Glucagon-like peptide-1 (GLP-1) mediates cardioprotection by remote ischaemic conditioning

Abstract

Aims: Although the nature of the humoral factor which mediates cardioprotection established by remote ischaemic conditioning (RIc) remains unknown, parasympathetic (vagal) mechanisms appear to play a critical role. As the production and release of many gut hormones is modulated by the vagus nerve, here we tested the hypothesis that RIc cardioprotection is mediated by the actions of glucagon-like peptide-1 (GLP-1).

Methods and results: A rat model of myocardial infarction (coronary artery occlusion followed by reperfusion) was used. Remote ischaemic pre- (RIPre) or perconditioning (RIPer) was induced by 15 min occlusion of femoral arteries applied prior to or during the myocardial ischaemia. The degree of RIPre and RIPer cardioprotection was determined in conditions of cervical or subdiaphragmatic vagotomy, or following blockade of GLP-1 receptors (GLP-1R) using specific antagonist Exendin(9-39). Phosphorylation of PI3K/AKT and STAT3 was assessed. RIPre and RIPer reduced infarct size by ∼50%. In conditions of bilateral cervical or subdiaphragmatic vagotomy RIPer failed to establish cardioprotection. GLP-1R blockade abolished cardioprotection induced by either RIPre or RIPer. Exendin(9-39) also prevented RIPre-induced AKT phosphorylation. Cardioprotection induced by GLP-1R agonist Exendin-4 was preserved following cervical vagotomy, but was abolished in conditions of M3 muscarinic receptor blockade.

Conclusions: These data strongly suggest that GLP-1 functions as a humoral factor of remote ischaemic conditioning cardioprotection. This phenomenon requires intact vagal innervation of the visceral organs and recruitment of GLP-1R-mediated signalling. Cardioprotection induced by GLP-1R activation is mediated by a mechanism involving M3 muscarinic receptors.

Keywords: Cardioprotection; Glucagon-like peptide-1; Myocardial infarction; Myocardial ischaemia; Parasympathetic; Remote ischaemic conditioning; Reperfusion; Vagus nerve.

Figure 1

Cardioprotection induced by remote ischaemic perconditioning requires intact parasympathetic innervation of visceral organs. (A) Illustration of the experimental protocols. In all the protocols, the rat model of myocardial infarction involved 30 min of left anterior descending coronary artery occlusion followed by 120 min of reperfusion. Arrows indicate time (15 min before myocardial ischaemia) of bilateral cervical (cerv.) or subdiaphragmatic (subd.) vagotomy. Remote ischaemic perconditioning (RIPer) was induced by occlusion of both femoral arteries for 15 min starting 10 min after the onset of myocardial ischaemia. (B) Infarct size is presented as a percentage of the area at risk. Individual data and means ± SD are shown. **P < 0.01; ***P < 0.001.

Figure 2

GLP-1 receptors mediate remote ischaemic conditioning cardioprotection. (A) Illustration of the experimental protocols. Myocardial ischaemic preconditioning (IPre) was induced by three episodes of myocardial ischaemia (3 + 5 + 5 min) separated by 5-min periods of reperfusion. Remote ischaemic preconditioning (RIPre) was induced by occlusion of both femoral arteries for 15 min starting 25 min before the onset of myocardial ischaemia. Arrows indicate the time (15 min before IPre, RIPre or myocardial ischaemia) of intravenous administration of GLP-1 receptor antagonist Exendin(9–39) (Ex(9–39)). (B) Infarct size is presented as a percentage of the area at risk. Individual data and means ± SD are shown. **P < 0.01; ***P < 0.001. (C) Left: representative immunoblots showing total AKT and phospho-AKT (Ser473) protein expression in left ventricular lysates at 15 min of myocardial reperfusion in rats subjected to preparative sham surgery (sham-RIPre), application of RIPre stimulus, or application of RIPre stimulus in conditions of systemic GLP-1R blockade with Ex(9–39). Right: summary data illustrating means ± SD of the densitometry of phospho-AKT-to-AKT ratio. *P < 0.05. (D) Left: representative immunoblots showing total STAT3 and phospho-STAT3 (Tyr705) protein expression in left ventricular lysates at 15 min of myocardial reperfusion in rats subjected to preparative sham surgery (sham-RIPre), application of RIPre stimulus, or application of RIPre stimulus in conditions of systemic GLP-1R blockade with Ex(9–39). Right: summary data illustrating means ± SD of the densitometry of phospho-STAT3-to-STAT3 ratio.

Figure 3

Cardioprotection induced by GLP-1 receptor activation is mediated by a muscarinic mechanism. (A) Illustration of the experimental protocols. Downward arrows indicate time (15 min before myocardial ischaemia) of intravenous administration of GLP-1 receptor agonist Exendin-4 (Ex4). Upward arrows indicate time (30 min before myocardial ischaemia) of cervical vagotomy, start of atropine infusion or administration of M3 muscarinic receptor antagonist 4DAMP. (B) Infarct size is presented as a percentage of the area at risk. Individual data and means ± SD are shown. **P < 0.01; ***P < 0.001.