Inhibiting epigenetic enzymes to improve atherogenic macrophage functions

Histone deacetylases and their inhibitors in inflammatory diseases

Despite considerable research efforts, inflammatory diseases remain a heavy burden on human health, causing significant economic losses annually. Histone deacetylases (HDACs) play a significant role in regulating inflammation (via histone and non-histone protein deacetylation) and chromatin structure and gene expression regulation. Herein, we present a detailed description of the different HDACs and their functions and analyze the role of HDACs in inflammatory diseases, including pro-inflammatory cytokine production reduction, immune cell function modulation, and anti-inflammatory cell activity enhancement. Although HDAC inhibitors have shown broad inflammatory disease treatment potentials, their clinical applicability remains limited because of their non-specific effects, adverse effects, and drug resistance. With further research and insight, these inhibitors are expected to become important tools for the treatment of a wide range of inflammatory diseases. This review aims to explore the mechanisms and application prospects of HDACs and their inhibitors in multiple inflammatory diseases.

Impact of HDAC inhibitors on macrophage polarization to enhance innate immunity against infections

Innate immunity plays an important role in host defense against pathogenic infections. It involves macrophage polarization into either the pro-inflammatory M1 or the anti-inflammatory M2 phenotype, influencing immune stimulation or suppression, respectively. Epigenetic changes during immune reactions contribute to long-term innate immunity imprinting on macrophage polarization. It is becoming increasingly evident that epigenetic modulators, such as histone deacetylase (HDAC) inhibitors (HDACi), enable the enhancement of innate immunity by tailoring macrophage polarization in response to immune stressors. In this review, we summarize current literature on the impact of HDACi and other epigenetic modulators on the functioning of macrophages during diseases that have a strong immune component, such as infections. Depending on the disease context and the chosen therapeutic intervention, HDAC1, HDAC2, HDAC3, HDAC6, or HDAC8 are particularly important in influencing macrophage polarization towards either M1 or M2 phenotypes. We anticipate that therapeutic strategies based on HDAC epigenetic mechanisms will provide a unique approach to boost immunity against disease challenges, including resistant infections.

Epigenetically regulated inflammation in vascular senescence and renal progression of chronic kidney disease

Chronic kidney disease (CKD) and its complications, including vascular senescence and progressive renal fibrosis, are associated with inflammation. Vascular senescence, in particular, has emerged as an instrumental mediator of vascular inflammation that potentially worsens renal function. Epigenetically regulated inflammation involving histone modification, DNA methylation, actions of microRNAs and other non-coding RNAs, and their reciprocal reactions during vascular senescence and inflammaging are underappreciated. Their synergistic effects can contribute to CKD progression. Vascular senotherapeutics or pharmacological anti-senescent therapies based on epigenetic machineries can therefore be plausible options for ameliorating vascular aging and even halting the worsening of renal fibrosis. These include histone deacetylase modulators, histone methyltransferase modulators, other histone modification effectors, DNA methyltransferase inhibitors, telomerase reverse transcriptase enhancers, microRNA mimic delivery, and small molecules with microRNA-regulating potentials. Some of these molecules have already been tested and have shown anecdotal evidence for treating uremic vasculopathy and renal fibrosis, supporting the feasibility of this approach.

Role of immune inflammation regulated by macrophage in the pathogenesis of age-related macular degeneration

Age-related macular degeneration (AMD) can lead to irreversible impairment of visual function, and the number of patients with AMD has been increasing globally. The immunoinflammatory theory is an important pathogenic mechanism of AMD, with macrophages serving as the primary inflammatory infiltrating cells in AMD lesions. Its powerful immunoinflammatory regulatory function has attracted considerable attention. Herein, we provide an overview of the involvement of macrophage-regulated immunoinflammation in different stages of AMD. Additionally, we summarize novel therapeutic approaches for AMD, focusing on targeting macrophages, such as macrophage/microglia modulators, reduction of macrophage aggregation in the subretinal space, modulation of macrophage effector function, macrophage phenotypic alterations, and novel biomimetic nanocomposites development based on macrophage-associated functional properties. We aimed to provide a basis and reference for the further exploration of AMD pathogenesis, developmental influences, and new therapeutic approaches.

DNA methylation and histone post-translational modifications in atherosclerosis and a novel perspective for epigenetic therapy

Atherosclerosis, which is a vascular pathology characterized by inflammation and plaque build-up within arterial vessel walls, acts as the important cause of most cardiovascular diseases. Except for a lipid-depository and chronic inflammatory, increasing evidences propose that epigenetic modifications are increasingly associated with atherosclerosis and are of interest from both therapeutic and biomarker perspectives. The chronic progressive nature of atherosclerosis has highlighted atherosclerosis heterogeneity and the fact that specific cell types in the complex milieu of the plaque are, by far, not the only initiators and drivers of atherosclerosis. Instead, the ubiquitous effects of cell type are tightly controlled and directed by the epigenetic signature, which, in turn, is affected by many proatherogenic stimuli, including low-density lipoprotein, proinflammatory, and physical forces of blood circulation. In this review, we summarize the role of DNA methylation and histone post-translational modifications in atherosclerosis. The future research directions and potential therapy for the management of atherosclerosis are also discussed. Video Abstract.

HDAC3 and HDAC8 PROTAC dual degrader reveals roles of histone acetylation in gene regulation

HDAC3 and HDAC8 have critical biological functions and represent highly sought-after therapeutic targets. Because histone deacetylases (HDACs) have a very conserved catalytic domain, developing isozyme-selective inhibitors remains challenging. HDAC3/8 also have deacetylase-independent activity, which cannot be blocked by conventional enzymatic inhibitors. Proteolysis-targeting chimeras (PROTACs) can selectively degrade a target enzyme, abolishing both enzymatic and scaffolding function. Here, we report a novel HDAC3/8 dual degrader YX968 that induces highly potent, rapid, and selective degradation of both HDAC3/8 without triggering pan-HDAC inhibitory effects. Unbiased quantitative proteomic experiments confirmed its high selectivity. HDAC3/8 degradation by YX968 does not induce histone hyperacetylation and broad transcriptomic perturbation. Thus, histone hyperacetylation may be a major factor for altering transcription. YX968 promotes apoptosis and kills cancer cells with a high potency in vitro. YX968 thus represents a new probe for dissecting the complex biological functions of HDAC3/8.

Regulation of Acetylation States by Nutrients in the Inhibition of Vascular Inflammation and Atherosclerosis

Atherosclerosis (AS) is a chronic metabolic disorder and primary cause of cardiovascular diseases, resulting in substantial morbidity and mortality worldwide. Initiated by endothelial cell stimulation, AS is characterized by arterial inflammation, lipid deposition, foam cell formation, and plaque development. Nutrients such as carotenoids, polyphenols, and vitamins can prevent the atherosclerotic process by modulating inflammation and metabolic disorders through the regulation of gene acetylation states mediated with histone deacetylases (HDACs). Nutrients can regulate AS-related epigenetic states via sirtuins (SIRTs) activation, specifically SIRT1 and SIRT3. Nutrient-driven alterations in the redox state and gene modulation in AS progression are linked to their protein deacetylating, anti-inflammatory, and antioxidant properties. Nutrients can also inhibit advanced oxidation protein product formation, reducing arterial intima-media thickness epigenetically. Nonetheless, knowledge gaps remain when it comes to understanding effective AS prevention through epigenetic regulation by nutrients. This work reviews and confirms the underlying mechanisms by which nutrients prevent arterial inflammation and AS, focusing on the epigenetic pathways that modify histones and non-histone proteins by regulating redox and acetylation states through HDACs such as SIRTs. These findings may serve as a foundation for developing potential therapeutic agents to prevent AS and cardiovascular diseases by employing nutrients based on epigenetic regulation.

