Hippocampal focal knockout of CBP affects specific histone modifications, long-term potentiation, and long-term memory

The Lysine Acetyltransferase PCAF Functionally Interacts with Estrogen Receptor Alpha in the Hippocampus of Gonadally Intact Male-But Not Female-Rats to Enhance Short-Term Memory

Acetylation of histone proteins by histone acetyltransferases (HATs), and the resultant change in gene expression, is a well-established mechanism necessary for long-term memory (LTM) consolidation, which is not required for short-term memory (STM). However, we previously demonstrated that the HAT p300/CBP-associated factor (PCAF) also influences hippocampus (HPC)-dependent STM in male rats. In addition to their epigenetic activity, HATs acetylate nonhistone proteins involved in nongenomic cellular processes, such as estrogen receptors (ERs). Given that ERs have rapid, nongenomic effects on HPC-dependent STM, we investigated the potential interaction between ERs and PCAF for STM mediated by the dorsal hippocampus (dHPC). Using a series of pharmacological agents administered directly into the dHPC, we reveal a functional interaction between PCAF and ERα in the facilitation of short-term object-in-place memory in male but not female rats. This interaction was specific to ERα, while ERβ agonism did not enhance STM. It was further specific to dHPC STM, as the effect was not present in the dHPC for LTM or in the perirhinal cortex. Further, while STM required local (i.e., dHPC) estrogen synthesis, the facilitatory interaction effect appeared independent of estrogens. Finally, western blot analyses demonstrated that PCAF activation in the dHPC rapidly (5 min) activated downstream estrogen-related cell signaling kinases (c-Jun N-terminal kinase and extracellular signal-related kinase). Collectively, these findings indicate that PCAF, which is typically implicated in LTM through epigenetic processes, also influences STM in the dHPC, possibly via nongenomic ER activity. Critically, this novel PCAF-ER interaction might exist as a male-specific mechanism supporting STM.

Exercise epigenetics is fueled by cell bioenergetics: Supporting role on brain plasticity and cognition

Exercise has the unique aptitude to benefit overall health of body and brain. Evidence indicates that the effects of exercise can be saved in the epigenome for considerable time to elevate the threshold for various diseases. The action of exercise on epigenetic regulation seems central to building an "epigenetic memory" to influence long-term brain function and behavior. As an intrinsic bioenergetic process, exercise engages the function of the mitochondria and redox pathways to impinge upon molecular mechanisms that regulate synaptic plasticity and learning and memory. We discuss how the action of exercise uses mechanisms of bioenergetics to support a "epigenetic memory" with long-term implications for neural and behavioral plasticity. This information is crucial for directing the power of exercise to reduce the burden of neurological and psychiatric disorders.

The Role of Histone H2B Acetylation Modification in Aluminum-Induced Cognitive Dysfunction

Aluminum (Al) is a low toxic trace element that can accumulate in the nervous system and induce cognitive disorders characterized by reduced learning and memory ability. Neuroepigenetic effects are structural changes in cellular function by the brain in response to environmental stimuli by altering the expression of specific genes and repressing normal cellular transcription, leading to abnormalities in a variety of biological processes within the nervous system and affecting neurobehavioral responses. One of the most important mechanisms of epigenetic control on chromatin shape is histone modification. In the present study, we established an offspring rat model of Al intoxication to investigate the changes in spatial learning and memory retention abilities and the relationship with histone H2B acetylation modification in rats exposed to different doses of Al over a long period of time. The results demonstrated that long-term AlCl3 staining resulted in decreased CBP gene and protein expression, increased HDAC3 gene and protein levels, as well as decreased histone H2B and acH2BK20 protein expression levels in the hippocampus of rats. In conclusion, long-term exposure to Al may vary the expression of histone H2B and acH2BK20 through the regulation of enzymes that specifically regulate histone acetylation, hence hastening the deterioration of the nervous system that impairs cognitive function.

Contributions of site- and sex-specific LTPs to everyday memory

Commentaries about long-term potentiation (LTP) generally proceed with an implicit assumption that largely the same physiological effect is sampled across different experiments. However, this is clearly not the case. We illustrate the point by comparing LTP in the CA3 projections to CA1 with the different forms of potentiation in the dentate gyrus. These studies lead to the hypothesis that specialized properties of CA1-LTP are adaptations for encoding unsupervised learning and episodic memory, whereas the dentate gyrus variants subserve learning that requires multiple trials and separation of overlapping bodies of information. Recent work has added sex as a second and somewhat surprising dimension along which LTP is also differentiated. Triggering events for CA1-LTP differ between the sexes and the adult induction threshold is significantly higher in females; these findings help explain why males have an advantage in spatial learning. Remarkably, the converse is true before puberty: Females have the lower LTP threshold and are better at spatial memory problems. A mechanism has been identified for the loss-of-function in females but not for the gain-of-function in males. We propose that the many and disparate demands of natural environments, with different processing requirements across ages and between sexes, led to the emergence of multiple LTPs. This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.

The Intellectual Disability Risk Gene Kdm5b Regulates Long-Term Memory Consolidation in the Hippocampus

The histone lysine demethylase KDM5B is implicated in recessive intellectual disability disorders, and heterozygous, protein-truncating variants in KDM5B are associated with reduced cognitive function in the population. The KDM5 family of lysine demethylases has developmental and homeostatic functions in the brain, some of which appear to be independent of lysine demethylase activity. To determine the functions of KDM5B in hippocampus-dependent learning and memory, we first studied male and female mice homozygous for a Kdm5b Δ ARID allele that lacks demethylase activity. Kdm5b Δ ARID/ Δ ARID mice exhibited hyperactivity and long-term memory deficits in hippocampus-dependent learning tasks. The expression of immediate early, activity-dependent genes was downregulated in these mice and hyperactivated upon a learning stimulus compared with wild-type (WT) mice. A number of other learning-associated genes were also significantly dysregulated in the Kdm5b Δ ARID/ Δ ARID hippocampus. Next, we knocked down Kdm5b specifically in the adult, WT mouse hippocampus with shRNA. Kdm5b knockdown resulted in spontaneous seizures, hyperactivity, and hippocampus-dependent long-term memory and long-term potentiation deficits. These findings identify KDM5B as a critical regulator of gene expression and synaptic plasticity in the adult hippocampus and suggest that at least some of the cognitive phenotypes associated with KDM5B gene variants are caused by direct effects on memory consolidation mechanisms.

Specific exercise patterns generate an epigenetic molecular memory window that drives long-term memory formation and identifies ACVR1C as a bidirectional regulator of memory in mice

Exercise has beneficial effects on cognition throughout the lifespan. Here, we demonstrate that specific exercise patterns transform insufficient, subthreshold training into long-term memory in mice. Our findings reveal a potential molecular memory window such that subthreshold training within this window enables long-term memory formation. We performed RNA-seq on dorsal hippocampus and identify genes whose expression correlate with conditions in which exercise enables long-term memory formation. Among these genes we found Acvr1c, a member of the TGF ß family. We find that exercise, in any amount, alleviates epigenetic repression at the Acvr1c promoter during consolidation. Additionally, we find that ACVR1C can bidirectionally regulate synaptic plasticity and long-term memory in mice. Furthermore, Acvr1c expression is impaired in the aging human and mouse brain, as well as in the 5xFAD mouse model, and over-expression of Acvr1c enables learning and facilitates plasticity in mice. These data suggest that promoting ACVR1C may protect against cognitive impairment.

