Glucocorticoid responsiveness of the rat phenylethanolamine N-methyltransferase gene

Beta2-Adrenergic Suppression of Neuroinflammation in Treatment of Parkinsonism, with Relevance for Neurodegenerative and Neoplastic Disorders

There is a preliminary record suggesting that β2-adrenergic agonists may have therapeutic value in Parkinson's disease; recent studies have proposed a possible role of these agents in suppressing the formation of α-synuclein protein, a component of Lewy bodies. The present study focuses on the importance of the prototypical β2-adrenergic agonist epinephrine in relation to the incidence of Parkinson's disease in humans, and its further investigation via synthetic selective β2-receptor agonists, such as levalbuterol. Levalbuterol exerts significant anti-inflammatory activity, a property that may suppress cytokine-mediated degeneration of dopaminergic neurons and progression of Parkinsonism. In a completely novel finding, epinephrine and certain other adrenergic agents modeled in the Harvard/MIT Broad Institute genomic database, CLUE, demonstrated strong associations with the gene-expression signatures of anti-inflammatory glucocorticoids. This prompted in vivo confirmation in mice engrafted with human peripheral blood mononuclear cells (PBMCs). Upon toxic activation with mononuclear antibodies, levalbuterol inhibited (1) the release of the eosinophil attractant chemokine eotaxin-1, which is implicated in CNS and peripheral inflammatory disorders, (2) elaboration of the tumor-promoting angiogenic factor VEGFa, and (3) release of the pro-inflammatory cytokine IL-13 from activated PBMCs. These observations suggest possible translation to Parkinson's disease, other neurodegenerative syndromes, and malignancies, via several mechanisms.

Impact of Prenatal LPS and Early-life Constant Light Exposure on Circadian Gene Expression Profiles in Various Rat Tissues

Exposure to lipopolysaccharide (LPS) during prenatal development leads to various changes in neurobiological and behavioural patterns. Similarly, continuous exposure to constant light (LL) during the critical developmental period of the circadian system affects gene expression in various tissues in adulthood. Given the reciprocal nature of the interaction between the circadian and the immune systems, our study primarily investigated the individual effects of both interventions and, more importantly, their combined effect. We aimed to explore whether there might be a potential synergistic effect on circadian rhythms and their parameters, focussing on the expression of clock genes, immune-related genes, and specific genes in the hippocampus, pineal gland, spleen and adrenal gland of rats at postnatal day 30. Our results show a significant influence of prenatal LPS and postnatal LL on the expression profiles of all genes assessed. However, the combination of prenatal LPS and postnatal LL only revealed an enhanced negative effect in a minority of the comparisons. In most cases, it appeared to attenuate the changes induced by the individual interventions, restoring the measured parameters to values closer to those of the control group. In particular, genes such as Nr1d1, Aanat and Tph1 showed increased amplitude in the pineal gland and spleen, while the kynurenine enzymes Kynu and KatII developed circadian rhythmicity in the adrenal glands only after the combined interventions. Our data suggest that a mild immunological challenge during prenatal development may play a critical role in triggering an adaptive response of the circadian clock later in life.

The 3D in vitro Adrenoid cell model recapitulates the complexity of the adrenal gland

The crosstalk between the chromaffin and adrenocortical cells is essential for the endocrine activity of the adrenal glands. This interaction is also likely important for tumorigenesis and progression of adrenocortical cancer and pheochromocytoma. We developed a unique in vitro 3D model of the whole adrenal gland called Adrenoid consisting in adrenocortical carcinoma H295R and pheochromocytoma MTT cell lines. Adrenoids showed a round compact morphology with a growth rate significantly higher compared to MTT-spheroids. Confocal analysis of differential fluorescence staining of H295R and MTT cells demonstrated that H295R organized into small clusters inside Adrenoids dispersed in a core of MTT cells. Transmission electron microscopy confirmed the strict cell-cell interaction occurring between H295R and MTT cells in Adrenoids, which displayed ultrastructural features of more functional cells compared to the single cell type monolayer cultures. Adrenoid maintenance of the dual endocrine activity was demonstrated by the expression not only of cortical and chromaffin markers (steroidogenic factor 1, and chromogranin) but also by protein detection of the main enzymes involved in steroidogenesis (steroidogenic acute regulatory protein, and CYP11B1) and in catecholamine production (tyrosine hydroxylase and phenylethanolamine N-methyltransferase). Mass spectrometry detection of steroid hormones and liquid chromatography measurement of catecholamines confirmed Adrenoid functional activity. In conclusion, Adrenoids represent an innovative in vitro 3D-model that mimics the spatial and functional complexity of the adrenal gland, thus being a useful tool to investigate the crosstalk between the two endocrine components in the pathophysiology of this endocrine organ.

Hyper-reactivity of HPA axis in Fischer 344 rats is associated with impaired cardiovascular and behavioral adaptation to repeated restraint stress

Fischer 344 (F344) rats are characterized by the hyper-reactive hypothalamic-pituitary-adrenal axis to stressful stimuli, while Lewis (LEW) rats are considered to be hypo-reactive. We studied stress-induced cardiovascular, neuroendocrine, and behavioral responses of adult male F344 and LEW rats subjected to the single (120 min) or the repeated restraint stress (daily 120 min for 1 week). Mean arterial pressure (MAP) and heart rate (HR) were measured in the restrained rats (n = 7-8 for each group) via a catheter inserted into the femoral artery. Baroreceptor sensitivity was evaluated using NO donor sodium nitroprusside and α₁-adrenoceptor agonist phenylephrine. The plasma levels of adrenocorticotropic hormone (ACTH), corticosterone, aldosterone, and adrenaline were determined before and during the restraint. Exploratory behavior was tested in open field test. F344 rats exerted the augmented stress-induced increase in plasma ACTH, corticosterone, and adrenaline as well as the impaired endocrine adaptation to the repeated stress compared to LEW rats. F344 rats exhibited higher MAP than LEW rats during single and repeated restraint. Moreover, repeatedly restrained F344 showed elevated HR and diminished baroreflex sensitivity. F344 and LEW rats exhibited similar total locomotor activity and the time spent in the center of open field arena, both parameters being decreased by the repeated restraint. The detailed analysis revealed altered pattern of locomotor behavior in F344 rats subjected to repeated restraint. In conclusion, F344 rats showed the impaired endocrine adaptation that resulted in allostatic overload, which might contribute to the impaired cardiovascular and behavioral adaptation to chronic stress observed in this strain. Lay summary F344 rats, characterized by HPA axis hyper-reactivity, exhibited higher blood pressure during restraint than LEW rats. Moreover, repeatedly restrained F344 rats showed elevated heart rate and impaired baroreflex sensitivity. It can be concluded that a poor adaptation to the repeated stress in F344 rats is not only limited to the neuroendocrine response but also has important cardiovascular consequences.

Fetal programming of adrenal PNMT and hypertension by glucocorticoids in WKY rats is dose and sex-dependent

Biochemical changes in utero may alter normal fetal development, resulting in disease later in life, a phenomenon known as fetal programming. Recent epidemiological studies link fetal programming to negative health outcomes, such as low birth weight and hypertension in adulthood. Here, we used a WKY rat model and studied the molecular changes triggered by prenatal glucocorticoid (GC) exposure on the development of hypertension, and on the regulation of phenylethanolamine N-methyl transferase (PNMT), the enzyme responsible for biosynthesis of epinephrine, and a candidate gene linked to hypertension. Clinically, high doses of the synthetic GC dexamethasone (DEX) are used to treat infant respiratory distress syndrome. Elevated maternal GCs have been correlated with fetal programming of hypertension. The aim of this study was to determine if lower doses of DEX would not lead to detrimental fetal programming effects such as hypertension. Our data suggests that prenatal stress programs for increased expression of PNMT and altered regulation of PNMT in males and females. Importantly, we identified that DEX mediated programming was more apparent in the male rats, and the lower dose 10μg/kg/day of DEX did not lead to changes in blood pressure (BP) in female rats suggesting that this dose is below the threshold for programming of hypertension. Furthermore, sex-specific differences were observed in regards to programming mechanisms that may account for hypertension in males.

