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

Effects of acute and chronic exposures of fluoxetine on the Chinese fish, topmouth gudgeon Pseudorasbora parva

Fluoxetine is a selective serotonin reuptake inhibitor used as an antidepressant and has been frequently detected in aquatic environments. However, its effects in fish from Asia remain relatively less studied. In this study, the topmouth gudgeon Pseudorasbora parva was exposed to 0, 50, and 200 µg/L of fluoxetine for 4 h and 42 d. The effects of fluoxetine on biometrics were compared to biochemical endpoints indicative of stress in different fish tissues (brain, liver, gills and intestine) following exposures. In fish exposed for 42 d, lipid peroxidation endpoints were enhanced 80% in the liver and gills. Acetylcholinesterase (AChE) activity was increased 40% after exposure to 50 µg/L and 55% at 200 µg/L following 4 h exposure. In contrast AChE was increased 26% (at 50 µg/L) after 42 d of exposures. Enhanced ethoxyresorufin-O-deethylase activity (EROD) was detected only in fish exposed to 50 µg/L of fluoxetine for 4 h. The activity of α-glucosidase (α-Glu) was also induced (at 200 µg/L) after 4 h of exposure. After 4 h of exposure, the activities of proteases in the intestine were generally inhibited at 200 µg/L. Both 4 h and 42 d exposures resulted in an increased hepatosomatic index (HSI) but did not affect the condition factor (CF). Our results demonstrate that fluoxetine significantly altered biochemical endpoints in P. parva after acute exposure and the morphological changes in liver size were not observed until 42 d of exposure.

Perinatal hypoxia as a risk factor for psychopathology later in life: the role of dopamine and neurotrophins

Brain development is influenced by various prenatal, intrapartum, and postnatal events which may interact with genotype to affect the neural and psychophysiological systems related to emotions, specific cognitive functions (e.g., attention, memory), and language abilities and thereby heighten the risk for psychopathology later in life. Fetal hypoxia (intrapartum oxygen deprivation), hypoxia-related obstetric complications, and hypoxia during the early neonatal period are major environmental risk factors shown to be associated with an increased risk for later psychopathology. Experimental models of perinatal hypoxia/ischemia (PHI) showed that fetal hypoxia-a consequence common to many birth complications in humans-results in selective long-term disturbances of the dopaminergic systems that persist in adulthood. On the other hand, neurotrophic signaling is critical for pre- and postnatal brain development due to its impact on the process of neuronal development and its reaction to perinatal stress. The aim of this review is (a) to summarize epidemiological data confirming an association of PHI with an increased risk of a range of psychiatric disorders from childhood through adolescence to adulthood, (b) to present immunohistochemical findings on human autopsy material indicating vulnerability of the dopaminergic neurons of the human neonate to PHI that could predispose infant survivors of PHI to dopamine-related neurological and/or cognitive deficits in adulthood, and

The Effect of Perinatal Hypoxic/Ischemic Injury on Tyrosine Hydroxylase Expression in the Locus Coeruleus of the Human Neonate

We have previously shown that perinatal hypoxic/ischemic injury (HII) may cause selective vulnerability of the mesencephalic dopaminergic neurons of human neonate. In the present study, we investigated the effect of perinatal HII on the noradrenergic neurons of the locus coeruleus (LC) of the same sample. We studied immunohistochemically the expression of tyrosine hydroxylase (TH, first limiting enzyme for catecholamine synthesis) in LC neurons of 15 autopsied infants (brains collected from the Greek Brain Bank) in relation to the neuropathological changes of acute or chronic HII of the neonatal brain. Our results showed that perinatal HII appears to affect the expression of TH and the size of LC neurons of the human neonate. In subjects with neuropathological lesions consistent with abrupt/severe HII, intense TH immunoreactivity was found in almost all neurons of the LC. In most of the neonates with neuropathological changes of prolonged or older injury, however, reduction in cell size and a decrease or absence of TH staining were observed in the LC. Intense TH immunoreactivity was found in the LC of 3 infants of the latter group, who interestingly had a longer survival time and had been treated with anticonvulsant drugs. Based on our observations and in view of experimental evidence indicating that the reduction of TH-immunoreactive neurons occurring in the LC after perinatal hypoxic insults persists into adulthood, we suggest that a dysregulation of monoaminergic neurotransmission in critical periods of brain development in humans is likely to predispose the survivors of perinatal HII, in combination with genetic susceptibility, to psychiatric and/or neurological disorders later in life.