Transcriptional Expression of Histone Acetyltransferases and Deacetylases During the Recovery of Acute Exercise in Mouse Hippocampus

Protein acetylation, which is dynamically maintained by histone acetyltransferases (HATs) and deacetylases (HDACs), might play essential roles in hippocampal exercise physiology. However, whether HATs/HDACs are imbalanced during the recovery phase following acute exercise has not been determined. Groups of exercised mice with different recovery periods after acute exercise (0 h, 0.5 h, 1 h, 4 h, 7 h, and 24 h) were constructed, and a group of sham-exercised mice was used as the control. The mRNA levels of HATs and HDACs were detected via real-time quantitative polymerase chain reaction. Lysine acetylation on the total proteins and some specific locations on histones were detected via western blotting, as were various acylation modifications on the total proteins. Except for four unaffected genes (Hdac4, Ncoa1, Ncoa2, and Sirt1), the mRNA expression trajectories of 21 other HATs or HDACs affected by exercise could be categorized into three clusters. The genes in Cluster 1 increased quickly following exercise, with a peak at 0.5 h and/or 1 h, and remained at high levels until 24 h. Cluster 2 genes presented a gradual increase with a delayed peak at 4 h or 7 h postexercise before returning to baseline. The expression of Cluster 3 genes decreased at 0.5 h and/or 1 h, with some returning to overexpression (Hdac1 and Sirt3). Although most HATs were upregulated and half of the affected HDACs were downregulated at 0.5 h postexercise, the global or residue-specific histone acetylation levels were unchanged. In contrast, the levels of several metabolism-related acylation products of total proteins, including acetylation, succinylation, 2-hydroxyisobutyryllysine, β-hydroxybutyryllysine, and lactylation, decreased and mainly occurred on nonhistones immediately after exercise. During the 24-h recovery phase after acute exercise, the transcriptional trajectory of HATs or the same class of HDACs in the hippocampus exhibited heterogeneity. Although acute exercise did not affect the selected sites on histone lysine residues, it possibly incurred changes in acetylation and other acylation on nonhistone proteins.

Inhibition of Cpeb3 ribozyme elevates CPEB3 protein expression and polyadenylation of its target mRNAs and enhances object location memory

A self-cleaving ribozyme that maps to an intron of the cytoplasmic polyadenylation element-binding protein 3 (Cpeb3) gene is thought to play a role in human episodic memory, but the underlying mechanisms mediating this effect are not known. We tested the activity of the murine sequence and found that the ribozyme's self-scission half-life matches the time it takes an RNA polymerase to reach the immediate downstream exon, suggesting that the ribozyme-dependent intron cleavage is tuned to co-transcriptional splicing of the Cpeb3 mRNA. Our studies also reveal that the murine ribozyme modulates maturation of its harboring mRNA in both cultured cortical neurons and the hippocampus: inhibition of the ribozyme using an antisense oligonucleotide leads to increased CPEB3 protein expression, which enhances polyadenylation and translation of localized plasticity-related target mRNAs, and subsequently strengthens hippocampal-dependent long-term memory. These findings reveal a previously unknown role for self-cleaving ribozyme activity in regulating experience-induced co-transcriptional and local translational processes required for learning and memory.

Epigenetics of Fear, Anxiety and Stress - Focus on Histone Modifications

Fear-, anxiety- and stress-related disorders are among the most frequent mental disorders. Given substantial rates of insufficient treatment response and often a chronic course, a better understanding of the pathomechanisms of fear-, anxiety- and stress-related disorders is urgently warranted. Epigenetic mechanisms such as histone modifications - positioned at the interface between the biological and the environmental level in the complex pathogenesis of mental disorders - might be highly informative in this context. The current state of knowledge on histone modifications, chromatin-related pharmacology and animal models modified for genes involved in the histone-related epigenetic machinery will be reviewed with respect to fear-, anxiety- and stress-related states. Relevant studies, published until 30th June 2022, were identified using a multi-step systematic literature search of the Pub- Med and Web of Science databases. Animal studies point towards histone modifications (e.g., H3K4me3, H3K9me1/2/3, H3K27me2/3, H3K9ac, H3K14ac and H4K5ac) to be dynamically and mostly brain region-, task- and time-dependently altered on a genome-wide level or gene-specifically (e.g., Bdnf) in models of fear conditioning, retrieval and extinction, acute and (sub-)chronic stress. Singular and underpowered studies on histone modifications in human fear-, anxiety- or stress-related phenotypes are currently restricted to the phenotype of PTSD. Provided consistent validation in human phenotypes, epigenetic biomarkers might ultimately inform indicated preventive interventions as well as personalized treatment approaches, and could inspire future innovative pharmacological treatment options targeting the epigenetic machinery improving treatment response in fear-, anxiety- and stressrelated disorders.

Cerebral glucagon-like peptide-1 receptor activation alleviates traumatic brain injury by glymphatic system regulation in mice

AIM

We aimed to assess the effects of cerebral glucagon-like peptide-1 receptor (GLP-1R) activation on the glymphatic system and whether this effect was therapeutic for traumatic brain injury (TBI).

METHODS

Immunofluorescence was employed to evaluate glymphatic system function. The blood-brain barrier (BBB) permeability, microvascular basement membrane, and tight junction expression were assessed using Evans blue extravasation, immunofluorescence, and western blot. Immunohistochemistry was performed to assess axonal damage. Neuronal apoptosis was evaluated using Nissl staining, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining, and western blot. Cognitive function was assessed using behavioral tests.

RESULTS

Cerebral GLP-1R activation restored glymphatic transport following TBI, alleviating BBB disruption and neuronal apoptosis, thereby improving cognitive function following TBI. Glymphatic function suppression by treatment using aquaporin 4 inhibitor TGN-020 abolished the protective effect of the GLP-1R agonist against cognitive impairment.

CONCLUSION

Cerebral GLP-1R activation can effectively ameliorate neuropathological changes and cognitive impairment following TBI; the underlying mechanism could involve the repair of the glymphatic system damaged by TBI.

Connecting the Dots: Potential Interactions Between Sex Hormones and the Circadian System During Memory Consolidation

Both the circadian clock and sex hormone signaling can strongly influence brain function, yet little is known about how these 2 powerful modulatory systems might interact during complex neural processes like memory consolidation. Individually, the molecular components and action of each of these systems have been fairly well-characterized, but there is a fundamental lack of information about how these systems cooperate. In the circadian system, clock genes function as timekeeping molecules that convey time-of-day information on a well-stereotyped cycle that is governed by the suprachiasmatic nucleus. Keeping time is particularly important to synchronize various physiological processes across the brain and body, including those that regulate memory consolidation. Similarly, sex hormones are powerful modulators of memory, with androgens, estrogens, and progestins, all influencing memory consolidation within memory-relevant brain regions like the hippocampus. Despite clear evidence that each system can influence memory individually, exactly how the circadian and hormonal systems might interact to impact memory consolidation remains unclear. Research investigating either sex hormone action or circadian gene function within memory-relevant brain regions has unveiled several notable places in which the two systems could interact to control memory. Here, we bring attention to known interactions between the circadian clock and sex hormone signaling. We then review sex hormone-mediated control of memory consolidation, highlighting potential nodes through which the circadian system might interact during memory formation. We suggest that the bidirectional relationship between these two systems is essential for proper control of memory formation based on an animal's hormonal and circadian state.

A mouse model of ATRX deficiency with cognitive deficits and autistic traits

BACKGROUND

ATRX is an ATP-dependent chromatin remodeling protein with essential roles in safeguarding genome integrity and modulating gene expression. Deficiencies in this protein cause ATR-X syndrome, a condition characterized by intellectual disability and an array of developmental abnormalities, including features of autism. Previous studies demonstrated that deleting ATRX in mouse forebrain excitatory neurons postnatally resulted in male-specific memory deficits, but no apparent autistic-like behaviours.

METHODS

We generated mice with an earlier embryonic deletion of ATRX in forebrain excitatory neurons and characterized their behaviour using a series of memory and autistic-related paradigms.

