Histone deacetylases in memory and cognition

A Triple combination formulation of an HDAC inhibitor treats chronic pain in rodent spared nerve injury model

Histone deacetylase inhibitors (HDACi) that modulate epigenetic regulation and are approved for treating rare cancers have, in disease models, also been shown to mitigate neurological conditions, including chronic pain. They are of interest as non-opioid treatments, but achieving long-term efficacy with limited dosing has remained elusive. Here we employ a triple combination formulation (TCF) that includes the pan-HDAC vorinostat (Vo) administered at its FDA-approved daily dosage of 50 mg/Kg, along with the caging agent 2-hydroxypropyl-β-cyclodextrin (HPBCD) and polyethylene glycol (PEG). This formulation enhances plasma and brain exposure of Vo in mice and rat models and shows specific activity in the spared nerve injury (SNI) model of chronic neuropathic pain. TCF (but not HPBCD and PEG) decreased mechanical allodynia for 4 weeks without antagonizing weight, anxiety, or mobility. This was achieved at less than 1% of the total dose of Vo approved for 4 weeks of tumor treatment, decreased RNA levels of two major inflammatory markers (CD11b and GFAP), and reduced proliferation of microglia in the ipsilateral (but not contralateral) spinal cord. A single TCF injection was sufficient for 3-4 weeks of efficacy. Pharmacodynamics suggested pain relief was sustained for weeks after Vo elimination. Doubling Vo in a single TCF injection tripled the response amplitude and remained effective for > 2 months in male rats. Together, these data suggest that the TCF enables single-dose effectiveness with extended action, reduces long-term HDACi dosage, and presents excellent potential to develop as a non-opioid treatment option for chronic pain. PERSPECTIVE: An epigenetic drug formulation (TCF) tested in rat and mouse chronic neuropathic pain models shows adequate and persistent pain relief, engaging spinal cord inflammatory mechanisms.

Cholinesterase-based inhibitors as multitarget small molecules for the therapy of Alzheimer's disease

Herein, we have summarized the most significant results that we have communicated from our laboratories in the last thirty years, highlighting the most potent and attractive ChEIs based hit(lead)-Multitarget Small Molecules, such as (S)-p-methoxytacripyrine (1), ASS234 (2), Contilisant (3), and Contilistat (4), that we have identified in the search for new chemical entities for the therapy of Alzheimer's disease.

Down-regulating HDAC2-LTA4H pathway ameliorates renal ischemia-reperfusion injury

BACKGROUND

The activation of histone deacetylase 2 (HDAC2) is the main pathogenesis of acute kidney injury (AKI), one of the leading causes of end-stage kidney disease. However, the regulatory role of HDAC2 upregulation on inflammation in AKI is still unclear.

RESULTS

In this study, we found that treatment with HDAC2 inhibitor BRD6688 could mitigate the degree of mesangial sclerosis, interstitial infiltration and tubular atrophy, reduce the concentration of blood urea nitrogen (BUN) and serum creatinine (Scr), improve the proliferation, anti-apoptotic, anti-oxidative stress and angiogenesis effects of renal cells. Our results mainly indicated that renal HDAC2 activity was increased by casein kinase 2 (CK2) in renal ischemia reperfusion (I/R) models, and HDAC2 genetic ablation in HREpiC cells suppressed the leukotriene B4 (LTB4) production. Renal leukotriene A4 hydrolase (LTA4H) activity was increased in AKI mice in a HDAC2-dependent manner. LTB4 could induce monocytes to differentiate into M1 macrophages, while BRD6688 could suppress this effect and force the M1 macrophages polarize to M2 macrophages.

CONCLUSION

Inhibition of HDAC2 activities by BRD6688 could suppress the progression of renal I/R injury through the regulation of LTA4H and macrophage polarization.

Upregulation of HDAC3 mediates behavioral impairment in the bile duct ligation model of hepatic encephalopathy

Hepatic encephalopathy (HE), an outcome of chronic liver disease is characterized by behavioral impairments. The present study investigated the role of HDAC-mediated transcriptional regulation causing behavioral impairments in the bile duct ligation (BDL) model of HE. Post-BDL surgery in rats, dynamic alterations in liver function tests, liver morphology were observed. In BDL rats, histological staining in brain demonstrated reduced neuronal viability and warped neuronal architecture. Additionally, BDL animals showed impaired spatial learning, memory, and increased anxiety in the open field, Barnes maze, and Y maze tests. Further, the Golgi cox staining revealed a significantly altered spine density and spine clustering patterns of granular neuron in dentate gyrus of BDL rats. Concordantly, a significant downregulation of memory encoding genes was also observed in BDL rats that may account for aberrant behavior. Molecular analysis of modifiers, such as HDAC, showed significant changes in the expression of HDAC3 and HDAC6 in both the cortex and hippocampus of BDL rats. Upregulation of HDAC3 promoted its localization on the promoter of genes like c-Fos, NPAS4, Arc, and others, likely causing their decreased expression. Our findings suggest that increased HDAC3 activity downregulates key synaptic plasticity and memory-related genes, potentially driving neurobehavioral changes in BDL rats.

The Mechanism of HDAC2 Inhibitors on Chronic Pancreatitis Pain

Background

Chronic pancreatitis (CP) is marked by persistent inflammation and fibrosis of the pancreas, often causing severe abdominal pain. The pain mechanism involves complex interactions between pancreatic inflammation and spinal nerve activity. Histone deacetylase 2 (HDAC2) is implicated in neural processes and pain modulation, making it a potential target for CP pain management.

Aim

This study investigates HDAC2's role in CP pain and evaluates the effects of its inhibition in a CP rat model.

Methods

CP was induced in male Sprague-Dawley rats using dibutyltin dichloride (DBTC). HDAC2 expression in spinal and pancreatic tissues was assessed through western blotting, quantitative Real-Time PCR, and enzyme-linked immunosorbent assay (ELISA). Pain sensitivity was evaluated using paw withdrawal tests. Co-cultures of AR42J pancreatic acinar cells and F11 spinal neurons were used to explore pancreatic-neural interactions. Chromatin immunoprecipitation (ChIP) and promoter assays examined HDAC2 transcriptional regulation.

Results

HDAC2 expression was significantly elevated in CP rats, which also displayed increased pain sensitivity and higher inflammatory markers (interleukin [IL]-1β [IL-1β], tumor necrosis factor-α [TNF-α], IL-6, and chemokine ligand 2 [CCL-2]). HDAC2 inhibition reduced pain sensitivity and pancreatitis. Co-culture experiments revealed that pancreatic inflammatory mediators upregulate HDAC2 in neurons. ChIP identified Sp1 as a regulatory factor for HDAC2, with the extracellular signal-regulated kinase-Specific protein 1 (ERK-Sp1) pathway critical for its expression.

Conclusion

HDAC2 is crucial in CP pain sensitization and inflammation. Its inhibition reduces pain and inflammation, offering potential for targeted pain management in CP.

DNA Methylation and Histone Acetylation Contribute to the Maintenance of LTP in the Withdrawal Behavior Interneurons in Terrestrial Snails

Accumulated data indicate that epigenetic regulations, including histone modifications and DNA methylation, are important means for adjusting the expression of genes in response to various stimuli. In contrast to the success in studying the role of DNA methylation in laboratory rodents, the role of DNA methylation in the terrestrial snail Helix lucorum has been studied only in behavioral experiments. This prompted us to further investigate the role of DNA methylation and the interaction between DNA methylation and histone acetylation in the mechanisms of neuroplasticity in terrestrial snails using in vitro experiments. Dysregulation of DNA methylation by the DNMT inhibitor RG108 significantly suppressed the long-term potentiation (LTP) of synaptic inputs in identified neurons. We then tested whether the RG108-induced weakening of potentiation can be reversed under co-application of histone deacetylase inhibitors sodium butyrate or trichostatin A. It was found that increased histone acetylation significantly compensated for RG108-induced LTP deficiency. These data bring important insights into the functional role of DNA methylation as an important regulatory mechanism and a necessary condition for the development and maintenance of long-term synaptic changes in withdrawal interneurons of terrestrial snails. Moreover, these results support the idea of the interaction of DNA methylation and histone acetylation in the epigenetic regulation of synaptic plasticity.

