Chemically distinct HDAC inhibitors prevent adipose conversion of subcutaneous human white preadipocytes at an early stage of the differentiation program

Bioactive Compounds as Inhibitors of Inflammation, Oxidative Stress and Metabolic Dysfunctions via Regulation of Cellular Redox Balance and Histone Acetylation State

Bioactive compounds (BCs) are known to exhibit antioxidant, anti-inflammatory, and anti-cancer properties by regulating the cellular redox balance and histone acetylation state. BCs can control chronic oxidative states caused by dietary stress, i.e., alcohol, high-fat, or high-glycemic diet, and adjust the redox balance to recover physiological conditions. Unique functions of BCs to scavenge reactive oxygen species (ROS) can resolve the redox imbalance due to the excessive generation of ROS. The ability of BCs to regulate the histone acetylation state contributes to the activation of transcription factors involved in immunity and metabolism against dietary stress. The protective properties of BCs are mainly ascribed to the roles of sirtuin 1 (SIRT1) and nuclear factor erythroid 2-related factor 2 (NRF2). As a histone deacetylase (HDAC), SIRT1 modulates the cellular redox balance and histone acetylation state by mediating ROS generation, regulating nicotinamide adenine dinucleotide (NAD+)/NADH ratio, and activating NRF2 in metabolic progression. In this study, the unique functions of BCs against diet-induced inflammation, oxidative stress, and metabolic dysfunction have been considered by focusing on the cellular redox balance and histone acetylation state. This work may provide evidence for the development of effective therapeutic agents from BCs.

Shp2 suppresses fat accumulation in white adipose tissue by activating Wnt/β‑catenin signaling following vertical sleeve gastrectomy in obese rats with type‑2 diabetes

Adipogenesis and fat accumulation are closely associated with the development of obesity. Sleeve gastrectomy (SG) is an effective treatment for obesity and associated metabolic disorders. Leptin is downregulated after SG and Src homology phosphatase 2 (Shp2) has an important role in leptin signaling. The role of Shp2 in SG and the mechanisms of fat reduction following SG were further investigated in the current study. Sham and SG operations were performed on obese type-2 diabetes model Sprague-Dawley rats. Primary pre-adipocytes were isolated from the inguinal white adipose tissue (ingWAT) of the rats. Shp2 expression in ingWAT pre-adipocytes was silenced using small interfering RNA transfection. Shp2 function was inhibited using the specific inhibitor, SHP099. In addition, Shp2 was overexpressed using lentivirus. Gene and protein expression analysis was performed after adipocyte differentiation. Furthermore, Shp2-overexpressing ingWAT pre-adipocytes treated with the β-catenin inhibitor, PNU-74654, were also used for gene and protein expression analysis. Adipogenic markers, including triglycerides, peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer-binding protein α (Cebpα), adiponectin, fatty acid-binding protein 4 and leptin, were examined. Compared with the sham, triglyceride, leptin, PPARγ and Cebpα levels were significantly reduced in the ingWAT from the SG group. Shp2 expression levels were reduced following leptin treatment. Moreover, genetic analysis demonstrated depot-specific adipogenesis following Shp2 silencing or inhibition in ingWAT pre-adipocytes. Conversely, Shp2 overexpression decreased the expression of adipogenic markers by enhancing β-catenin expression. PNU-74654 treatment abolished the downregulation of adipogenic markers caused by Shp2 overexpression. SG decreased leptin levels in ingWAT, which in turn upregulated Shp2, and Shp2 suppressed fat accumulation and adipogenic differentiation by activating the Wnt/β-catenin signaling pathway. Overall, this may represent a potential mechanism of fat reduction in SG, and Shp2 may serve as a potential therapeutic target for the treatment of obesity and type-2 diabetes.

The role of HDAC11 in obesity-related metabolic disorders: A critical review

At present, metabolic diseases, such as obesity and diabetes, have become the world's top health threats. These diseases are closely related to the abnormal development and function of adipocytes and metabolic inflammation associated with obesity. Histone deacetylase 11 (HDAC11), with a relatively unique structure and function in the HDAC family, plays a vital role in regulating cell growth, migration, and cell death. Currently, research on new key regulatory functions of HDAC11 in metabolic homeostasis is receiving more and more attention, and HDAC11 has also become a potential therapeutic target in the treatment of obesity and obesity-related diseases. Here, we summarized the latest literature on the role of HDAC11 in regulating the progress of obesity-related metabolic disorders.

