Class IIa HDACs regulate learning and memory through dynamic experience-dependent repression of transcription

Transcription and epigenetic factor dynamics in neuronal activity-dependent gene regulation

Neuronal activity, including sensory-evoked and spontaneous firing, regulates the expression of a subset of genes known as activity-dependent genes. A key issue in this process is the activation and accumulation of transcription factors (TFs), which bind to cis-elements at specific enhancers and promoters, ultimately driving RNA synthesis through transcription machinery. Epigenetic factors such as histone modifiers also play a crucial role in facilitating the specific binding of TFs. Recent evidence from epigenome analyses and imaging studies have revealed intriguing mechanisms: the default chromatin structure at activity-dependent genes is formed independently of neuronal activity, while neuronal activity modulates spatiotemporal dynamics of TFs and their interactions with epigenetic factors (EFs). In this article we review new insights into activity-dependent gene regulation that affects brain development and plasticity.

Activity-dependent synthesis of Emerin gates neuronal plasticity by regulating proteostasis

Neurons dynamically regulate their proteome in response to sensory input, a key process underlying experience-dependent plasticity. We characterized the visual experience-dependent nascent proteome in mice within a brief, defined time window after stimulation using an optimized metabolic labeling approach. Visual experience induced cell-type-specific and age-dependent alterations in the nascent proteome, including proteostasis-related proteins. Emerin is the top activity-induced candidate plasticity protein. Activity-induced neuronal Emerin synthesis is rapid and transcription independent. Emerin broadly inhibits protein synthesis, decreasing translation regulators and synaptic proteins. Decreasing Emerin shifted the dendritic spine population from a predominantly mushroom morphology to filopodia and decreased network connectivity. Blocking visual experience-induced Emerin reduced visually evoked electrophysiological responses and impaired behaviorally assessed visual information processing. Our findings support a proteostatic model in which visual experience-induced Emerin provides a feedforward block on further protein synthesis, refining temporal control of activity-induced plasticity proteins and optimizing visual system function.

A method for HDAC activity screening in postmortem human brain. A proof-of-concept study with antipsychotics

BACKGROUND

Histone deacetylase (HDAC) density and activity are altered in different brain disorders. Antipsychotic drugs (APs) might modulate HDAC activity in brains of schizophrenia subjects.

NEW METHOD

HDAC activity assay amenable for enzyme kinetics and HDAC inhibitor (HDACi) screening studies in postmortem human brain samples.

RESULTS

The optimization and characterization work involved several steps. The nucleosolic subcellular fraction and total protein amount needed for an optimal HDAC activity on Boc-Lys(Ac)-AMC substrate were characterized. Signal-to-noise ratio (1.8) and Z-score values (0.82) were indicators of the assay quality. Inhibition studies with non-selective (belinostat, vorinostat, valproic acid) and selective (apicidin, MS275, romidepsin, tacedinaline and EX527) HDACis showed that the optimized assay detected class I HDAC activity. The obtained IC50 values were similar to those previously reported, proving the assay reliability. We used the optimized assay to study the effect of APs on HDAC activity. Inhibition studies with APs in postmortem human brain, together with enzyme kinetic studies in brains of rats chronically treated with APs observed no modulation of class I HDAC activity.

COMPARISON WITH EXISTING METHODS

This study describes the optimization of a reliable and cost efficient HDAC activity assay for its use in postmortem human brain samples. The assay does not depend on antibody specificity and it is valid for enzyme kinetic studies and for the screening of new potential class I HDACis.

CONCLUSIONS

We optimized and characterized an assay to measure HDAC activity in postmortem human brain samples. We did not observe any modulatory effect of APs on HDAC activity.

Synaptic architecture of a memory engram in the mouse hippocampus

Memory engrams are formed through experience-dependent plasticity of neural circuits, but their detailed architectures remain unresolved. Using three-dimensional electron microscopy, we performed nanoscale reconstructions of the hippocampal CA3-CA1 pathway after chemogenetic labeling of cellular ensembles recruited during associative learning. Neurons with a remote history of activity coinciding with memory acquisition showed no strong preference for wiring with each other. Instead, their connectomes expanded through multisynaptic boutons independently of the coactivation state of postsynaptic partners. The rewiring of ensembles representing an initial engram was accompanied by input-specific, spatially restricted upscaling of individual synapses, as well as remodeling of mitochondria, smooth endoplasmic reticulum, and interactions with astrocytes. Our findings elucidate the physical hallmarks of long-term memory and offer a structural basis for the cellular flexibility of information coding.

HDAC5 controls a hypothalamic STAT5b-TH axis, the sympathetic activation of ATP-consuming futile cycles and adult-onset obesity in male mice

With age, metabolic perturbations accumulate to elevate our obesity burden. While age-onset obesity is mostly driven by a sedentary lifestyle and high calorie intake, genetic and epigenetic factors also play a role. Among these, members of the large histone deacetylase (HDAC) family are of particular importance as key metabolic determinants for healthy ageing, or metabolic dysfunction. Here, we aimed to interrogate the role of class 2 family member HDAC5 in controlling systemic metabolism and age-related obesity under non-obesogenic conditions. Starting at 6 months of age, we observed adult-onset obesity in chow-fed male global HDAC5-KO mice, that was accompanied by marked reductions in adrenergic-stimulated ATP-consuming futile cycles, including BAT activity and UCP1 levels, WAT-lipolysis, skeletal muscle, WAT and liver futile creatine and calcium cycles, and ultimately energy expenditure. Female mice did not differ between genotypes. The lower peripheral sympathetic nervous system (SNS) activity in mature male KO mice was linked to higher dopaminergic neuronal activity within the dorsomedial arcuate nucleus (dmARC) and elevated hypothalamic dopamine levels. Mechanistically, we reveal that hypothalamic HDAC5 acts as co-repressor of STAT5b over the control of Tyrosine hydroxylase (TH) gene transactivation, which ultimately orchestrates the activity of dmARH dopaminergic neurons and energy metabolism in male mice under non-obesogenic conditions.