Structural and transcriptional signatures of arithmetic abilities in children

Arithmetic ability is critical for daily life, academic achievement, career development, and future economic success. Individual differences in arithmetic skills among children and adolescents are related to variations in brain structures. Most existing studies have used hypothesis-driven region of interest analysis. To identify distributed brain regions related to arithmetic ability, we used data-driven cross-validated predictive models to analyze cross-sectional behavioral and structural MRI data in children and adolescents. The gray matter volume (GMV) of widespread brain regions reliably predicted arithmetic abilities measured by the Comprehensive Mathematical Abilities Test. Furthermore, we applied neuroimaging-transcriptome association analysis to explore transcriptional signatures associated with structural patterns of arithmetic ability. Structural patterns of arithmetic ability primarily correlated with transcriptional profiles enriched for genes involved in transmembrane transport and synaptic signaling. Our findings enhance our understanding of the neural and genetic mechanisms underlying children's arithmetic ability and offer a practical predictor for arithmetic skills during development.

Contilisant+Tubastatin A Hybrids: Polyfunctionalized Indole Derivatives as New HDAC Inhibitor-Based Multitarget Small Molecules with In Vitro and In Vivo Activity in Neurodegenerative Diseases

Herein, we describe the design, synthesis, and biological evaluation of 15 Contilisant+Tubastatin A hybrids. These ligands are polyfunctionalized indole derivatives developed by juxtaposing selected pharmacophoric moieties of Contilisant and Tubastatin A to act as multifunctional ligands. Compounds 3 and 4 were identified as potent HDAC6 inhibitors (IC50 = 0.012 μM and 0.035 μM, respectively), so they were further evaluated in Drosophila and human cell models of Parkinson's disease (PD). Both compounds attenuated PD-like phenotypes, such as motor defects, oxidative stress, and mitochondrial dysfunction in PD model flies. Ligands 3 and 4 were also studied in the transgenic Caenorhabditis elegans CL2006 model of Alzheimer's disease (AD). Both compounds were nontoxic, did not induce undesirable animal functional changes, inhibited age-related paralysis, and improved cognition in the thrashing assay. These results highlight 3 and 4 as novel multifunctional ligands that improve the features of PD and AD hallmarks in the respective animal models.

Dysregulation of lysine acetylation in the pathogenesis of digestive tract cancers and its clinical applications

Recent advances in high-resolution mass spectrometry-based proteomics have improved our understanding of lysine acetylation in proteins, including histones and non-histone proteins. Lysine acetylation, a reversible post-translational modification, is catalyzed by lysine acetyltransferases (KATs) and lysine deacetylases (KDACs). Proteins comprising evolutionarily conserved bromodomains (BRDs) recognize these acetylated lysine residues and consequently activate transcription. Lysine acetylation regulates almost all cellular processes, including transcription, cell cycle progression, and metabolic functions. Studies have reported the aberrant expression, translocation, and mutation of genes encoding lysine acetylation regulators in various cancers, including digestive tract cancers. These dysregulated lysine acetylation regulators contribute to the pathogenesis of digestive system cancers by modulating the expression and activity of cancer-related genes or pathways. Several inhibitors targeting KATs, KDACs, and BRDs are currently in preclinical trials and have demonstrated anti-cancer effects. Digestive tract cancers, including encompass esophageal, gastric, colorectal, liver, and pancreatic cancers, represent a group of heterogeneous malignancies. However, these cancers are typically diagnosed at an advanced stage owing to the lack of early symptoms and are consequently associated with poor 5-year survival rates. Thus, there is an urgent need to identify novel biomarkers for early detection, as well as to accurately predict the clinical outcomes and identify effective therapeutic targets for these malignancies. Although the role of lysine acetylation in digestive tract cancers remains unclear, further analysis could improve our understanding of its role in the pathogenesis of digestive tract cancers. This review aims to summarize the implications and pathogenic mechanisms of lysine acetylation dysregulation in digestive tract cancers, as well as its potential clinical applications.

HDAC1/2/3-mediated downregulation of neurogranin is involved in cognitive impairment in offspring exposed to maternal subclinical hypothyroidism

Subclinical hypothyroidism (SCH) in pregnancy is the most common form of thyroid dysfunction in pregnancy, which can affect fetal nervous system development and increase the risk of neurodevelopmental disorders after birth. However, the mechanism of the effect of maternal subclinical hypothyroidism on fetal brain development and behavioral phenotypes is still unclear and requires further study. In this study, we constructed a mouse model of maternal subclinical hypothyroidism by exposing dams to drinking water containing 50 ppm propylthiouracil (PTU) during pregnancy and found that its offspring were accompanied by severe cognitive deficits by behavioral testing. Mechanistically, gestational SCH resulted in the upregulation of protein expression and activity of HDAC1/2/3 in the hippocampus of the offspring. ChIP analysis revealed that H3K9ac on the neurogranin (Ng) promoter was reduced in the hippocampus of the offspring of SCH, with a significant reduction in Ng protein, leading to reduced expression levels of synaptic plasticity markers PSD95 (a membrane-associated protein in the postsynaptic density) and SYN (synaptophysin, a specific marker for presynaptic terminals), and impaired synaptic plasticity. In addition, administration of MS-275 (an HDAC1/2/3-specific inhibitor) to SCH offspring alleviated impaired synaptic plasticity and cognitive dysfunction in offspring. Thus, our study suggests that maternal subclinical hypothyroidism may mediate offspring cognitive dysfunction through the HDAC1/2/3-H3K9ac-Ng pathway. Our study contributes to the understanding of the signaling mechanisms underlying maternal subclinical hypothyroidism-mediated cognitive impairment in the offspring.

First in Class Dual Non-ATP-Competitive Glycogen Synthase Kinase 3β/Histone Deacetylase Inhibitors as a Potential Therapeutic to Treat Alzheimer's Disease

Despite recent FDA approvals, Alzheimer's disease (AD) still represents an unmet medical need. Among the different available therapeutic approaches, the development of multitarget molecules represents one of the most widely pursued. In this work, we present a second generation of dual ligands directed toward highly networked targets that are deeply involved in the development of the disease, namely, Histone Deacetylases (HDACs) and Glycogen Synthase Kinase 3β (GSK-3β). The synthesized compounds are highly potent GSK-3β, HDAC2, and HDAC6 inhibitors with IC50 values in the nanomolar range of concentrations. Among them, compound 4 inhibits histone H3 and tubulin acetylation at 0.1 μM concentration, blocks hyperphosphorylation of tau protein, and shows interesting immunomodulatory and neuroprotective properties. These features, together with its ability to cross the blood-brain barrier and its favorable physical-chemical properties, make compound 4 a promising hit for the development of innovative disease-modifying agents.

Targeting SIK3 to modulate hippocampal synaptic plasticity and cognitive function by regulating the transcription of HDAC4 in a mouse model of Alzheimer's disease

Cognitive deterioration and memory decline associated with the progression of Alzheimer's disease (AD) primarily results from synaptic failure. However, current understanding of the upstream regulatory mechanisms controlling synaptic plasticity remains limited. Salt-inducible kinase 3 (SIK3) is central to the signal pathway and is involved in neuronal regulation of sleep duration in mice. We speculated that the SIK3 cascade signaling pathway might contribute to the pathogenesis of AD. Thus, the present study employed AD transgenic mouse models, Morris Water Maze, virus-mediated gene transfer, electrophysiology, co-immunoprecipitation, western blotting, quantitative polymerase chain reaction, immunofluorescence, ChIP-qPCR, Golgi-Cox staining and dendritic spine analysis to investigate this connection. Our results revealed that SIK3 mRNA/protein expression was significantly reduced in middle-aged AD transgenic mouse models and AD patients. Conditional deletion of SIK3 gene in dorsal hippocampal neurons of 5×FAD mice further accelerated cognitive deterioration and impaired synaptic plasticity. In hippocampal neuronal cultures, SIK3 formed a complex with HDAC4, directly phosphorylated HDAC4 and regulated its nuclear cytoplasmic shuttle. Overexpression of SIK3 could facilitate the expression of synaptic plasticity-related genes by directly repressing mef2c or involving the recruitment of histone deacetylase to promoter regions of target genes through regulation of p-HDAC4, and vice versa. Moreover, up-regulation of SLP-S, the truncated fragment of SIK3, in dorsal hippocampal neurons, restored the synaptic plasticity and alleviates the cognitive impairment in 5×FAD mice. Collectively, these findings revealed a novel and important role of SIK3-HDAC4 regulation of synaptic plasticity and propose a new target for therapeutic approaches of cognitive deficits associated with AD.

