|Guan, Xin Fu|
|Burrin, Douglas - Doug|
Submitted to: Gastroenterology
Publication Type: Abstract Only
Publication Acceptance Date: 2/20/2006
Publication Date: 3/20/2006
Citation: Guan, X., Zhang, K., Karpen, H., Bukowski, J., Bian, X., Galligan, J., Burrin, D. 2006. Glucagon-like peptide-2 intracellularly stimulates eNOS phosphorylation and specifically induces submucosal arteriole vasodilation via a sheer strees-independent, local neural mechanism [abstract]. Gastroenterology. 130:A686. Interpretive Summary:
Technical Abstract: Glucagon-like peptide-2 (GLP-2) is a nutrient-responsive neuropeptide that exerts diverse actions in the gastrointestinal tract, including enhancing mucosal cell survival and proliferation, mucosal blood flow, luminal nutrient uptake, and suppressing gastric motility and secretion. We have shown that GLP-2-stimulated mucosal blood flow is associated in vivo with increased activation of endothelial nitric oxide synthase (eNOS), but not neuronal nitric oxide synthase (nNOS), in the neonatal pig intestine. We have also shown that the GLP-2 receptor (GLP-2R) is co-localized with eNOS in enteric neurons. However, it is well established that blood flow-induced sheer stress is a key stimulator of endothelial eNOS activity. Thus, the GLP-2-induced increase in blood flow may indirectly activate endothelial eNOS. We hypothesized that GLP-2R activation intracellularly stimulates eNOS phosphorylation in enteric neurons and is independent of blood flow-mediated sheer stress. Our aim was to establish whether the GLP-2-mediated activation of eNOS occurs intracellularly via a neural-dependent mechanism, independent of blood flow-induced sheer stress. We first studied an ex vivo submucosal preparation from the young guinea-pig jejunum to quantify individual submucosal arteriole diameter with a computer-aided, real-time videomicroscopy system. Under pre-constriction with KCl (60 mM), super-perfusion of human GLP-2 (at 100 nM) immediately increased the submucosal arteriole dilation by approximately 30%, but did not alter mesenteric artery dilation. However, GLP-2-induced vasodilation was completely blocked with co-superfusion of either a NOS inhibitor (NG-nitro-L-arginine at 300 uM) or a neuronal Na channel blocker (tetrodotoxin at 300 nM), implying that the GLP-2-mediated vascular action was localized specifically on the submucosal arteriole (the final and major resistance vessel in the gut) via a nitric oxide-dependent local neural mechanism. We next defined whether GLP-2R activation activates eNOS intracellularly in HEK 293T cells transiently transfected with full-length cDNA clones of human GLP-2R and eNOS. GLP-2 treatment dose-dependently induced eNOS phosphorylation on Ser1177 in the double transfected HEK 293T cells, and this was maximal within 15 min at 20 nM GLP-2. Thus, we concluded that GLP-2-induced submucosal arteriole dilation is locally mediated via a neural-dependent mechanism, independent of blood flow-mediated sheer stress. Moreover, GLP-2R activation intracellularly leads to stimulation of eNOS phosphorylation, independently from sheer stress.