Activity-dependent transcriptional programs in memory regulate motor recovery after stroke

Stroke causes death of brain tissue leading to long-term deficits. Behavioral evidence from neurorehabilitative therapies suggest learning-induced neuroplasticity can lead to beneficial outcomes. However, molecular and cellular mechanisms that link learning and stroke recovery are unknown. We show that in a mouse model of stroke, which exhibits enhanced recovery of function due to genetic perturbations of learning and memory genes, animals display activity-dependent transcriptional programs that are normally active during formation or storage of new memories. The expression of neuronal activity-dependent genes are predictive of recovery and occupy a molecular latent space unique to motor recovery. With motor recovery, networks of activity-dependent genes are co-expressed with their transcription factor targets forming gene regulatory networks that support activity-dependent transcription, that are normally diminished after stroke. Neuronal activity-dependent changes at the circuit level are influenced by interactions with microglia. At the molecular level, we show that enrichment of activity-dependent programs in neurons lead to transcriptional changes in microglia where they differentially interact to support intercellular signaling pathways for axon guidance, growth and synaptogenesis. Together, these studies identify activity-dependent transcriptional programs as a fundamental mechanism for neural repair post-stroke.

Class 1 histone deacetylases differentially modulate memory and synaptic genes in a spatial and temporal manner in aged and APP/PS1 mice

Epigenetics plays a vital role in aging and Alzheimer's disease (AD); however, whether epigenetic alterations during aging can initiate AD and exacerbate AD progression remains unclear. In this study, using 3-, 12- and 18- month-old APP/PS1 mice and age matched WT littermates, we conducted a series of memory tests, measured synapse-related gene expression, class 1 histone deacetylases (HDACs) abundance, and H3K9ac levels at target gene promoters in the hippocampus and prefrontal cortex (PFC). Our results showed impaired recognition and long-term spatial memory in 18-month-old WT mice and impaired recognition, short-term working, and long-term spatial reference memory in 12-and 18- month-old APP/PS1 mice. These memory impairments are associated with changes of synapse-related gene (nr2a, glur1, glur2, psd95) expression, HDAC abundance, and H3K9ac levels; more specifically, increased HDAC2 was associated with synapse-related gene expression changes through modulation of H3K9ac at the gene promoters during aging and AD progression in the hippocampus. Conversely, increased HDAC3 was associated with synapse-related gene expression changes through modulation of H3K9ac at the gene promoters during AD progression in the PFC. These findings suggest memory impairments in aging and AD may associated with a differential HDAC modulation of synapse-related gene expression in the brain.

Phospholipase C beta 1 in the dentate gyrus gates fear memory formation through regulation of neuronal excitability

Memory processes rely on a molecular signaling system that balances the interplay between positive and negative modulators. Recent research has focused on identifying memory-regulating genes and their mechanisms. Phospholipase C beta 1 (PLCβ1), highly expressed in the hippocampus, reportedly serves as a convergence point for signal transduction through G protein-coupled receptors. However, the detailed role of PLCβ1 in memory function has not been elucidated. Here, we demonstrate that PLCβ1 in the dentate gyrus functions as a memory suppressor. We reveal that mice lacking PLCβ1 in the dentate gyrus exhibit a heightened fear response and impaired memory extinction, and this excessive fear response is repressed by upregulation of PLCβ1 through its overexpression or activation using a newly developed optogenetic system. Last, our results demonstrate that PLCβ1 overexpression partially inhibits exaggerated fear response caused by traumatic experience. Together, PLCβ1 is crucial in regulating contextual fear memory formation and potentially enhancing the resilience to trauma-related conditions.

Activity-dependent synthesis of Emerin gates neuronal plasticity by regulating proteostasis

Neurons dynamically regulate their proteome in response to sensory input, a key process underlying experience-dependent plasticity. We characterized the visual experience-dependent nascent proteome within a brief, defined time window after stimulation using an optimized metabolic labeling approach. Visual experience induced cell type-specific and age-dependent alterations in the nascent proteome, including proteostasis-related processes. We identified Emerin as the top activity-induced candidate plasticity protein and demonstrated that its rapid activity-induced synthesis is transcription-independent. In contrast to its nuclear localization and function in myocytes, activity-induced neuronal Emerin is abundant in the endoplasmic reticulum and broadly inhibits protein synthesis, including translation regulators and synaptic proteins. Downregulating Emerin shifted the dendritic spine population from predominantly mushroom morphology to filopodia and decreased network connectivity. In mice, decreased Emerin reduced visual response magnitude and impaired visual information processing. Our findings support an experience-dependent feed-forward role for Emerin in temporally gating neuronal plasticity by negatively regulating translation.

Nr4a1 regulates cell-specific transcriptional programs in inhibitory GABAergic interneurons

The patterns of synaptic connectivity and physiological properties of diverse neuron types are shaped by distinct gene sets. Our study demonstrates that, in the mouse forebrain, the transcriptional profiles of inhibitory GABAergic interneurons are regulated by Nr4a1, an orphan nuclear receptor whose expression is transiently induced by sensory experiences and is required for normal learning. Nr4a1 exerts contrasting effects on the local axonal wiring of parvalbumin- and somatostatin-positive interneurons, which innervate different subcellular domains of their postsynaptic partners. The loss of Nr4a1 activity in these interneurons results in bidirectional, cell-type-specific transcriptional switches across multiple gene families, including those involved in surface adhesion and repulsion. Our findings reveal that combinatorial synaptic organizing codes are surprisingly flexible and highlight a mechanism by which inducible transcription factors can influence neural circuit structure and function.

