Aberrant Expression of Histone Deacetylases 4 in Cognitive Disorders: Molecular Mechanisms and a Potential Target

Design and synthesis of peptides as stabilizers of histone deacetylase 4

Histone deacetylase 4 (HDAC4) contributes to gene repression by complex formation with HDAC3 and the corepressor silencing mediator for retinoid or thyroid hormone receptors (SMRT). We hypothesized that peptides derived from the class IIa specific binding site of SMRT would stabilize a specific conformation of its target protein and modulate its activity. Based on the SMRT-motif 1 (SM1) involved in the interaction of SMRT with HDAC4, we systematically developed cyclic peptides that exhibit Ki values that are 9 to 56 times lower than that of the linear SMRT peptide. The peptide macrocycles stabilize the wildtype of the catalytic domain of HDAC4 (cHDAC4) considerably better than its thermally more stable 'gain-of-function' (GOF) variant, cHDAC4-H976Y. Molecular docking and mutagenesis studies indicated that the cyclic peptides bind in a similar but not identical manner as the linear SMRT peptide to a discontinuous binding site. Ion mobility mass spectrometry showed no major changes in the protein fold upon peptide binding. Consistent with these results, preliminary hydrogen-deuterium exchange mass spectrometry measurements indicated only minor conformational changes. Taken together, the cyclic SMRT peptides most likely stabilize the apo form of cHDAC4.

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

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

Permissive epigenetic regulatory mechanisms at the histone level are enhanced in postmortem dorsolateral prefrontal cortex of individuals with schizophrenia

BACKGROUND

Susceptibility to schizophrenia is determined by interactions between genes and environment, possibly via epigenetic mechanisms. Schizophrenia has been associated with a restrictive epigenome, and histone deacetylase (HDAC) inhibitors have been postulated as coadjuvant agents to potentiate the efficacy of current antipsychotic drugs. We aimed to evaluate global histone posttranslational modifications (HPTMs) and HDAC expression and activity in the dorsolateral prefrontal cortex (DLPFC) of individuals with schizophrenia.

METHODS

We used postmortem DLPFC samples of individuals with schizophrenia and controls matched for sex, age, and postmortem interval. Schizophrenia samples were classified into antipsychotic-treated or antipsychotic-free subgroups according to blood toxicology. Expression of HPTMs and HDAC was quantified by Western blot. HDAC activity was measured with a fluorometric assay.

RESULTS

H3K9ac, H3K27ac, and H3K4me3 were globally enhanced in the DLPFC of individuals with schizophrenia (+24%-42%, p < 0.05). HDAC activity (-17%, p < 0.01) and HDAC4 protein expression (-20%, p < 0.05) were downregulated in individuals with schizophrenia. Analyses of antipsychotic-free and antipsychotic-treated subgroups revealed enhanced H3K4me3 and H3K27ac (+24%-49%, p < 0.05) and reduced HDAC activity in the antipsychotic-treated, but not in the antipsychotic-free subgroup.

LIMITATIONS

Special care was taken to control the effect of confounding factors: age, sex, postmortem interval, and storage time. However, replication studies in bigger cohorts might strengthen the association between permissive HPTMs and schizophrenia.

CONCLUSION

We found global HPTM alterations consistent with an aberrantly permissive epigenome in schizophrenia. Further studies to elucidate the significance of enhanced permissive HPTMs in schizophrenia and its association with the mechanism of action of antipsychotic drugs are encouraged.

Interleukin-17A stimulation induces alterations in Microglial microRNA expression profiles

BACKGROUND

Increased maternal interleukin (IL)-17A and activated microglia are pivotal factors contributing to the pathological phenotypes of maternal immune activation (MIA), developing neurodevelopmental disorders in offspring. This study aimed to determine whether IL-17A affects the microglial microRNA (miRNA) profiles.

METHODS

The miRNA expression profiles of primary cultured microglia stimulated with recombinant IL-17A were examined comprehensively using miRNA sequencing and validated through qRT-PCR. The expressions of miRNAs target genes identified using bioinformatics, were investigated in microglia transfected with mimic miRNA. The target gene's expression was also examined in the fetal brains of the MIA mouse model induced by maternal lipopolysaccharide (LPS) administration.

RESULTS

Primary cultured microglia expressed the IL-17A receptor and increased proinflammatory cytokines and nitric oxide synthase 2 upon treatment with IL-17A. Among the three miRNAs with |log2FC | >1, only mmu-miR-206-3p expression was significantly up-regulated by IL-17A. Transfection with the mmu-miR-206-3p mimic resulted in a significant decrease in the expression of Hdac4 and Igf1, target genes of mmu-miR-206-3p. Hdac4 expression also significantly decreased in the LPS-induced MIA model.

