Human variants in the neuronal basic helix-loop-helix/Per-Arnt-Sim (bHLH/PAS) transcription factor complex NPAS4/ARNT2 disrupt function

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.

Molecular characterisation of rare loss-of-function NPAS3 and NPAS4 variants identified in individuals with neurodevelopmental disorders

Aberrations in the excitatory/inhibitory balance within the brain have been associated with both intellectual disability (ID) and schizophrenia (SZ). The bHLH-PAS transcription factors NPAS3 and NPAS4 have been implicated in controlling the excitatory/inhibitory balance, and targeted disruption of either gene in mice results in a phenotype resembling ID and SZ. However, there are few human variants in NPAS3 and none in NPAS4 that have been associated with schizophrenia or neurodevelopmental disorders. From a clinical exome sequencing database we identified three NPAS3 variants and four NPAS4 variants that could potentially disrupt protein function in individuals with either developmental delay or ID. The transcriptional activity of the variants when partnered with either ARNT or ARNT2 was assessed by reporter gene activity and it was found that variants which truncated the NPAS3/4 protein resulted in a complete loss of transcriptional activity. The ability of loss-of-function variants to heterodimerise with neuronally enriched partner protein ARNT2 was then determined by co-immunoprecipitation experiments. It was determined that the mechanism for the observed loss of function was the inability of the truncated NPAS3/4 protein to heterodimerise with ARNT2. This further establishes NPAS3 and NPAS4 as candidate neurodevelopmental disorder genes.

Chronic treatment with the antipsychotic drug blonanserin modulates the responsiveness to acute stress with anatomical selectivity

RATIONALE

Patients diagnosed with schizophrenia typically receive life-long treatments with antipsychotic drugs (APDs). However, the impact of chronic APDs treatment on neuroplastic mechanisms in the brain remains largely elusive.

OBJECTIVE

Here, we focused on blonanserin, a second-generation antipsychotic (SGA) that acts as an antagonist at dopamine D2, D3, and serotonin 5-HT2A receptors, and represents an important tool for the treatment of schizophrenia.

METHODS

We used rats to investigate the ability of chronic treatment blonanserin to modulate the activity of brain structures relevant for schizophrenia, under baseline conditions or in response to an acute forced swim session (FSS). We measured the expression of different immediate early genes (IEGs), including c-Fos, Arc/Arg 3.1, Zif268 and Npas4.

RESULTS

Blonanserin per se produced limited changes in the expression of these genes under basal conditions, while, as expected, FSS produced a significant elevation of IEGs transcription in different brain regions. The response of blonanserin-treated rats to FSS show anatomical and gene-selective differences. Indeed, the upregulation of IEGs was greatly reduced in the striatum, a brain structure enriched in dopamine receptors, whereas the upregulation of some genes (Zif268, Npas4) was largely preserved in other regions, such as the prefrontal cortex and the ventral hippocampus.

CONCLUSIONS

Taken together, our findings show that chronic exposure to blonanserin modulates selective IEGs with a specific anatomical profile. Moreover, the differential activation of specific brain regions under challenging conditions may contribute to specific clinical features of the drug.

Preoperative anxiety-induced glucocorticoid signaling reduces GABAergic markers in spinal cord and promotes postoperative hyperalgesia by affecting neuronal PAS domain protein 4

