Objectives Diabetic presents higher ischaemic heart disease morbidity and mortality, lacking of effective strategies of prevention and cure. Recently, a small peptide, helix B surface peptide (HBSP), derived from erythropoietin (EPO) was developed and shown to be tissue protective but avoiding property of elevating red blood cell which might become additional cardiovascular risks for already vulnerable patients. Our preliminary experiment results proved that HBSP could dramatically reduce the myocardial infarction size induced by ischaemia/reperfusion injury (I/RI) of Zucker diabetic fatty rat and the protective effect was superior to EPO. Nevertheless, the specific cardio-protective mechanisms of HBSP still unknown. Purpose of this study was to future elucidate the cardio-protective mechanisms of HBSP against I/RI of diabetic rats.
Methods Adult Zucker diabetic fatty rat hearts were subjected 30 min hearts ischaemia and 4h reperfusion. The hearts were randomized to receive EPO-derived peptides HBSP, EPO, HBSP plusLY294002 (specific inhibitor of PI3K), HBSP plus PD98059 (specific inhibitor ofERK1/2) or HBSP plus AG-490 (specific inhibitor of JAK2) at the start of reperfusion. To further confirm the correlation between survivin and myocardial survival in vitro and in vivo, cardiomyocytes were infected with adenovirusencoding survivin or transfected with siRNA targeting survivin. Phosphorylation of Akt, ERK1/2, STAT3 and the expression of protein survivin were determined by Western Blotting and myocardial infarction/area at risk was assessed using TTC staining, cardiomyocytes apoptosis were evaluated after reperfusion by TUNEL staining.
Results A single bolus injection of 60 μg/kg of HBSP before reperfusion reduced myocardial infarction size examined 4 h after reperfusion, by (33 ± 5.2)% and apoptosis of cardiomyocytes by (46 ± 2.5)% which was superior to that of EPO (P<0.05) and plus no RBC increasing. HBSP treatment enhanced phosphorylation of all three critical signaling pathways of cell survival, including Akt, ERK1/2, and STAT3 respectively (P<0.05 vs. control). Meanwhile HBSP reperfusion resulted in a4.1-fold increase in survivin expression of myocardium (P<0.05 vs. I/Ralone), which was almost completely blocked by LY294002. Moreover, over-expressed survivin provides protection against simulate dischaemia/reperfusion-induced cardiomyocyte apoptosis, while targeting survivin blunted the anti-apoptotic effect of HBSP.
Conclusions This study demonstrates that HBSP up-regulates myocardial survivin expression, mainlyvia PI3K/Akt mechanism, which contributes to the anti-apoptotic effect of HBSPagainst the myocardial I/RI of diabetic rats.