The secreted protein P75 of Lactobacillus rhamnosus GG regulates the SERT expression via EGFR and NF-kappa B pathway

Aim To investigate the mechanism of Lactobacillus rhamnosus GG (LGG)-secreted protein, P75, on the regulation of the expression of serotonin transporter (SERT) through the epidermal growth factor receptor (EGFR) and nuclear factor-kappa B (NF-kappa B) pathway. Methods Caco-2 cells were stimulated with LGG supernatant (LGG-super), protein P75, AG1478, and TNF-alpha. A rat model of post-infectious irritable bowel syndrome (PI-IBS) was constructed and treated with phosphate-buffered saline and LGG-super for 4 weeks. The levels of SERT, p-EGFR, EGFR, p-NF-kappa B, NF-kappa B, p-I kappa B-alpha, and I kappa B-alpha were detected by quantitative real-time polymerase chain reaction, Western blot, immunofluorescence, and immunochemistry. Luciferase assay was used to verify the link between NF-kappa B and SERT promoter. Results LGG-super and P75 upregulated the expression levels of SERT and p-EGFR and decreased the expression levels of p-I kappa B-alpha and p-NF-kappa B. Dual luciferase assay result suggested that NF-kappa B inhibited the activity of SERT promoter. In the animal experiments, 5-HT concentration increased in the PI-IBS Model group but decreased in the Model +LGG-super group compared with the control. On the contrary, the expression of SERT protein was downregulated in the PI-IBS Model group and improved in the Model +LGG-super group. The expression of p-EGFR was reduced and p-NF-kappa B was enhanced in the PI-IBS Model group, whereas the expression of p-EGFR and p-NF-kappa B was the opposite in the Model +LGG-super group. Conclusion LGG supernatant and its secreted protein, P75, upregulate the expression of SERT by activating EGFR and inhibiting the NF-kappa B pathway.