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

Roles of Histone Deacetylase 4 in the Inflammatory and Metabolic Processes

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

Class IIa HDAC4 and HDAC7 cooperatively regulate gene transcription in Th17 cell differentiation

Class II histone deacetylases (HDACs) are important in regulation of gene transcription during T cell development. However, our understanding of their cell-specific functions is limited. In this study, we reveal that class IIa Hdac4 and Hdac7 (Hdac4/7) are selectively induced in transcription, guiding the lineage-specific differentiation of mouse T-helper 17 (Th17) cells from naive CD4+ T cells. Importantly, Hdac4/7 are functionally dispensable in other Th subtypes. Mechanistically, Hdac4 interacts with the transcription factor (TF) JunB, facilitating the transcriptional activation of Th17 signature genes such as Il17a/f. Conversely, Hdac7 collaborates with the TF Aiolos and Smrt/Ncor1-Hdac3 corepressors to repress transcription of Th17 negative regulators, including Il2, in Th17 cell differentiation. Inhibiting Hdac4/7 through pharmacological or genetic methods effectively mitigates Th17 cell-mediated intestinal inflammation in a colitis mouse model. Our study uncovers molecular mechanisms where HDAC4 and HDAC7 function distinctively yet cooperatively in regulating ordered gene transcription during Th17 cell differentiation. These findings suggest a potential therapeutic strategy of targeting HDAC4/7 for treating Th17-related inflammatory diseases, such as ulcerative colitis.

The catalytic domain of free or ligand bound histone deacetylase 4 occurs in solution predominantly in closed conformation

Human histone deacetylase 4 (HDAC4) is a key epigenetic regulator involved in a number of important cellular processes. This makes HDAC4 a promising target for the treatment of several cancers and neurodegenerative diseases, in particular Huntington's disease. HDAC4 is highly regulated by phosphorylation and oxidation, which determine its nuclear or cytosolic localization, and exerts its function through multiple interactions with other proteins, forming multiprotein complexes of varying composition. The catalytic domain of HDAC4 is known to interact with the SMRT/NCOR corepressor complex when the structural zinc-binding domain (sZBD) is intact and forms a closed conformation. Crystal structures of the HDAC4 catalytic domain have been reported showing an open conformation of HDAC4 when bound to certain ligands. Here, we investigated the relevance of this HDAC4 conformation under physiological conditions in solution. We show that proper zinc chelation in the sZBD is essential for enzyme function. Loss of the structural zinc ion not only leads to a massive decrease in enzyme activity, but it also has serious consequences for the overall structural integrity and stability of the protein. However, the Zn2+ free HDAC4 structure in solution is incompatible with the open conformation. In solution, the open conformation of HDAC4 was also not observed in the presence of a variety of structurally divergent ligands. This suggests that the open conformation of HDAC4 cannot be induced in solution, and therefore cannot be exploited for the development of HDAC4-specific inhibitors.

Exercise Alleviates Fluoride-Induced Learning and Memory Impairment in Mice: Role of miR-206-3p and PREG

Fluorosis decreases the learning and memory ability in humans and animals, while exercise can reduce the risk of cognitive decline. However, the effect of exercise on learning and memory in fluoride-exposed mice is unclear. For this purpose, in this study, mice were randomly allotted into four groups (16 mice per group, half male and half female): control group (group C), fluoride group (group F, 100 mg/L sodium fluoride (NaF)), exercise group (group E, treadmill exercise), and E plus F group (group EF, treadmill exercise, and 100 mg/L NaF). During 6 months of exposure, exercise alleviated the NaF-induced decline in memory and learning. In addition, NaF induced injuries in mitochondria and myelin sheath ultrastructure and reduced the neurons number, while exercise restored them. Metabolomics results showed that phosphatidylethanolamine, pregnenolone (PREG), and lysophosphatidic acid (LysoPA) were altered among groups C, F, and EF. Combined with previous studies, it can be suggested that PREG might be a biomarker in response to exercise-relieving fluorine neurotoxicity. The miRNA sequencing results indicated that in the differently expressed miRNAs (DEmiRNAs), miR-206-3p, miR-96-5p, and miR-144-3p were shared in groups C, F, and EF. After the QRT-PCR validation and in vitro experiments, it was proved that miR-206-3p could reduce cell death and regulate AP-1 transcription factor subunit (JunD) and histone deacetylase 4 (HDAC4) to alleviate fluoride neurotoxicity. To sum up, the current study reveals that exercise could alleviate NaF-induced neurotoxicity by targeting miR-206-3p or PREG, which will contribute to revealing the pathogenesis and therapeutic method of fluoride neurotoxicity.

Alterations in DNA methylation associate with reduced migraine and headache days after medication withdrawal treatment in chronic migraine patients: a longitudinal study

BACKGROUND

Chronic migraine, a highly disabling migraine subtype, affects nearly 2% of the general population. Understanding migraine chronification is vital for developing better treatment and prevention strategies. An important factor in the chronification of migraine is the overuse of acute headache medication. However, the mechanisms behind the transformation of episodic migraine to chronic migraine and vice versa have not yet been elucidated. We performed a longitudinal epigenome-wide association study to identify DNA methylation (DNAm) changes associated with treatment response in patients with chronic migraine and medication overuse as part of the Chronification and Reversibility of Migraine clinical trial. Blood was taken from patients with chronic migraine (n = 98) at baseline and after a 12-week medication withdrawal period. Treatment responders, patients with ≥ 50% reduction in monthly headache days (MHD), were compared with non-responders to identify DNAm changes associated with treatment response. Similarly, patients with ≥ 50% versus < 50% reduction in monthly migraine days (MMD) were compared.

RESULTS

At the epigenome-wide significant level (p < 9.42 × 10-8), a longitudinal reduction in DNAm at an intronic CpG site (cg14377273) within the HDAC4 gene was associated with MHD response following the withdrawal of acute medication. HDAC4 is highly expressed in the brain, plays a major role in synaptic plasticity, and modulates the expression and release of several neuroinflammation markers which have been implicated in migraine pathophysiology. Investigating whether baseline DNAm associated with treatment response, we identified lower baseline DNAm at a CpG site (cg15205829) within MARK3 that was significantly associated with MMD response at 12 weeks.

CONCLUSIONS

Our findings of a longitudinal reduction in HDAC4 DNAm status associated with treatment response and baseline MARK3 DNAm status as an early biomarker for treatment response, provide support for a role of pathways related to chromatin structure and synaptic plasticity in headache chronification and introduce HDAC4 and MARK3 as novel therapeutic targets.

Difluoromethyl-1,3,4-oxadiazoles Are Selective, Mechanism-Based, and Essentially Irreversible Inhibitors of Histone Deacetylase

Histone deacetylase 6 (HDAC6) is an important drug target in oncological and non-oncological diseases. Most available HDAC6 inhibitors (HDAC6i) utilize hydroxamic acids as a zinc-binding group, which limits therapeutic opportunities due to its genotoxic potential. Recently, difluoromethyl-1,3,4-oxadiazoles (DFMOs) were reported as potent and selective HDAC6i but their mode of inhibition remained enigmatic. Herein, we report that DFMOs act as mechanism-based and essentially irreversible HDAC6i. Biochemical data confirm that DFMO 6 is a tight-binding HDAC6i capable of inhibiting HDAC6 via a two-step slow-binding mechanism. Crystallographic and mechanistic experiments suggest that the attack of 6 by the zinc-bound water at the sp2 carbon closest to the difluoromethyl moiety followed by a subsequent ring opening of the oxadiazole yields deprotonated difluoroacetylhydrazide 13 as active species. The strong anionic zinc coordination of 13 and the binding of the difluoromethyl moiety in the P571 pocket finally result in an essentially irreversible inhibition of HDAC6.

Upregulated ribosome pathway plays a key role in HDAC4, improving the survival rate and biofunction of chondrocytes

Aims

To explore the novel molecular mechanisms of histone deacetylase 4 (HDAC4) in chondrocytes via RNA sequencing (RNA-seq) analysis.

