Impaired insulin signaling accelerates cardiac mitochondrial dysfunction after myocardial infarction.

ABSTRACT

Diabetes increases mortality and accelerates left ventricular (LV) dysfunction following myocardial infarction (MI). This study sought to determine the impact of impaired myocardial insulin signaling, in the absence of diabetes, on the development of LV dysfunction following MI. Mice with cardiomyocyte-restricted knock out of the insulin receptor (CIRKO) and wildtype (WT) mice were subjected to proximal left coronary artery ligation (MI) and followed for 14 days. Despite equivalent infarct size, mortality was increased in CIRKO-MI vs. WT-MI mice (68% vs. 40%, respectively). In surviving mice, LV ejection fraction and dP/dt were reduced by >40% in CIRKO-MI vs. WT-MI. Relative to shams, isometric developed tension in LV papillary muscles increased in WT-MI but not in CIRKO-MI. Time to peak tension and relaxation times were prolonged in CIRKO-MI vs. WT-MI suggesting impaired, load-independent myocardial contractile function. To elucidate mechanisms for impaired LV contractility, mitochondrial function was examined in permeabilized cardiac fibers. Whereas maximal ADP-stimulated mitochondrial O(2) consumption rates (V(ADP)) with palmitoyl carnitine were unchanged in WT-MI mice relative to sham-operated animals, V(ADP) was significantly reduced in CIRKO-MI (13.17+/-0.94 vs. 9.14+/-0.88 nmol O(2)/min/mgdw, p<0.05). Relative to WT-MI, expression levels of GLUT4, PPAR-alpha, SERCA2, and the FA-Oxidation genes MCAD, LCAD, CPT2 and the electron transfer flavoprotein ETFDH were repressed in CIRKO-MI. Thus reduced insulin action in cardiac myocytes accelerates post-MI LV dysfunction, due in part to a rapid decline in mitochondrial FA oxidative capacity, which combined with limited glucose transport capacity that may reduce substrate utilization and availability.