[Fecal microbiota transplantation inhibits colonic tumor growth in mice by suppressing the TLR4/MyD88/NF-κB signaling pathway].

OBJECTIVES

To explore the effects of fecal microbiota transplantation (FMT) on immune function and tumor inhibition in mice.

METHODS

C57BL/6N mice were divided into blank control group, tumor bearing model group, and FMT intervention group (n=6). In the latter two groups, the mice bearing subcutaneous MC38 colon cancer cell xenografts were treated with daily gavage of normal saline or 0.1 mL of bacterial suspension. The changes in tumor mass and volume were recorded, and peripheral blood natural killer (NK) cell counts and NKG2A and NKG2D receptor expressions were analyzed using flow cytometry; serum lipopolysaccharide (LPS) levels were measured with ELISA. The binding ability of NF‑κB to the TGF‑β1 gene promoter was analyzed with JASPAR. The mRNA and protein expressions of TLR4, MyD88, NF‑κB, TGF‑β1, perforin and granzyme in the tumor tissues were detected using RT qPCR and Western blotting, and the changes in gut microbiota were analyzed using 16S high throughput sequencing.

RESULTS

FMT significantly reduced tumor mass and volume in the tumor-bearing mice. Peripheral CD3⁻NK1.1⁺ cell counts were significantly decreased in the tumor-bearing mice regardless of FMT treatment, which, however, reversed the increase of CD3-NKG2A+ cells and reduction of CD3-NKG2D+ cells and reduced serum LPS levels in the mouse models. Molecular docking and JASPAR analysis confirmed LPS-TLR4 binding (binding energy: -13.1 kcal/mol) and identified NF-κB binding sites on TGF‑β1 promoter. FMT downregulated mRNA and protein expressions of TLR4, MyD88, NF‑κB and TGF‑β1 and upregulated perforin and granzyme mRNA expressions in the xenografts. FMT also restored gut microbiota diversity and composition, and reversed the increase of Proteobacteria and decrease of Lactobacillus murinus in the tumor-bearing mice.

CONCLUSIONS

FMT modulates the relative abundances of intestinal Proteobacteria and Lactobacillus murinus in tumor-bearing mice, and inhibits tumor growth by suppressing the TLR4/MyD88/NF‑κB signaling axis, down-regulating TGF-β1 expression, and promoting NK cell activation.