High dietary cholesterol and ovariectomy in rats repress gene expression of key markers of VLDL and bile acid metabolism in liver

Thrombospondin 1 improves hepatic steatosis in diet-induced insulin-resistant mice and is associated with hepatic fat content in humans

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is associated with altered production of secreted proteins. Increased understanding of secreted proteins could lead to improved prediction and treatment of NAFLD. Here, we aimed to discover novel secreted proteins in humans that are associated with hepatic fat content using unbiased proteomic profiling strategy, and how the identified Thbs1 modulates lipid metabolism and hepatic steatosis.

METHOD

NAFLD patients were enrolled and treated with lifestyle intervention. Patients who underwent liver biopsy were enrolled for analyzing the correlation between circulating Thbs1 and liver steatosis. Mice were fed on high-fat, high-sucrose diet and treated with recombinant Thbs1. Primary hepatocytes isolated from CD36 knockout (CD36-/-) mice and their wild-type littermates (controls) were treated with glucose plus insulin for 24 h together with or without recombinant Thbs1.

FINDING

Serum Thbs1 levels are increased in participants with NAFLD and positively associated with liver steatosis grades. Improvement of liver steatosis after lifestyle intervention was accompanied with significant reduction of serum Thbs1 levels. Pharmacological administration of recombinant human Thbs1 attenuates hepatic steatosis in diet-induced obese mice. Treatment with Thbs1 protein or stably overexpression of Thbs1 causes a significant reduction of lipid accumulation in primary hepatocytes or HepG2 cells exposed to high glucose plus insulin, suggesting that Thbs1 regulates lipid metabolism in a hepatocyte-autonomous manner. Mechanistically, Thbs1 inhibits cleavage and processing of SREBP-1, leading to a reduction of target lipogenic gene expression and hepatic steatosis. Inhibitory effects of Thbs1 on lipogenesis and triglyceride accumulation are abrogated in CD36 deficient primary hepatocytes exposed to high glucose plus insulin. Interestingly, beneficial effects of Thbs1 on lipid accumulation are observed in primary hepatocytes treated with a Thbs1 nonapeptide mimetic ABT-526.

INTERPRETATION

Thbs1 is a biomarker for NAFLD in humans, and pharmacological and genetic approaches for the modulation of Thbs1 activity may have the therapeutic potential for treating hepatic steatosis. FUND: A full list of funding bodies that contributed to this study can be found in the Funding Sources section.

Metformin ameliorates body mass gain and early metabolic changes in ovariectomized rats

Estradiol has been used to prevent metabolic diseases, bone loss and menopausal symptoms, even though it might raise the risk of cancer. Metformin is usually prescribed for type 2 diabetes mellitus and lowers food intake and body mass while improving insulin resistance and the lipid profile. Ovariectomized rats show increased body mass, insulin resistance and changes in the lipid profile. Thus, the aim of this work was to evaluate whether metformin could prevent the early metabolic dysfunction that occurs early after ovariectomy. Female Wistar rats were divided into the following groups: SHAM-operated (SHAM), ovariectomized (OVX), ovariectomized + estradiol (OVX + E2) and ovariectomized + metformin (OVX + M). Treatment with metformin diminished approximately 50% of the mass gain observed in ovariectomized animals and reduced both the serum and hepatic triglyceride levels. The hepatic levels of phosphorylated AMP-activated protein kinase (pAMPK) decreased after OVX, and the expression of the inactive form of hepatic acetyl-CoA carboxylase (ACC) was also reduced. Metformin was able to increase the levels of pAMPK in the liver of OVX animals, sustaining the balance between the inactive and total forms of ACC. Estradiol effects were similar to those of metformin but with different proportions. Our results suggest that metformin ameliorates the early alterations of metabolic parameters and rescues hepatic AMPK phosphorylation and ACC inactivation observed in ovariectomized rats.

The effect of exercise training on upregulation of molecular markers of bile acid metabolism in the liver of ovariectomized rats fed a cholesterol-rich diet

BACKGROUND

Small heterodimer partner (SHP) is an important transcriptional factor involved in the regulation of glucose, lipid, and bile acid metabolism in the liver. SHP has been reported to be down-regulated in ovariectomized (Ovx) mice and up-regulated by estrogens suggesting a link between estrogens and SHP. The aim of the present study was to determine the effects of exercise training on SHP and key molecular markers of cholesterol and bile acid homeostasis in Ovx rats under cholesterol feeding.