Methods

Empty adenovirus (EP) and a HDAC4 overexpression adenovirus were transfected into cultured human chondrocytes. The cell survival rate was examined by real-time cell analysis (RTCA) and EdU and flow cytometry assays. Cell biofunction was detected by Western blotting. The expression profiles of messenger RNAs (mRNAs) in the EP and HDAC4 transfection groups were assessed using whole-transcriptome sequencing (RNA-seq). Volcano plot, Gene Ontology, and pathway analyses were performed to identify differentially expressed genes (DEGs). For verification of the results, the A289E/S246/467/632 A sites of HDAC4 were mutated to enhance the function of HDAC4 by increasing HDAC4 expression in the nucleus. RNA-seq was performed to identify the molecular mechanism of HDAC4 in chondrocytes. Finally, the top ten DEGs associated with ribosomes were verified by quantitative polymerase chain reaction (QPCR) in chondrocytes, and the top gene was verified both in vitro and in vivo.

Results

HDAC4 markedly improved the survival rate and biofunction of chondrocytes. RNA-seq analysis of the EP and HDAC4 groups showed that HDAC4 induced 2,668 significant gene expression changes in chondrocytes (1,483 genes upregulated and 1,185 genes downregulated, p < 0.05), and ribosomes exhibited especially large increases. The results were confirmed by RNA-seq of the EP versus mutated HDAC4 groups and the validations in vitro and in vivo.

Conclusion

The enhanced ribosome pathway plays a key role in the mechanism by which HDAC4 improves the survival rate and biofunction of chondrocytes.

Perspectives and new aspects of histone deacetylase inhibitors in the therapy of CNS diseases

Many populations worldwide are suffering from central nervous system (CNS) diseases such as brain tumors, neurodegenerative diseases (Alzheimer's disease, Parkinson's disease and Huntington's disease) and stroke. There is a shortage of effective drugs for most CNS diseases. As one of the regulatory mechanisms of epigenetics, the particular role and therapeutic benefits of histone deacetylases (HDACs) in the CNS have been extensively studied. In recent years, HDACs have attracted increasing attention as potential drug targets for CNS diseases. In this review, we summarize the recent applications of representative histone deacetylases inhibitors (HDACis) in CNS diseases and discuss the challenges in developing HDACis with different structures and better blood-brain barrier (BBB) permeability, hoping to promote the development of more effective bioactive HDACis for the treatment of CNS diseases.

Exploring the Genetic Predisposition to Epigenetic Changes in Alzheimer's Disease

Alzheimer's disease (AD) is a prevalent type of dementia in elderly populations with a significant genetic component. The accumulating evidence suggests that AD involves a reconfiguration of the epigenetic landscape, including DNA methylation, post-translational modification of histone proteins, and chromatin remodeling. Along with environmental factors, individual specific genetic features play a considerable role in the formation of epigenetic architecture. In this study, we attempt to identify the non-coding regulatory SNPs (rSNPs) able to affect the epigenetic mechanisms in AD. To this end, the multi-omics approach is used. The GEO (Gene Expression Omnibus) available data (GSE153875) for AD patients and controls are integrated to reveal the rSNPs that display allele-specific features in both ChIP-seq profiles of four histone modifications and RNA-seq. Furthermore, we analyze the presence of rSNPs in the promoters of genes reported to be differentially expressed between AD and the normal brain (AD-related genes) and involved in epigenetic regulation according to the EpiFactors database. We also searched for the rSNPs in the promoters of the genes coding for transcription regulators of the identified AD-related genes. These regulators were selected based on the corresponding ChIP-seq peaks (ENCODE) in the promoter regions of these genes. Finally, we formed a panel of rSNPs localized to the promoters of genes that contribute to the epigenetic landscape in AD and, thus, to the genetic predisposition for this disease.

Histone Deacetylase 4 Inhibition Reduces Rotenone-Induced Alpha-Synuclein Accumulation via Autophagy in SH-SY5Y Cells

(1) Background: Parkinson's disease (PD) is the most common movement disorder. Imbalanced protein homeostasis and α-syn aggregation are involved in PD pathogenesis. Autophagy is related to the occurrence and development of PD and can be regulated by histone deacetylases (HDACs). Various inhibitors of HDACs exert neuroprotective effects within in vitro and in vivo models of PD. HDAC4, a class Ⅱ HDAC, colocalizes with α-synuclein and ubiquitin in Lewy bodies and also accumulates in the nuclei of dopaminergic neurons in PD models. (2) Methods: In the present study, the gene expression profile of HDACs from two previously reported datasets in the GEO database was analyzed, and the RNA levels of HDAC4 in brain tissues were compared between PD patients and healthy controls. In vitro, SH-SY5Y cells transfected with HDAC4 shRNA or pretreated with mc1568 were treated with 1 μM of rotenone for 24 h. Then, the levels of α-syn, LC3, and p62 were detected using Western blot analysis and immunofluorescent staining, and cell viabilities were detected using Cell Counting Kit-8 (CCK-8). (3) Results: HDAC4 was highly expressed in PD substantia nigra and locus coeruleus. Mc1568, an inhibitor of HDAC4, decreased α-synuclein levels in rotenone-treated SH-SY5Y cells in a concentration-dependent manner and activated autophagy, which was impaired by rotenone. The knockdown of HDAC4 reversed rotenone-induced α-syn accumulation in SH-SY5Y cells and protected the neurons by enhancing autophagy. (4) Conclusions: HDAC4 is a potential therapeutic target for PD. The inhibition of HDAC4 by mc1568 or a gene block can reduce α-syn levels by regulating the autophagy process in PD. Mc1568 is a promising therapeutic agent for PD and other disorders related to α-syn accumulation.

Tip60's Novel RNA-Binding Function Modulates Alternative Splicing of Pre-mRNA Targets Implicated in Alzheimer's Disease

The severity of Alzheimer's disease (AD) progression involves a complex interplay of genetics, age, and environmental factors orchestrated by histone acetyltransferase (HAT)-mediated neuroepigenetic mechanisms. While disruption of Tip60 HAT action in neural gene control is implicated in AD, alternative mechanisms underlying Tip60 function remain unexplored. Here, we report a novel RNA binding function for Tip60 in addition to its HAT function. We show that Tip60 preferentially interacts with pre-mRNAs emanating from its chromatin neural gene targets in the Drosophila brain and this RNA binding function is conserved in human hippocampus and disrupted in Drosophila brains that model AD pathology and in AD patient hippocampus of either sex. Since RNA splicing occurs co-transcriptionally and alternative splicing (AS) defects are implicated in AD, we investigated whether Tip60-RNA targeting modulates splicing decisions and whether this function is altered in AD. Replicate multivariate analysis of transcript splicing (rMATS) analysis of RNA-Seq datasets from wild-type and AD fly brains revealed a multitude of mammalian-like AS defects. Strikingly, over half of these altered RNAs are identified as bona-fide Tip60-RNA targets that are enriched for in the AD-gene curated database, with some of these AS alterations prevented against by increasing Tip60 in the fly brain. Further, human orthologs of several Tip60-modulated splicing genes in Drosophila are well characterized aberrantly spliced genes in human AD brains, implicating disruption of Tip60's splicing function in AD pathogenesis. Our results support a novel RNA interaction and splicing regulatory function for Tip60 that may underly AS impairments that hallmark AD etiology.SIGNIFICANCE STATEMENT Alzheimer's disease (AD) has recently emerged as a hotbed for RNA alternative splicing (AS) defects that alter protein function in the brain yet causes remain unclear. Although recent findings suggest convergence of epigenetics with co-transcriptional AS, whether epigenetic dysregulation in AD pathology underlies AS defects remains unknown. Here, we identify a novel RNA interaction and splicing regulatory function for Tip60 histone acetyltransferase (HAT) that is disrupted in Drosophila brains modeling AD pathology and in human AD hippocampus. Importantly, mammalian orthologs of several Tip60-modulated splicing genes in Drosophila are well characterized aberrantly spliced genes in human AD brain. We propose that Tip60-mediated AS modulation is a conserved critical posttranscriptional step that may underlie AS defects now characterized as hallmarks of AD.

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

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

Synthesis and Characterization of Reversible Covalent HDAC4 Inhibitors

Cyanoacrylates define a class of inhibitors which are capable to form a transient covalent bond with a cysteine flanking the binding site, thereby increasing the residence time and prolonging the inhibitory effect on the target protein under nonequilibrium conditions. Herein, we describe the synthetic access to cyanoacrylate-based HDAC4 inhibitors and the procedures for the characterization of the transient nature of the covalent bond between cyanoacrylates and thiols or cysteines in HDAC4.