CONCLUSIONS

IL-17A affected microglial miRNA profiles with upregulated mmu-miR-206-3p. These findings suggest that targeting the IL-17A/mmu-miR-206-3p pathway may be a new strategy for predicting MIA-related neurodevelopmental deficits and providing preventive interventions.

IMPACT

Despite the growing evidence of interleukin (IL)-17A and microglia in the pathology of maternal immune activation (MIA), the downstream of IL-17A in microglia is not fully known. IL-17A altered microRNA profiles and upregulated the mmu-miR-206-3p expression in microglia. The mmu-miR-206-3p reduced autism spectrum disorder (ASD) related gene expressions, Hdac4 and Igf1. The Hdac4 expression was also reduced in the brain of MIA offspring. The hsa-miR-206 sequence is consistent with that of mmu-miR-206-3p. This study may provide clues to pathological mechanisms leading to predictions and interventions for ASD children born to mothers with IL-17A-related disorders.

Epigenetics of Alzheimer’s Disease: Past, Present and Future

Alzheimer’s disease (AD) exemplifies a looming epidemic lacking effective treatment and manifests with the accumulation of neurofibrillary tangles, amyloid-β plaques, neuroinflammation, behavioral changes, and acute cognitive impairments. It is a complex, multifactorial disorder that arises from the intricate interaction between environment and genetic factors, restrained via epigenetic machinery. Though the research progress has improved the understanding of clinical manifestations and disease advancement, the causal mechanism of detrimental consequences remains undefined. Despite the substantial improvement in recent diagnostic modalities, it is challenging to distinguish AD from other forms of dementia. Accurate diagnosis is a major glitch in AD as it banks on the symptoms and clinical criteria. Several studies are underway in exploring novel and reliable biomarkers for AD. In this direction, epigenetic alterations have transpired as key modulators in AD pathogenesis with the impeding inferences for the management of this neurological disorder. The present chapter aims to discuss the significance of epigenetic modifications reported in the pathophysiology of AD such as DNA methylation, hydroxy-methylation, methylation of mtDNA, histone modifications, and noncoding RNAs. Additionally, the chapter also describes the possible therapeutic avenues that target epigenetic modifications in AD.

Disruption of histone acetylation homeostasis triggers cognitive dysfunction in experimental diabetes

Epigenetic mechanisms related to diabetes-afflicted CNS complications are largely unknown. The present study investigated the role of histone acetylation mechanisms triggering cognitive dysfunction in the Type 1 and 2 diabetic mice model. Dynamic changes in diabetic parameters like fasting blood glucose levels, glucose tolerance test, and insulin levels were observed after the induction of diabetes. Cognitive performance was significantly diminished in T1D and T2D mice examined by the Morris water maze, novel object recognition test, and Y Maze as compared to controls. Histone profiling revealed a significant reduction in H3K9/14 and H4K12 acetylation in the cortex and hippocampus of T1D and T2D mice vs Controls. While histone deacetylase (HDAC) activity was significantly elevated in brain regions of T1D and T2D mice, the histone acetyltransferase (HAT) activity remain unchanged. Significantly increased HDAC 2, HDAC 3 protein and mRNA expression observed in T1D and T2D brain regions may corroborate for increased HDAC activity. No significant change was observed in protein and mRNA expression of HDAC 1, 5, 6, and 7 in diabetic brains. Reduced H3K9/14 and H4K12 acetylation paralleled transcriptional repression of memory-related markers BDNF, SYP, and PSD-95 in the cortex and hippocampus of T1D and T2D. Pharmacological inhibition of HDAC activity by Trichostatin A enhanced the cognitive changes observed in T1D and T2D by ameliorating BDNF, SYP, Psd-95. The present study provides a better insight into molecular mechanisms related to diabetes-dependent memory changes that can help to generate new advances for therapeutics to be developed in this area.

Targeting epigenetics: A novel promise for Alzheimer's disease treatment

So far, the search for a cure for Alzheimer Disease (AD) has been unsuccessful. The only approved drugs attenuate some symptoms, but do not halt the progress of this disease, which affects 50 million people worldwide and will increase its incidence in the coming decades. Such scenario demands new therapeutic approaches to fight against this devastating dementia. In recent years, multi-omics research and the analysis of differential epigenetic marks in AD subjects have contributed to our understanding of AD; however, the impact of epigenetic research is yet to be seen. This review integrates the most recent data on pathological processes and epigenetic changes relevant for aging and AD, as well as current therapies targeting epigenetic machinery in clinical trials. Evidence shows that epigenetic modifications play a key role in gene expression, which could provide multi-target preventative and therapeutic approaches in AD. Both novel and repurposed drugs are employed in AD clinical trials due to their epigenetic effects, as well as increasing number of natural compounds. Given the reversible nature of epigenetic modifications and the complexity of gene-environment interactions, the combination of epigenetic-based therapies with environmental strategies and drugs with multiple targets might be needed to properly help AD patients.

