In vivo destabilization of dynamic microtubules by HDAC6-mediated deacetylation

HDAC6 modulates myofibril stiffness and diastolic function of the heart

Passive stiffness of the heart is determined largely by extracellular matrix and titin, which functions as a molecular spring within sarcomeres. Titin stiffening is associated with the development of diastolic dysfunction (DD), while augmented titin compliance appears to impair systolic performance in dilated cardiomyopathy. We found that myofibril stiffness was elevated in mice lacking histone deacetylase 6 (HDAC6). Cultured adult murine ventricular myocytes treated with a selective HDAC6 inhibitor also exhibited increased myofibril stiffness. Conversely, HDAC6 overexpression in cardiomyocytes led to decreased myofibril stiffness, as did ex vivo treatment of mouse, rat, and human myofibrils with recombinant HDAC6. Modulation of myofibril stiffness by HDAC6 was dependent on 282 amino acids encompassing a portion of the PEVK element of titin. HDAC6 colocalized with Z-disks, and proteomics analysis suggested that HDAC6 functions as a sarcomeric protein deacetylase. Finally, increased myofibril stiffness in HDAC6-deficient mice was associated with exacerbated DD in response to hypertension or aging. These findings define a role for a deacetylase in the control of myofibril function and myocardial passive stiffness, suggest that reversible acetylation alters titin compliance, and reveal the potential of targeting HDAC6 to manipulate the elastic properties of the heart to treat cardiac diseases.

Direct and indirect effects of tubulin post-translational modifications on microtubule stability: Insights and regulations

Microtubules (MTs) mediate various cellular functions such as structural support, chromosome segregation, and intracellular transport. To achieve this, the pivotal properties of MTs have to be changeable and tightly controlled. This is enabled by a high variety of tubulin posttranslational modifications, which influence MT properties directly, via altering the MT lattice structurally, or indirectly by changing MT interaction partners. Here, the distinction between these direct and indirect effects of MT PTMs are exemplified by acetylation of the luminal α-tubulin K40 resulting in decreased rigidity of MTs, and by MT detyrosination which decreases interaction with depolymerizing proteins, thus causing more stable MTs. We discuss how these PTMs are reversed and regulated, e.g. on the level of enzyme transcription, localization, and activity via various signalling pathways including the conventional calcium-dependent proteases calpains and how advances in microscopy techniques and development of live-sensors facilitate the understanding of MT PTM interaction and effects.

Structure-based prediction of HDAC6 substrates validated by enzymatic assay reveals determinants of promiscuity and detects new potential substrates

Histone deacetylases play important biological roles well beyond the deacetylation of histone tails. In particular, HDAC6 is involved in multiple cellular processes such as apoptosis, cytoskeleton reorganization, and protein folding, affecting substrates such as ɑ-tubulin, Hsp90 and cortactin proteins. We have applied a biochemical enzymatic assay to measure the activity of HDAC6 on a set of candidate unlabeled peptides. These served for the calibration of a structure-based substrate prediction protocol, Rosetta FlexPepBind, previously used for the successful substrate prediction of HDAC8 and other enzymes. A proteome-wide screen of reported acetylation sites using our calibrated protocol together with the enzymatic assay provide new peptide substrates and avenues to novel potential functional regulatory roles of this promiscuous, multi-faceted enzyme. In particular, we propose novel regulatory roles of HDAC6 in tumorigenesis and cancer cell survival via the regulation of EGFR/Akt pathway activation. The calibration process and comparison of the results between HDAC6 and HDAC8 highlight structural differences that explain the established promiscuity of HDAC6.

Development of a NanoBRET assay to validate dual inhibitors of Sirt2-mediated lysine deacetylation and defatty-acylation that block prostate cancer cell migration

Sirtuin2 (Sirt2) with its NAD⁺-dependent deacetylase and defatty-acylase activities plays a central role in the regulation of specific cellular functions. Dysregulation of Sirt2 activity has been associated with the pathogenesis of many diseases, thus making Sirt2 a promising target for pharmaceutical intervention. Herein, we present new high affinity Sirt2 selective Sirtuin-Rearranging Ligands (SirReals) that inhibit both Sirt2-dependent deacetylation and defatty-acylation in vitro and in cells. We show that simultaneous inhibition of both Sirt2 activities results in strongly reduced levels of the oncoprotein c-Myc and an inhibition of cancer cell migration. Furthermore, we describe the development of a NanoBRET-based assay for Sirt2, thereby providing a method to study cellular target engagement for Sirt2 in a straightforward and accurately quantifiable manner. Applying this assay, we could confirm cellular Sirt2 binding of our new Sirt2 inhibitors and correlate their anticancer effects with their cellular target engagement.

Sirt2 inhibitors that show simultaneous inhibition of Sirt2 deacetylase and defatty-acylase activity block prostate cancer cell migration and their target engagement is shown by a newly developed NanoBRET assay.

HDAC inhibitor ameliorates behavioral deficits in Mecp2308/y mouse model of Rett syndrome

Rett syndrome (RTT) is a rare X-linked neurodevelopmental disorder. More than 95% of classic RETT syndrome cases result from pathogenic variants in the methyl-CpG binding protein 2 (MECP2) gene. Nevertheless, it has been established that a spectrum of neuropsychiatric phenotypes is associated with MECP2 variants in both females and males. We previously reported that microtubule growth velocity and vesicle transport directionality are altered in Mecp2-deficient astrocytes from newborn Mecp2-deficient mice compared to that of their wild-type littermates suggesting deficit in microtubule dynamics. In this study, we report that administration of tubastatin A, a selective HDAC6 inhibitor, restored microtubule dynamics in Mecp2-deficient astrocytes. We furthermore report that daily doses of tubastatin A reversed early impaired exploratory behavior in male Mecp2^308/y mice. These findings are a first step toward the validation of a novel treatment for RTT.

Protein lysine acetylation and its role in different human pathologies: a proteomic approach

INTRODUCTION

Lysine acetylation is a reversible post-translational modification (PTM) regulated through the action of specific types of enzymes: lysine acetyltransferases (KATs) and lysine deacetylases (HDACs), in addition to bromodomains, which are a group of conserved domains which identify acetylated lysine residues, several of the players in the process of protein acetylation, including enzymes and bromodomain-containing proteins, have been related to the progression of several diseases. The combination of high-resolution mass spectrometry-based proteomics, and immunoprecipitation to enrich acetylated peptides has contributed in recent years to expand the knowledge about this PTM described initially in histones and nuclear proteins, and is currently reported in more than 5000 human proteins, that are regulated by this PTM.

AREAS COVERED

This review presents an overview of the main participant elements, the scenario in the development of protein lysine acetylation, and its role in different human pathologies.

EXPERT OPINION

Acetylation targets are practically all cellular processes in eukaryotes and prokaryotes organisms. Consequently, this modification has been linked to many pathologies like cancer, viral infection, obesity, diabetes, cardiovascular, and nervous system-associated diseases, to mention a few relevant examples. Accordingly, some intermediate mediators in the acetylation process have been projected as therapeutic targets.

