Abstract
Postweaning pigs are subjected to nutrient deprivation during which intestinal epithelial cells undergo increased turnover. To preserve intestinal function, intestinal epithelial cells must activate adaptive mechanisms that allow them to cope with starvation-induced stress; most importantly, the preservation of intestinal barrier function. The objective of this study was to investigate the underlying mechanisms involved in starvation-induced alteration of tight junction protein abundance and function in IPEC-J2 cells. Cells were subjected to total nutrient starvation in Krebs-Ringer bicarbonate (KRB) buffer for 0, 3, 6, 12 and 24 h. Abundance of tight junction proteins was determined by RT-PCR, western blotting and immunofluorescence. Compared with control group (0 h), the protein expression of claudin 1, claudin 3 and claudin 4 protein was downregulated up to 6 h of starvation and then increased thereafter (P < 0.01). However, there was no change in the protein level of occludin and ZO-1. To determine the contribution of the lysosome and the ubiquitin proteasome pathways to regulation of tight junction protein abundance, the lysosome (Bafilomycin A1) and the proteasome (MG132) inhibitors were used in nutrient starved cells. Results showed the degradation of claudin 1, 3 and 4 up to 6 h of starvation was through the lysosomal pathway. Surprisingly, re-synthesis of claudins 4 and claudin 3 after prolonged starvation (12 and 24 h) was prevented when cells were treated with bafilomycin A1 and MG132, respectively. The autophagy-lysosome pathway inhibitors (Wortmannin and MHY1485) and endosome-lysosome pathway inhibitors (Dynasore and Pitstop 2) were further used to determine the specific roles of these pathways. In summary, the degradation of claudin 3 and claudin 4 during short-term starvation (up to 6 h) was through the dynamin-dependent endocytic pathway. However, re-synthesis of these proteins after prolonged starvation relies on both the lysosome and proteasome pathways.
Down-regulated expression of intestinal epithelial tight junction protein occludin in mice with fulminant hepatic failure