Development of Fluorinated Peptoid-Based Histone Deacetylase (HDAC) Inhibitors for Therapy-Resistant Acute Leukemia

Using a microwave-assisted protocol, we synthesized 16 peptoid-capped HDAC inhibitors (HDACi) with fluorinated linkers and identified two hit compounds. In biochemical and cellular assays, 10h stood out as a potent unselective HDACi with remarkable cytotoxic potential against different therapy-resistant leukemia cell lines. 10h demonstrated prominent antileukemic activity with low cytotoxic activity toward healthy cells. Moreover, 10h exhibited synergistic interactions with the DNA methyltransferase inhibitor decitabine in AML cell lines. The comparison of crystal structures of HDAC6 complexes with 10h and its nonfluorinated counterpart revealed a similar occupation of the L1 loop pocket but slight differences in zinc coordination. The substitution pattern of the acyl residue turned out to be crucial in terms of isoform selectivity. The introduction of an isopropyl group onto the phenyl ring provided the highly HDAC6-selective inhibitor 10p, which demonstrated moderate synergy with decitabine and exceeded the HDAC6 selectivity of tubastatin A.

Ubiquitin Proteasome Gene Signatures in Ependymoma Molecular Subtypes

The ubiquitin proteasome system (UPS) is critically important for cellular homeostasis and affects virtually all key functions in normal and neoplastic cells. Currently, a comprehensive review of the role of the UPS in ependymoma (EPN) brain tumors is lacking but may provide valuable new information on cellular networks specific to different EPN subtypes and reveal future therapeutic targets. We have reviewed publicly available EPN gene transcription datasets encoding components of the UPS pathway. Reactome analysis of these data revealed genes and pathways that were able to distinguish different EPN subtypes with high significance. We identified differential transcription of several genes encoding ubiquitin E2 conjugases associated with EPN subtypes. The expression of the E2 conjugase genes UBE2C, UBE2S, and UBE2I was elevated in the ST_EPN_RELA subtype. The UBE2C and UBE2S enzymes are associated with the ubiquitin ligase anaphase promoting complex (APC/c), which regulates the degradation of substrates associated with cell cycle progression, whereas UBE2I is a Sumo-conjugating enzyme. Additionally, elevated in ST_EPN_RELA were genes for the E3 ligase and histone deacetylase HDAC4 and the F-box cullin ring ligase adaptor FBX031. Cluster analysis demonstrated several genes encoding E3 ligases and their substrate adaptors as EPN subtype specific genetic markers. The most significant Reactome Pathways associated with differentially expressed genes for E3 ligases and their adaptors included antigen presentation, neddylation, sumoylation, and the APC/c complex. Our analysis provides several UPS associated factors that may be attractive markers and future therapeutic targets for the subtype-specific treatment of EPN patients.

Clinical relevance of biomarkers, new therapeutic approaches, and role of post-translational modifications in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder that causes progressive loss of cognitive functions like thinking, memory, reasoning, behavioral abilities, and social skills thus affecting the ability of a person to perform normal daily functions independently. There is no definitive cure for this disease, and treatment options available for the management of the disease are not very effective as well. Based on histopathology, AD is characterized by the accumulation of insoluble deposits of amyloid beta (Aβ) plaques and neurofibrillary tangles (NFTs). Although several molecular events contribute to the formation of these insoluble deposits, the aberrant post-translational modifications (PTMs) of AD-related proteins (like APP, Aβ, tau, and BACE1) are also known to be involved in the onset and progression of this disease. However, early diagnosis of the disease as well as the development of effective therapeutic approaches is impeded by lack of proper clinical biomarkers. In this review, we summarized the current status and clinical relevance of biomarkers from cerebrospinal fluid (CSF), blood and extracellular vesicles involved in onset and progression of AD. Moreover, we highlight the effects of several PTMs on the AD-related proteins, and provide an insight how these modifications impact the structure and function of proteins leading to AD pathology. Finally, for disease-modifying therapeutics, novel approaches, and targets are discussed for the successful treatment and management of AD.

Early postnatal serotonin modulation prevents adult-stage deficits in Arid1b-deficient mice through synaptic transcriptional reprogramming

Autism spectrum disorder is characterized by early postnatal symptoms, although little is known about the mechanistic deviations that produce them and whether correcting them has long-lasting preventive effects on adult-stage deficits. ARID1B, a chromatin remodeler implicated in neurodevelopmental disorders, including autism spectrum disorder, exhibits strong embryonic- and early postnatal-stage expression. We report here that Arid1b-happloinsufficient (Arid1b^+/–) mice display autistic-like behaviors at juvenile and adult stages accompanied by persistent decreases in excitatory synaptic density and transmission. Chronic treatment of Arid1b^+/– mice with fluoxetine, a selective serotonin-reuptake inhibitor, during the first three postnatal weeks prevents synaptic and behavioral deficits in adults. Mechanistically, these rescues accompany transcriptomic changes, including upregulation of FMRP targets and normalization of HDAC4/MEF2A-related transcriptional regulation of the synaptic proteins, SynGAP1 and Arc. These results suggest that chronic modulation of serotonergic receptors during critical early postnatal periods prevents synaptic and behavioral deficits in adult Arid1b^+/– mice through transcriptional reprogramming.

ARID1B is a chromatin remodeler associated with autism spectrum disorders. Here the authors demonstrate that early postnatal serotonin modulation prevents adult stage deficits in Arid1b-deficient mice through synaptic transcriptional reprogramming.

Specific epigenetic regulators serve as potential therapeutic targets in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF), a disorder observed mostly in older human beings, is characterised by chronic and progressive lung scarring leading to an irreversible decline in lung function. This health condition has a dismal prognosis and the currently available drugs only delay but fail to reverse the progression of lung damage. Consequently, it becomes imperative to discover improved therapeutic compounds and their cellular targets to cure IPF. In this regard, a number of recent studies have targeted the epigenetic regulation by histone deacetylases (HDACs) to develop and categorise antifibrotic drugs for lungs. Therefore, this review focuses on how aberrant expression or activity of Classes I, II and III HDACs alter TGF-β signalling to promote events such as epithelial-mesenchymal transition, differentiation of activated fibroblasts into myofibroblasts, and excess deposition of the extracellular matrix to propel lung fibrosis. Further, this study describes how certain chemical compounds or dietary changes modulate dysregulated HDACs to attenuate five faulty TGF-β-dependent profibrotic processes, both in animal models and cell lines replicating IPF, thereby identifying promising means to treat this lung disorder.

A Nutraceutical Product Based on a Mixture of Algae and Extra Virgin Olive Oils and Olive Leaf Extract Attenuates Sepsis-Induced Cardiovascular and Muscle Alterations in Rats

Nutraceuticals are products of natural origin widely used for the treatment and/or prevention of some chronic diseases that are highly prevalent in Western countries, such as obesity or type II diabetes, among others. However, its possible use in the prevention of acute diseases that can put life at risk has been poorly studied. Sepsis is an acute condition that causes cardiovascular and skeletal muscle damage due to a systemic inflammatory state. The aim of this work was to evaluate the possible beneficial effect of a new nutraceutical based on a mixture of algae oil (AO) and extra virgin olive oil (EVOO) supplemented with an olive leaf extract (OLE) in the prevention of cardiovascular alterations and skeletal muscle disorders induced by sepsis in rats. For this purpose, male Wistar rats were treated with the nutraceutical or with water p.o. for 3 weeks and after the treatment they were injected with 1mg/kg LPS twice (12 and 4 h before sacrifice). Pretreatment with the nutraceutical prevented the LPS-induced decrease in cardiac contractility before and after the hearts were subjected to ischemia-reperfusion. At the vascular level, supplementation with the nutraceutical did not prevent hypotension in septic animals, but it attenuated endothelial dysfunction and the increased response of aortic rings to the vasoconstrictors norepinephrine and angiotensin-II induced by LPS. The beneficial effects on cardiovascular function were associated with an increased expression of the antioxidant enzymes SOD-1 and GSR in cardiac tissue and SOD-1 and Alox-5 in arterial tissue. In skeletal muscle, nutraceutical pretreatment prevented LPS-induced muscle proteolysis and autophagy and significantly increased protein synthesis as demonstrated by decreased expression of MURF-1, atrogin-1, LC3b and increased MCH-I and MCH -IIa in gastrocnemius muscle. These effects were associated with a decrease in the expression of TNFα, HDAC4 and myogenin. In conclusion, treatment with a new nutraceutical based on a mixture of AO and EVOO supplemented with OLE is useful to prevent cardiovascular and muscular changes induced by sepsis in rats. Thus, supplementation with this nutraceutical may constitute an interesting strategy to reduce the severity and mortality risk in septic patients.

