Abstract P2021: Blockade Or Deletion Of The Thromboxane/Prostanoid Receptor Reduces Right Ventricular Stiffness To Maintain Function In Right Ventricular Pressure Overload

Abstract

The increased afterload of pulmonary arterial hypertension (PAH) impairs right ventricular function, as the RV struggles to adapt to increased pressure with remodeling and fibrosis. RV failure is the primary cause of death in PAH, and a frequent cause of death in pulmonary hypertension secondary to pulmonary embolism, emphysema, pulmonary fibrosis, and left-heart failure. There is currently no RV-specific therapeutic to maintain function and prolong patient life. During PAH, cardiomyocytes upregulate cell-surface expression of the G αq /IP 3 -coupled thromboxane/prostanoid receptor (TPr), which is activated by multiple endogenous ligands increased in PAH, and leads to calcium influx. TPr activation is also pro-fibrotic in multiple cell types and models. Previous studies have shown reduced fibrosis following TPr antagonism in mouse models of short-term pulmonary hypertension; however this effect has been variable in long-term studies. To more precisely determine the functional effects of TPr activation in RV pressure overload, we used pulmonary arterial banding (PAB) for a direct, sustained increase in pressure, antagonism or deletion of the TPr, and murine cardiac MRI for simultaneous evaluation of the RV and LV. TPr antagonism in a long-term PAB model improved RV ejection fraction and restored LV volume and output by preventing septal bulging and LV eccentricity. This occurred with even short-term antagonism, and was associated with decreased fibrosis in the septum and RV insertion points. Similar results were seen following PAB of universal or cardiomyocyte-specific TPr knockout mice; in all cases, decreasing TPr activation during RV pressure overload reduced RV stiffness even when RV fibrosis remained unchanged. In long-term pressure overload, the improved compliance with antagonism normalized expression of Yap/Taz-associated genes. These results suggest that TPr activation contributes to cardiomyocyte mechanotransduction and deleterious remodeling in response to the RV pressure overload of pulmonary hypertension, and that antagonism of the TPr may preserve RV function to prolong life in PAH patients.