NPAS4 Exacerbates Pyroptosis via Transcriptionally Regulating NLRP6 in the Acute Phase of Intracerebral Hemorrhage in Mice

Intracerebral hemorrhage (ICH) is a severe cerebrovascular disease with a high disability rate and high mortality, and pyroptosis is a type of programmed cell death in the acute phase of ICH. Neuronal Per-Arnt-Sim domain protein 4 (Npas4) is a specific transcription factor highly expressed in the nervous system, yet the role of NPAS4 in ICH-induced pyroptosis is not fully understood. NLR family Pyrin-domain-containing 6 (NLRP6), a new member of the Nod-like receptor family, aggravates pyroptosis via activating cysteine protease-1 (Caspase-1) and Caspase-11. In this study, we found that NPAS4 was upregulated in human and mouse peri-hematoma brain tissues and peaked at approximately 24 h after ICH modeling. Additionally, NPAS4 knockdown improved neurologic dysfunction and brain damage induced by ICH in mice after 24 h. Meanwhile, inhibiting NPAS4 expression reduced the levels of myeloperoxidase (MPO)-positive cells and Caspase-1/TUNEL-double-positive cells and decreased cleaved Caspase-1, cleaved Caspase-11, and N-terminal GSDMD levels. Consistently, NPAS4 overexpression reversed the above alternations after ICH in the mice. Moreover, NPAS4 could interact with the Nlrp6 promoter region (-400--391 bp and -33--24 bp) and activate the transcription of Nlrp6. Altogether, our study demonstrated that NPAS4, as a transcription factor, can exacerbate pyroptosis and transcriptionally activate NLRP6 in the acute phase of intracerebral hemorrhage in mice.

NPAS4 in the medial prefrontal cortex mediates chronic social defeat stress-induced anhedonia-like behavior and reductions in excitatory synapses

Chronic stress can produce reward system deficits (i.e., anhedonia) and other common symptoms associated with depressive disorders, as well as neural circuit hypofunction in the medial prefrontal cortex (mPFC). However, the molecular mechanisms by which chronic stress promotes depressive-like behavior and hypofrontality remain unclear. We show here that the neuronal activity-regulated transcription factor, NPAS4, in the mPFC is regulated by chronic social defeat stress (CSDS), and it is required in this brain region for CSDS-induced changes in sucrose preference and natural reward motivation in the mice. Interestingly, NPAS4 is not required for CSDS-induced social avoidance or anxiety-like behavior. We also find that mPFC NPAS4 is required for CSDS-induced reductions in pyramidal neuron dendritic spine density, excitatory synaptic transmission, and presynaptic function, revealing a relationship between perturbation in excitatory synaptic transmission and the expression of anhedonia-like behavior in the mice. Finally, analysis of the mice mPFC tissues revealed that NPAS4 regulates the expression of numerous genes linked to glutamatergic synapses and ribosomal function, the expression of upregulated genes in CSDS-susceptible animals, and differentially expressed genes in postmortem human brains of patients with common neuropsychiatric disorders, including depression. Together, our findings position NPAS4 as a key mediator of chronic stress-induced hypofrontal states and anhedonia-like behavior.

Structures of NPAS4-ARNT and NPAS4-ARNT2 heterodimers reveal new dimerization modalities in the bHLH-PAS transcription factor family

Neuronal PER-ARNT-SIM (PAS) domain protein 4 (NPAS4) is a protective transcriptional regulator whose dysfunction has been linked to a variety of neuropsychiatric and metabolic diseases. As a member of the basic helix-loop-helix PER-ARNT-SIM (bHLH-PAS) transcription factor family, NPAS4 is distinguished by an ability to form functional heterodimers with aryl hydrocarbon receptor nuclear translocator (ARNT) and ARNT2, both of which are also bHLH-PAS family members. Here, we describe the quaternary architectures of NPAS4-ARNT and NPAS4-ARNT2 heterodimers in complexes involving DNA response elements. Our crystallographic studies reveal a uniquely interconnected domain conformation for the NPAS4 protein itself, as well as its differentially configured heterodimeric arrangements with both ARNT and ARNT2. Notably, the PAS-A domains of ARNT and ARNT2 exhibit variable conformations within these two heterodimers. The ARNT PAS-A domain also forms a set of interfaces with the PAS-A and PAS-B domains of NPAS4, different from those previously noted in ARNT heterodimers formed with other class I bHLH-PAS family proteins. Our structural observations together with biochemical and cell-based interrogations of these NPAS4 heterodimers provide molecular glimpses of the NPAS4 protein architecture and extend the known repertoire of heterodimerization patterns within the bHLH-PAS family. The PAS-B domains of NPAS4, ARNT, and ARNT2 all contain ligand-accessible pockets with appropriate volumes required for small-molecule binding. Given NPAS4's linkage to human diseases, the direct visualization of these PAS domains and the further understanding of their relative positioning and interconnections within the NPAS4-ARNT and NPAS4-ARNT2 heterodimers may provide a road map for therapeutic discovery targeting these complexes.

