Hippocampal Histone Acetylation Research Articles

An enriched environment improves maternal sleep deprivation-induced cognitive deficits and synaptic plasticity via hippocampal histone acetylation.

Growing evidence clearly demonstrates that maternal rodents exposure to sleep deprivation (SD) during late pregnancy impairs learning and memory in their offspring. Epigenetic mechanisms, particularly histone acetylation, are known to be involved in synaptic plasticity, learning, and memory. We hypothesize that the cognitive decline induced by SD during late pregnancy is associated with histone acetylation dysfunction, and this effect could be reversed by an enriched environment (EE). In the present study, pregnant CD-1 mice were exposed to SD during the third trimester of pregnancy. After weaning, all offspring were randomly assigned to two subgroups in either a standard environment or an EE. When offspring were 3 months old, the Morris water maze was used to evaluate hippocampal-dependent learning and memory ability. Molecular biological techniques, including western blot and real-time fluorescence quantitative polymerase chain reaction, were used to examine the histone acetylation pathway and synaptic plasticity markers in the hippocampus of offspring. The results showed that the following were all reversed by EE treatment: maternal SD (MSD)-induced cognitive deficits including spatial learning and memory; histone acetylation dysfunction including increased histone deacetylase 2 (HDAC2) and decreased histone acetyltransferase (CBP), and the acetylation levels of H3K9 and H4K12; synaptic plasticity dysfunction including decreased brain-derived neurotrophic factor; and postsynaptic density protein-95. Our findings suggested that MSD could damage learning ability and memory in offspring via the histone acetylation pathway. This effect could be reversed by EE treatment.

Enriched environment improves sevoflurane-induced cognitive impairment during late-pregnancy via hippocampal histone acetylation.

Fetal exposure to sevoflurane induces long-term cognitive impairment. Histone acetylation regulates the transcription of genes involved in memory formation. We investigated whether sevoflurane exposure during late-pregnancy induces neurocognitive impairment in offspring, and if this is related to histone acetylation dysfunction. We determined whether the effects could be reversed by an enriched environment (EE). Pregnant rats were exposed to 2.5% sevoflurane or control for 1, 3, or 6 h on gestational day 18 (G18). Sevoflurane reduced brain-derived neurotrophic factor (BDNF), acetyl histone H3 (Ac-H3), and Ac-H4 levels and increased histone deacetylases-2 (HDAC2) and HDAC3 levels in the hippocampus of the offspring on postnatal day 1 (P1) and P35. Long-term potentiation was inhibited, and spatial learning and memory were impaired in the 6-h sevoflurane group at P35. EE alleviated sevoflurane-induced cognitive dysfunction and increased hippocampal BDNF, Ac-H3, and Ac-H4. Exposure to 2.5% sevoflurane for 3 h during late-pregnancy decreased hippocampal BDNF, Ac-H3, and Ac-H4 in the offspring but had no effect on cognitive function. However, when the exposure time was 6 h, impaired spatial learning and memory were linked to reduced BDNF, Ac-H3, and Ac-H4, which could be reversed by EE.

Effects of hippocampal histone acetylation and HDAC inhibition on spatial learning and memory in the Morris water maze in rats.

In recent years, it has been pointed out that epigenetic changes affect learning and memory formation. Particularly, it has been shown that histone acetylation and DNA methylation work in concert to regulate learning and memory formation. We aimed to examine whether acetylation of H2B within the rat hippocampus alters by trainings in the Morris water maze test. Male, 2-3months old, Sprague Dawley rats were trained in Morris water maze task. Animals were given four trials per day for five consecutive days to locate a hidden platform. On the sixth day, the platform was removed and the animals were swum for 60s. The effects of sodium butyrate, histone deacetylase inhibitor, were tested on normal and scopolamine-induced memory-impaired rats. The histone deacetylase inhibitor, sodium butyrate, increased histone H2B acetylation in normal rats. Sodium butyrate had no effect on learning and memory performance of normal rats; however, it partially ameliorated learning and memory disruption induced by scopolamine. So, the histone deacetylase inhibitors can be new treatment agent for cognitive disorders.