Class I histone deacetylases inhibition reverses memory impairment induced by acute stress in mice

While chronic stress induces learning and memory impairments, acute stress may facilitate or prevent memory consolidation depending on whether it occurs during the learning event or before it, respectively. On the other hand, it has been shown that histone acetylation regulates long-term memory formation. This study aimed to evaluate the effect of two inhibitors of class I histone deacetylases (HDACs), 4-phenylbutyrate (PB) and IN14 (100 mg/kg/day, ip for 2 days), on memory performance in mice exposed to a single 15-min forced swimming stress session. Plasma corticosterone levels were determined 30 minutes after acute swim stress in one group of mice. In another experimental series, independent groups of mice were trained in one of three different memory tasks: Object recognition test, Elevated T maze, and Buried food location test. Subsequently, the hippocampi were removed to perform ELISA assays for histone deacetylase 2 (HDAC2) expression. Acute stress induced an increase in plasma corticosterone levels, as well as hippocampal HDAC2 content, along with an impaired performance in memory tests. Moreover, PB and IN14 treatment prevented memory loss in stressed mice. These findings suggest that HDAC2 is involved in acute stress-induced cognitive impairment. None of the drugs improved memory in non-stressed animals, indicating that HDACs inhibitors are not cognitive boosters, but rather potentially useful drugs for mitigating memory deficits.

Abdominal surgery under ketamine anesthesia during second trimester impairs hippocampal learning and memory of offspring by regulating dendrite spine remodeling in rats

Recent evidence showed that general anesthesia produces long-term neurotoxicity and cognitive dysfunction. However, it remains unclear whether maternal non-obstetric surgery under ketamine anesthesia during second trimester causes cognitive impairment in offspring. The present study assigned pregnant rats into three groups: 1) normal control group receiving no anesthesia and no surgery, 2) ketamine group receiving ketamine anesthesia for 2 h on the 14th day of gestation but no surgery, and 3) surgery group receiving abdominal surgery under ketamine anesthesia on the 14th day of gestation. On postnatal day 1, the offspring rats in Ketamine group and surgery group were assigned to receive intra-peritoneal injection of Senegenin (15 mg/kg), once per day for consecutive 14 days. The offspring's spatial perception, anxiety-like behavior, and learning and memory were evaluated. Then the offspring's hippocampal tissues were collected. The offspring of the surgery group were impaired in the spatial perception in the cliff avoidance test and the spatial learning and memory in the Morris water maze test. Accordingly, the activity of histone deacetylases increased, the protein levels of NEDD9, BDNF, p-TrkB, Syn and PSD-95 decreased, and the density of dendritic spines reduced in the hippocampus of the offspring of the surgery group, and such effects were not seen in the offspring of the ketamine group, neither in the offspring of control group. Senegenin alleviated the learning and memory impairment, and increased the protein levels of NEDD9, BDNF, p-TrkB, Syn and PSD-95 and the density of dendritic spines in the offspring of the surgery group. ketamine anesthesia plus surgery during second trimester impairs hippocampus-dependent learning and memory, and the deficits could be rescued by treatment with Senegenin.

Long-range action of an HDAC inhibitor treats chronic pain in a spared nerve injury rat model

Histone deacetylase inhibitors (HDACi) that modulate epigenetic regulation and are approved for treating rare cancers have, in disease models, also been shown to mitigate neurological conditions, including chronic pain. They are of interest as non-opioid treatments, but achieving long-term efficacy with limited dosing has remained elusive. Here we utilize a triple combination formulation (TCF) comprised of a pan-HDACi vorinostat (Vo at its FDA-approved daily dose of 50mg/Kg), the caging agent 2-hydroxypropyl-β-cyclodextrin (HPBCD) and polyethylene glycol (PEG) known to boost plasma and brain exposure and efficacy of Vo in mice and rats, of various ages, spared nerve injury (SNI) model of chronic neuropathic pain. Administration of the TCF (but not HPBCD and PEG) decreased mechanical allodynia for 4 weeks without antagonizing weight, anxiety, or mobility. This was achieved at less than 1% of the total dose of Vo approved for 4 weeks of tumor treatment and associated with decreased levels of major inflammatory markers and microglia in ipsilateral (but not contralateral) spinal cord regions. A single TCF injection was sufficient for 3-4 weeks of efficacy: this was mirrored in repeat injections, specific for the injured paw and not seen on sham treatment. Pharmacodynamics in an SNI mouse model suggested pain relief was sustained for days to weeks after Vo elimination. Doubling Vo in a single TCF injection proved effectiveness was limited to male rats, where the response amplitude tripled and remained effective for > 2 months, an efficacy that outperforms all currently available chronic pain pharmacotherapies. Together, these data suggest that through pharmacological modulation of Vo, the TCF enables single-dose effectiveness with extended action, reduces long-term HDACi dosage, and presents excellent potential to develop as a non-opioid treatment option for chronic pain.

DNA Methylation Inhibition Reversibly Impairs the Long-Term Context Memory Maintenance in Helix

This work aims to study the epigenetic mechanisms of regulating long-term context memory in the gastropod mollusk: Helix. We have shown that RG108, an inhibitor of DNA methyltransferase (DNMT), impaired long-term context memory in snails, and this impairment can be reversed within a limited time window: no more than 48 h. Research on the mechanisms through which the long-term context memory impaired by DNMT inhibition could be reinstated demonstrated that this effect depends on several biochemical mechanisms: nitric oxide synthesis, protein synthesis, and activity of the serotonergic system. Memory recovery did not occur if at least one of these mechanisms was impaired. The need for the joint synergic activity of several biochemical systems for a successful memory rescue confirms the assumption that the memory recovery process depends on the process of active reconsolidation, and is not simply a passive weakening of the effect of RG108 over time. Finally, we showed that the reactivation of the impaired memory by RG108, followed by administration of histone deacetylase inhibitor sodium butyrate, led to memory recovery only within a narrow time window: no more than 48 h after memory disruption.

The computational power of the human brain

At the end of the 20th century, analog systems in computer science have been widely replaced by digital systems due to their higher computing power. Nevertheless, the question keeps being intriguing until now: is the brain analog or digital? Initially, the latter has been favored, considering it as a Turing machine that works like a digital computer. However, more recently, digital and analog processes have been combined to implant human behavior in robots, endowing them with artificial intelligence (AI). Therefore, we think it is timely to compare mathematical models with the biology of computation in the brain. To this end, digital and analog processes clearly identified in cellular and molecular interactions in the Central Nervous System are highlighted. But above that, we try to pinpoint reasons distinguishing in silico computation from salient features of biological computation. First, genuinely analog information processing has been observed in electrical synapses and through gap junctions, the latter both in neurons and astrocytes. Apparently opposed to that, neuronal action potentials (APs) or spikes represent clearly digital events, like the yes/no or 1/0 of a Turing machine. However, spikes are rarely uniform, but can vary in amplitude and widths, which has significant, differential effects on transmitter release at the presynaptic terminal, where notwithstanding the quantal (vesicular) release itself is digital. Conversely, at the dendritic site of the postsynaptic neuron, there are numerous analog events of computation. Moreover, synaptic transmission of information is not only neuronal, but heavily influenced by astrocytes tightly ensheathing the majority of synapses in brain (tripartite synapse). At least at this point, LTP and LTD modifying synaptic plasticity and believed to induce short and long-term memory processes including consolidation (equivalent to RAM and ROM in electronic devices) have to be discussed. The present knowledge of how the brain stores and retrieves memories includes a variety of options (e.g., neuronal network oscillations, engram cells, astrocytic syncytium). Also epigenetic features play crucial roles in memory formation and its consolidation, which necessarily guides to molecular events like gene transcription and translation. In conclusion, brain computation is not only digital or analog, or a combination of both, but encompasses features in parallel, and of higher orders of complexity.

ACSS2-dependent histone acetylation improves cognition in mouse model of Alzheimer's disease

BACKGROUND

Nuclear acetyl-CoA pools govern histone acetylation that controls synaptic plasticity and contributes to cognitive deterioration in patients with Alzheimer's disease (AD). Nuclear acetyl-CoA pools are generated partially from local acetate that is metabolized by acetyl-CoA synthetase 2 (ACSS2). However, the underlying mechanism of histone acetylation dysregulation in AD remains poorly understood.

METHODS

We detected ACSS2 expression and histone acetylation levels in the brains of AD patients and 5 × FAD mice. When we altered ACSS2 expression by injecting adeno-associated virus into the dorsal hippocampus of 5 × FAD mice and replenished ACSS2 substrate (acetate), we observed changes in cognitive function by Morris water maze. We next performed RNA-seq, ChIP-qPCR, and electrophysiology to study molecular mechanism underlying ACSS2-mediated spatial learning and memory in 5 × FAD mice.