RESULTS

We found that mutant mice displayed a broader spectrum of impairments, including fear memory, decreased anxiety-like behaviour, hyperactivity, as well as self-injurious and repetitive grooming. Sex-specific alterations were also observed, including male-specific aggression, sensory gating impairments, and decreased social memory.

CONCLUSIONS

Collectively, the findings indicate that early developmental abnormalities arising from ATRX deficiency in forebrain excitatory neurons contribute to the presentation of fear memory deficits as well as autistic-like behaviours.

Effects of a True Prophylactic Treatment on Hippocampal and Amygdala Synaptic Plasticity and Gene Expression in a Rodent Chronic Stress Model of Social Defeat

Post-traumatic stress disorder (PTSD) is a complex stress-related disorder induced by exposure to traumatic stress that is characterized by symptoms of re-experiencing, avoidance, and hyper-arousal. While it is widely accepted that brain regions involved in emotional regulation and memory-e.g., the amygdala and hippocampus-are dysregulated in PTSD, the pathophysiology of the disorder is not well defined and therefore, pharmacological interventions are extremely limited. Because stress hormones norepinephrine and cortisol (corticosterone in rats) are heavily implicated in the disorder, we explored whether preemptively and systemically antagonizing β-adrenergic and glucocorticoid receptors with propranolol and mifepristone are sufficient to mitigate pathological changes in synaptic plasticity, gene expression, and anxiety induced by a modified social defeat (SD) stress protocol. Young adult, male Sprague Dawley rats were initially pre-screened for anxiety. The rats were then exposed to SD and chronic light stress to induce anxiety-like symptoms. Drug-treated rats were administered propranolol and mifepristone injections prior to and continuing throughout SD stress. Using competitive ELISAs on plasma, field electrophysiology at CA1 of the ventral hippocampus (VH) and the basolateral amygdala (BLA), quantitative RT-PCR, and behavior assays, we demonstrate that our SD stress increased anxiety-like behavior, elevated long-term potentiation (LTP) in the VH and BLA, and altered the expression of mineralocorticoid, glucocorticoid, and glutamate receptors. These measures largely reverted to control levels with the administration of propranolol and mifepristone. Our findings indicate that SD stress increases LTP in the VH and BLA and that prophylactic treatment with propranolol and mifepristone may have the potential in mitigating these and other stress-induced effects.

Degenerate mapping of environmental location presages deficits in object-location encoding and memory in the 5xFAD mouse model for Alzheimer's disease

A key challenge in developing diagnosis and treatments for Alzheimer's disease (AD) is to detect abnormal network activity at as early a stage as possible. To date, behavioral and neurophysiological investigations in AD model mice have yet to conduct a longitudinal assessment of cellular pathology, memory deficits, and neurophysiological correlates of neuronal activity. We therefore examined the temporal relationships between pathology, neuronal activities and spatial representation of environments, as well as object location memory deficits across multiple stages of development in the 5xFAD mice model and compared these results to those observed in wild-type mice. We performed longitudinal in vivo calcium imaging with miniscope on hippocampal CA1 neurons in behaving mice. We find that 5xFAD mice show amyloid plaque accumulation, depressed neuronal calcium activity during immobile states, and degenerate and unreliable hippocampal neuron spatial tuning to environmental location at early stages by 4 months of age while their object location memory (OLM) is comparable to WT mice. By 8 months of age, 5xFAD mice show deficits of OLM, which are accompanied by progressive degradation of spatial encoding and, eventually, impaired CA1 neural tuning to object-location pairings. Furthermore, depressed neuronal activity and unreliable spatial encoding at early stage are correlated with impaired performance in OLM at 8-month-old. Our results indicate the close connection between impaired hippocampal tuning to object-location and the presence of OLM deficits. The results also highlight that depressed baseline firing rates in hippocampal neurons during immobile states and unreliable spatial representation precede object memory deficits and predict memory deficits at older age, suggesting potential early opportunities for AD detecting.

Object location learning in mice requires hippocampal somatostatin interneuron activity and is facilitated by mTORC1-mediated long-term potentiation of their excitatory synapses

Hippocampus-dependent learning and memory originate from long-term synaptic changes in hippocampal networks. The activity of CA1 somatostatin interneurons (SOM-INs) during aversive stimulation is necessary for contextual fear memory formation. In addition, mTORC1-dependent long-term potentiation (LTP) of SOM-IN excitatory input synapses from local pyramidal cells (PC-SOM synapses) contributes to the consolidation of fear motivated spatial and contextual memories. Although, it remains unknown if SOM-IN activity and LTP are necessary and sufficient for novelty motivated spatial episodic memory such as the object location memory, and if so when it is required. Here we use optogenetics to examine whether dorsal CA1 SOM-IN activity and LTP are sufficient to regulate object location memory. First, we found that silencing SOM-INs during object location learning impaired memory. Second, optogenetic induction of PC-SOM synapse LTP (TBS_opto) given 30 min before object location training, resulted in facilitation of memory. However, in mice with mTORC1 pathway genetically inactivated in SOM-INs, which blocks PC-SOM synapse LTP, TBS_opto failed to facilitate object location memory. Our results indicate that SOM-IN activity is necessary during object location learning and that optogenetic induction of PC-SOM synapse LTP is sufficient to facilitate consolidation of object location memory. Thus, hippocampal somatostatin interneuron activity is required for object location learning, a hippocampus-dependent form of novelty motivated spatial learning that is facilitated by plasticity at PC-SOM synapses.

CBP Is Required for Establishing Adaptive Gene Programs in the Adult Mouse Brain

Environmental factors and life experiences impinge on brain circuits triggering adaptive changes. Epigenetic regulators contribute to this neuroadaptation by enhancing or suppressing specific gene programs. The paralogous transcriptional coactivators and lysine acetyltransferases CREB binding protein (CBP) and p300 are involved in brain plasticity and stimulus-dependent transcription, but their specific roles in neuroadaptation are not fully understood. Here we investigated the impact of eliminating either CBP or p300 in excitatory neurons of the adult forebrain of mice from both sexes using inducible and cell type-restricted knock-out strains. The elimination of CBP, but not p300, reduced the expression and chromatin acetylation of plasticity genes, dampened activity-driven transcription, and caused memory deficits. The defects became more prominent in elderly mice and in paradigms that involved enduring changes in transcription, such as kindling and environmental enrichment, in which CBP loss interfered with the establishment of activity-induced transcriptional and epigenetic changes in response to stimulus or experience. These findings further strengthen the link between CBP deficiency in excitatory neurons and etiopathology in the nervous system.SIGNIFICANCE STATEMENT How environmental conditions and life experiences impinge on mature brain circuits to elicit adaptive responses that favor the survival of the organism remains an outstanding question in neurosciences. Epigenetic regulators are thought to contribute to neuroadaptation by initiating or enhancing adaptive gene programs. In this article, we examined the role of CREB binding protein (CBP) and p300, two paralogous transcriptional coactivators and histone acetyltransferases involved in cognitive processes and intellectual disability, in neuroadaptation in adult hippocampal circuits. Our experiments demonstrate that CBP, but not its paralog p300, plays a highly specific role in the epigenetic regulation of neuronal plasticity gene programs in response to stimulus and provide unprecedented insight into the molecular mechanisms underlying neuroadaptation.