Preoperative anxiety is common in patients undergoing elective surgery and is closely related to postoperative hyperalgesia. In this study, a single prolonged stress model was used to induce preoperative anxiety-like behavior in rats 24 h before the surgery. We found that single prolonged stress exacerbated the postoperative pain and elevated the level of serum corticosterone. Previous studies have shown that glucocorticoid is associated with synaptic plasticity, and decreased spinal GABAergic activity can cause hyperalgesia in rodents. Here, single prolonged stress rats’ lumbar spinal cord showed reduced glutamic acid decarboxylase-65, glutamic acid decarboxylase-67, GABA type A receptor alpha 1 subunit, and GABA type A receptor gamma 2 subunit, indicating an impairment of GABAergic system. Furthermore, neuronal PAS domain protein 4 was also reduced in rats after single prolonged stress stimulation, which has been reported to promote GABAergic synapse development. Then, intraperitoneal injection of RU486 (a glucocorticoid receptor antagonist) rather than spironolactone (a mineralocorticoid receptor antagonist) was found to relieve single prolonged stress-induced hyperalgesia and reverse neuronal PAS domain protein 4 reduction and the impairment of GABAergic system. Furthermore, overexpressing neuronal PAS domain protein 4 could also restore the damage of GABAergic system caused by single prolonged stress while interfering with neuronal PAS domain protein 4 caused an opposite effect. Finally, after stimulation of rat primary spinal cord neurons with exogenous corticosterone in vitro, neuronal PAS domain protein 4 and GABAergic markers were also downregulated, and RU486 reversed that. Together, our results demonstrated that preoperative anxiety led to GABAergic system impairment in spinal cord and thus caused hyperalgesia due to glucocorticoid-induced downregulation of neuronal PAS domain protein 4.

A viable hypomorphic Arnt2 mutation causes hyperphagic obesity, diabetes and hepatic steatosis

Aryl hydrocarbon receptor nuclear translocator 2 (ARNT2) is a member of the basic helix-loop-helix/PER-ARNT-SIM (bHLH/PAS) transcription factor family. ARNT2 heterodimerizes with several members of the family, including single-minded homolog-1 (SIM1) and neuronal PAS domain protein 4 (NPAS4), primarily in neurons of the central nervous system. We screened 64,424 third-generation germline mutant mice derived from N-ethyl-N-nitrosourea (ENU)-mutagenized great-grandsires for weight abnormalities. Among 17 elevated body weight phenotypes identified and mapped, one strongly correlated with an induced missense mutation in Arnt2 using a semidominant model of inheritance. Causation was confirmed by CRISPR/Cas9 gene targeting to recapitulate the original ENU allele, specifying Arg74Cys (R74C). The CRISPR/Cas9-targeted (Arnt2^R74C/R74C) mice demonstrated hyperphagia and increased adiposity as well as hepatic steatosis and abnormalities in glucose homeostasis. The mutant ARNT2 protein showed decreased transcriptional activity when coexpressed with SIM1. These findings establish a requirement for ARNT2-dependent genes in the maintenance of the homeostatic feeding response, necessary for prevention of obesity and obesity-related diseases.

Summary: A forward genetic approach identified genes involved in maintaining normal body weight. A mutation in Arnt2 caused obesity by regulating food intake.

Expression of the neuroprotective protein aryl hydrocarbon receptor nuclear translocator 2 correlates with neuronal stress and disability in models of multiple sclerosis

Background

Axonal degeneration and neuronal loss have been described as the major causes of irreversible clinical disability in multiple sclerosis (MS). The aryl-hydrocarbon receptor nuclear translocator 2 (ARNT2) protein has been associated with neuroprotection in models of ischemia and neuronal responses to stressors.

Methods

To characterize its potential to influence inflammatory neurodegeneration, we examined ARNT2 expression in the experimental autoimmune encephalomyelitis (EAE) model of MS and characterized mediators that influence ARNT2 expression as well as plausible partners and targets.

