Optic neuropathy arising from the synergy between YARS2 and mitochondrial COX1 mutations

Leber hereditary optic neuropathy (LHON) is a paradigm for mitochondrial retinopathy. Here, we investigate the mechanism underlying the interaction between nuclear modifier and mtDNA mutation(s) that manifests optic neuropathy in vivo to develop an effective therapeutic approach for this disease, using mouse models bearing LHON-linked Yars2^G186V or COI^V421A mutation alone and double mutations. Yars2^G186V alters mitochondrial translation and assembly and activities of complex I, III, and IV, while COI^V421A reduces complex IV activity. However, a single Yars2^G186V or COI^V421A mutation causes mild declines in ATP production and yields relatively mild degeneration of retinal ganglion cells (RGCs). Notably, the synergy between COI^V421A and Yars2^G186V mutations aggravates mitochondrial dysfunction and oxidative stress. Interestingly, COI^V421A mainly promotes apoptosis, and Yars2^G186V contributes to ferroptosis. The combination of two mutations accelerates the degeneration of RGCs and photoreceptors. Strikingly, AAV-mediated Yars2 expression in the mouse retina carrying both Yars2^G186V and COI^V421A mutations corrects the defective translation and ferroptosis arising from the Yars2^G186V mutation and remarkably improves mitochondrial function and causes morphologic and functional recovery of RGCs and photoreceptors. These findings provide mechanistic insights into the pathophysiology of LHON arising from nuclear modifiers and mtDNA mutation(s) and potential therapeutic strategies for LHON and other mitochondrial diseases.