HDAC6 is a specific deacetylase of peroxiredoxins and is involved in redox regulation. Proc Natl Acad Sci U S A. 2008;105:9633-9638. [PMID: 18606987 DOI: 10.1073/pnas.0803749105]

Biological and structural investigation of tetrahydro-β-carboline-based selective HDAC6 inhibitors with improved stability

Our previously reported HDAC6 inhibitor (HDAC6i) Marbostat-100 (4) has provided many arguments for further clinical evaluation. By the substitution of the acidic hydrogen of 4 for different carbon residues, we were able to generate an all-carbon stereocenter, which significantly improves the hydrolytic stability of the inhibitor. Further asymmetric synthesis has shown that the (S)-configured inhibitors preferentially bind to HDAC6. This led to the highly selective and potent methyl-substituted derivative S-29b, which elicited a long-lasting tubulin hyperacetylation in MV4-11 cells. Finally, a crystal structure of the HDAC6/S-29b complex provided mechanistic explanation for the high potency and stereoselectivity of synthesized compound series.

Design of Multi-Target drugs of HDACs and other Anti-Alzheimer related Targets: Current strategies and future prospects in Alzheimer's diseases therapy

Alzheimer disease (AD) is the most prevalent form of dementia that develops spontaneously in the elderly. It's worth mentioning that as people age, the epigenetic profile of the central nervous system cells changes, which may speed up the development of various neurodegenerative disorders including AD. Histone deacetylases (HDACs) are a class of epigenetic enzymes that can control gene expression without altering the gene sequence. Moreover, a promising strategy for multi-target hybrid design was proposed to potentially improve drug efficacy and reduce side effects. These hybrids are monocular drugs that contain various pharmacophore components and have the ability to bind to different targets at the same time. The HDACs ability to synergistically boost the performance of other anti-AD drugs, as well as the ease with which HDACs inhibitor cap group, can be modified. This has prompted numerous medicinal chemists to design a novel generation of HDACs multi-target inhibitors. Different HDACs inhibitors and other ones such as acetylcholinesterase, butyryl-cholinesterase, phosphodiesterase 9, phosphodiesterase 5 or glycogen synthase kinase 3β inhibitors were merged into hybrids for treatment of AD. This review goes over the scientific rationale for targeting HDACs along with several other crucial targets in AD therapy. This review presents the latest hybrids of HDACs and other AD target pharmacophores.

MOF-mediated PRDX1 acetylation regulates inflammatory macrophage activation

Signaling-dependent changes in protein phosphorylation are critical to enable coordination of transcription and metabolism during macrophage activation. However, the role of acetylation in signal transduction during macrophage activation remains obscure. Here, we identify the redox signaling regulator peroxiredoxin 1 (PRDX1) as a substrate of the lysine acetyltransferase MOF. MOF acetylates PRDX1 at lysine 197, preventing hyperoxidation and thus maintaining its activity under stress. PRDX1 K197ac responds to inflammatory signals, decreasing rapidly in mouse macrophages stimulated with bacterial lipopolysaccharides (LPSs) but not with interleukin (IL)-4 or IL-10. The LPS-induced decrease of PRDX1 K197ac elevates cellular hydrogen peroxide accumulation and augments ERK1/2, but not p38 or AKT, phosphorylation. Concomitantly, diminished PRDX1 K197ac stimulates glycolysis, potentiates H3 serine 28 phosphorylation, and ultimately enhances the production of pro-inflammatory mediators such as IL-6. Our work reveals a regulatory role for redox protein acetylation in signal transduction and coordinating metabolic and transcriptional programs during inflammatory macrophage activation.

Therapeutic indications for HDAC6 inhibitors in the peripheral and central nervous disorders

INTRODUCTION

Inhibition of the enzymatic function of HDAC6 is currently being explored in clinical trials ranging from peripheral neuropathies to cancers. Advances in selective HDAC6 inhibitor discovery allowed studying highly efficacious brain penetrant and peripheral restrictive compounds for treating PNS and CNS indications.

AREAS COVERED

This review explores the multifactorial role of HDAC6 in cells, the common pathological hallmarks of PNS and CNS disorders, and how HDAC6 modulates these mechanisms. Pharmacological inhibition of HDAC6 and genetic knockout/knockdown studies as a therapeutic strategy in PNS and CNS indications were analyzed. Furthermore, we describe the recent developments in HDAC6 PET tracers and their utility in CNS indications. Finally, we explore the advancements and challenges with HDAC6 inhibitor compounds, such as hydroxamic acid, fluoromethyl oxadiazoles, HDAC6 degraders, and thiol-based inhibitors.

EXPERT OPINION

Based on extensive preclinical evidence, pharmacological inhibition of HDAC6 is a promising approach for treating both PNS and CNS disorders, given its involvement in neurodegeneration and aging-related cellular processes. Despite the progress in the development of selective HDAC6 inhibitors, safety concerns remain regarding their chronic administration in PNS and CNS indications, and the development of novel compound classes and modalities inhibiting HDAC6 function offer a way to mitigate some of these safety concerns.

Multimechanism biological profiling of tetrahydro-β-carboline analogues as selective HDAC6 inhibitors for the treatment of Alzheimer's disease

With the intensive research on the pathogenesis of Alzheimer's disease (AD), inhibition of HDAC6 appears to be a potential therapeutic approach for AD. In this paper, a series of tetrahydro-β-carboline derivatives with hydroxamic acid group were fast synthesized. Among all, the most potent 15 selectively inhibited HDAC6 with IC50 of 15.2 nM and markedly increased acetylated alpha-tubulin levels. In cellular assay, 15 showed excellent neurotrophic effect by increasing the expression of GAP43 and Beta-3 tubulin markers. Besides, 15 showed neuroprotective effects in PC12 or SH-SY5Y cells against H2O2 and 6-OHDA injury through activation of Nrf2, catalase and Prx II, and significantly reduced H2O2-induced reactive oxygen species (ROS) production. In vivo, 15 significantly attenuated zebrafish anxiety-like behaviour and memory deficits in a SCOP-induced zebrafish model of AD. To sum up, multifunctional 15 might be a good lead to develop novel tetrahydrocarboline-based agents for the treatment of AD.

Histone deacetylases: potential therapeutic targets for idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive disease of unknown origin and the most common interstitial lung disease. However, therapeutic options for IPF are limited, and novel therapies are urgently needed. Histone deacetylases (HDACs) are enzymes that participate in balancing histone acetylation activity for chromatin remodeling and gene transcription regulation. Increasing evidence suggests that the HDAC family is linked to the development and progression of chronic fibrotic diseases, including IPF. This review aims to summarize available information on HDACs and related inhibitors and their potential applications in treating IPF. In the future, HDACs may serve as novel targets, which can aid in understanding the etiology of PF, and selective inhibition of single HDACs or disruption of HDAC genes may serve as a strategy for treating PF.

Restoring the epigenome in Alzheimer's disease: advancing HDAC inhibitors as therapeutic agents

Current treatment options for Alzheimer's disease (AD) focus on symptom relief rather than halting disease progression. In this context, targeting histone deacetylation emerges as a promising therapeutic alternative. Dysregulation of histone deacetylase (HDAC) activity is present in AD, contributing to cognitive decline. Pharmacological HDAC inhibition has shown benefits in preclinical models, namely reduced amyloid beta plaque formation, lower phosphorylation and aggregation of tau protein, greater microtubule stability, less neuroinflammation, and improved metabolic homeostasis and cell survival. Nonetheless, clinical trials evidenced limitations such as insufficient selectivity or blood-brain barrier penetration. Hence, future innovative strategies are required to enhance their efficacy/safety.