RESULTS

We reported that ACSS2 expression and histone acetylation (H3K9, H4K12) were reduced in the hippocampus and prefrontal cortex of 5 × FAD mice. Reduced ACSS2 levels were also observed in the temporal cortex of AD patients. 5 × FAD mice exhibited a low enrichment of acetylated histones on the promoters of NMDARs and AMPARs, together with impaired basal and activity-dependent synaptic plasticity, all of which were rescued by ACSS2 upregulation. Moreover, acetate replenishment enhanced ac-H3K9 and ac-H4K12 in 5 × FAD mice, leading to an increase of NMDARs and AMPARs and a restoration of synaptic plasticity and cognitive function in an ACSS2-dependent manner.

CONCLUSION

ACSS2 is a key molecular switch of cognitive impairment and that targeting ACSS2 or acetate administration may serve as a novel therapeutic strategy for the treatment of intermediate or advanced AD. Nuclear acetyl-CoA pools are generated partly from local acetate that is metabolized by acetyl-CoA synthetase 2 (ACSS2). Model depicts that ACSS2 expression is downregulated in the brains of 5×FAD model mice and AD patients. Of note, ACSS2 downregulation mediates a reduction in ionotropic glutamate receptor expression through histone acetylation, which exacerbates synaptic plasticity impairment in AD. These deficits can be rescued by ACSS2 upregulation or acetate supplementation (GTA, an FDA-approved food additive), which may serve as a promising therapeutic strategy for AD treatment.

The Beneficial Effect of Mitochondrial Transfer Therapy in 5XFAD Mice via Liver–Serum–Brain Response

We recently reported the benefit of the IV transferring of active exogenous mitochondria in a short-term pharmacological AD (Alzheimer’s disease) model. We have now explored the efficacy of mitochondrial transfer in 5XFAD transgenic mice, aiming to explore the underlying mechanism by which the IV-injected mitochondria affect the diseased brain. Mitochondrial transfer in 5XFAD ameliorated cognitive impairment, amyloid burden, and mitochondrial dysfunction. Exogenously injected mitochondria were detected in the liver but not in the brain. We detected alterations in brain proteome, implicating synapse-related processes, ubiquitination/proteasome-related processes, phagocytosis, and mitochondria-related factors, which may lead to the amelioration of disease. These changes were accompanied by proteome/metabolome alterations in the liver, including pathways of glucose, glutathione, amino acids, biogenic amines, and sphingolipids. Altered liver metabolites were also detected in the serum of the treated mice, particularly metabolites that are known to affect neurodegenerative processes, such as carnosine, putrescine, C24:1-OH sphingomyelin, and amino acids, which serve as neurotransmitters or their precursors. Our results suggest that the beneficial effect of mitochondrial transfer in the 5XFAD mice is mediated by metabolic signaling from the liver via the serum to the brain, where it induces protective effects. The high efficacy of the mitochondrial transfer may offer a novel AD therapy.

Histone Deacetylase Inhibitors as Cognitive Enhancers and Modifiers of Mood and Behavior

BACKGROUND

Epigenetic regulation of gene signalling is one of the fundamental molecular mechanisms for the generation and maintenance of cellular memory. Histone acetylation is a common epigenetic mechanism associated with increased gene transcription in the central nervous system (CNS). Stimulation of gene transcription by histone acetylation is important for the development of CNS-based long-term memory. Histone acetylation is a target for cognitive enhancement via the application of histone deacetylase (HDAC) inhibitors. The promising potential of HDAC inhibitors has been observed in the treatment of several neurodevelopmental and neurodegenerative diseases.

OBJECTIVE

This study assessed the current state of HDAC inhibition as an approach to cognitive enhancement and treatment of neurodegenerative diseases. Our analysis provides insights into the mechanism of action of HDAC inhibitors, associated epigenetic priming, and describes the therapeutic success and potential complications after unsupervised use of the inhibitors.

RESULTS AND CONCLUSION

Several chromatin-modifying enzymes play key roles in the regulation of cognitive processes. The importance of HDAC signaling in the brain is highlighted in this review. Recent advancements in the field of cognitive epigenetics are supported by the successful development of various HDAC inhibitors, demonstrating effective treatment of mood-associated disorders. The current review discusses the therapeutic potential of HDAC inhibition and observed complications after mood and cognitive enhancement therapies.

Neuroprotective Epigenetic Changes Induced by Maternal Treatment with an Inhibitor of Soluble Epoxide Hydrolase Prevents Early Alzheimer's Disease Neurodegeneration

Modulation of Alzheimer's disease (AD) risk begins early in life. During embryo development and postnatal maturation, the brain receives maternal physiological influences and establishes epigenetic patterns that build its level of resilience to late-life diseases. The soluble epoxide hydrolase inhibitor N-[1-(1-oxopropyl)-4-piperidinyl]-N'-[4-(trifluoromethoxy)phenyl] urea (TPPU), reported as ant-inflammatory and neuroprotective against AD pathology in the adult 5XFAD mouse model of AD, was administered to wild-type (WT) female mice mated to heterozygous 5XFAD males during gestation and lactation. Two-month-old 5XFAD male and female offspring of vehicle-treated dams showed memory loss as expected. Remarkably, maternal treatment with TPPU fully prevented memory loss in 5XFAD. TPPU-induced brain epigenetic changes in both WT and 5XFAD mice, modulating global DNA methylation (5-mC) and hydroxymethylation (5-hmC) and reducing the gene expression of some histone deacetylase enzymes (Hdac1 and Hdac2), might be on the basis of the long-term neuroprotection against cognitive impairment and neurodegeneration. In the neuropathological analysis, both WT and 5XFAD offspring of TPPU-treated dams showed lower levels of AD biomarkers of tau hyperphosphorylation and microglia activation (Trem2) than the offspring of vehicle-treated dams. Regarding sex differences, males and females were similarly protected by maternal TPPU, but females showed higher levels of AD risk markers of gliosis and neurodegeneration. Taken together, our results reveal that maternal treatment with TPPU impacts in preventing or delaying memory loss and AD pathology by inducing long-term modifications in the epigenetic machinery and its marks.

Contribution of histone acetylation to the serotonin-mediated long-term synaptic plasticity in terrestrial snails

Serotonin plays a decisive role in long-term synaptic plasticity and long-term memory in mollusks. Previously, we demonstrated that histone acetylation is a regulatory mechanism of long-term memory in terrestrial snail. At the behavioral level, many studies were done in Helix to elucidate the role of histone acetylation and serotonin. However, the impact of histone acetylation on long-term potentiation of synaptic efficiency in electrophysiological studies in Helix has been studied only in one paper. Here we investigated effects of serotonin, histone deacetylases inhibitors sodium butyrate and trichostatin A, and a serotonergic receptor inhibitor methiothepin on long-term potentiation of synaptic responses in vitro. We demonstrated that methiothepin drastically declined the EPSPs amplitudes when long-term potentiation was induced, while co-application either of histone deacetylase inhibitors sodium butyrate or trichostatin A with methiothepin prevented the weakening of potentiation. We showed that single serotonin application in combination with histone deacetylase blockade could mimic the effect of repeated serotonin applications and be enough for sustained long-lasting synaptic changes. The data obtained demonstrated that histone deacetylases blockade ameliorated deficits in synaptic plasticity induced by different paradigms (methiothepin treatment, the weak training protocol with single application of serotonin), suggesting that histone acetylation contributes to the serotonin-mediated synaptic plasticity.

High levels of HDAC expression correlate with microglial aging

BACKGROUND

Cellular damage gradually accumulates with aging, promoting a time-dependent functional decline of the brain. Microglia play an essential regulatory role in maintaining cognitive activity by phagocytosing cell debris and apoptotic cells during neurogenesis. The activities of different histone deacetylases (HDACs) regulate microglial function during development and neurodegeneration. However, no studies have described the role of HDACs in microglia during physiological aging.

RESEARCH DESIGN AND METHODS

HDAC and microglial marker levels were examined in microglial cells after inducing senescence in vitro and in mouse and human hippocampal biopsies in vivo, using quantitative real-time PCR. Publicly available datasets were used to determine HDAC expression in different brain areas during physiological aging.

RESULTS

HDAC expression increased upon the induction of senescence with bleomycin or serial passage in microglial cultures. High levels of HDACs were detected in mice and aged human brain samples. Human hippocampal samples showed a positive correlation between the expression of HDAC1, 3, and 7 and microglial and senescence markers. HDAC1 and 3 levels are enriched in the purified aged microglial population.

CONCLUSIONS

Several HDACs, particularly HDAC1, are elevated in microglia upon senescence induction in vitro and with aging in vivo, and correlate with microglial and senescence biomarkers.