Microtubules as Major Regulators of Endothelial Function: Implication for Lung Injury

Endothelial dysfunction has been attributed as one of the major complications in COVID-19 patients, a global pandemic that has already caused over 4 million deaths worldwide. The dysfunction of endothelial barrier is characterized by an increase in endothelial permeability and inflammatory responses, and has even broader implications in the pathogenesis of acute respiratory syndromes such as ARDS, sepsis and chronic illnesses represented by pulmonary arterial hypertension and interstitial lung disease. The structural integrity of endothelial barrier is maintained by cytoskeleton elements, cell-substrate focal adhesion and adhesive cell junctions. Agonist-mediated changes in endothelial permeability are directly associated with reorganization of actomyosin cytoskeleton leading to cell contraction and opening of intercellular gaps or enhancement of cortical actin cytoskeleton associated with strengthening of endothelial barrier. The role of actin cytoskeleton remodeling in endothelial barrier regulation has taken the central stage, but the impact of microtubules in this process remains less explored and under-appreciated. This review will summarize the current knowledge on the crosstalk between microtubules dynamics and actin cytoskeleton remodeling, describe the signaling mechanisms mediating this crosstalk, discuss epigenetic regulation of microtubules stability and its nexus with endothelial barrier maintenance, and overview a role of microtubules in targeted delivery of signaling molecules regulating endothelial permeability and inflammation.

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.

Molecular Profiling of Spermatozoa Reveals Correlations between Morphology and Gene Expression: A Novel Biomarker Panel for Male Infertility

Choosing spermatozoa with an optimum fertilizing potential is one of the major challenges in assisted reproductive technologies (ART). This selection is mainly based on semen parameters, but the addition of molecular approaches could allow a more functional evaluation. To this aim, we used sixteen fresh sperm samples from patients undergoing ART for male infertility and classified them in the high- and poor-quality groups, on the basis of their morphology at high magnification. Then, using a DNA sequencing method, we analyzed the spermatozoa methylome to identify genes that were differentially methylated. By Gene Ontology and protein-protein interaction network analyses, we defined candidate genes mainly implicated in cell motility, calcium reabsorption, and signaling pathways as well as transmembrane transport. RT-qPCR of high- and poor-quality sperm samples allowed showing that the expression of some genes, such as AURKA, HDAC4, CFAP46, SPATA18, CACNA1C, CACNA1H, CARHSP1, CCDC60, DNAH2, and CDC88B, have different expression levels according to sperm morphology. In conclusion, the present study shows a strong correlation between morphology and gene expression in the spermatozoa and provides a biomarker panel for sperm analysis during ART and a new tool to explore male infertility.

Naturally occurring small molecule compounds that target histone deacetylases and their potential applications in cancer therapy

Epigenetics is defined as the heritable alteration of gene expression without change to the DNA sequence. Epigenetic abnormalities play a role in various diseases, including cancer. Epigenetic regulation of gene expression occurs through histone chemical modifications and DNA methylation. Lysine acetylation is one of the major histone chemical modifications essential for epigenetic gene expression. Histone acetylation is reversibly regulated by histone acetyltransferases and histone deacetylases, which are molecular targets for cancer therapy. There has been an explosion of research in epigenetic-related drug discovery, and accordingly many small molecule compounds have been developed. Notably, several small molecule inhibitors of histone deacetylases have been approved for the treatment of cancer. This review will introduce natural products, their derivative inhibitors of histone deacetylases, and their clinical development.

Posttranslational modification and beyond: interplay between histone deacetylase 6 and heat-shock protein 90

Posttranslational modification (PTM) and regulation of protein stability are crucial to various biological processes. Histone deacetylase 6 (HDAC6), a unique histone deacetylase with two functional catalytic domains (DD1 and DD2) and a ZnF-UBP domain (ubiquitin binding domain, BUZ), regulates a number of biological processes, including gene expression, cell motility, immune response, and the degradation of misfolded proteins. In addition to the deacetylation of histones, other nonhistone proteins have been identified as substrates for HDAC6. Hsp90, a molecular chaperone that is a critical modulator of cell signaling, is one of the lysine deacetylase substrates of HDAC6. Intriguingly, as one of the best-characterized regulators of Hsp90 acetylation, HDAC6 is the client protein of Hsp90. In addition to regulating Hsp90 at the post-translational modification level, HDAC6 also regulates Hsp90 at the gene transcription level. HDAC6 mainly regulates the Hsp90-HSF1 complex through the ZnF-UBP domain, thereby promoting the HSF1 entry into the nucleus and activating gene transcription. The mutual interaction between HDAC6 and Hsp90 plays an important role in the regulation of protein stability, cell migration, apoptosis and other functions. Plenty of of studies have indicated that blocking HDAC6/Hsp90 has a vital regulatory role in multifarious diseases, mainly in cancers. Therefore, developing inhibitors or drugs against HDAC6/Hsp90 becomes a promising development direction. Herein, we review the current knowledge on molecular regulatory mechanisms based on the interaction of HDAC6 and Hsp90 and inhibition of HDAC6 and/or Hsp90 in oncogenesis and progression, antiviral and immune-related diseases and other vital biological processes.

The molecular chaperone Hsp90 maintains Golgi organization and vesicular trafficking by regulating microtubule stability

Hsp90 is an abundant and special molecular chaperone considered to be the regulator of many transcription factors and signaling kinases. Its high abundance is indicative of its involvement in some more fundamental processes. In this study, we provide evidence that Hsp90 is required for microtubule stabilization, Golgi organization, and vesicular trafficking. We showed that Hsp90 is bound to microtubule-associated protein 4 (MAP4), which is essential for maintaining microtubule acetylation and stabilization. Hsp90 depletion led to the decrease in MAP4, causing microtubule deacetylation and destabilization. Furthermore, in Hsp90-depleted cells, the Golgi apparatus was fragmented and anterograde vesicle trafficking was impaired, with phenotypes similar to those induced by silencing MAP4. These disruptive effects of Hsp90 depletion could be rescued by the expression of exogenous MAP4 or the treatment of trichostatin A that increases microtubule acetylation as well as stability. Thus, microtubule stability is an essential cellular event regulated by Hsp90.

Role of acetylation in doxorubicin-induced cardiotoxicity

As a potent chemotherapeutic agent, doxorubicin (DOX) is widely used for the treatment of a variety of cancers However, its clinical utility is limited by dose-dependent cardiotoxicity, and pathogenesis has traditionally been attributed to the formation of reactive oxygen species (ROS). Accordingly, the prevention of DOX-induced cardiotoxicity is an indispensable goal to optimize therapeutic regimens and reduce morbidity. Acetylation is an emerging and important epigenetic modification regulated by histone deacetylases (HDACs) and histone acetyltransferases (HATs). Despite extensive studies of the molecular basis and biological functions of acetylation, the application of acetylation as a therapeutic target for cardiotoxicity is in the initial stage, and further studies are required to clarify the complex acetylation network and improve the clinical management of cardiotoxicity. In this review, we summarize the pivotal functions of HDACs and HATs in DOX-induced oxidative stress, the underlying mechanisms, the contributions of noncoding RNAs (ncRNAs) and exercise-mediated deacetylases to cardiotoxicity. Furthermore, we describe research progress related to several important SIRT activators and HDAC inhibitors with potential clinical value for chemotherapy and cardiotoxicity. Collectively, a comprehensive understanding of specific roles and recent developments of acetylation in doxorubicin-induced cardiotoxicity will provide a basis for improved treatment outcomes in cancer and cardiovascular diseases.

