Persistent Regional Downregulation in Mitochondrial Enzymes and Upregulation of Stress Proteins in Swine With Chronic Hibernating Myocardium

Abstract

Abstract-Hibernating myocardium is accompanied by a downregulation in energy utilization that prevents the immediate development of ischemia during stress at the expense of an attenuated level of regional contractile function. We used a discovery based proteomic approach to identify novel regional molecular adaptations responsible for this phenomenon in subendocardial samples from swine instrumented with a chronic LAD stenosis. After 3 months (nϭ8), hibernating myocardium was present as reflected by reduced resting LAD flow (0.75Ϯ0.14 versus 1.19Ϯ0.14 mL ⅐ min Ϫ1 ⅐ g Ϫ1 in remote) and wall thickening (1.93Ϯ0.46 mm versus 5.46Ϯ0.41 mm in remote, PϽ0.05). Regionally altered proteins were quantified with 2D Differential-in-Gel Electrophoresis (2D-DIGE) using normal myocardium as a reference with identification of candidates using MALDI-TOF mass spectrometry. Hibernating myocardium developed a significant downregulation of many mitochondrial proteins and an upregulation of stress proteins. Of particular note, the major entry points to oxidative metabolism (eg, pyruvate dehydrogenase complex and Acyl-CoA dehydrogenase) and enzymes involved in electron transport (eg, complexes I, III, and V) were reduced (PϽ0.05). Multiple subunits within an enzyme complex frequently showed a concordant downregulation in abundance leading to an amplification of their cumulative effects on activity (eg, "total" LAD PDC activity was 21.9Ϯ3.1 versus 42.8Ϯ1.9 mU, PϽ0.05). After 5-months (nϭ10), changes in mitochondrial and stress proteins persisted whereas cytoskeletal proteins (eg, desmin and vimentin) normalized. These data indicate that the proteomic phenotype of hibernating myocardium is dynamic and has similarities to global changes in energy substrate metabolism and function in the advanced failing heart. These proteomic changes may limit oxidative injury and apoptosis and impact functional recovery after revascularization. Key Words: metabolism Ⅲ proteomics Ⅲ hibernating myocardium Ⅲ ischemic heart disease H ibernating myocardium is characterized by viable, chronically dysfunctional myocardium that develops in response to repetitive myocardial ischemia. 1,2 We have previously demonstrated that the relation between regional oxygen consumption, coronary flow, and function in response to stress is attenuated in hibernating myocardium and thus dissociated from the usual determinants of myocardial oxygen demand. 3 By reducing regional energy utilization, hibernation prevents the development of ischemia after submaximal stress. This is supported by a lack of biochemical markers of ischemia and preservation of total ATP and creatine phosphate content in swine with hibernating myocardium 3,4 as well as human biopsies from patients without significant fibrosis. 5 Although there has been interest in identifying the role of increased glucose uptake in these responses, maximal insulin stimulated glucose uptake is unchanged in chronic hibernating myocardium, and alterations in other metabolic pathways responsible for the attenuated increase...

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