TNFSF13 insuffiency causes epithelial and immune disruption in the human colon II
Objective: Cytokines produced by epithelial and immune cells can act upon one another to promote mucosal healing- a process that goes awry with chronic inflammation as in inflammatory bowel disease. TNFSF13 is a cytokine important for B cell function, but its role in epithelial cell behavior and contribution to inflammatory bowel disease is poorly understood.  Design: We performed histological and functional assays, single cell transcriptomics, and imaging mass cytometry on tissue-derived colonoids or biopsies from a patient with very early onset inflammatory bowel disease (VEO-IBD) harboring a novel TNFSF13 variant. To confirm causal, variant-driven phenotypes, parallel experiments were performed in induced pluripotent stem cell (iPSC)- derived colon organoids engineered with the same TNFSF13 variant.  Results: TNFSF13 variant colonoids exhibited reduced TNFSF13 expression associated with increased proliferation and reduced apoptosis, which was confirmed in iPSC-derived colon organoids. Single cell RNA-sequencing and flow cytometry defined FAS as the predominant colonic epithelial receptor for TNFSF13. TNFSF13 variant colon biopsies demonstrated a shift in tissue B cell populations consistent with altered differentiation of memory B cells. Finally, imaging mass cytometry revealed an increase in epithelial-associated B cells in TNFSF13 variant colon tissue sections compared to healthy and non-monogenic VEO-IBD controls.  Conclusions: The current study defines a previously unknown role for the cytokine TNFSF13 as a regulator of colonic epithelial proliferation and apoptosis. Furthermore, this study suggests that variant TNFSF13 can contribute to aberrant epithelial- B cell crosstalk in the human colon. Overall design: scRNA-seq analysis of epithelial and stromal cells from colon biopsies of a patient with VEO-IBD and a healthy control