Nicotine-mediated activation of α2 nAChR-expressing OLM cells in developing mouse brains disrupts OLM cell-mediated control of LTP in adolescence

Early postnatal nicotine exposure, a rodent model of smoking during pregnancy, affects hippocampal synaptic plasticity and memory. Here, we investigated the role of α2 nAChR-expressing OLM (α2-OLM) cells in LTP in unexposed and postnatal nicotine-exposed mice. We found that reduced α2 nAChR-dependent activation of OLM cells in α2 heterozygous knockout mice prevented LTP, whereas enhanced α2 nAChR-dependent activation of OLM cells in heterozygous knockin mice expressing hypersensitive α2 nAChRs facilitated LTP. Both optogenetic and chemogenetic activation of α2-OLM cells facilitated LTP as nicotine did. However, in postnatal nicotine-exposed mice, expressing chemogenetic hM3Dq receptors in α2-OLM cells, LTP was facilitated and both nicotinic and chemogenetic activation of α2-OLM cells prevented rather than facilitated LTP. These results demonstrate a critical role of α2-OLM cell activation in LTP as well as altered α2-OLM cell function in postnatal nicotine-exposed mice. To determine whether nicotine-mediated α2 nAChR activation in developing brains causes facilitated LTP and altered nicotinic modulation of LTP in adolescence, we used homozygous knockin mice expressing hypersensitive α2 nAChRs as a way to selectively activate α2-OLM cells. In the knockin mice, postnatal exposure to a low dose of nicotine, which had no effect on LTP in wild-type mice, is sufficient to cause facilitated LTP and altered nicotinic modulation of LTP as found in wild-type mice exposed to a higher dose of nicotine. Thus, the nicotine-mediated activation of α2 nAChRs on OLM cells in developing brains disrupts the α2-OLM cell-mediated control of LTP in adolescence that might be linked to impaired memory.

Glucose derived carbon nanosphere (CSP) conjugated TTK21, an activator of the histone acetyltransferases CBP/p300, ameliorates amyloid-beta 1-42 induced deficits in plasticity and associativity in hippocampal CA1 pyramidal neurons

The master epigenetic regulator lysine acetyltransferase (KAT) p300/CBP plays a pivotal role in neuroplasticity and cognitive functions. Recent evidence has shown that in several neurodegenerative diseases, including Alzheimer's disease (AD), the expression level and function of p300/CBP are severely compromised, leading to altered gene expression causing pathological conditions. Here, we show that p300/CBP activation by a small-molecule TTK21, conjugated to carbon nanosphere (CSP) ameliorates Aβ-impaired long-term potentiation (LTP) induced by high-frequency stimulation, theta burst stimulation, and synaptic tagging/capture (STC). This functional rescue was correlated with CSP-TTK21-induced changes in transcription and translation. Mechanistically, we observed that the expression of a large number of synaptic plasticity- and memory-related genes was rescued, presumably by the restoration of p300/CBP mediated acetylation. Collectively, these results suggest that small-molecule activators of p300/CBP could be a potential therapeutic molecule for neurodegenerative diseases like AD.

Targeting acetyl-CoA metabolism attenuates the formation of fear memories through reduced activity-dependent histone acetylation

Histone acetylation is a key component in the consolidation of long-term fear memories. Histone acetylation is fueled by acetyl-coenzyme A (acetyl-CoA), and recently, nuclear-localized metabolic enzymes that produce this metabolite have emerged as direct and local regulators of chromatin. In particular, acetyl-CoA synthetase 2 (ACSS2) mediates histone acetylation in the mouse hippocampus. However, whether ACSS2 regulates long-term fear memory remains to be determined. Here, we show that Acss2 knockout is well tolerated in mice, yet the Acss2-null mouse exhibits reduced acquisition of long-term fear memory. Loss of Acss2 leads to reductions in both histone acetylation and expression of critical learning and memory-related genes in the dorsal hippocampus, specifically following fear conditioning. Furthermore, systemic administration of blood-brain barrier-permeable Acss2 inhibitors during the consolidation window reduces fear-memory formation in mice and rats and reduces anxiety in a predator-scent stress paradigm. Our findings suggest that nuclear acetyl-CoA metabolism via ACSS2 plays a critical, previously unappreciated, role in the formation of fear memories.

The role of histone modifications: from neurodevelopment to neurodiseases

Epigenetic regulatory mechanisms, including DNA methylation, histone modification, chromatin remodeling, and microRNA expression, play critical roles in cell differentiation and organ development through spatial and temporal gene regulation. Neurogenesis is a sophisticated and complex process by which neural stem cells differentiate into specialized brain cell types at specific times and regions of the brain. A growing body of evidence suggests that epigenetic mechanisms, such as histone modifications, allow the fine-tuning and coordination of spatiotemporal gene expressions during neurogenesis. Aberrant histone modifications contribute to the development of neurodegenerative and neuropsychiatric diseases. Herein, recent progress in understanding histone modifications in regulating embryonic and adult neurogenesis is comprehensively reviewed. The histone modifications implicated in neurodegenerative and neuropsychiatric diseases are also covered, and future directions in this area are provided.

Role of type I interferon signaling and microglia in the abnormal long term potentiation and object place recognition deficits of male mice with a mutation of the Tuberous Sclerosis 2 gene

Background

Tuberous sclerosis complex is a genetic disorder associated with high rates of intellectual disability and autism. Mice with a heterozygous null mutation of the Tsc2 gene (Tsc2^+/-) show deficits in hippocampal-dependent tasks and abnormal long-term potentiation (LTP) in the hippocampal CA1 region. Although previous studies focused on the role of neuronal deficits in the memory phenotypes of rodent models of tuberous sclerosis complex, the results presented here demonstrate a role for microglia in these deficits.

Methods

To test the possible role of microglia and type I interferon in abnormal hippocampal-dependent memory and LTP of Tsc2^+/- mice, we used field recordings in CA1 and the object place recognition (OPR) task. We used the colony stimulating factor 1 receptor inhibitor PLX5622 to deplete microglia in Tsc2^+/- mice and interferon alpha/beta receptor alpha chain null mutation (Ifnar1^-/-) to manipulate a signaling pathway known to modulate microglia function.

Results

Unexpectedly, we demonstrate that male, but not female, Tsc2^+/- mice show OPR deficits. These deficits can be rescued by depletion of microglia and by the Ifnar1^-/- mutation. In addition to rescuing OPR deficits, depletion of microglia also reversed abnormal LTP of the Tsc2^+/- mice. Altogether, our results suggest that altered IFNAR1 signaling in microglia causes the abnormal LTP and OPR deficits of male Tsc2^+/- mice.

Conclusions

Microglia and IFNAR1 signaling have a key role in the hippocampal-dependent memory deficits and abnormal hippocampal LTP of Tsc2^+/- male mice.

p53-mediated neurodegeneration in the absence of the nuclear protein Akirin2

Proper gene regulation is critical for both neuronal development and maintenance as the brain matures. We previously demonstrated that Akirin2, an essential nuclear protein that interacts with transcription factors and chromatin remodeling complexes, is required for the embryonic formation of the cerebral cortex. Here we show that Akirin2 plays a mechanistically distinct role in maintaining healthy neurons during cortical maturation. Restricting Akirin2 loss to excitatory cortical neurons resulted in progressive neurodegeneration via necroptosis and severe cortical atrophy with age. Comparing transcriptomes from Akirin2-null postnatal neurons and cortical progenitors revealed that targets of the tumor suppressor p53, a regulator of both proliferation and cell death encoded by Trp53, were consistently upregulated. Reduction of Trp53 rescued neurodegeneration in Akirin2-null neurons. These data: (1) implicate Akirin2 as a critical neuronal maintenance protein, (2) identify p53 pathways as mediators of Akirin2 functions, and (3) suggest Akirin2 dysfunction may be relevant to neurodegenerative diseases.

