Decreased tetrahydrobiopterin and disrupted association of Hsp90 with eNOS by hyperglycemia impair myocardial ischemic preconditioning

Abstract

PF, Kersten JR. Decreased tetrahydrobiopterin and disrupted association of Hsp90 with eNOS by hyperglycemia impair myocardial ischemic preconditioning. Am J Physiol Heart Circ Physiol 301: H2130 -H2139, 2011. First published September 9, 2011 doi:10.1152/ajpheart.01078.2010.-Cardioprotection by ischemic preconditioning (IPC) is impaired during hyperglycemia, but the mechanisms underlying this phenomenon are poorly understood. This study investigated the role of hyperglycemia to adversely modulate tetrahydrobiopterin (BH 4) and heat shock protein 90 (Hsp90) during cardioprotection by IPC. Rabbits or mice underwent 30 min of coronary occlusion followed by reperfusion with or without IPC in the presence or absence of hyperglycemia. IPC significantly (P Ͻ 0.05) decreased myocardial infarct size (46 Ϯ 1 to 19 Ϯ 2% of the area at risk in control and IPC rabbits, respectively) and increased BH 4 concentrations (HPLC; 7.6 Ϯ 0.2 to 10.2 Ϯ 0.3 pmol/mg protein, respectively), Hsp90-endothelial nitric oxide synthase (eNOS) association (coimmunoprecipitation and Western blotting in mice; 4.0 Ϯ 0.3 to 5.4 Ϯ 0.1, respectively), and the ratio of phosphorylated eNOS/total eNOS. These beneficial actions of IPC on infarct size, BH 4, Hsp90/eNOS, and phosphorylated eNOS were eliminated by hyperglycemia. Pretreatment of animals with the Hsp90 inhibitor geldanamycin (0.6 mg/kg) or the BH4 synthesis inhibitor diamino-6-hydroxypyrimidine (1.0 g/kg) also eliminated cardioprotection produced by IPC. In contrast, the BH4 precursor sepiapterin (2 mg/kg iv) restored the beneficial effects of IPC on myocardial BH4 concentrations, eNOS dimerization, and infarct size during hyperglycemia. A-23871 increased Hsp90-eNOS association (0.33 Ϯ 0.06 to 0.59 Ϯ 0.3) and nitric oxide production (184 Ϯ 17%) in human coronary artery endothelial cells cultured in normal (5.5 mM) but not high (20 mM) glucose media. These data indicate that hyperglycemia eliminates protection by IPC via decreases in myocardial BH4 concentration and disruption of the association of Hsp90 with eNOS. The results suggest that eNOS dysregulation may be a central mechanism of impaired cardioprotection during hyperglycemia. hyperglycemia; ischemia reperfusion; tetrahydrobiopterin; heat shock protein; nitric oxide; endothelial nitric oxide synthase HYPERGLYCEMIA (HG) is an independent risk factor for increased cardiovascular morbidity and mortality (9, 12, 13). Previous studies have suggested that HG-associated risk of death is greater in patients with acute myocardial infarction who do not have antecedent diabetes than in those with diabetes, although the responsible mechanisms are not entirely clear (9, 32, 52). Available evidence indicates that endogenous cardioprotective mechanisms such as ischemic preconditioning (IPC) and pharmacological activation of cardioprotective signal transduction pathways are eliminated by HG in animals and in humans (2,16,26,29,31). We tested the hypothesis that regulation of endothelial nitric oxide synthase (eNOS) by its cofactors and protein chape...

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