Epigenetic regulation of white adipose tissue in the onset of obesity and metabolic diseases

Obesity and metabolic syndrome are among the most prevalent health problems in developed countries. The impairment of adipose tissue (AT) function is partially responsible for the aetiology of these conditions. Epigenetics refers to several processes that add modifications to either the DNA or chromatin architectural proteins (histones). These processes can regulate gene expression, chromatin compaction and DNA repair. Epigenetics includes mechanisms by which the cell can adapt the cellular response to the environmental conditions. Here, we review the role of epigenetics in the onset of obesity and related metabolic disorders, with special focus on AT. We highlight the importance of nutrients and lifestyle in the regulation of the epigenetic mechanisms and how they can impact on AT plasticity and function in obesity and metabolic diseases. Thus, the epigenetic landscape emerges as a fine-tune regulator of the cellular responses according to the energetic, metabolic and physiological conditions of the cell. Alterations in metabolic pathways deregulated during obesity and metabolic syndrome could in part explain the disturbances in the epigenetic marks of the AT in these disorders. The understanding of how this epigenetic deregulation may affect AT biology and function could lead to new therapeutic approaches based on epigenetic strategies.

Concise Review: The Regulatory Mechanism of Lysine Acetylation in Mesenchymal Stem Cell Differentiation

Nowadays, the use of MSCs has attracted considerable attention in the global science and technology field, with the self-renewal and multidirectional differentiation potential for diabetes, obesity treatment, bone repair, nerve repair, myocardial repair, and so on. Epigenetics plays an important role in the regulation of mesenchymal stem cell differentiation, which has become a research hotspot in the medical field. This review focuses on the role of lysine acetylation modification on the determination of MSC differentiation direction. During this progress, the recruitment of lysine acetyltransferases (KATs) and lysine deacetylases (KDACs) is the crux of transcriptional mechanisms in the dynamic regulation of key genes controlling MSC multidirectional differentiation.

Molecular Insight into the Interaction between Epigenetics and Leptin in Metabolic Disorders

Nowadays, it is well-known that the deregulation of epigenetic machinery is a common biological event leading to the development and progression of metabolic disorders. Moreover, the expression level and actions of leptin, a vast adipocytokine regulating energy metabolism, appear to be strongly associated with epigenetics. Therefore, the aim of this review was to summarize the current knowledge of the epigenetic regulation of leptin as well as the leptin-induced epigenetic modifications in metabolic disorders and associated phenomena. The collected data indicated that the deregulation of leptin expression and secretion that occurs during the course of metabolic diseases is underlain by a variation in the level of promoter methylation, the occurrence of histone modifications, along with miRNA interference. Furthermore, leptin was proven to epigenetically regulate several miRNAs and affect the activity of the histone deacetylases. These epigenetic modifications were observed in obesity, gestational diabetes, metabolic syndrome and concerned various molecular processes like glucose metabolism, insulin sensitivity, liver fibrosis, obesity-related carcinogenesis, adipogenesis or fetal/early postnatal programming. Moreover, the circulating miRNA profiles were associated with the plasma leptin level in metabolic syndrome, and miRNAs were found to be involved in hypothalamic leptin sensitivity. In summary, the evidence suggests that leptin is both a target and a mediator of epigenetic changes that develop in numerous tissues during metabolic disorders.

Harnessing the HDAC-histone deacetylase enzymes, inhibitors and how these can be utilised in tissue engineering

There are large knowledge gaps regarding how to control stem cells growth and differentiation. The limitations of currently available technologies, such as growth factors and/or gene therapies has led to the search of alternatives. We explore here how a cell's epigenome influences determination of cell type, and potential applications in tissue engineering. A prevalent epigenetic modification is the acetylation of DNA core histone proteins. Acetylation levels heavily influence gene transcription. Histone deacetylase (HDAC) enzymes can remove these acetyl groups, leading to the formation of a condensed and more transcriptionally silenced chromatin. Histone deacetylase inhibitors (HDACis) can inhibit these enzymes, resulting in the increased acetylation of histones, thereby affecting gene expression. There is strong evidence to suggest that HDACis can be utilised in stem cell therapies and tissue engineering, potentially providing novel tools to control stem cell fate. This review introduces the structure/function of HDAC enzymes and their links to different tissue types (specifically bone, cardiac, neural tissues), including the history, current status and future perspectives of using HDACis for stem cell research and tissue engineering, with particular attention paid to how different HDAC isoforms may be integral to this field.

