Vicious cycle of hemodynamic perturbation and endothelial injury in development and progression of pulmonary arterial hypertension

BackgroundPulmonary arterial hypertension (PAH) is a devastating disease caused by loss of effective lung microvasculature for which there is no curative treatment. Evidence from preclinical models and human disease-causing genetic mutations point to endothelial cell (EC) injury and apoptosis as a central trigger for the initiation of PAH. However, how EC apoptosis leads to pulmonary hypertension (PH) and complex arteriolar remodeling is uncertain. MethodsRats were subjected to SU5416-hypoxia (SUHx) and EC apoptosis, pulmonary vascular remodeling and arterial volume was assessed by immunohistochemistry, histology and microCT, respectively. Left pulmonary artery banding (LPAB) was performed, either 1 week before (prevention) or 5 weeks after SU injection (reversal), to study the effect of hemodynamic offloading. ResultsIn the SUHx model, EC apoptosis was markedly increased as early as 3 days post-SU, persisting through PAH development, and this was associated with a profound arterial pruning with reduction in lung arterial volume ([~]80%). LPAB abrogated lung EC apoptosis in the banded left lung and prevented as well as reversed arteriolar pruning. Moreover, in the reversal protocol, removal of the band at 10 weeks resulted in improvement in pulmonary hemodynamics and RV function at 13 weeks. ConclusionThese data demonstrate that perturbed hemodynamic factors triggered by lung microvascular arteriolar loss play a requisite role in perpetuating endothelial injury in experimental PAH, leading to persistent arterial EC injury and disease progression. Importantly, vascular loss, arterial remodeling and PH are reversible once the cycle of perturbed hemodynamics and EC injury is broken by unilateral lung banding.