Histone deacetylase 6 structure and molecular basis of catalysis and inhibition

Unusual zinc-binding mode of HDAC6-selective hydroxamate inhibitors

Histone deacetylases (HDACs) regulate myriad cellular processes by catalyzing the hydrolysis of acetyl-l-lysine residues in histone and nonhistone proteins. The Zn²⁺-dependent class IIb enzyme HDAC6 regulates microtubule function by deacetylating α-tubulin, which suppresses microtubule dynamics and leads to cell cycle arrest and apoptosis. Accordingly, HDAC6 is a target for the development of selective inhibitors that might be useful in new therapeutic approaches for the treatment of cancer, neurodegenerative diseases, and other disorders. Here, we present high-resolution structures of catalytic domain 2 from Danio rerio HDAC6 (henceforth simply "HDAC6") complexed with compounds that selectively inhibit HDAC6 while maintaining nanomolar inhibitory potency: N-hydroxy-4-[(N(2-hydroxyethyl)-2-phenylacetamido)methyl)-benzamide)] (HPB), ACY-1215 (Ricolinostat), and ACY-1083. These structures reveal that an unusual monodentate Zn²⁺ coordination mode is exploited by sterically bulky HDAC6-selective phenylhydroxamate inhibitors. We additionally report the ultrahigh-resolution structure of the HDAC6-trichostatin A complex, which reveals two Zn²⁺-binding conformers for the inhibitor: a major conformer (70%) with canonical bidentate hydroxamate-Zn²⁺ coordination geometry and a minor conformer (30%) with monodentate hydroxamate-Zn²⁺ coordination geometry, reflecting a free energy difference of only 0.5 kcal/mol. The minor conformer is not visible in lower resolution structure determinations. Structural comparisons of HDAC6-inhibitor complexes with class I HDACs suggest active site features that contribute to the isozyme selectivity observed in biochemical assays.

Largazole Analogues as Histone Deacetylase Inhibitors and Anticancer Agents: An Overview of Structure-Activity Relationships

Since the time of its identification, the natural compound largazole rapidly caught the attention of the medicinal chemistry community for its impressive potency as an inhibitor of histone deacetylases (HDACs) and its strong antiproliferative activity against a broad panel of cancer cell lines. The design of largazole analogues is an expanding field of study, due to their remarkable potential as novel anticancer therapeutics. At present, a large ensemble of largazole analogues has been reported, allowing the identification of important structure-activity relationships (SAR) that can guide the design of novel compounds with improved HDAC inhibitory profiles, anticancer activity, and pharmacokinetic properties. The aim of this review is to concisely summarize the information obtained by biological evaluations of the various largazole analogues reported to date, with particular attention given to the latest analogues, as well as to analyze the various SAR obtained from this data, with the purpose of providing useful guidelines for the development of novel potent and selective HDAC inhibitors to be used as anticancer agents.

Anti-cancer effects of naturally derived compounds targeting histone deacetylase 6-related pathways

Alterations of the epigenetic machinery, affecting multiple biological functions, represent a major hallmark enabling the development of tumors. Among epigenetic regulatory proteins, histone deacetylase (HDAC)6 has emerged as an interesting potential therapeutic target towards a variety of diseases including cancer. Accordingly, this isoenzyme regulates many vital cellular regulatory processes and pathways essential to physiological homeostasis, as well as tumor multistep transformation involving initiation, promotion, progression and metastasis. In this review, we will consequently discuss the critical implications of HDAC6 in distinct mechanisms relevant to physiological and cancerous conditions, as well as the anticancer properties of synthetic, natural and natural-derived compounds through the modulation of HDAC6-related pathways.