The human neurosecretory neurones under perinatal hypoxia: a quantitative immunohistochemical study of the supraoptic nucleus in autopsy material

In the rat, experimental manipulations that cause activation of the magnocellular neurosecretory neurones result in the synthesis, in addition to vasopressin (AVP) and oxytocin (OXY), of other neurotransmitters or peptides, including tyrosine hydroxylase (TH), the first and rate limiting enzyme for catecholamine biosynthesis. In the human neonate, our previous study showed that TH was selectively increased in AVP neurones of subjects that died from prolonged perinatal hypoxia. The purpose of the present study was to quantitatively investigate the expression of TH, AVP, OXY and neurophysin in magnocellular neurones of the human neonate in relation to the severity/duration of perinatal hypoxia, as estimated by neuropathological criteria. Autopsy was performed after obtaining parental written consent for diagnostic and research purposes. The intensity of the immunohistochemical reactions and the cellular/nuclear size were measured in the dorsolateral supraoptic nucleus using a computerised image analysis system. We showed that prolonged perinatal hypoxia resulted in the activation of the magnocellular neuroendocrine neurones of the human neonate, as indicated by their increased neuronal and nuclear size. OXY neurones appeared larger than the AVP ones at birth, possibly indicating an active role of foetal OXY during labour or even earlier. The gradual increase in the duration of the insult resulted in the reduction of intracellular AVP content, in parallel with a dramatic increase in the expression of TH, indicating a functional interaction of these peptides under neuronal activation. Ιsolated evidence in our series, obtained from an infant of a diabetic mother, raises the probability that in the case of hyperglycaemia the above pathogenetic mechanisms are diversified.

Vulnerability of the mesencephalic dopaminergic neurons of the human neonate to prolonged perinatal hypoxia: an immunohistochemical study of tyrosine hydroxylase expression in autopsy material

Experimental studies indicate that hypoxia to the fetus, a common occurrence in many birth complications in humans, results in long-term disturbances of the central dopaminergic (DA) systems that persist in adulthood. Because dysregulation of DA systems is involved in the pathophysiology of many neurological and psychiatric disorders, we investigated the effects of perinatal hypoxia on the mesencephalic DA neurons of the human neonate using immunohistochemistry. We studied the expression of tyrosine hydroxylase (TH), the first and rate-limiting enzyme in catecholamine synthesis, in substantia nigra, and ventral tegmental area of 18 neonates in relation to the age and severity/duration of hypoxic injury estimated by neuropathological criteria. In severe/abrupt perinatal hypoxia, intense TH staining was observed in substantia nigra, ventral tegmental area, and, surprisingly, in the nonpreganglionic Edinger-Westphal nucleus. In severe/prolonged hypoxia, there was a striking reduction or even absence of TH immunoreactivity in all the mesencephalic nuclei. These observations suggest that at early states of perinatal hypoxia, there is a massive increase in dopamine synthesis and release that is followed by feedback blockage of dopamine synthesis through inhibition of TH by the end product dopamine. Early dysregulation of DA neurotransmission could predispose infant survivors of severe perinatal hypoxia to dopamine-related neurological and/or cognitive deficits later in life.

Differential regulation of tyrosine hydroxylase by continuous and intermittent hypoxia

Although continuous hypoxia (CH) and intermittent hypoxia (IH) cause reduction in oxygen availability, organisms adapt to the effects of chronic CH whereas IH adversely impacts autonomic functions. Catecholamines are expressed both in the central and peripheral nervous systems and they play important roles in the regulation of cardio-respiratory functions during hypoxia. Tyrosine hydroxylase (TH) is the rate-limiting enzyme for catecholamine synthesis. Several studies have examined the effects of hypoxia on catecholamines by focusing on the regulation of TH. In this article, we present a brief overview of the impact of chronic CH and IH on TH expression, activity and the associated cellular mechanism(s).

