**Acknowledgements**

This work was supported by National Institutes of Health grant (HL098256), by a National Mentored Research Science Development Award (K01 AR052840), and Independent Scientist Award (K02 HL105799) from the NIH awarded to J.P. Konhilas, the Interdisciplinary Training in Cardiovascular Research (HL007249), and the Cardiovascular Biomedical Engineering Training Grant (HL007955). Support was received from the Sarver Heart Center at the University of Arizona and the Steven M. Gootter Foundation.

### **Author details**

Marissa Lopez-Pier1,3, Yulia Lipovka2,3, Eleni Constantopoulos2,3 and John P. Konhilas2,3\*

\*Address all correspondence to: konhilas@arizona.edu

1 Department of Biomedical Engineering, University of Arizona, Tucson, Arizona

2 Department of Physiology, University of Arizona, Tucson, Arizona

3 Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, Arizona

### **References**

[1] Maron BJ. Hypertrophic cardiomyopathy: a systematic review. JAMA 287: 1308-1320, 2002.

[2] Tardiff JC. Thin filament mutations: developing an integrative approach to a complex disorder. Circ Res 108: 765-782, 2011.

evident from studies of FHC is that although the primary defect may reside in the sarcomere, the development of an HCM, DCM, or RCM phenotype depends on the interaction of the initiated signaling pathways, environmental stressors, and individual genotype (including sex/gender). For example, pathways downstream of Ca2+ activation such as Ca2+-sensitivity or actin-myosin cycling kinetics represent functional parameter that is the summation of multiple

Despite an increasing appreciation of sex dimorphisms in the pathophysiology of FHC, many inconsistenciesplague the cellular andmolecularmechanismsunderlyingthese sexdifferences. Taken together, there is a clear necessity in elucidating the cellular and molecular actions of estrogen and how this relates to the sex dimorphisms in FHC. Finally, although murine models of FHC do not exactly mimic the human *genotype*, they have proven as useful tools to elucidate

This work was supported by National Institutes of Health grant (HL098256), by a National Mentored Research Science Development Award (K01 AR052840), and Independent Scientist Award (K02 HL105799) from the NIH awarded to J.P. Konhilas, the Interdisciplinary Training in Cardiovascular Research (HL007249), and the Cardiovascular Biomedical Engineering Training Grant (HL007955). Support was received from the Sarver Heart Center at the

Marissa Lopez-Pier1,3, Yulia Lipovka2,3, Eleni Constantopoulos2,3 and John P. Konhilas2,3\*

1 Department of Biomedical Engineering, University of Arizona, Tucson, Arizona

3 Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson,

[1] Maron BJ. Hypertrophic cardiomyopathy: a systematic review. JAMA 287: 1308-1320,

2 Department of Physiology, University of Arizona, Tucson, Arizona

signals.

the mechanisms underlying the FHC *phenotype*.

University of Arizona and the Steven M. Gootter Foundation.

\*Address all correspondence to: konhilas@arizona.edu

**Acknowledgements**

90 Cardiomyopathies - Types and Treatments

**Author details**

Arizona

**References**

2002.


increases calcium sensitivity of force and ATPase in transgenic mice. J Cell Sci 118: 3675-3683, 2005.


[28] de Tombe PP and Stienen GJ. Protein kinase A does not alter economy of force maintenance in skinned rat cardiac trabeculae. Circ Res 76: 734-741, 1995.

increases calcium sensitivity of force and ATPase in transgenic mice. J Cell Sci 118:

[16] Yar S, Monasky MM, and Solaro RJ. Maladaptive modifications in myofilament proteins and triggers in the progression to heart failure and sudden death. Pflugers Arch 466:

[17] Stehle R and Iorga B. Kinetics of cardiac sarcomeric processes and rate-limiting steps

[18] Szczesna-Cordary D, Jones M, Moore JR, Watt J, Kerrick WG, Xu Y, Wang Y, Wagg C, and Lopaschuk GD. Myosin regulatory light chain E22K mutation results in decreased cardiac intracellular calcium and force transients. FASEB J

[19] Tardiff JC, Hewett TE, Palmer BM, Olsson C, Factor SM, Moore RL, Robbins J, and Leinwand LA. Cardiac troponin T mutations result in allele-specific phenotypes in a mouse model for hypertrophic cardiomyopathy. J Clin Invest 104: 469-481, 1999.

[20] Witjas-Paalberends ER, Ferrara C, Scellini B, Piroddi N, Montag J, Tesi C, Stienen GJ, Michels M, Ho CY, Kraft T, Poggesi C, and van der Velden J. Faster cross-bridge detachment and increased tension cost in human hypertrophic cardiomyopathy with

[21] McKee LA, Chen H, Regan JA, Behunin SM, Walker JW, Walker JS, and Konhilas JP. Sexually dimorphic myofilament function and cardiac troponin I phosphospecies distribution in hypertrophic cardiomyopathy mice. Arch Biochem Biophys 535: 39-48,

[22] Tesi C, Colomo F, Nencini S, Piroddi N, and Poggesi C. The effect of inorganic phosphate on force generation in single myofibrils from rabbit skeletal muscle. Biophys J 78:

[23] Hill TL, Eisenberg E, and Greene L. Theoretical model for the cooperative equilibrium binding of myosin subfragment 1 to the actin-troponin-tropomyosin complex. Proc

[24] Huxley AF. Muscle structure and theories of contraction. Prog Biophys 7: 255-318, 1957.

[25] Podolsky RJ, Nolan AC, and Zaveler SA. Cross-bridge properties derived from muscle

[26] de Tombe PP and Stienen GJ. Impact of temperature on cross-bridge cycling kinetics in

[27] Birch CL, Behunin SM, Lopez-Pier MA, Danilo C, Lipovka Y, Saripalli C, Granzier H, and Konhilas JP. Sex dimorphisms of crossbridge cycling kinetics in transgenic hypertrophic cardiomyopathy mice. Am J Physiol Heart Circ Physiol 311: H125-136,

isotonic velocity transients. Proc Natl Acad Sci U S A 64: 504-511, 1969.

in contraction and relaxation. J Mol Cell Cardiol 48: 843-850, 2010.

the R403Q MYH7 mutation. J Physiol 592: 3257-3272, 2014.

3675-3683, 2005.

92 Cardiomyopathies - Types and Treatments

1189-1197, 2014.

21: 3974-3985, 2007.

2013.

2016.

3081-3092, 2000.

Natl Acad Sci U S A 77: 3186-3190, 1980.

rat myocardium. J Physiol 584: 591-600, 2007.


[52] Declercq JP, Evrard C, Lamzin V, and Parello J. Crystal structure of the EF-hand parvalbumin at atomic resolution (0.91 Å) and at low temperature (100 K). Evidence for conformational multistates within the hydrophobic core. Protein Sci 8: 2194-2204, 1999.

[41] Belus A, Piroddi N, Scellini B, Tesi C, D'Amati G, Girolami F, Yacoub M, Cecchi F, Olivotto I, and Poggesi C. The familial hypertrophic cardiomyopathy-associated myosin mutation R403Q accelerates tension generation and relaxation of human

[42] Palmer BM, Fishbaugher DE, Schmitt JP, Wang Y, Alpert NR, Seidman CE, Seidman JG, VanBuren P, and Maughan DW. Differential cross-bridge kinetics of FHC myosin mutations R403Q and R453C in heterozygous mouse myocardium. Am J Physiol Heart

[43] Palmer BM, Wang Y, Teekakirikul P, Hinson JT, Fatkin D, Strouse S, Vanburen P, Seidman CE, Seidman JG, and Maughan DW. Myofilament mechanical performance is enhanced by R403Q myosin in mouse myocardium independent of sex. Am J Physiol

[44] Blanchard E, Seidman C, Seidman JG, LeWinter M, and Maughan D. Altered crossbridge kinetics in the alphaMHC403/+ mouse model of familial hypertrophic cardio-

[45] Semsarian C, Ahmad I, Giewat M, Georgakopoulos D, Schmitt JP, McConnell BK, Reiken S, Mende U, Marks AR, Kass DA, Seidman CE, and Seidman JG. The L-type calcium channel inhibitor diltiazem prevents cardiomyopathy in a mouse model. J Clin

[46] Georgakopoulos D, Christe ME, Giewat M, Seidman CM, Seidman JG, and Kass DA. The pathogenesis of familial hypertrophic cardiomyopathy: early and evolving effects from an alpha-cardiac myosin heavy chain missense mutation. Nat Med 5: 327-330,

[47] Harris SP, Bartley CR, Hacker TA, McDonald KS, Douglas PS, Greaser ML, Powers PA, and Moss RL. Hypertrophic cardiomyopathy in cardiac myosin binding protein-C

[48] Korte FS, McDonald KS, Harris SP, and Moss RL. Loaded shortening, power output, and rate of force redevelopment are increased with knockout of cardiac myosin binding

[49] van Dijk SJ, Boontje NM, Heymans MW, Ten Cate FJ, Michels M, Dos Remedios C, Dooijes D, van Slegtenhorst MA, van der Velden J, and Stienen GJ. Preserved crossbridge kinetics in human hypertrophic cardiomyopathy patients with MYBPC3

[50] Sequeira V, Witjas-Paalberends ER, Kuster DW, and van der Velden J. Cardiac myosinbinding protein C: hypertrophic cardiomyopathy mutations and structure-function

[51] van Dijk SJ, Bezold KL, and Harris SP. Earning stripes: myosin binding protein-C

cardiac myofibrils. J Physiol 586: 3639-3644, 2008.

Circ Physiol 287: H91-99, 2004.

94 Cardiomyopathies - Types and Treatments

Heart Circ Physiol 294: H1939-1947, 2008.

myopathy. Circ Res 84: 475-483, 1999.

knockout mice. Circ Res 90: 594-601, 2002.

mutations. Pflugers Arch 466: 1619-1633, 2014.

relationships. Pflugers Arch 466: 201-206, 2014.

interactions with actin. Pflugers Arch 466: 445-450, 2014.

protein-C. Circ Res 93: 752-758, 2003.

Invest 109: 1013-1020, 2002.

1999.


[76] Stauffer BL, Konhilas JP, Luczak ED, and Leinwand LA. Soy diet worsens heart disease in mice. J Clin Invest 116: 209-216, 2006.

[64] Olivotto I, Maron MS, Adabag AS, Casey SA, Vargiu D, Link MS, Udelson JE, Cecchi F, and Maron BJ. Gender-related differences in the clinical presentation and outcome

[65] Konhilas JP and Leinwand LA. The effects of biological sex and diet on the development

[66] Yang XP and Reckelhoff JF. Estrogen, hormonal replacement therapy and cardiovas-

[67] Thomas P, Pang Y, Filardo EJ, and Dong J. Identity of an estrogen membrane receptor coupled to a G protein in human breast cancer cells. Endocrinology 146: 624-632, 2005.

[68] Widder J, Pelzer T, von Poser-Klein C, Hu K, Jazbutyte V, Fritzemeier KH, Hegele-Hartung C, Neyses L, and Bauersachs J. Improvement of endothelial dysfunction by selective estrogen receptor-alpha stimulation in ovariectomized SHR. Hypertension 42:

[69] Cavasin MA, Sankey SS, Yu AL, Menon S, and Yang XP. Estrogen and testosterone have opposing effects on chronic cardiac remodeling and function in mice with myocardial

[70] van Eickels M, Grohe C, Cleutjens JP, Janssen BJ, Wellens HJ, and Doevendans PA. 17beta-estradiol attenuates the development of pressure-overload hypertrophy.

