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Intestinal homeostasis is maintained by a hierarchy of immune defenses acting in concert to minimize contact between luminal microorganisms and the intestinal epithelial cell surface. The intestinal mucus layer, covering the gastrointestinal tract epithelial cells, contributes to mucosal homeostasis by limiting bacterial invasion. In this study, we used γδ T-cell-deficient (TCRδ−/−) mice to examine whether and how γδ T-cells modulate the properties of the intestinal mucus layer. Increased susceptibility of TCRδ−/− mice to dextran sodium sulfate (DSS)-induced colitis is associated with a reduced number of goblet cells. Alterations in the number of goblet cells and crypt lengths were observed in the small intestine and colon of TCRδ−/− mice compared with C57BL/6 wild-type (WT) mice. Addition of keratinocyte growth factor to small intestinal organoid cultures from TCRδ−/− mice showed a marked increase in crypt growth and in both goblet cell number and redistribution along the crypts. There was no apparent difference in the thickness or organization of the mucus layer between TCRδ−/− and WT mice, as measured in vivo. However, γδ T-cell deficiency led to reduced sialylated mucins in association with increased gene expression of gel-secreting Muc2 and membrane-bound mucins, including Muc13 and Muc17. Collectively, these data provide evidence that γδ T cells play an important role in the maintenance of mucosal homeostasis by regulating mucin expression and promoting goblet cell function in the small intestine.

Summary The mucus layer covering the gastrointestinal (GI) epithelium is critical in selecting and maintaining homeostatic interactions with our gut bacteria. However, the underpinning mechanisms of these interactions are not understood. Here, we provide structural and functional insights into the canonical mucus-binding protein (MUB), a multi-repeat cell-surface adhesin found in Lactobacillus inhabitants of the GI tract. X-ray crystallography together with small-angle X-ray scattering demonstrated a ‘beads on a string’ arrangement of repeats, generating 174 nm long protein fibrils, as shown by atomic force microscopy. Each repeat consists of tandemly arranged Ig- and mucin-binding protein (MucBP) modules. The binding of full-length MUB was confined to mucus via multiple interactions involving terminal sialylated mucin glycans. While individual MUB domains showed structural similarity to fimbrial proteins from Gram-positive pathogens, the particular organization of MUB provides a structural explanation for the mechanisms in which lactobacilli have adapted to their host niche by maximizing interactions with the mucus receptors, potentiating the retention of bacteria within the mucus layer. Together, this study reveals functional and structural features which may affect tropism of microbes across mucus and along the GI tract, providing unique insights into the mechanisms adopted by commensals and probiotics to adapt to the mucosal environment.

Intestinal γδ T-cell receptor-bearing intraepithelial lymphocytes (γδ IELs) play a multifaceted role in maintaining mucosal homeostasis. In order to investigate the relationship between O-glycosylation and inflammation, we carried out an in-depth mass spectrometric comparison of the intestinal O-glycosylation profile of mice lacking γδ IELs (TCRδ(-/-)) and of their wild-type (WT) littermates. A total of 69 nonsulfated and 59 sulfated compositional types of O-glycans were identified in the small intestine and colon of TCRδ(-/-) and WT mice. Our results demonstrated structural differences in intestinal glycosylation in TCRδ(-/-) mice compared with WT littermates. TCRδ(-/-) colons contained a lower proportion of core-2 structures and an increased proportion of core-1 structures whereas TCRδ(-/-) small intestines had a decreased percentage of core-3 structures. The glycan antennae in TCRδ(-/-) colon and small intestine showed altered structural diversity compared with WT mice. There were significant differences in the sialylated species between the TCRδ(-/-) and WT mice with the sialylated Tn antigen found exclusively in the TCRδ(-/-)small intestine, whereas the sulfation pattern remained mostly unchanged. These findings provide novel molecular insights underpinning the role of γδ IELs in maintaining gut homeostasis.

Background & Aims β3 Adrenoceptor (β3-AR) is expressed on adipocytes and enteric neurons. GW427353 is a human selective β3-AR agonist with visceral analgesic effects. Some of its effects may involve release of somatostatin (SST) and actions on enteric neurons. The aim of this study was to investigate the mode of action of GW427353 in human submucous neurons. Methods Voltage sensitive dye imaging was used to record from human submucous neurons. SST release from human primary adipocytes was measured with enzyme-linked immunoabsorbent assay. Immunohistochemistry was used to detect adiponectin, β3-AR, SST, SST2 receptors, tyrosine hydroxylase (TH), and protein gene product 9.5. Results Confocal imaging showed cytoplasmic β3-AR labeling in somata of submucous neurons and nerve varicosities. GW427353 had no direct postsynaptic actions but decreased fast synaptic input to submucous neurons. Tissue perfusion with GW427353 reduced nicotine-evoked neuronal spike frequency, an effect prevented by the β3-AR antagonist SR-59230 and the SST2-receptor antagonist CYN154806 and mimicked by the SST2 receptor agonist octreotide. Adipocytes expressed adiponectin, β3-AR, and SST. TH-positive fibers were in close proximity to adipocytes. Submucous neurons expressed SST2 receptors. Human primary adipocytes released SST in response to GW427353 in a concentration-dependent manner, an effect abolished by SR-59230. Conclusions Inhibitory action of GW427353 involves release of SST which stimulates inhibitory SST2 receptors on human submucous neurons. Adipocytes are a potential source for SST. β3-AR activation may be a promising approach to reduce enteric neuron hyperexcitability. The action of GW427353 may be the neurophysiologic correlate of its beneficial effect in patients with irritable bowel syndrome.

The activating transcription factor 6 (ATF6) is one of the major transducers of the endoplasmic reticulum unfolded protein response (ER UPR). To study how ATF6 signaling affects intestinal epithelial cells (IEC) and intestinal health, nATF6IEC mice were investigated. These mice express the activated form of ATF6 (nATF6) specifically in IEC. The dissertation shows that nATF6 expression in IEC promotes tumorigenesis in the large intestine which is linked to dysbiosis of the intestinal microbiota. The nATF6IEC model and the analysis of ATF6 in colon cancer patients provide evidence for a contribution of ATF6 signaling to the pathogenesis of intestinal cancer.