Interactions between Egr1 and AP1 factors in regulation of tyrosine hydroxylase transcription

SifiNet: a robust and accurate method to identify feature gene sets and annotate cells

SifiNet is a robust and accurate computational pipeline for identifying distinct gene sets, extracting and annotating cellular subpopulations, and elucidating intrinsic relationships among these subpopulations. Uniquely, SifiNet bypasses the cell clustering stage, commonly integrated into other cellular annotation pipelines, thereby circumventing potential inaccuracies in clustering that may compromise subsequent analyses. Consequently, SifiNet has demonstrated superior performance in multiple experimental datasets compared with other state-of-the-art methods. SifiNet can analyze both single-cell RNA and ATAC sequencing data, thereby rendering comprehensive multi-omic cellular profiles. It is conveniently available as an open-source R package.

Unraveling the impact of 27-hydroxycholesterol in autoimmune diseases: Exploring promising therapeutic approaches

The role of 27-hydroxycholesterol (27-OHC) in autoimmune diseases has become a subject of intense research in recent years. This oxysterol, derived from cholesterol, has been identified as a significant player in modulating immune responses and inflammation. Its involvement in autoimmune pathogenesis has drawn attention to its potential as a therapeutic target for managing autoimmune disorders effectively. 27-OHC, an oxysterol derived from cholesterol, has emerged as a key player in modulating immune responses and inflammatory processes. It exerts its effects through various mechanisms, including activation of nuclear receptors, interaction with immune cells, and modulation of neuroinflammation. Additionally, 27-OHC has been implicated in the dysregulation of lipid metabolism, neurotoxicity, and blood-brain barrier (BBB) disruption. Understanding the intricate interplay between 27-OHC and autoimmune diseases, particularly neurodegenerative disorders, holds promise for developing targeted therapeutic strategies. Additionally, emerging evidence suggests that 27-OHC may interact with specific receptors and transcription factors, thus influencing gene expression and cellular processes in autoimmune disorders. Understanding the intricate mechanisms by which 27-OHC influences immune dysregulation and tissue damage in autoimmune diseases is crucial for developing targeted therapeutic interventions. Further investigations into the molecular pathways and signaling networks involving 27-OHC are warranted to unravel its full potential as a therapeutic target in autoimmune diseases, thereby offering new avenues for disease intervention and management.

The JNK-EGR1 signaling axis promotes TNF-α-induced endothelial differentiation of human mesenchymal stem cells via VEGFR2 expression

Mesenchymal stem cells (MSCs) can differentiate into endothelial cells; however, the mechanisms underlying this process in the tumor microenvironment (TME) remain elusive. This study shows that tumor necrosis factor alpha (TNF-α), a key cytokine present in the TME, promotes the endothelial differentiation of MSCs by inducing vascular endothelial growth factor receptor 2 (VEGFR2) gene expression. EGR1 is a member of the zinc-finger transcription factor family induced by TNF-α. Our findings indicate that EGR1 directly binds to the VEGFR2 promoter and transactivates VEGFR2 expression. We also demonstrate that EGR1 forms a complex with c-JUN activated by c-JUN N-terminal kinase (JNK) to promote VEGFR2 transcription and endothelial differentiation in MSCs in response to TNF-α stimulation. The shRNA-mediated silencing of EGR1 or c-JUN abrogates TNF-α-induced VEGFR2 transcription and the endothelial differentiation of MSCs. To further evaluated the role of EGR1 in the endothelial differentiation of BM-MSCs, we used a syngenic tumor implantation model. 4T1 mouse mammary tumor cells were injected subcutaneously into BALB/c mice with primary mBM-MSCs isolated from wild-type (Egr1+/+) or Egr1-null (Egr1-/-) mice. CD31-positive cells were predominantly observed at the border of the tumor in the 4T1 plus wild-type MSC group, while staining less in the 4T1 alone or 4T1 plus Egr1-null MSC group. Collectively, these findings demonstrate that the JNK-EGR1 signaling axis plays a crucial role in the TNF-α-induced endothelial differentiation of MSCs in the TME, which could be a potential therapeutic target for solid tumors vasculatures.

Genetic or siRNA inhibition of MBD2 attenuates the UUO- and I/R-induced renal fibrosis via downregulation of EGR1

DNA methylation plays a pivotal role in the progression of renal fibrosis. Methyl-CpG–binding domain protein 2 (MBD2), a protein reader of methylation, is involved in the development of acute kidney injury (AKI) caused by vancomycin. However, the role and mechanism of action of MBD2 in renal remain unclear. In this study, MBD2 mediated extracellular matrix (ECM) production induced by TGF-β1 in Boston University mouse proximal tubule (BUMPT) cells，and upregulated the expression EGR1 to promote ECM production in murine embryonic NIH 3T3 fibroblasts. ChIP analysis demonstrated that MBD2 physically interacted with the promoter region of the CpG islands of EGR1 genes and then activated their expression by inducing hypomethylation of the promoter region. In vivo, PT-MBD2-KO attenuated unilateral ureteral obstruction (UUO)-induced renal tubulointerstitial fibrosis via downregulation of EGR1, which was demonstrated by the downregulation of fibronectin (FN), collagen I and IV, α-SMA, and EGR1. Injection of MBD2-siRNA attenuated the UUO- and I/R-induced renal fibrosis. Those molecular changes were verified by biopsies from patients with obstructive nephropathy (OB). These data collectively demonstrated that inhibition of MBD2 reduces renal fibrosis via downregulating EGR1, which could be a target for treatment of fibrotic kidney disease.

Crosstalk between dopamine and insulin signaling in growth control of the oyster

Neuroendocrine hormones such as dopamine and insulin/insulin-like peptides play indispensable roles in growth regulation of animals, while the interplay between dopamine and insulin signaling pathways remains largely unknown in invertebrates. In the present study, we showed that tyrosine hydroxylase (TH), the rate-limiting enzyme of dopamine synthesis, was highly expressed in all tissues of the fast-growing oysters, and gradually increased with the development, which indicated the potential role of dopamine in growth regulation. Incubated with dopamine hydrochloride and insulin-like peptide recombinant proteins in vitro induced the expression of TH, suggesting a mutual regulatory relationship between insulin and dopamine signaling. Fasting and re-feeding experiments confirmed the role of TH in food intake regulation, also provide a clue about the potential regulatory relationship between the FoxO and TH. Further luciferase assay experiment confirmed that FoxO was involved in transcriptional regulation of TH gene through binding to its specific promoter region. This work provided insights into the crosstalk between dopamine and insulin signaling in growth control of mollusks.

Bmal1 in the striatum influences alcohol intake in a sexually dimorphic manner

Alcohol consumption has been strongly associated with circadian clock gene expression in mammals. Analysis of clock genes revealed a potential role of Bmal1 in the control of alcohol drinking behavior. However, a causal role of Bmal1 and neural pathways through which it may influence alcohol intake have not yet been established. Here we show that selective ablation of Bmal1 (Cre/loxP system) from medium spiny neurons of the striatum induces sexual dimorphic alterations in alcohol consumption in mice, resulting in augmentation of voluntary alcohol intake in males and repression of intake in females. Per2mRNA expression, quantified by qPCR, decreases in the striatum after the deletion of Bmal1. To address the possibility that the effect of striatal Bmal1 deletion on alcohol intake and preference involves changes in the local expression of Per2, voluntary alcohol intake (two-bottle, free-choice paradigm) was studied in mice with a selective ablation of Per2 from medium spiny neurons of the striatum. Striatal ablation of Per2 increases voluntary alcohol intake in males but has no effect in females. Striatal Bmal1 and Per2 expression thus may contribute to the propensity to consume alcohol in a sex -specific manner in mice.

Glucagon-like peptide-1 receptor controls exocytosis in chromaffin cells by increasing full-fusion events

Agonists for glucagon-like-peptide-1 receptor (GLP-1R) are currently used for the treatment of type 2 diabetes and obesity. Their benefits have been centered on pancreas and hypothalamus, but their roles in other organ systems are not well understood. We studied the action of GLP-1R on secretions of adrenal medulla. Exendin-4, a synthetic analog of GLP-1, increases the synthesis and the release of catecholamines (CAs) by increasing cyclic AMP (cAMP) production, without apparent participation of cAMP-regulated guanine nucleotide exchange factor (Epac). Exendin-4, when incubated for 24 h, increases CA synthesis by promoting the activation of tyrosine hydroxylase. Short incubation (20 min) increases the quantum size of exocytotic events by switching exocytosis from partial to full fusion. Our results give a strong support to the role of GLP-1 in the fine control of exocytosis.