The Role of miRNAs in Dexmedetomidine's Neuroprotective Effects against Brain Disorders

There are limited neuroprotective strategies for various central nervous system conditions in which fast and sustained management is essential. Neuroprotection-based therapeutics have become an intensively researched topic in the neuroscience field, with multiple novel promising agents, from natural products to mesenchymal stem cells, homing peptides, and nanoparticles-mediated agents, all aiming to significantly provide neuroprotection in experimental and clinical studies. Dexmedetomidine (DEX), an α2 agonist commonly used as an anesthetic adjuvant for sedation and as an opioid-sparing medication, stands out in this context due to its well-established neuroprotective effects. Emerging evidence from preclinical and clinical studies suggested that DEX could be used to protect against cerebral ischemia, traumatic brain injury (TBI), spinal cord injury, neurodegenerative diseases, and postoperative cognitive disorders. MicroRNAs (miRNAs) regulate gene expression at a post-transcriptional level, inhibiting the translation of mRNA into functional proteins. In vivo and in vitro studies deciphered brain-related miRNAs and dysregulated miRNA profiles after several brain disorders, including TBI, ischemic stroke, Alzheimer’s disease, and multiple sclerosis, providing emerging new perspectives in neuroprotective therapy by modulating these miRNAs. Experimental studies revealed that some of the neuroprotective effects of DEX are mediated by various miRNAs, counteracting multiple mechanisms in several disease models, such as lipopolysaccharides induced neuroinflammation, β-amyloid induced dysfunction, brain ischemic-reperfusion injury, and anesthesia-induced neurotoxicity models. This review aims to outline the neuroprotective mechanisms of DEX in brain disorders by modulating miRNAs. We address the neuroprotective effects of DEX by targeting miRNAs in modulating ischemic brain injury, ameliorating the neurotoxicity of anesthetics, reducing postoperative cognitive dysfunction, and improving the effects of neurodegenerative diseases.

Modifier pathways in polyglutamine (PolyQ) diseases: from genetic screens to drug targets

Polyglutamine (PolyQ) diseases include a group of inherited neurodegenerative disorders caused by unstable expansions of CAG trinucleotide repeats in the coding region of specific genes. Such genetic alterations produce abnormal proteins containing an unusually long PolyQ tract that renders them more prone to aggregate and cause toxicity. Although research in the field in the last years has contributed significantly to the knowledge of the biological mechanisms implicated in these diseases, effective treatments are still lacking. In this review, we revisit work performed in models of PolyQ diseases, namely the yeast Saccharomyces cerevisiae, the nematode worm Caenorhabditis elegans and the fruit fly Drosophila melanogaster, and provide a critical overview of the high-throughput unbiased genetic screens that have been performed using these systems to identify novel genetic modifiers of PolyQ diseases. These approaches have revealed a wide variety of cellular processes that modulate the toxicity and aggregation of mutant PolyQ proteins, reflecting the complexity of these disorders and demonstrating how challenging the development of therapeutic strategies can be. In addition to the unbiased large-scale genetic screenings in non-vertebrate models, complementary studies in mammalian systems, closer to humans, have contributed with novel genetic modifiers of PolyQ diseases, revealing neuronal function and inflammation as key disease modulators. A pathway enrichment analysis, using the human orthologues of genetic modifiers of PolyQ diseases clustered modifier genes into major themes translatable to the human disease context, such as protein folding and transport as well as transcription regulation. Innovative genetic strategies of genetic manipulation, together with significant advances in genomics and bioinformatics, are taking modifier genetic studies to more realistic disease contexts. The characterization of PolyQ disease modifier pathways is of extreme relevance to reveal novel therapeutic possibilities to delay disease onset and progression in patients.

Epigenetics in inflammatory liver diseases: A clinical perspective (Review)

Inflammatory liver diseases are, nowadays, multifactorial and wide-spread, thus having an important socio-economic impact. Although the therapeutic algorithms are well-known in hepatitis, regardless of etiology, strategies to identify inflammatory hepatic lesions in early stages and to develop new epigenetic therapies should be prioritized. The main entities of inflammatory liver disease are: alcoholic and non-alcoholic fatty liver disease, autoimmune hepatitis, viral hepatitis and Wilson disease. The main epigenetic processes include: DNA methylation/demethylation, which imply changes in DNA tertiary structure; post-translational histone covalent changes (methylation/demethylation, acetylation/deacetylation, ubiquitination), that cause DNA-histone instability; synthesis of small, non-coding RNA molecules, called microRNAs, that modulate translational potential of transcripts (mRNAs) and post-translational modification of polypeptide chains. Consequently, the epigenetic interactions aforementioned, play an important modulatory role in disease progression and response to conventional therapies The present review focused on the main epigenetic changes in inflammatory liver conditions, considering a new perspective: Epigenetic therapy. This approach is more than welcomed, taking into consideration that conventional therapeutic strategies are almost exhausted.

Role of Glucocorticoid Signaling and HDAC4 Activation in Diaphragm and Gastrocnemius Proteolytic Activity in Septic Rats

Sepsis increases glucocorticoid and decreases IGF-1, leading to skeletal muscle wasting and cachexia. Muscle atrophy mainly takes place in locomotor muscles rather than in respiratory ones. Our study aimed to elucidate the mechanism responsible for this difference in muscle proteolysis, focusing on local inflammation and IGF-1 as well as on their glucocorticoid response and HDAC4-myogenin activation. Sepsis was induced in adult male rats by lipopolysaccharide (LPS) injection (10 mg/kg), and 24 h afterwards, rats were euthanized. LPS increased TNFα and IL-10 expression in both muscles studied, the diaphragm and gastrocnemius, whereas IL-6 and SOCS3 mRNA increased only in diaphragm. In comparison with gastrocnemius, diaphragm showed a lower increase in proteolytic marker expression (atrogin-1 and LC3b) and in LC3b protein lipidation after LPS administration. LPS increased the expression of glucocorticoid induced factors, KLF15 and REDD1, and decreased that of IGF-1 in gastrocnemius but not in the diaphragm. In addition, an increase in HDAC4 and myogenin expression was induced by LPS in gastrocnemius, but not in the diaphragm. In conclusion, the lower activation of both glucocorticoid signaling and HDAC4-myogenin pathways by sepsis can be one of the causes of lower sepsis-induced proteolysis in the diaphragm compared to gastrocnemius.

Lysine 63-linked ubiquitination of tau oligomers contributes to the pathogenesis of Alzheimer's disease

Ubiquitin-modified tau aggregates are abundantly found in human brains diagnosed with Alzheimer's disease (AD) and other tauopathies. Soluble tau oligomers (TauO) are the most neurotoxic tau species that propagate pathology and elicit cognitive deficits, but whether ubiquitination contributes to tau formation and spreading is not fully understood. Here, we observed that K63-linked, but not K48-linked, ubiquitinated TauO accumulated at higher levels in AD brains compared with age-matched controls. Using mass spectrometry analyses, we identified 11 ubiquitinated sites on AD brain-derived TauO (AD TauO). We found that K63-linked TauO are associated with enhanced seeding activity and propagation in human tau-expressing primary neuronal and tau biosensor cells. Additionally, exposure of tau-inducible HEK cells to AD TauO with different ubiquitin linkages (wild type, K48, and K63) resulted in enhanced formation and secretion of K63-linked TauO, which was associated with impaired proteasome and lysosome functions. Multipathway analysis also revealed the involvement of K63-linked TauO in cell survival pathways, which are impaired in AD. Collectively, our study highlights the significance of selective TauO ubiquitination, which could influence tau aggregation, accumulation, and subsequent pathological propagation. The insights gained from this study hold great promise for targeted therapeutic intervention in AD and related tauopathies.

MS275 as Class I HDAC inhibitor displayed therapeutic potential on malignant ascites by iTRAQ-based quantitative proteomic analysis

Background

Malignant ascites is a manifestation of end stage events in a variety of cancers and is associated with significant morbidity. Epigenetic modulators play a key role in cancer initiation and progression, among which histone deacetylases (HDACs) are considered as one of the most important regulators for various cancer development, such as liver cancer, ovarian cancer, and pancreatic cancer et al. Thus, in this paper, we sought to explore the therapeutic effect of HDAC inhibitor on malignant ascites.