NPAS4 Polymorphisms Contribute to Coronary Heart Disease (CHD) Risk

As genetic inheritance is an inevitable risk factor in the development of coronary heart disease (CHD), it is critical to identify the polymorphisms of CHD risk. This study explored whether the NPAS4 polymorphisms are related to the CHD risk in the Chinese Han population. Five SNPs in NPAS4 were genotyped using Agena Mass ARRAY from 499 CHD and 500 controls. RT-PCR detected the NPAS4 expression levels in peripheral blood mononuclear cells from 50 CHD and 50 controls. χ² test compared the distributions of gender, allele and genotypes frequencies between cases and controls. Logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (95% CIs). MDR analyzed the SNP-SNP interactions on risk of CHD. U test compared the differences in gene expression between different groups. The results showed that rs4466842 was correlated with an increased CHD risk in overall, males and age ≤ 60; rs117186164 and rs12785321 were significantly related to an increased CHD risk in male and age ≤ 60, respectively; haplotype A_rs117186164C_rs4466842 was significantly correlated with an increased CHD risk. SNP-SNP interactions results showed that the best model was the four-locus model was the combination of rs117770654, rs117957381, rs12785321, and rs4466842 (CVC = 10/10, Testing Sensitivity = 0.647). The expression levels of NPAS4 in the case group (0.365 ± 0.139) were significantly lower than that in the control group (0.782 ± 0.224) (P < 0.001). The results revealed that SNPs in NPAS4 may play an important role in the occurrence and development of CHD.

REST/NRSF drives homeostatic plasticity of inhibitory synapses in a target-dependent fashion

The repressor-element 1-silencing transcription/neuron-restrictive silencer factor (REST/NRSF) controls hundreds of neuron-specific genes. We showed that REST/NRSF downregulates glutamatergic transmission in response to hyperactivity, thus contributing to neuronal homeostasis. However, whether GABAergic transmission is also implicated in the homeostatic action of REST/NRSF is unknown. Here, we show that hyperactivity-induced REST/NRSF activation, triggers a homeostatic rearrangement of GABAergic inhibition, with increased frequency of miniature inhibitory postsynaptic currents (IPSCs) and amplitude of evoked IPSCs in mouse cultured hippocampal neurons. Notably, this effect is limited to inhibitory-onto-excitatory neuron synapses, whose density increases at somatic level and decreases in dendritic regions, demonstrating a complex target- and area-selectivity. The upscaling of perisomatic inhibition was occluded by TrkB receptor inhibition and resulted from a coordinated and sequential activation of the Npas4 and Bdnf gene programs. On the opposite, the downscaling of dendritic inhibition was REST-dependent, but BDNF-independent. The findings highlight the central role of REST/NRSF in the complex transcriptional responses aimed at rescuing physiological levels of network activity in front of the ever-changing environment.

NPAS4 suppresses propofol-induced neurotoxicity by inhibiting autophagy in hippocampal neuronal cells

