Dietary Fatty Acid Composition Alters Gut Microbiome in Mice with Obesity-Induced Peripheral Neuropathy

Abstract

Background: Peripheral neuropathy (PN), a complication of diabetes and obesity, progresses through a complex pathophysiology. Lifestyle interventions to manage systemic metabolism are recommended to prevent or slow PN, given the multifactorial risks of diabetes and obesity. A high-fat diet rich in saturated fatty acids (SFAs) induces PN, which a diet rich in monounsaturated fatty acids (MUFAs) rescues, independent of weight loss, suggesting factors beyond systemic metabolism impact nerve health. Interest has grown in gut microbiome mechanisms in PN, which is characterized by a distinct microbiota signature that correlates with sciatic nerve lipidome.

Methods: Herein, we postulated that SFA- versus MUFA-rich diet would impact gut microbiome composition and correlate with PN development. To assess causality, we performed fecal microbiota transplantation (FMT) from donor mice fed SFA- versus MUFA-rich diet to lean recipient mice and assessed metabolic and PN phenotypes.

Results: We found that the SFA-rich diet altered the microbiome community structure, which the MUFA-rich diet partially reversed. PN metrics correlated with several microbial families, some containing genera with feasible mechanisms of action for microbiome-mediated effects on PN. SFA and MUFA FMT did not impact metabolic phenotypes in recipient mice although SFA FMT marginally induced motor PN.

Conclusions: The involvement of diet-mediated changes in the microbiome on PN and gut-nerve axis may warrant further study.

Keywords: fecal microbiota transplantation; inflammation; monounsaturated fatty acid; prediabetes; saturated fatty acid.

Figure 1

MUFA diet protects against SFA-induced PN in mice. WT mice aged 6 weeks received a standard diet (SD, red) or saturated fatty acid (SFA)-rich diet (SFA, blue) for 10 weeks. Half the SFA mice were then placed on a diet rich in monounsaturated fatty acids (MUFA, gray) for 8 weeks while the remaining mice stayed on their respective diets. Terminal assessment of large fiber neuropathy by (A) sural sensory and (B) sciatic motor nerve conduction velocity (NCV). (C) Terminal assessment of small fiber neuropathy by intraepidermal nerve fiber density. Black circles represent individual animals. All data presented as mean ± standard deviation; n = 5–7 mice per group; * p < 0.05, ** p < 0.01, **** p < 0.0001 for SD vs. SFA; SFA vs. MUFA; one-way ANOVA with Tukey’s multiple comparisons test. Figure adapted ref. [4].

Figure 2

Different fatty acid-rich diets associated with distinct gut microbiome community structures. (A) Intra-group microbial diversity assessed by alpha diversity in fecal samples using observed counts and Shannon and Simpson indices from standard diet (SD, red), saturated fatty acid-rich diet (SFA, blue), and monounsaturated fatty acid-rich diet (MUFA, gray) mice. Data in box plots represented with horizontal line for median, box for first and third quartiles, and whiskers for minimum and maximum values. (B) Inter-group microbial diversity assessed by beta diversity. Principal coordinate analysis based on ASV clustering of gut microbiome from cecum (circle), colon (triangle), and fecal (square) samples in SD (red), SFA (blue), and MUFA (gray) mice. Ellipses comprise 85% of samples. (C) Stacked bar plot of relative abundance of the most abundant gut microbiome phyla in fecal samples from SD, SFA, and MUFA mice. (D) Heatmap clustering based on log₁₀-transformed ASV genera abundance in gut microbiome from cecum (green), colon (yellow), and fecal (purple) samples in SD (red), SFA (blue), and MUFA (gray) mice. Legend indicates lower (blue) to higher (red) genera (g_) or family (f_) abundance. Data from SD (n = 7), SFA (n = 4–5), and MUFA (n = 7) cecum, colon, and fecal microbial samples.