Methods

In this report, we tested the therapeutic effect of different isoform selective HDAC inhibitors (Class I HDACI MS275, Class IIa HDACI MC1568, pan-HDAC inhibitors SAHA) on malignant ascites in vitro and in vivo. We further used proteome analysis to find the potential mechanisms for malignant ascites therapy.

Results

Among the different isoform-selective HDAC inhibitors, the class I selective HDACI, MS275, exhibited preferential inhibition on various ascites cells. MS275 could induce cell cycle arrest in G0/G1 phase and promote apoptosis on ascites cells. Through proteome analysis, we found MS275 could downregulate proteins related to cell cycle progression, such as CDK4, CDC20, CCND1; MS275 could upregulate pro-apoptosis proteins such as PAPR1, LMNB2 and AIFM1; in addition, MS275 could change the expression of tumorigenic proteins related to the specific malignant ascites bearing tumors, such as TSP1 and CDK4 for bladder cancer. We then confirmed that abemaciclib (CDK4/6 selective inhibitor) could inhibit the proliferation of ascites cells, and the combination of abemaciclib and MS275 had synergistic anti-tumor effect. Finally, we found that MS275 could in vivo inhibit malignant ascites progression (ascites volume: 2.9 ± 1.0 mL vs 7.5 ± 1.2 mL, p < 0.01), tumor growth, and prolong 66% of the life-span when compared with the untreated group.

Conclusion

This present research revealed that the class I selective HDAC inhibitor, MS275, could effectively inhibit malignant ascites development and tumor growth via multiple pathways. These results indicated that HDACI could have great potential for clinical therapy of malignant ascites.

Mesenchymal Stem Cell-Originated Exosomal Circular RNA circFBXW7 Attenuates Cell Proliferation, Migration and Inflammation of Fibroblast-Like Synoviocytes by Targeting miR-216a-3p/HDAC4 in Rheumatoid Arthritis

Background

Rheumatoid arthritis (RA) is a chronic autoimmune disease of articular joint damage and elevated synovial hyperplasia. Abnormal proliferation, invasion inflammatory response of rheumatoid fibroblast-like synoviocytes (RA-FLS) play a critical role in RA progression. Mesenchymal stem cell (MSC)–derived exosomal circular RNAs are promising therapeutic manner for disease treatment. This work aimed to decipher the role of exosomal circFBXW7 in RA.

Methods

The expression of circFBXW7, miR-216a-3p, and HDAC4 were detected in clinical RA samples. The RA rat model was established. Isolation and identification of exosomes from MSCs was conducted. The effects of exosomal circFBXW7 on RA was evaluated by qPCR, CCK-8, transwell assays, flow cytometry, Western blotting, ELISA, and immunohistochemical assay. Interaction between miR-216a-3p and circFBXW7 or HDAC4 was determined by luciferase reporter gene assay and RNA pulldown.

Results

Exosomal circFBXW7 treatment suppressed proliferation, migration and inflammatory response of RA-FLSs and damage of RA model. CircFBXW7 could directly sponge miR-216a-3p to upregulate the expression of HDAC4. Inhibition of HDAC4 or upregulation of miR-216a-3p abolished the therapeutic function of exosomal circFBXW7. Our data demonstrated that circFBXW7 and HDAC4 were decreased, and miR-216a-3p was elevated in clinical RA sample compared with healthy samples.

Conclusion

We concluded that MSC-derived exosomal circFBXW7 suppressed proliferation, migration and inflammatory response of RA-FLSs and damage of RA rats via sponging miR-216a-3p and release the activation of HDAC4. These findings may provide a novel therapeutic target for RA.

Mechanistic Insights into Binding of Ligands with Thiazolidinedione Warhead to Human Histone Deacetylase 4

Recently, we have reported that non-hydroxamate thiazolidinedione (TZD) analogs are capable of inhibiting human deacetylase 4 (HDAC4). This study aims at the dissection of the molecular determinants and kinetics of the molecular recognition of TZD ligands by HDAC4. For this purpose, a structure activity relationship analysis of 225 analogs was combined with a comprehensive study of the enzyme and binding kinetics of a variety of HDAC4 mutant variants. The experimental data were rationalized by docking to the two major conformations of HDAC4. TZD ligands are competitive inhibitors and bind via a two-step mechanism involving principal molecular recognition and induced fit. The residence time of 24 g is (34 ± 3) min and thus much larger than that of the canonical pan-HDAC inhibitor SAHA ((5 ± 2) min). Importantly, the binding kinetics can be tuned by varying the structure of the CAP group.

Evaluation of Class IIa Histone Deacetylases Expression and In Vivo Epigenetic Imaging in a Transgenic Mouse Model of Alzheimer's Disease

Epigenetic regulation by histone deacetylase (HDAC) is associated with synaptic plasticity and memory formation, and its aberrant expression has been linked to cognitive disorders, including Alzheimer's disease (AD). This study aimed to investigate the role of class IIa HDAC expression in AD and monitor it in vivo using a novel radiotracer, 6-(tri-fluoroacetamido)-1-hexanoicanilide ([¹⁸F]TFAHA). A human neural cell culture model with familial AD (FAD) mutations was established and used for in vitro assays. Positron emission tomography (PET) imaging with [¹⁸F]TFAHA was performed in a 3xTg AD mouse model for in vivo evaluation. The results showed a significant increase in HDAC4 expression in response to amyloid-β (Aβ) deposition in the cell model. Moreover, treatment with an HDAC4 selective inhibitor significantly upregulated the expression of neuronal memory-/synaptic plasticity-related genes. In [¹⁸F]TFAHA-PET imaging, whole brain or regional uptake was significantly higher in 3xTg AD mice compared with WT mice at 8 and 11 months of age. Our study demonstrated a correlation between class IIa HDACs and Aβs, the therapeutic benefit of a selective inhibitor, and the potential of using [¹⁸F]TFAHA as an epigenetic radiotracer for AD, which might facilitate the development of AD-related neuroimaging approaches and therapies.

Functional Duality of Chondrocyte Hypertrophy and Biomedical Application Trends in Osteoarthritis

Chondrocyte hypertrophy is one of the key indicators in the progression of osteoarthritis (OA). However, compared with other OA indications, such as cartilage collapse, sclerosis, inflammation, and protease activation, the mechanisms by which chondrocyte hypertrophy contributes to OA remain elusive. As the pathological processes in the OA cartilage microenvironment, such as the alterations in the extracellular matrix, are initiated and dictated by the physiological state of the chondrocytes, in-depth knowledge of chondrocyte hypertrophy is necessary to enhance our understanding of the disease pathology and develop therapeutic agents. Chondrocyte hypertrophy is a factor that induces OA progression; it is also a crucial factor in the endochondral ossification. This review elaborates on this dual functionality of chondrocyte hypertrophy in OA progression and endochondral ossification through a description of the characteristics of various genes and signaling, their mechanism, and their distinguishable physiological effects. Chondrocyte hypertrophy in OA progression leads to a decrease in chondrogenic genes and destruction of cartilage tissue. However, in endochondral ossification, it represents an intermediate stage at the process of differentiation of chondrocytes into osteogenic cells. In addition, this review describes the current therapeutic strategies and their mechanisms, involving genes, proteins, cytokines, small molecules, three-dimensional environments, or exosomes, against the OA induced by chondrocyte hypertrophy. Finally, this review proposes that the contrasting roles of chondrocyte hypertrophy are essential for both OA progression and endochondral ossification, and that this cellular process may be targeted to develop OA therapeutics.

