Glycolysis-dependent histone deacetylase 4 degradation regulates inflammatory cytokine production

Histone deacetylases: the critical enzymes for microglial activation involved in neuropathic pain

Neuropathic pain is a common health problem in clinical practice that can be caused by many different factors, including infection, ischemia, trauma, diabetes mellitus, nerve compression, autoimmune disorders, cancer, trigeminal neuralgia, and abuse of certain drugs. This type of pain can persistently affect patients for a long time, even after the rehabilitation of their damaged tissues. Researchers have identified the crucial role of microglial activation in the pathogenesis of neuropathic pain. Furthermore, emerging evidence has shown that the expression and/or activities of different histone deacetylases (HDACs) can modulate microglial function and neuropathic pain. In this review, we will summarize and discuss the functions and mechanisms of HDACs in microglial activation and neuropathic pain development. Additionally, we will also list the emerging HDAC inhibitors or activators that may contribute to therapeutic advancement in alleviating neuropathic pain.

Inflammation and aging-related disease: A transdisciplinary inflammaging framework

Inflammaging, a state of chronic, progressive low-grade inflammation during aging, is associated with several adverse clinical outcomes, including frailty, disability, and death. Chronic inflammation is a hallmark of aging and is linked to the pathogenesis of many aging-related diseases. Anti-inflammatory therapies are also increasingly being studied as potential anti-aging treatments, and clinical trials have shown benefits in selected aging-related diseases. Despite promising advances, significant gaps remain in defining, measuring, treating, and integrating inflammaging into clinical geroscience research. The Clin-STAR Inflammation Research Interest Group was formed by a group of transdisciplinary clinician-scientists with the goal of advancing inflammaging-related clinical research and improving patient-centered care for older adults. Here, we integrate insights from nine medical subspecialties to illustrate the widespread impact of inflammaging on diseases linked to aging, highlighting the extensive opportunities for targeted interventions. We then propose a transdisciplinary approach to enhance understanding and treatment of inflammaging that aims to improve comprehensive care for our aging patients.

Genetic Commonalities Between Metabolic Syndrome and Rheumatic Diseases Through Disease Interactome Modules

This study aims to elucidate the potential genetic commonalities between metabolic syndrome (MetS) and rheumatic diseases through a disease interactome network, according to publicly available large-scale genome-wide association studies (GWAS). The analysis included linkage disequilibrium score regression analysis, cross trait meta-analysis and colocalisation analysis to identify common genetic overlap. Using modular partitioning, the network-based association between the two disease proteins in the protein-protein interaction set was divided and quantified. Clinical samples from public databases were used to confirm the mapped genes. Mendelian randomisation analyses were conducted using genetic instrumental variables for causal inference. MetS and rheumatoid arthritis (RA), ankylosing spondylitis (AS), systemic lupus erythematosus (SLE), Sjogren's syndrome (SS) and their primary module networks shared topological overlap and genetic correlation. Functional analysis highlighted the significance of these shared targets in processes such as a diverse array of metabolic pathways involving glucose, lipids, energy, protein transport, inflammatory response, autophagy and cytokine regulation, elucidating the pathways through which MetS intersects with rheumatic diseases. Causal associations were determined between MetS phenotypes and rheumatic diseases. The persistence of MetS effects on rheumatic diseases remained evident even after adjusting for alcohol consumption and smoking. We have highlighted specific genetic associations between MetS and rheumatic diseases. Several genes (e.g., PRRC2A, PSMB8, BAG6, GPSM3, PBX2, etc.) have been identified with molecular commonalities in MetS and RA, AS, SLE and SS, which may serve as potential targets for shared treatments.

A novel inhibitor of class IIa histone deacetylases attenuates collagen-induced arthritis

BACKGROUND AND PURPOSE

Most inhibitors of histone deacetylases (HDACs) are not selective and are cytotoxic. Some have anti-inflammatory activity in disease models, but cytotoxicity prevents long-term uses in non-fatal diseases. Inhibitors selective for class IIa HDACs are much less cytotoxic and may have applications in management of chronic inflammatory diseases.

EXPERIMENTAL APPROACH

LL87 is a novel HDAC inhibitor examined here for HDAC enzyme selectivity. It was also investigated in macrophages for cytotoxicity and for inhibition of lipopolysaccharide (LPS)-stimulated cytokine secretion. In a rat model of collagen-induced arthritis, LL87 was investigated for effects on joint inflammation in Dark Agouti rats. Histological, immunohistochemical, micro-computed tomography and molecular analyses characterise developing arthritis and anti-inflammatory efficacy.

KEY RESULTS

LL87 was significantly more inhibitory against class IIa than class I or IIb HDAC enzymes. In macrophages, LL87 was not cytotoxic and reduced both LPS-induced secretion of pro-inflammatory cytokines, and IL6-induced class IIa HDAC activity. In rats, LL87 attenuated paw swelling and clinical signs of arthritis, reducing collagen loss and histological damage in ankle joints. LL87 decreased immune cell infiltration, especially pro-inflammatory macrophages and osteoclasts, into synovial joints and significantly reduced expression of pro-inflammatory cytokines and tissue-degrading proteases.

CONCLUSION AND IMPLICATIONS

A novel inhibitor of class IIa HDACs has been shown to have an anti-inflammatory and anti-arthritic profile distinct from current therapies. It is efficacious in reducing macrophage infiltration and joint inflammation in a chronic model of rat arthritis.

Rethinking the role of microglia in obesity

Microglia are the macrophages of the central nervous system (CNS), implying their role in maintaining brain homeostasis. To achieve this, these cells are sensitive to a plethora of endogenous and exogenous signals, such as neuronal activity, cellular debris, hormones, and pathological patterns, among many others. More recent research suggests that microglia are highly responsive to nutrients and dietary variations. In this context, numerous studies have demonstrated their significant role in the development of obesity under calorie surfeit. Because many reviews already exist on this topic, we have chosen to present the state of our reflections on various concepts put forth in the literature, bringing a new perspective whenever possible. Our literature review focuses on studies conducted in the arcuate nucleus of the hypothalamus, a key structure in the control of food intake. Specifically, we present the recent data available on the modifications of microglial energy metabolism following the consumption of an obesogenic diet and their consequences on hypothalamic neuron activity. We also highlight the studies unraveling the mechanisms underlying obesity-related sexual dimorphism. The review concludes with a list of questions that remain to be addressed in the field to achieve a comprehensive understanding of the role of microglia in the regulation of body energy metabolism. This article is part of the Special Issue on "Microglia".