Histone deacetylases up-regulate C/EBPα expression through reduction of miR-124-3p and miR-25 in hepatocellular carcinoma

BACKGROUND

CCAAT enhancer binding protein α (C/EBPα), as an important transcription factor involved in cell proliferation, differentiation and metabolism, was up-regulated in primary hepatocellular carcinoma (HCC) and predicted poorer prognosis. In this study, we explored how histone deacetylases (HDACs) up-regulated C/EBPα in HCC.

METHODS

The protein expressions of HDAC1, HDAC2 were associated with C/EBPα by immunohistochemistry staining in a HCC tissue microarray. HCC cells were then treated with HDAC inhibitors or siRNAs to determine the roles of miR-124-3p and miR-25 in the regulation of C/EBPα mRNA expression.

RESULTS

Both HDAC1 and HDAC2 proteins were significantly associated with C/EBPα. Inhibition of HDAC by either pharmacological inhibitors or siRNAs decreased C/EBPα mRNA expression in dose-dependent manners in HCC cells. HDAC inhibitors reduced C/EBPα mRNA stability as shown by pmiRGLO luciferase reporter assays. HDAC inhibition consistently induced miR-124-3p and miR-25 expression. Conversely, blockage of miR-124-3p and/or miR-25 by treatment with specific synthetic inhibitors abolished C/EBPα reduction. More importantly, C/EBPα mRNA stability could be rescued by site-directed mutations of miR-124-3p or miR-25 recognition sites in the C/EBPα 3'UTR sequence. In summary, HDAC may up-regulate C/EBPα expression through miR-124-3p and miR-25 in HCC.

Histone deacetylase inhibition attenuates hepatic steatosis in rats with experimental Cushing's syndrome

Cushing's syndrome (CS) is a collection of symptoms caused by prolonged exposure to excess cortisol. Chronically elevated glucocorticoid (GC) levels contribute to hepatic steatosis. We hypothesized that histone deacetylase inhibitors (HDACi) could attenuate hepatic steatosis through glucocorticoid receptor (GR) acetylation in experimental CS. To induce CS, we administered adrenocorticotropic hormone (ACTH; 40 ng/kg/day) to Sprague-Dawley rats by subcutaneous infusion with osmotic mini-pumps. We administered the HDACi, sodium valproate (VPA; 0.71% w/v), in the drinking water. Treatment with the HDACi decreased steatosis and the expression of lipogenic genes in the livers of CS rats. The enrichment of GR at the promoters of the lipogenic genes, such as acetyl-CoA carboxylase (Acc), fatty acid synthase (Fasn), and sterol regulatory element binding protein 1c (Srebp1c), was markedly decreased by VPA. Pan-HDACi and an HDAC class I-specific inhibitor, but not an HDAC class II a-specific inhibitor, attenuated dexamethasone (DEX)-induced lipogenesis in HepG2 cells. The transcriptional activity of Fasn was decreased by pretreatment with VPA. In addition, pretreatment with VPA decreased DEX-induced binding of GR to the glucocorticoid response element (GRE). Treatment with VPA increased the acetylation of GR in ACTH-infused rats and DEX-induced HepG2 cells. Taken together, these results indicate that HDAC inhibition attenuates hepatic steatosis hrough GR acetylation in experimental CS.

Nutriepigenomics and malnutrition

Epigenetics is defined as the modulation of gene expression without changes to the underlying DNA sequence. Epigenetic alterations, as a consequence of in utero malnutrition, may play a role in susceptibility to develop adulthood diseases and inheritance. However, the mechanistic link between epigenetic modifications and abnormalities in nutrition remains elusive. This review provides an update on the association of suboptimal nutritional environment and the high propensity to produce adult-onset chronic illnesses with a particular focus on modifications in genome functions that occur without alterations to the DNA sequence. We will mention the drivers of the phenotype and pattern of epigenetic markers set down during the reprogramming along with novel preventative and therapeutic strategies. New knowledge of epigenetic alterations is opening a gate toward personalized medicine.

