Inhibition of histone deacetylase 3 via RGFP966 facilitates cortical plasticity underlying unusually accurate auditory associative cue memory for excitatory and inhibitory cue-reward associations

Pharmacological HDAC3 inhibition alters memory updating in young and old male mice

Long-term memories are not stored in a stable state but must be flexible and dynamic to maintain relevance in response to new information. Existing memories are thought to be updated through the process of reconsolidation, in which memory retrieval initiates destabilization and updating to incorporate new information. Memory updating is impaired in old age, yet little is known about the mechanisms that go awry. One potential mechanism is the repressive histone deacetylase 3 (HDAC3), which is a powerful negative regulator of memory formation that contributes to age-related impairments in memory formation. Here, we tested whether HDAC3 also contributes to age-related impairments in memory updating using the Objects in Updated Locations (OUL) paradigm. We show that blocking HDAC3 immediately after updating with the pharmacological inhibitor RGFP966 ameliorated age-related impairments in memory updating in 18-m.o. male mice. Surprisingly, we found that post-update HDAC3 inhibition in young (3-m.o.) male mice had no effect on memory updating but instead impaired memory for the original information, suggesting that the original and updated information may compete for expression at test and HDAC3 helps regulate which information is expressed. To test this idea, we next assessed whether HDAC3 inhibition would improve memory updating in young male mice given a weak, subthreshold update. Consistent with our hypothesis, we found that HDAC3 blockade strengthened the subthreshold update without impairing memory for the original information, enabling balanced expression of the original and updated information. Together, this research suggests that HDAC3 may contribute to age-related impairments in memory updating and may regulate the strength of a memory update in young mice, shifting the balance between the original and updated information at test.

Pharmacological HDAC3 inhibition alters memory updating in young and old mice

Long-term memories are not stored in a stable state but must be flexible and dynamic to maintain relevance in response to new information. Existing memories are thought to be updated through the process of reconsolidation, in which memory retrieval initiates destabilization and updating to incorporate new information. Memory updating is impaired in old age, yet little is known about the mechanisms that go awry. One potential mechanism is the repressive histone deacetylase 3 (HDAC3), which is a powerful negative regulator of memory formation that contributes to age-related impairments in memory formation. Here, we tested whether HDAC3 also contributes to age-related impairments in memory updating using the Objects in Updated Locations (OUL) paradigm. We show that blocking HDAC3 immediately after updating with the pharmacological inhibitor RGFP966 ameliorated age-related impairments in memory updating in 18-m.o. mice. Surprisingly, we found that post-update HDAC3 inhibition in young (3-m.o.) mice had no effect on memory updating but instead impaired memory for the original information, suggesting that the original and updated information may compete for expression at test and HDAC3 helps regulate which information is expressed. To test this idea, we next assessed whether HDAC3 inhibition would improve memory updating in young mice given a weak, subthreshold update. Consistent with our hypothesis, we found that HDAC3 blockade strengthened the subthreshold update without impairing memory for the original information, enabling balanced expression of the original and updated information. Together, this research suggests that HDAC3 may contribute to age-related impairments in memory updating and may regulate the strength of a memory update in young mice, shifting the balance between the original and updated information at test.

Functional diversities within neurons and astrocytes in the adult rat auditory cortex revealed by single-nucleus RNA sequencing

The mammalian cerebral cortex is composed of a rich diversity of cell types. Cortical cells are organized into networks that rely on their functional diversity to ultimately carry out a variety of sophisticated cognitive functions. To investigate the breadth of transcriptional diverse cell types in the sensory cortex, we have used single-nucleus RNA sequencing (snRNA-seq) in the auditory cortex of the adult rat. A variety of unique excitatory and inhibitory neuron types were identified. In addition, we report for the first time a diversity of astrocytes in the auditory cortex that may represent functionally unique subtypes. Together, these results pave the way for building models of how neurons in the sensory cortex work in concert with astrocytes at synapses to fulfill high-cognitive functions like learning and memory.

Learning induces unique transcriptional landscapes in the auditory cortex

Learning can induce neurophysiological plasticity in the auditory cortex at multiple timescales. Lasting changes to auditory cortical function that persist over days, weeks, or even a lifetime, require learning to induce de novo gene expression. Indeed, transcription is the molecular determinant for long-term memories to form with a lasting impact on sound-related behavior. However, auditory cortical genes that support auditory learning, memory, and acquired sound-specific behavior are largely unknown. Using an animal model of adult, male Sprague-Dawley rats, this report is the first to identify genome-wide changes in learning-induced gene expression within the auditory cortex that may underlie long-lasting discriminative memory formation of acoustic frequency cues. Auditory cortical samples were collected from animals in the initial learning phase of a two-tone discrimination sound-reward task known to induce sound-specific neurophysiological and behavioral effects. Bioinformatic analyses on gene enrichment profiles from bulk RNA sequencing identified cholinergic synapse (KEGG rno04725), extra-cellular matrix receptor interaction (KEGG rno04512), and neuroactive receptor interaction (KEGG rno04080) among the top biological pathways are likely to be important for auditory discrimination learning. The findings characterize candidate effectors underlying the early stages of changes in cortical and behavioral function to ultimately support the formation of long-term discriminative auditory memory in the adult brain. The molecules and mechanisms identified are potential therapeutic targets to facilitate experiences that induce long-lasting changes to sound-specific auditory function in adulthood and prime for future gene-targeted investigations.