Results

Arnt2 message and protein levels dropped significantly in EAE spinal cords as disease developed and were lowest at peak disability. ARNT2 expression is prominent in neuronal cell bodies within the gray matter with some staining in glial fibrillary acidic protein (GFAP)⁺ astrocytes in healthy animals. At peak disease, ARNT2 expression is reduced by 20–50% in gray matter neurons compared to healthy controls. ARNT2 intensity in neurons throughout the EAE spinal cord correlated inversely with the degree of immune cell infiltration (r = − 0.5085, p < 0.01) and axonal damage identified with SMI32 staining (r = − 0.376, p = 0.032). To understand the relationship between ARNT2 expression and neuronal health, we exposed enriched cortical cultures of neurons to hydrogen peroxide (H₂O₂) to mimic oxidative stress. H₂O₂ at lower doses rapidly increased ARNT2 protein levels which returned to baseline within 3–4 h. Exposure to higher doses of H₂O₂) dropped ARNT2 levels below baseline, preceding cytotoxicity measured by morphological changes and lactate dehydrogenase release from cells. Decreases in ARNT2 secondary to staurosporine and H₂O₂ preceded increases in cleaved caspase 3 and associated apoptosis. We also examined expression of neuronal pas 4 (Npas4), whose heterodimerization with ARNT2 drives expression of the neurotrophic factor brain-derived neurotrophic factor (Bdnf). Like ARNT2, Npas4 levels also decline at the onset of EAE and are linked to decreases in Bdnf. In vitro, H₂O₂ exposure drives Npas4 expression that is tied to increases in Bdnf.

Conclusion

Our data support ARNT2 as a neuronal transcription factor whose sustained expression is linked to neuronal and axonal health, protection that may primarily be driven through its partnering with Npas4 to influence BDNF expression.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1290-6) contains supplementary material, which is available to authorized users.

Structural insights and characterization of human Npas4 protein

Npas4 is an activity dependent transcription factor which is responsible for gearing the expression of target genes involved in neuro-transmission. Despite the importance of Npas4 in many neuronal diseases, the tertiary structure of Npas4 protein along with its physico-chemical properties is limited. In the current study, first we perfomed the phylogenetic analysis of Npas4 and determined the content of hydrophobic, flexible and order-disorder promoting amino acids. The protein binding regions, post-translational modifications and crystallization propensity of Npas4 were predicted through different in-silico methods. The three dimensional model of Npas4 was predicted through LOMET, SPARSKS-X, I-Tasser, RaptorX, MUSTER and Pyhre and the best model was selected on the basis of Ramachandran plot, PROSA, and Qmean scores. The best model was then subjected to further refinement though MODREFINER. Finally the interacting partners of Npas4 were identified through STRING database. The phylogenetic analysis showed the human Npas4 gene to be closely related to other primates such as chimpanzees, monkey, gibbon. The physiochemical properties of Npas4 showed that it is an intrinsically disordered protein with N-terminal ordered region. The post-translational modification analyses indicated absence of acetylation and mannosylation sites. Three potential phosphorylation sites (S108, T130 and T136) were found in PAS A domain whilst a single phosphorylation site (S273) was present in PAS B domain. The predicted tertiary structure of Npas4 showed that bHLH domain and PAS domain possess tertiary structures while the rest of the protein exhibited disorder property. Protein-protein interaction analysis revealed NPas4 interaction with various proteins which are mainly involved in nuclear trafficking of proteins to cytoplasm, activity regulated gene transcription and neurodevelopmental disorders. Moreover the analysis also highlighted the direct relation to proteins involved in promoting neuronal survival, plasticity and cAMP responsive element binding protein proteins. The current study helps in understanding the physicochemical properties and reveals the neuro-modulatory role of Npas4 in crucial pathways involved in neuronal survival and neural signalling hemostasis.

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.

