HIF Upregulates AQP1 Expression in Pulmonary Arterial Smooth Muscle Cells (PASMCs) in a Calcium‐Dependent Manner

Prolonged exposure to hypoxia can have adverse effects on the pulmonary vasculature, including structural remodeling and sustained contraction, resulting in the development of pulmonary hypertension. Both PASMC proliferation and migration contribute to the vascular remodeling. The expression of AQP1, a membrane water channel protein, is elevated during hypoxia. Studies in other cell types suggest that AQP1 is a direct transcriptional target of hypoxia inducible factor (HIF)‐1. Moreover, an increase in intracellular calcium ([Ca 2+ ] i ) concentration is a hallmark of hypoxic exposure in PASMCs. Thus, we wanted to determine whether HIF regulates AQP1 in PASMCs and, if so, whether the process was Ca 2+ ‐dependent. PASMCs were incubated with DMOG, which inhibits HIF protein degradation. DMOG produced a time‐dependent increase in AQP1 protein, but not mRNA. Interestingly, incubation with DMOG increased [Ca 2+ ] i in PASMCs, and this elevation was prevented by the voltage‐gated Ca 2+ channel inhibitor, verapamil (VER). VER also blocked upregulation of AQP1 protein by DMOG, but had no effect on expression of GLUT1, a canonical HIF transcriptional target. Thus, our results show that contrary to reports in other cell types, in PASMCs, AQP1 does not appear to be a direct target for HIF transcriptional regulation. Instead, AQP1 protein may be upregulated by a mechanism involving HIF‐dependent increases in [Ca 2+ ] i .