Melatonin treatment affects changes in adrenal gene expression of catecholamine biosynthesizing enzymes and norepinephrine transporter in the rat model of chronic-stress-induced depression

This study investigated the effects of melatonin treatment on adrenal catecholamine content, synthesis, uptake, and vesicular transport induced by the chronic unpredictable mild stress (CUMS) model of depression in rats. This entailed quantifying the norepinephrine, epinephrine, mRNA, and protein levels of tyrosine hydroxylase (TH), dopamine-β-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT), norepinephrine transporter (NET), and vesicular monoamine transporter 2 (VMAT2) in the adrenal medulla. CUMS caused a significant depletion of norepinephrine stores and protein levels of TH, DBH, and NET, whereas the gene expression of PNMT was increased. It was observed that melatonin treatment in the CUMS rats prevented the stress-induced decrease in norepinephrine content and the protein expression of TH, DBH, and NET in the adrenal medulla of chronically stressed rats. The present study demonstrates the stimulatory effect of melatonin on adrenomedullary synthesis, the uptake and content of catecholamine in the rat model of chronic stress-induced depression.

Inflammatory Signaling in Hypertension: Regulation of Adrenal Catecholamine Biosynthesis

The immune system is increasingly recognized for its role in the genesis and progression of hypertension. The adrenal gland is a major site that coordinates the stress response via the hypothalamic-pituitary-adrenal axis and the sympathetic-adrenal system. Catecholamines released from the adrenal medulla function in the neuro-hormonal regulation of blood pressure and have a well-established link to hypertension. The immune system has an active role in the progression of hypertension and cytokines are powerful modulators of adrenal cell function. Adrenal medullary cells integrate neural, hormonal, and immune signals. Changes in adrenal cytokines during the progression of hypertension may promote blood pressure elevation by influencing catecholamine biosynthesis. This review highlights the potential interactions of cytokine signaling networks with those of catecholamine biosynthesis within the adrenal, and discusses the role of cytokines in the coordination of blood pressure regulation and the stress response.

Effects of Trilostane on urinary Catecholamines and their metabolites in dogs with Hypercortisolism

BACKGROUND

Glucocorticoids influence the synthesis and metabolism of catecholamines (epinephrine and norepinephrine) and metanephrines (metanephrine and normetanephrine). The aim of this study was to measure urinary catecholamines and metanephrines in dogs with hypercortisolism before and during trilostane therapy. Urine samples were collected during initial work up and during therapy with trilostane in 14 dogs with hypercortisolism and in 25 healthy dogs. Epinephrine, norepinephrine, metanephrine and normetanephrine were measured using high-pressure liquid chromatography and expressed as ratios to urinary creatinine concentration.

RESULTS

Untreated dogs with hypercortisolism had significantly higher epinephrine, norepinephrine, and normetanephrine:creatinine ratios compared to healthy dogs. During trilostane therapy, urinary catecholamines and their metabolites did not decrease significantly. However, dogs with low post-ACTH cortisol concentrations during trilostane therapy had less increased epinephrine, norepinephrine and normetanephrine:creatinine ratios compared to healthy dogs. There was no correlation of urinary catecholamines and their metabolites with baseline or post-ACTH cortisol or endogenous ACTH concentrations during trilostane therapy.

CONCLUSION

Influences between steroid hormones and catecholamines seem to occur, as dogs with hypercortisolism have significantly higher urinary epinephrine, norepinephrine, and normetanephrine:creatinine ratios. Once-daily trilostane therapy does not lead to a significant decrease in catecholamines and their metabolites. Trilostane-treated dogs still have increased urinary epinephrine, norepinephrine and normetanephrine:creatinine ratios during trilostane therapy.

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.

Prenatal glucocorticoid exposure programs adrenal PNMT expression and adult hypertension

Prenatal exposure to glucocorticoids (GCs) programs for hypertension later in life. The aim of the current study was to examine the impact of prenatal GC exposure on the postnatal regulation of the gene encoding for phenylethanolamine N-methyltransferase (PNMT), the enzyme involved in the biosynthesis of the catecholamine, epinephrine. PNMT has been linked to hypertension and is elevated in animal models of hypertension. Male offspring of Wistar-Kyoto dams treated with dexamethasone (DEX) developed elevated systolic, diastolic and mean arterial blood pressure compared to saline-treated controls. Plasma epinephrine levels were also elevated in adult rats exposed to DEX in utero. RT-PCR analysis revealed adrenal PNMT mRNA was higher in DEX exposed adult rats. This was associated with increased mRNA levels of transcriptional regulators of the PNMT gene: Egr-1, AP-2, and GR. Western blot analyses showed increased expression of PNMT protein, along with increased Egr-1 and GR in adult rats exposed to DEX in utero. Furthermore, gel mobility shift assays showed increased binding of Egr-1 and GR to DNA. These results suggest that increased PNMT gene expression via altered transcriptional activity is a possible mechanism by which prenatal exposure to elevated levels of GCs may program for hypertension later in life.

Cardiac phenylethanolamine N-methyltransferase: localization and regulation of gene expression in the spontaneously hypertensive rat

Phenylethanolamine N-methyltransferase (PNMT) is the terminal enzyme in the catecholamine biosynthetic pathway responsible for adrenaline biosynthesis. Adrenaline is involved in the sympathetic control of blood pressure; it augments cardiac function by increasing stroke volume and cardiac output. Genetic mapping studies have linked the PNMT gene to hypertension. This study examined the expression of cardiac PNMT and changes in its transcriptional regulators in the spontaneously hypertensive (SHR) and wild type Wistar-Kyoto (WKY) rats. SHR exhibit elevated levels of corticosterone, and lower levels of the cytokine IL-1β, revealing systemic differences between SHR and WKY. PNMT mRNA was significantly increased in all chambers of the heart in the SHR, with the greatest increase in the right atrium. Transcriptional regulators of the PNMT promoter show elevated expression of Egr-1, Sp1, AP-2, and GR mRNA in all chambers of the SHR heart, while protein levels of Sp1, Egr-1, and GR were elevated only in the right atrium. Interestingly, only AP-2 protein-DNA binding was increased, suggesting it may be a key regulator of cardiac PNMT in SHR. This study provides the first insights into the molecular mechanisms involved in the dysregulation of cardiac PNMT in a genetic model of hypertension.

Fetal endocrine and metabolic adaptations to hypoxia: the role of the hypothalamic-pituitary-adrenal axis

In utero, hypoxia is a significant yet common stress that perturbs homeostasis and can occur due to preeclampsia, preterm labor, maternal smoking, heart or lung disease, obesity, and high altitude. The fetus has the extraordinary capacity to respond to stress during development. This is mediated in part by the hypothalamic-pituitary-adrenal (HPA) axis and more recently explored changes in perirenal adipose tissue (PAT) in response to hypoxia. Obvious ethical considerations limit studies of the human fetus, and fetal studies in the rodent model are limited due to size considerations and major differences in developmental landmarks. The sheep is a common model that has been used extensively to study the effects of both acute and chronic hypoxia on fetal development. In response to high-altitude-induced, moderate long-term hypoxia (LTH), both the HPA axis and PAT adapt to preserve normal fetal growth and development while allowing for responses to acute stress. Although these adaptations appear beneficial during fetal development, they may become deleterious postnatally and into adulthood. The goal of this review is to examine the role of the HPA axis in the convergence of endocrine and metabolic adaptive responses to hypoxia in the fetus.

