Remodeling of the endothelial extracellular matrix drives smooth muscle cell hyperplasia in pulmonary hypertension due to left heart disease

Introduction: Pulmonary hypertension (PH) due to left heart disease (PH-LHD) is first initiated by passive congestion of blood from the left heart into the pulmonary vasculature, but subsequently progresses by pulmonary arterial (PA) remodeling characterized by smooth muscle cell (SMC) hyperplasia. Yet, underlying pathomechanisms driving SMC hyperplasia in PH-LHD are poorly understood and intervention strategies are lacking. Here, we addressed the role of the endothelial cell (EC)-derived basement membrane (BM) in regulating SMC hyperplasia in PH-LHD.

Methods and Results: PA samples were obtained from patients with end-stage left-heart disease (LHD) meeting clinical criteria of PH (PH-LHD) or not (LHD w/o PH), or from healthy-heart donors during orthotopic heart transplantation. Histological analyses of these samples revealed SMC hyperplasia in the PA intima as a hallmark of PH-LHD that correlated with patients’ pulmonary hemodynamics, namely mean pulmonary arterial pressure and pulmonary vascular resistance. SMC hyperplasia increased PH-LHD PA wall thickness by up to 10%, and primary isolated SMC from PH-LHD PAs showed increased cell migration and proliferation rates as compared to isolated control SMC. Concomitantly, immunohistological detection of the BM markers collagen IV and laminin identified endothelial BM remodeling as an early event in PA remodeling in LHD w/o PH patients prior to SMC hyperplasia and clinical PH. Based on these findings we hypothesized that early remodeling of the endothelial BM may enhance SMC migration and proliferation via extracellular matrix (ECM)-to-cell signaling. Consistent with this hypothesis, EC-produced decellularized ECM (dECM) from PAs of LHD w/o PH patients increased proliferation and migration in control SMC, while control BM inhibited these responses in PH-LHD SMC. We next considered an activation of mechanosensitive transcriptional co-activator YAP-1 as a mediator of BM effects on SMC. Indeed, culturing cells on dECM produced by LHD w/o PH or PH-LHD EC increased nuclear (active) YAP-1 abundance in control SMC, while culturing on dECM produced by control EC decreased nuclear YAP-1 in LHD w/o PH and PH-LHD SMC. Inhibition of YAP-1 by Verteporfin abolished the effects of LHD w/o PH and PH-LHD endothelial dECM on proliferation and migration of human PA SMC cultured in vitro, and reduced PA SMC proliferation and migration in a rat model of PH-LHD secondary to surgical aortic banding.

Conclusion: Our findings identify endothelial BM (ECM) remodeling as an important pathomechanism driving SMC proliferation and migration in PH-LHD via activation of YAP-1. ECM remodeling and/or YAP-1 activation may present promising therapeutic targets for preventing SMC hyperplasia in PH-LHD.

Acknowledgements: This research was supported by the German Center for Cardiovascular Research (DZHK), the State Ministry for Education and Research (BMBF), the German Foundation for Cardiac Research (DSHF), the German Society for Cardiology and Cardiovascular Research (DGK), and the German Research Foundation (DFG).