PD-L1 promotes oncolytic virus infection via a metabolic shift that inhibits the type I IFN pathway

While conventional wisdom initially postulated that PD-L1 serves as the inert ligand for PD-1, an emerging body of literature suggests that PD-L1 has cell-intrinsic functions in immune and cancer cells. In line with these studies, here we show that engagement of PD-L1 via cellular ligands or agonistic antibodies, including those used in the clinic, potently inhibits the type I interferon pathway in cancer cells. Hampered type I interferon responses in PD-L1-expressing cancer cells resulted in enhanced efficacy of oncolytic viruses in vitro and in vivo. Consistently, PD-L1 expression marked tumor explants from cancer patients that were best infected by oncolytic viruses. Mechanistically, PD-L1 promoted a metabolic shift characterized by enhanced glycolysis rate that resulted in increased lactate production. In turn, lactate inhibited type I IFN responses. In addition to adding mechanistic insight into PD-L1 intrinsic function, our results will also help guide the numerous ongoing efforts to combine PD-L1 antibodies with oncolytic virotherapy in clinical trials.

Roles of Histone Deacetylase 4 in the Inflammatory and Metabolic Processes

Histone deacetylase 4 (HDAC4), a class IIa HDAC, has gained attention as a potential therapeutic target in treating inflammatory and metabolic processes based on its essential role in various biological pathways by deacetylating non-histone proteins, including transcription factors. The activity of HDAC4 is regulated at the transcriptional, post-transcriptional, and post-translational levels. The functions of HDAC4 are tissue-dependent in response to endogenous and exogenous factors and their substrates. In particular, the association of HDAC4 with non-histone targets, including transcription factors, such as myocyte enhancer factor 2, hypoxia-inducible factor, signal transducer and activator of transcription 1, and forkhead box proteins, play a crucial role in regulating inflammatory and metabolic processes. This review summarizes the regulatory modes of HDAC4 activity and its functions in inflammation, insulin signaling and glucose metabolism, and cardiac muscle development.

Stress and Microglia: A Double-edged Relationship

Microglia are highly dynamic cells and acquire different activation states to modulate their multiple functions, which are tightly regulated by the central nervous system microenvironment in which they reside. In response to stress, that is to the appearance of non-physiological signals in their vicinity, microglia will adapt their function in order to promote a return to brain homeostasis. However, when these stress signals are chronically present, microglial response may not be adapted and lead to the establishment of a pathological state. The aim of this book chapter is to examine the substantial literature around the ability of acute and chronic stressors to affect microglial structure and function, with a special focus on psychosocial and nutritional stresses. We also discuss the molecular mechanisms known to date that explain the link between exposure to stressors and microglial activation.

Interleukin 1β triggers synaptic and memory deficits in Herpes simplex virus type-1-infected mice by downregulating the expression of synaptic plasticity-related genes via the epigenetic MeCP2/HDAC4 complex

Extensive research provides evidence that neuroinflammation underlies numerous brain disorders. However, the molecular mechanisms by which inflammatory mediators determine synaptic and cognitive dysfunction occurring in neurodegenerative diseases (e.g., Alzheimer's disease) are far from being fully understood. Here we investigated the role of interleukin 1β (IL-1β), and the molecular cascade downstream the activation of its receptor, to the synaptic dysfunction occurring in the mouse model of multiple Herpes simplex virus type-1 (HSV-1) reactivations within the brain. These mice are characterized by neuroinflammation and memory deficits associated with a progressive accumulation of neurodegenerative hallmarks (e.g., amyloid-β protein and tau hyperphosphorylation). Here we show that mice undergone two HSV-1 reactivations in the brain exhibited increased levels of IL-1β along with significant alterations of: (1) cognitive performances; (2) hippocampal long-term potentiation; (3) expression synaptic-related genes and pre- and post-synaptic proteins; (4) dendritic spine density and morphology. These effects correlated with activation of the epigenetic repressor MeCP2 that, in association with HDAC4, affected the expression of synaptic plasticity-related genes. Specifically, in response to HSV-1 infection, HDAC4 accumulated in the nucleus and promoted MeCP2 SUMOylation that is a post-translational modification critically affecting the repressive activity of MeCP2. The blockade of IL-1 receptors by the specific antagonist Anakinra prevented the MeCP2 increase and the consequent downregulation of gene expression along with rescuing structural and functional indices of neurodegeneration. Collectively, our findings provide novel mechanistic evidence on the role played by HSV-1-activated IL-1β signaling pathways in synaptic deficits leading to cognitive impairment.

Lyn-mediated glycolysis enhancement of microglia contributes to neuropathic pain through facilitating IRF5 nuclear translocation in spinal dorsal horn

The pro-inflammatory phenotype of microglia usually induces neuroinflammatory reactions in neuropathic pain. Glycometabolism shift to glycolysis can promote the pro-inflammatory phenotype transition of microglia. The omics data analysis suggest a critical role for Lyn dysregulation in neuropathic pain. The present study aimed at exploring the mechanism of Lyn-mediated glycolysis enhancement of microglia in neuropathic pain. Neuropathic pain model was established by chronic constriction injury (CCI), then pain thresholds and Lyn expression were measured. Lyn inhibitor Bafetinib and siRNA-lyn knockdown were administrated intrathecally to evaluate the effects of Lyn on pain thresholds, glycolysis and interferon regulatory factor 5 (IRF5) nuclear translocation of microglia in vivo and in vitro. ChIP was carried out to observe the binding of transcription factors SP1, PU.1 to glycolytic gene promoters by IRF5 knockdown. Finally, the relationship between glycolysis and pro-inflammatory phenotype transition of microglia was evaluated. CCI led to the upregulation of Lyn expression and glycolysis enhancement in microglia of spinal dorsal horn. Bafetinib or siRNA-lyn knockdown intrathecally alleviated pain hyperalgesia, suppressed glycolysis enhancement and inhibited nuclear translocation of IRF5 in CCI mice. Also, IRF5 promoted the binding of transcription factors SP1, PU.1 to glycolytic gene promoters, and then the enhanced glycolysis facilitated the proliferation and pro-inflammatory phenotype transition of microglia and contributed to neuropathic pain. Lyn-mediated glycolysis enhancement of microglia contributes to neuropathic pain through facilitating IRF5 nuclear translocation in spinal dorsal horn.