Learning induces unique transcriptional landscapes in the auditory cortex

Learning can induce neurophysiological plasticity in the auditory cortex at multiple timescales. Lasting changes to auditory cortical function that persist over days, weeks, or even a lifetime, require learning to induce de novo gene expression. Indeed, transcription is the molecular determinant for long-term memories to form with a lasting impact on sound-related behavior. However, auditory cortical genes that support auditory learning, memory, and acquired sound-specific behavior are largely unknown. This report is the first to identify in young adult male rats (Sprague-Dawley) genome-wide changes in learning-induced gene expression within the auditory cortex that may underlie the formation of long-lasting discriminative memory for acoustic frequency cues. Auditory cortical samples were collected from animals in the initial learning phase of a two-tone discrimination sound-reward task known to induce sound-specific neurophysiological and behavioral effects (e.g., Shang et al., 2019). Bioinformatic analyses on gene enrichment profiles from bulk RNA sequencing identified cholinergic synapse (KEGG 04725), extra-cellular matrix receptor interaction (KEGG 04512) , and neuroactive ligand-receptor interaction (KEGG 04080) as top biological pathways for auditory discrimination learning. The findings characterize key candidate effectors underlying changes in cortical function that support the initial formation of long-term discriminative auditory memory in the adult brain. The molecules and mechanisms identified are potential therapeutic targets to facilitate lasting changes to sound-specific auditory function in adulthood and prime for future gene-targeted investigations.

Epigenetic mechanisms regulate cue memory underlying discriminative behavior

The burgeoning field of neuroepigenetics has introduced chromatin modification as an important interface between experience and brain function. For example, epigenetic mechanisms like histone acetylation and DNA methylation operate throughout a lifetime to powerfully regulate gene expression in the brain that is required for experiences to be transformed into long-term memories. This review highlights emerging evidence from sensory models of memory that converge on the premise that epigenetic regulation of activity-dependent transcription in the sensory brain facilitates highly precise memory recall. Chromatin modifications may be key for neurophysiological responses to transient sensory cue features experienced in the "here and now" to be recapitulated over the long term. We conclude that the function of epigenetic control of sensory system neuroplasticity is to regulate the amount and type of sensory information retained in long-term memories by regulating neural representations of behaviorally relevant cues that guide behavior. This is of broad importance in the neuroscience field because there are few circumstances in which behavioral acts are devoid of an initiating sensory experience.

HDAC3 of dorsal hippocampus induces postoperative cognitive dysfunction in aged mice

Postoperative cognitive dysfunction (POCD) affects a substantial number of aged individuals. Although advanced age has been regarded as the only independent risk factor for cognitive decline following anesthesia and surgery, the exact cellular and molecular mechanisms remain poorly understood. Histone deacetylase 3 (HDAC3), an epigenetic regulator of memory plays an important role in age-dependent disease. In this study, we investigated the role of HDAC3 in POCD using a laparotomy mouse model. The results showed that the level of HDAC3 in the dorsal hippocampus (DH) was elevated in aged mice compared with young mice. The surgery impaired the spatial-temporal memory in aged mice, as indicated in the object location memory (OLM) and temporal order memory (TOM) tests. Model mice also exhibited increased expression of HDAC3 protein and decreased levels of dendritic spine density and synaptic plasticity-related proteins in the DH. Selectively blocking HDAC3 in the DH of aged mice reversed spatial-temporal memory impairment induced by surgery and restored dendritic spine density and synaptic plasticity-related proteins in the DH. Overexpression of HDAC3 by adeno-associated virus in the DH of young mice mimicked the behavioral deficits induced by anesthesia and surgery. Our results indicated that HDAC3 negatively regulates spatial-temporal memory in aged mice after anesthesia and surgery. Targeting HDAC3 might represent a potential therapy to avoid POCD.

