Abstract Rationale Pulmonary arterial hypertension (PAH) is a fatal disease for which current pharmacotherapies, including emerging agents such as sotatercept, are not effective for all patients. Further development of PAH therapeutics requires a deeper understanding of disease mechanisms, particularly pulmonary vascular remodeling. We previously reported that VPS34, a key component of the phosphatidylinositol-3 kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway, is activated—evidenced by decreased Ser164 phosphorylation—in pulmonary arterial smooth muscle cells (PAVSMCs) from PAH patients. VPS34 activation is required for the hyperproliferative phenotype of PAH PAVSMCs, and our prior findings suggest that Akt-induced VPS34 activation may be mediated by protein phosphatases (PPPs). However, the precise mechanisms remain unclear. Methods and Results Experimental pulmonary hypertension was induced in 6-8-week-old male and female C57BL/6 mice by exposure to SU5416 and chronic hypoxia (10% O2, SuHx) for three weeks. While still under hypoxia, mice were randomized to receive either vehicle or SAR405 (a VPS34 inhibitor) for two additional weeks. Age- and sex-matched normoxic (21% O2) mice served as controls. Lung tissues were analyzed by immunohistochemistry (IHC) for P-Ser164-VPS34, smooth muscle (SM) actin, fibronectin (FN), and PPP1CA. Preliminary data by IHC revealed that SM FN expression positively correlated with VPS34 activation (i.e., decreased P-Ser164-VPS34). SAR405 treatment reduced SM FN expression, indicating that VPS34 regulates FN expression. Consistent with our in silico simulations showing interactions among PPP1CA, Akt, and VPS34, we also observed a positive correlation between SM PPP1CA expression and VPS34 activation, suggesting that PPP1CA may facilitate Akt-induced VPS34 activation. Conclusions These preliminary findings suggest that Akt-induced VPS34 activation is associated with upregulation of SM PPP1CA and FN. Ongoing studies will assess the signaling mechanisms underlying these regulations in human PAVSMCs. This abstract is funded by: NIH
Shen et al. (Fri,) studied this question.