| Studies have shown that high methionine diet(HMD)induces liver lipid accumulation and promotes the development of nonalcoholic fatty liver disease(NAFLD);whereas methionine restricted diet(MRD)can reduce liver lipid accumulation by improving the composition of intestinal microbiota.However,whether there is a dose-dependent relationship between dietary methionine levels and liver lipid accumulation and whether its mechanism of action is related to intestinal microbiota remain unclear.Choline can act as a methyl donor to the body and participate in the re-methylation of homocysteine to methionine in the methionine cycle.However,high choline diet(HCD)can lead to dyslipidemia and lipid accumulation in the liver and body.Based on this,the present study investigated the intestinal microbiota based regulatory effects of methionine on liver lipid accumulation and the mechanism of methionine restriction regarding improving lipid metabolism in high-choline-diet-fed mice,and the main methods,results,and conclusions are as follows:1.First,the effects of different dietary methionine levels on liver lipid accumulation were investigated by feeding diets with different methionine levels to intervene normal mice and analyze the phenotype,organ weight and index,histomorphological changes,and combined with metabolomics and multivariate statistical techniques and biochemical analysis.The results showed that MRD significantly decreased body weight,liver weight,hepatic and plasma lipid levels,liver fatty infiltration area,and perirenal fat cell volume;whereas HMD significantly increased liver weight and index,hepatic and plasma lipid levels,liver fatty infiltration area,and perirenal fat cell volume in mice.The results of metabolomic analysis showed that MRD significantly promoted lipolysis and fatty acid oxidation in the body,increased plasma short chain fatty acids(SCFAs)levels,changed protein synthesis and amino acid-related metabolism,and improved oxidative stress;whereas the results of HMD were opposite to those of MRD.Meanwhile,the results of correlation analysis showed that methionine intake was positively correlated with liver lipid accumulation,MRD reduced liver lipid accumulation,whereas HMD increased liver lipid accumulation.2.Subsequently,16 S r DNA high-throughput sequencing was employed to analyze the composition of fecal microbiota in mice,and the levels of SCFAs in the feces and plasma as well as energy metabolism-,oxidative stress-,and inflammation-related indicators in the liver were examined.The results showed that MRD significantly increased the abundance of SCFAs-producing bacteria(Roseburia,Blautia,Faecalibaculum,and Bifidobacterium)and SCFAs level,and significantly decreased the abundance of the pro-inflammatory bacteria Escherichia-Shigella.In addition,MRD promoted hepatic lipid catabolism and glycolysis metabolism,inhibited lipid anabolism,increased the activity of mitochondrial respiratory chain enzyme complexes(I and V),and the production of adenosine triphosphate(ATP),and improved oxidative stress in the liver and reduced liver lipid accumulation;whereas the results of HMD were opposite to those of MRD.Meanwhile,correlation analysis showed that methionine intake was negatively correlated with SCFAs-producing bacteria and SCFAs levels.These results suggest that different dietary methionine levels can modulate the composition of intestinal microbiota,regulate the production of SCFAs in a dose-dependent manner,and regulate liver lipid accumulation.3.Furthermore,MRD was used to intervene HCD mice to investigate the effects of MRD on lipid metabolism in HCD mice by measuring body weight,body composition analysis,energy metabolism monitoring,biochemical index detection,and histomorphological observation.The results showed that MRD significantly reduced body weight and percent fat mass and increased percent lean mass in HCD mice;increased body energy expenditure and ambulatory activity,reduced hepatic and plasma lipid levels and liver fatty infiltration area,and improved liver function in mice.Meanwhile,MRD significantly reduced the weight and index of white adipose tissue,increased the weight and index of brown adipose tissue,and significantly reduced fat cell volume.These results suggest that MRD can improve lipid metabolism in the liver and adipose tissue of HCD mice and reduce body fat deposition.4.Finally,the composition of microbiota in mouse cecum contents was analyzed,and the expression of key genes of lipid metabolism in the liver and adipose tissue as well as oxidative stress-and inflammation-related indexes in the liver and plasma of mice were examined to investigate the potential mechanism of MRD improving lipid metabolism in HCD mice.The results showed that MRD significantly increased the abundance of SCFAs-producing bacteria Bacteroidetes,Lachnospiraceae＿NK4A136＿group,Faecalibaculum,Bifidobacterium,and Roseburia,and significantly decreased the abundance of inflammation-producing bacteria Escherichia-Shigella,[Eubacterium]＿coprostanoligenes group,Ruminiclostridium＿9,Anaerotruncus,and Oscillibacter.Meanwhile,MRD significantly increased the level of SCFAs in mice cecum,increased the expression of lipolysis-related genes in the liver and adipose tissue,decreased the expression of liposynthesis-related genes,increased energy production in the body,and improved oxidative stress and inflammation in the liver and plasma of HCD mice.These results suggest that MRD can regulate intestinal microbiota composition,increase the level of SCFAs in the body,promote lipid metabolism in the liver and adipose tissue,and reduce lipid accumulation in the body of HCD mice.In conclusion,different dietary methionine levels can alter the composition of intestinal microbiota,regulate SCFAs production in a dose-dependent manner,and regulate liver lipid accumulation;MRD can improve the composition of intestinal microbiota,increase SCFAs production,improve lipid metabolism in the liver and adipose tissue,and reduce lipid accumulation in the body of HCD mice. |
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