Collagen sponge scaffolds loaded with Trichostatin A pretreated BMSCs-derived exosomes regulate macrophage polarization to promote skin wound healing

The process of wound healing includes the inflammatory stage, which plays an important role. Macrophages can promote inflammatory response and also promote angiogenesis, wound contraction and tissue remodeling required for wound healing. It is crucial to promote macrophages to polarize from M1 pro-inflammatory phenotype to M2 anti-inflammatory phenotype at a critical time for the quality of wound healing. Because mesenchymal stem cell-derived exosomes have broad therapeutic prospects in the field of tissue repair and regeneration, in this study, we explored whether trichostatin A pretreated bone marrow mesenchymal stem cells (BMSCs)-derived exosomes (T-Exo) could promote wound healing by binding to biomaterial scaffolds through certain anti-inflammatory effects. In the cell experiment, we established macrophage inflammation model and then treated with T-Exo, and finally detected the expression levels of macrophage polarization proteins CD206, CD86 and TNF-α, iNOS, and Arg-1 by Western Blot and immunofluorescence staining; detected the expression levels of inflammation-related genes TNF-α, iNOS, IL-1β, IL-10 and anti-inflammatory genes CD206 and Arg-1 by qRT-PCR; explored the promoting ability of T-Exo to promote cell migration and tube formation by cell scratch experiment and angiogenesis experiment. The results showed that T-Exo could promote the polarization of M1 macrophages to M2 macrophages, and promote the migration and angiogenesis of HUVECs. Because TSA pretreatment may bring about changes in the content and function of BMSCs-derived exosomes, proteomic analysis was performed on T-Exo and unpretreated BMSCs-derived exosomes (Exo). The results showed that the differentially expressed proteins in T-Exo were related to some pathways that promote angiogenesis, cell migration, proliferation, and re-epithelialization. Then, exosome/collagen sponge (T-Exo/Col) biological scaffolds were prepared, and the physicochemical properties and biocompatibility of the scaffolds were investigated. Animal skin wound models were established, and the therapeutic effect and anti-inflammatory effect of T-Exo/Col in wound repair were evaluated by small animal in vivo imaging, H&E staining, Masson trichrome staining, immunohistochemical staining, Western Blot, and qRT-PCR. The results showed that T-Exo significantly promoted wound healing by inhibiting inflammation, thereby further promoting angiogenesis and collagen formation in vivo. Moreover, the existence of Col scaffold in T-Exo/Col enabled T-Exo to achieve a certain sustained release effect. Finally, we further explored whether TSA exerts beneficial effects by inhibiting HDAC6 gene of BMSCs, but the results showed that knockdown of HDAC6 gene would cause oxidative stress damage to BMSCs, which means that TSA does not produce these beneficial effects by inhibiting HDAC6 gene. What molecular mechanisms TSA exerts beneficial effects through needs to be further elucidated in the future.

Histone deacetylase as emerging pharmacological therapeutic target for neuropathic pain: From epigenetic to selective drugs

BACKGROUND

Neuropathic pain remains a formidable challenge for modern medicine. The first-line pharmacological therapies exhibit limited efficacy and unfavorable side effect profiles, highlighting an unmet need for effective therapeutic medications. The past decades have witnessed an explosion in efforts to translate epigenetic concepts into pain therapy and shed light on epigenetics as a promising avenue for pain research. Recently, the aberrant activity of histone deacetylase (HDAC) has emerged as a key mechanism contributing to the development and maintenance of neuropathic pain.

AIMS

In this review, we highlight the distinctive role of specific HDAC subtypes in a cell-specific manner in pain nociception, and outline the recent experimental evidence supporting the therapeutic potential of HDACi in neuropathic pain.

METHODS

We have summarized studies of HDAC in neuropathic pain in Pubmed.

RESULTS

HDACs, widely distributed in the neuronal and non-neuronal cells of the dorsal root ganglion and spinal cord, regulate gene expression by deacetylation of histone or non-histone proteins and involving in increased neuronal excitability and neuroinflammation, thus promoting peripheral and central sensitization. Importantly, pharmacological manipulation of aberrant acetylation using HDAC-targeted inhibitors (HDACi) has shown promising pain-relieving properties in various preclinical models of neuropathic pain. Yet, many of which exhibit low-specificity that may induce off-target toxicities, underscoring the necessity for the development of isoform-selective HDACi in pain management.

CONCLUSIONS

Abnormally elevated HDACs promote neuronal excitability and neuroinflammation by epigenetically modulating pivotal gene expression in neuronal and immune cells, contributing to peripheral and central sensitization in the progression of neuropathic pain, and HDACi showed significant efficacy and great potential for alleviating neuropathic pain.

Central inhibition of HDAC6 re-sensitizes leptin signaling during obesity to induce profound weight loss

Leptin resistance during excess weight gain significantly contributes to the recidivism of obesity to leptin-based pharmacological therapies. The mechanisms underlying the inhibition of leptin receptor (LepR) signaling during obesity are still elusive. Here, we report that histone deacetylase 6 (HDAC6) interacts with LepR, reducing the latter's activity, and that pharmacological inhibition of HDAC6 activity disrupts this interaction and augments leptin signaling. Treatment of diet-induced obese mice with blood-brain barrier (BBB)-permeable HDAC6 inhibitors profoundly reduces food intake and leads to potent weight loss without affecting the muscle mass. Genetic depletion of Hdac6 in Agouti-related protein (AgRP)-expressing neurons or administration with BBB-impermeable HDAC6 inhibitors results in a lack of such anti-obesity effect. Together, these findings represent the first report describing a mechanistically validated and pharmaceutically tractable therapeutic approach to directly increase LepR activity as well as identifying centrally but not peripherally acting HDAC6 inhibitors as potent leptin sensitizers and anti-obesity agents.

Potent hydroxamate-derived compounds arrest endodyogeny of Toxoplasma gondii tachyzoites

Toxoplasmosis is a zoonosis that is a worldwide health problem, commonly affecting fetal development and immunodeficient patients. Treatment is carried out with a combination of pyrimethamine and sulfadiazine, which can cause cytopenia and intolerance and does not lead to a parasitological cure of the infection. Lysine deacetylases (KDACs), which remove an acetyl group from lysine residues in histone and non-histone proteins are found in the Toxoplasma gondii genome. Previous work showed the hydroxamate-type KDAC inhibitors Tubastatin A (TST) and Vorinostat (Suberoylanilide Hydroxamic Acid, SAHA) were effective against T. gondii. In the present study, the effects of three hydroxamates (KV-24, KV-30, KV-46), which were originally designed to inhibit human KDAC6, showed different effects against T. gondii. These compounds contain a heterocyclic cap group and a benzyl linker bearing the hydroxamic acid group in para-position. All compounds showed selective activity against T. gondii proliferation, inhibiting tachyzoite proliferation with IC50 values in a nanomolar range after 48h treatment. Microscopy analyses showed that after treatment, tachyzoites presented mislocalization of the apicoplast, disorganization of the inner membrane complex, and arrest in the completion of new daughter cells. The number of dividing cells with incomplete endodyogeny increased significantly after treatment, indicating the compounds can interfere in the late steps of cell division. The results obtained in this work that these new hydroxamates should be considered for future in vivo tests and the development of new compounds for treating toxoplasmosis.

Emerging therapeutic strategies in cancer therapy by HDAC inhibition as the chemotherapeutic potent and epigenetic regulator

In developing new cancer medications, attention has been focused on novel epigenetic medicines called histone deacetylase (HDAC) inhibitors. Our understanding of cancer behavior is being advanced by research on epigenetics, which also supplies new targets for improving the effectiveness of cancer therapy. Most recently published patents emphasize HDAC selective drugs and multitarget HDAC inhibitors. Though significant progress has been made in emerging HDAC selective antagonists, it is urgently necessary to find new HDAC blockers with novel zinc-binding analogues to avoid the undesirable pharmacological characteristics of hydroxamic acid. HDAC antagonists have lately been explored as a novel approach to treating various diseases, including cancer. The complicated terrain of HDAC inhibitor development is summarized in this article, starting with a discussion of the many HDAC isotypes and their involvement in cancer biology, followed by a discussion of the mechanisms of action of HDAC inhibitors, their current level of development, effect of miRNA, and their combination with immunotherapeutic.