Memory Specific to Temporal Features of Sound Is Formed by Cue-Selective Enhancements in Temporal Coding Enabled by Inhibition of an Epigenetic Regulator

Recent investigation of memory-related functions in the auditory system have capitalized on the use of memory-modulating molecules to probe the relationship between memory and substrates of memory in auditory system coding. For example, epigenetic mechanisms, which regulate gene expression necessary for memory consolidation, are powerful modulators of learning-induced neuroplasticity and long-term memory (LTM) formation. Inhibition of the epigenetic regulator histone deacetylase 3 (HDAC3) promotes LTM, which is highly specific for spectral features of sound. The present work demonstrates for the first time that HDAC3 inhibition also enables memory for temporal features of sound. Adult male rats trained in an amplitude modulation (AM) rate discrimination task and treated with a selective inhibitor of HDAC3 formed memory that was highly specific to the AM rate paired with reward. Sound-specific memory revealed behaviorally was associated with a signal-specific enhancement in temporal coding in the auditory system; stronger phase locking that was specific to the rewarded AM rate was revealed in both the surface-recorded frequency following response and auditory cortical multiunit activity in rats treated with the HDAC3 inhibitor. Furthermore, HDAC3 inhibition increased trial-to-trial cortical response consistency (relative to naive and trained vehicle-treated rats), which generalized across different AM rates. Stronger signal-specific phase locking correlated with individual behavioral differences in memory specificity for the AM signal. These findings support that epigenetic mechanisms regulate activity-dependent processes that enhance discriminability of sensory cues encoded into LTM in both spectral and temporal domains, which may be important for remembering spectrotemporal features of sounds, for example, as in human voices and speech.SIGNIFICANCE STATEMENT Epigenetic mechanisms have recently been implicated in memory and information processing. Here, we use a pharmacological inhibitor of HDAC3 in a sensory model of learning to reveal the ability of HDAC3 to enable precise memory for amplitude-modulated sound cues. In so doing, we uncover neural substrates for memory's specificity for temporal sound cues. Memory specificity was supported by auditory cortical changes in temporal coding, including greater response consistency and stronger phase locking. HDAC3 appears to regulate effects across domains that determine specific cue saliency for behavior. Thus, epigenetic players may gate how sensory information is stored in long-term memory and can be leveraged to reveal the neural substrates of sensory details stored in memory.

Precise memory for pure tones is predicted by measures of learning-induced sensory system neurophysiological plasticity at cortical and subcortical levels

Despite identical learning experiences, individuals differ in the memory formed of those experiences. Molecular mechanisms that control the neurophysiological bases of long-term memory formation might control how precisely the memory formed reflects the actually perceived experience. Memory formed with sensory specificity determines its utility for selectively cueing subsequent behavior, even in novel situations. Here, a rodent model of auditory learning capitalized on individual differences in learning-induced auditory neuroplasticity to identify and characterize neural substrates for sound-specific (vs. general) memory of the training signal's acoustic frequency. Animals that behaviorally revealed a naturally induced signal-"specific" memory exhibited long-lasting signal-specific neurophysiological plasticity in auditory cortical and subcortical evoked responses. Animals with "general" memories did not exhibit learning-induced changes in these same measures. Manipulating a histone deacetylase during memory consolidation biased animals to have more signal-specific memory. Individual differences validated this brain-behavior relationship in both natural and manipulated memory formation, such that the degree of change in sensory cortical and subcortical neurophysiological responses could be used to predict the behavioral precision of memory.

β-adrenergic modulation of discrimination learning and memory in the auditory cortex

Despite vast literature on catecholaminergic neuromodulation of auditory cortex functioning in general, knowledge about its role for long‐term memory formation is scarce. Our previous pharmacological studies on cortex‐dependent frequency‐modulated tone‐sweep discrimination learning of Mongolian gerbils showed that auditory‐cortical D_1/5‐dopamine receptor activity facilitates memory consolidation and anterograde memory formation. Considering overlapping functions of D_1/5‐dopamine receptors and β‐adrenoceptors, we hypothesised a role of β‐adrenergic signalling in the auditory cortex for sweep discrimination learning and memory. Supporting this hypothesis, the β_1/2‐adrenoceptor antagonist propranolol bilaterally applied to the gerbil auditory cortex after task acquisition prevented the discrimination increment that was normally monitored 1 day later. The increment in the total number of hurdle crossings performed in response to the sweeps per se was normal. Propranolol infusion after the seventh training session suppressed the previously established sweep discrimination. The suppressive effect required antagonist injection in a narrow post‐session time window. When applied to the auditory cortex 1 day before initial conditioning, β₁‐adrenoceptor‐antagonising and β₁‐adrenoceptor‐stimulating agents retarded and facilitated, respectively, sweep discrimination learning, whereas β₂‐selective drugs were ineffective. In contrast, single‐sweep detection learning was normal after propranolol infusion. By immunohistochemistry, β₁‐ and β₂‐adrenoceptors were identified on the neuropil and somata of pyramidal and non‐pyramidal neurons of the gerbil auditory cortex. The present findings suggest that β‐adrenergic signalling in the auditory cortex has task‐related importance for discrimination learning of complex sounds: as previously shown for D_1/5‐dopamine receptor signalling, β‐adrenoceptor activity supports long‐term memory consolidation and reconsolidation; additionally, tonic input through β₁‐adrenoceptors may control mechanisms permissive for memory acquisition.

