Date on Master's Thesis/Doctoral Dissertation

5-2011

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Physiology and Biophysics

Committee Chair

Epstein, Paul N.

Author's Keywords

Glycolysis; F-2; 6-P2; Glucose oxidation; Pyruvate dehydrogenase; Heart failure; PFK2

Subject

Heart failure; Glycolysis; Glucose--Metabolism

Abstract

Heart failure is the most frequent cause of mortality in western countries. Currently, there is no cure treatment for heart failure and the long term survival rate following heart failure is poor, with one third of patients dying within a year of diagnosis. Thus, new therapeutic targets have to be developed. Enhanced glycolysis is a very common phenomenon in the development of heart failure and maybe a target for drug development. However it is not know whether the increased glycolysis is a cause or an effect of heart failure. Also, metabolic modulators to increase glucose use by the heart have been used acutely in treatment in heart failure but the long term impact of increased glycolysis is not known. To understand whether chronically increased glycolysis specifically in the heart is beneficial or detrimental, glycolysis was chronically elevated by cardiac-specific overexpression of a modified, phosphatase-deficient 6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase (PFK-2) in transgenic mice. PFK-2 controls the level offructose-2, 6-bisphosphate (Fru-2, 6-P2), an important regulator of phosphofructokinase and glycolysis. These transgenic mice were used to test two hypotheses: (1) Long term elevation of cardiac Fru-2, 6-P2 will increase glycolysis and alter glucose oxidation. (2) Chronically increased cardiac glycolysis will be detrimental to the heart. To test these hypotheses we carried out three specific aims: Aim I was to produce transgenic mice with overexpression of phosphatase-deficient 6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase (PFK-2). Aim 2 was to compare metabolites and glucose metabolism in transgenic and control samples using whole hearts, Langendorff perfused hearts and cultured adult cardiomyocytes. Aim 3 was to assess whether chronically increased glycolysis promotes cardiac fibrosis, hypertrophy or impaired function. The results demonstrated a new line of transgenic mice called Mk, with cardiac expression of modified PFK2 and increased levels of Fru-2, 6-P2. Mk hearts had elevated glycolysis that was less sensitive to inhibition by palmitate. Mk cardiomyocytes had increased glucose oxidation despite reduced pyruvate dehydrogenase complex (PDC) activity. PDC activity was decreased because of reduced protein levels of PDC subunit Ela and because of increased PDC Ela phosphorylation. Mk hearts had increased mitochondrial level of MCT -2 transporter protein and malate content. The increased malate content and elevated MCT2 expression suggested that anaplerosis pathways in transgenic hearts might explain the paradoxical finding of reduced PDC activity and elevated glucose oxidation. Functional studies revealed that the elevation in glycolysis made transgenic cardiomyocytes highly resistant to contractile inhibition by hypoxia, in vitro. However, in vivo the transgene had no protective effects on ischemia-reperfusion injury. Furthermore, the transgenic hearts exhibited pathologic changes that included a 17% increase of the heart weight-to-body weight ratio, greater cardiomyocyte length and increased cardiac fibrosis. Therefore, chronic elevation of glycolysis produced more pathological effects than protective effects on the heart.

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