Abstract 3669: The Glucagon Like Peptide-1 (GLP-1) Metabolite GLP-1(9–36) Protects Cardiomyocytes and Endothelial Cells From Myocardial Ischemia Reperfusion Injury via GLP-1 Receptor-independent Mechanisms
Background: Cardioprotective effects of glucagon-like peptide-1 (GLP-1), GLP-1 receptor (GLP-1R) agonists, and GLP-1(9 –36), a cleavage product of GLP-1, have been reported. However, mechanisms underlying the effects of these diverse peptides on specific cardiovascular cells remain unknown.
Methods & Results: Mass spectrometry was used to assay conversion of GLP-1 to GLP-1(9 –36) in coronary effluents of isolated mouse hearts. Within 15 min of infusing GLP-1(7–36), significant amounts of GLP-1(9 –36) were generated by the heart. By 30 min, only trace amounts of intact GLP-1 remained in coronary effluents. Next, cardioprotective effects of GLP-1(9 –36) and the GLP-1R agonist exendin-4 (Ex-4) were examined in a global ischemia (30 min)-reperfusion (120 min) model (I/R) in isolated mouse hearts. GLP-1(9 –36) and the degradation resistant GLP-1R agonist Ex-4 significantly improved functional recovery and reduced infarct size vs. untreated controls when administered during reperfusion. Subsequently, effects of these agents on cultured neonatal mouse cardiomyocytes (CM) and human aortic endothelial cells (HAEC) were tested. In CM, both GLP-1(9 –36) and Ex-4 significantly increased cAMP levels and phosphorylation of the PI3K targets PKB/Akt and the mitogen activated protein kinases ERK1/2. In CM undergoing simulated I/R injury, both agents significantly improved cell viability, as determined by the MTT assay, LDH release and caspase-3 activation. These effects were significantly attenuated by co-treatments with LY294002 and PD98059, inhibitors of PI3K and ERK1/2 respectively. The actions of Ex-4, but not GLP-1(9 –36) were lost in CM isolated from Glp1r−/− mice. Of interest, only GLP-1(9 –36) (i.e. not Ex-4), improved the survival of HAEC undergoing simulated I/R injury, a beneficial effect that was abrogated by co-treatment with the NOS inhibitor, L-NAME.
Summary: These data show that the heart rapidly converts GLP-1 to GLP-1(9 –36), which exerts cytoprotective actions on CM via a PI3K- and ERK1/2-dependent mechanism, and on HAEC via a NOS-dependent mechanism. Our findings that GLP-1(9 –36), but not Ex4, protects both CM from Glp1r−/− mice, and HAEC from I/R injury, further implicate the existence of an alternative receptor for GLP-1(9 –36).