**4. Conclusion**

256 Endometriosis - Basic Concepts and Current Research Trends

reduced angiogenesis *per se*. However, overexpression of the enzymatically inactive, dominant-negative ISG20 mutant inhibited angiogenesis in this system and potentiated the anti-angiogenic properties of interferon. How ISG20 might be involved in angiogenesis is

The ISG20 protein mediates antiviral effects of interferons by inhibiting the replication of several RNA viruses, like vesicular stomatitis virus, influenza virus, encephalomyocarditis virus, West Nile virus, Dengue virus, hepatitis A and C viruses, yellow fever virus, and bovine viral diarrhea virus (Zhou et al., 2011). The antiviral activity of ISG20 is only observed with enzymatically active ISG20 expression, since expression of an ISG20 mutant

Importantly, ISG20 mRNA was found to be up-regulated in the uterine epithelium during the implantation window in mouse (Pan et al., 2006). Whether abolished ISG20 enzyme activity is implicated in the pathogenesis of endometriosis or a marker of altered hormonal

The HOX proteins encoded by the homeobox genes are DNA binding transcription factors known to regulate embryonic development. In addition, the *HOX* genes are dynamically expressed in the endometrium during the menstrual cycle, where they are necessary for endometrial growth, differentiation, and implantation (Cakmak & Taylor, 2010; Zanatta et al., 2010). Furthermore, HOX proteins are molecular mediators of the steroid hormones

It has been suggested that a HOX gene-related defect in endometrial development exists in patients with endometriosis (Zanatta et al., 2010). According to this theory, endometriosis might originate from estrogen stimulated metaplasia of mesenchymal embryonic cells distributed in the pelvis during organogenesis. However, transcriptional dysregulation of the HOX genes in the adult endometrium compatible with the more well-supported retrograde menstruation pathogenesis model is also well substantiated. Recently, a systematic dysregulation of *HOX* genes in the endometrium from healthy women compared with the endometrium in women with endometriosis has been demonstrated (Borghese et al., 2008). A down-regulation of *HOXA* and *HOXB* genes and an up-regulation of HOXC genes were found in endometrium from women with endometriosis compared with

The HOXA10 protein is up-regulated in response to circulating estrogen and progesterone in the healthy endometrium, thus indicating a role in endometrial maturation, implantation and maintenance of pregnancy implantation (Cakmak & Taylor, 2010; Zanatta et al., 2010). *HOXA10* transcription is normally up-regulated in the endometrium during the window of implantation but this up-regulation is abolished in women with endometriosis. Low levels of HOXA10 could explain the lower fertility of women with endometriosis, and this is further supported by studies of the HOXA10 knock-out mice, in which the targeted disruption of the *HOXA10* gene generated uterine factor infertility. Also in the endometriotic tissue, the HOXA10 transcriptional levels were found to be low

without enzymatic activity, did not possess the same antiviral activities.

expression, or both, needs to be further investigated.

currently not clear.

**3.2 The HOX proteins** 

during endometrial cell development.

endometrium from healthy women.

The pathogenesis and the similarity to cancer invasiveness suggested that a viral background could be part of the pathogenesis of endometriosis, but so far no investigations have demonstrated this connection in the aetiology. The prevalence of pathogenic dsDNA viruses in the human endometrium was found to be generally low (0-10%), and nothing points towards any evidence that endometriosis is caused by currently known DNA viruses (Oppelt et al., 2010; Vestergaard et al., 2010). It can be speculated that the endometrium and endometriotic tissue is difficult to access or simply an unfavorable environment for virus progression, leading to a generally low prevalence in these deeper tissues. It is possible that viruses can infect the endometrium transiently but subsequently be either shed with the endometrial tissue during menstruation or be rapidly cleared by an efficient immune response. Thus stable infections of the endometrium would not be frequent. However, a pathogenic virus could theoretically initiate a malignant cell process during a shorter infectious period and then flee the scene. This "hit-and-run" strategy has been previously shown *e.g.* for CMV *in vitro* and indicated in clinical studies of both polyomaviruses and papillomaviruses (see Vestergaard et al., 2010). This could explain why no virus DNA so far has been found associated with endometriosis lesions.

