Background:

Adiponectin mediates cardioprotection through anti-inflammatory, anti-oxidant and anti-apoptotic effects. The CTRPs (C1q/tumor necrosis factor-alpha-related proteins), a family of adiponectin paralogs, were recently described but a comprehensive analysis of their cardioprotective effects has not been performed so far.

Methods:

Adult rat cardiomyocytes and H9C2 cardiomyoblasts were stimulated with full-length CTRP1, 2, 7 and 9 or recombinant adiponectin in a time- and dose-dependent manner. Putative activated signaling cascades were analyzed by Western Blotting. Protection from H2O2-induced cell death and changes in cellular/mitochondrial ROS-production were analyzed. In addition, promoter activation and expression of various antioxidative enzymes was determined by luciferase assay, RT-PCR and Western Blotting.

Results:

Adiponectin and most CTRPs were able to phosphorylate AMPK, p44/42 MAPK and Akt, although time-course and dose differed significantly. Adiponectin and CTRP1, 7 and 9 reduced the number of necrotic and apoptotic cells after exposure to hydrogen peroxide and diminished cellular and mitochondrial ROS-production. Pre-treatment with the AMPK-inhibitor AraA or knockdown of alpha-AMPK inhibited these effects. CTRP7 and 9 activated the promoter of some anti-oxidative enzymes (MnSOD, Trx1) and significantly increased the mRNA and protein expression of various anti-oxidative enzymes. Mutation of the FOXO3-binding site or the antioxidant-response element within the Trx1 or MnSOD promoter abolished the effects of CTRP7 and 9 partially.

Conclusions:

These results suggest that CTRP7 and 9 protect isolated cardiac cells from cell death and reduce ROS levels by inducing Trx1/MnSOD expression through activation of the AMPK-FOXO3 pathway. Thus, CTRPs may play a cardioprotective role in vivo as well.