Endothelial Injury in a Transforming Growth Factor β-Dependent Mouse Model of Scleroderma Induces Pulmonary Arterial Hypertension

ObjectiveTo delineate the constitutive pulmonary vascular phenotype of the TRIIk-fib mouse model of scleroderma, and to selectively induce pulmonary endothelial cell injury using vascular endothelial growth factor (VEGF) inhibition to develop a model with features characteristic of pulmonary arterial hypertension (PAH). MethodsThe TRIIk-fib mouse strain expresses a kinase-deficient transforming growth factor (TGF) receptor type II driven by a fibroblast-specific promoter, leading to ligand-dependent up-regulation of TGF signaling, and replicates key fibrotic features of scleroderma. Structural, biochemical, and functional assessments of pulmonary vessels, including in vivo hemodynamic studies, were performed before and following VEGF inhibition, which induced pulmonary endothelial cell apoptosis. These assessments included biochemical analysis of the TGF and VEGF signaling axes in tissue sections and explanted smooth muscle cells. ResultsIn the TRIIk-fib mouse strain, a constitutive pulmonary vasculopathy with medial thickening, a perivascular proliferating chronic inflammatory cell infiltrate, and mildly elevated pulmonary artery pressure resembled the well-described chronic hypoxia model of pulmonary hypertension. Following administration of SU5416, the pulmonary vascular phenotype was more florid, with pulmonary arteriolar luminal obliteration by apoptosis-resistant proliferating endothelial cells. These changes resulted in right ventricular hypertrophy, confirming hemodynamically significant PAH. Altered expression of TGF and VEGF ligand and receptor was consistent with a scleroderma phenotype. ConclusionIn this study, we replicated key features of systemic sclerosis-related PAH in a mouse model. Our results suggest that pulmonary endothelial cell injury in a genetically susceptible mouse strain triggers this complication and support the underlying role of functional interplay between TGF and VEGF, which provides insight into the pathogenesis of this disease.