Transcription factor EGR-1 transactivates the MMP1 gene promoter in response to TNFα in HaCaT keratinocytes

Matrix metalloproteinase 1 (MMP-1), a calcium-dependent zinc- containing collagenase, is involved in the initial degradation of native fibrillar collagen. Tissue necrosis factor-alpha (TNFα) is a pro-inflammatory cytokine that is rapidly produced by dermal fibroblasts, monocytes/macrophages, and keratinocytes and regulates inflammation and damaged-tissue remodeling. MMP-1 is induced by TNFα and plays a critical role in tissue remodeling and skin aging processes. However, the regulation of the MMP1 gene by TNFα is not fully understood. We aimed to find additional cis-acting elements involved in the regulation of TNFα-induced MMP1 gene transcription in addition to the nuclear factor-kappa B (NF-kB) and activator protein 1 (AP1) sites. Assessments of the 5’-regulatory region of the MMP1 gene, using a series of deletion constructs, revealed the requirement of the early growth response protein 1 (EGR-1)-binding sequence (EBS) in the proximal region for proper transcription by TNFα. Ectopic expression of EGR-1, a zinc-finger transcription factor that binds to G-C rich sequences, stimulated MMP1 promoter activity. The silencing of EGR-1 by RNA interference reduced TNFα-induced MMP-1 expression. EGR-1 directly binds to the proximal region and transactivates the MMP1 gene promoter. Mutation of the EBS within the MMP1 promoter abolished EGR-1-mediated MMP-1 promoter activation. These data suggest that EGR-1 is required for TNFα-induced MMP1 transcriptional activation. In addition, we found that all three MAPKs, ERK1/2, JNK, and p38 kinase, mediate TNFα-induced MMP-1 expression via EGR-1 upregulation. These results suggest that EGR-1 may represent a good target for the development of pharmaceutical agents to reduce inflammation-induced MMP-1 expression.

Potential role of insulin on the pathogenesis of depression

The regulation of insulin on depression and depression-like behaviour has been widely reported. Insulin and activation of its receptor can promote learning and memory, affect the hypothalamic-pituitary-adrenal axis (HPA) balance, regulate the secretion of neurotrophic factors and neurotransmitters, interact with gastrointestinal microbiome, exert neuroprotective effects and have an impact on depression. However, the role of insulin on depression remains largely unclear. Therefore, in this review, we summarized the potential role of insulin on depression. It may provide new insight for clarifying role of insulin on the pathogenesis of depression.

Role of the HIF-1α/Nur77 axis in the regulation of the tyrosine hydroxylase expression by insulin in PC12 cells

Tyrosine hydroxylase (TH), catalyzing the conversion of tyrosine into l-DOPA, is the rate-limiting enzyme in dopamine synthesis. Defects in insulin action contribute to alterations of TH expression and/or activity in the brain and insulin increases TH levels in 1-methyl-4-phenylpyridinium (MPP+)-treated neuronal cells. However, the molecular mechanisms underlying the regulation of TH by insulin have not been elucidated yet. Using PC12 cells, we show for the first time that insulin increases TH expression in a biphasic manner, with a transient peak at 2 hr and a delayed response at 16 hr, which persists for up to 24 hr. The use of a dominant negative hypoxia-inducible factor 1-alpha (HIF-1α) and its pharmacological inhibitor chetomin, together with chromatin immunoprecipitation (ChIP) experiments for the specific binding to TH promoter, demonstrate the direct role of HIF-1α in the early phase. Moreover, ChIP experiments and transfection of a dominant negative of the nerve growth factor IB (Nur77) indicate the involvement of Nur77 in the late phase insulin response, which is mediated by HIF-1α. In conclusion, the present study shows that insulin regulates TH expression through HIF-1α and Nur77 in PC12 cells, supporting the critical role of insulin signaling in maintaining an appropriate dopaminergic tone by regulating TH expression in the central nervous system.

Intrinsic and Extrinsic Thymic Adrenergic Networks: Sex Steroid-Dependent Plasticity

The thymus is sexually differentiated organ providing microenvironment for T-cell precursor differentiation/maturation in the major histocompatibility complex-restricted self-tolerant T cells. With increasing age, the thymus undergoes involution leading to the decline in efficacy of thymopoiesis. Noradrenaline from thymic nerve fibers and "(nor)adrenergic" cells is involved in the regulation of thymopoiesis. In rodents, noradrenaline concentration in thymus and adrenoceptor (AR) expression on thymic cells depend on sex and age. These differences are suggested to be implicated in the development of sexual diergism and the age-related decline in thymopoiesis. The programming of both thymic sexual differentiation and its involution occurs during the critical early perinatal period and may be reprogrammed during peripubertal development. The thymic (re)programming is critically dependent on circulating levels of gonadal steroids. Although the underlying molecular mechanisms have not yet been elucidated fully, it is assumed that the gonadal steroid action during the critical perinatal/peripubertal developmental periods leads to long-lasting changes in the efficacy of thymopoiesis partly through (re)programming of "(nor)adrenergic" cell networks and AR expression on thymic cells.

miR-375 negatively regulates the synthesis and secretion of catecholamines by targeting Sp1 in rat adrenal medulla

The adrenal gland is an important endocrine gland in balancing homeostasis and the response to stress by synthesizing and secreting catecholamines (CATs), and it has been confirmed that microRNA-375 (miR-375) is highly expressed in adrenal medulla. However, up to now there are few reports about the functions and related mechanisms in adrenal medulla. The present study was thus designed to study the roles and related mechanisms in rat adrenal medulla. Our results showed that miR-375 was specifically expressed in rat adrenal medulla chromaffin cells, and its expression was downregulated when rats were exposed to stress. The further functional studies demonstrated that the inhibition of endogenous miR-375 induced the secretion of CATs in primary rat medulla chromaffin cells and PC12 cells, whereas miR-375 overexpression resulted in a decline of CAT secretion. In addition, our results showed that miR-375 negatively regulated tyrosine hydroxylase (TH) and dopamine-β-hydroxylase (DBH) and mediated adrenomedullary CAT biosynthesis. These functions of miR-375 were accomplished by its binding to the 3'-untranslated region of Sp1, which was involved in the regulation of TH and DBH expressions. These novel findings suggest that miR-375 acts as a potent negative mediator in regulating the synthesis and secretion of CATs in the adrenal medulla during the maintenance of homeostasis under stress.

Phenylethanolamine N-methyltransferase gene expression in adrenergic neurons of spontaneously hypertensive rats

Epinephrine is synthesised by the catecholamine biosynthetic enzyme, phenylethanolamine N-methyltransferase (PNMT), primarily in chromaffin cells of the adrenal medulla and secondarily in brainstem adrenergic neurons of the medulla oblongata. Epinephrine is an important neurotransmitter/neurohormone involved in cardiovascular regulation; however, overproduction is detrimental with negative outcomes such as cellular damage, cardiovascular dysfunction, and hypertension. Genetic mapping studies have linked elevated expression of PNMT to hypertension. Adrenergic neurons are responsible for blood pressure regulation and are the only PNMT containing neurons in the brainstem. The purpose of the current study was to determine whether elevated blood pressure found in adult spontaneously hypertensive rats (SHR) is associated with altered regulation of the PNMT gene in catecholaminergic neurons. C1, C2, and C3 adrenergic regions of 16 week old Wistar Kyoto (WKY) and SHR rats were excised using micropunch microdissection for mRNA expression analyses. Results from the current study confirm high PNMT mRNA expression in all three brainstem adrenergic regions (C1: 2.96-fold; C2: 2.17-fold; C3 1.20-fold) of the SHR compared to normotensive WKY rats. Furthermore, the immediate early gene transcription factor (Egr-1) mRNA was elevated in the C1 (1.84-fold), C2 (8.57-fold) and C3 (2.41-fold) regions in the brainstem of the SHR. Low mRNA expression for transcription factors Sp1 and GR was observed, while no change was observed for AP-2. The findings presented propose that alterations in the PNMT gene regulation in the brainstem contribute to enhanced PNMT production and epinephrine synthesis in the SHR, a genetic model of hypertension.

