| Multiple Sclerosis [MS] is a CNS disorder with unknown etiology. Deficient mitochondrial energy production is implicated in primary neurodegeneration seen in MS cortex. Previous studies have identified decreased expression of 26 electron transport chain [ETC] genes in MS motor cortex. In order to understand if this change was more global, the expression and transcriptional regulation of select ETC genes was studied here. Using RT-PCR, a significant decrease in the expression of transcripts for subunits of Complexes I, III, IV and V was observed in MS parietal and frontal cortices. Additionally, all the genes under study were transcriptionally regulated by NRF-2. Using EMSA studies, NRF-2 binding, but not its expression, was seen to be decreased in the presence of oxidative stress in MS. In order to better study the effects of oxidative stress on NRF-2 function, two possible models for MS, namely the human neuroblastoma SH-SY5Y cell line and the EAE mouse were studied, but both were found to be unsuitable. A comparative study of protein expression between MS and EAE showed that while it models inflammatory demyelinating events well, EAE does not model the respiratory deficits observed in MS and other factors such as oxidative stress and epigenetic influences may play a role in the evolution of MS. In line with this thought, DNA methylation was studied using ChIP and PCR for its effects on the regulation of electron transport chain gene expression in MS. A significant increase in the methylation of the promoter regions of the genes associated with respiration, namely GAD67 and ATP5I was seen. This indicates that it may play a role in the decreased expression of the ETC proteins and contribute to mitochondrial dysfunction seen in MS. Overall this study has found that there is a global oxidative stress and increased DNA methylation in the MS brain which could contribute to impaired ETC function which can adversely impact ATP production and create an energy imbalance. SH-SY5Y and the EAE mouse are unsuitable for studying oxidative stress in MS. This implies that events other than pro-inflammatory attacks play a role in primary neurodegeneration seen in MS cortex. |
