Regulated expression of the tyrosine hydroxylase gene by membrane depolarization. Identification of the responsive element and possible second messengers

Role of dopamine neuron activity in Parkinson's disease pathophysiology

Neural activity is finely tuned to produce normal behaviors, and disruptions in activity likely occur early in the course of many neurodegenerative diseases. However, how neural activity is altered, and how these changes influence neurodegeneration is poorly understood. Here, we focus on evidence that the activity of dopamine neurons is altered in Parkinson's disease (PD), either as a compensatory response to degeneration or as a result of circuit dynamics or pathologic proteins, based on available human data and studies in animal models of PD. We then discuss how this abnormal activity may augment other neurotoxic phenomena in PD, including mitochondrial deficits, protein aggregation and spread, dopamine toxicity, and excitotoxicity. A more complete picture of how activity is altered and the resulting effects on dopaminergic neuron health and function may inform future therapeutic interventions to target and protect dopamine neurons from degeneration.

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.

DDC-Promoter-Driven Chemogenetic Activation of SNpc Dopaminergic Neurons Alleviates Parkinsonian Motor Symptoms

Parkinson's disease (PD) is a neurodegenerative disorder with typical motor symptoms. Recent studies have suggested that excessive GABA from reactive astrocytes tonically inhibits dopaminergic neurons and reduces the expression of tyrosine hydroxylase (TH), the key dopamine-synthesizing enzyme, in the substantia nigra pars compacta (SNpc). However, the expression of DOPA decarboxylase (DDC), another dopamine-synthesizing enzyme, is relatively spared, raising a possibility that the live but non-functional TH-negative/DDC-positive neurons could be the therapeutic target for rescuing PD motor symptoms. However, due to the absence of a validated DDC-specific promoter, manipulating DDC-positive neuronal activity has not been tested as a therapeutic strategy for PD. Here, we developed an AAV vector expressing mCherry under rat DDC promoter (AAV-rDDC-mCherry) and validated the specificity in the rat SNpc. Modifying this vector, we expressed hM3Dq (Gq-DREADD) under DDC promoter in the SNpc and ex vivo electrophysiologically validated the functionality. In the A53T-mutated alpha-synuclein overexpression model of PD, the chemogenetic activation of DDC-positive neurons in the SNpc significantly alleviated the parkinsonian motor symptoms and rescued the nigrostriatal TH expression. Altogether, our DDC-promoter will allow dopaminergic neuron-specific gene delivery in rodents. Furthermore, we propose that the activation of dormant dopaminergic neurons could be a potential therapeutic strategy for PD.

Aberrant Tonic Inhibition of Dopaminergic Neuronal Activity Causes Motor Symptoms in Animal Models of Parkinson's Disease

Current pharmacological treatments for Parkinson's disease (PD) are focused on symptomatic relief, but not on disease modification, based on the strong belief that PD is caused by irreversible dopaminergic neuronal death. Thus, the concept of the presence of dormant dopaminergic neurons and its possibility as the disease-modifying therapeutic target against PD have not been explored. Here we show that optogenetic activation of substantia nigra pars compacta (SNpc) neurons alleviates parkinsonism in acute PD animal models by recovering tyrosine hydroxylase (TH) from the TH-negative dormant dopaminergic neurons, some of which still express DOPA decarboxylase (DDC). The TH loss depends on reduced dopaminergic neuronal firing under aberrant tonic inhibition, which is attributed to excessive astrocytic GABA. Blocking the astrocytic GABA synthesis recapitulates the therapeutic effect of optogenetic activation. Consistently, SNpc of postmortem PD patients shows a significant population of TH-negative/DDC-positive dormant neurons surrounded by numerous GABA-positive astrocytes. We propose that disinhibiting dormant dopaminergic neurons by blocking excessive astrocytic GABA could be an effective therapeutic strategy against PD.

Identification of Novel Pathways Associated with Patterned Cerebellar Purkinje Neuron Degeneration in Niemann-Pick Disease, Type C1

Niemann-Pick disease, type C1 (NPC1) is a lysosomal disease characterized by progressive cerebellar ataxia. In NPC1, a defect in cholesterol transport leads to endolysosomal storage of cholesterol and decreased cholesterol bioavailability. Purkinje neurons are sensitive to the loss of NPC1 function. However, degeneration of Purkinje neurons is not uniform. They are typically lost in an anterior-to-posterior gradient with neurons in lobule X being resistant to neurodegeneration. To gain mechanistic insight into factors that protect or potentiate Purkinje neuron loss, we compared RNA expression in cerebellar lobules III, VI, and X from control and mutant mice. An unexpected finding was that the gene expression differences between lobules III/VI and X were more pronounced than those observed between mutant and control mice. Functional analysis of genes with anterior to posterior gene expression differences revealed an enrichment of genes related to neuronal cell survival within the posterior cerebellum. This finding is consistent with the observation, in multiple diseases, that posterior Purkinje neurons are, in general, resistant to neurodegeneration. To our knowledge, this is the first study to evaluate anterior to posterior transcriptome-wide changes in gene expression in the cerebellum. Our data can be used to not only explore potential pathological mechanisms in NPC1, but also to further understand cerebellar biology.

Effects of asarinin on dopamine biosynthesis and 6-hydroxydopamine-induced cytotoxicity in PC12 cells

This study investigated the effects of asarinin on dopamine biosynthesis and 6-hydroxydopamine (6-OHDA)-induced cytotoxicity in rat adrenal pheochromocytoma (PC12) cells. Treatment with asarinin (25-50 μM) increased intracellular dopamine levels and enhanced L-DOPA-induced increases in dopamine levels. Asarinin (25 μM) induced cyclic AMP-dependent protein kinase A (PKA) signaling, leading to increased cyclic AMP-response element binding protein (CREB) and tyrosine hydroxylase (TH) phosphorylation, which in turn stimulated dopamine production. Asarinin (25 μM) also activated transient phosphorylation of extracellular signal-regulated kinase (ERK1/2) and Bad phosphorylation at Ser 112, both of which have been shown to promote cell survival. In contrast, asarinin (25 μM) inhibited sustained ERK1/2, Bax, c-Jun N-terminal kinase (JNK1/2) and p38 mitogen-activated protein kinase (p38MAPK) phosphorylation and caspase-3 activity, which were induced by 6-OHDA (100 μM). These results suggest that asarinin induces dopamine biosynthesis via activation of the PKA-CREB-TH system and protects against 6-OHDA-induced cytotoxicity by inhibiting the sustained activation of the ERK-p38MAPK-JNK1/2-caspase-3 system in PC12 cells.