SIRT7 regulates hepatocellular carcinoma response to therapy by altering the p53-dependent cell death pathway

Background

Optimal therapeutic strategies for hepatocellular carcinoma (HCC) patients are still challenging due to the high recurrence rate after surgical resection and chemotherapy resistance. Growing evidence shows that genetic and epigenetic alterations are involved in HCC progression and resistance to therapy, however the molecular mechanisms underlying resistance to therapy have not been fully understood.

Methods

Expression of SIRT7 in 17 paired paraffin-embedded HCC tissues and adjacent nontumoral liver tissues was examined by immunohistochemistry and Western blot. The mRNA expression of SIRT7 in 20 paired frozen HCC tissues and adjacent nontumoral liver tissues was analyzed by quantitative RT-PCR. The biologic consequences of overexpression and knockdown of SIRT7 in HCC therapy sensitivity were studied in vitro and in vivo. Interaction between SIRT7 and p53 were studied in HCC cell lines.

Results

SIRT7 expression was frequently upregulated in clinical HCC samples, and its expression was highly associated with TACE-resistance and poor survival (P = 0.008.) Depletion of SIRT7 from multiple liver cancer cell lines significantly increased doxorubicin toxicity while overexpression of SIRT7 largely abolished doxorubicin induced apoptosis. At the molecular level, we observed that SIRT7 interacts with and induces deacetylation of p53 at lysines 320 and 373. Deacetylated p53 showed significantly less affinity for the NOXA promoter and its transcription. In mouse xenografts, SIRT7 suppression increased doxorubicin induced p53 activation, inhibited tumor growth and induced apoptosis.

Conclusion

The newly identified SIRT7-p53-NOXA axis partially illustrates the molecular mechanism of HCC resistance to therapy and represents a novel potential therapeutic target for HCC treatment.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1246-4) contains supplementary material, which is available to authorized users.

The effect of silymarin supplementation on cognitive impairment induced by diabetes in rats

Background The objective of this investigation was to examine the impact of silymarin supplementation on locomotion, anxiety-related behavior, learning, and memory via several behavioral tests, such as open field, elevated plus maze, and Morris water maze tests in streptozotocin-induced diabetic rats. Methods The rats were divided into the control, diabetes, silymarin, and diabetes plus silymarin groups. On the 30th-35th days of the study, several behavioral tests were performed and blood and brain tissue samples were taken and brain-derived neurotrophic factor (BDNF) and histone deacetylase 3 (HDAC3) levels were analyzed. Results There was no significant difference in locomotor activity between the groups (p = 0.534). Spatial memory was lower (p = 0.000) but anxiety scores were higher (p = 0.005) in the diabetes group than in the control, silymarin, and diabetes plus silymarin groups. Plasma (p = 0.000) and brain tissue (p = 0.007) BDNF levels were lower in the diabetes group than in the control, silymarin, and diabetes plus silymarin groups; however, plasma (p = 0.432) and brain tissue (p = 0.321) HDAC3 levels did not significantly differ between the groups. Conclusions The findings obtained from this study suggest that silymarin supplementation could improve anxiety-related behavior, and learning and memory in diabetic rats by increasing the BDNF levels.

A Natural Isoquinoline Alkaloid With Antitumor Activity: Studies of the Biological Activities of Berberine

Coptis, a traditional medicinal plant, has been used widely in the field of traditional Chinese medicine for many years. More recently, the chemical composition and bioactivity of Coptis have been studied worldwide. Berberine is a main component of Rhizoma Coptidis. Modern medicine has confirmed that berberine has pharmacological activities, such as anti-inflammatory, analgesic, antimicrobial, hypolipidemic, and blood pressure-lowering effects. Importantly, the active ingredient of berberine has clear inhibitory effects on various cancers, including colorectal cancer, lung cancer, ovarian cancer, prostate cancer, liver cancer, and cervical cancer. Cancer, ranked as one of the world’s five major incurable diseases by WHO, is a serious threat to the quality of human life. Here, we try to outline how berberine exerts antitumor effects through the regulation of different molecular pathways. In addition, the berberine-mediated regulation of epigenetic mechanisms that may be associated with the prevention of malignant tumors is described. Thus, this review provides a theoretical basis for the biological functions of berberine and its further use in the clinical treatment of cancer.