CTPR9 Exerts Cardiac Protection via Activation of CRT Against I/R Injury

Background The underlying mechanisms of cardioprotection of C1q tumor necrosis factor-related

protein 9 (CTRP9) against ischemia/reperfusion (I/R) injury remain largely unknown. The present study aimed to investigate whether calreticulin (CRT) mediated CTRP9’s cardioprotection against I/R injury.

Method and results We inhibited mice cardiac CRT expression via intra-myocardial injection of CRT SiRNA, performed transient LAD ligation, measured the cardiac function, apoptosis and oxidative stress to identify CRT’s effects on cardioprotective actions of CTRP9 against I/R injury in vivo. LDH release and expression of CRT were measured in neonatal cardiomyocytes (NCM) subjected to simulated I/R (SI/R) and CTRP9. CRT specific SiRNA was also utilized in vitro. CRT inhibition partially blunted cardioprotection of CTRP9 against I/R injury (evidenced by left ventricular ejection fraction and myocardial infarct size). It also blunted CTRP9’s function against I/R induced apoptosis and oxidative stress (evidenced by TUNEL positive staining and reactive oxygen species production). In addition, SI/R increased LDH release, and administration of CTRP9 attenuated SI/R-induced cell death significantly. However, neither SI/R nor CTRP9 altered CRT expression in NCM. Inhibition of CRT expression blunted cardioprotective action of CTRP9 against SI/R induced apoptotic events (evidenced by TUNEL positive staining, LDH release and Caspase 3 activity). Furthermore, CRT inhibition significantly blunted CTRP9’s anti-oxidative action (evidenced by gp91phox expression and superoxide generation). However, CRT inhibition did not attenuate AMPK phosphorylation by CTRP9 administration in NCM.

Conclusion Therefore, these novel findings strongly indicate that CTRP9 exerts cardioprotective effects against I/R injury partially via CRT mediated anti-apoptotic and anti-oxidative actions.