Histone deacetylases as regulators of inflammation and immunity

The Depsipeptide Romidepsin Reverses HIV-1 Latency In Vivo

Pharmacologically-induced activation of replication competent proviruses from latency in the presence of antiretroviral treatment (ART) has been proposed as a step towards curing HIV-1 infection. However, until now, approaches to reverse HIV-1 latency in humans have yielded mixed results. Here, we report a proof-of-concept phase Ib/IIa trial where 6 aviremic HIV-1 infected adults received intravenous 5 mg/m² romidepsin (Celgene) once weekly for 3 weeks while maintaining ART. Lymphocyte histone H3 acetylation, a cellular measure of the pharmacodynamic response to romidepsin, increased rapidly (maximum fold range: 3.7–7.7 relative to baseline) within the first hours following each romidepsin administration. Concurrently, HIV-1 transcription quantified as copies of cell-associated un-spliced HIV-1 RNA increased significantly from baseline during treatment (range of fold-increase: 2.4–5.0; p = 0.03). Plasma HIV-1 RNA increased from <20 copies/mL at baseline to readily quantifiable levels at multiple post-infusion time-points in 5 of 6 patients (range 46–103 copies/mL following the second infusion, p = 0.04). Importantly, romidepsin did not decrease the number of HIV-specific T cells or inhibit T cell cytokine production. Adverse events (all grade 1–2) were consistent with the known side effects of romidepsin. In conclusion, romidepsin safely induced HIV-1 transcription resulting in plasma HIV-1 RNA that was readily detected with standard commercial assays demonstrating that significant reversal of HIV-1 latency in vivo is possible without blunting T cell-mediated immune responses. These finding have major implications for future trials aiming to eradicate the HIV-1 reservoir.

One proposed way of curing HIV is to activate virus transcription and kill latently infected cells while the presence of antiretroviral therapy prevents spreading the infection. Induction of global T cell activation by mitogenic or other potent activators effectively reverses HIV-1 from latency ex vivo, but such compounds are generally too toxic for clinical use. Therefore, investigating the capacity of small molecule latency reversing agents to induce production of virus without causing global T cell activation has been a top research priority for scientists in recent years. In the present clinical trial, we demonstrate that significant viral reactivation can be safely induced using the depsipeptide romidepsin (HDAC inhibitor) in long-term suppressed HIV-1 individuals on antiretroviral therapy. Following each romidepsin infusion, we observed clear increases in lymphocyte H3 acetylation, HIV-1 transcription, and plasma HIV-1 RNA. Importantly, this reversal of HIV-1 latency could be measured using standard clinical assays for detection of plasma HIV-1 RNA. Furthermore, romidepsin did not alter the proportion of HIV-specific T cells or inhibit T cell cytokine production which is critically important for future trials combining HDAC inhibitors with interventions (e.g. therapeutic HIV-1 vaccination) designed to enhance killing of latently infected cells.

Manipulation of the host protein acetylation network by human immunodeficiency virus type 1

Over the past 15 years, protein acetylation has emerged as a globally important post-translational modification that fine-tunes major cellular processes in many life forms. This dynamic regulatory system is critical both for complex eukaryotic cells and for the viruses that infect them. HIV-1 accesses the host acetylation network by interacting with several key enzymes, thereby promoting infection at multiple steps during the viral life cycle. Inhibitors of host histone deacetylases and bromodomain-containing proteins are now being pursued as therapeutic strategies to enhance current antiretroviral treatment. As more acetylation-targeting compounds are reaching clinical trials, it is time to review the role of reversible protein acetylation in HIV-infected CD4(+) T cells.

Changes in the Peripheral Blood Gene Expression Profile Induced by 3 Months of Valproate Treatment in Patients with Newly Diagnosed Epilepsy

Valproic acid (VPA) is a widely used antiepileptic drug with a broad range of effects and broad clinical efficacy. As a well-known histone deacetylase (HDAC) inhibitor, VPA regulates epigenetic programming by altering the expression of many genes. The aim of study was to analyze differences in gene expression profiles before and after the start of VPA treatment in patients with newly diagnosed epilepsy. RNA sequencing was used to compare whole-genome gene expression patterns of peripheral blood from nine patients with epilepsy before and 3 months after the start of treatment with VPA. Of the 23,099 analyzed genes, only 11 showed statistically significant differential expression with false discovery rate-adjusted p-values below 0.1. Functional annotation and network analyses showed activation of only one genetic network (enrichment score = 30), which included genes for cardiovascular system development and function, cell morphology, and hematological system development and function. The finding of such a small number of differently expressed genes between before and after the start of treatment suggests a lack of HDAC inhibition in these patients, which could be explained by the relatively low doses of VPA that were used. In conclusion, VPA at standard therapeutic dosages modulates the expression of a small number of genes. Therefore, to minimize the potential side effects of HDAC inhibition, it is recommended that the lowest effective dose of VPA be used for treating epilepsy.

HDAC inhibitor-dependent transcriptome and memory reinstatement in cognitive decline models

Aging and increased amyloid burden are major risk factors for cognitive diseases such as Alzheimer's disease (AD). Effective therapies for these diseases are lacking. Here, we evaluated mouse models of age-associated memory impairment and amyloid deposition to study transcriptome and cell type-specific epigenome plasticity in the brain and peripheral organs. We determined that aging and amyloid pathology are associated with inflammation and impaired synaptic function in the hippocampal CA1 region as the result of epigenetic-dependent alterations in gene expression. In both amyloid and aging models, inflammation was associated with increased gene expression linked to a subset of transcription factors, while plasticity gene deregulation was differentially mediated. Amyloid pathology impaired histone acetylation and decreased expression of plasticity genes, while aging altered H4K12 acetylation-linked differential splicing at the intron-exon junction in neurons, but not nonneuronal cells. Furthermore, oral administration of the clinically approved histone deacetylase inhibitor vorinostat not only restored spatial memory, but also exerted antiinflammatory action and reinstated epigenetic balance and transcriptional homeostasis at the level of gene expression and exon usage. This study provides a systems-level investigation of transcriptome plasticity in the hippocampal CA1 region in aging and AD models and suggests that histone deacetylase inhibitors should be further explored as a cost-effective therapeutic strategy against age-associated cognitive decline.

Inhibition of Histone Deacetylase Activity Aggravates Coxsackievirus B3-Induced Myocarditis by Promoting Viral Replication and Myocardial Apoptosis

Viral myocarditis, which is most prevalently caused by coxsackievirus B3 (CVB3), is a serious clinical condition characterized by excessive myocardial inflammation. Recent studies suggest that regulation of protein acetylation levels by inhibiting histone deacetylase (HDAC) activity modulates inflammatory response and shows promise as a therapy for several inflammatory diseases. However, the role of HDAC activity in viral myocarditis is still not fully understood. Here, we aim to investigate the role of HDAC activity in viral myocarditis and its underlying mechanism. CVB3-infected BALB/c mice were treated with the HDAC inhibitor (HDACI) suberoylanilide hydroxamic acid (SAHA) or trichostatin A (TSA). We found inhibition of HDAC activity aggravated rather than ameliorated the severity of CVB3-induced myocarditis, which was contrary to our expectations. The aggravated myocarditis by HDACI treatment seemed not to be caused by an elevated inflammatory response but by the increased CVB3 replication. Further, it was revealed that the increased CVB3 replication was closely associated with the HDACI-enhanced autophagosome formation. Inhibition of autophagosome formation by wortmannin or ATG5 short hairpin RNA dramatically suppressed the HDACI-increased CVB3 replication. The increased viral replication subsequently elevated CVB3-induced myocardial apoptosis. Conversely, inhibition of CVB3 replication and ensuing myocardial apoptosis by the antiviral drug ribavirin significantly reversed the HDACI-aggravated viral myocarditis. In conclusion, we elucidate that the inhibition of HDAC activity increases CVB3 replication and ensuing myocardial apoptosis, resulting in aggravated viral myocarditis. Possible adverse consequences of administering HDACI should be considered in patients infected (or coinfected) with CVB3.

