Involvement of calpain isoforms in ischemia-reperfusion injury in rat retina

Purpose. Much evidence has accumulated suggesting that activation of calpai n causes neuronal cell death in ischemic brain. However, little is known ab out the involvement of calpain in retinal cell death in ischemic injury. Th us, the purpose of present study was to investigate the involvement of calp ain isoforms (m- and mu-calpain) in ischemia-reperfusion injury in retina f rom rat. Methods. Retinal ischemia was produced by occlusion of the central retinal artery for one hour, and this was followed by reperfusion for seven days. C alpain mRNAs, calpain activities, total calcium content and proteolysis of alpha-spectrin were determined in retina. Effect of a calpain inhibitor SJA 6017 was histologically tested in retinal injury after ischemia-reperfusion . Results. Following retinal ischemia, most of cells in the ganglion cell lay er were sloughed off by day 1 after reperfusion, followed by loss of cells in the inner plexiform layer on day 3 and loss of cells in the inner nuclea r layer by day 5. These morphologic changes were accompanied by several pre sumptive biochemical indicators of calpain activation: increased calcium, p roteolysis of alpha-spectrin (a sensitive substrate for calpains), decrease d caseinolytic activity for both calpains (suggesting calpain activation fo llowed by autolytic degradation), increased mRNA levels for mu-calpain and calpastatin - the endogenous inhibitor of calpains - and decreased mRNA lev els for mu-calpain. Moreover, the calpain inhibitor SJA6017 protected the r eduction of cell density in the ganglion cell layer after ischemia-reperfus ion. Conclusion. These results suggest that calpain isoforms may play an importa nt role in neuronal cell death induced by retinal ischemia-reperfusion inju ry in rat.