Propofol, a general intravenous anesthetic, has been demonstrated to cause a profound neuroapoptosis in the developing brain followed by long-term neurocognitive impairment. Our study aimed to examine the neuroprotective effect of neuronal PAS domain protein 4 (NPAS4), an activity-dependent neuron-specific transcription factor, on propofol-induced neurotoxicity in hippocampal neuronal HT22 cells. The differentially expressed genes in HT22 cells after treatment with propofol were screened from Gene Expression Omnibus dataset GSE106799. NPAS4 expression in HT22 cells treated with different doses of propofol was investigated by qRT-PCR and Western blot analysis. Cell viability, lactate dehydrogenase (LDH) release, caspase-3 activity, and apoptosis were evaluated by MTT, a LDH-Cytotoxicity Assay Kit, a Caspase-3 Colorimetric Assay Kit, and TUNEL assay, respectively. The protein levels of LC3-I, LC3-II, Beclin 1, p62 and NPAS4 were detected using Western blot analysis. Propofol treatment concentration-dependently decreased NPAS4 expression in HT22 cells. Propofol treatment inhibited cell viability, increased LDH release and caspase-3 activity, and induced apoptosis and autophagy in HT22 cells. NPAS4 overexpression suppressed propofol-induced cell injury and autophagy in HT22 cells. Mechanistically, autophagy agonist rapamycin attenuated the neuroprotective effect of NPAS4 in propofol-treated HT22 cells. In conclusion, NAPS4 overexpression protected hippocampal neuronal HT22 cells against propofol-induced neurotoxicity by reducing autophagy.

NPAS4 regulates the transcriptional response of the suprachiasmatic nucleus to light and circadian behavior

The suprachiasmatic nucleus (SCN) is the master circadian pacemaker in mammals and is entrained by environmental light. However, the molecular basis of the response of the SCN to light is not fully understood. We used RNA/chromatin immunoprecipitation/single-nucleus sequencing with circadian behavioral assays to identify mouse SCN cell types and explore their responses to light. We identified three peptidergic cell types that responded to light in the SCN: arginine vasopressin (AVP), vasoactive intestinal peptide (VIP), and cholecystokinin (CCK). In each cell type, light-responsive subgroups were enriched for expression of neuronal Per-Arnt-Sim (PAS) domain protein 4 (NPAS4) target genes. Further, mice lacking Npas4 had a longer circadian period under constant conditions, a damped phase response curve to light, and reduced light-induced gene expression in the SCN. Our data indicate that NPAS4 is necessary for normal transcriptional responses to light in the SCN and critical for photic phase-shifting of circadian behavior.

Single Exposure to the Cathinones MDPV and α-PVP Alters Molecular Markers of Neuroplasticity in the Adult Mouse Brain

Synthetic cathinones have gained popularity among young drug users and are widely used in the clandestine market. While the cathinone-induced behavioral profile has been extensively investigated, information on their neuroplastic effects is still rather fragmentary. Accordingly, we have exposed male mice to a single injection of MDPV and α-PVP and sacrificed the animals at different time points (i.e., 30 min, 2 h, and 24 h) to have a rapid readout of the effect of these psychostimulants on neuroplasticity in the frontal lobe and hippocampus, two reward-related brain regions. We found that a single, low dose of MDPV or α-PVP is sufficient to alter the expression of neuroplastic markers in the adult mouse brain. In particular, we found increased expression of the transcription factor Npas4, increased ratio between the vesicular GABA transporter and the vesicular glutamate transporter together with changes in the expression of the neurotrophin Bdnf, confirming the widespread impact of these cathinones on brain plasticity. To sum up, exposure to low dose of cathinones can impair cortical and hippocampal homeostasis, suggesting that abuse of these cathinones at much higher doses, as it occurs in humans, could have an even more profound impact on neuroplasticity.

The Participation of the Intrinsically Disordered Regions of the bHLH-PAS Transcription Factors in Disease Development

The basic helix–loop–helix/Per-ARNT-SIM (bHLH-PAS) proteins are a family of transcription factors regulating expression of a wide range of genes involved in different functions, ranging from differentiation and development control by oxygen and toxins sensing to circadian clock setting. In addition to the well-preserved DNA-binding bHLH and PAS domains, bHLH-PAS proteins contain long intrinsically disordered C-terminal regions, responsible for regulation of their activity. Our aim was to analyze the potential connection between disordered regions of the bHLH-PAS transcription factors, post-transcriptional modifications and liquid-liquid phase separation, in the context of disease-associated missense mutations. Highly flexible disordered regions, enriched in short motives which are more ordered, are responsible for a wide spectrum of interactions with transcriptional co-regulators. Based on our in silico analysis and taking into account the fact that the functions of transcription factors can be modulated by posttranslational modifications and spontaneous phase separation, we assume that the locations of missense mutations inducing disease states are clearly related to sequences directly undergoing these processes or to sequences responsible for their regulation.