HDAC4 in cancer: A multitasking platform to drive not only epigenetic modifications

Controlling access to genomic information and maintaining its stability are key aspects of cell life. Histone acetylation is a reversible epigenetic modification that allows access to DNA and the assembly of protein complexes that regulate mainly transcription but also other activities. Enzymes known as histone deacetylases (HDACs) are involved in the removal of the acetyl-group or in some cases of small hydrophobic moieties from histones but also from the non-histone substrate. The main achievement of HDACs on histones is to repress transcription and promote the formation of more compact chromatin. There are 18 different HDACs encoded in the human genome. Here we will discuss HDAC4, a member of the class IIa family, and its possible contribution to cancer development.

Epigenomic and transcriptomic analyses reveal differences between low-grade inflammation and severe exhaustion in LPS-challenged murine monocytes

Emerging studies suggest that monocytes can be trained by bacterial endotoxin to adopt distinct memory states ranging from low-grade inflammation to immune exhaustion. While low-grade inflammation may contribute to the pathogenesis of chronic diseases, exhausted monocytes with pathogenic and immune-suppressive characteristics may underlie the pathogenesis of polymicrobial sepsis including COVID-19. However, detailed processes by which the dynamic adaption of monocytes occur remain poorly understood. Here we exposed murine bone-marrow derived monocytes to chronic lipopolysaccharide (LPS) stimulation at low-dose or high-dose, as well as a PBS control. The cells were profiled for genome-wide H3K27ac modification and gene expression. The gene expression of TRAM-deficient and IRAK-M-deficient monocytes with LPS exposure was also analyzed. We discover that low-grade inflammation preferentially utilizes the TRAM-dependent pathway of TLR4 signaling, and induces the expression of interferon response genes. In contrast, high dose LPS uniquely upregulates exhaustion signatures with metabolic and proliferative pathways. The extensive differences in the epigenomic landscape between low-dose and high-dose conditions suggest the importance of epigenetic regulations in driving differential responses. Our data provide potential targets for future mechanistic or therapeutic studies.

Epigenetic Regulation in Sepsis, Role in Pathophysiology and Therapeutic Perspective

Sepsis is characterized by an initial hyperinflammatory response, with intense cell activation and cytokine storm. In parallel, a prolonged compensatory anti-inflammatory response, known as immunological tolerance, can lead to immunosuppression. Clinically, this condition is associated with multiple organ failure, resulting in the patient's death. The mechanisms underlying the pathophysiology of sepsis are not yet fully understood, but evidence is strong showing that epigenetic changes, including DNA methylation and post-translational modifications of histones, modulate the inflammatory response of sepsis. During the onset of infection, host cells undergo epigenetic changes that favor pathogen survival. Besides, epigenetic changes in essential genes also orchestrate the patient's inflammatory response. In this review, we gathered studies on sepsis and epigenetics to show the central role of epigenetic mechanisms in various aspects of the pathogenesis of sepsis and the potential of epigenetic interventions for its treatment.

Glycogen Synthase Kinase 3β Modulates the Inflammatory Response Activated by Bacteria, Viruses, and Parasites

Knowledge of glycogen synthase kinase 3β (GSK3β) activity and the molecules identified that regulate its function in infections caused by pathogenic microorganisms is crucial to understanding how the intensity of the inflammatory response can be controlled in the course of infections. In recent years many reports have described small molecular weight synthetic and natural compounds, proteins, and interference RNA with the potential to regulate the GSK3β activity and reduce the deleterious effects of the inflammatory response. Our goal in this review is to summarize the most recent advances on the role of GSK3β in the inflammatory response caused by bacteria, bacterial virulence factors (i.e. LPS and others), viruses, and parasites and how the regulation of its activity, mainly its inhibition by different type of molecules, modulates the inflammation.

Epigenetic Modifiers: Anti-Neoplastic Drugs With Immunomodulating Potential

Cancer cells are under the surveillance of the host immune system. Nevertheless, a number of immunosuppressive mechanisms allow tumors to escape protective responses and impose immune tolerance. Epigenetic alterations are central to cancer cell biology and cancer immune evasion. Accordingly, epigenetic modulating agents (EMAs) are being exploited as anti-neoplastic and immunomodulatory agents to restore immunological fitness. By simultaneously acting on cancer cells, e.g. by changing expression of tumor antigens, immune checkpoints, chemokines or innate defense pathways, and on immune cells, e.g. by remodeling the tumor stroma or enhancing effector cell functionality, EMAs can indeed overcome peripheral tolerance to transformed cells. Therefore, combinations of EMAs with chemo- or immunotherapy have become interesting strategies to fight cancer. Here we review several examples of epigenetic changes critical for immune cell functions and tumor-immune evasion and of the use of EMAs in promoting anti-tumor immunity. Finally, we provide our perspective on how EMAs could represent a game changer for combinatorial therapies and the clinical management of cancer.

Role of Epigenetics in the Regulation of Immune Functions of the Skin

This review is intended to illuminate the emerging understanding of epigenetic modifications that regulate both adaptive and innate immunity in the skin. Host defense of the epidermis and dermis involves the interplay of many cell types to enable homeostasis; tolerance to the external environment; and appropriate response to transient microbial, chemical, and physical insults. To understand this process, the study of cutaneous immunology has focused on immune responses that reflect both adaptive learned and genetically programmed innate defense systems. However, recent advances have begun to reveal that epigenetic modifications of chromatin structure also have a major influence on the skin immune system. This deeper understanding of how enzymatic changes in chromatin structure can modify the skin immune system and may explain how environmental exposures during life, and the microbiome, lead to both short-term and long-term changes in cutaneous allergic and other inflammatory processes. Understanding the mechanisms responsible for alterations in gene and chromatin structure within skin immunocytes could provide key insights into the pathogenesis of inflammatory skin diseases that have thus far evaded understanding by dermatologists.

Inhibition of alcohol-induced inflammation and oxidative stress by astaxanthin is mediated by its opposite actions in the regulation of sirtuin 1 and histone deacetylase 4 in macrophages

We previously demonstrated that astaxanthin (ASTX), a xanthophyll carotenoid, repressed ethanol-induced inflammation and oxidative stress in macrophages. We explored the role of sirtuin 1 (SIRT1) and histone deacetylase 4 (HDAC4) in the inhibitory effect of ASTX on inflammation and oxidative stress in macrophages exposed to ethanol. Ethanol decreased mRNA and protein of SIRT1 while increasing those of HDAC4, which was attenuated by ASTX in RAW 264.7 macrophages and mouse bone marrow-derived macrophages (BMDMs). Inhibition of SIRT1 expression or activity augmented ethanol-induced Hdac4 expression, but SIRT1 activation elicited the opposite effect. Consistently, Hdac4 knockdown increased Sirt1 expression with decreases in ethanol-induced inflammatory gene expression, but its overexpression resulted in the opposite effects. Furthermore, BMDMs from mice with macrophage specific-deletion of Hdac4 (Hdac4^MKO) showed significant decreases in ethanol-induced inflammatory genes and ROS accumulation but an increase in Sirt1 expression. Macrophage specific deletion of Hdac4 or ASTX abolished the changes in genes for mitochondrial biogenesis and glycolysis by ethanol. Ethanol increased mitochondrial respiration, ATP production, and proton leak, but decreased maximal respiration and spare respiratory capacity, all of which were abolished by ASTX in RAW 264.7 macrophages. The ethanol-induced alterations in mitochondrial respiration were abrogated in Hdac4^MKO BMDMs. In conclusion, the anti-inflammatory and antioxidant properties of ASTX in ethanol-treated macrophages may be mediated, at least partly, by its opposite effect on SIRT1 and HDAC4 to empower SIRT1 to counteract ethanol-induced activation of HDAC4.