Dysregulation of Npas4 and Inhba expression and an altered excitation-inhibition balance are associated with cognitive deficits in DBA/2 mice

Differences in the learning associated transcriptional profiles between mouse strains with distinct learning abilities could provide insight into the molecular basis of learning and memory. The inbred mouse strain DBA/2 shows deficits in hippocampus-dependent memory, yet the transcriptional responses to learning and the underlying mechanisms of the impairments are unknown. Comparing DBA/2J mice with the reference standard C57BL/6N mouse strain we verify an enhanced susceptibility to kainic acid induced seizures, confirm impairments in hippocampus-dependent spatial memory tasks and uncover additional behavioral abnormalities including deficits in hippocampus-independent learning. Surprisingly, we found no broad dysfunction of the DBA/2J strain in immediate early gene (IEG) activation but instead report brain region-specific and gene-specific alterations. The learning-associated IEGs Arc, c-Fos, and Nr4a1 showed no DBA/2J deficits in basal or synaptic activity induced gene expression in hippocampal or cortical primary neuronal cultures or in the CA1, CA3, or retrosplenial cortex following spatial object recognition (SOR) training in vivo. However, the parietal cortex showed reduced and the dentate gyrus showed enhanced SOR-evoked induction of most IEGs. All DBA/2J hippocampal regions exhibited elevated basal expression of inhibin β A (Inhba) and a learning-associated superinduction of the transcription factor neuronal Per-Arnt-Sim domain protein 4 (Npas4) known to regulate the synaptic excitation-inhibition balance. In line with this, CA1 pyramidal neurons of DBA/2J mice showed fewer inhibitory and more excitatory miniature postsynaptic currents but no alteration in most other electrophysiological properties or gross dendritic morphology. The dysregulation of Npas4 and Inhba expression and synaptic connectivity may underlie the cognitive deficits and increased susceptibility to seizures of DBA/2J mice.

Prepubescent female rodents have enhanced hippocampal LTP and learning relative to males, reversing in adulthood as inhibition increases

Multiple studies indicate that adult male rodents perform better than females on spatial problems and have a lower threshold for long-term potentiation (LTP) of hippocampal CA3-to-CA1 synapses. We report here that, in rodents, prepubescent females rapidly encode spatial information and express low-threshold LTP, whereas age-matched males do not. The loss of low-threshold LTP across female puberty was associated with three inter-related changes: increased densities of α5 subunit-containing GABAARs at inhibitory synapses, greater shunting of burst responses used to induce LTP and a reduction of NMDAR-mediated synaptic responses. A negative allosteric modulator of α5-GABAARs increased burst responses to a greater degree in adult than in juvenile females and markedly enhanced both LTP and spatial memory in adults. The reasons for the gain of functions with male puberty do not involve these mechanisms. In all, puberty has opposite consequences for plasticity in the two sexes, albeit through different routes.

Morris water maze: a versatile and pertinent tool for assessing spatial learning and memory

Since its development about 40 years ago (1981–2021), Morris water maze has turned into a very popular tool for assessing spatial learning and memory. Its many advantages have ensured its pertinence to date. These include its effectiveness in evaluating hippocampal-dependent learning and memory, exemption from motivational differences across diverse experimental manipulations, reliability in various cross-species studies, and adaptability to many experimental conditions with various test protocols. Nonetheless, throughout its establishment, several experimental and analysis loopholes have galvanized researchers to assess ways in which it could be improved and adapted to fill this gap. Therefore, in this review, we briefly summarize these developments since the early years of its establishment through to the most recent advancements in computerized analysis, offering more comprehensive analysis paradigms. In addition, we discuss the adaptability of the Morris water maze across different test versions and analysis paradigms, providing suggestions with regard to the best paradigms for particular experimental conditions. Hence, the proper selection of the experimental protocols, analysis paradigms, and consideration of the assay’s limitations should be carefully considered. Given that appropriate measures are taken, with various adaptations made, the Morris water maze will likely remain a relevant tool to assess the mechanisms of spatial learning and memory.

Mechanistic insight into sevoflurane-associated developmental neurotoxicity

With the development of technology, more infants receive general anesthesia for surgery, other interventions, or clinical examination at an early stage after birth. However, whether general anesthetics can affect the function and structure of the developing infant brain remains an important, complex, and controversial issue. Sevoflurane is the most-used anesthetic in infants, but this drug is potentially neurotoxic. Short or single exposure to sevoflurane has a weak effect on cognitive function, while long or repeated exposure to general anesthetics may cause cognitive dysfunction. This review focuses on the mechanisms by which sevoflurane exposure during development may induce long-lasting undesirable effects on the brain. We review neural cell death, neural cell damage, impaired assembly and plasticity of neural circuits, tau phosphorylation, and neuroendocrine effects as important mechanisms for sevoflurane-induced developmental neurotoxicity. More advanced technologies and methods should be applied to determine the underlying mechanism(s) and guide prevention and treatment of sevoflurane-induced neurotoxicity.

1. We discuss the mechanisms underlying sevoflurane-induced developmental neurotoxicity from five perspectives: neural cell death, neural cell damage, assembly and plasticity of neural circuits, tau phosphorylation, and neuroendocrine effects. 2. Tau phosphorylation, IL-6, and mitochondrial dysfunction could interact with each other to cause a nerve damage loop. 3. miRNAs and lncRNAs are associated with sevoflurane-induced neurotoxicity.

Persistent sexually dimorphic effects of adolescent THC exposure on hippocampal synaptic plasticity and episodic memory in rodents

There is evidence that cannabis use during adolescence leads to memory and cognitive problems in young adulthood but little is known about effects of early life cannabis exposure on synaptic operations that are critical for encoding and organizing information. We report here that a 14-day course of daily Δ⁹-tetrahydrocannabinol treatments administered to adolescent rats and mice (aTHC) leads to profound but selective deficits in synaptic plasticity in two axonal systems in female, and to lesser extent male, hippocampus as assessed in adulthood. Adolescent-THC exposure did not alter basic synaptic transmission (input/output curves) and had only modest effects on frequency facilitation. Nevertheless, aTHC severely impaired the endocannabinoid-dependent long-term potentiation in the lateral perforant path in females of both species, and in male mice; this was reliably associated with impaired acquisition of a component of episodic memory that depends on lateral perforant path function. Potentiation in the Schaffer-commissural (S-C) projection to field CA1 was disrupted by aTHC treatment in females only and this was associated with both a deficit in estrogen effects on S-C synaptic responses and impairments to CA1-dependent spatial (object location) memory. In all the results demonstrate sexually dimorphic and projection system-specific effects of aTHC exposure that could underlie discrete effects of early life cannabinoid usage on adult cognitive function. Moreover they suggest that some of the enduring, sexually dimorphic effects of cannabis use reflect changes in synaptic estrogen action.

Examining age-dependent DNA methylation patterns and gene expression in the male and female mouse hippocampus

DNA methylation is a well-characterized epigenetic modification involved in numerous molecular and cellular functions. Methylation patterns have also been associated with aging mechanisms. However, how DNA methylation patterns change within key brain regions involved in memory formation in an age- and sex-specific manner remains unclear. Here, we performed reduced representation bisulfite sequencing (RRBS) from mouse dorsal hippocampus - which is necessary for the formation and consolidation of specific types of memories - in young and aging mice of both sexes. Overall, our findings demonstrate that methylation levels within the dorsal hippocampus are divergent between sexes during aging in genomic features correlating to mRNA functionality, transcription factor binding sites, and gene regulatory elements. These results define age-related changes in the methylome across genomic features and build a foundation for investigating potential target genes regulated by DNA methylation in an age- and sex-specific manner.

HMGB1 mediates cognitive impairment caused by the NLRP3 inflammasome in the late stage of traumatic brain injury

Background

Cognitive impairment in the late stage of traumatic brain injury (TBI) is associated with the NOD-, LRR and pyrin domain-containing protein 3 (NLRP3) inflammasome, which plays an important role in neuroinflammation. Although classical inflammatory pathways have been well-documented in the late stage of TBI (4–8 weeks post-injury), the mechanism by which the NLRP3 inflammasome impairs cognition is still unclear.

Methods

Mice lacking the gene encoding for NLRP3 (NLRP3-knockout mice) and their wild-type littermates were used in a controlled cortical impact model of TBI. Levels of NLRP3 inflammasome and inflammatory factors such as IL-1β and HMGB1 were detected in post-injury hippocampal tissue, as well as long-term potentiation. Behaviors were assessed by T-maze test, novel object recognition, and nesting tests. Glycyrrhizin was used to antagonize HMGB1. Calcium imaging were performed on primary neuronal cultures.

