Mitochondrial dysfunction in fibroblasts of Multiple System Atrophy

Abstract

Multiple System Atrophy is a severe neurodegenerative disorder which is characterized by a variable clinical presentation and a broad neuropathological spectrum. The pathogenic mechanisms are almost completely unknown. In the present study, we established a cellular model of MSA by using fibroblasts' primary cultures and performed several experiments to investigate the causative mechanisms of the disease, with a particular focus on mitochondrial functioning. Fibroblasts' analyses (7 MSA-P, 7 MSA-C and 6 healthy controls) displayed several anomalies in patients: an impairment of respiratory chain activity, in particular for succinate Coenzyme Q reductase (p < 0.05), and a reduction of complex II steady-state level (p < 0.01); a reduction of Coenzyme Q10 level (p < 0.001) and an up-regulation of some CoQ10 biosynthesis enzymes, namely COQ5 and COQ7; an impairment of mitophagy, demonstrated by a decreased reduction of mitochondrial markers after mitochondrial inner membrane depolarization (p < 0.05); a reduced basal autophagic activity, shown by a decreased level of LC3 II (p < 0.05); an increased mitochondrial mass in MSA-C, demonstrated by higher TOMM20 levels (p < 0.05) and suggested by a wide analysis of mitochondrial DNA content in blood of large cohorts of patients. The present study contributes to understand the causative mechanisms of Multiple System Atrophy. In particular, the observed impairment of respiratory chain activity, mitophagy and Coenzyme Q10 biosynthesis suggests that mitochondrial dysfunction plays a crucial role in the pathogenesis of the disease. Furthermore, these findings will hopefully contribute to identify novel therapeutic targets for this still incurable disorder.

MSA: From basic mechanisms to experimental therapeutics

“…Di Fonzo and colleagues showed mitochondrial dysfunction, neuronal damage and severe impairment of the autophagic machinery in iPSCs-derived dopaminergic neurons of MSA patients compared to healthy controls [66]. Similar findings were observed by the same group in MSA fibroblasts [67]. Mitochondrial dysfunction was also described in iPSC-derived neurons of a patient with a heterozygous mutation in COQ2 and a patient with idiopathic MSA compared to healthy individuals.…”

“…However, based on pathological and molecular evidence from MSA human studies and animal models, several factors seem to be definitely associated with the disease and may serve as therapeutic targets for disease modification (Fig. 1), including the abnormal accumulation of α-syn [30][31][32][33]43,44], microglial activation and neuroinflammation [52,[54][55][56][57][58][59][60][61]89], autophagy disturbances [64][65][66][67], mitochondrial dysfunction [12,15,66,[68][69][70][71][72][73][74] and oxidative stress [76]. Yet the primary event which triggers the whole pathogenic cascade is still unknown.…”

“…Finally, MSA patients showed reduced levels of CoQ10 in cerebrospinal fluid, plasma/serum and cerebellum [68][69][70][71][72][73], which may lead to decreased electron transport in mitochondria and increased vulnerability to oxidative stress [68,69]. Recent studies with MSA fibroblast and iPSCs-derived dopaminergic neurons observed reduced CoQ10 levels and up-regulation of some CoQ10 biosynthesis enzymes in MSA patients compared to healthy controls [66,67,74]. These changes were associated with mitochondrial dysfunction, impaired autophagy and neuronal damage [66,74] and partially rescued by CoQ10 supplementation [74].…”

“…It is thought that the neurodegenerative process underlying MSA results from the interaction of multiple factors, including the abnormal accumulation of α-syn, microglial activation and neuroinflammation, genetic polymorphisms, dysregulation of myelin lipids [62,63], disturbances of autophagy [64][65][66][67], mitochondrial [12,15,66,[68][69][70][71][72][73][74] and proteasomal dysfunction [75,76] and oxidative stress [74,76]. At present there is no cure for MSA and only mitigation of some symptoms is feasible.…”

Mitochondrial disorders in neuromuscular pathology

“…Используют колориметрический анализ оксидоредуктаз в дыхательной цепи митохондрий [19], изучают митохондриальный мембранный потенциал [20]. В фибробластах возможно определение активности ферментов дыхательной цепи (сукцинат-коэнзим-Qредуктазы, II комплекcа, уровня коэнзима Q 10 , ферментов биосинтеза CoQ10, а именно COQ5 и COQ7) [21]. Также применяют цитохимический метод исследования активности митохондрильных ферментов в лимфоцитах периферической крови [22], который позволяет определить количество окрашенных гранул (продукт реакции дегидрогеназ митохондрий) в клетках, характеристики этих гранул, провести исследование цитоморфоденситометрических показателей митохондриальной активности лимфоцитов (активность объединенных митохондрий (кластеров), общий продукт реакции в отдельных митохондриях и т. д. С помощью этого метода можно определять среднюю активность ферментов, коэффициент ассимметрии, коэффициент вариации и другие показатели.…”