Figure 3

Different fatty acid-rich diets associated with differential fecal bacterial genera abundance. (A–F) Relative abundance of the most and differentially abundant genera in fecal microbial samples from the standard diet (SD, red, n = 7), saturated fatty acid-rich diet (SFA, blue, n = 5), and monounsaturated fatty acid-rich diet (MUFA, gray, n = 7) mice. Data in box plots represented with horizontal line for median, box for first and third quartiles, and whiskers for minimum and maximum values. Black circles represent individual animals. * p < 0.05, ** p < 0.01, *** p < 0.001; Kruskal–Wallis with Dunn’s multiple comparisons test for panels (A, C, and F); one-way ANOVA with Tukey’s multiple comparisons test for panels (B, D, and E).

Figure 4

Sural and sciatic nerve conduction velocities correlate with distinct microbiota families in different fatty acid-rich diet mouse groups. Heatmap of Pearson correlation analysis of (A) sural sensory and (B) sciatic motor nerve conduction velocities to family taxa in cecum (green), colon (yellow), and fecal (purple) microbial samples from standard diet (SD, n = 7), saturated fatty acid-rich diet (SFA, n = 4–5), and monounsaturated fatty acid-rich (MUFA, gray, n = 7) mice. Legend indicates negative (blue) and positive (red) correlations. Unadjusted p-values, * p < 0.05, ** p < 0.01, *** p < 0.001; Pearson correlation analysis.

Figure 5

Different FMT transplants do not substantially affect metabolic and PN phenotypes in recipient mice. (A) FMT study design and mouse groups. Longitudinal (B) body weight and (C) fasting blood glucose levels for all mouse groups at study start (aged 5 weeks), after microbiota depletion (aged 7 weeks), and towards study end (aged 15 weeks). (D) Blood glucose levels following glucose tolerance test for all mouse groups towards study end (aged 15 weeks). Data presented as mean ± standard deviation; n = 11–12 mice per group; *** p < 0.001, **** p < 0.0001 for “no antibiotics, no FMT” versus other groups, otherwise few other statistically significant between-group differences; two-way ANOVA with Dunnett’s multiple comparisons. Terminal assessment of large fiber neuropathy by (E) sciatic motor and (F) sural sensory nerve conduction velocity (NVC). Data presented as mean ± standard deviation; n = 10–12 mice per group; * p < 0.05 for “no antibiotics, no FMT” versus SFA FMT, Kruskal–Wallis with Dunn’s multiple comparisons. (G) Terminal assessment of small fiber neuropathy by intraepidermal nerve fiber density. Black circles represent individual animals. Data presented as mean ± standard deviation; n = 3 mice per group; Kruskal–Wallis with Dunn’s multiple comparisons. No-anti-no-FMT, no antibiotics, no FMT; no FMT, no fecal microbiota transplant; SD FMT, standard diet FMT; SFA FMT, saturated fatty acid FMT; MUFA FMT, monounsaturated fatty acid FMT.

Figure 6

MUFA FMT transplant affects inflammatory gene expression in colon but not fatty acid transporter expression in colon or sciatic nerve of recipient mice. Terminal (A) Tlr4, (B) Il1β, and (C) Gpr43 mRNA expression by qPCR of colon tissue from all mouse groups. mRNA calculated against 18S reference gene and expressed relative to the “no antibiotics, no FMT” group. (D) Terminal FXR protein expression by Western blot of sciatic nerve from all mouse groups. Protein calculated against HSC70 loading control and expressed relative to the “no antibiotics, no FMT group”. Black circles represent individual animals. n = 3–10 mice per group; * p < 0.05, ** p < 0.01 for “no antibiotics; no FMT” versus other groups; Kruskal–Wallis with Dunn’s multiple comparisons. No-anti-no-FMT, no antibiotics, no FMT; no FMT, no fecal microbiota transplant; SD FMT, standard diet FMT; SFA FMT, saturated fatty acid FMT; MUFA FMT, monounsaturated fatty acid FMT.