Transcriptional, Epigenetic and Metabolic Programming of Tumor-Associated Macrophages

Macrophages are key innate immune cells in the tumor microenvironment (TME) that regulate primary tumor growth, vascularization, metastatic spread and tumor response to various types of therapies. The present review highlights the mechanisms of macrophage programming in tumor microenvironments that act on the transcriptional, epigenetic and metabolic levels. We summarize the latest knowledge on the types of transcriptional factors and epigenetic enzymes that control the direction of macrophage functional polarization and their pro- and anti-tumor activities. We also focus on the major types of metabolic programs of macrophages (glycolysis and fatty acid oxidation), and their interaction with cancer cells and complex TME. We have discussed how the regulation of macrophage polarization on the transcriptional, epigenetic and metabolic levels can be used for the efficient therapeutic manipulation of macrophage functions in cancer.

Functional Inhibition of Host Histone Deacetylases (HDACs) Enhances in vitro and in vivo Anti-mycobacterial Activity in Human Macrophages and in Zebrafish

The rapid and persistent increase of drug-resistant Mycobacterium tuberculosis (Mtb) infections poses increasing global problems in combatting tuberculosis (TB), prompting for the development of alternative strategies including host-directed therapy (HDT). Since Mtb is an intracellular pathogen with a remarkable ability to manipulate host intracellular signaling pathways to escape from host defense, pharmacological reprogramming of the immune system represents a novel, potentially powerful therapeutic strategy that should be effective also against drug-resistant Mtb. Here, we found that host-pathogen interactions in Mtb-infected primary human macrophages affected host epigenetic features by modifying histone deacetylase (HDAC) transcriptomic levels. In addition, broad spectrum inhibition of HDACs enhanced the antimicrobial response of both pro-inflammatory macrophages (Mϕ1) and anti-inflammatory macrophages (Mϕ2), while selective inhibition of class IIa HDACs mainly decreased bacterial outgrowth in Mϕ2. Moreover, chemical inhibition of HDAC activity during differentiation polarized macrophages into a more bactericidal phenotype with a concomitant decrease in the secretion levels of inflammatory cytokines. Importantly, in vivo chemical inhibition of HDAC activity in Mycobacterium marinum-infected zebrafish embryos, a well-characterized animal model for tuberculosis, significantly reduced mycobacterial burden, validating our in vitro findings in primary human macrophages. Collectively, these data identify HDACs as druggable host targets for HDT against intracellular Mtb.

Temporal modulation of host aerobic glycolysis determines the outcome of Mycobacterium marinum infection

Macrophages are the first-line host defense that the invading Mycobacterium tuberculosis (Mtb) encounters. It has been recently reported that host aerobic glycolysis was elevated post the infection by a couple of virulent mycobacterial species. However, whether this metabolic transition is required for host defense against intracellular pathogens and the underlying mechanisms remain to be further investigated. A pathogenic mycobacterial species, M. marinum, is genetically close to Mtb and was utilized in this study. Through analyzing cellular carbon metabolism of RAW 264.7 (a murine macrophage-like cell line) post M. marinum infection, a strong elevation of glycolysis was observed. Next, three glycolysis inhibitors were examined for their ability to inhibit mycobacterial proliferation inside RAW264.7 macrophages. Among them, a glucose analog, 2-deoxyglucose (2-DG) displayed a protective role against mycobacterial infection. Treatment with 2-DG at concentrations of 0.5 or 1 mM significantly induced autophagy and decreased the phagocytosis of M. marinum by macrophages. Moreover, 2-DG pre-treatment exerted a significantly protective effect on zebrafish larvae by limiting the proliferation of M. marinum, and such effect was correlated to tumor necrosis factor alpha (TNF-α) as the 2-DG pre-treatment increased the expression of TNF-α in both mouse peritoneal macrophages and zebrafish. On the contrary, the 2-DG treatment post infection did not restrain proliferation of M. marinum in WT zebrafish, and even accelerated bacterial replication in TNF-α-/- zebrafish. Together, modulation of glycolysis prior to infection boosts host immunity against M. marinum infection, indicating a potential intervention strategy to control mycobacterial infection.

miR-29b attenuates histone deacetylase-4 mediated podocyte dysfunction and renal fibrosis in diabetic nephropathy

Purpose

As epigenetic modifications like chromatin histone modifications have been suggested to play a role in the pathophysiology of Diabetic Nephropathy (DN) and are also found to be regulated by microRNAs. Our main purpose was to explore the role of microRNA in histone modulations associated with DN. There is downregulation of miR-29b due to advanced glycation end products in diabetes. Histone Deacetylase-4 (HDAC4) is amongst the histone modulators which promotes podocytes' impairment and upregulates transforming growth factor-1 (TGF-β1) leading to renal fibrosis. Moreover, macrophage infiltration causes podocytes' apoptosis and IL-6 mediated inflammation. As miR-29b is downregulated in diabetes and HDAC4, TGF-β1 and IL-6 could be the possible therapeutic targets in DN, our study was focussed on unveiling the role of miR-29b in modulation of HDAC4 and hence, in podocyte dysfunction and renal fibrosis in DN.

Methods

In silico analysis and luciferase assay were done to study the interaction between miR-29b and HDAC4. In-vitro DN model was developed in podocytes and miR-29b mimics were transfected. Also, podocytes were co-cultured with macrophage and miR-29b mimics were transfected. At the end, in-vivo DN model was generated in C57BL/6 J male mice and the effect of miR-29b mimics was reconfirmed.

Results

It was found that miR-29b targets the 3' untranslated region of HDAC4. In both in-vitro and in-vivo DN model, downregulation of miR-29b and subsequent increase in HDAC4 expression was observed. The miR-29b mimics suppressed podocytes' inflammation mediated through macrophages and attenuated HDAC4 expression, glomerular damage and renal fibrosis.

