Histone deacetylase in neuropathology

Exploring histone deacetylases in type 2 diabetes mellitus: pathophysiological insights and therapeutic avenues

Diabetes mellitus is a chronic disease that impairs metabolism, and its prevalence has reached an epidemic proportion globally. Most people affected are with type 2 diabetes mellitus (T2DM), which is caused by a decline in the numbers or functioning of pancreatic endocrine islet cells, specifically the β-cells that release insulin in sufficient quantity to overcome any insulin resistance of the metabolic tissues. Genetic and epigenetic factors have been implicated as the main contributors to the T2DM. Epigenetic modifiers, histone deacetylases (HDACs), are enzymes that remove acetyl groups from histones and play an important role in a variety of molecular processes, including pancreatic cell destiny, insulin release, insulin production, insulin signalling, and glucose metabolism. HDACs also govern other regulatory processes related to diabetes, such as oxidative stress, inflammation, apoptosis, and fibrosis, revealed by network and functional analysis. This review explains the current understanding of the function of HDACs in diabetic pathophysiology, the inhibitory role of various HDAC inhibitors (HDACi), and their functional importance as biomarkers and possible therapeutic targets for T2DM. While their role in T2DM is still emerging, a better understanding of the role of HDACi may be relevant in improving insulin sensitivity, protecting β-cells and reducing T2DM-associated complications, among others.

Acetylation of p53 in the Cerebral Cortex after Photothrombotic Stroke

p53 expression and acetylation are crucial for the survival and death of neurons in penumbra. At the same time, the outcome of ischemia for penumbra cells depends largely on the histone acetylation status, but the effect of histone acetyltransferases and deacetylases on non-histone proteins like p53 is largely understudied. With combined in silico and in vitro approach, we have identified enzymes capable of acetylation/deacetylation, distribution, stability, and pro-apoptotic activity of p53 in ischemic penumbra in the course of post-stroke recovery, and also detected involved loci of acetylation in p53. The dynamic regulation of the acetylation of p53 at lysine 320 is controlled by acetyltransferase PCAF and histone deacetylases HDAC1 and HDAC6. The in silico simulation have made it possible to suggest the acetylation of p53 at lysine 320 acetylation may facilitate the shuttling of p53 between the nucleus and cytoplasm in penumbra neurons. Acetylation of p53 at lysine 320 is more preferable than acetylation at lysine 373 and probably promotes survival and repair of penumbra neurons after stroke. Strategies to increase p53 acetylation at lysine 320 via increasing PCAF activity, inhibiting HDAC1 or HDAC6, inhibiting p53, or a combination of these interventions may have therapeutic benefits for stroke recovery and would be promising for neuroprotective therapy of stroke.

N-Acetylaspartate Drives Oligodendroglial Differentiation via Histone Deacetylase Activation

An unmet clinical goal in demyelinating pathologies is to restore the myelin sheath prior to neural degeneration. N-acetylaspartate (NAA) is an acetylated derivative form of aspartate, abundant in the healthy brain but severely reduced during traumatic brain injury and in patients with neurodegenerative pathologies. How extracellular NAA variations impact the remyelination process and, thereby, the ability of oligodendrocytes to remyelinate axons remains unexplored. Here, we evaluated the remyelination properties of the oligodendroglial (OL) mouse cell line Oli-neuM under different concentrations of NAA using a combination of biochemical, qPCR, immunofluorescence assays, and in vitro engagement tests, at NAA doses compatible with those observed in healthy brains and during brain injury. We observed that oligodendroglia cells respond to decreasing levels of NAA by stimulating differentiation and promoting gene expression of myelin proteins in a temporally regulated manner. Low doses of NAA potently stimulate Oli-neuM to engage with synthetic axons. Furthermore, we show a concentration-dependent expression of specific histone deacetylases essential for MBP gene expression under NAA or Clobetasol treatment. These data are consistent with the idea that oligodendrocytes respond to lowering the NAA concentration by activating the remyelination process via deacetylase activation.

Aging-related histone modification changes in brain function

Aging can be defined as a decline of physiological function that is more difficult to reverse, characterized by the loss of the physiological integrity of tissues, organs, and cells of an organism over time. Normal aging is associated with structural and functional changes in the brain, involving neuronal apoptosis, synaptic structure, neurotransmission, and metabolism alterations, leading to impairment in sleep, cognitive functions, memory, learning, and motor and sensory systems. Histone modification is a significant aging-related epigenetic change that influences synaptic and mitochondrial function and immune and stress responses in the brain. This review discusses the changes in histone modifications that occur during brain aging, specifically methylation and acetylation, and the associated changes in gene transcription and protein expression. We observed that genes related to synaptic and mitochondrial function are downregulated in the aging brain, while genes related to immune response and inflammatory functions are upregulated.