Role of Altered Expression, Activity and Sub-cellular Distribution of Various Histone Deacetylases (HDACs) in Mesial Temporal Lobe Epilepsy with Hippocampal Sclerosis

Histone deacetylases (HDACs) have been described to have both neurotoxic and neuroprotective roles, and partly, depend on its sub-cellular distribution. HDAC inhibitors have a long history of use in the treatment of various neurological disorders including epilepsy. Key role of HDACs in GABAergic neurotransmission, synaptogenesis, synaptic plasticity and memory formation was demonstrated whereas very less is known about their role in drug-resistant epilepsy pathologies. The present study was aimed to investigate the changes in the expression of HDACs, activity and its sub-cellular distribution in mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) patients. For this study, surgically resected hippocampal tissue specimens of 28 MTLE-HS patients and 20 hippocampus from post-mortem cases were obtained. Real-time PCR was done to analyse the mRNA expression. HDAC activity and the protein levels of HDACs in cytoplasm as well as nucleus were measured spectrophotometrically. Further, sub-cellular localization of HDACs was characterized by immunofluorescence. Significant upregulation of HDAC1, HDAC2, HDAC4, HDAC5, HDAC6, HDAC10 and HDAC11 mRNA were observed in MTLE-HS. Alterations in the mRNA expression of glutamate and gamma-aminobutyric acid (GABA) receptor subunits have been also demonstrated. We observed significant increase of HDAC activity and nuclear level of HDAC1, HDAC2, HDAC5 and HDAC11 in the hippocampal samples obtained from patients with MTLE-HS. Moreover, we found altered cytoplasmic level of HDAC4, HDAC6 and HDAC10 in the hippocampal sample obtained from patients with MTLE-HS. Alterations in the level of HDACs could potentially be part of a dynamic transcription regulation associated with MTLE-HS. Changes in cytoplasmic level of HDAC4, 6 and 10 suggest that cytoplasmic substrates may play a crucial role in the pathophysiology of MTLE-HS. Knowledge regarding expression pattern and sub-cellular distribution of HDACs may help to devise specific HDACi therapy for epilepsy.

Therapeutic role of curcumin in adult neurogenesis for management of psychiatric and neurological disorders: a scientometric study to an in-depth review

Aberrant neurogenesis is a major factor in psychiatric and neurological disorders that have significantly attracted the attention of neuroscientists. Curcumin is a primary constituent of curcuminoid that exerts several positive pharmacological effects on aberrant neurogenesis. First, it is important to understand the different processes of neurogenesis, and whether their dysfunction promotes etiology as well as the development of many psychiatric and neurological disorders; then investigate mechanisms by which curcumin affects neurogenesis as an active participant in pathophysiological events. Based on scientometric studies and additional extensive research, we explore the mechanisms by which curcumin regulates adult neurogenesis and in turn affects psychiatric diseases, i.e., depression and neurological disorders among them traumatic brain injury (TBI), stroke, Alzheimer's disease (AD), Gulf War Illness (GWI) and Fragile X syndrome (FXS). This review aims to elucidate the therapeutic effects and mechanisms of curcumin on adult neurogenesis in various psychiatric and neurological disorders. Specifically, we discuss the regulatory role of curcumin in different activities of neural stem cells (NSCs), including proliferation, differentiation, and migration of NSCs. This is geared toward providing novel application prospects of curcumin in treating psychiatric and neurological disorders by regulating adult neurogenesis.

Identification of potent HDAC 2 inhibitors using E-pharmacophore modelling, structure-based virtual screening and molecular dynamic simulation

Histone deacetylase 2 (HDAC 2) of class I HDACs plays a major role in embryonic and neural developments. However, HDAC 2 overexpression triggers cell proliferation by diverse mechanisms in cancer. Over the decades, many pan and class-specific inhibitors of HDAC were discovered. Limitations such as toxicity and differential cell localization of each isoform led researchers to hypothesize that isoform selective inhibitors may be relevant to bring about desired effects. In this study, we have employed the PHASE module to develop an e-pharmacophore model and virtually screened four focused libraries of around 300,000 compounds to identify isoform selective HDAC 2 inhibitors. The compounds with phase fitness score greater than or equal to 2.4 were subjected to structure-based virtual screening with HDAC 2. Ten molecules with docking score greater than  -12 kcal/mol were chosen for selectivity study, QikProp module (ADME prediction) and dG/bind energy identification. Compound 1A with the best dock score of  -13.3 kcal/mol and compound 1I with highest free binding energy,  -70.93 kcal/mol, were selected for molecular dynamic simulation studies (40 ns simulation). The results indicated that compound 1I may be a potent and selective HDAC 2 inhibitor. Further, in vitro and in vivo studies are necessary to validate the potency of selected lead molecule and its derivatives.

Histone Deacetylases 1 and 2 in Memory Function

Histone deacetylases (HDACs) have been implicated in learning and memory, and their dysregulation has been linked to cognitive impairment in brain aging and neurodegenerative diseases. In this review, we focus on HDAC1 and HDAC2, highlighting recent progress on their roles in regulating brain function through distinct mechanisms, including gene repression and DNA repair pathways. Moreover, we discuss evidence demonstrating how HDAC1 and HDAC2 could be modulated and their potential as targets to combat memory deficits.

TIP60 buffers acute stress response and depressive behaviour by controlling PPARγ-mediated transcription

Tat-interacting protein 60 (TIP60) as nuclear receptors (NRs) coregulator, acts as a tumor suppressor and also has promising therapeutic potential to target Alzheimer's disease. Stress has been implicated in many psychiatric disorders, and these disorders are characterized by impairments in cognitive function. Until now, there are no experimental data available on the regulatory effect of TIP60 in acute stress and depression. There is also no definitive explanation on which specific modulation of target gene expression is achieved by TIP60. Here, we identify TIP60 as a novel positive regulator in response to acute restraint stress (ARS) and a potentially effective target of antidepressants. Firstly, we discovered increased hippocampal TIP60 expressions in the ARS model. Furthermore, using the TIP60 inhibitor, MG149, we proved that TIP60 function correlates with behavioral and synaptic activation in the two-hour ARS. Secondly, the lentivirus vector (LV)-TIP60overexpression (OE) was injected into the hippocampus prior to the chronic restraint stress (CRS) experiments and it was found that over-expressed TIP60 compensates for TIP60 decrease and improves depression index in CRS. Thirdly, through the intervention of TIP60 expression in vitro, we established the genetic regulation of TIP60 on synaptic proteins, confirmed the TIP60 function as a specific coactivator for PPARγ and found that the PPARγ-mediated TIP60 function modulates transcriptional activation of synaptic proteins. Finally, the LV-TIP60OE and PPARγ antagonist, GW9662, were both administered in the CRS model and the data indicated that blocking PPARγ significantly weakened the protective effect of TIP60 against the CRS-induced depression. Conclusively, these findings together support TIP60 as a novel positive factor in response to acute stress and interacts with PPARγ to modulate the pathological mechanism of CRS-induced depression.

Epigenetic Mechanisms of Neural Plasticity in Chronic Neuropathic Pain

Neuropathic pain is a challenging clinical problem and remains difficult to treat. Altered gene expression in peripheral sensory nerves and neurons due to nerve injury is well documented and contributes critically to the synaptic plasticity in the spinal cord and the initiation and maintenance of chronic pain. However, our understanding of the epigenetic mechanisms regulating the transcription of pro-nociceptive (e.g., NMDA receptors and α2δ-1) and antinociceptive (e.g., potassium channels and opioid and cannabinoid receptors) genes are still limited. In this review, we summarize recent studies determining the roles of histone modifications (including methylation, acetylation, and ubiquitination), DNA methylation, and noncoding RNAs in neuropathic pain development. We review the epigenetic writer, reader, and eraser proteins that participate in the transcriptional control of the expression of key ion channels and neurotransmitter receptors in the dorsal root ganglion after traumatic nerve injury, which is commonly used as a preclinical model of neuropathic pain. A better understanding of epigenetic reprogramming involved in the transition from acute to chronic pain could lead to the development of new treatments for neuropathic pain.

How to Slow down the Ticking Clock: Age-Associated Epigenetic Alterations and Related Interventions to Extend Life Span

Epigenetic alterations pose one major hallmark of organismal aging. Here, we provide an overview on recent findings describing the epigenetic changes that arise during aging and in related maladies such as neurodegeneration and cancer. Specifically, we focus on alterations of histone modifications and DNA methylation and illustrate the link with metabolic pathways. Age-related epigenetic, transcriptional and metabolic deregulations are highly interconnected, which renders dissociating cause and effect complicated. However, growing amounts of evidence support the notion that aging is not only accompanied by epigenetic alterations, but also at least in part induced by those. DNA methylation clocks emerged as a tool to objectively determine biological aging and turned out as a valuable source in search of factors positively and negatively impacting human life span. Moreover, specific epigenetic signatures can be used as biomarkers for age-associated disorders or even as targets for therapeutic approaches, as will be covered in this review. Finally, we summarize recent potential intervention strategies that target epigenetic mechanisms to extend healthy life span and provide an outlook on future developments in the field of longevity research.