IMPORTANCE Viral myocarditis, which is most prevalently caused by CVB3, is characterized by excessive myocardial inflammation. Inhibition of HDAC activity was originally identified as a powerful anti-cancer therapeutic strategy and was recently found to be implicated in the regulation of inflammatory response. HDACI has been demonstrated to be efficacious in animal models of several inflammatory diseases. Thus, we hypothesize that inhibition of HDAC activity also protects against CVB3-induced viral myocarditis. Surprisingly, we found inhibition of HDAC activity enhanced myocardial autophagosome formation, which led to the elevated CVB3 viral replication and ensuing increased myocardial apoptosis. Viral myocarditis was eventually aggravated rather than ameliorated by HDAC inhibition. In conclusion, we elucidate the role of HDAC activity in viral myocarditis. Moreover, given the importance of HDACI in preclinical and clinical treatments, the possible unfavorable effect of HDACI should be carefully evaluated in patients infected with viruses, including CVB3.

Contribution of metabolic reprogramming to macrophage plasticity and function

Macrophages display a spectrum of functional activation phenotypes depending on the composition of the microenvironment they reside in, including type of tissue/organ and character of injurious challenge they are exposed to. Our understanding of how macrophage plasticity is regulated by the local microenvironment is still limited. Here we review and discuss the recent literature regarding the contribution of cellular metabolic pathways to the ability of the macrophage to sense the microenvironment and to alter its function. We propose that distinct alterations in the microenvironment induce a spectrum of inducible and reversible metabolic programs that might form the basis of the inducible and reversible spectrum of functional macrophage activation/polarization phenotypes. We highlight that metabolic pathways in the bidirectional communication between macrophages and stromals cells are an important component of chronic inflammatory conditions. Recent work demonstrates that inflammatory macrophage activation is tightly associated with metabolic reprogramming to aerobic glycolysis, an altered TCA cycle, and reduced mitochondrial respiration. We review cytosolic and mitochondrial mechanisms that promote initiation and maintenance of macrophage activation as they relate to increased aerobic glycolysis and highlight potential pathways through which anti-inflammatory IL-10 could promote macrophage deactivation. Finally, we propose that in addition to their role in energy generation and regulation of apoptosis, mitochondria reprogram their metabolism to also participate in regulating macrophage activation and plasticity.

Tumor necrosis factor-related apoptosis-inducing ligand induces the expression of proinflammatory cytokines in macrophages and re-educates tumor-associated macrophages to an antitumor phenotype

This study reveals that tumor necrosis factor–related apoptosis-inducing ligand (TRAIL) induces expression of IL-1β, IL-6, and tumor necrosis factor α in macrophages, especially in tumor-associated macrophages (TAMs). TRAIL re-educates TAMs to an M1-like phenotype and induces their cytotoxicity to tumor cells. This study provides new evidence for TRAIL in immune regulation of macrophages and sheds light on TRAIL-based antitumor therapy in human patients.

Tumor necrosis factor–related apoptosis-inducing ligand (TRAIL) is a promising candidate for cancer therapy, because it can induce apoptosis in various tumor cells but not in most normal cells. Although it is well known that TRAIL and its receptors are expressed in many types of normal cells, including immune cells, their immunological effects and regulatory mechanisms are still obscure. In the present study, we demonstrated that TRAIL affected the activity of NF-κB (nuclear factor-κB) and the expression of its downstream proinflammatory cytokines IL-1β (interleukin-1β), IL-6, and tumor necrosis factor α in macrophages. TRAIL also induced microRNA-146a (miR-146a) expression in an NF-κB–dependent manner. As a result, miR-146a was involved as a negative-feedback regulator in the down-regulation of proinflammatory cytokine expression. In addition, the suppression of histone deacetylase (HDAC) activities by trichostatin A improved miR-146a expression due to the up-regulation of the DNA-binding activity of NF-κB at the miR-146a promoter in TRAIL-induced macrophages, suggesting that histone acetylation was involved in the suppression of miR-146a expression. Further investigation revealed that the HDAC subtype HDAC1 directly regulated the expression of miR-146a in TRAIL-stimulated macrophages. Finally, the TRAIL-sensitive human non small cell lung carcinoma cell line NCI-H460 was used to elucidate the physiological significance of TRAIL with respect to tumor-associated macrophages (TAMs). We demonstrated that TRAIL re-educated TAMs to an M1-like phenotype and induced cytotoxic effects in the tumor cells. These data provide new evidence for TRAIL in the immune regulation of macrophages and may shed light on TRAIL-based antitumor therapy in human patients.

Valproic Acid Ameliorates Graft-versus-Host Disease by Downregulating Th1 and Th17 Cells

Graft-versus-host disease (GVHD) is the major complication after allogeneic bone marrow transplantation. Valproic acid (VPA) was described as a histone deacetylase inhibitor that had anti-inflammatory effects and reduced the production of proinflammatory cytokines in experimental autoimmune disease models. Using well-characterized mouse models of MHC-mismatched transplantation, we studied the effects of VPA on GVHD severity and graft-versus-leukemia (GVL) activity. Administration of VPA significantly attenuated the clinical severity of GVHD, the histopathology of GVHD-involved organs, and the overall mortality from GVHD. VPA downregulated Th1 and Th17 cell responses and cytokine production in vitro and in vivo, whereas its effect on GVHD was regulatory T cell independent. The effect of VPA was related to its ability to directly reduce the activity of Akt, an important regulator of T cell immune responses. Importantly, when mice received lethal doses of host-type acute leukemia cells, administration of VPA did not impair GVL activity and resulted in significantly improved leukemia-free survival. These findings reveal a unique role for VPA as a histone deacetylase inhibitor in reducing the donor CD4(+) T cells that contribute to GVHD, which may provide a strategy to reduce GVHD while preserving the GVL effect.