Cellular mechanisms of MR regulation of adipose tissue physiology and pathophysiology

In addition to the well-documented expression and activity of the mineralocorticoid receptor (MR) in the kidney, in the last decade research on MR has also revealed its important role in regulating functions of extrarenal tissues, including adipose tissue, where MR is involved in adipocyte fundamental processes such as differentiation, autophagy and adipokine secretion. MR expression is increased in adipose tissue of murine models of obesity and in obese human subjects, suggesting that over-activation of the mineralocorticoid signaling leads to dysfunctional adipocyte and associated metabolic disorders. Notably, pharmacological blockade of MR prevents metabolic dysfunctions observed in obese mice and suggests a potential therapeutic use of MR antagonists in the treatment of obesity and metabolic syndrome. However, the molecular pathways affected by MR blockade have been poorly investigated. This review summarizes the functions of MR in the adipocyte, discusses potential signaling pathways mediating MR action, and describes post-translational modifications regulating its activity.

Enhanced Ca(2+) response and stimulation of prostaglandin release by the bradykinin B2 receptor in human retinal pigment epithelial cells primed with proinflammatory cytokines

Kallikrein, kininogen and kinin receptors are present in human ocular tissues including the retinal pigment epithelium (RPE), suggesting a possible role of bradykinin (BK) in physiological and/or pathological conditions. To test this hypothesis, kinin receptors expression and function was investigated for the first time in human fetal RPE cells, a model close to native RPE, in both control conditions and after treatment with proinflammatory cytokines. Results showed that BK evoked intracellular Ca(2+) transients in human RPE cells by activating the kinin B2 receptor. Pretreatment of the cells with TNF-α and/or IL-1β enhanced Ca(2+) response in a time- and concentration-dependent additive manner, whereas the potency of BK and that of the selective B2 receptor antagonist, fasitibant chloride, both in the nanomolar range, remained unaffected. Cytokines have no significant effect on cell number and viability and on the activity of other GPCRs such as the kinin B1, acetylcholine, ATP and thrombin receptors. Immunoblot analysis and immunofluorescence studies revealed that cytokines treatment was associated with an increase in both kinin B2 receptor and COX-2 expression and with the secretion of prostaglandin E1 and E2 into the extracellular medium. BK, through activation of the kinin B2 receptor, potentiated the COX-2 mediated prostaglandin release in cytokines-primed RPE cells while new protein synthesis and prostaglandin production contribute to the potentiating effect of cytokines on BK-induced Ca(2+) response. In conclusion, overall data revealed a cross-talk between the kinin B2 receptor and cytokines in human RPE in promoting inflammation, a key feature in retinal pathologies including diabetic retinopathy and macular edema.

The Ontogeny of Brown Adipose Tissue

There are three different types of adipose tissue (AT)-brown, white, and beige-that differ with stage of development, species, and anatomical location. Of these, brown AT (BAT) is the least abundant but has the greatest potential impact on energy balance. BAT is capable of rapidly producing large amounts of heat through activation of the unique uncoupling protein 1 (UCP1) located within the inner mitochondrial membrane. White AT is an endocrine organ and site of lipid storage, whereas beige AT is primarily white but contains some cells that possess UCP1. BAT first appears in the fetus around mid-gestation and is then gradually lost through childhood, adolescence, and adulthood. We focus on the interrelationships between adipocyte classification, anatomical location, and impact of diet in early life together with the extent to which fat development differs between the major species examined. Ultimately, novel dietary interventions designed to reactivate BAT could be possible.

Melatonin in the regulation of liver steatosis following prenatal glucocorticoid exposure

Nonalcoholic fatty liver disease patients are characterized by hepatic steatosis. Prenatal glucocorticoid overexposure can result in steatosis. In this study, we aimed to determine the mechanism and cellular apoptosis of prenatal glucocorticoid overexposure in rats and whether melatonin can rescue the prenatal glucocorticoid-induced steatosis and apoptosis in neonatal rats. Pregnant Sprague-Dawley rats at gestational days 14 to 21 were administered dexamethasone. Acute effects of prenatal programming liver were assessed at postnatal day 7. The expression of proteins involved in the apoptotic and methylation pathways was analyzed by RT-PCR and Western blotting. Apoptosis and steatosis were examined by histology staining. The liver steatosis and apoptosis were increased in prenatal glucocorticoid group more than in control group and decreased in melatonin group. The expression of leptin decreased in prenatal glucocorticoid and increased in melatonin group by liver RT-PCR and Western blot study. Caspase 3, TNF-α proteins expression, and TUNEL stains increased in prenatal glucocorticoid compared with control and decreased in melatonin group. The liver histone deacetylase, DNA methyltransferase activity, and DNA methylation were increased in prenatal glucocorticoid and decreased in melatonin group. The present study showed that the prenatal glucocorticoid induced programming liver steatosis at day 7 after delivery, possibly via altered leptin expression. Melatonin can reverse the methylation of leptin and decreased liver steatosis.