A novel orally active HDAC6 inhibitor T-518 shows a therapeutic potential for Alzheimer's disease and tauopathy in mice

Accumulation of tau protein is a key pathology of age-related neurodegenerative diseases such as Alzheimer's disease and progressive supranuclear palsy. Those diseases are collectively termed tauopathies. Tau pathology is associated with axonal degeneration because tau binds to microtubules (MTs), a component of axon and regulates their stability. The acetylation state of MTs contributes to stability and histone deacetylase 6 (HDAC6) is a major regulator of MT acetylation status, suggesting that pharmacological HDAC6 inhibition could improve axonal function and may slow the progression of tauopathy. Here we characterize N-[(1R,2R)-2-{3-[5-(difluoromethyl)-1,3,4-oxadiazol-2-yl]-5-oxo-5H,6H,7H-pyrrolo[3,4-b]pyridin-6-yl}cyclohexyl]-2,2,3,3,3-pentafluoropropanamide (T-518), a novel, potent, highly selective HDAC6 inhibitor with clinically favorable pharmacodynamics. T-518 shows potent inhibitory activity against HDAC6 and superior selectivity over other HDACs compared with the known HDAC6 inhibitors in the enzyme and cellular assays. T-518 showed brain penetration in an oral dose and blocked HDAC6-dependent tubulin deacetylation at Lys40 in mouse hippocampus. A 2-week treatment restored impaired axonal transport and novel object recognition in the P301S tau Tg mouse, tauopathy model, while a 3-month treatment also decreased RIPA-insoluble tau accumulation. Pharmaceutical inhibition of HDAC6 is a potential therapeutic strategy for tauopathy, and T-518 is a particularly promising drug candidate.

Myocardin-related transcription factor and serum response factor regulate cilium turnover by both transcriptional and local mechanisms

Turnover of the primary cilium (PC) is critical for proliferation and tissue homeostasis. Each key component of the PC resorption machinery, the HEF1/Aurora kinase A (AurA)/HDAC6 pathway harbors cis-elements potentially targeted by the transcriptional co-activator myocardin-related transcription factor (MRTF) and/or its partner serum response factor (SRF). Thus we investigated if MRTF and/or SRF regulate PC turnover. Here we show that (1) both MRTF and SRF are indispensable for serum-induced PC resorption, and (2) they act via both transcriptional and local mechanisms. Intriguingly, MRTF and SRF are present in the basal body and/or the PC, and serum facilitates ciliary MRTF recruitment. MRTF promotes the stability and ciliary accumulation of AurA and facilitates SRF phosphorylation. Ciliary SRF interacts with AurA and HDAC6. MRTF also inhibits ciliogenesis. It interacts with and is required for the correct localization of the ciliogenesis modulator CEP290. Thus, MRTF and SRF are critical regulators of PC assembly and/or disassembly, acting both as transcription factors and as PC constituents.

How Influenza Virus Uses Host Cell Pathways during Uncoating

Influenza is a zoonotic respiratory disease of major public health interest due to its pandemic potential, and a threat to animals and the human population. The influenza A virus genome consists of eight single-stranded RNA segments sequestered within a protein capsid and a lipid bilayer envelope. During host cell entry, cellular cues contribute to viral conformational changes that promote critical events such as fusion with late endosomes, capsid uncoating and viral genome release into the cytosol. In this focused review, we concisely describe the virus infection cycle and highlight the recent findings of host cell pathways and cytosolic proteins that assist influenza uncoating during host cell entry.

Loss of Deacetylation Enzymes Hdac6 and Sirt2 Promotes Acetylation of Cytoplasmic Tubulin, but Suppresses Axonemal Acetylation in Zebrafish Cilia

Cilia are evolutionarily highly conserved organelles with important functions in many organs. The extracellular component of the cilium protruding from the plasma membrane comprises an axoneme composed of microtubule doublets, arranged in a 9 + 0 conformation in primary cilia or 9 + 2 in motile cilia. These microtubules facilitate transport of intraflagellar cargoes along the axoneme. They also provide structural stability to the cilium, which may play an important role in sensory cilia, where signals are received from the movement of extracellular fluid. Post-translational modification of microtubules in cilia is a well-studied phenomenon, and acetylation on lysine 40 (K40) of alpha tubulin is prominent in cilia. It is believed that this modification contributes to the stabilization of cilia. Two classes of enzymes, histone acetyltransferases and histone deacetylases, mediate regulation of tubulin acetylation. Here we use a genetic approach, immunocytochemistry and behavioral tests to investigate the function of tubulin deacetylases in cilia in a zebrafish model. By mutating three histone deacetylase genes (Sirt2, Hdac6, and Hdac10), we identify an unforeseen role for Hdac6 and Sirt2 in cilia. As expected, mutation of these genes leads to increased acetylation of cytoplasmic tubulin, however, surprisingly it caused decreased tubulin acetylation in cilia in the developing eye, ear, brain and kidney. Cilia in the ear and eye showed elevated levels of mono-glycylated tubulin suggesting a compensatory mechanism. These changes did not affect the length or morphology of cilia, however, functional defects in balance was observed, suggesting that the level of tubulin acetylation may affect function of the cilium.

Mini-Review: Mitochondrial dysfunction and chemotherapy-induced neuropathic pain

Chemotherapy-induced peripheral neuropathy (CIPN) is a somatosensory axonopathy in cancer patients receiving any of a variety of widely-use antitumor agents. CIPN can lead to long-lasting neuropathic pain that limits the dose or length of otherwise life-saving cancer therapy. Accumulating evidence over the last two decades indicates that many chemotherapeutic agents cause mitochondrial injury in the peripheral sensory nerves by disrupting mitochondrial structure and bioenergetics, increasing nitro-oxidative stress and altering mitochondrial transport, fission, fusion and mitophagy. The accumulation of abnormal and dysfunctional mitochondria in sensory neurons are linked to axonal growth defects resulting in the loss of intraepidermal nerve fibers in the hands and feet, increased spontaneous discharge and the sensitization of peripheral sensory neurons that provoke and promote changes in the central nervous system that establish a chronic neuropathic pain state. This has led to the propose mitotoxicity theory of CIPN. Strategies that improve mitochondrial function have shown success in preventing and reversing CIPN in pre-clinical animal models and have begun to show some progress toward translation to the clinic. In this review, we will review the evidence for, the causes and effects of and current strategies to target mitochondrial dysfunction in CIPN.

Response to stress in biological disorders: Implications of stress granule assembly and function

It is indispensable for cells to adapt and respond to environmental stresses, in order for organisms to survive. Stress granules (SGs) are condensed membrane‐less organelles dynamically formed in the cytoplasm of eukaryotes cells to cope with diverse intracellular or extracellular stress factors, with features of liquid‐liquid phase separation. They are composed of multiple constituents, including translationally stalled mRNAs, translation initiation factors, RNA‐binding proteins and also non‐RNA‐binding proteins. SG formation is triggered by stress stimuli, viral infection and signal transduction, while aberrant assembly of SGs may contribute to tissue degenerative diseases. Recently, a growing body of evidence has emerged on SG response mechanisms for cells facing high temperatures, oxidative stress and osmotic stress. In this review, we aim to summarize factors affecting SGs assembly, present the impact of SGs on germ cell development and other biological processes. We particularly emphasize the significance of recently reported RNA modifications in SG stress responses. In parallel, we also review all current perspectives on the roles of SGs in male germ cells, with a particular focus on the dynamics of SG assembly.