Epigenetic regulation of CC-chemokine ligand 2 in nonresolving inflammation

Inflammation mediated by the crosstalk between leukocytes and resident tissue cells is crucial for the maintenance of homeostasis. Because chemokine ligands and receptors, which recruit a variety of leukocytes, are widely distributed among tissues, it is important to understand the mechanisms regulating inflammatory disease. Chemokines such as CC-chemokine ligand 2 (CCL2) amplify and maintain inflammation through chemokine-cytokine networks after the recruitment of circulating leukocytes. Chemokine-dependent nonresolving inflammation occurs in the peripheral and central nervous systems, and underlies several intractable diseases, including cancer and neuropathic pain. The chronic upregulation of chemokines is often mediated by epigenetic mechanisms consisting of DNA methylation, histone modification, and nucleosome positioning. In particular, histone acetylation and methylation have been shown to play important roles in the upregulation of chemokine expression. In addition to CCL2, several other chemokines strongly contribute to neuropathic pain through epigenetic induction. Consequently, targeting epigenetic changes may have therapeutic potential for nonresolving inflammatory diseases such as neuropathic pain. Further research into the epigenetics of inflammatory diseases should promote the development of novel and effective treatment strategies for intractable inflammatory diseases.

New Insights into the Role of Histone Deacetylases as Coactivators of Inflammatory Gene Expression

SIGNIFICANCE

The expression and/or activity of histone deacetylases (HDACs) can be regulated by a variety of environmental conditions, including inflammation and oxidative stress. These events result in diminished or exaggerated protein acetylation, both of which can be causative for many ailments. While the anti-inflammatory activity of HDAC inhibitors (HDACis) is well known, recent studies started unraveling details of the molecular mechanisms underlying the pro-inflammatory function of HDACs.

RECENT ADVANCES

Recent evidence shows that HDACs are found in association with transcribed regions and ensure proper transcription by maintaining acetylation homeostasis. We also discuss current insights in the molecular mechanisms mediating acetylation-dependent inhibition of pro-inflammatory transcription factors of the NF-κB, HIF-1, IRF, and STAT families.

CRITICAL ISSUES

The high number of acetylations and the complexity of the regulatory consequences make it difficult to assign biological effects directly to a single acetylation event. The vast majority of acetylated proteins are nonhistone proteins, and it remains to be shown whether the therapeutic effects of HDACis are attributable to altered histone acetylation.

FUTURE DIRECTIONS

In the traditional view, only exaggerated acetylation is harmful and causative for diseases. Recent data show the relevance of acetylation homeostasis and suggest that both diminished and inflated acetylation can enable the development of ailments. Since acetylation of nonhistone proteins is essential for the induction of a substantial part of the inflammatory gene expression program, HDACis are more than "epigenetic drugs." The identification of substrates for individual HDACs will be the prerequisite for the adequate use of highly specific HDACis.

New approaches to manipulating the epigenome

Cellular processes that control transcription of genetic information are critical for cellular function, and are often implicated in psychiatric and neurological disease states. Among the most critical of these processes are epigenetic mechanisms, which serve to link the cellular environment with genomic material. Until recently our understanding of epigenetic mechanisms has been limited by the lack of tools that can selectively manipulate the epigenome with genetic, cellular, and temporal precision, which in turn diminishes the potential impact of epigenetic processes as therapeutic targets. This review highlights an emerging suite of tools that enable robust yet selective interrogation of the epigenome. In addition to allowing site-specific epigenetic editing, these tools can be paired with optogenetic approaches to provide temporal control over epigenetic processes, allowing unparalleled insight into the function of these mechanisms. This improved control promises to revolutionize our understanding of epigenetic modifications in human health and disease states.

Epigenetic Aspects of Systemic Lupus Erythematosus

Autoimmune diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis, multiple sclerosis, autoimmune hepatitis, and inflammatory bowel disease have complex pathogeneses and the courses of events leading to these diseases are not well understood. The immune surveillance is a delicate balance between self and foreign as well as between tolerance and immune response. Exposure to certain environmental factors may impair this equilibrium, leading to autoimmune diseases, cancer, and the so-called “lifestyle diseases” such as atherosclerosis, heart attack, stroke, and obesity, among others. These external stimuli may also alter the epigenetic status quo and may trigger autoimmune diseases such as SLE in genetically susceptible individuals. This review aims to highlight the role of epigenetic (dys-)regulation in the pathogenesis of SLE.

Targeting macrophage Histone deacetylase 3 stabilizes atherosclerotic lesions

Macrophages are key immune cells found in atherosclerotic plaques and critically shape atherosclerotic disease development. Targeting the functional repertoire of macrophages may hold novel approaches for future atherosclerosis management. Here, we describe a previously unrecognized role of the epigenomic enzyme Histone deacetylase 3 (Hdac3) in regulating the atherosclerotic phenotype of macrophages. Using conditional knockout mice, we found that myeloid Hdac3 deficiency promotes collagen deposition in atherosclerotic lesions and thus induces a stable plaque phenotype. Also, macrophages presented a switch to anti-inflammatory wound healing characteristics and showed improved lipid handling. The pro-fibrotic phenotype was directly linked to epigenetic regulation of the Tgfb1 locus upon Hdac3 deletion, driving smooth muscle cells to increased collagen production. Moreover, in humans, HDAC3 was the sole Hdac upregulated in ruptured atherosclerotic lesions, Hdac3 associated with inflammatory macrophages, and HDAC3 expression inversely correlated with pro-fibrotic TGFB1 expression. Collectively, we show that targeting the macrophage epigenome can improve atherosclerosis outcome and we identify Hdac3 as a potential novel therapeutic target in cardiovascular disease.

Epigenetic pathways in macrophages emerge as novel targets in atherosclerosis

Atherosclerosis is a lipid-driven chronic inflammatory disorder. Monocytes and macrophages are key immune cells in the development of disease and clinical outcome. It is becoming increasingly clear that epigenetic pathways govern many aspects of monocyte and macrophage differentiation and activation. The dynamic regulation of epigenetic patterns provides opportunities to alter disease-associated epigenetic states. Therefore, pharmaceutical companies have embraced the targeting of epigenetic processes as new approaches for interventions. Particularly histone deacetylase (Hdac) inhibitors and DNA-methyltransferase inhibitors have long received attention and several of them have been approved for clinical use in relation to hematological malignancies. The key focus is still on oncology, but Alzheimer's disease, Huntington's disease and inflammatory disorders are coming in focus as well. These developments raise opportunities for the epigenetic targeting in cardiovascular disease (CVD). In this review we discuss the epigenetic regulation of the inflammatory pathways in relation to atherosclerosis with a specific attention to monocyte- and macrophage-related processes. What are the opportunities for future therapy of atherosclerosis by epigenetic interventions?

Inhibition of histone deacetylase 6 improves long-term survival in a lethal septic model

BACKGROUND

We recently demonstrated that suberoylanilide hydroxamic acid, a broad-spectrum histone deacetylase (HDAC) inhibitor that inhibits HDACs 1, 2, 3, and 6, improves survival in a mouse model of cecal ligation and puncture (CLP)-induced lethal sepsis. The current study was undertaken to determine the effect of selective inhibition of HDAC isoform on survival, key cytokine production, organ injury, bacteria clearance, and cell apoptosis.

METHODS

In Experiment 1, C57BL/6J mice were subjected to CLP and, 1 hour later, given intraperitoneal injections of (1) Tubastatin A (inhibitor of HDAC6) dissolved in dimethyl sulfoxide (DMSO), (2) MS-275 (inhibitor of HDACs 1, 2, and 3) in DMSO, and (3) DMSO only. Survival was monitored for 10 days. In Experiment 2, 1 hour after CLP, animals were treated with DMSO vehicle or Tubastatin A. Sham-operated animals served as control. Peritoneal fluid and blood samples were collected for measurement of cytokines at 24 hours or 48 hours. Blood at 48 hours was also used to determine bacteria load. Liver was harvested to evaluate acute liver injury. In Experiment 3, Primary splenocytes were used to assess cytokine responses and phagocytosis. Macrophages were cultured and harvested 3 hours and 6 hours after lipopolysaccharide stimulation in the absence or presence of Tubastatin A to analyze cell apoptosis.

