Dysregulated bile acid metabolism impairs intestinal barrier integrity via defective GPBAR1 signaling in low-birth-weight suckling piglet.

Low birth weight (LBW) is closely associated with postnatal inflammation and disruption of intestinal barrier function. However, the molecular mechanisms underlying these associations remain incompletely understood. This study aimed to investigate whether bile acid (BA) metabolism influences intestinal epithelial homeostasis. Using eight pairs of LBW and normal-birth-weight (NBW) piglets selected from twelve litters (Duroc × Landrace × Large White crossbreed), with LBW piglets weighing 0.85 ± 0.05 kg at birth (d 1) and NBW piglets weighing 1.49 ± 0.08 kg, all piglets were raised under normal maternal nursing until postnatal d 7 (at which LBW and NBW weighed 1.38 ± 0.30 kg and 2.70 ± 0.25 kg, respectively) and then sampled for further investigation (n = 8 per group). It was demonstrated that disrupted bile acid metabolism impairs epithelial homeostasis via the gut-liver axis. At both the mRNA and protein levels, compared with NBW piglets, LBW piglets exhibited significant upregulation of hepatic Cyp7a1, accompanied by marked suppression of GPBAR1 in liver and ileum (P < 0.05). Serum primary bile acids (PBAs) and interferons (interferon [IFN]-α and IFN-γ) were significantly elevated compared with NBW piglets (P < 0.05). A downward trend in ileal secondary bile acid (SBA; approximately 0.31-fold compared with NBW piglets) was observed, coinciding with shortened villi, shallow crypts, sparse microvilli, and reduced tight junction proteins occludin, ZO-1, and claudin-4 (P < 0.05). Ileal transcriptomics and protein data further indicated IFN-linked signaling and MLCK mediated cytoskeletal stress. In vitro, pharmacological inhibition of GPBAR1 sensitized the intestinal barrier to pro-inflammatory cytokine injury, particularly IFN-γ, through enhancing the MLCK expression (P < 0.001) and downregulating the tight junction proteins, including occludin (P = 0.008), ZO-1 (P = 0.024), claudin-1 (P < 0.001), and claudin-4 (P < 0.001). Overall, these findings demonstrate that BA dysregulation and IFN signaling converge on GPBAR1-MLCK pathways to compromise epithelial integrity in LBW piglets, highlighting GPBAR1 as a potential target for maintaining intestinal homeostasis.