Synaptic architecture of a memory engram in the mouse hippocampus

Memory engrams are formed through experience-dependent remodeling of neural circuits, but their detailed architectures have remained unresolved. Using 3D electron microscopy, we performed nanoscale reconstructions of the hippocampal CA3-CA1 pathway following chemogenetic labeling of cellular ensembles with a remote history of correlated excitation during associative learning. Projection neurons involved in memory acquisition expanded their connectomes via multi-synaptic boutons without altering the numbers and spatial arrangements of individual axonal terminals and dendritic spines. This expansion was driven by presynaptic activity elicited by specific negative valence stimuli, regardless of the co-activation state of postsynaptic partners. The rewiring of initial ensembles representing an engram coincided with local, input-specific changes in the shapes and organelle composition of glutamatergic synapses, reflecting their weights and potential for further modifications. Our findings challenge the view that the connectivity among neuronal substrates of memory traces is governed by Hebbian mechanisms, and offer a structural basis for representational drifts.

Interleukin 1β triggers synaptic and memory deficits in Herpes simplex virus type-1-infected mice by downregulating the expression of synaptic plasticity-related genes via the epigenetic MeCP2/HDAC4 complex

Extensive research provides evidence that neuroinflammation underlies numerous brain disorders. However, the molecular mechanisms by which inflammatory mediators determine synaptic and cognitive dysfunction occurring in neurodegenerative diseases (e.g., Alzheimer's disease) are far from being fully understood. Here we investigated the role of interleukin 1β (IL-1β), and the molecular cascade downstream the activation of its receptor, to the synaptic dysfunction occurring in the mouse model of multiple Herpes simplex virus type-1 (HSV-1) reactivations within the brain. These mice are characterized by neuroinflammation and memory deficits associated with a progressive accumulation of neurodegenerative hallmarks (e.g., amyloid-β protein and tau hyperphosphorylation). Here we show that mice undergone two HSV-1 reactivations in the brain exhibited increased levels of IL-1β along with significant alterations of: (1) cognitive performances; (2) hippocampal long-term potentiation; (3) expression synaptic-related genes and pre- and post-synaptic proteins; (4) dendritic spine density and morphology. These effects correlated with activation of the epigenetic repressor MeCP2 that, in association with HDAC4, affected the expression of synaptic plasticity-related genes. Specifically, in response to HSV-1 infection, HDAC4 accumulated in the nucleus and promoted MeCP2 SUMOylation that is a post-translational modification critically affecting the repressive activity of MeCP2. The blockade of IL-1 receptors by the specific antagonist Anakinra prevented the MeCP2 increase and the consequent downregulation of gene expression along with rescuing structural and functional indices of neurodegeneration. Collectively, our findings provide novel mechanistic evidence on the role played by HSV-1-activated IL-1β signaling pathways in synaptic deficits leading to cognitive impairment.

The Epigenetics of Migraine

Migraine is a complex neurological disorder and a major cause of disability. A wide range of different drug classes such as triptans, antidepressants, anticonvulsants, analgesics, and beta-blockers are used in acute and preventive migraine therapy. Despite a considerable progress in the development of novel and targeted therapeutic interventions during recent years, e.g., drugs that inhibit the calcitonin gene-related peptide (CGRP) pathway, therapy success rates are still unsatisfactory. The diversity of drug classes used in migraine therapy partly reflects the limited perception of migraine pathophysiology. Genetics seems to explain only to a minor extent the susceptibility and pathophysiological aspects of migraine. While the role of genetics in migraine has been extensively studied in the past, the interest in studying the role of gene regulatory mechanisms in migraine pathophysiology is recently evolving. A better understanding of the causes and consequences of migraine-associated epigenetic changes could help to better understand migraine risk, pathogenesis, development, course, diagnosis, and prognosis. Additionally, it could be a promising avenue to discover new therapeutic targets for migraine treatment and monitoring. In this review, we summarize the state of the art regarding epigenetic findings in relation to migraine pathogenesis and potential therapeutic targets, with a focus on DNA methylation, histone acetylation, and microRNA-dependent regulation. Several genes and their methylation patterns such as CALCA (migraine symptoms and age of migraine onset), RAMP1, NPTX2, and SH2D5 (migraine chronification) and microRNA molecules such as miR-34a-5p and miR-382-5p (treatment response) seem especially worthy of further study regarding their role in migraine pathogenesis, course, and therapy. Additionally, changes in genes including COMT, GIT2, ZNF234, and SOCS1 have been linked to migraine progression to medication overuse headache (MOH), and several microRNA molecules such as let-7a-5p, let-7b-5p, let-7f-5p, miR-155, miR-126, let-7g, hsa-miR-34a-5p, hsa-miR-375, miR-181a, let-7b, miR-22, and miR-155-5p have been implicated with migraine pathophysiology. Epigenetic changes could be a potential tool for a better understanding of migraine pathophysiology and the identification of new therapeutic possibilities. However, further studies with larger sample sizes are needed to verify these early findings and to be able to establish epigenetic targets as disease predictors or therapeutic targets.