RESULTS

Animals treated with Tubastatin A, but not MS-275, displayed a significant improvement in survival. Moreover, Tubastatin A significantly inhibited cytokine production in peritoneal fluid and plasma as well as in supernatant from splenocytes stimulated with lipopolysaccharide. Tubastatin A significantly attenuated acute liver injury, increased blood bacteria clearance and splenocyte phagocytosis, and decreased macrophage apoptosis.

CONCLUSION

HDAC6 inhibition significantly improves survival, reduces "cytokine storm," attenuates acute livery injury, increases bacteria clearance and immune cell phagocytosis, and inhibits macrophage apoptosis in a lethal mouse CLP model.

Sulforaphane epigenetically regulates innate immune responses of porcine monocyte-derived dendritic cells induced with lipopolysaccharide

Histone acetylation, regulated by histone deacetylases (HDACs) is a key epigenetic mechanism controlling gene expressions. Although dendritic cells (DCs) are playing pivotal roles in host immune responses, the effect of epigenetic modulation of DCs immune responses remains unknown. Sulforaphane (SFN) as a HDAC inhibitor has anti-inflammatory properties, which is used to investigate the epigenetic regulation of LPS-induced immune gene and HDAC family gene expressions in porcine monocyte-derived dendritic cells (moDCs). SFN was found to inhibit the lipopolysaccharide LPS induced HDAC6, HDAC10 and DNA methyltransferase (DNMT3a) gene expression, whereas up-regulated the expression of DNMT1 gene. Additionally, SFN was observed to inhibit the global HDAC activity, and suppressed moDCs differentiation from immature to mature DCs through down-regulating the CD40, CD80 and CD86 expression and led further to enhanced phagocytosis of moDCs. The SFN pre-treated of moDCs directly altered the LPS-induced TLR4 and MD2 gene expression and dynamically regulated the TLR4-induced activity of transcription factor NF-κB and TBP. SFN showed a protective role in LPS induced cell apoptosis through suppressing the IRF6 and TGF-ß1 production. SFN impaired the pro-inflammatory cytokine TNF-α and IL-1ß secretion into the cell culture supernatants that were induced in moDCs by LPS stimulation, whereas SFN increased the cellular-resident TNF-α accumulation. This study demonstrates that through the epigenetic mechanism the HDAC inhibitor SFN could modulate the LPS induced innate immune responses of porcine moDCs.

The epigenetic memory of monocytes and macrophages as a novel drug target in atherosclerosis

PURPOSE

Atherosclerosis is characterized by a persistent inflammation of the arterial wall. Monocyte-derived macrophages are the most abundant immune cells in atherosclerotic plaques. After stimulation, monocytes can adopt a long-term proinflammatory phenotype. This nonspecific memory of innate immune cells is mediated by epigenetic reprogramming and has recently been termed "trained innate immunity." The goal of this study was to describe the potential role of trained immunity in the development of atherosclerosis and to discuss the potential clinical implications of this concept.

METHODS

We performed a comprehensive literature search (PubMed) on the role of epigenetic programming of histones, and of trained immunity in particular, in atherogenesis.

FINDINGS

In vitro studies demonstrate that modified LDL particles can induce a long-term proinflammatory phenotype in monocytes/macrophages by epigenetic reprogramming at the level of histone methylation. This scenario is associated with increased production of proatherogenic cytokines and chemokines and increased formation of foam cells.

IMPLICATIONS

Preclinical evidence suggests that trained innate immunity may contribute to vascular wall inflammation in patients with risk factors for atherosclerosis. Epigenetic reprogramming is regulated by enzymes that are amenable to pharmacologic modulation. Therefore, this mechanism could be used to develop novel pharmacologic targets for the prevention or treatment of atherosclerotic vascular disease.

Histone deacetylases: structural determinants of inhibitor selectivity

Histone deacetylases (HDACs) are epigenetic targets with an important role in cancer, neurodegeneration, inflammation, and metabolic disorders. Although clinically effective HDAC inhibitors have been developed, the design of inhibitors with the desired isoform(s) selectivity remains a challenge. Selective inhibitors could help clarify the function of each isoform, and provide therapeutic agents having potentially fewer adverse effects. Crystal structures of several HDACs have been reported, enabling structure-based drug design and providing important information to understand enzyme function. Here, we provide a comprehensive review of the structural information available on HDACs, discussing both conserved and isoform-specific structural and mechanistic features. We focus on distinctive aspects that help rationalize inhibitor selectivity, and provide structure-based recommendations for achieving the desired selectivity.

Suppression of monosodium urate crystal-induced cytokine production by butyrate is mediated by the inhibition of class I histone deacetylases

OBJECTIVES

Acute gouty arthritis is caused by endogenously formed monosodium urate (MSU) crystals, which are potent activators of the NLRP3 inflammasome. However, to induce the release of active interleukin (IL)-1β, an additional stimulus is needed. Saturated long-chain free fatty acids (FFAs) can provide such a signal and stimulate transcription of pro-IL-1β. In contrast, the short-chain fatty acid butyrate possesses anti-inflammatory effects. One of the mechanisms involved is inhibition of histone deacetylases (HDACs). Here, we explored the effects of butyrate on MSU+FFA-induced cytokine production and its inhibition of specific HDACs.

METHODS

Freshly isolated peripheral blood mononuclear cells (PBMCs) from healthy donors were stimulated with MSU and palmitic acid (C16.0) in the presence or absence of butyrate or a synthetic HDAC inhibitor. Cytokine responses were measured with ELISA and quantitative PCR. HDAC activity was measured with fluorimetric assays.

RESULTS

Butyrate decreased C16.0+MSU-induced production of IL-1β, IL-6, IL-8 and IL-1β mRNA in PBMCs from healthy donors. Similar results were obtained in PBMCs isolated from patients with gout. Butyrate specifically inhibited class I HDACs. The HDAC inhibitor, panobinostat and the potent HDAC inhibitor, ITF-B, also decreased ex vivo C16.0+MSU-induced IL-1β production.

CONCLUSIONS

In agreement with the reported low inhibitory potency of butyrate, a high concentration was needed for cytokine suppression, whereas synthetic HDAC inhibitors showed potent anti-inflammatory effects at nanomolar concentrations. These novel HDAC inhibitors could be effective in the treatment of acute gout. Moreover, the use of specific HDAC inhibitors could even improve the efficacy and reduce any potential adverse effects.

The histone deacetylase Hdac1 regulates inflammatory signalling in intestinal epithelial cells

Background

It has recently been found that both nuclear epithelial-expressed histone deacetylases Hdac1 and Hdac2 are important to insure intestinal homeostasis and control the mucosal inflammatory response in vivo. In addition, HDAC inhibitors modulate epithelial cell inflammatory responses in cancer cells. However, little is known of the specific role of different HDAC, notably Hdac1, in the regulation of inflammatory gene expression in intestinal epithelial cells (IEC).

