Time-dependent effects of focal retinal ischemia on axonal cytoskeleton proteins.

PURPOSE To examine the time-dependent effects of focal axonal ischemia on the retinal ganglion cell (RGC) cytoskeleton. METHODS Eight pigs were used. Small retinal arteriolar branches were occluded by argon laser to induce focal ischemic insults that were maintained for a period of 6 hours or 1 hour. Treated and untreated retinal segments were dissected from the eye after euthanatization. Each retinal segment followed the longitudinal projection of RGC axons from peripheral retina to the optic disc. Antibodies to phosphorylated neurofilament heavy, phosphorylation-independent neurofilament heavy (NFH), neurofilament light, neurofilament medium, microtubule, and microtubule-associated proteins were used to study the axonal cytoskeleton. Glial fibrillary acidic protein and TUNEL staining were also used to examine astrocyte and apoptotic changes, respectively. Comparisons were made between treated and untreated retinal segments. RESULTS Cytoskeleton protein changes occurred within ischemic regions and also within retinal tissue on the disc side and peripheral side of the ischemic regions. NFH and microtubule proteins were the earliest cytoskeleton subunits that underwent change. Changes to all cytoskeleton proteins, apart from NFH, occurred in a time-dependent manner within regions of ischemia. In the time points studied, cytoskeleton changes occurred in the absence of detectable astrocyte changes and RGC apoptosis. CONCLUSIONS An ischemic insult induces RGC cytoskeleton protein change, implying that the local environment plays an important role in modulating axonal structure and function. Cytoskeleton proteins are likely to be important pathogenic mediators of neuronal dysfunction in diseases such as glaucoma and retinal vascular disease.