[71] Sharkey LC, Holycross BJ, Park S, Shiry LJ, Hoepf TM, McCune SA, and Radin MJ. Effect of ovariectomy and estrogen replacement on cardiovascular disease in heart

[72] de Jager T, Pelzer T, Muller-Botz S, Imam A, Muck J, and Neyses L. Mechanisms of estrogen receptor action in the myocardium. Rapid gene activation via the ERK1/2

[73] Grady D, Applegate W, Bush T, Furberg C, Riggs B, and Hulley SB. Heart and Estrogen/ progestin Replacement Study (HERS): design, methods, and baseline characteristics.

[74] Rossouw JE, Anderson GL, Prentice RL, LaCroix AZ, Kooperberg C, Stefanick ML, Jackson RD, Beresford SA, Howard BV, Johnson KC, Kotchen JM, and Ockene J. Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results from the Women's Health Initiative randomized controlled trial. JAMA 288:

[75] Vikstrom KL, Factor SM, and Leinwand LA. Mice expressing mutant myosin heavy chains are a model for familial hypertrophic cardiomyopathy. Mol Med 2: 556-567,

failure-prone SHHF/Mcc- fa cp rats. J Mol Cell Cardiol 31: 1527-1537, 1999.

pathway and serum response elements. J Biol Chem 276: 27873-27880, 2001.

infarction. Am J Physiol Heart Circ Physiol 284: H1560-1569, 2003.

of hypertrophic cardiomyopathy. J Am Coll Cardiol 46: 480-487, 2005.

cular disease. Curr Opin Nephrol Hypertens 20: 133-138, 2011.

of heart failure. Circulation 116: 2747-2759, 2007.

991-996, 2003.

96 Cardiomyopathies - Types and Treatments

Circulation 104: 1419-1423, 2001.

Control Clin Trials 19: 314-335, 1998.

321-333, 2002.

1996.


[100] Fliegner D, Schubert C, Penkalla A, Witt H, Kararigas G, Dworatzek E, Staub E, Martus P, Ruiz Noppinger P, Kintscher U, Gustafsson JA, and Regitz‐Zagrosek V. Female sex and estrogen receptor‐beta attenuate cardiac remodeling and apoptosis in pressure overload. Am J Physiol Regul Integr Comp Physiol 298: R1597‐1606, 2010.

[90] Satoh M, Matter CM, Ogita H, Takeshita K, Wang CY, Dorn GW, 2nd, and Liao JK. Inhibition of apoptosis-regulated signaling kinase-1 and prevention of congestive heart

[91] Shen T, Ding L, Ruan Y, Qin W, Lin Y, Xi C, Lu Y, Dou L, Zhu Y, Cao Y, Man Y, Bian Y, Wang S, Xiao C, and Li J. SIRT1 functions as an important regulator of estrogenmediated cardiomyocyte protection in angiotensin II-induced heart hypertrophy. Oxid

[92] Patten RD, Pourati I, Aronovitz MJ, Baur J, Celestin F, Chen X, Michael A, Haq S, Nuedling S, Grohe C, Force T, Mendelsohn ME, and Karas RH. 17beta-estradiol reduces cardiomyocyte apoptosis in vivo and in vitro via activation of phospho-inositide-3

[93] Donaldson C, Eder S, Baker C, Aronovitz MJ, Weiss AD, Hall-Porter M, Wang F, Ackerman A, Karas RH, Molkentin JD, and Patten RD. Estrogen attenuates left ventricular and cardiomyocyte hypertrophy by an estrogen receptor-dependent pathway that increases calcineurin degradation. Circ Res 104: 265-275, 211p following

[94] Pedram A, Razandi M, Aitkenhead M, and Levin ER. Estrogen inhibits cardiomyocyte hypertrophy in vitro. Antagonism of calcineurin-related hypertrophy through induc-

[95] Voloshenyuk TG and Gardner JD. Estrogen improves TIMP-MMP balance and collagen distribution in volume-overloaded hearts of ovariectomized females. Am J Physiol

[96] Pelzer T, Loza PA, Hu K, Bayer B, Dienesch C, Calvillo L, Couse JF, Korach KS, Neyses L, and Ertl G. Increased mortality and aggravation of heart failure in estrogen receptor-beta knockout mice after myocardial infarction. Circulation 111: 1492-1498,

[97] Bolego C, Rossoni G, Fadini GP, Vegeto E, Pinna C, Albiero M, Boscaro E, Agostini C, Avogaro A, Gaion RM, and Cignarella A. Selective estrogen receptor-alpha agonist provides widespread heart and vascular protection with enhanced endothelial progenitor cell mobilization in the absence of uterotrophic action. FASEB J 24:

[98] Westphal C, Schubert C, Prelle K, Penkalla A, Fliegner D, Petrov G, and Regitz-Zagrosek V. Effects of estrogen, an ERalpha agonist and raloxifene on pressure overload induced

[99] Babiker FA, Lips D, Meyer R, Delvaux E, Zandberg P, Janssen B, van Eys G, Grohe C, and Doevendans PA. Estrogen receptor beta protects the murine heart against left ventricular hypertrophy. Arterioscler Thromb Vasc Biol 26:

failure by estrogen. Circulation 115: 3197-3204, 2007.

kinase/Akt signaling. Circ Res 95: 692-699, 2004.

tion of MCIP1. J Biol Chem 280: 26339-26348, 2005.

Regul Integr Comp Physiol 299: R683-693, 2010.

cardiac hypertrophy. PLoS One 7: e50802, 2012.

Med Cell Longev 2014: 713894, 2014.

98 Cardiomyopathies - Types and Treatments

275, 2009.

2005.

2262-2272, 2010.

1524-1530, 2006.


### **Idiopathic Dilated Cardiomyopathy: Molecular Basis and Distilling Complexity to Advance Idiopathic Dilated Cardiomyopathy: Molecular Basis and Distilling Complexity to Advance**

Santiago Roura, Carolina Gálvez-Montón, Santiago Roura, Carolina Gálvez-Montón, Josep Lupón and Antoni Bayes-Genis

Josep Lupón and Antoni Bayes-Genis Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/64996

#### **Abstract**

[111] Rivera Z, Christian PJ, Marion SL, Brooks HL, and Hoyer PB. Steroidogenic capacity of residual ovarian tissue in 4-vinylcyclohexene diepoxide-treated mice. Biol Reprod

[112] Mayer LP, Devine PJ, Dyer CA, and Hoyer PB. The follicle-deplete mouse ovary

[113] Morris PD and Channer KS. Testosterone and cardiovascular disease in men. Asian J

[114] Erickson GF, Magoffin DA, Dyer CA, and Hofeditz C. The ovarian androgen producing cells: a review of structure/function relationships. Endocr Rev 6: 371-399, 1985. [115] Liu Y, Ding J, Bush TL, Longenecker JC, Nieto FJ, Golden SH, and Szklo M. Relative androgen excess and increased cardiovascular risk after menopause: a hypothesized

[116] Pollow DP, Jr., Romero-Aleshire MJ, Sanchez JN, Konhilas JP, and Brooks HL. ANG IIinduced hypertension in the VCD mouse model of menopause is prevented by estrogen replacement during perimenopause. Am J Physiol Regul Integr Comp Physiol 309:

[117] Rundell VL, Geenen DL, Buttrick PM, and de Tombe PP. Depressed cardiac tension cost in experimental diabetes is due to altered myosin heavy chain isoform expression. Am

produces androgen. Biol Reprod 71: 130-138, 2004.

relation. Am J Epidemiol 154: 489-494, 2001.

J Physiol Heart Circ Physiol 287: H408-413, 2004.

80: 328-336, 2009.

100 Cardiomyopathies - Types and Treatments

R1546-1552, 2015.

Androl 14: 428-435, 2012.

Cardiomyopathies are heterogeneous diseases of the myocardium associated with abnormal findings of chamber size, wall thickness, and/or functional contractility. In particular, dilated cardiomyopathy (DCM) is mainly characterized by ventricular chamber enlargement with systolic dysfunction and normal left ventricular (LV) wall thickness. Although DCM is thought to be induced mainly by genetic or environmental factors, in the majority of cases, the cause is unknown. With an estimated prevalence of 1:2500 and an incidence of 1:18,000 per year in adults, DCM is the most frequent indication for heart transplantation, which represents an enormous cost burden on healthcare systems. These figures warrant greater accuracy in patient diagnosis and prognosis and further insight into the underlying basis of DCM. Here, we discuss past and recent findings on the molecular mechanisms involved in DCM. Dilated cardio‐ myopathy has been linked to the overactivation of extracellular signal‐regulated kinase (ERK1/2), which in turn is related to activation of low‐density lipoprotein receptor– related protein‐1 (LRP‐1). Moreover, a redistribution of LRP‐1 into cholesterol‐enriched plasma membrane domains (lipid rafts) and alterations in cardiac DNA methylation have been reported in failing hearts. In conclusion, more comprehensive analyses of myocardial lipid rafts and epigenetic mechanisms may advance our understanding of DCM causes and progression. In turn, this understanding may promote the develop‐ ment of innovative treatments.

**Keywords:** dilated cardiomyopathy, heart failure, lipid rafts, LRP‐1, molecular basis, cardiac muscle, vasculature

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

### **1. Introduction**

Cardiomyopathies are heterogeneous diseases of the myocardium associated with abnormal findings of chamber size, wall thickness, and/or functional contractility [1]. Currently, cardio‐ myopathy is classified based on the dominant pathophysiology or by aetiological/pathogenetic factors. This system defines four distinct categories of cardiomyopathy: dilated, hypertrophic, restrictive, and arrhythmogenic (**Figure 1**) [2]. In particular, dilated cardiomyopathy (DCM) is mainlycharacterizedbyventricularchamberenlargementordilatationwithsystolicdysfunction andnormalleftventricular(LV)wallthickness.Ingeneral,theseabnormalitiesleadtoprogressive heart failure, a decline in LV contractile function, abnormalities in ventricular and supraven‐ tricularrhythm and conduction,thromboembolism, and finally, sudden or heartfailure‐related death [3]. Indeed, DCM is a common, largely irreversible cause of myocardial damage. It is thought to be induced by genetic or environmental factors that may manifest clinically over a wide range of ages (most commonly in the third or fourth decade, but also in young children). Dilated cardiomyopathy affects both sexes and all ethnic groups; it is typically identified when patients exhibit severe limiting symptoms and incapacity [4].

**Figure 1.** Heterogeneous diseases of the myocardium. The different types of cardiomyopathies fall into four principal categories, based on the muscle disorder involved. This chapter is confined to dilated cardiomyopathy.

This chapter summarizes the most important traits (aetiology, diagnosis, treatment, and pathophysiology) that characterize DCM. We focus on studies that provided novel insights into the underlying molecular basis of this extremely complex human disorder. In a sense, we will present new pieces of an intriguing puzzle, with the aim of bringing some order into the chaos of the molecular reality.