Novel pyrrolo[2,1-c][1,4]benzodiazepine-3,11-dione (PBD) derivatives as selective HDAC6 inhibitors to suppress tumor metastasis and invasion in vitro and in vivo

Selective inhibition of histone deacetylase 6 (HDAC6) has been emerged as a promising approach to cancer treatment. As a pivotal strategy for drug discovery,molecular hybridization was introduced in this study and a series of pyrrolo[2,1-c][1,4] benzodiazepine-3,11-diones (PBDs) based hydroxamic acids was rationally designed and synthesizedas novel selective HDAC6 inhibitors. Preliminary in vitro enzyme inhibition assay and structure-activity relationship (SAR) discussion confirmed our design strategy and met the expectation. Several of the compounds showed high potent against HDAC6 enzyme in vitro, and compound A7 with a long aliphatic linker was revealed to have the similar activity as the positive control tubastatin A. Further in vitro characterization of A7 demonstrates the metastasis inhibitory potency in MDA-MB-231 cell line and western blotting showed that A7 could induce the upregulation of Ac-α-tubulin, but not induce the excessive acetylation of histone H3, which indicated that the compound had HDAC6 targeting effect in MDA-MB-231 cells. In vivo study revealed that compound A7 has satisfactory inhibitory effects onliver and lung metastasis of breast cancer in mice. Molecular docking released that A7 could fit well with the receptor and interact with some key residues, which lays a foundation for further structural modifications to elucidate the interaction mode between compounds and target protein. This pharmacological investigation workflow provided a reasonable and reference methodto examine the pharmacological effects of inhibiting HDAC6 with a single molecule, either in vitro or in vivo. All of these results suggested that A7 is a promising lead compound that could lead to the further development of novel selective HDAC6 inhibitors for the treatment of tumor metastasis.

SIRT2-knockdown rescues GARS-induced Charcot-Marie-Tooth neuropathy

Charcot‐Marie‐Tooth disease is the most common inherited peripheral neuropathy. Dominant mutations in the glycyl‐tRNA synthetase (GARS) gene cause peripheral nerve degeneration and lead to CMT disease type 2D. The underlying mechanisms of mutations in GARS (GARS^CMT2D) in disease pathogenesis are not fully understood. In this study, we report that wild‐type GARS binds the NAD⁺‐dependent deacetylase SIRT2 and inhibits its deacetylation activity, resulting in the acetylated α‐tubulin, the major substrate of SIRT2. The catalytic domain of GARS tightly interacts with SIRT2, which is the most CMT2D mutation localization. However, CMT2D mutations in GARS cannot inhibit SIRT2 deacetylation, which leads to a decrease of acetylated α‐tubulin. Genetic reduction of SIRT2 in the Drosophila model rescues the GARS‐induced axonal CMT neuropathy and extends the life span. Our findings demonstrate the pathogenic role of SIRT2‐dependent α‐tubulin deacetylation in mutant GARS‐induced neuropathies and provide new perspectives for targeting SIRT2 as a potential therapy against hereditary axonopathies.

Kinase-anchoring proteins in ciliary signal transduction

Historically, the diffusion of chemical signals through the cell was thought to occur within a cytoplasmic soup bounded by the plasma membrane. This theory was predicated on the notion that all regulatory enzymes are soluble and moved with a Brownian motion. Although enzyme compartmentalization was initially rebuffed by biochemists as a 'last refuge of a scoundrel', signal relay through macromolecular complexes is now accepted as a fundamental tenet of the burgeoning field of spatial biology. A-Kinase anchoring proteins (AKAPs) are prototypic enzyme-organizing elements that position clusters of regulatory proteins at defined subcellular locations. In parallel, the primary cilium has gained recognition as a subcellular mechanosensory organelle that amplifies second messenger signals pertaining to metazoan development. This article highlights advances in our understanding of AKAP signaling within the primary cilium and how defective ciliary function contributes to an increasing number of diseases known as ciliopathies.

S6K1 Is Indispensible for Stress-Induced Microtubule Acetylation and Autophagic Flux

Autophagy is a specific macromolecule and organelle degradation process. The target macromolecule or organelle is first enclosed in an autophagosome, and then delivered along acetylated microtubules to the lysosome. Autophagy is triggered by stress and largely contributes to cell survival. We have previously shown that S6K1 kinase is essential for autophagic flux under stress conditions. Here, we aimed to elucidate the underlying mechanism of S6K1 involvement in autophagy. We stimulated autophagy in S6K1/2 double-knockout mouse embryonic fibroblasts by exposing them to different stress conditions. Transient gene overexpression or silencing, immunoblotting, immunofluorescence, flow cytometry, and ratiometric fluorescence analyses revealed that the perturbation of autophagic flux in S6K1-deficient cells did not stem from impaired lysosomal function. Instead, the absence of S6K1 abolished stress-induced tubulin acetylation and disrupted the acetylated microtubule network, in turn impairing the autophagosome-lysosome fusion. S6K1 overexpression restored tubulin acetylation and autophagic flux in stressed S6K1/2-deficient cells. Similar effect of S6K1 status was observed in prostate cancer cells. Furthermore, overexpression of an acetylation-mimicking, but not acetylation-resistant, tubulin variant effectively restored autophagic flux in stressed S6K1/2-deficient cells. Collectively, S6K1 controls tubulin acetylation, hence contributing to the autophagic flux induced by different stress conditions and in different cells.

Acetylation/deacetylation and microtubule associated proteins influence flagellar axonemal stability and sperm motility

PTMs and microtubule-associated proteins (MAPs) are known to regulate microtubule dynamicity in somatic cells. Reported literature on modulation of α-tubulin acetyl transferase (αTAT1) and histone deacetylase 6 (HDAC6) in animal models and cell lines illustrate disparity in correlating tubulin acetylation status with stability of MT. Our earlier studies showed reduced acetyl tubulin in sperm of asthenozoospermic individuals. Our studies on rat sperm showed that on inhibition of HDAC6 activity, although tubulin acetylation increased, sperm motility was reduced. Studies were therefore undertaken to investigate the influence of tubulin acetylation/deacetylation on MT dynamicity in sperm flagella using rat and human sperm. Our data on rat sperm revealed that HDAC6 specific inhibitor Tubastatin A (T) inhibited sperm motility and neutralized the depolymerizing and motility debilitating effect of Nocodazole. The effect on polymerization was further confirmed in vitro using pure MT and recHDAC6. Also polymerized axoneme was less in sperm of asthenozoosperm compared to normozoosperm. Deacetylase activity was reduced in sperm lysates and axonemes exposed to T and N+T but not in axonemes of sperm treated similarly suggesting that HDAC6 is associated with sperm axonemes or MT. Deacetylase activity was less in asthenozoosperm. Intriguingly, the expression of MDP3 physiologically known to bind to HDAC6 and inhibit its deacetylase activity remained unchanged. However, expression of acetyl α-tubulin, HDAC6 and microtubule stabilizing protein SAXO1 was less in asthenozoosperm. These observations suggest that MAPs and threshold levels of MT acetylation/deacetylation are important for MT dynamicity in sperm and may play a role in regulating sperm motility.

Analysis of Key Distinct Biological Characteristics of Human Placenta-Derived Mesenchymal Stromal Cells and Individual Heterogeneity Attributing to Donors

For potential clinical applications in the future, we investigated the distinct biological features of mesenchymal stromal cells (MSCs) derived from different origin areas of human placenta and individual heterogeneity among different donors. Chorionic plate MSCs (CP-MSCs), amniotic membrane MSCs (AM-MSCs), and decidual plate MSCs (DP-MSCs) were isolated from 5 human placentae and were analyzed in terms of main features of MSCs including surface marker profile, growth, differentiation potential, immune regulation capability, and tubulin acetylation (Ac-tubulin). The expression profile of surface markers in the 3 types of MSCs derived from the 5 donors was relatively stable. Heterogeneity was found in growth, differentiation potential, and immune regulation among MSCs according to the different areas of isolation and different donors. CP-MSCs and AM-MSCs derived from the placentae of donors 1-3 had a higher osteogenic differentiation potential than the corresponding DP-MSCs, but those derived from the placentae of donors 4 and 5 had a markedly lower osteogenic differentiation potential than DP-MSCs. All CP-MSCs derived from donors 1-3 had the highest adipogenic differentiation potential, but CP-MSCs derived from donors 4 and 5 did not show strong capability of adipogenic differentiation. CP-MSCs markedly inhibited the proliferation of peripheral blood mononuclear cells (PBMCs) induced by phytohemagglutinin, whereas AM- and DP-MSCs did not. All MSCs decreased the proportion of CD3+/CD8-/IFN-γ+ Th1 and CD3+/CD8-/IL17+ Th17 cells, but increased the proportion of Treg cells in PBMCs, with individual differences among the 5 donors. DP-MSCs from donors 1 and 2 had higher levels of Ac-tubulin compared with CP- and AM-MSCs. However, the levels of Ac-tubulin in AM-MSCs from donors 3 and 5 were higher than those of the other 2 types of MSCs. Our results revealed that there was tissue-specific heterogeneity among the 3 types of MSCs from different origin tissues of placenta and individual heterogeneity among donors. In future, the pre-selected placenta-derived MSCs with specific biological advantages may improve the curative effect of cell therapy in different situations.

