Repeated immobilization stress increases nur77 expression in the bed nucleus of the stria terminalis

Chronic stress induces cell type-selective transcriptomic and electrophysiological changes in the bed nucleus of the stria terminalis

Distinct regions and cell types in the anterolateral group of the bed nucleus of the stria terminalis (BNST_ALG) act to modulate anxiety in opposing ways. A history of chronic stress increases anxiety-like behavior with lasting electrophysiological effects on the BNST_ALG. However, the opposing circuits within the BNST_ALG suggest that stress may have differential effects on the individual cell types that comprise these circuits to shift the balance to favor anxiogenesis. Yet, the effects of stress are generally examined by treating all neurons within a particular region of the BNST as a homogenoeus population. We used patch-clamp electrophysiology and single-cell quantitative reverse transcriptase PCR (scRT-PCR) to determine how chronic shock stress (CSS) affects electrophysiological and neurochemical properties of Type I, Type II, and Type III neurons in the BNST_ALG. We report that CSS resulted in changes in the input resistance, time constant, action potential waveform, and firing rate of Type III but not Type I or II neurons. Additionally, only the Type III neurons exhibited an increase in Crf mRNA and a decrease in striatal-enriched protein tyrosine phosphatase (Ptpn5) mRNA after CSS. In contrast, only non-Type III cells showed a reduction in calcium-permeable AMPA receptor (CP-AMPAR) current and changes in mRNA expression of genes encoding AMPA receptor subunits after CSS. Importantly, none of the effects of CSS observed were seen in all cell types. Our results suggest that Type III neurons play a unique role in the BNST_ALG circuit and represent a population of CRF neurons particularly sensitive to chronic stress.

The Stress-Induced Transcription Factor NR4A1 Adjusts Mitochondrial Function and Synapse Number in Prefrontal Cortex

The energetic costs of behavioral chronic stress are unlikely to be sustainable without neuronal plasticity. Mitochondria have the capacity to handle synaptic activity up to a limit before energetic depletion occurs. Protective mechanisms driven by the induction of neuronal genes likely evolved to buffer the consequences of chronic stress on excitatory neurons in prefrontal cortex (PFC), as this circuitry is vulnerable to excitotoxic insults. Little is known about the genes involved in mitochondrial adaptation to the buildup of chronic stress. Using combinations of genetic manipulations and stress for analyzing structural, transcriptional, mitochondrial, and behavioral outcomes, we characterized NR4A1 as a stress-inducible modifier of mitochondrial energetic competence and dendritic spine number in PFC. NR4A1 acted as a transcription factor for changing the expression of target genes previously involved in mitochondrial uncoupling, AMP-activated protein kinase activation, and synaptic growth. Maintenance of NR4A1 activity by chronic stress played a critical role in the regressive synaptic organization in PFC of mouse models of stress (male only). Knockdown, dominant-negative approach, and knockout of Nr4a1 in mice and rats (male only) protected pyramidal neurons against the adverse effects of chronic stress. In human PFC tissues of men and women, high levels of the transcriptionally active NR4A1 correlated with measures of synaptic loss and cognitive impairment. In the context of chronic stress, prolonged expression and activity of NR4A1 may lead to responses of mitochondria and synaptic connectivity that do not match environmental demand, resulting in circuit malfunction between PFC and other brain regions, constituting a pathological feature across disorders.

SIGNIFICANCE STATEMENT The bioenergetic cost of chronic stress is too high to be sustainable by pyramidal prefrontal neurons. Cellular checkpoints have evolved to adjust the responses of mitochondria and synapses to the buildup of chronic stress. NR4A1 plays such a role by controlling the energetic competence of mitochondria with respect to synapse number. As an immediate-early gene, Nr4a1 promotes neuronal plasticity, but sustained expression or activity can be detrimental. NR4A1 expression and activity is sustained by chronic stress in animal models and in human studies of neuropathologies sensitive to the buildup of chronic stress. Therefore, antagonism of NR4A1 is a promising avenue for preventing the regressive synaptic reorganization in cortical systems in the context of chronic stress.

Transcription factor Nr4a1 couples sympathetic and inflammatory cues in CNS-recruited macrophages to limit neuroinflammation

The molecular mechanisms that link the sympathetic stress response and inflammation remain obscure. Here we found that the transcription factor Nr4a1 regulated the production of norepinephrine (NE) in macrophages and thereby limited experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. Lack of Nr4a1 in myeloid cells led to enhanced NE production, accelerated infiltration of leukocytes into the central nervous system (CNS) and disease exacerbation in vivo. In contrast, myeloid-specific deletion of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, protected mice against EAE. Furthermore, we found that Nr4a1 repressed autocrine NE production in macrophages by recruiting the corepressor CoREST to the Th promoter. Our data reveal a new role for macrophages in neuroinflammation and identify Nr4a1 as a key regulator of catecholamine production by macrophages.

