Targeted GLUT-4 deficiency in the heart induces cardiomyocyte hypertrophy and impaired contractility linked with Ca(2+) and proton flux dysregulation

• Published in: Journal of molecular and cellular cardiology 2010-04, Vol.48 (4), p.663-672
• Main Authors: Domenighetti, Andrea A, Danes, Vennetia R, Curl, Claire L, Favaloro, Jennifer M, Proietto, Joseph, Delbridge, Lea M D
• Format: Article
• Language: English
• Subjects: Animals; Calcium - chemistry; Calcium - metabolism; Glucose Transporter Type 4 - genetics; Glucose Transporter Type 4 - metabolism; Glucose Transporter Type 4 - physiology; Heart; Hydrogen-Ion Concentration; Hypertrophy - pathology; Insulin - metabolism; Male; Mice; Mice, Knockout; Microscopy, Fluorescence - methods; Myocardium - pathology; Myocytes, Cardiac - metabolism; Myocytes, Cardiac - pathology; Patch-Clamp Techniques
• ISSN: 1095-8584
• DOI: 10.1016/j.yjmcc.2009.11.017

There is clinical evidence to suggest that impaired myocardial glucose uptake contributes to the pathogenesis of hypertrophic, insulin-resistant cardiomyopathy. The goal of this study was to determine whether cardiac deficiency of the insulin-sensitive glucose transporter, GLUT4, has deleterious effect on cardiomyocyte excitation-contraction coupling. Cre-Lox mouse models of cardiac GLUT4 knockdown (KD, 85% reduction) and knockout (KO, >95% reduction), which exhibit similar systemic hyperinsulinemic and hyperglycemic states, were investigated. The Ca(2+) current (I(Ca)) and Na(+)-Ca(2+) exchanger (NCX) fluxes, Na(+)-H(+) exchanger (NHE) activity, and contractile performance of GLUT4-deficient myocytes was examined using whole-cell patch-clamp, epifluorescence, and imaging techniques. GLUT4-KO exhibited significant cardiac enlargement characterized by cardiomyocyte hypertrophy (40% increase in cell area) and fibrosis. GLUT4-KO myocyte contractility was significantly diminished, with reduced mean maximum shortening (5.0+/-0.4% vs. 6.2+/-0.6%, 5 Hz). Maximal rates of shortening and relaxation were also reduced (20-25%), and latency was delayed. In GLUT4-KO myocytes, the I(Ca) density was decreased (-2.80+/-0.29 vs. -5.30+/-0.70 pA/pF), and mean I(NCX) was significantly increased in both outward (by 60%) and inward (by 100%) directions. GLUT4-KO expression levels of SERCA2 and RyR2 were reduced by approximately 50%. NHE-mediated H(+) flux in response to NH(4)Cl acid loading was markedly elevated GLUT4-KO myocytes, associated with doubled expression of NHE1. These findings demonstrate that, independent of systemic endocrinological disturbance, cardiac GLUT4 deficiency per se provides a lesion sufficient to induce profound alterations in cardiomyocyte Ca(2+) and pH homeostasis. Our investigation identifies the cardiac GLUT4 as a potential primary molecular therapeutic target in ameliorating the functional deficits associated with insulin-resistant cardiomyopathy.