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

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

Low- and high-cocaine intake affects the spatial and temporal dynamics of class IIa HDAC expression-activity in the nucleus accumbens and hippocampus of male rats as measured by [18F]TFAHA PET/CT neuroimaging

Repeated cocaine alters neuronal function in the nucleus accumbens (NAc), a brain region involved in cocaine taking, and in hippocampus (HC), known for contextual and associative learning. [¹⁸F]TFAHA is a histone deacetylase (HDAC) class IIa-specific radiotracer for positron emission tomography (PET)-imaging developed by our group to study epigenetic mechanisms. Here, [¹⁸F]TFAHA was used to conduct PET-imaging coupled with computed tomography (CT) of rat brains at baseline and after repeated cocaine intravenous self-administration (cocaine-IVSA) in low-intake versus high-intake cocaine groups. A 3 h-access FR1-schedule of cocaine-IVSA (0.5 mg/kg/infusion) for 12 continuous days was used with male Sprague Dawley rats following jugular vein catheterization. PET/CT neuroimaging with [¹⁸F]TFAHA was acquired in a dynamic mode over 40 min post-radiotracer administration at baseline and on day 12 of cocaine-IVSA using a longitudinal, repeated design. This study shows that high-cocaine intake significantly decreases class IIa HDAC expression-activity in NAc, while low-cocaine intake significantly decreases expression-activity in HC in male rats. These findings suggest the individual rats with low-cocaine intake had epigenetic changes in HC, where drug-associative changes occur. Alternatively, individuals with high-cocaine intake had robust epigenetic changes in NAc, where rewared-related behaviors originate. These findings are the first longitudinal data obtained in vivo to implicate class IIa HDACs in the persistent behavioral effects of cocaine. Furthermore, our results are consistent with published research implicating class IIa HDACs in cocaine-induced brain changes and studies suggesting a relationship between an individual's drug-taking behavior and regional pattern of epigenetic changes in the brain.

Activity-Induced Cortical Glutamatergic Neuron Nascent Proteins

Neuronal activity initiates signaling cascades that culminate in diverse outcomes including structural and functional neuronal plasticity, and metabolic changes. While studies have revealed activity-dependent neuronal cell type-specific transcriptional changes, unbiased quantitative analysis of cell-specific activity-induced dynamics in newly synthesized proteins (NSPs) synthesis in vivo has been complicated by cellular heterogeneity and a relatively low abundance of NSPs within the proteome in the brain. Here we combined targeted expression of mutant MetRS (methionine tRNA synthetase) in genetically defined cortical glutamatergic neurons with tight temporal control of treatment with the noncanonical amino acid, azidonorleucine, to biotinylate NSPs within a short period after pharmacologically induced seizure in male and female mice. By purifying peptides tagged with heavy or light biotin-alkynes and using direct tandem mass spectrometry detection of biotinylated peptides, we quantified activity-induced changes in cortical glutamatergic neuron NSPs. Seizure triggered significant changes in ∼300 NSPs, 33% of which were decreased by seizure. Proteins mediating excitatory and inhibitory synaptic plasticity, including SynGAP1, Pak3, GEPH1, Copine-6, and collybistin, and DNA and chromatin remodeling proteins, including Rad21, Smarca2, and Ddb1, are differentially synthesized in response to activity. Proteins likely to play homeostatic roles in response to activity, such as regulators of proteastasis, intracellular ion control, and cytoskeleton remodeling proteins, are activity induced. Conversely, seizure decreased newly synthetized NCAM, among others, suggesting that seizure induced degradation. Overall, we identified quantitative changes in the activity-induced nascent proteome from genetically defined cortical glutamatergic neurons as a strategy to discover downstream mediators of neuronal plasticity and generate hypotheses regarding their function.SIGNIFICANCE STATEMENT Activity-induced neuronal and synaptic plasticity are mediated by changes in the protein landscape, including changes in the activity-induced newly synthesized proteins; however, identifying neuronal cell type-specific nascent proteome dynamics in the intact brain has been technically challenging. We conducted an unbiased proteomic screen from which we identified significant activity-induced changes in ∼300 newly synthesized proteins in genetically defined cortical glutamatergic neurons within 20 h after pharmacologically induced seizure. Bioinformatic analysis of the dynamic nascent proteome indicates that the newly synthesized proteins play diverse roles in excitatory and inhibitory synaptic plasticity, chromatin remodeling, homeostatic mechanisms, and proteasomal and metabolic functions, extending our understanding of the diversity of plasticity mechanisms.

Norepinephrine, beyond the Synapse: Coordinating Epigenetic Codes for Memory

The noradrenergic system is implicated in neuropathologies contributing to major disorders of the memory, including post-traumatic stress disorder and Alzheimer’s disease. Determining the impact of norepinephrine on cellular function and plasticity is thus essential for making inroads into our understanding of these brain conditions, while expanding our capacity for treating them. Norepinephrine is a neuromodulator within the mammalian central nervous system which plays important roles in cognition and associated synaptic plasticity. Specifically, norepinephrine regulates the formation of memory through the stimulation of β-ARs, increasing the dynamic range of synaptic modifiability. The mechanisms through which NE influences neural circuit function have been extended to the level of the epigenome. This review focuses on recent insights into how the noradrenergic recruitment of epigenetic modifications, including DNA methylation and post-translational modification of histones, contribute to homo- and heterosynaptic plasticity. These advances will be placed in the context of synaptic changes associated with memory formation and linked to brain disorders and neurotherapeutic applications.

