Singh, A.; Poling, H. M.; Foulke-Abel, J.; Sundaram, N.; Al Reza, A.; Joseph, S.; Elseht, A.; Srivasta, K.; Krutko, M.; Mayhew, C. N.; Breault, D.; Wells, J. M.; Thiagarajah, J. R.; O'Connell, A. E.; Kovbasnjuk, O.; Helmrath, M. A.

Background and Aims: WNT2B mutations result in Diarrhea-9 (DIAR9), a congenital diarrhea syndrome with an extreme phenotype and unique histological defects. Attempts to model DIAR9 in rodents and study patient epithelial tissue have not been able to fully reproduce the human phenotype, making understanding this condition challenging. Here, we aimed to interrogate the mechanisms and the specific cellular compartment contributing to DIAR9 using a human intestinal organoid model. Methods: Human intestinal organoids (HIOs) generated from both a patient-derived WNT2BR69*iPSC line and a control line were transplanted into immunocompromised mice for 10 weeks. Grafts were harvested and histologically compared. Bulk RNA sequencing was performed on both organoid groups and on patient-biopsy derived enteroids. In vitro recombination experiments were performed to describe the causative cellular compartment. Results: Live and histological imaging revealed partial epithelial delamination in WNT2BR69*HIOs, which was absent in controls. A significant number of crypts in WNT2BR69* HIOs lacked OLFM4, a surrogate marker of stem cell activity. Key transcriptomic pathways altered between groups included trafficking of apical digestion proteins, which was confirmed via immunofluorescence. Patient derived enteroid proteomic analysis revealed similar results. Recombination experiments in HIOs revealed that while both epithelial and mesenchymal WNT2B are important for stem cell function, lack of mesenchymal WNT2B was sufficient to elicit the phenotype. Conclusion: We demonstrated that mesenchymal WNT2B is critical for supporting human intestinal epithelial development and function.