Targeting frataxin deficiency in DRG neurons and fibroblasts: omaveloxolone restores metabolic and iron balance to reduce ferroptosis

Abstract

Friedreich ataxia (FA) is a rare, multisystemic neurodegenerative disorder caused by a deficiency of the mitochondrial protein frataxin. It is characterized by degeneration of the large sensory neurons in the dorsal root ganglia (DRG) and spinocerebellar tracts, leading to progressive neurodegeneration and muscle weakness. Frataxin deficiency induces iron dyshomeostasis, defective energy production, and oxidative stress, all regulated by NRF2. Omaveloxolone, an NRF2 activator, is currently the only approved therapy for FA; however, its effects on DRG neurons remain unknown. Here we used frataxin-deficient DRG neurons to better understand the drug's role in these sensory neurons. Omaveloxolone improved most of the analyzed parameters, including frataxin levels, cell survival, mitochondrial respiratory activity, iron homeostasis, oxidative stress, transferrin receptor 1 and glutathione peroxidase 4 levels, as well as the GSH/GSSG ratio. Moreover, lipid peroxidation, a key marker of ferroptosis that was increased in frataxin-deficient neurons, was almost completely rescued by omaveloxolone. Both total and nuclear NRF2 levels were decreased in frataxin-deficient neurons, and omaveloxolone treatment fully prevented this alteration. In addition, most of these results were validated in fibroblasts from FA patients. We also evaluated a combinatorial treatment using low doses of omaveloxolone together with honokiol, a SIRT3 activator with known neuroprotective properties. This combination enhanced cell survival and produced a synergistic effect increasing mitochondrial respiration in frataxin-deficient DRG neurons. In summary, these findings demonstrate the beneficial effects of omaveloxolone and further suggest that combination therapy with honokiol may provide an effective strategy for the treatment of FA, potentially mitigating adverse effects.

Keywords: Friedreich ataxia; dorsal root ganglia; ferroptosis; fibroblasts; honokiol; omaveloxolone.