Imaging studies on dopamine transporter and depression: a review of literature and suggestions for future research

We review the conflicting results from imaging studies of dopamine transporter availability in depressed patients and also discuss the heterogeneity of the variables involved. Major depression includes diverse clinical manifestations and in recent years there has been an increasing interest in the identification of homogeneous phenotypes and different clinical subtypes of depression, e.g. anhedonic depression, retarded depression, etc. In addition, the use of different radioligands and imaging techniques, diverse rating scales, together with the lack of control of clinical variables (clinical course, recent or past use of substances of abuse, etc.) make it difficult to clearly identify neuronal regions or networks with consistently abnormal structures or functions in major depressive disorder. It is probably necessary to build a shared approach between clinicians and researchers in order to identify standardized procedures to better understand the role of the dopamine transporter in depression. We outline a list of major issues and also suggest some standardized procedures in collecting clinical and imaging data on major depressed patients. Our aim is to delineate a possible "modus operandi" that would be a proposal for neuroreceptor studies on major depression.

Prolonged membrane depolarization enhances midbrain dopamine neuron differentiation via epigenetic histone modifications

Understanding midbrain dopamine (DA) neuron differentiation is of importance, because of physiological and clinical implications of this neuronal subtype. We show that prolonged membrane depolarization induced by KCl treatment promotes DA neuron differentiation from neural precursor cells (NPCs) derived from embryonic ventral midbrain (VM). Interestingly, the depolarization-induced increase of DA neuron yields was not abolished by L-type calcium channel blockers, along with no depolarization-mediated change of intracellular calcium level in the VM-derived NPCs (VM-NPCs), suggesting that the depolarization effect is due to a calcium-independent mechanism. Experiments with labeled DA neuron progenitors indicate that membrane depolarization acts at the differentiation fate determination stage and promotes the expression of DA phenotype genes (tyrosine hydroxylase [TH] and DA transporter [DAT]). Recruitment of Nurr1, a transcription factor crucial for midbrain DA neuron development, to the promoter of TH gene was enhanced by depolarization, along with increases of histone 3 acetylation (H3Ac) and trimethylation of histone3 on lysine 4 (H3K4m3), and decreases of H3K9m3 and H3K27m3 in the consensus Nurr1 binding regions of TH promoter. Depolarization stimuli on differentiating VM-NPCs also induced dissociation of methyl CpG binding protein 2 and related repressor complex molecules (repressor element-1 silencing transcription factor corepressor and histone deacetylase 1) from the CpG sites of TH and DAT promoters. Based on these findings, we suggest that membrane depolarization promotes DA neuron differentiation by opening chromatin structures surrounding DA phenotype genes and inhibiting the binding of corepressors, thus allowing transcriptional activators such as Nurr1 to access DA neuron differentiation gene promoter regions.

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.

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.

Decrease of prestin expression by increased potassium concentration in organotypic cultures of the organ of Corti of newborn rats

Prestin is the motor protein of the outer hair cells of the organ of Corti and a key factor in ensuring a high sensitivity level of mammalian hearing. In the present study, we examined the effects of increased extracellular potassium (K(+)) concentration on the expression of prestin mRNA and the transcription factors Gata-3 and Carf in the organotypic culture of the organ of Corti of newborn rats. Mannitol and NaCl were used to analyze possible effects of hyperosmotic stress or ion-specific changes, respectively. An increase in prestin expression by a factor of 1.5-2.0 was seen in cultures grown in the presence of 5mM K(+). Potassium concentration of 35 and 55 mM induced a parallel decrease in prestin and Carf expression, but Gata-3 expression increased. Mannitol had no effect on gene expression whereas increased NaCl concentrations decreased prestin, but not Carf expression. The data suggest that chronic depolarization might decrease the prestin expression and possibly contribute to hearing loss and tinnitus.

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.

Effects of scoparone on dopamine biosynthesis and L-DOPA-induced cytotoxicity in PC12 cells

The effects of scoparone on dopamine biosynthesis and L-DOPA-induced cytotoxicity in PC12 cells were investigated. PC12 cells treated with scoparone at concentrations of 100-200 microM showed a 128-136% increase in dopamine levels over the course of 24 hr. Scoparone significantly increased the secretion of dopamine into the culture medium. Under the same conditions, the activities of tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC) were enhanced by treatment with 200 microM scoparone for 6-48 hr, but the activity of TH was regulated for a longer period than that of AADC. The intracellular levels of cyclic AMP and Ca(2+) were increased by treatment with 200 microM scoparone. The levels of TH mRNA and the phosphorylation of cyclic AMP-response element-binding protein (CREB) were also significantly increased by treatment with 200 microM scoparone. In addition, scoparone at a concentration of 200 microM stimulated the activities of cyclic AMP-dependent protein kinase (PKA), protein kinase C (PKC), and Ca(2+)/calmodulin kinase II (CaMK II). Finally, pretreatment with 200 microM scoparone reduced the cytotoxicity induced by L-DOPA (20-100 microM) at 24 hr. These results suggest that scoparone enhances dopamine biosynthesis by regulating TH activity and TH gene expression, which is mediated by the PKA, CREB, PKC, and CaMK II pathways, and protects cells from L-DOPA-induced cytotoxicity by inducing cyclic AMP-PKA systems in PC12 cells.

Pogo: a novel spontaneous ataxic mutant mouse

The Pogo (pogo/pogo) mouse is a naturally occurring neurological mutant from a Korean wild-type mouse characterized by loss of balance and motor coordination due to dysfunction of the cerebellum. The Pogo mutation is believed to be an allele of P/Q-type calcium channel mutants such as tottering, leaner, and rolling mouse Nagoya. These mutants have been served as mouse models for a group of neurodegenerative diseases. The overall aim of this minireview is to summarize our current understanding of the ataxic Pogo mouse. To address this issue, we first describe the discovery of Pogo mouse and its morphological and behavioral defects. Then, we focus on the abnormal expression of several molecules in the Pogo cerebellum, including tyrosine hydroxylase, glutamate, corticotrophin-releasing factor, and 5-hydroxytryptamine. Much of this review is concerned with the functional implications of these ectopic molecules in the Pogo cerebellum.