To address the viral "hit-and-run" strategy hypothesis, one could analyse for an elevated level of serum antibodies against the viruses, which would then show previous viral infections. Even though a broad selection of the most common pathogenic DNA viruses have been tested for, other more rare or even undiscovered viruses or bacteria might still be involved. Conclusively, the prevalence of pathogenic DNA viruses in the endometrium

Virus Infection and Type I Interferon in Endometriosis 259

Acién, P., Quereda, F., Campos, A., Gomez-Torres, M.-J., Velasco, I., & Gutierrez, M. (2002).

Boimel, P. J., Cruz, C., & Segall, J. E. (2011). A functional in vivo screen for regulators of

cancer. *Genomics*, Vol. 98, No. 3, (September 2011), pp. 164-172, 0888-7543 Bondza, P. K., Maheux, R., & Akuom, A. (2009). Insights into endometriosis-associated

Borghese, B., Mondon, F., Noel, J.-C., Fayt, I., Mignot, T.-M., Vaiman, D., & Chapron, C.

Brown, H. L., & Abernathy, M. P. (1998). Cytomegalovirus infection. *Semin Perinatol*, Vol. 22,

Bulun, S. E. (2009). Endometriosis. *N Engl J Med*, Vol. 360, No. 3, (January 2009), pp. 268-279,

Cakmak, H., & Taylor, H. S. (2010). Molecular Mechanisms of Treatment Resistance in

Dolcetti, R., & Masucci, M. G. (2003). Epstein-Barr virus: induction and control of cell

Fang, C.-L., Han, S.-P., Fu, S.-L., Wang, W., Kong, N., & Wang, X.-L. (2009). Ectopic,

Faquhar, C. (2007). Endometriosis. *BMJ*, Vol. 334, No. 7587, (February 2007), pp. 249-253,

Haber, E., Danenberg, H. D., Koroukhov, N., Ron-El, R., Golomb, G., & Schachter, M. (2009).

Haider, S., & Knöfler, M. (2009). Human Tumour Necrosis Factor: Physiological and

Hall, J. C., & Rosen, A. (2010). Type I interferons: crucial participants in disease

Hu, L., Hornung, D., Kurek, R., Ostman, H., Blomberg, J., & Bergqvist, A. (2006). Expression

(October 2002), pp. 705-711, 0015-0282

11, (November 2008), pp. 2557-2562, 0888-8809

Vol. 28, No. 1, (January 2010), pp. 69-74, 1526-8004

No. 4, (August 1997), pp. 260-6, 0146-0005

1, (March 2009), pp. 55-60, 0301-2115

pp. 415-428, 1093-0046

0028-4793

9541

0959-8138

398-407, 0268-1161

40-49, 1759-4790

2009), pp. 111-123, 0143-4004

Use of intraperitoneal interferon α-2b therapy after conservative surgery for endometriosis and postoperative medical treatment with depot gonadotropinreleasing hormone analog: a randomized clinical trial. *Fertil Steril*, Vol. 78, No. 4,

tumor progression identifies HOXB2 as a regulator of tumor growth in breast

endometrial dysfunction: a review. *Frontiers in Bioscience*, Vol. 1, No. -, (June 2009),

(2008). Gene Expression Profile for Ectopic Versus Eutopic Endometrium Provides New Insights into Endometriosis Oncogenic Potential. *Mol Endocrinol*, Vol. 22, No.

Endometriosis: The Role of Progesterone-Hox Gene Interactions. *Semin Reprod Med*,

transformation. *J Cell Physiol*, Vol. 196, No. 2, (August 2003), pp. 207-18, 0021-

autologous eutopic and normal endometrial stromal cells have altered expression and chemotactic activity of RANTES. *Eur J Obstet Gynecol Reprod Biol*, Vol. 143, No.

Peritoneal macrophage depletion by liposomal bisphosphonate attenuates endometriosis in the rat model. *Hum Reprod*, Vol. 24, No. 2, (February 2009), pp.