### **2. Dilated cardiomyopathy: characteristic features**

**1. Introduction**

102 Cardiomyopathies - Types and Treatments

Cardiomyopathies are heterogeneous diseases of the myocardium associated with abnormal findings of chamber size, wall thickness, and/or functional contractility [1]. Currently, cardio‐ myopathy is classified based on the dominant pathophysiology or by aetiological/pathogenetic factors. This system defines four distinct categories of cardiomyopathy: dilated, hypertrophic, restrictive, and arrhythmogenic (**Figure 1**) [2]. In particular, dilated cardiomyopathy (DCM) is mainlycharacterizedbyventricularchamberenlargementordilatationwithsystolicdysfunction andnormalleftventricular(LV)wallthickness.Ingeneral,theseabnormalitiesleadtoprogressive heart failure, a decline in LV contractile function, abnormalities in ventricular and supraven‐ tricularrhythm and conduction,thromboembolism, and finally, sudden or heartfailure‐related death [3]. Indeed, DCM is a common, largely irreversible cause of myocardial damage. It is thought to be induced by genetic or environmental factors that may manifest clinically over a wide range of ages (most commonly in the third or fourth decade, but also in young children). Dilated cardiomyopathy affects both sexes and all ethnic groups; it is typically identified when

**Figure 1.** Heterogeneous diseases of the myocardium. The different types of cardiomyopathies fall into four principal

categories, based on the muscle disorder involved. This chapter is confined to dilated cardiomyopathy.

patients exhibit severe limiting symptoms and incapacity [4].

Dilated cardiomyopathy has an estimated prevalence of 1:2500, an incidence of 1:15,000–18,000 per year in adults, and an estimated prevalence of 2:3 among children with unknown diseases [4, 5]. The clinical course of DCM can be progressive; one study reported that about 35% of individuals died within 5 years after diagnosis [1]. The origin of death is divided evenly between sudden death and pump failure. To date, prolonged survival has been achieved with neurohormone blockers (angiotensin‐converting enzyme inhibitors and β‐adrenoceptor antagonists) and devices (cardiac resynchronization and implanted defibrillators). Neverthe‐ less, the only definitive treatment is heart transplantation, which is hampered in many instances by the limited number of heart donors and by graft rejection over time. Therefore, DCM is the most frequent indication for heart transplantation, which results in an enormous cost burden for healthcare systems throughout the world. Diagnosis is typically based on patient history and the presence of LV dilatation and impaired ejection fraction, with or without regurgitation; these signs are detected with echocardiography, cardiac magnetic resonance imaging, or both.

At the histological level, the main pathological derangements observed in explanted diseased hearts are patchy interstitial fibrosis surrounding myocardial filaments, marked lipid deposi‐ tion, cardiac muscle atrophy, and lipid accumulation [6–8]. Moreover, further investigations of both patient samples and animal disease models have shown that DCM hearts exhibit marked vascular alterations [9, 10]. In most cases, the causal mechanism of disease is poorly understood. This reality has induced some authors to argue that heart disease in DCM arises from an obscure origin, and this viewpoint has given rise to the term 'idiopathic' DCM. Recently, relevant advances have been made in our understanding of the causes of this disease. The main causes include familial and genetic disorders, infectious and toxicity‐related processes, autoimmunity, and inflammation [4].

Frequently, DCM has been defined as the result of an extremely complex genetic architecture that involves disruptions in a variety of myocardial proteins, which are provoked by rare variants in some genes; moreover, many of these genes are also involved in other cardiomyo‐ pathies, such as muscular dystrophy or syndromic diseases [11]. In brief, numerous DCM‐ associated genes have been identified. This information has provided a better understanding of disease pathogenesis, and it has promoted advances in mutation analytical techniques to facilitate the recognition of subjects and progeny that carry these mutations [12]. Alterations in more than 50 loci and genes have been identified, which mostly encode either cardiac myocyte‐specific proteins or structural, nuclear membrane, and calcium metabolism proteins. However, it is estimated that genetic disorders account for only 20–35% of DCM cases [12, 13]. Some researchers have predicted that genetic associations may have been missed due to the limited nature of previous studies; accordingly, they point to a need for more comprehen‐ sive studies in much larger cohorts of families that are rigorously phenotyped [11]. In addition, some cases of DCM are believed to be related to autoimmune and inflammatory processes [14– 16]; metabolic, nutritional, and endocrine deficiencies; or heart muscle damage following exposure to viruses, exogenous drugs, or toxins (e.g., chronic alcohol consumption) [2]. Peripartum cardiomyopathy also represents a subset of LV systolic dysfunction. In the latter cases, initial symptoms of heart failure occur during the late stages of pregnancy [17]. Although there may be a variety of causes for DCM, the clinical presentation of this disease seems to be uniform, both in humans and in animal models that have been used to dissect DCM develop‐ ment, progression, and treatment [10].

Standard treatment of DCM involves neurohormonal inhibition of the renin‐angiotensin‐ aldosterone system (i.e., angiotensin‐converting enzyme inhibitors, angiotensin II receptor type 1 blockers, or mineralocorticoid receptor blockers) or blocking the sympathetic nervous system with β‐blockers. In patients, it is crucial to focus on improving cardiac function and reducing mechanical stress. Although progress has been made in arrhythmia therapy and in sudden death prevention, many impediments for improving patient outcomes remain unresolved [4]. Innovative therapies, such as stem cell‐based applications, are also being investigated [18].

### **3. Dilated cardiomyopathy affects both cardiac muscle and the vasculature**

Dilated cardiomyopathy is associated with pronounced remodelling of one or both ventricles, which results in large changes in the shapes of ventricles and in the architecture of myocardial fibres. As mentioned previously, the main microscopic hallmarks of failing hearts are marked collagen deposition, patchy interstitial fibrosis, degenerated cardiac muscle cells, and sparse blood vessels. At the ultrastructural level, remodelling comprises mitochondrial abnormali‐ ties, T‐tubular dilatation, and intracellular lipid droplet accumulation [10]. Because the mitochondrion is the main site of ATP production and cardiac myocytes are particularly sensitive to the supply of energy, deficits in mitochondrial function have been linked to DCM [19]. Additionally, altered levels of connexin‐43 and modulation of its phosphorylation state can induce electromechanical uncoupling between neighbouring cardiac muscle cells [20].

A number of studies have indicated that programmed cell death or apoptosis contributes actively to human end‐stage heart failure. Indeed, cell death occurs in myocardial ischemia‐ reperfusion [21], ischemia‐reperfusion injury [22], and fatal myocarditis [23]. However, the role of apoptosis in the DCM myocardium remains controversial, due to some limitations in the techniques that have been used to measure apoptosis [24–26]. A positive Terminal deoxy‐ nucleotidyl transferase dUTP nick end labeling (TUNEL) signal seems to require fragmenta‐ tion of only 10% of all DNA; as a result, the level of apoptosis may be highly overestimated [24]. Furthermore, cells that are apoptotic, necrotic, undergoing DNA repair, or living can emit equivalent signals in the TUNEL assay [27], which renders the use of this method even more questionable. Consequently, although some authors have reported putative increases in apoptotic markers with different methodologies, including caspase‐3 activity, DNA fragmen‐ tation (TUNEL), and electron microscopy [28], others have failed to detect changes in apop‐ tosis. For instance, Bott‐Flügel *et al*. did not detect any correlations between caspase‐3 activity, the induction of DNA fragmentation, and haemodynamic or echocardiographic variables in patients with end‐stage heart failure, including DCM. Moreover, they did not find significant differences in caspase‐3 activation between DCM and control myocardium [26]. **Figure 2** shows that only slight amounts of caspase‐3 mRNA and protein were detected in LV samples from patients (unpublished results). These findings suggest that cardiac muscle cells might trigger apoptotic self‐destruction, without completing the process. Hence, DCM is characterized by marked abnormalities in the function and integrity of cardiac muscle.

However, it is estimated that genetic disorders account for only 20–35% of DCM cases [12, 13]. Some researchers have predicted that genetic associations may have been missed due to the limited nature of previous studies; accordingly, they point to a need for more comprehen‐ sive studies in much larger cohorts of families that are rigorously phenotyped [11]. In addition, some cases of DCM are believed to be related to autoimmune and inflammatory processes [14– 16]; metabolic, nutritional, and endocrine deficiencies; or heart muscle damage following exposure to viruses, exogenous drugs, or toxins (e.g., chronic alcohol consumption) [2]. Peripartum cardiomyopathy also represents a subset of LV systolic dysfunction. In the latter cases, initial symptoms of heart failure occur during the late stages of pregnancy [17]. Although there may be a variety of causes for DCM, the clinical presentation of this disease seems to be uniform, both in humans and in animal models that have been used to dissect DCM develop‐

Standard treatment of DCM involves neurohormonal inhibition of the renin‐angiotensin‐ aldosterone system (i.e., angiotensin‐converting enzyme inhibitors, angiotensin II receptor type 1 blockers, or mineralocorticoid receptor blockers) or blocking the sympathetic nervous system with β‐blockers. In patients, it is crucial to focus on improving cardiac function and reducing mechanical stress. Although progress has been made in arrhythmia therapy and in sudden death prevention, many impediments for improving patient outcomes remain unresolved [4]. Innovative therapies, such as stem cell‐based applications, are also being

**3. Dilated cardiomyopathy affects both cardiac muscle and the vasculature**

Dilated cardiomyopathy is associated with pronounced remodelling of one or both ventricles, which results in large changes in the shapes of ventricles and in the architecture of myocardial fibres. As mentioned previously, the main microscopic hallmarks of failing hearts are marked collagen deposition, patchy interstitial fibrosis, degenerated cardiac muscle cells, and sparse blood vessels. At the ultrastructural level, remodelling comprises mitochondrial abnormali‐ ties, T‐tubular dilatation, and intracellular lipid droplet accumulation [10]. Because the mitochondrion is the main site of ATP production and cardiac myocytes are particularly sensitive to the supply of energy, deficits in mitochondrial function have been linked to DCM [19]. Additionally, altered levels of connexin‐43 and modulation of its phosphorylation state can induce electromechanical uncoupling between neighbouring cardiac muscle cells [20].

A number of studies have indicated that programmed cell death or apoptosis contributes actively to human end‐stage heart failure. Indeed, cell death occurs in myocardial ischemia‐ reperfusion [21], ischemia‐reperfusion injury [22], and fatal myocarditis [23]. However, the role of apoptosis in the DCM myocardium remains controversial, due to some limitations in the techniques that have been used to measure apoptosis [24–26]. A positive Terminal deoxy‐ nucleotidyl transferase dUTP nick end labeling (TUNEL) signal seems to require fragmenta‐ tion of only 10% of all DNA; as a result, the level of apoptosis may be highly overestimated [24]. Furthermore, cells that are apoptotic, necrotic, undergoing DNA repair, or living can emit

ment, progression, and treatment [10].

104 Cardiomyopathies - Types and Treatments

investigated [18].

**Figure 2.** Comparative analysis of apoptosis in left ventricle samples collected from human explanted DCM hearts and control hearts from non‐cardiac decedents. Representative caspase‐3 gene (**A**) and protein (**B**) expression levels by quantitative RT‐PCR and Western blotting, respectively.

Cardiac endothelial dysfunction was also associated with disease progression and a poor prognosis in patients with DCM. In the late 1940s, preliminary observations showed a correlation between heart weight and the total cross‐sectional size of the main coronary vessels [29]. Since then, a number of studies have recognized that cardiac vasculature is a key regulator of the integrity and function of the myocardium. In an attempt to take this a step further, Brutsaert *et al*. studied the mechanical properties of the mammalian ventricular myocardium before and after damaging the endocardial surface [30]. Those authors speculated that the endocardium could affect myocardial performance by either forming an electrochem‐ ical barrier, releasing a chemical substance or messenger, or both. They subsequently demon‐ strated that nitric oxide synthase activity regulated the contractile responsiveness of ventricular myocytes [31]. Perhaps more significantly, additional studies in Langendorff‐ perfused and post‐infarcted rat hearts confirmed that endothelial damage led to progressive myocardial dysfunction and that, conversely, protecting the associated vasculature preserved global myocardial homeostasis [32, 33].