Epigenetic regulation of macrophage polarization in wound healing

The immune microenvironment plays a critical role in regulating skin wound healing. Macrophages, the main component of infiltrating inflammatory cells, play a pivotal role in shaping the immune microenvironment in the process of skin wound healing. Macrophages comprise the classic proinflammatory M1 subtype and anti-inflammatory M2 population. In the early inflammatory phase of skin wound closure, M1-like macrophages initiate and amplify the local inflammatory response to disinfect the injured tissue. In the late tissue-repairing phase, M2 macrophages are predominant in wound tissue and limit local inflammation to promote tissue repair. The biological function of macrophages is tightly linked with epigenomic organization. Transcription factors are essential for macrophage polarization. Epigenetic modification of transcription factors determines the heterogeneity of macrophages. In contrast, transcription factors also regulate the expression of epigenetic enzymes. Both transcription factors and epigenetic enzymes form a complex network that regulates the plasticity of macrophages. Here, we describe the latest knowledge concerning the potential epigenetic mechanisms that precisely regulate the biological function of macrophages and their effects on skin wound healing.

Innate Immune Memory in Monocytes and Macrophages: The Potential Therapeutic Strategies for Atherosclerosis

Atherosclerosis is a complex metabolic disease characterized by the dysfunction of lipid metabolism and chronic inflammation in the intimal space of the vessel. As the most abundant innate immune cells, monocyte-derived macrophages play a pivotal role in the inflammatory response, cholesterol metabolism, and foam cell formation. In recent decades, it has been demonstrated that monocytes and macrophages can establish innate immune memory (also termed trained immunity) via endogenous and exogenous atherogenic stimuli and exhibit a long-lasting proinflammatory phenotype. The important cellular metabolism processes, including glycolysis, oxidative phosphorylation (OXPHOS), the tricarboxylic acid (TCA) cycle, fatty acid synthesis, and cholesterol synthesis, are reprogrammed. Trained monocytes/macrophages with innate immune memory can be persistently hyperactivated and can undergo extensive epigenetic rewiring, which contributes to the pathophysiological development of atherosclerosis via increased proinflammatory cytokine production and lipid accumulation. Here, we provide an overview of the regulation of cellular metabolic processes and epigenetic modifications of innate immune memory in monocytes/macrophages as well as the potential endogenous and exogenous stimulations involved in the progression of atherosclerosis that have been reported recently. These elucidations might be beneficial for further understanding innate immune memory and the development of therapeutic strategies for inflammatory diseases and atherosclerosis.

New Insight in HDACs: Potential Therapeutic Targets for the Treatment of Atherosclerosis

Atherosclerosis (AS) features include progressive hardening and reduced elasticity of arteries. AS is the leading cause of morbidity and mortality. An increasing amount of evidence showed that epigenetic modifications on genes serve are a main cause of several diseases, including AS. Histone deacetylases (HDACs) promote the deacetylation at lysine residues, thereby condensing the chromatin structures and further inhibiting the transcription of downstream genes. HDACs widely affect various physiological and pathological processes through transcriptional regulation or deacetylation of other non-histone proteins. In recent years, the role of HDACs in vascular systems has been revealed, and their effects on atherosclerosis have been widely reported. In this review, we discuss the members of HDACs in vascular systems, determine the diverse roles of HDACs in AS, and reveal the effects of HDAC inhibitors on AS progression. We provide new insights into the potential of HDAC inhibitors as drugs for AS treatment.

Diverse Epigenetic Regulations of Macrophages in Atherosclerosis

Emerging research on epigenetics has resulted in many novel discoveries in atherosclerosis (AS), an inflammaging-associated disease characterized by chronic inflammation primarily driven by macrophages. The bulk of evidence has demonstrated the central role of epigenetic machinery in macrophage polarization to pro- (M1-like) or anti-inflammatory (M2-like) phenotype. An increasing number of epigenetic alterations and their modifiers involved in reprogramming macrophages by regulating DNA methylation or histone modifications (e.g., methylation, acetylation, and recently lactylation) have been identified. They may act to determine or skew the direction of macrophage polarization in AS lesions, thereby representing a promising target. Here we describe the current understanding of the epigenetic machinery involving macrophage polarization, to shed light on chronic inflammation-driving onset and progression of inflammaging-associated diseases, using AS as a prototypic example, and discuss the challenge for developing effective therapies targeting the epigenetic modifiers against these diseases, particularly highlighting a potential strategy based on epigenetically-governed repolarization from M1-like to M2-like phenotype.

Remembering your A, B, C's: Alzheimer's disease and ABCA1

The function of ATP binding cassette protein A1 (ABCA1) is central to cholesterol mobilization. Reduced ABCA1 expression or activity is implicated in Alzheimer's disease (AD) and other disorders. Therapeutic approaches to boost ABCA1 activity have yet to be translated successfully to the clinic. The risk factors for AD development and progression, including comorbid disorders such as type 2 diabetes and cardiovascular disease, highlight the intersection of cholesterol transport and inflammation. Upregulation of ABCA1 can positively impact APOE lipidation, insulin sensitivity, peripheral vascular and blood–brain barrier integrity, and anti-inflammatory signaling. Various strategies towards ABCA1-boosting compounds have been described, with a bias toward nuclear hormone receptor (NHR) agonists. These agonists display beneficial preclinical effects; however, important side effects have limited development. In particular, ligands that bind liver X receptor (LXR), the primary NHR that controls ABCA1 expression, have shown positive effects in AD mouse models; however, lipogenesis and unwanted increases in triglyceride production are often observed. The longstanding approach, focusing on LXRβ vs. LXRα selectivity, is over-simplistic and has failed. Novel approaches such as phenotypic screening may lead to small molecule NHR modulators that elevate ABCA1 function without inducing lipogenesis and are clinically translatable.

Histone Deacetylase 3: A Potential Therapeutic Target for Atherosclerosis

Atherosclerosis, the pathological basis of most cardiovascular disease, is characterized by plaque formation in the intima. Secondary lesions include intraplaque hemorrhage, plaque rupture, and local thrombosis. Vascular endothelial function impairment and smooth muscle cell migration lead to vascular dysfunction, which is conducive to the formation of macrophage-derived foam cells and aggravates inflammatory response and lipid accumulation that cause atherosclerosis. Histone deacetylase (HDAC) is an epigenetic modifying enzyme closely related to chromatin structure and gene transcriptional regulation. Emerging studies have demonstrated that the Class I member HDAC3 of the HDAC super family has cell-specific functions in atherosclerosis, including 1) maintenance of endothelial integrity and functions, 2) regulation of vascular smooth muscle cell proliferation and migration, 3) modulation of macrophage phenotype, and 4) influence on foam cell formation. Although several studies have shown that HDAC3 may be a promising therapeutic target, only a few HDAC3-selective inhibitors have been thoroughly researched and reported. Here, we specifically summarize the impact of HDAC3 and its inhibitors on vascular function, inflammation, lipid accumulation, and plaque stability in the development of atherosclerosis with the hopes of opening up new opportunities for the treatment of cardiovascular diseases.

Preclinical and clinical progress for HDAC as a putative target for epigenetic remodeling and functionality of immune cells

Genetic changes are difficult to reverse; thus, epigenetic aberrations, including changes in DNA methylation, histone modifications, and noncoding RNAs, with potential reversibility, have attracted attention as pharmaceutical targets. The current paradigm is that histone deacetylases (HDACs) regulate gene expression via deacetylation of histone and nonhistone proteins or by forming corepressor complexes with transcription factors. The emergence of epigenetic tools related to HDACs can be used as diagnostic and therapeutic markers. HDAC inhibitors that block specific or a series of HDACs have proven to be a powerful therapeutic treatment for immune-related diseases. Here, we summarize the various roles of HDACs and HDAC inhibitors in the development and function of innate and adaptive immune cells and their implications for various diseases and therapies.

