|Burrin, Douglas - Doug|
Submitted to: Gastroenterology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2006
Publication Date: 1/1/2006
Citation: Guan, X., Karpen, H.E., Bukowski, J.T., Stephens, J., Niu, S., Zhang, G., Stoll, B., Finegold, M.J., Holst, J.J., Burrin, D.G. 2006. GLP-2 receptor localizes to enteric neurons and endocrine cells expressing vasoactive peptides and mediates increased blood flow. Gastroenterology. 130:150-164. Interpretive Summary: The growth and development of the intestine is critical for premature infants, many of which are unable to tolerate oral feedings at birth. Most premature infants are fed intravenously for several days or weeks before being fed oral food and this delays their gut development and increases the hospital cost. We have demonstrated that a key gut hormone, glucagon-like peptide 2 (GLP-2), secreted when infants are fed orally is a potent intestinal growth factor. We have also shown that administering this hormone even during intravenous nutrition stimulates intestinal growth and blood flow. In order to understand the cellular mechanism that explains how GLP-2 stimulates intestinal growth and blood flow, we used several molecular and cellular approaches to characterize on which cells the receptor for GLP-2 is located in the intestine. We found that the GLP-2 receptor is located on nerve cells and epithelial cells that also contain hormones called neurotransmitters that are capable of stimulating blood flow. Our results suggest that GLP-2 stimulates intestinal growth and blood flow by activating these specific neurotransmitters, which then indirectly cause dilation of blood vessels and proliferation of epithelial cells. These studies provide important new clues about how this critical gut growth factor functions in the neonatal gut.
Technical Abstract: Background & Aims: Glucagon-like peptide-2 (GLP-2) is a nutrient-responsive hormone that exerts diverse actions in the gastrointestinal tract including enhancing epithelial cell survival and proliferation, mucosal blood flow, nutrient uptake and suppressing gastric motility and secretion. These actions are mediated by the G protein-coupled receptor, GLP-2R. Cellular localization of the GLP-2R and nature of its signaling network in the gut, however, are poorly defined. Thus, our aim was to establish cellular localization of GLP-2R and functional connection to vascular action of GLP-2 in the gut. Methods: Intestinal cellular GLP-2R localization was determined with real-time, quantitative reverse-transcription polymerase chain reaction (qRT-PCR) of laser capture microdissected sub-tissue and fluorescence in situ hybridization and also with double and/or triple immunostaining of human and pig tissue using a validated GLP-2R polyclonal antibody. Superior mesenteric arterial blood flow and intestinal eNOS expression and phosphorylation were measured in TPN-fed pigs acutely (4 h) infused with GLP-2. Results: We show that the porcine GLP-2R mRNA was expressed in the villus epithelium and myenteric plexus. GLP-2R protein was co-localized by confocal immunohistochemistry with serotonin in enteroendocrine cells and also with endothelial nitric oxide synthase (eNOS)-expressing and vasoactive intestinal polypeptide-positive enteric neurons. In neonatal pigs, GLP-2 infusion dose-dependently stimulated intestinal blood flow and coordinately upregulated the expression of intestinal eNOS mRNA, protein, and phosphorylation (eNOS-Ser1117). Conclusions: We conclude that the GLP-2-induced stimulation of blood flow is mediated by vasoactive neurotransmitters that are co-localized with GLP-2R in two functionally distinct cell types within the gastrointestinal tract.