Mouse mtDNA mutant model of Leber hereditary optic neuropathy

Abstract

An animal model of Leber hereditary optic neuropathy (LHON) was produced by introducing the human optic atrophy mtDNA ND6 P25L mutation into the mouse. Mice with this mutation exhibited reduction in retinal function by elecroretinogram (ERG), age-related decline in central smaller caliber optic nerve fibers with sparing of larger peripheral fibers, neuronal accumulation of abnormal mitochondria, axonal swelling, and demyelination. Mitochondrial analysis revealed partial complex I and respiration defects and increased reactive oxygen species (ROS) production, whereas synaptosome analysis revealed decreased complex I activity and increased ROS but no diminution of ATP production. Thus, LHON pathophysiology may result from oxidative stress.eber hereditary optic neuropathy (LHON), the first inherited mitochondrial (mt)DNA disease reported (1), is thought to be one of the most prevalent diseases caused by mtDNA missense mutations, having an estimated frequency of 15 in 100,000 (2). Most European LHON mutations occur in the mtDNA oxidative phosphorylation (OXPHOS) complex I (NADH:ubiquinone oxidoreductase or NADH dehydrogenase) genes, the three most common being the ND4 gene mutation at nucleotide G11778A causing an arginine 340 to histidine (R340H) substitution (1), the ND1 G3460A (A52T) mutation (3), and the ND6 T14484C (M64V) mutation (4). Milder LHON mutations are generally homoplasmic (pure mutant). In contrast, more severe mtDNA complex I ND gene mutations can cause basal ganglia degeneration presenting as dystonia or Leigh syndrome when homoplasmic but optic atrophy when heteroplasmic (mixed mutant and normal mtDNAs). Two examples of such mutations are ND6 G14459A (A72V) (5) and ND6 G14600A (P25L) (6).LHON generally presents in the second or third decade of life as acute or subacute onset of central vision loss, first in one eye and then in the other. The percentage of optic atrophy in patients varies markedly among pedigrees. Male patients are two to five times more likely to develop blindness than female patients (2), and maternal relatives who have not progressed to subacute optic atrophy can still show signs of visual impairment (7,8).In LHON, optic atrophy is associated with preferential loss of the central small-caliber optic nerve fibers of the papillomacular bundle, resulting in central scotoma but with sparing of the largercaliber peripheral fibers and retention of peripheral vision. The loss of the optic nerve fibers is attributed to the death of retinal ganglion cells (RGC) as a result of the high energy demand placed on the unmyelinated portion of the optic nerve fibers anterior to the lamina cribosa, an area associated with high mitochondrial density (2).Complex I is the largest and most intricate of the mitochondrial OXPHOS complexes. It is comprised of 45 subunits, 7 (ND1, -2, -3, -4, -4L, -5, and -6) of which are coded by the mtDNA (9). Complex I transfers electrons from NADH to ubiquinone, and the energy released from this redox reaction is coupled to pumping protons across the mitochondrial in...

Consequences of zygote injection and germline transfer of mutant human mitochondrial DNA in mice

“…Moreover, therapies for disorders caused by mutated mtDNA are inadequate, in large part because of the absence of animal models with mutated mtDNA and with the same genotype and phenotype as the human disorder that would help uncover the pathogenesis of disease and test potential avenues for treatment (11)(12)(13). Current procedures for the introduction of artificially mutagenized mtDNA into mitochondria have generated optic neuropathy in mice with a gene [ND6 G14600A (P25L)] that, when homoplasmic, is responsible for Leigh syndrome in humans (14).…”

Cell therapy using retinal progenitor cells shows therapeutic effect in a chemically-induced rotenone mouse model of Leber hereditary optic neuropathy

“…2 Complex I deficit results in reduced oxygen consumption, increased reactive oxygen species, decreased energy supply and sensitization of the mitochondrial permeability transition pore (mtPTP) to apoptosis. 3,5 The retina is uniquely vulnerable to such insults, given its high energy demands and the nonreplicating nature of mammalian retinal neurons. 2,3,5 LHON is similar in etiology to dominant optic atrophy (DOA), which has been mapped to seven loci, with three genes (OPA1, OPA3 and TMEM126A/OPA7) identified to date.…”

“…3,5 The retina is uniquely vulnerable to such insults, given its high energy demands and the nonreplicating nature of mammalian retinal neurons. 2,3,5 LHON is similar in etiology to dominant optic atrophy (DOA), which has been mapped to seven loci, with three genes (OPA1, OPA3 and TMEM126A/OPA7) identified to date. These DOA genes are nuclear encoded, but have mitochondrial functions.…”

“…8 Therapeutic development for LHON has been impeded by the need to target therapeutic agents to mitochondria, and the difficulty of engineering animal models carrying specific mtDNA mutations, although recently a mouse model carrying a mtDNA mutation has been shown to demonstrate LHON-like symptoms. 5 We have utilized a chemically-induced model, the complex I inhibitor rotenone, to model LHON in mice. Rotenone inhibits the reduction of ubiquinone and causes specific and irreversible retinal effects in mice, which mimic those of LHON, when administered intravitreally.…”

Mitochondrial disorders: aetiologies, models systems, and candidate therapies

“…These so-called 'mito-mice' carrying a mtDNA deletion encompassing 6tRNA and seven structural genes, a mutation in the genes encoding cytochrome oxidase I (COI) or NADH dehydrogenase 4 (ND6) have been generated [56]. Recently, using a homoplasmic G14600A ND6 mutant cell line, cybrids from this cell line were fused with ES cells depleted of mtDNA to generate a mouse with a mitochondrial mutation in ND6 [57] that recapitulates many features of LHON. The model suggests that LHON is due to oxidative stress rather than to ATP deficiency, because in this model, no reduction in ATP production was evident.…”