Catecholamine metabolism in paraganglioma and pheochromocytoma: similar tumors in different sites?

Pheochromocytoma (PHEO) and paraganglioma (PGL) are catecholamine-producing neuroendocrine tumors that arise respectively inside or outside the adrenal medulla. Several reports have shown that adrenal glucocorticoids (GC) play an important regulatory role on the genes encoding the main enzymes involved in catecholamine (CAT) synthesis i.e. tyrosine hydroxylase (TH), dopamine β-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT). To assess the influence of tumor location on CAT metabolism, 66 tissue samples (53 PHEO, 13 PGL) and 73 plasma samples (50 PHEO, 23 PGL) were studied. Western blot and qPCR were performed for TH, DBH and PNMT expression. We found a significantly lower intra-tumoral concentration of CAT and metanephrines (MNs) in PGL along with a downregulation of TH and PNMT at both mRNA and protein level compared with PHEO. However, when PHEO were partitioned into noradrenergic (NorAd) and mixed tumors based on an intra-tumoral CAT ratio (NE/E >90%), PGL and NorAd PHEO sustained similar TH, DBH and PNMT gene and protein expression. CAT concentration and composition were also similar between NorAd PHEO and PGL, excluding the use of CAT or MNs to discriminate between PGL and PHEO on the basis of biochemical tests. We observed an increase of TH mRNA concentration without correlation with TH protein expression in primary cell culture of PHEO and PGL incubated with dexamethasone during 24 hours; no changes were monitored for PNMT and DBH at both mRNA and protein level in PHEO and PGL. Altogether, these results indicate that long term CAT synthesis is not driven by the close environment where the tumor develops and suggest that GC alone is not sufficient to regulate CAT synthesis pathway in PHEO/PGL.

Stress-triggered changes in peripheral catecholaminergic systems

The sympathetic nervous system not only regulates cardiovascular and metabolic responses to stress but also is altered by stress. The sympathoneural and sympathoadrenomedullary systems are modified by different metabolic pathways and have different responses to short- and to long-term stressors. Stress also induces nonneuronal catecholamine enzymes, primarily through corticosteroids. Catecholamine synthetic enzymes are induced by different pathways in response to short- and long-term acting stressors, like cold exposure or immobilization, and differently in the sympathetic ganglia and the adrenal medulla. However, a long-term exposure to one stressor can increase the response to a second, different stressor. Tyrosine hydroxylase gene transcription increases after only 5min of immobilization through phosphorylation of CREB, but this response is short lived. However, repeated stress gives a longer-lived response utilizing transcription factors such as Egr-1 and Fra-2. Glucocorticoids and ACTH also induce sympathoneural enzymes leading to distinct patterns of short-term and long-lived activation of the sympathetic nervous system. Nonneuronal phenylethanolamine N-methyltransferase (PNMT) develops early in the heart and then diminishes. However, intrinsic cardiac adrenergic cells remain and nonneuronal PNMT is present in many cells of the adult organism and increases in response to glucocorticoids. Both stress-induced and administered glucocorticoids induce fetal PNMT and hypertension. Human stressors such as caring for an ill spouse or sleep apnea cause a persistent increase in blood norepinephrine, increased blood pressure, and downregulated catecholamine receptors. Hypertension is associated with a loss of slow-wave sleep, when sympathetic nerve activity is lowest. These findings indicate that stress-induced alteration of the sympathetic nervous system occurs in man as in experimental animals.

Epinephrine: a short- and long-term regulator of stress and development of illness : a potential new role for epinephrine in stress

Epinephrine (Epi), which initiates short-term responses to cope with stress, is, in part, stress-regulated via genetic control of its biosynthetic enzyme, phenylethanolamine N-methyltransferase (PNMT). In rats, immobilization (IMMO) stress activates the PNMT gene in the adrenal medulla via Egr-1 and Sp1 induction. Yet, elevated Epi induced by acute and chronic stress is associated with stress induced, chronic illnesses of cardiovascular, immune, cancerous, and behavioral etiologies. Major sources of Epi include the adrenal medulla and brainstem. Although catecholamines do not cross the blood-brain barrier, circulating Epi from the adrenal medulla may communicate with the central nervous system and stress circuitry by activating vagal nerve β-adrenergic receptors to release norepinephrine, which could then stimulate release of the same from the nucleus tractus solitarius and locus coeruleus. In turn, the basal lateral amygdala (BLA) may activate to stimulate afferents to the hypothalamus, neocortex, hippocampus, caudate nucleus, and other brain regions sequentially. Recently, we have shown that repeated IMMO or force swim stress may evoke stress resiliency, as suggested by changes in expression and extinction of fear memory in the fear-potentiated startle paradigm. However, concomitant adrenergic changes seem stressor dependent. Present studies aim to identify stressful conditions that elicit stress resiliency versus stress sensitivity, with the goal of developing a model to investigate the potential role of Epi in stress-associated illness. If chronic Epi over expression does elicit illness, possibilities for alternative therapeutics exist through regulating stress-induced Epi expression, adrenergic receptor function and/or corticosteroid effects on Epi, adrenergic receptors and the stress axis.

Role of reactive oxygen species in the neural and hormonal regulation of the PNMT gene in PC12 cells

The stress hormone, epinephrine, is produced predominantly by adrenal chromaffin cells and its biosynthesis is regulated by the enzyme phenylethanolamine N-methyltransferase (PNMT). Studies have demonstrated that PNMT may be regulated hormonally via the hypothalamic-pituitary-adrenal axis and neurally via the stimulation of the splanchnic nerve. Additionally, hypoxia has been shown to play a key role in the regulation of PNMT. The purpose of this study was to examine the impact of reactive oxygen species (ROS) produced by the hypoxia mimetic agent CoCl₂, on the hormonal and neural stimulation of PNMT in an in vitro cell culture model, utilizing the rat pheochromocytoma (PC12) cell line. RT-PCR analyses show inductions of the PNMT intron-retaining and intronless mRNA splice variants by CoCl₂ (3.0- and 1.76-fold, respectively). Transient transfection assays of cells treated simultaneously with CoCl₂ and the synthetic glucocorticoid, dexamethasone, show increased promoter activity (18.5-fold), while mRNA levels of both splice variants do not demonstrate synergistic effects. Similar results were observed when investigating the effects of CoCl₂-induced ROS on the neural stimulation of PNMT via forskolin. Our findings demonstrate that CoCl₂-induced ROS have synergistic effects on hormonal and neural activation of the PNMT promoter.

Developmental and stress-induced remodeling of cell–cell communication in the adrenal medullary tissue

The adrenal medullary tissue contributes to maintain body homeostasis in reaction to stressful environmental changes via the release of catecholamines into the blood circulation in response to splanchnic nerve activation. Accordingly, chromaffin cell stimulus-secretion coupling undergoes temporally restricted periods of anatomo- functional remodeling in response to prevailing hormonal requirements of the organism. The postnatal development of the adrenal medulla and response to stress are remarkable physiological situations in which the stimulus- secretion coupling is critically affected. Catecholamine secretion from rat chromaffin cells is under a dual control involving an incoming initial command arising from the sympathetic nervous system that releases acetylcholine at the splanchnic nerve terminal-chromaffin cell synapses and a local gap junction-mediated intercellular communication. Interestingly, these two communication pathways are functionally interconnected within the gland and exhibit coordinated plasticity mechanisms. This article reviews the physiological and molecular evidence that the adrenal medullary tissue displays anatomical and functional adaptative remodeling of cell–cell communications upon physiological (postnatal development) and/or physiopathological (stress) situations associated with specific needs in circulating catecholamine levels.