Targeting epigenetic modifiers to reprogramme macrophages in non-resolving inflammation-driven atherosclerosis

Epigenomic and epigenetic research has been providing several new insights into a variety of diseases caused by non-resolving inflammation, including cardiovascular diseases. Atherosclerosis (AS) has long been recognized as a chronic inflammatory disease of the arterial walls, characterized by local persistent and stepwise accelerating inflammation without resolution, also known as uncontrolled inflammation. The pathogenesis of AS is driven primarily by highly plastic macrophages via their polarization to pro- or anti-inflammatory phenotypes as well as other novel subtypes recently identified by single-cell sequencing. Although emerging evidence has indicated the key role of the epigenetic machinery in the regulation of macrophage plasticity, the investigation of epigenetic alterations and modifiers in AS and related inflammation is still in its infancy. An increasing number of the epigenetic modifiers (e.g. TET2, DNMT3A, HDAC3, HDAC9, JMJD3, KDM4A) have been identified in epigenetic remodelling of macrophages through DNA methylation or histone modifications (e.g. methylation, acetylation, and recently lactylation) in inflammation. These or many unexplored modifiers function to determine or switch the direction of macrophage polarization via transcriptional reprogramming of gene expression and intracellular metabolic rewiring upon microenvironmental cues, thereby representing a promising target for anti-inflammatory therapy in AS. Here, we review up-to-date findings involving the epigenetic regulation of macrophages to shed light on the mechanism of uncontrolled inflammation during AS onset and progression. We also discuss current challenges for developing an effective and safe anti-AS therapy that targets the epigenetic modifiers and propose a potential anti-inflammatory strategy that repolarizes macrophages from pro- to anti-inflammatory phenotypes.

Role of Histone Deacetylases in Monocyte Function in Health and Chronic Inflammatory Diseases

Histone deacetylases (HDACs) are a family of 18 members that participate in the epigenetic regulation of gene expression. In addition to histones, some HDACs also deacetylate transcription factors and specific cytoplasmic proteins.Monocytes, as part of the innate immune system, maintain tissue homeostasis and help fight infections and cancer. In these cells, HDACs are involved in multiple processes including proliferation, migration, differentiation, inflammatory response, infections, and tumorigenesis. Here, a systematic description of the role that most HDACs play in these functions is reviewed. Specifically, some HDACs induce a pro-inflammatory response and play major roles in host defense. Conversely, other HDACs reprogram monocytes and macrophages towards an immunosuppressive phenotype. The right balance between both types helps monocytes to respond correctly to the different physiological/pathological stimuli. However, aberrant expressions or activities of specific HDACs are associated with autoimmune diseases along with other chronic inflammatory diseases, infections, or cancer.This paper critically reviews the interesting and extensive knowledge regarding the role of some HDACs in these pathologies. It also shows that as yet, very little progress has been made toward the goal of finding effective HDAC-targeted therapies. However, given their obvious potential, we conclude that it is worth the effort to develop monocyte-specific drugs that selectively target HDAC subtypes with the aim of finding effective treatments for diseases in which our innate immune system is involved.

Inhibition of myeloid HDAC2 upregulates glutaredoxin 1 expression, improves protein thiol redox state and protects against high-calorie diet-induced monocyte dysfunction and atherosclerosis

BACKGROUND AND AIMS

The thiol transferase glutaredoxin 1 controls redox signaling and cellular functions by regulating the S-glutathionylation status of critical protein thiols. Here we tested the hypothesis that by derepressing the expression of glutaredoxin 1, inhibition of histone deacetylase 2 prevents nutrient stress-induced protein S-glutathionylation and monocyte dysfunction and protects against atherosclerosis.

METHODS

Using both a pharmacological inhibitor and shRNA-mediated knockdown of histone deacetylase 2, we determine the role of this deacetylase on glutaredoxin 1 expression and nutrient stress-induced inactivation of mitogen-activated protein kinase phosphatase 1 activity and monocyte and macrophage dysfunction. To assess whether histone deacetylase 2 inhibition in myeloid cells protects against atherosclerosis, we fed eight-week-old female and male HDAC2^-/-_MyeloidLDLR^-/- mice and age and sex-matched LysMcre^tg/wtLDLR^-/- control mice a high-calorie diet for 12 weeks and assessed monocyte function and atherosclerotic lesion size.

RESULTS

Myeloid histone deacetylase 2 deficiency in high-calorie diet-fed LDLR^-/- mice reduced atherosclerosis in males by 39% without affecting plasma lipid and lipoprotein profiles or blood glucose levels but had no effect on atherogenesis in female mice. Macrophage content in plaques of male mice was reduced by 31%. Histone deacetylase 2-deficient blood monocytes from male mice showed increased acetylation on histone 3, and increased Grx1 expression, and was associated with increased MKP-1 activity and reduced recruitment of monocyte-derived macrophages, whereas in females, myeloid HDAC2 deficiency had no effect on Grx1 expression, did not prevent nutrient stress-induced loss of MKP-1 activity in monocytes and was not atheroprotective.

CONCLUSIONS

Specific histone deacetylase 2 inhibitors may represent a potential novel therapeutic strategy for the prevention and treatment of atherosclerosis, but any benefits may be sexually dimorphic.

MicroRNA-328-5p Alleviates Macrophage Lipid Accumulation through the Histone Deacetylase 3/ATP-binding cassette transporter A1 pathway

MicroRNA-328 (miR-328) was reported to protect against atherosclerosis, but its role in foam cell formation remains unknown. The aim of this study was to investigate the effect of miR-328-5p on macrophage lipid accumulation and the underlying mechanisms. The results showed that miR-328-5p expression was robustly decreased in oxidized low-density lipoprotein (ox-LDL)-treated macrophages. Treatment of human acute monocytic leukemia cel (THP-1) macrophage-derived foam cells with a miR-328-5p mimic markedly increased [³ H]-cholesterol efflux, inhibited lipid droplet accumulation, and decreased intracellular total cholesterol (TC), free cholesterol (FC) and cholesteryl ester (CE) contents. Upregulation of miR-328-5p also reduced the expression of histone deacetylase 3 (HDAC3) but increased the levels of ATP-binding cassette transporter A1 (ABCA1) in THP-1 macrophage-derived foam cells. Mechanistically, miR-328-5p inhibited HDAC3 expression by directly targeting its 3'UTR, thereby promoting ABCA1 expression and the subsequent cholesterol efflux. Furthermore, miR-328-5p mimic treatment did not affect the uptake of Dil-ox-LDL or the expression of scavenger receptor-A (SR-A), thrombospondin receptor (CD36) and ABCG1. Taken together, these findings suggest that miR-328-5p alleviates macrophage lipid accumulation through the HDAC3/ABCA1 pathway.

