The Function Of Gpr177 In The Mouse Intestinal Epithelium And Bowel Cancer

Wnt,a kind of secretory proteins,is indispensable for the homeostasis of intestine.Gpr177,also known as Wntless,has a multipass transmembrane protein structure,which is similar to that of classic G-protein coupled receptor.Gpr177 is essential to the proper secretion of Wnt proteins.Currently,the understanding of the biological function of Gpr177 in intestine is yet limited.Thus,this project would aim to explore the role of Gpr177 in the mouse intestinal epithelium and bowel cancer.In order to well study the Gpr177 function in intestine and circumvent problem of mouse embryonic lethality caused by homozygous Gpr177 knockout,we established a mice model of Gpr177 conditional knockout in the intestinal epithelium.Our results showed that in Gpr177 conditional knockout mice,the morphology and structure of intestinal tissues,the proliferation and differentiation of intestinal stem cells were as normal as those in control mice.To exclude the compensation effects by the peripheral mesenchyme,we used the method of culturing three-dimensional(3D)intestinal epithelial organoids in vitro for further studies.We found that the small intestinal organoids had growth defect and intestinal stem cells lost the self-renewal and differentiated abnormally without Gpr177.This demonstrates that Gpr177 plays an important role in the maintainance of small intestinal stem cells homeostasis in vitro.Mechanistical study showed that Notch signaling pathway was significantly suppressed in the small intestinal organoids when Gpr177 was knocked out,which caused the aberrant differentiation of goblet cells.Moreover,we found that exogenously added WNT3 a could partly rescue the growth defect of small intestinal organoids caused by Gpr177 conditional knockout,thereby indicating that Gpr177 regulates the homeostasis of small intestine by altering secretory WNT3 a.However,it is interesting to note that the deletion of Gpr177 has no influence on the proliferation and differentiation of colon organoids,thus suggesting that small intestine and colon differentially depends on Gpr177.In order to explore the function of Gpr177 in the development of bowel cancer,we established the Apcfloxp/+ spontaneous bowel cancer model and inflammation induced cancer model.We found that the size and number of tumors in Gpr177 conditional knockout mice were comparable to those in control mice,which implies that intestinal epithelial Gpr177 does not play a key role in the development of bowel cancer.Collectively,this project shows that intesitinal epithelial Gpr177 is required for the homeostasis maintenance of small intestinal in vitro without mesenchymal cells,by increasing the secretion of WNT3a.However,intestinal epithelial Gpr177 does not strikingly affect the intestinal homeostasis and bowel cancer development in vivo.Thus,this study expands the current understanding of Gpr177 and providing theoretical evidence for therapy and diagnosis of bowel cancer.