Pulmonary arterial hypertension (PAH) is a lethal disease that is characterized by functional and structural abnormalities involving distal pulmonary arterioles that result in increased pulmonary vascular resistance and ultimately right heart failure. In experimental models of pulmonary hypertension, endothelial cell (EC) apoptosis is a necessary trigger for the development of obliterative lung arteriopathy, inducing the emergence of hyperproliferative and apoptosis-resistant vascular cells. However, it has not been established whether EC apoptosis is sufficient for the induction of complex lung arteriolar lesions. We generated a conditional transgenic system in mice to test the hypothesis that lung endothelial cell apoptosis is sufficient to induce a PAH phenotype. The Fas-induced apoptosis (FIA) construct was expressed under the control of endothelial-specific Tie2 promoter (i.e., EFIA mice), and administration of a small molecule dimerizing agent, AP20187, resulted in modest pulmonary hypertension, which was associated with obliterative vascular lesions localized to distal lung arterioles in a proportion of transgenic mice. These lesions were characterized by proliferating cells, predominantly CD68 macrophages. Although endothelial cell apoptosis was also seen in the kidney, evidence of subsequent arteriopathy was seen only in the lung. This model provides direct evidence that lung endothelial cell apoptosis acts as a trigger to initiate a PAH phenotype and provides initial insight into the potential mechanisms that underlie a lung-specific arterial response to endothelial injury.
ObjectivePulmonary arterial hypertension (PAH) is a lethal disease, characterized by complex vascular lesions and increased pulmonary vascular resistance. To test the hypothesis that lung EC apoptosis at the level of distal pulmonary arterioles is necessary and sufficient to cause PAH phenotype we developed a novel transgenic model.Methods and ResultsThe Fas‐Induced Apoptosis (FIA) construct was expressed under the control of endothelial‐specific, Tie2 promoter in transgenic mice (i.e. EFIA mice). Two transgenic lines characterized by low and high expression levels (LE and HE, respectively) were generated. LE‐EFIA exhibited normal pulmonary hemodynamics and vascular structure at baseline; however, administration of a small molecule dimerizing agent, AP20187, resulted in lung microvascular apotosis and modest dose‐dependent increase in RVSP. Interestingly, HE‐EFIA transgenic mice showed significant elevation in baseline RVSP compared to wild‐type controls even in the absence of the AP compound (34± vs. 24±4 mm Hg, respectively; p<0.005). 40% of HE‐EFIA mice also exhibited perivascular lesions, localized to distal lung arterioles which were highly proliferative by Ki67 and EDU staining, and exhibited variable degrees of apoptosis.ConclusionOur data suggest that EC apoptosis is sufficient to induce PAH, which is associated with marked inflammation and remodeling of lung arterioles.
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