EGR-1 and DUSP-1 are important negative regulators of pro-allergic responses in airway epithelium

BACKGROUND

Primary nasal epithelium of house dust mite allergic individuals is in a permanently activated inflammatory transcriptional state.

OBJECTIVE

To investigate whether a deregulated expression of EGR-1 and/or DUSP-1, two potential negative regulators of pro-inflammatory responses, could contribute to the activation of the inflammatory state.

METHODS

We silenced the expression of EGR-1 or DUSP-1 in the airway epithelial cell line NCI-H292. The cell lines were stimulated in a 24-h time course with the house dust mite allergen or poly(I:C). RNA expression profiles of cytokines were established using q-PCR and protein levels were determined in supernatants with ELISA.

RESULTS

The shRNA-mediated gene silencing reduced expression levels of EGR-1 by 92% (p<0.0001) and of DUSP-1 by 76% (p<0.0001). Both mutant cells lines showed an increased and prolonged response to the HDM allergen. The mRNA induction of IL-6 was 4.6 fold (p=0.02) and 2.4 fold higher (p=0.01) in the EGR-1 and DUSP-1 knock-down, respectively when compared to the induced levels in the control cell line. For IL-8, the induction levels were 4.6 fold (p=0.01) and 13.0 (p=0.001) fold higher. The outcome was largely similar, yet not identical at the secreted protein levels. Furthermore, steroids were able to suppress the poly(I:C) induced cytokine levels by 70-95%.

CONCLUSIONS

Deregulation of EGR-1 and/or DUSP-1 in nasal epithelium could be responsible for the prolonged activated transcriptional state observed in vivo in allergic disease. This could have clinical consequences as cytokine levels after the steroid treatment in EGR-1 or DUSP-1 knock-down remained higher than in the control cell line.

Nucleotide sequence conservation of novel and established cis-regulatory sites within the tyrosine hydroxylase gene promoter

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in catecholamine biosynthesis and its gene proximal promoter ( < 1 kb upstream from the transcription start site) is essential for regulating transcription in both the developing and adult nervous systems. Several putative regulatory elements within the TH proximal promoter have been reported, but evolutionary conservation of these elements has not been thoroughly investigated. Since many vertebrate species are used to model development, function and disorders of human catecholaminergic neurons, identifying evolutionarily conserved transcription regulatory mechanisms is a high priority. In this study, we align TH proximal promoter nucleotide sequences from several vertebrate species to identify evolutionarily conserved motifs. This analysis identified three elements (a TATA box, cyclic AMP response element (CRE) and a 5'-GGTGG-3' site) that constitute the core of an ancient vertebrate TH promoter. Focusing on only eutherian mammals, two regions of high conservation within the proximal promoter were identified: a ∼250 bp region adjacent to the transcription start site and a ∼85 bp region located approximately 350 bp further upstream. Within both regions, conservation of previously reported cis-regulatory motifs and human single nucleotide variants was evaluated. Transcription reporter assays in a TH -expressing cell line demonstrated the functionality of highly conserved motifs in the proximal promoter regions and electromobility shift assays showed that brain-region specific complexes assemble on these motifs. These studies also identified a non-canonical CRE binding (CREB) protein recognition element in the proximal promoter. Together, these studies provide a detailed analysis of evolutionary conservation within the TH promoter and identify potential cis-regulatory motifs that underlie a core set of regulatory mechanisms in mammals.

A systems approach identifies co-signaling molecules of early growth response 1 transcription factor in immobilization stress

Background

Adaptation to stress is critical for survival. The adrenal medulla, the major source of epinephrine, plays an important role in the development of the hyperadenergic state and increased risk for stress associated disorders, such as hypertension and myocardial infarction. The transcription factor Egr1 plays a central role in acute and repeated stress, however the complexity of the response suggests that other transcription factor pathways might be playing equally important roles during acute and repeated stress. Therefore, we sought to discover such factors by applying a systems approach.

Results

Using microarrays and network analysis we show here for the first time that the transcription factor signal transducer and activator of transcription 3 (Stat3) gene is activated in acute stress whereas the prolactin releasing hormone (Prlh11) and chromogranin B (Chgb) genes are induced in repeated immobilization stress and that along with Egr1 may be critical mediators of the stress response.

Conclusions

Our results suggest possible involvement of Stat3 and Prlh1/Chgb up-regulation in the transition from short to repeated stress activation.

Complex molecular regulation of tyrosine hydroxylase

Tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, is strictly controlled by several interrelated regulatory mechanisms. Enzyme synthesis is controlled by epigenetic factors, transcription factors, and mRNA levels. Enzyme activity is regulated by end-product feedback inhibition. Phosphorylation of the enzyme is catalyzed by several protein kinases and dephosphorylation is mediated by two protein phosphatases that establish a sensitive process for regulating enzyme activity on a minute-to-minute basis. Interactions between tyrosine hydroxylase and other proteins introduce additional layers to the already tightly controlled production of catecholamines. Tyrosine hydroxylase degradation by the ubiquitin-proteasome coupled pathway represents yet another mechanism of regulation. Here, we revisit the myriad mechanisms that regulate tyrosine hydroxylase expression and activity and highlight their physiological importance in the control of catecholamine biosynthesis.

High degree of overlap between responses to a virus and to the house dust mite allergen in airway epithelial cells

BACKGROUND

Airway epithelium is widely considered to play an active role in immune responses through its ability to detect changes in the environment and to generate a microenvironment for immune competent cells. Therefore, besides its role as a physical barrier, epithelium affects the outcome of the immune response by the production of various pro-inflammatory mediators.

METHODS

We stimulated airway epithelial cells with viral double stranded RNA analogue poly(I:C) or with house dust mite in a time course of 24 hours. In order to determine cytokines production by stimulated cells, we performed multiplex enzyme linked immunosorbant assay (ELISA).

RESULTS

We demonstrate that the temporal pattern of the genes that respond to virus exposure in airway epithelium resembles to a significant degree their pattern of response to HDM. The gene expression pattern of EGR1, DUSP1, FOSL1, JUN, MYC, and IL6 is rather similar after viral (poly(I:C)) and HDM exposure. However, both triggers also induce a specific response (e.g. ATF3, FOS, and NFKB1). We confirmed these data by showing that epithelial cells produce a variety of similar mediators in response to both poly(I:C) and HDM challenge (IL1-RA, IL-17, IFN-α and MIP1-α), sometimes with a quantitative difference in response (IL2-R, IL-6, IL-8, MCP-1, MIG, and HGF). Interestingly, only four mediators (IL-12, IP-10, RANTES and VEGF) where up-regulated specifically by poly(I:C) and not by HDM. Additionally, we report that pre-exposure to HDM deregulates production of cytokines and mediators in response to poly(I:C).

CONCLUSIONS

Epithelial cells responses to the HDM-allergen and a virus strongly resemble both in gene expression and in protein level explaining why these two responses may affect each other.

COUP-TFI controls activity-dependent tyrosine hydroxylase expression in adult dopaminergic olfactory bulb interneurons

COUP-TFI is an orphan nuclear receptor acting as a strong transcriptional regulator in different aspects of forebrain embryonic development. In this study, we investigated COUP-TFI expression and function in the mouse olfactory bulb (OB), a highly plastic telencephalic region in which continuous integration of newly generated inhibitory interneurons occurs throughout life. OB interneurons belong to different populations that originate from distinct progenitor lineages. Here, we show that COUP-TFI is highly expressed in tyrosine hydroxylase (TH)-positive dopaminergic interneurons in the adult OB glomerular layer (GL). We found that odour deprivation, which is known to downregulate TH expression in the OB, also downregulates COUP-TFI in dopaminergic cells, indicating a possible correlation between TH- and COUP-TFI-activity-dependent action. Moreover, we demonstrate that conditional inactivation of COUP-TFI in the EMX1 lineage results in a significant reduction of both TH and ZIF268 expression in the GL. Finally, lentiviral vector-mediated COUP-TFI deletion in adult-generated interneurons confirmed that COUP-TFI acts cell-autonomously in the control of TH and ZIF268 expression. These data indicate that COUP-TFI regulates TH expression in OB cells through an activity-dependent mechanism involving ZIF268 induction and strongly argue for a maintenance rather than establishment function of COUP-TFI in dopaminergic commitment. Our study reveals a previously unknown role for COUP-TFI in the adult brain as a key regulator in the control of sensory-dependent plasticity in olfactory dopaminergic neurons.