Carbamazepine directly inhibits adipocyte differentiation through activation of the ERK 1/2 pathway

BACKGROUND AND PURPOSE

Carbamazepine (CBZ), known for its anti-epileptic, analgesic and mood-stabilizing properties, is also known to induce weight gain but the pathophysiology of this adverse effect is still largely unknown. We tested the hypothesis that CBZ could have a direct effect on adipocyte development and metabolism. EXPERIMENTAL RESEARCH: We studied the effects of CBZ on morphological biochemical and molecular markers of adipogenesis, using several pre-adipocyte murine cell lines (3T3-L1, 3T3-F442A and T37i cells) and primary cultures of human pre-adipocytes. To delineate the mechanisms underlying the effect of CBZ, clonal expansion of pre-adipocytes, pro-adipogenic transcription factors, glucose uptake and lipolysis were also examined.

KEY RESULTS

CBZ strongly inhibited pre-adipocyte differentiation and triglyceride accumulation in a time- and dose-dependent manner in all models. Pleiotropic mechanisms were at the basis of the inhibitory effects of CBZ on adipogenesis and cell lipid accumulation. They included suppression of both clonal expansion and major adipogenic transcription factors such as PPAR-γ and CCAAT/enhancer binding protein-α, activation of basal lipolysis and decrease in insulin-stimulated glucose transport.

CONCLUSIONS AND IMPLICATIONS

The effect of CBZ on adipogenesis involves activation of the ERK1/2 pathway. Our results show that CBZ acts directly on pre-adipocytes and adipocytes to alter adipose tissue development and metabolism.

Human skeletal muscle fibroblasts, but not myogenic cells, readily undergo adipogenic differentiation

We characterised the adherent cell types isolated from human skeletal muscle by enzymatic digestion, and demonstrated that even at 72 hours after isolation these cultures consisted predominantly of myogenic cells (CD56(+), desmin(+)) and fibroblasts (TE-7(+), collagen VI(+), PDGFRα(+), vimentin(+), fibronectin(+)). To evaluate the behaviour of the cell types obtained, we optimised a double immuno-magnetic cell-sorting method for the separation of myogenic cells from fibroblasts. This procedure gave purities of >96% for myogenic (CD56(+), desmin(+)) cells. The CD56(-) fraction obtained from the first sort was highly enriched in TE-7(+) fibroblasts. Using quantitative analysis of immunofluorescent staining for lipid content, lineage markers and transcription factors, we tested if the purified cell populations could differentiate into adipocytes in response to treatment with either fatty acids or adipocyte-inducing medium. Both treatments caused the fibroblasts to differentiate into adipocytes, as shown by loss of intracellular TE-7, upregulation of the adipogenic transcription factors PPARγ and C/EBPα, and adoption of a lipid-laden adipocyte morphology. By contrast, myogenic cells did not undergo adipogenesis and showed differential regulation of PPARγ and C/EBPα in response to these adipogenic treatments. Our results show that human skeletal muscle fibroblasts are at least bipotent progenitors that can remain as extracellular-matrix-producing cells or differentiate into adipocytes.

