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
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