Differential in vivo regulation of TH and DBH mRNA in rat atria by maprotiline and fluoxetine

It is well known that antidepressants affect central monoaminergic neurotransmission and that they also modulate hormone release in peripheral tissues. Repeated maprotiline (a noradrenaline reuptake inhibitor) and fluoxetine (a serotonin reuptake inhibitor) treatment on gene expression of the catecholamine biosynthetic enzymes were examined in rat atria and ventricles in vivo. Maprotiline decreased the gene expression of tyrosine hydroxylase (TH) and dopamine?-hydroxylase (DBH) in the rat atrium. Fluoxetine increased gene expression of TH and DBH, but not of phenylethanolamine N-methyltransferase (PNMT). Chronic application of antidepressants did not change the expression of these enzymes in the ventricles. We conclude that repeated administration of fluoxetine enhances gene transcription of TH and DBH and subsequently stimulates noradrenaline synthesis in rat atria in vivo.

Stress and adrenergic function: HIF1α, a potential regulatory switch

Stress elicits adrenal epinephrine and cortisol release into the bloodstream to initiate physiological and behavioral responses to counter and overcome stress, the classic "fight or flight" response (Cannon and De La Paz, Am J Physiol 28:64-70, 1911). Stress and the stress hormone epinephrine also contribute to the pathophysiology of illness, e.g., behavioral disorders, cardiovascular disease, and immune dysfunction. Epinephrine itself is regulated by stress through its biosynthesis by phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28). Single and repeated immobilization (IMMO) stress in rats stimulates adrenal PNMT mRNA and protein expression via the transcription factors, Egr-1 and Sp1. Moderate hypoxic stress increases PNMT promoter-driven gene expression and endogenous PNMT mRNA and protein in PC12 cells. Induction is initiated through cAMP and PLC signaling, with PKA, PKC, PI3K, ERK1/2 MAPK, and p38 MAPK continuing downstream signal transduction, followed by activation of HIF1α, Egr-1, and Sp1. While functional Egr-1 and Sp1 binding sites exist within the proximal PNMT promoter, a putative hypoxia response element is a weak HIF binding site. Yet, HIF1α overexpression increases PNMT promoter-driven luciferase activity and endogenous PNMT. When the Egr-1 or Sp1 sites are mutated, HIF1α does not stimulate the PNMT promoter. siRNA knock down of Egr-1 or Sp1 prevents promoter activation while siRNA knock down of HIF1α inhibits Egr-1 and Sp1 induction. Findings suggest that hypoxia activates the PNMT gene indirectly via HIF1α stimulation of Egr-1 and Sp1. Thus, for stress-induced illnesses where adrenergic dysfunction is implicated, HIF1α may be an "on-off" switch regulating adrenergic responses to stress and a potential target for therapeutic intervention.

Hypoxia and adrenergic function: molecular mechanisms related to Egr-1 and Sp1 activation

Hypoxia is shown to regulate the stress hormone epinephrine through its biosynthesis by phenylethanolamine N-methyltransferase (PNMT) via PNMT gene activation and transcription factors Egr-1 and Sp1 in adrenal medulla-derived PC12 cells. Moderate hypoxia (5% oxygen) markedly stimulates PNMT promoter-driven luciferase activity in the cells. Hypoxia increases Egr-1 and Sp1 mRNA and nuclear protein content and Egr-1 and Sp1 protein-DNA binding complex formation. Subsequent to transcription factor induction, endogenous PNMT mRNA and protein also increase. Egr-1 and Sp1 binding site inactivation or Egr-1 and Sp1 siRNA inhibit PNMT promoter stimulation by hypoxia. Hypoxia elevates protein kinase A (PKA), phospholipase C (PLC), phosphoinositide 3-kinase, protein kinase C, ERK1/2 mitogen-activated protein kinase and p38 mitogen-activated protein kinase expression while selective inhibitors of these signaling enzymes abrogate hypoxic induction of the PNMT promoter and the rise in Egr-1, Sp1 and PNMT mRNA and protein. PC12 cells lacking PKA or PLCgamma-1 show significant reduction in PNMT promoter activation by hypoxia. Signaling inhibitors do not affect these responses or reduce hypoxic induction of the PNMT promoter to a lesser extent. Findings suggest that Egr-1 and Sp1 through synergistic interaction are critical transcriptional activators for hypoxic stress-regulated adrenergic function controlled via cAMP/PKA and PLC signaling. Identification of Sp1 as a mediator of hypoxia-induced transcriptional activation of PNMT has not been previously been shown. The effects of hypoxia on PNMT and thereby epinephrine may have important ramifications for the stress hormone epinephrine, its ability to regulate behavioral and physiological processes associated with stress and stress-elicited illness.

Effects of repeated maprotiline and fluoxetine treatment on gene expression of catecholamine synthesizing enzymes in adrenal medulla of unstressed and stressed rats

1 Repeated maprotiline (a noradrenaline reuptake inhibitor) and fluoxetine (a serotonin reuptake inhibitor) treatment on gene expression of catecholamine biosynthetic enzymes were examined in adrenal medulla of unstressed control and chronic unpredictable mild stressed rats. 2 Maprotiline did not change gene expression of catecholamine biosynthetic enzymes in control and stressed rats. 3 Fluoxetine increased gene expression of tyrosine hydroxylase (TH) and dopamine-β-hydroxylase (DBH), but did not phenylethanolamine N-methyltransferase in both unstressed and chronic unpredictable mild stressed animals. 4 In conclusion, we have demonstrated that repeated administration of fluoxetine enhanced gene transcription of TH and DBH and subsequently stimulates noradrenaline synthesis in adrenal medulla of control and stressed rats.

Glucocorticoids and phenobarbital induce murine CYP2B genes by independent mechanisms

BACKGROUND

Genes for CYP of the 2B subfamily (CYP2B genes) have long been known to be inducible in murine liver by phenobarbital and phenobarbital-like inducers. More recently, it has become clear that glucocorticoids can also induce these genes by a mechanism independent of that of phenobarbital-like inducers.

OBJECTIVE

To summarize the evidence for the existence of two distinct molecular mechanisms for induction of murine CYP2B genes and to analyze the wider implications of this situation for inducible xenobiotic metabolism.

METHODS

The mechanism of action of phenobarbital-like inducers of murine CYP2B genes is first briefly summarized. The role of glucocorticoids in the induction of various proteins, particularly rat phosphoenolpyruvate carboxykinase, where transcriptional activation is achieved via a glucocorticoid response unit, is also discussed. Finally, recent results are presented on glucocorticoid induction of murine CYP2B genes, including evidence for the presence of a functional glucocorticoid response unit in the rat CYP2B2 gene and for the role of constitutive androstane receptor as an accessory factor in this response.

RESULTS/CONCLUSION

Murine CYP2B genes are seen to respond to two distinct regulatory mechanisms, but much remains to be learned concerning the interactions between these two regulatory loops, as well as the details of glucocorticoid induction.