Genetics of Combined Pituitary Hormone Deficiency: Roadmap into the Genome Era

The genetic basis for combined pituitary hormone deficiency (CPHD) is complex, involving 30 genes in a variety of syndromic and nonsyndromic presentations. Molecular diagnosis of this disorder is valuable for predicting disease progression, avoiding unnecessary surgery, and family planning. We expect that the application of high throughput sequencing will uncover additional contributing genes and eventually become a valuable tool for molecular diagnosis. For example, in the last 3 years, six new genes have been implicated in CPHD using whole-exome sequencing. In this review, we present a historical perspective on gene discovery for CPHD and predict approaches that may facilitate future gene identification projects conducted by clinicians and basic scientists. Guidelines for systematic reporting of genetic variants and assigning causality are emerging. We apply these guidelines retrospectively to reports of the genetic basis of CPHD and summarize modes of inheritance and penetrance for each of the known genes. In recent years, there have been great improvements in databases of genetic information for diverse populations. Some issues remain that make molecular diagnosis challenging in some cases. These include the inherent genetic complexity of this disorder, technical challenges like uneven coverage, differing results from variant calling and interpretation pipelines, the number of tolerated genetic alterations, and imperfect methods for predicting pathogenicity. We discuss approaches for future research in the genetics of CPHD.

NPAS1-ARNT and NPAS3-ARNT crystal structures implicate the bHLH-PAS family as multi-ligand binding transcription factors

The neuronal PAS domain proteins NPAS1 and NPAS3 are members of the basic helix-loop-helix-PER-ARNT-SIM (bHLH-PAS) family, and their genetic deficiencies are linked to a variety of human psychiatric disorders including schizophrenia, autism spectrum disorders and bipolar disease. NPAS1 and NPAS3 must each heterodimerize with the aryl hydrocarbon receptor nuclear translocator (ARNT), to form functional transcription complexes capable of DNA binding and gene regulation. Here we examined the crystal structures of multi-domain NPAS1-ARNT and NPAS3-ARNT-DNA complexes, discovering each to contain four putative ligand-binding pockets. Through expanded architectural comparisons between these complexes and HIF-1α-ARNT, HIF-2α-ARNT and CLOCK-BMAL1, we show the wider mammalian bHLH-PAS family is capable of multi-ligand-binding and presents as an ideal class of transcription factors for direct targeting by small-molecule drugs.

DOI:http://dx.doi.org/10.7554/eLife.18790.001

Transcription factors are proteins that can bind to DNA to regulate the activity of genes. One family of transcription factors in mammals is known as the bHLH-PAS family, which consists of sixteen members including NPAS1 and NPAS3. These two proteins are both found in nerve cells, and genetic mutations that affect NPAS1 or NPAS3 have been linked to psychiatric conditions in humans. Therefore, researchers would like to discover new drugs that can bind to these proteins and control their activities in nerve cells. Understanding the three-dimensional structure of a protein can aid the discovery of small molecules that can bind to these proteins and act as drugs. Proteins in the bHLH-PAS family have to form pairs in order to bind to DNA: NPAS1 and NPAS3 both interact with another bHLH-PAS protein called ARNT, but it is not clear exactly how this works.

In 2015, a team of researchers described the shapes that ARNT adopts when it forms pairs with two other bHLH-PAS proteins that are important for sensing when oxygen levels drop in cells. Here, Wu et al. – including many of the researchers involved in the earlier work – have used a technique called X-ray crystallography to determine the three-dimensional shapes of NPAS1 when it is bound to ARNT, and NPAS3 when it is bound to both ARNT and DNA. The experiments show that each of these structures contains four distinct pockets that certain small molecules might be able to bind to. The NPAS1 and NPAS3 structures are similar to each other and to the previously discovered bHLH-PAS structures involved in oxygen sensing.

Further analysis of other bHLH-PAS proteins suggests that all the members of this protein family are likely to be able to bind to small molecules and should therefore be considered as potential drug targets. The next step following on from this work is to identify small molecules that bind to bHLH-PAS proteins, which will help to reveal the genes that are regulated by this family. In the future, these small molecules may have the potential to be developed into new drugs to treat psychiatric conditions and other diseases in humans.

