PLCγ1-PKCε-IP₃R1 signaling plays an important role in hypoxia-induced calcium response in pulmonary artery smooth muscle cells

<jats:p>Hypoxia-induced pulmonary vasoconstriction (HPV) is attributed to an increase in intracellular Ca<jats:sup>2+</jats:sup>concentration ([Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub>) 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<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub>in PASMCs and attendant HPV. In this study, we intended to determine molecular mechanisms for hypoxic Ca<jats:sup>2+</jats:sup>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<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub>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<jats:sub>3</jats:sub>) generation. Exogenous ROS, hydrogen peroxide (H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>), increases PLCγ1 phosphorylation at tyrosine-783 and IP<jats:sub>3</jats:sub>production. IP<jats:sub>3</jats:sub>receptor-1 (IP<jats:sub>3</jats:sub>R1) knock-down remarkably diminishes hypoxia- or H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>-induced increase in [Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub>. Hypoxia or H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>increases the activity of IP<jats:sub>3</jats:sub>Rs, which is significantly reduced in protein kinase C-ε (PKCε) knockout PASMCs. A higher PLCγ1 expression, activity, and basal [Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub>are found in PASMCs, but not in mesenteric artery smooth muscle cells from mice exposed to chronic hypoxia (CH) for 21 days. CH enhances H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>- and ATP-induced increase in [Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub>in PASMCs and PLC-dependent, norepinephrine-evoked pulmonary vasoconstriction. In conclusion, acute hypoxia uniquely causes ROS-dependent PLCγ1 activation, IP<jats:sub>3</jats:sub>production, PKCε activation, IP<jats:sub>3</jats:sub>R1 opening, Ca<jats:sup>2+</jats:sup>release, and contraction in mouse PASMCs; CH enhances PASM PLCγ1 expression, activity, and function, playing an essential role in pulmonary hypertension in mice.</jats:p>