Blockade of L-Type Ca2+ Channel Activity Alleviates Oligodendrocyte Pathology following Brain Injury in Male Rats

A growing body of studies suggests that Ca²⁺ signaling controls a variety of biological processes in brain elements. Activation of L-type voltage-operated Ca²⁺ channels (VOCCs) plays a role in the development of oligodendrocyte (OL) lineage loss, and indicates that the blocking of these channels may be an effective way to inhibit OL lineage cell loss. For this study, 10.5-day-old male Sprague-Dawley rats were used to generate cerebellar tissue slices. The slice tissues were cultured and randomly allocated to one of four groups (six each) and treated as follows: Group I, (sham control); Group II, 0.1% dimethyl sulfoxide (DMSO) only (vehicle control); Group III, injury (INJ); Group IV, (INJ and treatment with NIF). The injury was simulated by exposing the slice tissues to 20 min of oxygen-glucose deprivation (OGD). At 3 days post-treatment, the survival, apoptosis, and proliferation of the OL lineages were measured and compared. Results: In the INJ group, there was a decrease in mature myelin basic protein+ OLs (MBP+ OLs) and their precursors, NG2⁺ OPCs (Nerve-glia antigen 2+ oligodendrocyte precursor cell), compared with controls. A significant elevation was observed in the NG2⁺ OPCs and apoptotic MBP⁺ OLs as confirmed by a TUNEL assay. However, the cell proliferation rate was decreased in NG2⁺ OPCs. NIF increased OL survival as measured by apoptosis rate in both OL lineages and preserved the rate of proliferation in the NG2⁺ OPCs. Conclusions: Activation of L-type VOCCs may contribute to OL pathology in association with reduced mitosis of OPCs following brain injury as a strategy to treat demyelinating diseases.

Epigenetic Mechanisms Involved in the Effects of Maternal Hyperhomocysteinemia on the Functional State of Placenta and Nervous System Plasticity in the Offspring

According to modern view, susceptibility to diseases, specifically to cognitive and neuropsychiatric disorders, can form during embryonic development. Adverse factors affecting mother during the pregnancy increase the risk of developing pathologies. Despite the association between elevated maternal blood homocysteine (Hcy) and fetal brain impairments, as well as cognitive deficits in the offspring, the role of brain plasticity in the development of these pathologies remains poorly studied. Here, we review the data on the negative impact of hyperhomocysteinemia (HHcy) on the neural plasticity, in particular, its possible influence on the offspring brain plasticity through epigenetic mechanisms, such as changes in intracellular methylation potential, activity of DNA methyltransferases, DNA methylation, histone modifications, and microRNA expression in brain cells. Since placenta plays a key role in the transport of nutrients and transmission of signals from mother to fetus, its dysfunction due to aberrant epigenetic regulation can affect the development of fetal CNS. The review also presents the data on the impact of maternal HHcy on the epigenetic regulation in the placenta. The data presented in the review are not only interesting from purely scientific point of view, but can help in understanding the role of HHcy and epigenetic mechanisms in the pathogenesis of diseases, such as pregnancy pathologies resulting in the delayed development of fetal brain, cognitive impairments in the offspring during childhood, and neuropsychiatric and neurodegenerative disorders later in life, as well as in the search for approaches for their prevention using neuroprotectors.

Selective Targeting of Class I HDAC Reduces Microglial Inflammation in the Entorhinal Cortex of Young APP/PS1 Mice