DOI:http://dx.doi.org/10.7554/eLife.18790.002

miR-744 and miR-224 Downregulate Npas4 and Affect Lineage Differentiation Potential and Neurite Development During Neural Differentiation of Mouse Embryonic Stem Cells

Neuronal PAS domain protein 4 (Npas4) is a brain-specific transcription factor whose expression is enriched in neurogenic regions of the brain. In addition, it was demonstrated that Npas4 expression is dynamic and highly regulated during neural differentiation of embryonic stem cells (ESCs). While these findings implicate a role for Npas4 in neurogenesis, the underlying mechanisms of regulation remain unknown. Given that growing evidence suggests that microRNAs (miRNAs) play important roles in both embryonic and adult neurogenesis, we reasoned that miRNAs are good candidates for regulating Npas4 expression during neural differentiation of ESCs. In this study, we utilized the small RNA sequencing method to profile miRNA expression during neural differentiation of mouse ESCs. Two differentially expressed miRNAs were identified to be able to significantly reduce reporter gene activity by targeting the Npas4 3'UTR, namely miR-744 and miR-224. More importantly, ectopic expression of these miRNAs during neural differentiation resulted in downregulation of endogenous Npas4 expression. Subsequent functional analysis revealed that overexpression of either miR-744 or miR-224 delayed early neural differentiation, reduced GABAergic neuron production and inhibited neurite outgrowth. Collectively, our findings indicate that Npas4 not only functions at the early stages of neural differentiation but may also, in part, contribute to neuronal subtype specification and neurite development.

Npas4: Linking Neuronal Activity to Memory

Immediate-early genes (IEGs) are rapidly activated after sensory and behavioral experience and are believed to be crucial for converting experience into long-term memory. Neuronal PAS domain protein 4 (Npas4), a recently discovered IEG, has several characteristics that make it likely to be a particularly important molecular link between neuronal activity and memory: it is among the most rapidly induced IEGs, is expressed only in neurons, and is selectively induced by neuronal activity. By orchestrating distinct activity-dependent gene programs in different neuronal populations, Npas4 affects synaptic connections in excitatory and inhibitory neurons, neural circuit plasticity, and memory formation. It may also be involved in circuit homeostasis through negative feedback and psychiatric disorders. We summarize these findings and discuss their implications.

Npas4 deficiency increases vulnerability to juvenile stress in mice

During specific windows of postnatal brain development, individuals are particularly susceptible to developing mental illnesses in adulthood. Adolescence is such a window during which environmental stress can have long-lasting consequences on social and cognitive functions. In individuals, highly vulnerable to stress, a relatively mild stressful situation can trigger the onset of psychiatric conditions. The genetic factors and mechanisms underlying vulnerability to stress are not well understood. Here, we show that variations in expression of the brain-specific transcription factor Npas4 contributes to the long-term consequences of juvenile stress on cognitive abilities. We observed that transgenic Npas4-deficient mice exposed to chronic mild stress during adolescence (but not during adulthood) develop prefrontal cortex-dependent cognitive deficits in adulthood, while the same stress did not affect Npas4 wild-type mice. These cognitive deficits were accompanied by fewer neuroblasts in the subventricular zone, and reduced ability of these immature neuronal cells to migrate away from this neurogenic zone toward cortical regions. These findings suggest for the first time that the transcription factor Npas4 could play a significant role in coping with juvenile stress. They also suggest that Npas4 could modulate resilience or vulnerability to stress by mediating the effects of stress on neurogenesis.

Inducible and reversible lentiviral and Recombination Mediated Cassette Exchange (RMCE) systems for controlling gene expression

Manipulation of gene expression to invoke loss of function (LoF) or gain of function (GoF) phenotypes is important for interrogating complex biological questions both in vitro and in vivo. Doxycycline (Dox)-inducible gene expression systems are commonly used although success is often limited by high background and insufficient sensitivity to Dox. Here we develop broadly applicable platforms for reliable, tightly controlled and reversible Dox-inducible systems for lentiviral mediated generation of cell lines or FLP Recombination-Mediated Cassette Exchange (RMCE) into the Collagen 1a1 (Col1a1) locus (FLP-In Col1a1) in mouse embryonic stem cells. We significantly improve the flexibility, usefulness and robustness of the Dox-inducible system by using Tetracycline (Tet) activator (Tet-On) variants which are more sensitive to Dox, have no background activity and are expressed from single Gateway-compatible constructs. We demonstrate the usefulness of these platforms in ectopic gene expression or gene knockdown in multiple cell lines, primary neurons and in FLP-In Col1a1 mouse embryonic stem cells. We also improve the flexibility of RMCE Dox-inducible systems by generating constructs that allow for tissue or cell type-specific Dox-inducible expression and generate a shRNA selection algorithm that can effectively predict potent shRNA sequences able to knockdown gene expression from single integrant constructs. These platforms provide flexible, reliable and broadly applicable inducible expression systems for studying gene function.

