Evolutionary conservation of glucose-dependent insulinotropic polypeptide (GIP) gene regulation and the enteroinsular axis

In vivo drug discovery for increasing incretin-expressing cells identifies DYRK inhibitors that reinforce the enteroendocrine system

Analogs of the incretin hormones Gip and Glp-1 are used to treat type 2 diabetes and obesity. Findings in experimental models suggest that manipulating several hormones simultaneously may be more effective. To identify small molecules that increase the number of incretin-expressing cells, we established a high-throughput in vivo chemical screen by using the gip promoter to drive the expression of luciferase in zebrafish. All hits increased the numbers of neurogenin 3-expressing enteroendocrine progenitors, Gip-expressing K-cells, and Glp-1-expressing L-cells. One of the hits, a dual-specificity tyrosine phosphorylation-regulated kinase (DYRK) inhibitor, additionally decreased glucose levels in both larval and juvenile fish. Knock-down experiments indicated that nfatc4, a downstream mediator of DYRKs, regulates incretin+ cell number in zebrafish, and that Dyrk1b regulates Glp-1 expression in an enteroendocrine cell line. DYRK inhibition also increased the number of incretin-expressing cells in diabetic mice, suggesting a conserved reinforcement of the enteroendocrine system, with possible implications for diabetes.

The drug target genes show higher evolutionary conservation than non-target genes

Although evidence indicates that drug target genes share some common evolutionary features, there have been few studies analyzing evolutionary features of drug targets from an overall level. Therefore, we conducted an analysis which aimed to investigate the evolutionary characteristics of drug target genes. We compared the evolutionary conservation between human drug target genes and non-target genes by combining both the evolutionary features and network topological properties in human protein-protein interaction network. The evolution rate, conservation score and the percentage of orthologous genes of 21 species were included in our study. Meanwhile, four topological features including the average shortest path length, betweenness centrality, clustering coefficient and degree were considered for comparison analysis. Then we got four results as following: compared with non-drug target genes, 1) drug target genes had lower evolutionary rates; 2) drug target genes had higher conservation scores; 3) drug target genes had higher percentages of orthologous genes and 4) drug target genes had a tighter network structure including higher degrees, betweenness centrality, clustering coefficients and lower average shortest path lengths. These results demonstrate that drug target genes are more evolutionarily conserved than non-drug target genes. We hope that our study will provide valuable information for other researchers who are interested in evolutionary conservation of drug targets.

Gastric inhibitory polypeptide immunoneutralization attenuates development of obesity in mice

Previous reports have suggested that the abrogation of gastric inhibitory polypeptide (GIP) signaling could be exploited to prevent and treat obesity and obesity-related disorders in humans. This study was designed to determine whether immunoneutralization of GIP, using a newly developed specific monoclonal antibody (mAb), would prevent the development of obesity. Specific mAb directed against the carboxy terminus of mouse GIP was identified, and its effects on the insulin response to oral and to intraperitoneal (ip) glucose and on weight gain were evaluated. Administration of mAb (30 mg/kg body wt, BW) to mice attenuated the insulin response to oral glucose by 70% and completely eliminated the response to ip glucose coadministered with human GIP. Nine-week-old C57BL/6 mice injected with GIP mAbs (60 mg·kg BW(-1)·wk(-1)) for 17 wk gained 46.5% less weight than control mice fed an identical high-fat diet (P < 0.001). No significant differences in the quantity of food consumed were detected between the two treatment groups. Furthermore, magnetic resonance imaging demonstrated that subcutaneous, omental, and hepatic fat were 1.97-, 3.46-, and 2.15-fold, respectively, lower in mAb-treated animals than in controls. Moreover, serum insulin, leptin, total cholesterol (TC), low-density lipoprotein (LDL), and triglycerides were significantly reduced, whereas the high-density lipoprotein (HDL)/TC ratio was 1.25-fold higher in treated animals than in controls. These studies support the hypothesis that a reduction in GIP signaling using a GIP-neutralizing mAb might provide a useful method for the treatment and prevention of obesity and related disorders.

Obesity and the gastrointestinal tract: you are what you eat

Obesity represents a complex multifactorial syndrome that develops from interactions among genetic and environmental factors and is a leading cause of illness and death. The prevalence of obesity in the United States has increased dramatically since 1975. Although often ignored, the gastrointestinal tract, and the gastrointestinal regulatory peptides in particular, constitutes an ideal starting point for defining and investigating obesity as it represents the route by which all nutrients are ingested, processed, and absorbed. Another important factor to consider when evaluating the etiology of obesity is the capacity for all animals to store nutrients. Insulin is the most potent anabolic hormone, and it appears to have evolved from the need to maximize energy efficiency, obviating the requirement to continuously forage for food. Organisms expressing this important peptide possessed a distinct survival advantage and flourished. During the course of evolution, insulin biosynthesis translocated from the intestine to pancreatic islets, which necessitated a messenger from the intestine to complete the "enteroinsular axis." The eventual development of glucose-dependent insulinotropic polypeptide (GIP) and other incretins fulfilled this requirement. GIP appears to offer an additional survival benefit by not only stimulating intestinal glucose transport and maximally releasing insulin to facilitate nutrient storage but also by its insulin-mimetic properties, including enhanced uptake of glucose by adipocytes. This physiological redundancy offered by insulin and GIP ensured the survival of organisms during times when food was scarce. As food is no longer scarce, at least in the West, this survival advantage appears to have contributed to the current obesity epidemic.

Overlap of endocrine hormone expression in the mouse intestine revealed by transcriptional profiling and flow cytometry

The intestine secretes a range of hormones with important local and distant actions, including the control of insulin secretion and appetite. A number of enteroendocrine cell types have been described, each characterized by a distinct hormonal signature, such as K-cells producing glucose-dependent insulinotropic polypeptide (GIP), L-cells producing glucagon-like peptide-1 (GLP-1), and I-cells producing cholecystokinin (CCK). To evaluate similarities between L-, K-, and other enteroendocrine cells, primary murine L- and K-cells, and pancreatic α- and β-cells, were purified and analyzed by flow cytometry and microarray-based transcriptomics. By microarray expression profiling, L cells from the upper small intestinal (SI) more closely resembled upper SI K-cells than colonic L-cells. Upper SI L-cell populations expressed message for hormones classically localized to different enteroendocrine cell types, including GIP, CCK, secretin, and neurotensin. By immunostaining and fluorescence-activated cell sorting analysis, most colonic L-cells contained GLP-1 and PeptideYY In the upper SI, most L-cells contained CCK, approximately 10% were GIP positive, and about 20% were PeptideYY positive. Upper SI K-cells exhibited approximately 10% overlap with GLP-1 and 6% overlap with somatostatin. Enteroendocrine-specific transcription factors were identified from the microarrays, of which very few differed between the enteroendocrine cell populations. Etv1, Prox1, and Pax4 were significantly enriched in L-cells vs. K cells by quantitative RT-PCR. In summary, our data indicate a strong overlap between upper SI L-, K-, and I-cells and suggest they may rather comprise a single cell type, within which individual cells exhibit a hormonal spectrum that may reflect factors such as location along the intestine and exposure to dietary nutrients.