Epigenetic repression of Wnt receptors in AD: a role for Sirtuin2-induced H4K16ac deacetylation of Frizzled1 and Frizzled7 promoters

Growing evidence supports a role for deficient Wnt signalling in Alzheimer's disease (AD). First, the Wnt antagonist DKK1 is elevated in AD brains and is required for amyloid-β-induced synapse loss. Second, LRP6 Wnt co-receptor is required for synapse integrity and three variants of this receptor are linked to late-onset AD. However, the expression/role of other Wnt signalling components remain poorly explored in AD. Wnt receptors Frizzled1 (Fzd1), Fzd5, Fzd7 and Fzd9 are of interest due to their role in synapse formation/plasticity. Our analyses showed reduced FZD1 and FZD7 mRNA levels in the hippocampus of human early AD stages and in the hAPP^NLGF/NLGF mouse model. This transcriptional downregulation was accompanied by reduced levels of the pro-transcriptional histone mark H4K16ac and a concomitant increase of its deacetylase Sirt2 at Fzd1 and Fzd7 promoters in AD. In vitro and in vivo inhibition of Sirt2 rescued Fzd1 and Fzd7 mRNA expression and H4K16ac levels at their promoters. In addition, we showed that Sirt2 recruitment to Fzd1 and Fzd7 promoters is dependent on FoxO1 activity in AD, thus acting as a co-repressor. Finally, we found reduced levels of SIRT2 inhibitory phosphorylation in nuclear samples from human early AD stages with a concomitant increase in the SIRT2 phosphatase PP2C. This results in hyperactive nuclear Sirt2 and favours Fzd1 and Fzd7 repression in AD. Collectively, our findings define a novel role for nuclear hyperactivated SIRT2 in repressing Fzd1 and Fzd7 expression via H4K16ac deacetylation in AD. We propose SIRT2 as an attractive target to ameliorate AD pathology.

Histone Deacetylase 2 Knockdown Ameliorates Morphological Abnormalities of Dendritic Branches and Spines to Improve Synaptic Plasticity in an APP/PS1 Transgenic Mouse Model

Disease-modifying therapies, such as neuroprotective and neurorestorative interventions, are strongly desired for Alzheimer’s disease (AD) treatment. Several studies have suggested that histone deacetylase 2 (HDAC2) inhibition can exhibit disease-modifying effects in AD patients. However, whether HDAC2 inhibition shows neuroprotective and neurorestorative effects under neuropathic conditions, such as amyloid β (Aβ)-elevated states, remains poorly understood. Here, we performed HDAC2-specific knockdown in CA1 pyramidal cells and showed that HDAC2 knockdown increased the length of dendrites and the number of mushroom-like spines of CA1 basal dendrites in APP/PS1 transgenic mouse model. Furthermore, HDAC2 knockdown also ameliorated the deficits in hippocampal CA1 long-term potentiation and memory impairment in contextual fear conditioning tests. Taken together, our results support the notion that specific inhibition of HDAC2 has the potential to slow the disease progression of AD through ameliorating Aβ-induced neuronal impairments.

Overexpressing Histone Deacetylase 5 in Rat Dorsal Striatum Alters Reward-Guided Decision-Making and Associated Neural Encoding

Accumulating evidence in the past decade implicates histone-modifying enzymes, such as class I histone deacetylases (HDACs), in learning and memory and, recently, habit formation. However, it is unclear whether HDACs play roles in complex cognitive function. To address this issue, we examined the role of dorsal striatal HDAC5, a class II HDAC, in reward-guided decision-making and associated neural encoding in rats. We first injected adeno-associated virus to overexpress a nuclear-localized HDAC5 in dorsal striatum (DS). We then recorded neural correlates from dorsolateral striatum (DLS) as rats performed two reward-guided choice tasks, in which we manipulated either the size of or delay to reward. During these tasks, rats first learned which of two options led to the better reward and then reversed those contingencies in a second block of trials. We found that rats with HDAC5 overexpression in DS responded faster and chose higher value reward more often during the first block of trials but were less able to reverse those contingencies in the second block of trials. At the neural level, HDAC5 overexpression in DS elevated and reduced the number of cells in DLS that increased firing to stimuli and reward, respectively, and shifted encoding toward cues that predicted more immediate reward. These results suggest that the HDAC5 overexpression in DS contributes to inflexible decision-making, demonstrating a role of histone-modifying enzymes in complex cognitive function.SIGNIFICANCE STATEMENT HDACs are important for learning and habit formation. Here, we expanded on these functions and found that overexpression of HDAC5 produced faster and more automatic behavior, and related changes in dorsolateral striatal neural firing in rats performing a value-based decision-making task. These results implicate HDAC5 as a potential therapeutic target for psychiatric conditions that impair decision-making and executive function.

Effects of Manipulation of Noradrenergic Activities on the Expression of Dopaminergic Phenotypes in Aged Rat Brains

This study investigated the effects of the pharmacological manipulation of noradrenergic activities on dopaminergic phenotypes in aged rats. Results showed that the administration of L-threo-3,4-dihydroxyphenylserine (L-DOPS) for 21 days significantly increased the expression of tyrosine hydroxylase (TH) and dopamine transporter (DAT) in the striatum and substantia nigra (SN) of 23-month-old rats. Furthermore, this treatment significantly increased norepinephrine/DA concentrations in the striatum and caused a deficit of sensorimotor gating as measured by prepulse inhibition (PPI). Next, old rats were injected with the α2-adrenoceptor antagonist 2-methoxy idazoxan or β2-adrenoceptor agonist salmeterol for 21 days. Both drugs produced similar changes of TH and DAT in the striatum and SN. Moreover, treatments with L-DOPS, 2-methoxy idazoxan, or salmeterol significantly increased the protein levels of phosphorylated Akt in rat striatum and SN. However, although a combination of 2-methoxy idazoxan and salmeterol resulted in a deficit of PPI in these rats, the administration of 2-methoxy idazoxan alone showed an opposite behavioral change. The in vitro experiments revealed that treatments with norepinephrine markedly increased mRNAs and proteins of ATF2 and CBP/p300 and reduced mRNA and proteins of HDAC2 and HDAC5 in MN9D cells. A ChIP assay showed that norepinephrine significantly increased CBP/p300 binding or reduced HDAC2 and HDAC5 binding on the TH promoter. The present results indicate that facilitating noradrenergic activity in the brain can improve the functions of dopaminergic neurons in aged animals. While this improvement may have biochemically therapeutic indication for the status involving the degeneration of dopaminergic neurons, it may not definitely include behavioral improvements, as indicated by using 2-methoxy idazoxan only.

A putative role for lncRNAs in epigenetic regulation of memory

The central dogma of molecular genetics is defined as encoded genetic information within DNA, transcribed into messenger RNA, which contain the instructions for protein synthesis, thus imparting cellular functionality and ultimately life. This molecular genetic theory has given birth to the field of neuroepigenetics, and it is now well established that epigenetic regulation of gene transcription is critical to the learning and memory process. In this review, we address a potential role for a relatively new player in the field of epigenetic crosstalk - long non-coding RNAs (lncRNAs). First, we briefly summarize epigenetic mechanisms in memory formation and examine what little is known about the emerging role of lncRNAs during this process. We then focus discussions on how lncRNAs interact with epigenetic mechanisms to control transcriptional programs under various conditions in the brain, and how this may be applied to regulation of gene expression necessary for memory formation. Next, we explore how epigenetic crosstalk in turn serves to regulate expression of various individual lncRNAs themselves. To highlight the importance of further exploring the role of lncRNA in epigenetic regulation of gene expression, we consider the significant relationship between lncRNA dysregulation and declining memory reserve with aging, Alzheimer's disease, and epilepsy, as well as the promise of novel therapeutic interventions. Finally, we conclude with a discussion of the critical questions that remain to be answered regarding a role for lncRNA in memory.

