Diabetes is one of the most prevalent metabolic disorders, and its incidence has been experiencing a steady annual rise in recent years. Diabetic peripheral neuropathy (DPN) represents the most frequent adverse complication, exerting a profound impact on the quality of life for those suffering from diabetes. The etiology of DPN is complex, including impaired mitochondrial function. Iron-sulfur clusters (Fe–S) are essential cofactors for numerous essential enzymes crucial for mitochondrial function. Our previous study showed that expression of Frataxin, encoded by the Fxn gene, is downregulated in leptin receptor knockout (so-called db/db) mice, a commonly used DPN mouse model. Fxn is one of the core components of Fe–S biogenesis machinery. Here, we found that the mitochondria-targeted antioxidant SS-31 markedly improved the behavioral indices and significantly mitigated the damage to the sciatic nerve. SS-31 treatment effectively elevated Fxn expression, meliorated mitochondrial function, and inflammation in the sciatic nerve (SCN). We also found that SS-31 effectively mitigated high glucose-induced disruption of iron and redox homeostasis in RSC96 cells, a typical cell model of DPN, thereby improving mitochondrial function. These findings suggest enhancing Fe–S biogenesis could be an effective therapeutic strategy for treating DPN.
Friedreich ataxia is a progressive neurodegenerative disease caused by the expansion of GAA trinucleotide repeats within the first intron of the FXN gene, which encodes frataxin. The pathophysiology of the disease is thought to be derived from the decrease of Fe-S cluster biogenesis due to frataxin deficiency. There is currently no effective treatment for the disease. In our study, we demonstrated that treatment with the mitochondrion-targeted peptide SS-31 reduced frataxin deficiency-induced oxidative stress in lymphoblasts and fibroblasts derived from patients. Interestingly, SS-31 treatment translationally upregulated the protein level of frataxin in a dose-dependent manner. Furthermore, SS-31 treatment increased the enzymatic activities of the iron-sulphur enzymes, including aconitase and complex II and III of the respiratory chain. Further evaluation of the quality of mitochondria showed that mitochondrial membrane potential, ATP content, NAD + /NADH, and the morphology of mitochondria all improved. Our results suggest that SS-31 might potentially be a new drug for the early treatment of Friedreich ataxia.
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