Retinal cell death induced by over-stimulation of
glutamate receptors is related to the programmed cell death or apoptosis. However, little is known about the intracellular events that lead to this cell death process in the retina. In this study, we asked if
caspase-3 family
cysteine proteases regulate cell death in an explant culture of adult rat retina after exposure to excessive
glutamate. Cells with DNA fragmentation were first detected in the
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
glutamate lesion. Caspase-3-like activity, as indicated by immunostaining of the fractin antibody that recognizes actin fragments generated by
caspase-3 family
proteases, was seen 40 min after
glutamate treatment. Staining was first detected in the
ganglion cell layer and then in the inner nuclear layer, preceding the appearance of cells with DNA fragmentation in these layers. Colocalization study showed that all cells with DNA breaks were fractin positive, indicating that
caspase-3 family activity was involved in the
glutamate-induced cell death in the adult rat retina. Furthermore,
DEVD-CHO, a tetrapeptide inhibitor for
caspase-3 family members, reduced dramatically the fractin staining and significantly alleviated
glutamate-induced cell death and DNA fragmentation in the
ganglion cell layer and inner nuclear layer. Inhibitor for caspase-1-like activity,
YVAD-CHO, neither reduced the fractin staining nor showed comparable
neuroprotective effects to the retina. We conclude that
glutamate-induced apoptotic cell death in adult rat retina is mediated by a specific activation of
cysteine proteases related to the
caspase-3 family, and an intervention to the
caspase-3 proteases provides effective protection to retinal neurons against
glutamate excitotoxicity.