**13. Acknowledgements**

The authors thank the Carolinas HealthCare Foundation and Carolinas ALS Research Fund for financial support of this study. The authors thank Dr. Richelle Hemendinger and Dr. Nataliya Kubalik for testing in 2010 the tgSOD1 rats for the time of development of ALS symptoms.

### **14. References**

242 Amyotrophic Lateral Sclerosis

release large amounts of calcium. The tissue calcium content in the spinal cord from presymptomatic tgSOD1 rats was diminished by 26% (Panov et al., 2011b). Thus, oxidatively damaged mitochondria may encounter increased amounts of Ca2+ released during demyelination and undergo permeability transition. Halestrap (2005) has pointed out that when mitochondria massively undergo permeability transition, the cells will die by necrosis,

The results presented by us in this and other papers (Panov et al., 2009, 20011a, 2011b) lead us to suggest the role of the brain and spinal cord mitochondria in the loss of motor neurons in ALS. We hypothesize that increased oxidative stress associated with specific metabolic phenotypes, which promote reverse electron transport due to reduction of the membrane pool of ubiquinone by succinate (Panov et al., 2009, 2011a, 2011b) or fatty acids (Panov et al., 2010c), is a prerequisite for cases of sporadic ALS. The energy-dependent reverse electron transport is a way of dissipation of the mitochondrial membrane potential, which increases the rate of resting mitochondrial respiration. In mammals, the standard metabolic rate depends on the intrinsic (in state 4) mitochondrial proton conductivity (Rolfe & Brown , 1997). Therefore in patients with ALS hypermetabolism could be associated with the systemically increased dissipation of mitochondrial membrane potential. The specific vulnerability of motor neurons in ALS is, more likely than not, associated with the specific

Normally, SCM produce significantly more ROS than BM when oxidizing physiologically relevant mixture of neuromediator glutamate and the tricarboxylic acid cycle substrates pyruvate, succinate and malate. Mutated SOD1 is extremely sensitive to the damaging effect of H2O2, which in tgBM and tgSCM were dramatically increased. This results in demetallation of mSOD1 and association with mitochondria, thus changing the physical properties of the mitochondrial membranes and further enhancing production of ROS. Increased oxidative stress initiates damage to myelin and released the tissue calcium. Finally, oxidatively damaged mitochondria undergo the Ca2+-induced permeability transition, and motor neurons die by apoptotic or necrotic pathway. Thus, mitochondria are early and directly involved in the pathogenesis of ALS. We suggest that sporadic ALS is preferentially acquired by individuals with the mitochondrial metabolic phenotype, that promotes very high levels of ROS production. In individuals with mutated SOD1 gene, the abnormal SOD1 protein has high sensitivity to deleterious effect of H2O2 and the disease

The results and the hypothesis presented in this article highlight the importance to consider determination of metabolic phenotypes together with the disease mechanisms when

The authors thank the Carolinas HealthCare Foundation and Carolinas ALS Research Fund for financial support of this study. The authors thank Dr. Richelle Hemendinger and Dr.

which was documented Martin et al.(2009) for ALS animals.

features of spinal cord described in Panov et al. (2011a, 2011b).

may develop even at normal levels of ROS production.

working with patients or animal models of the ALS.

**12. Proposals for future studies** 

**13. Acknowledgements** 

**11. Conclusions** 


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**10** 

*Finland* 

**Lateral Sclerosis** 

Jari Koistinaho and Gundars Goldsteins

**Mutant Cu/Zn-Superoxide Dismutase Induced** 

Mutations in Cu/Zn superoxide dismutase (SOD1) gene are linked to the motor neuron death in familial amyotrophic lateral sclerosis (FALS). More than 100 missense mutations have been described to cause the disease and are distributed throughout the whole 153 amino acid sequence of SOD1 molecule (Valentine et al., 2005; Boillée et al., 2006). Mutant SOD1 molecules can be grouped according to their biochemical characteristics into wild type-like proteins, that bind metal ions and possess enzymatic dismutase activity (e.g. G93A-SOD1 and G37R-SOD1), and mutant molecules with impaired metal binding capacity, which have significantly reduced dismutase activity (e.g. G85R-SOD1) (Valentine et al., 2005). Therefore, the toxicity of mutant SOD1 is not thought to be mediated by a lack of

The exact nature of the toxic gain of function for mutant SOD1 has not been identified yet. Most of the studies demonstrate a link between the disease pathology and increased oxidative stress. Augmented generation of free radicals and reactive oxygen species (ROS) is thought to be a major contributor to the destruction of motor neurons (Beckman et al., 1994;

The suggested toxic mechanisms include aberrant mutant SOD1 enzymatic activities (Beckman et al., 1993; Wiedau-Pazos et al., 1996) as well as destabilized SOD1 protein misfolding, causing enhanced aggregation of SOD1 or pathological interaction of SOD1 with

In a number of studies mitochondrial localization of mutant SOD1 has been implicated in ALS pathogenesis (Liu et al., 2004; Vijayvergiya et al., 2005; Bergemalm et al., 2006; Deng et al., 2006; Ferri et al., 2006) and increased recruitment of mutant SOD1 into mitochondria in the spinal cord might be a reason for death of motor neurons in some forms of familial ALS. However, the detailed mechanisms for toxicity of the mitochondria resident mutant SOD1 are not entirely clear yet. Here we review the current state of the art in the studies on

**2. Factors controlling SOD1 translocation to mitochondria and SOD1 activity** 

Although the majority of SOD1 is present in the cytosol (Okado-Matsumoto & Fridovich, 2001), a fraction of SOD1 is translocated into the mitochondrial intermembrane space (IMS)

dismutase activity, but rather by gain of one or more detrimental functions.

Wiedau-Pazos et al., 1996; Estévez et al., 1999).

mitochondrial toxicity of SOD1 in ALS.

**in mitochondrial intermembrane space** 

other proteins (Stathopulos et al., 2003; Liu et al., 2004).

**1. Introduction** 

**Mitochondrial Dysfunction in Amyotrophic** 

*A.I.Virtanen Institute for Molecular Sciences, University of Eastern Finland,* 