Life-long norepinephrine transporter (NET) knock-out leads to the increase in the NET mRNA in brain regions rich in norepinephrine terminals

These studies aimed to identify the genes differentially expressed in the frontal cortex of mice bearing a life-long norepinephrine transporter knock-out (NET-KO) and wild-type animals (WT). Differences in gene expression in the mouse frontal cortex were studied using a whole-genome microarray approach. Using an alternative approach, i.e. RT-PCR (reverse transcription polymerase chain reaction) with primers complementary to various exons of the NET gene, as well as TaqMan arrays, the level of mRNA encoding the NET in other brain regions of the NET-KO mice was also examined. The analyses revealed a group of 92 transcripts (27 genes) that differentiated the NET-KO mice from the WT mice. Surprisingly, the studies have shown that the mRNA encoding NET accumulated in the brain regions rich in norepinephrine nerve endings in the NET-KO mice. Because there is no other source of NET mRNA besides the noradrenergic terminals in the brain regions studied, these results might speak in favor of the presence of mRNA in axon terminals. RNA-Binding Protein Immunoprecipitation approach indicated that mRNA encoding NET was detected in the Ago2 protein/mRNA complex. In addition, the amount of Ago2 protein in the frontal cortex was significantly higher in NET-KO mice as compared with that of the WT animals. These results are important for further characterization of the NET-KO mice, which - besides other merits - might serve as a good model to study the fate of truncated mRNA in neurons.

Decreased Expression of CoREST1 and CoREST2 Together with LSD1 and HDAC1/2 during Neuronal Differentiation

CoREST (CoREST1, rcor1) transcriptional corepressor together with the histone demethylase LSD1 (KDM1A) and the histone deacetylases HDAC1/2 form LSD1-CoREST-HDAC (LCH) transcriptional complexes to regulate gene expression. CoREST1 belong to a family that also comprises CoREST2 (rcor2) and CoREST3 (rcor3). CoREST1 represses the expression of neuronal genes during neuronal differentiation. However, the role of paralogs CoREST2 and CoREST3 in this process is just starting to emerge. Here, we report the expression of all CoRESTs and partners LSD1 and HDAC1/2 in two models of neuronal differentiation: Nerve-Growth-Factor (NGF)-induced neuronal phenotype of PC12 cells, and in vitro maturation of embryonic rat cortical neurons. In both models, a concomitant and gradual decrease of LSD1, HDAC1, HDAC2, CoREST1, and CoREST2, but not CoREST3 was observed. As required by the study, full-length rat rcor1 gene was identified using in silico analysis of available rat genome. The work was also complemented by the analysis of rat RNA-seq databases. The analysis showed that all CoRESTs, including the identified four splicing variants of rat CoREST3, display a wide expression in adult tissues. Moreover, the analysis of RNA-seq databases showed that CoREST2 displays a higher expression than CoREST1 and CoREST3 in the mature brain. Immunofluorescent assays and immunoblots of adult rat brain showed that all CoRESTs are present in both glia and neurons. Regarding functional partnership, CoREST2 and CoREST3 interact with all LSD1 splicing variants. In conclusion, neuronal differentiation is accompanied by decreased expression of all core components of LCH complexes, but not CoREST3. The combination of the differential transcriptional repressor capacity of LCH complexes and variable protein levels of its different components should result in a finely tuned gene expression during neuronal differentiation and in the adult brain.

Differential properties of transcriptional complexes formed by the CoREST family

Mammalian genomes harbor three CoREST genes. rcor1 encodes CoREST (CoREST1), and the paralogues rcor2 and rcor3 encode CoREST2 and CoREST3, respectively. Here, we describe specific properties of transcriptional complexes formed by CoREST proteins with the histone demethylase LSD1/KDM1A and histone deacetylases 1 and 2 (HDAC1/2) and the finding that all three CoRESTs are expressed in the adult rat brain. CoRESTs interact equally strongly with LSD1/KDM1A. Structural analysis shows that the overall conformation of CoREST3 is similar to that of CoREST1 complexed with LSD1/KDM1A. Nonetheless, transcriptional repressive capacity of CoREST3 is lower than that of CoREST1, which correlates with the observation that CoREST3 leads to a reduced LSD1/KDM1A catalytic efficiency. Also, CoREST2 shows a lower transcriptional repression than CoREST1, which is resistant to HDAC inhibitors. CoREST2 displays lower interaction with HDAC1/2, which is barely present in LSD1/KDM1A-CoREST2 complexes. A nonconserved leucine in the first SANT domain of CoREST2 severely weakens its association with HDAC1/2. Furthermore, CoREST2 mutants with increased HDAC1/2 interaction and those without HDAC1/2 interaction exhibit equivalent transcriptional repression capacities, indicating that CoREST2 represses in an HDAC-independent manner. In conclusion, differences among CoREST proteins are instrumental in the modulation of protein-protein interactions and catalytic activities of LSD1/KDM1A-CoREST-HDAC complexes, fine-tuning gene expression regulation.

