Humanin analogue, S14G-humanin, has neuroprotective effects against oxygen glucose deprivation/reoxygenation by reactivating Jak2/Stat3 signaling through the PI3K/AKT pathway

Stroke, characterized by a disruption of blood supply to the brain, is a major cause of morbidity and mortality worldwide. Although humanin, a 24-amino acid polypeptide, has been identified to have multiple neuroprotective functions, the level of humanin in plasma has been demonstrated to decrease with age, which likely limits the effects against stroke injury. A potent humanin analogue, S14G-humanin (HNG), generated by replacement of Ser14 with glycine, has been demonstrated to have 1,000-fold stronger biological activity than humanin. The present study established an in vitro oxygen glucose deprivation/reoxygenation (OGD/R) model using SH-SY5Y neuroblastoma cells to mimic the in vivo ischemia/reperfusion injury in stroke. Adding HNG (0-10 mu g/l) to SH-SY5Y cells to different extents blocked OGD/R-induced reduction of cell viability and antioxidative capacity, as well as decreased the elevated apoptosis rate induced by OGD/R, with the most evident effects at 1 mu g/l HNG. Janus kinase 2 (Jak2)/signal transducer and activator of transcription 3 (Stat3) signaling was attenuated in OGD/R processes, yet reactivated with HNG treatment. FLLL32 (5 mu M), a specific inhibitor of the signal, abolished effects of HNG on anti-apoptosis and antioxidation in OGD/R processes. Co-treatment with HNG and FLLL32 failed to interrupt upregulation of cytochrome c, B-cell lymphoma 2-associated X protein and cleaved caspase-3 provoked by OGD/R. Similar to FLLL32, Jak2/Stat3 signaling activated by HNG was also repressed by inhibitor of phosphoinositide 3-kinase (PI3K; 10 mu M LY294002) or protein kinase B (AKT; 5 mu M MK-2206 2HCl). These data collectively indicated that HNG has neuroprotective effects against OGD/R by reactivating Jak2/Stat3 signaling through the PI3K/AKT pathway, suggesting that HNG may be a promising agent in the management of stroke.