My long-term goal is to identify the physiological function and signaling network of glucagon-like peptide 2 receptor (GLP-2R) in the gastrointestinal tract. GLP-2 is an intestinotrophic growth factor that stimulates mucosal growth by increasing crypt cell proliferation and decreasing enterocyte cell apoptosis. GLP-2 also stimulates intestinal blood flow, improves nutrient absorption, and inhibits gut motility. Based largely on evidence from pharmacological dosing of GLP-2 or its antagonist, it is suggested that GLP-2 may be a key mediator for intestinal growth and function. Dual localization of the GLP-2R protein to enteric neurons and enteroendocrine cells, but not enterocytes, suggests that the GLP-2-mediated trophic actions on the epithelium are mediated indirectly through an unidentified secondary signaling molecule. However, the GLP- 2R-mediated physiological function and signaling network are poorly defined in vivo. This proposal will test two hypotheses: (1) GLP-2R is required for maintaining intestinal epithelial integrity and absorptive function in the postnatal mouse. (2) GLP-2-induced trophic and vasoactive actions in vivo are mediated through local neurotransmitter (nitric oxide, NO).
Aim 1 - Develop a global glp2r gene knockout mouse model to establish the physiological role of the GLP-2R in intestinal growth and function. We will test if the GLP-2R activation is required for intestinal growth (adaptation) and absorptive function in two conditions: [1] where mice receive a 36-h enteral nutrition after a 36-h fast;and [2] where mice receive either a 50% small bowel resection or a sham operation.
Aim 2 - Identify if local neuronal NO is a key downstream mediator in the GLP-2R-activated enteric signaling network by using a glp2r and eNOS double knockout approach in combination with cultured neuron model. This proposal will be the first to elucidate the glp2r gene in vivo physiological function, to identify key GLP-2R-activated downstream mediator(s), and to establish if GLP-2R is a key mediator involved in intestinal disease (e.g. short bowel syndrome), which may facilitate to develop new drugs to treat intestinal disease/ dysfunction. I submitted an R21 application earlier this year, which was not funded (Score 227). However, the Study Section advised strongly that I submit a K01 application to acquire expertise in molecular biology and genetics from an experienced mentor. I have selected Dr. Lawrence Chan, a leader in the application of molecular genetics to molecular endocrinology and medicine for this K01 application. Under the mentorship of Dr. Chan and the guidance of a scientific advisory committee, I hope to generate transgenic/gene knockout mouse models to investigate GLP-2R function at the molecular level. A K01 award would facilitate my transition to become a fully independent investigator. Toward the end of this award, I will take advantage of my newly acquired expertise and the novel genetically modified mouse models to submit an R01 grant application to investigate gastrointestinal function and disease.
