Therapeutic Effects of PXR Agonists in a Novel Adenine-Induced HFsnEF Mouse Model

Heart failure (HF) with supranormal ejection fraction (HFsnEF, LVEF ≥ 65%) is a newly defined subtype of HF. Its pathophysiological complexity and lack of effective animal models have hindered its treatment research progress. The aim of this study is to explore the characteristics of the HFsnEF mouse model induced by an adenine diet and elucidate the cardioprotective effect of pregnane X receptor (PXR) agonist and its molecular mechanism. C57BL/6J mice were fed with a 0.2% adenine diet for 28 days to establish HFsnEF model. Cardiac function parameters (left ventricular ejection fraction, cardiac output, interventricular septal thickness, left ventricular volume, and left ventricular diameter) were evaluated by small animal ultrasound (Vevo 3100), and the degree of myocardial injury and fibrosis were analyzed by histopathology. Tunel staining was used to detect the level of apoptosis. Immunofluorescence, RT-PCR, and western blot were used to detect the expression of myocardial cell apoptosis markers (p53, Bax, Bcl2, Caspase3, and cleave-Caspase3), cardiac capillary density marker (CD31), and cardiomyocyte hypertrophy-related markers (ANP and β-MHC). In vitro, the adenine was used to simulate the injury model of H9c2 cardiomyocytes. CCK-8 was used to detect cell viability. Adenine diet successfully induced the phenotype of HFsnEF in mice, which was characterized by smaller hearts, significantly increased ejection fraction (≥ 65%), reduced cardiac output, specific ventricular posterior wall thickening during systole, impaired diastolic function, ventricular shrinkage, myocardial fibrosis and hypertrophy, and decreased blood pressure and heart rate. Mechanistically, the Tunel staining and the expression of p53, Bax, cleave-Caspase3/Caspase3, and Bcl2 indicated that adenine induced cardiomyocyte apoptosis. However, these adenine-induced changes were reversed by PXR agonists. This is the first study to establish an HFsnEF mouse model induced by an adenine diet, and reveals that PXR agonists can alleviate myocardial injury by regulating the p53-Bax/Bcl2 apoptosis pathway, providing a new basis for the mechanism and targeted therapy of HFsnEF.