Short-term hypoxia transiently increases dopamine β-hydroxylase immunoreactivity in glomus cells of the rat carotid body

Under long-term hypoxia, noradrenaline (NA) content in the carotid body (CB) increases, suggesting that NA plays an important role in CB chemotransduction. However, it is unknown whether short-term hypoxia upregulates NA biosynthesis in CB. Therefore, we examined dopamine β-hydroxylase (DBH) expression in the CB of rats exposed to hypoxia (10% O(2)) for 0 to 24 hr with immunoblotting and immunohistochemistry. Using immunoblotting, the signal intensity for DBH appeared to be the most intense in rats exposed to hypoxia for 12 hr. Using immunohistochemistry, DBH immunoreactivity was observed in the cytoplasm of some glomus cells and varicosities in controls and rats exposed to hypoxia for 6 hr. In rats exposed to hypoxia for 12 hr, DBH immunoreactive intensities in DBH-positive glomus cells were significantly higher compared with controls (p<0.05). In the CB of rats exposed to hypoxia for 18 and 24 hr, DBH immunoreactive intensities in DBH-positive glomus cells were significantly lower than that of rats exposed to hypoxia for 12 hr (p<0.05). These results demonstrate that DBH immunoreactivity is transiently increased in glomus cells by short-term hypoxia, suggesting that NA biosynthesis is transiently facilitated in glomus cells at an early stage of hypoxia.

Heme oxygenase-1 and chronic hypoxia

A myriad of changes are necessary to adapt to chronic hypoxemia. Key among these changes increases in arterial oxygen carrying capacity, ventilation and sympathetic activity. This requires the induction of several gene products many of which are regulated by the activity of HIF-1α, including HO-1. Induction of HO-1 during chronic hypoxia is necessary for the continued breakdown of heme for the enhanced production of hemoglobin and the increased respiratory and sympathetic responses. Several human HO-1 polymorphisms have been identified that can affect the expression or activity of HO-1. Associations between these polymorphisms and the prevalence of hypertension have recently been assessed in specific populations. There are major gaps in our understanding of the mechanisms of how HO-1 mediates changes in the activity of the hypoxia-sensitive chemosensors and whether HO-1 polymorphisms are an important factor in the integrated response to chronic hypoxia. Understanding how HO-1 mediates cardiorespiratory responses could provide important insights into clinical syndromes such as obstructive sleep apnea.

Beyond the antioxidant: the double life of vitamin C

When considering the history of vitamin C, and the names given to this molecule in early days, the Latin proverb nomen est omen suddenly comes to mind. Around 1920, when Casimir Funk introduced the term Vitamin C to indicate the nutritional factor necessary to prevent the pathological state known as scurvy, the nature of the active molecule was still unknown (Davies MB, Austin J, Partridge DA (1991) Vitamin C: Its chemistry and biochemistry. The Royal Society of Chemistry, Cambridge UK). Almost in the same years, Albert Szent-Giörgyi was striving to identify a new 6-carbon sugar he had obtained in crystal form from oranges, lemons, cabbage and adrenal glands. As humorously described by Szent-Giörgyi himself (Szent-Giörgyi A (1963) Lost in the twentieth century. Annu Rev Biochem 36:1-15), he intended to name this yet unknown carbohydrate "ignose". When this name was rejected by Sir Arthur Harden, editor of the Biochemical Journal, he suggested to name it "godnose", meaning that only God could know the real identity of the molecule. Obviously, also this choice was considered inappropriate by Harden, who suggested the plain name "hexuronic acid". Only later, when the structure of "hexuronic acid" had been completely elucidated, and biological tests performed by Swirbely identified this molecule as the anti-scurvy factor vitamin C, Szent-Giörgyi and Walter Norman Haworth decided to eventually name it ascorbic acid (Szent-Giörgyi A (1963) Lost in the twentieth century. Annu Rev Biochem 36:1-15). "Ascorbic" literally means "against scurvy", and scurvy is known to be mainly due to the inactivation of some important dioxygenases involved in the synthesis of a few key molecules, including different collagen forms (De Tullio MC (2004) How does ascorbic acid prevent scurvy? A survey of the nonantioxidant functions of vitamin C. In: Asard H, May J, Smirnoff N (eds) Vitamin C, its functions and biochemistry in animals and plants. Bios Scientific Publishers, Oxford, UK, pp. 159-172). All this has very little to do with the celebrated role of ascorbic acid (ASC) as an antioxidant. So, if the fate of ASC had to be found in its name, its role in the prevention of scurvy (i.e. beyond the antioxidant function) should be considered its main feature. But, in spite of more than 80 years of extensive research (34,424 hits in a PubMed query on January 6 2007), an unprecedented popularity among the general public, an estimated market of several billion dollars (Hancock RD, Viola R (2005) Improving the nutritional value of crops through enhancement of l-ascorbic acid (vitamin C) content: Rationale and biotechnological opportunities. J Agr Food Chem 53:5248-5257), we should honestly conclude that the fate of vitamin C is still in the first name it received, many years ago: we still ignore much of its actual relevance in cell metabolism, although we are progressively getting aware of the many facets of this fascinating molecule, and its direct involvement in the regulation of apparently unrelated pathways (Arrigoni O, De Tullio MC (2002) Ascorbic acid, much more than just an antioxidant. Biochim Biophys Acta 1569:1-9; De Tullio MC, Arrigoni O (2004) Hopes, disillusions and more hopes from vitamin C. Cell Mol Life Sci 61:209-219; Duarte TL, Lunec J (2005) When is an antioxidant not an antioxidant? A review of novel actions and reactions of vitamin C. Free Rad Res 39:671-686). Recent data on ASC involvement in cell signalling and gene expression open new perspectives, that will be presented and discussed in this chapter.