BG45 is a class Ⅰ histone deacetylase inhibitor (HDACI) with selectivity for HDAC3. Our previous study demonstrated that BG45 can upregulate the expression of synaptic proteins and reduce the loss of neurons in the hippocampus of APPswe/PS1dE9 (APP/PS1) transgenic mice (Tg). The entorhinal cortex is a pivotal region that, along with the hippocampus, plays a critical role in memory in the Alzheimer's disease (AD) pathology process. In this study, we focused on the inflammatory changes in the entorhinal cortex of APP/PS1 mice and further explored the therapeutic effects of BG45 on the pathologies. The APP/PS1 mice were randomly divided into the transgenic group without BG45 (Tg group) and the BG45-treated groups. The BG45-treated groups were treated with BG45 at 2 months (2 m group), at 6 months (6 m group), or twice at 2 and 6 months (2 and 6 m group). The wild-type mice group (Wt group) served as the control. All mice were killed within 24 h after the last injection at 6 months. The results showed that amyloid-β (Aβ) deposition and IBA1-positive microglia and GFAP-positive astrocytes in the entorhinal cortex of the APP/PS1 mice progressively increased over time from 3 to 8 months of age. When the APP/PS1 mice were treated with BG45, the level of H3K9K14/H3 acetylation was improved and the expression of histonedeacetylase1, histonedeacetylase2, and histonedeacetylase3 was inhibited, especially in the 2 and 6 m group. BG45 alleviated Aβ deposition and reduced the phosphorylation level of tau protein. The number of IBA1-positive microglia and GFAP-positive astrocytes decreased with BG45 treatment, and the effect was more significant in the 2 and 6 m group. Meanwhile, the expression of synaptic proteins synaptophysin, postsynaptic density protein 95, and spinophilin was upregulated and the degeneration of neurons was alleviated. Moreover, BG45 reduced the gene expression of inflammatory cytokines interleukin-1β and tumor necrosis factor-α. Closely related to the CREB/BDNF/NF-kB pathway, the expression of p-CREB/CREB, BDNF, and TrkB was increased in all BG45 administered groups compared with the Tg group. However, the levels of p-NF-kB/NF-kB in the BG45 treatment groups were reduced. Therefore, we deduced that BG45 is a potential drug for AD by alleviating inflammation and regulating the CREB/BDNF/NF-kB pathway, and the early, repeated administration of BG45 can play a more effective role.

Evaluation of advanced, pathophysiologic new targets for imaging of CNS

The inadequate information about the in vivo pathological, physiological, and neurological impairments, as well as the absence of in vivo tools for assessing brain penetrance and the efficiency of newly designed drugs, has hampered the development of new techniques for the treatment for variety of new central nervous system (CNS) diseases. The searching sites such as Science Direct and PubMed were used to find out the numerous distinct tracers across 16 CNS targets including tau, synaptic vesicle glycoprotein, the adenosine 2A receptor, the phosphodiesterase enzyme PDE10A, and the purinoceptor, among others. Among the most encouraging are [¹⁸ F]FIMX for mGluR imaging, [¹¹ C]Martinostat for Histone deacetylase, [¹⁸ F]MNI-444 for adenosine 2A imaging, [¹¹ C]ER176 for translocator protein, and [¹⁸ F]MK-6240 for tau imaging. We also reviewed the findings for each tracer's features and potential for application in CNS pathophysiology and therapeutic evaluation investigations, including target specificity, binding efficacy, and pharmacokinetic factors. This review aims to present a current evaluation of modern positron emission tomography tracers for CNS targets, with a focus on recent advances for targets that have newly emerged for imaging in humans.

Isozyme-specific histone deacetylase 1/2 inhibitor K560 attenuates oxidative stress-induced retinal cell death

Oxidative stress-induced damage is an underlying mechanism in the pathogenesis of age-related retinal diseases. Here, we examined the effects of K560, a potential candidate drug for the treatment of these diseases, on oxidative stress-induced retinal cell death. K560 is a novel isozyme-specific inhibitor of histone deacetylase 1 and 2 (HDAC1/2). Histone acetylation in retinal lysates and dissociated retinal cells was detected with a western blot analysis and cell-based enzyme-linked immunosorbent assay (ELISA), respectively. The viability of mouse retinal cells was measured with an alamarBlue assay. We used immunohistochemistry for RNA binding protein with multiple splicing (RBPMS) to visualize the retinal ganglion cells (RGCs) of mice. An ELISA analysis indicated that histone acetylation was enhanced in dissociated mouse retinal cells treated with K560. The cell viability assay indicated that K560 attenuated both exogenous hydrogen peroxide-induced and endogenous oxidative stress-induced cell death in dissociated retinal cells. Western blot analysis indicated that intravitreal K560 administration enhanced the acetylation of histones H3 and H4 in mouse retinal lysates. To examine the effect of K560 on oxidative stress-induced RGC death, we performed whole-mount immunohistochemistry for RBPMS on retinas dissected from eyes treated with K560 or vehicle on day one, and K560 or vehicle and NMDA on day two. Quantification of RBPMS-immunopositive cells indicated that K560 attenuated NMDA-induced RGC death. Taken together, our findings suggest that administration of a HDAC1/2-specific inhibitor K560 may be effective in the treatment of oxidative stress-mediated retinal degeneration and have less cytotoxicity than other known HDAC inhibitors, which are known to target a wide range of HDAC family members.