Pharmacological strategies for improving the efficacy and therapeutic ratio of glucocorticoids in inflammatory lung diseases

Glucocorticoids are widely used to treat various inflammatory lung diseases. Acting via the glucocorticoid receptor (GR), they exert clinical effects predominantly by modulating gene transcription. This may be to either induce (transactivate) or repress (transrepress) gene transcription. However, certain individuals, including those who smoke, have certain asthma phenotypes, chronic obstructive pulmonary disease (COPD) or some interstitial diseases may respond poorly to the beneficial effects of glucocorticoids. In these cases, high dose, often oral or parental, glucocorticoids are typically prescribed. This generally leads to adverse effects that compromise clinical utility. There is, therefore, a need to enhance the clinical efficacy of glucocorticoids while minimizing adverse effects. In this context, a long-acting beta(2)-adrenoceptor agonist (LABA) can enhance the clinical efficacy of an inhaled corticosteroid (ICS) in asthma and COPD. Furthermore, LABAs can augment glucocorticoid-dependent gene expression and this action may account for some of the benefits of LABA/ICS combination therapies when compared to ICS given as a monotherapy. In addition to metabolic genes and other adverse effects that are induced by glucocorticoids, there are many other glucocorticoid-inducible genes that have significant anti-inflammatory potential. We therefore advocate a move away from the search for ligands of GR that dissociate transactivation from transrepression. Instead, we submit that ligands should be functionally screened by virtue of their ability to induce or repress biologically-relevant genes in target tissues. In this review, we discuss pharmacological methods by which selective GR modulators and "add-on" therapies may be exploited to improve the clinical efficacy of glucocorticoids while reducing potential adverse effects.

Effect of immobilization stress on gene expression of catecholamine biosynthetic enzymes in heart auricles of socially isolated rats

Chronic stress is associated with the development of cardiovascular diseases. The sympathoneural system plays an important role in the regulation of cardiac function both in health and disease. In the present study, the changes in gene expression of the catecholamine biosynthetic enzymes tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) and protein levels in the right and left heart auricles of naive control and long-term (12 weeks) socially isolated rats were investigated by Taqman RT-PCR and Western blot analysis. The response of these animals to additional immobilization stress (2 h) was also examined. Long-term social isolation produced a decrease in TH mRNA level in left auricles (about 70%) compared to the corresponding control. Expression of the DBH gene was markedly decreased both in the right (about 62%) and left (about 81%) auricles compared to the corresponding control, group-maintained rats, whereas PNMT mRNA levels remained unchanged. Exposure of group-housed rats to acute immobilization for 2 h led to a significant increase of mRNA levels of TH (about 267%), DBH (about 37%) and PNMT (about 60%) only in the right auricles. Additional 2-h immobilization of individually housed rats did not affect gene expression of these enzymes in either the right or left auricle. Protein levels of TH, DBH and PNMT in left and right heart auricles were unchanged either in both individually housed and immobilized rats. The unchanged mRNA levels of the enzymes examined after short-term immobilization suggest that the catecholaminergic system of the heart auricles of animals previously exposed to chronic psychosocial stress was adapted to maintain appropriate cardiovascular homeostasis.

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.

Hypoxic stress-induced changes in adrenergic function: role of HIF1 alpha

Sustaining epinephrine-elicited behavioral and physiological responses during stress requires replenishment of epinephrine stores. Egr-1 and Sp1 contribute by stimulating the gene encoding the epinephrine-synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT), as shown for immobilization stress in rats in adrenal medulla and for hypoxic stress in adrenal medulla-derived PC12 cells. Hypoxia (5% O(2)) also activates hypoxia inducible factor (HIF) 1alpha, increasing mRNA, nuclear protein and nuclear protein/hypoxia response element binding complex formation. Hypoxia and HIF1alpha over-expression also elevate PNMT promoter-driven luciferase activity in PC12 cells. Hypoxia may be limiting as HIF1alpha over-expression increases luciferase expression to no greater extent than oxygen reduction alone. HIF1alpha inducers CoCl(2) or deferoxamine elevate luciferase as well. PC12 cells harboring a HIF1alpha expression construct show markedly higher levels of Egr-1 and Sp1 mRNA and nuclear protein and PNMT mRNA and cytoplasmic protein. Inactivation of Egr-1 and Sp1 binding sites in the proximal -893 bp of PNMT promoter precludes HIF1alpha stimulation while a potential hypoxia response element (-282 bp) in the promoter shows weak HIF1alpha affinity at best. These findings are the first to suggest that hypoxia activates the proximal rat PNMT promoter primarily via HIF1alpha induction of Egr-1 and Sp1 rather than by co-activation by Egr-1, Sp1 and HIF1alpha. In addition, the rise in HIF1alpha protein leading to Egr-1 and Sp1 stimulation of PNMT appears to include HIF1alpha gene activation rather than simply prevention of HIF1alpha proteolytic degradation.

Regulation of gene expression of catecholamine biosynthetic enzymes in dopamine-beta-hydroxylase- and CRH-knockout mice exposed to stress

Norepinephrine-deficient mice harbor a disruption of the gene for dopamine-beta-hydroxylase (DBH-KO). Corticotropin-releasing hormone knockout mice (CRH-KO) have markedly reduced HPA activity. The aim of the present work was to study how deficiency of DBH and CRH would affect tyrosine hydroxylase (TH), DBH, and phenylethanolamine N-methyltransferase (PNMT) gene expression and protein levels in the adrenal medulla (AM) and stellate ganglia (SG) of control and stressed mice. Both in AM and SG, single immobilization significantly increased TH and DBH mRNA and protein levels both in wild-type (WT) and CRH-KO mice. On the other hand, the stress-triggered increase in PNMT mRNA and protein levels seen in WT mice was absent in CRH-KO mice. DBH-KO mice are more sensitive to stress but survive a single 2 h restraint stress in a tube. The increase in TH mRNA levels induced by restraint stress in WT was not observed in DBH-KO mice. PNMT mRNA and especially PNMT protein levels were significantly elevated in AM of DBH-KO mice. In SG of DBH-KO mice, TH mRNA levels were not affected; however, PNMT gene expression was highly elevated. Thus, disruption of the DBH gene surprisingly blocks the stress-induced elevation of TH mRNA levels in AM but increases PNMT gene expression in both AM and SG. Our data indicate that adrenergic signaling is required for stress-induced increase in TH mRNA and that this signaling restrains stress-induced increase in PNMT mRNA. They also confirm that the HPA system plays a crucial role in the stress-induced regulation of PNMT gene expression.

Adrenergic responses to stress: transcriptional and post-transcriptional changes

Stress effects on adrenergic responses in rats were examined in adrenal medulla, the primary source of circulating epinephrine (Epi). Irrespective of duration, immobilization (IMMO) increased adrenal corticosterone to the same extent. In contrast, Epi changed little, suggesting that Epi synthesis replenishes adrenal pools and sustains circulating levels for the heightened alertness and physiological changes required of the "flight or fight" response. IMMO also induced the Epi-synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT). The rise in its mRNA and protein was preceded by increases in Egr-1 and Sp1 mRNA, protein, and protein-DNA binding complex formation. With repeated and prolonged stress, PNMT protein did not reflect the magnitude of change in mRNA. The latter suggests that post-transcriptional, in addition to transcriptional mechanisms, regulate PNMT responses to stress. To further reveal molecular mechanisms underlying stress-induced changes in adrenergic function, the effects of hypoxia on PNMT promoter-driven gene expression are being examined in adrenal medulla-derived PC12 cells. Hypoxia activates the PNMT promoter to increase PNMT promoter-driven luciferase reporter gene expression and endogenous PNMT in PC12 cells. Induction of both appear mediated via activation of multiple signaling pathways and downstream activation of hypoxia inducible factor and PNMT transcriptional activators, Egr-1 and Sp1. Hypoxia generates both partially and fully processed forms of PNMT mRNA. The former reportedly is translated into a truncated, nonfunctional protein, and the latter into enzymatically active PNMT. Together, findings suggest that stress increases PNMT gene transcriptional activity but post-transcriptional regulatory mechanisms limit the biological end-point of functional PNMT enzyme and, thereby, Epi.

