Abstract 1612: Humanin is a Novel Protector against Myocardial Infarction
Humanin is a 24 amino-acid peptide that is best known for its neuroprotective effects in Alzheimer’s disease. Our hypothesis is that humanin has a cardioprotective effect that is mediated by the activation of a Gi-protein-coupled receptor (GPCR) and PLCβ. This activation, in turn, leads to the activation of two pathways, one involving PKC and ATP-sensitive potassium channels, and the other involving PI3K and Akt. Our studies demonstrated that pretreatment of mouse hearts with humanin (10 nM) for as short as 5 min protected the heart against I/R injury in a mouse heart perfusion model. Functional recovery was significantly improved in humanin-treated hearts. The percentages of recovery, control vs. humanin-treated hearts were 30 ± 2% vs. 75 ± 3% for LVDP x HR. When mouse hearts were subjected to 60 min of LAD ligation followed by 4 h of reperfusion, humanin pretreatment (3.3 μg/kg) 15 min before ligation was able to reduce the infarct size/risk area from 49 ± 4% in the control to 20 ± 2% (P<0.05). We also found that humanin pretreatment reduced troponin-I levels from 160 ± 25 ng/ml in the control plasma to 34.4 ± 5.5 ng/ml (P<0.001). Interestingly, humanin pretreatment (33 μg/kg) 24 h before ligation reduced the infarct size/risk area from 49 ± 4% in the control to 35 ± 3% (P<0.05). This intriguing data suggest that humanin has a late preconditioning effect, which could have great clinical significance. The protective effect of humanin was blocked by pretreatment with pertussis toxin (0.1 mg/kg), an endotoxin that inactivates Gi protein by ADP-ribosylation. The protective effect was also abolished by a specific PLC inhibitor, U-73122 (0.2 mg/kg), a PI3K inhibitor, wortmannin (0.4 mg/kg), and an Akt inhibitor, tribicribine (6.6 mg/kg). Akt kinase-deficient mutant mice nullified humanin’s protective action. In addition, the protective effect was also blocked by chelerythrine (5 mg/kg), a PKC inhibitor, and ϵV1–2 (0.2 mg/kg), a PKCϵ inhibitor. Finally, the protective effect was inhibited by 5-hydroxydecanoate (5 mg/kg), which blocks the opening of mitoKATP channels. In conclusion, our studies demonstrate that the cardioprotective action of humanin is mediated by Gi-protein coupled receptor/PLC/PI3K/Akt/PKCϵ/KATP-channel dependent pathways.