Impact of Environmental and Epigenetic Changes on Mesenchymal Stem Cells during Aging

Many crucial epigenetic changes occur during early skeletal development and throughout life due to aging, disease and are heavily influenced by an individual’s lifestyle. Epigenetics is the study of heritable changes in gene expression as the result of changes in the environment without any mutation in the underlying DNA sequence. The epigenetic profiles of cells are dynamic and mediated by different mechanisms, including histone modifications, non-coding RNA-associated gene silencing and DNA methylation. Given the underlining role of dysfunctional mesenchymal tissues in common age-related skeletal diseases such as osteoporosis and osteoarthritis, investigations into skeletal stem cells or mesenchymal stem cells (MSC) and their functional deregulation during aging has been of great interest and how this is mediated by an evolving epigenetic landscape. The present review describes the recent findings in epigenetic changes of MSCs that effect growth and cell fate determination in the context of aging, diet, exercise and bone-related diseases.

Cytoplasmic HDAC4 recovers synaptic function in the 3×Tg mouse model of Alzheimer's disease

AIMS

Early dysfunction in Alzheimer's disease (AD) is characterised by alterations of synapse structure and function leading to dysmorphic neurites, decreased spine density, impaired synaptic plasticity and cognitive deficits. The class II member HDAC4, which recently emerged as a crucial factor in shaping synaptic plasticity and memory, was found to be altered in AD. We investigated how the modulation of HDAC4 may contribute to counteracting AD pathogenesis.

METHODS

Using a cytoplasmic HDAC4 mutant (HDAC4^SD ), we studied the recovery of synaptic function in hippocampal tissue and primary neurons from the triple-transgenic mouse model of AD (3×Tg-AD).

RESULTS

Here, we report that in wild-type mice, HDAC4 is localised at synapses and interacts with postsynaptic proteins, whereas in the 3×Tg-AD, it undergoes nuclear import, reducing its interaction with synaptic proteins. Of note, HDAC4 delocalisation was induced by both amyloid-β and tau accumulation. Overexpression of the HDAC4^SD mutant in CA1 pyramidal neurons of organotypic hippocampal slices obtained from 3×Tg-AD mice increased dendritic length and promoted the enrichment of N-cadherin, GluA1, PSD95 and CaMKII proteins at the synaptic level compared with AD neurons transfected with the empty vector. Moreover, HDAC4 overexpression recovered the level of SUMO2/3ylation of PSD95 in AD hippocampal tissue, and in AD organotypic hippocampal slices, the HDAC4^SD rescued spine density and synaptic transmission.

CONCLUSIONS

These results highlight a new role of cytoplasmic HDAC4 in providing a structural and enzymatic regulation of postsynaptic proteins. Our findings suggest that controlling HDAC4 localisation may represent a promising strategy to rescue synaptic function in AD, potentially leading to memory improvement.

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.

Histone deacetylase 4 inhibition ameliorates the social deficits induced by Ephrin-B2 mutation

Deterioration of inhibitory synapse may be an essential neurological basis underlying abnormal social behaviours. Manipulations that regulate GABAergic transmission are associated with improved behavioural phenotypes in sociability. The synaptic protein, Ephrin-B2 (EB2), plays an important role in the maintenance and reconfiguration of inhibitory synapses in the medial prefrontal cortex (mPFC). However, the inhibitory cell-type specific role of EB2 in the pathophysiology and treatment of social deficits remains unknown. As expected, we revealed that tdTomato-expressing cells were only found in GABAergic neurons instead of excitatory neurons in transgenic EB2-vGATCre mice. This result indicated that depletion of EB2 would occur in those neurons, which further contribute to social deficits. In addition, specific over-expression of mPFC EB2 restored the defective social behaviour abnormalities. These results suggest that the effect of EB2 on social deficits is anatomically and cell-type specific. More importantly, the global upregulation of HDAC4 expression was found in EB2-vGATCre mice. Significant subcellular nuclear shuttling of HDAC4 in vGAT+ neurons was examined and quantified, suggesting a role of nuclear HDAC4 in mediating the mechanism underlying EB2 impairment in vGAT+ neurons. Treatment with LMK235 led to a remarkable rescue of social deficits, thus our data revealed a new domain for the potential utility of HDAC targeting agents to treat social deficits. In conclusion, these results not only revealed a novel molecular mechanism underlying the pathophysiology of social deficits, but also suggested a potential intervention avenue for the treatment of social deficits.