Complexity of dopamine metabolism

: Parkinson's disease (PD) coincides with a dramatic loss of dopaminergic neurons within the substantia nigra. A key player in the loss of dopaminergic neurons is oxidative stress. Dopamine (DA) metabolism itself is strongly linked to oxidative stress as its degradation generates reactive oxygen species (ROS) and DA oxidation can lead to endogenous neurotoxins whereas some DA derivatives show antioxidative effects. Therefore, DA metabolism is of special importance for neuronal redox-homeostasis and viability.In this review we highlight different aspects of dopamine metabolism in the context of PD and neurodegeneration. Since most reviews focus only on single aspects of the DA system, we will give a broader overview by looking at DA biosynthesis, sequestration, degradation and oxidation chemistry at the metabolic level, as well as at the transcriptional, translational and posttranslational regulation of all enzymes involved. This is followed by a short overview of cellular models currently used in PD research. Finally, we will address the topic from a medical point of view which directly aims to encounter PD.

A synopsis on the role of tyrosine hydroxylase in Parkinson's disease

Parkinson's disease (PD) is a common chronic progressive neurodegenerative disorder in elderly people. A consistent neurochemical abnormality in PD is degeneration of dopaminergic neurons in substantia nigra pars compacta, leading to a reduction of striatal dopamine (DA) levels. As tyrosine hydroxylase (TH) catalyses the formation of L-dihydroxyphenylalanine (L-DOPA), the rate-limiting step in the biosynthesis of DA, the disease can be considered as a TH-deficiency syndrome of the striatum. Problems related to PD usually build up when vesicular storage of DA is altered by the presence of either α-synuclein protofibrils or oxidative stress. Phosphorylation of three physiologically-regulated specific sites of N-terminal domain of TH is vital in regulating its kinetic and protein interaction. The concept of physiological significance of TH isoforms is another interesting aspect to be explored further for a comprehensive understanding of its role in PD. Thus, a logical and efficient strategy for PD treatment is based on correcting or bypassing the enzyme deficiency by the treatment with L-DOPA, DA agonists, inhibitors of DA metabolism or brain grafts with cells expressing a high level of TH. Neurotrophic factors are also attracting the attention of neuroscientists because they provide the essential neuroprotective and neurorestorative properties to the nigrostriatal DA system. PPAR-γ, a key regulator of immune responses, is likewise a promising target for the treatment of PD, which can be achieved by the use of agonists with the potential to impact the expression of pro- and anti-inflammatory cytokines at the transcriptional level in immune cells via expression of TH. Herein, we review the primary biochemical and pathological features of PD, and describe both classical and developing approaches aimed to ameliorate disease symptoms and its progression.

The oxysterol 27-hydroxycholesterol regulates α-synuclein and tyrosine hydroxylase expression levels in human neuroblastoma cells through modulation of liver X receptors and estrogen receptors--relevance to Parkinson's disease

Loss of dopaminergic neurons and α-synuclein accumulation are the two major pathological hallmarks of Parkinson's disease. Currently, the mechanisms governing depletion of dopamine content and α-synuclein accumulation are not well understood. We showed that the oxysterol 27-hydroxycholesterol (27-OHC) reduces the expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine synthesis, and increases α-synuclein levels in SH-SY5Y cells. However, the cellular mechanisms involved in 27-OHC effects were not elucidated. In this study, we demonstrate that 27-OHC regulates TH and α-synuclein expression levels through the estrogen receptors (ER) and liver X receptors (LXR). We specifically show that inhibition of ERβ mediates 27-OHC-induced decrease in TH expression, an effect reversed by the ER agonist estradiol. We also show that 27-OHC and the LXR agonist GW3965 increase α-synuclein while the LXR antagonist 5α-6α-epoxycholesterol-3-sulfate significantly attenuated the 27-OHC-induced increase in α-synuclein expression. We further demonstrate that LXRβ positively regulates α-synuclein expression and 27-OHC increases LXRβ-mediated α-synuclein transcription. Our results demonstrate the involvement of two distinct pathways that are involved in the 27-OHC regulation of TH and α-synuclein levels. Concomitant activation of ERβ and inhibition of LXRβ prevent 27-OHC effects and may therefore reduce the progression of Parkinson's disease by precluding TH reduction and α-synuclein accumulation.

Exposure to extremely low frequency magnetic fields induces fos-related antigen-immunoreactivity via activation of dopaminergic d1 receptor

We previously demonstrated that repeated exposure to extremely low frequency magnetic fields (ELF-MF) increases locomotor activity via stimulation of dopaminergic D1 receptor (J. Pharmacol. Sci., 2007;105:367-371). Since it has been demonstrated that activator protein-1 (AP-1) transcription factors, especially 35-kDa fos-related antigen (FRA), play a key role in the neuronal and behavioral adaptation in response to various stimuli, we examined whether repeated ELF-MF exposure induces FRA-immunoreactivity (FRA-IR) in the striatum and nucleus accumbens (striatal complex) of the mice. Repeated exposure to ELF-MF (0.3 or 2.4 mT, 1 h/day, for consecutive fourteen days) significantly induced hyperlocomotor activity and FRA-IR in the striatal complex in a field intensity-dependent manner. ELF-MF-induced FRA-IR lasted for at least 1 year, while locomotor activity returned near control level 3 months after the final exposure to ELF-MF. Pretreatment with SCH23390, a dopaminergic D1 receptor antagonist, but not with sulpiride, a dopaminergic D2 receptor antagonist, significantly attenuated hyperlocomotor activity and FRA-IR induced by ELF-MF. Our results suggest that repeated exposure to ELF-MF leads to prolonged locomotor stimulation and long-term expression of FRA in the striatal complex of the mice via stimulation of dopaminergic D1 receptor.

Epigenetic, transcriptional and posttranscriptional regulation of the tyrosine hydroxylase gene

The activity of tyrosine hydroxylase (TH, EC 1.14.16.2) gene and protein determines the catecholamine level, which, in turn, is crucial for the organism homeostasis. The TH gene expression is regulated by near all possible regulatory mechanisms on epigenetic, transcriptional and posttranscriptional levels. Ongoing molecular characteristic of the TH gene reveals some of the cis and trans elements necessary for its proper expression but most of them especially these responsible for tissue specific expression remain still obscure. This review will focus on some aspects of TH regulation including spatial chromatin organization of the TH locus and TH gene, regulatory elements mediating basal, induced and cell-specific activity, transcriptional elongation, alternative TH RNA processing, and the regulation of TH RNA stability in the cell.

Human tyrosine hydroxylase natural genetic variation: delineation of functional transcriptional control motifs disrupted in the proximal promoter

BACKGROUND

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in catecholamine biosynthesis. Common genetic variation at the human TH promoter predicts alterations in autonomic activity and blood pressure, but how such variation influences human traits and, specifically, whether such variation affects transcription are not yet known.

METHODS AND RESULTS

Pairwise linkage disequilibrium across the TH locus indicated that common promoter variants (C-824T, G-801C, A-581G, and G-494A) were located in a single 5' linkage disequilibrium block in white, black, Hispanic, and Asian populations. Polymorphisms C-824T and A-581G were located in highly conserved regions and were predicted to disrupt known transcriptional control motifs myocyte enhancer factor-2 (MEF2), sex-determining region Y (SRY), and forkhead box D1 (FOXD1) at C-824T and G/C-rich binding factors specificity protein 1 (SP1), activating enhancer-binding protein 2 (AP2)], early growth response protein 1 (EGR1) at A-581G. At C-824T and A-581G, promoter and luciferase reporter plasmids indicated differential allele strength (T>C at C-824T; G>A at A-581G) under both basal circumstances and secretory stimulation. C-824T and A-581G displayed the most pronounced effects on both transcription in cella and catecholamine secretion in vivo. We further probed the functional significance of C-824T and A-581G by cotransfection of trans-activating factors in cella; MEF2, SRY, and FOXD1 differentially activated C-824T, whereas the G/C-rich binding factors SP1, AP2, and EGR1 differentially activated A-581G. At C-824T, factor MEF2 acted in a directionally coordinate fashion (at T>C) to explain the in vivo trait associations, whereas at A-581G, factors SP1, AP2, and EGR1 displayed similar differential actions (at G>A). Finally, chromatin immunoprecipitation demonstrated that the endogenous factors bound to the motifs in cella.