Activity-dependent regulation of tyrosine hydroxylase expression in the enteric nervous system

The regulation of neuromediator expression by neuronal activity in the enteric nervous system (ENS) is currently unknown. Using primary cultures of ENS derived from rat embryonic intestine, we have characterized the regulation of tyrosine hydroxylase (TH), a key enzyme involved in the synthesis of dopamine. Depolarization induced either by 40 mm KCl, veratridine or by electrical field stimulation produced a robust and significant increase in the proportion of TH immunoreactive (TH-IR) neurons (total neuronal population was identified with PGP9.5 or Hu) compared to control. This increase in the proportion of TH-IR neurons was significantly reduced by the sodium channel blocker tetrodotoxin (0.5 microm), demonstrating that neuronal activity was critically involved in the effects of these depolarizing stimuli. KCl also increased the proportion of VIP-IR but not nNOS-IR enteric neurons. The KCl-induced increase in TH expression was partly reduced in the presence of the nicotinic receptor antagonist hexamethonium (100 microm), of noradrenaline (1 microm) and of the alpha(2)-adrenoreceptor agonist clonidine (1 microm). Combining pharmacological and calcium imaging studies, we have further shown that L-type calcium channels were involved in the increase of TH expression induced by KCl. Finally, using specific inhibitors, we have shown that both protein kinases A and C as well as the extracellular signal-regulated kinases were required for the increase in the proportion of TH-IR neurons induced by KCl. These results are the first demonstration that TH phenotype of enteric neurons can be regulated by neuronal activity. They could also set the basis for the study of the pathways and mechanisms involved in the neurochemical plasticity observed both during ENS development and in inflammatory enteric neuropathies.

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.

Regulation of Expression of Dopamine β-Hydroxylase in PC12 Cells by Glucocorticoids and Cyclic AMP Analogues

Regulation of catecholamine biosynthesis is crucial in the adaptation to various physiological conditions, such as stress, and in several disorders, including hypertension and depression. In this study we have found that in PC12 cells, the mRNA levels of dopamine beta-hydroxylase (DBH), the enzyme that catalyzes the formation of norepinephrine from dopamine, can be regulated by glucocorticoids and cyclic AMP (cAMP) analogues. Treatment with dexamethasone increased DBH mRNA levels by 6 h. with maximal elevation (four- to fivefold) obtained after 1 day of exposure, and these levels were maintained for up to 4 days. DBH mRNA levels were also elevated on treatment of PC12 cells with 8-bromo cAMP for 8 h to 1 day. The response to 8-bromo cAMP, however, was bimodal, because DBH mRNA levels declined below control values on treatment for > 1 day. In combined treatments with 8-bromo cAMP and dexamethasone, the cAMP effect was dominant. To begin to characterize the regulation of DBH mRNA, genomic clones for rat DBH were isolated, and 1 kb of the 5' flanking region was sequenced. Several putative regulatory elements, which may be involved in cAMP and glucocorticoid regulation, were identified, including two adjacent cAMP response elements, another element that can also bind members of the ATF/CREB family of transcription factors, a NF-kappa B-like sequence, several AP-2 sites, and three core glucocorticoid receptor binding sequences.

Dense-core secretory granule biogenesis

The dense-core secretory granule is a key organelle for secretion of hormones and neuropeptides in endocrine cells and neurons, in response to stimulation. Cholesterol and granins are critical for the assembly of these organelles at the trans-Golgi network, and their biogenesis is regulated quantitatively by posttranscriptional and posttranslational mechanisms.

A tyrosine hydroxylase-yellow fluorescent protein knock-in reporter system labeling dopaminergic neurons reveals potential regulatory role for the first intron of the rodent tyrosine hydroxylase gene

Degeneration of the dopaminergic neurons of the substantia nigra is a hallmark of Parkinson's disease. To facilitate the study of the differentiation and maintenance of this population of dopaminergic neurons both in vivo and in vitro, we generated a knock-in reporter line in which the yellow fluorescent protein (YFP) replaced the first exon and the first intron of the tyrosine hydroxylase (TH) gene in one allele by homologous recombination. Expression of YFP under the direct control of the entire endogenous 5' upstream region of the TH gene was predicted to closely match expression of TH from the wild type allele, thus marking functional dopaminergic neurons. We found that YFP was expressed in dopaminergic neurons differentiated in vitro from the knock-in mouse embryonic stem cell line and in dopaminergic brain regions in knock-in mice. Surprisingly, however, YFP expression did not overlap completely with TH expression, and the degree of overlap varied in different TH-expressing brain regions. Thus, the reporter gene did not identify functional TH-expressing cells with complete accuracy. A DNaseI hypersensitivity assay revealed a cluster of hypersensitivity sites in the first intron of the TH gene, which was deleted by insertion of the reporter gene, suggesting that this region may contain cis-acting regulatory sequences. Our results suggest that the first intron of the rodent TH gene may be important for accurate expression of TH.

Stress triggered changes in gene expression in adrenal medulla: transcriptional responses to acute and chronic stress

1. Stress elicits activation of several transcription factors involved in the regulation of catecholamine biosynthetic enzyme gene expression depending on its duration or repetition. However, the dynamic of the conversion of transient transcriptional activation with acute stress to sustained changes in transcription in response to repeated exposure to stress in adrenomedullary catecholaminergic systems is not clear. 2. Here, we analyzed changes in levels of phospho-CREB (P-CREB), phospho-ERK1/2 (P-ERK1/2) and Fra-2 by Western Blot analysis in adrenal medulla of Sprague Dawley male rats exposed to single or repeated immobilization stress (IMO). For single stress, rats were immobilized for 5 min, 30 min, or 2 h and sacrificed immediately afterwards. In the repeated stress conditions, animals were immobilized for 2 h daily on each consecutive day prior to the final day (day 2 for 2x IMO, day 6 for 6x IMO) in which the rats were immobilized for a session lasting 5 min, 30 min or 2 h. There were two control groups, an absolute control (AC) not exposed to stress, and a handled control (HC) gently handled daily for 6 days. 3. Phosphorylation of CREB was rapid and elevated at the earliest time examined, even with single stress. However, with a second daily episode of stress the increase in P-CREB was observed for at least the entire duration of the stress. In contrast, phosphorylation of ERK1/2 was only significant after brief exposure to a single IMO. The elevation of Fra-2 protein level was slower, but was significant after 2 h of a single IMO. With repeated IMO, there were marked elevations of Fra-2 throughout the 2 h IMO, which were especially pronounced at the end of the immobilization. 4. The transient nature of the phosphorylation of CREB may be responsible for the short-lived induction of transcription of catecholamine biosynthetic enzymes after brief exposure to a single immobilization stress. The sustained phosphorylation of CREB throughout the repeated stress coupled with induction of Fra-2 may mediate the longer lasting responses to repeated stress.