Exploration of Mutated Genes and Prediction of Potential Biomarkers for Childhood-Onset Schizophrenia Using an Integrated Bioinformatic Analysis

Childhood-onset schizophrenia (COS) is an unusual severe neurodevelopmental disorder of unknown etiology. In this study, we aimed to survey the missense variants in new cases of COS and also identify possible pathology biomarkers for COS. We found one list of mutated genes such as TTN, MUC12, and MUC2, which are the candidates to be involved in the etiology of COS. Next, we used WGSNA to predict COS disease-related genes and identified differential DNA methylation among COS disease groups, COS dangerous groups, and normal groups and found eight methylation sites that can be used as the diagnostic biomarkers. A total of six key genes are obtained through the intersection analysis between weighted correlation network analysis (WGCNA) mode, methylation-related genes, and differentially expressed genes (DGenes). These genes may play important roles in the progression of COS and serve as the potential biomarkers for future diagnosis. Our results might help to design the molecule or gene-targeted drugs for COS.

Alzheimer’s Disease-Related Genes Identified by Linking Spatial Patterns of Pathology and Gene Expression

Background

Alzheimer’s Disease (AD) is an age-related neurodegenerative disease with a poorly understood etiology, shown to be partly genetic. Glucose hypometabolism, extracellular Amyloid-beta (Aβ) deposition, and intracellular Tau deposition are cardinal features of AD and display characteristic spatial patterns in the brain. We hypothesize that regional differences in underlying gene expression confer either resistance or susceptibility to AD pathogenic processes and are associated with these spatial patterns. Data-driven methods for the identification of genes involved in AD pathogenesis complement hypothesis-driven approaches that reflect current theories about the disease. Here we present a data driven method for the identification of genes involved in AD pathogenesis based on comparing spatial patterns of normal gene expression to Positron Emission Tomography (PET) images of glucose hypometabolism, Aβ deposition, and Tau deposition.

Methods

We performed correlations between the cerebral cortex microarray samples from the six cognitively normal (CN) post-mortem Allen Human Brain Atlas (AHBA) specimens and PET FDG-18, AV-45, and AV-1451 tracer images from AD and CN participants in the Alzheimer’s Disease and Neuroimaging Initiative (ADNI) database. Correlation coefficients for each gene by each ADNI subject were then entered into a partial least squares discriminant analysis (PLS-DA) to determine sets that best classified the AD and CN groups. Pathway analysis via BioPlanet 2019 was then used to infer the function of implicated genes.

Results

We identified distinct sets of genes strongly associated with each PET modality. Pathway analyses implicated novel genes involved in mitochondrial function, and Notch signaling, as well as genes previously associated with AD.

Conclusion

Using an unbiased approach, we derived sets of genes with expression patterns spatially associated with FDG hypometabolism, Aβ deposition, and Tau deposition in AD. This methodology may complement population-based approaches for identifying the genetic underpinnings of AD.

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.

Antidepressant-like Effects of Combined Fluoxetine and Zinc Treatment in Mice Exposed to Chronic Restraint Stress Are Related to Modulation of Histone Deacetylase

Chronic stress is the key factor contributing to the development of depressive symptoms. Chronic restraint stress (CRS) is well validated and is one of the most commonly used models to induce depressive-like behavior in rodents. The present study aimed to evaluate whether fluoxetine (FLU 5 mg/kg) and zinc (Zn 10mg/kg) given simultaneously induce a more pronounced antidepressant-like effect in the CRS model than both those compounds given alone. Behavioral assessment was performed using the tail suspension and splash tests (TST and ST, respectively). Furthermore, the effects of CRS, FLU and Zn given alone and combined treatment with FLU + Zn on the expression of proteins involved in the apoptotic, inflammatory, and epigenetic processes were evaluated in selected brain structures (prefrontal cortex, PFC; and hippocampus, Hp) using Western blot analysis or enzyme-linked immunosorbent assays (ELISA). The results obtained indicated that three hours (per day) of immobilization for 4 weeks induced prominent depressive symptoms that manifested as increased immobility time in the TST, as well as decreased number and grooming time in the ST. Behavioral changes induced by CRS were reversed by both FLU (5 and 10 mg/kg) or Zn (10 mg/kg). Zinc supplementation (10 mg/kg) slightly increases the effectiveness of FLU (5 mg/kg) in the TST. However, it significantly increased the activity of FLU in the ST compared to the effect induced by FLU and Zn alone. Biochemical studies revealed that neither CRS nor FLU and Zn given alone or in combined treatment alter the expression of proteins involved in apoptotic or inflammatory processes. CRS induced major alterations in histone deacetylase (HDAC) levels by increasing the level of HADC1 and decreasing the level of HADC4 in the PFC and Hp, decreasing the level of HADC6 in the PFC but increasing it in Hp. Interestingly, FLU + Zn treatment reversed CRS-induced changes in HDAC levels in the Hp, indicating that HDAC modulation is linked to FLU + Zn treatment and this effect is structure-specific.

