Role of Calpains in Hypoxia-Induced Cell Death in Monkey Retina

Abstract

Abstract: : Purpose In rats, calpain-induced proteolysis is a major factor in retinal cell death induced by hypoxia in vitro and by ischemia-reperfusion injury in vivo. Ubiquitous calpain 1 and 2 from monkey retina were previously shown to be homologous to rat calpains, and they were activated by calcium. In contrast, expression patterns for variants of tissue-specific calpain 3 were different between monkey and rat retinas. These differences might be related to different functions for the variants in the two species. Thus, the purpose of present study was to determine the role of calpains in cell death in monkey retinas. Methods Monkey retinas were incubated in RPMI medium with glucose under conditions supplying oxygen sufficient for retinal cell survival (95% O₂/5 % CO₂). To induce a hypoxia, retinas were incubated in RPMI medium without glucose and under 95% N₂/5 % CO₂. Leakage of LDH into the medium assessed retinal cell death. Calpain activation and proteolysis of calpain substrates were assessed by casein zymography and immunoblotting. Results Leakage of LDH from retinas into the medium increased under hypoxic conditions. Decreased caseinolytic activity was observed under hypoxic conditions, suggesting calpain activation and subsequent autodegradation. Calpain preferred substrates such as α-spectrin were proteolyzed in hypoxic retina. To directly confirm that retinal cell death was induced by activated calpain, retinal soluble protein from monkey retina was incubated with calcium. Calpain activation and proteolysis were observed by addition of calcium, and both changes were inhibited by calpain inhibitor. Conclusions These results suggested that calpain plays an important role in cell death in monkey retina. Dr. Shearer has a significant financial interest (research contract and consulting fee) in Senju Pharmaceutical Co., Ltd.

Keywords: calcium • retinal degenerations: cell biology • proteolysis