Recent advances in the discovery of potent and selective HDAC6 inhibitors

Histone deacetylase HDAC6, a member of the class IIb HDAC family, is unique among HDAC enzymes in having two active catalytic domains, and has unique physiological function. In addition to the modification of histone, HDAC6 targets specific substrates including α-tubulin and HSP90, and are involved in protein trafficking and degradation, cell shape and migration. Selective HDAC6 inhibitors are an emerging class of pharmaceuticals due to the involvement of HDAC6 in different pathways related to neurodegenerative diseases, cancer, and immunology. Therefore, extensive investigations have been made in the discovery of selective HDAC6 inhibitors. Based on their different zinc binding groups (ZBGs), in this review, HDAC6 inhibitors are grouped as hydroxamic acids, a sulfur containing ZBG based derivatives and other ZBG-derived compounds, and their enzymatic inhibitory activity, selectivity and other biological activities are introduced and summarized.

Synthesis and Pharmacological Evaluation of Selective Histone Deacetylase 6 Inhibitors in Melanoma Models

Only a handful of therapies offer significant improvement in the overall survival in cases of melanoma, a cancer whose incidence has continued to rise in the past 30 years. In our effort to identify potent and isoform-selective histone deacetylase (HDAC) inhibitors as a therapeutic approach to melanoma, a series of new HDAC6 inhibitors based on the nexturastat A scaffold were prepared. The new analogues 4d, 4e, and 7b bearing added hydrophilic substituents, so as to establish additional hydrogen bonding on the rim of the HDAC6 catalytic pocket, exhibit improved potency against HDAC6 and retain selectivity over HDAC1. Compound 4d exhibits antiproliferative effects on several types of melanoma and lymphoma cells. Further studies indicates that 4d selectively increases acetylated tubulin levels in vitro and elicits an immune response through down-regulating cytokine IL-10. A preliminary in vivo efficacy study indicates that 4d possesses improved capability to inhibit melanoma tumor growth and that this effect is based on the regulation of inflammatory and immune responses.

HDAC6 Brain Mapping with [18F]Bavarostat Enabled by a Ru-Mediated Deoxyfluorination

Histone deacetylase 6 (HDAC6) function and dysregulation have been implicated in the etiology of certain cancers and more recently in central nervous system (CNS) disorders including Rett syndrome, Alzheimer's and Parkinson's diseases, and major depressive disorder. HDAC6-selective inhibitors have therapeutic potential, but in the CNS drug space the development of highly brain penetrant HDAC inhibitors has been a persistent challenge. Moreover, no tool exists to directly characterize HDAC6 and its related biology in the living human brain. Here, we report a highly brain penetrant HDAC6 inhibitor, Bavarostat, that exhibits excellent HDAC6 selectivity (>80-fold over all other Zn-containing HDAC paralogues), modulates tubulin acetylation selectively over histone acetylation, and has excellent brain penetrance. We further demonstrate that Bavarostat can be radiolabeled with ¹⁸F by deoxyfluorination through in situ formation of a ruthenium π-complex of the corresponding phenol precursor: the only method currently suitable for synthesis of [¹⁸F]Bavarostat. Finally, by using [¹⁸F]Bavarostat in a series of rodent and nonhuman primate imaging experiments, we demonstrate its utility for mapping HDAC6 in the living brain, which sets the stage for first-in-human neurochemical imaging of this important target.

Binding of the Microbial Cyclic Tetrapeptide Trapoxin A to the Class I Histone Deacetylase HDAC8

Trapoxin A is a microbial cyclic tetrapeptide that is an essentially irreversible inhibitor of class I histone deacetylases (HDACs). The inhibitory warhead is the α,β-epoxyketone side-chain of (2S,9S)-2-amino-8-oxo-9,10-epoxydecanoic acid (l-Aoe), which mimics the side-chain of the HDAC substrate acetyl-l-lysine. We now report the crystal structure of the HDAC8-trapoxin A complex at 1.24 Å resolution, revealing that the ketone moiety of l-Aoe undergoes nucleophilic attack to form a zinc-bound tetrahedral gem-diolate that mimics the tetrahedral intermediate and its flanking transition states in catalysis. Mass spectrometry, activity measurements, and isothermal titration calorimetry confirm that trapoxin A binds tightly (K_d = 3 ± 1 nM) and does not covalently modify the enzyme, so the epoxide moiety of l-Aoe remains intact. Comparison of the HDAC8-trapoxin A complex with the HDAC6-HC toxin complex provides new insight regarding the inhibitory potency of l-Aoe-containing natural products against class I and class II HDACs.

