Induction of Rapid and Highly Efficient Expression of the Human ND4 Complex I Subunit in the Mouse Visual System by Self-complementary Adeno-Associated Virus

Abstract

Leber hereditary optic neuropathy (LHON) is a maternally inherited disease characterized by acute bilateral loss of central vision.¹ In approximately 95% of the cases worldwide, LHON is caused by 3 pathogenic point mutations in mitochondrial DNA (mtDNA) coding for the respiratory chain subunits of complex I genes (the reduced form of nicotinamide adenine dinucleotide–ubiquinone-oxidoreductase), namely m.3460G>A in ND1, m.11778G>A in ND4, and m.14484T>C in ND6.² Of these 3 mutations, 11778G>A, resulting in an arginine to histidine substitution at amino acid 340, is responsible for half of all LHON cases. Patients with this mutation exhibit the poorest prognosis for spontaneous visual improvement, and there is no effective therapy.³ Most patients with LHON carry the mtDNA mutations in homoplasmic condition, that is, they have no normal ND4 mtDNA. Thus, an effective therapeutic approach would be introduction of normal mtDNA into the affected cells (ganglion cells of the retina) in these patients. One of the major limitations in this aspect is that few practical methods for delivering genes to the mitochondria are available.^4,5 To address this, we and other groups adapted an approach termed allotopic expression, in which the mutant mitochondrial gene (in this case ND4) is expressed in the nucleus, translated on cytoplasmic polyribosomes, and transported into mitochondria with the addition of an N-terminal mitochondrial targeting sequence.^6-8 Allotopic expression of the normal ND4 gene normalized the defective adenosine triphosphate (ATP) synthesis of LHON cells and improved cell survival.⁹