Altered Non‐Coding RNA‐Histone Acetylation Regulatory Circuit Is Associated With Cognitive Impairment via Gut Dysbiosis in Aging Mice

Advancing age is the top risk factor for the development of neurodegenerative disorders such as Alzheimer's Disease (AD). However, the contribution of the aging process to Alzheimer's disease (AD) pathology remain unclear. It is also unclear, whether age‐related disruption of the gut‐barrier integrity or dysbiosis causes impaired hippocampal memory. Allyl sulfide (AS), an organic sulfur compound in garlic, has many health benefits and is known for its detoxifying agents. However, the precise role of allyl sulfide in regulating hippocampal memory function at mechanistic levels in mice still needs to be investigated. Here we show that memory disturbances with altered hippocampal chromatin plasticity in the aging brain of the mouse are associated with gut‐microbiota changes and intragastric administration of allyl sulfide retards age‐related defects. To test the hypothesis, we employed 4‐months age‐matched male wild‐type C57BJ/L6 (WT) mice as control group (Young), 24‐months old age‐matched male WT mice group as aging group (AG) and another 24‐months old age‐matched male WT mice group received daily AS at the dosage of 2mg/kg/b.wt through oral gavage (AG+AS). The results show that Young and AG+AS mice showed higher behavioral proficiency and more robust long‐term and short‐term memory compared to AG mice. Gut microbiota is significantly altered as assessed by the denaturing gradient gel electrophoresis (DGGE) analysis in AG group in compared with Young and AG+AS group. The mechanistic study shows that AG mice display an increased plasma level of circulating non‐coding RNA‐Hotair (lncRNA‐Hotair), as assessed by RT2 lncRNA qPCR Assay. To test whether memory impairment correlates with altered hippocampal chromatin plasticity in a lncRNA‐Hotair dependent manner, we first investigated the hippocampal histone acetylation pattern in the AG group. The data suggest that lncRNA‐Hotair causes a specific deregulation of histone H3 lysine 27 (H3K27) acetylation (ac) at the neuronal derived natriuretic factor (NDNF) promoter of hippocampal tissue of AG group and, therefore, fail to initiate a hippocampal gene transcription associated with memory consolidation. However, administration of AS in the AG group could ameliorate gut dysbiosis and memory functions. In lncRNA‐Hotair‐deficient mice, which are protected from age‐related microbiota changes and memory impairment. Furthermore, restoration of NDNF using recombinant NDNF‐therapy reinstates to the recovery of cognitive abilities. In conclusion, our data suggest that lncRNA‐Hotair upregulation and H3K27ac regulatory activity may represent an early biomarker in the aging mouse brain. In addition, AS could serve as potential anti‐aging therapeutics in treating aging individuals.Support or Funding InformationThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Neonatal Lipopolysaccharide Challenge Induces Long-lasting Spatial Cognitive Impairment and Dysregulation of Hippocampal Histone Acetylation in Mice

Neonatal inflammation induces long-term effects on brain function. We investigated the effects of systematic neonatal inflammation using lipopolysaccharide (LPS) injection at postnatal day 3 (P3) and P5 in a mouse model of spatial memory capacity measured using a Morris water maze (MWM) task in adulthood. Subsequently, we assessed histone acetylation and immediate-early response gene expression (c-Fos and brain-derived neurotrophic factor) in the hippocampus in response to MWM acquisition training. The LPS-treated mice exhibited a significant spatial cognitive impairment, which was accompanied by insufficient histone acetylation of the H4K12-specific lysine residue and repressed c-Fos gene expression immediately after acquisition training. Moreover, the enrichment of acetyl-H4K12 on the c-Fos promoter following acquisition training was decreased in LPS-treated mice. Administration of trichostatin A (TSA), a histone deacetylase inhibitor, 2 h before each MWM acquisition training session effectively enhanced hippocampal histone acetylation levels and enrichment of acetyl-H4K12 on the c-Fos promoter following acquisition training in LPS-treated mice. TSA also increased c-Fos gene expression underlying synaptic plasticity and memory formation, and consequently rescued impaired spatial cognitive function. These results indicate that the dysregulation of H4K12 acetylation during the ongoing process of memory formation plays a key role in the spatial cognitive impairment associated with a neonatal LPS challenge. The histone deacetylase inhibitor TSA exhibits therapeutic potential for treating cognitive impairment induced by neonatal inflammation, by means of improving hippocampal histone acetylation and downstream c-Fos gene expression in response to a learning task.