Dual role of PRDX1 in redox-regulation and tumorigenesis: Past and future

Tumour cells often display an active metabolic profile, leading to the intracellular accumulation of reactive oxygen species. As a member of the peroxidase family, peroxiredoxin 1 (PRDX1) functions generally in protecting against cell damage caused by H2O2. Additionally, PRDX1 plays a role as a molecular chaperone in various malignant tumours, exhibiting either tumour-promoting or tumour-suppressing effects. Currently, PRDX1-targeting drugs have demonstrated in vitro anticancer effects, indicating the potential of PRDX1 as a molecular target. Here we discussed the diverse functions of PRDX1 in tumour biology and provided a comprehensive analysis of the therapeutic potential of targeting PRDX1 signalling across various types of cancer.

Role of Histone Deacetylase 6 and Histone Deacetylase 6 Inhibition in Colorectal Cancer

Histone deacetylase 6 (HDAC6), by deacetylation of multiple substrates and association with interacting proteins, regulates many physiological processes that are involved in cancer development and invasiveness such as cell proliferation, apoptosis, motility, epithelial to mesenchymal transition, and angiogenesis. Due to its ability to remove misfolded proteins, induce autophagy, and regulate unfolded protein response, HDAC6 plays a protective role in responses to stress and enables tumor cell survival. The scope of this review is to discuss the roles of HDCA6 and its implications for the therapy of colorectal cancer (CRC). As HDAC6 is overexpressed in CRC, correlates with poor disease prognosis, and is not essential for normal mammalian development, it represents a good therapeutic target. Selective inhibition of HDAC6 impairs growth and progression without inducing major adverse events in experimental animals. In CRC, HDAC6 inhibitors have shown the potential to reduce tumor progression and enhance the therapeutic effect of other drugs. As HDAC6 is involved in the regulation of immune responses, HDAC6 inhibitors have shown the potential to improve antitumor immunity by increasing the immunogenicity of tumor cells, augmenting immune cell activity, and alleviating immunosuppression in the tumor microenvironment. Therefore, HDAC6 inhibitors may represent promising candidates to improve the effect of and overcome resistance to immunotherapy.

Endoplasmic reticulum stress: molecular mechanism and therapeutic targets

The endoplasmic reticulum (ER) functions as a quality-control organelle for protein homeostasis, or "proteostasis". The protein quality control systems involve ER-associated degradation, protein chaperons, and autophagy. ER stress is activated when proteostasis is broken with an accumulation of misfolded and unfolded proteins in the ER. ER stress activates an adaptive unfolded protein response to restore proteostasis by initiating protein kinase R-like ER kinase, activating transcription factor 6, and inositol requiring enzyme 1. ER stress is multifaceted, and acts on aspects at the epigenetic level, including transcription and protein processing. Accumulated data indicates its key role in protein homeostasis and other diverse functions involved in various ocular diseases, such as glaucoma, diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, achromatopsia, cataracts, ocular tumors, ocular surface diseases, and myopia. This review summarizes the molecular mechanisms underlying the aforementioned ocular diseases from an ER stress perspective. Drugs (chemicals, neurotrophic factors, and nanoparticles), gene therapy, and stem cell therapy are used to treat ocular diseases by alleviating ER stress. We delineate the advancement of therapy targeting ER stress to provide new treatment strategies for ocular diseases.

Mitochondrial NIR imaging probe mitigating oxidative damage by targeting HDAC6

Despite the apparent copious fluorescent probes targeting mitochondria, the development of low cytotoxic probes is still needed for improving validation of mitochondrial function assessment. Herein, we report a novel cyanine-based NIR fluorescent probe, T2, which selectively targets mitochondria with significantly low toxicity by modulating the intracellular redox status. Additionally, T2 inhibits oxidative stress-induced cell death in cortical neurons. This study provides new insight into developing low-toxic mitochondrial imaging agents by regulating redox homeostasis.

Histone deacetylase 6's function in viral infection, innate immunity, and disease: latest advances

In the family of histone-deacetylases, histone deacetylase 6 (HDAC6) stands out. The cytoplasmic class IIb histone deacetylase (HDAC) family is essential for many cellular functions. It plays a crucial and debatable regulatory role in innate antiviral immunity. This review summarises the current state of our understanding of HDAC6's structure and function in light of the three mechanisms by which it controls DNA and RNA virus infection: cytoskeleton regulation, host innate immune response, and autophagy degradation of host or viral proteins. In addition, we summed up how HDAC6 inhibitors are used to treat a wide range of diseases, and how its upstream signaling plays a role in the antiviral mechanism. Together, the findings of this review highlight HDAC6's importance as a new therapeutic target in antiviral immunity, innate immune response, and some diseases, all of which offer promising new avenues for the development of drugs targeting the immune response.

Discovery of the First Irreversible HDAC6 Isoform Selective Inhibitor with Potent Anti-Multiple Myeloma Activity

In our previous research, a series of phenylsulfonylfuroxan-based hydroxamates were developed, among which compound 1 exhibited remarkable in vitro and in vivo antitumor potency due to its histone deacetylase (HDAC) inhibitory and nitric oxide (NO)-donating activities. Herein, the in-depth study of compound 1 revealed that this HDAC inhibitor-NO donor hybrid could enduringly increase the intracellular levels of acetyl histones and acetyl α-tubulin, which could be ascribed to its irreversible inhibition toward class I HDACs and HDAC6. Structural modification of compound 1 led to a novel phenylsulfonylfuroxan-based hydroxamate 4, which exhibited considerable HDAC6 inhibitory activity and selectivity. Furthermore, compound 4 could inhibit intracellular HDAC6 both selectively and irreversibly. To the best of our knowledge, this is the first research reporting the irreversible inhibition of HDAC6. It was also demonstrated that compared with ACY-241 (a reversible HDAC6 inhibitor in clinical trials), the irreversible HDAC6 selective inhibitor 4 exhibited not only superior anti-multiple myeloma activity but also improved therapeutic index.

Chemoproteomic target deconvolution reveals Histone Deacetylases as targets of (R)-lipoic acid

Lipoic acid is an essential enzyme cofactor in central metabolic pathways. Due to its claimed antioxidant properties, racemic (R/S)-lipoic acid is used as a food supplement but is also investigated as a pharmaceutical in over 180 clinical trials covering a broad range of diseases. Moreover, (R/S)-lipoic acid is an approved drug for the treatment of diabetic neuropathy. However, its mechanism of action remains elusive. Here, we performed chemoproteomics-aided target deconvolution of lipoic acid and its active close analog lipoamide. We find that histone deacetylases HDAC1, HDAC2, HDAC3, HDAC6, HDAC8, and HDAC10 are molecular targets of the reduced form of lipoic acid and lipoamide. Importantly, only the naturally occurring (R)-enantiomer inhibits HDACs at physiologically relevant concentrations and leads to hyperacetylation of HDAC substrates. The inhibition of HDACs by (R)-lipoic acid and lipoamide explain why both compounds prevent stress granule formation in cells and may also provide a molecular rationale for many other phenotypic effects elicited by lipoic acid.

The role of P21-activated kinase (Pak1) in sinus node function

Sinoatrial node (SAN) dysfunction (SND) and atrial arrhythmia frequently occur simultaneously with a hazard ratio of 4.2 for new onset atrial fibrillation (AF) in SND patients. In the atrial muscle attenuated activity of p21-activated kinase 1 (Pak1) increases the risk for AF by enhancing NADPH oxidase 2 dependent production of reactive oxygen species (ROS). However, the role of Pak1 dependent ROS regulation in SAN function has not yet been determined. We hypothesize that Pak1 activity maintains SAN activity by regulating the expression of the hyperpolarization activated cyclic nucleotide gated cation channel (HCN). To determine Pak1 dependent changes in heart rate (HR) regulation we quantified the intrinsic sinus rhythm in wild type (WT) and Pak1 deficient (Pak1-/-) mice of both sexes in vivo and in isolated Langendorff perfused hearts. Pak1-/- hearts displayed an attenuated HR in vivo after autonomic blockage and in isolated hearts. The contribution of the Ca2+ clock to pacemaker activity remained unchanged, but Ivabradine (3 μM), a blocker of HCN channels that are a membrane clock component, eliminated the differences in SAN activity between WT and Pak1-/- hearts. Reduced HCN4 expression was confirmed in Pak1-/- right atria. The reduced HCN activity in Pak1-/- could be rescued by class II HDAC inhibition (LMK235), ROS scavenging (TEMPOL) or attenuation of Extracellular Signal-Regulated Kinase (ERK) 1/2 activity (SCH772984). No sex specific differences in Pak1 dependent SAN regulation were determined. Our results establish Pak1 as a class II HDAC regulator and a potential therapeutic target to attenuate SAN bradycardia and AF susceptibility.

