Role of Na+/H+ Exchanger 1 in Regulating Resistance to Apoptosis in Pulmonary Arterial Smooth Muscle Cells

Abstract

Vascular remodeling within the pulmonary arterioles is a key component of pulmonary arterial hypertension (PAH). In a rat model of severe PAH, the SU5416‐Hypoxia (SuHx) model, pulmonary arterial smooth muscle cells (PASMCs) demonstrate resistance to apoptosis and contribute to vascular remodeling. Na+/H+ exchange (NHE) is increased in SuHx PASMCs; however, few studies have elucidated the functional role of NHE in these cells. Previous studies have shown a link between NHE and the expression of CHOP, a critical mediator of apoptosis. Therefore, we tested the hypothesis that altering NHE1 expression and or activity is sufficient to modulate apoptosis in PASMCs. PASMCs were isolated from distal pulmonary arteries dissected from vehicle‐treated, male, Wistar rats or rats exposed to hypoxia after an injection of SU5416 (SuHx rats). PASMCs were treated with vehicle, a combination of a pharmacologic inhibitor of NHE (EIPA) and hydrogen peroxide (H2O2), an apoptosis‐inducing agent, or either EIPA or H2O2 alone. Apoptosis was measured via Hoechst staining. In other experiments, control PASMCs were infected with a viral construct to overexpress wild‐type NHE1 (AdNHE1), a translocation‐disabled NHE1 mutant (AdE266I), or green fluorescent protein (AdGFP) as a control. NHE activity was measured via the ammonium‐pulse technique. SuHx PASMCs exhibited decreased CHOP expression and minimal apoptosis rates in response to H2O2 when compared to control PASMCs. EIPA had no effect on unstimulated apoptosis in control cells, but induced apoptosis in SuHx PASMCs at baseline and sensitized the cells to H2O2. AdNHE1, but not AdE266I, increased NHE1 activity. Interestingly, both AdNHE1 and AdE266I conferred a resistance to H2O2‐induced apoptosis when compared to the AdGFP‐infected cells. Overall, these findings suggest that increased NHE1 may be responsible for attenuating apoptotic responses in SuHx PASMCs and that increasing NHE1 levels in normal PASMCs is sufficient to promote increased survival via an ion‐translocation‐independent function.Support or Funding InformationSupported by NIH grants HL073859, HL126514 and HL084762