Functional Study Of Intestinal Epithelial-specific IGF1 On Intestinal Development And Mucosal Immunity In Mice

Gastrointestinal tract is the organ for food digestion,nutrient uptake and host defense against various bacterial pathogens.It has the largest surface,allowing cross-talking between the outside world and inside parts of our body.It is essential for maintaning the normal metabolism of our body.The rapid turnover of intestinal epithelial cells(IECs)every three to five days is driven by intestinal epithelial stem cells(ISCs)at the base of the crypt.IECs maintain gut immune homeostasis by regulating the interaction between the intestinal microbiota and intestinal immunity.Deregulation of intestinal homeostasis results in short bowel syndrome(SBS),chronic or acute inflammatory bowel diseases(3BD),and even colorectal cancer(CRC).Insulin-like growth factor 1(IGF1)had trophic hormone action on small intestine under both physiological and pathophysiological conditions.The potent proliferative effects of IGF1 on intestinal epithelium have been extensively studied using both enteral and parenteral IGF1.IGFlalso has potent therapeutic effects against gastrointestinal disorders including SBS,IBD and radiation enteritis.However,little is known about the in vivo function of intestinal epithelial cell-specific IGF1 in normal gut,ISCs,and gastrointestinal disorders.Particularly,the IGF1 functional role in regulating gut microbiota and the host immune system is entirely unknown.In this study we first generated IEC-specific knockout IGF1(cKO)mice by crossing Villin-Cre transgenic mice and IGF1flox/flox mice.These cKO mice,together with the Lgr5-EGFP-CreERT mouse model were used to study the in vivo roles of intestinal intrinsic IGF1 on intestinal growth,ISC and mucosal protection.In addition,the IGF1 roles in regulating gut microbiota,metabolites,and host immunity were also investigated.Our results demonstrated that IEC-specific IGF1 has following functional roles:1)enhanced the nutrient uptake,2)reduced the protein catabolism and energy consumption.3)increased villus height and crypt depth with enhanced cell proliferation,and 4)expanded numbers of ISC and intestinal secretory cells,including Paneth cells,goblet cells,enteroendocrine cells.Mouse radiation experiments showed that IEC-specific IGF1 enhanced radio-resistant capacity of intestinal epithelial cells and promoted the epithelial regeneration.DSS-induced colitis in cKO mice showed that the loss of intestinal IGF1 resulted in more severe damage in colonic epithelium,higher mortality rate,and slower epithelial regeneration.These results indicated that that IEC-specific IGF1 played an important role in epithelial regeneration caused by irradiation and DSS treatment.Furthermore,we determined transcriptome profiles of intestine and colon and compared them between cKO and control mice.The results revealed that the most ennriched differentially expressed genes were associated with intestinal mucosal immunity in both tissues.Particularly,these genes involved in differentiation and maturation processes of lymphoid lineages were significantly suppressed in the intestine of cKO mice as compared to controls.Meanwhile,intestinal bacteria analysis was performed using 16S ribosomal DNA high-throughput sequencing.We observed that IEC-specific IGF1 loss profoundly affects the gut microbial composition at different classification levels of bacteria.Lefse analysis screened out that Oscillospira bacteria significantly decreased in cKO mice compared to controls.Taken together,our results demonstrated the role of IEC-specific IGF1 in host immunities and gut microbiota for first time from transcriptome level in vivo.Overall,the above experimental results sufficiently demonstrated that the irreplaceable role of intestinal paracrine/autocrine IGF1,compared to endocrine IGF1.Both types of IGF1 are essential for maintaining the basic metabolic homeostasis.Understanding the precise role of the IEC specific IGF1 on intestinal epithelial homeostasis,regeneration and immunity would help developing of new therapeutic strategy and drug designation for acute or chronic gastrointestinal diseases or intestinal inflammatory disorders.