Peroxiredoxin 2: An Important Element of the Antioxidant Defense of the Erythrocyte

Peroxiredoxin 2 (Prdx2) is the third most abundant erythrocyte protein. It was known previously as calpromotin since its binding to the membrane stimulates the calcium-dependent potassium channel. Prdx2 is present mostly in cytosol in the form of non-covalent dimers but may associate into doughnut-like decamers and other oligomers. Prdx2 reacts rapidly with hydrogen peroxide (k > 10⁷ M^-1 s^-1). It is the main erythrocyte antioxidant that removes hydrogen peroxide formed endogenously by hemoglobin autoxidation. Prdx2 also reduces other peroxides including lipid, urate, amino acid, and protein hydroperoxides and peroxynitrite. Oxidized Prdx2 can be reduced at the expense of thioredoxin but also of other thiols, especially glutathione. Further reactions of Prdx2 with oxidants lead to hyperoxidation (formation of sulfinyl or sulfonyl derivatives of the peroxidative cysteine). The sulfinyl derivative can be reduced by sulfiredoxin. Circadian oscillations in the level of hyperoxidation of erythrocyte Prdx2 were reported. The protein can be subject to post-translational modifications; some of them, such as phosphorylation, nitration, and acetylation, increase its activity. Prdx2 can also act as a chaperone for hemoglobin and erythrocyte membrane proteins, especially during the maturation of erythrocyte precursors. The extent of Prdx2 oxidation is increased in various diseases and can be an index of oxidative stress.

Augmentation of Histone Deacetylase 6 Activity Impairs Mitochondrial Respiratory Complex I in Ischemic/Reperfused Diabetic Hearts

BACKGROUND

Diabetes augments activity of histone deacetylase 6 (HDAC6) and generation of tumor necrosis factor α (TNFα) and impairs the physiological function of mitochondrial complex I (mCI) which oxidizes reduced nicotinamide adenine dinucleotide (NADH) to nicotinamide adenine dinucleotide to sustain the tricarboxylic acid cycle and β-oxidation. Here we examined how HDAC6 regulates TNFα production, mCI activity, mitochondrial morphology and NADH levels, and cardiac function in ischemic/reperfused diabetic hearts.

METHODS

HDAC6 knockout, streptozotocin-induced type 1 diabetic, and obese type 2 diabetic db/db mice underwent myocardial ischemia/reperfusion injury in vivo or ex vivo in a Langendorff-perfused system. H9c2 cardiomyocytes with and without HDAC6 knockdown were subjected to hypoxia/reoxygenation injury in the presence of high glucose. We compared the activities of HDAC6 and mCI, TNFα and mitochondrial NADH levels, mitochondrial morphology, myocardial infarct size, and cardiac function between groups.

RESULTS

Myocardial ischemia/reperfusion injury and diabetes synergistically augmented myocardial HDCA6 activity, myocardial TNFα levels, and mitochondrial fission and inhibited mCI activity. Interestingly, neutralization of TNFα with an anti-TNFα monoclonal antibody augmented myocardial mCI activity. Importantly, genetic disruption or inhibition of HDAC6 with tubastatin A decreased TNFα levels, mitochondrial fission, and myocardial mitochondrial NADH levels in ischemic/reperfused diabetic mice, concomitant with augmented mCI activity, decreased infarct size, and ameliorated cardiac dysfunction. In H9c2 cardiomyocytes cultured in high glucose, hypoxia/reoxygenation augmented HDAC6 activity and TNFα levels and decreased mCI activity. These negative effects were blocked by HDAC6 knockdown.

CONCLUSIONS

Augmenting HDAC6 activity inhibits mCI activity by increasing TNFα levels in ischemic/reperfused diabetic hearts. The HDAC6 inhibitor, tubastatin A, has high therapeutic potential for acute myocardial infarction in diabetes.

Wounds under diabetic milieu: The role of immune cellar components and signaling pathways

A major challenge in the field of diabetic wound healing is to confirm the body's intrinsic mechanism that could sense the immune system damage promptly and protect the wound from non-healing. Accumulating literature indicates that macrophage, a contributor to prolonged inflammation occurring at the wound site, might play such a role in hindering wound healing. Likewise, other immune cell dysfunctions, such as persistent neutrophils and T cell infection, may also lead to persistent oxidative stress and inflammatory reaction during diabetic wound healing. In this article, we discuss recent advances in the immune cellular components in wounds under the diabetic milieu, and the role of key signaling mechanisms that compromise the function of immune cells leading to persistent wound non-healing.

Advances in the Mechanistic Study of the Control of Oxidative Stress Injury by Modulating HDAC6 Activity

Oxidative stress is defined as an injury resulting from a disturbance in the dynamic equilibrium of the redox environment due to the overproduction of active/radical oxygen exceeding the antioxidative ability of the body. This is a key step in the development of various diseases. Oxidative stress is modulated by different factors and events, including the modification of histones, which are the cores of nucleosomes. Histone modification includes acetylation and deacetylation of certain amino acid residues; this process is catalyzed by different enzymes. Histone deacetylase 6 (HDAC6) is a unique deacetylating protease that also catalyzes the deacetylation of different nonhistone substrates to regulate various physiologic processes. The intimate relationship between HDAC6 and oxidative stress has been demonstrated by different studies. The present paper aims to summarize the data obtained from a mechanistic study of HDAC6 and oxidative stress to guide further investigations on mechanistic characterization and drug development.

Immunoprecipitation of HDAC6 and Interacting Proteins

The lysine deacetylase HDAC6 has unique structural and functional properties: It contains tandem catalytic domains that can deacetylate a variety of proteins and a zinc finger domain that binds ubiquitin. HDAC6 has been implicated in a variety of biological processes, normal or pathological, such as cellular motility, stress response, cancer, neurodegeneration, or viral infection. Due to this, HDAC6 is considered an attractive therapeutic target, and there is a major interest to identify small molecule inhibitors. To gain a mechanistic understanding of how HDAC6 impacts these different biological processes, there is a continued need to discover additional substrates as well as interacting proteins in different paradigms. One approach to achieve this is to perform HDAC6 immunoprecipitations to identify partner proteins. We describe here our optimized protocols to immunoprecipitate HDAC6 with the goal to identify or validate interacting proteins.

In silico design of HDAC6 inhibitors with neuroprotective effects

HDAC6 has emerged as a molecular target to treat neurodegenerative disorders, due to its participation in protein aggregate degradation, oxidative stress process, mitochondrial transport, and axonal transport. Thus, in this work we have designed a set of 485 compounds with hydroxamic and bulky-hydrophobic moieties that may function as HDAC6 inhibitors with a neuroprotective effect. These compounds were filtered by their predicted ADMET properties and their affinity to HDAC6 demonstrated by molecular docking and molecular dynamics simulations. The combination of in silico with in vitro neuroprotective results allowed the identification of a lead compound (FH-27) which shows neuroprotective effect that could be due to HDAC6 inhibition. Further, FH-27 chemical moiety was used to design a second series of compounds improving the neuroprotective effect from 2- to 10-fold higher (YSL-99, YSL-109, YSL-112, YSL-116 and YSL-121; 1.25 ± 0.67, 1.82 ± 1.06, 7.52 ± 1.78, 5.59 and 5.62 ± 0.31 µM, respectively). In addition, the R enantiomer of FH-27 (YSL-106) was synthesized, showing a better neuroprotective effect (1.27 ± 0.60 µM). In conclusion, we accomplish the in silico design, synthesis, and biological evaluation of hydroxamic acid derivatives with neuroprotective effect as suggested by an in vitro model. Communicated by Ramaswamy H. Sarma.