The effect of sevoflurane anesthesia on learning and memory and hippocampal histone acetylation in mice

Objective To investigate the effect of sevoflurane anesthesia on learning and memory in mice and the relationship with histone acetylation. Methods Thirty-six adult male C57BL/6 mice were randomly divided into control group(mice inhaled 95% O2 for 6 h), sevoflurane (Sevo) group (1.5% Sevo group, 2% Sevo group, 3% Sevo group: mice inhaled 1.5%, 2% and 3% sevoflurane for 6 h respectively), sevoflurane + SAHA (Sevo + SAHA) group (mice were intraperitoneally injected with histone deacetylase inhibitor SAHA (25 mg/kg). And 1 h later, 3% Sevo was inhaled continuously for 6 hours.)and SAHA group(mice were intraperitoneally injected with histone deacetylase inhibitor SAHA (25 mg/kg)). The ability of learning and memory in mice was estimated by Morris water maze. The expression levels of Ac-H3, BDNF and Syt-I protein in the hippocampus were detected by Western blot. Results In Morris water maze, 3% sevoflurane anesthesia significantly prolonged the escape latency((46.91±1.84)s), and significantly decreased the ratio of target time((35.84±5.40)%) compared with that of control group((23.46±2.67)s, (49.74±4.91)%, P<0.05). Compared with 3% Sevo group, the ratio of target time in Sevot+ SAHA group((46.86±4.37)%) was increased(P<0.05). Moreover, 3% sevoflurane anesthesia significantly decreased the expression levels of Ac-H3 (10.23±2.45), BDNF (6.72±1.21) and Syt-I (8.25±2.11) in the hippocampus compared with that of control group((15.45±2.58), (10.17±1.45) and (15.02±3.38), P<0.05). However, pre-administration of the histone deacetylase inhibitor SAHA significantly increased the ratio of target time in Morris water maze, and improved the expression levels of Ac-H3 (14.06±2.79), BDNF (10.13±1.06) and Syt-I (14.16±3.66) in Sevo+ SAHA group compared with that of Sevo group (P<0.05). Conclusion The high dose of sevoflurane anesthesia can induce learning and memory impairment through the inhibitation of histone acetylation in the hippocampus. Key words: Sevoflurane; Histone acetylation; Learning and memory

Neuroprotective effects of artemisinin against isoflurane-induced cognitive impairments and neuronal cell death involve JNK/ERK1/2 signalling and improved hippocampal histone acetylation in neonatal rats.

This study was performed to assess the effect of artemisinin against isoflurane-induced neuronal apoptosis and cognitive impairment in neonatal rats. Artemisinin (50, 100 or 200 mg/kg b.wt/day; oral gavage) was administered to separate groups of neonatal rats starting from postnatal day 3 (P3) to postnatal day 21 (P21). On postnatal day 7 (P7), animals were exposed to inhalation anaesthetic isoflurane (0.75%) for 6 h. Neuronal apoptosis following anaesthetic exposure was significantly reduced by artemisinin. Isoflurane-induced upregulated cleaved caspase-3, Bax and Bad expression were downregulated. Western blotting analysis revealed that treatment with artemisinin significantly enhanced the expression of anti-apoptotic proteins (Bcl-2, Bcl-xL, c-IAP-1, c-IAP-2, xIAP and survivin). Artemisinin increased the acetylation of H3K9 and H4K12 while reducing the expression of histone deacetlyases (HDACs) - HDAC-2 and HDAC-3. Isoflurane-induced activation of JNK signalling and downregulated ERK1/2 expression was effectively modulated by artemisinin. General behaviour of the animals in open-field and T-maze test were improved. Morris water maze test and object recognition test revealed better learning, working memory and also better memory retention on artemisinin treatment. Artemisinin effectively inhibited neuronal apoptosis and improved cognition and memory via regulating histone acetylation and JNK/ERK1/2 signalling.

