Henner F. Farin

Redundant sources of wnt regulate intestinal stem cells and promote formation of paneth cells

BACKGROUND & AIMS Wnt signaling regulates multiple aspects of intestinal physiology, including stem cell maintenance. Paneth cells support stem cells by secreting Wnt, but little is known about the exact sources and primary functions of individual Wnt family members. METHODS We analyzed intestinal tissues and cultured epithelial cells from adult mice with conditional deletion of Wnt3 (Vil-CreERT2;Wnt3fl/fl mice). We also analyzed intestinal tissues and cells from Atoh1 mutant mice, which lack secretory cells. RESULTS Unexpectedly, Wnt3 was dispensable for maintenance of intestinal stem cells in mice, indicating a redundancy of Wnt signals. By contrast, cultured crypt organoids required Paneth cell-derived Wnt3. Addition of exogenous Wnt, or coculture with mesenchymal cells, restored growth of Vil-CreERT2;Wnt3fl/fl crypt organoids. Intestinal organoids from Atoh1 mutant mice did not grow or form Paneth cells; addition of Wnt3 allowed growth in the absence of Paneth cells. Wnt signaling had a synergistic effect with the Lgr4/5 ligand R-spondin to induce formation of Paneth cells. Mosaic expression of Wnt3 in organoids using a retroviral vector promoted differentiation of Paneth cells in a cell-autonomous manner. CONCLUSIONS Wnt is part of a signaling loop that affects homeostasis of intestinal stem and Paneth cells in mice. Wnt3 signaling is required for growth and development of organoid cultures, whereas nonepithelial Wnt signals could provide a secondary physiological source of Wnt.

Niche-independent high-purity cultures of Lgr5+ intestinal stem cells and their progeny

Although Lgr5+ intestinal stem cells have been expanded in vitro as organoids, homogeneous culture of these cells has not been possible thus far. Here we show that two small molecules, CHIR99021 and valproic acid, synergistically maintain self-renewal of mouse Lgr5+ intestinal stem cells, resulting in nearly homogeneous cultures. The colony-forming efficiency of cells from these cultures is ∼100-fold greater than that of cells cultured in the absence of CHIR99021 and valproic acid, and multilineage differentiation ability is preserved. We made use of these homogeneous cultures to identify conditions employing simultaneous modulation of Wnt and Notch signaling to direct lineage differentiation into mature enterocytes, goblet cells and Paneth cells. Expansion in these culture conditions may be feasible for Lgr5+ cells from the mouse stomach and colon and from the human small intestine. These methods provide new tools for the study and application of multiple intestinal epithelial cell types.

Controlled gene expression in primary Lgr5 organoid cultures

The study of gene function in endodermal epithelia such as of stomach, small intestine and colon relies heavily on transgenic approaches. Establishing such animal models is laborious, expensive and time-consuming. We present here a method based on Cre recombinase–inducible retrovirus vectors that allows the conditional manipulation of gene expression in primary mouse organoid culture systems.

Paneth cell extrusion and release of antimicrobial products is directly controlled by immune cell–derived IFN-γ

IFN-γ directly triggers degranulation and death of Paneth cells, which do not respond to microbial stimulation in primary culture.

TTC7A mutations disrupt intestinal epithelial apicobasal polarity

Multiple intestinal atresia (MIA) is a rare cause of bowel obstruction that is sometimes associated with a combined immunodeficiency (CID), leading to increased susceptibility to infections. The factors underlying this rare disease are poorly understood. We characterized the immunological and intestinal features of 6 unrelated MIA-CID patients. All patients displayed a profound, generalized lymphocytopenia, with few lymphocytes present in the lymph nodes. The thymus was hypoplastic and exhibited an abnormal distribution of epithelial cells. Patients also had profound disruption of the epithelial barrier along the entire gastrointestinal tract. Using linkage analysis and whole-exome sequencing, we identified 10 mutations in tetratricopeptide repeat domain–7A (TTC7A), all of which potentially abrogate TTC7A expression. Intestinal organoid cultures from patient biopsies displayed an inversion of apicobasal polarity of the epithelial cells that was normalized by pharmacological inhibition of Rho kinase. Our data indicate that TTC7A deficiency results in increased Rho kinase activity, which disrupts polarity, growth, and differentiation of intestinal epithelial cells, and which impairs immune cell homeostasis, thereby promoting MIA-CID development.

Generation of L cells in mouse and human small intestine organoids.

Upon a nutrient challenge, L cells produce glucagon-like peptide 1 (GLP-1), a powerful stimulant of insulin release. Strategies to augment endogenous GLP-1 production include promoting L-cell differentiation and increasing L-cell number. Here we present a novel in vitro platform to generate functional L cells from three-dimensional cultures of mouse and human intestinal crypts. We show that short-chain fatty acids selectively increase the number of L cells, resulting in an elevation of GLP-1 release. This is accompanied by the upregulation of transcription factors associated with the endocrine lineage of intestinal stem cell development. Thus, our platform allows us to study and modulate the development of L cells in mouse and human crypts as a potential basis for novel therapeutic strategies in patients with type 2 diabetes.

Germline deletions in the tumour suppressor gene FOCAD are associated with polyposis and colorectal cancer development

Heritable genetic variants can significantly affect the lifetime risk of developing cancer, including polyposis and colorectal cancer (CRC). Variants in genes currently known to be associated with a high risk for polyposis or CRC, however, explain only a limited number of hereditary cases. The identification of additional genetic causes is, therefore, crucial to improve CRC prevention, detection and treatment. We have performed genome‐wide and targeted DNA copy number profiling and resequencing in early‐onset and familial polyposis/CRC patients, and show that deletions affecting the open reading frame of the tumour suppressor gene FOCAD are recurrent and significantly enriched in CRC patients compared with unaffected controls. All patients carrying FOCAD deletions exhibited a personal or family history of polyposis. RNA in situ hybridization revealed FOCAD expression in epithelial cells in the colonic crypt, the site of tumour initiation, as well as in colonic tumours and organoids. Our data suggest that monoallelic germline deletions in the tumour suppressor gene FOCAD underlie moderate genetic predisposition to the development of polyposis and CRC.