The higher prevalence of metabolic syndrome (MetS) in women after menopause is associated with a decrease in circulating 17β-oestradiol. To explore novel treatments for MetS in women with oestrogen deficiency, we studied the effect of exogenous butyrate on diet-induced obesity and metabolic dysfunctions using ovariectomized (OVX) mice as a menopause model. Oral administration of sodium butyrate (NaB) reduced the body fat content and blood lipids, increased whole-body energy expenditure, and improved insulin sensitivity. Additionally, NaB induced oestrogen receptor alpha (ERα) expression, activated the phosphorylation of AMPK and PGC1α, and improved mitochondrial aerobic respiration in cultured skeletal muscle cells. In conclusion, oral NaB improves metabolic parameters in OVX mice with diet-induced obesity. Oral supplementation with NaB might provide a novel therapeutic approach to treating MetS in women with menopause. Graphical Abstract

Background：The incidence of nonalcoholic fatty liver disease (NAFLD) in postmenopausal women has increased significantly. NAFLD can be effectively inhibited by estrogen, but the severe side effects, especially the increased risk of malignant tumors, limit its application. Thus, it is of great clinical significance to explore the mechanism by which estrogen inhibits NAFLD. Gut microbiota and its metabolites short chain fatty acids (SCFA) have been shown to play important roles in the development of NAFLD.Objective：In this study, we investigated the impact of estrogen deficiency on the gut microbiome and SCFA in both NAFLD patients and an experimental NAFLD model in premenopause.Methods：The levels of estrogen，insulin and leptin was measured using ELISA. Gut microbiota was analyzed by 16S rRNA gene sequence analysis. Tissue sections were stained with hematoxylin and eosin. SCFAs were determined with Agilent 6890 N gas chromatography (GC). We quantified mRNA levels of genes in our study by quantitative real time-PCR. Additionally, Western Blotting was used to validate protein expression.Results：We showed that female NAFLD patients had much lower estrogen levels. Estrogen deficient mice, due to ovariectomy (OVX), suffered more severe liver steatosis with an elevated body weight, abdominal fat weight, and serum triglycerides with deterioration in histological hepatic steatosis. Altered gut microbiota composition and decreased butyrate content were found in patients with NAFLD and in OVX mice. Furthermore, fecal microbiota transplantation (FMT) or supplementing with butyrate markedly alleviated NAFLD in OVX mice. The production of antimicrobial peptides (AMP) RegIIIg, β-defensins 1, 3 and the expression of intestinal epithelial tight junction, including ZO-1 and occludin5, were decreased in the OVX mice compared to control mice. Upregulation of PPAR-ɣ and VLDLR and downregulation of PPAR-ɑ indicated that OVX mice suffered from abnormal lipid metabolism.Conclusions：These data indicate that changes in the gut microbiota and SCFA caused by estrogen reduction, together with a disorder in AMP production and lipid metabolism, promote NAFLD, thus provide microbiota derived SCFAs as new therapeutic targets for the clinical prevention and treatment of NAFLD.