Effect of fecal microbiota transplantation on type 1 diabetes mellitus in non-obese diabetic mice and its underlying mechanism

Abstract

Objective: To investigate the effects of fecal microbiota transplantation (FMT) on non-obese diabetic (NOD) mice of type 1 diabetes mellitus (T1DM) and its underlying mechanisms. Methods: A total of 8-9 week-female NOD mice were randomly divided into control (n=36) and FMT groups (n=36) according to the random number table. Fecal microbiota from C57BL/6 mice were transplanted into FMT group, and control group were transplanted with microbiota from themselves, once every two days for 5 times. The insulitis score and incidence of T1DM were compared between two groups;16S rRNA gene sequencing was used to evaluate the structure of fecal bacteria in NOD mice. The expressions of intestinal barrier related genes were detected by real-time quantitative PCR. The proportions of regulatory T cells (Tregs), helper T cell (Th)-1 and Th17 in the enteric-pancreatic immune axis were detected by flow cytometry. Amino acid in serum was measured by amino acid metabolomics. Results: Incidence of T1DM in NOD mice from FMT group was 40.9% (9/22), lower than 72.7% (13/22) from control group at 26 weeks of age (P=0.034). FMT promoted colonization of probiotics such as Lactobacillus, Clostridium_sp_ND2, Candidatus_Arthromitus and Clostridiaceae_1; mRNA of intestinal barrier related genes were up-regulated in FMT group [ mucins(Muc)-1: 0.93±0.29 vs 2.97±0.79, P=0.036; Muc2: 0.72±0.39 vs 10.70±3.54, P=0.019;Muc3: 1.79±0.69 vs 10.97±2.78, P=0.009;Muc4: 1.01±0.23 vs 2.42±0.49, P=0.029;Occludin(Ocln): 0.96±0.08 vs 1.81±0.36, P=0.045; Claudin(Cldn)-1:0.94±0.17 vs 2.20±0.43, P=0.022] compared to control. The proportions of Treg in mesenteric lymphoid node, pancreatic lymph node and peyer's patches of FMT group [(6.10±0.49)% vs (7.54±0.27)%, P=0.020;(5.28±0.39)% vs (6.42±0.34)%, P=0.048;(6.78±0.42)% vs (7.88±0.13)%, P=0.029] were increased compared to control,while proportions of Th1 [(1.02±0.06)% vs (0.83±0.06)%, P=0.040;(0.82±0.10)% vs (0.56±0.05)%, P=0.038;(1.28±0.12) vs (0.85±0.07), P=0.012] and proportions of Th17 [(0.40±0.01)% vs (0.30±0.02)%, P=0.004;(0.40±0.02)% vs (0.31±0.02)%, P=0.008;(0.51±0.06) vs (0.36±0.02), P=0.027] were decreased. The contents of leucine [(92.86±7.32) vs (91.87±12.62) μmol/L, P=0.027], valine [(162.74±15.97) vs (155.89±25.70) μmol/L, P=0.046] and isoleucine [(75.65±5.59) vs (73.61±9.67) μmol/L, P=0.048] in serum were decreased in FMT group. Conclusions: FMT can alleviate insulitis and T1DM occurrence in NOD mice, of which mechanism may be related to remodeling gut microbiota and improving intestinal barrier function, affecting immune response of enteric-pancreatic immune axis, correcting amino acid metabolism disorder and reducing the accumulation of branch chain amino acids in NOD mice.