Methods

We investigated the role of Hdac1 in non-transformed IEC-6 rat cells infected with lentiviral vectors expressing specific Hdac1 shRNAs, to suppress Hdac1 expression. Proliferation was assessed by cell counting. Deacetylase activity was measured with a colorimetric HDAC assay. Cells were treated with IL-1β and/or the JQ1 bromodomain acetyl-binding inhibitor. Nuclear protein levels of Hdac1, Hdac2, phosphorylated or unphosphorylated NF-κB p65 or C/EBPβ, and NF-κB p50 and actin were determined by Western blot. Chemokine and acute phase protein expression was assessed by semi-quantitative RT-PCR analysis. Secreted cytokine and chemokine levels were assessed with a protein array. Chromatin immunoprecipitation experiments were done to assess RNA polymerase II recruitment.

Results

Reduced Hdac1 protein levels led to Hdac2 protein increases and decreased cell proliferation. Hdac1 depletion prolonged nuclear IL-1β-induced phosphorylation of NF-κB p65 protein on Ser536 as opposed to total p65, and of C/EBPβ on Ser105. In addition, semi-quantitative RT-PCR analysis revealed three patterns of expression caused by Hdac1 depletion, namely increased basal and IL-1β-stimulated levels (Hp, Kng1), increased IL-1β-stimulated levels (Cxcl2) and decreased basal levels with normal IL-1β induction levels (Ccl2, Ccl5, Cxcl1, C3). Secreted cytokine and chemokine measurements confirmed that Hdac1 played roles both as an IL-1β signalling repressor and activator. Hdac1 depletion did not alter the JQ1 dependent inhibition of basal and IL-1β-induced inflammatory gene expression. Hdac1 depletion led to decreased basal levels of RNA polymerase II enrichment on the Ccl2 promoter, as opposed to the Gapdh promoter, correlating with decreased Ccl2 basal mRNA expression.

Conclusions

Hdac1 is a major nuclear HDAC controlling IL-1β-dependent inflammatory response in IEC, notably by regulating gene-specific transcriptional responses. Hdac1 may be important in restricting basal and inflammatory-induced gene levels to defined ranges of expression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12950-014-0043-2) contains supplementary material, which is available to authorized users.

Deficiency of the stroke relevant HDAC9 gene attenuates atherosclerosis in accord with allele-specific effects at 7p21.1

BACKGROUND AND PURPOSE

Recent genome-wide association studies identified the histone deacetylase 9 (HDAC9) gene region as a major risk locus for large-vessel stroke and coronary artery disease. However, the mechanisms linking variants at this locus to vascular risk are poorly understood. In this study, we investigated the candidacy and directionality of HDAC9 in atherosclerosis and analyzed associations between risk alleles at 7p21.1 and plaque characteristics.

METHODS

Allele-dependent expression of HDAC9 was analyzed in human peripheral blood mononuclear cells of healthy donors. Effects of HDAC9 deficiency on atherosclerotic plaques were investigated in 18- and 28-week-old ApoE(-/-) mice by histology and immunohistochemistry. We further performed detailed plaque phenotyping and genotyping of rs2107595, the lead single-nucleotide polymorphism for large-vessel stroke, in carotid endarterectomy samples of 1858 subjects from the Athero-Express study.

RESULTS

Gene expression studies in peripheral blood mononuclear cells revealed increased mRNA levels of HDAC9 but not of neighboring genes (TWIST1/FERD3L) in risk allele carriers of rs2107595. Compared with HDAC9(+/+)ApoE(-/-) mice, HDAC9(-/-)ApoE(-/-) mice exhibited markedly reduced lesion sizes throughout atherosclerotic aortas and significantly less advanced lesions. The proportion of Mac3-positive macrophages was higher in plaques from HDAC9(-/-)ApoE(-/-) mice, but this was largely because of a lower proportion of advanced lesions. Analysis of human atherosclerotic plaques revealed no association between rs2107595 and specific plaque characteristics.

CONCLUSIONS

Our results suggest that HDAC9 represents the disease-relevant gene at the stroke and coronary artery disease risk locus on 7p21.1, and that risk alleles in this region mediate their effects through increased HDAC9 expression. Targeted inhibition of HDAC9 might be a viable strategy to prevent atherosclerosis.

HDAC1 controls CD8+ T cell homeostasis and antiviral response

Reversible lysine acetylation plays an important role in the regulation of T cell responses. HDAC1 has been shown to control peripheral T helper cells, however the role of HDAC1 in CD8⁺ T cell function remains elusive. By using conditional gene targeting approaches, we show that LckCre-mediated deletion of HDAC1 led to reduced numbers of thymocytes as well as peripheral T cells, and to an increased fraction of CD8⁺CD4^– cells within the CD3/TCRβ^lo population, indicating that HDAC1 is essential for the efficient progression of immature CD8⁺CD4^– cells to the DP stage. Moreover, CD44^hi effector CD8⁺ T cells were enhanced in mice with a T cell-specific deletion of HDAC1 under homeostatic conditions and HDAC1-deficient CD44^hi CD8⁺ T cells produced more IFNγ upon ex vivo PMA/ionomycin stimulation in comparison to wild-type cells. Naïve (CD44^l°CD62L⁺) HDAC1-null CD8⁺ T cells displayed a normal proliferative response, produced similar amounts of IL-2 and TNFα, slightly enhanced amounts of IFNγ, and their in vivo cytotoxicity was normal in the absence of HDAC1. However, T cell-specific loss of HDAC1 led to a reduced anti-viral CD8⁺ T cell response upon LCMV infection and impaired expansion of virus-specific CD8⁺ T cells. Taken together, our data indicate that HDAC1 is required for the efficient generation of thymocytes and peripheral T cells, for proper CD8⁺ T cell homeostasis and for an efficient in vivo expansion and activation of CD8⁺ T cells in response to LCMV infection.

Creating a prosurvival phenotype through a histone deacetylase inhibitor in a lethal two-hit model

OBJECTIVES

Hemorrhagic shock (HS) can initiate an exaggerated systemic inflammatory response and multiple organ failure, especially if followed by a subsequent inflammatory insult ("second hit"). We have recently shown that histone deacetylase inhibitors can improve survival in rodent models of HS or septic shock, individually. In the present study, we examined whether valproic acid (VPA), a histone deacetylase inhibitor, could prolong survival in a rodent "two-hit" model: HS followed by septic shock from cecal ligation and puncture (CLP).

METHODS

Male Sprague-Dawley rats (250-300 g) were subjected to sublethal HS (40% blood loss) and then randomly divided into two groups (n = 7/group): VPA and control. The VPA group was treated intraperitoneally with VPA (300 mg/kg in normal saline [NS], volume = 750 μL/kg). The control group was injected with 750 μL/kg NS. After 24 h, all rats received CLP followed immediately by injection of the same dose of VPA (VPA group) or NS (vehicle group). Survival was monitored for 10 days. In a parallel study, serum and peritoneal irrigation fluid from VPA- or vehicle-treated rats were collected 3, 6, and 24 h after CLP, and enzyme-linked immunosorbent assay was performed to analyze myeloperoxidase activity and determine tumor necrosis factor α and interleukin 6 concentrations. Hematoxylin-eosin staining of lungs at 24-h time point was performed to investigate the grade of acute lung injury.