Trichostatin A modulates thiazolidinedione-mediated suppression of tumor necrosis factor α-induced lipolysis in 3T3-L1 adipocytes

In obesity, high levels of tumor necrosis factor α (TNFα) stimulate lipolysis in adipocytes, leading to hyperlipidemia and insulin resistance. Thiazolidinediones (TZDs), the insulin-sensitizing drugs, antagonize TNFα-induced lipolysis in adipocytes, thereby increasing insulin sensitivity in diabetes patients. The cellular target of TZDs is peroxisome proliferator-activated receptor γ (PPARγ), a nuclear receptor that controls many adipocyte functions. As a transcription factor, PPARγ is closely modulated by coregulators, which include coactivators and corepressors. Previous studies have revealed that in macrophages, the insulin-sensitizing effect of PPARγ may involve suppression of proinflammatory gene expression by recruiting the corepressor complex that contains corepressors and histone deacetylases (HDACs). Therefore, we investigated whether the corepressor complex is involved in TZD-mediated suppression of TNFα-induced lipolysis in 3T3-L1 adipocytes. Trichostatin A (TSA), a pan HDAC inhibitor (HDACI) that inhibits class I and II HDACs, was used to examine the involvement of HDACs in the actions of TZDs. TSA alone increased basal lipolysis and attenuated TZD-mediated suppression of TNFα-induced lipolysis. Increased basal lipolysis may in part result from class I HDAC inhibition because selective class I HDACI treatment had similar results. However, attenuation of TZD-mediated TNFα antagonism may be specific to TSA and related hydroxamate-based HDACI rather than to HDAC inhibition. Consistently, corepressor depletion did not affect TZD-mediated suppression. Interestingly, TSA treatment greatly reduced PPARγ levels in differentiated adipocytes. Finally, extracellular signal-related kinase 1/2 (ERK1/2) mediated TNFα-induced lipolysis, and TZDs suppressed TNFα-induced ERK phosphorylation. We determined that TSA increased basal ERK phosphorylation, and attenuated TZD-mediated suppression of TNFα-induced ERK phosphorylation, consistent with TSA's effects on lipolysis. These studies suggest that TSA, through down-regulating PPARγ, attenuates TZD-mediated suppression of TNFα-induced ERK phosphorylation and lipolysis in adipocytes.

Trichostatin A modulates thiazolidinedione-mediated suppression of tumor necrosis factor α-induced lipolysis in 3T3-L1 adipocytes

In obesity, high levels of tumor necrosis factor α (TNFα) stimulate lipolysis in adipocytes, leading to hyperlipidemia and insulin resistance. Thiazolidinediones (TZDs), the insulin-sensitizing drugs, antagonize TNFα-induced lipolysis in adipocytes, thereby increasing insulin sensitivity in diabetes patients. The cellular target of TZDs is peroxisome proliferator-activated receptor γ (PPARγ), a nuclear receptor that controls many adipocyte functions. As a transcription factor, PPARγ is closely modulated by coregulators, which include coactivators and corepressors. Previous studies have revealed that in macrophages, the insulin-sensitizing effect of PPARγ may involve suppression of proinflammatory gene expression by recruiting the corepressor complex that contains corepressors and histone deacetylases (HDACs). Therefore, we investigated whether the corepressor complex is involved in TZD-mediated suppression of TNFα-induced lipolysis in 3T3-L1 adipocytes. Trichostatin A (TSA), a pan HDAC inhibitor (HDACI) that inhibits class I and II HDACs, was used to examine the involvement of HDACs in the actions of TZDs. TSA alone increased basal lipolysis and attenuated TZD-mediated suppression of TNFα-induced lipolysis. Increased basal lipolysis may in part result from class I HDAC inhibition because selective class I HDACI treatment had similar results. However, attenuation of TZD-mediated TNFα antagonism may be specific to TSA and related hydroxamate-based HDACI rather than to HDAC inhibition. Consistently, corepressor depletion did not affect TZD-mediated suppression. Interestingly, TSA treatment greatly reduced PPARγ levels in differentiated adipocytes. Finally, extracellular signal-related kinase 1/2 (ERK1/2) mediated TNFα-induced lipolysis, and TZDs suppressed TNFα-induced ERK phosphorylation. We determined that TSA increased basal ERK phosphorylation, and attenuated TZD-mediated suppression of TNFα-induced ERK phosphorylation, consistent with TSA's effects on lipolysis. These studies suggest that TSA, through down-regulating PPARγ, attenuates TZD-mediated suppression of TNFα-induced ERK phosphorylation and lipolysis in adipocytes.