Corticotropin-Releasing Factor Immunoreactivity Increases in the Cerebellar Climbing Fibers in the Novel Ataxic Mutant Mouse, Pogo

The ataxic pogo mouse (pogo/pogo) is a novel neurological mutant, which was derived as an inbred strain (KJR/MsKist) from a Korean wild mouse. The pathological manifestations include a difficulty in maintaining a normal posture, the failure of inter-limb coordination and an inability to walk straight. In this study, we examined the distribution of corticotropin-releasing factor (CRF) immunoreactive cerebellar climbing fibres and their projections to tyrosine hydroxylase (TH) immunoreactive Purkinje cells in the cerebellum of the pogo mutant mouse using immunohistochemistry. In the pogo/pogo mouse, a subset of climbing fibres was stained more intensely for CRF than in the control. Moreover, ataxic pogo mouse, neurons of the inferior olivary nucleus projecting climbing fibres were also more intensely stained for CRF than in the control. In the pogo/pogo mouse, TH immunoreactivity was located in the Purkinje cells, whereas no TH expression was found in the control. Double immunostaining for CRF and TH in the pogo/pogo cerebellum revealed that the distribution of TH-immunoreactive Purkinje cells corresponded to terminal fields of CRF-immunoreactive climbing fibres but not to the CRF-immunoreactive mossy fibres. Therefore, we suggest that an increase of CRF level may alter the function of targeted Purkinje cells and that it is related to the ataxic phenotype in the pogo mutant mouse.

Genomic profiling of the neuronal target genes of the plasticity-related transcription factor -- Zif268

The later phases of neuronal plasticity are invariably dependent on gene transcription. Induction of the transcription factor Zif268 (Egr-1) in neurones is closely associated with many forms of functional plasticity, yet the neuronal target genes modulated by Zif268 have not been characterized. After transfection of a neuronal cell line with Zif268 we identified genes that show altered expression using high density microarrays. Although some of the genes identified have previously been associated with forms of neuronal plasticity, the majority have not been linked with neuronal plasticity or Zif268 action. Altered expression of a representative sample of the novel target genes was confirmed in Zif268-transfected PC12 neurones, and in in vitro and in vivo models of Zif268-associated neuronal plasticity. In particular, altered expression of the protease inhibitor Cystatin C and the chemokine Cxcl10 was observed in striatal tissue after haloperidol administration. Surprisingly, the group of identified genes is enriched for components of the proteasome and the major histocompatibility complex. Our findings suggest that altered expression of these genes following Zif268 induction may be a key component of long lasting plasticity in the CNS.

Protease nexin-1 promotes secretory granule biogenesis by preventing granule protein degradation

Dense-core secretory granule (DCG) biogenesis is a prerequisite step for the sorting, processing, and secretion of neuropeptides and hormones in (neuro)endocrine cells. Previously, chromogranin A (CgA) has been shown to play a key role in the regulation of DCG biogenesis in vitro and in vivo. However, the underlying mechanism of CgA-mediated DCG biogenesis has not been explored. In this study, we have uncovered a novel mechanism for the regulation of CgA-mediated DCG biogenesis. Transfection of CgA into endocrine 6T3 cells lacking CgA and DCGs not only recovered DCG formation and regulated secretion but also prevented granule protein degradation. Genetic profiling of CgA-expressing 6T3 versus CgA- and DCG-deficient 6T3 cells, followed by real-time reverse transcription-polymerase chain reaction and Western blotting analyses, revealed that a serine protease inhibitor, protease nexin-1 (PN-1), was significantly up-regulated in CgA-expressing 6T3 cells. Overexpression of PN-1 in CgA-deficient 6T3 cells prevented degradation of DCG proteins at the Golgi apparatus, enhanced DCG biogenesis, and recovered regulated secretion. Moreover, depletion of PN-1 by antisense RNAs in CgA-expressing 6T3 cells resulted in the specific degradation of DCG proteins. We conclude that CgA increases DCG biogenesis in endocrine cells by up-regulating PN-1 expression to stabilize granule proteins against degradation.

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.

Induction of tyrosine hydroxylase in the locus coeruleus of transgenic mice in response to stress or nicotine treatment: lack of activation of tyrosine hydroxylase promoter activity

Prolonged stress or chronic nicotine administration leads to induction of tyrosine hydroxylase (TH) in adrenal medulla and locus coeruleus (LC) of the rat. In this study we use mice that express a transgene encoding 4.5 kb of TH gene 5'-flanking region fused upstream of the reporter gene, human alkaline phosphatase (hAP) to test whether TH gene promoter activity is stimulated by immobilization stress, cold exposure or nicotine administration in adrenal medulla and LC. TH-hAP transgene expression is increased in response to all three stimuli in the adrenal medulla. In contrast, TH-hAP expression does not increase in response to either immobilization stress or nicotine administration in the LC and only a small induction of LC TH-hAP mRNA is observed in response to cold exposure. TH mRNA is induced 2-3 fold and TH activity is increased significantly by all three stimuli in both the adrenal and LC. These results support the hypothesis that TH expression is induced by stress or nicotine treatment in both the adrenal medulla and LC of the mouse. The induction in the adrenal is dependent primarily on transcriptional mechanisms, whereas that in the LC is apparently dependent primarily on post-transcriptional mechanisms.

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.