Pathological Roles in Placenta and Endometrium. *Placenta*, Vol. 30, No. 2, (February

amplification in autoimmunity. *Nat Rev Rheumatol*, Vol. 6, No. 1, (January 2010), pp.

of Human Endogenous Gammaretroviral Sequences in Endometriosis and Ovarian

**5. References** 

and endometriosis lesions is very low and does not indicate a virological cause of endometriosis. However, the existence of a causative infectious agent can still not be ruled out at this point.

The altered expression of a large number of genes has been reported in endometriosis (Kao et al., 2003; Matsuzaki et al., 2006), an imbalance mediated by altered levels of a number of signaling molecules as well as by epigenetic alterations. Dysregulation of a large number of hormones, cytokines, chemokines, and growth factors is a feature of endometriosis. The abolished expression of *HOXA10*, *HOXB2* and *ISG20* in the endometriosis tissue seems to be influenced by a number of these factors, which regulate gene transcription via complex, overlapping mechanisms, possibly in combination with the action of estrogen and progesterone. The observed abolishment of *ISG20* and *HOXB2* expression in endometriosis lesions indicates that they fail to be induced by estrogen. The altered ERα/ERβ ratio in endometriosis could be important in this mechanism. The lack of *HOXA10* expression in the endometrium as well as in endometriotic lesions is probably due to epigenetic changes in the gene promoter, resulting in abolished response to estrogen and progesterone. Moreover, the expression of other *HOX* genes in endometriosis might shed a light on the function of this family of proteins in the development of this disease.

As the aetiology of endometriosis is unknown, and as several factors are thought to influence the course of the disease, the pathogenesis of endometriosis is still a challenge. One of the main problems is the lack of a non-invasive test to diagnose endometriosis. Several markers have been investigated. The best known is CA125, which is not specific to endometriosis but frequently also elevated in cancer. CA125 is often elevated in endometriosis, and the level is to some extend related to the degree of the infiltration in active endometriosis. However, the CA125 levels are individual, and change in intensity of pain or other symptoms related to endometriosis are not automatically reflected in the level. Therefore, the identification of a non-invasive marker able to diagnose endometriosis would be of great importance. Furthermore, if this marker could indicate changes in disease intensity this would be a great help both for the patient and the doctor. The success of different treatments could also be measured more objectively e.g. by an independent marker. So far hormonal treatment is the first line of treatment, and if pain cannot be resolved by medication, surgery may be performed. However, the endometriosis often reoccurs and more operations are needed, thus bringing the risk of complications.

As clarified in this chapter, many possibilities for causative or aetiological mechanism for the pathogenesis of endometriosis are in focus. If the aetiology of endometriosis is to be found related to virus, we can probably in the future prevent the disease or at least weaken the intensity. A marker for the disease based on virus aetiology would most likely be possible to develop, and the development of a specific treatment could be feasible. If HOX genes and/or ISG20 are involved in the aetiology of endometriosis, this would also give possibilities for new diagnostic tools and medical treatments.

In conclusion, the possible involvement of viruses, type I IFNs, and the innate immune system in the pathogenesis of endometriosis is yet unclear. More investigations are needed in order to resolve the riddle of endometriosis.

#### **5. References**

258 Endometriosis - Basic Concepts and Current Research Trends

and endometriosis lesions is very low and does not indicate a virological cause of endometriosis. However, the existence of a causative infectious agent can still not be ruled

The altered expression of a large number of genes has been reported in endometriosis (Kao et al., 2003; Matsuzaki et al., 2006), an imbalance mediated by altered levels of a number of signaling molecules as well as by epigenetic alterations. Dysregulation of a large number of hormones, cytokines, chemokines, and growth factors is a feature of endometriosis. The abolished expression of *HOXA10*, *HOXB2* and *ISG20* in the endometriosis tissue seems to be influenced by a number of these factors, which regulate gene transcription via complex, overlapping mechanisms, possibly in combination with the action of estrogen and progesterone. The observed abolishment of *ISG20* and *HOXB2* expression in endometriosis lesions indicates that they fail to be induced by estrogen. The altered ERα/ERβ ratio in endometriosis could be important in this mechanism. The lack of *HOXA10* expression in the endometrium as well as in endometriotic lesions is probably due to epigenetic changes in the gene promoter, resulting in abolished response to estrogen and progesterone. Moreover, the expression of other *HOX* genes in endometriosis might shed a light on the function of

