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This Article Full Text Full Text (PDF) All Versions of this Article: 295/5/H2079    most recent 00092.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Ohori, K. Articles by Shimamoto, K. PubMed PubMed Citation Articles by Ohori, K. Articles by Shimamoto, K.

Ser9 phosphorylation of mitochondrial GSK-3β is a primary mechanism of cardiomyocyte protection by erythropoietin against oxidant-induced apoptosis

¹Second Department of Internal Medicine and ²Department of Pharmacology, Sapporo Medical University School of Medicine, Sapporo, Japan

Submitted 28 January 2008 ; accepted in final form 11 September 2008

The aim of this study was to determine the role of GSK-3β in cardiomyocyte protection afforded by erythropoietin (EPO) against oxidant stress-induced apoptosis. Treatment with EPO (10 units/ml) induced Ser473 phosphorylation of Akt and Ser9 phosphorylation of GSK-3β and significantly reduced the proportion of apoptotic H9c2 cardiomyocytes after exposure to H₂O₂ from 38.3 ± 2.7% to 26.0 ± 2.9%. This protection was not detected in cells transfected with constitutively active GSK-3β (S9A), which lacks Ser9 for inhibitory phosphorylation. The antiapoptotic effect of EPO was mimicked completely by GSK-3β knockdown using small interfering RNA and partly by the transfection with kinase-deficient GSK-3β (K85R). The level of colocalization of intracellular GSK-3β with mitochondria assessed by enhanced green fluorescent protein-tagged GSK-3β or immunocytochemistry was not altered by EPO treatment. However, EPO increased the level of Ser9-phospho-GSK-3β colocalized with mitochondria by 50% in a phosphatidylinositol 3-kinase-dependent manner. Mitochondrial translocation of Bcl-2-associated X protein (BAX) after exposure to H₂O₂ was inhibited by EPO pretreatment and by GSK-3β knockdown. These results suggest that the suppression of GSK-3β activity by Akt-mediated Ser9 phosphorylation in the mitochondria affords cardiomyocytes tolerance against oxidant-induced apoptosis, possibly by inhibiting the access of BAX to the mitochondria.

oxidant stress; glycogen synthase kinase-3β