Abstract Rationale Pulmonary Arterial Hypertension (PAH) is a progressive fatal disease characterized by the remodeling of small pulmonary arteries (PAs), primarily driven by excessive proliferation and reduced apoptosis of pulmonary arterial smooth muscle cells (PASMCs). PASMCs in PAH undergo a metabolic shift to glycolysis, leading to elevated lactate production. Lactate is known to promote tumor growth and progression via post-translational protein modification (lysine lactylation). Protein arginine methyltransferase 5 (PRMT5) is the primary enzyme responsible for generating symmetric dimethylarginine (SDMA) marks on histone and non-histone proteins. PRMT5 dysregulation is implicated in various oncogenic processes, but its role and potential link with lactate in PAH is not known. Methods/Results Immunohistochemical analysis demonstrated that PRMT5 protein levels were markedly higher in smooth muscle alpha-actin (SMA)-positive areas of small muscularized PAs of human PAH lungs. Immunoblot and RNA sequencing analyses demonstrated that PRMT5 was selectively upregulated in early-passage distal PASMCs, but not PA endothelial cells and adventitial fibroblasts, from PAH patients compared to non-diseased controls. This was associated with increased protein SDMA modification, hyper-proliferation, and deficiency of pro-apoptotic protein Bcl-2 interacting mediator of cell death (Bim). Proteomic analysis of anti-lysine lactylation (anti-Kla) immunoprecipitates from nucleus-enriched fractions identified PRMT5 as one of most significantly hyper-lactylated proteins in PAH compared to control PASMCs. siRNA-induced depletion of lactate dehydrogenase (LDHA), an enzyme converting pyruvate into lactate, downregulated PRMT5, inhibited proliferation (Ki67), restored Bim, and induced apoptosis (In situ cell death detection kit) in human PAH PASMCs. In contrast, treatment with lactate or pro-PH factor PDGF-BB upregulated PRMT5 and proliferation of control PASMCs. Importantly, siRNA PRMT5 reduced phosphorylation of S473-Akt and ribosomal protein S6, molecular signatures of Akt-mTORC1 activity, inhibited proliferation, restored Bim protein levels, and induced apoptosis in human PAH PASMCs. These data demonstrate that LDHA/lactate axis promotes hyper-proliferation, and apoptosis resistance of human PASMCs via PRMT5. Furthermore, pharmacological inhibition of PRMT5 with GSK3326595 significantly inhibited proliferation and induced apoptosis in human PAH PASMCs, and attenuated SuHx-induced PA remodeling and PH in mice as evidenced by significant decrease in medial wall thickness (PA MT) and systolic RV pressure (sRVP) compared to vehicle-treated group. Conclusion 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. This abstract is funded by: 10.58275/AHA.25CDA1450516.pc.gr.229627
Jiang et al. (Fri,) studied this question.