The anti-diarrheal role of iron in piglets: Regulation of colonic goblet cell function

Diarrhea is a common condition in piglets. The intestinal mucosal barrier is the primary protective mechanism against external challenges. Iron-an essential trace element for the growth and metabolism of living organisms-is crucial for enhancing host defense functions. Newborn piglets and porcine colonic organoids were employed as experimental models to investigate the mechanisms underlying the regulation of the intestinal mucosal barrier by iron supplementation. A total of 24 seven-d-old piglets (body weight 1.75 ± 0.20 kg) were orally administered formula milk powder supplemented with different concentrations of iron (FeSO₄) for 2 weeks. The treatment groups were low (without), middle (70 mg/kg), and high (700 mg/kg) iron (n = 8). Compared with the low group, iron supplementation significantly reduced fecal scores (P = 0.016), increased the number of colonic goblet cells (P = 0.009), and enhanced MUC2 production (P = 0.049). Additionally, fecal scores were negatively correlated with both the number of colonic goblet cells (P = 0.003, |r| = 0.772) and MUC2 production (P = 0.026, |r| = 0.636). To investigate the mechanism by which iron regulates goblet cells, a hypothesis was proposed that iron exerts its effects through both the gut microbiota and the host. Specific microbial taxa and metabolites were identified as potential regulators of goblet cell function. However, organoid-based in vitro experiments demonstrated that iron regulates goblet cells regardless of microbial metabolites. Additionally, porcine colonic organoids were treated with deferoxamine (DFO; 100 μmol/L), ammonium iron citrate (FAC; 100 or 200 μmol/L), or a mock treatment for 48 h, which was followed by gene expression profiling and transcriptome sequencing. Elevated iron concentrations increased MUC2 expression (P < 0.001). In the group with increased MUC2 expression, the MAPK and PI3K-Akt signaling pathways were downregulated (P = 0.001), whereas the mucin-type O-glycan biosynthesis pathway was upregulated (P = 0.002). Subsequent treatment of porcine colonic organoids with inhibitors specific to these pathways validated the crucial role of the PI3K-Akt signaling pathway in the iron-regulated goblet cell function. Therefore, dietary iron intake increased colonic goblet cell MUC2 production by inhibiting the PI3K-Akt signaling pathway, thereby alleviating diarrhea in piglets.