Adenosine A(2)A receptor but not HIF-1 mediates Tyrosine hydroxylase induction in hypoxic PC12 cells

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the biosynthesis of catecholamines released by oxygen-sensitive cells in response to hypoxic conditions. Adenosine is released in response to hypoxia in the central nervous system and CGS21680, an adenosine A(2)A receptor agonist, induces TH transcription. As we have previously demonstrated the A(2)A receptor-mediated induction of HIF-1 in macrophages and hepatocytes, we investigated the involvement of HIF-1 in the adenosine-mediated activation of TH expression. Exposure to adenosine or CGS21680 increased TH mRNA and protein levels in PC12 cells. Transcription of a reporter gene under the control of the wild type rat TH promoter was induced 3.5-fold in CGS21680-treated cells, but neither the mutation of the hypoxia responsive element in the TH promoter nor the co-transfection of a dominant negative of the HIF-1 beta subunit prevented the increase in transcription; furthermore, CGS21680 increased CREB binding activity but did not induce HIF-1 DNA binding activity or protein levels. To investigate whether HIF-1 was involved in the hypoxia-mediated induction of TH, PC12 cells were exposed to hypoxia in the presence of the A(2)A receptor antagonist ZM241385, which prevented hypoxia-dependent TH induction despite HIF-1 activation; in line with this finding, the inhibition of HIF-1 did not abolish TH induction in hypoxic PC12 cells. These results indicate that, under hypoxic conditions, TH (a key factor in systemic adaptation to reduced oxygen availability) is not regulated by HIF-1, the primary modulator of the response to hypoxia, but by the adenosine A(2)A receptor-mediated signalling pathway.

The Ventilatory Response to Hypoxia in Mammals: Mechanisms, Measurement, and Analysis

The respiratory response to hypoxia in mammals develops from an inhibition of breathing movements in utero into a sustained increase in ventilation in the adult. This ventilatory response to hypoxia (HVR) in mammals is the subject of this review. The period immediately after birth contains a critical time window in which environmental factors can cause long-term changes in the structural and functional properties of the respiratory system, resulting in an altered HVR phenotype. Both neonatal chronic and chronic intermittent hypoxia, but also chronic hyperoxia, can induce such plastic changes, the nature of which depends on the time pattern and duration of the exposure (acute or chronic, episodic or not, etc.). At adult age, exposure to chronic hypoxic paradigms induces adjustments in the HVR that seem reversible when the respiratory system is fully matured. These changes are orchestrated by transcription factors of which hypoxia-inducible factor 1 has been identified as the master regulator. We discuss the mechanisms underlying the HVR and its adaptations to chronic changes in ambient oxygen concentration, with emphasis on the carotid bodies that contain oxygen sensors and initiate the response, and on the contribution of central neurotransmitters and brain stem regions. We also briefly summarize the techniques used in small animals and in humans to measure the HVR and discuss the specific difficulties encountered in its measurement and analysis.