Role of Epigenetic Mechanisms in Chronic Pain

Pain is an unpleasant but essential-to-life sensation, usually resulting from tissue damage. When pain persists long after the injury has resolved, it becomes pathological. The precise molecular and cellular mechanisms causing the transition from acute to chronic pain are not fully understood. A key aspect of pain chronicity is that several plasticity events happen along the neural pathways involved in pain. These long-lasting adaptive changes are enabled by alteration in the expression of relevant genes. Among the different modulators of gene transcription in adaptive processes in the nervous system, epigenetic mechanisms play a pivotal role. In this review, I will first outline the main classes of epigenetic mediators and then discuss their implications in chronic pain.

HDAC4 Inhibitors as Antivascular Senescence Therapeutics

Aging is an inevitable consequence of life, and during this process, the epigenetic landscape changes and reactive oxygen species (ROS) accumulation increases. Inevitably, these changes are common in many age-related diseases, including neurodegeneration, hypertension, and cardiovascular diseases. In the current research, histone deacetylation 4 (HDAC4) was studied as a potential therapeutic target in vascular senescence. HDAC4 is a specific class II histone deacetylation protein that participates in epigenetic modifications and deacetylation of heat shock proteins and various transcription factors. There is increasing evidence to support that HDAC4 is a potential therapeutic target, and developments in the synthesis and testing of HDAC4 inhibitors are now gaining interest from academia and the pharmaceutical industry.

ADRAM is an experience-dependent long noncoding RNA that drives fear extinction through a direct interaction with the chaperone protein 14-3-3

Here, we used RNA capture-seq to identify a large population of lncRNAs that are expressed in the infralimbic prefrontal cortex of adult male mice in response to fear-related learning. Combining these data with cell-type-specific ATAC-seq on neurons that had been selectively activated by fear extinction learning, we find inducible 434 lncRNAs that are derived from enhancer regions in the vicinity of protein-coding genes. In particular, we discover an experience-induced lncRNA we call ADRAM (activity-dependent lncRNA associated with memory) that acts as both a scaffold and a combinatorial guide to recruit the brain-enriched chaperone protein 14-3-3 to the promoter of the memory-associated immediate-early gene Nr4a2 and is required fear extinction memory. This study expands the lexicon of experience-dependent lncRNA activity in the brain and highlights enhancer-derived RNAs (eRNAs) as key players in the epigenomic regulation of gene expression associated with the formation of fear extinction memory.

Emerging Role of HDACs in Regeneration and Ageing in the Peripheral Nervous System: Repair Schwann Cells as Pivotal Targets

The peripheral nervous system (PNS) has a remarkable regenerative capacity in comparison to the central nervous system (CNS), a phenomenon that is impaired during ageing. The ability of PNS axons to regenerate after injury is due to Schwann cells (SC) being reprogrammed into a repair phenotype called Repair Schwann cells. These repair SCs are crucial for supporting axonal growth after injury, myelin degradation in a process known as myelinophagy, neurotropic factor secretion, and axonal growth guidance through the formation of Büngner bands. After regeneration, repair SCs can remyelinate newly regenerated axons and support nonmyelinated axons. Increasing evidence points to an epigenetic component in the regulation of repair SC gene expression changes, which is necessary for SC reprogramming and regeneration. One of these epigenetic regulations is histone acetylation by histone acetyl transferases (HATs) or histone deacetylation by histone deacetylases (HDACs). In this review, we have focused particularly on three HDAC classes (I, II, and IV) that are Zn²⁺-dependent deacetylases. These HDACs are important in repair SC biology and remyelination after PNS injury. Another key aspect explored in this review is HDAC genetic compensation in SCs and novel HDAC inhibitors that are being studied to improve nerve regeneration.

Organic anion transporter 1 is an HDAC4-regulated mediator of nociceptive hypersensitivity in mice

Persistent pain is sustained by maladaptive changes in gene transcription resulting in altered function of the relevant circuits; therapies are still unsatisfactory. The epigenetic mechanisms and affected genes linking nociceptive activity to transcriptional changes and pathological sensitivity are unclear. Here, we found that, among several histone deacetylases (HDACs), synaptic activity specifically affects HDAC4 in murine spinal cord dorsal horn neurons. Noxious stimuli that induce long-lasting inflammatory hypersensitivity cause nuclear export and inactivation of HDAC4. The development of inflammation-associated mechanical hypersensitivity, but neither acute nor basal sensitivity, is impaired by the expression of a constitutively nuclear localized HDAC4 mutant. Next generation RNA-sequencing revealed an HDAC4-regulated gene program comprising mediators of sensitization including the organic anion transporter OAT1, known for its renal transport function. Using pharmacological and molecular tools to modulate OAT1 activity or expression, we causally link OAT1 to persistent inflammatory hypersensitivity in mice. Thus, HDAC4 is a key epigenetic regulator that translates nociceptive activity into sensitization by regulating OAT1, which is a potential target for pain-relieving therapies.

Chronic pain is sustained by alterations in gene transcription. Here, the authors show that increased expression of Organic Anionic Transporter 1 in the spinal cord is epigenetically controlled and key to hypersensitivity in pathological pain.

Unlocking the Memory Component of Alzheimer’s Disease:Biological Processes and Pathways across Brain Regions

Alzheimer’s Disease (AD) is a neurodegenerative disorder characterized by a progressive loss of memory and a general cognitive decline leading to dementia. AD is characterized by changes in the behavior of the genome and can be traced across multiple brain regions and cell types. It is mainly associated with β-amyloid deposits and tau protein misfolding, leading to neurofibrillary tangles. In recent years, however, research has shown that there is a high complexity of mechanisms involved in AD neurophysiology and functional decline enabling its diverse presentation and allowing more questions to arise. In this study, we present a computational approach to facilitate brain region-specific analysis of genes and biological processes involved in the memory process in AD. Utilizing current genetic knowledge we provide a gene set of 265 memory-associated genes in AD, combinations of which can be found co-expressed in 11 different brain regions along with their functional role. The identified genes participate in a spectrum of biological processes ranging from structural and neuronal communication to epigenetic alterations and immune system responses. These findings provide new insights into the molecular background of AD and can be used to bridge the genotype–phenotype gap and allow for new therapeutic hypotheses.

