HDAC1 negatively regulates Bdnf and Pvalb required for parvalbumin interneuron maturation in an experience-dependent manner

Gene-environmental regulation of the postnatal post-mitotic neuronal maturation

Embryonic neurodevelopment, particularly neural progenitor differentiation into post-mitotic neurons, has been extensively studied. While the number and composition of post-mitotic neurons remain relatively constant from birth to adulthood, the brain undergoes significant postnatal maturation marked by major property changes frequently disrupted in neural diseases. This review first summarizes recent characterizations of the functional and molecular maturation of the postnatal nervous system. We then review regulatory mechanisms controlling the precise gene expression changes crucial for the intricate sequence of maturation events, highlighting experience-dependent versus cell-intrinsic genetic timer mechanisms. Despite significant advances in understanding of the gene-environmental regulation of postnatal neuronal maturation, many aspects remain unknown. The review concludes with our perspective on exciting future research directions in the next decade.

Azadiradione up-regulates the expression of parvalbumin and BDNF via Ube3a

Azadiradione is a small bioactive limonoid found in the seed of Azadirachta Indica, an Indian medicinal plant commonly known as Neem. Recently, it has been shown to ameliorate the disease pathology in fly and mouse model of Huntington's disease by restoring impaired proteostasis. Here we report that the azadiradione could be involved in modulating the synaptic function through increased expression of Ube3a, a dual function protein having ubiquitin ligase and co-activator functions and associated with Angelman syndrome and autism. Treatment of azadiradione to HT22 hippocampal cell line and in adult mice induced the expression of Ube3a as well as two important synaptic function and plasticity regulating proteins, parvalbumin and brain-derived neurotropic factor (BDNF). Interestingly, another synaptic plasticity modulating protein Arc (activity-regulated cytoskeletal associated protein) was down-regulated by azadiradione. Partial knockdown of Ube3a in HT22 cell abrogated azadiradione induced expression of parvalbumin and BDNF. Ube3a-maternal deficient mice also exhibited significantly decreased expression of parvalbumin and BDNF in their brain and treatment of azadiradione in these animals did not rescue the altered expression of either parvalbumin or BDNF. These results indicate that azadiradione-induced expression of parvalbumin and BDNF in the brain is mediated through Ube3a and suggest that azadiradione could be implicated in restoring synaptic dysfunction in many neuropsychiatric/neurodegenerative disorders.

Smilagenin induces expression and epigenetic remodeling of BDNF in alzheimer's disease

BACKGROUND

Smilagenin (SMI) is a lipid-soluble steroidal sapogenin, extracted from traditional Chinses medicinal herbs Radix Asparagi, which is extracted from the dry root of Asparagus cochinchinensis (Lour.) Merr. We previously found that SMI significantly increased brain-derived neurotrophic factor (BDNF) expression in Aβ-intoxicated SH-SY5Y cells.

METHODS

In this study, we performed behavioral tests to analyze cognitive function of WT and APP/PS1 mice treated with or without SMI, and found that SMI could significantly improve the learning and memory ability of APP/PS1 mice. Moreover, immunofluorescence and ELISA results showed that SMI pretreatment could effectively reduce the deposition of β-amyloid plaques in the cortex and hippocampus of APP/PS1 mice (26 mg/kg/day for 60 days) and inhibit the secretion of Aβ1-42 in N2a/APPswe cells (10 μM concentration for 24 hours).

RESULTS

Mechanistically, SMI enhanced BDNF mRNA expression, elevated the global level of H3AC and H4AC, and increased the expression of P300 in AD models. Furthermore, chromatin immunoprecipitation results showed that SMI could increase the levels of H3AC and H4AC at the promoter of BDNF promoter Ⅱ and Ⅳ, indicating that SMI epigenetically regulates BDNF expression through HAT enhancement. To further verify the critical role of P300 by which SMI upregulated histone acetylation in BDNF, AD mice were treated with SMI and C646 simultaneously. Behavioral experiments showed that the improvement effects of SMI on cognitive impairment were abolished after P300 inhibition in APP/PS1 mice.

