Inhibition of protein translation as a mechanism of acidotic pH protection against ischaemic injury through inhibition of CREB mediated tRNA synthetase expression

Ischaemia associated reduction in local tissue pH is well documented but the mechanisms through which it influences cell survival remain poorly understood. Using renal epithelial HK-2 cells we demonstrate acidotic pH6.4 protects against oxygen glucose deprivation (OGD) induced cell death. Initial exploration of the mechanisms responsible using microarray analysis revealed acidotic inhibition of OGD induced aminoacyl-tRNA synthetase (ARS) gene expression. These genes are key components of protein translation, which was markedly attenuated by reduced pH. Inhibition of protein synthesis using the ARS inhibitor halofuginone or cycloheximide protected against OGD induced injury. To explore further we focussed on the transcription factor CREB, identified by pathway analysis of microarray data and observed a pH dependent decrease in OGD induced activation. Inhibition of CREB/CBP interaction prevented OGD induced isoleucyl-ARS (IARS) expression, reduced protein synthesis and protected against OGD induced cellular injury. In addition we also observed that acidotic pH attenuated the OGD induced pro-apoptotic unfolded protein response (UPR) activated gene DDIT3. We suggest that maladaptive activation of CREB and ARS gene expression, through the maintenance of protein synthesis contributes to ER stress and UPR activation and that acidotic pH through inhibition of CREB activation inhibits protein synthesis and ultimately UPR activated apoptotic signals.