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.

Transcription factors in neurodevelopmental and associated psychiatric disorders: A potential convergence for genetic and environmental risk factors

Neurodevelopmental disorders (NDDs) are a heterogeneous and highly prevalent group of psychiatric conditions marked by impairments in the nervous system. Their onset occurs during gestation, and the alterations are observed throughout the postnatal life. Although many genetic and environmental risk factors have been described in this context, the interactions between them challenge the understanding of the pathways associated with NDDs. Transcription factors (TFs)-a group of over 1,600 proteins that can interact with DNA, regulating gene expression through modulation of RNA synthesis-represent a point of convergence for different risk factors. In addition, TFs organize critical processes like angiogenesis, blood-brain barrier formation, myelination, neuronal migration, immune activation, and many others in a time and location-dependent way. In this review, we summarize important TF alterations in NDD and associated disorders, along with specific impairments observed in animal models, and, finally, establish hypotheses to explain how these proteins may be critical mediators in the context of genome-environment interactions.

Class IIa HDAC Downregulation Contributes to Surgery-Induced Cognitive Impairment Through HMGB1-Mediated Inflammatory Response in the Hippocampi of Aged Mice

Objective

Perioperative neurocognitive disorders (PND) are a common complication in the elderly. Histone deacetylases (HDACs) are a class of enzymes that control the acetylation status of intracellular proteins. Thus, we explored whether HDACs trigger the release of high mobility group box 1 (HMGB1) through altering the acetylation status in the hippocampi of aged mice.

Materials and Methods

The effect of the Class IIa HDAC in PND was explored using an in vivo form of splenectomy. Sixteen-month-old healthy male C57BL/6J mice were randomly divided into five groups: control, anesthesia plus sham surgery, anesthesia plus splenectomy, LMK235 treatment, and PBS treatment. The hippocampi were harvested on either first, third, or seventh postoperative day. Cognitive function was assessed via a Morris water maze (MWM) test. Quantitative RT-PCR, Western blots and ELISAs were carried out to assess the targeted gene expression at transcriptional and translational levels.

Results

Splenectomy led to a significant deficiency in spatial memory acquisition, marked decreases in mRNA and protein levels of HDAC4 and HDAC5 in the hippocampus, and increases in the levels of total HMGB1 and acetylated HMGB1. In a similar fashion to splenectomy, treatment with the HDAC4/5 inhibitor LMK235 produced impaired spatial memory and an increase in the expression of HMGB1 and its acetylated counterpart in the hippocampus.

Conclusion

These results suggest that surgery leads to PND through class IIa HDAC downregulation-triggered HMGB1 release in hippocampus of aged mice. HDACs may be a potential therapeutic target for postoperative cognitive dysfunction.

Increased Histone Acetylation and Decreased Expression of Specific Histone Deacetylases in Ultraviolet-Irradiated and Intrinsically Aged Human Skin In Vivo

Histone deacetylases (HDACs) are conserved enzymes that remove acetyl groups from lysine side chains in histones and other proteins and play a crucial role in epigenetic regulation. Previously, we showed that histone acetylation is implicated in ultraviolet (UV)-induced inflammation and matrix impairment. To elucidate the histone acetylation status and specific HDACs involved in skin aging, we examined the changes in histone acetylation, global HDAC activity, and the expression of HDACs and sirtuins (SIRTs) in intrinsically aged and photoaged human skin as well as in UV-irradiated human skin in vivo. Following acute UV irradiation, the acetylated histone H3 (AcH3) level was increased, but HDAC activity and the expression levels of HDAC4, HDAC11, and SIRT4 were significantly decreased. In intrinsically aged skin, AcH3 levels were increased, but HDAC activity and the expression levels of HDAC4, HDAC5, HDAC10, HDAC11, SIRT6, and SIRT7 were significantly decreased. However, histone acetylation and HDAC expression in photoaged skin were not significantly different from those in intrinsically aged skin. Collectively, HDAC4 and HDAC11 were decreased in both UV-irradiated and intrinsically aged skin, suggesting that they may play a universal role in increased histone acetylation associated with skin aging.