Role of HDAC6 inhibition in sepsis-induced acute respiratory distress syndrome (Review)

Acute respiratory distress syndrome (ARDS) induced by sepsis contributes remarkably to the high mortality rate observed in intensive care units, largely due to a lack of effective drug therapies. Histone deacetylase 6 (HDAC6) is a class-IIb deacetylase that modulates non-nuclear protein functions via deacetylation and ubiquitination. Importantly, HDAC6 has been shown to exert anti-cancer, anti-neurodegeneration, and immunological effects, and several HDAC6 inhibitors have now entered clinical trials. It has also been recently shown to modulate inflammation, and HDAC6 inhibition has been demonstrated to markedly suppress experimental sepsis. The present review summarizes the role of HDAC6 in sepsis-induced inflammation and endothelial barrier dysfunction in recent years. It is proposed that HDAC6 inhibition predominantly ameliorates sepsis-induced ARDS by directly attenuating inflammation, which modulates the innate and adaptive immunity, transcription of pro-inflammatory genes, and protects endothelial barrier function. HDAC6 inhibition protects against sepsis-induced ARDS, thereby making HDAC6 a promising therapeutic target. However, HDAC inhibition may be associated with adverse effects on the embryo sac and oocyte, necessitating further studies.

Histone deacetylase 6 inhibition improves survival in a swine model of lethal hemorrhage, polytrauma, and bacteremia

BACKGROUND

Trauma is the leading cause of death for young Americans. Nonspecific histone deacetylase inhibitors, such as valproic acid, have been shown to improve survival in preclinical models of lethal trauma, hemorrhage, and sepsis. The doses needed to achieve a survival benefit are higher than Food and Drug Administration-approved doses, and the nonspecificity raises concerns about unintended adverse effects. The isoform-specific histone deacetylase 6 inhibitor, ACY-1083, has been found to be as efficacious as valproic acid in a rodent model of hemorrhagic shock. We hypothesized that ACY-1083 treatment would improve survival in a swine model of lethal hemorrhage, polytrauma, and bacteremia.

METHODS

Swine were subjected to 45% blood volume hemorrhage, brain injury, femur fracture, rectus crush, splenic and liver lacerations, and colon injury. After 1 hour of shock (mean arterial pressure, 30-35 mm Hg), animals were randomized to normal saline resuscitation (control) or normal saline plus ACY-1083 30 mg/kg treatment (n = 5/group). After 3 hours (simulating delayed evacuation), packed red blood cells and antibiotics were administered, the colon injury was repaired, and the abdomen was closed. Animals were then monitored for another 4 hours. Survival was assessed using Kaplan-Meier and log-rank test.

RESULTS

This combination of injuries was lethal. All animals became bacteremic, in addition to the severe hemorrhagic shock. Survival in the control group was 0%, and ACY-1083 treatment increased survival to 80% (p = 0.019). There was no difference in the brain lesion size between the groups.

CONCLUSION

A single dose of ACY-1083 markedly improves survival in an otherwise lethal model of polytrauma, hemorrhagic shock, and bacteremia.

Activation of TRPV4 by mechanical, osmotic or pharmaceutical stimulation is anti-inflammatory blocking IL-1β mediated articular cartilage matrix destruction

OBJECTIVE

Cartilage health is maintained in response to a range of mechanical stimuli including compressive, shear and tensile strains and associated alterations in osmolality. The osmotic-sensitive ion channel Transient Receptor Potential Vanilloid 4 (TRPV4) is required for mechanotransduction. Mechanical stimuli inhibit interleukin-1β (IL-1β) mediated inflammatory signalling, however the mechanism is unclear. This study aims to clarify the role of TRPV4 in this response.

DESIGN

TRPV4 activity was modulated glycogen synthase kinase (GSK205 antagonist or GSK1016790 A (GSK101) agonist) in articular chondrocytes and cartilage explants in the presence or absence of IL-1β, mechanical (10% cyclic tensile strain (CTS), 0.33 Hz, 24hrs) or osmotic loading (200mOsm, 24hrs). Nitric oxide (NO), prostaglandin E₂ (PGE₂) and sulphated glycosaminoglycan (sGAG) release and cartilage biomechanics were analysed. Alterations in post-translational tubulin modifications and primary cilia length regulation were examined.

RESULTS

In isolated chondrocytes, mechanical loading inhibited IL-1β mediated NO and PGE₂ release. This response was inhibited by GSK205. Similarly, osmotic loading was anti-inflammatory in cells and explants, this response was abrogated by TRPV4 inhibition. In explants, GSK101 inhibited IL-1β mediated NO release and prevented cartilage degradation and loss of mechanical properties. Upon activation, TRPV4 cilia localisation was increased resulting in histone deacetylase 6 (HDAC6)-dependent modulation of soluble tubulin and altered cilia length regulation.

CONCLUSION

Mechanical, osmotic or pharmaceutical activation of TRPV4 regulates HDAC6-dependent modulation of ciliary tubulin and is anti-inflammatory. This study reveals for the first time, the potential of TRPV4 manipulation as a novel therapeutic mechanism to supress pro-inflammatory signalling and cartilage degradation.

Succinyl-CoA Ligase Deficiency in Pro-inflammatory and Tissue-Invasive T Cells

Autoimmune T cells in rheumatoid arthritis (RA) have a defect in mitochondrial oxygen consumption and ATP production. Here, we identified suppression of the GDP-forming β subunit of succinate-CoA ligase (SUCLG2) as an underlying abnormality. SUCLG2-deficient T cells reverted the tricarboxylic acid (TCA) cycle from the oxidative to the reductive direction, accumulated α-ketoglutarate, citrate, and acetyl-CoA (AcCoA), and differentiated into pro-inflammatory effector cells. In AcCoA^hi RA T cells, tubulin acetylation stabilized the microtubule cytoskeleton and positioned mitochondria in a perinuclear location, resulting in cellular polarization, uropod formation, T cell migration, and tissue invasion. In the tissue, SUCLG2-deficient T cells functioned as cytokine-producing effector cells and were hyperinflammatory, a defect correctable by replenishing the enzyme. Preventing T cell tubulin acetylation by tubulin acetyltransferase knockdown was sufficient to inhibit synovitis. These data link mitochondrial failure and AcCoA oversupply to autoimmune tissue inflammation.

