A deficiency in the gene for endonuclease G (Endog) was recently described as a genetic determinant of cardiac hypertrophy. The mechanisms involved in the regulation of Endog, however, are still to be elucidated. Therefore we hypothesised that Endog, being regulated by small regulatory non-coding RNAs called microRNAs (miRNAs), could contribute to the cardiac hypertrophy of the Hypertrophic Heart Rat (HHR), a human polygenic model of cardiac hypertrophy. From birth the HHR has less and smaller cardiomyocytes, which leads to hypertrophy and cardiac failure later in life. In this study, we examined genome-wide miRNA expression by Agilent Rat miRNA Microarray Kit Release 16.0 and Endog mRNA levels by real-time PCR in the left ventricle of neonatal HHR compared to age-matched rats from its authentic control, the Normal Heart Rat (NHR). Endog mRNA was significantly under-expressed in the HHR (fold change=−4.7; P=0.0001). Sixty-seven miRNAs (FDR P<0.05 and fold change>1.1) were differentially expressed between HHR and NHR (n=16). We then performed an in silico analysis to predict the miRNAs that are able to bind to the 3′ untranslated region of Endog mRNA, and therefore could regulate Endog levels. We discovered that the miRNAs let-7b, miR-338 and miR-347 are predicted to bind to Endog mRNA. Functional studies are being undertaken to determine whether these miRNAs can regulate Endog mRNA levels in vitro and their role in the pathological processes leading to cardiac hypertrophy. These miRNAs could be a new target for the prevention and treatment of cardiac hypertrophy in humans
Objective: The molecular processes associated with cardiac hypertrophy independent of blood pressure are still largely unknown. The hypertrophic heart rate (HHR) is normotensive and born with a reduced complement of cardiomyocytes that predisposes to cardiac hypertrophy and failure in later life. We investigated the expression of c-kit gene, a marker of cardiac stem cells and myocardial regeneration that could contribute to hypertrophy. Methods: Left ventricular c-kit mRNA expression was measured by real-time PCR in HHR and control strain in neonatal and 38-week old rats (n=7-12/group). We tested for linkage of c-kit expression with neonatal cardiac size in 197 second generation crosses (F2) of HHR and control strain. Results: c-kit mRNA was slightly up-regulated in neonatal (fold change +1.3, P=0.02) and markedly so in 38-week old HHR (+35.5, P=0.0003). Cardiac weight index was positively correlated with neonatal myocardial c-kit mRNA in the F2 population (r=0.19, P=0.007). Conclusions: In HHR hearts c-kit expression appears increased throughout life, but more so in the adult where cardiac hypertrophy is established and leading to failure. In aged hypertrophic hearts, over-expression of c-kit is likely a compensatory mechanism of the failing heart. Previous studies showed an activation of cardiac stem cells in the hypertrophic myocardium. Our study suggests that c-kit might be involved from an early age in mechanisms that lead to cardiac hypertrophy in adulthood.