As the aetiology of endometriosis is unknown, and as several factors are thought to influence the course of the disease, the pathogenesis of endometriosis is still a challenge. One of the main problems is the lack of a non-invasive test to diagnose endometriosis. Several markers have been investigated. The best known is CA125, which is not specific to endometriosis but frequently also elevated in cancer. CA125 is often elevated in endometriosis, and the level is to some extend related to the degree of the infiltration in active endometriosis. However, the CA125 levels are individual, and change in intensity of pain or other symptoms related to endometriosis are not automatically reflected in the level. Therefore, the identification of a non-invasive marker able to diagnose endometriosis would be of great importance. Furthermore, if this marker could indicate changes in disease intensity this would be a great help both for the patient and the doctor. The success of different treatments could also be measured more objectively e.g. by an independent marker. So far hormonal treatment is the first line of treatment, and if pain cannot be resolved by medication, surgery may be performed. However, the endometriosis often reoccurs and more operations are needed, thus bringing the risk of

As clarified in this chapter, many possibilities for causative or aetiological mechanism for the pathogenesis of endometriosis are in focus. If the aetiology of endometriosis is to be found related to virus, we can probably in the future prevent the disease or at least weaken the intensity. A marker for the disease based on virus aetiology would most likely be possible to develop, and the development of a specific treatment could be feasible. If HOX genes and/or ISG20 are involved in the aetiology of endometriosis, this would also give

In conclusion, the possible involvement of viruses, type I IFNs, and the innate immune system in the pathogenesis of endometriosis is yet unclear. More investigations are needed

this family of proteins in the development of this disease.

possibilities for new diagnostic tools and medical treatments.

in order to resolve the riddle of endometriosis.

out at this point.

complications.


Virus Infection and Type I Interferon in Endometriosis 261

Osuga, Y., Koga, K., Hirota, Y., Hirata, T., Yaoshino, O., & Taketani, Y. (2011). Lymphocytes

Pan, H., Zhu, L., Deng, Y., & Pollard, J. (2006). Microarray analysis of uterine epithelial gene

Platanias, L. C. (2005). Mechanisms of type-I- and type-II-interferon-mediated signalling.

Prober, C. G. (2011). Human Herpesvirus 6, In *Hot Topics in Infection and Immunity in* 

Simpson, J. L., Eklias, S., Malinak, L. R., & Buttram, V. C., Jr. (1980). Heritable aspects of

Taylor, K. L., Leaman, D. W., Grane, R., Mechti, N., Borden, E. C., & Lindner, D. J. (2008).

Vestergaard, A. L., Knudsen, U. B., Munk, T., Rosbach, H., & Martensen, P. M. (2011).

Wilson, S. S., Fakioglu, E., & Herold, B. C. (2009). Novel approaches in fighting herpes

Wu, M.-H., Yang, B.-C., Lee, Y.-C., Wu, P.-L., & Hsu, C.-C. (2004). The Differential

Zanatta, A., Rocha, A. M., Carvalho, F. M., Pereira, R. M. A., Taylor, H. S., Motta, E., Baracat,

Zhou, Z., Wang, N., Woodson, S. E., Dong, Q., Wang, J., Liang, Y., Rijnbrand, R., Wei, L.,

*Reprod*, Vol. 17, No. 4, (April 2011), pp. 243-254, 1360-9947

*Immunol*, Vol. 51, No. 5, (May 2004), pp. 373-380, 1600-0897

No. 12, (December 2010), pp. 701-710, 1058-0468

(January 2011), pp. 175-188, 0042-6822

Nat Rev Immunol, Vol. 5, No. 5, (May 2005), pp. 375-386, 1474-1733

*and Sterility*, Vol. 93, No. 6, (April 2010), pp. 1778-1786, 0015-0282

No.(October 2006), pp. 4904-4916, 0013-7227

1046-7408

5, New York, USA

pp. 327-331, 0002-9378

pp. 695-703, 0304-8608

559-68, 1744-8336

not of herpes viruses or Chlamydia trachomatis with endometriosis lesions. *Fertility* 

in endometriosis. *Am. J. Reprod. Immunol*., Vol. 65, No. 1, (January 2011), pp. 1-10,

expression during the implantation window in the mouse. *Endocrinology*, Vol. 147,

