β-sitosterol alleviates pulmonary arterial hypertension by altering smooth muscle cell phenotype and DNA damage/cGAS/STING signaling

Background: Pulmonary arterial smooth muscle cells (PASMCs) have a neoplastic phenotype characterized by hyperproliferative and anti-apoptotic features that contribute to pulmonary hypertension (PH) development. DNA-sensing adapter protein stimulator of interferon genes (STING) regulate the phenotypic switch of vessel smooth muscle cells. beta-sitosterol (SITO) is a nutrient derived from plants that inhibits vascular smooth muscle cell proliferation without notable toxicity. However, the effect of SITO on cancer-like PH-associated pulmonary vascular remodeling and the specific mechanism has not yet be studied. Purpose: This study investigated the in vitro and in vivo effects of SITO against PH, and its underlying mechanisms. Methods: The therapeutic efficacy of SITO was assessed, and its underlying mechanisms were explored in hypoxia-induced and platelet-derived growth factor (PDGF)-BB-stimulated primary PASMCs and in a monocrotaline (MCT)-induced preclinical PH rat model. SITO or sildenafil (SID) were administered after the MCT intraperitoneal injection. Pulmonary parameters, right heart function, morphology, and PASMCs were cultured for verification. The expression levels of DNA damage/cyclic GMP-AMP synthase (cGAS)/STING were determined using immunofluorescence and Western blotting. STING agonists that interfere with PASMCs were used to determine whether STING mediates the effects of SITO. Results: SITO prevented PASMCs proliferation, promoted apoptosis and suppressed phenotypic switching in a dose-dependent manner in vitro and in vivo. In vivo results in rats demonstrated that four weeks of intragastric SITO administration effectively mitigated the MCT-induced elevation of hemodynamic parameters, improved right cardiac function, and reduced pulmonary arteries remodeling. Mechanistically, DNA damage and cGAS/STING/nuclear factor kappa-B signaling activation were observed in rats with PH and cultured PASMCs. SITO exhibited protective effects by suppressing the DNA damage, potentially via inhibiting the expression level of the cGAS/STING signaling pathway. Pharmacological overexpression of STING abolished the anti-proliferative effects of SITO treatment in hypoxia-induced and PDGF-stimulated PASMCs by downregulating PCNA. Conclusion: SITO may be an attractive agent for PH vascular remodeling by inhibiting proliferation and modulating the phenotypic switch in PASMCs via the DNA damage/cGAS/STING signaling pathway. This study provides a novel therapeutic agent and mediator of the pathological development of PASMCs and PH.