METHODS

Our main experimental group was composed of Ovx rats fed a high-cholesterol diet (Ovx-Chol) that was compared to a group of Ovx rats fed a standard diet (Ovx-SD) and a group of sham operated rats fed the cholesterol diet (Sham-Chol). These three groups of Ovx and sham rats were subdivided into either voluntary wheel running (Tr) or sedentary (Sed) groups for 5 weeks. The mRNA expression of all genes was measured by quantitative real-time polymerase chain reaction.

RESULTS

Liver total cholesterol levels were not affected by exercise training in any of the experimental conditions. Cholesterol feeding in both sham and Ovx rats resulted in significantly higher hepatic cholesterol accumulation than in Ovx-SD (P < 0.001). Hepatic low density lipoprotein receptor (LDL-R) involved in cholesterol uptake from circulation was not influenced by training. A main effect of training was, however, found for transcripts of SHP and cholesterol 7 alpha-hydroxylase (CYP7A1, P < 0.050). CYP7A1 is the main gene involved in bile acid biosynthesis from cholesterol.

CONCLUSION

These results suggest that voluntary wheel running modulates cholesterol metabolism in Ovx animals through up-regulation of SHP and bile acid formation.

Dynamics of hepatic and intestinal cholesterol and bile acid pathways: The impact of the animal model of estrogen deficiency and exercise training

Plasma cholesterol level is determined by a complex dynamics that involves transport lipoproteins which levels are tightly dependent on how the liver and the intestine regulate cholesterol and biliary acid metabolism. Regulation of cholesterol and biliary acids by the liver and the intestine is in turn coupled to a large array of enzymes and transporters that largely influence the inflow and the outflow of cholesterol and biliary acids through these organs. The activity of the key regulators of cholesterol and biliary acids may be influenced by several external factors such as pharmacological drugs and the nutritional status. In recent years, more information has been gathered about the impact of estrogens on regulation of cholesterol in the body. Exposure to high levels of estrogens has been reported to promote cholesterol gallstone formation and women are twice as likely as men to develop cholesterol gallstones. The impact of estrogen withdrawal, such as experienced by menopausal women, is therefore of importance and more information on how the absence of estrogens influence cholesterol regulation is started to come out, especially through the use of animal models. An interesting alternative to metabolic deterioration due to estrogen deficiency is exercise training. The present review is intended to summarize the present information that links key regulators of cholesterol and biliary acid pathways in liver and intestine to the absence of estrogens in an animal model and to discuss the potential role of exercise training as an alternative.

High-Cholesterol Diet Disrupts the Levels of Hormones Derived from Anterior Pituitary Basophilic Cells

Emerging evidence shows that elevated cholesterol levels are detrimental to health. However, it is unclear whether there is an association between cholesterol and the pituitary. We investigated the effects of a high-cholesterol diet on pituitary hormones using in vivo animal studies and an epidemiological study. In the animal experiments, rats were fed a high-cholesterol or control diet for 28 weeks. In rats fed the high-cholesterol diet, serum levels of thyroid-stimulating hormone (TSH; also known as thyrotrophin), luteinising hormone (LH) and follicle-stimulating hormone (FSH) produced by the basophilic cells of the anterior pituitary were elevated in a time-dependent manner. Among these hormones, TSH was the first to undergo a significant change, whereas adrenocorticotrophic hormone (ACTH), another hormone produced by basophilic cells, was not changed significantly. As the duration of cholesterol feeding increased, cholesterol deposition increased gradually in the pituitary. Histologically, basophilic cells, and especially thyrotrophs and gonadotrophs, showed an obvious increase in cell area, as well as a potential increase in their proportion of total pituitary cells. Expression of the β-subunit of TSH, FSH and LH, which controls hormone specificity and activity, exhibited a corresponding increase. In the epidemiological study, we found a similar elevation of serum TSH, LH and FSH and a decrease in ACTH in patients with hypercholesterolaemia. Significant positive correlations existed between serum total cholesterol and TSH, FSH or LH, even after adjusting for confounding factors. Taken together, the results of the present study suggest that the high-cholesterol diet affected the levels of hormones derived from anterior pituitary basophilic cells. This phenomenon might contribute to the pituitary functional disturbances described in hypercholesterolaemia.