CONCLUSIONS

We conclude that common genetic variants in the proximal TH promoter, especially at C-824T and A-581G, are functional in cella and alter transcription so as to explain promoter marker-on-trait associations in vivo. MEF2, FOXD1, and SRY contribute to functional differences in C-824T expression, whereas SP1, AP2, and EGR1 mediate those of A-581G. The SRY effect on TH transcription suggests a mechanism whereby male and female sex may differ in sympathetic activity and hence blood pressure. These results point to new strategies for diagnostic and therapeutic intervention into disorders of human autonomic function and their cardiovascular consequences.

Membrane-initiated estradiol signaling increases tyrosine hydroxylase promoter activity with ER alpha in PC12 cells

Tyrosine hydroxylase (TH) promoter activity is induced by 17beta-estradiol (E(2)) in PC12 cells expressing estradiol receptor-alpha (ERalpha) requiring a cAMP/calcium response element (CRE/CaRE) at -45. To examine whether membrane-initiated estradiol signaling is underlying this induction, cells co-transfected with TH reporter construct and ERalpha expression vector were exposed to membrane-impermeant estradiol conjugate (beta-estradiol-6-(O-carboxy-methyl) oxime-bovine serum albumin, E(2)BSA). TH promoter activity was elevated by E(2)BSA in dose- and time-dependent manner. E(2)BSA also elicited rapid phosphorylation of CRE binding protein (CREB) and increased CRE-driven promoter activity. Over-expression of dominant negative forms of CREB, with mutations in DNA binding or phosphorylation site, prevented TH promoter response to E(2)BSA. Pre-treatment with protein kinase A (PKA) and MEK inhibitors reduced E(2) dependent phosphorylation of CREB and ERK, and also decreased induction of TH promoter activity by E(2) or E(2)BSA. Blocking S-palmitoylation of ERalpha with C451A mutation and/or pre-treatment with 2-Bromopalmitate did not prevent but instead enhanced E(2) or E(2)BSA-elicited induction of TH promoter activity. These findings reveal, for the first time, that estradiol induction of TH gene transcription with ERalpha in PC12 cells involves membrane-initiated estradiol signaling, rapid activation of dual PKA/MEK signaling pathways, leading to CREB phosphorylation, acting at CRE/CaRE. The data demonstrate possible mechanism whereby estradiol affects catecholaminergic systems in vivo.

Divergent effects of estradiol on gene expression of catecholamine biosynthetic enzymes

Within the catecholaminergic systems, there are contradictory findings regarding ability of estradiol to regulate expression of genes related to catecholamine biosynthesis. Several parameters important for effects of estradiol on the catecholamine (CA) related enzyme gene expression were examined in two CA regions. Ovariectomized (OVX) female rats were given prolonged estradiol treatments, either in a pulsatile fashion by injections or continuously by pellets. The mode affected the response of tyrosine hydroxylase (TH) and GTP cyclohydrolase I (GTPCH) mRNAs differentially in the nucleus of solitary tract (NTS) and the locus coeruleus (LC). In rostral-medial NTS, TH mRNA levels were increased with injections, but declined in rats administered estradiol by pellets. In LC, a significant change was only observed in GTPCH with injections. These differences may reflect activation of different estrogen receptors (ER). The response to estradiol in the presence of ERalpha and ER beta was examined in PC12 cell culture. Estradiol directly regulated promoter activity of TH, GTPCH and dopamine beta-hydroxylase (DBH) genes. With ERalpha, 17 beta-estradiol elevated TH promoter activity, while there was a decline with ERbeta. In contrast, both DBH and GTPCH promoters were enhanced by 17 beta-estradiol over a wide range of concentrations with either ER subtype. Thus, mode of administration, location examined and ER subtype expressed are important considerations in the overall response of catecholamine related enzymes to estradiol.

Social contact elicits immediate-early gene expression in dopaminergic cells of the male prairie vole extended olfactory amygdala

Male prairie voles (Microtus ochrogaster) are a valuable model in which to study the neurobiology of sociality because, unlike most mammals, they pair bond after mating and display paternal behaviors. Research on the regulation of these social behaviors has highlighted dopamine (DA) neurotransmission in both pair bonding and parenting. We recently described large numbers of dopaminergic cells in the male prairie vole principal nucleus of the bed nucleus of the stria terminalis (pBST) and posterodorsal medial amygdala (MeApd), but such cells were very few in number or absent in the non-monogamous species we examined, including meadow voles. This suggests that DA cells in these sites may be important for sociosexual behaviors in male prairie voles. To gain some insight into the function of these DAergic neurons in male prairie voles, we examined expression of the immediate-early genes (IEGs) Fos and Egr-1 in tyrosine hydroxylase (TH)-immunoreactive (TH-ir) cells of the pBST and MeApd after males interacted or not with one of several social stimuli. We found that IEGs were constitutively expressed in some TH-ir neurons under any social condition, but that IEG expression in these cells decreased after a 3.5-h social isolation. Thirty-minute mating bouts (but not 6- or 24-h bouts) that included ejaculation elicited greater IEG expression in TH-ir cells than did non-ejaculatory mating, interactions with a familiar female sibling, or interactions with pups. Furthermore, Fos expression in TH-ir cells was positively correlated with the display of copulatory, but not parental, behaviors. These effects of mating were not found in other DA-rich sites of the forebrain (including the anteroventral periventricular preoptic area, periventricular anterior hypothalamus, zona incerta, and arcuate nucleus). Thus, activity in DAergic cells of the male prairie vole pBST and MeApd is influenced by their social environment, and may be particularly involved in mating and its consequences, including pair bonding.

Catecholaminergic systems in stress: structural and molecular genetic approaches

Stressful stimuli evoke complex endocrine, autonomic, and behavioral responses that are extremely variable and specific depending on the type and nature of the stressors. We first provide a short overview of physiology, biochemistry, and molecular genetics of sympatho-adrenomedullary, sympatho-neural, and brain catecholaminergic systems. Important processes of catecholamine biosynthesis, storage, release, secretion, uptake, reuptake, degradation, and transporters in acutely or chronically stressed organisms are described. We emphasize the structural variability of catecholamine systems and the molecular genetics of enzymes involved in biosynthesis and degradation of catecholamines and transporters. Characterization of enzyme gene promoters, transcriptional and posttranscriptional mechanisms, transcription factors, gene expression and protein translation, as well as different phases of stress-activated transcription and quantitative determination of mRNA levels in stressed organisms are discussed. Data from catecholamine enzyme gene knockout mice are shown. Interaction of catecholaminergic systems with other neurotransmitter and hormonal systems are discussed. We describe the effects of homotypic and heterotypic stressors, adaptation and maladaptation of the organism, and the specificity of stressors (physical, emotional, metabolic, etc.) on activation of catecholaminergic systems at all levels from plasma catecholamines to gene expression of catecholamine enzymes. We also discuss cross-adaptation and the effect of novel heterotypic stressors on organisms adapted to long-term monotypic stressors. The extra-adrenal nonneuronal adrenergic system is described. Stress-related central neuronal regulatory circuits and central organization of responses to various stressors are presented with selected examples of regulatory molecular mechanisms. Data summarized here indicate that catecholaminergic systems are activated in different ways following exposure to distinct stressful stimuli.

Expression of EGR-1 in a subset of olfactory bulb dopaminergic cells

In the adrenal medulla, binding of the immediate early gene (IEG) proteins, EGR-1 (ZIF-268/KROX-24/NGFI-A) and AP-1, to the tyrosine hydroxylase (Th) proximal promoter mediate inducible Th expression. The current study investigated the potential role of EGR-1 in inducible Th expression in the olfactory bulb (OB) since IEGs bound to the AP-1 site in the Th proximal promoter are also necessary for activity-dependent OB TH expression. Immunohistochemical analysis of a naris-occluded mouse model of odor deprivation revealed weak EGR-1 expression levels in the OB glomerular layer that were activity-dependent. Immunofluorescence analysis indicated that a majority of glomerular cells expressing EGR-1 also co-expressed TH, but only small subset of TH-expressing cells contained EGR-1. By contrast, granule cells, which lack TH, exhibited EGR-1 expression levels that were unchanged by naris closure. Together, these finding suggest that EGR-1 mediates activity-dependent TH expression in a subset of OB dopaminergic neurons, and that there is differential regulation of EGR-1 in periglomerular and granule cells.