Human histone deacetylase 6 shows strong preference for tubulin dimers over assembled microtubules

Human histone deacetylase 6 (HDAC6) is the major deacetylase responsible for removing the acetyl group from Lys40 of α-tubulin (αK40), which is located lumenally in polymerized microtubules. Here, we provide a detailed kinetic analysis of tubulin deacetylation and HDAC6/microtubule interactions using individual purified components. Our data unequivocally show that free tubulin dimers represent the preferred HDAC6 substrate, with a K _M value of 0.23 µM and a deacetylation rate over 1,500-fold higher than that of assembled microtubules. We attribute the lower deacetylation rate of microtubules to both longitudinal and lateral lattice interactions within tubulin polymers. Using TIRF microscopy, we directly visualized stochastic binding of HDAC6 to assembled microtubules without any detectable preferential binding to microtubule tips. Likewise, indirect immunofluorescence microscopy revealed that microtubule deacetylation by HDAC6 is carried out stochastically along the whole microtubule length, rather than from the open extremities. Our data thus complement prior studies on tubulin acetylation and further strengthen the rationale for the correlation between tubulin acetylation and microtubule age.

Lysine Deacetylases Exhibit Distinct Changes in Activity Profiles Due to Fluorophore Conjugation of Substrates

Lysine deacetylases (KDACs) are enzymes that reverse the post-translational modification of lysine acetylation. Thousands of potential substrates, acetylated protein sequences, have been identified in mammalian cells. Properly regulated acetylation and deacetylation have been linked to many biological processes, while aberrant KDAC activity has also been linked to numerous diseases. Commercially available peptide substrates that are conjugated to fluorescent dye molecules, such as 7-amino-4-methylcoumarin (AMC), are commonly used to monitor deacetylation in studies addressing both substrate specificity and small molecule modulators of activity. Here, we have compared the activity of several KDACs, representing all major classes of KDACs, with substrates in the presence and absence of AMC as well as peptides for which tryptophan has been substituted for AMC. Our results unequivocally demonstrate that AMC has a significant effect on activity for all KDACs tested. Furthermore, in neither the nature of the effect nor the magnitude is consistent across KDACs, making it impossible to predict the effect of AMC on a particular enzyme-substrate pair. AMC did not affect acetyllysine preference in a multiply acetylated substrate. In contrast, AMC significantly enhanced KDAC6 substrate affinity, greatly reduced Sirt1 activity, eliminated the substrate sequence specificity of KDAC4, and had no consistent effect with KDAC8 substrates. These results indicate that profiling of KDAC activity with labeled peptides is unlikely to produce biologically relevant data.

ARID1A-mutated ovarian cancers depend on HDAC6 activity

ARID1A , encoding a subunit of the SWI/SNF chromatin-remodelling complex, is the most frequently mutated epigenetic regulator across all human cancers. ARID1A and TP53 mutations are typically mutually exclusive. Therapeutic approaches that correlate with this genetic characteristic remain to be explored. Here, we show that HDAC6 activity is essential in ARID1A-mutated ovarian cancers. Inhibition of HDAC6 activity using a clinically applicable small molecule inhibitor significantly improved the survival of mice bearing ARID1A-mutated tumours. This correlated with the suppression of growth and dissemination of ARID1A-mutated, but not wildtype, tumours. The dependence on HDAC6 activity in ARID1A-mutated cells correlated with a direct transcriptional repression of HDAC6 by ARID1A. HDAC6 inhibition selectively promoted apoptosis of ARID1A-mutated cells. HDAC6 directly deacetylates Lys-120 of p53, a pro-apoptotic post-translational modification. Thus, ARID1A mutation inactivates p53’s apoptosis-promoting function by upregulating HDAC6. Together, these results indicate that pharmacological inhibition of HDAC6 is a therapeutic strategy for ARID1A-mutated cancers.

