Spotlight: TMEM219 signaling promotes intestinal stem cell death and exacerbates colitis

Introduction

Regulation of cell proliferation, differentiation and death in the intestinal epithelium has been the focus of intense research for many years. In addition to epithelial-intrinsic factors, the roles of the mucosal immune system, enteric nervous system and intestinal microbiota in controlling cell fate have been established. Dysregulation of the relationship between the different cell types underlies the development of pathologies such as Crohn’s Disease. In a recent paper, D’Addio et al examine the hypothesis that a stem cell-specific defect disrupts the ability of the intestinal epithelium to regenerate following injury, facilitating the establishment of an inflammatory response.

Main Points

• Patients with active Crohn’s disease (CD) had fewer intestinal epithelial crypts that contained fewer stem cells, based on expression of EPHB2 and LGR5. Organoids derived from patients with active CD demonstrated less branching.
• A higher proportion of intestinal stem cells were apoptotic in samples from patients with active/non-responsive CD. This was associated with an increase in cleaved (activated) caspase 8, also observed in organoids derived from the same samples. Organiods from non-IBD pateints showed increased caspase 8 activation when cultured with serum from patients with active CD.
• Bioinformatic analysis led to the proposal that the transmembrane receptor, TMEM219, was as essential component of the pathway triggering caspase 8 activation.
• Expression of TMEM219 was demonstrated in intestinal cells and shown to be increased in samples from patients with active CD, in particular in inflamed areas.
• Incubation of Caco2 cells with the TMEM219 ligand, IGFBP3, resulted in activation of caspase 8 (but not 1, 3, 7 or 9), which was inhibited by a TMEM219 siRNA and by a soluble TMEM219 EC domain only protein (Ecto-TMEM219).
• Ecto-TMEM219 increased branching of organoids derived from active CD biospy samples, with an associated increase in the expression of stem cell markers LGR5 and EPHB2.
• Ecto-TMEM219 ameliorated clinical signs and histopathological changes in DSS-induced acute and chronic colitis models and enhanced organoid development from intestinal cells isolated from DSS-treated mice. Efficacy was also demonstrated in a T cell transfer-mediated colitis model.
• Mice with conditional deletion of Tmem219 gene in Lgr5+ cells demonstrated greatly reduced expression of Tmem219 in intestinal crypts, together with a decrease in Casp8 and an increase in Lgr5. Organoids derived from Tmem219 conditional KO mice were less sensitive to the pro-apoptotic TMEM219 ligand, IGFBP3.
• Tmem219 conditional KOs were less sensitive to DSS compared to control mice.

Conclusion

Epithelial crypt loss is an obvious feature of IBD-associated intestinal pathology that is also replicated in animal models. Crypt loss is a result of crypt sterilisation i.e. death of all stem cells within the crypt. D’Addio et al provide evidence that a TMEM219/Caspase 8-dependent pathway may play a role in enhanced stem cell apoptosis and a failure of epithelial regeneration in Crohn’s disease.

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Epistem can offer more than 25 years of experience in gastrointestinal stem cell biology, apoptosis and IBD, including 15 years running intestinal organoid models. Our preclinical models are supported by GCLP-accredited PGx and histology laboratories and a range of analytical services including NGS, bioinformatics, RNAScope, flow cytometry, multiplex cytokine analysis and live cell imaging capabilities. We are used to working a wide range of clients from large pharma to academia on a variety of studies including clinical trials sample analysis, IND-enabling efficacy studies, POC studies and in vitro GI toxicity screening.