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E Nakajima, Y Tamada, C Fukiage, M Azuma, TR Shearer; Cleavage of p35, Regulator of CDK5, to p25 by Calpain in Retinal Cell Death . Invest. Ophthalmol. Vis. Sci. 2002;43(13):783.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Our previous study suggested that calpains played an important role in retinal cell death induced by ischemia-reperfusion in rat. However, the relationship between changes in signaling pathways caused by activation of calpain and retinal cell death is not clear. Recently, calpain-induced proteolysis of p35, a regulator of cdk5, to p25 was reported in Alzheimer's disease. Thus, the purpose of present study to determine if p35 was similarly proteolyzed by m-calpain to p25 during retinal cell damage occurring in vitro. Methods: Rat retinas were incubated in RPMI medium with glucose under conditions supplying oxygen sufficient for retinal cell survival. To induce a hypoxia, retinas were incubated in RPMI medium without glucose under 95 % N2/5 % CO2 instead of 95 % O2/5 % CO2. Leakage of LDH into the medium assessed membrane damage and cell death. Casein zymography and immunoblotting assessed activation of calpain and proteolysis of α-spectrin and p35. Results: Results Leakage of LDH into the medium from retinas increased under hypoxic conditions. Decreased caseinolytic activity was observed under hypoxic conditions, and this was indirect evidence of calpain activation and subsequent autodegradation. Calpain activation was well correlated with the proteolysis of α-spectrin. p25 accumulated in retinas under hypoxic conditions. We speculate that accumulation of p25 may lead to over activation of cdk5, hyperphosphorylation and disassembly of retinal cytoskeletal proteins, and cell death. Conclusion: These results suggested that proteolysis of p35 to p25 by calpain may play an important role in retinal cell death in the rat.
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