Non-histone substrates of histone deacetylases as potential therapeutic targets in epilepsy

Introduction: Epilepsy is a network-level neurological disorder characterized by unprovoked recurrent seizures and associated comorbidities. Aberrant activity and localization of histone deacetylases (HDACs) have been reported in epilepsy and HDAC inhibitors (HDACi) have been used for therapeutic purposes. Several non-histone targets of HDACs have been recognized whose reversible acetylation can modulate protein functions and can contribute to disease pathology. Areas covered: This review provides an overview of HDACs in epilepsy and reflects its action on non-histone substrates involved in the pathogenesis of epilepsy and explores the effectiveness of HDACi as anti-epileptic drugs (AEDs). It also covers the efforts undertaken to target the interaction of HDACs with their substrates. We have further discussed non-deacetylase activity possessed by specific HDACs that might be essential in unraveling the molecular mechanism underlying the disease. For this purpose, relevant literature from 1996 to 2020 was derived from PubMed. Expert opinion: The interaction of HDACs and their non-histone substrates can serve as a promising therapeutic target for epilepsy. Pan-HDACi offers limited benefits to the epileptic patients. Thus, identification of novel targets of HDACs contributing to the disease and designing inhibitors targeting these complexes would be more effective and holds a greater potential as an anti-epileptogenic therapy.

Repeated stress exposure in mid-adolescence attenuates behavioral, noradrenergic, and epigenetic effects of trauma-like stress in early adult male rats

Stress in adolescence can regulate vulnerability to traumatic stress in adulthood through region-specific epigenetic activity and catecholamine levels. We hypothesized that stress in adolescence would increase adult trauma vulnerability by impairing extinction-retention, a deficit in PTSD, by (1) altering class IIa histone deacetylases (HDACs), which integrate effects of stress on gene expression, and (2) enhancing norepinephrine in brain regions regulating cognitive effects of trauma. We investigated the effects of adolescent-stress on adult vulnerability to severe stress using the single-prolonged stress (SPS) model in male rats. Rats were exposed to either (1) adolescent-stress (33-35 postnatal days) then SPS (58-60 postnatal days; n = 14), or (2) no adolescent-stress and SPS (58-60 postnatal days; n = 14), or (3) unstressed conditions (n = 8). We then measured extinction-retention, norepinephrine, HDAC4, and HDAC5. As expected, SPS exposure induced an extinction-retention deficit. Adolescent-stress prior to SPS eliminated this deficit, suggesting adolescent-stress conferred resiliency to adult severe stress. Adolescent-stress also conferred region-specific resilience to norepinephrine changes. HDAC4 and HDAC5 were down-regulated following SPS, and these changes were also modulated by adolescent-stress. Regulation of HDAC levels was consistent with the pattern of cognitive effects of SPS; only animals exposed to SPS without adolescent-stress exhibited reduced HDAC4 and HDAC5 in the prelimbic cortex, hippocampus, and striatum. Thus, HDAC regulation caused by severe stress in adulthood interacts with stress history such that seemingly conflicting reports describing effects of adolescent stress on adult PTSD vulnerability may stem in part from dynamic HDAC changes following trauma that are shaped by adolescent stress history.

Nuclear accumulation of histone deacetylase 4 (HDAC4) by PP1-mediated dephosphorylation exerts neurotoxicity in Pb-exposed neural cells

Lead (Pb) is an environmental contaminant that primarily affects the central nervous system, particularly the developing brain. Recently, increasing evidence indicates the important roles of histone deacetylases (HDACs) in Pb-induced neurotoxicity. However, the precise molecular mechanisms involving HDAC4 remains unknown. The purpose of this study was to investigate the role of HDAC4 in Pb-induced neurotoxicity both in vivo and in vitro. In vitro study, PC12 cells were exposed to Pb (10 μM) for 24 h, then the mRNA and protein levels of HDAC4 were analyzed. In vivo study, pregnant rats and their female offspring were treated with lead (50 ppm) until postnatal day 30. Then the pups were sacrificed and the mRNA and protein levels of HDAC4 in the hippocampus were analyzed. The results showed that HDAC4 was significantly increased in both PC12 cells and rat hippocampus upon Pb exposure. Blockade of HDAC4 with either LMK-235 (an inhibitor of HDAC4) or shHDAC4 (HDAC4-knocking down plasmid) ameliorated the Pb-induced neurite outgrowth deficits. Interestingly, HDAC4 was aberrantly accumulated in the nucleus upon Pb exposure. By contrast, blocking the HDAC4 shuffling from the cytosol to the nucleus with ΔNLS2-HDAC4 (the cytosol-localized HDAC4 mutant) was able to rescue the neuronal impairment. In addition, Pb increased PP1 (protein phosphatase 1) expression which in turn influenced the subcellular localization of HDAC4 by dephosphorylation of specific serine/threonine residues. What's more, blockade of PP1 with PP1-knocking down construct (shPP1) ameliorated Pb-induced neurite outgrowth deficits. Taken together, nuclear accumulation of HDAC4 by PP1-mediated dephosphorylation involved in Pb-induced neurotoxicity. This study might provide a promising molecular target for medical intervention with environmental cues.

