Probiotics up-regulate MUC-2 mucin gene expression in a Caco-2 cell-culture model

Enteral probiotics such as Lactobacillus casei GG (LGG) have been used in the treatment of a variety of intestinal disorders in infants and children, including diarrhea, malabsorption, and Clostridium difficile colitis. Previous studies have identified the gene locus for mucin (MUC-2) and its expression in Caco-2 cells. Others have demonstrated that mucin, located on the surface of the intestinal epithelium, inhibits bacterial translocation (BT). We previously demonstrated that both mucin and the probiotic bacterium LGG have an inhibitory effect on BT in both an in-vitro Caco-2 cell model and a neonatal rabbit model. We hypothesized that the decline in BT by LGG is mediated by up-regulation of epithelial MUC-2. Human enterocyte Caco-2 cells were grown to confluence and incubated at 37 °C with either medium (control group) or 10⁴ or 10⁸ LGG for 180 min. Nonadherent LGG was washed away. Caco-2 cells were then lysed, purified, and quantified for MUC-2 protein and mRNA. The addition of LGG to the enterocyte monolayer surface resulted in significantly (P < 0.05) increased MUC-2 expression compared to the untreated monolayers. Protein densities for MUC-2 significantly (P < 0.05) increased with LGG. Density (expressed as ratio to control group) was 8.6 ± 1.3 in the low-dose group (10⁴ LGG) and 15.6 ± 2.3 in the high-dose group (108 LGG). LGG may thus bind to specific receptor sites on the enterocyte and stimulate the up-regulation of MUC-2, resulting in increased inhibition of BT.