LncRNA kcnq1ot1 promotes lipid accumulation and accelerates atherosclerosis via functioning as a ceRNA through the miR-452-3p/HDAC3/ABCA1 axis

Kcnq1 overlapping transcript 1 (kcnq1ot1), an imprinted antisense lncRNA in the kcnq1 locus, acts as a potential contributor to cardiovascular disease, but its role in atherosclerosis remains unknown. The aim of this study was to explore the effects of kcnq1ot1 on atherogenesis and the underlying mechanism. Our results showed that kcnq1ot1 expression was significantly increased in mouse aorta with atherosclerosis and lipid-loaded macrophages. Lentivirus-mediated kcnq1ot1 overexpression markedly increased atherosclerotic plaque area and decreased plasma HDL-C levels and RCT efficiency in apoE^-/- mice fed a Western diet. Upregulation of kcnq1ot1 also reduced the expression of miR-452-3p and ABCA1 but increased HDAC3 levels in mouse aorta and THP-1 macrophages. Accordingly, kcnq1ot1 overexpression inhibited cholesterol efflux and promoted lipid accumulation in THP-1 macrophages. In contrast, kcnq1ot1 knockdown protected against atherosclerosis in apoE^-/- mice and suppressed lipid accumulation in THP-1 macrophages. Mechanistically, kcnq1ot1 enhanced HDAC3 expression by competitively binding to miR-452-3p, thereby inhibiting ABCA1 expression and subsequent cholesterol efflux. Taken together, these findings suggest that kcnq1ot1 promotes macrophage lipid accumulation and accelerates the development of atherosclerosis through the miR-452-3p/HDAC3/ABCA1 pathway.

Targeting epigenetics as atherosclerosis treatment: an updated view

PURPOSE OF REVIEW

This review discusses the current developments on epigenetic inhibition as treatment for atherosclerosis.

RECENT FINDINGS

The first phase III clinical trial targeting epigenetics in cardiovascular disease (CVD), BETonMACE, using the bromodomain inhibitor apabetalone (RVX-208) showed no significant effect on major adverse cardiovascular events (MACE) in patients with type II diabetes, low HDL-c and a recent acute coronary artery event compared with its placebo arm.

SUMMARY

Preclinical and clinical studies suggest that targeting epigenetics in atherosclerosis is a promising novel therapeutic strategy against CVD. Interfering with histone acetylation by targeting histone deacetylates (HDACs) and bromodomain and extraterminal domain (BET) proteins demonstrated encouraging results in modulating disease progression in model systems. Although the first phase III clinical trial targeting BET in CVD showed no effect on MACE, we suggest that there is sufficient potential for future clinical usage based on the outcomes in specific subgroups and the fact that the study was slightly underpowered. Lastly, we propose that there is future window for targeting repressive histone modifications in atherosclerosis.

Histone Deacetylases (HDACs) and Atherosclerosis: A Mechanistic and Pharmacological Review

Atherosclerosis (AS), the most common underlying pathology for coronary artery disease, is a chronic inflammatory, proliferative disease in large- and medium-sized arteries. The vascular endothelium is important for maintaining vascular health. Endothelial dysfunction is a critical early event leading to AS, which is a major risk factor for stroke and myocardial infarction. Accumulating evidence has suggested the critical roles of histone deacetylases (HDACs) in regulating vascular cell homeostasis and AS. The purpose of this review is to present an updated view on the roles of HDACs (Class I, Class II, Class IV) and HDAC inhibitors in vascular dysfunction and AS. We also elaborate on the novel therapeutic targets and agents in atherosclerotic cardiovascular diseases.

Local Delivery of Minocycline and Vorinostat Targets the Tumor Microenvironment to Inhibit the Recurrence of Glioma

Background

Postoperative recurrence is the main reason for poor clinical outcomes in glioma patients, so preventing tumor recurrence is crucial in the management of gliomas.

Methods

In this study, the expression of matrix metalloproteinases (MMPs) in normal tissues was detected via RNA-seq analysis. Glioma cases from the public databases (The Cancer Genome Atlas (TCGA), the Chinese Glioma Genome Atlas (CGGA)) were included in this study. The hydrogel contains minocycline (Mino) and vorinostat (Vor) (G/Mino+Vor) was formed under 365 nm when the photoinitiator was added. High-performance liquid chromatography (HPLC) was used to assess the release of drugs in the G/Mino+Vor hydrogel. An MTT assay was used to explore the biosecurity of GelMA. Immunohistochemistry, ELISA, and TUNEL assays were used to demonstrate the antitumor effect of the G/Mino+Vor hydrogel.

Results

We successfully developed a G/Mino+Vor hydrogel. The experiments in vitro and in vivo confirmed the MMPs-responsive delivery of minocycline and vorinostat in hydrogel and the anti-glioma effect on an incomplete tumor operation model, which indicated that the G/Mino+Vor hydrogel effectively inhibited the recurrence of glioma after surgery.

Conclusion

In summary, the G/Mino+Vor hydrogel could continuously release drugs and improve the therapy effects against recurrent glioma.

Targeting foam cell formation in inflammatory brain diseases by the histone modifier MS-275

OBJECTIVE

To assess class I-histone deacetylase (HDAC) inhibition on formation of lipid-accumulating, disease-promoting phagocytes upon myelin load in vitro, relevant for neuroinflammatory disorders like multiple sclerosis (MS) and cerebral X-linked adrenoleukodystrophy (X-ALD).

METHODS

Immunohistochemistry on postmortem brain tissue of acute MS (n = 6) and cerebral ALD (n = 4) cases to analyze activation and foam cell state of phagocytes. RNA-Seq of in vitro differentiated healthy macrophages (n = 8) after sustained myelin-loading to assess the metabolic shift associated with foam cell formation. RNA-Seq analysis of genes linked to lipid degradation and export in MS-275-treated human HAP1 cells and RT-qPCR analysis of HAP1 cells knocked out for individual members of class I HDACs or the corresponding enzymatically inactive knock-in mutants. Investigation of intracellular lipid/myelin content after MS-275 treatment of myelin-laden human foam cells. Analysis of disease characteristic very long-chain fatty acid (VLCFA) metabolism and inflammatory state in MS-275-treated X-ALD macrophages.

RESULTS

Enlarged foam cells coincided with a pro-inflammatory, lesion-promoting phenotype in postmortem tissue of MS and cerebral ALD patients. Healthy in vitro myelin laden foam cells upregulated genes linked to LXRα/PPARγ pathways and mimicked a program associated with tissue repair. Treating these cells with MS-275, amplified this gene transcription program and significantly reduced lipid and cholesterol accumulation and, thus, foam cell formation. In macrophages derived from X-ALD patients, MS-275 improved the disease-associated alterations of VLCFA metabolism and reduced the pro-inflammatory status of these cells.

INTERPRETATION

These findings identify class I-HDAC inhibition as a potential novel strategy to prevent disease promoting foam cell formation in CNS inflammation.

HDAC3 Mediates the Inflammatory Response and LPS Tolerance in Human Monocytes and Macrophages

Histone deacetylases (HDACs) are a group of enzymes that control histone deacetylation and bear potential to direct expression of large gene sets. We determined the effect of HDAC inhibitors (HDACi) on human monocytes and macrophages, with respect to their polarization, activation, and their capabilities of inducing endotoxin tolerance. To address the role for HDACs in macrophage polarization, we treated monocytes with HDAC3i, HDAC6i or pan-HDACi prior to polarization into M1 or M2 macrophages using IFNγ or IL-4 respectively. To study the HDAC inhibition effect on cytokine expression, macrophages were treated with HDACi prior to LPS-stimulation. TNFα, IL-6, and p40 were measured with ELISA, whereas modifications of Histone 3 and STAT1 were assessed using western blot. To address the role for HDAC3 in repeated LPS challenge induction, HDAC3i or HDAC3 siRNA was added to monocytes prior to incubation with IFNγ, which were then repeatedly challenged with LPS and analyzed by means of protein analyses and transcriptional profiling. Pan-HDACi and HDAC3i reduced cytokine secretion in monocytes and M1 macrophages, whereas HDAC6i yielded no such effect. Notably, neither pan-HDACi nor HDAC3i reduced cytokine secretion in M2 macrophages. In contrast to previous reports in mouse macrophages, HDAC3i did not affect macrophage polarization in human cells. Likewise, HDAC3 was not required for IFNγ signaling or IFNβ secretion. Cytokine and gene expression analyses confirmed that IFNγ-treated macrophages consistently develop a cytokine response after LPS repeated challenge, but pretreatment with HDAC3i or HDAC3 siRNA reinstates a state of tolerance reflected by general suppression of tolerizable genes, possibly through decreasing TLRs expression, and particularly TLR4/CD14. The development of endotoxin tolerance in macrophages is important to reduce exacerbated immune response and limit tissue damage. We conclude that HDAC3 is an attractive protein target to mediate macrophage reactivity and tolerance induction in inflammatory macrophages.

