Bromodomain-containing protein 4 regulates a cascade of lipid-accumulation-related genes at the transcriptional level in the 3T3-L1 white adipocyte-like cell line

Effects of feeding the medium-chain triacylglycerol on GLP-1 secretion in aged Brd4-heterozygous mice, which are a mouse model of aging

OBJECTIVES

Gastrointestinal hormones, such as glucagon-like peptide 1 (GLP-1), gastric inhibitory polypeptide, and peptide YY (PYY) are important for reducing malnutrition at older ages because they are related to assimilation and feeding behavior. Medium-chain triacylglycerol (MCT) ameliorates metabolic symptoms and frailty in adults; however, whether it has the same effect in old age is unknown. To address this, we examined the changes in insulin and gastrointestinal hormones in aged Brd4 (+/-) mice exhibiting symptoms of old age.

RESEARCH METHODS AND PROCEDURES

Aged male wild-type and Brd4 (+/-) mice were fed a long-chain triacylglycerol (LCT)- or MCT diet. Feeding, blood glucose, and plasma active GLP-1 protein concentrations were determined at 9 weeks using a meal tolerance test, and those gastrointestinal hormone genes were determined at 10 weeks.

RESULTS

The liver and stomach weights and mRNA expression of Gcg (encodes GLP-1 protein) and Pyy in the colon were lower in LCT-fed Brd4 (+/-) mice than those in LCT-fed wild-type mice; these were restored by the MCT diet. The blood concentration of active GLP-1 protein at 15 and 30 minutes postload was higher in MCT-fed Brd4 (+/-) mice than that in those fed an LCT diet.

CONCLUSIONS

Aged Brd4 (+/-) mice showed lower mRNA expression of Gcg and Pyy genes, and active GLP-1 protein secretion in the blood, which were as restored and enhanced with MCT feeding.

Medium-chain fatty acids enhance expression and histone acetylation of genes related to lipid metabolism in insulin-resistant adipocytes

Background

The expressions of genes related to lipid metabolism are decreased in adipocytes with insulin resistance. In this study, we examined the effects of fatty acids on the reduced expressions and histone acetylation of lipid metabolism-related genes in 3T3-L1 adipocytes treated with insulin resistance induced by tumor necrosis factor (TNF)-α.

Methods

Short-, medium-, and long-chain fatty acid were co-administered with TNF-α in 3T3-L1 adipocytes. Then, mRNA expressions and histone acetylation of genes involved in lipid metabolism were determined using mRNA microarrays, qRT-PCR, and chromatin immunoprecipitation assays.

Results

We found in microarray and subsequent qRT-PCR analyses that the expression levels of several lipid metabolism-related genes, including Gpd1, Cidec, and Cyp4b1, were reduced by TNF-α treatment and restored by co-treatment with a short-chain fatty acid (C4: butyric acid) and medium-chain fatty acids (C8: caprylic acid and C10: capric acid). The pathway analysis of the microarray showed that capric acid enhanced mRNA levels of genes in the PPAR signaling pathway and adipogenesis genes in the TNF-α-treated adipocytes. Histone acetylation around Cidec and Gpd1 genes were also reduced by TNF-α treatment and recovered by co-administration with short- and medium-chain fatty acids.

General significance

Medium- and short-chain fatty acids induce the expressions of Cidec and Gpd1, which are lipid metabolism-related genes in insulin-resistant adipocytes, by promoting histone acetylation around these genes.

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Expressions of lipid metabolism genes are reduced in insulin-resistant adipocytes.

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Short- and medium-chain fatty acids inhibit lipid metabolism gene downregulation.

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Capric acid enhances expressions of PPAR signaling and adipogenesis genes.

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This mechanism involves recovery of histone acetylation in lipid metabolism genes.

Regulation of Carbohydrate-Responsive Metabolic Genes by Histone Acetylation and the Acetylated Histone Reader BRD4 in the Gene Body Region

Studies indicate that induction of metabolic gene expression by nutrient intake, and in response to subsequently secreted hormones, is regulated by transcription factors binding to cis-elements and associated changes of epigenetic memories (histone modifications and DNA methylation) located in promoter and enhancer regions. Carbohydrate intake-mediated induction of metabolic gene expression is regulated by histone acetylation and the histone acetylation reader bromodomain-containing protein 4 (BRD4) on the gene body region, which corresponds to the transcribed region of the gene. In this review, we introduce carbohydrate-responsive metabolic gene regulation by (i) transcription factors and epigenetic memory in promoter/enhancer regions (promoter/enhancer-based epigenetics), and (ii) histone acetylation and BRD4 in the gene body region (gene body-based epigenetics). Expression of carbohydrate-responsive metabolic genes related to nutrient digestion and absorption, fat synthesis, inflammation in the small intestine, liver and white adipose tissue, and in monocytic/macrophage-like cells are regulated by various transcription factors. The expression of these metabolic genes are also regulated by transcription elongation via histone acetylation and BRD4 in the gene body region. Additionally, the expression of genes related to fat synthesis, and the levels of acetylated histones and BRD4 in fat synthesis-related genes, are downregulated in white adipocytes under insulin resistant and/or diabetic conditions. In contrast, expression of carbohydrate-responsive metabolic genes and/or histone acetylation and BRD4 binding in the gene body region of these genes, are upregulated in the small intestine, liver, and peripheral leukocytes (innate leukocytes) under insulin resistant and/or diabetic conditions. In conclusion, histone acetylation and BRD4 binding in the gene body region as well as transcription factor binding in promoter/enhancer regions regulate the expression of carbohydrate-responsive metabolic genes in many metabolic organs. Insulin resistant and diabetic conditions induce the development of metabolic diseases, including type 2 diabetes, by reducing the expression of BRD4-targeted carbohydrate-responsive metabolic genes in white adipose tissue and by inducing the expression of BRD4-targeted carbohydrate-responsive metabolic genes in the liver, small intestine, and innate leukocytes including monocytes/macrophages and neutrophils.