Treadmill exercise induces selective changes in hippocampal histone acetylation during the aging process in rats

Physical exercise and the aging process have been shown to induce opposite effects on epigenetic marks, such as histone acetylation. The impact of exercise on hippocampal histone acetylation on specific lysine residues, especially during the aging process, is rarely studied. The aim of this study was to investigate the effect of treadmill exercise (20min/day during 2 weeks) on H3K9, H4K5 and H4K12 acetylation levels in hippocampi of young adult and aged rats. Male Wistar rats aged 3 or 20–21 months were assigned to sedentary and exercise groups. Single-trial step-down inhibitory avoidance conditioning was employed as an aversive memory paradigm. Hippocampal H3K9, H4K5 and H4K12 acetylation was determined by Western blotting. The daily moderate exercise protocol improved the aversive memory performance and increased hipocampal H4K12 acetylation levels in both tested ages. Exercise was also able to increase H3K9 acetylation levels in aged rats. An age-related decline in memory performance was observed, without any effect of the aging process on histone acetylation state. Our data suggest that treadmill exercise can impact hippocampal the histone acetylation profile in an age- and lysine-dependent manner. In addition, higher hippocampal H4K12 acetylation levels at both ages may be related to improvement of aversive memory performance.

Accelerated reduction of serum thyroxine and hippocampal histone acetylation links to exacerbation of spatial memory impairment in aged CD-1 mice pubertally exposed to bisphenol-a.

Age-related cognitive decline has been associated with changes in endogenous hormones and epigenetic modification of chromatin, including histone acetylation. Developmental exposure to endocrine disrupting chemicals, such as bisphenol-A (BPA) that produces endocrine disruption and epigenetic changes, may be a risk factor for accelerating cognitive deficits during aging. Thus, we exposed CD-1 mice to BPA (0, 1, and 100mg/l BPA in the drinking water) orally during puberty (from postnatal days 28 to 56) and investigated whether pubertal BPA exposure exacerbates the age-related impairment of spatial cognition in old age (18months old) and whether serum sex and thyroid hormones or hippocampal histone acetylation (H3K9ac and H4K8ac) are associated with cognitive effects. A young control group (6months old) was added to analyze the age effect. Results showed untreated aged mice had marked decline of spatial learning and memory in the novel location recognition and radial six-arm water maze tasks, with decreased levels of these hormones and hippocampal H3K9ac and H4K8ac compared to young controls. The BPA treatment exacerbated age-related spatial cognitive impairment and accelerated the reduction of free thyroxine (FT4), H3K9ac, and H4K8ac, and the 100mg/l BPA group showed more significant impact. Additionally, correlation analyses revealed that lower levels of FT4, H3K9ac, and H4K8ac were accompanied by decreased spatial memory abilities. We concluded that accelerated reduction of serum FT4 and hippocampal H3K9ac and H4K8ac might be linked to exacerbation of age-related spatial cognitive impairment due to pubertal BPA exposure.

Role of histone acetylation in long-term neurobehavioral effects of neonatal Exposure to sevoflurane in rats