Norepinephrine transporter knock-out alters expression of the genes connected with antidepressant drugs action

Norepinephrine transporter knock-out mice (NET-KO) exhibit depression-resistant phenotypes. They manifest significantly shorter immobility times in both the forced swim test and the tail suspension test. Moreover, biochemical studies have revealed the up-regulation of other monoamine transporters (dopamine and serotonin) in the brains of NET-KO mice, similar to the phenomenon observed after the chronic pharmacological blockade of norepinephrine transporter by desipramine in wild-type (WT) animals. NET-KO mice are also resistant to stress, as we demonstrated previously by measuring plasma corticosterone concentration. In the present study, we used a microdissection technique to separate target brain regions and the TaqMan Low Density Array approach to test the expression of a group of genes in the NET-KO mice compared with WT animals. A group of genes with altered expression were identified in four brain structures (frontal and cingulate cortices, dentate gyrus of hippocampus and basal-lateral amygdala) of NET-KO mice compared with WT mice. These genes are known to be altered by antidepressant drugs administration. The most interesting gene is Crh-bp, which modulates the activity of corticotrophin--releasing hormone (CRH) and several CRH-family members. Generally, genetic disturbances within noradrenergic neurons result in biological changes, such as in signal transduction and intercellular communication, and may be linked to changes in noradrenaline levels in the brains of NET-KO mice.

Stress and glucocorticoid regulation of NR4A genes in mice

The NR4A nuclear receptors subgroup, comprising Nur77 (NR4A1), Nurr1 (NR4A2), and Nor1 (NR4A3), are orphan receptors induced by a variety of signals, including stress. These receptors are described as early response genes and in vitro studies have shown that they take part in regulation of the hypothalamic-pituitary-adrenal (HPA) axis, the major stress-responsive neuroendocrine system. This study analyzes further the interweaving of NR4A receptors with the HPA axis at rest and after a restraint stress in vivo in mice. We show that each NR4A member has a similar mRNA expression pattern and low levels of expression at rest except, in particular in hippocampus for Nurr1 and in adrenals for Nur77. After restraint stress, mRNA expression of each NR4A is markedly induced in adrenals and pituitary and significantly in hypothalamus. In higher cerebral regions, such as cortex, hippocampus, and amygdala, induction of NR4A mRNA elicited by stress was very moderate or undetected. The influence of glucocorticoids on NR4A mRNA expression was analyzed by comparing wild-type and Cbg k.o. mice used as a model of glucocorticoid hyposignaling. Nur77 mRNA and protein expression and a downstream Nur77 target gene were found to be affected in the hypothalamus and pituitary of the Cbg k.o. mice but not in hippocampus and cortex. These results further support a physiological role of NR4A orphan receptors in the glucocorticoid response to stress.

Haloperidol-induced Nur77 expression in striatopallidal neurons is under the control of protein phosphatase 1 regulation by DARPP-32

Impaired dopaminergic signaling in the striatum is involved in diseases as diverse as Parkinson's disease, addiction, and schizophrenia. An important pathophysiological aspect is the loss of balance between striatopallidal and striatonigral pathways. Nur77 is an orphan nuclear receptor and dopamine-regulated immediate-early gene. Classical antipsychotic drugs widely used in the treatment of schizophrenia, such as haloperidol, increase Nur77 mRNA expression in the striatum. However, little is known about the intracellular signaling pathways involved in Nur77 induction. Here, using pharmacological approaches and transgenic mutant mice, we investigated the mechanisms underlying the up-regulation of Nur77 protein expression in the dorsal striatum after haloperidol injection. In drd1a::EGFP transgenic mice that express GFP in D1 neurons, Nur77 up-regulation induced by haloperidol occurred predominantly in GFP-negative neurons. In Gαolf heterozygous mutant mice, in which cAMP production in response to A2A stimulation is impaired in the striatum, haloperidol effect was not altered. In contrast, in DARPP-32 knock-in mutant mice bearing a T34A point mutation of the site responsible for cAMP-dependent phosphatase 1 inhibition, Nur77 up-regulation by haloperidol was prevented. Haloperidol also induced Nur77 protein in D2 neurons of the nucleus accumbens core of wild type but not T34A knock-in mice. Thus, our results show that expression of Nur77 is induced by haloperidol in D2 receptors-expressing medium-sized spiny neurons, through cAMP-dependent regulation of protein phosphatase 1, which is likely to modulate the effects of other protein kinases. Our results clarify the mechanisms of Nur77 induction by antipsychotic and its possible contribution to extrapyramidal effects.

Nur transcription factors in stress and addiction

The Nur transcription factors Nur77 (NGFI-B, NR4A1), Nurr1 (NR4A2), and Nor-1 (NR4A3) are a sub-family of orphan members of the nuclear receptor superfamily. These transcription factors are products of immediate early genes, whose expression is rapidly and transiently induced in the central nervous system by several types of stimuli. Nur factors are present throughout the hypothalamus-pituitary-adrenal (HPA) axis where are prominently induced in response to stress. Drugs of abuse and stress also induce the expression of Nur factors in nuclei of the motivation/reward circuit of the brain, indicating their participation in the process of drug addiction and in non-hypothalamic responses to stress. Repeated use of addictive drugs and chronic stress induce long-lasting dysregulation of the brain motivation/reward circuit due to reprogramming of gene expression and enduring alterations in neuronal function. Here, we review the data supporting that Nur transcription factors are key players in the molecular basis of the dysregulation of neuronal circuits involved in chronic stress and addiction.