Inhibiting Histone Deacetylases in Human Macrophages Promotes Glycolysis, IL-1β, and T Helper Cell Responses to Mycobacterium tuberculosis

Tuberculosis (TB) is the leading infectious killer in the world. Mycobacterium tuberculosis (Mtb), the bacteria that causes the disease, is phagocytosed by alveolar macrophages (AM) and infiltrating monocyte-derived macrophages (MDM) in the lung. Infected macrophages then upregulate effector functions through epigenetic modifications to make DNA accessible for transcription. The metabolic switch to glycolysis and the production of proinflammatory cytokines are key effector functions, governed by epigenetic changes, that are integral to the ability of the macrophage to mount an effective immune response against Mtb. We hypothesised that suberanilohydroxamic acid (SAHA), an FDA-approved histone deacetylase inhibitor (HDACi), can modulate epigenetic changes upstream of the metabolic switch and support immune responses during Mtb infection. The rate of glycolysis in human MDM, infected with Mtb and treated with SAHA, was tracked in real time on the Seahorse XFe24 Analyzer. SAHA promoted glycolysis early in the response to Mtb. This was associated with significantly increased production of IL-1β and significantly reduced IL-10 in human MDM and AM. Since innate immune function directs downstream adaptive immune responses, we used SAHA-treated Mtb-infected AM or MDM in a co-culture system to stimulate T cells. Mtb-infected macrophages that had previously been treated with SAHA promoted IFN-γ, GM-CSF, and TNF co-production in responding T helper cells but did not affect cytotoxic T cells. These results indicate that SAHA promoted the early switch to glycolysis, increased IL-1β, and reduced IL-10 production in human macrophages infected with Mtb. Moreover, the elevated proinflammatory function of SAHA-treated macrophages resulted in enhanced T helper cell cytokine polyfunctionality. These data provide an in vitro proof-of-concept for the use of HDACi to modulate human immunometabolic processes in macrophages to promote innate and subsequent adaptive proinflammatory responses.

Histone Deacetylase 9 Activates IKK to Regulate Atherosclerotic Plaque Vulnerability

RATIONALE

Arterial inflammation manifested as atherosclerosis is the leading cause of mortality worldwide. Genome-wide association studies have identified a prominent role of HDAC (histone deacetylase)-9 in atherosclerosis and its clinical complications including stroke and myocardial infarction.

OBJECTIVE

To determine the mechanisms linking HDAC9 to these vascular pathologies and explore its therapeutic potential for atheroprotection.

METHODS AND RESULTS

We studied the effects of Hdac9 on features of plaque vulnerability using bone marrow reconstitution experiments and pharmacological targeting with a small molecule inhibitor in hyperlipidemic mice. We further used 2-photon and intravital microscopy to study endothelial activation and leukocyte-endothelial interactions. We show that hematopoietic Hdac9 deficiency reduces lesional macrophage content while increasing fibrous cap thickness thus conferring plaque stability. We demonstrate that HDAC9 binds to IKK (inhibitory kappa B kinase)-α and β, resulting in their deacetylation and subsequent activation, which drives inflammatory responses in both macrophages and endothelial cells. Pharmacological inhibition of HDAC9 with the class IIa HDAC inhibitor TMP195 attenuates lesion formation by reducing endothelial activation and leukocyte recruitment along with limiting proinflammatory responses in macrophages. Transcriptional profiling using RNA sequencing revealed that TMP195 downregulates key inflammatory pathways consistent with inhibitory effects on IKKβ. TMP195 mitigates the progression of established lesions and inhibits the infiltration of inflammatory cells. Moreover, TMP195 diminishes features of plaque vulnerability and thereby enhances plaque stability in advanced lesions. Ex vivo treatment of monocytes from patients with established atherosclerosis reduced the production of inflammatory cytokines including IL (interleukin)-1β and IL-6.

CONCLUSIONS

Our findings identify HDAC9 as a regulator of atherosclerotic plaque stability and IKK activation thus providing a mechanistic explanation for the prominence of HDAC9 as a vascular risk locus in genome-wide association studies. Its therapeutic inhibition may provide a potent lever to alleviate vascular inflammation. Graphical Abstract: A graphical abstract is available for this article.

The important role of histone deacetylases in modulating vascular physiology and arteriosclerosis

Cardiovascular diseases are the leading cause of deaths in the world. Endothelial dysfunction followed by inflammation of the vessel wall leads to atherosclerotic lesion formation that causes ischemic heart and myocardial hypertrophy, which ultimately progress into cardiac dysfunction and failure. Histone deacetylases (HDACs) have been recognized to play crucial roles in cardiovascular disease, particularly in the epigenetic regulation of gene transcription in response to a variety of stresses. The unique nature of HDAC regulation includes that HDACs form a complex co-regulatory network with other transcription factors, deacetylate histones and non-histone proteins to facilitate the regulatory mechanism of the vascular system. The selective HDAC inhibitors are considered as the most promising target in cardiovascular disease, especially for preventing cardiac hypertrophy. In this review, we discuss our present knowledge of the cellular and molecular basis of HDACs in mediating the biological function of vascular cells and related pharmacologic interventions in vascular disease.

Targeting Histone Deacetylases in Myeloid Cells Inhibits Their Maturation and Inflammatory Function With Limited Effects on Atherosclerosis

Monocytes and macrophages are key drivers in the pathogenesis of inflammatory diseases. Epigenetic targets have been shown to control the transcriptional profile and phenotype of these cells. Since histone deacetylase protein inhibitors demonstrate profound anti-inflammatory activity, we wanted to test whether HDAC inhibition within monocytes and macrophages could be applied to suppress inflammation in vivo. ESM technology conjugates an esterase-sensitive motif (ESM) onto small molecules to allow targeting of cells that express carboxylesterase 1 (CES1), such as mononuclear myeloid cells. This study utilized an ESM-HDAC inhibitor to target monocytes and macrophages in mice in both an acute response model and an atherosclerosis model. We demonstrate that the molecule blocks the maturation of peritoneal macrophages and inhibits pro-inflammatory cytokine production in both models but to a lesser extent in the atherosclerosis model. Despite regulating the inflammatory response, ESM-HDAC528 did not significantly affect plaque size or phenotype, although histological classification of the plaques demonstrated a significant shift to a less severe phenotype. We hereby show that HDAC inhibition in myeloid cells impairs the maturation and activation of peritoneal macrophages but shows limited efficacy in a model of atherosclerosis.

Epigenetic regulation of macrophages: from homeostasis maintenance to host defense

Macrophages are crucial members of the innate immune response and important regulators. The differentiation and activation of macrophages require the timely regulation of gene expression, which depends on the interaction of a variety of factors, including transcription factors and epigenetic modifications. Epigenetic changes also give macrophages the ability to switch rapidly between cellular programs, indicating the ability of epigenetic mechanisms to affect phenotype plasticity. In this review, we focus on key epigenetic events associated with macrophage fate, highlighting events related to the maintenance of tissue homeostasis, responses to different stimuli and the formation of innate immune memory. Further understanding of the epigenetic regulation of macrophages will be helpful for maintaining tissue integrity, preventing chronic inflammatory diseases and developing therapies to enhance host defense.