Design, Multicomponent Synthesis, and Anticancer Activity of a Focused Histone Deacetylase (HDAC) Inhibitor Library with Peptoid-Based Cap Groups

In this work, we report the multicomponent synthesis of a focused histone deacetylase (HDAC) inhibitor library with peptoid-based cap groups and different zinc-binding groups. All synthesized compounds were tested in a cellular HDAC inhibition assay and an MTT assay for cytotoxicity. On the basis of their noteworthy activity in the cellular HDAC assays, four compounds were further screened for their inhibitory activity against recombinant HDAC1-3, HDAC6, and HDAC8. All four compounds showed potent inhibition of HDAC1-3 as well as significant inhibition of HDAC6 with IC₅₀ values in the submicromolar concentration range. Compound 4j, the most potent HDAC inhibitor in the cellular HDAC assay, revealed remarkable chemosensitizing properties and enhanced the cisplatin sensitivity of the cisplatin-resistant head-neck cancer cell line Cal27CisR by almost 7-fold. Furthermore, 4j almost completely reversed the cisplatin resistance in Cal27CisR. This effect is related to a synergistic induction of apoptosis as seen in the combination of 4j with cisplatin.

Histone deacetylase 10 structure and molecular function as a polyamine deacetylase

Cationic polyamines such as spermidine and spermine are critical in all forms of life, as they regulate the function of biological macromolecules. Intracellular polyamine metabolism is regulated by reversible acetylation and dysregulated polyamine metabolism is associated with neoplastic diseases such as colon cancer, prostate cancer and neuroblastoma. Here we report that histone deacetylase 10 (HDAC10) is a robust polyamine deacetylase, using recombinant enzymes from Homo sapiens (human) and Danio rerio (zebrafish). The 2.85 Å-resolution crystal structure of zebrafish HDAC10 complexed with a transition-state analogue inhibitor reveals that a glutamate gatekeeper and a sterically constricted active site confer specificity for N⁸-acetylspermidine hydrolysis and disfavour acetyllysine hydrolysis. Both HDAC10 and spermidine are known to promote cellular survival through autophagy. Accordingly, this work sets a foundation for studying the chemical biology of autophagy through the structure-based design of inhibitors that may also serve as new leads for cancer chemotherapy.

Polyamines bind to nucleic acids and their function is regulated by reversible acetylation. Here, the authors show that histone deacetylase 10 is a polyamine deacetylase and present its crystal structure with a bound polyamine transition state analogue inhibitor.

Hydroxyl Ketone-Based Histone Deacetylase Inhibitors To Gain Insight into Class I HDAC Selectivity versus That of HDAC6

Little is known about the biological and structural features that govern the isoform selectivity for class I histone deacetylases (HDACs) over HDAC6. In addition to that for known inhibitors, like benzamides, psammaplin A, and cyclodepsipeptide-derived thiols, selectivity was also observed for naturally occurring cyclopeptide HDAC inhibitors with an aliphatic flexible linker and ketonelike zinc-binding group (ZBG). The present study reports that this isoform selectivity is mainly due to the linker and ZBG, as replacement of the cyclopeptide cap region by a simple aniline retained class I HDAC isoform selectivity toward HDAC6 in enzymatic assays. The best cyclopeptide-free analogues preserved efficacy against Plasmodium falciparum and cancer cell lines. Molecular modeling provided hypotheses to explain this selectivity and suggests different behaviors of the flexible linker on HDAC1 and HDAC6 pockets, which may influence, on the basis of the strength of the ZBG, its coordination with the zinc ion.

