Mannan Oligosaccharides Promoted Skeletal Muscle Hypertrophy through the Gut Microbiome and Microbial Metabolites in Mice

Abstract

Mannan oligosaccharides (MOSs) have been implicated in the animal growth rate, health indices, and lipid oxidative stability. MOSs have been indicated to maintain intestinal health and anti-inflammatory effects via modulation of gut microbiota. Furthermore, the role of MOSs in modulating skeletal muscle function is largely unknown. Here, this study aimed to investigate the effects of MOS supplementation on muscle function and muscle mass in mice. Additionally, the possible underlying mechanisms, including the contributions of gut microbiota and microbial metabolites, were explored. In our study, 3-week-old C57BL/6J male mice (body weight of approximately 10.7 ± 1.1 g) were given pure water or pure water with 1% MOS. To study the effect of MOSs on gut-microbiota-derived metabolites, serum metabolic profiles were analyzed through untargeted metabolomic profiling. Moreover, we detected the downstream signals of differential metabolites, and decanoic acid (DA) was selected as our target spot. Then, DA was used to treat C2C12 cells, and we found that DA promotes C2C12 cell differentiation via the GPR84 and PI3K/AKT signaling pathways. In conclusion, these results showed that MOS supplementation improves muscle function and muscle mass. Additionally, gut microbiome and microbial metabolites were regulated by MOSs, and DA may be one of the most important links between the gut microbiome and skeletal muscle function regulation.

Keywords: C2C12; decanoic acid; gut microbiome; mannan oligosaccharides; metabolite profile; skeletal muscle.

Figure 1

Mannan oligosaccharide supplementation shows positive effects on the gastrocnemius. (A) Body weight of mice. (B) Average daily food intake. (C) Average daily water intake. (D,E) QMR analyses of body composition of mice. (F) The grip strength of mice. (G) The weight test of mice. (H) The GAS, TA, SOL and EDL tissue indices of mice. (I,J) Staining of ATPase in GAS. * p < 0.05 versus the control group, ** p < 0.01 versus the control group.

Figure 2

Serum metabolic profiles of mice fed mannan oligosaccharides. (A) The serum metabolome by OPLS–DA. (B) Metabolites in mice serum of volcano plot. (C–I) The box charts show the detailed serum metabolites and significant changes between the control and MOS groups (μM). Up, upregulated; FC, fold change.

Figure 3

Gut microbiome of mice fed mannan oligosaccharides. (A) Relative abundance analysis at the phylum level. (B) OTU Venn analysis. (C) Principal coordinate analysis (PCOA). (D) Hierarchical clustering analysis. (E) Chao1 value. (F,G) Shannon and Simpson index of gut microbiota. (H) LDA score of gut microbiota. (I) Correlations between serum differential metabolites and differential gut microbiota. * p < 0.05 versus the control group.

Figure 4

Decanoic acid may be the key metabolite that mediates the effects of mannan oligosaccharides on skeletal muscle. (A,B) The protein expression level of FXR and TGR5 in the GAS. (C,D) cAMP and L-carnosine concentrations in the GAS. (E,F) The protein expression level of TLR4, GPR84 and PI3K/AKT signaling pathways in the GAS. * p < 0.05 versus the control group.

Figure 5

Decanoic acid mediates C2C12 cell differentiation through the GPR84 and PI3K/AKT signaling pathways. (A,B) The protein expression level of GPR84 and PI3K/AKT signaling pathways in C2C12 cells. (C–E) Immunocytochemistry of myotubes in C2C12 cells. Red: MyHC; blue: DAPI. (F,G) The protein expression level of MyHC, MyHC 1 and MyHC 2a in C2C12 cells. NS indicates no significant differences. * p < 0.05 versus the control group, ** p < 0.01 versus the control group.