Expression and distribution of glucocorticoid receptors in the ovine fetal adrenal cortex: effect of long-term hypoxia

This study was designed to determine if long-term hypoxia (LTH) alters adrenal glucocorticoid receptor (GR) expression in the ovine fetal adrenal cortex. Ewes were maintained at 3820 m from approximately 30 to 138 to 140 days' gestation, and fetal adrenals were collected. Western analysis revealed two approximately 94-kDa GR-alpha isoforms and a lower molecular weight (45 kDa) form. A decreasing trend in the ratio of 94-kDa/45-kDa bands following LTH suggested an increase in GR turnover. Immunohistochemistry demonstrated dense GR staining in the zona glomerulosa with minimal staining in the zona fasciculata in the control group, while dense staining was observed throughout the cortex in LTH. Western analysis and reverse transcription polymerase chain reaction confirmed that the GR- beta isoform is not present or expressed at extremely low levels in the fetal adrenal, hypothalamus, pituitary, and placenta. These data indicate that LTH alters GR-alpha function in the fetal adrenal cortex and suggest that GR-beta is not expressed in sheep.

Long-term hypoxia modulates expression of key genes regulating adrenomedullary function in the late gestation ovine fetus

We previously communicated that long-term hypoxia (LTH) resulted in a selective reduction in plasma epinephrine following acute stress in fetal sheep. The present study tested the hypothesis that LTH selectively reduces adrenomedullary expression of phenylethanolamine-N-methyltransferase (PNMT), the rate-limiting enzyme for epinephrine synthesis. We also examined the effect of LTH on adrenomedullary nicotinic, muscarinic, and glucocorticoid receptor (GR) expression. Ewes were maintained at high altitude (3,820 m) from 30 to 138 days gestation (dGA); adrenomedullary tissue was collected from LTH and age-matched, normoxic control fetuses at 139-141 dGA. Contrary to our hypothesis, in addition to PNMT, adrenomedullary expression (mRNA, protein) of tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) were reduced in the LTH fetus. Immunocytochemistry indicated that TH and DBH expression was lower throughout the medulla, while PNMT appeared to reflect a reduction in PNMT-expressing cells. Nicotinic receptor alpha 1, 2, 3, 5, 6, 7, beta 1, 2, and 4 subunits were expressed in the medulla of LTH and control fetuses. Messenger RNA for alpha 1 and 7 and beta 1 and 2 subunits was lower in LTH fetuses. Muscarinic receptors M1, M2, and M3 as well as the GR were also expressed, and no differences were noted between groups. In summary, LTH in fetal sheep has a profound effect on expression of key enzymes mediating adrenomedullary catecholamine synthesis. Further, LTH impacts nicotinic receptor subunit expression potentially altering cholinergic neurotransmission within the medulla. These findings have important implications regarding fetal cardiovascular and metabolic responses to stress in the LTH fetus.

Separating transrepression and transactivation: a distressing divorce for the glucocorticoid receptor?

Glucocorticoids (corticosteroids) are highly effective in combating inflammation in the context of a variety of diseases. However, clinical utility can be compromised by the development of side effects, many of which are attributed to the ability of the glucocorticoid receptor (GR) to induce the transcription of, or transactivate, certain genes. By contrast, the anti-inflammatory effects of glucocorticoids are due largely to their ability to reduce the expression of pro-inflammatory genes. This effect has been predominantly attributed to the repression of key inflammatory transcription factors, including AP-1 and NF-kappaB, and is termed transrepression. The ability to functionally separate these transcriptional functions of GR has prompted a search for dissociated GR ligands that can differentially induce transrepression but not transactivation. In this review, we present evidence that post-transcriptional mechanisms of action are highly important to the anti-inflammatory actions of glucocorticoids. Furthermore, we present the case that mechanistically distinct forms of glucocorticoid-inducible gene expression are critical to the development of anti-inflammatory effects by repressing inflammatory signaling pathways and inflammatory gene expression at multiple levels. Considerable care is therefore required to avoid loss of anti-inflammatory effectiveness in the development of novel transactivation-defective ligands of GR.

Stress-induced catecholaminergic function: transcriptional and post-transcriptional control

This review summarizes knowledge on the effects of stress on two catecholamine biosynthetic enzymes, tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT). Information is presented on differential responses of the enzymes to a variety of stressors as well as differential responses of the enzymes localized to the central nervous system vs. peripheral nervous system and tissues. Changes in mRNA and protein or activity are described, including species- and stressor-specific effects. While temporal changes in these parameters may differ for the particular stressor or enzyme, in general, maximal changes in mRNA and protein content occur at 6-8 and 24 h after stressor exposure, respectively. Elevation of TH and PNMT transcriptional activators prior to mRNA induction and nuclear run-on assays show that stress activates the genes encoding these enzymes. Yet, extents of induction of mRNA, protein and enzyme activity are often discordant depending on the stress, its duration and repetition of exposure. The extremes are concordant changes in mRNA and protein/activity vs. highly elevated mRNA with no change in protein/activity. Post-transcriptional and/or post-translational regulatory influences that may contribute to the complex effects of stress on TH, PNMT and the stress hormone epinephrine are explored.

Adrenergic and calcium modulation of the heart in stress: from molecular biology to function

There is strong evidence about the importance of catecholamines and calcium signaling in heart function. Also, interaction of these two systems is well documented. Catecholamines signal through adrenergic receptors, and further activate calcium transport either from the extracellular space, or from the intracellular calcium stores. This review summarizes current knowledge on catecholamine production in the heart, with special focus on the final enzyme in the catecholamine synthesizing pathway, phenylethanolamine N-methyltransferase (PNMT), in different cell types in the heart. Further, signaling through different types of adrenergic receptors in physiological conditions and after exposure to different stressors is discussed. Also, part of this review considers activation of an intracellular calcium transport system via inositol 1,4,5-trisphosphate receptor and to possible functional consequences in control and stress conditions.

Stress-induced changes in epinephrine expression in the adrenal medulla in vivo

Immobilization (IMMO) stress was used to examine how stress alters the stress hormone epinephrine (EPI) in the adrenal medulla in vivo. In rats subjected to IMMO for 30 or 120 min, adrenal corticosterone increased to the same extent. In contrast, EPI changed very little, suggesting that EPI synthesis replenishes adrenal pools and sustains circulating levels for the heightened alertness and physiological responses of the 'flight or fight' response. In part, stress activates EPI via the phenylethanolamine N-methyltransferase (PNMT) gene as single or repeated IMMO elevated PNMT mRNA. The rise in PNMT mRNA was preceded by induction of the PNMT gene activator, Egr-1, with increases in Egr-1 mRNA, protein, and protein-DNA binding complex apparent. IMMO also evoked changes in Sp1 mRNA, protein, and Sp1-DNA complex formation, although for chronic IMMO changes were not entirely coincident. In contrast, glucocorticoid receptor and AP-2 mRNA, protein, and protein-DNA complex were unaltered. Finally, IMMO stress elevated PNMT protein. However, with seven daily IMMOs for 120 min and delayed killing, protein stimulation did not attain the highly elevated levels expected based on mRNA changes. The latter may perhaps suggest initiation of adrenergic desensitization to prolonged and repeated IMMO stress and/or dissociation of transcriptional and post-transcriptional regulatory mechanisms.