Pharmacological inhibition of histone deacetylase reduces NADPH oxidase expression, oxidative stress and the progression of atherosclerotic lesions in hypercholesterolemic apolipoprotein E-deficient mice; potential implications for human atherosclerosis

NADPH oxidase (Nox)-derived reactive oxygen species (ROS) are instrumental in all inflammatory phases of atherosclerosis. Dysregulated histone deacetylase (HDAC)-related epigenetic pathways have been mechanistically linked to alterations in gene expression in experimental models of cardiovascular disorders. Hitherto, the relation between HDAC and Nox in atherosclerosis is not known. We aimed at uncovering whether HDAC plays a role in mediating Nox up-regulation, oxidative stress, inflammation, and atherosclerotic lesion progression. Human non-atherosclerotic and atherosclerotic arterial samples, ApoE-/- mice, and in vitro polarized monocyte-derived M1/M2-macrophages (Mac) were examined. Male ApoE-/- mice, maintained on normal or high-fat, cholesterol-rich diet, were randomized to receive 10 mg/kg suberoylanilide hydroxamic acid (SAHA), a pan-HDAC inhibitor, or its vehicle, for 4 weeks. In the human/animal studies, real-time PCR, Western blot, lipid staining, lucigenin-enhanced chemiluminescence assay, and enzyme-linked immunosorbent assay were employed. The protein levels of class I, class IIa, class IIb, and class IV HDAC isoenzymes were significantly elevated both in human atherosclerotic tissue samples and in atherosclerotic aorta of ApoE-/- mice. Treatment of ApoE-/- mice with SAHA reduced significantly the extent of atherosclerotic lesions, and the aortic expression of Nox subtypes, NADPH-stimulated ROS production, oxidative stress and pro-inflammatory markers. Significantly up-regulated HDAC and Nox subtypes were detected in inflammatory M1-Mac. In these cells, SAHA reduced the Nox1/2/4 transcript levels. Collectively, HDAC inhibition reduced atherosclerotic lesion progression in ApoE-/- mice, possibly by intertwined mechanisms involving negative regulation of Nox expression and inflammation. The data propose that HDAC-oriented pharmacological interventions could represent an effective therapeutic strategy in atherosclerosis.

Targeting epigenetics and non-coding RNAs in atherosclerosis: from mechanisms to therapeutics

Atherosclerosis, the principal cause of cardiovascular death worldwide, is a pathological disease characterized by fibro-proliferation, chronic inflammation, lipid accumulation, and immune disorder in the vessel wall. As the atheromatous plaques develop into advanced stage, the vulnerable plaques are prone to rupture, which causes acute cardiovascular events, including ischemic stroke and myocardial infarction. Emerging evidence has suggested that atherosclerosis is also an epigenetic disease with the interplay of multiple epigenetic mechanisms. The epigenetic basis of atherosclerosis has transformed our knowledge of epigenetics from an important biological phenomenon to a burgeoning field in cardiovascular research. Here, we provide a systematic and up-to-date overview of the current knowledge of three distinct but interrelated epigenetic processes (including DNA methylation, histone methylation/acetylation, and non-coding RNAs), in atherosclerotic plaque development and instability. Mechanistic and conceptual advances in understanding the biological roles of various epigenetic modifiers in regulating gene expression and functions of endothelial cells (vascular homeostasis, leukocyte adhesion, endothelial-mesenchymal transition, angiogenesis, and mechanotransduction), smooth muscle cells (proliferation, migration, inflammation, hypertrophy, and phenotypic switch), and macrophages (differentiation, inflammation, foam cell formation, and polarization) are discussed. The inherently dynamic nature and reversibility of epigenetic regulation, enables the possibility of epigenetic therapy by targeting epigenetic "writers", "readers", and "erasers". Several Food Drug Administration-approved small-molecule epigenetic drugs show promise in pre-clinical studies for the treatment of atherosclerosis. Finally, we discuss potential therapeutic implications and challenges for future research involving cardiovascular epigenetics, with an aim to provide a translational perspective for identifying novel biomarkers of atherosclerosis, and transforming precision cardiovascular research and disease therapy in modern era of epigenetics.

Murine models of sleep apnea: functional implications of altered macrophage polarity and epigenetic modifications in adipose and vascular tissues

Obstructive sleep apnea (OSA) is a highly prevalent disease across the lifespan, is characterized by chronic intermittent hypoxia and sleep fragmentation, and has been independently associated with substantial cardiometabolic morbidity. However, the reversibility of end-organ morbidity with treatment is not always apparent, suggesting that both tissue remodeling and epigenetic mechanisms may be operationally involved. Here, we review the cumulative evidence focused around murine models of OSA to illustrate the temporal dependencies of cardiometabolic dysfunction and its reversibility, and more particularly to discuss the critical contributions of tissue macrophages to adipose tissue insulin resistance and vascular atherogenesis. In addition, we describe initial findings potentially implicating epigenetic alterations in both the emergence of the cardiometabolic morbidity of OSA, and in its reversibility with treatment. We anticipate that improved understanding of macrophage biology and epigenetics in the context of intermittent hypoxia and sleep fragmentation will lead to discovery of novel therapeutic targets and improved cardiovascular and metabolic outcomes in OSA.

Cell‑specific histone modifications in atherosclerosis (Review)

Histone modifications are the key epigenetic mechanisms that have been identified to regulate gene expression in many human diseases. However, in the early developmental stages, such as in utero and the postnatal stages, histone modifications are essential for gene regulation and cell growth. Atherosclerosis represents a classical example of the involvement of different cell types, and their cumulative effects in the development of atheroma and the progression of the disease. Post translational modifications on proteins either induces their functional activity or renders them inactive. Post translational modifications such as methylation or acetylation on histones have been well characterized, and their role in enhancing or inhibiting specific gene expression was clearly elucidated. In the present review article, the critical roles of different histone modifications that occur in atherosclerosis have been summarized. Different histone proteins have been identified to serve a critical role in the development of atherosclerosis. Specifically, histone methylation and histone acetylation in monocytes, macrophages, vascular smooth muscle cells and in endothelial cells during the progression of atherosclerosis, have been well reported. In recent years, different target molecules and genes that regulate histone modifications have been examined for their effects in the treatment of atherosclerosis in animal models and in clinical trials. An increasing body of evidence suggests that these epigenetic changes resulting from DNA methylation and non-coding RNA may also be associated with histone modifications, thereby indicating that novel therapeutic strategies can be developed by targeting these post translational modifications, which may in turn aid in the treatment of atherosclerosis.

Targeting macrophage immunometabolism: Dawn in the darkness of sepsis

Sepsis is known since the time (470 BC) of great Greek physician, Hippocrates. Advancement in modern medicine and establishment of separate branches of medical science dealing with sepsis research have improved its outcome. However, mortality associated with sepsis still remains higher (25-30%) that further increases to 40-50% in the presence of septic shock. For example, sepsis-associated deaths account more in comparison to deaths-associated with myocardial-infarction and certain cancers (i.e. breast and colorectal cancer). However, it is now well established that profound activation of innate immune cells including macrophages play a very important role in the immunopathogenesis of sepsis. Macrophages are sentinel cells of the innate immune system with their location varying from peripheral blood to various target organs including lungs, liver, brain, kidneys, skin, testes, vascular endothelium etc. Thus, profound and dysregulated activation of these cells during sepsis can directly impact the outcome of sepsis. However, the emergence of the concept of immunometabolism as a major controller of immune response has raised a new hope for identifying new targets for immunomodulatory therapeutic approaches. Thus this present review starts with an introduction of sepsis as a major medical problem worldwide and signifies the role of dysregulated innate immune response including macrophages in its immunopathogenesis. Thereafter, subsequent sections describe changes in immunometabolic stage of macrophages (both M1 and M2) during sepsis. The article ends with the discussion of novel macrophage-specific therapeutic targets targeting their immunometabolism during sepsis and epigenetic regulation of macrophage immunometabolism and vice versa.

