Inhibition of caspase-3-like activity reduces glutamate induced cell deathin adult rat retina

Retinal cell death induced by over-stimulation of glutamate receptors is re lated to the programmed cell death or apoptosis. However, little is known a bout the intracellular events that lead to this cell death process in the r etina. In this study, we asked if caspase-3 family cysteine proteases regul ate cell death in an explant culture of adult rat retina after exposure to excessive glutamate. Cells with DNA fragmentation were first detected in th e ganglion cell layer 3 h after a brief exposure to 20 mM glutamate, whilst those in the inner nuclear layer were first observed 6 h after the glutama te lesion. Caspase-3-like activity, as indicated by immunostaining of the f ractin antibody that recognizes actin fragments generated by caspase-3 fami ly proteases, was seen 40 min after glutamate treatment. Staining was first detected in the ganglion cell layer and then in the inner nuclear layer, p receding the appearance of cells with DNA fragmentation in these layers. Co localization study showed that all cells with DNA breaks were fractin posit ive, indicating that caspase-3 family activity was involved in the glutamat e-induced cell death in the adult rat retina. Furthermore, DEVD-CHO, a tetr apeptide inhibitor for caspase-3 family members, reduced dramatically the f ractin staining and significantly alleviated glutamate-induced cell death a nd DNA fragmentation in the ganglion cell layer and inner nuclear layer. In hibitor for caspase-1-like activity, YVAD-CHO, neither reduced the fractin staining nor showed comparable neuroprotective effects to the retina. We co nclude that glutamate-induced apoptotic cell death in adult rat retina is m ediated by a specific activation of cysteine proteases related to the caspa se-3 family, and an intervention to the caspase-3 proteases provides effect ive protection to retinal neurons against glutamate excitotoxicity. (C) 200 1 Elsevier Science B.V. All rights reserved.