Glucagon-like peptide-1 increases myocardial glucose uptake via p38alpha MAP kinase-mediated, nitric oxide-dependent mechanisms in conscious dogs with dilated cardiomyopathy

Abstract

Background: We have shown that glucagon-like peptide-1 (GLP-1[7-36] amide) stimulates myocardial glucose uptake in dilated cardiomyopathy (DCM) independent of an insulinotropic effect. The cellular mechanisms of GLP-1-induced myocardial glucose uptake are unknown.

Methods and results: Myocardial substrates and glucoregulatory hormones were measured in conscious, chronically instrumented dogs at control (n=6), DCM (n=9) and DCM after treatment with a 48-hour infusion of GLP-1 (7-36) amide (n=9) or vehicle (n=6). GLP-1 receptors and cellular pathways implicated in myocardial glucose uptake were measured in sarcolemmal membranes harvested from the 4 groups. GLP-1 stimulated myocardial glucose uptake (DCM: 20+/-7 nmol/min/g; DCM+GLP-1: 61+/-12 nmol/min/g; P=0.001) independent of increased plasma insulin levels. The GLP-1 receptors were upregulated in the sarcolemmal membranes (control: 98+/-2 density units; DCM: 256+/-58 density units; P=0.046) and were expressed in their activated (65 kDa) form in DCM. The GLP-1-induced increases in myocardial glucose uptake did not involve adenylyl cyclase or Akt activation but was associated with marked increases in p38alpha MAP kinase activity (DCM+vehicle: 97+/-22 pmol ATP/mg/min; DCM+GLP-1: 170+/-36 pmol ATP/mg/min; P=0.051), induction of nitric oxide synthase 2 (DCM+vehicle: 151+/-13 density units; DCM+GLP-1: 306+/-12 density units; P=0.001), and GLUT-1 translocation (DCM+vehicle: 21+/-3% membrane bound; DCM+GLP-1: 39+/-3% membrane bound; P=0.005). The effects of GLP-1 on myocardial glucose uptake were blocked by pretreatment with the p38alpha MAP kinase inhibitor or the nonspecific nitric oxide synthase inhibitor nitro-l-arginine.

Conclusions: GLP-1 stimulates myocardial glucose uptake through a non-Akt-1-dependent mechanism by activating cellular pathways that have been identified in mediating chronic hibernation and the late phase of ischemic preconditioning.

Figures

Figure 1

The sarcolemmal expression of GLP-1 receptor isoforms (Figure 1A) and basal and agonist stimulated myocardial adenylyl cyclase activity (Figure 1B) in Control dogs (n=6), DCM alone (n=6), DCM+Veh (n=6) and DCM+GLP-1 (n=6). * p=0.046 Control compared to DCM

Figure 2

Akt-1 protein expression and activation as measured by serine 473 phosphorylation in Control dogs (n=6), DCM alone (n=9), DCM+Veh (n=6) and DCM+GLP-1 (n=9). One way ANOVA, p=0.001. * p=0.003 Control compared to DCM

Figure 3

GLUT–4 and GLUT–1 translocation in response to GLP-1 treatment in Control dogs (n=6), DCM alone (n=9), DCM+Veh (n=6) and DCM+GLP-1 (n=9). Transporter translocation is expressed as the % membrane bound/total transporter concentration in membrane and cytosolic fractions. One way ANOVA p=0.0013 for GLUT-1. **p=0.0013 DCM+ Veh compared to DCM+GLP-1.

Figure 4

The effects of GLP-1 treatment on AMP kinase protein expression (4A) and activity (4B) in Control dogs (n=6), DCM alone (n=9), DCM+Veh (n=6) and DCM+GLP-1 (n=9). One way ANOVA for AMP kinase activity p=0.0590. *p=0.0181 Control compared to DCM.

Figure 5

The effects of GLP-1 treatment on p38α MAP kinase expression (5A) and activity (5B) in Control dogs (n=6), DCM alone (n=9), DCM+Veh (n=6) and DCM+GLP-1 (n=9). One way ANOVA p=0.2869 for p38 MAP kinase activity. **p=0.0431 DCM+ Veh compared to DCM+GLP-1.

Figure 6

The effects of GLP-1 treatment on myocardial NOS isoform expression (6A) and on myocardial NO uptake (6B) in Control dogs (n=6), DCM alone (n=9), DCM+Veh (n=6) and DCM+GLP-1 (n=9). One way ANOVA NOS1 p=0.0111, NOS2 p=0.0002; NOS3 p=0.4371. One way ANOVA NO uptake p=0.0001. *p=0.0042 Control compared to DCM. ** **p=0.0010 DCM+ Veh compared to DCM+GLP-1.

Figure 7

The effects of p38 MAP kinase inhibition with SB 203580 (7A) and NOS inhibition with nitro L-arginine (N-LA; 7B) on GLP-1 mediated myocardial glucose uptake in Control (n=6) and DCM (n=6). *p

Figure 8

The effects of GLP-1 treatment on mitochondrial protein expression (8A) and lipid peroxidation (8B) in Control dogs (n=5), DCM alone (n=5), DCM+Veh (n=4) and DCM+GLP-1 (n=5). mCO = mitochrondrial cytochrome oxidase; SDH = succinate dehydrogenase;UCP-3 = uncoupling protein-3, Mn SOD= manganese superoxide dismutase. One way ANOVA MCO p=0.001; SDH p=0.001; UCP-3 p=0.001; MnSOD p=0.00

Figure 8

The effects of GLP-1 treatment on mitochondrial protein expression (8A) and lipid peroxidation (8B) in Control dogs (n=5), DCM alone (n=5), DCM+Veh (n=4) and DCM+GLP-1 (n=5). mCO = mitochrondrial cytochrome oxidase; SDH = succinate dehydrogenase;UCP-3 = uncoupling protein-3, Mn SOD= manganese superoxide dismutase. One way ANOVA MCO p=0.001; SDH p=0.001; UCP-3 p=0.001; MnSOD p=0.00