Comprehensive Analysis of Mouse Hippocampal Lysine Acetylome Mediated by Sea Cucumber Peptides Preventing Memory Impairment

Memory impairment is becoming a potential health issue with the delicacy of diet and social stress. Sea cucumber peptides (SCP) prevent memory impairment, as previously reported. In this study, further research was performed using hippocampal lysine-acetylome to explore molecular regulation mechanisms. C57BL/6 mice were treated with scopolamine via intraperitoneal injection to simulate memory impairment. To determine the influence of SCP on the total acetylated-protein level of the hippocampus, acetylated-proteomics was performed. SCP increased the acetylation level of histone (H3 and H4). Meanwhile, for non-histones, the differentially acetylated proteins were involved in multiple memory-related pathways, as shown by KEGG enrichment analysis. Additionally, long-term potentiation was confirmed by western blotting. Finally, a combined analysis of proteome and lysine acetylome revealed that SCP contributed to synaptic vesicle cycle regulation and dopamine metabolism. Consequently, our findings revealed that SCP was potentially neuroprotective by regulating post-transcriptional hippocampal protein acetylation.

DNA methylome perturbations: an epigenetic basis for the emergingly heritable neurodevelopmental abnormalities associated with maternal smoking and maternal nicotine exposure†

Maternal smoking during pregnancy is associated with an ensemble of neurodevelopmental consequences in children and therefore constitutes a pressing public health concern. Adding to this burden, contemporary epidemiological and especially animal model research suggests that grandmaternal smoking is similarly associated with neurodevelopmental abnormalities in grandchildren, indicative of intergenerational transmission of the neurodevelopmental impacts of maternal smoking. Probing the mechanistic bases of neurodevelopmental anomalies in the children of maternal smokers and the intergenerational transmission thereof, emerging research intimates that epigenetic changes, namely DNA methylome perturbations, are key factors. Altogether, these findings warrant future research to fully elucidate the etiology of neurodevelopmental impairments in the children and grandchildren of maternal smokers and underscore the clear potential thereof to benefit public health by informing the development and implementation of preventative measures, prophylactics, and treatments. To this end, the present review aims to encapsulate the burgeoning evidence linking maternal smoking to intergenerational epigenetic inheritance of neurodevelopmental abnormalities, to identify the strengths and weaknesses thereof, and to highlight areas of emphasis for future human and animal model research therein.

Histone deacetylase in neuropathology

Neuroepigenetics, a new branch of epigenetics, plays an important role in the regulation of gene expression. Neuroepigenetics is associated with holistic neuronal function and helps in formation and maintenance of memory and learning processes. This includes neurodevelopment and neurodegenerative defects in which histone modification enzymes appear to play a crucial role. These modifications, carried out by acetyltransferases and deacetylases, regulate biologic and cellular processes such as apoptosis and autophagy, inflammatory response, mitochondrial dysfunction, cell-cycle progression and oxidative stress. Alterations in acetylation status of histone as well as non-histone substrates lead to transcriptional deregulation. Histone deacetylase decreases acetylation status and causes transcriptional repression of regulatory genes involved in neural plasticity, synaptogenesis, synaptic and neural plasticity, cognition and memory, and neural differentiation. Transcriptional deactivation in the brain results in development of neurodevelopmental and neurodegenerative disorders. Mounting evidence implicates histone deacetylase inhibitors as potential therapeutic targets to combat neurologic disorders. Recent studies have targeted naturally-occurring biomolecules and micro-RNAs to improve cognitive defects and memory. Multi-target drug ligands targeting HDAC have been developed and used in cell-culture and animal-models of neurologic disorders to ameliorate synaptic and cognitive dysfunction. Herein, we focus on the implications of histone deacetylase enzymes in neuropathology, their regulation of brain function and plausible involvement in the pathogenesis of neurologic defects.

Histone hypoacetylation contributes to neurotoxicity induced by chronic nickel exposure in vivo and in vitro

Nickel (Ni) is a heavy metal that is both an environmental pollutant and a threat to human health. However, the effects of Ni on the central nervous system in susceptible populations have not been well established. In the present study, the neurotoxicity of Ni and its underlying mechanism were investigated in vivo and in vitro. Ni exposure through drinking water (10 mg Ni/L, 12 weeks) caused learning and memory impairment in mice. Reduced dendrite complexity was observed in both Ni-exposed mouse hippocampi and Ni-treated (200 μM, 72 h) primary cultured hippocampal neurons. The levels of histone acetylation, especially at histone H3 lysine 9 (H3K9ac), were reduced in Ni-exposed mouse hippocampi and cultured neurons. RNA sequencing and chromatin immunoprecipitation (ChIP) sequencing analyses revealed that H3K9ac-modulated gene expression were downregulated. Treatment with sodium butyrate, a histone deacetylase inhibitor, attenuated Ni-induced H3K9 hypoacetylation, neural gene downregulation and dendrite complexity reduction in cultured neurons. Sodium butyrate also restored Ni-induced memory impairment in mice. These results indicate that Ni-induced H3K9 hypoacetylation may be a contributor to the neurotoxicity of Ni. The finding that Ni disturbs histone acetylation in the nervous system may provide new insight into the health risk of chronic Ni exposure.

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.

Sodium butyrate enhances fear extinction and rescues hippocampal acetylcholinesterase activity in a rat model of posttraumatic stress disorder

It is believed that impaired extinction of fear memories is an underlying cause for the development of posttraumatic stress disorder (PTSD). Histone deacetylases (HDAC) are enzymes that modulate extinction by changing the chromatin structure and altering protein synthesis in the brain. Studies show that stress modifies both HDAC activity and cerebral cholinergic neurotransmission. The present work aims to evaluate the effect of sodium butyrate (NaBu), an HDAC inhibitor, on behavioral markers of extinction and biochemical changes in HDAC and acetylcholinesterase activity in the hippocampus. NaBu was administered for 7 days in a group of rats that were exposed to single prolonged stress (SPS), as a model for PTSD. Contextual fear conditioning was performed on the 8th day, and fear extinction was measured in the next 4 consecutive days. Other behavioral tests to measure anxiety, locomotor activity and working memory were performed for further interpretation of the results. Hippocampal acetylcholinesterase and HDAC activity were also measured through biochemical tests. Behavioral results showed that treatment with NaBu can reverse the SPS-induced extinction deficits. Biochemical data indicated that while SPS induced overactivity in hippocampal HDAC, it decreased acetylcholinesterase activity in the region. Both effects were reversed after NaBu treatment. It seems that at least part of extinction deficiency in SPS exposed rats is related to hypoacetylation of acetylcholinesterase in the hippocampus. Preemptive therapy with an HDAC inhibitor reverses this process and is worth further evaluation as a possible therapeutic approach in PTSD.

Acetylation of the influenza A virus polymerase subunit PA in the N-terminal domain positively regulates its endonuclease activity

The post-translational acetylation of lysine residues is found in many nonhistone proteins and is involved in a wide range of biological processes. Recently, we showed that the nucleoprotein of the influenza A virus is acetylated by histone acetyltransferases (HATs), a phenomenon that affects viral transcription. Here, we report that the PA subunit of influenza A virus RNA-dependent RNA polymerase is acetylated by the HATs, P300/CREB-binding protein-associated factor (PCAF), and general control nonderepressible 5 (GCN5), resulting in accelerated endonuclease activity. Specifically, the full-length PA subunit expressed in cultured 293T cells was found to be strongly acetylated. Moreover, the partial recombinant protein of the PA N-terminal region containing the endonuclease domain was also acetylated by PCAF and GCN5 in vitro, which facilitated its endonuclease activity. Mass spectrometry analyses identified K19 as a candidate acetylation target in the PA N-terminal region. Notably, the substitution of the lysine residue at position 19 with glutamine, a mimic of the acetyl-lysine residue, enhanced its endonuclease activity in vitro; this point mutation also accelerated influenza A virus RNA-dependent RNA polymerase activity in the cell. Our findings suggest that PA acetylation is important for the regulation of the endonuclease and RNA polymerase activities of the influenza A virus.

Epigenetic Modulation of Microglia Function and Phenotypes in Neurodegenerative Diseases

Microglia-mediated neuroinflammation is one of the most remarkable hallmarks of neurodegenerative diseases (NDDs), including AD, PD, and ALS. Accumulating evidence indicates that microglia play both neuroprotective and detrimental roles in the onset and progression of NDDs. Yet, the specific mechanisms of action surrounding microglia are not clear. Modulation of microglia function and phenotypes appears to be a potential strategy to reverse NDDs. Until recently, research into the epigenetic mechanisms of diseases has been gradually developed, making it possible to elucidate the molecular mechanisms underlying the epigenetic regulation of microglia in NDDs. This review highlights the function and phenotypes of microglia, elucidates the relationship between microglia, epigenetic modifications, and NDDs, as well as the possible mechanisms underlying the epigenetic modulation of microglia in NDDs with a focus on potential intervention strategies.