RESULTS

Rats treated with VPA (300 mg/kg) showed significantly higher survival rates (85.7%) compared with the control (14.3%). Moreover, VPA significantly suppressed myeloperoxidase activity (marker of neutrophil-mediated oxidative damage) and inhibited levels of proinflammatory cytokine tumor necrosis factor α and interleukin 6 in the serum and peritoneal cavity. Meanwhile, the severity of acute lung injury was significantly reduced in VPA-treated animals.

CONCLUSIONS

We have demonstrated that VPA treatment improves survival and attenuates inflammation in a rodent two-hit model.

Macrophage polarization: the epigenetic point of view

PURPOSE OF REVIEW

The first functions of macrophages to be identified by Metchnikoff were phagocytosis and microbial killing. Although these are important features, macrophages are functionally very complex and involved in virtually all aspects of life, from immunity and host defense, to homeostasis, tissue repair and development. To accommodate for this, macrophages adopt a plethora of polarization states. Understanding their transcriptional regulation and phenotypic heterogeneity is vital because macrophages are critical in many diseases and have emerged as attractive targets for therapy. Here, we review how epigenetic mechanisms control macrophage polarization.

RECENT FINDINGS

It is becoming increasingly clear that chromatin remodelling governs multiple aspects of macrophage differentiation, activation and polarization. In recent years, independent research groups highlighted the importance of epigenetic mechanisms to regulate enhancer activity. Moreover, distinct histone-modifying enzymes were identified that control macrophage activation and polarization.

SUMMARY

We recap epigenetic features of distinct enhancers and describe the role of Jumonji domain-containing protein 3 (Jmjd3) and Hdac3 as crucial mediators of macrophage differentiation, activation and polarization. We hypothesize that epigenetic enzymes could serve as the link between environment, cellular metabolism and macrophage phenotype. To conclude, we propose epigenetic intervention as a future pharmacological target to modulate macrophage polarization and to treat inflammatory diseases such as atherosclerosis.

Histone deacetylases and their inhibitors in cancer, neurological diseases and immune disorders

Epigenetic aberrations, which are recognized as key drivers of several human diseases, are often caused by genetic defects that result in functional deregulation of epigenetic proteins, their altered expression and/or their atypical recruitment to certain gene promoters. Importantly, epigenetic changes are reversible, and epigenetic enzymes and regulatory proteins can be targeted using small molecules. This Review discusses the role of altered expression and/or function of one class of epigenetic regulators--histone deacetylases (HDACs)--and their role in cancer, neurological diseases and immune disorders. We highlight the development of small-molecule HDAC inhibitors and their use in the laboratory, in preclinical models and in the clinic.

Novel mechanism of attenuation of LPS-induced NF-κB activation by the heat shock protein 90 inhibitor, 17-N-allylamino-17-demethoxygeldanamycin, in human lung microvascular endothelial cells

Heat shock protein (hsp) 90 inhibition attenuates NF-κB activation and blocks inflammation. However, the precise mechanism of NF-κB regulation by hsp90 in the endothelium is not clear. We investigated the mechanisms of hsp90 inhibition by 17-N-allylamino-17-demethoxygeldanamycin (17-AAG) on NF-κB activation by LPS in primary human lung microvascular endothelial cells. Transcriptional activation of NF-κB was measured by luciferase reporter assay, gene expression by real-time RT-PCR, DNA binding of transcription factors by chromatin immunoprecipitation assay, protein-protein interaction by coimmunoprecipitation/immunoblotting, histone deacetylase (HDAC)/histone acetyltransferase enzyme activity by fluorometry, and nucleosome eviction by partial microccocal DNase digestion. In human lung microvascular endothelial cells, 17-AAG-induced degradation of IKBα was accomplished regardless of the phosphorylation/ubiquitination state of the protein. Hence, 17-AAG did not block LPS-induced NF-κB nuclear translocation and DNA binding activity. Instead, 17-AAG blocked the recruitment of the coactivator, cAMP response element binding protein binding protein, and prevented the assembly of a transcriptionally competent RNA polymerase II complex at the κB elements of the IKBα (an NF-κB-responsive gene) promoter. The effect of LPS on IKBα mRNA expression was associated with rapid deacetylation of histone-H3(Lys9) and a dramatic down-regulation of core histone H3 binding. Even though treatment with an HDAC inhibitor produced the same effect as hsp90 inhibition, the effect of 17-AAG was independent of HDAC. We conclude that hsp90 inhibition attenuates NF-κB transcriptional activation by preventing coactivator recruitment and nucleosome eviction from the target promoter in human lung endothelial cells.

Effect of histone deacetylase inhibitor JNJ-26481585 in pain

Recent studies have shown that histone deacetylase (HDAC) inhibitors can alleviate inflammatory and neuropathic pain. We investigated the effects of JNJ-26481585, a pan-HDAC inhibitor on basal mechanical sensitivity. Unlike previous reports for HDAC inhibitors, JNJ-26481585 induced mechanical hypersensitivity in mice. This effect was reversible with gabapentin. Voltage-dependent calcium channel subunit alpha-2/delta-1, one of the putative targets for gabapentin, was upregulated in the spinal cord from JNJ-26481585-treated mice. Transcriptional profiling of spinal cord from JNJ-26481585-treated mice showed significant alterations in pathways involved in axon guidance, suggesting overlap in mechanisms underlying neurotoxicity caused by other known chemotherapeutic agents. To investigate the mechanisms underlying the development of pain, RAW 264.7 mouse macrophage cells were treated with JNJ-26481585. There was a dose- and time-dependent activation of nuclear factor-kappaB and interleukin-1β increase. Thus, alterations in the axon guidance pathway, increase in voltage-dependent calcium channel alpha(2)delta-1 subunit, and the induction of proinflammatory mediators by JNJ-26481585 could all contribute to increased mechanical sensitivity. Our data indicate that the effect of HDAC inhibitors may be unique to the compound studied and highlights the potential to develop chemotherapy-induced peripheral neuropathy with the use of a pan-HDAC inhibitor for cancer treatment, and this pain may be alleviated by gabapentin.

Denbinobin upregulates miR-146a expression and attenuates IL-1β-induced upregulation of ICAM-1 and VCAM-1 expressions in osteoarthritis fibroblast-like synoviocytes

Interleukin-1β (IL-1β) upregulates intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expressions in osteoarthritis fibroblast-like synoviocytes (OA-FLS) via nuclear factor (NF)-κB-mediated mechanism; enhancement of leukocyte infiltration and upregulation of proinflammatory mediators play a crucial role in OA pathophysiology. MicroRNA (miR)-146a suppresses inflammatory responses by inhibiting NF-κB activity and target gene expression, and epigenetic mechanisms are reportedly involved in miR expression regulation. Here, we aimed to verify the inhibition of ICAM-1/VCAM-1 expression in OA-FLS on denbinobin treatment and to determine whether this inhibition was due to the miR-146a-dependent pathway. We also assessed the epigenetic regulation caused by histone acetyltransferases involved in denbinobin action. Denbinobin attenuated the upregulation of IL-1β-induced ICAM-1/VCAM-1 expression and monocyte adhesion to OA-FLS. The mechanism underlying the inhibitory effects of denbinobin involved miR-146a induction, which in turn inhibited NF-κB signaling. This is because miR-146a inhibitor abrogated the inhibitory effects of denbinobin. Furthermore, histone acetyltransferase inhibitor attenuated the denbinobin-induced upregulation of miR-146a expression and inhibited the acetylation of NF-κB-binding sites located within the miR-146a promoter region. These data suggest that an epigenetic mechanism plays a crucial role in the upregulation of miR-146a expression in response to denbinobin treatment. Our overall findings suggest that denbinobin can be used as a potent anti-inflammatory agent.