Magnesium deficiency causes loss of response to intermittent hypoxia in paraganglion cells

Magnesium deficiency is suggested to contribute to many age-related diseases. Hypoxia-inducible factor 1alpha (HIF-1alpha) is known to be a master regulator of hypoxic response. Here we show that hypomagnesemia suppresses reactive oxygen species (ROS)-induced HIF-1alpha activity in paraganglion cells of the adrenal medulla and carotid body. In PC12 cells cultured in the low magnesium medium and treated with cobalt chloride (CoCl(2)) or exposed to intermittent hypoxia, ROS-mediated HIF-1alpha activity was suppressed. This suppression was due to up-regulation of inhibitory PAS (Per/Arnt/Sim) domain protein (IPAS) that was caused by NF-kappaB activation, which resulted from ROS and calcium influx mainly through the T-type calcium channels. Induction of tyrosine hydroxylase, a target of HIF-1, by CoCl(2) injection was suppressed in the adrenal medulla of magnesium-deficient mice because of up-regulation of IPAS. Also in the carotid body of magnesium-deficient mice, CoCl(2) and chronic intermittent hypoxia failed to enhance the tyrosine hydroxylase expression. These results demonstrate that serum magnesium levels are a key determinant for ROS-induced hypoxic responses.

Chemical dissection of an essential redox switch in yeast

Saccharomyces cerevisiae responds to elevated levels of hydrogen peroxide in its environment via a redox relay system comprising the thiol peroxidase Gpx3 and transcription factor Yap1. In this signaling pathway, a central unresolved question is whether cysteine sulfenic acid modification of Gpx3 is required for Yap1 activation in cells. Here we report that cell-permeable chemical probes, which are selective for sulfenic acid, inhibit peroxide-dependent nuclear accumulation of Yap1, trap the Gpx3 sulfenic acid intermediate, and block formation of the Yap1-Gpx3 intermolecular disulfide directly in cells. In addition, we present electrostatic calculations that show cysteine oxidation is accompanied by significant changes in charge distribution, which might facilitate essential conformational rearrangements in Gpx3 during catalysis and intermolecular disulfide formation with Yap1.

Developmental plasticity of the hypoxic ventilatory response after perinatal hyperoxia and hypoxia

Both genetic and environmental factors influence the normal development of the respiratory control system. This review examines the role perinatal O2 plays in the development of normoxic breathing and the hypoxic ventilatory response in mammals. Hyperoxia and hypoxia elicit plasticity in respiratory control that is unique to development and may persist weeks to years after return to normoxia. Specifically, both hyperoxia and hypoxia during early postnatal development attenuate the adult hypoxic ventilatory response, but the underlying mechanisms for this plasticity differ. Hyperoxia attenuates the hypoxic ventilatory response through potentially life-long changes in carotid body function. Neonatal hypoxia appears to have short-term effects on carotid body function, but persistent changes in the hypoxic ventilatory response may instead reflect changes in respiratory mechanics or related neural pathways. Overall, it appears that a relatively narrow range of environmental O2 is consistent with "normal" postnatal respiratory control development, predisposing animals to potentially maladaptive plasticity in the face of disease or atypical environmental conditions.

Tyrosine hydroxylase expression and activity in the rat brain: differential regulation after long-term intermittent or sustained hypoxia

