Alpha-fodrin is cleaved by caspase-3 in a chronic ocular hypertensive (COH) rat model of glaucoma

Purpose: α-Fodrin is a neuronal cytoskeletal protein and a known caspase-3 target. We sought to determine whether caspase-3 cleaves α-fodrin in COH rat retinas and whether this process is reduced by adeno-associated virus (AAV)-induced retinal ganglion cell expression of baculovirus inhibitory repeat-containing 4 (BIRC4), a potent caspase-3 inhibitor.Methods: Ocular hypertension was induced unilaterally in five rat eyes by limbal injection of hypertonic saline. In a similar experiment, ocular hypertension was induced in four eyes pre-treated with an intravitreal injection of AAV-BIRC4 to assess α-fodrin cleavage. Western immunoblotting was performed on all retinas.Results: Caspase-3 cleavage of α-fodrin yields a specific 120 kDa protein fragment. COH retina immunoblots indicated significantly more caspase-3 cleavage of α-fodrin than controls (P<0.01, paired t-test). Inhibition of retinal caspase-3 activity with BIRC4 reduced caspase-3-mediated α-fodrin cleavage compared to controls.Conclusion: This confirms our previous finding of caspase-3 cleavage of α-fodrin in COH retinas and parallels pathology seen in Alzheimer’s disease, in which neurons undergo chronic caspase activation, slow build-up of cleavage products, and delayed apoptosis. If caspase activation in glaucoma leads to protracted rather than rapid retinal ganglion cell apoptosis, a much longer therapeutic window exists for apoptosis inhibition with caspase inhibitors such as BIRC4.