Designing HDAC-PROTACs: lessons learned so far

Proteolysis-targeting chimeras (PROTACs) are a powerful tool to hijack the endogenous ubiquitin-proteasome system (UPS) and to degrade the intracellular proteins of therapeutic importance. Recently, two heterobifunctional degraders targeting hormone receptors headed into Phase II clinical trials. Compared to traditional drug design and common modes of action, the PROTAC approach offers new opportunities for the drug research field. Histone deacetylase inhibitors (HDACi) are well-established drugs for the treatment of hematological malignancies. The integration of HDAC binding motifs in PROTACs explores the possibility of targeted, chemical HDAC degradation. This review provides an overview and a perspective about the key steps in the structure development of HDAC-PROTACs. In particular, the influence of the three canonical PROTAC elements on HDAC-PROTAC efficacy and selectivity are discussed, the HDACi, the linker and the E3 ligase ligand.

Combining histone deacetylase inhibitors (HDACis) with other therapies for cancer therapy

Histone deacetylases (HDACs) play an important role in regulating the expression of genes involved in tumorigenesis and tumor maintenance, and hence they have been considered as key targets in cancer therapy. As a novel category of antitumor agents, histone deacetylase inhibitors (HDACis) can induce cell cycle arrest, apoptosis, and differentiation in cancer cells, ultimately combating cancer. Although in the United States, the use of HDACis for the treatment of certain cancers has been approved, the therapeutic efficacy of HDACis as a single therapeutic agent in solid tumorshas been unsatisfactory and drug resistance may yet occur. To enhance therapeutic efficacy and limit drug resistance, numerous combination therapies involving HDACis in synergy with other antitumor therapies have been studied. In this review, we describe the classification of HDACs. Moreover, we summarize the antitumor mechanism of the HDACis for targeting key cellular processes of cancers (cell cycle, apoptosis, angiogenesis, DNA repair, and immune response). In addition, we outline the major developments of other antitumor therapies in combination with HDACis, including chemotherapy, radiotherapy, phototherapy, targeted therapy, and immunotherapy. Finally, we discuss the current state and challenges of HDACis-drugs combinations in future clinical studies, with the aim of optimizing the antitumor effect of such combinations.

Histone Deacetylases and Immediate Early Genes: Key Players in Psychostimulant-Induced Neuronal Plasticity

IEGs play a critical functional role of in molecular, cellular, and behavioral alterations induced by psychostimulants. IEGs appear to have specific chromatin structures that may contribute to the rapid activation of their transcription. HDAC enzymes regulate reversible acetylation of lysine residues of histones and non-histone proteins. Dysregulation of HDACs has been proposed to modulate the establishment and maintenance of aberrant transcriptional programs and behaviors associated with cognitive dysfunctions and drug addiction. In this mini-review we focus our attention on recent discoveries concerning networks of protein-protein interactions for the two classes of HDAC protein family members that are highly expressed in neurons, class I and IIa HDACs. Because dynamic histone acetylation appears to be critical to IEG expression in the brain, we discuss the role of these epigenetic regulators on IEG expression induced by cocaine and methamphetamine intake.

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.

A schizophrenia risk factor induces marked anatomical deficits at GABAergic-dopaminergic synapses in the rat ventral tegmental area: Essential evidence for new targeted therapies

To develop new therapies for schizophrenia, evidence accumulated over decades highlights the essential need to investigate the GABAergic synapses that presynaptically influence midbrain dopaminergic neurons. Since current technology restricts these studies to animals, and evidence accumulated in recent decades indicates a developmental origin of schizophrenia, we investigated synaptic changes in male rat offspring exposed to maternal immune activation (MIA), a schizophrenia risk factor. Using a novel combination of lentiviruses, peroxidase-immunogold double labeling, three-dimensional serial section transmission electron microscopy and stereology, we observed clear anatomical alterations in synaptic inputs on dopaminergic neurons in the midbrain posterior ventral tegmental area (pVTA). These changes relate directly to a characteristic feature of schizophrenia: increased dopamine release. In 3-month-old and 14-month-old MIA rats, we found a marked decrease in the volume of presynaptic GABAergic terminals from the rostromedial tegmental nucleus (RMTg) and in the length of the synapses they made, when innervating pVTA dopaminergic neurons. In MIA rats in the long-term, we also discovered a decrease in the volume of the postsynaptic density (PSD) and in the maximum thickness of the PSD at the same synapses. These marked deficits were evident in conventional GABA-dopamine synapses and in synaptic triads that we discovered involving asymmetric synapses that innervated RMTg GABAergic presynaptic terminals, which in turn innervated pVTA dopaminergic neurons. In triads, the PSD thickness of asymmetric synapses was significantly decreased in MIA rats in the long-term cohort. The extensive anatomical deficits provide a potential basis for new therapies targeted at synaptic inputs on midbrain pVTA dopaminergic neurons, in contrast to current striatum-targeted antipsychotic drugs.