CONCLUSIONS

Our research for the first time demonstrated that SMI showed neuroprotective effects by increasing the expression of P300 protein, thus upregulating histone acetylation levels in the promoter region of BDNF and promoting its transcription. Our findings provide an important theoretical basis for the treatment of Alzheimer's disease with SMI extracted from Asparagus cochinchinensis (Lour.) Merr.

HDAC1-mediated regulation of GABA signaling within the lateral septum facilitates long-lasting social fear extinction in male mice

Social anxiety disorder (SAD) is caused by traumatic social experiences. It is characterized by intense fear and avoidance of social contexts, which can be robustly mimicked by the social fear conditioning (SFC) paradigm. The extinction phase of the SFC paradigm is akin to exposure therapy for SAD and requires learning to disassociate the trauma with the social context. Learning-induced acetylation of histones is critical for extinction memory formation and its endurance. Although class I histone deacetylases (HDACs) regulate the abovementioned learning process, there is a lack of clarity in isoforms and spatial specificity in HDAC function in social learning. Utilizing the SFC paradigm, we functionally characterized the role of HDAC1, specifically in the lateral septum (LS), in regulating the formation of long-term social fear extinction memory. We measured a local increase in activity-inducing HDAC1 phosphorylation at serine residues of social fear-conditioned (SFC⁺) mice in response to the extinction of social fear. We also found that LS-HDAC1 function negatively correlates with acute social fear extinction learning using pharmacological and viral approaches. Further, inhibition of LS-HDAC1 enhanced the expression of the GABA-A receptor β1 subunit (Gabrb1) in SFC⁺ mice, and activation of GABA-A receptors facilitated acute extinction learning. Finally, the facilitation of extinction learning by HDAC1 inhibition or GABA-A receptor activation within the LS led to the formation of long-lasting extinction memory, which persisted even 30 days after extinction. Our results show that HDAC1-mediated regulation of GABA signaling in the LS is crucial for the formation of long-lasting social fear extinction memory.

Age- and sex-specific effects of stress on parvalbumin interneurons in preclinical models: Relevance to sex differences in clinical neuropsychiatric and neurodevelopmental disorders

Stress is a major risk factor for neurodevelopmental and neuropsychiatric disorders, with the capacity to impact susceptibility to disease as well as long-term neurobiological and behavioral outcomes. Parvalbumin (PV) interneurons, the most prominent subtype of GABAergic interneurons in the cortex, are uniquely responsive to stress due to their protracted development throughout the highly plastic neonatal period and into puberty and adolescence. Additionally, PV + interneurons appear to respond to stress in a sex-specific manner. This review aims to discuss existing preclinical studies that support our overall hypothesis that the sex-and age-specific impacts of stress on PV + interneurons contribute to differences in individual vulnerability to stress across the lifespan, particularly in regard to sex differences in the diagnostic rate of neurodevelopmental and neuropsychiatric diseases in clinical populations. We also emphasize the importance of studying sex as a biological variable to fully understand the mechanistic and behavioral differences between males and females in models of neuropsychiatric disease.

The interplay of seizures-induced axonal sprouting and transcription-dependent Bdnf repositioning in the model of temporal lobe epilepsy

