P4476Cardiovascular benefits of GLP-1 (liraglutide) treatment in experimental arterial hypertension are mediated by the endothelial GLP-1 receptor
Authors: Steven S , Helmstaedter J , Filippou K , Pawelke F , Katie F , Vujacic-Mirski K , Kalinovic S S , Kroeller-Schoen S , Oelze M , Munzel T , Daiber A 
Published: October 2019

Abstract

Objective
The LEADER trial demonstrated that glucagon-like peptide-1 (GLP-1) analogs like Liraglutide (Lira) reduce the risk of cardiovascular events in T2DM, an effect beyond glycemic control. A detailed evaluation of the precise mechanisms underlying the cardiovascular protective effects of GLP-1 has been hampered by the fact that the GLP-1 receptor is expressed on different cell types in the vasculature including platelets, neuronal, endothelial and inflammatory cells. We used endothelial and myeloid cell-specific knockout mice of the GLP-1 receptor (GLP-1r) in an angiotensin-II (ATII)-induced model of hypertension. The aim of the recent study was to investigate the cardioprotective effects of GLP-1 in ATII-induced arterial hypertension and to characterize the cell-specific contribution of GLP-1r signaling.

Methods
Arterial hypertension was induced by s.c. ATII administration (0.5mg/kg/d; 7 days) in WT (C57/BL6J) as well as endothelial and myeloid cell-specific GLP-1r knockout mice (Cdh5crexGLP-1rfl/fl and LysMcrexGLP-1rfl/fl mice). Animals were treated with Lira (2x30μg/d; 7 days). Blood pressure was measured by tail-cuff. Vascular function was tested by isometric tension recording. Aortic and cardiac tissue was used for Western blotting, qRT-PCR, FACS, IHC and HPLC to determine the extent of inflammation, oxidative stress and fibrosis. ELISA was used to determine GLP-1 and insulin levels in plasma.

Results
Endogenous GLP-1 (7–36 and 9–36) was reduced in hypertensive animals. Lira ameliorated blood pressure and improved endothelial dysfunction, vascular oxidative stress and inflammation caused by ATII, in both WT and myeloid cell-specific GLP-1r knockout mice. Hypertension led to infiltration of inflammatory monocytes (Ly6G-Ly6Chigh) and neutrophils (Ly6G+Ly6C+) into the vascular wall, which was prevented by Lira. In accordance, Lira suppressed vascular oxidative stress and mRNA expression of iNOS, CD11b and Nox2. Endothelial NO synthase (eNOS) was S-glutathionylated with ATII treatment indicating uncoupled eNOS. Thus, aortic NO levels were reduced, all of which was restored by Lira. Furthermore, vascular fibrosis and cardiac hypertrophy were tremendously reduced by GLP-1. Interestingly, all of these beneficial cardiovascular effects of GLP-1 were abolished in endothelial cell-specific GLP-1r knockout mice.

Conclusion
We show that Lira reduces blood pressure and improves vascular function, fibrosis and cardiac hypertrophy in experimental arterial hypertension in mice. Mechanistically, Lira prevents the infiltration of inflammatory cells to the vascular wall, leading to reduced oxidative stress and improved NO bioavailability. Beneficial effects of GLP-1 are mediated by the GLP-1r expressed on endothelial and not myeloid cells. With the present study we provide a mechanistic approach to explain the cardioprotective effects of GLP-1 analogs like Lira, for which the endothelial GLP-1 receptor is indispensable.

Acknowledgement/Funding
Deutsche Forschungsgesellschaft (DFG), Bundesministerium für Bildung und Forschung (BMBF)