An integrated multi-omics approach identifies epigenetic alterations associated with Alzheimer's disease

Protein aggregation is the hallmark of neurodegeneration but the molecular mechanisms underlying late-onset Alzheimer’s disease (AD) remain unclear. Here we integrated transcriptomic, proteomic and epigenomic analyses of post-mortem human brains to identify molecular pathways involved in AD. RNA-seq analysis revealed upregulation of transcription- and chromatin-related genes, including the histone acetyltransferases for H3K27ac and H3K9ac. An unbiased proteomic screening singled out H3K27ac and H3K9ac as main enrichments specific to AD. In turn, epigenomic profiling revealed gains of H3K27ac and H3K9ac linked to transcription, chromatin, and disease pathways in AD. Increasing genome-wide H3K27ac and H3K9ac in a fly model of AD exacerbated amyloid-β42-driven neurodegeneration. Together, these findings suggest that AD involves a reconfiguration of the epigenome, where H3K27ac and H3K9ac impact disease pathways by dysregulating transcription- and chromatin-gene feedback loops. The identification of this process highlights potential epigenetic strategies for early-stage disease treatment.

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.

STVNa Attenuates Isoproterenol-Induced Cardiac Hypertrophy Response through the HDAC4 and Prdx2/ROS/Trx1 Pathways

Recent data show that cardiac hypertrophy contributes substantially to the overall heart failure burden. Mitochondrial dysfunction is a common feature of cardiac hypertrophy. Recent studies have reported that isosteviol inhibits myocardial ischemia-reperfusion injury in guinea pigs and H9c2 cells. This work investigated the protective mechanisms of isosteviol sodium (STVNa) against isoproterenol (Iso)-induced cardiac hypertrophy. We found that STVNa significantly inhibited H9c2 cell and rat primary cardiomyocyte cell surface, restored mitochondrial membrane potential (MMP) and morphological integrity, and decreased the expression of mitochondrial function-related proteins Fis1 and Drp1. Furthermore, STVNa decreased reactive oxygen species (ROS) levels and upregulated the expression of antioxidant factors, Thioredoxin 1 (Trx1) and Peroxiredoxin 2 (Prdx2). Moreover, STVNa restored the activity of histone deacetylase 4 (HDAC4) in the nucleus. Together, our data show that STVNa confers protection against Iso-induced myocardial hypertrophy primarily through the Prdx2/ROS/Trx1 signaling pathway. Thus, STVNA is a potentially effective treatment for cardiac hypertrophy in humans.

Opioid and chemokine regulation of cortical synaptodendritic damage in HIV-associated neurocognitive disorders

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) persist despite effective antiretroviral therapies (ART). Evidence suggests that modern HAND is driven by subtle synaptodendritic damage in select brain regions, as ART-treated patients do not display overt neuronal death in postmortem brain studies. HAND symptoms are also aggravated by drug abuse, particularly with injection opioids. Opioid use produces region-specific synaptodendritic damage in similar brain regions, suggesting a convergent mechanism that may enhance HAND progression in opioid-using patients. Importantly, studies indicate that synaptodendritic damage and cognitive impairment in HAND may be reversible. Activation of the homeostatic chemokine receptor CXCR4 by its natural ligand CXCL12 positively regulates neuronal survival and dendritic spine density in cortical neurons, reducing functional deficits. However, the molecular mechanisms that underlie CXCR4, as well as opioid-mediated regulation of dendritic spines are not completely defined. Here, we will consolidate studies that describe the region-specific synaptodendritic damage in the cerebral cortex of patients and animal models of HAND, describe the pathways by which opioids may contribute to cortical synaptodendritic damage, and discuss the prospects of using the CXCR4 signaling pathway to identify new approaches to reverse dendritic spine deficits. Additionally, we will discuss novel research questions that have emerged from recent studies of CXCR4 and µ-opioid actions in the cortex. Understanding the pathways that underlie synaptodendritic damage and rescue are necessary for developing novel, effective therapeutics for this growing patient population.

The posttranslational modification of HDAC4 in cell biology: Mechanisms and potential targets

Histone deacetylase 4 (HDAC4) is a member of the HDACs family, its expression is closely related to the cell development. The cell is an independent living entity that undergoes proliferation, differentiation, senescence, apoptosis, and pathology, and each process has a strict and complex regulatory system. With deepening of its research, the expression of HDAC4 is critical in the life process. This review focuses on the posttranslational modification of HDAC4 in cell biology, providing an important target for future disease treatment.