**Figure 3.** Foundation of DCM as a two‐hit heart disease. The integrity and function of both cardiac muscle and vascu‐ lature are adversely compromised in DCM, which leads to LV remodelling and pump failure.

Advances in medical imaging techniques have become crucial for performing more compre‐ hensive analyses of vascular derangements in DCM. Angiography revealed that a mismatch between artery size and LV mass in patients with DCM contributed to myocardial hypoper‐ fusion [34–37]. Computed tomography measurements of DCM cardiac vasculature on a multislice scanner have also clearly shown side branch paucity and shortened, thinned epicardial arteries [9]. Therefore, the epicardial coronary arteries in patients with DCM are not adequately sized for the enlarged LV mass. Notably, a variety of studies described significantly reduced, sparse microvasculature in diseased myocardium samples [9, 38, 39]. In this context, numerous studies in patients with DCM have reported that the circulating levels of distinct bone marrow‐derived cell populations are peripherally increased after vascular damage [40]. Although there is a correlation between the circulating levels of these progenitor cells and the progression and clinical outcomes of DCM, the clinical usefulness of this overrepresentation awaits further validation.

Cardiac endothelial dysfunction was also associated with disease progression and a poor prognosis in patients with DCM. In the late 1940s, preliminary observations showed a correlation between heart weight and the total cross‐sectional size of the main coronary vessels [29]. Since then, a number of studies have recognized that cardiac vasculature is a key regulator of the integrity and function of the myocardium. In an attempt to take this a step further, Brutsaert *et al*. studied the mechanical properties of the mammalian ventricular myocardium before and after damaging the endocardial surface [30]. Those authors speculated that the endocardium could affect myocardial performance by either forming an electrochem‐ ical barrier, releasing a chemical substance or messenger, or both. They subsequently demon‐ strated that nitric oxide synthase activity regulated the contractile responsiveness of ventricular myocytes [31]. Perhaps more significantly, additional studies in Langendorff‐ perfused and post‐infarcted rat hearts confirmed that endothelial damage led to progressive myocardial dysfunction and that, conversely, protecting the associated vasculature preserved

**Figure 3.** Foundation of DCM as a two‐hit heart disease. The integrity and function of both cardiac muscle and vascu‐

Advances in medical imaging techniques have become crucial for performing more compre‐ hensive analyses of vascular derangements in DCM. Angiography revealed that a mismatch between artery size and LV mass in patients with DCM contributed to myocardial hypoper‐ fusion [34–37]. Computed tomography measurements of DCM cardiac vasculature on a multislice scanner have also clearly shown side branch paucity and shortened, thinned

lature are adversely compromised in DCM, which leads to LV remodelling and pump failure.

global myocardial homeostasis [32, 33].

106 Cardiomyopathies - Types and Treatments

Collectively, these findings led to a re‐examination of the pathophysiology of DCM. In 2009, Roura and Bayes‐Genis [10] reviewed the extensive data from animal models and patients and concluded that DCM is a two‐hit disease, where both cardiac muscle and endothelial altera‐ tions contribute equally to contractile deficiency and pump failure (**Figure 3**).

### **4. Molecular basis of dilated cardiomyopathy: past and new actors**

Molecularly, in humans, DCM has been related to intramyocardial accumulation of α‐2 macroglobulin (α‐2M) [41] and increased activation of extracellular signal‐regulated kinase (ERK1/2) [42]. In a mouse model of DCM, the disease was generated by a mutation in the lamin A/C gene [43, 44]. In these mice, chemically suppressing ERK1/2 activation prevented LV dilatation and greatly restored the cardiac ejection fraction.

The α‐2M protein is a highly abundant plasma protease inhibitor, which has been shown to activate various tyrosine kinases and mitogen‐activated protein kinases [45]. Moreover, α‐2M was one of the first molecules to be described as a ligand of low‐density lipoprotein (LDL) receptor‐related protein 1 (LRP‐1) [46]. A recent review described LRP‐1 as a multifunctional receptor of the LDL‐receptor family that mediates the clearance of a variety of structurally diverse extracellular molecules [47]. Moreover, LRP‐1 plays key roles in various biological processes by interacting with multiple intracellular signalling pathways [48, 49]. As a result, LRP‐1 tyrosine phosphorylation can be activated in response to diverse extracellular mole‐ cules, such as platelet‐derived growth factor [50–52]. In particular, ERK1/2 activation is recognized as one of the main LRP‐1 molecular relays [53–55]. In the following pages, we present and discuss novel data demonstrating that, together with the pivotal role of LRP‐1 in the vascular wall and in the aetiology of atherosclerosis [56], LRP‐1 is redistributed and overactivated within some specialized plasma membrane domains, termed lipid rafts, in DCM myocardium.

The decreased capillary density found in patients with DCM was shown to arise from impairments in myocardial endothelial cell survival and insufficient revascularization. These processes involve several intracellular signalling pathways, including those mediated by vascular endothelial (VE)‐cadherin/β‐catenin, angiopoietins, and vascular endothelial growth factors (VEGFs). In particular, VE‐cadherin, β‐catenin, angiopoietin‐2, VEGF‐A, VEGF‐B, and VEGF receptor‐1 (VEGFR‐1) expression levels were downregulated in DCM [9, 57, 58]. Roura *et al*. [9] further demonstrated that reduced expression of β‐catenin, an important angiogenic regulator [59], occurred exclusively in myocardial vascular cells in failing hearts.

Remarkably, different DNA methylation patterns have been detected in genes that regulate pathways related to heart disease and in genes with unknown functions in DCM. For example, variations in DNA methylation were observed in lymphocyte antigen 75, tyrosine kinase‐type cell surface receptor HER3, homeobox B13, and adenosine receptor A2A [60]. These validated targets are most likely involved in modifying DCM rather than independently causing disease. Furthermore, other authors found differentially methylated gene promoters and a depletion of mitochondrial DNA that resulted in a thymidine kinase deficiency in DCM hearts [61, 62]. Indeed, investigating epigenetic mechanisms represents an attractive approach for finding novel mechanisms of disease.

**Figure 4.** Potential impact of lipid raft–associated signalling on DCM. Schematic illustration of a lipid raft domain in a portion of the cell surface. Proteins potentially involved in disease progression are either packed into or excluded from these specialized plasma membrane areas.

For more than 40 years, the Singer and Nicolson model of the cell membrane, where proteins are viewed as icebergs floating in a sea of lipids, has provided a solid foundation for studying cell membrane properties [63]. This enduring model was subsequently reinterpreted with the discovery of localized, highly cholesterol‐ and glycosphingolipid‐enriched plasma membrane areas, referred to as 'lipid rafts' [64]. Many proteins, particularly those involved in cell signalling and cytokine presentation, were found to be densely packed together in these specialized surface domains [65]. Accordingly, lipid rafts facilitate interactions between protein receptors and mediators by maintaining them tightly packed together in one location. Interestingly, LRP‐1 was reported to be associated with lipid rafts [66, 67].

As previously mentioned, recent research has given us new molecular aspects of the disease. Particularly, in patients with DCM, LRP‐1 was seen redistributed and further activated, through tyrosine phosphorylation, within lipid rafts enriched in caveolin‐3 and flotillin‐1 [68]. Of note, these observations suggested that movement of LRP‐1 within these specialized membrane domains contribute to the overactivation of ERK1/2‐mediated signalling described in DCM. However, further confirmatory exploration is warranted to determine whether this overactive signalling leads to the characteristic promotion of extracellular matrix metallopro‐ teinase activity and subsequent LV remodelling (**Figure 4**) [69, 70].

To investigate this novel regulatory impact of lipid rafts on DCM, Roura *et al*. extracted lipid rafts from failing myocardium and detected elevated amounts of the mobilizing cytokine, stromal cell‐derived factor (SDF)‐1 [71]. In that same study, the authors showed that deficien‐ cies in ILK and ERK1/2 signalling impeded SDF‐1‐mediated migration of circulating progen‐ itor cells. As a result, impaired cell migration compromised endothelial maintenance and recovery, which contributed to the marked vascular derangements observed in diseased myocardium [72].

Taken together, these observations support the growing body of data that led to the recognition of myocardial lipid rafts and their associated proteins as modulators of cardiac performance and as novel therapeutic targets [73–75].

### **5. Conclusions**

*et al*. [9] further demonstrated that reduced expression of β‐catenin, an important angiogenic

Remarkably, different DNA methylation patterns have been detected in genes that regulate pathways related to heart disease and in genes with unknown functions in DCM. For example, variations in DNA methylation were observed in lymphocyte antigen 75, tyrosine kinase‐type cell surface receptor HER3, homeobox B13, and adenosine receptor A2A [60]. These validated targets are most likely involved in modifying DCM rather than independently causing disease. Furthermore, other authors found differentially methylated gene promoters and a depletion of mitochondrial DNA that resulted in a thymidine kinase deficiency in DCM hearts [61, 62]. Indeed, investigating epigenetic mechanisms represents an attractive approach for finding

**Figure 4.** Potential impact of lipid raft–associated signalling on DCM. Schematic illustration of a lipid raft domain in a portion of the cell surface. Proteins potentially involved in disease progression are either packed into or excluded from

For more than 40 years, the Singer and Nicolson model of the cell membrane, where proteins are viewed as icebergs floating in a sea of lipids, has provided a solid foundation for studying cell membrane properties [63]. This enduring model was subsequently reinterpreted with the discovery of localized, highly cholesterol‐ and glycosphingolipid‐enriched plasma membrane areas, referred to as 'lipid rafts' [64]. Many proteins, particularly those involved in cell signalling and cytokine presentation, were found to be densely packed together in these specialized surface domains [65]. Accordingly, lipid rafts facilitate interactions between protein receptors and mediators by maintaining them tightly packed together in one location.

Interestingly, LRP‐1 was reported to be associated with lipid rafts [66, 67].

regulator [59], occurred exclusively in myocardial vascular cells in failing hearts.

novel mechanisms of disease.

108 Cardiomyopathies - Types and Treatments

these specialized plasma membrane areas.

Heart failure has become an increasingly common disorder worldwide, and it is associated with substantial morbidity and mortality. Many causes of heart failure are easily identified in clinical practice, including abnormal heart valves, inherited cardiomyopathies, severe coro‐ nary artery disease, or hypertensive heart disease. However, the precise mechanisms that govern the progression of heart failure and ventricular remodelling in DCM remain obscure. Some authors have appropriately pointed out that, for both clinicians and researchers, attempting to discover the underlying genetic and environmental causes linked to complex human diseases, such as DCM, is like facing a drawer filled with thousands of puzzle pieces mixed together from an unknown number of jigsaw puzzles [76, 77]. The question remains, how can they begin to solve it?

