Cross-talk between TSC2 and the extracellular matrix controls pulmonary vascular proliferation and pulmonary hypertension

Increased proliferation and survival of cells in small pulmonary arteries (PAs) drive pulmonary arterial hypertension (PAH). Because cell growth mediated by the mTOR-containing mTORC1 complex is inhibited by tuberous sclerosis complex 2 (TSC2), we investigated the role of this GTPase-activating protein in PAH pathology. TSC2 abundance was decreased in remodeled small PAs and PA vascular smooth muscle cells (PAVSMCs) from patients with PAH or from rodent pulmonary hypertension (PH) models, as well as PAVSMCs maintained on substrates that reproduced pathology-induced stiffness. Accordingly, mice with smooth muscle–specific reduction in TSC2 developed PH. At the molecular level, decreased TSC2 abundance led to stiffness-induced PAVSMC proliferation, increased abundance of the mechanosensitive transcriptional coactivators YAP/TAZ, and enhanced mTOR kinase activity. Moreover, extracellular matrix (ECM) produced by TSC2-deficient PAVSMCs stimulated the proliferation of nondiseased PA adventitial fibroblasts and PAVSMCs through fibronectin and its receptor, the α5β1 integrin. Reconstituting TSC2 in PAVSMCs from patients with PAH through overexpression or treatment with the SIRT1 activator SRT2104 decreased YAP/TAZ abundance, mTOR activity, and ECM production, as well as inhibited proliferation and induced apoptosis. In two rodent models of PH, SRT2104 treatment restored TSC2 abundance, attenuated pulmonary vascular remodeling, and ameliorated PH. Thus, TSC2 in PAVSMCs integrates ECM composition and stiffness with pro-proliferative and survival signaling, and restoring TSC2 abundance could be an attractive therapeutic option to treat PH. Description TSC2 limits mechanosensitive and cell growth signaling that drives pulmonary hypertension. Protection from pulmonary hypertension Pulmonary arterial hypertension (PAH) is partially driven by the proliferation of pulmonary arterial vascular smooth muscle cells (PAVSMCs) induced by stiffening of pulmonary arteries. The GTPase-activating protein TSC2 inhibits cell growth–promoting signaling, leading Shen et al. to characterize how TSC2 might prevent the pathogenesis of PAH. Pulmonary arteries and PAVSMCs from PAH patients had reduced TSC2 abundance, and pulmonary artery remodeling and hypertension developed in mice with partial deficiency of TSC2 in smooth muscle. Analysis of PAVSMCs suggested that the stiffening of pulmonary arteries in PAH led to a decrease in TSC2 content in smooth muscle, triggering remodeling of the extracellular matrix, activation of mechanosensitive and cell growth signaling pathways, and increased PAVSMC proliferation. Restoring TSC2 abundance in rodent models with a drug currently in clinical trials improved lung function and reduced pulmonary hypertension. Thus, strategies that increase TSC2 abundance in PAVSMCs may reverse PAH, a condition that is ultimately fatal and that currently lacks effective treatments. –WW