Understanding the role of histone deacetylase and their inhibitors in neurodegenerative disorders: Current targets and future perspective

Neurodegenerative diseases are a group of pathological conditions that cause motor inc-ordination (jerking movements), cognitive and memory impairments result from degeneration of neurons in a specific area of the brain. Oxidative stress, mitochondrial dysfunction, excitotoxicity, neuroinflammation, neurochemical imbalance and histone deacetylase enzymes (HDAC) are known to play a crucial role in neurodegeneration. HDAC is classified into four categories (class I, II, III and class IV) depending upon their location and functions. HDAC1 and 2 are involved in neurodegeneration, while HDAC3-11 and class III HDACs are beneficial as neuroprotective. HDACs are localized in different parts of the brain- HDAC1 (hippocampus and cortex), HDAC2 (nucleus), HDAC3, 4, 5, 7 and 9 (nucleus and cytoplasm), HDAC6 & HDAC7 (cytoplasm) and HDAC11 (Nucleus, cornus ammonis 1 and spinal cord). In pathological conditions, HDAC up-regulates glutamate, phosphorylation of tau, and glial fibrillary acidic proteins while down-regulating BDNF, Heat shock protein 70 and Gelsolin. Class III HDACs are divided into seven sub-classes (SIRT1-SIRT7). Sirtuins are localized in the different parts of the brain and neuron -Sirt1 (nucleus), Sirt2 (cortex, striatum, hippocampus and spinal cord), Sirt3 (mitochondria and cytoplasm), Sirt4, Sirt5 & Sirt6 (mitochondria), Sirt7 (nucleus) and Sirt8 (nucleolus). SIRTs (1, 3, 4, and 6) are involved in neuronal survival, proliferation and modulating stress response, and SIRT2 is associated with Parkinsonism, Huntington’s disease and Alzheimer’s disease, whereas SIRT6 is only associated with Alzheimer’s disease. In this critical review, we have discussed the mechanisms and therapeutic targets of HDACs that would be beneficial for the management of neurodegenerative disorders.

Melatonin and Melatonergic Influence on Neuronal Transcription Factors: Implications for the Development of Novel Therapies for Neurodegenerative Disorders

Melatonin is a multifunctional signalling molecule that is secreted by the mammalian pineal gland, and also found in a number of organisms including plants and bacteria. Research has continued to uncover an ever-increasing number of processes in which melatonin is known to play crucial roles in mammals. Amongst these functions is its contribution to cell multiplication, differentiation and survival in the brain. Experimental studies show that melatonin can achieve these functions by influencing transcription factors which control neuronal and glial gene expression. Since neuronal survival and differentiation are processes that are important determinants of the pathogenesis, course and outcome of neurodegenerative disorders; the known and potential influences of melatonin on neuronal and glial transcription factors are worthy of constant examination. In this review, relevant scientific literature on the role of melatonin in preventing or altering the course and outcome of neurodegenerative disorders, by focusing on melatonin's influence on transcription factors is examined. A number of transcription factors whose functions can be influenced by melatonin in neurodegenerative disease models have also been highlighted. Finally, the therapeutic implications of melatonin's influences have also been discussed and the potential limitations to its applications have been highlighted.

When Good Kinases Go Rogue: GSK3, p38 MAPK and CDKs as Therapeutic Targets for Alzheimer's and Huntington's Disease

Alzheimer's disease (AD) is a mostly sporadic brain disorder characterized by cognitive decline resulting from selective neurodegeneration in the hippocampus and cerebral cortex whereas Huntington's disease (HD) is a monogenic inherited disorder characterized by motor abnormalities and psychiatric disturbances resulting from selective neurodegeneration in the striatum. Although there have been numerous clinical trials for these diseases, they have been unsuccessful. Research conducted over the past three decades by a large number of laboratories has demonstrated that abnormal actions of common kinases play a key role in the pathogenesis of both AD and HD as well as several other neurodegenerative diseases. Prominent among these kinases are glycogen synthase kinase (GSK3), p38 mitogen-activated protein kinase (MAPK) and some of the cyclin-dependent kinases (CDKs). After a brief summary of the molecular and cell biology of AD and HD this review covers what is known about the role of these three groups of kinases in the brain and in the pathogenesis of the two neurodegenerative disorders. The potential of targeting GSK3, p38 MAPK and CDKS as effective therapeutics is also discussed as is a brief discussion on the utilization of recently developed drugs that simultaneously target two or all three of these groups of kinases. Multi-kinase inhibitors either by themselves or in combination with strategies currently being used such as immunotherapy or secretase inhibitors for AD and knockdown for HD could represent a more effective therapeutic approach for these fatal neurodegenerative diseases.

Increased Abundance of Nuclear HDAC4 Impairs Neuronal Development and Long-Term Memory

Dysregulation of the histone deacetylase HDAC4 is associated with both neurodevelopmental and neurodegenerative disorders, and a feature common to many of these disorders is impaired cognitive function. HDAC4 shuttles between the nucleus and cytoplasm in both vertebrates and invertebrates and alterations in the amounts of nuclear and/or cytoplasmic HDAC4 have been implicated in these diseases. In Drosophila, HDAC4 also plays a critical role in the regulation of memory, however, the mechanisms through which it acts are unknown. Nuclear and cytoplasmically-restricted HDAC4 mutants were expressed in the Drosophila brain to investigate a mechanistic link between HDAC4 subcellular distribution, transcriptional changes and neuronal dysfunction. Deficits in mushroom body morphogenesis, eye development and long-term memory correlated with increased abundance of nuclear HDAC4 but were associated with minimal transcriptional changes. Although HDAC4 sequesters MEF2 into punctate foci within neuronal nuclei, no alteration in MEF2 activity was observed on overexpression of HDAC4, and knockdown of MEF2 had no impact on long-term memory, indicating that HDAC4 is likely not acting through MEF2. In support of this, mutation of the MEF2 binding site within HDAC4 also had no impact on nuclear HDAC4-induced impairments in long-term memory or eye development. In contrast, the defects in mushroom body morphogenesis were ameliorated by mutation of the MEF2 binding site, as well as by co-expression of MEF2 RNAi, thus nuclear HDAC4 acts through MEF2 to disrupt mushroom body development. These data provide insight into the mechanisms through which dysregulation of HDAC4 subcellular distribution impairs neurological function and provides new avenues for further investigation.

Histone Deacetylases (HDACs) in Gastric Cancer: An Update of their Emerging Prognostic and Therapeutic Role

Chemotherapy resistance is a rising concern in Gastric Cancer (GC) and has led to the investigation of various cellular compounds. Α functional equilibrium of histone acetylation and deacetylation was discovered in all cells, regulated by Histone Acetyltransferases and Deacetylases (HDACs), controlling chromatin coiling status and changing gene expression appropriately. In accordance with recent research, this equilibrium can be dysregulated in cancer cells aiding in the process of carcinogenesis and tumor progression by altering histone and non-histone proteins affecting gene expression, cell cycle control, differentiation, and apoptosis in various malignancies. In addition, increased HDAC expression in GC cells has been associated with increased stage, tumor invasion, nodal metastases, increased distant metastatic potential, and decreased overall survival. HDAC inhibitors could be used as treatment regimens for GC patients and could develop important synergistic interactions with chemotherapy drugs. The aim of this article is to review the molecular identity and mechanism of action of HDAC inhibitors, as well as highlight their potential utility as anti-cancer agents in GC.

Impaired Regulation of Histone Methylation and Acetylation Underlies Specific Neurodevelopmental Disorders

Epigenetic processes are critical for governing the complex spatiotemporal patterns of gene expression in neurodevelopment. One such mechanism is the dynamic network of post-translational histone modifications that facilitate recruitment of transcription factors or even directly alter chromatin structure to modulate gene expression. This is a tightly regulated system, and mutations affecting the function of a single histone-modifying enzyme can shift the normal epigenetic balance and cause detrimental developmental consequences. In this review, we will examine select neurodevelopmental conditions that arise from mutations in genes encoding enzymes that regulate histone methylation and acetylation. The methylation-related conditions discussed include Wiedemann-Steiner, Kabuki, and Sotos syndromes, and the acetylation-related conditions include Rubinstein-Taybi, KAT6A, genitopatellar/Say-Barber-Biesecker-Young-Simpson, and brachydactyly mental retardation syndromes. In particular, we will discuss the clinical/phenotypic and genetic basis of these conditions and the model systems that have been developed to better elucidate cellular and systemic pathological mechanisms.

