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Mutations in the optic atrophy type 1 (OPA1) gene give rise to human autosomal dominant optic atrophy. The purpose of this study is to investigate OPA1 protein expression in the human retina and optic nerve. A rabbit polyclonal antiserum was generated using a fusion protein covering amino acids 647 to 808 of the human OPA1 protein as the immunogenic antigen. Western blot and immunofluorescence staining were performed to examine OPA1 expression in the human retina and optic nerve. In human retina, we found that OPA1 expression was clearly present in retinal ganglion cells and photoreceptors. OPA1 immunoreactivity was also present in the nerve fiber layer, inner plexiform layer and outer plexiform layer. However, OPA1 protein was not detected in the choline acetyltransferase-positive, calretinin-positive, and calbindin-positive amacrine cells, nor in the calbindin-positive horizontal cells. In the human optic nerve, expression of OPA1 was present in the axonal tract that was labeled with neurofilament specific antibody. In conclusion, expression of OPA1 gene is present in the mitochondria-rich regions of the retina and optic nerve. This suggests that OPA1 protein might be involved in the functioning of the mitochondria that are present in both inner and outer retinal neurons.

The purpose of this study is to investigate the cytochrome oxidase (COX) activity in the retina and optic nerve following an optic nerve injury. The optic nerve crush of one eye was carried out in Balb/c mice. A semi-quantitative RT-PCR method was then adopted to evaluate the mRNA expression of cytochrome oxidase subunit 1 (COX1) in the retina after surgery. Up-regulation of COX1 mRNA in the retina was detected by RT-PCR at 24 hr following the optic nerve injury. Total retinal mitochondrial mass measured by fluorescent intensity of MitoTracker green was not altered following the injury. COX histochemistry performed on cryostat sections showed an elevated enzyme activity of COX in the retina and in the optic nerve. In the retina, elevation of the COX activity was observed in the retinal ganglion cell layer and the overlying nerve fibre layer. The increase of COX activity began from 24 hr after injury, peaked around day 3, and maintained up to 1 week after the operation. In the optic nerve, increase of COX activity was observed in regions distal to the crush line and distributed either randomly or in a cone shape. In conclusion, both the expression of COX1 mRNA in retina and the activity of COX in inner plexiform layer and retinal ganglion cell layer were elevated following optic nerve injury without affecting total retinal mitochondrial mass. These findings suggested that one of early responses in the retina and in the optic nerve after the optic nerve injury is to scale up the energy production., (Copyright 2002 Elsevier Science Ltd.)