Circular RNA circ_0003420 mediates inflammation in sepsis-induced liver damage by downregulating neuronal PAS domain protein 4

OBJECTIVE

Our aim was to investigate whether circular RNA (circRNA) circ_0003420 mediates inflammation in sepsis-induced liver damage and to determine the mechanism involved.

MATERIALS AND METHODS

Liver tissue samples from patients with sepsis and healthy subjects were used to identify differentially expressed circRNAs. Additionally, Kupffer cells were treated with lipopolysaccharide (LPS) to establish an in vitro model of sepsis-induced liver damage. Cell viability and proliferation were measured with a cell counting kit-8 and 5-ethynyl-2'-deoxyuridine (EdU) labeling, respectively. Relative mRNA and protein levels of IL-6, IL-1β, tumor necrosis factor (TNF)-α, and neuronal PAS domain protein 4 (NPAS4) were determined via reverse-transcription quantitative PCR and western blotting, respectively.

RESULTS

We observed circ_0003420 upregulation accompanied by NPAS4 downregulation in liver samples from patients with sepsis-associated damage and in Kupffer cells treated with LPS. Results of in vitro experiments indicated that LPS treatment reduced cell viability and induced well-pronounced apoptosis and inflammatory signs. Circ_0003420 silencing counteracted LPS's influence on cell proliferation, apoptosis, and inflammation signs. Bioinformatics and a dual-luciferase reporter assay revealed that circ_0003420 targets NPAS4 mRNA and negatively correlates with NPAS4 expression. Moreover, NPAS4 knockdown recovered the apoptosis rate and expression levels of inflammatory cytokines in the LPS-treated circ_0003420 knockdown cells, whereas NPAS4 overexpression had similar effects on Kupffer cell properties as circ_0003420 silencing.

CONCLUSION

We demonstrate that circ_0003420 targets NPAS4 mRNA thereby mediating the cell damage and inflammation caused by LPS. This study provides a possible target for treatment of liver damage induced by sepsis.

Neuroprotective Effects Against Cerebral Ischemic Injury Exerted by Dexmedetomidine via the HDAC5/NPAS4/MDM2/PSD-95 Axis

Numerous evidences have highlighted the efficient role of dexmedetomidine (DEX) in multi-organ protection. In the present study, the neuroprotective role of DEX on cerebral ischemic injury and the underlining signaling mechanisms were explored. In order to simulate cerebral ischemic injury, we performed middle cerebral artery occlusion in mice and oxygen-glucose deprivation in neurons. Immunohistochemistry, Western blot analysis, and RT-qPCR were used to examine expression of HDAC5, NPAS4, MDM2, and PSD-95 in hippocampus tissues of MCAO mice and OGD-treated neurons. MCAO mice received treatment with DEX and sh-PSD-95, followed by neurological function evaluation, behavioral test, infarct volume detection by TTC staining, and apoptosis by TUNEL staining. Additionally, gain- and loss-of-function approaches were conducted in OGD-treated neuron after DEX treatment. Cell viability and apoptosis were assessed with the application of CCK-8 and flow cytometry. The interaction between MDM2 and PSD-95 was evaluated using Co-IP assay, followed by ubiquitination of PSD-95 detection. As per the results, HDAC5 and MDM2 were abundantly expressed, while NPAS4 and PSD-95 were poorly expressed in hippocampus tissues of MCAO mice and OGD-treated neurons. DEX elevated viability, and reduced LDH leakage rate and apoptosis rate of OGD-treated neurons, which was reversed following the overexpression of HDAC5. Moreover, HDAC5 augmented MDM2 expression via NPAS4 inhibition. MDM2 induced PSD-95 ubiquitination and degradation. In MCAO mice, DEX improved neurological function and behaviors and decreased infarct volume and apoptosis, which was negated as a result of PSD-95 silencing. DEX plays a neuroprotective role against cerebral ischemic injury by disrupting MDM2-induced PSD-95 ubiquitination and degradation via HDAC5 and NPAS4.