Epigenetic control of macrophage polarization: implications for targeting tumor-associated macrophages

The progression of cancer is a result of not only the growth of the malignant cells but also the behavior of other components of the tumor microenvironment (TME). Tumor-associated macrophages (TAMs) are key components of the TME that influence tumor growth and disease progression. TAMs can either inhibit or support tumor growth depending on their polarization to classically-activated macrophages (M1s) or alternatively-activated macrophages (M2s), respectively. Epigenetic regulation plays a significant role in determining this polarization and manipulating the epigenetic regulation in macrophages would provide a means for selectively targeting M2s thereby eliminating tumor-supporting TAMs while sparing tumor-inhibiting M1 TAMs. Many pharmacologic modulators of epigenetic enzymes are currently used clinically and could be repurposed for treating tumors with high TAM infiltrate. While much research involving epigenetic enzymes and their modulators has been performed in M1s, significantly less is known about the epigenetic regulation of M2s. This review highlights the field’s current knowledge of key epigenetic enzymes and their pharmacologic modulators known to influence macrophage polarization.

Carcinogenesis-relevant biological events in the pathophysiology of the efferocytosis phenomenon

The effective removal of cells undergoing programmed cell death, which is referred to as efferocytosis, prevents the leakage of intracellular contents into the surrounding tissue, which could lead to tissue damage and inflammation. Efferocytosis involves a coordinated orchestration of multiple steps that lead to a swift, coherent and immunologically silent removal of dying cells. The release of wound healing cytokines, which resolve inflammation and enhance tissue repair, is an important feature of efferocytosis. However, in addition to the healing cytokines released during efferocytosis, the immunosuppressive action of cytokines promotes the tumor microenvironment, enhances the motility of cancer cells and promotes the evasion of antitumor immunity. The aim of the present review was to comprehensively discuss the efferocytosis phenomenon, the important players associated with this process and their role in cancer-related biological events.

Pathophysiological relevance of macrophage subsets in atherogenesis

Macrophages are highly heterogeneous and plastic cells. They were shown to play a critical role in all stages of atherogenesis, from the initiation to the necrotic core formation and plaque rupture. Lesional macrophages primarily derive from blood monocyte, but local macrophage proliferation as well as differentiation from smooth muscle cells have also been described. Within atherosclerotic plaques, macrophages rapidly respond to changes in the microenvironment, shifting between pro- (M1) or anti-inflammatory (M2) functional phenotypes. Furthermore, different stimuli have been associated with differentiation of newly discovered M2 subtypes: IL-4/IL-13 (M2a), immunecomplex (M2b), IL-10/glucocorticoids (M2c), and adenosine receptor agonist (M2d). More recently, additional intraplaque macrophage phenotypes were also recognized in response to CXCL4 (M4), oxidized phospholipids (Mox), haemoglobin/haptoglobin complexes (HAmac/M(Hb)), and heme (Mhem). Such macrophage polarization was described as a progression among multiple phenotypes, which reflect the activity of different transcriptional factors and the cross-talk between intracellular signalling. Finally, the distribution of macrophage subsets within different plaque areas was markedly associated with cardiovascular (CV) vulnerability. The aim of this review is to update the current knowledge on the role of macrophage subsets in atherogenesis. In addition, the molecular mechanisms underlying macrophage phenotypic shift will be summarised and discussed. Finally, the role of intraplaque macrophages as predictors of CV events and the therapeutic potential of these cells will be discussed.

Epigenetic Changes in Diabetes and Cardiovascular Risk

Cardiovascular complications remain the leading causes of morbidity and premature mortality in patients with diabetes mellitus. Studies in humans and preclinical models demonstrate lasting gene expression changes in the vasculopathies initiated by previous exposure to high glucose concentrations and the associated overproduction of reactive oxygen species. The molecular signatures of chromatin architectures that sensitize the genome to these and other cardiometabolic risk factors of the diabetic milieu are increasingly implicated in the biological memory underlying cardiovascular complications and now widely considered as promising therapeutic targets. Atherosclerosis is a complex heterocellular disease where the contributing cell types possess distinct epigenomes shaping diverse gene expression. Although the extent that pathological chromatin changes can be manipulated in human cardiovascular disease remains to be established, the clinical applicability of epigenetic interventions will be greatly advanced by a deeper understanding of the cell type-specific roles played by writers, erasers, and readers of chromatin modifications in the diabetic vasculature. This review details a current perspective of epigenetic mechanisms of macrovascular disease in diabetes mellitus and highlights recent key descriptions of chromatinized changes associated with persistent gene expression in endothelial, smooth muscle, and circulating immune cells relevant to atherosclerosis. Furthermore, we discuss the challenges associated with pharmacological targeting of epigenetic networks to correct abnormal or deregulated gene expression as a strategy to alleviate the clinical burden of diabetic cardiovascular disease.

Macrophage Immunometabolism: Where Are We (Going)?

A growing number of findings highlight the crucial role of metabolic reprogramming in macrophage activation. Metabolic pathways are closely interconnected and recent literature demonstrates the need for glucose metabolism in anti-inflammatory as well as inflammatory macrophages. Moreover, fatty acid oxidation (FAO) not only supports anti-inflammatory responses as described formerly but also drives inflammasome activation in inflammatory macrophages. Hence, defining glycolysis as proinflammatory and FAO as anti-inflammatory may be an oversimplification. Here we review how the rapid growth of the immunometabolism field has improved our understanding of macrophage activation and at the same time has led to an increase in the appearance of contradictory observations. To conclude we discuss current challenges in immunometabolism and present crucial areas for future research.

The acetyl code in rheumatoid arthritis and other rheumatic diseases

Growing evidence supports the idea that aberrancies in epigenetic processes contribute to the onset and progression of human immune-mediated inflammatory diseases, such as rheumatoid arthritis (RA). Epigenetic regulators of histone tail modifications play a role in chromatin accessibility and transcriptional responses to inflammatory stimuli. Among these, histone deacetylases (HDACs) regulate the acetylation status of histones and nonhistone proteins, essential for immune responses. Broad-spectrum HDAC inhibitors are well-known anti-inflammatory agents and reduce disease severity in animal models of arthritis; however, selective HDAC inhibitors remain poorly studied. In this review, we describe emerging findings regarding the aberrant acetyl code in RA and other rheumatic disorders which may help identify not only novel diagnostic and prognostic clinical biomarkers for RA, but also new targets for epigenetic pharmacological applications.

FTY720/fingolimod increases NPC1 and NPC2 expression and reduces cholesterol and sphingolipid accumulation in Niemann-Pick type C mutant fibroblasts

Niemann-Pick type C (NPC) disease is a fatal neurodegenerative disorder caused by mutations in NPC1 or NPC2 with decreased functions leading to lysosomal accumulation of cholesterol and sphingolipids. FTY720/fingolimod, used for treatment of multiple sclerosis, is phosphorylated by nuclear sphingosine kinase 2, and its active phosphorylated form (FTY720-P) is an inhibitor of class I histone deacetylases. In this study, administration of clinically relevant doses of FTY720 to mice increased expression of NPC1 and -2 in brain and liver and decreased cholesterol in an SphK2-dependent manner. FTY720 greatly increased expression of NPC1 and -2 in human NPC1 mutant fibroblasts that correlated with formation of FTY720-P and significantly reduced the accumulation of cholesterol and glycosphingolipids. In agreement with this finding, FTY720 pretreatment of human NPC1 mutant fibroblasts restored transport of the cholera toxin B subunit, which binds ganglioside GM1, to the Golgi apparatus. Together, these findings suggest that FTY720 administration can ameliorate cholesterol and sphingolipid storage and trafficking defects in NPC1 mutant fibroblasts. Because neurodegeneration is the main clinical feature of NPC disease, and FTY720 accumulates in the CNS and has several advantages over available histone deacetylase inhibitors now in clinical trials, our work provides a potential opportunity for treatment of this incurable disease.-Newton, J., Hait, N. C., Maceyka, M., Colaco, A., Maczis, M., Wassif, C. A., Cougnoux, A., Porter, F. D., Milstien, S., Platt, N., Platt, F. M., Spiegel, S. FTY720/fingolimod increases NPC1 and NPC2 expression and reduces cholesterol and sphingolipid accumulation in Niemann-Pick type C mutant fibroblasts.