Identifying the stress transcriptome in the adrenal medulla following acute and repeated immobilization

Stress triggers changes in gene expression mediating important adaptive and maladaptive responses. The full repertoire of genes whose expression in the adrenal medulla is altered by stress has not been previously determined. In this study, gene profiling (RAE 230 2.0 Affymetrix) was applied to elucidate global changes in gene expression in adrenal medulla of rats exposed to 2-h immobilization (IMO) stress once or repeatedly for 6 consecutive days. The number of transcripts significantly (P < 0.01) altered with single IMO (651 up, 487 down) was more than with repeated IMO (370 up, 195 down). The annotated transcripts were further analyzed and categorized. The largest numbers of changes were in mRNA levels in the transcription factor and cell signaling categories. Robust changes were also observed in transcripts related to growth factors, apoptosis, neurosecretion/neuropeptides, heat shock proteins, structural proteins, chemokines, cytokines, metabolism/lipid-metabolism, and proteases. Many (>80%) were uniquely induced by single IMO. About half of transcripts changed by repeated IMO were also responsive to single IMO. Pathway analysis was applied to identify direct interactions and common targets among gene products altered by single and repeated IMO. In this paper, we briefly describe the most pronounced changes observed, with emphasis on those that may provide new insight into the common and distinct mechanisms whereby the adrenal medulla responses to a first encounter with stress compared to repeated exposure to the same stressor.

Identification of an activator protein-1-like sequence as the glucocorticoid response element in the rat tyrosine hydroxylase gene

Glucocorticoids (GCs) generally stimulate gene transcription via consensus glucocorticoid response elements (GREs) located in the promoter region. To identify the GRE in the rat tyrosine hydroxylase (TH) gene promoter, we transiently transfected PC12 cells with a 9-kilobase (kb) TH promoter-luciferase (Luc) construct. Dexamethasone (Dex) stimulated Luc activity, which was abolished by mifepristone (RU486). Serial deletion mutations revealed a Dex-responsive 7-base pair (bp) sequence, TGACTAA, located at -5734 to -5728. Deletion of just these seven nucleotides from the 9-kb promoter completely abolished the Dex response and partially reduced the response to phorbol ester but not to forskolin. The Dex response was fully retained in a construct in which most of the 9-kb promoter was deleted, except for 100 bp around the -5.7-kb region, clearly identifying this 7-bp sequence as solely responsible for GC responsiveness. Conversely, deletion of the proximal cAMP-response element (-45/-38) or activator protein-1 (AP-1) (-207/-201) sites in the 9-kb promoter did not affect Dex and phorbol ester responses. A radiolabeled 25-bp promoter fragment bearing the 7-bp TH-GRE/AP-1 showed specific binding to PC12 nuclear proteins. Using antibodies against the glucocorticoid receptors and AP-1 family of proteins and primers for the TH-GRE/AP-1 region, we detected a specific DNA amplicon in a chromatin immunoprecipitation assay. This 7-bp TH-GRE/AP-1 sequence (TGACTAA) does not bear similarity to any known GRE but closely resembles the consensus AP-1 binding site, TGACTCA. Our studies describe for the first time a novel GRE/AP-1 site present in the TH gene promoter that is critical for glucocorticoid regulation of the TH gene.

Differential effects of 24-hydroxycholesterol and 27-hydroxycholesterol on tyrosine hydroxylase and alpha-synuclein in human neuroblastoma SH-SY5Y cells

Evidence suggests that environmental and dietary factors may contribute to the pathogenesis of Parkinson's disease (PD). High dietary intake of cholesterol is such a factor that has been shown to increase or decrease the risk of PD. However, because circulating cholesterol does not cross the blood-brain barrier, the mechanisms linking dietary cholesterol to the pathogenesis of PD remain to be understood. In contrast to cholesterol, the oxidized cholesterol metabolites (oxysterols), 24S-hydroxycholesterol (24-OHC) and 27-hydroxycholesterol (27-OHC), can cross the blood-brain barrier and may place the brain at risk of degeneration. In this study, we incubated the human neuroblastoma SH-SY5Y cells for 24 h with 24-OHC, 27-OHC, or a mixture of 24-OHC plus 27-OHC, and have determined effects on tyrosine hydroxylase (the rate-limiting enzyme in dopamine synthesis) levels, alpha-synuclein levels, and apoptosis. We demonstrate that while 24-OHC increases the levels of tyrosine hydroxylase, 27-OHC increases levels of alpha-synuclein, and induces apoptosis. Our findings show for the first time that oxysterols trigger changes in levels of proteins that are associated with the pathogenesis of PD. As steady state levels of 24-OHC and 27-OHC are tightly regulated in the brain, disturbances in these levels may contribute to the pathogenesis of PD.

Concomitant activation of adenylyl cyclase suppresses the opposite influences of CB(1) cannabinoid receptor agonists on tyrosine hydroxylase expression

The CB(1) cannabinoid receptor shows complex interactions with intracellular signalling partners, and responses to cannabinoid ligands are likely to be influenced by concomitant inputs modifying the overall tone of signalling cascades. This appears even more relevant as we previously evidenced opposite regulations of tyrosine hydroxylase (TH) expression by the two common cannabinoid agonists HU 210 and CP 55,940. Therefore, we studied the consequences of manipulating adenylyl cyclase activity with forskolin on the regulation of TH gene transcription in neuroblastoma cells (N1E-115). Reporter gene experiments performed with the luciferase sequence cloned under the control of modified fragments of the TH gene promoter revealed that the AP-1 consensus sequence is essential for cannabinoid-mediated regulation of TH expression. Consistently, inhibition of PKC totally blocked the responses mediated by both HU 210 and CP 55,940. In addition, forskolin which boosts adenylyl cyclase activity remarkably modified the responses to the cannabinoid agonists. Thus, in these conditions, both agonists efficiently reduced TH gene promoter activity, a response requiring functional PKA/CRE-dependent signallings. Finally, the modulations of the promoter were inhibited in pertussis toxin treated cells, suggesting that responses to both agonists are mediated through G(i/o)-dependent mechanisms. Emphasising on the importance of functional selectivity at GPCRs, these data demonstrate that the concomitant activation of adenylyl cyclase by forskolin strongly influences the biochemical responses triggered by distinct cannabinoid agonists. Together our results suggest that the physiological modulation of TH expression by cannabinoid agonists in dopaminergic neurons would be influenced by additional endogenous inputs.

Adrenocorticotropic hormone elevates gene expression for catecholamine biosynthesis in rat superior cervical ganglia and locus coeruleus by an adrenal independent mechanism

Classically, upon hypothalamic stimulation, adrenocorticotropic hormone (ACTH) is released from the pituitary and acts on melanocortin 2 receptors (MC2R) in the adrenal cortex, stimulating glucocorticoid synthesis and release. Our earlier studies suggested that ACTH might have a direct effect on sympathetic ganglia. To analyze further the involvement of ACTH in regulation of gene expression of norepinephrine (NE) biosynthetic enzymes, we examined the effect of bilateral adrenalectomy (ADX) of Sprague-Dawley male rats. Fourteen days post-ADX, as expected, plasma ACTH was elevated, and levels of tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH) and MC2R mRNAs in superior cervical ganglia (SCG), and TH mRNA in locus coeruleus (LC) were increased compared with sham-operated animals. To determine effect of pulsatile elevation of ACTH, corticosterone pellets were implanted to ADX rats. Similar to immobilization (IMO) stress ACTH injections to these animals caused a rise in ACTH in plasma and triggered elevation of TH and DBH mRNAs in SCG and in LC with single and repeated daily injections, and MC2R mRNA in SCG with single injections. To study the effect of ACTH in isolated cells, primary cultures of rat SCG were transfected with TH and DBH promoter constructs and treated with ACTH. In agreement with the in vivo data, ACTH elevated their promoter activities similar to levels triggered by cyclic AMP analog. ACTH in the human SK-N-SH neuroblastoma cells increased TH and DBH promoter activity and endogenous DBH mRNA levels. The results show that ACTH can have a direct effect on transcription and gene expression of NE biosynthetic enzymes even without contribution of adrenal hormones.