Results

By using the NLRP3-knockout TBI model, we found that the continuous activation of the NLRP3 inflammasome and high mobility group box 1 (HMGB1) release were closely related to cognitive impairment. We also found that inhibition of HMGB1 improved LTP reduction and cognitive function by increasing the phosphorylation level of the NMDAR1 subunit at serine 896 while reducing NLRP3 inflammasome activation.

Conclusion

NLRP3 inflammasome damages memory in the late stage of TBI primarily through HMGB1 upregulation and provides an explanation for the long-term progression of cognitive dysfunction.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02274-0.

Long-term molecular differences between resilient and susceptible mice after a single traumatic exposure

BACKGROUND AND PURPOSE

PTSD is a heterogeneous disorder induced by trauma, resulting in severe long-term impairments of an individual's mental health. Interestingly, PTSD does not develop in every individual; thus, some individuals are more resilient than others. However, the underlying molecular mechanisms are poorly understood. Here, we aimed at shedding light on these processes.

EXPERIMENTAL APPROACH

We used a single-trauma PTSD model in mice to induce long-term maladaptive behaviours and profiled the mice four weeks post-trauma into resilient or susceptible individuals. The phenotype's classification was based on their individual responses in different behavioural experiments. We analysed microbiome, circulating endocannabinoids, and long-term changes in brain phospholipid and transcript levels.

KEY RESULTS

We found a plethora of molecular differences between resilient and susceptible individuals across multiple molecular domains, including lipidome, transcriptome, and gut microbiome. Some of these differences were stable even several weeks after the trauma, indicating the long-term impact of traumatic stimuli on the organism's physiology. Furthermore, the integration of these multi-layered molecular data revealed that resilient and susceptible individuals have very distinct molecular signatures across various physiological systems.

CONCLUSIONS AND IMPLICATIONS

We showed that trauma induces individual-specific behavioural responses that, in combination with a longitudinal characterization of mice, can be used to identify distinct sub-phenotypes within the trauma-exposed group. These groups differ significantly not only in their behaviour but also in specific molecular aspects across a variety of tissues and brain regions. This approach may reveal new targets and predictive biomarkers for the pharmacological treatment and prognosis of stress-related disorders.

HDAC inhibition prevents hypobaric hypoxia-induced spatial memory impairment through PΙ3K/GSK3β/CREB pathway

Hypobaric hypoxia at higher altitudes usually impairs cognitive function. Previous studies suggested that epigenetic modifications are the culprits for this condition. Here, we set out to determine how hypobaric hypoxia mediates epigenetic modifications and how this condition worsens neurodegeneration and memory loss in rats. In the current study, different duration of hypobaric hypoxia exposure showed a discrete pattern of histone acetyltransferases and histone deacetylases (HDACs) gene expression in the hippocampus when compared with control rat brains. The level of acetylation sites in histone H2A, H3 and H4 was significantly decreased under hypobaric hypoxia exposure compared to the control rat's hippocampus. Additionally, inhibiting the HDAC family with sodium butyrate administration (1.2 g/kg body weight) attenuated neurodegeneration and memory loss in hypobaric hypoxia-exposed rats. Moreover, histone acetylation increased at the promoter regions of brain-derived neurotrophic factor (BDNF); thereby its protein expression was enhanced significantly in hypobaric hypoxia exposed rats treated with HDAC inhibitor compared with hypoxic rats. Thus, BDNF expression upregulated cAMP-response element binding protein (CREB) phosphorylation by stimulation of PI3K/GSK3β/CREB axis, which counteracts hypobaric hypoxia-induced spatial memory impairment. In conclusion, these results suggested that sodium butyrate is a novel therapeutic agent for the treatment of spatial memory loss associated with hypobaric hypoxia, and also further studies are warranted to explore specific HDAC inhibitors in this condition.

The Mechanisms and Boundary Conditions of Drug Memory Reconsolidation

Drug addiction can be seen as a disorder of maladaptive learning characterized by relapse. Therefore, disrupting drug-related memories could be an approach to improving therapies for addiction. Pioneering studies over the last two decades have revealed that consolidated memories are not static, but can be reconsolidated after retrieval, thereby providing candidate pathways for the treatment of addiction. The limbic-corticostriatal system is known to play a vital role in encoding the drug memory engram. Specific structures within this system contribute differently to the process of memory reconsolidation, making it a potential target for preventing relapse. In addition, as molecular processes are also active during memory reconsolidation, amnestic agents can be used to attenuate drug memory. In this review, we focus primarily on the brain structures involved in storing the drug memory engram, as well as the molecular processes involved in drug memory reconsolidation. Notably, we describe reports regarding boundary conditions constraining the therapeutic potential of memory reconsolidation. Furthermore, we discuss the principles that could be employed to modify stored memories. Finally, we emphasize the challenge of reconsolidation-based strategies, but end with an optimistic view on the development of reconsolidation theory for drug relapse prevention.

Rubinstein-Taybi Syndrome: A Model of Epigenetic Disorder

The Rubinstein-Taybi syndrome (RSTS) is a rare congenital developmental disorder characterized by a typical facial dysmorphism, distal limb abnormalities, intellectual disability, and many additional phenotypical features. It occurs at between 1/100,000 and 1/125,000 births. Two genes are currently known to cause RSTS, CREBBP and EP300, mutated in around 55% and 8% of clinically diagnosed cases, respectively. To date, 500 pathogenic variants have been reported for the CREBBP gene and 118 for EP300. These two genes encode paralogs acting as lysine acetyltransferase involved in transcriptional regulation and chromatin remodeling with a key role in neuronal plasticity and cognition. Because of the clinical heterogeneity of this syndrome ranging from the typical clinical diagnosis to features overlapping with other Mendelian disorders of the epigenetic machinery, phenotype/genotype correlations remain difficult to establish. In this context, the deciphering of the patho-physiological process underlying these diseases and the definition of a specific episignature will likely improve the diagnostic efficiency but also open novel therapeutic perspectives. This review summarizes the current clinical and molecular knowledge and highlights the epigenetic regulation of RSTS as a model of chromatinopathy.

CB1 receptor neutral antagonist treatment epigenetically increases neuropeptide Y expression and decreases alcohol drinking

Alcohol consumption is mediated by several important neuromodulatory systems, including the endocannabinoid and neuropeptide Y (NPY) systems in the limbic brain circuitry. However, molecular mechanisms through which cannabinoid-1 (CB1) receptors regulate alcohol consumption are still unclear. Here, we investigated the role of the CB1 receptor-mediated downstream regulation of NPY via epigenetic mechanisms in the amygdala. Alcohol drinking behavior was measured in adult male C57BL/6J mice treated with a CB1 receptor neutral antagonist AM4113 using a two-bottle choice paradigm while anxiety-like behavior was assessed in the light-dark box (LDB) test. The CB1 receptor-mediated changes in the protein levels of phosphorylated cAMP-responsive element binding protein (pCREB), CREB binding protein (CBP), H3K9ac, H3K14ac and NPY, and the mRNA levels of Creb1, Cbp, and Npy were measured in amygdaloid brain structures. Npy-specific changes in the levels of acetylated histone (H3K9/14ac) and CBP in the amygdala were also measured. We found that the pharmacological blockade of CB1 receptors with AM4113 reduced alcohol consumption and, in an ethanol-naïve cohort, reduced anxiety-like behavior in the LDB test. Treatment with AM4113 also increased the mRNA levels of Creb1 and Cbp in the amygdala as well as the protein levels of pCREB, CBP, H3K9ac and H3K14ac in the central and medial nucleus of amygdala, but not in the basolateral amygdala. Additionally, AM4113 treatment increased occupancy of CBP and H3K9/14ac at the Npy gene promoter, leading to an increase in both mRNA and protein levels of NPY in the amygdala. These novel findings suggest that CB1 receptor-mediated CREB signaling plays an important role in the modulation of NPY function through an epigenetic mechanism and further support the potential use of CB1 receptor neutral antagonists for the treatment of alcohol use disorder.