Amyloid Precursor Protein (APP) Controls the Expression of the Transcriptional Activator Neuronal PAS Domain Protein 4 (NPAS4) and Synaptic GABA Release

The amyloid precursor protein (APP) has been extensively studied as the precursor of the β-amyloid (Aβ) peptide, the major component of the senile plaques found in the brain of Alzheimer’s disease (AD) patients. However, the function of APP per se in neuronal physiology remains to be fully elucidated. APP is expressed at high levels in the brain. It resembles a cell adhesion molecule or a membrane receptor, suggesting that its function relies on cell-cell interaction and/or activation of intracellular signaling pathways. In this respect, the APP intracellular domain (AICD) was reported to act as a transcriptional regulator. Here, we used a transcriptome-based approach to identify the genes transcriptionally regulated by APP in the rodent embryonic cortex and on maturation of primary cortical neurons. Surprisingly, the overall transcriptional changes were subtle, but a more detailed analysis pointed to genes clustered in neuronal-activity dependent pathways. In particular, we observed a decreased transcription of neuronal PAS domain protein 4 (NPAS4) in APP−/− neurons. NPAS4 is an inducible transcription factor (ITF) regulated by neuronal depolarization. The downregulation of NPAS4 co-occurs with an increased production of the inhibitory neurotransmitter GABA and a reduced expression of the GABA_A receptors α1. CRISPR-Cas-mediated silencing of NPAS4 in neurons led to similar observations. Patch-clamp investigation did not reveal any functional decrease of GABA_A receptors activity, but long-term potentiation (LTP) measurement supported an increased GABA component in synaptic transmission of APP−/− mice. Together, NPAS4 appears to be a downstream target involved in APP-dependent regulation of inhibitory synaptic transmission.

Genomic Decoding of Neuronal Depolarization by Stimulus-Specific NPAS4 Heterodimers

Cells regulate gene expression in response to salient external stimuli. In neurons, depolarization leads to the expression of inducible transcription factors (ITFs) that direct subsequent gene regulation. Depolarization encodes both a neuron's action potential (AP) output and synaptic inputs, via excitatory postsynaptic potentials (EPSPs). However, it is unclear if distinct types of electrical activity can be transformed by an ITF into distinct modes of genomic regulation. Here, we show that APs and EPSPs in mouse hippocampal neurons trigger two spatially segregated and molecularly distinct induction mechanisms that lead to the expression of the ITF NPAS4. These two pathways culminate in the formation of stimulus-specific NPAS4 heterodimers that exhibit distinct DNA binding patterns. Thus, NPAS4 differentially communicates increases in a neuron's spiking output and synaptic inputs to the nucleus, enabling gene regulation to be tailored to the type of depolarizing activity along the somato-dendritic axis of a neuron.

ARNT2 Tunes Activity-Dependent Gene Expression through NCoR2-Mediated Repression and NPAS4-Mediated Activation

Neuronal activity-dependent transcription is tuned to ensure precise gene induction during periods of heightened synaptic activity, allowing for appropriate responses of activated neurons within neural circuits. The consequences of aberrant induction of activity-dependent genes on neuronal physiology are not yet clear. Here, we demonstrate that, in the absence of synaptic excitation, the basic-helix-loop-helix (bHLH)-PAS family transcription factor ARNT2 recruits the NCoR2 co-repressor complex to suppress neuronal activity-dependent regulatory elements and maintain low basal levels of inducible genes. This restricts inhibition of excitatory neurons, maintaining them in a state that is receptive to future sensory stimuli. By contrast, in response to heightened neuronal activity, ARNT2 recruits the neuronal-specific bHLH-PAS factor NPAS4 to activity-dependent regulatory elements to induce transcription and thereby increase somatic inhibitory input. Thus, the interplay of bHLH-PAS complexes at activity-dependent regulatory elements maintains temporal control of activity-dependent gene expression and scales somatic inhibition with circuit activity.

NPAS4 recruits CCK basket cell synapses and enhances cannabinoid-sensitive inhibition in the mouse hippocampus

Experience-dependent expression of immediate-early gene transcription factors (IEG-TFs) can transiently change the transcriptome of active neurons and initiate persistent changes in cellular function. However, the impact of IEG-TFs on circuit connectivity and function is poorly understood. We investigate the specificity with which the IEG-TF NPAS4 governs experience-dependent changes in inhibitory synaptic input onto CA1 pyramidal neurons (PNs). We show that novel sensory experience selectively enhances somatic inhibition mediated by cholecystokinin-expressing basket cells (CCKBCs) in an NPAS4-dependent manner. NPAS4 specifically increases the number of synapses made onto PNs by individual CCKBCs without altering synaptic properties. Additionally, we find that sensory experience-driven NPAS4 expression enhances depolarization-induced suppression of inhibition (DSI), a short-term form of cannabinoid-mediated plasticity expressed at CCKBC synapses. Our results indicate that CCKBC inputs are a major target of the NPAS4-dependent transcriptional program in PNs and that NPAS4 is an important regulator of plasticity mediated by endogenous cannabinoids.

