Abstract 17220: Functional Roles and Molecular Mechanisms of Calcium Release Signaling in Hypoxic Cellular Responses in Pulmonary Artery Smooth Muscle Cells

Abstract

Introduction: Hypoxia causes contractile and proliferative responses in pulmonary arterial smooth muscle cells (PASMCs), but not systemic artery SMCs, thereby leading to pulmonary hypertension (PH), but not systemic hypertension. However, the underlying mechanisms remain unclear. Hypothesis: Ca 2+ release signaling in PASMCs may mediate hypoxic pulmonary artery vasoconstriction, remodeling and hypertension. Methods: Single cell RT-PCR and Western blot analysis, FRET and immunoprecipitation, tissue contraction assay, immunohistochemistry staining and pressure-volume loop analysis, and genetic and pharmacological approaches, were, respectively, used to determine targeted molecular expression, interaction and function. Results: All ryanodine receptor (RyR1, RyR2 and RyR3) Ca 2+ release channels are expressed in mouse PASMCs. RyR1 or RyR3 knockout (KO) partially inhibits, while RyR2 KO completely blocks, hypoxic cellular responses. SMC-specific RyR2 KO restores abolishes hypoxic pulmonary artery vasoconstriction, remodeling and hypertension in mice. RyR2 KO also inhibits hypoxic nuclear factor (NF)-κB and downstream cyclin D1 activation. FK506 binding protein 12.6 (FKBP12.6) is an endogenous RyR2 inhibitor; its KO or FK506 treatment enhances, and treatment of S107 (a specific RyR2/FKBP12.6 stabilizer) inhibits hypoxic PH. Lentiviral shRNA-mediated SMC-specific Rieske iron-sulfur protein (RISP) knockdown diminishes mitochondrial reactive oxygen species (ROS) generation, RyR2/FKBP12.6 complex dissociation, and RyR2 activation, thereby blocking hypoxic PH. Conclusions: RyR1, RyR2 and RyR3 are all involved in hypoxic contractile and proliferative responses in PASMCs, but RyR2 is a most important player. RISP-dependent mitochondrial ROS - FKBP12.6/RyR2 complex dissociation - RyR2 hyperfunction signaling mediate PA vasoconstriction. RyR2 hyperfunction also activates Ca2+-dependent NF-κB/cyclinD1 pathway to provoke PA remodeling; PA vasoconstriction and remodeling together cause PH. Furthermore, RISP-mediated ROS inhibition, RyR2/FKBP12.6 complex stabilization and Ca2+ release blockade may be novel and effective options for the treatment of PH.