Late-life intermittent fasting decreases aging-related frailty and increases renal hydrogen sulfide production in a sexually dimorphic manner

Global average life expectancy continues to rise. As aging increases the likelihood of frailty, which encompasses metabolic, musculoskeletal, and cognitive deficits, there is a need for effective anti-aging treatments. It is well established in model organisms that dietary restriction (DR), such as caloric restriction or protein restriction, enhances health and lifespan. However, DR is not widely implemented in the clinic due to patient compliance and its lack of mechanistic underpinnings. Thus, the present study tested the effects of a somewhat more clinically applicable and adoptable DR regimen, every-other-day (EOD) intermittent fasting, on frailty in 20-month-old male and female C57BL/6 mice. Frailty was determined by a series of metabolic, musculoskeletal, and cognitive tasks performed prior to and toward the end of the 2.5-month dietary intervention. Late-life EOD fasting attenuated overall energy intake, hypothalamic inflammatory gene expression, and frailty in males. However, it failed to reduce overall caloric intake and had a little positive effect in females. Given that the selected benefits of DR are dependent on augmented production of the gasotransmitter hydrogen sulfide (H₂S) and that renal H₂S production declines with age, we tested the effects of EOD fasting on renal H₂S production capacity and its connection to frailty in males. EOD fasting boosted renal H₂S production, which positively correlated with improvements in multiple components of frailty tasks. Therefore, late-life initiated EOD fasting is sufficient to reduce aging-related frailty, at least in males, and suggests that renal H₂S production capacity may modulate the effects of late-life EOD fasting on frailty.

From Circuits to Chromatin: The Emerging Role of Epigenetics in Mental Health

A central goal of neuroscience research is to understand how experiences modify brain circuits to guide future adaptive behavior. In response to environmental stimuli, neural circuit activity engages gene regulatory mechanisms within each cell. This activity-dependent gene expression is governed, in part, by epigenetic processes that can produce persistent changes in both neural circuits and the epigenome itself. The complex interplay between circuit activity and neuronal gene regulation is vital to learning and memory, and, when disrupted, is linked to debilitating psychiatric conditions, such as substance use disorder. To develop clinical treatments, it is paramount to advance our understanding of how neural circuits and the epigenome cooperate to produce behavioral adaptation. Here, we discuss how new genetic tools, used to manipulate neural circuits and chromatin, have enabled the discovery of epigenetic processes that bring about long-lasting changes in behavior relevant to mental health and disease.

Administration of branched-chain amino acids alters epigenetic regulatory enzymes in an animal model of Maple Syrup Urine Disease

Maple Syrup Urine Disease (MSUD) is an autosomal recessive inherited disorder that affects the activity of the branched-chainα-keto acid dehydrogenase complex (BCDK). This deficiency on BCDK complex results in the accumulation of branched-chain amino acids (BCAA) leucine, isoleucine, valine, and their corresponding α-keto acids. Epigenetic changes can negatively affect the metabolism of BCAA. These changes are catalyzed by the epigenetic regulatory enzymes, e.g., DNA methyltransferase (DNMT), histone deacetylases (HDAC), and histone acetyltransferases (HAT). However, the impacts of BCAA administration on the activity of epigenetic regulatory enzymes in the brain of MSUD patients are still unknown. In this study, we aimed to demonstrate the impact of BCAA administration on the activity of DNMT, HDAC, and HAT in the brain structures of infant rats, an animal model of MSUD. For that, we administered a BCAA pool to infant rats for 21 days. We demonstrated that BCAA administration significantly increased the DNMT and HDAC activities in the hippocampus and striatum, but not in the cerebral cortex of MSUD infant rats. A positive correlation was observed between HDAC and DNMT activities in the hippocampus and striatum of animals exposed to BCAA injections. Our results showed that the BCAA administration could modulate epigenetic regulatory enzymes, mainly DNMT and HDAC, in the brains of infant rats. Therefore, we suggest that the increase in the activity of DNMT and HDAC in the hippocampus and striatum could partially explain the neurological impairments presented in animal models of MSUD.

Systemic HDAC3 inhibition ameliorates impairments in synaptic plasticity caused by simulated galactic cosmic radiation exposure in male mice

Deep space travel presents a number of measurable risks including exposure to a spectrum of radiations of varying qualities, termed galactic cosmic radiation (GCR) that are capable of penetrating the spacecraft, traversing through the body and impacting brain function. Using rodents, studies have reported that exposure to simulated GCR leads to cognitive impairments associated with changes in hippocampus function that can persist as long as one-year post exposure with no sign of recovery. Whether memory can be updated to incorporate new information in mice exposed to GCR is unknown. Further, mechanisms underlying long lasting impairments in cognitive function as a result of GCR exposure have yet to be defined. Here, we examined whether whole body exposure to simulated GCR using 6 ions and doses of 5 or 30 cGy interfered with the ability to update an existing memory or impact hippocampal synaptic plasticity, a cellular mechanism believed to underlie memory processes, by examining long term potentiation (LTP) in acute hippocampal slices from middle aged male mice 3.5-5 months after radiation exposure. Using a modified version of the hippocampus-dependent object location memory task developed by our lab termed "Objects in Updated Locations" (OUL) task we find that GCR exposure impaired hippocampus-dependent memory updating and hippocampal LTP 3.5-5 months after exposure. Further, we find that impairments in LTP are reversed through one-time systemic subcutaneous injection of the histone deacetylase 3 inhibitor RGFP 966 (10 mg/kg), suggesting that long lasting impairments in cognitive function may be mediated at least in part, through epigenetic mechanisms.

Impaired Regulation of Histone Methylation and Acetylation Underlies Specific Neurodevelopmental Disorders

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

Carbamazepine Restores Neuronal Signaling, Protein Synthesis, and Cognitive Function in a Mouse Model of Fragile X Syndrome

Fragile X syndrome (FXS) is a leading genetic disorder of intellectual disability caused by the loss of the functional fragile X mental retardation protein (FMRP). To date, there is no efficacious mechanism-based medication for FXS. With regard to potential disease mechanisms in FXS, it is widely accepted that the lack of FMRP causes elevated protein synthesis and deregulation of neuronal signaling. Abnormal enhancement of the ERK½ (extracellular signal-regulated kinase ½) and PI3K-Akt (Phosphoinositide 3 kinase-protein kinase B) signaling pathways has been identified in both FXS patients and FXS mouse models. In this study, we show that carbamazepine, which is an FDA-approved drug and has been mainly used to treat seizure and neuropathic pain, corrects cognitive deficits including passive avoidance and object location memory in FXS mice. Carbamazepine also rescues hyper locomotion and social deficits. At the cellular level, carbamazepine dampens the elevated level of ERK½ and Akt signaling as well as protein synthesis in FXS mouse neurons. Together, these results advocate repurposing carbamazepine for FXS treatment.

Rho Guanine Nucleotide Exchange Factor 4 (Arhgef4) Deficiency Enhances Spatial and Object Recognition Memory

Guanine nucleotide exchange factors (GEFs) play multiple functional roles in neurons. In a previous study, we reported that Arhgef4 (Rho guanine nucleotide exchange factor 4) functioned as a negative regulator of the excitatory synaptic function by sequestering postsynaptic density protein 95 (PSD-95). However, the role of Arhgef4 in behavior has not been examined. We performed comprehensive behavioral tests in knockout (KO) mice to investigate of the effects of Arhgef4 deficiency. We found that the expressed PSD-95 particle size was significantly increased in hippocampal neuronal cultures from Arhgef4 KO mice, which is consistent with the previous in vitro findings. Arhgef4 KO mice exhibited general motor activity and anxiety-like behavior comparable to those of the wild type littermates. However, spatial memory and object recognition memory were significantly enhanced in the Arhgef4 KO mice. Taken together, these data confirm the role of Arhgef4 as a negative synaptic regulator at the behavioral level.