There is a growing body of data that describes the multifaceted genetic diversity involved in DCM and the alterations in both cardiac muscle and vasculature that contribute to the disease. However, several crucial issues remain to be addressed. For example, it is not clear whether the marked vascular deficiencies observed in patients with DCM develop secondary to heart remodelling, or whether they directly contribute to myocardial alterations and to the temporal evolution of LV dilatation. Accordingly, researchers are providing novel mechanistic insights that might bring some order to this 'disordered' collection of data. For example, they have shown that lipid rafts participate in the mechanism underlying the spatial regulation of LRP‐1‐ mediated ERK1/2 activity. Undoubtedly, further work is needed to increase our comprehension of the causes underlying this 'obscure' disease. To that end, the current state of knowledge summarized in the present review provides a starting point for addressing the remaining questions in the pathophysiology of this disease. Moreover, we highlight new avenues for discovering potentially effective treatments.

### **Funding sources**

This work was supported by grants from the Ministerio de Educación y Ciencia (SAF2014‐59892), Fundació La MARATÓ de TV3 (201502 and 201516), Fundació Daniel Bravo Andreu, Sociedad Española de Cardiología, Societat Catalana de Cardiologia, Generalitat de Catalunya (SGR 2014), and Acadèmia de Ciències Mèdiques i de la Salut de Catalunya i de Balears. This work was also funded by the Red de Terapia Celular ‐ TerCel (RD12/0019/0029), Red de Investigación Cardiovascular ‐ RIC (RD12/0042/0047), and Fondo de Investigación Sanitaria, Instituto de Salud Carlos III (FIS PI14/01682) projects as part of the Plan Nacional de I+D+I and cofounded by ISCIII‐Sudirección General de Evaluación y el Fondo Europeo de Desarrollo Regional (FEDER).

## **Author details**

Santiago Roura1,2\*, Carolina Gálvez‐Montón1 , Josep Lupón3,4 and Antoni Bayes‐Genis1,3,4

\*Address all correspondence to: sroura@igtp.cat

1 ICREC Research Program, Germans Trias i Pujol Health Science Research Institute, Badalona, Spain

2 Center of Regenerative Medicine in Barcelona, Barcelona,Spain

3 Cardiology Service, Germans Trias i Pujol University Hospital, Badalona, Spain

4 Department of Medicine, Autonomous University of Barcelona, Barcelona, Spain

### **References**


of the cardiomyopathies: an American Heart Association Scientific Statement from the Council on Clinical Cardiology, Heart Failure and Transplantation Committee; Quality of Care and Outcomes Research and Functional Genomics and Translational Biology Interdisciplinary Working Groups; and Council on Epidemiology and Prevention. Circulation. 2006;113:1807‐1816.


summarized in the present review provides a starting point for addressing the remaining questions in the pathophysiology of this disease. Moreover, we highlight new avenues for

This work was supported by grants from the Ministerio de Educación y Ciencia (SAF2014‐59892), Fundació La MARATÓ de TV3 (201502 and 201516), Fundació Daniel Bravo Andreu, Sociedad Española de Cardiología, Societat Catalana de Cardiologia, Generalitat de Catalunya (SGR 2014), and Acadèmia de Ciències Mèdiques i de la Salut de Catalunya i de Balears. This work was also funded by the Red de Terapia Celular ‐ TerCel (RD12/0019/0029), Red de Investigación Cardiovascular ‐ RIC (RD12/0042/0047), and Fondo de Investigación Sanitaria, Instituto de Salud Carlos III (FIS PI14/01682) projects as part of the Plan Nacional de I+D+I and cofounded by ISCIII‐Sudirección General de Evaluación y el Fondo Europeo de

1 ICREC Research Program, Germans Trias i Pujol Health Science Research Institute, Badalona,

[2] Maron BJ, Towbin JA, Thiene G, Antzelevitch C, Corrado D, Arnett D, Moss AJ, Seidman CE, Young JB; American Heart Association; Council on Clinical Cardiology, Heart Failure and Transplantation Committee; Quality of Care and Outcomes Research and Functional Genomics and Translational Biology Interdisciplinary Working Groups; Council on Epidemiology and Prevention. Contemporary definitions and classification

3 Cardiology Service, Germans Trias i Pujol University Hospital, Badalona, Spain

4 Department of Medicine, Autonomous University of Barcelona, Barcelona, Spain

[1] Towbin JA, Bowles NE: The failing heart. Nature. 2002;415:227‐233.

, Josep Lupón3,4 and Antoni Bayes‐Genis1,3,4

discovering potentially effective treatments.

**Funding sources**

110 Cardiomyopathies - Types and Treatments

Desarrollo Regional (FEDER).

Santiago Roura1,2\*, Carolina Gálvez‐Montón1

\*Address all correspondence to: sroura@igtp.cat

2 Center of Regenerative Medicine in Barcelona, Barcelona,Spain

**Author details**

Spain

**References**


[30] Brutsaert DL, Meulemans AL, Sipido KR, Sys SU: Effects of damaging the endocardial surface on the mechanical performance of isolated cardiac muscle. Circ Res. 1988;62:358‐366.

[16] Kaya Z, Katus HA: Role of autoimmunity in dilated cardiomyopathy. Basic Res Cardiol.

[17] Bachelier‐Walenta K, Hilfiker‐Kleiner D, Sliwa K: Peripartum cardiomyopathy: update

[18] Roura S, Gálvez‐Montón C, Bayes‐Genis A: Umbilical cord blood‐derived mesenchy‐ mal stem cells: new therapeutic weapons for idiopathic dilated cardiomyopathy? Int J

[19] Limongelli G, Masarone D, D'Alessandro R, Elliott PM: Mitochondrial diseases and the heart: an overview of molecular basis, diagnosis, treatment and clinical course. Future

[20] Ai X, Pogwizd SM: Connexin 43 downregulation and dephosphorylation in nonische‐ mic heart failure is associated with enhanced colocalized protein phosphatase type 2A.

[21] Gottlieb RA, Engler RL: Apoptosis in myocardial ischemia‐reperfusion. Ann N Y Acad

[22] Saraste A, Pulkki K, Kallajoki M, Henriksen K, Parvinen M, Voipio‐Pulkki LM: Apoptosis in human acute myocardial infarction. Circulation. 1997;95:320‐323.

[23] Kytö V, Saraste A, Saukko P, Henn V, Pulkki K, Vuorinen T, Voipio‐Pulkki LM: Apop‐ totic cardiomyocyte death in fatal myocarditis. Am J Cardiol. 2004;94:746‐750.

[24] Schaper J, Lorenz‐Meyer S, Suzuki K: The role of apoptosis in dilated cardiomyopathy.

[25] Westphal E, Rohrbach S, Buerke M, Behr H, Darmer D, Silber RE, Werdan K, Loppnow H: Altered interleukin‐1 receptor antagonist and interleukin‐18 mRNA expression in myocardial tissues of patients with dilatated cardiomyopathy. Mol Med. 2008;14:55‐63.

[26] Bott‐Flügel L, Weig HJ, Uhlein H, Nabauer M, Laugwitz KL, Seyfarth M: Quantitative analysis of apoptotic markers in human end‐stage heart failure. Eur J Heart Fail.

[27] Kanoh M, Takemura G, Misao J, Hayakawa Y, Aoyama T, Nishigaki K, Noda T, Fujiwara T, Fukuda K, Minatoguchi S, Fujiwara H: Significance of myocytes with positive DNA in situ nick end‐labeling (TUNEL) in hearts with dilated cardiomyopathy: not apoptosis

[28] Narula J, Haider N, Virmani R, DiSalvo TG, Kolodgie FD, Hajjar RJ, Schmidt U, Semigran MJ, Dec GW, Khaw BA: Apoptosis in myocytes in end‐stage heart failure. N

[29] Harrison CV, Wood P: Hypertensive and ischaemic heart disease; a comparative clinical

but DNA repair. Circulation. 1999;99:2757‐2764.

and pathological study. Br Heart J. 1949;11:205‐229.

Engl J Med. 1996;335:1182‐1189.

2010;105:7‐8.

112 Cardiomyopathies - Types and Treatments

Cardiol. 2014;177:809‐818.

Cardiol. 2012;8:71‐88.

Circ Res. 2005;96:54‐63.

Sci. 1999;874:412‐426.

Herz. 1999;24:219‐224.

2008;10:129‐132.

2012. Curr Opin Crit Care. 2013;19:397‐403.


[53] Langlois B, Perrot G, Schneider C, Henriet P, Emonard H, Martiny L, Dedieu S: LRP‐1 promotes cancer cell invasion by supporting ERK and inhibiting JNK signaling pathways. PLoS One. 2010;5:e11584.

[41] Sharma S, Adrogue JV, Golfman L, Uray I, Lemm J, Youker K, Noon GP, Frazier OH, Taegtmeyer H: Intramyocardial lipid accumulation in the failing human heart resem‐

[42] Haq S, Choukroun G, Lim H, Tymitz KM, del Monte F, Gwathmey J, Grazette L, Michael A, Hajjar R, Force T, Molkentin JD: Differential activation of signal transduction pathways in human hearts with hypertrophy versus advanced heart failure. Circula‐

[43] Muchir A, Shan J, Bonne G, Lehnart SE, Worman HJ: Inhibition of extracellular signal‐ regulated kinase signaling to prevent cardiomyopathy caused by mutation in the gene

[44] Wu W, Muchir A, Shan J, Bonne G, Worman HJ: Mitogen‐activated protein kinase inhibitors improve heart function and prevent fibrosis in cardiomyopathy caused by

[45] Herz J, Strickland DK: LRP: a multifunctional scavenger and signaling receptor. J. Clin

[46] Cáceres LC, Bonacci GR, Sánchez MC, Chiabrando GA: Activated α(2) macroglobulin induces matrix metalloproteinase 9 expression by low‐density lipoprotein receptor‐ related protein 1 through MAPK‐ERK1/2 and NF‐kB activation in macrophage‐derived

[47] Huang W, Dolmer K, Liao X, Gettins PG: NMR solution structure of the receptor binding domain of human alpha(2)‐macroglobulin. J Biol Chem. 2000;275:1089‐1094.

[48] Lillis AP, Van Duyn LB, Murphy‐Ullrich JE, Strickland DK: LDL receptor‐related protein 1: unique tissue‐specific functions revealed by selective gene knockout studies.

[49] Franchini M, Montagnana M: Low‐density lipoprotein receptor‐related protein 1: new

[50] Boucher P, Liu P, Gotthardt M, Hiesberger T, Anderson RG, Herz J: Platelet‐derived growth factor mediates tyrosine phosphorylation of the cytoplasmic domain of the low density lipoprotein receptor‐related protein in caveolae. J Biol Chem.

[51] Loukinova E, Ranganathan S, Kuznetsov S, Gorlatova N, Migliorini MM, Loukinov D, Ulery PG, Mikhailenko I, Lawrence DA, Strickland DK: Platelet‐derived growth factor (PDGF)‐induced tyrosine phosphorylation of the low density lipoprotein receptor‐ related protein (LRP). Evidence for integrated co‐receptor function between LRP and

[52] van der Geer P: Phosphorylation of LRP‐1: regulation of transport and signal trans‐

functions for an old molecule. Clin Chem Lab Med. 2011;49:967‐970.

bles the lipotoxic rat heart. FASEB J. 2004;18:1692‐1700.

encoding A‐type lamins. Hum Mol Genet. 2009;18:241‐247.

mutation in lamin A/C gene. Circulation. 2011;123:53‐61.

cell lines. J Cell Biochem. 2010;111:607‐617.

the PDGF. J Biol Chem. 2002;18:15499‐15506.

duction. Trends Cardiovasc Med. 2002;12:160‐165.

tion. 2001;103:670‐677.