Characterization of a novel proinflammatory effect mediated by BK and the kinin B₂ receptor in human preadipocytes

Obesity and adipose tissue contribute to local and systemic inflammation. However the role of the inflammatory mediator bradykinin (BK) in this context is not known. We therefore evaluated the effect of BK on adipokines secretion in human preadipocytes during the course of differentiation and characterized the receptors involved. Results obtained from antibody array and ELISA experiments showed that several adipokines are released by human preadipocytes under basal conditions while BK specifically stimulated the production of interleukin(IL)-6 and IL-8. The effect of BK diminished with the progression of differentiation, being almost inactive on adipocytes. In preadipocytes, BK also induced a rapid and transient [Ca²⁺](i) mobilization, a rapid and sustained increase in ERK1/2 activation and enhanced forskolin-stimulated cAMP accumulation. BK was without effect on cell proliferation and viability as assessed by bromodeoxyuridine incorporation, WST-1 conversion, or lactate dehydrogenase leakage and was without effect on adipogenesis as measured by triglyceride accumulation, GPDH activity and leptin release. The B₁ receptor agonist, Lys-[des-Arg⁹]-BK, displayed poor activity or was without effect while overall BK effects were prevented by the selective B₂ receptor antagonist, fasitibant chloride, but not by the B₁ selective antagonist, Lys-[Leu⁸][des-Arg⁹]-BK. Immunoblot analysis and immunofluorescence studies showed that the kinin B₂ receptor was essentially expressed at the beginning of the differentiation program. In conclusion, human preadipocytes expressed kinin B₂ receptors linked to multiple signaling pathways, IL-6 and IL-8 production, and BK proinflammatory response in adipose tissue could be prevented by fasitibant chloride.

Temporal analysis of protein lysine acetylation during adipocyte differentiation

The post-translational modification of protein by acetylation has been emerging as a prevalent modification in enzymes that catalyze intermediary metabolism. However, the dynamics of protein acetylation during adipocyte differentiation that involves a major shift in cellular metabolism is not known. In this study, we investigated the temporal changes in acetylation during adipocyte differentiation. Almost all acetylated proteins identified showed a sequential change in acetylation during the differentiation process. While the majority of the acetylated proteins showed a sequential upregulation during adipocyte differentiation, in a few proteins a sequential downregulation of protein acetylation was also observed. Our findings suggest that a wide-ranging temporal change in protein acetylation occurs during adipocyte differentiation including differentially expressed proteins signifying an important role in adipocyte differentiation.

Metabolic reprogramming by class I and II histone deacetylases

Accumulating evidence suggests that protein acetylation plays a major regulatory role in many facets of transcriptional control of metabolism. The enzymes that catalyze the addition and removal of acetyl moieties are the histone acetyl transferases (HATs) and histone deacetylases (HDACs), respectively. Several recent studies have uncovered novel mechanisms and contexts in which different HDACs play crucial roles in metabolic control. Understanding the role of class I and II HDACs in different metabolic programs during development, as well as in the physiology and pathology of the adult organism, will lead to novel therapeutics for metabolic disease. Here, we review the current understanding of how class I and class II HDACs contribute to metabolic control.

Dietary regulation of histone acetylases and deacetylases for the prevention of metabolic diseases

Age-related diseases such as type 2 diabetes, cardiovascular disease, and cancer involve epigenetic modifications, where accumulation of minute changes in the epigenome over time leads to disease manifestation. Epigenetic changes are influenced by life style and diets. This represents an avenue whereby dietary components could accelerate or prevent age-related diseases through their effects on epigenetic modifications. Histone acetylation is an epigenetic modification that is regulated through the opposing action of histone acetylases (HATs) and deacetylases (HDACs). These two families of enzymes play critical roles in metabolic processes and their dysregulation is associated with pathogenesis of several diseases. Dietary components, such as butyrate, sulforaphane, and curcumin, have been shown to affect HAT and HDAC activity, and their health benefits are attributed, at least in part, to epigenetic modifications. Given the decades that it takes to accumulate epigenetic changes, it is unlikely that pharmaceuticals could undo epigenetic changes without side effects. Therefore, long term consumption of dietary components that can alter the epigenome could be an attractive means of disease prevention. The goal of this review is to highlight the roles of diets and food components in epigenetic modifications through the regulation of HATs and HDACs for disease prevention.

