Maintenance of intestinal epithelium homeostasis is a complex process because of the multicellular and molecular composition of the gastrointestinal wall and the involvement of surrounding interactive signals. The complex nature of this intestinal barrier system poses challenges in the detailed mechanistic understanding of intestinal morphogenesis and the onset of several gut pathologies, including intestinal inflammatory disorders, food allergies, and cancer. For several years, the gut scientific community has explored different alternatives in research involving animals and in vitro models consisting of cultured monolayers derived from the immortalized or cancerous origin cell lines. The recent ability to recapitulate intestinal epithelial dynamics from mini-gut cultures has proven to be a promising step in the field of scientific research and biomedicine. The organoids can be grown as two- or three-dimensional structures, and are derived from adult or pluripotent stem cells that ultimately establish an intestinal epithelium that is composed of all differentiated cell types present in the normal epithelium. In this review, we summarize the different origins and recent use of organoids in modeling intestinal epithelial differentiation and barrier properties.

FoxL1+-Telocytes (TCFoxL1+) are subepithelial cells that form a network underneath the epithelium. We have shown that without inflammatory stress, mice with loss of function in the BMP signalling pathway in TCFoxL1+ (BmpR1aΔFoxL1+) initiated colonic neoplasia. Although TCFoxL1+ are modulated in IBD patients, their specific role in this pathogenesis remains unclear. Thus, we investigated how the loss of BMP signalling in TCFoxL1+ influences the severity of inflammation and fosters epithelial recovery after inflammatory stress. BmpR1a was genetically ablated in mouse colonic TCFoxL1+. Experimental colitis was performed using a DSS challenge followed by recovery steps to assess wound healing. Physical barrier properties, including mucus composition and glycosylation, were assessed by alcian blue staining, immunofluorescences and RT-qPCR. We found that BmpR1aΔFoxL1+ mice had impaired mucus quality, and upon exposure to inflammatory challenges, they had increased susceptibility to experimental colitis and delayed healing. In addition, defective BMP signalling in TCFoxL1+ altered the functionality of goblet cells, thereby affecting mucosal structure and promoting bacterial invasion. Following inflammatory stress, TCFoxL1+ with impaired BMP signalling lose their homing signal for optimal distribution along the epithelium, which is critical in tissue regeneration after injury. Overall, our findings revealed key roles of BMP signalling in TCFoxL1+ in IBD pathogenesis.

Background Inflammatory bowel diseases (IBD) are a group of chronic disorders that affect more than 233 000 Canadians and for which there is not yet an effective treatment. In addition, IBD is a multifactorial disease depending on genetic, immune and environmental dysregulations. The gastrointestinal epithelium plays an important role as a barrier that protects against antigens and bacterial products that are in the lumen. It is well recognized that a defect in the integrity of the barrier and its functions may be involved in the development of these diseases. On the other hand, our laboratory has shown that the conditional deletion of HNF4alpha nuclear receptor (Hnf4a) in the intestinal epithelium of mice can lead to the development of chronic inflammation of the intestine. However, the impact of the loss of this transcriptional factor on the epithelial barrier is still controversial. Aims To evaluate the impact of Hnf4a deletion on the epithelial barrier during bacterial infections. Methods We used a tamoxifen-inducible Cre-loxP system to delete the Hnf4a gene in the intestinal epithelium of 2-month-old mice, that were then infected with an attenuated strain of Salmonella typhimurium (SB1003) during 4 days. S. typhimurium loads were determined in cecum and colon content, and in liver, spleen tissues by plating homogenates on LB agar supplemented with streptomycin. Also, histological examinations and gene expression of selected targets were assessed between mutant (Hnf4aΔIEC) and control mice. Results The tamoxifen-inducible Cre-loxP system was able to delete intestinal Hnf4a gene expression with almost 100% of efficacy. Analysis by qPCR showed that the infection caused significant changes on the response of different infection responsive components (Relmβ, Muc2 and IL-33) in mutant mice. In addition, morphological analyses revealed an increase in the infiltration of immune cells and the number of goblets cells, indicative of an increase in the susceptibility to Salmonella typhimurium (SB1003) infection of the mutant mice. Conclusions Altogether, our results suggest that Hnf4a could be involved or play an important role as a modulator of the intestinal epithelial barrier function during Salmonella typhimurium (SB1003) infection. Therefore, understanding the mechanisms involved in this process could allow the development of better therapies for IBD. Funding Agencies CIHR

NOT PUBLISHED AT AUTHOR’S REQUEST Funding Agencies: CIHR