Erythropoietin affords additional cardioprotection to preconditioned hearts by enhanced phosphorylation of glycogen synthase kinase-3 beta.
The aim of this study was to determine whether erythropoietin (EPO) affords additional cardioprotection to the preconditioned myocardium by enhanced phosphorylation of Akt, STAT3, or glycogen synthase kinase-3beta (GSK-3 beta). Preconditioning (PC) with 5-min ischemia/5-min reperfusion and EPO (5,000 U/kg iv) reduced infarct size (as % of area at risk, %IS/AR) after 20-min ischemia in rat hearts in situ from 56.5 +/- 1.8% to 25.2 +/- 2.1% and to 36.2 +/- 2.8%, respectively. PC-induced protection was significantly inhibited by a protein kinase C inhibitor, chelerythrine (5 mg/kg), and slightly blunted by a phosphatidylinositol-3-kinase inhibitor, wortmannin (15 microg/kg). The opposite pattern of inhibition was observed for EPO-induced protection. The combination of PC and EPO further reduced %IS/AR to 8.9 +/- 1.9%, and this protection was inhibited by chelerythrine and wortmannin. The additive effects of PC and EPO on infarct size were mirrored by their effects on the level of phosphorylated GSK-3 beta at 5 min after reperfusion but not their effects on the level of phospho-Akt or phospho-STAT3. To mimic phosphorylation-induced inhibition of GSK-3 beta activity, SB-216763 (SB), a GSK-3 beta inhibitor, was administered before ischemia or 5 min before reperfusion. Infarct size was significantly reduced by preischemic injection (%IS/AR = 40.4 +/- 2.2% by 0.6 mg/kg SB and 34.0 +/- 1.8% by 1.2 mg/kg SB) and also by prereperfusion injection (%IS/AR = 32.0 +/- 2.0% by 1.2 mg/kg SB). These results suggest that EPO and PC afford additive infarct size-limiting effects by additive phosphorylation of GSK-3beta at the time of reperfusion by Akt-dependent and -independent mechanisms.
Second Dept. of Internal Medicine, Sapporo Medical Univ. School of Medicine, Sapporo 060-8543, Japan.
Masahiro
M
Nishihara
Tetsuji
T
Miura
Takayuki
T
Miki
Jun
J
Sakamoto
Masaya
M
Tanno
Hironori
H
Kobayashi
Yoshihiro
Y
Ikeda
Katsuhiko
K
Ohori
Akari
A
Takahashi
Kazuaki
K
Shimamoto
D000818:Animals; D015153:Blotting, Western; D002316:Cardiotonic Agents; D004921:Erythropoietin / Q000494:pharmacology*; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D000071679:Glycogen Synthase Kinase 3 beta; D006439:Hemodynamics / Q000502:physiology; D019157:Ischemic Preconditioning, Myocardial; D008297:Male; D009203:Myocardial Infarction / Q000473:pathology; D009206:Myocardium / Q000473:pathology; D009929:Organ Size / Q000502:physiology; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D050796:STAT3 Transcription Factor / Q000096:biosynthesis
D002316:Cardiotonic Agents; D050796:STAT3 Transcription Factor; D004921:Erythropoietin; D000071679:Glycogen Synthase Kinase 3 beta; C000605508:Gsk3b protein, rat; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3