Cellular defence or viral assist: the dilemma of HDAC6

Histone deacetylase 6 (HDAC6) is a unique cytoplasmic deacetylase that regulates various important biological processes by preventing protein aggregation and deacetylating different non-histone substrates including tubulin, heat shock protein 90, cortactin, retinoic acid inducible gene I and β-catenin. Growing evidence has indicated a dual role for HDAC6 in viral infection and pathogenesis: HDAC6 may represent a host defence mechanism against viral infection by modulating microtubule acetylation, triggering antiviral immune response and stimulating protective autophagy, or it may be hijacked by the virus to enhance proinflammatory response. In this review, we will highlight current data illustrating the complexity and importance of HDAC6 in viral pathogenesis. We will summarize the structure and functional specificity of HDAC6, and its deacetylase- and ubiquitin-dependent activity in key cellular events in response to virus infection. We will also discuss how HDAC6 exerts its direct or indirect histone modification ability in viral lytic-latency switch.

Structural Requirements of HDAC Inhibitors: SAHA Analogues Modified at the C2 Position Display HDAC6/8 Selectivity

Histone deacetylase (HDAC) proteins are epigenetic regulators that deacetylate protein substrates, leading to subsequent changes in cell function. HDAC proteins are implicated in cancers, and several HDAC inhibitors have been approved by the FDA as anticancer drugs, including SAHA (suberoylanilide hydroxamic acid; Vorinostat and Zolinza). Unfortunately, SAHA inhibits most HDAC isoforms, which limits its use as a pharmacological tool and may lead to side effects in the clinic. In this work SAHA analogues substituted at the C2 position were synthesized and screened for HDAC isoform selectivity in vitro and in cells. The most potent and selective compound, C2-n-hexyl SAHA, displayed submicromolar potency with 49- to 300-fold selectivity for HDAC6 and HDAC8 compared to HDAC1, -2, and -3. Docking studies provided a structural rationale for selectivity. Modification of the nonselective inhibitor SAHA generated HDAC6/HDAC8 dual selective inhibitors, which can be useful lead compounds toward developing pharmacological tools and more effective anticancer drugs.

Melatonin and sirtuins: A "not-so unexpected" relationship

Epigenetic modifications, including methylation or acetylation as well as post-transcriptional modifications, are mechanisms used by eukaryotic cells to increase the genome diversity in terms of differential gene expression and protein diversity. Among these modifying enzymes, sirtuins, a class III histone deacetylase (HDAC) enzymes, are of particular importance. Sirtuins regulate the cell cycle, DNA repair, cell survival, and apoptosis, thus having important roles in normal and cancer cells. Sirtuins can also regulate metabolic pathways by changing preference for glycolysis under aerobic conditions as well as glutaminolysis. These actions make sirtuins a major target in numerous physiological processes as well as in other contexts such as calorie restriction-induced anti-aging, cancer, or neurodegenerative disease. Interestingly, melatonin, a nighttime-produced indole synthesized by pineal gland and many other organs, has important cytoprotective effects in many tissues including aging, neurodegenerative diseases, immunomodulation, and cancer. The pleiotropic actions of melatonin in different physiological and pathological conditions indicate that may be basic cellular targeted for the indole. Thus, much research has focused attention on the potential mechanisms of the indole in modulating expression and/or activity of sirtuins. Numerous findings report a rise in activity, especially on SIRT1, in a diversity of cells and animal models after melatonin treatment. This contrasts, however, with data reporting an inhibitory effect of melatonin on this sirtuin in some tumor cells. This review tabulates and discusses the recent findings relating melatonin with sirtuins, particularly SIRT1 and mitochondrial SIRT3, showing the apparent dichotomy with the differential actions documented in normal and in cancer cells.