Regulation of rat dopamine beta-hydroxylase gene transcription by early growth response gene 1 (Egr1)

Egr1, a transcription factor rapidly induced by various stimuli including stress, can elevate transcription of genes for the catecholamine biosynthetic enzymes TH and PNMT. To examine if Egr1 also regulates dopamine beta-hydroxylase (DBH) gene expression, PC12 cells were transfected with expression vector for full length or truncated inactive Egr1 and various DBH promoter-driven luciferase constructs. While Egr1 elevated TH promoter activity, DBH promoter activity was reduced. The reduction occurred as early as 4 h and reached maximal inhibition 16-40 h after transfection. Egr1 also reduced the expression of endogenous DBH mRNA and the induction of DBH promoter activity by cAMP. These effects were not observed with truncated Egr1 lacking the DNA binding domain. The first 247, but not 200, nucleotides of DBH promoter are sufficient for this suppression. Several putative Egr1 motifs were identified, and mutagenesis showed that the motif at -227/-224 is required. Binding of Egr1 to this region of the DBH promoter was verified by chromatin immunoprecipitation and electrophoretic mobility shift assays. This study demonstrates that DBH promoter contains at least one functional Egr1 motif; and indicates, for the first time, that Egr1 can play an inhibitory role in regulation of DBH gene transcription.

Evidence for circadian regulation of activating transcription factor 5 but not tyrosine hydroxylase by the chromaffin cell clock

In mammals, adrenal medulla chromaffin cells constitute a fundamental component of the sympathetic nervous system outflow, producing most of the circulating adrenaline. We recently found that the rhesus monkey adrenal gland expresses several genes in a 24-h rhythmic pattern, including TH (the rate-limiting enzyme in catecholamine synthesis) and Atf5 (a transcription factor involved in apoptosis and neural cell differentiation) together with the core-clock genes. To examine whether these core-clock genes play a role in adrenal circadian function, we exposed rat pheochromocytoma PC12 cells to a serum shock and found that it triggered rhythmic oscillation of the clock genes rBmal1, rPer1, rRev-erbalpha, and rCry1 and induced the circadian expression of Atf5 but not TH. Furthermore, we found that the CLOCK/brain and muscle Arnt-like protein-1 (BMAL1) heterodimer could regulate Atf5 expression by binding to an E-box motif and repressing activity of its promoter. The physiological relevance of this interaction was evident in Bmal1 -/- mice, in which blunted circadian rhythm of Atf5 mRNA was observed in the liver, together with significantly higher expression levels in both liver and adrenal glands. Although we found no compelling evidence for rhythmic expression of TH in chromaffin cells being regulated by an intrinsic molecular clock mechanism, the Atf5 results raise the possibility that other aspects of chromaffin cell physiology, such as cell survival and cell differentiation, may well be intrinsically regulated.

Neuronal PAS domain protein 1 regulates tyrosine hydroxylase level in dopaminergic neurons

Catecholamines (dopamine, norepinephrine, and epinephrine) are all synthesized from a common pathway in which tyrosine hydroxylase (TH) is the rate-limiting enzyme. Dopamine is the main neurotransmitter present in dopaminergic neurons of the ventral midbrain, where dysfunction of these neurons can lead to Parkinson's disease and schizophrenia. Neuronal PAS domain protein 1 (NPAS1) was identified as one of the genes up-regulated during dopaminergic MN9D cell differentiation. We found that there was a corresponding decrease in TH level during MN9D differentiation. Overexpression and siRNA experiments revealed that NPAS1, in concert with ARNT, negatively regulates the expression of TH and that this regulation is mediated by a direct binding of NPAS1 on the TH promoter. Expression studies also confirmed a decrease in TH level in the ventral midbrain during mouse development, concomitant with an increase in NPAS1 level. These results suggest that NPAS1 plays a novel and important role in regulating TH level of dopaminergic neurons in the ventral midbrain during development.

Molecular basis of neuroendocrine cell type-specific expression of the chromogranin B gene: Crucial role of the transcription factors CREB, AP-2, Egr-1 and Sp1

The molecular basis of neuroendocrine-specific expression of chromogranin B gene (Chgb) has remained elusive. Utilizing wild-type and mutant Chgb promoter/luciferase reporter constructs, this study established a crucial role for the cAMP response element (CRE) box at -102/-95 bp in endocrine [rat pheochromocytoma (chromaffin) cell line (PC12) and rat pituitary somatotrope cell line (GC)] and neuronal [rat dorsal root ganglion/mouse neuroblastoma hybrid cell line (F-11), cortical and hippocampal primary neurons] cells. Additionally, G/C-rich domains at -134/-127, -125/-117 and -115/-110 bp played especially important roles for endocrine-specific expression of the Chgb gene. Co-transfection of expression plasmids for CREB, activator protein-2 (transcription factor) (AP-2), early growth response protein (transcription factor) (Egr-1) or specificity protein 1 (transcription factor) (Sp1) with the Chgb promoter constructs trans-activated expression of the Chgb gene. Nuclear extracts from either PC12 or F-11 cells formed specific complexes with the Chgb (-110/-87 bp) (CRE) oligonucleotide, which were either supershifted or disrupted by anti-CREB antibodies. In addition PC12 nuclear extracts also formed a specific complex with a Chgb (-140/-104-bp) oligonucleotide containing three G/C-rich regions, which was dose-dependently disrupted by anti-AP-2, anti-Egr-1 or anti-Sp1 antibodies; indeed, any one of these three antibodies completely abolished the complex, suggesting that all three factors bind the region simultaneously, at least in vitro. Chromatin immunoprecipitation assays documented the binding of the transcription factors CREB, AP-2, Egr-1 and Sp1 to the chromosomal Chgb gene promoter in vivo in PC12 cells within the context of chromatin. We conclude that the neuroendocrine-specific expression of Chgb is mediated by the CRE and G/C boxes in cis and the transcription factors CREB, AP-2, Egr-1 and Sp1 in trans.

Chronic high-dose haloperidol has qualitatively similar effects to risperidone and clozapine on immediate-early gene and tyrosine hydroxylase expression in the rat locus coeruleus but not medial prefrontal cortex

Acute administration of clozapine has been reported to activate the locus coeruleus (LC) and beta-adrenoceptor-dependent Fos immunoreactivity in the medial prefrontal cortex (mPFC) in rodents. Haloperidol is reported to exhibit a similar acute effect on LC firing and beta-adrenoceptor dependent Fos immunoreactivity in the mPFC but only at high doses. We compared the effects of chronic 4-week treatment with risperidone (1mg/kg/day s.c.), clozapine (10mg/kg/day s.c.) or a high dose of haloperidol (4mg/kg/day s.c.) on immediate-early gene protein (c-Fos, Egr-1 and Egr-2) and tyrosine hydroxylase (TH) expression. In the mPFC, haloperidol decreased, whereas clozapine increased, c-Fos immunoreactivity. Only haloperidol increased Egr-1 immunoreactivity. There was no significant effect on Egr-2 immunoreactivity. In the LC, both Egr-1 and Egr-2 expression was down regulated by all three antipsychotics. Clozapine and risperidone increased TH immunoreactivity in both mPFC and LC. Haloperidol caused a smaller increase in TH expression in the LC, but did not alter expression in the mPFC. In conclusion, despite qualitatively similar effects in the LC, chronic treatment with haloperidol had different effects to clozapine and risperidone in the mPFC. This may relate to the reported advantage of clozapine and risperidone over haloperidol against prefrontal cortical-dependent cognitive and negative symptoms.

