Extracellular Acidification Activates cAMP Responsive Element Binding Protein via Na+/H+ Exchanger Isoform 1–Mediated Ca 2+ Oscillation in Central Nervous System Pericytes

Abstract

Objective— We have previously shown that Na + /H + exchanger isoform 1 (NHE1) plays an important role in Ca 2+ signaling and cell proliferation in human central nervous system (CNS) pericytes. The aims of the present study were to elucidate how NHE1–induced Ca 2+ signaling during acidosis is transformed into cellular responses in CNS pericytes. Methods and Results— Human CNS pericytes were cultured, and the activation of cAMP responsive element–binding protein (CREB) was evaluated by Western blotting analysis, immunofluorescence, and luciferase assays. In human CNS pericytes, low extracellular Na + or low pH generated Ca 2+ oscillation and subsequently phosphorylated Ca 2+ /calmodulin-dependent kinase II (CaMKII) and CREB in a time-dependent manner. Focal cerebral ischemia was applied using photothrombotic distal middle cerebral artery occlusion in mice, and the phosphorylation of CREB and the production of interleukin-6 were observed in pericytes migrating into the peri-infarct penumbra during the early phase after ischemic insult. Conclusion— Our results indicate that extracellular acidosis induces Ca 2+ oscillation via NHE1, leading to Ca 2+ /CaMKII–dependent CREB activation in human CNS pericytes. Acidosis may upregulate a variety of proteins, such as interleukin-6, through the NHE1-Ca2+/CaMKII–CREB pathway in brain pericytes and may thus modulate brain ischemic insult.