iPSC modeling of pulmonary arterial hypertension to uncover pathomechanisms and unrecognized modes of action of sotatercept

Pulmonary arterial hypertension (PAH) is a potentially fatal disease characterized by obliterative remodeling of distal pulmonary arteries, commonly associated with bone morphogenetic receptor type 2 (BMPR2) gene mutations. In patients with PAH, sotatercept, an activin signaling inhibitor, improves hemodynamics and outcomes, but clinical responses vary and sometimes occur within weeks, suggesting additional mechanisms beyond its anti-proliferative, pro-apoptotic and anti-remodeling effects. Using patient-specific induced pluripotent stem cell-derived smooth muscle cells (iSMCs) with BMPR2 extracellular- or kinase-domain mutations, we were able to reproduce Activin A-driven PAH traits, including hyperproliferation, reduced apoptosis, enhanced contraction and excessive matrix production. We identified smooth muscle cell-to-myofibroblast transition as a previously unknown contributor to pulmonary vascular remodeling and demonstrate that it is blocked by sotatercept. Beyond its established effects, sotatercept rapidly reduced contractility, collagen-integrin mechanotransduction and TGF{beta} receptor expression, disrupting a pathological positive feedback loop, reflected by lower levels of circulating TGF{beta}1 in patients on sotatercept. Taken together, our patient-derived iSMC platform links mutation-dependent mechanisms of pulmonary vascular remodeling to variable drug responsiveness and reveals previously unrecognized, potentially rapid-acting modes of sotatercept in PAH. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=80 SRC="FIGDIR/small/711267v1_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@18d5e53org.highwire.dtl.DTLVardef@2bc80dorg.highwire.dtl.DTLVardef@5ace98org.highwire.dtl.DTLVardef@1b16171_HPS_FORMAT_FIGEXP M_FIG C_FIG