Individual differences in the expression of tyrosine hydroxylase mRNA in neurosecretory neurons of the human paraventricular and supraoptic nuclei: positive correlation with vasopressin mRNA

Previous studies indicated that in the human paraventricular nucleus (PVN) and in the supraoptic nucleus (SON) tyrosine hydroxylase (TH) - the first and rate-limiting enzyme in catecholamine synthesis - is localized mainly in magnocellular neurosecretory neurons. Individual differences were observed among control subjects in number and distribution of TH-immunoreactive (IR) perikarya, indicating that antemortem factors may regulate TH expression. Since a large number of TH-IR perikarya were observed in subjects who suffered from somatic illnesses leading to prolonged osmotic or nonosmotic stimulation of vasopressin (VP) release, we suggested that TH expression is related to the activation of VP neurons. The purpose of our study was to apply (1) in situ hybridization for TH mRNA on human PVN and SON to investigate how the previously reported individual differences in TH protein expression are depicted at the transcriptional level and (2) quantitative TH immunohistochemistry and in situ hybridization for VP mRNA throughout the dorsolateral part of the SON (dl-SON) in order to elucidate whether indeed expression of TH in neurosecretory nuclei depends on activation of VP neurons. Postmortem formalin-fixed, paraffin-embedded hypothalamic sections of 16 control subjects were studied for TH protein and TH and VP mRNAs. For 6 of the above cases, the number of TH-IR neurons and the total VP mRNA levels were estimated throughout the entire dl-SON using an image analysis system. Individual variation was observed in TH mRNA expression which appears to parallel the expression of TH-protein. Using Spearman's bivariate test, a positive correlation was found between the number of TH-IR- and TH-mRNA-expressing neurons in both PVN and SON (p < 0.01) as well as between the number of TH-IR neurons and the total VP mRNA in the dl-SON (p < 0.05). Our results show (1) that the individual variability in the number of TH-IR neurons within the neurosecretory nuclei might be due to differential expression and/or stability of TH mRNA and (2) that expression of TH-immunoreactivity in human PVN and SON depends on the activation of VP neurons.

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.

Functional genomics approach to hypoxia signaling

Mammalian cells require a constant supply of oxygen to maintain energy balance, and sustained hypoxia can result in cell death. It is therefore not surprising that sophisticated adaptive mechanisms have evolved that enhance cell survival during hypoxia. During the past few years, there have been a growing number of reports on hypoxia-induced transcription of specific genes. In this review, we describe a unique experimental approach that utilizes focused cDNA libraries coupled to microarray analyses to identify hypoxia-responsive signal transduction pathways and genes that confer the hypoxia-tolerant phenotype. We have used the subtractive suppression hybridization (SSH) method to create a cDNA library enriched in hypoxia-regulated genes in oxygen-sensing pheochromocytoma cells and have used this library to create microarrays that allow us to examine hundreds of genes at a time. This library contains over 300 genes and expressed sequence tags upregulated by hypoxia, including tyrosine hydroxylase, vascular endothelial growth factor, and junB. Hypoxic regulation of these and other genes in the library has been confirmed by microarray, Northern blot, and real-time PCR analyses. Coupling focused SSH libraries with microarray analyses allows one to specifically study genes relevant to a phenotype of interest while reducing much of the biological noise associated with these types of studies. When used in conjunction with high-throughput, dye-based assays for cell survival and apoptosis, this approach offers a rapid method for discovering validated therapeutic targets for the treatment of cardiovascular disease, stroke, and tumors.

Catecholamine-independent transient expression of tyrosine hydroxylase in primary auditory neurons is coincident with the onset of hearing in the rat cochlea

During the last stages of neuronal maturation, tyrosine hydroxylase is transiently expressed in the absence of the other catecholamine-synthesizing enzymes. We show here that it is expressed in rat spiral ganglion neurons between postnatal days 8 and 20, with a peak of expression at postnatal day 12. These tyrosine hydroxylase-immunoreactive neurons did not display aromatic amino acid decarboxylase- or dopamine-beta-hydroxylase-immunoreactivities, ruling out the possibilities of dopamine or noradrenaline synthesis. They also did not display peripherin- or intense neurofilament 200-kDa-immunoreactivities, two indicators of type II primary auditory neurons. Tyrosine hydroxylase-immunoreactive dendrites were seen in synaptic contact with the inner hair cells and expressed the GluR2 subunit of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors, further confirming the type I nature of the neurons transiently expressing the enzyme. The end of the tyrosine hydroxylase expression was not due to cell death because the immunoreactive neurons did not show TUNEL-labelled nuclei. Finally, all the type I neurons expressed the tyrosine hydroxylase mRNA at postnatal day 12, suggesting that the expression of the enzyme is a maturational step common to all these neurons and that the expression of the protein is not synchronized. Because the period of transient expression of tyrosine hydroxylase in type I neurons parallels the periods of maturation of evoked exocytosis in inner hair cells and of appearance and maturation of the cochlear potentials, we propose that the expression of the enzyme indicates the onset of hearing in individual type I primary auditory neurons. This enzyme expression could rely on a Ca2+ activation of its encoding gene subsequent to a sudden and massive Ca2+ entry through voltage-activated Ca2+ channels.

Integrative nuclear FGFR1 signaling (INFS) as a part of a universal ?feed-forward-and-gate? signaling module that controls cell growth and differentiation

A novel signaling mechanism is described through which extracellular signals and intracellular signaling pathways regulate proliferation, growth, differentiation, and other functions of cells in the nervous system. Upon cell stimulation, fibroblast growth factor receptor-1 (FGFR1), a typically plasma membrane-associated protein, is released from ER membranes into the cytosol and translocates to the cell nucleus by an importin-beta-mediated transport pathway along with its ligand, FGF-2. The nuclear accumulation of FGFR1 is activated by changes in cell contacts and by stimulation of cells with growth factors, neurotransmitters and hormones as well as by a variety of different second messengers and thus was named integrative nuclear FGFR1 signaling (INFS). In the nucleus, FGFR1 localizes specifically within nuclear matrix-attached speckle-domains, which are known to be sites for RNA Pol II-mediated transcription and co-transcriptional pre-mRNA processing. In these domains, nuclear FGFR1 colocalizes with RNA transcription sites, splicing factors, modified histones, phosphorylated RNA Pol II, and signaling kinases. Within the nucleus, FGFR1 serves as a general transcriptional regulator, as indicated by its association with the majority of active nuclear centers of RNA synthesis and processing, by the ability of nuclear FGFR1 to activate structurally distinct genes located on different chromosomes and by its stimulation of multi-gene programs for cell growth and differentiation. We propose that FGFR1 is part of a universal "feed-forward-and-gate" signaling module in which classical signaling cascades initiated by specific membrane receptors transmit signals to sequence specific transcription factors (ssTFs), while INFS elicited by the same stimuli feeds the signal forward to the common coactivator, CREB-binding protein (CBP). Activation of CBP by INFS, along with the activation of ssTFs by classical signaling cascades brings about coordinated responses from structurally different genes located at different genomic loci.

c-Fos is essential for the response of the tyrosine hydroxylase gene to depolarization or phorbol ester