Tyrosine hydroxylase, a hypoxia-regulated gene, may be involved in tissue adaptation to hypoxia. Intermittent hypoxia, a characteristic feature of sleep apnea, leads to significant memory deficits, as well as to cortex and hippocampal apoptosis that are absent after sustained hypoxia. To examine the hypothesis that sustained and intermittent hypoxia induce different catecholaminergic responses, changes in tyrosine hydroxylase mRNA, protein expression, and activity were compared in various brain regions of male rats exposed for 6 h, 1 day, 3 days, and 7 days to sustained hypoxia (10% O2), intermittent hypoxia (alternating room air and 10% O2), or normoxia. Tyrosine hydroxylase activity, measured at 7 days, increased in the cortex as follows: sustained > intermittent > normoxia. Furthermore, activity decreased in the brain stem and was unchanged in other brain regions of sustained hypoxia-exposed rats, as well as in all regions from animals exposed to intermittent hypoxia, suggesting stimulus-specific and heterotopic catecholamine regulation. In the cortex, tyrosine hydroxylase mRNA expression was increased, whereas protein expression remained unchanged. In addition, significant differences in the time course of cortical Ser40tyrosine hydroxylase phosphorylation were present in the cortex, suggesting that intermittent and sustained hypoxia-induced enzymatic activity differences are related to different phosphorylation patterns. We conclude that long-term hypoxia induces site-specific changes in tyrosine hydroxylase activity and that intermittent hypoxia elicits reduced tyrosine hydroxylase recruitment and phosphorylation compared with sustained hypoxia. Such changes may not only account for differences in enzyme activity but also suggest that, with differential regional brain susceptibility to hypoxia, recruitment of different mechanisms in response to hypoxia will elicit region-specific modulation of catecholamine response.

Comparative gene expression profile of mouse carotid body and adrenal medulla under physiological hypoxia

The carotid body (CB) is an arterial chemoreceptor, bearing specialized type I cells that respond to hypoxia by closing specific K+ channels and releasing neurotransmitters to activate sensory axons. Despite having detailed information on the electrical and neurochemical changes triggered by hypoxia in CB, the knowledge of the molecular components involved in the signalling cascade of the hypoxic response is fragmentary. This study analyses the mouse CB transcriptional changes in response to low PO2 by hybridization to oligonucleotide microarrays. The transcripts were obtained from whole CBs after mice were exposed to either normoxia (21% O2), or physiological hypoxia (10% O2) for 24 h. The CB transcriptional profiles obtained under these environmental conditions were subtracted from the profile of control non-chemoreceptor adrenal medulla extracted from the same animals. Given the common developmental origin of these two organs, they share many properties but differ specifically in their response to O2. Our analysis revealed 751 probe sets regulated specifically in CB under hypoxia (388 up-regulated and 363 down-regulated). These results were corroborated by assessing the transcriptional changes of selected genes under physiological hypoxia with quantitative RT-PCR. Our microarray experiments revealed a number of CB-expressed genes (e.g. TH, ferritin and triosephosphate isomerase) that were known to change their expression under hypoxia. However, we also found novel genes that consistently changed their expression under physiological hypoxia. Among them, a group of ion channels show specific regulation in CB: the potassium channels Kir6.1 and Kcnn4 are up-regulated, while the modulatory subunit Kcnab1 is down-regulated by low PO2 levels.

Urocortin 2 induces tyrosine hydroxylase phosphorylation in PC12 cells

Urocotins (Ucns) are newly discovered members of the corticotropin-releasing factor (CRF) neuropeptide family. Ucn 2 is expressed in the adrenal medulla, and its receptor, CRF2 receptor, is also expressed in the adrenal gland. To predict the physiological significance of Ucn 2 expression in the adrenal medulla, we examined the effects of Ucn 2 on catecholamine secretion and intracellular signaling using PC12 cells, a rat pheochromocytoma cell line. PC12 cells were found to express CRF2 receptor, but not CRF1 receptor. Treatment with Ucn 2 increased noradrenaline secretion and induced phosphorylation of PKA and Erk1/2. Tyrosine hydroxylase (TH), a rate-limiting enzyme for catecholamine synthesis, was also phosphorylated by Ucn 2. Pretreatment with a PKA inhibitor blocked Ucn 2-induced NA secretion, and Erk1/2 and TH phosphorylation. Pretreatment with a MEK inhibitor did not block Ucn 2-induced noradrenaline secretion or PKA phosphorylation, although TH phosphorylation was blocked. Thus, Ucn 2 induces noradrenaline secretion and TH phosphorylation through the PKA pathway and the PKA-Erk1/2 pathway, respectively. These results suggest Ucn 2 in the adrenal gland may be involved in the regulation of catecholamine release and synthesis.