The liver plays a central role in regulating cholesterol homeostasis. High fat diets have been shown to induce obesity and hyperlipidemia. Despite considerable advances in our understanding of cholesterol metabolism, the regulation of liver cholesterol biosynthesis in response to high fat diet feeding has not been fully addressed. The aim of the present study was to investigate mechanisms by which a high fat diet caused activation of liver 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) leading to increased cholesterol biosynthesis. Mice were fed a high fat diet (60% kcal fat) for 5weeks. High fat diet feeding induced weight gain and elevated lipid levels (total cholesterol and triglyceride) in both the liver and serum. Despite cholesterol accumulation in the liver, there was a significant increase in hepatic HMG-CoA reductase mRNA and protein expression as well as enzyme activity. The DNA binding activity of sterol regulatory element binding protein (SREBP)-2 and specific protein 1 (Sp1) were also increased in the liver of mice fed a high fat diet. To validate the in vivo findings, HepG2 cells were treated with palmitic acid. Such a treatment activated SREBP-2 as well as increased the mRNA and enzyme activity of HMG-CoA reductase leading to intracellular cholesterol accumulation. Inhibition of Sp1 by siRNA transfection abolished palmitic acid-induced SREBP-2 and HMG-CoA reductase mRNA expression. These results suggest that Sp1-mediated SREBP-2 activation contributes to high fat diet induced HMG-CoA reductase activation and increased cholesterol biosynthesis. This may play a role in liver cholesterol accumulation and hypercholesterolemia.

Cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE) catalyze homocysteine (Hcy) metabolism via the trans-sulfuration pathway. They are also responsible for hydrogen sulfide (H2S) production via desulfuration reactions. The liver contributes significantly to the regulation of Hcy and H2S homeostasis, which might participate in many physiological and pathological processes. The aim of this study was to investigate the effect of a high-fat diet (HFD) on hepatic CBS and CSE expression and its impact on Hcy and H2S metabolism. Mice (C57BL/6) fed a HFD (60% kcal fat) for 5 weeks developed fatty liver. The mRNA and protein levels of CBS and CSE in the liver were significantly elevated in mice fed a HFD. Subsequently the metabolism of Hcy by CBS and CSE was increased in the liver, and its level decreased in the circulation. Increased CBS and CSE expression also caused a significant elevation in H2S production in the liver. The level of lipid peroxides was elevated, indicating oxidative stress, while the level of total glutathione remained unchanged in the liver of HFD-fed mice. Upregulation of the trans-sulfuration pathway might play an adaptive role against oxidative stress by maintaining total glutathione levels in the liver.

The gut microbiota is proposed as a "metabolic organ" involved in energy utilization and is associated with obesity. Dietary intervention is one of the approaches for obesity management. Changes in dietary components have significant impacts on host metabolism and gut microbiota. In the present study, we examined the influence of dietary fat intervention on the modification of gut mucosa-associated microbiota profile along with body weight and metabolic parameter changes. Male C57BL/6J mice (6-week old) were fed a low fat diet (10% kcal fat) as a control or a high fat diet (HFD 60% kcal fat) for 7 weeks. In another group, mice were fed HFD for 5 weeks followed by low fat control diet for 2 weeks (HFD + Control). At 7 weeks, body weight gain, blood glucose and hepatic triacylglycerol levels of mice fed a HFD were significantly higher than that of the control group and the HFD + Control group. There were significant differences in the diversity and predicted functional properties of microbiota in the cecum and colon mucosa between the control group and the HFD group. HFD feeding reduced the ratio of Bacteroidetes to Firmicutes, a microbiota pattern often associated with obesity. The HFD + Control diet partially restored the diversity and composition of microbiota in the cecum to the pattern observed in mice fed a control diet. These results suggest that short-term high fat diet withdrawal can restore metabolic changes and prevent excess body weight gain, however, long-term dietary intervention may be required to optimize the restoration of gut microbiota in mouse.