KEY MESSAGE

Denbinobin inhibited IL-1β-induced ICAM-1/VCAM-1 expression and monocyte adhesion to OA-FLS. It was due to denbinobin increased miR-146a level, which in turn inhibited NF-κB signaling. Our overall findings suggest that denbinobin can be used as a potent anti-inflammatory agent.

MS-275, a class I histone deacetylase inhibitor, protects the p53-deficient mouse against ischemic injury

The administration of pan histone deacetylase (HDAC) inhibitors reduces ischemic damage to the CNS, both in vitro and in animal models of stroke, via mechanisms which we are beginning to understand. The acetylation of p53 is regulated by Class I HDACs and, because p53 appears to play a role in ischemic pathology, the purpose of this study was to discover, using an in vitro white matter ischemia model and an in vivo cerebral ischemia model, if neuroprotection mediated by HDAC inhibition depended on p53 expression. Optic nerves were excised from wild-type and p53-deficient mice, and then subjected to oxygen-glucose deprivation in the presence and absence of a specific inhibitor of Class I HDACs (MS-275, entinostat) while compound action potentials were recorded. Furthermore, transient focal ischemia was imposed on wild-type and p53-deficient mice, which were subsequently treated with MS-275. Interestingly, and in both scenarios, the beneficial effects of MS-275 were most pronounced when p53 was absent. These results suggest that modulation of p53 activity is not responsible for MS-275-mediated neuroprotection, and further illustrate how HDAC inhibitors variably influence p53 and associated apoptotic pathways. Optic nerves from wild-type and p53-deficient mice, engineered to express cyan fluorescent protein (CFP) in neuronal mitochondria, were subjected to oxygen-glucose deprivation (OGD) in the presence and absence of a specific inhibitor of Class I histone deacetylases. The protective effect of MS-275 was evidenced by mitochondrial preservation, and this was most pronounced in the absence of p53.

CD4(+) T cell lineage integrity is controlled by the histone deacetylases HDAC1 and HDAC2

Molecular mechanisms that maintain lineage integrity of helper T cells are largely unknown. Here we show histone deacetylases 1 and 2 (HDAC1 and HDAC2) as crucial regulators of this process. Loss of HDAC1 and HDAC2 during late T cell development led to the appearance of major histocompatibility complex (MHC) class II-selected CD4(+) helper T cells that expressed CD8-lineage genes such as Cd8a and Cd8b1. HDAC1 and HDAC2-deficient T helper type 0 (TH0) and TH1 cells further upregulated CD8-lineage genes and acquired a CD8(+) effector T cell program in a manner dependent on Runx-CBFβ complexes, whereas TH2 cells repressed features of the CD8(+) lineage independently of HDAC1 and HDAC2. These results demonstrate that HDAC1 and HDAC2 maintain integrity of the CD4 lineage by repressing Runx-CBFβ complexes that otherwise induce a CD8(+) effector T cell-like program in CD4(+) T cells.

Preclinical anti-arthritic study and pharmacokinetic properties of a potent histone deacetylase inhibitor MPT0G009

The pathology of rheumatoid arthritis includes synoviocyte proliferation and inflammatory mediator expression, which may result from dysregulated epigenetic control by histone deacetylase (HDAC). Thus, HDAC inhibitors may be useful for treating inflammatory disease. This was a preclinical study of the HDAC inhibitor, MPT0G009. The IC50 values of MPT0G009 for HDAC1, 2, 3, 6 and 8 enzymatic activities were significantly lower than those for the currently marketed HDAC inhibitor suberoylanilide hydroxamic acid (SAHA; vorinostat). In addition, MPT0G009 markedly inhibited cytokine secretion and macrophage colony-stimulating factor/receptor activator of nuclear factor kappa B ligand-induced osteoclastogenesis by macrophages (50 ng/ml each). These MPT0G009 effects on cytokine secretion and osteoclast formation were reduced by the overexpression of HDAC 1 (class I HDAC) and 6 (class II HDAC) in cells, suggesting that these effects were due to the inhibition of its activity. In an in vivo rat model, oral administration of MPT0G009 (25 mg/kg) significantly inhibited paw swelling and bone destruction. Furthermore, compared with SAHA, MPT0G009 exhibited longer half-life (9.53 h for oral administration) and higher oral bioavailability (13%) in rats. These results established the preclinical anti-arthritic efficacy and pharmacokinetic parameters of MPT0G009, which may provide a new therapeutic approach for treating inflammatory arthritis.

Expression of IL-33 and its epigenetic regulation in Multiple Sclerosis

Objective

We examined the expression of IL-33 as an indicator of an innate immune response in relapsing remitting MS (RRMS) and controls. We proposed a link between the expression of IL-33 and IL-33 regulated genes to histone deacetylase (HDAC) activity and in particular HDAC3, an enzyme that plays a role in the epigenetic regulation of a number genes including those which regulate inflammation.

Methods

Using TaqMan low density arrays, flow cytometry and ELIZA, expression of IL-33, and family of innate immune response genes which regulate cytokine gene expression was examined in RRMS patients and controls.

Results

Intracellular expression of IL-33 and IL-33 regulated genes are increased in patients with RRMS. In addition, following in vitro culture with TLR agonist lipopolysaccharide (LPS), there is increased induction of both IL-33 and HDAC3 in RRMS patients over that seen in controls. Also, culture of PBMC with IL-33 led to the expression of genes which overlapped with that seen in RRMS patients suggesting that the gene expression signature seen in RRMS is likely to be driven by IL-33 mediated innate immune pathways. Expression of levels of IL-33 but not IL-1 (another gene regulated by TLR agonists) is completely inhibited by Trichostatin A (TSA) establishing a closer regulation of IL-33 but not IL-1 with HDAC.

Interpretation

These results demonstrate the over expression of innate immune genes in RRMS and offer a causal link between the epigenetic regulation by HDAC and the induction of IL-33.

Regulation of type I interferon responses

Type I interferons (IFNs) activate intracellular antimicrobial programmes and influence the development of innate and adaptive immune responses. Canonical type I IFN signalling activates the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway, leading to transcription of IFN-stimulated genes (ISGs). Host, pathogen and environmental factors regulate the responses of cells to this signalling pathway and thus calibrate host defences while limiting tissue damage and preventing autoimmunity. Here, we summarize the signalling and epigenetic mechanisms that regulate type I IFN-induced STAT activation and ISG transcription and translation. These regulatory mechanisms determine the biological outcomes of type I IFN responses and whether pathogens are cleared effectively or chronic infection or autoimmune disease ensues.