Transcriptional regulation of phenylethanolamine N-methyltransferase in pheochromocytomas from patients with von Hippel-Lindau syndrome and multiple endocrine neoplasia type 2

Pheochromocytomas in multiple endocrine neoplasia type 2 (MEN-2) express phenylethanolamine N-methyltransferase (PNMT), the enzyme that catalyzes conversion of norepinephrine to epinephrine, whereas those in von Hippel-Lindau (VHL) syndrome do not. Consequently, pheochromocytomas in MEN-2 produce epinephrine, whereas those in VHL syndrome produce mainly norepinephrine. This study examined whether transcription factors known to regulate expression of PNMT explain the different tumor phenotypes in these syndromes. Quantitative polymerase chain reaction (PCR) and Western blotting were used to assess levels of mRNA and protein for the glucocorticoid receptor, early growth response 1 (Egr-1), the Sp1 transcription factor (Sp1), and MYC-associated zinc finger protein (MAZ) in 6 MEN-2 and 13 VHL tumors. Results were cross-checked with data obtained using microarray gene expression profiling in a further set of 10 MEN-2 and 12 VHL tumors. Pheochromocytomas in MEN-2 and VHL syndrome did not differ in expression of the glucocorticoid receptor, Egr-1, Sp1, or MAZ as assessed by quantitative PCR and Western blotting. Microarray data also indicated no relevant differences in expression of the glucocorticoid receptor, Egr-1, MAZ, and the AP2 transcription factor. Thus, our results do not support a role for the above transcription factors in determining differences in expression of PNMT in pheochromocytomas from patients with VHL syndrome and MEN-2. Microarray analysis, however, did indicate differences in expression of genes involved in neural crest cell lineage and chromaffin cell development, consistent with differential survival of PNMT-expressing cells in the two syndromes.

Low glucocorticoid receptor (GR), high Dig2 and low Bcl-2 expression in double positive thymocytes of BALB/c mice indicates their endogenous glucocorticoid hormone exposure

Several studies have shown that of the four major thymocyte subsets, the CD4/CD8 double positive (DP) thymocytes are the most sensitive to in vivo glucocorticoid hormone (GC)-induced apoptosis. Our aim was to analyse fine molecular differences among thymocyte subgroups that could underlie this phenomenon. Therefore, we characterised the glucocorticoid hormone receptor (GR) expression of thymocyte subgroups both at the mRNA and protein levels by real-time PCR and flow cytometry, and correlated these features to their apoptotic sensitivity. We also investigated the time-dependent effects of the GC agonist dexamethasone (DX) with or without GC antagonist (RU486) treatments on GR mRNA/protein expression. We also analysed the expression of two apoptosis-related gene products: dexamethasone-induced gene 2 (Dig2) mRNA and Bcl-2 protein. We found that DN thymocytes had the highest GR expression, followed by CD8 single positive (SP), CD4 SP and DP thymocytes in 4-week-old BALB/c mice, both at the mRNA and protein levels, respectively. In DP cells, the Dig2 expression was significantly higher, while the Bcl-2 expression was significantly lower than in DN, CD4 SP and CD8 SP thymocytes. Single high dose DX treatment caused time-dependent depletion of DP thymocytes due to their higher apoptosis rate, which could not be abolished with RU486 pretreatment. After a single high dose DX treatment, there was a transient, significant increase of the GR mRNA and protein level of unsorted thymocytes after 8 and 16 h, followed by a significant decrease at 24 h, respectively. The time-dependent GR expression changes after DX administration could not be inhibited by the GC antagonist RU486. Twenty-four hours after exposure to high dose DX the DN, CD4 SP and CD8 SP cells showed a significant decrease of GR mRNA and protein expression, whereas the DP thymocytes, showed no significant alteration of GR mRNA or protein expression. The kinetical analysis of GR expression and apoptotic marker changes upon single high dose GC analogue administration revealed a two-phase process in thymocytes: early events, within 4-8 h, include GR upregulation and early apoptosis induction, while the late events appear most prominently at 16-20 h, when the GR is already downregulated and apoptotic cell ratio reaches its peak, with marked DP cell depletion. The low GR, high Dig2 and low Bcl-2 expression, coupled with the absence of homologous downregulation of GR after exogenous GC analogue treatment, could contribute to the high GC sensitivity of DP thymocytes. The downregulated GR and Bcl-2 together with the upregulated Dig2 level in DP cells indicates the significance of intrathymic GC effects at this differentiation stage. Since GR expression changes and apoptotic events could not be completely inhibited by GC antagonist, we propose the involvement of non-genomic GR mechanisms in these processes.

Nerve Growth Factor Regulates Adrenergic Expression

The mechanism by which nerve growth factor (NGF) regulates adrenergic expression was examined in PC-12 cells transfected with a rat phenylethanolamine N-methyl-transferase (PNMT) promoter-luciferase reporter gene construct pGL3RP893. NGF treatment increased PNMT promoter-driven luciferase activity in a dose- and time-dependent manner. Induction was attenuated by inhibition of the extracellular signal-regulated kinase mitogen-activated protein kinase (MAPK) pathway ( approximately 60%) but not by inhibition of the protein kinase A (PKA), protein kinase C, phosphoinositol kinase, or p38 MAPK pathways. Deletion PNMT promoter-luciferase reporter gene constructs showed that the NGF-responsive sequences lay within the proximal -392 base pairs (bp) of PNMT promoter, wherein binding elements for Egr-1 (-165 bp) and Sp1 (-48 bp) reside. Western analysis further showed that NGF increased nuclear levels of Egr-1, but not Sp1 or the catalytic subunit of PKA. Gel mobility shift assays showed increased potential for Egr-1, but not Sp1, protein-DNA binding complex formation. Mutation of either the Egr-1 or Sp1 binding sites in the PNMT promoter attenuated NGF activation. NGF, combined with pituitary adenylyl cyclase-activating protein (PACAP), another PNMT transcriptional activator, cooperatively stimulated PNMT promoter driven-luciferase activity beyond levels observed with either neurotrophin alone. Finally, post-transcriptional control seems to be another important mechanism by which neurotrophins regulate the adrenergic phenotype. NGF, PACAP, and a combination of the two stimulated both intron-retaining and intronless PNMT mRNA and PNMT protein, but to different extents.

Gene expression of phenylethanolamine N-methyltransferase in corticotropin-releasing hormone knockout mice during stress exposure

AIMS

Epinephrine (EPI) synthesizing enzyme phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28) is primarily localized in the adrenal medulla (AM). We have recently described existence of the PNMT gene expression in cardiac atria and ventricles and in sympathetic ganglia of adult rats and mice. The aim of the present work was to study regulation of the PNMT gene expression in corticotropin-releasing hormone knockout mice (CRH KO) and matched control wild-type mice (WT) under normal and stress conditions.

METHODS

Levels of the PNMT mRNA were determined by RT-PCR; PNMT immunoprotein and protein of transcription factor EGR-1 by Western Blot. Plasma EPI and corticosterone (CORT) levels were determined by radioenzymatic and RIA methods. Immobilization (IMMO) was used as a stressor.

RESULTS

Stress-induced increases in the PNMT mRNA and protein levels observed in WT mice were almost completely absent in CRH KO mouse adrenal medulla, stellate ganglia, and cardiac atria, while ventricular PNMT mRNA elevation was not CRH-dependent. Plasma EPI and CORT levels were markedly reduced in CRH KO compared to WT mice both before and after the stress. Levels of EGR-1, crucial transcription factor for regulation of the PNMT were highly increased in stressed WT and CRH KO mice in cardiac areas, but not in the adrenal medulla.

CONCLUSIONS

Data show that the CRH deficiency can markedly prevent immobilization-triggered induction of the PNMT mRNA and protein levels in the adrenal medulla and stellate ganglia. Reduced plasma epinephrine and corticosterone levels and adrenal medullary EGR-1 protein levels in CRH knockout versus WT mice during stress indicate that the HPA axis plays a crucial role in regulation of the PNMT gene expression in these organs. Cardiac atrial PNMT gene expression with stress is also dependent on intact HPA axis. However, in cardiac ventricles, especially after the single stress exposure, its expression is not impaired by CRH deficiency. Since cardiac EGR-1 protein levels in CRH KO mice are also not affected by the single stress exposure, we propose existence of different regulation of the PNMT gene expression, especially in the cardiac ventricles.Overall, our findings reveal that the PNMT gene expression is regulated through the HPA in both sympathoadrenal system and the heart and also via EGR-1 in the adrenal medulla, but apparently not in the heart. Regulation of the PNMT gene expression in various compartments of heart includes both corticosterone-dependent and independent mechanisms.

