P362Pathological cardiac remodeling caused by cardiomyocyte/vascular smooth muscle glucocorticoid receptor deficiency

Abstract

Variation in the human glucocorticoid receptor (GR) gene associates with relative glucocorticoid resistance, hypertension and increased cardiovascular disease risk. Here, the contribution of cardiovascular GR to disease risk was assessed in male and female mice with cardiomyocyte and vascular smooth muscle deletion of GR. SMGRKO mice, generated by crossing GR “floxed” mice (congenic on C57BL/6J) with SM22α-Cre mice, have reduced cardiac GR protein and mRNA levels (by 52% and 57%, respectively), compared to Cre-negative littermate controls. Loss of cardiovascular GR impairs viability. There are fewer SMGKRO mice than controls at weaning with a greater effect in females [SMGRKO:Control; females 27:79(25% vs expected 50%); males 37:68(35%) p<0.0001]. Doppler measurements (Visualsonics Vevo770 ultrasound) of blood flow within the left ventricle show a detrimental increase in the myocardial performance index, which measures combined systolic and diastolic function, in both sexes of adult SMGRKO mice. This is primarily due to prolonged isovolumetric contraction time (p<0.05) indicating impairment of the initial left ventricular contractile phase. In male SMGRKO mice (but not female) heart weight (% body weight) was increased (Control:0.50±0.02%; SMGRKO:0.55±0.01%, p<0.05) as was cardiomyocyte cross sectional area (Control:180±4μm2; SMGRKO:194±4μm2, p<0.01). Furthermore, cardiac levels of mRNA encoding myosin heavy chain-β, a marker of pathological cardiac hypertrophy, were elevated in male SMGRKO mice only (p<0.05). Both sexes showed left ventricular fibrosis (histopathology) and elevated levels of cardiac mRNA encoding pro-fibrotic factors. Thus, cardiomyocyte/smooth muscle GR-deficiency causes the same functional impairment of isovolumetric contraction but differential pathological changes in the left ventricle of surviving male and female mice. Whether pathology is worse in neonatal or fetal SMGRKO females is under investigation. These findings support a role for cardiovascular GR in determination of cardiovascular disease risk, though without overt signs of cardiac hypertrophy in females.