Abstract 4364408: Protein Arginine Methyltransferase 5 Drives Pulmonary Arterial Remodeling in Pulmonary Arterial Hypertension

Background: Pulmonary arterial hypertension (PAH) is a progressive and fatal disease characterized by excessive proliferation and reduced apoptosis of pulmonary arterial smooth muscle cells (PASMCs) and pulmonary vascular remodeling. In PAH, PASMCs undergo a metabolic shift to glycolysis, resulting in lactate over-production. Lactate promotes tumor progression through a post-translational protein modification called lysine lactylation. Protein arginine methyltransferase 5 (PRMT5), the primary enzyme responsible for symmetric dimethylarginine (SDMA) modifications of histone and non-histone proteins, is implicated in cancer. However, the role of PRMT5 and its potential interplay with lactate in PAH remains unknown. Goal: To determine the role of PRMT5 in PA remodeling and PAH. Methods: Immunohistochemical, immunoblot, proteomic analyses, proliferation, apoptosis assays; SU5416/Hypoxia (SuHx) mouse and rat models of PH. Results: PRMT5 was over-accumulated in SMα-actin-positive areas of small muscular PAs from PAH patients and rats with SuHx PH, and distal human PAH PASMCs compared to non-diseased controls, supporting increased protein SDMA modification, PASMC hyper-proliferation, and apoptosis resistance. Proteomic analysis of nuclear fraction anti-Kla immunoprecipitates identified PRMT5 as one of most significantly hyper-lactylated nuclear proteins in PAH PASMCs compared to controls. siRNA-induced depletion of lactate dehydrogenase (LDHA), an enzyme converting pyruvate into lactate, downregulated PRMT5, inhibited proliferation and induced apoptosis in human PAH PASMCs. Treatment of control PASMCs with lactate or pro-PH factor PDGF-BB upregulated PRMT5 and cell proliferation. Importantly, siRNA PRMT5 reduced P-S6 and P-S473-Akt, inhibited proliferation and induced apoptosis of human PAH PASMCs. Furthermore, pharmacological inhibition of PRMT5 with GSK3326595 significantly inhibited proliferation and induced apoptosis of human PAH PASMCs, and significantly decreased PA remodeling and PH, as assessed by medial wall thickness (PA MT) and systolic RV pressure (sRVP), in mice with SuHx-induced PH compared to vehicle-treated group. Conclusions: Collectively, our data suggest that LDHA/lactate and PDGF-BB-driven PRMT5 up-regulation promotes PASMC hyper-proliferation, survival, PA remodeling, and PH via activating Akt/mTOR. Targeting PRMT5 signaling could represent potentially attractive strategy to treat PAH.