Microtubule Dysfunction: A Common Feature of Neurodegenerative Diseases

Neurons are particularly susceptible to microtubule (MT) defects and deregulation of the MT cytoskeleton is considered to be a common insult during the pathogenesis of neurodegenerative disorders. Evidence that dysfunctions in the MT system have a direct role in neurodegeneration comes from findings that several forms of neurodegenerative diseases are associated with changes in genes encoding tubulins, the structural units of MTs, MT-associated proteins (MAPs), or additional factors such as MT modifying enzymes which modulating tubulin post-translational modifications (PTMs) regulate MT functions and dynamics. Efforts to use MT-targeting therapeutic agents for the treatment of neurodegenerative diseases are underway. Many of these agents have provided several benefits when tested on both in vitro and in vivo neurodegenerative model systems. Currently, the most frequently addressed therapeutic interventions include drugs that modulate MT stability or that target tubulin PTMs, such as tubulin acetylation. The purpose of this review is to provide an update on the relevance of MT dysfunctions to the process of neurodegeneration and briefly discuss advances in the use of MT-targeting drugs for the treatment of neurodegenerative disorders.

Recent advances in small molecular modulators targeting histone deacetylase 6

Histone deacetylase 6 (HDAC6) is a unique isozyme in the HDAC family with various distinguished characters. HDAC6 is predominantly localized in the cytoplasm and has several specific nonhistone substrates, such as α-tubulin, cortactin, Hsp90, tau and peroxiredoxins. Accumulating evidence reveals that targeting HDAC6 may serve as a promising therapeutic strategy for the treatment of cancers, neurological disorders and immune diseases, making the development of HDAC6 inhibitors particularly attractive. Recently, multitarget drug design and proteolysis targeting chimera technology have also been applied in the discovery of novel small molecular modulators targeting HDAC6. In this review, we briefly describe the structural features and biological functions of HDAC6 and discuss the recent advances in HDAC6 modulators, including selective inhibitors, chimeric inhibitors and proteolysis targeting chimeras for multiple therapeutic purposes.

The dual functions of α-tubulin acetylation in cellular apoptosis and autophage induced by tanespimycin in lung cancer cells

Background

Reversible acetylation of α-tubulin has been implicated in modulating microtuble structures and functions, which may subsequently involve in cellular apoptosis and autophage. But how to trigger apoptosis or autophage at what level of acetylated α-tubulin (Ac-α-tubulin) are not known. This study aims to demonstrate the dual functions and molecular mechanisms of α-tubulin acetylation in cellular apoptosis and autophage induced by tanespimycin in Calu-1 cells simultaneously.

Methods

Calu-1 cells were treated with tanespimycin alone or combined administrations of different agents (including TSA, Docetaxel, Rapamycin, 3-MA and Z-vad) respectively and cell lysates were prepared to detect the given proteins by Western Blot. The cell survival was observed by inverted phase contrast microscope and estimated by SRB assay. HDAC6, TAT1 and Hsp90α/β proteins were knocked down by siRNA technique.

Results

By combination administration of tanespimycin with TSA or Docetaxel, the expression of Ac-α-tubulin and cellular apoptosis were enhanced markedly. While combination of tanespimycin and Rapamycin, α-tubulin acetylation and apoptosis were inhibited, but LC3B-II expression was facilitated substantially. When tanespimycin was combined with autophage inhibitor 3-MA, α-tubulin acetylation elevation was apparently, but LC3B-II was attenuated. Apoptosis inhibitor Z-vad blocked partially Caspases activation induced by tanespimycin, but failed to hinder α-tubulin acetylation elevation. According to results of RNA interference, acetyltransferase TAT1, deacetylase HDAC6 and Hsp90 modulated the expression level of α-tubulin acetylation.

Conclusion

We have elucidated that acetylation of α-tubulin induced by tanespimycin has dual functions in cellular apoptosis and autophage and the level of α-tubulin acetylation reaches a degree Calu-1 cells undergo cell apoptosis rather than autophage, implying that the level of acetylated α-tubulin may determine cell fate for survival or apoptosis.

Honokiol ameliorates angiotensin II-induced hypertension and endothelial dysfunction by inhibiting HDAC6-mediated cystathionine γ-lyase degradation

Hypertension and endothelial dysfunction are associated with various cardiovascular diseases. Hydrogen sulphide (H₂S) produced by cystathionine γ‐lyase (CSE) promotes vascular relaxation and lowers hypertension. Honokiol (HNK), a natural compound in the Magnolia plant, has been shown to retain multifunctional properties such as anti‐oxidative and anti‐inflammatory activities. However, a potential role of HNK in regulating CSE and hypertension remains largely unknown. Here, we aimed to demonstrate that HNK co‐treatment attenuated the vasoconstriction, hypertension and H₂S reduction caused by angiotensin II (AngII), a well‐established inducer of hypertension. We previously found that histone deacetylase 6 (HDAC6) mediates AngII‐induced deacetylation of CSE, which facilitates its ubiquitination and proteasomal degradation. Our current results indicated that HNK increased endothelial CSE protein levels by enhancing its stability in a sirtuin‐3‐independent manner. Notably, HNK could increase CSE acetylation levels by inhibiting HDAC6 catalytic activity, thereby blocking the AngII‐induced degradative ubiquitination of CSE. CSE acetylation and ubiquitination occurred mainly on the lysine 73 (K73) residue. Conversely, its mutant (K73R) was resistant to both acetylation and ubiquitination, exhibiting higher protein stability than that of wild‐type CSE. Collectively, our findings suggested that HNK treatment protects CSE against HDAC6‐mediated degradation and may constitute an alternative for preventing endothelial dysfunction and hypertensive disorders.

Inhibition of cell migration and induction of apoptosis by a novel class II histone deacetylase inhibitor, MCC2344

Epigenetic modifiers provide a new target for the development of anti-cancer drugs. The eraser histone deacetylase 6 (HDAC6) is a class IIb histone deacetylase that targets various non-histone proteins such as transcription factors, nuclear receptors, cytoskeletal proteins, DNA repair proteins, and molecular chaperones. Therefore, it became an attractive target for cancer treatment. In this study, virtual screening was applied to the MicroCombiChem database with 1162 drug-like compounds to identify new HDAC6 inhibitors. Five compounds were tested in silico and in vitro as HDAC6 inhibitors. Both analyses revealed 1-cyclohexene-1-carboxamide, 2-hydroxy-4,4-dimethyl-N-1-naphthalenyl-6-oxo- (MCC2344) as the best HDAC6 inhibitor among the five ligands. The binding affinity of MCC2344 to HDAC6 was further confirmed by microscale thermophoresis. Additionally, the anti-cancer activity of MCC2344 was tested in several tumor cell lines. Leukemia cells were the most sensitive cells towards MCC2344, particularly the P-glycoprotein-overexpressing multidrug-resistant cell line CEM/ADR5000 exhibited remarkable collateral sensitivity towards MCC2344. Transcriptome analysis using microarray hybridization was performed for investigating downstream mechanisms of action of MCC2344 in leukemia cells. MCC2344 affected microtubule dynamics and suppressed cell migration in the wound healing assay as well as in a spheroid model by hyper-acetylation of tubulin and HSP-90. MCC2344 induced cell death in CEM/ADR5000 cells by activation of PARP, caspase-3, and p21 in addition to the downregulation of p62. MCC2344 significantly inhibited tumor growth in vivo in zebrafish larvae without mortality until 20 pM. We propose MCC2344 as a novel HDAC6 inhibitor for cancer treatment.