Conclusion

This study concludes that miR-29b regulates the expression of HDAC4 which plays a role in controlling renal fibrosis and podocytes' impairment in DN.

Particles from the Echinococcus granulosus Laminated Layer Inhibit CD40 Upregulation in Dendritic Cells by Interfering with Akt Activation

The larval stage of the cestode Echinococcus granulosus causes cystic echinococcosis in humans and livestock. This larva is protected by the millimeter-thick, mucin-based laminated layer (LL), from which materials have to be shed to allow parasite growth. We previously reported that dendritic cells (DCs) respond to microscopic pieces of the mucin gel of the LL (pLL) with unconventional maturation phenotypes, in the absence or presence of Toll-like receptor (TLR) agonists, including lipopolysaccharide (LPS).

The larval stage of the cestode Echinococcus granulosus causes cystic echinococcosis in humans and livestock. This larva is protected by the millimeter-thick, mucin-based laminated layer (LL), from which materials have to be shed to allow parasite growth. We previously reported that dendritic cells (DCs) respond to microscopic pieces of the mucin gel of the LL (pLL) with unconventional maturation phenotypes, in the absence or presence of Toll-like receptor (TLR) agonists, including lipopolysaccharide (LPS). We also reported that the presence of pLL inhibited the activating phosphorylation of the phosphatidylinositol 3-kinase (PI3K) effector Akt induced by granulocyte-macrophage colony-stimulating factor or interleukin-4. We now show that the inhibitory effect of pLL extends to LPS as a PI3K activator, and results in diminished phosphorylation of GSK3 downstream from Akt. Functionally, the inhibition of Akt and GSK3 phosphorylation are linked to the blunted upregulation of CD40, a major feature of the unconventional maturation phenotype. Paradoxically, all aspects of unconventional maturation induced by pLL depend on PI3K class I. Additional components of the phagocytic machinery are needed, but phagocytosis of pLL particles is not required. These observations hint at a DC response mechanism related to receptor-independent mechanisms proposed for certain crystalline and synthetic polymer-based particles; this would fit the previously reported lack of detection of molecular-level motifs necessary of the effects of pLL on DCs. Finally, we report that DCs exposed to pLL are able to condition DCs not exposed to the material so that these cannot upregulate CD40 in full in response to LPS.

Acetylome profiling reveals extensive involvement of lysine acetylation in the conversion of muscle to meat

Protein lysine acetylation is an post-translational modification that regulates gene expression, metabolism, cell signaling, and diseases, but its implication in the postmortem (PM) meat quality development is basically unclear. In the present study, a quantitative proteomic analysis was conducted to profile acetylome in porcine muscle within 24 h PM. In total 595 acetylation sites assigned to 163 proteins were identified in porcine muscle, of which 460 sites distributing to 110 proteins significantly changed in acetylation levels in the conversion of muscle to meat. The dynamic acetylation/deacetylaion of muscle proteins was closely associated with critical chemical-biophysical changes in PM muscle. Bioinformatic analysis revealed that protein lysine acetylation likely regulated postmortem meat quality development by regulating glycolysis and muscle pH, cell stress reponse and apoptosis, muscle contraction and rigor mortis, calcium signaling and proteolysis, IMP synthesis and meat flavor development, and even the stability of pigment proteins and meat color. This study provided the first overview of protein lysine acetylation in PM muscle and revealed its significance in the conversion of muscle to meat. Future exploration of the exact role of protein lysine acetylation at specific sites will further our understanding regarding the underlying mechanisms and be helpful for meat quality control. SIGNIFICANCE: This is the first analysis of acetylome in farm animal and postmortem muscle. Our data showed that the dynamic acetylation/deacetylation of muscle proteins was closely related to the postmortem changes of muscle that affect the final quality of raw meat. Proteins related to glucose metabolism and muscle contraction were the two largest clusters of acetylproteins identified in postmortem porcine muscle. Networks of acetylproteins involved in apoptosis, calcium signaling and IMP synthesis were identified in postmortem porcine muscle at the same time. Our results revealed that protein lysine acetylation regulated the conversion of muscle to meat. It likely regulated meat quality development by regulating postmortem glycolysis, mitochondrion initiated cell apoptosis, calcium signaling, rigor mortis, meat flavor compound sysnthesis and meat tenderization. Our study broadened our understanding of the biochemistry regulating the postmortem conversion of muscle to meat and final meat quality development, which may be helpful for future meat quality control.

Ammonia exposure induced abnormal expression of cytokines and heat shock proteins via glucose metabolism disorders in chicken neutrophils

Ammonia (NH₃) is a highly irritant, alkaline gas. Atmospheric emission of NH₃ was recognized as an environmental challenge. As a global issue, the NH₃ emission survey with spatially detailed information demonstrated that the sources of atmospheric NH₃ include agriculture (livestock wastes, fertilizers) and some industrial activities. As an environmental pollution, excessive NH₃ exposure can induce many bird dysfunction. Neutrophils respond to multiple invading pathogens through different mechanisms. In order to investigate the effect of NH₃ exposure on broilers' neutrophil, 1-day-old broilers were treated with/without NH₃ for 28 days. We extracted neutrophils from peripheral blood of chicken with/without NH₃ exposure and subsequently stimulated with PMA. Changes of cytokines and inflammatory bodies, heat shock proteins (HSPs), and glucose metabolism of neutrophil were examined in both cases. We not only explored that the index associated with inflammation changed due to NH₃ exposure but also observed the status of neutrophils which was treated with PMA stimulation. After NH₃ exposure, IL-1β and IL-6 were significantly increased on broilers neutrophil. Inflammatory-related factors (NLRP3, ASC, and caspase-1) were significantly elevated. The mRNA expression of HSP70 and HSP90 was increased significantly. All glucose metabolism indicators were reduced. In summary, we concluded that NH₃ enhanced inflammation and disrupted glucose metabolism, and increased the expression of HSPs and inflammatory factors. In addition, the sensitivity of neutrophils to exogenous stimuli was diminished. This information can not only be used to evaluate the damage of NH₃-spiked neutrophils to chickens, but also provide clues for human health pathophysiology caused by excess NH₃, providing valuable information for NH₃ risk management.

