title: Limitation of infarct size by erythropoietin is associated with translocation of Akt to the mitochondria after reperfusion.
abstract: 1. The aim of the present study was to determine the critical timing of Akt activation and its interaction with the mitochondrial permeability transition pore (mPTP) in the mechanism of infarct size limitation by erythropoietin (Epo). 2. In an isolated, buffer-perfused preparation, rabbit hearts were subjected to 30 min ischaemia/2 h reperfusion. Infusion of Epo (1 unit/mL) before ischaemia reduced infarct size from 36.6 +/- 2.6% of the risk area to 15.4 +/- 3.2%, whereas a 10-fold higher dose of Epo infused for 65 min commencing 5 min before reperfusion failed to afford significant cardioprotection. The protection afforded by Epo pretreatment was abolished by coinfusion of 5 micromol/L LY294002, a phosphatidylinositol 3-kinase (PI3-K) inhibitor. Infusion of Epo induced phosphorylation of Akt, extracellular signal-regulated kinase, glycogen synthase kinase 3beta and p70s6 kinase before ischaemia and tended to enhance reperfusion-induced phosphorylation of these protein kinases. Erythropoietin increased phospho-Akt in the mitochondria and induced complex formation of Akt with adenine nucleotide translocase (ANT), a major subunit of mPTP, upon reperfusion. 3. In another series of experiments, cardiomyocytes were isolated from rat hearts and loaded with Rhod-2 to determine mitochondrial Ca(2+) levels. Increases in mitochondrial Ca(2+) levels following exposure to 1 mmol/L ouabain for 30 min were similar in untreated and Epo-pretreated cells. However, ouabain-induced hypercontracture was significantly suppressed from 45.1 +/- 1.6 to 39.2 +/- 1.9% by Epo. 4. In conclusion, activation of PI3-K-Akt signalling before ischaemia is crucial for Epo-induced myocardial protection and this protection may be achieved by complex formation of activated Akt with mPTP components upon reperfusion, leading to elevation of the threshold for opening of mPTP.
authors.affiliation: Second Department of Internal Medicine, Sapporo Medical University School of Medicine, Sapporo, Japan.
authors.forename: Hironori
authors.initials: H
authors.lastname: Kobayashi
authors.forename: Tetsuji
authors.initials: T
authors.lastname: Miura
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Ishida
authors.forename: Takayuki
authors.initials: T
authors.lastname: Miki
authors.forename: Masaya
authors.initials: M
authors.lastname: Tanno
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Yano
authors.forename: Takahiro
authors.initials: T
authors.lastname: Sato
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Hotta
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Shimamoto
mesh_terms: D000818:Animals; D004921:Erythropoietin / Q000494:pharmacology / Q000627:therapeutic use*; D008297:Male; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism*; D009203:Myocardial Infarction / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D015428:Myocardial Reperfusion Injury / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D011817:Rabbits
chemical_list: D004921:Erythropoietin; D051057:Proto-Oncogene Proteins c-akt