Human studies, and especially laboratory studies, provide evidence that early life exposure to general anesthesia may affect neurocognitive development via largely unknown mechanisms. We explored whether hippocampal histone acetylation had a role in neurodevelopmental effects of sevoflurane administered to neonatal rats. Male Sprague–Dawley rats were exposed to 3% sevoflurane or were subjected to maternal separation only for 2h daily at postnatal days 6, 7, and 8. The histone deacetylase inhibitor, sodium butyrate (250mg/kg, intraperitoneally), or saline was administered starting 2h prior to anesthesia or maternal separation and continued daily until the end of behavioral tests, which were performed between postnatal days 33 and 50. Upon completion of the behavioral tests, the brain tissues were harvested for further analysis. Rats neonatally exposed to sevoflurane exhibited decreased freezing time in the fear conditioning contextual test and increased escape latency, decreased time in target quadrant, and number of platform crossings in the Morris water maze test. The sevoflurane-exposed rats had lower hippocampal density of dendritic spines, reduced levels of the brain-derived neurotrophic factor, c-fos protein, microtubule-associated protein 2, synapsin1, postsynaptic density protein 95, pCREB/CREB, CREB binding protein, and acetylated histones H3 and H4, and increased levels of histone deacetylases 3 and 8. These neurobehavioral abnormalities were normalized in the sevoflurane-exposed rats treated with sodium butyrate. Our findings provide evidence that neonatal exposure to sevoflurane induces neurobehavioral abnormalities and long-lasting alterations in histone acetylation; normalization of histone acetylation may alleviate the neurodevelopmental side effects of the anesthetic.

Swimming exercise ameliorates neurocognitive impairment induced by neonatal exposure to isoflurane and enhances hippocampal histone acetylation in mice

Isoflurane-induced neurocognitive impairment in the developing rodent brain is well documented, and regular physical exercise has been demonstrated to be a viable intervention for some types of neurocognitive impairment. This study was designed to investigate the potential protective effect of swimming exercise on both neurocognitive impairment caused by repeated neonatal exposure to isoflurane and the underlying molecular mechanism. Mice received 0.75% isoflurane exposures for 4h on postnatal days 7, 8, and 9. From the third month after anesthesia, the mice were subjected to regular swimming exercise for 4weeks, followed by a contextual fear condition (CFC) trial. We found that repeated neonatal exposure to isoflurane reduced freezing behavior during CFC testing and deregulated hippocampal histone H4K12 acetylation. Conversely, mice subjected to regular swimming exercise showed enhanced hippocampal H3K9, H4K5, and H4K12 acetylation levels, increased numbers of c-Fos-positive cells 1h after CFC training, and less isoflurane-induced memory impairment. We also observed increases in histone acetylation and of cAMP-response element-binding protein (CREB)-binding protein (CBP) during the swimming exercise program. The results suggest that neonatal isoflurane exposure-induced memory impairment was associated with dysregulation of H4K12 acetylation, which may lead to less hippocampal activation following learning tasks. Swimming exercise was associated with enhanced hippocampal histone acetylation and CBP expression. Exercise most likely ameliorated isoflurane-induced memory impairment by enhancing hippocampal histone acetylation and activating more neuron cells during memory formation.

Neonatal isoflurane exposure induces neurocognitive impairment and abnormal hippocampal histone acetylation in mice.

BackgroundNeonatal exposure to isoflurane may induce long-term memory impairment in mice. Histone acetylation is an important form of chromatin modification that regulates the transcription of genes required for memory formation. This study investigated whether neonatal isoflurane exposure-induced neurocognitive impairment is related to dysregulated histone acetylation in the hippocampus and whether it can be attenuated by the histone deacetylase (HDAC) inhibitor trichostatin A (TSA).MethodsC57BL/6 mice were exposed to 0.75% isoflurane three times (each for 4 h) at postnatal days 7, 8, and 9. Contextual fear conditioning (CFC) was tested at 3 months after anesthesia administration. TSA was intraperitoneally injected 2 h before CFC training. Hippocampal histone acetylation levels were analyzed following CFC training. Levels of the neuronal activation and synaptic plasticity marker c-Fos were investigated at the same time point.ResultsMice that were neonatally exposed to isoflurane showed significant memory impairment on CFC testing. These mice also exhibited dysregulated hippocampal H4K12 acetylation and decreased c-Fos expression following CFC training. TSA attenuated isoflurane-induced memory impairment and simultaneously increased histone acetylation and c-Fos levels in the hippocampal cornu ammonis (CA)1 area 1 h after CFC training.ConclusionsMemory impairment induced by repeated neonatal exposure to isoflurane is associated with dysregulated histone H4K12 acetylation in the hippocampus, which probably affects downstream c-Fos gene expression following CFC training. The HDAC inhibitor TSA successfully rescued impaired contextual fear memory, presumably by promoting histone acetylation and histone acetylation-mediated gene expression.