Alpha-synuclein induces microglial migration via PKM2-dependent glycolysis

After spinal cord injury, microglial cells are activated and converted to an M1 phenotype. Emerging evidence supports the hypothesis that glucose reprogramming accompanies microglial activation. What contributes to the activation of microglia and glucose reprogramming, however, remains unclear. In the current study, we investigated the role and underlying mechanism of a-synuclein in regulating the aerobic glycolysis in microglia. We found that a-synuclein contributed to the reprogramming of glucose metabolism in microglia by promoting glycolysis and inhibiting mitochondrial biogenesis and oxidative phosphorylation. Further studies demonstrated that pyruvate kinase M2 (PKM2), a rate-limiting enzyme in glycolysis, mediated glucose reprogramming regulated by a-synuclein. A co-immunoprecipitation assay and Western blot assay demonstrated that a-synuclein interacted with PKM2. Further studies demonstrated that knockdown of PKM2 in a-synuclein-exposed microglia markedly reduced glycolysis and lactate production. Additionally, a-synuclein exposure promoted migration abilities in glucose-cultured microglia, whereas migration ability was suppressed in PKM2 knockdown microglia. Additionally, the PKM2 activator TEPP-46 promoted migration ability in a-synuclein-treated microglia, compared to treatment with a-synuclein alone. In conclusion, we demonstrate a PKM2-dependent glycolysis of a-synuclein in microglial.

Acute exercise and periodized training in different environments affect histone deacetylase activity and interleukin-10 levels in peripheral blood of patients with type 2 diabetes

AIMS

Our purpose was to investigate the effects of aerobic periodized training in aquatic and land environments on plasma histone deacetylase (HDAC) activity and cytokines levels in peripheral blood of diabetes mellitus type 2 (T2DM) patients.

METHODS

The patients underwent 12 weeks of periodized training programs that including walking or running in a swimming pool (aquatic group) or in a track (dry land group). Blood samples were collected immediately before and after both first and last sessions. Plasma cytokine levels and HDAC activity in peripheral blood mononuclear cell (PBMC) was measured.

RESULTS

The exercise performed in both environments similarly modulated the evaluated acetylation mark, global HDAC activity. However, a differential profile depending on the evaluated time point was detected, since exercise increased acutely HDAC activity in sedentary and after 12 weeks of training period, while a reduced HDAC activity was observed following periodized training (samples collected before the last session). Additionally, the 12 weeks of periodized exercise in both environments increased IL-10 levels.

CONCLUSIONS

Our data support the hypothesis that the modulation of HDAC activity and inflammatory status might be at least partially related to exercise effects on T2DM. The periodized training performed in both aquatic and land environments impacts similarly epigenetic and inflammatory status.

Bisphenol A and Phthalates Modulate Peritoneal Macrophage Function in Female Mice Involving SYMD2-H3K36 Dimethylation

Ample evidence suggests that environmental and occupational exposure to bisphenol A (BPA) and phthalate, two chemicals widely used in the plastics industry, disturbs homeostasis of innate immunity and causes inflammatory diseases. However, the underlying molecular mechanisms of these toxicants in the regulation of macrophage inflammatory functions remain poorly understood. In this study, we addressed the effect of chronic exposure to BPA or phthalate at levels relevant to human exposure, either in vitro or in vivo, on the inflammatory reprograming of peritoneal macrophages. Our studies revealed that BPA and phthalates adversely affected expression levels of the proinflammatory cytokines and mediators in response to lipopolysaccharide stimulation. Exposure to these toxicants also affected gene expression of scavenger receptors and phagocytic capacity of peritoneal macrophages. Our studies revealed that the epigenetic inhibitors differentially modulated target gene expression in these cells. Further analysis revealed that certain histone modification enzymes were aberrantly expressed in response to BPA or phthalate exposure, leading to alteration in the levels of H3K36 acetylation and dimethylation, two chromatin modifications that are critical for transcriptional efficacy and accuracy. Our results further revealed that silencing of H3K36-specific methyltransferase Smyd2 expression or inhibition of SMYD2 enzymatic activity attenuated H3K36 dimethylation and enhanced interleukin-6 and tumor necrosis factor-α expression but dampened the phagocytic capacity of peritoneal macrophages. In summary, our results indicate that peritoneal macrophages are vulnerable to BPA or phthalate at levels relevant to human exposure. These environmental toxicants affect phenotypic programming of macrophages via epigenetic mechanisms involving SMYD2-mediated H3K36 modification.

A shift to glycolysis accompanies the inflammatory changes in PBMCs from individuals with an IQ-discrepant memory

Identification of a blood-based biomarker that can detect early cognitive decline presents a significant healthcare challenge. We prepared peripheral blood mononuclear cells (PBMCs) from individuals who had a poorer than predicted performance in their delayed recall performance on the Logical Memory II Subtest of the Wechsler Memory Scale (WMS) relative to their IQ estimated by the National Adult Reading Test (NART); we described these individuals as IQ-discrepant, compared with IQ-consistent, individuals. Stimulation with Aβ + LPS increased production of TNFα to a greater extent in cells from IQ-discrepant, compared with IQ-consistent, individuals. This was associated with a shift towards glycolysis and the evidence indicates that 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase (PFKFB)3 plays a role in driving glycolysis. A similar shift towards glycolysis was observed in MDMs prepared from IQ-discrepant, compared with IQ-consistent, individuals. The important finding here is that we have established an increased sensitivity to Aβ + LPS stimulation in PBMCs from individuals that under-perform on a memory task, relative to their estimated premorbid IQ, which may be an indicator of early cognitive decline. This may be a useful tool in determining the presence of early cognitive dysfunction.

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.

Lysine Deacetylases and Regulated Glycolysis in Macrophages

Regulated cellular metabolism has emerged as a fundamental process controlling macrophage functions, but there is still much to uncover about the precise signaling mechanisms involved. Lysine acetylation regulates the activity, stability, and/or localization of metabolic enzymes, as well as inflammatory responses, in macrophages. Two protein families, the classical zinc-dependent histone deacetylases (HDACs) and the NAD-dependent HDACs (sirtuins, SIRTs), mediate lysine deacetylation. We describe here mechanisms by which classical HDACs and SIRTs directly regulate specific glycolytic enzymes, as well as evidence that links these protein deacetylases to the regulation of glycolysis-related genes. In these contexts, we discuss HDACs and SIRTs as key control points for regulating immunometabolism and inflammatory outputs from macrophages.

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.

