Targeting the glucagon receptor improves cardiac function and enhances insulin sensitivity following a myocardial infarction

Abstract

Background: In heart failure the myocardium becomes insulin resistant which negatively influences cardiac energy metabolism and function, while increasing cardiac insulin signalling improves cardiac function and prevents adverse remodelling in the failing heart. Glucagon's action on cardiac glucose and lipid homeostasis counteract that of insulin's action. We hypothesised that pharmacological antagonism of myocardial glucagon action, using a human monoclonal antibody (mAb A) against glucagon receptor (GCGR), a G-protein coupled receptor, will enhance insulin sensitivity and improve cardiac energy metabolism and function post myocardial infarction (MI). Methods: Male C57BL/6 mice were subjected to a permanent left anterior descending coronary artery ligation to induce MI, following which they received either saline or mAb A (4 mg kg −1 week −1 starting at 1 week post-MI) for 3 weeks. Results: Echocardiographic assessment at 4 weeks post-MI showed that mAb A treatment improved % ejection fraction (40.0 ± 2.3% vs 30.7 ± 1.7% in vehicle-treated MI heart, p < 0.05) and limited adverse remodelling (LV mass: 129 ± 7 vs 176 ± 14 mg in vehicle-treated MI hearts, p < 0.05) post MI. In isolated working hearts an increase in insulin-stimulated glucose oxidation was evident in the mAb A-treated MI hearts (1661 ± 192 vs 924 ± 165 nmol g dry wt −1 min −1 in vehicle-treated MI hearts, p < 0.05), concomitant with a decrease in ketone oxidation and fatty acid oxidation rates. The increase in insulin stimulated glucose oxidation was accompanied by activation of the IRS-1/Akt/ AS160/GSK-3β pathway, an increase in GLUT4 expression and a reduction in pyruvate dehydrogenase phosphorylation. This enhancement in insulin sensitivity occurred in parallel with a reduction in cardiac branched chain amino acids content (374 ± 27 vs 183 ± 41 µmol g protein −1 in vehicle-treated MI hearts, p < 0.05) and inhibition of the mTOR/P70S6K hypertrophic signalling pathway. The MI-induced increase in the phosphorylation of transforming growth factor β-activated kinase 1 (p-TAK1) and p38 MAPK was also reduced by mAb A treatment. Conclusions: mAb A-mediated cardioprotection post-myocardial infarction is associated with improved insulin sensitivity and a selective enhancement of glucose oxidation via, at least in part, enhancing branched chain amino acids catabolism. Antagonizing glucagon action represents a novel and effective pharmacological intervention to alleviate cardiac dysfunction and adverse remodelling post-myocardial infarction.

Weight loss enhances cardiac energy metabolism and function in heart failure associated with obesity

“…Hearts were isolated from mice at 14 weeks of the study protocol and were quickly cannulated as an isolated working heart preparation, as described previously . Hearts were perfused with Krebs‐Henseleit solution containing 2.5 mM Ca 2+ , 5 mM [U‐ 14 C]glucose and 0.8 mM [9,10‐ 3 H]palmitate pre‐bound to 3% albumin.…”

“…The acetylation status of cardiac energy metabolic enzymes was examined using an immunoprecipitation technique, as previously reported …”

“…Hearts were isolated from mice at 14 weeks of the study protocol and were quickly cannulated as an isolated working heart preparation, as described previously. 27 Hearts were perfused with Krebs-Henseleit solution containing 2.5 mM Ca 2+ , 5 mM [U- 14 respectively. At the end of perfusion, the hearts were quickly frozen with tongs cooled to the temperature of liquid N 2 .…”

“…Myocardial biopsies were collected at the end of perfusion for biochemical characterization, as previously described. [27][28][29] Briefly, protein samples (30 μg/well) were loaded onto 10% SDS-PAGE to be separated based on molecular weight, and were then transferred onto a nitrocellulose membrane using a wet-transfer method. The membrane was incubated with one of the following primary antibodies…”

“…The acetylation status of cardiac energy metabolic enzymes was examined using an immunoprecipitation technique, as previously reported. 27 . Briefly, protein processing procedures were conducted at 4 C to ensure protein integrity.…”