Abstract Body (Do not enter title and authors here): Introduction: Pulmonary arterial hypertension (PAH) is characterized by progressive obstruction and decreased compliance of pulmonary arteries (PA), leading to right ventricular failure and premature death. Sustained proliferation and resistance to apoptosis of PAs smooth muscle and endothelial cells (PASMCs, PAECs) and accumulation of extracellular matrix (ECM) elements are key features contributing to vascular remodeling. Integrins, members of the cell adhesion receptor superfamily, are known to promote cell proliferation and survival through ECM binding. Despite the recognition of the role of ECM elements in vascular remodeling in PAH, the contribution of integrins remains poorly studied. We hypothesized that integrin signaling could promote PAH-PASMCs and PAH-PAECs proliferation and resistance to apoptosis contributing to vascular remodeling.

Methods & Results: Using Western blot (WB) and Meso Scale Discovery, we found that α5β1 was upregulated in distal PAs, PA smooth muscle cells (PASMC) and PA endothelial cells (PAEC) from PAH patients compared to controls. Small molecule, antibody (M200), or siRNA-mediated inhibition of α5β1 decreased PAH-PASMC and PAH-PAEC proliferation (WB, MCM2 and Ki67 labeling), resistance to apoptosis (WB, Survivin and Annexin V labeling) and migration (scratch test assay). RNA sequencing analysis revealed that inhibition of α5β1 regulates a FOXM1-dependant gene network through the activation of focal adhesion kinase, resulting in mitotic defects (Immunofluorescence: α-tubulin and pericentrin labeling). In vivo, in both monocrotaline and Sugen/hypoxia rats with established PAH, inhibition of α5β1 using a small molecule inhibitor or a neutralizing antibody alone or in combination with macitentan and tadalafil improved hemodynamics (RHC and echocardiography: mean pulmonary arterial pressure, cardiac output, pulmonary artery acceleration time) and vascular remodeling (Elastica Van Gieson staining). Ex vivo, inhibition of α5β1 decreased vascular remodeling in human precision-cut lung slices (PCLS) from PAH patients and attenuated growth factors-induced vascular remodeling in control PCLS.

Conclusion: Integrin α5β1 plays a key role in vascular remodeling in PAH and represents a novel therapeutic target.