Bioenergetic state regulates innate inflammatory responses through the transcriptional co-repressor CtBP

The innate inflammatory response contributes to secondary injury in brain trauma and other disorders. Metabolic factors such as caloric restriction, ketogenic diet, and hyperglycemia influence the inflammatory response, but how this occurs is unclear. Here, we show that glucose metabolism regulates pro-inflammatory NF-κB transcriptional activity through effects on the cytosolic NADH:NAD⁺ ratio and the NAD(H) sensitive transcriptional co-repressor CtBP. Reduced glucose availability reduces the NADH:NAD⁺ ratio, NF-κB transcriptional activity, and pro-inflammatory gene expression in macrophages and microglia. These effects are inhibited by forced elevation of NADH, reduced expression of CtBP, or transfection with an NAD(H) insensitive CtBP, and are replicated by a synthetic peptide that inhibits CtBP dimerization. Changes in the NADH:NAD⁺ ratio regulate CtBP binding to the acetyltransferase p300, and regulate binding of p300 and the transcription factor NF-κB to pro-inflammatory gene promoters. These findings identify a mechanism by which alterations in cellular glucose metabolism can influence cellular inflammatory responses.

Several metabolic factors affect cellular glucose metabolism as well as the innate inflammatory response. Here, the authors show that glucose metabolism regulates pro-inflammatory responses through effects on the cytosolic NADH:NAD+ ratio and the NAD(H)-sensitive transcription co-repressor CtBP.

Enhanced glycolysis, regulated by HIF-1α via MCT-4, promotes inflammation in arsenite-induced carcinogenesis

Arsenite is well established as a human carcinogen, but the molecular mechanisms leading to arsenite-induced carcinogenesis are complex and elusive. Accelerated glycolysis, a common process in tumor cells called the Warburg effect, is associated with various biological phenomena. However, the role of glycolysis induced by arsenite is unknown. We have found that, with chronic exposure to arsenite, L-02 cells undergo a metabolic shift to glycolysis. In liver cells exposed to arsenite, hypoxia inducible factor-1α (HIF-1α) and monocarboxylate transporter-4 (MCT-4) are over-expressed. MCT-4, directly mediated by HIF-1α, maintains a high level of glycolysis, and the enhanced glycolysis promotes pro-inflammatory properties, which are involved in arsenite carcinogenesis. In addition, serum lactate and cytokines are higher in arsenite-exposed human populations, and there is a positive correlation between them. Moreover, there is a positive relationship between lactate and cytokines with arsenic in hair. In sum, these findings indicate that MCT-4, mediated by HIF-1α, enhances the glycolysis induced by arsenite. Lactate, the end product of glycolysis, is released into the extracellular environment. The acidic microenvironment promotes production of pro-inflammatory cytokines, which contribute to arsenite-induced liver carcinogenesis. These results provide a link between the induction of glycolysis and inflammation in liver cells exposed to arsenite, and thus establish a previously unknown mechanism for arsenite-induced hepatotoxicity.

Role of cellular metabolism in regulating type I interferon responses: Implications for tumour immunology and treatment

Type I interferons (IFN) are increasingly recognized for their role in regulating anti-tumour immune responses. However, chronic activation of these pathways can result in immunosuppression and has been linked to poor responses to genotoxic and radiotoxic therapies. Emerging evidence suggests energy, lipid and amino acid metabolism play an important role in regulating and fine tuning type I IFN responses. Further, dysregulation of these processes has been implicated in the pathogenesis of chronic viral infections and autoimmune disorders. Systematic evaluation of these interrelationships in cancer models and patients may have important implications for the development of targeted IFN based anti-cancer therapeutics with minimal toxicity and limited off target effects.

A seasonal switch in histone deacetylase gene expression in the hypothalamus and their capacity to modulate nuclear signaling pathways

Seasonal animals undergo changes in physiology and behavior between summer and winter conditions. These changes are in part driven by a switch in a series of hypothalamic genes under transcriptional control by hormones and, of recent interest, inflammatory factors. Crucial to the control of transcription are histone deacetylases (HDACs), generally acting to repress transcription by local histone modification. Seasonal changes in hypothalamic HDAC transcripts were investigated in photoperiod-sensitive F344 rats by altering the day-length (photoperiod). HDAC4, 6 and 9 were found to change in expression. The potential influence of HDACs on two hypothalamic signaling pathways that regulate transcription, inflammatory and nuclear receptor signaling, was investigated. For inflammatory signaling the focus was on NF-κB because of the novel finding made that its expression is seasonally regulated in the rat hypothalamus. For nuclear receptor signaling it was discovered that expression of retinoic acid receptor beta was regulated seasonally. HDAC modulation of NF-κB-induced pathways was examined in a hypothalamic neuronal cell line and primary hypothalamic tanycytes. HDAC4/5/6 inhibition altered the control of gene expression (Fos, Prkca, Prkcd and Ptp1b) by inducers of NF-κB that activate inflammation. These inhibitors also modified the action of nuclear receptor ligands thyroid hormone and retinoic acid. Thus seasonal changes in HDAC4 and 6 have the potential to epigenetically modify multiple gene regulatory pathways in the hypothalamus that could act to limit inflammatory pathways in the hypothalamus during long-day summer-like conditions.

Transformation by different oncogenes relies on specific metabolic adaptations

Metabolic adaptations are emerging as common traits of cancer cells and tumor progression. In vitro transformation of NIH 3T3 cells allows the analysis of the metabolic changes triggered by a single oncogene. In this work, we have compared the metabolic changes induced by H-RAS and by the nuclear resident mutant of histone deacetylase 4 (HDAC4). RAS-transformed cells exhibit a dominant aerobic glycolytic phenotype characterized by up-regulation of glycolytic enzymes, reduced oxygen consumption and a defect in complex I activity. In this model of transformation, glycolysis is strictly required for sustaining the ATP levels and the robust cellular proliferation. By contrast, in HDAC4/TM transformed cells, glycolysis is only modestly up-regulated, lactate secretion is not augmented and, instead, mitochondrial oxygen consumption is increased. Our results demonstrate that cellular transformation can be accomplished through different metabolic adaptations and HDAC4/TM cells can represent a useful model to investigate oncogene-driven metabolic changes besides the Warburg effect.

Histone deacetylases in monocyte/macrophage development, activation and metabolism: refining HDAC targets for inflammatory and infectious diseases

Macrophages have central roles in danger detection, inflammation and host defense, and consequently, these cells are intimately linked to most disease processes. Major advances in our understanding of the development and function of macrophages have recently come to light. For example, it is now clear that tissue-resident macrophages can be derived from either blood monocytes or through local proliferation of phagocytes that are originally seeded during embryonic development. Metabolic state has also emerged as a major control point for macrophage activation phenotypes. Herein, we review recent literature linking the histone deacetylase (HDAC) family of enzymes to macrophage development and activation, particularly in relation to these recent developments. There has been considerable interest in potential therapeutic applications for small molecule inhibitors of HDACs (HDACi), not only for cancer, but also for inflammatory and infectious diseases. However, the enormous range of molecular and cellular processes that are controlled by different HDAC enzymes presents a potential stumbling block to clinical development. We therefore present examples of how classical HDACs control macrophage functions, roles of specific HDACs in these processes and approaches for selective targeting of drugs, such as HDACi, to macrophages. Development of selective inhibitors of macrophage-expressed HDACs and/or selective delivery of pan HDACi to macrophages may provide avenues for enhancing efficacy of HDACi in therapeutic applications, while limiting unwanted side effects.