Epinephrine biosynthesis: hormonal and neural control during stress

1. Stress contributes to the pathophysiology of many diseases, including psychiatric disorders, immune dysfunction, nicotine addiction and cardiovascular illness. Epinephrine and the glucocorticoids, cortisol and corticosterone, are major stress hormones. 2. Release of epinephrine from the adrenal medulla and glucocorticoids from the adrenal cortex initiate the biological responses permitting the organism to cope with adverse psychological, physiological and environmental stressors. Following its massive release during stress, epinephrine must be restored to replenish cellular pools and sustain release to maintain the heightened awareness and sequelae of responses to re-establish homeostasis and ensure survival. 3. Epinephrine is regulated in part through its biosynthesis catalyzed by the final enzyme in the catecholamine pathway, phenylethanolamine N-methyltransferase (E.C. 2.1.1.28, PNMT). PNMT expression, in turn, is controlled through hormonal and neural stimuli, which exert their effects on gene transcription through protein stability. 4. The pioneering work of Julius Axelrod forged the path to our present understanding of how the stress hormone and neurotransmitter epinephrine, is regulated, in particular via its biosynthesis by PNMT.

Understanding stress through the genome

Stress-induced glucocorticoid hormones support coping with and adaptation to different stressors. They act to modulate gene expression in a tissue and stressor-specific manner through activation of corticosteroid receptors, which act as transcription factors. Here, a number of recent insights in gene regulation under the influence of glucocorticoids are discussed. Emphasis is put on distinct classes of target genes that may be defined, based on categorization of (combinations of) transcription factor binding sites in responsive genes. These categories depend on insights into different mechanisms of transcriptional regulation, such as transactivation vs transrepression, and high affinity vs low affinity hormone receptor response elements. It is argued that such classes, based on mechanistic understanding of transcription regulation, in combination with the availability of complete genomic sequences and expression data from different organs, may enhance our understanding of the way in which organisms deal with different forms of stress.

Identification of phenylethanolamine N-methyltransferase gene expression in stellate ganglia and its modulation by stress

Phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28) is the terminal enzyme of the catecholaminergic pathway converting noradrenaline to adrenaline. Although preferentially localized in adrenal medulla, evidence exists that PNMT activity and gene expression are also present in the rat heart, kidney, spleen, lung, skeletal muscle, thymus, retina and different parts of the brain. However, data concerning PNMT gene expression in sympathetic ganglia are still missing. In this study, our effort was focused on identification of PNMT mRNA and/or protein in stellate ganglia and, if present, testing the effect of stress on PNMT mRNA and protein levels in this type of ganglia. We identified both PNMT mRNA and protein in stellate ganglia of rats and mice, although in much smaller amounts compared with adrenal medulla. PNMT gene expression and protein levels were also increased after repeated stress exposure in stellate ganglia of rats and wild-type mice. Similarly to adrenal medulla, the immobilization-induced increase was probably regulated by glucocorticoids, as determined indirectly using corticotropin-releasing hormone knockout mice, where immobilization-induced increase of PNMT mRNA was suppressed. Thus, glucocorticoids might play an important role in regulation of PNMT gene expression in stellate ganglia under stress conditions.

Increases in preproenkephalin mRNA levels in the Syrian hamster: The influence of glucocorticoids is dependent on age and tissue

In adult hamsters, basal proenkephalin (Penk) gene expression in adrenals is independent of glucocorticoids and glucocorticoid receptor blockade, by RU 486, increases striatal preproenkephalin (PPenk) mRNA levels. However, glucocorticoids maintain both basal and induced Penk gene expression in rat adrenal (medulla) and striatum. This suggests species and tissue-specific differences in Penk gene regulation. Since studies show temporal coordination in Penk gene expression in developing hamster adrenal and striatum, we tested the hypothesis that increasing PPenk mRNA levels are dependent, while basal levels are independent of glucocorticoids in developing hamsters. To facilitate this study, we examined the influence of glucocorticoids on the temporal increases in developing hamster PPenk mRNA observed in adrenals between postnatal days 0 and 4 and in striatum between postnatal days 12 and 48. PPenk mRNA levels were determined in hamster pups after treatment with increasing doses of metyrapone (an 11beta hydroxylase inhibitor) or with the glucocorticoid receptor antagonist RU 486 +/- metyrapone between postnatal days 2 and 4. Levels were also determined 36 days after hypophysectomy at age 16-17 days. Although plasma glucocorticoid levels and/or the influence from glucocorticoids were reduced, only developmental increases in PPenk mRNA are influenced by glucocorticoids in hamster adrenals, while basal adrenal mRNA levels are unchanged. However, pituitary influence on striatal PPenk mRNA levels appears complex and may involve steroid and/or non-steroid factors. These results suggest that glucocorticoids regulate hamster Penk gene expression via a mechanism that varies with age and tissue and functions during the induction of the Penk gene and not to maintain basal gene expression. Possible mechanisms and species variation are discussed.

Genome-wide expression analysis of therapy-resistant tumors reveals SPARC as a novel target for cancer therapy

Overcoming resistance to chemotherapy and radiation therapy has been a difficult but important goal in the effort to cure cancer. We used gene-expression microarrays to identify differentially expressed genes involved in colorectal cancer resistance to chemotherapy and identified secreted protein, acidic and rich in cysteine (osteonectin) (SPARC) as a putative resistance-reversal gene by demonstrating low SPARC expression in refractory human MIP101 colon cancer cells. We were able to achieve restoration of their radiosensitivity and sensitivity to 5-fluorouracil and irinotecan by reexpression of SPARC in tumor xenografts. Moreover, treatment of mice with SPARC conferred increased sensitivity to chemotherapy and led to significant regression of xenografted tumors. The results show that modulation of SPARC expression affects colorectal cancer sensitivity to radiation and chemotherapy. SPARC-based gene or protein therapy may ameliorate the emergence of resistant clones and eradicate existing refractory clones and offers a novel approach to treating cancer.

Gene expression profiling of dexamethasone-treated RBL-2H3 cells: induction of anti-inflammatory molecules

Glucocorticoids are well known for their anti-inflammatory effect through the regulation of gene expression in many types of immune cells, including mast cells. However, the genes that are involved in suppression of mast cell-mediated inflammation by glucocorticoids have not been fully identified. Therefore, we examined the dexamethasone (Dex)-responsive genes in RBL-2H3 mast cells using a high-density oligonucleotide microarray technique. Gene expression profiling revealed that the antigen-induced up-regulation of pro-inflammatory factors, including monocyte chemoattractant protein-1, was markedly inhibited by 100 nM Dex. On the other hand, Dex treatment itself caused the substantial up-regulation of many genes, including phenylethanolamine-N-methyl transferase (PNMT) and cytokine-inducible SH2-containing protein (CISH), in the mast cells. The expression of these two genes significantly increased 6 h after Dex exposure and lasted for more than 24 h. Considering that PNMT is the rate-determining enzyme in epinephrine synthesis and that CISH is a suppressor of cytokine signaling, these Dex-responsive genes may be potential anti-inflammatory factors. Thus, gene expression profiling suggested that Dex might exert its anti-inflammatory effect through two pathways in mast cells: the suppression and induction of potentially pro- and anti-inflammatory factors, respectively.