FZD5 controls intestinal crypt homeostasis and colonic Wnt surrogate agonist response.

The rapidly regenerating intestinal epithelium requires crypt intestinal stem cells (ISCs). Wnt/β-catenin signaling maintains crypt homeostasis and Lgr5+ ISCs, and WNT ligands bind Frizzled receptors (FZD1-10). Identifying specific FZD(s) essential for intestinal homeostasis has been elusive; however, bioengineered antagonists blocking Wnt binding to FZD5 and FZD8 deplete the gut epithelium in vivo, highlighting potential roles. Here, an epithelial-specific Fzd5 knockout (KO) elicited lethal pan-intestinal crypt and villus loss, whereas an Lgr5+ ISC-specific Fzd5 KO depleted Lgr5+ ISCs via premature differentiation and repressed Wnt target genes. Fzd5-null phenotypes were rescued by constitutive β-catenin activation in vivo and in both mouse and human enteroids. KO of Fzd5, not Fzd8, in enteroids ablated responsiveness to dual-specificity FZD5/FZD8-selective Wnt surrogate agonists, which ameliorated DSS-induced colitis in wild-type and Fzd8 KO mice. Overall, FZD5 is a dominant and essential regulator of crypt homeostasis, Lgr5+ ISCs, and intestinal response to Wnt surrogate agonists, with implications for therapeutic mucosal repair.