Normalization of Hepatic Homeostasis in the Npc1nmf164 Mouse Model of Niemann-Pick Type C Disease Treated with the Histone Deacetylase Inhibitor Vorinostat

Niemann-Pick type C (NP-C) disease is a fatal genetic lipidosis for which there is no Food and Drug Administration (FDA)-approved therapy. Vorinostat, an FDA-approved inhibitor of histone deacetylases, ameliorates lysosomal lipid accumulation in cultured NP-C patient fibroblasts. To assess the therapeutic potential of histone deacetylase inhibition, we pursued these in vitro observations in two murine models of NP-C disease. Npc1^nmf164 mice, which express a missense mutation in the Npc1 gene, were treated intraperitoneally, from weaning, with the maximum tolerated dose of vorinostat (150 mg/kg, 5 days/week). Disease progression was measured via gene expression, liver function and pathology, serum and tissue lipid levels, body weight, and life span. Transcriptome analyses of treated livers indicated multiple changes consistent with reversal of liver dysfunction that typifies NP-C disease. Significant improvements in liver pathology and function were achieved by this treatment regimen; however, NPC1 protein maturation and levels, disease progression, weight loss, and animal morbidity were not detectably altered. Vorinostat concentrations were >200 μm in the plasma compartment of treated animals but were almost 100-fold lower in brain tissue. Apolipoprotein B metabolism and the expression of key components of lipid homeostasis in primary hepatocytes from null (Npc1^-/-) and missense (Npc1^nmf164 ) mutant mice were altered by vorinostat treatment, consistent with a response by these cells independent of the status of the Npc1 locus. These results suggest that HDAC inhibitors have utility to treat visceral NP-C disease. However, it is clear that improved blood-brain barrier penetration will be required to alleviate the neurological symptoms of human NP-C disease.

Epigenetic Regulation of Monocyte and Macrophage Function

SIGNIFICANCE

Monocytes and macrophages are key players in tissue homeostasis and immune responses. Epigenetic processes tightly regulate cellular functioning in health and disease. Recent Advances: Recent technical developments have allowed detailed characterizations of the transcriptional circuitry underlying monocyte and macrophage regulation. Upon differentiation and activation, enhancers are selected by lineage-determining and signal-dependent transcription factors. Enhancers are shown to be very dynamic and activation of these enhancers underlies the differences in gene transcription between monocytes and macrophages and their subtypes.

CRITICAL ISSUES

It has been shown that epigenetic enzymes regulate the functioning of these cells and targeting of epigenetic enzymes has been proven to be a valuable tool to dampen inflammatory responses. We give a comprehensive overview of recent developments and understanding of the epigenetic pathways that control monocyte and macrophage function and of the epigenetic enzymes involved in monocyte and macrophage differentiation and activation.

FUTURE DIRECTIONS

The key challenges in the upcoming years will be to study epigenetic changes in human disease and to better understand how epigenetic pathways control the inflammatory repertoire in disease. Antioxid. Redox Signal. 25, 758-774.

Epigenetic mechanisms of macrophage activation in type 2 diabetes

The alarming rise of obesity and type 2 diabetes (T2D) has put a tremendous strain on global healthcare systems. Over the past decade extensive research has focused on the role of macrophages as key mediators of inflammation in T2D. The inflammatory environment in the obese adipose tissue and pancreatic β-cell islets creates and perpetuates imbalanced inflammatory macrophage activation. Consequences of this chronic low-grade inflammation include insulin resistance in the adipose tissue and pancreatic β-cell dysfunction. Recently, the emerging field of epigenetics has provided new insights into the pathogenesis of T2D, while also affording potential new opportunities for treatment. In macrophages, epigenetic mechanisms are increasingly being recognized as crucial controllers of their phenotype. Here, we first describe the role of macrophages in T2D. Then we elaborate on epigenetic mechanisms that regulate macrophage activation, thereby focusing on T2D. Next, we highlight how diabetic conditions such as hyperlipidemia and hyperglycemia could induce epigenetic changes that promote an inflammatory macrophage phenotype. In conclusion we discuss possible therapeutic interventions by targeting macrophage epigenetics and speculate on future research directions.

Histone deacetylase 3 regulates the inflammatory gene expression programme of rheumatoid arthritis fibroblast-like synoviocytes

Objectives

Non-selective histone deacetylase (HDAC) inhibitors (HDACi) have demonstrated anti-inflammatory properties in both in vitro and in vivo models of rheumatoid arthritis (RA). Here, we investigated the potential contribution of specific class I and class IIb HDACs to inflammatory gene expression in RA fibroblast-like synoviocytes (FLS).

Methods

RA FLS were incubated with pan-HDACi (ITF2357, givinostat) or selective HDAC1/2i, HDAC3/6i, HDAC6i and HDAC8i. Alternatively, FLS were transfected with HDAC3, HDAC6 or interferon (IFN)-α/β receptor alpha chain (IFNAR1) siRNA. mRNA expression of interleukin (IL)-1β-inducible genes was measured by quantitative PCR (qPCR) array and signalling pathway activation by immunoblotting and DNA-binding assays.

Results

HDAC3/6i, but not HDAC1/2i and HDAC8i, significantly suppressed the majority of IL-1β-inducible genes targeted by pan-HDACi in RA FLS. Silencing of HDAC3 expression reproduced the effects of HDAC3/6i on gene regulation, contrary to HDAC6-specific inhibition and HDAC6 silencing. Screening of the candidate signal transducers and activators of transcription (STAT)1 transcription factor revealed that HDAC3/6i abrogated STAT1 Tyr701 phosphorylation and DNA binding, but did not affect STAT1 acetylation. HDAC3 activity was required for type I IFN production and subsequent STAT1 activation in FLS. Suppression of type I IFN release by HDAC3/6i resulted in reduced expression of a subset of IFN-dependent genes, including the chemokines CXCL9 and CXCL11.

Conclusions

Inhibition of HDAC3 in RA FLS largely recapitulates the effects of pan-HDACi in suppressing inflammatory gene expression, including type I IFN production in RA FLS. Our results identify HDAC3 as a potential therapeutic target in the treatment of RA and type I IFN-driven autoimmune diseases.

Epigenetic mechanisms involved in modulation of inflammatory diseases

PURPOSE OF REVIEW

The activation of inflammatory response is dependent upon genetic factors and epigenetic control mechanisms. This overview will highlight recent advances in the understanding of epigenetic dynamics during cellular inflammation.

RECENT FINDINGS

There is a growing body of evidence indicating that alterations of the chromatin state associate with an increased risk of chronic disease development and inflammation. Epigenetic alterations respond rapidly to environmental changes and have a profound effect on gene regulatory cross-wirings and transcriptional regulation.

SUMMARY

Systematic dissection of the mechanisms underlying epigenetic effects during inflammatory response is a critical step toward elucidation of the cell's molecular processes and holds potential for the development of novel therapies for the treatment of chronic diseases.