*Children VII, Curtis*, N., Finn, A. & Pollard, A., pp. 87-90, Springer, 978-1-4419-7184-

endometriosis. I. Genetic studies. *Am J Obstet Gynecol* Vol. 137, No. 3, (June 1980),

Identification of interferon-β-stimulated genes that inhibit angiogenesis in vitro. *J Interferon Cytokine Res*, Vol. 28, No. 12, (December 2008), pp. 733-740, 1079-9907 Vestergaard, A. L., Knudsen, U. B., Munk, T., Rosbach, H., Bialasiewicz, S., Sloots, T. P.,

Martensen, P. M., & Antonsson, A. (2010). Low prevalence of DNA viruses in the human endometrium and endometriosis. *Arch Virol,* Vol. 155, No. 5, (May 2010),

Transcriptional expression of type-I interferon response genes and stability of housekeeping genes in the human endometrium and endometriosis. *Mol Hum* 

simplex virus infections. *Expert Rev Anti Infect Ther*, Vol. 7, No. 5, (June 2009), pp.

Expression of Intercellular Adhesion Molecule-1 (ICAM-1) and Regulation by Interferon-Gamma during the Pathogenesis of Endometriosis. *Am J Reprod* 

E. C., & Serafini, P. C. (2010). The role of *Hoxa10/HOXA10* gene in the etiology of endometriosis and its related infertility: a review. *J. Assist Reprod. Genet.,* Vol. 27,

Nichols, J. E., Guo, J.-T., Holbrook, M. R., Lemon, S. M., & Li, K. (2011). Antiviral activities of ISG20 in positive-strand RNA virus infection. *Virology*, Vol. 409, No. 2,

Cancer. *AIDS Research and Human Retroviruses*, Vol. 22, No. 6, (November 2006), pp. 551-557, 0889-2229


Kao, L. C., Germeyer, A., Tulac, S., Lobo, S., Yang, J. P., Taylor, R. N., Osteen, K., Lessey,

Kennedy, P. G. E., & Cohrs, R. J. (2010). Varicella-zoster virus human ganglionic latency: a

Kyama, C. M., Debrock, S., Mwenda, J. M., & D'Hooghe, T. M. (2003). Potential involvement

Langendonckt, A. V., Lyuckx, M., Gonzalez, M.-D., Defrère, S., Donnez, J., & Squifflet, J.

Li, Q., Zhang, M., Kumar, S., Zhu, L. J., Chen, D., Bagchi, M. K., & Bagchi, I. C. (2001).

Liu, Y.-g., Tekmal, R. R., Binkley, P. A., Nair, H. B., Schenken, R. S., & Kirma, N. B. (2009).

Matsuzaki, S., Canis, M., Pouly, J.-L., Botchorishvili, R., Déchelotte, P. J., & Mage, G. (2006).

Moens, U., & Johannessen, M. (2008). Human polyomaviruses and cancer: expanding

Muir, A., Lever, A., & Moffett, A. (2004). Expression and function of human endogenous

Omwandho, C. O. A., Konrad, L., Halis, G., Oehmke, F., & Tinneberg, H.-R. (2009). Role of

Oppelt, P., Strick, R., Strissel, P. L., Winzierl, K., Beckmann, M. W., & Renner, S. P. (2009).

Oppelt, P., Renner, S. P., Strick, R., Valletta, D., Mehlhorn, G., Fasching, P. A., Beckmann, M.

Vol. 1, No. -, (December 2003), pp. 123, 1477-7827

(November 2010), pp. 1995-2000, 0015-0282

(June 2001), pp. 2390-400, 0013-7227

(September 2008), pp. 704-708, 1610-0387

No. 1, (November 2009), pp. 101-109, 0268-1161

665-673, 1360-9947

553, 0015-0282

747, 0951-3590

pp. S16-S25, 0143-4004

551-557, 0889-2229

0013-7227

0284

Cancer. *AIDS Research and Human Retroviruses*, Vol. 22, No. 6, (November 2006), pp.

