HspB8 is neuroprotective during oxygen glucose deprivation and reperfusion

Heat shock protein B8 (HspB8) is a chaperone protein that is highly and constitutively expressed in the brain, cardiac tissue and many other organs. Recently, it has been shown that HspB8 can enhance cardiac function and render cardioprotection. However, the potential benefits of HspB8 action on ischemic stroke and the underlying mechanism(s) are largely unknown. To investigate whether HspB8 exerts protective effects on in vitro ischemia/ reperfusion (I/R) injury, mouse neuroblastoma cells were subjected to oxygen-glucose deprivation and reoxygenation (OGD/R). At first, we investigated and described the HspB8 expression and distribution in N2A cells exposed to OGD/R. Expressions of HspB8 were upregulated in mouse N2A cells after OGD/R, both at mRNA and protein levels. The level of HspB8 began increased after the OGD/R and peaked at 12 hour (12h) after the reperfusion, then declined at 24-hour time points, however, the level of HspB8 was still significantly increased compared to controls. Immunofluorescence analysis revealed that the expressed HspB8 was constitutively localized in the cytoplasm and at the periphery of the nucleus. Nuclear HspB8 levels increased after OGD/R compared with levels in the control, beginning as early as 4h reperfusion, the most conspicuous nuclear HspB8 staining was observed after 24h of reperfusion. Furthermore, overexpression of HspB8 reduced OGD/R -induced apoptosis by reducing the release of cytochrome c from mitochondria to cytosol. In conclusion, our data demonstrated that increased HspB8 expression and its nuclear shift in mouse N2A neuroblastoma cells protected against I/R injury, resulting in reduced apoptosis with the decrease of the release of cytochrome c from mitochondria to cytosol. Therefore, HspB8 might play a fundamental role in opposing and alleviating I/R injury in primary myocardial cells, and it may constitute a new therapeutic target for cerebral ischemic diseases.