Optimized ND4 allotopic expression for gene therapy of Leber’s hereditary optic neuropathy

Leber’s hereditary optic neuropathy (LHON) is a mitochondrial disorder characterized by central vision loss, primarily resulting from mutations disrupting the electron transport chain. The most prevalent LHON-causing mutation is mt.11778G>A in the mitochondrial MT-ND4 gene, which encodes a critical subunit of complex I. Allotopic expression, a promising gene therapy strategy, aims to deliver a functional nuclear version of ND4 into the cell nucleus and target the resulting protein to the mitochondria. The efficiency of this approach critically depends on the mitochondrial targeting signal used. In this study, we screened five different MTS sequences to optimize the allotopic expression of ND4 in a HEK-293 cellular model of LHON harboring the mt.11778G>A mutation. We identified MTS-cox8k as the most effective signal for restoring mitochondrial function. Treatment with this construct significantly mitigated key pathological hallmarks: reactive oxygen species decreased by 72%, mitochondrial calcium levels dropped by 47%, and mitochondrial membrane potential (ΔΨm) increased by 38%. These results underscore the therapeutic potential of allotopic ND4 expression and highlight the critical importance of MTS optimization for developing effective treatments for mitochondrial diseases like LHON.