Repression of contexual fear memory induced by isoflurane is accompanied by reduction in histone acetylation and rescued by sodium butyrate

Isoflurane produces amnesia in mice during contextual fear conditioning (CFC) trials. Histone acetylation is a form of chromatin modification involved in the transcriptional regulation underlying memory formation. We investigated whether isoflurane-induced repression of contextual fear memory is related to altered histone acetylation in the hippocampus, and whether it can be rescued by the histone deacetylases inhibitor sodium butyrate (SB). Adult C57BL/6 mice were chronically given intraperitoneal injections of SB or vehicle for 28 days. Immediately before CFC training, the mice were exposed to isoflurane or air for 30 min and CFC testing was performed the next day. Hippocampal histone acetylation was analysed 1 h after CFC training. c-Fos, an immediate early gene (IEG) suggested to participate in learning and memory formation, was also investigated at the same timepoint. Mice exposed to isoflurane showed a reduction in freezing time during the CFC test. These mice also exhibited reduced hippocampal H3K14, H4K5, and H4K12 acetylation 1 h after CFC training, and also decreased c-Fos expression. All of these changes were attenuated in isoflurane-exposed mice that were chronically treated with SB. Isoflurane suppresses histone acetylation and down-regulates c-Fos gene expression in CA1 of the hippocampus after CFC training. These changes are associated with isoflurane-induced amnesia. The HDAC inhibitor SB prevented repressed contextual fear memory, presumably by promoting histone acetylation and histone acetylation-mediated gene expression in response to CFC training.

Total Levels of Hippocampal Histone Acetylation Predict Normal Variability in Mouse Behavior

BackgroundGenetic, pharmacological, and environmental interventions that alter total levels of histone acetylation in specific brain regions can modulate behaviors and treatment responses. Efforts have been made to identify specific genes that are affected by alterations in total histone acetylation and to propose that such gene specific modulation could explain the effects of total histone acetylation levels on behavior — the implication being that under naturalistic conditions variability in histone acetylation occurs primarily around the promoters of specific genes.Methods/ResultsHere we challenge this hypothesis by demonstrating with a novel flow cytometry based technique that normal variability in open field exploration, a hippocampus-related behavior, was associated with total levels of histone acetylation in the hippocampus but not in other brain regions.ConclusionsResults suggest that modulation of total levels of histone acetylation may play a role in regulating biological processes. We speculate in the discussion that endogenous regulation of total levels of histone acetylation may be a mechanism through which organisms regulate cellular plasticity. Flow cytometry provides a useful approach to measure total levels of histone acetylation at the single cell level. Relating such information to behavioral measures and treatment responses could inform drug delivery strategies to target histone deacetylase inhibitors and other chromatin modulators to places where they may be of benefit while avoiding areas where correction is not needed and could be harmful.

Reassessing the effects of histone deacetylase inhibitors on hippocampal memory and cognitive aging.

Converging results link histone acetylation dynamics to hippocampus-dependent memory, including evidence that histone deacetylase inhibitor (HDACi) administration enhances long-term memory. Previously, we demonstrated that aging disrupts the coordinated epigenetic response to recent experience observed in the young adult hippocampus. Here, we extended that work to test the cognitive effects of a novel, brain-penetrant HDACi (EVX001688; EVX) that we confirmed yields robust, relatively long lasting dose-dependent increases in histone acetylation in the hippocampus. In young rats, acute systemic EVX administration, scheduled to yield elevated histone acetylation levels during training in a contextual fear conditioning (CFC) task, had no effect on memory retention at 24 h at any dose examined (10, 30, or 60 mg/kg). Pretraining injection of another HDACi, sodium butyrate, also failed to affect fear memory, and CFC training itself had no influence on hippocampal histone acetylation at 1 hour in mice or two strains of rats. EVX administration before water maze training in young rats yielded a modest effect such that the middle dose produced marginally better 24-h retention than either the low or high dose, but only a small numerical benefit relative to vehicle. Guided by those findings, a final experiment tested the influence of pretraining EVX treatment on age-related spatial memory impairment. The results, revealing no effect on performance, are consistent with the idea that effective procognitive HDACi treatments in aging may require intervention aimed at restoring coordinated epigenetic regulation rather than bulk increases in hippocampal histone acetylation.