Psychostimulants and opioids differentially influence the epigenetic modification of histone acetyltransferase and histone deacetylase in astrocytes

Illicit drugs are known to affect central nervous system (CNS). Majorly psychostimulants such as cocaine, methamphetamine (METH) and opioids such as morphine are known to induce epigenetic changes of histone modifications and chromatin remodeling which are mediated by histone acetyltransferase (HAT) and histone deacetylase (HDAC). Aberrant changes in histone acetylation-deacetylation process further exacerbate dysregulation of gene expression and protein modification which has been linked with neuronal impairments including memory formation and synaptic plasticity. In CNS, astrocytes play a pivotal role in cellular homeostasis. However, the impact of psychostimulants and opioid mediated epigenetic changes of HAT/HADCs in astrocytes has not yet been fully elucidated. Therefore, we have investigated the effects of the psychostimulants and opioid on the acetylation-regulating enzymes- HAT and HDACs role in astrocytes. In this study, Class I and II HDACs and HATs gene expression, protein changes and global level changes of acetylation of H3 histones at specific lysines were analyzed. In addition, we have explored the neuroprotective “nootropic” drug piracetam were exposed with or without psychostimulants and opioid in the human primary astrocytes. Results revealed that psychostimulants and opioid upregulated HDAC1, HDAC4 and p300 expression, while HDAC5 and GCN5 expression were downregulated. These effects were reversed by piracetam coexposure. Psychostimulants and opioid exposure upregulated global acetylation levels of all H3Ks, except H3K14. These results suggest that psychostimulants and opioids differentially influence HATs and HDACs.

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

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

Medulloblastoma recurrence and metastatic spread are independent of colony-stimulating factor 1 receptor signaling and macrophage survival

PURPOSE

Tumor infiltration by immunosuppressive myeloid cells or tumor-associated macrophages (TAMs) contributes to tumor progression and metastasis. In contrast to their adult counterparts, higher TAM signatures do not correlate with aggressive tumor behavior in pediatric brain tumors. While prominent TAM infiltrates exist before and after radiation, the degree to which irradiated macrophages and microglia support progression or leptomeningeal metastasis remains unclear. Patients with medulloblastoma often present with distant metastases and tumor recurrence is largely incurable, making them prime candidates for the study of novel approaches to prevent neuroaxis dissemination and recurrence.

METHODS

Macrophage depletion was achieved using CSF-1 receptor inhibitors (CSF-1Ri), BLZ945 and AFS98, with or without whole brain radiation in a variety of medulloblastoma models, including patient-derived xenografts bearing Group 3 medulloblastoma and a transgenic Sonic Hedgehog (Ptch1^+/-, Trp53^-/-) medulloblastoma model.

RESULTS

Effective reduction of microglia, TAM, and spinal cord macrophage with CSF-1Ri resulted in negligible effects on the rate of local and spinal recurrences or survival following radiation. Results were comparable between medulloblastoma subgroups. While notably few tumor-infiltrating lymphocytes (TILs) were detected, average numbers of CD3+ TILs and FoxP3+ Tregs did not differ between groups following treatment and tumor aggressiveness by Ki67 proliferation index was unaltered.

CONCLUSION

In the absence of other microenvironmental influences, medulloblastoma-educated macrophages do not operate as tumor-supportive cells or promote leptomeningeal recurrence in these models. Our data add to a growing body of literature describing a distinct immunophenotype amid the medulloblastoma microenvironment and highlight the importance of appropriate pediatric modeling prior to clinical translation.

The role of nuclear Ca2+ in maintaining neuronal homeostasis and brain health

Nuclear Ca2+ has emerged as one of the most potent mediators of the dialogue between neuronal synapses and the nucleus that regulates heterochromatin states, transcription factor activity, nuclear morphology and neuronal gene expression induced by synaptic activity. Recent studies underline the importance of nuclear Ca2+ signaling in long-lasting, activity-induced adaptation and maintenance of proper brain function. Diverse forms of neuroadaptation require transient nuclear Ca2+ signaling and cyclic AMP-responsive element-binding protein (CREB1, referred to here as CREB) as its prime target, which works as a tunable switch to drive and modulate specific gene expression profiles associated with memory, pain, addiction and neuroprotection. Furthermore, a reduction of nuclear Ca2+ levels has been shown to be neurotoxic and a causal factor driving the progression of neurodegenerative disorders, as well as affecting neuronal autophagy. Because of its central role in the brain, deficits in nuclear Ca2+ signaling may underlie a continuous loss of neuroprotection in the aging brain, contributing to the pathophysiology of Alzheimer's disease. In this Review, we discuss the principles of the 'nuclear calcium hypothesis' in the context of human brain function and its role in controlling diverse forms of neuroadaptation and neuroprotection. Furthermore, we present the most relevant and promising perspectives for future studies.

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

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

Role of histone deacetylases in bone development and skeletal disorders

Bone cells must constantly respond to hormonal and mechanical cues to change gene expression programs. Of the myriad of epigenomic mechanisms used by cells to dynamically alter cell type-specific gene expression, histone acetylation and deacetylation has received intense focus over the past two decades. Histone deacetylases (HDACs) represent a large family of proteins with a conserved deacetylase domain first described to deacetylate lysine residues on histone tails. It is now appreciated that multiple classes of HDACs exist, some of which are clearly misnamed in that acetylated lysine residues on histone tails is not the major function of their deacetylase domain. Here, we will review the roles of proteins bearing deacetylase domains in bone cells, focusing on current genetic evidence for each individual HDAC gene. While class I HDACs are nuclear proteins whose primary role is to deacetylate histones, class IIa and class III HDACs serve other important cellular functions. Detailed knowledge of the roles of individual HDACs in bone development and remodeling will set the stage for future efforts to specifically target individual HDAC family members in the treatment of skeletal diseases such as osteoporosis.