The Brain-Derived Neurotrophic Factor is one of the most important trophic proteins in the brain. The role of this growth factor in neuronal plasticity, in health and disease, has been extensively studied. However, mechanisms of epigenetic regulation of Bdnf gene expression in epilepsy are still elusive. In our previous work, using a rat model of neuronal activation upon kainate-induced seizures, we observed a repositioning of Bdnf alleles from the nuclear periphery towards the nuclear center. This change of Bdnf intranuclear position was associated with transcriptional gene activity. In the present study, using the same neuronal activation model, we analyzed the relation between the percentage of the Bdnf allele at the nuclear periphery and clinical and morphological traits of epilepsy. We observed that the decrease of the percentage of the Bdnf allele at the nuclear periphery correlates with stronger mossy fiber sprouting-an aberrant form of excitatory circuits formation. Moreover, using in vitro hippocampal cultures we showed that Bdnf repositioning is a consequence of transcriptional activity. Inhibition of RNA polymerase II activity in primary cultured neurons with Actinomycin D completely blocked Bdnf gene transcription and repositioning occurring after neuronal excitation. Interestingly, we observed that histone deacetylases inhibition with Trichostatin A induced a slight increase of Bdnf gene transcription and its repositioning even in the absence of neuronal excitation. Presented results provide novel insight into the role of BDNF in epileptogenesis. Moreover, they strengthen the statement that this particular gene is a good candidate to search for a new generation of antiepileptic therapies.

Deep Learning-Based Classification of GAD67-Positive Neurons Without the Immunosignal

Excitatory neurons and GABAergic interneurons constitute neural circuits and play important roles in information processing. In certain brain regions, such as the neocortex and the hippocampus, there are fewer interneurons than excitatory neurons. Interneurons have been quantified via immunohistochemistry, for example, for GAD67, an isoform of glutamic acid decarboxylase. Additionally, the expression level of other proteins varies among cell types. For example, NeuN, a commonly used marker protein for postmitotic neurons, is expressed differently across brain regions and cell classes. Thus, we asked whether GAD67-immunopositive neurons can be detected using the immunofluorescence signals of NeuN and the fluorescence signals of Nissl substances. To address this question, we stained neurons in layers 2/3 of the primary somatosensory cortex (S1) and the primary motor cortex (M1) of mice and manually labeled the neurons as either cell type using GAD67 immunosignals. We then sought to detect GAD67-positive neurons without GAD67 immunosignals using a custom-made deep learning-based algorithm. Using this deep learning-based model, we succeeded in the binary classification of the neurons using Nissl and NeuN signals without referring to the GAD67 signals. Furthermore, we confirmed that our deep learning-based method surpassed classic machine-learning methods in terms of binary classification performance. Combined with the visualization of the hidden layer of our deep learning algorithm, our model provides a new platform for identifying unbiased criteria for cell-type classification.

Regulation of Thyroid-disrupting Chemicals to Protect the Developing Brain

Synthetic chemicals with endocrine disrupting properties are pervasive in the environment and are present in the bodies of humans and wildlife. As thyroid hormones (THs) control normal brain development, and maternal hypothyroxinemia is associated with neurological impairments in children, chemicals that interfere with TH signaling are of considerable concern for children's health. However, identifying thyroid-disrupting chemicals (TDCs) in vivo is largely based on measuring serum tetraiodothyronine in rats, which may be inadequate to assess TDCs with disparate mechanisms of action and insufficient to evaluate the potential neurotoxicity of TDCs. In this review 2 neurodevelopmental processes that are dependent on TH action are highlighted, neuronal migration and maturation of gamma amino butyric acid-ergic interneurons. We discuss how interruption of these processes by TDCs may contribute to abnormal brain circuitry following developmental TH insufficiency. Finally, we identify issues in evaluating the developmental neurotoxicity of TDCs and the strengths and limitations of current approaches designed to regulate them. It is clear that an enhanced understanding of how THs affect brain development will lead to refined toxicity testing, reducing uncertainty and improving our ability to protect children's health.

Endocannabinoid Signaling Contributes to Experience-Induced Increase of Synaptic Release Sites From Parvalbumin Interneurons in Mouse Visual Cortex

During postnatal development of the visual cortex between eye-opening to puberty, visual experience promotes a gradual increase in the strength of inhibitory synaptic connections from parvalbumin-positive interneurons (PV-INs) onto layer 2/3 pyramidal cells. However, the detailed connectivity properties and molecular mechanisms underlying these developmental changes are not well understood. Using dual-patch clamp in brain slices from G42 mice, we revealed that both connection probability and the number of synaptic release sites contributed to the enhancement of synaptic strength. The increase of release site number was hindered by dark rearing from eye-opening and rescued by 3-days re-exposure to the normal visual environment. The effect of light re-exposure on restoring synaptic release sites in dark reared mice was mimicked by the agonist of cannabinoid-1 (CB1) receptors and blocked by an antagonist of these receptors, suggesting a role for endocannabinoid signaling in light-induced maturation of inhibitory connectivity from PV-INs to pyramidal cells during postnatal development.

