Intestinal Microbiota Increases Cell Proliferation of Colonic Mucosa in Human-Flora-Associated (HFA) Mice

Intestinal epithelium renewal strictly depends on fine regulation between cell proliferation, differentiation, and apoptosis. While murine intestinal microbiota has been shown to modify some epithelial cell kinetics parameters, less is known about the role of the human intestinal microbiota. Here, we investigated the rate of intestinal cell proliferation in C3H/HeN germ-free mice associated with human flora (HFA, n = 8), and in germ-free (n = 15) and holoxenic mice (n = 16). One hour before sacrifice, all mice were intraperitoneally inoculated with 5-bromodeoxyuridine (BrdU), and the number of BrdU-positive cells/total cells (labelling index, LI), both in the jejunum and the colon, was evaluated by immunohistochemistry. Samples were also observed by scanning electron microscopy (SEM). Moreover, the microbiota composition in the large bowel of the HFA mice was compared to that of of human donor's fecal sample. No differences in LI were found in the small bowels of the HFA, holoxenic, and germ-free mice. Conversely, the LI in the large bowel of the HFA mice was significantly higher than that in the germ-free and holoxenic counterparts (p = 0.017 and p = 0.048, respectively). In the holoxenic and HFA mice, the SEM analysis disclosed different types of bacteria in close contact with the intestinal epithelium. Finally, the colonic microbiota composition of the HFA mice widely overlapped with that of the human donor in terms of dominant populations, although Bifidobacteria and Lactobacilli disappeared. Despite the small sample size analyzed in this study, these preliminary findings suggest that human intestinal microbiota may promote a high proliferation rate of colonic mucosa. In light of the well-known role of uncontrolled proliferation in colorectal carcinogenesis, these results may deserve further investigation in a larger population study.