Tyrosine hydroxylase (TH) gene transcription rate increases in response to numerous pharmacological and physiological stimuli. The AP1 site within the TH gene proximal promoter is thought to play an important role in mediating many of these responses; however, it is unclear which AP1 factors are required. To investigate whether c-Fos is essential for the response of the TH gene to different stimuli, c-Fos-deficient PC12 cell lines were produced utilizing an antisense RNA strategy. In these cell lines, stimulus-induced increases in c-Fos protein levels were dramatically attenuated, while c-Jun and CREB levels remained unchanged. TH gene transcription rate increased from four- to eight-fold in control cells after treatment with either 50 mM KCl or TPA. These responses were dramatically decreased in the c-Fos-deficient cell lines. In contrast, c-Fos down-regulation had little effect on the response of the TH gene to forskolin. Stimulation of TH gene promoter activity, which was observed in control cell lines treated with either 50 mm KCl or TPA was also dramatically inhibited in the c-Fos-deficient cells. These results suggest that c-Fos induction is essential for maximal stimulation of the TH gene in response to either depolarization or PKC activation in PC12 cells.

Angiotensin II AT(1) and AT(2) receptors contribute to maintain basal adrenomedullary norepinephrine synthesis and tyrosine hydroxylase transcription

Angiotensin II (Ang II) AT(1) receptors have been proposed to mediate the Ang II-dependent and the stress-stimulated adrenomedullary catecholamine synthesis and release. However, in this tissue, most of the Ang II receptors are of the AT(2) type. We asked the question whether AT(1) and AT(2) receptors regulate basal catecholamine synthesis. Long-term AT(1) receptor blockade decreased adrenomedullary AT(1) receptor binding, AT(2) receptor binding and AT(2) receptor protein, rat tyrosine hydroxylase (TH) mRNA, norepinephrine (NE) content, Fos-related antigen 2 (Fra-2) protein, phosphorylated cAMP response element binding protein (pCREB), and ERK2. Long-term AT(2) receptor blockade decreased AT(2) receptor binding, TH mRNA, NE content and Fra-2 protein, although not affecting AT(1) receptor binding or receptor protein, pCREB or ERK2. Angiotensin II colocalized with AT(1) and AT(2) receptors in ganglion cell bodies. AT(2) receptors were clearly localized to many, but not all, chromaffin cells. Our data support the hypothesis of an AT(1)/AT(2) receptor cross-talk in the adrenomedullary ganglion cells, and a role for both receptor types on the selective regulation of basal NE, but not epinephrine formation, and in the regulation of basal TH transcription. Whereas AT(1) and AT(2) receptors involve the Fos-related antigen Fra-2, AT(1) receptor transcriptional effects include pCREB and ERK2, indicating common as well as different regulatory mechanisms for each receptor type.

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

Several treatments which regulate tyrosine hydroxylase (TH) transcription, such as stress in vivo, or 12-O-tetradecanoylphorbol-13-acetate (TPA) in cell culture, induce both Egr1 and AP1 factors. Previously, we identified a functional Egr1 motif overlapping with Sp1 site in the rat TH promoter. Its response to Egr1 also required the presence of an AP1/Ebox motif. Here, we further examined the cross-talk between these sites. Insertion of 10- or 20-bp between the Sp1/Egr1 and AP1/Ebox elements, reduced the ability of Egr1 to upregulate luciferase reporter activity controlled by the proximal 272 nucleotides of the rat TH promoter in PC12 cells. Electrophoretic mobility shift assays with nuclear extracts from TPA treated cells were used to identify the composition of the factors which bound the AP1/Ebox motif and whether there is competition with factors which bind the Sp1/Egr1 motif. The complexes formed with labeled AP1/E box oligonucleotide were reduced or supershifted with antisera to Fos family, c-Fos, Fra-2, and Jun D. Excess Sp1/Egr1 oligonucleotide or anti Egr1 antisera did not compete. Fra-2 was a major component of the complex after 2-4 h TPA. Transfection of PC12 cells with Fra-2 induced reporter activity requiring the AP1, but not the Egr1 motif. However, when cotransfected with Fra-2, Egr1 expression plasmids elicited lower induction of luciferase activity than observed with Egr1 alone. Our results suggest that although it does not compete for binding to the promoter, Egr1 can modulate the regulation of TH transcription by AP1 factors.

Regulation of tyrosine hydroxylase expression in tottering mouse Purkinje cells

Tottering (tg) mice inherit a missense mutation in the Alpha1A subunit of P/Q-type calcium channels. This mutation results in an increased density of L-type calcium channels in the cerebellum and abnormal regulation of tyrosine hydroxylase (TH) gene expression in a subset of cerebellar Purkinje cells, a cell type that does not normally express TH. The behavioral phenotype includes attacks of dyskinesia, which can be blocked by L-type calcium channel antagonists. To test the hypothesis that cerebellar TH mRNA expression can be manipulated in vivo by L-type calcium channel blockade, control and tottering mice were chronically treated with the L-type calcium channel antagonist nimodipine. Chronic nimodipine treatment significantly reduced the expression of TH mRNA in tottering mouse Purkinje cells. This effect was observed without altering the increased density of L-type calcium channels in tottering mouse cerebella. Chronic nimodipine treatment had no effect on TH mRNA expression in tottering mouse catecholaminergic neurons, including those of the locus coeruleus and substantia nigra. However, a small reduction in TH mRNA expression in the substantia nigra of control mice was observed after drug treatment. These data suggest that the abnormal expression of TH in tottering mouse Purkinje cells is regulated by Purkinje cell excitability.

Regulation of gene expression for neurotransmitters during adaptation to hypoxia in oxygen-sensitive neuroendocrine cells

Reduced oxygen tension (hypoxia) in the environment stimulates oxygen-sensitive cells in the carotid body (CB). Upon exposure to hypoxia, the CB immediately triggers a reflexive physiological response, thereby increasing respiration. Adaptation to hypoxia involves changes in the expression of various CB genes, whose products are involved in the transduction and modulation of the hypoxic signal to the central nervous system (CNS). Genes encoding neurotransmitter-synthesizing enzymes and receptors are particularly important in this regard. The cellular response to hypoxia correlates closely with the release and biosynthesis of catecholamines. The gene expression of tyrosine hydroxylase (TH), the rate-limiting enzyme for catecholamine biosynthesis, is regulated by hypoxia in the CB and in the oxygen-sensitive cultured PC12 cell line. Recently, genomic microarray studies have identified additional genes regulated by hypoxia. Patterns of gene expression vary, depending on the type of applied hypoxia, e.g., intermittent vs. chronic. Construction of a hypoxia-regulated, CB-specific, subtractive cDNA library will enable us to further characterize regulation of gene expression in the CB.

