Localization and Activation of Glucagon-Like Peptide-2 Receptors on Vagal Afferents in the Rat

Abstract

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent proglucagon-derived hormone that stimulates intestinal growth through poorly understood paracrine and/or neural pathways. The relationship between GLP-2 action and a vagal pathway is unclear. Our aims were to determine whether 1) the GLP-2 receptor (GLP-2R) is expressed on vagal afferents by localizing it to the nodose ganglia; 2) exogenous GLP-2 stimulates the vagal afferent pathway by determining immunoreactivity for c-fos protein in the nucleus of the solitary tract (NTS); and 3) functional ablation of vagal afferents attenuates GLP-2-mediated intestinal growth in rats maintained with total parenteral nutrition (TPN). A polyclonal antibody against the N terminus of the rat GLP-2R was raised and characterized. The GLP-2R was localized to vagal afferents in the nodose ganglia and confirmed in enteroendocrine cells, enteric neurons, and nerve fibers in the myenteric plexus using immunohistochemistry. Activation of the vagal afferent pathway, as indicated by c-fos protein immunoreactivity in the NTS, was determined by immunohistochemistry after ip injection of 200 microg human GLP-2. GLP-2 induced a significant 5-fold increase in the number of c-fos protein immunoreactive neurons in the NTS compared with saline. Ablation of vagal afferent function by perivagal application of capsaicin, a specific afferent neurotoxin, abolished c-fos protein immunoreactivity, suggesting that activation of the NTS due to GLP-2 is dependent on vagal afferents. Exogenous GLP-2 prevented TPN-induced mucosal atrophy, but ablation of vagal afferent function with capsaicin did not attenuate this effect. This suggests that vagal-independent pathways are responsible for GLP-2 action in the absence of luminal nutrients during TPN, possibly involving enteric neurons or endocrine cells. This study shows for the first time that the GLP-2R is expressed by vagal afferents, and ip GLP-2 activates the vagal afferent pathway.

Exogenous Glucagon‐Like Peptide‐2 (GLP‐2) Augments GLP‐2 Receptor mRNA and Maintains Proglucagon mRNA Levels in Resected Rats

“…36,37 The GLP-2R has also been identified in the brain and on vagal afferents, enteroendocrine cells, and enteric neurons in the unresected rat jejunum and ileum; in enteric neurons in a rat model of inflammatory bowel disease; and in subepithelial myofibroblasts in mice. 28,38,39 Of interest, the GLP-2R is not found on GI epithelial cells, which are the cells most responsive to the trophic actions of GLP-2. This finding suggests the presence of a downstream mediator linking the GLP-2R on enteroendocrine cells, enteric neurons, and subepithelial myofibroblasts to its target tissue, the intestinal epithelium.…”

“…Slides were prepared as previously described. 28 Cryostat tissue sections (10μm) of jejunum and ileum were mounted on Superfrost/Plus slides (Fisher Scientific, Pittsburgh, PA). Slides were dried for 3 minutes on a warming table, washed with phosphate buffered saline (PBS) for three 5-minute intervals, and then blocked with 10% goat serum (GS; Vector Laboratories, Burlingame, CA), in 0.2% Triton X-100, and 0.1% bovine serum albumin in PBS (ICC buffer) at room temperature for 30 minutes.…”

Central and peripheral control of food intake

“…Th e DVC consists of the dorsal motor nucleus of the vagus (DVN), the area postrema (AP), and the NTS within which POMC neurons exist (Schwartz 2010). Receptors for a variety of hormones controlling food intake have been found to be expressed in the brainstem vagal aff erent neurons including cholecystokinin (CCK) 1R and CCK 2R at which both CCK and gastrin act (Moriarty et al 1997), insulin receptors, GLP-1 (Nakagawa et al 2004) and GLP-2R (Nelson et al 2007), growth hormone secretagogue receptor (GHS)-R1 at which ghrelin acts (Date et al 2002), the orexin receptor, OX-R1 (Burdyga et al 2003), and leptin (Burdyga et al 2002).…”

The role of gut hormones and the hypothalamus in appetite regulation

“…Within the brainstem, vagal afferent neurons have been shown to express a variety of receptors including cholecystokinin (CCK) 1R and CCK2R (at which both CCK and gastrin act) [42], Ob-R [43], Y2R [44], GLP-1 [45] and GLP-2R [46], growth hormone secretagogue receptor (GHS)-R1 at which ghrelin acts [47] and the orexin receptor, OX-R1 [48].…”