Histone deacetylase 9 is a negative regulator of adipogenic differentiation.
ABSTRACT Differentiation of preadipocytes into mature adipocytes capable of efficiently storing lipids is an important regulatory mechanism in obesity. Here, we examined the involvement of histone deacetylases (HDACs) and histone acetyltransferases (HATs) in the regulation of adipogenesis. We find that among the various members of the HDAC and HAT families, only HDAC9 exhibited dramatic down-regulation preceding adipogenic differentiation. Preadipocytes from HDAC9 gene knock-out mice exhibited accelerated adipogenic differentiation, whereas HDAC9 overexpression in 3T3-L1 preadipocytes suppressed adipogenic differentiation, demonstrating its direct role as a negative regulator of adipogenesis. HDAC9 expression was higher in visceral as compared with subcutaneous preadipocytes, negatively correlating with their potential to undergo adipogenic differentiation in vitro. HDAC9 localized in the nucleus, and its negative regulation of adipogenesis segregates with the N-terminal nuclear targeting domain, whereas the C-terminal deacetylase domain is dispensable for this function. HDAC9 co-precipitates with USF1 and is recruited with USF1 at the E-box region of the C/EBPα gene promoter in preadipocytes. Upon induction of adipogenic differentiation, HDAC9 is down-regulated, leading to its dissociation from the USF1 complex, whereas p300 HAT is up-regulated to allow its association with USF1 and accumulation at the E-box site of the C/EBPα promoter in differentiated adipocytes. This reciprocal regulation of HDAC9 and p300 HAT in the USF1 complex is associated with increased C/EBPα expression, a master regulator of adipogenic differentiation. These findings provide new insights into mechanisms of adipogenic differentiation and document a critical regulatory role for HDAC9 in adipogenic differentiation through a deacetylase-independent mechanism.
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ABSTRACT: Valproic acid (VPA) is the drug of choice for treating epilepsy, but has the unwanted effects of inducing weight gain and increasing the risk of developing insulin resistance. The mechanism through which these side effects occur is unknown. VPA inhibits histone deacetylase (HDAC), but also decreases the transcriptional activity of CCAAT enhancer binding protein alpha (CEBPalpha). Given the possible association between VPA, CEBPalpha and adipokine gene regulation, we hypothesized that they would alter the expression of resistin (rstn), fasting-induced adipose factor (fiaf) and suppressor of cytokine signaling-3 (socs-3), genes implicated in the development of leptin and insulin resistance. We investigated the effects of VPA (1 mM; 24 or 48 h) on gene expression using real-time RT-PCR in 3 distinct models: N-1 hypothalamic neurons, 3T3-L1 adipocytes and male CD-1 mice. Subsequently, cells were treated with 5 nM of the more specific HDAC inhibitor trichostatin A (TSA). CEBPalpha expression was also modified in N-1 neurons using either RNA interference (RNAi) or an overexpression vector to evaluate its effects on target gene expression. In N-1 neurons, VPA induced significant increases in CEBPalpha and socs-3, but inhibited rstn and fiaf gene expression. In contrast, TSA induced rstn and socs-3, but inhibited fiaf. VPA also induced the expression of CEBPalphain 3T3-L1 adipocytes, but had no effect on other target genes, and TSA suppressed fiaf and socs-3.Subsequently, CEBPalpha was overexpressed (24 h) or silenced using RNAi (24 and 48 h) in N-1 neurons. The silencing of CEBPalpha led to significant decreases in rstn mRNA, but increased fiaf and socs-3 expression, whereas its overexpression had the opposite effect. When male CD-1 mice were treated with either a single (100 mg/kg; 24 h), or multiple (200 mg/kg; 72 h) daily injections of VPA, no changes in body weight or gene expression were detected in either hypothalamic or adipose tissues. In summary, these experiments reveal a potentially important role for CEBPalpha in the regulation of hypothalamic gene expression in N-1 neurons and suggest that it might modulate central energy metabolism. Although VPA also modified hypothalamic gene expression in vitro, it remains to be determined whether it has similar effects in vivo.Neuroendocrinology 02/2008; 88(1):25-34. · 3.54 Impact Factor
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ABSTRACT: Adipose cell size and the glucose and insulin response to an oral glucose load have been studied in 26 obese children. Adipose cells were found to be enlarged, and hyperinsulinaemia was demonstrated both in the fasting state and also after oral glucose. The degree of hyperinsulinaemia could not be predicted by adipose cell size.In 14 children studies were repeated after a period of weight loss. A marked fall in fasting serum insulin occurred in all children over the first week of treatment. A reduction in adipose cell size was demonstrated over a longer period, but there was no change in the total number of adipose cells. In 7 children who were still losing weight when a second glucose tolerance test was performed, insulin levels after oral glucose were reduced, but there was no reduction in insulin levels in 7 children studied after they had stopped losing weight. The reduction in body fat and adipose cell size in these two groups of children was no different. Thus it was not possible to predict the fall in insulin levels from changes in body composition or adipose cell size.These data do not support the hypothesis of a direct causal relation between the increase in adipose cell size and the hyperinsulinaemia of obesity.Archives of Disease in Childhood 05/1973; 48(4):301-4. · 3.05 Impact Factor
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ABSTRACT: White adipose tissue (fat) is the primary organ for energy storage and its regulation has serious implications on human health. Excess fat tissue causes significant morbidity, and adipose tissue dysfunction caused by excessive adipocyte hypertrophy has been proposed to play a significant role in the pathogenesis of metabolic disease. Studies in both humans and animal models show that metabolic dysfunction is more closely associated with visceral than subcutaneous fat accumulation. Here, we show that in mice fed a high-fat diet, visceral fat (VAT) grows mostly by hypertrophy and subcutaneous fat (SAT) by hyperplasia, providing a rationale for the different effects of specific adipose depots on metabolic health. To address whether depot expansion is controlled at the level of stem/progenitor cells, we developed a strategy to prospectively identify adipogenic progenitors (APs) from both depots. Clonogenic assays and in vivo bromodeoxyuridine (BrdU) studies show that APs are eightfold more abundant in SAT than VAT, and that AP proliferation is significantly increased in SAT but not VAT in response to high-fat diet. Our results suggest that depot-specific differences in AP abundance and proliferation underlie whether a fat depot expands by hypertrophy or hyperplasia, and thus may have important implications on the development of metabolic disease. In addition, we provide the first evidence that dietary inputs can modulate the proliferation of adipogenic progenitors in adults.Stem Cells 09/2009; 27(10):2563-70. · 7.70 Impact Factor