Epigenetic histone acetylation modulating prenatal Poly I:C induced neuroinflammation in the prefrontal cortex of rats: a study in a maternal immune activation model

Introduction: Neuroinflammation in the central nervous system, particularly the prefrontal cortex (PFC), plays a role in the pathogenesis of schizophrenia, which has been found to be associated with maternal immune activation (MIA). Recent evidence suggests that epigenetic regulation involves in the MIA-induced neurodevelopmental disturbance. However, it is not well-understood how epigenetic modulation is involved in the neuroinflammation and pathogenesis of schizophrenia.

Methods: This study explored the modulation of histone acetylation in both neuroinflammation and neurotransmission using an MIA rat model induced by prenatal polyriboinosinic-polyribocytidylic acid (Poly I:C) exposure, specifically examining those genes that were previously observed to be impacted by the exposure, including a subunit of nuclear factor kappa-B (Rela), Nod-Like-Receptor family Pyrin domain containing 3 (Nlrp3), NMDA receptor subunit 2A (Grin2a), 5-HT2A (Htr2a), and GABAA subunit β3 (Gabrb3).

Results: Our results revealed global changes of histone acetylation on H3 (H3ace) and H4 (H4ace) in the PFC of offspring rats with prenatal Poly I:C exposure. In addition, it revealed enhancement of both H3ace and H4ace binding on the promoter region of Rela, as well as positive correlations between Rela and genes encoding histone acetyltransferases (HATs) including CREB-binding protein (CBP) and E1A-associated protein p300 (EP300). Although there was no change in H3ace or H4ace enrichment on the promoter region of Nlrp3, a significant enhancement of histone deacetylase 6 (HDAC6) binding on the promoter region of Nlrp3 and a positive correlation between Nlrp3 and Hdac6 were also observed. However, prenatal Poly I:C treatment did not lead to any specific changes of H3ace and H4ace on the promoter region of the target genes encoding neurotransmitter receptors in this study.

Discussion: These findings demonstrated that epigenetic modulation contributes to NF-κB/NLRP3 mediated neuroinflammation induced by prenatal Poly I:C exposure via enhancement of histone acetylation of H3ace and H4ace on Rela and HDAC6-mediated NLRP3 transcriptional activation. This may further lead to deficits in neurotransmissions and schizophrenia-like behaviors observed in offspring.

Tanshinone IIA Microemulsion Protects against Cerebral Ischemia Reperfusion Injury via Regulating H3K18ac and H4K8ac In Vivo and In Vitro

Tanshinone IIA (TanIIA) has neuroprotective effects against cerebral ischemia reperfusion injury (CIRI), but its clinical application is limited due to poor water solubility and robust first pass elimination property. In this study, we developed microemulsion loaded with TanIIA (TanIIA ME) to break through these limitations, and explored the neuroprotective effect of TanIIA ME against CIRI and the epigenetic regulation mechanism of this neuroprotection. In vivo, middle cerebral artery occlusion (MCAO) models were treated with TanIIA ME and TanIIA solution or sodium valproate as a control. The effect of TanIIA ME on HDAC activity was determined by ELISA assay. In addition, we used primary hippocampal neurons to establish oxygen-glucose deprivation and reoxygenation (OGD/R) models. Lactate dehydrogenase (LDH) assay and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay were performed to investigate the neuroprotective efficacy of TanIIA ME. Subsequently, the expression of H3K18ac, H4K8ac, NMDAR1, caspase-3, and MAP-2 were investigated in MCAO or OGD/R models treated with TanIIA ME, TanIIA solution or sodium valproate. In vivo experimental results indicated that TanIIA ME significantly reduced neurological scores, infarction volume, and HDAC activity compared with TanIIA solution and MCAO group, accompanied by upregulation of H3K18ac, H4K8ac, and MAP-2 expression and downregulation of NMDAR1 and caspase-3 expression. Additionally, in OGD/R models, the results demonstrated that TanIIA ME treatment had a better neuroprotective effect along with increased H3K18ac, H4K8ac, and MAP-2 expression and decreased NMDAR1 and caspase-3 expression, compared with the other treatments except sodium valproate. Overall, TanIIA ME treatment exhibited superior efficacy in protecting against CIRI through mechanisms that might involve the inhibition of NMDAR1 and caspase-3 expression and the enhancement of MAP-2 expression by regulating histone H3K18 and H4K8 acetylation. Thus, TanIIA ME could be potentially used to develop a promising drug for the treatment of ischemic stroke.