Mesenchymal Stem Cell-Derived Exosomes Ameliorate Alzheimer's Disease Pathology and Improve Cognitive Deficits

The accumulation of extracellular β-amyloid (Aβ) plaques within the brain is unique to Alzheimer’s disease (AD) and thought to induce synaptic deficits and neuronal loss. Optimal therapies should tackle the core AD pathophysiology and prevent the decline in memory and cognitive functions. This study aimed to evaluate the therapeutic performance of mesenchymal stem cell-derived exosomes (MSC-exosomes), which are secreted membranous elements encapsulating a variety of MSC factors, on AD. A human neural cell culture model with familial AD (FAD) mutations was established and co-cultured with purified MSC-exosomes. 2-[¹⁸F]Fluoro-2-deoxy-d-glucose ([¹⁸F]FDG) and novel object recognition (NOR) testing were performed before/after treatment to evaluate the therapeutic effect in vivo. The AD-related pathology and the expression of neuronal memory/synaptic plasticity-related genes were also evaluated. The results showed that MSC-exosomes reduced Aβ expression and restored the expression of neuronal memory/synaptic plasticity-related genes in the cell model. [¹⁸F]FDG-PET imaging and cognitive assessment revealed a significant improvement in brain glucose metabolism and cognitive function in AD transgenic mice. The phase of neurons and astrocytes in the brain of AD mice were also found to be regulated after treatment with MSC-exosomes. Our study demonstrates the therapeutic mechanism of MSC-exosomes and provides an alternative therapeutic strategy based on cell-free MSC-exosomes for the treatment of AD.

Chronic restraint stress impairs cognition via modulating HDAC2 expression

Background

To investigate the effects of chronic restraint stress on cognition and the probable molecular mechanism in mice.

Methods

In the current work, a restraining tube was used as a way to induce chronic stress in mice. The protein levels were determined with ELISA and western blot. A series of behavior tests, including the Morris water maze, elevated plus maze, open field test, and novel object recognition test, were also performed to examine the anxiety and the ability of learning and memory. Moreover, murine neuroblastoma N2a cells were used to confirm the findings from mice under chronic stress.

Results

Decreased synaptic functions were impaired in chronic stress with the downregulation of PSD95, GluR-1, the neurotrophic factor BDNF, and immediate-onset genes Arc and Egr. Chronic restraint decreased the histone acetylation level in hippocampal neurons while HDAC2 was increased and was co-localized with glucocorticoid receptors. Moreover, chronic stress inhibited the PI3K/AKT signaling pathway and induced energy metabolism dysfunctions.

Conclusion

This work examining the elevated levels of HDAC2 in the hippocampus may provide new insights and targets for drug development for treating many neurodegenerative diseases.

Identification of the ZEB2 gene as a potential target for epilepsy therapy and the association between rs10496964 and ZEB2 expression

Objective

An association between the rs10496964 polymorphism and the ZEB2 gene has not yet been reported, and the role of ZEB2 in epilepsy therapy is also unclear. The aims of this research were to evaluate the role of ZEB2 in the therapy of epilepsy and to explore the association between rs10496964 and ZEB2 expression.

Methods

We used the expression quantitative trait loci (eQTL) dataset resource from the Brain eQTL Almanac to evaluate the association between rs10496964 and ZEB2 expression in human brain tissue. Pathway and process enrichment analysis, protein–protein interaction analysis, and PhosphoSitePlus® analysis were then performed to further evaluate the role of ZEB2 in the therapy of epilepsy.

Results

The rs10496964 polymorphism was found to regulate the expression of ZEB2 in human brain tissue. The ZEB2 protein interacts with the targets of approved antiepileptic drugs, and a post-translational acetylation modification of ZEB2 was associated with an epilepsy drug therapy.

Conclusion

Our findings suggest that ZEB2 may be involved in the therapy of epilepsy, and rs10496964 regulates ZEB2 expression in human brain tissue.

Maternal Separation-Induced Histone Acetylation Correlates with BDNF-Programmed Synaptic Changes in an Animal Model of PTSD with Sex Differences

Maternal separation (MS) causes long-lasting epigenetic changes in the brain and increases vulnerability to traumatic events in adulthood. Of interest, there may be sex-specific differences in these epigenetic changes. In this study, the extent of histone acetylation in the hippocampus (HIP) and the expression of BDNF were measured to determine whether BDNF influences risk of PTSD following MS in early life. Rat offspring were separated from their dams (3 h/day or 6 h/day from PND2~PND14). Then, pups were treated with a single prolonged stress (SPS) procedure when they reached adulthood (PND80). In animals stressed with the SPS procedure in adulthood, those that had increased MS intensity in childhood demonstrated more significant changes in performance on tests of anxiety, depression, and contextual fear memory. Reduced levels of total BDNF mRNA and protein were observed after SPS treatment and further declined in groups with greater MS time in childhood. Interestingly, these changes were correlated with decreased H3K9ac levels and increased HDAC2 levels. Additional MS also led to more severe ultrastructural synaptic damage in rats that experienced the SPS procedure, particularly in the CA1 and CA3 region of the HIP, reflecting impaired synaptic plasticity in these regions. Interestingly, male rats in the MS3h-PTSD group showed decreased anxiety, but no similar changes were found in female rats, suggesting a degree of gender specificity in coping with stress after mild MS. In summary, this study suggests that the epigenetic signatures of the BDNF genes can be linked to HIP responses to stress, providing insights that may be relevant for people at risk of stress-related psychopathologies.

Melatonin- and Ferulic Acid-Based HDAC6 Selective Inhibitors Exhibit Pronounced Immunomodulatory Effects In Vitro and Neuroprotective Effects in a Pharmacological Alzheimer's Disease Mouse Model

The structures of melatonin and ferulic acid were merged into tertiary amide-based histone deacetylase 6 (HDAC6) inhibitors to develop multi-target-directed inhibitors for neurodegenerative diseases to incorporate antioxidant effects without losing affinity and selectivity at HDAC6. Structure-activity relationships led to compound 10b as a hybrid molecule showing pronounced and selective inhibition of HDAC6 (IC50 = 30.7 nM, > 25-fold selectivity over other subtypes). This compound shows comparable DPPH radical scavenging ability to ferulic acid, comparable ORAC value to melatonin and comparable Cu²⁺ chelating ability to EDTA. It also lacks neurotoxicity on HT-22 cells, exhibits a pronounced immunomodulatory effect, and is active in vivo showing significantly higher efficacy in an AD mouse model to prevent both Aβ25-35-induced spatial working and long-term memory dysfunction at lower dose (0.3 mg/kg) compared to positive control HDAC6 inhibitor ACY1215 and an equimolar mixture of the three entities ACY1215, melatonin and ferulic acid, suggesting potentially disease-modifying properties.

Knock-Down of HDAC2 in Human Induced Pluripotent Stem Cell Derived Neurons Improves Neuronal Mitochondrial Dynamics, Neuronal Maturation and Reduces Amyloid Beta Peptides

Histone deacetylase 2 (HDAC2) is a major HDAC protein in the adult brain and has been shown to regulate many neuronal genes. The aberrant expression of HDAC2 and subsequent dysregulation of neuronal gene expression is implicated in neurodegeneration and brain aging. Human induced pluripotent stem cell-derived neurons (hiPSC-Ns) are widely used models for studying neurodegenerative disease mechanisms, but the role of HDAC2 in hiPSC-N differentiation and maturation has not been explored. In this study, we show that levels of HDAC2 progressively decrease as hiPSCs are differentiated towards neurons. This suppression of HDAC2 inversely corresponds to an increase in neuron-specific isoforms of Endophilin-B1, a multifunctional protein involved in mitochondrial dynamics. Expression of neuron-specific isoforms of Endophilin-B1 is accompanied by concomitant expression of a neuron-specific alternative splicing factor, SRRM4. Manipulation of HDAC2 and Endophilin-B1 using lentiviral approaches shows that the knock-down of HDAC2 or the overexpression of a neuron-specific Endophilin-B1 isoform promotes mitochondrial elongation and protects against cytotoxic stress in hiPSC-Ns, while HDAC2 knock-down specifically influences genes regulating mitochondrial dynamics and synaptogenesis. Furthermore, HDAC2 knock-down promotes enhanced mitochondrial respiration and reduces levels of neurotoxic amyloid beta peptides. Collectively, our study demonstrates a role for HDAC2 in hiPSC-neuronal differentiation, highlights neuron-specific isoforms of Endophilin-B1 as a marker of differentiating hiPSC-Ns and demonstrates that HDAC2 regulates key neuronal and mitochondrial pathways in hiPSC-Ns.