Integrative nuclear FGFR1 signaling (INFS) pathway mediates activation of the tyrosine hydroxylase gene by angiotensin II, depolarization and protein kinase C

The integrative nuclear FGFR1 signaling (INFS) pathway functions in association with cellular growth, differentiation, and regulation of gene expression, and is activated by diverse extracellular signals. Here we show that stimulation of angiotensin II (AII) receptors, depolarization, or activation protein kinase C (PKC) or adenylate cyclase all lead to nuclear accumulation of fibroblast growth factor 2 (FGF-2) and FGFR1, association of FGFR1 with splicing factor-rich domains, and activation of the tyrosine hydroxylase (TH) gene promoter in bovine adrenal medullary cells (BAMC). The up-regulation of endogenous TH protein or a transfected TH promoter-luciferase construct by AII, veratridine, or PMA (but not by forskolin) is abolished by transfection with a dominant negative FGFR1TK-mutant which localizes to the nucleus and plasma membrane, but not by extracellularly acting FGFR1 antagonists suramin and inositolhexakisphosphate (IP6). Mechanism of TH gene activation by FGF-2 and FGFR1 was further investigated in BAMC and human TE671 cultures. TH promoter was activated by co-transfected HMW FGF-2 (which is exclusively nuclear) but not by cytoplasmic FGF-1 or extracellular FGFs. Promoter transactivation by HMWFGF-2 was accompanied by an up-regulation of FGFR1 specifically in the cell nucleus and was prevented FGFR1(TK-) but not by IP6 or suramin. The TH promoter was also transactivated by co-transfected wild-type FGFR1, which localizes to both to the nucleus and the plasma membrane, and by an exclusively nuclear, soluble FGFR1(SP-/NLS) mutant with an inserted nuclear localization signal. Activation of the TH promoter by nuclear FGFR1 and FGF-2 was mediated through the cAMP-responsive element (CRE) and was associated with induction of CREB- and CBP/P-300-containing CRE complexes. We propose a new model for gene regulation in which nuclear FGFR1 acts as a mediator of CRE transactivation by AII, cell depolarization, and PKC.

Interaction of a glucocorticoid-responsive element with regulatory sequences in the promoter region of the mouse tyrosine hydroxylase gene

The purpose of the work reported here was to determine whether the tyrosine hydroxylase glucocorticoid-responsive element (TH-GRE) interacts with the cyclic AMP pathway and the CRE in regulating mouse TH promoter activity, and whether an additional, previously identified downstream GRE-like element also participates in the function of the TH-GRE and CRE. To determine the role of the cAMP pathway on TH-GRE function, we compared the effects of forskolin and dexamethasone on TH mRNA, TH gene transcription and TH promoter activity in a mutant PC12 cell line (A126-1B2) deficient in cAMP-dependent protein kinase A (PKA) with their effects in the wild-type parental strain. Forskolin treatment increased TH mRNA content, transcriptional activity and the activity of a chimeric gene with 3.6 kb of the TH promoter in wild-type cells, but not in PKA-deficient cells. In contrast, dexamethasone treatment stimulated equivalent increases in TH mRNA, TH gene transcription and TH promoter activity in each cell type. Mutation of the CRE in chimeric constructs containing 3.6 kb of the 5' flanking sequence of the mouse TH gene or coexpression of a dominant-negative mutant of CREB prevented the stimulation of TH promoter activity by forskolin. However, neither the mutation of the CRE nor inhibition of CREB influenced basal or dexamethasone-stimulated promoter activity. Site-directed mutagenesis of the TH-GRE eliminated the response of the promoter to dexamethasone. However, the mutagenesis of a more proximal 15-bp region with a GRE-like sequence had no demonstrable effect on the ability of dexamethasone to stimulate TH promoter activity. Neither mutagenesis of the TH-GRE or the downstream GRE-like sequence had an effect on the ability of forskolin to activate this chimeric gene. Taken together, these results provide evidence that a single GRE is sufficient for maximal induction of transcriptional activity by glucocorticoids and that the CRE is not required for either partial or full activity of this upstream GRE sequence.

Ectopic expression of tyrosine hydroxylase in Zebrin II immunoreactive Purkinje cells in the cerebellum of the ataxic mutant mouse, pogo

The pogo mouse is a new ataxic autosomal recessive mutant that arose in an inbred strain (KJR/MsKist) derived from a Korean wild mouse. The phenotype includes difficulty in maintaining normal posture and the inability to walk straight. Several previous studies have associated inherited ataxia with the ectopic expression of tyrosine hydroxylase (TH) in Purkinje cells. Therefore, in the present study, the distribution of TH expression was compared with that of zebrin II in Purkinje cells of adult pogo/pogo mutant mice. In normal control littermates, tyrosine hydroxylase immunoreactivity is confined to a delicate axonal plexus ramifying through the molecular layer. In pogo/pogo, in addition to the axonal plexus, TH-immunoreactive Purkinje cells were present in all lobules of the cerebellar vermis and hemispheres, distributed as series parasagittal bands. The general pattern of expression is reproducible between individuals and symmetrical about the midline. Alternating stripes of TH expression are also seen in the hemispheres, and most Purkinje cells in the paraflocculi and flocculi are immunoreactive. In pogo/+ mice, TH-immunoreactive Purkinje cells are rare. The pattern of zebrin II expression was used to map TH immunoreactive Purkinje cells in pogo/pogo mutant mice. Double immunofluorescence labeling combining anti-zebrin II fand anti-TH showed that all TH-immunoreactive Purkinje cells are zebrin II+, but that many zebrin II+ Purkinje cells within a band do not stain with anti-TH. Taken together with the morphological changes observed in the Purkinje cell axons, this suggests that abnormal Purkinje cell function may contribute to the ataxic phenotype in pogo/pogo mice.