Critical period regulation across multiple timescales

Brain plasticity is dynamically regulated across the life span, peaking during windows of early life. Typically assessed in the physiological range of milliseconds (real time), these trajectories are also influenced on the longer timescales of developmental time (nurture) and evolutionary time (nature), which shape neural architectures that support plasticity. Properly sequenced critical periods of circuit refinement build up complex cognitive functions, such as language, from more primary modalities. Here, we consider recent progress in the biological basis of critical periods as a unifying rubric for understanding plasticity across multiple timescales. Notably, the maturation of parvalbumin-positive (PV) inhibitory neurons is pivotal. These fast-spiking cells generate gamma oscillations associated with critical period plasticity, are sensitive to circadian gene manipulation, emerge at different rates across brain regions, acquire perineuronal nets with age, and may be influenced by epigenetic factors over generations. These features provide further novel insight into the impact of early adversity and neurodevelopmental risk factors for mental disorders.

Histone deacetylases 1, 2 and 3 in nervous system development

Although histone acetylases (HDACS) were initially believed to render chromatin in a transcriptionally repressed state by deacetylating histones, it is now known that they both repress and activate transcription. Moreover, HDACs regulate the activity and/or function of a large number of other cellular proteins localized in the nucleus and cytoplasm. Accumulating evidence indicates that HDACs also play a key role in the development of the nervous system. This review focuses on three classical HDACS - HDACs 1, 2 and 3. Although much evidence on the involvement of HDACs in neurodevelopment has come from the use of pharmacological inhibitors, because these agents are not specific in their action on individual HDAC proteins, this review only describes evidence derived from the use of molecular genetic approaches. Our review describes that HDACs 1, 2 and 3 play crucial roles in neurodevelopment by regulating neurogenesis, gliogenesis, the development of neural circuitry and synaptic transmission.

Role for calcium signaling in manganese neurotoxicity

BACKGROUND

Calcium is an essential macronutrient that is involved in many cellular processes. Homeostatic control of intracellular levels of calcium ions [Ca²⁺] is vital to maintaining cellular structure and function. Several signaling molecules are involved in regulating Ca²⁺ levels in cells and perturbation of calcium signaling processes is implicated in several neurodegenerative and neurologic conditions. Manganese [Mn] is a metal which is essential for basic physiological functions. However, overexposure to Mn from environmental contamination and workplace hazards is a global concern. Mn overexposure leads to its accumulation in several human organs particularly the brain. Mn accumulation in the brain results in a manganism, a Parkinsonian-like syndrome. Additionally, Mn is a risk factor for several neurodegenerative diseases including Parkinson's disease and Alzheimer's disease. Mn neurotoxicity also affects several neurotransmitter systems including dopaminergic, cholinergic and GABAergic. The mechanisms of Mn neurotoxicity are still being elucidated.

AIM

The review will highlight a potential role for calcium signaling molecules in the mechanisms of Mn neurotoxicity.

CONCLUSION

Ca²⁺ regulation influences the neurodegenerative process and there is possible role for perturbed calcium signaling in Mn neurotoxicity. Mechanisms implicated in Mn-induced neurodegeneration include oxidative stress, generation of free radicals, and apoptosis. These are influenced by mitochondrial integrity which can be dependent on intracellular Ca²⁺ homeostasis. Nevertheless, further elucidation of the direct effects of calcium signaling dysfunction and calcium-binding proteins activities in Mn neurotoxicity is required.

