Ctla-4 deficiency induces an inflammatory bowel disease-like phenotype in a zebrafish model [scRNA-seq]

Inflammatory bowel disease (IBD) is a chronic and relapsing immune-mediated disorder characterized by intestinal inflammation and epithelial injury. The underlying causes of IBD are not fully understood, but genetic factors have implicated in genome-wide association studies, including CTLA-4, an essential negative regulator of T cell activation. However, establishing a direct link between CTLA-4 and IBD has been challenging due to the early lethality of CTLA-4 knockout mice. In this study, we identified zebrafish Ctla-4 ortholog and investigated its role in maintaining intestinal immune homeostasis by generating a Ctla-4-deficient (ctla-4-/-) zebrafish line. These mutant zebrafish exhibit reduced weight, along with impaired epithelial barrier integrity and lymphocytic infiltration in their intestines. Transcriptomics analysis revealed upregulation of inflammation-related genes, disturbing immune system homeostasis. Moreover, single-cell RNA-sequencing analysis indicated increased Th2 cells and interleukin 13 expression, along with decreased innate lymphoid cells and upregulated proinflammatory cytokines. Additionally, Ctla-4-deficient zebrafish exhibited reduced diversity and an altered composition of the intestinal microbiota. All these phenotypes closely resemble those found in mammalian IBD. Lastly, supplementation with Ctla-4-Ig successfully alleviated intestinal inflammation in these mutants. Altogether, these findings offer substantial evidence linking CTLA-4 to IBD and establish a new model for investigating pathogenesis and potential treatments. intestine leukocyte (WT and KO (Ctla-4 deficiency) ) of the AB zebrafish were isolated by Ficoll-Hypaque (1.080 g/mL) density-gradient centrifugation and analyzed using scRNAseq.