Differential Expression of Intestinal Ion Transporters and Water Channel Aquaporins in Young Piglets Challenged with Enterotoxigenic Escherichia coli K88

Enterotoxigenic Escherichia coli K88 (ETEC K88) can induce severe watery diarrhea and subsequent growth retardation for neonatal and post-weaning piglets, which causes great economic loss in swine production. Our previous study has shown that the incidence of diarrhea in young piglets was significantly increased following ETEC K88 challenge. The study was to determine whether the expression of genes involved in water and ion transports would be affected by ETEC K88 both in vitro and in vivo. (1) Thirty-six male piglets (4-d-old) were randomly allotted to either Control or K88 group. Each group had 6 replicates with 3 piglets each replicate. All piglets were fed with the same diets for 18 days. On d 15, piglets in the K88 group were challenged with ETEC K88 (serotype O149: K91: K88ac) of 1×10⁸ CFU per pig, while those in the Control group received the same volume of sterilize PBS. After challenging with ETEC K88 for 72 h (d 18), one piglet from each replicate was selected for slaughter to collect samples from jejunum, ileum and colon. The mRNA expression and protein abundance of cystic fibrosis transmembrane conductance regulator (CFTR) in the ileum and colon were significantly increased compared to that in the control group (P<0.05). Furthermore, the mRNA expression of Na-K-Cl cotransporter 1 (NKCC1) in the ileum and colon were significantly increased, while in the jejunum both its mRNA and protein expression were significantly increased by ETEC K88 treatment (P<0.05). (2) Additionally, an established porcine intestinal epithelial cell line (IPEC-J2) was used to investigate the effect and possible mechanism of ETEC K88 on expression of water channel aquaporins (AQPs) and ion transporters. Cells (1.17 × 10⁶/well) were grown in 6-well plates, and treated with ETEC K88 (5.6× 10⁷ CFU/well) for 3 h. AQP3 and AQP11 mRNAs were abundantly expressed in IPEC-J2 cells. The mRNA expression of AQP3, AQP11, and Na⁺/H⁺ exchanger 3 (NHE3) in IPEC-J2 cells were significantly reduced after ETEC K88 treatment (P<0.05). Further analyses by immunofluorescence and western blotting also demonstrated that ETEC K88 significantly decreased the protein expression of AQP3, AQP9, and AQP11 in IPEC-J2 cells (P<0.05). Moreover, the phosphorylation level of protein kinase A (PKA) of cAMP pathway was significantly decreased by ETEC K88 challenge (P<0.05). The results indicate that the cAMP-PKA signaling pathway might regulate the differential expression of intestinal ion transporters and AQPs, therefore contributing to fluid imbalance and the development of ETEC diarrhea in young piglets.