Multiple sequences orchestrate subcellular trafficking of neuronal PAS domain-containing protein 4 (NPAS4)

Neuronal Per-Arnt-Sim (PAS) domain-containing protein 4 (NPAS4) is a basic helix-loop-helix (bHLH)-PAS transcription factor first discovered in neurons in the neuronal layer of the mammalian hippocampus and later discovered in pancreatic β-cells. NPAS4 has been proposed as a therapeutic target not only for depression and neurodegenerative diseases associated with synaptic dysfunction but also for type 2 diabetes and pancreas transplantation. The ability of bHLH-PAS proteins to fulfil their function depends on their intracellular trafficking, which is regulated by specific sequences, i.e. the nuclear localization signal (NLS) and the nuclear export signal (NES). However, until now, no study examining the subcellular localization signals of NPAS4 has been published. We show here that Rattus norvegicus NPAS4 was not uniformly localized in the nuclei of COS-7 and N2a cells 24 h after transfection. Additionally, cytoplasmic localization of NPAS4 was leptomycin B-sensitive. We demonstrate that NPAS4 possesses a unique arrangement of localization signals. Its bHLH domain contains an overlapping NLS and NES. We observed that its PAS-2 domain contains an NLS, an NES, and a second, proximally located, putative NLS. Moreover, the C terminus of NPAS4 contains two active NESs that overlap with a putative NLS. Our data indicate that glucose concentration could be one of the factors influencing NPAS4 localization. The presence of multiple localization signals and the differentiated localization of NPAS4 suggest a precise, multifactor-dependent regulation of NPAS4 trafficking, potentially crucial for its ability to act as a cellular stress sensor and transcription factor.

HDAC5 and Its Target Gene, Npas4, Function in the Nucleus Accumbens to Regulate Cocaine-Conditioned Behaviors

Individuals suffering from substance-use disorders develop strong associations between the drug's rewarding effects and environmental cues, creating powerful, enduring triggers for relapse. We found that dephosphorylated, nuclear histone deacetylase 5 (HDAC5) in the nucleus accumbens (NAc) reduced cocaine reward-context associations and relapse-like behaviors in a cocaine self-administration model. We also discovered that HDAC5 associates with an activity-sensitive enhancer of the Npas4 gene and negatively regulates NPAS4 expression. Exposure to cocaine and the test chamber induced rapid and transient NPAS4 expression in a small subpopulation of FOS-positive neurons in the NAc. Conditional deletion of Npas4 in the NAc significantly reduced cocaine conditioned place preference and delayed learning of the drug-reinforced action during cocaine self-administration, without affecting cue-induced reinstatement of drug seeking. These data suggest that HDAC5 and NPAS4 in the NAc are critically involved in reward-relevant learning and memory processes and that nuclear HDAC5 limits reinstatement of drug seeking independent of NPAS4.

MAGED1 is a novel regulator of a select subset of bHLH PAS transcription factors

Transcription factors of the basic helix-loop-helix (bHLH) PER-ARNT-SIM (PAS) family generally have critical and nonredundant biological roles, but some bHLH PAS proteins compete for common cofactors or recognise similar DNA elements. Identifying factors that regulate function of bHLH PAS proteins, particularly in cells where multiple family members are coexpressed, is important for understanding bHLH PAS factor biology. This study identifies and characterises a novel interaction between melanoma-associated antigen D1 (MAGED1) and select members of the bHLH PAS transcription factor family. MAGED1 binds and positively regulates the transcriptional activity of family members SIM1, SIM2, NPAS4 and ARNT2, but does not interact with AhR, HIF1α and ARNT. This interaction is mediated by PAS repeat regions which also form the interface for bHLH PAS dimerisation, and accordingly MAGED1 is not found in complex with bHLH PAS dimers. We show that MAGED1 does not affect bHLH PAS protein levels and cannot be acting as a coactivator of transcriptionally active heterodimers, but rather appears to interact with nascent bHLH PAS proteins in the cytoplasm to enhance their function prior to nuclear import. As a selective regulator, MAGED1 may play an important role in the biology of these specific factors and in general bHLH PAS protein dynamics.