Beneficial Effects of a Mixture of Algae and Extra Virgin Olive Oils on the Age-Induced Alterations of Rodent Skeletal Muscle: Role of HDAC-4

Aging is associated with a progressive decline in skeletal muscle mass, strength and function (sarcopenia). We have investigated whether a mixture of algae oil (25%) and extra virgin olive oil (75%) could exert beneficial effects on sarcopenia. Young (3 months) and old (24 months) male Wistar rats were treated with vehicle or with the oil mixture (OM) (2.5 mL/kg) for 21 days. Aging decreased gastrocnemius weight, total protein, and myosin heavy chain mRNA. Treatment with the OM prevented these effects. Concomitantly, OM administration decreased the inflammatory state in muscle; it prevented the increase of pro-inflammatory interleukin-6 (IL-6) and the decrease in anti-inflammatory interleukin-10 (IL-10) in aged rats. The OM was not able to prevent aging-induced alterations in either the insulin-like growth factor I/protein kinase B (IGF-I/Akt) pathway or in the increased expression of atrogenes in the gastrocnemius. However, the OM prevented decreased autophagy activity (ratio protein 1A/1B-light chain 3 (LC3b) II/I) induced by aging and increased expression of factors related with muscle senescence such as histone deacetylase 4 (HDAC-4), myogenin, and IGF-I binding protein 5 (IGFBP-5). These data suggest that the beneficial effects of the OM on muscle can be secondary to its anti-inflammatory effect and to the normalization of HDAC-4 and myogenin levels, making this treatment an alternative therapeutic tool for sarcopenia.

Synthesis and Evaluation of 18F-INER-1577-3 as a Central Nervous System (CNS) Histone Deacetylase Imaging Agent

BACKGROUND

Epigenetic dysfunction is implicated in many neurologic, psychiatric and oncologic diseases. Consequently, histone deacetylases (HDACs) inhibitors have been developed as therapeutic and imaging agents for these diseases. However, only a few radiotracers have been developed as HDACs imaging agents for the central nervous system (CNS). We report herein the synthesis and evaluation of [¹⁸F]INER-1577-3 ([¹⁸F]5) as an HDACs imaging agent for CNS.

METHODS

[¹⁸F]INER-1577-3 ([¹⁸F]5) was synthesized by two methods: one-step (A) and two-step (B) methods. Briefly, radiofluorination of the corresponding precursors (11, 12) with K[¹⁸F]/K2.2.2 followed by purifications with HPLC gave ([¹⁸F]5). The quality of [¹⁸F]INER- 1577-3 synthesized by these methods was verified by HPLC and TLC as compared to an authentic sample. The inhibitions of [¹⁸F]INER-1577-3 and related HDACs inhibitors on tumor cells growth were carried out with breast cancer cell line 4T1 and MCF-7. The whole-body and brain uptake of [¹⁸F]INER-1577-3 in rats and AD mice were determined using a micro-PET scanner and the data was analyzed using PMOD.

RESULTS

The radiochemical yield of [¹⁸F]INER-1577-3 synthesized by these two methods was 1.4 % (Method A) and 8.8% (Method B) (EOB), respectively. The synthesis time was 115 min and 100 min, respectively, from EOB. The inhibition studies showed that INER-1577-3 has a significant inhibitory effect in HDAC6 and HDAC8 but not HDAC2. PET studies in rats and AD mice showed a maximum at about 15 min postinjection for the whole brain of a rat (0.47 ± 0.03 %ID/g), SAMP8 mice (5.63 ± 1.09 %ID/g) and SAMR1 mice (7.23 ± 1.21 %ID/g).

CONCLUSION

This study showed that INER-1577-3 can inhibit tumor cell growth and is one of a few HDACs inhibitors that can penetrate the blood-brain barrier (BBB) and monitor HDAC activities in AD mice. Thus, [¹⁸F]INER-1577-3 may be a potent HDACs imaging agent, especially for CNS.

The role of histone deacetylase 4 during chondrocyte hypertrophy and endochondral bone development

Chondrocyte hypertrophy represents a crucial turning point during endochondral bone development. This process is tightly regulated by various factors, constituting a regulatory network that maintains normal bone development. Histone deacetylase 4 (HDAC4) is the most well-characterized member of the HDAC class IIa family and participates in different signalling networks during development in various tissues by promoting chromatin condensation and transcriptional repression. Studies have reported that HDAC4-null mice display premature ossification of developing bones due to ectopic and early-onset chondrocyte hypertrophy. Overexpression of HDAC4 in proliferating chondrocytes inhibits hypertrophy and ossification of developing bones, which suggests that HDAC4, as a negative regulator, is involved in the network regulating chondrocyte hypertrophy. Overall, HDAC4 plays a key role during bone development and disease. Thus, understanding the role of HDAC4 during chondrocyte hypertrophy and endochondral bone formation and its features regarding the structure, function, and regulation of this process will not only provide new insight into the mechanisms by which HDAC4 is involved in chondrocyte hypertrophy and endochondral bone development, but will also create a platform for developing a therapeutic strategy for related diseases.

Cite this article:Bone Joint Res. 2020;9(2):82–89.

MicroRNA-206 Regulates Stress-Provoked Aggressive Behaviors in Post-weaning Social Isolation Mice

When facing stressful conditions, some people tend to be impulsively aggressive whereas others are not. However, the causes and underlying mechanisms remain elusive. It has been reported that acute stress induces outbursts of aggression in post-weaning social isolation (SI) mice but not in group housing (GH) mice. Here we report epigenetic regulation of impulsive aggression in SI mice. At post-natal day 21, mice were randomly assigned to GH or SI groups. We found that SI mice exhibited a higher level of microRNA 206 (miR-206) compared with GH mice. Intra-hippocampal injection of AM206, an antagomir of miR-206, decreased stress-induced attack behavior in SI mice and increased BDNF expression. Moreover, BDNF expression was required for AM206 effects on the reduction of aggression. On the other hand, miR-206 overexpression in GH mice induced attack behavior. Intranasal administration of AM206 rather than a scramble control significantly reduced attack behavior and depression-like behavior in SI mice. Our results suggest that miR-206 mediates development of maladaptive impulsive aggression in early life adversity and that its antagomir could potentially be a therapeutic target against stress-exacerbated aggressive behavior.

Behavioral Alterations in Mice Carrying Homozygous HDAC4 A778T Missense Mutation Associated With Eating Disorder

Eating disorders (EDs) are serious mental illnesses thought to arise from the complex gene-environment interactions. DNA methylation patterns in histone deacetylase 4 (HDAC4) locus have been associated with EDs and we have previously identified a missense mutation in the HDAC4 gene (HDAC4^A786T) that increases the risk of developing an ED. In order to evaluate the biological consequences of this variant and establish a useful mouse model of EDs, here we performed behavioral characterization of mice homozygous for Hdac4^A778T (corresponding to human HDAC4^A786T) that were further backcrossed onto C57BL/6 background. When fed high-fat diet, male, but not female, homozygous mice showed a trend toward decreased weight gain compared to their wild-type littermates. Behaviorally, male, but not female, homozygous mice spent less time in eating and exhibited reduced motivation to work for palatable food and light phase-specific decrease in locomotor activity. Additionally, homozygous Hdac4^A778T female, but not male, mice display social subordination when subjected to a tube dominance test. Collectively, these results reveal a complex sex- and circadian-dependent role of ED-associated Hdac4^A778T mutation in affecting mouse behaviors. Homozygous Hdac4^A778T mice could therefore be a useful animal model to gain insight into the neurobiological basis of EDs.

Arginase Inhibition Supports Survival and Differentiation of Neuronal Precursors in Adult Alzheimer's Disease Mice

Adult neurogenesis is a complex physiological process, which plays a central role in maintaining cognitive functions, and consists of progenitor cell proliferation, newborn cell migration, and cell maturation. Adult neurogenesis is susceptible to alterations under various physiological and pathological conditions. A substantial decay of neurogenesis has been documented in Alzheimer’s disease (AD) patients and animal AD models; however, several treatment strategies can halt any further decline and even induce neurogenesis. Our previous results indicated a potential effect of arginase inhibition, with norvaline, on various aspects of neurogenesis in triple-transgenic mice. To better evaluate this effect, we chronically administered an arginase inhibitor, norvaline, to triple-transgenic and wild-type mice, and applied an advanced immunohistochemistry approach with several biomarkers and bright-field microscopy. Remarkably, we evidenced a significant reduction in the density of neuronal progenitors, which demonstrate a different phenotype in the hippocampi of triple-transgenic mice as compared to wild-type animals. However, norvaline showed no significant effect upon the progenitor cell number and constitution. We demonstrated that norvaline treatment leads to an escalation of the polysialylated neuronal cell adhesion molecule immunopositivity, which suggests an improvement in the newborn neuron survival rate. Additionally, we identified a significant increase in the hippocampal microtubule-associated protein 2 stain intensity. We also explore the molecular mechanisms underlying the effects of norvaline on adult mice neurogenesis and provide insights into their machinery.