Repetitive transcranial magnetic stimulation recovers cortical map plasticity induced by sensory deprivation due to deafferentiation

KEY POINTS

Partial sensory deprivation (deafferentation) by removing whiskers from the rat snout resulted in a reduced responsiveness of related cortical representations. Repetitive transcranial magnetic stimulation (three blocks of intermittent theta-burst) applied for 5 days in combination with sensory exploration restored the normal responsiveness level of the deafferented barrel cortex. However, intracortical inhibition (lateral and recurrent) appeared to be reduced after repetitive transcranial magnetic stimulation, probably as the cause of improved responsiveness. Repetitive transcranial magnetic stimulation also reduced the asymmetry of the lateral spread of sensory activity.

ABSTRACT

Repetitive transcranial magnetic stimulation (rTMS) modulates human cortical excitability. It has the potential to support recovery to normal cortical function when the excitation-inhibition balance is altered (e.g. after a stroke or loss of sensory input). We tested cortical map plasticity on the basis of sensory responses (local field potentials, LFPs) and expression of neuronal activity marker proteins within the barrel cortex of rats receiving either active or sham rTMS after selective unilateral deafferentation by whiskers plucking. Rats received daily rTMS [intermittent theta-burst (iTBS), active or sham] for 5 days before exploring an enriched environment. Our previous studies indicated a disinhibitory effect of iTBS on cortical activity. Therefore, we also expected disinhibitory effects if deafferentation causes depression of sensory responses. Deafferentation resulted in an acute general reduction of sensory responsiveness and enhanced expression of inhibitory activity markers (GAD67, parvalbumin) in the deafferented hemisphere. Active but not sham-iTBS-rTMS normalized these measures. The stronger caudal-to-frontal horizontal spread of activity across barrels was reduced after deafferentation but not restored after active iTBS, despite generally increased responses. Fitting the LFP data with a computational model of different strengths and types of excitatory and inhibitory connections further revealed an iTBS-induced reduction of lateral and recurrent inhibition as the most probable scenario. Whether the disinhibitory effect of iTBS for the restoration of normal cortical function in the acute phase of depression after deafferentiation is also beneficial in humans remains to be demonstrated. As recently discussed, disinhibition appears to be required to open a window for neuronal plasticity.

Adolescent social isolation affects parvalbumin expression in the medial prefrontal cortex in the MAM-E17 model of schizophrenia

Altered parvalbumin (PV) expression is observed in the prefrontal cortex of subjects with schizophrenia. Environmental context, particularly during adolescence, might regulate PV expression. In the present study, we investigated the effect of adolescent social isolation (SI) on PV expression in the medial prefrontal cortex in a neurodevelopmental model (MAM-E17) of schizophrenia. SI exposure occurred from postnatal day 30 to 40, followed by resocialization until late adolescence or early adulthood. PV mRNA and protein levels, as well as the number of PV cells, were analysed at these ages. Moreover, epigenetic regulation of PV expression by histone methylation was examined by measuring the total and PV gene-bound H3K4me3 levels. MAM only decreased levels of the PV mRNA and protein in adulthood. Decreases in total H3K4me3 levels and its level at the PV gene were also observed at this age. In contrast, in late adolescence, SI induced a decrease in the expression of the PV mRNA in the MAM group that was related to the reduction in total and PV gene-bound H3K4me3 levels. However, at this age, SI increased the levels of the PV protein in both the control and MAM groups. In adulthood, SI did not affect PV mRNA or H3K4me3 levels but decreased levels of the PV protein in both groups. Both MAM and SI failed to change the number of PV cells at any age. The results indicate that adolescent SI accelerated epigenetic impairments of PV expression in MAM-E17 rats; however, subsequent resocialization abolished this dysfunction, but failed to prevent alterations in PV protein.

Juvenile stress induces behavioral change and affects perineuronal net formation in juvenile mice

Background

Many neuropsychiatric disorders develop in early life. Although the mechanisms involved have not been elucidated, it is possible that functional abnormalities of parvalbumin-positive interneurons (PV neurons) are present. Several previous studies have shown that juvenile stress is implicated in the development of neuropsychiatric disorders. We aimed to clarify the effects of juvenile stress on behavior and on the central nervous system. We investigated behavioral abnormalities of chronically-stressed mice during juvenilehood and the effect of juvenile stress on PV neurons and WFA-positive perineuronal nets (PNNs), which are associated with vulnerability and plasticity in the mouse brain.