The Search for Potent, Small-Molecule HDACIs in Cancer Treatment: A Decade After Vorinostat

Histone deacetylases (HDACs) play a crucial role in the remodeling of chromatin, and are involved in the epigenetic regulation of gene expression. In the last decade, inhibition of HDACs came out as a target for specific epigenetic changes associated with cancer and other diseases. Until now, more than 20 HDAC inhibitors (HDACIs) have entered clinical studies, and some of them (e.g., vorinostat, romidepsin) have been approved for the treatment of cutaneous T-cell lymphoma. This review provides an overview of current knowledge, progress, and molecular mechanisms of HDACIs, covering a period from 2011 until 2015.

Photochromic histone deacetylase inhibitors based on dithienylethenes and fulgimides

The synthesis, photochromic properties, inhibition of different HDACs and corresponding molecular dockings of photochromic inhibitors are described.

Design and synthesis of benzodiazepine analogs as isoform-selective human lysine deacetylase inhibitors

A comprehensive investigation was performed to identify new benzodiazepine (BZD) derivatives as potent and selective human lysine deacetylase inhibitors (hKDACis). A total of 108 BZD compounds were designed, synthesized and from that 104 compounds were biologically evaluated against human lysine deacetylases (hKDACs) 1, 3 and 8 (class I) and 6 (class IIb). The most active compounds showed mid-nanomolar potencies against hKDACs 1, 3 and 6 and micromolar activity against hKDAC8, while a promising compound (6q) showed selectivity towards hKDAC3 among the different enzyme isoforms. An hKDAC6 homology model, refined by molecular dynamics simulation was generated, and molecular docking studies performed to rationalize the dominant ligand-residue interactions as well as to define structure-activity-relationships. Experimental results confirmed the usefulness of the benzodiazepine moiety as capping group when pursuing hKDAC isoform-selectivity inhibition, suggesting its continued use when designing new hKDACis.

Structural and Functional Influence of the Glycine-Rich Loop G302GGGY on the Catalytic Tyrosine of Histone Deacetylase 8

Histone deacetylase 8 (HDAC8) catalyzes the hydrolysis of acetyl-l-lysine to yield products l-lysine and acetate through a mechanism in which a nucleophilic water molecule is activated by a histidine general base and a catalytic metal ion (Zn²⁺ or Fe²⁺). Acetyl-l-lysine also requires activation by metal coordination and a hydrogen bond with catalytic tyrosine Y306, which also functions in transition state stabilization. Interestingly, Y306 is located in the conserved glycine-rich loop G³⁰²GGGY. The potential flexibility afforded by the tetraglycine segment may facilitate induced-fit conformational changes in Y306 between "in" and "out" positions, as observed in related deacetylases. To probe the catalytic importance of the glycine-rich loop in HDAC8, we rigidified this loop by preparing the G302A, G303A, G304A, and G305A mutants and measured their steady state kinetics and determined their X-ray crystal structures. Substantial losses of catalytic efficiency are observed (10-500-fold based on k_cat/K_M), particularly for G304A HDAC8 and G305A HDAC8. These mutants also exhibit the greatest structural changes for catalytic tyrosine Y306 (1.3-1.7 Å shifts of the phenolic hydroxyl group). Molecular dynamics simulations further indicate that G304 and G305 undergo pronounced structural changes as residue 306 undergoes a transition between "in" and "out" conformations. Thus, the G304A and G305A substitutions likely compromise the position and conformational changes of Y306 required for substrate activation and transition state stabilization. The G302A and G303A substitutions have less severe catalytic consequences, and these substitutions may influence an internal channel through which product acetate is believed to exit.