Phospho-HDAC6 Gathers Into Protein Aggregates in Parkinson's Disease and Atypical Parkinsonisms

HDAC6 is a unique histone deacetylase that targets cytoplasmic non-histone proteins and has a specific ubiquitin-binding activity. Both of these activities are required for HDAC6-mediated formation of aggresomes, which contain misfolded proteins that will ultimately be degraded via autophagy. HDAC6 deacetylase activity is increased following phosphorylation on serine 22 (phospho-HDAC6). In human, HDAC6 localizes in neuronal Lewy bodies in Parkinson’s disease (PD) and in oligodendrocytic Papp–Lantos bodies in multiple system atrophy (MSA). However, the expression of phospho-HDAC6 in post-mortem human brains is currently unexplored. Here, we evaluate and compare the distribution of HDAC6 and its phosphorylated form in human brains obtained from patients affected by three forms of parkinsonism: two synucleinopathies (PD and MSA) and a tauopathy (progressive supranuclear palsy, PSP). We find that both HDAC6 and its phosphorylated form localize with pathological protein aggregates, including α-synuclein-positive Lewy bodies in PD and Papp–Lantos bodies in MSA, and phospho-tau-positive neurofibrillary tangles in PSP. We further find a direct interaction of HDAC6 with α-synuclein with proximity ligation assay (PLA) in neuronal cell of PD patients. Taken together, our findings suggest that both HDAC6 and phospho-HDAC6 regulate the homeostasis of intra-neuronal proteins in parkinsonism.

AAV9-Stathmin1 gene delivery improves disease phenotype in an intermediate mouse model of spinal muscular atrophy

Spinal muscular atrophy (SMA) is a devastating infantile genetic disorder caused by the loss of survival motor neuron (SMN) protein that leads to premature death due to loss of motor neurons and muscle atrophy. The approval of an antisense oligonucleotide therapy for SMA was an important milestone in SMA research; however, effective next-generation therapeutics will likely require combinatorial SMN-dependent therapeutics and SMN-independent disease modifiers. A recent cross-disease transcriptomic analysis identified Stathmin-1 (STMN1), a tubulin-depolymerizing protein, as a potential disease modifier across different motor neuron diseases, including SMA. Here, we investigated whether viral-based delivery of STMN1 decreased disease severity in a well-characterized SMA mouse model. Intracerebroventricular delivery of scAAV9-STMN1 in SMA mice at P2 significantly increased survival and weight gain compared to untreated SMA mice without elevating Smn levels. scAAV9-STMN1 improved important hallmarks of disease, including motor function, NMJ pathology and motor neuron cell preservation. Furthermore, scAAV9-STMN1 treatment restored microtubule networks and tubulin expression without affecting tubulin stability. Our results show that scAAV9-STMN1 treatment improves SMA pathology possibly by increasing microtubule turnover leading to restored levels of stable microtubules. Overall, these data demonstrate that STMN1 can significantly reduce the SMA phenotype independent of restoring SMN protein and highlight the importance of developing SMN-independent therapeutics for the treatment of SMA.

Epigenetic Regulation of Multidrug Resistance Protein 1 and Breast Cancer Resistance Protein Transporters by Histone Deacetylase Inhibition

Multidrug resistance protein 1 (MDR1, ABCB1, P-glycoprotein) and breast cancer resistance protein (BCRP, ABCG2) are key efflux transporters that mediate the extrusion of drugs and toxicants in cancer cells and healthy tissues, including the liver, kidneys, and the brain. Altering the expression and activity of MDR1 and BCRP influences the disposition, pharmacodynamics, and toxicity of chemicals, including a number of commonly prescribed medications. Histone acetylation is an epigenetic modification that can regulate gene expression by changing the accessibility of the genome to transcriptional regulators and transcriptional machinery. Recently, studies have suggested that pharmacological inhibition of histone deacetylases (HDACs) modulates the expression and function of MDR1 and BCRP transporters as a result of enhanced histone acetylation. This review addresses the ability of HDAC inhibitors to modulate the expression and the function of MDR1 and BCRP transporters and explores the molecular mechanisms by which HDAC inhibition regulates these transporters. While the majority of studies have focused on histone regulation of MDR1 and BCRP in drug-resistant and drug-sensitive cancer cells, emerging data point to similar responses in nonmalignant cells and tissues. Elucidating epigenetic mechanisms regulating MDR1 and BCRP is important to expand our understanding of the basic biology of these two key transporters and subsequent consequences on chemoresistance as well as tissue exposure and responses to drugs and toxicants. SIGNIFICANCE STATEMENT: Histone deacetylase inhibitors alter the expression of key efflux transporters multidrug resistance protein 1 and breast cancer resistance protein in healthy and malignant cells.

BAG3 Pro209 mutants associated with myopathy and neuropathy relocate chaperones of the CASA-complex to aggresomes

Three missense mutations targeting the same proline 209 (Pro209) codon in the co-chaperone Bcl2-associated athanogene 3 (BAG3) have been reported to cause distal myopathy, dilated cardiomyopathy or Charcot-Marie-Tooth type 2 neuropathy. Yet, it is unclear whether distinct molecular mechanisms underlie the variable clinical spectrum of the rare patients carrying these three heterozygous Pro209 mutations in BAG3. Here, we studied all three variants and compared them to the BAG3_Glu455Lys mutant, which causes dilated cardiomyopathy. We found that all BAG3_Pro209 mutants have acquired a toxic gain-of-function, which causes these variants to accumulate in the form of insoluble HDAC6- and vimentin-positive aggresomes. The aggresomes formed by mutant BAG3 led to a relocation of other chaperones such as HSPB8 and Hsp70, which, together with BAG3, promote the so-called chaperone-assisted selective autophagy (CASA). As a consequence of their increased aggregation-proneness, mutant BAG3 trapped ubiquitinylated client proteins at the aggresome, preventing their efficient clearance. Combined, these data show that all BAG3_Pro209 mutants, irrespective of their different clinical phenotypes, are characterized by a gain-of-function that contributes to the gradual loss of protein homeostasis.

Insights of the tubulin code in gametes and embryos: from basic research to potential clinical applications in humans†

Microtubules are intracellular filaments that define in space and in time a large number of essential cellular functions such as cell division, morphology and motility, intracellular transport and flagella and cilia assembly. They are therefore essential for spermatozoon and oocyte maturation and function, and for embryo development. The dynamic and functional properties of the microtubules are in large part defined by various classes of interacting proteins including MAPs (microtubule associated proteins), microtubule-dependent motors, and severing and modifying enzymes. Multiple mechanisms regulate these interactions. One of them is defined by the high diversity of the microtubules themselves generated by the combination of different tubulin isotypes and by several tubulin post-translational modifications (PTMs). This generates a so-called tubulin code that finely regulates the specific set of proteins that associates with a given microtubule thereby defining the properties and functions of the network. Here we provide an in depth review of the current knowledge on the tubulin isotypes and PTMs in spermatozoa, oocytes, and preimplantation embryos in various model systems and in the human species. We focus on functional implications of the tubulin code for cytoskeletal function, particularly in the field of human reproduction and development, with special emphasis on gamete quality and infertility. Finally, we discuss some of the knowledge gaps and propose future research directions.

HDAC11 deficiency disrupts oncogene-induced hematopoiesis in myeloproliferative neoplasms

Protein acetylation is an important contributor to cancer initiation. Histone deacetylase 6 (HDAC6) controls JAK2 translation and protein stability and has been implicated in JAK2-driven diseases best exemplified by myeloproliferative neoplasms (MPNs). By using novel classes of highly selective HDAC inhibitors and genetically deficient mouse models, we discovered that HDAC11 rather than HDAC6 is necessary for the proliferation and survival of oncogenic JAK2-driven MPN cells and patient samples. Notably, HDAC11 is variably expressed in primitive stem cells and is expressed largely upon lineage commitment. Although Hdac11is dispensable for normal homeostatic hematopoietic stem and progenitor cell differentiation based on chimeric bone marrow reconstitution, Hdac11 deficiency significantly reduced the abnormal megakaryocyte population, improved splenic architecture, reduced fibrosis, and increased survival in the MPLW515L-MPN mouse model during primary and secondary transplantation. Therefore, inhibitors of HDAC11 are an attractive therapy for treating patients with MPN. Although JAK2 inhibitor therapy provides substantial clinical benefit in MPN patients, the identification of alternative therapeutic targets is needed to reverse MPN pathogenesis and control malignant hematopoiesis. This study establishes HDAC11 as a unique type of target molecule that has therapeutic potential in MPN.

