Vascular Smooth Muscle Vps34 in Pulmonary Arterial Hypertension - PROJECT SUMMARY/ABSTRACT Pulmonary arterial hypertension (PAH) is a progressive and rapidly fatal disease with no cure. PAH manifests by remodeling of small pulmonary arteries, leading to increased PA pressure, elevated right ventricular (RV) afterload, heart failure, and death. One of the key components of PA remodeling is increased proliferation and survival of PA vascular smooth muscle cells (PAVSMC). Recently, I found that activation of Class III Phosphatidylinositol 3-kinase vacuolar protein sorting 34 (Vps34), evidenced by lack of inhibitory phosphorylation at Ser164 (P-S164-Vps34), promotes hyper-proliferation of PAH PAVSMC, which is Akt- dependent and is associated with accumulation of Vps15, deficiency of TSC2, activation of mammalian target of rapamycin complex 1 (mTORC1), increased growth and proliferation of PAVSMC, and pulmonary vascular remodeling in PAH. Similar to human PAH, decreased P-S164-Vps34 was also observed in PA VSM from experimental rodent PH models, which is reversely correlated with increased PA medial thickness, and was associated with increased RV systolic pressure (RVSP) and RV hypertrophy. Further, I show that Vps34 inhibition by siRNA significantly decreased PAH PAVSMC proliferation and survival, reduced Vps15 and restored TSC2 protein levels, and inactivated mTORC1. Additionally, our data show that pharmacological inhibition of Vps34 reverses PAH-specific signaling abnormalities, selectively inhibits proliferation and promotes apoptosis in human PAH PAVSMC, and significantly attenuated established pulmonary vascular remodeling and reduced RV hypertrophy in mice with SU5416/hypoxia-induced PH. Based on our preliminary data, I hypothesize that Vps34 is activated in PAH PAVSMC in an Akt-dependent manner, leading to increased PAVSMC proliferation and survival, pulmonary vascular remodeling, and PH via modulating Vps15 and TSC2-mTORC1 axis. I also propose that pharmacological inhibition of Vps34 inhibits proliferation and induces apoptosis in PAH PAVSMC, and attenuates or reverses pulmonary vascular remodeling and PH. I will test my hypothesis using three specific aims: Aim 1 will examine the status and mechanisms of Vps34 regulation in PAH pulmonary vasculature, Aim 2 will determine the role of Vps34 in human PAVSMC proliferation and survival, and Aim 3 will evaluate whether molecular or pharmacological inhibition of Vps34 attenuates or reverses experimental PH in vivo. The proposed study will identify a new critical mechanism of pulmonary vascular remodeling and dissect a new remodeling- focused molecular target for therapeutic intervention.
