The Role of Collagen Synthesis in Ventricular and Vascular Adaptation to Hypoxic Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a rapidly fatal disease in which mortality is typically due to right ventricular (RV) failure. An excellent predictor of mortality in PAH is proximal pulmonary artery stiffening, which is mediated by collagen accumulation in hypoxia-induced pulmonary hypertension (HPH) in mice. We sought to investigate the impact of limiting vascular and ventricular collagen accumulation on RV function and the hemodynamic coupling efficiency between the RV and pulmonary vasculature. Inbred mice were exposed to chronic hypoxia for 10 days with either no treatment (HPH) or with treatment with a proline analog that impairs collagen synthesis (CHOP-PEG; HPH + CP). Both groups were compared to control mice (CTL) exposed only to normoxia (no treatment). An admittance catheter was used to measure pressure-volume loops at baseline and during vena cava occlusion, with mice ventilated with either room air or 8% oxygen, from which pulmonary hemodynamics, RV function, and ventricular-vascular coupling efficiency (η_vvc) were calculated. Proline analog treatment limited increases in RV afterload (neither effective arterial elastance E_a nor total pulmonary vascular resistance significantly increased compared to CTL with CHOP-PEG), limited the development of pulmonary hypertension (CHOP-PEG reduced right ventricular systolic pressure by 10% compared to HPH, p < 0.05), and limited RV hypertrophy (CHOP-PEG reduced RV mass by 18% compared to HPH, p < 0.005). In an acutely hypoxic state, treatment improved RV function (CHOP-PEG increased end-systolic elastance E_es by 43%, p < 0.05) and maintained η_vvc at control, room air levels. CHOP-PEG also decreased lung collagen content by 12% measured biochemically compared to HPH (p < 0.01), with differences evident in large and small pulmonary arteries by histology. Our results demonstrate that preventing new collagen synthesis limits pulmonary hypertension development by reducing collagen accumulation in the pulmonary arteries that affect RV afterload. In particular, the proline analog limited structural and functional changes in distal pulmonary arteries in this model of early and somewhat mild pulmonary hypertension. We conclude that collagen plays an important role in small pulmonary artery remodeling and, thereby, affects RV structure and function changes induced by chronic hypoxia.