Results

Due to juvenile stress, mice showed neurodevelopmental disorder-like behavior. Juvenile stressed mice did not show depressive-like behaviors, but on the contrary, they showed increased activity and decreased anxiety-like behavior. In the central nervous system of juvenile stressed mice, the fluorescence intensity of WFA-positive PNNs decreased, which may signify increased vulnerability.

Conclusion

This study suggested that juvenile stressed mice showed behavioral abnormalities, resembling those seen in neuropsychiatric disorders, and increased brain vulnerability.

Synaptic and circuit development of the primary sensory cortex

Animals, including humans, optimize their primary sensory cortex through the use of input signals, which allow them to adapt to the external environment and survive. The time window at the beginning of life in which external input signals are connected sensitively and strongly to neural circuit optimization is called the critical period. The critical period has attracted the attention of many neuroscientists due to the rapid activity-/experience-dependent circuit development that occurs, which is clearly differentiated from other developmental time periods and brain areas. This process involves various types of GABAergic inhibitory neurons, the extracellular matrix, neuromodulators, transcription factors, and neurodevelopmental factors. In this review, I discuss recent progress regarding the biological nature of the critical period that contribute to a better understanding of brain development.

Molecular mechanisms of experience-dependent maturation in cortical GABAergic inhibition

Critical periods (CP) in early post-natal life are periods of plasticity during which the neuronal circuitry is most receptive to environmental stimuli. These early experiences translate to a more permanent and sophisticated neuronal connection in the adult brain systems. Multiple studies have pointed to the development of inhibitory circuitry as one of the central factors for the onset of critical periods. We discuss several molecular mechanisms regulating inhibitory circuit maturation and CP, from gene transcription level to protein signaling level. Also, beyond the level of gene sequences, we briefly consider recent information on dynamic epigenetic regulation of gene expression through histone methylation and acetylation and their implication on timed development of the inhibitory circuitry for the onset of CP.

Defining a critical period for inhibitory circuits within the somatosensory cortex

Although experience-dependent changes in brain inhibitory circuits are thought to play a key role during the “critical period” of brain development, the nature and timing of these changes are poorly understood. We examined the role of sensory experience in sculpting an inhibitory circuit in the primary somatosensory cortex (S1) of mice by using optogenetics to map the connections between parvalbumin (PV) expressing interneurons and layer 2/3 pyramidal cells. Unilateral whisker deprivation decreased the strength and spatial range of inhibitory input provided to pyramidal neurons by PV interneurons in layers 2/3, 4 and 5. By varying the time when sensory input was removed, we determined that the critical period closes around postnatal day 14. This yields the first precise time course of critical period plasticity for an inhibitory circuit.

HDAC1 links early life stress to schizophrenia-like phenotypes

Schizophrenia is a devastating disease that arises on the background of genetic predisposition and environmental risk factors, such as early life stress (ELS). In this study, we show that ELS-induced schizophrenia-like phenotypes in mice correlate with a widespread increase of histone-deacetylase 1 (Hdac1) expression that is linked to altered DNA methylation. Hdac1 overexpression in neurons of the medial prefrontal cortex, but not in the dorsal or ventral hippocampus, mimics schizophrenia-like phenotypes induced by ELS. Systemic administration of an HDAC inhibitor rescues the detrimental effects of ELS when applied after the manifestation of disease phenotypes. In addition to the hippocampus and prefrontal cortex, mice subjected to ELS exhibit increased Hdac1 expression in blood. Moreover, Hdac1 levels are increased in blood samples from patients with schizophrenia who had encountered ELS, compared with patients without ELS experience. Our data suggest that HDAC1 inhibition should be considered as a therapeutic approach to treat schizophrenia.