NPAS4 Facilitates the Autophagic Clearance of Endogenous Tau in Rat Cortical Neurons

Tau, a microtubule-binding phosphoprotein, plays a critical role in the stabilisation of microtubules and neuronal function. However, hyperphosphorylated tau is involved in the pathogenesis of Alzheimer's disease (AD) and other tauopathies. The facilitation of tau clearance is now regarded as a valid therapeutic strategy for these neurodegenerative tauopathies. Here, we provide the first demonstration that the over-expression of neuronal PAS domain protein 4 (NPAS4)-induced autophagy and effectively facilitated the clearance of endogenous total and phosphorylated tau in rat primary cortical neurons. Moreover, the activation of autophagy by serum depletion significantly decreased endogenous total and phosphorylated tau levels. Autophagy inhibitors, such as 3-methyladenine (3-MA) and chloroquine (CQ), induced tau aggregation. However, NPAS4 over-expression reversed the aggregation of tau that was induced by the inhibition of autophagy. Interestingly, proteasome inhibition by MG132, had no effect on autophagy, but did reduce tau levels, indicating that NPAS4 may also degrade tau proteins through an unknown proteasome-mediated mechanism. Furthermore, NPAS4 did not alter the activity of two major tau kinases, glycogen synthase kinase 3β (GSK3β) and cyclin-dependent kinase 5 (CDK5). Taken together, the results indicate that targeting NPAS4 could provide a therapeutic approach for the treatment of AD and other tauopathies.

Repeated aripiprazole treatment regulates Bdnf, Arc and Npas4 expression under basal condition as well as after an acute swim stress in the rat brain

Despite the rapid control of schizophrenic symptoms is due to the ability of antipsychotic drugs (APDs) to block D2 receptors in the mesolimbic pathway, it is now well-established that the therapeutic effects rely on adaptive mechanisms set in motion by their long-term administration. Such neuroplastic mechanisms depend on the pharmacological profile of the drug employed, with marked differences existing between first and second generation APDs. On these bases, the major accomplishment of this work was to investigate neuroadaptive changes set in motion by repeated treatment with aripiprazole, a novel APD that is unique for being a partial agonist at dopamine D2 receptors. Moreover, given that stress plays a critical role in the exacerbation of disease symptoms, we also investigated whether aripiprazole could influence the dynamic response of the brain to an acute challenge. We found that repeated aripiprazole treatment in rats regulates the expression of different markers of neuroplasticity such as Bdnf, Arc and Npas4 in a brain-region specific fashion; more importantly, the expression of these molecules was significantly up-regulated by an acute swim stress only in aripiprazole-treated animals, which is suggestive of increased ability to cope with the adverse event. We indeed found an overall facilitation of Bdnf expression, an effect that is mainly evident in the prefrontal cortex on the pool of transcripts undergoing dendritic localization. Overall, our results provide novel information regarding the mechanisms through which aripiprazole may regulate brain function and could contribute to improve neuroplastic defects that are associated with schizophrenia symptomatology.

Regulation of the neuronal transcription factor NPAS4 by REST and microRNAs

NPAS4 is a brain restricted, activity-induced transcription factor which regulates the expression of inhibitory synapse genes to control homeostatic excitatory/inhibitory balance in neurons. NPAS4 is required for normal social interaction and contextual memory formation in mice. Protein and mRNA expression of NPAS4 is tightly coupled to neuronal depolarization and most prevalent in the cortical and hippocampal regions in the brain, however the precise mechanisms by which the NPAS4 gene is controlled remain unexplored. Here we show that expression of NPAS4 mRNA is actively repressed by RE-1 silencing transcription factor/neuron-restrictive silencer factor (REST/NRSF) in embryonic stem cells and non-neuronal cells by binding multiple sites within the promoter and Intron I of NPAS4. Repression by REST also appears to correlate with the binding of the zinc finger DNA binding protein CTCF within Intron I of NPAS4. In addition, we show that the 3' untranslated region (3'UTR) of NPAS4 can be targeted by two microRNAs, miR-203 and miR-224 to further regulate its expression. miR-224 is a midbrain/hypothalamus enriched microRNA which is expressed from an intron within the GABAA receptor epsilon (GABRE) gene and may further regionalize NPAS4 expression. Our results reveal REST and microRNA dependent mechanisms that restrict NPAS4 expression to the brain.