HAT- and HDAC-Targeted Protein Acetylation in the Occurrence and Treatment of Epilepsy

Epilepsy is a common and severe chronic neurological disorder. Recently, post-translational modification (PTM) mechanisms, especially protein acetylation modifications, have been widely studied in various epilepsy models or patients. Acetylation is regulated by two classes of enzymes, histone acetyltransferases (HATs) and histone deacetylases (HDACs). HATs catalyze the transfer of the acetyl group to a lysine residue, while HDACs catalyze acetyl group removal. The expression of many genes related to epilepsy is regulated by histone acetylation and deacetylation. Moreover, the acetylation modification of some non-histone substrates is also associated with epilepsy. Various molecules have been developed as HDAC inhibitors (HDACi), which have become potential antiepileptic drugs for epilepsy treatment. In this review, we summarize the changes in acetylation modification in epileptogenesis and the applications of HDACi in the treatment of epilepsy as well as the mechanisms involved. As most of the published research has focused on the differential expression of proteins that are known to be acetylated and the knowledge of whole acetylome changes in epilepsy is still minimal, a further understanding of acetylation regulation will help us explore the pathological mechanism of epilepsy and provide novel ideas for treating epilepsy.

HDAC6 Inhibition Alleviates Ischemia- and Cisplatin-Induced Acute Kidney Injury by Promoting Autophagy

Histone deacetylase (HDAC) 6 exists exclusively in cytoplasm and deacetylates cytoplasmic proteins such as α-tubulin. HDAC6 dysfunction is associated with several pathological conditions in renal disorders, including UUO-induced fibrotic kidneys and rhabdomyolysis-induced nephropathy. However, the role of HDAC6 in ischemic acute kidney injury (AKI) and the mechanism by which HDAC6 inhibition protects tubular cells after AKI remain unclear. In the present study, we observed that HDAC6 was markedly activated in kidneys subjected to ischemia- and cisplatin (cis)-induced AKI treatment. Pharmacological inhibition of HDAC6 alleviated renal impairment and renal tubular damage after ischemia and cisplatin treatment. HDAC6 dysfunction was associated with decreased acetylation of α-tubulin at the residue of lysine 40 and autophagy. HDAC6 inhibition preserved acetyl-α-tubulin-enhanced autophagy flux in AKI and cultured tubular cells. Genetic ablation of the renal tubular (RT) Atg7 gene or pharmacological inhibition of autophagy suppressed the protective effects of HDAC6. Taken together, our study indicates that HDAC6 contributes to ischemia- and cisplatin-induced AKI by inhibiting autophagy and the acetylation of α-tubulin. These results suggest that HDAC6 could be a potential target for ischemic and nephrotoxic AKI.

Tubulin deacetylase NDST3 modulates lysosomal acidification: Implications in neurological diseases

Neurological diseases (NDs), featured by progressive dysfunctions of the nervous system, have become a growing burden for the aging populations. N-Deacetylase and N-sulfotransferase 3 (NDST3) is known to catalyze deacetylation and N-sulfation on disaccharide substrates. Recently, NDST3 is identified as a novel deacetylase for tubulin, and its newly recognized role in modulating microtubule acetylation and lysosomal acidification provides fresh insights into ND therapeutic approaches using NDST3 as a target. Microtubule acetylation and lysosomal acidification have been reported to be critical for activities in neurons, implying that the regulators of these two biological processes, such as the previously known microtubule deacetylases, histone deacetylase 6 (HDAC6) and sirtuin 2 (SIRT2), could play important roles in various NDs. Aberrant NDST3 expression or tubulin acetylation has been observed in an increasing number of NDs, including amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD), schizophrenia and bipolar disorder, Alzheimer's disease (AD), and Parkinson's disease (PD), suggesting that NDST3 is a key player in the pathogenesis of NDs and may serve as a target for development of new treatment of NDs.

Telomere Shortening in Hypertensive Heart Disease Depends on Oxidative DNA Damage and Predicts Impaired Recovery of Cardiac Function in Heart Failure

BACKGROUND

Heart failure (HF) coincides with cardiomyocyte telomere shortening. Arterial hypertension is the most prominent risk factor for HF. Both HF and arterial hypertension are associated with dysregulation of the neurohormonal axis. How neurohormonal activation is linked to telomere shortening in the pathogenesis of HF is incompletely understood.

METHODS

Cardiomyocyte telomere length was assessed in a mouse model of hypertensive HF induced by excess neurohormonal activation (AngII [angiotensin II] infusion, high salt diet, and uninephrectomy), in AngII-stimulated cardiomyocytes and in endomyocardial biopsies from patients with HF. Superoxide production, expression of NOX2 (NADPH oxidase 2) and PRDX1 (peroxiredoxin 1) and HDAC6 (histone deacetylase 6) activity were assessed.

RESULTS

Telomere shortening occurred in vitro and in vivo, correlating with both left ventricular (LV) dilatation and LV systolic function impairment. Telomere shortening coincided with increased superoxide production, increased NOX2 expression, increased HDAC6 activity, loss of the telomere-specific antioxidant PRDX1, and increased oxidative DNA-damage. NOX2 knockout prevented PRDX1 depletion, DNA-damage and telomere shortening confirming this enzyme as a critical source of reactive oxygen species. Cotreatment with the NOX inhibitor apocynin ameliorated hypertensive HF and telomere shortening. Similarly, treatment with the HDAC6 inhibitor tubastatin A, which increases PRDX1 bioavailability, prevented telomere shortening in adult cardiomyocytes. To explore the clinical relevance of our findings, we examined endomyocardial biopsies from an all-comer population of patients with HF with reduced ejection fraction. Here, cardiomyocyte telomere length predicted the recovery of cardiac function.

CONCLUSIONS

Cardiomyocyte telomere shortening and oxidative damage in heart failure with reduced ejection fraction induced by excess neurohormonal activation depends on NOX2-derived superoxide and may help to stratify HF therapy.

Psychosocial stress and cannabinoid drugs affect acetylation of α-tubulin (K40) and gene expression in the prefrontal cortex of adult mice

The dynamics of neuronal microtubules are essential for brain plasticity. Vesicular transport and synaptic transmission, additionally, requires acetylation of α-tubulin, and aberrant tubulin acetylation and neurobiological deficits are associated. Prolonged exposure to a stressor or consumption of drugs of abuse, like marihuana, lead to neurological changes and psychotic disorders. Here, we studied the effect of psychosocial stress and the administration of cannabinoid receptor type 1 drugs on α-tubulin acetylation in different brain regions of mice. We found significantly decreased tubulin acetylation in the prefrontal cortex in stressed mice. The impact of cannabinoid drugs on stress-induced microtubule disturbance was investigated by administration of the cannabinoid receptor agonist WIN55,212–2 and/or antagonist rimonabant. In both, control and stressed mice, the administration of WIN55,212–2 slightly increased the tubulin acetylation in the prefrontal cortex whereas administration of rimonabant acted antagonistically indicating a cannabinoid receptor type 1 mediated effect. The analysis of gene expression in the prefrontal cortex showed a consistent expression of ApoE attributable to either psychosocial stress or administration of the cannabinoid agonist. Additionally, ApoE expression inversely correlated with acetylated tubulin levels when comparing controls and stressed mice treated with WIN55,212–2 whereas rimonabant treatment showed the opposite.

HDAC6 inhibition attenuates renal injury by reducing IL-1β secretion and RIP kinase mediated necroptosis in acute oxalate nephropathy

BACKGROUND

Pathogenesis of acute kidney injury is driven by necro-inflammation, which is comprised of IL-1β mediated inflammation and RIP-1 mediated tubular necroptosis. HDAC6 is reported to regulate both inflammation and cell death. In the present study, we explored the role of HDAC6 in the lysosomal exocytosis of IL-1β and RIP-1 mediated necroptosis in the context of oxalate nephropathy.

METHODS

Raw 264.7 macrophages and NRK52E stimulated with oxalate crystals and LPS with or without HDAC6 inhibitor for in vitro experiments. Acute oxalate nephropathy was induced in C57BL/6 mice by injecting sodium oxalate (75 mg/kg). For the drug intervention study, Tubastain A (TSA) was given an hour before injection of sodium oxalate. Mice were sacrificed 24 hrs after the oxalate injection, blood and kidney were harvested. Blood samples were analyzed for BUN and IL-1β levels. Renal tissues were analyzed for histology, immunohistochemistry, RNA, and protein expression.