114 Cardiomyopathies - Types and Treatments

Invest. 2001;108:779‐784.

Physiol Rev. 2008;88:887‐918.

2002;277:15507‐15513.


#### **Cardiomyopathy Caused by Mutations in Nuclear A-Type Lamin Gene** Cardiomyopathy Caused by Mutations in Nuclear A-Type Lamin Gene

Gisèle Bonne and Antoine Muchir Gisèle Bonne and Antoine Muchir

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/65315

#### Abstract

[64] Sonnino S, Prinetti A: Membrane domains and the "lipid raft" concept. Curr Med Chem.

[65] Chiantia S, London E: Sphingolipids and membrane domains: recent advances. Handb

[67] Parton RG, Simons: The multiple faces of caveolae. Nat. Rev. Mol. Cell. Biol.

[68] Roura S, Cal R, Gálvez‐Montón C, Revuelta‐Lopez E, Nasarre L, Badimon L, Bayes‐ Genis A, Llorente‐Cortés V: Inverse relationship between raft LRP1 localization and non‐raft ERK1,2/MMP9 activation in idiopathic dilated cardiomyopathy: potential

[69] Fedak PW, Moravec CS, McCarthy PM, Altamentova SM, Wong AP, Skrtic M, Verma S, Weisel RD, Li RK. Altered expression of disintegrin metalloproteinases and their

[70] Sivakumar P, Gupta S, Sarkar S, Sen S: Upregulation of lysyl oxidase and MMPs during cardiac remodeling in human dilated cardiomyopathy. Mol Cell Biochem.

[71] Roura S, Gálvez‐Montón C, Pujal JM, Casani L, Fernández MA, Astier L, Gastelurrutia P, Domingo M, Prat‐Vidal C, Soler‐Botija C, Llucià‐Valldeperas A, Llorente‐Cortés V, Bayes‐Genis A: New insights into lipid raft function regulating myocardial vasculari‐ zation competency in human idiopathic dilated cardiomyopathy. Atherosclerosis.

[72] Roura S, Gálvez‐Montón C, Bayes‐Genis A. The challenges for cardiac vascular precursor cell therapy: lessons from a very elusive precursor. J Vasc Res.

[73] Insel PA, Patel HH: Membrane rafts and caveolae in cardiovascular signaling. Curr

[74] Tsutsumi YM, Kawaraguchi Y, Horikawa YT, Niesman IR, Kidd MW, Chin‐Lee B, Head BP, Patel PM, Roth DM, Patel HH: Role of caveolin‐3 and glucose transporter‐4 in isoflurane‐induced delayed cardiac protection. Anesthesiology. 2010;112:1136‐1145.

[75] Gazzerro E, Bonetto A, Minetti C. Caveolinopathies: translational implications of caveolin‐3 in skeletal and cardiac muscle disorders. Handb Clin Neurol.

[76] Hunter DJ: Gene‐environment interactions in human diseases. Nat Rev Genet.

[77] Craig J: Complex diseases: Research and applications. Nature Education. 2008;1:1.

inhibitor in human dilated cardiomyopathy. Circulation. 2006;113:238‐245.

impact in ventricular remodeling. Int J Cardiol. 2014;176:805‐814.

[66] Simons K, Ikonen E: Functional rafts in cell membranes. Nature. 1997;387:569‐572.

2013;20:4‐21.

116 Cardiomyopathies - Types and Treatments

2007;8:185‐194.

2008;307:159‐167.

2013;230:354‐364.

2013;50:304‐323.

2011;101:135‐142.

2005;6:287‐298.

Opin Nephrol Hypertens. 2009;18:50‐56.

Exp Pharmacol. 2013;215:33‐55.

Heart disease is a major cause of morbidity and premature mortality. Cardiomyopathy is an anatomic and pathologic condition associated with muscle and electrical dysfunction of the heart, often leading to heart failure–related disability. Dilated cardiomyopathy caused by mutations in A-type lamin gene (i.e., LMNA cardiomyopathy) is characterized by an increase in both myocardial mass and volume. The ventricular walls become thin and stretched, compromising cardiac contractility and ultimately resulting in poor left ventricular function. Despite current strategies to aggressively manage "LMNA cardiomyopathy," the disorder remains a common cause of heart failure with decreased ejection fraction, and a prevalent diagnosis in individuals is referred for cardiac transplantation. Despite progress in reducing "LMNA cardiomyopathy"–related mortality, hospitalizations remain very frequent and rates of readmission continue to rise. It appears important and necessary to further increase our knowledge on the pathophysiology of "LMNA cardiomyopathy" to unveil novel molecular/cellular mechanisms to target future therapeutic approaches.

Keywords: Dilated cardiomyopathy, Genetics, LMNA, A-type lamins, Nuclear lamina

### 1. Introduction

Cardiomyopathy, a major cause of morbidity and premature mortality in developed countries, is an anatomic and pathologic condition associated with muscle and electrical dysfunction of the heart, often leading to heart failure-related disability, which is a staggering clinical and public health problem. The mechanical component of the heart is liable for pumping blood throughout the body. The electric component, as for it, produces a rhythm for the blood to be pumped correctly. Hence, both components are tightly connected and regulated. Most common symptoms of dilated cardiomyopathy are shortness of breath, leg swelling, decreased exercise tolerance, fatigue, dizziness, coughing or wheezing, weight gain, and palpitation. Given the diversity in severity of symptoms in dilated cardiomyopathy, the disease is not

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© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

distribution, and eproduction in any medium, provided the original work is properly cited.

always diagnosed. Cardiomyopathies are a clinically heterogeneous group of cardiac muscle disorders [1]. Cardiomyopathies have historically been broken down into several major phenotypic categories. Dilated cardiomyopathy, the most common form, is a condition where the heart muscle becomes enlarged and weakened, resulting in poor left ventricular function. Despite current strategies to aggressively manage dilated cardiomyopathy, the disorder remains a common cause of heart failure with a decrease below 45% of ejection fraction and a referring for cardiac transplantation. Notwithstanding progress in reducing heart failurerelated mortality, hospitalizations for heart failure remain very frequent and rates of readmissions continue to rise. It appears important and necessary to increase our knowledge on the pathophysiology of cardiomyopathies to unveil novel molecular/cellular mechanisms for future therapeutic approaches.

### 2. Inherited cardiomyopathies

While the most common cardiomyopathies are secondary to acquired conditions, many are inherited. Genetic mutations have been identified in 25–35% of patients presenting dilated cardiomyopathy. These mutations affect genes that encode components of a wide variety of cellular compartments and pathways, including the nuclear envelope (e.g., LMNA, EMD), the contractile apparatus (e.g., MYH7, ACTC1, TPM1, TTN), the force transduction apparatus (e.g., MLP, DES, TNNT2), and calcium handling (e.g., SERCA). The cardiac cell is composed of a complex network of proteins linking the sarcomere to the sarcolemma and the extracellular matrix, providing structural support for subcellular structures and transmitting mechanical signals within and between cells (Figure 1). Mutations in genes encoding proteins of the sarcolemma are disrupting the anchoring and hence abrogate the transmission of the force

Figure 1. Cellular localizations of proteins involved in dilated cardiomyopathies.

generated by muscle contraction. Muscle contraction is due to the interaction between an actin filament and myosin heavy chain. Mutations in genes encoding contractile elements were identified as the cause of dilated cardiomyopathy. Functional units of striated muscle are called sarcomeres. Because the generated power of muscle contraction is transmitted to adjacent sarcomeres through the Z-disk, mutations in genes encoding proteins of the Z-disk causes also dilated cardiomyopathy. Part of hereditary dilated cardiomyopathies is caused by mutations in the genes encoding proteins of the nuclear envelope. Hence, disruption of the links from the sarcolemma to the sarcomere and nucleus could have a "domino effect," which leads to the disruption of systolic function and to the development of dilated cardiomyopathy.

### 3. LMNA cardiomyopathy

always diagnosed. Cardiomyopathies are a clinically heterogeneous group of cardiac muscle disorders [1]. Cardiomyopathies have historically been broken down into several major phenotypic categories. Dilated cardiomyopathy, the most common form, is a condition where the heart muscle becomes enlarged and weakened, resulting in poor left ventricular function. Despite current strategies to aggressively manage dilated cardiomyopathy, the disorder remains a common cause of heart failure with a decrease below 45% of ejection fraction and a referring for cardiac transplantation. Notwithstanding progress in reducing heart failurerelated mortality, hospitalizations for heart failure remain very frequent and rates of readmissions continue to rise. It appears important and necessary to increase our knowledge on the pathophysiology of cardiomyopathies to unveil novel molecular/cellular mechanisms

While the most common cardiomyopathies are secondary to acquired conditions, many are inherited. Genetic mutations have been identified in 25–35% of patients presenting dilated cardiomyopathy. These mutations affect genes that encode components of a wide variety of cellular compartments and pathways, including the nuclear envelope (e.g., LMNA, EMD), the contractile apparatus (e.g., MYH7, ACTC1, TPM1, TTN), the force transduction apparatus (e.g., MLP, DES, TNNT2), and calcium handling (e.g., SERCA). The cardiac cell is composed of a complex network of proteins linking the sarcomere to the sarcolemma and the extracellular matrix, providing structural support for subcellular structures and transmitting mechanical signals within and between cells (Figure 1). Mutations in genes encoding proteins of the sarcolemma are disrupting the anchoring and hence abrogate the transmission of the force

for future therapeutic approaches.

118 Cardiomyopathies - Types and Treatments

2. Inherited cardiomyopathies

Figure 1. Cellular localizations of proteins involved in dilated cardiomyopathies.

Among the causing genes of dilated cardiomyopathy, it has been estimated that mutations in LMNA, encoding nuclear lamin A/C [2], accounts for about 5–10% of familial dilated cardiomyopathy, thus representing one of the major causative genes. Affected patients often exhibit early conduction defects before left ventricle dysfunction and dilatation occur [3]. "LMNA cardiomyopathy" usually presents in early to mid-adulthood with symptomatic conduction system disease or arrhythmias or with symptomatic dilated cardiomyopathy (Figure 2A). "LMNA cardiomyopathy" has an intrusive clinical progression with higher rates of aggressive arrhythmias and faster course toward heart failure than most other cardiac diseases. Given the increased awareness among physicians, cardiologists are now facing difficult queries regarding patient management. These queries concern the use of defibrillators in order to avoid sudden death from aggressive ventricular arrhythmias and pharmacological interventions to improve heart failure symptoms. Once dilated cardiomyopathy is detected clinically, the management for "LMNA cardiomyopathy" follows the standard of care for heart failure. It is unclear whether early institution of these therapeutic agents prior to detectable cardiac dysfunction can modify the aggressive nature of "LMNA cardiomyopathy." There is no definitive treatment for the progressive cardiac dilatation and loss of contractility in "LMNA cardiomyopathy" short of heart transplantation [4].