Role of hippocampal histone acetylation in isoflurane-induced amnestic effect in mice

Objective To evaluate the role of hippocampal histone acetylation in isoflurane-induced amnestic effect in mice.Methods Fifty-four male C57BL/6J mice,aged 8 weeks,weighing 18-22 g,were randomly divided into 3 groups (n =18 each) using a random number table:control group (group C),isoflurane group (group ISO) and histone deacetylase inhibitor sodium butyrate group (group SB).Group C inhaled 35％ oxygen for 30 ain,and ISO and SB groups inhaled the mixture of 35 ％ oxygen and 0.4％ isoflurane for 30 min,and then the animals underwent contextual fear conditioning training.After the end of training,normal saline 6 ml/kg was intraperitoneally injected in C and ISO groups,while in group SB,sodium butyrate 1.2 g/kg was intraperitoneally injected.One hour after the end of training,3 mice were sacrificed randomly in each group and their hippocampi were immediately removed for determination of the expression of acetylated histone-H3 (Ac-H3) and Ac-H4 by Western blot.Twenty-four hours after the end of training,contextual fear conditioning test and open field test were conducted.The freezing time,total distance and time of staying at the central zone were recorded.Results Compared with group C,Ac-H3 and Ac-H4 expression was significantly down-regulated,and the percentage of freezing time during testing was decreased in group ISO (P ＜ 0.05).Compared with group ISO,Ac-H3 and Ac-H4 expression was significantly up-regulated,and the percentage of freezing time during testing was increased in group SB (P ＜ 0.05).There was no significant difference in the percentage of freezing time during training,total distance and time of staying in the central zone among the 3 groups (P ＞ 0.05).Conclusion Hippocampal histone acetylation is involved in the regulation of isoflurane-induced amnestic effect in mice. Key words: Isoflurane; Amnesia; Acetylation; Histones

Genomic targets, and histone acetylation and gene expression profiling of neural HDAC inhibition

Histone deacetylase inhibitors (HDACis) have been shown to potentiate hippocampal-dependent memory and synaptic plasticity and to ameliorate cognitive deficits and degeneration in animal models for different neuropsychiatric conditions. However, the impact of these drugs on hippocampal histone acetylation and gene expression profiles at the genomic level, and the molecular mechanisms that underlie their specificity and beneficial effects in neural tissue, remains obscure. Here, we mapped four relevant histone marks (H3K4me3, AcH3K9,14, AcH4K12 and pan-AcH2B) in hippocampal chromatin and investigated at the whole-genome level the impact of HDAC inhibition on acetylation profiles and basal and activity-driven gene expression. HDAC inhibition caused a dramatic histone hyperacetylation that was largely restricted to active loci pre-marked with H3K4me3 and AcH3K9,14. In addition, the comparison of Chromatin immunoprecipitation sequencing and gene expression profiles indicated that Trichostatin A-induced histone hyperacetylation, like histone hypoacetylation induced by histone acetyltransferase deficiency, had a modest impact on hippocampal gene expression and did not affect the transient transcriptional response to novelty exposure. However, HDAC inhibition caused the rapid induction of a homeostatic gene program related to chromatin deacetylation. These results illuminate both the relationship between hippocampal gene expression and histone acetylation and the mechanism of action of these important neuropsychiatric drugs.