Structural aspects of HDAC8 mechanism and dysfunction in Cornelia de Lange syndrome spectrum disorders

Cornelia de Lange Syndrome (CdLS) encompasses a broad spectrum of phenotypes characterized by distinctive craniofacial abnormalities, limb malformations, growth retardation, and intellectual disability. CdLS spectrum disorders are referred to as cohesinopathies, with ∼70% of patients having a mutation in a gene encoding a core cohesin protein (SMC1A, SMC3, or RAD21) or a cohesin regulatory protein (NIPBL or HDAC8). Notably, the regulatory function of HDAC8 in cohesin biology has only recently been discovered. This Zn2+ -dependent hydrolase catalyzes the deacetylation of SMC3, a necessary step for cohesin recycling during the cell cycle. To date, 23 different missense mutants in the gene encoding HDAC8 have been identified in children with developmental features that overlap those of CdLS. Enzymological, biophysical, and structural studies of CdLS HDAC8 protein mutants have yielded critical insight on compromised catalysis in vitro. Most CdLS HDAC8 mutations trigger structural changes that directly or indirectly impact substrate binding and catalysis. Additionally, several mutations significantly compromise protein thermostability. Intriguingly, catalytic activity in many HDAC8 mutants can be partially or fully restored by an N-acylthiourea activator, suggesting a plausible strategy for the chemical rescue of compromised HDAC8 catalysis in vivo.

Ubiquitin in Influenza Virus Entry and Innate Immunity

Viruses are obligatory cellular parasites. Their mission is to enter a host cell, to transfer the viral genome, and to replicate progeny whilst diverting cellular immunity. The role of ubiquitin is to regulate fundamental cellular processes such as endocytosis, protein degradation, and immune signaling. Many viruses including influenza A virus (IAV) usurp ubiquitination and ubiquitin-like modifications to establish infection. In this focused review, we discuss how ubiquitin and unanchored ubiquitin regulate IAV host cell entry, and how histone deacetylase 6 (HDAC6), a cytoplasmic deacetylase with ubiquitin-binding activity, mediates IAV capsid uncoating. We also discuss the roles of ubiquitin in innate immunity and its implications in the IAV life cycle.

Impaired histone deacetylases 5 and 6 expression mimics the effects of obesity and hypoxia on adipocyte function

Objective

The goal of the study was to investigate the role of histone deacetylases (HDACs) in adipocyte function associated with obesity and hypoxia.

Methods

Total proteins and RNA were prepared from human visceral adipose tissues (VAT) of human obese and normal weight subjects and from white adipose tissue (WAT) of C57Bl6-Rj mice fed a normal or high fat diet (HFD) for 16 weeks. HDAC activity was measured by colorimetric assay whereas the gene and protein expression were monitored by real-time PCR and by western blotting, respectively. RNA interference (RNAi) was used to silence the expression of genes in 3T3-L1 adipocytes.

Results

Total HDAC activity was decreased in VAT and WAT from obese individuals and from mice fed a HFD, respectively. The HDAC activity reduction was associated with decreased HDAC5/Hdac5 and HDAC6/Hdac6 expression in human and mice adipocyte fraction. Similarly, hypoxia hampered total Hdac activity and reduced the expression of Hdac5 and Hdac6 in 3T3-L1 adipocytes. The decrease of both Hdac5 and Hdac6 by hypoxia was associated with altered expression of adipokines and of the inducible cAMP early repressor (Icer), a key repressor that is defective in human and mice obesity. Silencing of Icer in adipocytes reproduced the changes in adipokine levels under hypoxia and obesity, suggesting a causative effect. Finally, modeling the defect of the two Hdacs in adipocytes by RNAi or selective inhibitors mimicked the effects of hypoxia on the expression of Icer, leading to impairment of insulin-induced glucose uptake.

Conclusion

Hdac5 and Hdac6 expression are required for the adequate expression of Icer and adipocyte function. Altered adipose expression of the two Hdacs in obesity by hypoxia may contribute to the development of metabolic abnormalities.

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Impaired adipose HDAC activity in human obese subjects and obese mice.

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HDAC5 and HDAC6 expression is reduced in adipocytes of obese mice and human.

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The expression of HDAC5, HDAC6 and ICER is altered by hypoxia in 3T3-L1 adipocytes.

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ICER regulates hypoxia-sensitive adipokines expression.

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Hdac5 and Hdac6 control the expression of ICER and glucose uptake in adipocytes.