Telomere Length: A Potential Biomarker for the Risk and Prognosis of Stroke

Stroke is one of the leading causes of death and disability worldwide. Age is associated with increased risk of stroke, while telomere length shortening plays a pivotal role in the process of aging. Moreover, telomere length shortening is associated with many risk factors of stroke in addition to age. Accumulated evidence shows that short leukocyte telomere length is not only associated with stroke occurrence but also associated with post-stroke recovery in the elderly population. In this review, we aimed to summarize the association between leukocyte telomere length and stroke, and discuss that telomere length might serve as a potential biomarker to predict the risk and prognosis of stroke.

Regulation of global gene expression in brain by TMP21

TMP21, a type I transmembrane protein of thep24 protein family, mediates protein trafficking and maturation. Dysregulation of TMP21 is implicated in the pathogenesis of Alzheimer’s disease (AD). However, underlying mechanisms remain elusive. To reveal the function of TMP21 in the brain and the pathogenic role of TMP21 in the brain of AD, the global gene expression was profiled in the brain of TMP21 knockdown mice. We found that 8196 and 8195 genes are significantly altered in the hippocampus and cortex, respectively. The genes are involved in a number of brain function-related pathways, including glutamatergic synapse pathway, serotonergic synapse pathway, synaptic vesicle pathway, and long-term depression pathway. Moreover, the network analysis suggests that the TMP21 may contribute to the pathogenesis of AD by regulatingPI3K/Akt/GSK3β signalling pathway. Our study provides an insight into the physiological function of TMP21 in the brain and pathological role of TMP21 in AD.

Unravelling the GSK3β-related genotypic interaction network influencing hippocampal volume in recurrent major depressive disorder

OBJECTIVE

Glycogen synthase kinase 3β (GSK3β) has been implicated in mood disorders. We previously reported associations between a GSK3β polymorphism and hippocampal volume in major depressive disorder (MDD). We then reported similar associations for a subset of GSK3β-regulated genes. We now investigate an algorithm-derived comprehensive list of genes encoding proteins that directly interact with GSK3β to identify a genotypic network influencing hippocampal volume in MDD.

PARTICIPANTS AND METHODS

We used discovery (N=141) and replication (N=77) recurrent MDD samples. Our gene list was generated from the NetworKIN database. Hippocampal measures were derived using an optimized Freesurfer protocol. We identified interacting single nucleotide polymorphisms using the machine learning algorithm Random Forest and verified interactions using likelihood ratio tests between nested linear regression models.

RESULTS

The discovery sample showed multiple two-single nucleotide polymorphism interactions with hippocampal volume. The replication sample showed a replicable interaction (likelihood ratio test: P=0.0088, replication sample; P=0.017, discovery sample; Stouffer's combined P=0.0007) between genes associated previously with endoplasmic reticulum stress, calcium regulation and histone modifications.

CONCLUSION

Our results provide genetic evidence supporting associations between hippocampal volume and MDD, which may reflect underlying cellular stress responses. Our study provides evidence of biological mechanisms that should be further explored in the search for disease-modifying therapeutic targets for depression.

HDAC4 in ischemic stroke: mechanisms and therapeutic potential

Stroke is one of the leading causes of death and disability worldwide, and the majority of the cases are ischemic stroke. However, it still lacks effective treatment except for thrombolytic therapy in an extremely narrow time window. Increased evidence suggests that histone deacetylase 4 (HDAC4) was dysregulated in ischemic stroke, which plays a key role in the pathogenesis of ischemic stroke and post-stroke recovery by affecting neuronal death, angiogenesis, and neurogenesis. Therefore, we aim to review the dysregulation of HDAC4 in ischemic stroke and the role of dysregulated HDAC4 in the pathogenesis of ischemic stroke. Furthermore, the therapeutic potential of modulating HDAC4 in ischemic stroke is discussed.

The mechanism and potential targets of class II HDACs in angiogenesis

Angiogenesis refers to the new blood vessels deriving from the existing blood vessels, and it is a complex regulatory process. Angiogenesis is associated with the normal development of the body and tumor growth and migration. The imbalance of histone deacetylase, as an epigenetic modification, could induce the production of diseases, such as cancer, metabolic diseases, etc., and it also plays an important role in angiogenesis. Many researches indicate that class II HDACs nuclear shuttle and its phosphorylation are necessary for the diseases and the protection of the collective itself. This paper will make a review for the relationship between II HDACs and angiogenesis under physiological and pathologic categories, looking forward to the disease treatment in the future.