Abstract 182: CTRP9 - A Novel Cardiac Derived Secreted Factor With Anti-hypertrophic Properties
Background: CTRP9 (also called C1qtnf9) is a newly discovered secreted protein and a paralog of adiponectin. The biological functions of CTRP9, however, are still largely unknown.
Results: Although previous data from a semi-quantitative real-time PCR had suggested that CTRP9 is mainly secreted by adipose tissue, we found its mRNA to be predominantly expressed in the heart by quantitative real-time PCR. Interestingly, we identified CTRP9 mRNA as significantly upregulated in hypertrophied mouse hearts (after 2 weeks of aortic constriction, TAC) as well as in hypertrophied human hearts (24±4-fold versus healthy human myocardium; p<0.01). LacZ staining in myocardial sections of C1qtnf9tm1(KOMP)Vlcg mice (knock-out for CTRP9, containing a lacZ cassette to replace exon 1-3 of the gene) revealed exclusive expression of CTRP9 in capillary and venous endothelial cells. Adenoviral overexpression of CTRP9 or recombinant CTRP9 strongly inhibited cardiomyocyte hypertrophy (assessed as cell size, protein/DNA-ratio, expression of skeletal α-actin) after stimulation with phenylephrine (PE). Accordingly, myocardial overexpression of CTRP9 via a cardioselective adeno-associated virus (AAV9-CTRP9) in mice dramatically reduced cardiac hypertrophy after two weeks of pressure overload (heart weight/body weight ratio, HW/BW in mg/g: AAV9-control 6.5±0.2 versus AAV9-CTRP9 5.6±0.2; p<0.01). In turn, downregulation of CTRP9 by a specific siRNA aggravated cardiomyocyte growth in response to PE in vitro and CTRP9 knock-out (KO) mice exerted an enhanced hypertrophic response after two weeks of TAC in vivo (% increase in HW/BW versus sham: wild-type 77±13, KO 106±9; p<0.05). Mechanistically, we found that CTRP9 binds to the adiponectin receptor 1 (AdipoR1) and inhibits prohypertrophic mTOR signalling in cardiac myocytes. SiRNA mediated downregulation of AdipoR1 or mTOR in neonatal rat cardiomyocytes abolished the anti-hypertrophic effect of CTRP9.
Conclusion: Endothelial cell derived CTRP9 inhibits cardiac hypertrophy through binding to AdipoR1 and inhibition of the mTOR pathway in cardiomyocytes. Therefore, myocardial application of CTRP9 could be a novel strategy to combat pathological cardiac hypertrophy.
- © 2013 by American Heart Association, Inc.