Endothelial Extracellular Matrix Drives Smooth Muscle Cell Hyperplasia via YAP1 Activation in Pulmonary Hypertension Secondary to Left Heart Disease

Introduction: Pulmonary hypertension (PH) is characterized by hyperplasia of the pulmonary artery (PA), which increases pulmonary vascular resistance and imposes stress on the right ventricle (RV), ultimately leading to RV failure. The mechanisms driving PA hyperplasia in PH secondary to left heart disease (LHD) remain poorly characterized, and therapeutic options for PH-LHD are lacking. Here, we aimed to elucidate the role of endothelial extracellular matrix (ECM) in promoting PA smooth muscle cell (SMC) hyperplasia in PH-LHD.

Methods and Results: Human PA samples from LHD patients with or without PH (PH-LHD or LHD w/o PH, respectively) and from healthy heart donors (controls) were obtained when the PA was adjusted for surgical anastomosis during orthotopic heart transplantation. Histological analyses and atomic force microscopy revealed intimal SMC hyperplasia and progressive remodeling and stiffening of the endothelial ECM in LHD w/o PH and PH-LHD PA samples. Based on these findings, we hypothesized a regulatory role of endothelial ECM in promoting SMC hyperplasia. Further in vitro studies showed that culturing healthy SMCs on decellularized ECM (dECM) produced by LHD w/o PH or PH-LHD pulmonary arterial endothelial cells (ECs), or on commercial matrices with corresponding stiffness, promoted SMC proliferation and migration. In contrast, culturing on dECM produced by healthy ECs suppressed these cellular functions in PH-LHD SMCs, suggesting a mechanotransductive regulation of SMC hyperplasia in PH-LHD. These findings were corroborated by immunofluorescent detection of nuclear YAP1 – a mechanosensitive transcriptional coactivator – which increased in LHD w/o PH and PH-LHD SMCs as compared to control SMCs, and in control SMCs cultured on dECM produced by LHD w/o PH or PH-LHD ECs or stiff matrices. Importantly, pharmacological inhibition of YAP1 in PA SMCs by treatment with 1 µM Verteporfin for 72 h attenuated the effects of LHD w/o PH and PH-LHD dECM on SMC migration and proliferation in vitro. In a preclinical PH-LHD model, biweekly i.p. administration of 10 mg/kg of Verteporfin for 6 weeks effectively reduced SMC proliferation, migration, and reversed ECM remodeling and PH-LHD.

Conclusion: Remodeling and stiffening of the endothelial ECM trigger YAP1 activation, driving SMC hyperproliferation and migration, which contributes to SMC hyperplasia in PH-LHD. Our findings suggest that YAP1 inhibition could serve as a therapeutic strategy to (1) mitigate SMC hyperplasia, (2) counteract ECM remodeling, and (3) reverse PH-LHD in vivo.

Acknowledgements: This research was funded by the DZHK, BMBF, DSHF, DGK, and DFG.