B. A., & Giudice, L. C. (2003). Expression profiling of endometrium from women with endometriosis reveals candidate genes for disease-based implantation failure and infertility. *Endocrinology*, Vol. 144, No. 7, (July 2003), pp. 2870-81,

current summary. *J NeuroVirol,* Vol. 16, No. 6, (November 2010), pp. 411-418, 1355-

of the immune system in the development of endometriosis. *Reprod Biol Endocrinol*,

(2010). Differential expression of genes from the homeobox A cluster in deep endometriotic nodules and peritoneal lesions. *Fertil Steril*, Vol. 94, No. 6,

Identification and implantation stage-specific expression of an interferon-αregulated gene in human and rat endometrium. *Endocrinology*, Vol. 142, No. 6,

Induction of endometrial epithelial cell invasion and c-fms expression by transforming growth factor β. *Mol Hum Reprod*, Vol. 15, No. 10, (October 2009), pp.

Differential expression of genes in eutopic and ectopic endometrium from patients with ovarian endometriosis. *Fertil Steril*, Vol. 86, No. 3, (September 2006), pp. 548-

repertoire. *Journal der Deutschen Dermatologischen Gesellschaft*, Vol. 6, No. 9,

retroviruses in the placenta: An update. *Placenta*, Vol. 25, No. suppl. 1, (April 2004),

TGF-βs in normal human endometrium and endometriosis. *Hum Reprod*, Vol. 25,

Expression of the human endogenous retrovirus-W envelope gene syncytin in endometriosis lesion. *Gynecol Endocrinol*, Vol. 25, No. 11, (November 2007), pp. 741-

W., & Strissel, P. L. (2010). Correlation of high-risk human papilloma viruses but

not of herpes viruses or Chlamydia trachomatis with endometriosis lesions. *Fertility and Sterility*, Vol. 93, No. 6, (April 2010), pp. 1778-1786, 0015-0282


**13** 

**of Endometriosis** 

*Kaohsiung Medical University,* 

Eing-Mei Tsai

*Taiwan* 

**Stem Cell as the Novel Pathogenesis** 

Endometriosis is a common gynecological disease. It is unique to have benign histology but with malignant characteristics. Easy recurrence, multiple organ involvement and malignant transformation potential make endometriosis a complex disease. Multi-factors contribute to the pathophysiology. Recently, endometriosis has been regarded as a stem cell disease (Sasson & Taylor, 2008). Some studies have provided evidence of the possible existence of stem cells in endometrial tissue (Gargett et al., 2004, 2007). We successfully isolated eutopic and ectopic endometrial mesenchymal stem cells (EN-MSCs) derived from one donor to examine the genetic difference analysis that provided a powerful tool for investigating the disease origin (Kao et al., 2011). Our results are consistent with the concept that endometriosis is a stem cell disease. We identified and characterized the MSCs from ectopic and eutopic endometrium by *in vitro* cell characteristics, including serpiginous morphology, surface biomarkers, a lack of gap junctional intercellular communication and the ability of differentiation and transdifferentiation into adipocytes, osteocytes, chondrocytes, neural cell and cardiomyocytes. In an *in vivo* animal study, we found the ability of invasion in eutopic

The origins of endometrium stem cells are still under debate. Bone marrow is one of the origins. Bone marrow MSC circulates to the endometrium and reprograms into the

Aims of the chapter are to discuss about the endometrial stem cell identification and characterization and the stem cell theory of endometriosis will be discussed by search from the PubMed publications. The results will update our knowledge of the novel theory ---

The presence of endometrium stem cells can be identified by the property of clonogenicity, side population cells, stem cell markers, multipotent cells, xeno-transplantation. Expression of pluripotent marker such as Oct-4, and the stem cell factor in ectopic endometrium suggest

**2. Stem cells as the novel pathophysiology of endometriosis** 

**1. Introduction** 

and ectopic MSC.

endometrial MSC.

stem cell as the root of endometriosis.

**2.1 Evidence of stem cell in the endometrium** 

