No retinal apoptosis in mouse model of Opa1 dominant optic atrophy despite visual loss

Purpose Autosomal dominant optic atrophy (ADOA) due to mutations in OPA1 is a slowly progressive optic neuropathy. OPA1 is ubiquitously expressed and plays a key role in mitochondrial fusion. Heterozygous Opa1 mutant mice (B6;C3-Opa1Q285STOP), with previously reported visual defects and optic nerve changes on EM, were assessed for evidence of cellular effects and retinal sequelae. Methods The level and processing of Opa1 were studied by Western blot. Membrane potential was assessed by JC-1 in isolated mitochondria. Mitochondrial morphology was investigated using Mitotracker staining on E13.5 mouse embryonic fibroblasts (MEFS). End-organ evidence for apoptosis was explored on TUNEL stained retinal sections. Results The heterozygous mutation leads to ca. 50% reduction in Opa1 protein in mitochondria. Despite this there is no statistically significant reduction in the average mitochondrial membrane potential in the retina and brain by 5 months of age. Although Opa1 +/- MEFS demonstrate a 15% increase in the number of cells showing mitochondrial fragmentation their growth and survival characteristics after oxidative stress were not significantly affected. There was no increased apoptosis in retinal sections from mutant animals. Conclusion A 50% reduction in Opa1 protein, capable of causing a defect in mitochondrial morphology in MEFS, in the presence of visual dysfunction and morphological changes on electron microscopy in the optic nerve, nevertheless does not appear to lead to a significant increase in apoptosis in retina. This suggests that dysfunction of RGCs rather than overt loss may be important in the pathophysiology of the disease.