A novel long-galanin peptide from non-mammalian vertebrates mitigates the inflammatory response in IBD models via the biased GALR2/β-arrestin2 pathway

Galanin, a neuropeptide, regulates immune and inflammatory responses via GALR1-3. GALRs have emerged as potential therapeutic targets for inflammatory bowel disease (IBD), yet their mechanistic roles remain unclear. Based on evolutionary analysis, we identified a long galanin isoform (GAL53), generated by alternative splicing in non-mammalian vertebrates. Here we show that the chicken ortholog cGAL53 is robustly expressed in colonic tissue but downregulated upon dextran sulfate sodium (DSS)-induced colitis. Administration of cGAL53 alleviates colitis-associated weight loss, colon shortening, bleeding, and inflammation in both chickens and mice. These effects are abolished in Galr2-deficient mice, highlighting receptor dependency. Moreover, epithelial cell-specific Arrb2 and Gnaq knockout models demonstrate that cGAL53 protects the gut barrier and reduces inflammation by activating β-arrestin2-biased GALR2 signaling. Our findings reveal a naturally occurring long galanin peptide with potent anti-inflammatory activity and propose evolutionary medicine-guided biased GALR2 agonism as a therapeutic strategy for IBD.