The CBP KIX domain regulates long-term memory and circadian activity

Background

CREB-dependent transcription necessary for long-term memory is driven by interactions with CREB-binding protein (CBP), a multi-domain protein that binds numerous transcription factors potentially affecting expression of thousands of genes. Identifying specific domain functions for multi-domain proteins is essential to understand processes such as cognitive function and circadian clocks. We investigated the function of the CBP KIX domain in hippocampal memory and gene expression using CBP^KIX/KIX mice with mutations that prevent phospho-CREB (Ser133) binding.

Results

We found that CBP^KIX/KIX mice were impaired in long-term memory, but not learning acquisition or short-term memory for the Morris water maze. Using an unbiased analysis of gene expression in the dorsal hippocampus after training in the Morris water maze or contextual fear conditioning, we discovered dysregulation of CREB, CLOCK, and BMAL1 target genes and downregulation of circadian genes in CBP^KIX/KIX mice. Given our finding that the CBP KIX domain was important for transcription of circadian genes, we profiled circadian activity and phase resetting in CBP^KIX/KIX mice. CBP^KIX/KIX mice exhibited delayed activity peaks after light offset and longer free-running periods in constant dark. Interestingly, CBP^KIX/KIX mice displayed phase delays and advances in response to photic stimulation comparable to wildtype littermates. Thus, this work delineates site-specific regulation of the circadian clock by a multi-domain protein.

Conclusions

These studies provide insight into the significance of the CBP KIX domain by defining targets of CBP transcriptional co-activation in memory and the role of the CBP KIX domain in vivo on circadian rhythms.

Graphical abstract

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.

Epigenetic Mechanisms of Learning and Memory: Implications for Aging

The neuronal epigenome is highly sensitive to external events and its function is vital for producing stable behavioral outcomes, such as the formation of long-lasting memories. The importance of epigenetic regulation in memory is now well established and growing evidence points to altered epigenome function in the aging brain as a contributing factor to age-related memory decline. In this review, we first summarize the typical role of epigenetic factors in memory processing in a healthy young brain, then discuss the aspects of this system that are altered with aging. There is general agreement that many epigenetic marks are modified with aging, but there are still substantial inconsistencies in the precise nature of these changes and their link with memory decline. Here, we discuss the potential source of age-related changes in the epigenome and their implications for therapeutic intervention in age-related cognitive decline.

The Emerging Role of ATP-Dependent Chromatin Remodeling in Memory and Substance Use Disorders

Long-term memory formation requires coordinated regulation of gene expression and persistent changes in cell function. For decades, research has implicated histone modifications in regulating chromatin compaction necessary for experience-dependent changes to gene expression and cell function during memory formation. Recent evidence suggests that another epigenetic mechanism, ATP-dependent chromatin remodeling, works in concert with the histone-modifying enzymes to produce large-scale changes to chromatin structure. This review examines how histone-modifying enzymes and chromatin remodelers restructure chromatin to facilitate memory formation. We highlight the emerging evidence implicating ATP-dependent chromatin remodeling as an essential mechanism that mediates activity-dependent gene expression, plasticity, and cell function in developing and adult brains. Finally, we discuss how studies that target chromatin remodelers have expanded our understanding of the role that these complexes play in substance use disorders.

Molecular Mechanisms of Reconsolidation-Dependent Memory Updating

Memory is not a stable record of experience, but instead is an ongoing process that allows existing memories to be modified with new information through a reconsolidation-dependent updating process. For a previously stable memory to be updated, the memory must first become labile through a process called destabilization. Destabilization is a protein degradation-dependent process that occurs when new information is presented. Following destabilization, a memory becomes stable again through a protein synthesis-dependent process called restabilization. Much work remains to fully characterize the mechanisms that underlie both destabilization and subsequent restabilization, however. In this article, we briefly review the discovery of reconsolidation as a potential mechanism for memory updating. We then discuss the behavioral paradigms that have been used to identify the molecular mechanisms of reconsolidation-dependent memory updating. Finally, we outline what is known about the molecular mechanisms that support the memory updating process. Understanding the molecular mechanisms underlying reconsolidation-dependent memory updating is an important step toward leveraging this process in a therapeutic setting to modify maladaptive memories and to improve memory when it fails.

KAT3-dependent acetylation of cell type-specific genes maintains neuronal identity in the adult mouse brain

The lysine acetyltransferases type 3 (KAT3) family members CBP and p300 are important transcriptional co-activators, but their specific functions in adult post-mitotic neurons remain unclear. Here, we show that the combined elimination of both proteins in forebrain excitatory neurons of adult mice resulted in a rapidly progressing neurological phenotype associated with severe ataxia, dendritic retraction and reduced electrical activity. At the molecular level, we observed the downregulation of neuronal genes, as well as decreased H3K27 acetylation and pro-neural transcription factor binding at the promoters and enhancers of canonical neuronal genes. The combined deletion of CBP and p300 in hippocampal neurons resulted in the rapid loss of neuronal molecular identity without de- or transdifferentiation. Restoring CBP expression or lysine acetylation rescued neuronal-specific transcription in cultured neurons. Together, these experiments show that KAT3 proteins maintain the excitatory neuron identity through the regulation of histone acetylation at cell type-specific promoter and enhancer regions.

Neuronal identity maintenance is highly regulated. Here, the authors showed that CBP and p300 safeguard neuronal identity through histone acetylation at promoters and enhancers of neuronal specific genes. The loss of both CBP and p300 impairs gene expression, circuit activity, and behavior in mice.

The medial prefrontal cortex - hippocampus circuit that integrates information of object, place and time to construct episodic memory in rodents: Behavioral, anatomical and neurochemical properties

Rats and mice have been demonstrated to show episodic-like memory, a prototype of episodic memory, as defined by an integrated memory of the experience of an object or event, in a particular place and time. Such memory can be assessed via the use of spontaneous object exploration paradigms, variably designed to measure memory for object, place, temporal order and object-location inter-relationships. We review the methodological properties of these tests, the neurobiology about time and discuss the evidence for the involvement of the medial prefrontal cortex (mPFC), entorhinal cortex (EC) and hippocampus, with respect to their anatomy, neurotransmitter systems and functional circuits. The systematic analysis suggests that a specific circuit between the mPFC, lateral EC and hippocampus encodes the information for event, place and time of occurrence into the complex episodic-like memory, as a top-down regulation from the mPFC onto the hippocampus. This circuit can be distinguished from the neuronal component memory systems for processing the individual information of object, time and place.

Activity- and memory training-induced acetylation of α-tubulin in the hippocampus

Posttranslational modifications play crucial roles in synaptic plasticity and memory formation. The important role of histone acetylation is well established in these processes. However, activity-dependent regulation of acetylation of non-histone proteins is not well understood. We previously showed that α-tubulin is acetylated in an activity-dependent manner. Here, we show that cyclin-dependent kinase 5 (CDK5) plays an important role in α-tubulin acetylation induced by KCl depolarization or N-methyl-D-aspartate stimulation of the hippocampal slices. In addition, KCl depolarization inhibits the activity of SIRT2, an α-tubulin deacetylase. The inhibitory effect of KCl on SIRT2 activity requires CDK5 activity. Furthermore, α-tubulin acetylation is enhanced by memory training in object recognition task. These results suggest that memory formation may involve α-tubulin acetylation.