Hippocampal Histone Acetylation Regulates Object Recognition and the Estradiol-Induced Enhancement of Object Recognition

Histone acetylation has recently been implicated in learning and memory processes, yet necessity of histone acetylation for such processes has not been demonstrated using pharmacological inhibitors of histone acetyltransferases (HATs). As such, the present study tested whether garcinol, a potent HAT inhibitor in vitro, could impair hippocampal memory consolidation and block the memory-enhancing effects of the modulatory hormone 17β-estradiol E2. We first showed that bilateral infusion of garcinol (0.1, 1, or 10 μg/side) into the dorsal hippocampus (DH) immediately after training impaired object recognition memory consolidation in ovariectomized female mice. A behaviorally effective dose of garcinol (10 μg/side) also significantly decreased DH HAT activity. We next examined whether DH infusion of a behaviorally subeffective dose of garcinol (1 ng/side) could block the effects of DH E2 infusion on object recognition and epigenetic processes. Immediately after training, ovariectomized female mice received bilateral DH infusions of vehicle, E2 (5 μg/side), garcinol (1 ng/side), or E2 plus garcinol. Forty-eight hours later, garcinol blocked the memory-enhancing effects of E2. Garcinol also reversed the E2-induced increase in DH histone H3 acetylation, HAT activity, and levels of the de novo methyltransferase DNMT3B, as well as the E2-induced decrease in levels of the memory repressor protein histone deacetylase 2. Collectively, these findings suggest that histone acetylation is critical for object recognition memory consolidation and the beneficial effects of E2 on object recognition. Importantly, this work demonstrates that the role of histone acetylation in memory processes can be studied using a HAT inhibitor.

Sodium Butyrate Improves Memory Function in an Alzheimer's Disease Mouse Model When Administered at an Advanced Stage of Disease Progression

Dysregulation of histone acetylation has been implicated in the onset of age-associated memory impairment and the pathogenesis of neurodegenerative diseases. Elevation of histone acetylation via administration of histone deacetylase (HDAC) inhibitors is currently being pursued as a novel therapeutic avenue to treat memory impairment linked to Alzheimer's disease (AD). Here we show that severe amyloid pathology correlates with a pronounced dysregulation of histone acetylation in the forebrain of APPPS1-21 mice. Importantly, prolonged treatment with the pan-HDAC inhibitor sodium butyrate improved associative memory in APPPS1-21 mice even when administered at a very advanced stage of pathology. The recovery of memory function correlated with elevated hippocampal histone acetylation and increased expression of genes implicated in associative learning. These data advance our understanding of the potential applicability of HDAC inhibitors for the treatment of AD and suggest that HDAC inhibitors may have beneficial effects even when administered long after the onset of disease-associated symptoms.

Regulation of Histone Acetylation during Memory Formation in the Hippocampus

Formation of long term memory begins with the activation of many disparate signaling pathways that ultimately impinge on the cellular mechanisms regulating gene expression. We investigated whether mechanisms regulating chromatin structure were activated during the early stages of long term memory formation in the hippocampus. Specifically, we investigated hippocampal histone acetylation during the initial stages of consolidation of long term association memories in a contextual fear conditioning paradigm. Acetylation of histone H3 in area CA1 of the hippocampus was regulated in contextual fear conditioning, an effect dependent on activation of N-methyl-D-aspartic acid (NMDA) receptors and ERK, and blocked using a behavioral latent inhibition paradigm. Activation of NMDA receptors in area CA1 in vitro increased acetylation of histone H3, and this effect was blocked by inhibition of ERK signaling. Moreover, activation of ERK in area CA1 in vitro through either the protein kinase C or protein kinase A pathways, biochemical events known to be involved in long term memory formation, also increased histone H3 acetylation. Furthermore, we observed that elevating levels of histone acetylation through the use of the histone deacetylase inhibitors trichostatin A or sodium butyrate enhanced induction of long term potentiation at Schaffer-collateral synapses in area CA1 of the hippocampus, a candidate mechanism contributing to long term memory formation in vivo. In concert with our findings in vitro, injection of animals with sodium butyrate prior to contextual fear conditioning enhanced formation of long term memory. These results indicate that histone-associated heterochromatin undergoes changes in structure during the formation of long term memory. Mimicking memory-associated changes in heterochromatin enhances a cellular process thought to underlie long term memory formation, hippocampal long term potentiation, and memory formation itself.