Experience-regulated molecular mechanisms in cortical GABAergic interneurons: from cellular functions to control over circuit plasticity

Experience-induced changes in GABAergic interneurons (INs) are thought to control the plasticity of neural circuits in the developing and adult cortex. However, it remains poorly understood how experience and the ensuing neuronal activity alter the properties and connectivity of specific IN subtypes and how these cellular changes, in turn, control the plasticity of cortical circuits. Here, I discuss recent experimental and theoretical studies that point to specific experience-induced changes in select IN subtypes as central regulators of plasticity in the cortex. In particular, I focus on the recent identification of several experience-regulated secreted molecules that modulate specific sets of synapses in IN subtypes. I argue that elucidating these molecular mechanisms will allow us to test experimentally the predictions made by theoretical models about the plasticity functions of specific IN subtypes.

Epigenetic Regulation as a Basis for Long-Term Changes in the Nervous System: In Search of Specificity Mechanisms

Abstract

Adaptive long-term changes in the functioning of nervous system (plasticity, memory) are not written in the genome, but are directly associated with the changes in expression of many genes comprising epigenetic regulation. Summarizing the known data regarding the role of epigenetics in regulation of plasticity and memory, we would like to highlight several key aspects. (i) Different chromatin remodeling complexes and DNA methyltransferases can be organized into high-order multiprotein repressor complexes that are cooperatively acting as the “molecular brake pads”, selectively restricting transcriptional activity of specific genes at rest. (ii) Relevant physiological stimuli induce a cascade of biochemical events in the activated neurons resulting in translocation of different signaling molecules (protein kinases, NO-containing complexes) to the nucleus. (iii) Stimulus-specific nitrosylation and phosphorylation of different epigenetic factors is linked to a decrease in their enzymatic activity or changes in intracellular localization that results in temporary destabilization of the repressor complexes. (iv) Removing “molecular brakes” opens a “critical time window” for global and local epigenetic changes, triggering specific transcriptional programs and modulation of synaptic connections efficiency. It can be assumed that the reversible post-translational histone modifications serve as the basis of plastic changes in the neural network. On the other hand, DNA methylation and methylation-dependent 3D chromatin organization can serve a stable molecular basis for long-term maintenance of plastic changes and memory.

Environmental Stimulation Counteracts the Suppressive Effects of Maternal High-Fructose Diet on Cell Proliferation and Neuronal Differentiation in the Dentate Gyrus of Adult Female Offspring via Histone Deacetylase 4

Maternal high-fructose diets (HFD) impair the learning and memory capacity of adult female offspring via histone deacetylase 4 (HDAC4). Hippocampal adult neurogenesis is important for supporting the function of existing neural circuits. In this study, we investigated the effects of maternal HFD on hippocampal neural stem cell (NSC) proliferation and neuronal differentiation in adult offspring. Increased nuclear HDAC4 enzyme activity was detected in the hippocampus of HFD female offspring. The Western blot analyses indicated that the expressions of sex-determining region Y box2 (SOX2) and the transcription factor Paired Box 6 (PAX6), which are critical for the progression of NSC proliferation and differentiation, were downregulated. Concurrently, the expression of Ki67 (a cellular marker for proliferation) and doublecortin (DCX), which are related to NSC division and neuronal differentiation, was suppressed. Intracerebroventricular infusion with class II HDAC inhibitor (Mc1568, 4 weeks) led to the upregulation of these proteins. Environmental stimulation reversed the expression of Ki67 and DCX and the counts of Ki67- and DCX-positive cells in the hippocampi of HFD offspring as a result of providing the enriched housing for 4 weeks. Together, these results demonstrate that the suppressive effects of maternal HFD on hippocampal NSC proliferation and neuronal differentiation are reversibly mediated through HDAC4 and can be effectively reversed by environmental stimulation. The advantageous effects of environmental enrichment were possibly mediated by HDAC4 suppression.

Mechanisms that communicate features of neuronal activity to the genome

Stimulus-driven gene expression is a ubiquitous feature of biological systems, allowing cells and organisms to adapt their function in a stimulus-driven manner. Neurons exhibit complex and heterogeneous activity-dependent gene expression, but many of the canonical mechanisms that transduce electrical activity into gene regulation are promiscuous and convergent. We discuss literature that describes mechanisms that drive activity-dependent gene expression with a focus on those that allow the nucleus to decode complex stimulus-features into appropriate transcriptional programs.

Recent developments in transcriptional and translational regulation underlying long-term synaptic plasticity and memory

Formation of long-term synaptic plasticity that underlies long-term memory requires new protein synthesis. Years of research has elucidated some of the transcriptional and translational mechanisms that contribute to the production of new proteins. Early research on transcription focused on the transcription factor cAMP-responsive element binding protein. Since then, other transcription factors, such as the Nuclear Receptor 4 family of proteins that play a role in memory formation and maintenance have been identified. In addition, several studies have revealed details of epigenetic mechanisms consisting of new types of chemical alterations of DNA such as hydroxymethylation, and various histone modifications in long-term synaptic plasticity and memory. Our understanding of translational control critical for memory formation began with the identification of molecules that impinge on the 5′ and 3′ untranslated regions of mRNAs and continued with the appreciation for local translation near synaptic sites. Lately, a role for noncoding RNAs such as microRNAs in regulating translation factors and other molecules critical for memory has been found. This review describes the past research in brief and mainly focuses on the recent work on molecular mechanisms of transcriptional and translational regulation that form the underpinnings of long-term synaptic plasticity and memory.