Transcriptional and epigenetic regulation of ncx1 and ncx3 in the brain

Sodium-calcium exchanger (NCX) 1 and 3, have been demonstrated to play a relevant role in controlling the intracellular homeostasis of sodium and calcium ions in physiological and patho-physiological conditions. While NCX1 and NCX3 knocking-down have been both implicated in brain ischemia, several aspects of the epigenetic regulation of these two antiporters transcription were not yet well characterized. In response to stroke, NCX1 and NCX3 transcriptional regulation occurs from specific promoter sequences. Several evidences have shown that the expression of NCX1 and NCX3 can be determined by epigenetic modifications, consisting in changes of the histone acetylation levels on their promoter sequences. An interesting issue is that histone modifications at the NCX1 and NCX3 promoters could be linked to neurodegeneration occurring after stroke. Therefore, identifying the epigenetic regulation at the NCX1 and NCX3 promoters could permit to identify new molecular targets that can open new strategies for stroke treatment. The current review reassumes the recent knowledge of histone modifications of NCX1 and NCX3 genes in brain in physiological and patho-physiological conditions.

Discovery of specific HDAC6 inhibitor with anti-metastatic effects in pancreatic cancer cells through virtual screening and biological evaluation

Histone deacetylase 6 (HDAC6) has been demonstrated to play a major role in cell motility and aggresome formation, and HDAC6 inhibition is therefore considered as a promising epigenetic strategy for cancer treatment. At present, only a minority of compounds have been reported as HDAC6 inhibitors, so specific HDAC6 inhibitors with safety profile need to be discovered urgently. In this paper, HDAC6 inhibitors with diverse structures were used to generate the pharmacophore model by ligand-based method, which contained two hydrogen bond acceptors and two hydrophobic groups. A combined virtual screening based on pharmacophore model and molecular docking was adopted to screen potential HDAC6 inhibitors. Subsequently, the HDAC6 inhibitory activity of the hit compounds were evaluated using an in vitro enzyme binding inhibition assay. The experimental results illustrated that cefoperazone sodium had the strongest inhibitory effect on HDAC6 among the six screened compounds, and its IC₅₀ value was 8.59 ± 1.06 μM. Cefoperazone sodium significantly catalyzed the hyperacetylation of α-tubulin but not histone H3, proving that cefoperazone sodium was a selective inhibitor of HDAC6. Since the expression of HDAC6 plays an important role in cancer metastasis, the effects of cefoperazone sodium on migration and invasion of human pancreatic cancer PANC-1 cells were further investigated by wound healing and transwell chamber assays. It was found that cefoperazone sodium could evidently inhibit the migration and invasion of PANC-1 cells. Furthermore, the binding pattern of inhibitor at the active site of the crystal structure was revealed by molecular docking, providing a reference value for the structural design and optimization of HDAC6 inhibitors. This study provides a systematic virtual screening approach for discovering HDAC6 active inhibitors, and by which the specific effect of cefoperazone sodium against HDAC6 was found, suggesting its potential application on cancer therapy.

Much More Than a Scaffold: Cytoskeletal Proteins in Neurological Disorders

Recent observations related to the structure of the cytoskeleton in neurons and novel cytoskeletal abnormalities involved in the pathophysiology of some neurological diseases are changing our view on the function of the cytoskeletal proteins in the nervous system. These efforts allow a better understanding of the molecular mechanisms underlying neurological diseases and allow us to see beyond our current knowledge for the development of new treatments. The neuronal cytoskeleton can be described as an organelle formed by the three-dimensional lattice of the three main families of filaments: actin filaments, microtubules, and neurofilaments. This organelle organizes well-defined structures within neurons (cell bodies and axons), which allow their proper development and function through life. Here, we will provide an overview of both the basic and novel concepts related to those cytoskeletal proteins, which are emerging as potential targets in the study of the pathophysiological mechanisms underlying neurological disorders.

HDAC6-an Emerging Target Against Chronic Myeloid Leukemia?

Imatinib became the standard treatment for chronic myeloid leukemia (CML) about 20 years ago, which was a major breakthrough in stabilizing the pathology and improving the quality of life of patients. However, the emergence of resistance to imatinib and other tyrosine kinase inhibitors leads researchers to characterize new therapeutic targets. Several studies have highlighted the role of histone deacetylase 6 (HDAC6) in various pathologies, including cancer. This protein effectively intervenes in cellular activities by its primarily cytoplasmic localization. In this review, we will discuss the molecular characteristics of the HDAC6 protein, as well as its overexpression in CML leukemic stem cells, which make it a promising therapeutic target for the treatment of CML.

The disordered N-terminus of HDAC6 is a microtubule-binding domain critical for efficient tubulin deacetylation

Histone deacetylase 6 (HDAC6) is a multidomain cytosolic enzyme having tubulin deacetylase activity that has been unequivocally assigned to the second of the tandem catalytic domains. However, virtually no information exists on the contribution of other HDAC6 domains on tubulin recognition. Here, using recombinant protein expression, site-directed mutagenesis, fluorimetric and biochemical assays, microscale thermophoresis, and total internal reflection fluorescence microscopy, we identified the N-terminal, disordered region of HDAC6 as a microtubule-binding domain and functionally characterized it to the single-molecule level. We show that the microtubule-binding motif spans two positively charged patches comprising residues Lys-32 to Lys-58. We found that HDAC6-microtubule interactions are entirely independent of the catalytic domains and are mediated by ionic interactions with the negatively charged microtubule surface. Importantly, a crosstalk between the microtubule-binding domain and the deacetylase domain was critical for recognition and efficient deacetylation of free tubulin dimers both in vitro and in vivo Overall, our results reveal that recognition of substrates by HDAC6 is more complex than previously appreciated and that domains outside the tandem catalytic core are essential for proficient substrate deacetylation.

Emerging Role of Sirtuin 2 in Parkinson's Disease

Parkinson’s disease (PD), the main risk factor of which is age, is one of the most common neurodegenerative diseases, thus presenting a substantial burden on the health of affected individuals as well as an economic burden. Sirtuin 2 (SIRT2), a subtype in the family of sirtuins, belongs to class III histone deacetylases (HDACs). It is known that SIRT2 levels increase with aging, and a growing body of evidence has been accumulating, showing that the activity of SIRT2 mediates various processes involved in PD pathogenesis, including aggregation of α-synuclein (α-syn), microtubule function, oxidative stress, inflammation, and autophagy. There have been conflicting reports about the role of SIRT2 in PD, in that some studies indicate its potential to induce the death of dopaminergic (DA) neurons, and that inhibition of SIRT2 may, therefore, have protective effects in PD. Other studies suggest a protective role of SIRT2 in the context of neuronal damage. As current treatments for PD are directed at alleviating symptoms and are very limited, a comprehensive understanding of the enzymology of SIRT2 in PD may be essential for developing novel therapeutic agents for the treatment of this disease. This review article will provide an update on our knowledge of the structure, distribution, and biological characteristics of SIRT2, and highlight its role in the pathogenesis of PD.