Acetylation of malate dehydrogenase 1 promotes adipogenic differentiation via activating its enzymatic activity

Acetylation is one of the most crucial post-translational modifications that affect protein function. Protein lysine acetylation is catalyzed by acetyltransferases, and acetyl-CoA functions as the source of the acetyl group. Additionally, acetyl-CoA plays critical roles in maintaining the balance between carbohydrate metabolism and fatty acid synthesis. Here, we sought to determine whether lysine acetylation is an important process for adipocyte differentiation. Based on an analysis of the acetylome during adipogenesis, various proteins displaying significant quantitative changes were identified by LC-MS/MS. Of these identified proteins, we focused on malate dehydrogenase 1 (MDH1). The acetylation level of MDH1 was increased up to 6-fold at the late stage of adipogenesis. Moreover, overexpression of MDH1 in 3T3-L1 preadipocytes induced a significant increase in the number of cells undergoing adipogenesis. The introduction of mutations to putative lysine acetylation sites showed a significant loss of the ability of cells to undergo adipogenic differentiation. Furthermore, the acetylation of MDH1 dramatically enhanced its enzymatic activity and subsequently increased the intracellular levels of NADPH. These results clearly suggest that adipogenic differentiation may be regulated by the acetylation of MDH1 and that the acetylation of MDH1 is one of the cross-talk mechanisms between adipogenesis and the intracellular energy level.

Lysine acetylation in obesity, diabetes and metabolic disease

Histone acetyltransferases (HATs) and histone deacetylases (HDACs) mediate acetylation and deacetylation of histone proteins and transcription factors. There is abundant evidence that these enzymes regulate the acetylation state of many cytoplasmic proteins, including lysine residues in important metabolic enzymes. Lysine acetylation regulates major cellular functions as a common post-transcriptional modification of proteins, conserved from prokaryotes to humans. In this article, we refer to HATs and HDACs broadly as lysine acetyltransferases (KATs) and deacetylases (KDACs). Lysine acetylation is vitally important in both immunological and metabolic pathways and may regulate the balance between energy storage and expenditure. Obesity, type II diabetes and cardiovascular disease (metabolic syndrome) are widely recognised as features of a chronic low-grade inflammatory state, involving significant alterations in primary immunometabolism. Identifying effective therapeutic and preventive options to treat this multi-factorial syndrome has proven to be very challenging, with an emerging focus on developing anti-inflammatory agents that can combat adiposity and metabolic disease. Here, we summarise current evidence and understanding of innate immune and metabolic pathways relevant to adiposity and metabolic disease regulated by lysine acetylation. Developing this understanding in greater detail may facilitate strategic development of novel and enzyme-specific lysine deacetylase modulators that regulate both metabolic and immune systems.

Histone deacetylase 9 is a negative regulator of adipogenic differentiation

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.

Myocyte enhancer factor-2 interacting transcriptional repressor (MITR) is a switch that promotes osteogenesis and inhibits adipogenesis of mesenchymal stem cells by inactivating peroxisome proliferator-activated receptor gamma-2

EZH2, a catalytic subunit of Polycomb-repressive complex 2 (PRC2), is a histone lysine methyltransferase that methylates lysine 27 of histone H3, resulting in gene silencing. It has been shown that EZH2 plays a pivotal role in fostering self-renewal and inhibiting the differentiation of embryonic stem cells. Mesenchymal stem cells (MSCs) can be induced to differentiate into adipogenic and osteogenic lineages, which are mutually exclusive. However, it is not clear whether the molecular events of EZH2-mediated epigenetic silencing may coordinate differentiation between osteoblasts and adipocytes. Disruption of the balance between adipogenesis and osteogenesis is associated with many diseases; thus, identifying a switch that determines the fate of MSC is critical. In this study, we used EZH2-ChIP-on-chip assay to identify differential EZH2 targets in the two differentiation stages on a genome-wide scale. After validating the targets, we found that myocyte enhancer factor-2 interacting transcriptional repressor (MITR)/HDAC9c was expressed in osteoblasts and greatly decreased in adipocytes. We demonstrated that MITR plays a crucial role in the acceleration of MSC osteogenesis and attenuation of MSC adipogenesis through interaction with peroxisome proliferator-activated receptor (PPAR) γ-2 in the nucleus of osteoblasts, which interrupts PPARγ-2 activity and prevents adipogenesis. Together, our results demonstrated that MITR plays a master switch role to balance osteogenic and adipogenic differentiation of MSCs through regulation of PPARγ-2 transcriptional activity.