Abstract 241: Cardiac-Specific Overexpression of Runx2 Mediates Cardiac Hypertrophy and Dysfunction in Mice

Abstract

Backgrounds: Recent studies demonstrated that the osteopontin (OPN), an acid phosphoprotein plays pivotal roles in cardiac hypertrophy and failure. An osteogenic transcription factor Runx2 regulates the expression of OPN in osteoblasts. In the present study, we examined the pathological role of Runx2 in cardiac hypertrophy and failure. Methods and Results: Runx2 expression was detected in neonatal cardiomyocytes and upregulated in heart 14 days after myocardial infarction (MI) as well as 7days after transverse aortic constriction (TAC) procedures. To determine the functional role of Runx2 in heart, we generated transgenic mice (TG) with inducible cardiac-specific overexpression of Runx2. Two TG lines (low and high) were obtained and high-expressing TG (HE-TG) showed premature death within 8 weeks of age specifically in male mice. At two months of age, the survived male and female HE-TG displayed significant increases in heart weight/body weight ratio (mg/g) compared to controls (control; 4.95±0.26, n=6 vs HE-TG; 6.63±0.12, n=5, p<.05). Consistent with those results, the expression of hypertrophic marker genes such as atrial natriuretic factor (ANF) and αskeletal actin significantly increased in HE-TG heart assessed by real-time RT-PCR analysis. In addition, HE-TG mice demonstrated decreased fractional shortening assessed by echocardiography (control; 44.1±1.89%, n=9 vs HE-TG; 23.9±3.48%, n=7, p<.05). HE-TG mice demonstrated significantly lower heart rate (control; 630±18 bpm, vs HE-TG; 350±74 bpm, n=3 each, p<.05) and complete atrioventricular block by telemetry analysis. In response to pressure overload, low expressing TG (LE-TG) demonstrated higher mortality and enhanced cardiac hypertrophic response after TAC (control; 6.20±0.23, n=6 vs LE-TG; 6.90±0.26, n=4, p<.05). Conclusions: Targeted expression of Runx2 in heart mediates cardiac dysfunction and hypertrophy in mice. Thus, Runx2 could be a novel therapeutic target for heart failure.