GLP‐1 attenuates VEGF‐induced dilation of rat mesenteric resistance vessels by reducing PLCγ phosphorylation, Ca2+ signaling and NO synthesis in vascular endothelial cells
Authors: Egholm Cecilie , Aalkjær Christian , Michell Khammy Makhala , Dalsgaard Thomas , Hansen Anker Jon , Tritsaris Katerina , Dissing Steen 
Published: November 2023

The incretine GLP‐1 enhances insulin release and thereby causes a diminished blood glucose peak in response to food intake. We explored the potential roles of GLP‐1 in vascular function by studying signaling in human dermal microvascular endothelial cells (HDMEC), human retinal microvascular endothelial cells (HRMEC) and rat mesenteric resistance arteries. We found that HDMEC, and HRMEC and resistance vessels express the GLP‐1R by use of RT‐PCR. GLP‐1, on its own, induced phosphorylation of Src and ERK 1/2. By use of Ca2+ imaging we found that pre‐incubation for 15 min with GLP‐1 caused a reduction in VEGF‐A (25 ng/ml) induced Ca2+ signaling due to a reduction in phosphorylation of PLCγ. In addition, GLP‐1 also caused a reduction in the [Ca2+]i rise evoked by ATP4− which is partially due to PLC activation and IP3 synthesis through the P2X7 receptor. We also found a reduction in VEGF‐A induced Ca2+ increase in rat mesenteric resistance arteries preincubated with GLP‐1. A VEGFA induced increase in [Ca2+ ]i is mediated through PLCγ and it has been shown that PLCγ activation is uniquely dependent on a Gαi protein (Yang et al., J. Biol. Chem. (266:33, 1991). In accordance with this observation we found a strong inhibition of VEGFA‐induced Ca2+ signaling after preincubation with pertussin toxin (100 ng/ml), which is an inhibitor of Gαi. Our data are thus consistent with the GLP‐1 signaling being evoked through an enhanced Gs/βγ signaling over that of Gαi since the Gαi inhibition with pertussis toxin elicits a similar response thus favoring the Gs/βγ signaling pathway.In rat mesenteric resistance arteries mounted in a wire myograph and precontracted with the thromboxane analogue U46619 to 90% of their maximum contraction, VEGF‐A caused partial relaxation (−35±4%), an effect that was blocked by GLP‐1(7–36) (1000 pM). VEGF‐A induced relaxation was also inhibited in endothelial denuded arteries and in arteries pretreated with the NOS inhibitor Nω‐nitro‐l‐arginine methyl ester (100 μM). In addition, preincubation with GLP‐1 caused a reduction in VEGF‐A induced eNOS phosphorylation consistent with endothelial NO synthesis being responsible for the relaxation.In resistance vessels VEGF is released from smooth muscle cells. Our data are consistent with GLP‐1 inhibiting VEGFR signaling by modulating Gi induced processes such as PLCγ phosphorylation by enhancing signaling of Gs/βγ signaling over that of Gαi. The blockade of VEGF‐A vessel relaxation by GLP‐1 is in accordance with the diminished eNOS phosphorylation seen when endothelial cells are preincubated with GLP‐1. Thus, GLP‐1 can reduce relaxation induced by VEGF‐A in resistance vessels by inhibiting the VEGFR induced endothelial NO synthesis.We hypothesize that GLP‐1 released from intestinal L‐cells after food intake modulates physiological processes related to PLCγ activation such as endothelial control of vessel tone, endothelial cell migration and proliferation.