Mitochondrial localization and ocular expression of mutant Opa3 in a mouse model of 3-methylglutaconicaciduria type III.

PURPOSE: To investigate the developmental and ocular expression of Opa3 in a mouse model of 3-methylglutaconicaciduria type III and the effect of mutation on protein localization and mitochondrial morphology.
METHODS: The B6 C3-Opa3(L122P) mouse carrying a missense mutation in exon 2 (c.365T>C; p.L122P) of Opa3, which displays features of recessive 3-methylglutaconic aciduria type III was studied. The expression of Opa3 was determined with RT-PCR, quantitative PCR, and Western blot, in embryos (embryonic day [E]8 to postnatal day [P]0) and adult tissues, and by ocular immunohistochemistry. Mitochondria were stained using a mitochondrion-selective probe in mouse embryonic fibroblasts from Opa3(-/-) mutants and imaged by electron microscopy of the retinas.
RESULTS: The splice variants Opa3a and Opa3b were expressed in the lenses and the retinas in the Opa3(-/-) mice, with the expression of the Opa3a isoform predominant. Opa3 was expressed throughout embryonic development, with high levels of expression in the developing brain, retina, optic nerve, and lens. Opa3 localized to the mitochondria, and the L122P mutant protein did not mislocalize. Neither protein localized to the peroxisome. Opa3(-/-) mice displayed disrupted mitochondrial morphology in the retina. Wild-type Opa3 protein increased as the lenses aged, despite the reduction in Opa3 mRNA occurring as a part of lens differentiation. However, mutant Opa3 mRNA was upregulated in homozygous mutant lenses, suggesting a compensatory increase in expression, which may further increase Opa3 protein levels.
CONCLUSIONS: Mutant Opa3 protein retains its mitochondrial localization and induces disrupted mitochondrial morphology. Opa3 accumulates in the lens. The results may reflect a slow turnover of Opa3 protein in vivo and may be important in normal lens physiology.