In silico Design of Novel Histone Deacetylase 4 Inhibitors: Design Guidelines for Improved Binding Affinity

Histone deacetylases (HDAC) are being targeted for a number of diseases such as cancer, inflammatory disease, and neurological disorders. Within this family of 18 isozymes, HDAC4 is a prime target for glioma, one of the most aggressive brain tumors reported. Thus, the development of HDAC4 inhibitors could present a novel therapeutic route for glioma. In this work, molecular docking studies on cyclopropane hydroxamic acid derivatives identified five novel molecular interactions to the HDAC4 receptor that could be harnessed to enhance inhibitor binding. Thus, design guidelines for the optimization of potent HDAC4 inhibitors were developed which can be utilized to further the development of HDAC4 inhibitors. Using the developed guidelines, eleven novel cyclopropane hydroxamic acid derivatives were designed that outcompeted all original cyclopropane hydroxamic acids HDAC4 inhibitors studied in silico. The results of this work will be an asset to paving the way for further design and optimization of novel potent HDAC4 inhibitors for gliomas.

DDIT4 gene expression is switched on by a new HDAC4 function in ataxia telangiectasia

Ataxia telangiectasia (AT) is a rare, severe, and ineluctably progressive multisystemic neurodegenerative disease. Histone deacetylase 4 (HDAC4) nuclear accumulation has been related to neurodegeneration in AT. Since treatment with glucocorticoid analogues has been shown to improve the neurological symptoms that characterize this syndrome, the effects of dexamethasone on HDAC4 were investigated. In this paper, we describe a novel nonepigenetic function of HDAC4 induced by dexamethasone, through which it can directly modulate HIF-1a activity and promote the upregulation of the DDIT4 gene and protein expression. This new HDAC4 transcription regulation mechanism leads to a positive effect on autophagic flux, an AT-compromised biological pathway. This signaling was specifically induced by dexamethasone only in AT cell lines and can contribute in explaining the positive effects of dexamethasone observed in AT-treated patients.

Histone deacetylase 4 (HDAC4): a new player in anorexia nervosa?

Anorexia nervosa (AN) and other eating disorders continue to constitute significant challenges for individual and public health. AN is thought to develop as a result of complex interactions between environmental triggers, psychological risk factors, sociocultural influences, and genetic vulnerability. Recent research developments have highlighted a novel potentially relevant component in the AN etiology-activity of the histone deacetylase 4 (HDAC4) gene that has emerged in several recent studies related to AN. HDAC4 is a member of the ubiquitously important family of epigenetic modifier enzymes called histone deacetylases and has been implicated in processes related to the formation and function of the central nervous system (CNS), bone, muscle, and metabolism. In a family affected by eating disorders, a missense mutation in HDAC4 (A786T) was found to segregate with the illness. The relevance of this mutation in eating-related behaviors was further confirmed with mouse models. Despite  the fact that HDAC4 has not been identified as a significant signal in genome-wide association studies in AN, several studies have found significant or near-significant methylation differences in HDAC4 locus in peripheral tissues of actively ill AN patients in comparison with different control groups. Limitations of these studies include a lack of understanding of to what extent the changes in methylation are predictive of AN as such changes might also occur as a consequence of the disease. It remains to be determined how methylation in peripheral tissues correlates with that in the CNS and how different methylation patterns affect HDAC4 expression. The present review discusses the findings and potential roles of HDAC4 in AN. Its emerging roles in learning and neuroplasticity may be specific and relevant for the etiology of AN and potentially lead to novel therapeutic approaches.

Histone Deacetylase 4 Downregulation Elicits Post-Traumatic Psychiatric Disorders through Impairment of Neurogenesis

An enduring deficit in neurogenesis largely contributes to the development of severe post-traumatic psychiatric disorders such as anxiety, depression, and memory impairment following traumatic brain injury (TBI); however, the mechanism remains obscure. Here we have shown that an imbalance in the generation of γ-aminobutyric acid (GABA)ergic and glutamatergic neurons due to aberrant induction of vesicular glutamate transporter 1 (vGlut1)-positive glutamatergic cells is responsible for impaired neuronal differentiation in the hippocampus following TBI. To elucidate the molecular mechanism, we found that TBI activates a transcription factor, Pax3, by increasing its acetylation status, and subsequently induces Ngn2 transcription. This event, in turn, augments the vGlut1-expressing glutamatergic neurons and accumulation of excess glutamate in the hippocampus that can affect neuronal differentiation. In our study the acetylation of Pax3 was increased due to loss of its interaction with a deacetylase, histone deacetylase 4 (HDAC4), which was downregulated after TBI. TBI-induced activation of GSK3β was responsible for the degradation of HDAC4. We also showed that overexpression of HDAC4 before TBI reduces Pax3 acetylation by restoring an interaction between HDAC4 and Pax3 in the hippocampus. This event prevents the aberrant induction of vGlut1-positive glutamatergic neurons by decreasing the Ngn2 level and subsequently reinforces the balance between GABAergic and glutamatergic neurons following TBI. Further, we found that overexpression of HDAC4 in the hippocampus improves anxiety, depressive-like behavior, and memory functions following TBI.

Quality Control in Huntington's Disease: a Therapeutic Target

Huntington's disease (HD) is a fatal autosomal dominantly inherited brain disease caused by excessively expanded CAG repeats in gene which encodes huntingtin protein. These abnormally encoded huntingtin proteins and their truncated fragments result in disruption of cellular quality mechanism ultimately triggering neuronal death. Despite great efforts, a potential causative agent leading to genetic mutation in HTT, manifesting the neurons more prone to oxidative stress, cellular inflammation, energy depletion and apoptotic death, has not been established yet. Current scenario concentrates on symptomatic pathologies to improvise the disease progression and to better the survival. Most of the therapeutic developments have been converged to rescue the protein homeostasis. In HD, abnormal expansion of glutamine repeats in the protein huntingtin leads to toxic aggregation of huntingtin which in turn impairs the quality control mechanism of cells through damaging the machineries involved in removal of aggregated abnormal protein. Therapeutic approaches to improve the efficiency of aggregate clearance through quality control mechanisms involve protein folding machineries such as chaperones and protein degradation machineries such as proteasome and autophagy. Also, to reduce protein aggregation by enhancing proper folding, to degrade and eliminate the aggregates are suggested to negatively regulate the HD progression associated with the disruption of protein homeostasis. This review focuses on the collection of therapeutic strategies targeting enhancement of protein quality control activity to delay the HD pathogenesis.

Determination of the binding mechanism of histone deacetylase inhibitors

This article places its focus on methods and tools enabling the elucidation of the mechanism by which ligands, small-molecule inhibitors, or substrates interact with zinc-containing bacterial or human members of the histone deacetylase family (HDACs). These methods include biochemical and biophysical approaches and can be subdivided into equilibrium and kinetic methods. More information about the exact mode of action can be obtained by combining these methods with specific mutant variants of the enzymes and/or series of structural similar ligands. All available equilibrium and kinetic data including additional information from 3D structures of HDAC-ligand complexes can be beneficially combined in a data analysis procedure called Integrated Global-Fit analysis eventually providing the most likely binding mechanism.

Immunoepigenetics Combination Therapies: An Overview of the Role of HDACs in Cancer Immunotherapy

Long-standing efforts to identify the multifaceted roles of histone deacetylase inhibitors (HDACis) have positioned these agents as promising drug candidates in combatting cancer, autoimmune, neurodegenerative, and infectious diseases. The same has also encouraged the evaluation of multiple HDACi candidates in preclinical studies in cancer and other diseases as well as the FDA-approval towards clinical use for specific agents. In this review, we have discussed how the efficacy of immunotherapy can be leveraged by combining it with HDACis. We have also included a brief overview of the classification of HDACis as well as their various roles in physiological and pathophysiological scenarios to target key cellular processes promoting the initiation, establishment, and progression of cancer. Given the critical role of the tumor microenvironment (TME) towards the outcome of anticancer therapies, we have also discussed the effect of HDACis on different components of the TME. We then have gradually progressed into examples of specific pan-HDACis, class I HDACi, and selective HDACis that either have been incorporated into clinical trials or show promising preclinical effects for future consideration. Finally, we have included examples of ongoing trials for each of the above categories of HDACis as standalone agents or in combination with immunotherapeutic approaches.