Spexin-GALR2-Gq axis as a biased signaling pathway for colitis therapy.

Inflammatory bowel disease (IBD) remains a major clinical challenge worldwide. Spexin (SPX), a neuropeptide that signals through galanin receptors (GALR2/3), has been implicated in metabolic and behavioral regulation. Here, we report that SPX effectively alleviates colitis, primarily by suppressing inflammation and promoting intestinal epithelial repair, outperforming its relative peptide, galanin (GAL). Mechanistically, SPX exhibits G protein-biased agonism at GALR2, whereas GAL favors β-arrestin2 recruitment. Utilizing Galr2 -/- and Galr3 -/- mice, receptor-specific inhibitors, and intestinal epithelial-specific Gnaq and Arrb2 knockout mice, we establish that the SPX-GALR2-Gq axis drives the protective effects of SPX in colitis. Structure-guided mutagenesis further pinpointed key residues governing this signaling bias and enabled the design of SPX p.Lys11Leu, a high-affinity GALR2 agonist that exerts potent anti-colitis activity at significantly lower doses than wild-type SPX. Collectively, our work defines the SPX-GALR2-Gq axis as a therapeutically relevant biased signaling pathway for colitis, and nominates SPX, particularly its p.Lys11Leu mutant, as a promising peptide drug candidate for IBD.