RESULTS

HDAC6 and IL-1β upregulated in crystal stimulated macrophages and acute oxalate nephropathy. Pre-treatment of macrophages with TSA reduced IL-1β in supernatant without affecting the expression of pro-IL-1β and mature IL-1β in cell lysate. The effect of TSA on IL-1β secretion was influenced by tubulin acetylation. Renal epithelial cell NRK52E stimulated with crystals showed upregulation of necroptosis pathway markers and concentration-dependent cell death. TSA inhibited RIP-1, RIP3, and MLKL expression along with p-MLKL in stimulated epithelial cells. TSA treatment of oxalate nephropathy mice showed decreased inflammation and tubular cell death by regulating IL-1β and necroptosis and reduced renal injury.

CONCLUSION

This study highlights the role of HDAC6 in regulating the tubulin-mediated secretion of IL-1β and RIP kinase mediated necroptosis in acute oxalate nephropathy.

Pharmacological inhibition of HDAC6 overcomes cisplatin chemoresistance by targeting cancer stem cells in oral squamous cell carcinoma

BACKGROUND

Chemoresistance is associated with recurrence and metastasis in oral squamous cell carcinoma (OSCC). The cancer stem cell (CSC) subpopulation is highly resistant to therapy, and they are regulated by epigenetic mechanisms. HDACs are histone deacetylase enzymes that epigenetically regulate gene expression. HDAC6 acts on several physiological processes, including oxidative stress, autophagy and DNA damage response, and its accumulation is associated with cancer. Here, we investigate the role of HDAC6 in CSC-mediated chemoresistance in oral carcinoma in addition to its application as a therapeutic target to reverse chemoresistance.

METHODS

Wild-type oral carcinoma cell lines (CAL27 WT and SCC9 WT), cisplatin-resistant (CAL27 CisR and SCC9 CisR), and the subpopulations of cancer stem cells (CSC+) and non-stem (CSC-) derived from CisR cells were investigated. HDAC6 accumulation was analyzed by Western blot and immunofluorescence; DNA damage was evaluated by immunofluorescence of phospho-H2A.X; the qPCR for PRDX2, PRDX6, SOD2, and TXN and ROS assay assessed oxidative stress. Apoptosis and CSC accumulation were investigated by flow cytometry.

RESULTS

We identified the accumulation of HDAC6 in CisR cell lines and CSC. Cisplatin-resistant cell lines and CSC demonstrated a reduction in DNA damage and ROS and elevated expression of PRDX2. The administration of tubastatin A (a specific HDAC6 inhibitor) increased oxidative stress and DNA damage and decreased PRDX2. Tubastatin A as a monotherapy induced apoptosis in CisR and CSC and reduced the stemness phenotype.

CONCLUSION

High levels of HDAC6 sustain CSC subpopulation and chemoresistance in OSCC, suggesting HDAC6 as a pharmacological target to overcome resistance and perhaps prevent recurrence in OSCC.

Macrophage migration inhibitory factor (MIF) acetylation protects neurons from ischemic injury

Ischemia-induced neuronal death leads to serious lifelong neurological deficits in ischemic stroke patients. Histone deacetylase 6 (HDAC6) is a promising target for neuroprotection in many neurological disorders, including ischemic stroke. However, the mechanism by which HDAC6 inhibition protects neurons after ischemic stroke remains unclear. Here, we discovered that genetic ablation or pharmacological inhibition of HDAC6 reduced brain injury after ischemic stroke by increasing macrophage migration inhibitory factor (MIF) acetylation. Mass spectrum analysis and biochemical results revealed that HDAC6 inhibitor or aspirin treatment promoted MIF acetylation on the K78 residue. MIF K78 acetylation suppressed the interaction between MIF and AIF, which impaired MIF translocation to the nucleus in ischemic cortical neurons. Moreover, neuronal DNA fragmentation and neuronal death were impaired in the cortex after ischemia in MIF K78Q mutant mice. Our results indicate that the neuroprotective effect of HDAC6 inhibition and aspirin treatment results from MIF K78 acetylation; thus, MIF K78 acetylation may be a therapeutic target for ischemic stroke and other neurological diseases.

Expression of Protein Acetylation Regulators During Peripheral Nerve Development, Injury, and Regeneration

Protein acetylation, regulated by acetyltransferases and deacetylases, is an important post-translational modification that is involved in numerous physiological and pathological changes in peripheral nerves. There is still no systematical analysis on the expression changes of protein acetylation regulators during sciatic nerve development, injury, and regeneration. Here, we sequenced and analyzed the transcriptome of mouse sciatic nerves during development and after injury. We found that the changes in the expression of most regulators followed the rule that “development is consistent with regeneration and opposite to injury.” Immunoblotting with pan-acetylated antibodies also revealed that development and regeneration are a process of increased acetylation, while injury is a process of decreased acetylation. Moreover, we used bioinformatics methods to analyze the possible downstream molecules of two key regulators, histone deacetylase 1 (Hdac1) and lysine acetyltransferase 2b (Kat2b), and found that they were associated with many genes that regulate the cell cycle. Our findings provide an insight into the association of sciatic nerve development, injury, and regeneration from the perspective of protein acetylation.

Targeting Histone Deacetylases in Idiopathic Pulmonary Fibrosis: A Future Therapeutic Option

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease with limited therapeutic options, and there is a huge unmet need for new therapies. A growing body of evidence suggests that the histone deacetylase (HDAC) family of transcriptional corepressors has emerged as crucial mediators of IPF pathogenesis. HDACs deacetylate histones and result in chromatin condensation and epigenetic repression of gene transcription. HDACs also catalyse the deacetylation of many non-histone proteins, including transcription factors, thus also leading to changes in the transcriptome and cellular signalling. Increased HDAC expression is associated with cell proliferation, cell growth and anti-apoptosis and is, thus, a salient feature of many cancers. In IPF, induction and abnormal upregulation of Class I and Class II HDAC enzymes in myofibroblast foci, as well as aberrant bronchiolar epithelium, is an eminent observation, whereas type-II alveolar epithelial cells (AECII) of IPF lungs indicate a significant depletion of many HDACs. We thus suggest that the significant imbalance of HDAC activity in IPF lungs, with a "cancer-like" increase in fibroblastic and bronchial cells versus a lack in AECII, promotes and perpetuates fibrosis. This review focuses on the mechanisms by which Class I and Class II HDACs mediate fibrogenesis and on the mechanisms by which various HDAC inhibitors reverse the deregulated epigenetic responses in IPF, supporting HDAC inhibition as promising IPF therapy.

HDAC6 regulates NF-κB signalling to control chondrocyte IL-1-induced MMP and inflammatory gene expression

Elevated pro-inflammatory signalling coupled with catabolic metalloproteinase expression is a common feature of arthritis, leading to cartilage damage, deterioration of the joint architecture and the associated pain and immobility. Countering these processes, histone deacetylase inhibitors (HDACi) have been shown to suppress matrix metalloproteinase (MMP) expression, block cytokine-induced signalling and reduce the cartilage degradation in animal models of the arthritis. In order to establish which specific HDACs account for these chondro-protective effects an HDAC1-11 RNAi screen was performed. HDAC6 was required for both the interleukin (IL)-1 induction of MMP expression and pro-inflammatory interleukin expression in chondrocytes, implicating an effect on NF-κB signalling. Depletion of HDAC6 post-transcriptionally up-regulated inhibitor of κB (IκB), prevented the nuclear translocation of NF-κB subunits and down-regulated NF-κB reporter activation. The pharmacological inhibition of HDAC6 reduced MMP expression in chondrocytes and cartilage collagen release. This work highlights the important role of HDAC6 in pro-inflammatory signalling and metalloproteinase gene expression, and identifies a part for HDAC6 in the NF-κB signalling pathway. By confirming the protection of cartilage this work supports the inhibition of HDAC6 as a possible therapeutic strategy in arthritis.