Prolonged Activation of cAMP-response Element-binding Protein and ATF-2 Needed for Nicotine-triggered Elevation of Tyrosine Hydroxylase Gene Transcription in PC12 Cells

Phosphorylation (P-) of cAMP-response element-binding protein (CREB) by protein kinase A or mitogen-activated protein kinases was implicated in mediating the increased tyrosine hydroxylase (TH) gene expression after prolonged exposure to nicotine in vivo and in cell culture. We examined the time course and signaling pathways for phosphorylation of CREB and possible involvement of ATF-2. Treatment of PC12 cells with 200 microm nicotine triggered rapid but transient elevation of P-CREB followed by a second sustained rise after 2-5 h of continuous nicotine. In contrast, ERK1/2 was only phosphorylated with short term nicotine exposure. MEK inhibitor U0126 abolished nicotine-induced rise in P-ERK1/2, but not P-CREB, nor did it inhibit nicotine-evoked elevation in TH promoter activity, indicating that ERK1/2 was not needed for induction of TH gene expression by nicotine. In contrast, protein kinase A inhibitor H-89 or Ca(2+)/calmodulin-activated protein kinase inhibitor KN-93 reduced the nicotine-triggered rise in P-CREB and TH promoter activity. There was a delayed elevation of P-ATF-2 after 1 h of nicotine treatment, accompanied by increased ATF-2 protein. Upstream kinase JNK, but not p38, was phosphorylated especially after 5 min to 2 h of nicotine exposure. To examine the requirement for CREB and ATF-2, cells were transfected with dominant negative forms of ATF-2 or CREB. Both reduced the basal TH promoter activity and the response to nicotine. Knockdown of ATF-2 or CREB with siRNA did not alter basal TH promoter activity or mRNA but greatly attenuated the response to nicotine. The results suggest that both ATF-2 and CREB mediate activation of TH gene transcription by nicotine.

Single and repeated immobilization stress differentially trigger induction and phosphorylation of several transcription factors and mitogen-activated protein kinases in the rat locus coeruleus

The locus coeruleus (LC) is a critical stress-responsive location that mediates many of the responses to stress. We used immunoblotting and immunohistochemistry to investigate changes in induction and phosphorylation of several transcription factors and kinases in the LC that may mediate the stress-triggered induction of tyrosine hydroxylase (TH) transcription. Rats were exposed to single or repeated immobilization stress (IMO) for brief (5 min), intermediate (30 min) or sustained (2 h) duration. Single IMO elicited rapid induction of c-Fos and phosphorylation of cyclic AMP response element-binding protein (CREB) without changing the expression of early growth response (Egr)1, Fos-related antigen (Fra)-2 or phosphorylated activating transcription factor-2. Repeated IMO triggered increased phosphorylation and levels of CREB along with transient induction of c-Fos and increased Fra-2 expression. Several mitogen-activated protein kinases were activated by repeated IMO, shown by increased phosphorylation of p38, c-Jun N-terminal kinase (JNK)1/2/3 and extracellular signal-regulated kinase (ERK1/2). ERK1 was the major isoform expressed, and ERK2 the predominant isoform phosphorylated. Repeated IMO elicited hyperphosphorylation of ERK1/2 selectively in TH immunoreactive neurons, with substantial nuclear localization. These distinct alterations in transcriptional pathways following repeated compared with single stress may be involved in mediating long-lasting neuronal remodeling and are implicated in the mechanisms by which acute beneficial responses to stress are converted into prolonged adaptive or maladaptive responses.

Transcriptional regulation of tyrosine hydroxylase by estrogen: opposite effects with estrogen receptors alpha and beta and interactions with cyclic AMP

Reported effects of estrogen administration on tyrosine hydroxylase (TH) gene expression are confusing. Therefore, we studied the mechanism of regulation of TH transcription by estrogen with different estradiol receptor (ER) subtypes. PC12 cells, transiently co-transfected with expression vector for ERalpha or ERbeta, and luciferase gene under control of the TH promoter, were treated with 17 beta-estradiol (E2). E2 doubled luciferase activity with ERalpha; however, it was decreased with ERbeta. Mapping the TH promoter showed that the putative half estrogen response element (ERE) motif at - 675, as well as the activation protein 1 motif at - 205, were not required for response to E2 with either ER. The specificity protein 1/early growth response gene 1 (Egr 1) motif was required for the E2-elicited response with ERbeta, but not with ERalpha. Deletion of the cyclic AMP/Ca2+ response element (CRE/CaRE) nearly abolished E2-triggered responses with either ER. Further analysis revealed an imperfect canonical putative ERE overlapping with CRE/CaRE and Nurr1 response element. Oligonucleotides spanning this ERE displayed binding to ER, Cyclic AMP Response Element Binding Protein (CREB) and other proteins. Moreover, E2 attenuated the increase in TH transcription seen with cyclic AMP analogs. Thus, TH is transcriptionally regulated by estradiol in opposite directions depending on ER subtype. The overlapping ERE and CRE/CaRE may integrate interactions elicited by various regulators of TH transcription including cAMP and estrogens.

Differential effects of stress on gene transcription factors in catecholaminergic systems

Long-term changes in catecholamine levels and expression of their biosynthetic enzymes are associated with several stress-related disorders such as elevated plasma norepinephrine in posttraumatic stress disorder and increased postmortem tyrosine hydroxylase in the locus coeruleus with major depression. Stress elevates tyrosine hydroxylase gene expression in the CNS and periphery. Increased transcriptional initiation was involved in this induction in the rat adrenal medulla and locus coeruleus in response to single as well as repeated immobilization stress (IMO). We examined the stress-triggered induction or phosphorylation of several transcription factors, which were previously shown to be able to modulate tyrosine hydroxylase transcription. A single episode of IMO triggered elevations of c-fos in both the adrenal medulla and locus coeruleus. With repeated daily IMO, Fra-2 was a major AP-1 factor induced in the adrenal medulla, but not in the locus coeruleus. Egr1 levels were markedly elevated in the adrenal medulla with both single and repeated IMO stress, but not in the locus coeruleus. In the locus coeruleus, increased phosphorylation of CREB was observed after both single and repeated IMO. Results implicate differential transcription pathways in mediating elevation of gene expression of tyrosine hydroxylase, and other target genes, in these locations.

Regulation of tyrosine hydroxylase gene transcription by Sry

Testes determining factor Sry is encoded by the Sry locus on the Y chromosome and may be involved in the regulation of blood pressure. Here we tested the hypothesis that Sry regulates transcription of tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of catecholamines. Sry was found to be expressed in catecholaminergic regions, in male but not female rats. Co-transfection of PC12 cells with expression vector for Sry and the reporter construct [p5'TH(-773/+27)/Luc], containing 773 of the proximal nucleotides of the TH promoter directing luciferase reporter activity, led to elevation of reporter activity. The reporter activity of a shorter construct [p5'TH(-272/+27)/Luc] lacking putative Sry sites also responded to Sry. However, mutation of the AP1 site in the TH promoter greatly reduced induction by Sry, indicating that the regulation is primarily at this motif. The remaining, significantly increased expression with the mutated TH promoter construct may reflect Sry function at other sites in addition to the AP1 motif. These results reveal that Sry can regulate TH transcription and suggest that this may be one of the mechanisms of Sry mediated regulation of catecholamine biosynthesis in catecholaminergic neurons in males.

Nicotine and epibatidine triggered prolonged rise in calcium and TH gene transcription in PC12 cells

The effect of epibatidine on regulation of [Ca2+]i and tyrosine hydroxylase (TH) transcription was examined. Epibatidine triggers a biphasic rise in [Ca2+]i in PC12 cells similar to that observed with nicotine. There was an immediate transient increase in [Ca2+]i and a subsequent sustained second elevation. In contrast to nicotine, the epibatidine-triggered increase in [Ca2+]i was independent of activation of alpha7 nicotinic acetylcholine receptors, as it was not altered by either methyllycaconitine or alpha-bungarotoxin. The second [Ca2+]i elevation involves calcium release from intracellular stores and is inhibited by dantrolene or xestospongin C. Epibatidine, like nicotine, elevated TH promoter driven reporter transcription, mostly mediated by the cyclic-AMP responsive motifs. Elevation in TH promoter activity requires Ca2+ and cAMP since it is inhibited by 1,2-bis(o-Aminophenoxy)ethane-N,N,N',N'-tetraacetic Acid Tetra (acetoxymethyl ester) (BAPTA-AM) or 2',5'-dideoxyadenosine (DDA). The results reveal that epibatidine can elevate [Ca2+]i in an alpha7 independent manner and nevertheless induce TH transcription.