Gut Microbiota Contribution to Weight-Independent Glycemic Improvements after Gastric Bypass Surgery

Abstract

Roux-en-Y gastric bypass surgery (RYGB) leads to improved glycemic control in individuals with severe obesity beyond the effects of weight loss alone. Here, We addressed the potential contribution of gut microbiota in mediating this favourable surgical outcome by using an established preclinical model of RYGB. 16S rRNA sequencing revealed that RYGB-treated Zucker fatty rats had altered fecal composition of various bacteria at the phylum and species levels, including lower fecal abundance of an unidentified Erysipelotrichaceae species, compared with both sham-operated (Sham) and body weight-matched to RYGB-treated (BWM) rats. Correlation analysis further revealed that fecal abundance of this unidentified Erysipelotrichaceae species linked with multiple indices of glycemic control uniquely in RYGB-treated rats. Sequence alignment of this Erysipelotrichaceae species identified Longibaculum muris to be the most closely related species, and its fecal abundance positively correlated with oral glucose intolerance in RYGB-treated rats. In fecal microbiota transplant experiments, the improved oral glucose tolerance of RYGB-treated compared with BWM rats could partially be transferred to recipient germfree mice, independently of body weight. Unexpectedly, providing L. muris as a supplement to RYGB recipient mice further improved oral glucose tolerance, while administering L. muris alone to chow-fed or Western style diet-challenged conventionally raised mice had minimal metabolic impact. Taken together, our findings provide evidence that the gut microbiota contributes to weight loss-independent improvements in glycemic control after RYGB and demonstrate how correlation of a specific gut microbiota species with a host metabolic trait does not imply causation. IMPORTANCE Metabolic surgery remains the most effective treatment modality for severe obesity and its comorbidities, including type 2 diabetes. Roux-en-Y gastric bypass (RYGB) is a commonly performed type of metabolic surgery that reconfigures gastrointestinal anatomy and profoundly remodels the gut microbiota. While it is clear that RYGB is superior to dieting when it comes to improving glycemic control, the extent to which the gut microbiota contributes to this effect remains untested. In the present study, we uniquely linked fecal Erysipelotrichaceae species, including Longibaculum muris, with indices of glycemic control after RYGB in genetically obese and glucose-intolerant rats. We further show that the weight loss-independent improvements in glycemic control in RYGB-treated rats can be transmitted via their gut microbiota to germfree mice. Our findings provide rare causal evidence that the gut microbiota contributes to the health benefits of metabolic surgery and have implications for the development of gut microbiota-based treatments for type 2 diabetes.

Keywords: caloric restriction; gastric bypass surgery; germfree mice; glycemic control; gut microbiota.

FIG 1

Evidence that the gut microbiota contributes to the weight loss-independent improvement in glycemic control after RYGB. (A) Beta-diversity plot, measured by Bray-Curtis analysis, showing separation of the fecal microbiota in Sham (n = 12) and BWM (n = 5) rats from that in RYGB-treated (n = 16) rats at postoperative day 28. **, Q < 0.01 versus Sham rats, and ##, Q < 0.01, versus BWM rats, as determined by PERMANOVA followed by a pairwise post hoc test. (B) Relative abundance of phyla in Sham (n = 12), RYGB-treated (n = 16), and BWM (n = 5) rats. ****, Q < 0.0001, and **, Q < 0.01, for RYGB-treated versus Sham rats, and ###, P < 0.001, ##, P < 0.01, and #, P < 0.05, for RYGB-treated versus BWM rats, as determined by the Kruskal-Wallis test corrected for FDR by the Benjamini-Hochberg method. (C) Differential species abundance, expressed as log₂ fold change in RYGB-treated versus BWM rats. (D) Correlation matrix of fecal microbiota species with metabolic parameters in RYGB-treated rats. **, Q < 0.01, and *, Q < 0.05, as determined by the Mann-Whitney U test after adjusting for multiple comparisons. (E) Schematic diagram showing protocol for fecal microbiota transplant in GF mice. (F to H) Body weights at day 1 and day 14 (F), body weight difference (G), and OGTT (H) in GF mice (n = 9 or 10/group) transplanted with feces from BWM (n = 3) and RYGB-treated (n = 3) rats. ##, P < 0.01, as determined by two-way ANOVA followed by Bonferroni’s post hoc test. (I and J) Relative fecal abundance of the family Erysipelotrichaceae (I) and an unidentified species belonging to the family Erysipelotrichaceae (J) in recipient GF mice (n = 9 or 10/group) transplanted with feces from BWM (n = 3) and RYGB-treated (n = 3) rats. ##, P < 0.01, as determined by the Mann-Whitney U test.

FIG 2

Metabolic impact of L. muris on RYGB-recipient and conventionally raised mice. (A) qPCR analysis of Longibaculum muris in feces of BWM (n = 5) and RYGB-treated (n = 16) rats at postoperative day 28. ***, P < 0.001, as determined by the Mann-Whitney U test. (B) Correlation between abundance of fecal L. muris and OGTT AUC in RYGB-treated rats. (C) Protocol for L. muris administration in RYGB-recipient mice. (D and E) Body weights (BW) at day 1 and day 21 (D) and OGTT (E) in recipient GF mice transplanted with feces from one RYGB-treated rat and supplemented with heat-killed (n = 4) or live (n = 4) L. muris. *, P < 0.05, as determined by two-way ANOVA followed by Bonferroni’s post hoc test. (F) Protocol for L. muris administration in chow diet-fed and Western-style diet (WSD)-challenged mice. (G and H) Body weights at day 1 and day 21 (G) and OGTT (H) in chow-fed mice administered heat-killed (n = 10) or live (n = 10) L. muris. (I and J) Body weights at day 1 and day 21 (I) and OGTT (J) in WSD-challenged mice administered heat-killed (n = 10) or live (n = 10) L. muris.