Blockade of Ser16-Hsp20 phosphorylation attenuates neuroprotection dependent upon Bcl-2 and Bax.

Ischemic stroke causes a significant amount of cell damage resulting from an insufficient supply of glucose and oxygen to central nervous system tissue and finding more effective therapeutic neuroprotective agents has become a priority in the treatment of ischemic stroke. Hsp20, one of the small heat shock proteins, has been implicated in multiple physiological and pathophysiological processes and is a potential neuroprotective agents. To investigate whether Hsp20 exerts protective effects on in vitro ischemia-reperfusion injury, mouse neuroblastoma cells were subjected to oxygen-glucose deprivation/reoxygenation (OGDR) insult. The N2a cells transfected with Hsp20 and constitutively phosphorylated Hsp20 (S16D) had significantly less cell loss and less proportion of apoptotic cells compared to N2a cells transfected with pEGFP-N1 after oxygen-glucose deprivation (OGD) 4 h plus 12 and 24 h reperfusion, which showed no difference in N2a cells transfected with nonphosphorylatable Hsp20 (S16A). Meanwhile, transfected with Hsp20 and constitutively phosphorylated Hsp20 (S16D) also significantly attenuated mitochondrial fragmentation and modulated Bcl-2 and Bax expression level after OGD 4 h plus 12 reperfusion, which were not affected in N2a cells transfected with Hsp20 (S16A). In conclusion, our data demonstrated that increased Hsp20 and Hsp20 (S16D) expression in mouse N2A neuroblastoma cells protected against ischemia-reperfusion injury, the neuroprotective mechanism may be related to regulate Bcl-2 and Bax expression. However, blockade of Ser16-Hsp20 phosphorylation attenuated the neuroprotective effects of Hsp20. Therefore, Hsp20 and factors that contribute to regulation of phosphorylation on Ser16 of Hsp20 are potential new therapeutic targets for the treatment of cerebral ischemia-reperfusion injury.