PLCγ1-PKCε-IPR1 signaling plays an important role in hypoxia-induced calcium response in pulmonary artery smooth muscle cells.

Hypoxia-induced pulmonary vasoconstriction (HPV) is attributed to an increase in intracellular Ca concentration ([Ca]) in pulmonary artery smooth muscle cells (PASMCs). We have reported that phospholipase C-γ1 (PLCγ1) plays a significant role in the hypoxia-induced increase in [Ca] in PASMCs and attendant HPV. In this study, we intended to determine molecular mechanisms for hypoxic Ca and contractile responses in PASMCs. Our data reveal that hypoxic vasoconstriction occurs in pulmonary arteries, but not in mesenteric arteries. Hypoxia caused a large increase in [Ca] in PASMCs, which is diminished by the PLC inhibitor U73122 and not by its inactive analog U73433 . Hypoxia augments PLCγ1-dependent inositol 1,4,5-trisphosphate (IP) generation. Exogenous ROS, hydrogen peroxide (HO), increases PLCγ1 phosphorylation at tyrosine-783 and IP production. IP receptor-1 (IPR1) knock-down remarkably diminishes hypoxia- or HO-induced increase in [Ca]. Hypoxia or HO increases the activity of IPRs, which is significantly reduced in protein kinase C-ε (PKCε) knockout PASMCs. A higher PLCγ1 expression, activity, and basal [Ca] are found in PASMCs, but not in mesenteric artery smooth muscle cells from mice exposed to chronic hypoxia (CH) for 21 days. CH enhances HO- and ATP-induced increase in [Ca] in PASMCs and PLC-dependent, norepinephrine-evoked pulmonary vasoconstriction. In conclusion, acute hypoxia uniquely causes ROS-dependent PLCγ1 activation, IP production, PKCε activation, IPR1 opening, Ca release, and contraction in mouse PASMCs; CH enhances PASM PLCγ1 expression, activity, and function, playing an essential role in pulmonary hypertension in mice.