### 4. A-type nuclear lamins

The LMNA gene, on chromosome 1q21.2-21.3, encodes nuclear A-type lamins. Lamin A and lamin C, the major somatic A-type lamins, arise via alternative splicing of pre-mRNA [5] (Figure 3A). Lamin A is primarily synthesized as a precursor, the prelamin A. Prelamin A has a particular C-terminal amino acid tail, which undergoes several enzymatic reactions to produce mature lamin A. Two other genes, LMNB1 and LMNB2, encode lamins B1 and B2, respectively. Lamins are class V intermediate filament proteins that polymerize to form the nuclear lamina (Figure 3B), a fibrous network underlining the inner nuclear membrane of most eukaryotic cells (Figure 3C) [6–8]. The nuclear lamina is bounded to the inner nuclear membrane via interactions with integral proteins and to the chromatin. It has also been shown that lamin A/C can also interact with the cytoskeleton, through the linker of nucleoskeleton and cytoskeleton ("LINC") complex [9]. One function of the lamina is to provide structural

Figure 2. Cardiac symptoms of "LMNA cardiomyopathy (A) and pathological mechanisms (B).

support to the nucleus. Nuclear lamins have also been implicated in processes such as chromatin organization, gene regulation, DNA replication, and RNA splicing [10]. However, the specific mechanistic roles of lamins in these processes, particularly in a cell- or tissue-type– specific context, remain obscure.

Figure 3. Nuclear lamins: structure (A), organization (B), and cellular localization (C). Modified from [10].

### 5. Pathogenesis

support to the nucleus. Nuclear lamins have also been implicated in processes such as chromatin organization, gene regulation, DNA replication, and RNA splicing [10]. However, the specific mechanistic roles of lamins in these processes, particularly in a cell- or tissue-type–

Figure 2. Cardiac symptoms of "LMNA cardiomyopathy (A) and pathological mechanisms (B).

specific context, remain obscure.

120 Cardiomyopathies - Types and Treatments

Identification of disease-causing mutations in the heart has contributed to the delineation of "LMNA cardiomyopathy." However, much work remains in elucidating the specific cellular mechanisms of the disease. Several hypotheses have been proposed attempting to link the pathophysiology of "LMNA cardiomyopathy" to known or emerging functions of lamin A/C. Among these functions include those based on that lamin A/C likely have in maintaining the mechanical integrity of cells subject to external and internal cues and signal transduction (i.e., the mechanical stress hypothesis). The "mechanical stress hypothesis" is attractive when trying to explain striated muscle diseases. It is based on the premise that the striated muscles are constantly subjected to mechanical forces and that mutations in "nucleocytoskeletal" support elements make them susceptible to damage from recurrent stress. Mouse models have been extremely helpful in deciphering crucial mechanisms, which could partially explain the pathogenesis of the disease. The development of Lmna−/<sup>−</sup> mice by Sullivan and colleagues was the first animal model of the disease [11]. Since, other models (knock-in and transgenic) have been created to study the cardiac dysfunction caused by LMNA mutation [12–15]. We and others reported an aberrant cardiac activation of signaling pathways in "LMNA cardiomyopathy" [16, 17] in mice and human, which participate to the development of contractile dysfunction (mitogen-activated protein kinase (MAPK) signaling, AKT/mTOR signaling, TGF-β signaling, etc.) [16, 18, 19] and electrical disturbances (connexin 43 remodeling, apoptosis, Hf1b expression) (Figure 2B).

MAPK signaling—One of the most prevalent and best-characterized responses to mechanical stress is the phosphorylation of proteins, which could be mediated by mitogen-activated protein kinase (MAPK) signaling pathway. Genes encoding proteins in MAPK signaling pathway demonstrated significantly altered expression in hearts of Lmna H222P mice by transcriptomic analysis [16]. We demonstrated an aberrant activation of ERK1/2, JNK, and p38α signaling, three main branches of MAPK signaling pathway involved in cellular mechanotransduction, in hearts from Lmna H222P mice, as early as 4 weeks of age [16, 17]. Our work proved that the activation of MAPK signaling pathway preceded the cardiac dysfunction of Lmna H222P mice and that it is a consequence of alterations in lamin A/C and not secondary to nonspecific effects. Accordingly, lamin A/C-deficient fibroblasts subjected to cyclic strain respond with decreased expression of the mechanosensitive genes, which are downstream targets of the MAPK pathway [20].

AKT/mTOR signaling—We showed that the Lmna pH222P mutation results in aberrant activation of the AKT/mTOR signaling cascade, downstream of the MAPK pathway [18]. Given that activated mTOR inhibits autophagic responses and reduces tolerance to energy deficits, the heart is therefore unable to compensate for increased energy demand and, over time, develops muscle damage and dilated cardiomyopathy.

TGF-β signaling—Cardiac fibrosis exacerbates the clinical progression of heart failure. We showed that Lmna H222P mice had elevated expression of TGF-β signaling as early as 12 weeks of age, which is a time that preceded development of both cardiac fibrosis and the onset of overt cardiac dysfunction [13, 19]. Our observations indicate that TGF-β is a mediator of the cardiomyopathy that develops as a result of LMNA mutations.

Connexin 43 remodeling—Gap junction communications describe the electrical coupling of cells through specialized cell contacts called gap junctions. In adult heart, connexin 43 is expressed in the atrial and ventricular working (contractile) myocardium. The working cardiomyocytes of the ventricle are extensively interconnected by clusters of connexin 43 located at the intercalated disks. The intercalated disks of working ventricular myocardium have a step-like configuration, with the gap junctions situated predominantly in the "horizontal" facing segments of these steps rather than the vertical segments [21, 22]. Features of gap junction organization encourage preferential propagation of the impulse in the longitudinal axis, thus contributing to the normal pattern of anisotropic spread of the impulse of healthy ventricular myocardium. The most striking form of structural remodeling connexin 43 is typically scattered in disordered fashion over the lateral surfaces in the heart from Lmna N195K mice (i.e., lateralization) [12].

Apoptosis—Apoptosis in all metazoan cells is mediated by caspases, a multigene family of cysteine proteases that hydrolyzes peptide bonds carboxyl to aspartic acid residues. Once activated, caspases cut cellular proteins, leading to the apoptotic demise of the cell. During the past few years, there has been accumulating evidence in both human and animal models suggesting that apoptosis may be an important mode of cell death during heart failure [23]. Myocyte apoptosis has been reported in the atrioventricular tissue from Lmna+/<sup>−</sup> mice [24], which could account for the evolution of electrophysiologic dysfunction.

Hf1b/Sp4—This transcription factor has been described as important for the development of the cardiac conduction system [25]. Mounkes and colleagues found that expression and localization of Hf1b/Sp4 were altered in the heart from Lmna N195K mice [12]. Strikingly, this study reported that Hf1b/Sp4 was not found in the ventricles and was strongly expressed in the atria in the heart from Lmna N195K mice, which mirror the localization in control animals. This finding needs further analysis.

The exact mechanisms by which defects in nuclear lamins cause dysregulated signaling remain to be elucidated.

### 6. Treatments

pathophysiology of "LMNA cardiomyopathy" to known or emerging functions of lamin A/C. Among these functions include those based on that lamin A/C likely have in maintaining the mechanical integrity of cells subject to external and internal cues and signal transduction (i.e., the mechanical stress hypothesis). The "mechanical stress hypothesis" is attractive when trying to explain striated muscle diseases. It is based on the premise that the striated muscles are constantly subjected to mechanical forces and that mutations in "nucleocytoskeletal" support elements make them susceptible to damage from recurrent stress. Mouse models have been extremely helpful in deciphering crucial mechanisms, which could partially explain the pathogenesis of the disease. The development of Lmna−/<sup>−</sup> mice by Sullivan and colleagues was the first animal model of the disease [11]. Since, other models (knock-in and transgenic) have been created to study the cardiac dysfunction caused by LMNA mutation [12–15]. We and others reported an aberrant cardiac activation of signaling pathways in "LMNA cardiomyopathy" [16, 17] in mice and human, which participate to the development of contractile dysfunction (mitogen-activated protein kinase (MAPK) signaling, AKT/mTOR signaling, TGF-β signaling, etc.) [16, 18, 19] and electrical disturbances (connexin 43 remodeling, apoptosis, Hf1b expres-

MAPK signaling—One of the most prevalent and best-characterized responses to mechanical stress is the phosphorylation of proteins, which could be mediated by mitogen-activated protein kinase (MAPK) signaling pathway. Genes encoding proteins in MAPK signaling pathway demonstrated significantly altered expression in hearts of Lmna H222P mice by transcriptomic analysis [16]. We demonstrated an aberrant activation of ERK1/2, JNK, and p38α signaling, three main branches of MAPK signaling pathway involved in cellular mechanotransduction, in hearts from Lmna H222P mice, as early as 4 weeks of age [16, 17]. Our work proved that the activation of MAPK signaling pathway preceded the cardiac dysfunction of Lmna H222P mice and that it is a consequence of alterations in lamin A/C and not secondary to nonspecific effects. Accordingly, lamin A/C-deficient fibroblasts subjected to cyclic strain respond with decreased expression of the mechanosensitive genes, which are

AKT/mTOR signaling—We showed that the Lmna pH222P mutation results in aberrant activation of the AKT/mTOR signaling cascade, downstream of the MAPK pathway [18]. Given that activated mTOR inhibits autophagic responses and reduces tolerance to energy deficits, the heart is therefore unable to compensate for increased energy demand and, over time,

TGF-β signaling—Cardiac fibrosis exacerbates the clinical progression of heart failure. We showed that Lmna H222P mice had elevated expression of TGF-β signaling as early as 12 weeks of age, which is a time that preceded development of both cardiac fibrosis and the onset of overt cardiac dysfunction [13, 19]. Our observations indicate that TGF-β is a mediator of the

Connexin 43 remodeling—Gap junction communications describe the electrical coupling of cells through specialized cell contacts called gap junctions. In adult heart, connexin 43 is expressed in the atrial and ventricular working (contractile) myocardium. The working cardiomyocytes of the ventricle are extensively interconnected by clusters of connexin 43 located at the

sion) (Figure 2B).

122 Cardiomyopathies - Types and Treatments

downstream targets of the MAPK pathway [20].

develops muscle damage and dilated cardiomyopathy.

cardiomyopathy that develops as a result of LMNA mutations.

Advances in molecular techniques have improved the understanding of mechanisms responsible for cardiac dysfunction in "LMNA cardiomyopathy." It is clear that mutations in nuclear lamin A/C in cardiomyocytes can perturb cardiac function. Alterations in cardiomyocyte function initiate cascades of cellular responses that attempt to compensate for these insults. However, persistent responses at the cellular level lead to organ-wide alterations, which correlated with sudden cardiac death and heart failure. Although there exists no treatment to directly address the causes of "LMNA cardiomyopathy," basic studies of the processes that mediate cellular responses to cardiac stress have allowed the development of innovative treatments that address the reduction of symptoms that include drugs that decrease blood pressure (ACE inhibitors, angiotensin II receptor blockers, beta-blockers) and heart rate (betablockers, calcium channel blockers, digoxin) to reduce the strain on the ventricular walls. Utilization of animal and cellular models to further dissect the mechanisms of "LMNA cardiomyopathy" and demonstrate efficacy of drugs that specifically target disease-causing pathways holds promise that further reduction in the mortality associated with "LMNA cardiomyopathy" can be achieved [17–19, 26, 27].

### 7. Conclusion

In the past decade, there has been an extraordinary burst of researches on lamin A/C and the nuclear lamina, which has been accelerated by attempts to explain the pathogenesis of "LMNA cardiomyopathy." One important unanswered question is how mutations in genes expressed in most differentiated somatic cells lead to human disease affecting the cardiac tissue. Within the next several years, we will likely have more clues to answer this question, and these answers will hopefully lead to new ways to treat or prevent "LMNA cardiomyopathy."

