Tryptophan metabolic gatekeeping in epithelial repair: GPR35-KLF5 circuitry decodes mucosal damage signals for repair programming.

The impaired repair of intestinal mucosal damage is an important pathological feature of ulcerative colitis (UC). The critical role of intestinal epithelial cells (IECs) proliferation and migration in the repair of damaged mucosal epithelium has been well established. However, the molecular circuitry that decodes IECs sense intestinal mucosal damage signals to initiate and drive repair program remains elusive. Here, we identify a tryptophan (Trp) metabolic gatekeeping mechanism wherein G protein-coupled receptor 35 (GPR35) senses intestinal mucosal damage through monitoring Trp-kynurenine (KYN)-kynurenic acid (KA) axis metabolism with a unique "sandwich" structural binding mode. We delineate a GPR35-Kruppel-like factor 5 (KLF5) regulatory circuit in which KLF5 serves as the central effector, translating GPR35-mediated KA sensing into repair programming through PI3K-AKT-mTOR signaling cascade. This circuitry precisely orchestrates IECs proliferation and migration by regulating KLF5-dependent gene expression networks that essential for restoring damaged mucosa. Once this metabolic gatekeeping system is disrupted, either through impaired GPR35-mediated KA sensing or defective signal transduction, compromises damage signal decoding, leading to inadequate repair responses. Such dysregulation results in delayed intestinal mucosal repair and exacerbation of tissue damage. Our findings highlight GPR35 as a surveillant of abnormal Trp-KYN-KA axis metabolism, enabling IECs to detect intestinal mucosal damage and orchestrate repair through KLF5 response. This provides important implications for UC prevention and treatment by targeting GPR35-KLF5 circuit.