Chasing a Breath of Fresh Air in Cystic Fibrosis (CF): Therapeutic Potential of Selective HDAC6 Inhibitors to Tackle Multiple Pathways in CF Pathophysiology

Compelling new support has been provided for histone deacetylase isoform 6 (HDAC6) as a common thread in the generation of the dysregulated proinflammatory and fibrotic phenotype in cystic fibrosis (CF). HDAC6 also plays a crucial role in bacterial clearance or killing as a direct consequence of its effects on CF immune responses. Inhibiting HDAC6 functions thus eventually represents an innovative and effective strategy to tackle multiple aspects of CF-associated lung disease. In this Perspective, we not only showcase the latest evidence linking HDAC(6) activity and expression with CF phenotype but also track the new dawn of HDAC(6) modulators in CF and explore potentialities and future perspectives in the field.

Histone deacetylase 6 inhibitors with blood-brain barrier penetration as a potential strategy for CNS-Disorders therapy

Histone deacetylase 6 inhibitors (HDAC6is) have been applied to certain cancer diseases and more recently to central nervous system (CNS) disorders including Rett syndrome, Alzheimer's and Parkinson's diseases, and major depressive disorder. Brain penetrance is the major challenge for the development of HDAC6is as potential therapeutics for CNS disorders due in part to the polarity of hydroxamate ZBG. Hence, only a handful of brain-penetrant HDAC6is have been reported and a few display appropriate in vitro and in vivo activities in models of neurological diseases in last decades. This review summarizes the contemporary research being done on HADC6is with brain penetration both the biological pathways involved and the structural modification attempts.

An HDAC6 inhibitor reverses chemotherapy-induced mechanical hypersensitivity via an IL-10 and macrophage dependent pathway

Chemotherapy-induced peripheral neuropathy (CIPN) impacts a growing number of cancer survivors and treatment options are limited. Histone deacetylase 6 (HDAC6) inhibitors are attractive candidates because they reverse established CIPN and may enhance anti-tumor effects of chemotherapy. Before considering clinical application of HDAC6 inhibitors, the mechanisms underlying reversal of CIPN need to be identified. We showed previously that deletion of Hdac6 from sensory neurons did not prevent cisplatin-induced mechanical hypersensitivity, while global deletion of Hdac6 was protective, indicating involvement of HDAC6 in other cell types. Here we show that local depletion of MRC1 (CD206)-positive macrophages without affecting microglia by intrathecal administration of mannosylated clodronate liposomes reduced the capacity of an HDAC6 inhibitor to reverse cisplatin-induced mechanical hypersensitivity. The HDAC6 inhibitor increased spinal cord Il10 mRNA and this was M2-macrophage dependent. Intrathecal administration of anti-IL-10 antibody or genetic deletion of Il10 prevented resolution of mechanical hypersensitivity. Genetic deletion of the IL-10 receptor from Advillin+ neurons prevented resolution of mechanical hypersensitivity in mice treated with the HDAC6 inhibitor. These findings indicate that treatment with an HDAC6 inhibitor increases macrophage-derived IL-10 signaling to IL-10 receptors on Advillin+ sensory neurons to resolve mechanical hypersensitivity. Cisplatin decreases mitochondrial function in sensory axons, and HDAC6 inhibition can promote axonal transport of healthy mitochondria. Indeed, the HDAC6 inhibitor normalized cisplatin-induced tibial nerve mitochondrial deficits. However, this was independent of macrophages and IL-10 signaling. In conclusion, our findings indicate that administration of an HDAC6 inhibitor reverses cisplatin-induced mechanical hypersensitivity through two complementary pathways: macrophage HDAC6 inhibition to promote IL-10 production and IL-10 signaling to DRG neurons, and neuronal HDAC6 inhibition to restore axonal mitochondrial health.

Redox signaling, mitochondrial metabolism, epigenetics and redox active phytochemicals

Biological redox signaling plays an important role in many diseases. Redox signaling involves reductive and oxidative mechanisms. Oxidative stress occurs when reductive mechanism underwhelms oxidative challenges. Cellular oxidative stress occurs when reactive oxygen/nitrogen species (RO/NS) exceed the cellular reductive/antioxidant capacity. Endogenously produced RO/NS from mitochondrial metabolic citric-acid-cycle coupled with electron-transport-chain or exogenous stimuli trigger cellular signaling events leading to homeostatic response or pathological damage. Recent evidence suggests that RO/NS also modulate epigenetic machinery driving gene expression. RO/NS affect DNA methylation/demethylation, histone acetylation/deacetylation or histone methylation/demethylation. Many health beneficial phytochemicals possess redox capability that counteract RO/NS either by directly scavenging the radicals or via inductive mechanism of cellular defense antioxidant/reductive enzymes. Amazingly, these phytochemicals also possess epigenetic modifying ability. This review summarizes the latest advances on the interactions between redox signaling, mitochondrial metabolism, epigenetics and redox active phytochemicals and the future challenges of integrating these events in human health.

HDAC6 inhibition reverses long-term doxorubicin-induced cognitive dysfunction by restoring microglia homeostasis and synaptic integrity

Breast cancer is the most common female malignancy in both the developed and developing world. Doxorubicin is one of the most commonly used chemotherapies for breast cancer. Unfortunately, up to 60% of survivors report long-term chemotherapy-induced cognitive dysfunction (CICD) characterized by deficits in working memory, processing speed and executive function. Currently, no therapeutic standard for treating CICD exists. Here, we hypothesized that treatment with a blood-brain barrier permeable histone deacetylase 6 (HDAC6) inhibitor can successfully reverse long-term doxorubicin-induced cognitive dysfunction. Methods: The puzzle box test and novel object/place recognition test were used to assess cognitive function following a therapeutic doxorubicin dosing schedule in female mice. Mitochondrial function and morphology in neuronal synaptosomes were evaluated using the Seahorse XF24 extracellular flux analyzer and transmission electron microscopy, respectively. Hippocampal postsynaptic integrity was evaluated using immunofluorescence. Hippocampal microglia phenotype was determined using advanced imaging techniques and single-nucleus RNA sequencing. Results: A 14-day treatment with a blood-brain barrier permeable HDAC6 inhibitor successfully reversed long-term CICD in the domains of executive function, working and spatial memory. No significant changes in mitochondrial function or morphology in neuronal synaptosomes were detected. Long-term CICD was associated with a decreased expression of postsynaptic PSD95 in the hippocampus. These changes were associated with decreased microglial ramification and alterations in the microglia transcriptome that suggest a stage 1 disease-associated microglia (DAM) phenotype. HDAC6 inhibition completely reversed these doxorubicin-induced alterations, indicating a restoration of microglial homeostasis. Conclusion: Our results show that decreased postsynaptic integrity and a neurodegenerative microglia phenotype closely resembling stage 1 DAM microglia contribute to long-term CICD. Moreover, HDAC6 inhibition shows promise as an efficacious pharmaceutical intervention to alleviate CICD and improve quality of life of breast cancer survivors.

Synthesis and biological evaluation of selective histone deacetylase 6 inhibitors as multifunctional agents against Alzheimer's disease

Histone deacetylase 6 (HDAC6) is a potential target for Alzheimer's disease (AD). In this study, a series of novel phenothiazine-, memantine-, and 1,2,3,4-tetrahydro-γ-carboline-based HDAC6 inhibitors with a variety of linker moieties were designed and synthesized. As a hydrochloride salt, the phenothiazine-based hydroxamic acid W5 with a pyridyl-containing linker motif was identified as a high potent and selective HDAC6 inhibitor. It inhibited HDAC6 with an IC₅₀ of 2.54 nM and was more than 290- to 3300-fold selective over other HDAC isoforms. In SH-SY5Y cells, W5 dose-dependently increased the acetylated α-tubulin levels and reduced the hyperphosphorylated tau proteins at Ser396. As an effective metal chelator, W5 inhibited Cu²⁺-induced Aβ_1-42 aggregation and disaggregated Cu²⁺-Aβ_1-42 oligomers, and showed protective effects on the SH-SY5Y cells against Aβ_1-42- as well as Cu²⁺-Aβ_1-42 induced cell damages, serving as a potential ligand to target AD metal dyshomeostasis. Moreover, W5 promoted the differentiated neuronal neurite outgrowth, increased the mRNA expression of the recognized neurogenesis markers, GAP43, N-myc, and MAP-2. Therefore, W5 might be a good lead for the development of novel HDAC6 inhibitors targeting multi-facets of AD.

