Role of Ryanodine Receptor Channel and Mechanisms of Vascular Diseases

Abstract

The functional importance of ryanodine receptors (RyRs) is well established in cardiac and skeletal diseases, but not in smooth muscle diseases. Here we explored the potentially essential role of RyRs in pulmonary hypertension. Using real-time RT-PCR and Western blot analysis, we found that all three RyR subtypes (RyR1, RyR2 and RyR3) were expressed in pulmonary artery smooth muscle cells (PASMCs). Studies with gene knockout (KO) mice revealed that RyR1, RyR2 and RyR3 all showed their functional activity. Contractile and calcium responses in PASMCs following acute hypoxia for 5 and 30 min respectively were completely blocked in RyR2 KO mice, but only partially inhibited by RyR1 or RyR3 KO mice. RyR channel activity and calcium release were largely increased in PASMCs from mice with pulmonary hypertension induced by chronic hypoxia for 21 days. The chronic hypoxia-induced increases in RyR channel activity and calcium release are fully abolished in PASMCs from SMC-specific RyR2 KO mice. Pulmonary artery vasoconstriction, remodeling, and hypertension following chronic hypoxia are all nulled in RyR2 KO mice. FK506 binding protein 12.6 (FKBP12.6, the RyR2 channel inhibitor) is significantly dissociated from the channel in PASMCs from mice with hypoxia-induced pulmonary hypertension. FKBP12.6 KO promoted, while FKBP12.6 overexpression diminished, hypoxic pulmonary hypertension in mice. Treatment of S107, a specific RyR2/FKBP12.6 stabilizer, also protects against hypoxic pulmonary hypertension. Rieske iron-sulfur protein (RISP) in mitochondrial complex III serves as an essential, primary molecule in hypoxia-evoked reactive oxygen species (ROS) generation and subsequent FKBP12.6/RyR2 dissociation in PASMCs. Intravenous administration of lentiviral RISP shRNAs eliminates hypoxia-induced pulmonary hypertension in mice. Collectively, we conclude that hypoxia can cause RISP-mediated ROS production, FKBP12.6/RyR2 dissociation, RyR2 channel hyperfunction, sarcoplasmic reticulum calcium leaking, increased calcium signaling, PASMC proliferation and remodeling, and ultimately pulmonary hypertension.