Topological relationship between corticotropin-releasing factor-immunoreactive cerebellar afferents and tyrosine hydroxylase-immunoreactive Purkinje cells in a hereditary ataxic mutant, rolling mouse Nagoya

Using immunohistochemistry we examined the distribution of corticotropin-releasing factor-positive cerebellar afferents and the topological relationship between their projections and the distribution of tyrosine hydroxylase-positive Purkinje cells in an ataxic mutant, rolling mouse Nagoya. In the mutants, some climbing fibers were more intensely stained for corticotropin-releasing factor, but their zonal distribution remained the same as in non-ataxic littermates (control mice). These climbing fibers arose from the dorsal accessory nucleus, the ventral lamella of principal nucleus, the dorsomedial cell group, the subnucleus A, the beta subnucleus and the ventrolateral protrusion of the inferior olive, since perikarya in these olivary subdivisions were more intensely stained for corticotropin-releasing factor than in controls. Some mossy fiber rosettes in the vermal lobules, the simple lobule, the crus I of ansiform lobule, the copula pyramidis and the flocculus also exhibited corticotropin-releasing factor immunoreactivity and were more densely stained in the mutants than in controls. Double immunostaining for corticotropin-releasing factor and tyrosine hydroxylase in the mutant cerebellum revealed that the distribution of tyrosine hydroxylase-positive Purkinje cells corresponded to terminal fields of corticotropin-releasing factor-positive climbing fibers but not corticotropin-releasing factor-positive mossy fibers. This study indicated an increased corticotropin-releasing factor immunoreactivity in some climbing or mossy fibers in the cerebellum of rolling mouse Nagoya. We also found that the distribution of tyrosine hydroxylase-positive Purkinje cells corresponded to terminal fields of corticotropin-releasing factor-positive climbing fibers in the mutant cerebellum. As the transcription of the tyrosine hydroxylase gene is facilitated by Ca2+, abnormal tyrosine hydroxylase expression in the mutant Purkinje cells may indicate functional abnormality by alterations in intracellular Ca2+ concentrations. Therefore, we suggest that an increased level of corticotropin-releasing factor in a specific population of climbing fibers may alter the function of their target Purkinje cells.

NGF enhances depolarization effects on SNAP-25 expression: induction of SNAP-25b isoform

The 25 kDa synaptosomal associated protein (SNAP-25), which is implicated in neuronal plasticity and neurosecretion, exists as two isoforms generated by alternative splicing of exons 5a and 5b. The aim of the present study was to characterize factors influencing isoform expression. We report that chronic depolarization of PC12 cells alone or in the presence of NGF induces the expression of isoform-b, in addition to a 1.8- to 3-fold increase in SNAP-25 mRNA and protein as determined by immunoblotting and combined RT-PCR and Southern blot analysis. When cerebellar granule neurons were cultured in elevated K+, the predominant isoform switched from SNAP-25a to SNAP-25b. Taken together these results suggested that chronic depolarization regulates the transcription and processing of SNAP-25 mRNA.

The cAMP responsive element and CREB partially mediate the response of the tyrosine hydroxylase gene to phorbol ester

Tyrosine hydroxylase (TH) gene promoter activity is increased in PC12 cells that are treated with the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate (TPA). Mutagenesis of either the cAMP responsive element (CRE) or the activator protein-1 element (AP1) within the TH gene proximal promoter leads to a dramatic inhibition of the TPA response. The TH CRE and TH AP1 sites are also independently responsive to TPA in minimal promoter constructs. TPA treatment results in phosphorylation of cAMP responsive element binding protein (CREB) and activation of cAMP-dependent protein kinase (PKA) in PC12 cells; hence, we tested whether CREB and/or PKA are essential for the TPA response. In CREB-deficient cells, the response of the full TH gene proximal promoter or the independent response of the TH CRE by itself to TPA is inhibited. The TPA-inducibility of TH mRNA is also blocked in CREB-deficient cells. Expression of the PKA inhibitor protein, PKI, also inhibits the independent response of the TH CRE to TPA. Our results support the hypothesis that TPA stimulates the TH gene promoter via signaling pathways that activate either the TH AP1 or TH CRE sites. Both signaling pathways are dependent on CREB and the TH CRE-mediated pathway is dependent on PKA.

Identification of a glucocorticoid-responsive element in the promoter region of the mouse tyrosine hydroxylase gene

It has been known for nearly 30 years that glucocorticoid receptor stimulation induces increased tyrosine hydroxylase (TH) gene expression. However, the mechanism mediating this effect has remained elusive. Sequences with homology to known glucocorticoid-responsive elements (GRE) have been identified in the 5' flanking region of the TH gene of several vertebrate species, but none has been shown to be functional. To identify the GRE element(s) in the TH promoter, we generated chimeric constructs in which different lengths of the 5' flanking sequences of the mouse TH gene (3.6, 1.1 and 0.8 kb) were ligated to a luciferase reporter gene. Dexamethasone treatment increased luciferase expression only in cells transiently transfected with the construct containing 3.6 kb of the TH 5' flanking DNA. Co-administration of mifepristone (RU486), a glucocorticoid receptor antagonist, blocked this effect. We identified a TH-GRE sequence (5'-GGCACAGTGTGGTCT) in the mouse 5' flanking DNA between -2435 and -2421 from the transcription start. Responsiveness to dexamethasone was lost following deletion of this sequence. To determine the ability of this element to function in a heterologous promoter, we prepared a chimeric construct in which the TH-GRE sequence was cloned just upstream of a minimal thymidine kinase (TK) promoter. Promoter activity was increased 2-fold in dexamethasone-treated PC12 cells transfected with the TH-GRE-TK construct. These results provide strong evidence that the 15 base-pair sequence in the 5' flanking DNA of the mouse TH gene functions as a glucocorticoid response element. This is the first report identifying a functional glucocorticoid response element in the promoter region of the TH gene of any species.

Stress-triggered activation of gene expression in catecholaminergic systems: dynamics of transcriptional events

Stress triggers important adaptive responses that enable an organism to cope with a changing environment. However, when prolonged or repeated, stress can be extremely harmful. The release of catecholamines is a key initial event in responses to stressors and is followed by an increase in the expression of genes that encode catecholamine-synthesizing enzymes. This process is mediated by transcriptional mechanisms in the adrenal medulla and the locus coeruleus. The persistence of transcriptional activation depends on the duration and repetition of the stress. Recent work has begun to identify the various transcription factors that are associated with brief or intermediate duration of a single or repeated stress. These studies suggest that dynamic interplay is involved in converting the transient increases in the rate of transcription into prolonged (potentially adaptive or maladaptive) changes in gene expression.