### Author details

Gisèle Bonne and Antoine Muchir\*

\*Address all correspondence to: a.muchir@institut-myologie.org

Center of Research in Myology, Paris, France

### References


[6] Fisher DZ, Chaudhary N, Blobel G: cDNA sequencing of nuclear lamins A and C reveals primary and secondary structural homology to intermediate filament proteins. Proc Natl Acad Sci U S A 1986;83:6450–6454.

7. Conclusion

124 Cardiomyopathies - Types and Treatments

Author details

References

Gisèle Bonne and Antoine Muchir\*

Center of Research in Myology, Paris, France

\*Address all correspondence to: a.muchir@institut-myologie.org

DOI: 10.1161/CIRCULATIONAHA.106.174287

1724. DOI: 10.1056/NEJM199912023412302

and nuclear lamin C. J Biol Chem. 1993;268:16321–16326.

210. DOI: 10.1056/NEJMc052632

athy."

In the past decade, there has been an extraordinary burst of researches on lamin A/C and the nuclear lamina, which has been accelerated by attempts to explain the pathogenesis of "LMNA cardiomyopathy." One important unanswered question is how mutations in genes expressed in most differentiated somatic cells lead to human disease affecting the cardiac tissue. Within the next several years, we will likely have more clues to answer this question, and these answers will hopefully lead to new ways to treat or prevent "LMNA cardiomyop-

[1] Maron BJ, Towbin JA, Thiene G, Antzelevitch C, Corrado D, Arnett D, Moss AJ, Seidman CE, Young JB: Contemporary definitions and classification of the cardiomyopathies: an American Heart Association Scientific Statement from the Council on Clinical Cardiology, Heart Failure and Transplantation Committee; Quality of Care and Outcomes Research and Functional Genomics and Translational Biology Interdisciplinary Working Groups; and Council on Epidemiology and Prevention. Circulation. 2006;113:1807–1816.

[2] Fatkin D, MacRae C, Sasaki T, Wolff MR, Porcu M, Frenneaux M, Atherton J, Vidaillet HJ Jr, Spudich S, De Girolami U, Seidman JG, Seidman C, Muntoni F, Müehle G, Johnson W, McDonough B: Missense mutation in the rod domain of he lamin A/C gene as cause of dilated cardiomyopathy and conduction-system disease. N Engl J Med. 1999;341:1715–

[3] Meune C, Van Berlo JH, Anselme F, Bonne G, Pinto YM, Duboc D: Primary prevention of sudden death in patients with lamin A/C gene mutations. N Engl J Med. 2006;354:209–

[4] Ben Yaou R, Gueneau L, Demay L, Stora S, Chikaoui K, Richard P, Bonne G: Heart involvement in lamin A/C related diseases. Arch Mal Coeur Vaiss. 2006;99:848–855. [5] Lin F, Worman HJ: Structural organization of the human gene encoding nuclear lamin A


by mutation in the lamin A/C gene. Cardiovasc Res. 2012;93:311–319. DOI: 10.1093/cvr/ cvr301


### **Arrhythmogenic Right Ventricular Cardiomyopathy/ Dysplasia Arrhythmogenic Right Ventricular Cardiomyopathy/ Dysplasia**

Bandar Al‐Ghamdi Bandar Al‐Ghamdi

by mutation in the lamin A/C gene. Cardiovasc Res. 2012;93:311–319. DOI: 10.1093/cvr/

[18] Choi JC, Muchir A, Wu W, Iwata S, Homma S, Morrow JP, Worman HJ: Temsirolimus activates autophagy and ameliorates cardiomyopathy caused by lamin A/C gene muta-

[19] Chatzifrangkeskou M, Le Dour C, Wu W, Morrow JP, Joseph LC, Beuvin M, Sera F, Homma S, Vignier N, Mougenot N, Bonne G, Lipson KE, Worman HJ, Muchir A: ERK1/ 2 directly acts on CTGF/CCN2 expression to mediate myocardial fibrosis in cardiomyopathy caused by mutation in the lamin A/C gene. Hum Mol Genet. 2016;ddw090. DOI:

[20] Lammerding J, Schulze PC, Takahashi T, Kozlov S, Sullivan T, Kamm RD, Stewart CL, Lee RT: Lamin A/C deficiency causes defective nuclear mechanics and mechanotransduction.

[21] Severs NJ: Gap junction shape and orientation at the cardiac intercalated disk. Circ Res.

[22] Severs NJ: The cardiac gap junction and intercalated disc. Int J Cardiol. 1990;26:137–173. [23] Kang PM, Izumo S: Apoptosis and heart failure: a critical review of the literature. Circ

[24] Wolf CM, Wang L, Alcalai R, Pizard A, Burgon PG, Ahmad F, Sherwood M, Branco DM, Wakimoto H, Fishman GI, See V, Stewart CL, Conner DA, Berul CI, Seidman CE, Seidman JG: Lamin A/C haploinsufficiency causes dilated cardiomyopathy and apoptosis-triggered cardiac conduction system disease. J Mol Cell Cardiol. 2008;44:293–303.

[25] Nguyen-Tran VT, Kubalak SW, Minamisawa S, Fiset C, Wollert KC, Brown AB, Ruiz-Lozano P, Barrere-Lemaire S, Kondo R, Norman LW, Gourdie RG, Rahme MM, Feld GK, Clark RB, Giles WR, Chien KR: A novel genetic pathway for sudden cardiac death via defects in the transition between ventricular and conduction system cell lineages. Cell

[26] Muchir A, Shan J, Bonne G, Lehnart SE, Worman HJ: Inhibition of extracellular signalregulated kinase signaling to prevent cardiomyopathy caused by mutation in the gene encoding A-type lamins. Hum Mol Genet. 2009;18:241–247. DOI: 10.1093/hmg/ddn343

[27] Wu W, Muchir A, Shan J, Bonne G, Worman HJ: Mitogen activated protein kinase inhibitors improve heart function and prevent fibrosis in cardiomyopathy caused by lamin A/C gene mutation. Circulation 2011;123:53–61. DOI: 10.1161/CIRCULATIONAHA.110.

tion. Sci Transl Med. 2012;4:144ra102. DOI: 10.1126/scitranslmed.3003875

J Clin Invest. 2004;113:370–378. DOI: 10.1172/JCI19670

cvr301

126 Cardiomyopathies - Types and Treatments

10.1093/hmg/ddw090

1989;65:1458–1461.

Res. 2000;86:1107–1113.

2000;102:671–682.

970673

DOI: 10.1016/j.yjmcc.2007.11.008

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/65316

#### **Abstract**

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a rare disease characterized by progressive fibrofatty replacement of the myocardium, primarily involving the right ventricle (RV). The structural changes in the ventricular myocardium form a substrate for ventricular arrhythmia ranging from premature ventricular complexes to ventricular tachycardia typically of RV origin and may result in RV failure and progress to congestive heart failure at a later stage. ARVC/D is a recognized cause of sudden cardiac death in young people, but it may occur at any age. With the discovery of underlying pathogenic mutations involved in the disease development and insight from long‐term follow‐up of ARVC/D patients, ARVC/D is an inherited cardiomyopathy. Mutations in at least eight genes have been involved in ARVC/D genesis in 30–50% of patients. Most of these genes are involved in the function of desmosomes, which are structures that attach heart muscle cells to one another. Desmosomes provide strength to the myocardium and play a role in signaling between neighboring cells. Mutations in the genes responsible for ARVC/D often impair the normal desmosomal function. There has been significant advancement in the diagnosis and management of ARVC/D in the past few decades. This chapter provides an overview of ARVC/D pathophysiology, clinical presentations, diagnosis, and manage‐ ment.

**Keywords:** cardiomyopathy, arrhythmia, right ventricle, sudden cardiac death, heart failure

### **1. Introduction**

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a rare disease characterized by progressive fibrofatty replacement of the myocardium, primarily involving the right ventricle (RV) [1–4].

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The typical age of presentation is between the second and the fourth decade of life. The structural changes in the ventricular myocardium form a substrate for ventricular arrhythmia ranging from premature ventricular complexes (PVCs) to ventricular tachycardia (VT), typically of RV origin and may result in RV failure, and progress to congestive heart failure at a later stage. ARVC/D is a recognized cause of sudden cardiac death (SCD) in young individ‐ uals, but it may occur at any age [4].

ARVC/D was first described by Frank et al. [1], and the first clinical profile of the disease was published in 1982 [2]. It was described as a disease in which "the right ventricular musculature is partially or totally absent and is replaced by fatty and fibrous tissue [2]." With the discovery of underlying pathogenic mutations involved in the disease development and insight from long‐term follow‐up of ARVC/D patients, the ARVC/D is currently considered to be an inherited cardiomyopathy [4–6]. However, the presence of sporadic cases of ARVC/D in‐ creased the possibility of nongenetic causes.

Mutations in at least eight genes have been involved in the ARVC/D genesis in 30–50% patients. Most of these genes are involved in the function of desmosomes, which are structures that attach heart muscle to one another. Desmosomes provide strength to the myocardium and also play a role in signaling between neighboring cells. Mutations in the genes responsible for ARVC/D often impair the normal desmosomal function. This results in cells of the myocardium detaching from one another and dying (apoptosis). They are then replaced with fibrous and fibrofatty tissue. The apoptosis occurs predominantly when the heart muscle is placed under stress (such as during vigorous exercise). Most of these gene code for desmosome proteins plakoglobin (JUP), desmoplakin (DSP), plakophilin‐2 (PKP2), the desmoglein‐2 (DSG2), and desmocollin‐2 (DSC2)—and other genes that code for nondesmosomal protein (e.g., RYR2 and TMEM43) have also been associated with ARVC/D [7]. Additionally, an autosomal recessive variant of ARVC/D has been described. The first disease‐causing gene, encoding the desmo‐ somal protein plakoglobin (JUP), was identified in patients with Naxos disease and is an autosomal recessive variant of ARVC/D. It was first reported from the Greek island of Naxos and is associated with palmoplantar keratoderma and wooly hair [8]. Another recessive mutation of DSP has been reported and associated with Carvajal syndrome, another cardio‐ cutaneous disease [9].

In the past few decades, there has been a significant improvement in our understanding of this disease pathogenesis, natural course, diagnosis, and management.

This chapter provides an overview of ARVC/D pathophysiology, clinical presentations, diagnosis, and management.

### **2. Epidemiology**

The estimated prevalence of ARVC/D in the general population ranges from 1 in 2000 to 1 in 5000 individuals; men are more frequently affected than women, with an approximate ratio of 3:1 [10, 11].

The median age at onset of the disease is about 30 years, whereas it rarely manifests before the age of 12 or after the age of 60 years [12, 13]. ARVC/D is a leading cause of sudden cardiac death (SCD) accounting for 11–22% of cases of SCD in the young athlete patient population 8 [13–15]. However, this varies based on the geographic area as it accounts for approximately 22% of SCD cases in athletes in northern Italy [5] and about 17% of SCD in young people in the United States [16]. The genes involved and different mode of inheritance may explain the ARVC/D ethnic variations [17]. The most prevalent mode of inheritance of ARVC/D is an autosomal dominant; however, autosomal recessive form has also been described such as Naxos disease. This disease was first described in Naxos Island, Greece, and it is associated with cutaneous manifestations such as palmoplantar keratosis [8]. Although there are no genetic studies in ARVC/D Chinese patients, some studies showed a lower familial incidence of premature SCD among these patients [18].