Npas4 expression in two experimental models of the barrel cortex plasticity

Npas4 has recently been identified as an important factor in brain plasticity, particularly in mechanisms of inhibitory control. Little is known about Npas4 expression in terms of cortical plasticity. In the present study expressions of Npas4 and the archetypal immediate early gene (IEG) c-Fos were investigated in the barrel cortex of mice after sensory deprivation (sparing one row of whiskers for 7 days) or sensory conditioning (pairing stimulation of one row of whiskers with aversive stimulus). Laser microdissection of individual barrel rows allowed for analysis of IEGs expression precisely in deprived and nondeprived barrels (in deprivation study) or stimulated and nonstimulated barrels (in conditioning study). Cortex activation by sensory conditioning was found to upregulate the expression of both Npas4 and c-Fos. Reorganization of cortical circuits triggered by removal of selected rows of whiskers strongly affected c-Fos but not Npas4 expression. We hypothesize that increased inhibitory synaptogenesis observed previously after conditioning may be mediated by Npas4 expression.

Effects of Npas4 deficiency on anxiety, depression-like, cognition and sociability behaviour

The transcription factor neuronal PAS domain-containing protein 4 (Npas4), which regulates the formation of inhibitory synapses on excitatory neurons, has been suggested as a candidate gene for neurological and psychiatric conditions such as bipolar depression, autism spectrum and cognitive disorders. A mouse model of Npas4 deficiency has been developed to investigate any role in these disorders. Behavioural characterisation of Npas4(-/-), Npas4(+/-) and Npas4(+/+) mice has been conducted using the open field, elevated zero maze (EZM), Y-maze, sociability test and forced swim test (FST) to investigate a range of behaviours. Npas4(-/-) mice spent more time in the open arm of the EZM than other genotypes, suggesting decreased anxiety-like behaviour. Npas4(+/-) mice, however, were more immobile in the FST than other genotypes, suggesting increased depression-like behaviour, and also showed impaired spatial recognition memory in the Y-maze. There were no differences between genotype in social behaviour. These results suggest that differential levels of Npas4 expression in the brain may regulate anxiety, depression and cognition related disorders.

Decreased expression of neuronal Per-Arnt-Sim domain protein 4 gene in the hippocampus of a post-stroke depression rat model

Neuronal Per-Arnt-Sim domain protein 4 (NPAS4) is important in regulating transcription and function in the limbic system and in brain development. Post-stroke depression (PSD) is a common complication following a stroke. Furthermore, organic damage as a result of a stroke affects the restoration of nerve function and indicates that hippocampal neural activity may be associated with PSD. A PSD rat model was established via a middle cerebral artery occlusion procedure, which was combined with isolation and chronic unexpected mild stress, and was used to investigate the expression of the NPAS4 gene in the hippocampus. The neurological deficit and behavior were evaluated and NPAS4 mRNA expression was measured by semi-quantitative reverse transcription-polymerase chain reaction; furthermore, the association with cognitive impairment was analyzed. The PSD rats displayed neuropsychopathic disorders and the NPAS4 mRNA expression levels in the hippocampus were significantly lower in the depression and PSD groups compared with the control group. Therefore, the present study identified that NPAS4 expression was decreased in the hippocampus of PSD rats.