Intermittent or sustained systemic inflammation and the preterm brain

Exposure to perinatal infection and inflammation is associated with an increased risk for neonatal brain damage and developmental disabilities. In this integrated mechanism review, we discuss evidence in support of the contention that the preterm newborn is capable of intermittent or sustained systemic inflammation (ISSI), which appears to contribute more to adverse neurodevelopmental outcomes in preterm infants than does shorter duration inflammation.

Epigenetic enhancement of brain-derived neurotrophic factor signaling pathway improves cognitive impairments induced by isoflurane exposure in aged rats

Isoflurane-induced cognitive impairments are well documented in animal models; yet, the molecular mechanisms remain largely to be determined. In the present study, 22-month-old male Sprague-Dawley rats received 2 h of 1.5 % isoflurane or 100 % oxygen daily for 3 consecutive days. For the intervention study, the rats were intraperitoneally injected with 1.2 g/kg sodium butyrate 2 h before isoflurane exposure. Our data showed that repeated isoflurane exposure significantly decreased the freezing time to context and the freezing time to tone in the fear conditioning test, which was associated with upregulated histone deacetylase 2, reduced histone acetylation, and increased inflammation and apoptosis in the hippocampus, and impairments of brain-derived neurotrophic factor (BDNF)-tyrosine kinase receptor B (TrkB) and the downstream signaling pathway phospho-calmodulin-dependent protein kinase and phospho-cAMP response element-binding protein. These results suggest that isoflurane-induced cognitive impairments are associated with the declines in chromatin histone acetylation and the resulting downregulation of BDNF-TrkB signaling pathway. Moreover, the cognitive impairments and the signaling deficits can be rescued by histone deacetylase inhibitor sodium butyrate. Therefore, epigenetic enhancement of BDNF-TrkB signaling may be a promising strategy for reversing isoflurane-induced cognitive impairments.

Selective inhibition of histone deacetylase 6 alters the composition of circulating blood cells in a lethal septic model

BACKGROUND

Phagocytes, especially monocytes, macrophages, and dendritic cells, play a pivotal role in the innate and adaptive immune responses during sepsis. We have shown that inhibition of histone deacetylase 6 improves survival and increases bacterial clearance in a mouse model of cecal ligation and puncture (CLP). The aim of this study was to determine whether this effect was associated with changes in the number and composition of different blood cell types in the circulation.

METHODS

C57BL/6J mice were subjected to CLP, and 1 h later given an intraperitoneal injection of either Tubastatin A dissolved in dimethyl sulfoxide, or dimethyl sulfoxide only. Sham-operated animals were treated in an identical fashion but not subjected to CLP. Forty-eight hours later, peripheral blood was obtained via cardiac puncture and analyzed using a HemaTrue veterinary hematology analyzer.

RESULTS

Tubastatin A administration increased the number of circulating monocytes in the sham-operated and the CLP animals. In comparison with the sham, CLP animals displayed an increase in the granulocyte percentage in white blood cells and decrease in the lymphocyte number and percentage, with a resultant increase in the granulocyte-to-lymphocyte ratio. Treatment of CLP animals with Tubastatin A decreased the granulocyte percentage and restored the lymphocyte number and percentage, which decreased the granulocyte-to-lymphocyte ratio. In the sham animals, Tubastatin A increased red blood cell number, hematocrit, and hemoglobin. This effect was not seen in CLP animals.

CONCLUSIONS

Tubastatin A treatment has significant impact on the composition of circulating blood cells. It increases the number of circulating monocytes and the red blood cell mass in sham-operated animals. In the CLP animals, it increases the monocyte count, decreases the percentage of granulocytes, restores the lymphocyte population, and decreases the granulocyte-to-lymphocyte ratio. These results may explain why Tubastatin A treatment improves survival in the septic models.

Rapid changes in histone deacetylases and inflammatory gene expression in expert meditators

BACKGROUND

A growing body of research shows that mindfulness meditation can alter neural, behavioral and biochemical processes. However, the mechanisms responsible for such clinically relevant effects remain elusive.

METHODS

Here we explored the impact of a day of intensive practice of mindfulness meditation in experienced subjects (n=19) on the expression of circadian, chromatin modulatory and inflammatory genes in peripheral blood mononuclear cells (PBMC). In parallel, we analyzed a control group of subjects with no meditation experience who engaged in leisure activities in the same environment (n=21). PBMC from all participants were obtained before (t1) and after (t2) the intervention (t2-t1=8h) and gene expression was analyzed using custom pathway focused quantitative-real time PCR assays. Both groups were also presented with the Trier Social Stress Test (TSST).

RESULTS

Core clock gene expression at baseline (t1) was similar between groups and their rhythmicity was not influenced in meditators by the intensive day of practice. Similarly, we found that all the epigenetic regulatory enzymes and inflammatory genes analyzed exhibited similar basal expression levels in the two groups. In contrast, after the brief intervention we detected reduced expression of histone deacetylase genes (HDAC 2, 3 and 9), alterations in global modification of histones (H4ac; H3K4me3) and decreased expression of pro-inflammatory genes (RIPK2 and COX2) in meditators compared with controls. We found that the expression of RIPK2 and HDAC2 genes was associated with a faster cortisol recovery to the TSST in both groups.

CONCLUSIONS

The regulation of HDACs and inflammatory pathways may represent some of the mechanisms underlying the therapeutic potential of mindfulness-based interventions. Our findings set the foundation for future studies to further assess meditation strategies for the treatment of chronic inflammatory conditions.

Class I HDACs regulate angiotensin II-dependent cardiac fibrosis via fibroblasts and circulating fibrocytes

Fibrosis, which is defined as excessive accumulation of fibrous connective tissue, contributes to the pathogenesis of numerous diseases involving diverse organ systems. Cardiac fibrosis predisposes individuals to myocardial ischemia, arrhythmias and sudden death, and is commonly associated with diastolic dysfunction. Histone deacetylase (HDAC) inhibitors block cardiac fibrosis in pre-clinical models of heart failure. However, which HDAC isoforms govern cardiac fibrosis, and the mechanisms by which they do so, remains unclear. Here, we show that selective inhibition of class I HDACs potently suppresses angiotensin II (Ang II)-mediated cardiac fibrosis by targeting two key effector cell populations, cardiac fibroblasts and bone marrow-derived fibrocytes. Class I HDAC inhibition blocks cardiac fibroblast cell cycle progression through derepression of the genes encoding the cyclin-dependent kinase (CDK) inhibitors, p15 and p57. In contrast, class I HDAC inhibitors block agonist-dependent differentiation of fibrocytes through a mechanism involving repression of ERK1/2 signaling. These findings define novel roles for class I HDACs in the control of pathological cardiac fibrosis. Furthermore, since fibrocytes have been implicated in the pathogenesis of a variety of human diseases, including heart, lung and kidney failure, our results suggest broad utility for isoform-selective HDAC inhibitors as anti-fibrotic agents that function, in part, by targeting these circulating mesenchymal cells.

The structure based design of dual HDAC/BET inhibitors as novel epigenetic probes

DUAL946 (1) inhibits BET and HDAC proteins in chemoproteomic cell lysate experiments and in immune and cancer cells.