Mitochondrial Sirtuin TcSir2rp3 Affects TcSODA Activity and Oxidative Stress Response in Trypanosoma cruzi

Trypanosoma cruzi faces a variety of environmental scenarios during its life cycle, which include changes in the redox environment that requires a fine regulation of a complex antioxidant arsenal of enzymes. Reversible posttranslational modifications, as lysine acetylation, are a fast and economical way for cells to react to environmental conditions. Recently, we found that the main antioxidant enzymes, including the mitochondrial superoxide dismutase A (TcSODA) are acetylated in T. cruzi, suggesting that protein acetylation could participate in the oxidative stress response in T. cruzi. Therefore, we investigated whether mitochondrial lysine deacetylase TcSir2rp3 was involved in the activity control of TcSODA. We observed an increased resistance to hydrogen peroxide and menadione in parasites overexpressing TcSir2rp3. Increased resistance was also found for benznidazole and nifurtimox, known to induce reactive oxidative and nitrosactive species in the parasite, associated to that a reduction in the ROS levels was observed. To better understand the way TcSir2rp3 could contributes to oxidative stress response, we analyzed the expression of TcSODA in the TcSir2rp3 overexpressing parasites and did not detect any increase in protein levels of this enzyme. However, we found that these parasites presented higher levels of superoxide dismutase activity, and also that TcSir2rp3 and TcSODA interacts in vivo. Knowing that TcSODA is acetylated at lysine residues K44 and K97, and that K97 is located at a similar region in the protein structure as K68 in human manganese superoxide dismutase (MnSOD), responsible for regulating MnSOD activity, we generated mutated versions of TcSODA at K44 and K97 and found that replacing K97 by glutamine, which mimics an acetylated lysine, negatively affects the enzyme activity in vitro. By using molecular dynamics approaches, we revealed that acetylation of K97 induces specific conformational changes in TcSODA with respect to hydrogen-bonding pattern to neighbor residues, suggesting a key participation of this residue to modulate the affinity to O2−. Taken together, our results showed for the first time the involvement of lysine acetylation in the maintenance of homeostatic redox state in trypanosomatids, contributing to the understanding of mechanisms used by T. cruzi to progress during the infection.

The Role of HDAC6 in Autophagy and NLRP3 Inflammasome

Autophagy fights against harmful stimuli and degrades cytosolic macromolecules, organelles, and intracellular pathogens. Autophagy dysfunction is associated with many diseases, including infectious and inflammatory diseases. Recent studies have identified the critical role of the NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) inflammasomes activation in the innate immune system, which mediates the secretion of proinflammatory cytokines IL-1β/IL-18 and cleaves Gasdermin D to induce pyroptosis in response to pathogenic and sterile stimuli. Accumulating evidence has highlighted the crosstalk between autophagy and NLRP3 inflammasome in multifaceted ways to influence host defense and inflammation. However, the underlying mechanisms require further clarification. Histone deacetylase 6 (HDAC6) is a class IIb deacetylase among the 18 mammalian HDACs, which mainly localizes in the cytoplasm. It is involved in two functional deacetylase domains and a ubiquitin-binding zinc finger domain (ZnF-BUZ). Due to its unique structure, HDAC6 regulates various physiological processes, including autophagy and NLRP3 inflammasome, and may play a role in the crosstalk between them. In this review, we provide insight into the mechanisms by which HDAC6 regulates autophagy and NLRP3 inflammasome and we explored the possibility and challenges of HDAC6 in the crosstalk between autophagy and NLRP3 inflammasome. Finally, we discuss HDAC6 inhibitors as a potential therapeutic approach targeting either autophagy or NLRP3 inflammasome as an anti-inflammatory strategy, although further clarification is required regarding their crosstalk.

Oxidative Modification of Proteins: From Damage to Catalysis, Signaling, and Beyond

Significance: The systematic investigation of oxidative modification of proteins by reactive oxygen species started in 1980. Later, it was shown that reactive nitrogen species could also modify proteins. Some protein oxidative modifications promote loss of protein function, cleavage or aggregation, and some result in proteo-toxicity and cellular homeostasis disruption. Recent Advances: Previously, protein oxidation was associated exclusively to damage. However, not all oxidative modifications are necessarily associated with damage, as with Met and Cys protein residue oxidation. In these cases, redox state changes can alter protein structure, catalytic function, and signaling processes in response to metabolic and/or environmental alterations. This review aims to integrate the present knowledge on redox modifications of proteins with their fate and role in redox signaling and human pathological conditions. Critical Issues: It is hypothesized that protein oxidation participates in the development and progression of many pathological conditions. However, no quantitative data have been correlated with specific oxidized proteins or the progression or severity of pathological conditions. Hence, the comprehension of the mechanisms underlying these modifications, their importance in human pathologies, and the fate of the modified proteins is of clinical relevance. Future Directions: We discuss new tools to cope with protein oxidation and suggest new approaches for integrating knowledge about protein oxidation and redox processes with human pathophysiological conditions. Antioxid. Redox Signal. 35, 1016-1080.

Acetylated Thioredoxin Reductase 1 Resists Oxidative Inactivation

Thioredoxin Reductase 1 (TrxR1) is an enzyme that protects human cells against reactive oxygen species generated during oxidative stress or in response to chemotherapies. Acetylation of TrxR1 is associated with oxidative stress, but the function of TrxR1 acetylation in oxidizing conditions is unknown. Using genetic code expansion, we produced recombinant and site-specifically acetylated variants of TrxR1 that also contain the non-canonical amino acid, selenocysteine, which is essential for TrxR1 activity. We previously showed site-specific acetylation at three different lysine residues increases TrxR1 activity by reducing the levels of linked dimers and low activity TrxR1 tetramers. Here we use enzymological studies to show that acetylated TrxR1 is resistant to both oxidative inactivation and peroxide-induced multimer formation. To compare the effect of programmed acetylation at specific lysine residues to non-specific acetylation, we produced acetylated TrxR1 using aspirin as a model non-enzymatic acetyl donor. Mass spectrometry confirmed aspirin-induced acetylation at multiple lysine residues in TrxR1. In contrast to unmodified TrxR1, the non-specifically acetylated enzyme showed no loss of activity under increasing and strongly oxidating conditions. Our data suggest that both site-specific and general acetylation of TrxR1 regulate the enzyme’s ability to resist oxidative damage.

Thiol-disulphide independent in-cell trapping for the identification of peroxiredoxin 2 interactors

Hydrogen peroxide (H2O2) acts as a signalling molecule by oxidising cysteine thiols in proteins. Recent evidence has established a role for cytosolic peroxiredoxins in transmitting H2O2-based oxidation to a multitude of target proteins. Moreover, it is becoming clear that peroxiredoxins fulfil their function in organised microdomains, where not all interactors are covalently bound. However, most studies aimed at identifying peroxiredoxin interactors were based on methods that only detect covalently linked partners. Here, we explore the applicability of two thiol-disulphide independent in-cell trapping methodological approaches in combination with mass spectrometry for the identification of interaction partners of peroxiredoxin 2 (Prdx2). The first is biotin-dependent proximity-labelling (BioID) with a biotin ligase A (BirA*)-fused Prdx2, which has never been applied on redox-active proteins. The second is crosslinker co-immunoprecipitation with an N-terminally His-tagged Prdx2. During the initial characterisation of the tagged Prdx2 constructs, we found that the His-tag, but not BirA*, compromises the peroxidase and signalling activities of Prdx2. Further, the Prdx2 interactors identified with each approach showed little overlap. We therefore concluded that BioID is a more reliable method than crosslinker co-immunoprecipitation. After a stringent mass spec data filtering, BioID identified 13 interactors under elevated H2O2 conditions, including subunit five of the COP9 signalosome complex (CSN5). The Prdx2:CSN5 interaction was further confirmed in a proximity ligation assay. Taken together, our results demonstrate that BioID can be used as a method for the identification of interactors of Prdxs, and that caution should be exercised when interpreting protein-protein interaction results using tagged Prdxs.