Histone Deacetylase Inhibitors Promote Mitochondrial Reactive Oxygen Species Production and Bacterial Clearance by Human Macrophages

Broad-spectrum histone deacetylase inhibitors (HDACi) are used clinically as anticancer agents, and more isoform-selective HDACi have been sought to modulate other conditions, including chronic inflammatory diseases. Mouse studies suggest that HDACi downregulate immune responses and may compromise host defense. However, their effects on human macrophage antimicrobial responses are largely unknown. Here, we show that overnight pretreatment of human macrophages with HDACi prior to challenge with Salmonella enterica serovar Typhimurium or Escherichia coli results in significantly reduced intramacrophage bacterial loads, which likely reflect the fact that this treatment regime impairs phagocytosis. In contrast, cotreatment of human macrophages with HDACi at the time of bacterial challenge did not impair phagocytosis; instead, HDACi cotreatment actually promoted clearance of intracellular S. Typhimurium and E. coli. Mechanistically, treatment of human macrophages with HDACi at the time of bacterial infection enhanced mitochondrial reactive oxygen species generation by these cells. The capacity of HDACi to promote the clearance of intracellular bacteria from human macrophages was abrogated when cells were pretreated with MitoTracker Red CMXRos, which perturbs mitochondrial function. The HDAC6-selective inhibitor tubastatin A promoted bacterial clearance from human macrophages, whereas the class I HDAC inhibitor MS-275, which inhibits HDAC1 to -3, had no effect on intracellular bacterial loads. These data are consistent with HDAC6 and/or related HDACs constraining mitochondrial reactive oxygen species production from human macrophages during bacterial challenge. Our findings suggest that, whereas long-term HDACi treatment regimes may potentially compromise host defense, selective HDAC inhibitors may have applications in treating acute bacterial infections.

Pyruvate kinase M2 accelerates pro-inflammatory cytokine secretion and cell proliferation induced by lipopolysaccharide in colorectal cancer

Surgery-induced inflammation has been associated with cancer recurrence and metastasis in colorectal cancer (CRC). As a constituent of gram-negative bacteria, lipopolysaccharide (LPS) is frequently abundant in the peri-operative window. However, the definite roles of LPS in tumour progression remain elusive. Here we reported that LPS treatment increased PKM expression through activation of NF-κB signalling pathway, and knockdown of PKM reversed LPS-induced TNF-α, IL-1β production and cell proliferation in CRC cells. We further showed that the PKM2 but not PKM1 mediated the pro-inflammatory and proliferative effects of LPS. Interestingly, LPS promoted PKM2 binding to the STAT3 promoter to enhance STAT3 expression and its subsequent nuclear translocation. Depletion of STAT3 decreased PKM2-induced TNF-α and IL-1β expression, indicating that STAT3 mediates the pro-inflammatory effects of PKM2. Furthermore, it is the protein kinase activity but not the pyruvate kinase activity of PKM2 that is required for inflammatory cytokine production. Collectively, our findings reveal the NF-κB-PKM2-STAT3 axis as a novel mechanism for the regulation of TNF-α and IL-1β production and suggest the importance of PKM2 as a key inflammatory mediator in inflammatory microenvironment.

HDAC4 as a potential therapeutic target in neurodegenerative diseases: a summary of recent achievements

For the past decade protein acetylation has been shown to be a crucial post-transcriptional modification involved in the regulation of protein functions. Histone acetyltransferases (HATs) mediate acetylation of histones which results in the nucleosomal relaxation associated with gene expression. The reverse reaction, histone deacetylation, is mediated by histone deacetylases (HDACs) leading to chromatin condensation followed by transcriptional repression. HDACs are divided into distinct classes: I, IIa, IIb, III, and IV, on the basis of size and sequence homology, as well as formation of distinct repressor complexes. Implications of HDACs in many diseases, such as cancer, heart failure, and neurodegeneration, have identified these molecules as unique and attractive therapeutic targets. The emergence of HDAC4 among the members of class IIa family as a major player in synaptic plasticity raises important questions about its functions in the brain. The characterization of HDAC4 specific substrates and molecular partners in the brain will not only provide a better understanding of HDAC4 biological functions but also might help to develop new therapeutic strategies to target numerous malignancies. In this review we highlight and summarize recent achievements in understanding the biological role of HDAC4 in neurodegenerative processes.

HIV-1 pathogenicity and virion production are dependent on the metabolic phenotype of activated CD4+ T cells

BACKGROUND

HIV-1, like all viruses, is entirely dependent on the host cell for providing the metabolic resources for completion of the viral replication cycle and the production of virions. It is well established that HIV-1 replicates efficiently in activated CD4+ T cells, whereas resting CD4+ T cells are refractory to infection with HIV-1. A hallmark of T cell activation is the upregulation of glycolysis to meet the biosynthetic and bioenergetic needs of cell proliferation and the execution of effector functions by the secretion of cytokines. To date, it has remained unknown if HIV-1 requires the high glycolytic activity of activated T cells to support its replication.

RESULTS

We report that in primary CD4+ T cells, the flux through the glycolytic pathway is increased upon infection with HIV-1. This increase in glycolytic activity does not occur in T cell lines when infected with HIV-1. By providing cells with galactose instead of glucose, the former being a poor substrate for glycolysis, we monitored the effect of preventing glycolysis in CD4+ T cells on virus replication cycle and cell fate. We observed that HIV-1 infected primary CD4+ T cells cultured in galactose have a survival advantage over those cultured in glucose and this coincides with reduced caspase 3 activation and apoptosis in cultures with galactose. T cell lines do not recapitulate this difference in cell death. Finally, we demonstrate that virion production is dependent on glycolysis as cultures containing galactose yield reduced amounts of HIV-1 virions compared with cultures containing glucose.

CONCLUSIONS

The replication of HIV-1 in primary CD4+ T cells causes an increase in glycolytic flux of the cell. Glycolysis is particularly required for virion production and additionally increases the sensitivity of the infected cell to virus-induced cell death.