Comparison of circadian expression of tryptophan hydroxylase isoform mRNAs in the rat pineal gland using real-time PCR

Influence of photoperiod variations on the mRNA expression pattern of melatonin bio-synthesizing enzyme genes in the pineal organ and retina: A study in relation to the serum melatonin profile in the tropical carp Catla catla

Surface-dwelling C. catla were exposed to different photoperiods (8L:16D, 12L:12D, 12D:12L and 16L:8D) and the mRNA level profile of enzymes involved in melatonin synthesis was evaluated in the pineal gland and retina. Furthermore, a comparative analysis of the serum melatonin profile with the mRNA level was also performed. The results indicated diurnal variations in the transcripts of tph1, aanat and hiomt in the pineal organ and retina, and these variations change with the change in lighting regime. The serum melatonin profile showed rhythmicity in the natural photoperiod, but the serum melatonin level increased proportionally with increasing daylength. In short photoperiods, the peak value (though lower than in long photoperiods) of melatonin maintains a longer duration in serum. Moreover, the comparative analysis revealed a similar profile of mRNA of pineal aanat1 and aanat2 with serum melatonin under the same lighting conditions. This indicates that serum melatonin is produced by the pineal gland. Our results specify the importance of day length and the timing of onset or offset of the dark for maintaining the oscillating levels of serum melatonin and mRNA levels of melatonin biosynthesizing enzyme genes in the pineal organ and retina as well. The findings in this study highlight the distinctive pattern of mRNA levels in the pineal organ and retina under different photoperiods. The pineal melatonin biosynthesizing enzyme genes showed a similar pattern with serum melatonin levels while the retinal genes changed dramatically with photoperiod. We also revealed a light-dependent transcriptional regulation of pineal aanat genes in C. catla. Moreover, our results suggest that ALAN and skyglow can influence the levels of serum melatonin and its biosynthesis, resulting in desynchronization of the entire biological clock as well as the overall physiology of the animal.

Blast Exposure Dysregulates Nighttime Melatonin Synthesis and Signaling in the Pineal Gland: A Potential Mechanism of Blast-Induced Sleep Disruptions

Blast-induced traumatic brain injury (bTBI) frequently results in sleep-wake disturbances. However, limited studies have investigated the molecular signaling mechanisms underlying these sleep disturbances, and potentially efficacious therapies are lacking. We investigated the levels of melatonin and genes involved in melatonin synthesis pathway in the pineal glands of Sprague Dawley rats exposed to single and tightly coupled repeated blasts during the night and daytime. Rats were exposed to single and tightly coupled repeated blasts using an advanced blast simulator. The plasma, cerebrospinal fluid (CSF), and pineal gland were collected at 6 h, 24 h, or 1 month postblast at two different time points: one during the day (1000 h) and one at night (2200 h). Differential expressions of genes involved in pineal melatonin synthesis were quantified using quantitative real-time polymerase chain reaction (qRT-PCR). Plasma and CSF melatonin levels were assessed using a commercial melatonin ELISA kit. The plasma and CSF melatonin levels showed statistically significant decreases at 6 h and 24 h in the blast-exposed rats euthanized in the night (in dim light), with no significant alterations noted in rats euthanized in the morning (daylight) at all three-time points. Blast-exposed rats showed statistically significant decreases in Tph1, Aanat, Asmt, and Mtnr1b mRNA levels, along with increased Tph2 mRNA, in the pineal gland samples collected at night at 6 h and 24 h. No significant changes in the mRNA levels of these genes were noted at 1 month. These findings imply that the melatonin circadian rhythm is disrupted following blast exposure, which may be a factor in the sleep disturbances that blast victims frequently experience.

The role of melatonin and Tryptophan-5-hydroxylase-1 in different abiotic stressors in Apis cerana cerana

Tryptophan-5-hydroxylase-1 (T5H-1) is the rate-limiting enzyme in the biosynthesis of serotonin, which is involved in the biosynthesis of melatonin (Mel). Mel, a biological hormone, plays crucial roles in stressors tolerance, such as cold, hot, Ultraviolet (UV) and pesticide tolerance. However, the direct correlation between T5H-1 and Mel and the underlying mechanism in organisms remains elusive. Mel-mediated cold tolerance was studied extensively in plants and somewhat in insects, including bees. The present study isolated the Mel synthesis gene T5H-1 from Apis cerana cerana for the first time. qRT-PCR analysis indicated that AccT5H-1 played vital roles during some adverse conditions, including 4 °C, 8 °C, 10 °C, 45 °C, UV, cyhalothrin, abamectin, paraquat and bifenthrin exposure. Knockdown of AccT5H-1 using RNA interference (RNAi) technology upregulated most antioxidant genes. Additionally, an enzyme activity assay revealed higher contents of Malondialdehyde (MDA) and Hydrogen peroxide (H₂O₂), lower content of Vitamin C (VC), and higher activities of Glutathione S-transferase (GST), Superoxide dismutase (SOD), Catalase (CAT) and Peroxidase (POD) in the AccT5H-1 silenced group than the control group. These results suggest that AccT5H-1 is involved in the response to different oxidative stressors in A. cerana cerana. The survival rate of A. cerana cerana exposed to low temperature treatment revealed that the optimal concentration of Mel in the diet was 10 µg/mL. We also found that the antioxidant enzyme (GST, SOD, POD and CAT) concentrations at 10 µg/mL Mel increased to different degrees, and the content of oxidizing substances (MDA and H₂O₂) decreased, the content of VC increased, and the content of substances that promote cold resistance (glycerol and glycogen) increased. Mel increased the resistance of A. cerana cerana exposed to low temperatures. The expression of AccT5H-1 decreased after the feeding of exogenous Mel to bees. These results provide a reference for other insect studies on Mel and T5H-1.

Dysregulation of Circadian Rhythms in Autism Spectrum Disorders

Background:

The alterations in neurological and neuroendocrine functions observed in the autism spectrum disorder (ASD) involves environmentally dependent dysregulation of neurodevelopment, in interaction with multiple coding gene defects. Disturbed sleep-wake patterns, as well as abnormal melatonin and glucocorticoid secretion, show the relevance of an underlying impairment of the circadian timing system to the behavioral phenotype of ASD. Thus, understanding the mechanisms involved in the circadian dysregulation in ASD could help to identify early biomarkers to improve the diagnosis and therapeutics as well as providing a significant impact on the lifelong prognosis.

Objective:

In this review, we discuss the organization of the circadian timing system and explore the connection between neuroanatomic, molecular, and neuroendocrine responses of ASD and its clinical manifestations. Here we propose interconnections between circadian dysregulation, inflammatory baseline and behavioral changes in ASD. Taking into account, the high relevancy of melatonin in orchestrating both circadian timing and the maintenance of physiological immune quiescence, we raise the hypothesis that melatonin or analogs should be considered as a pharmacological approach to suppress inflammation and circadian misalignment in ASD patients.

Strategy:

This review provides a comprehensive update on the state-of-art of studies related to inflammatory states and ASD with a special focus on the relationship with melatonin and clock genes. The hypothesis raised above was analyzed according to the published data.

Conclusion:

Current evidence supports the existence of associations between ASD to circadian dysregulation, behavior problems, increased inflammatory levels of cytokines, sleep disorders, as well as reduced circadian neuroendocrine responses. Indeed, major effects may be related to a low melatonin rhythm. We propose that maintaining the proper rhythm of the circadian timing system may be helpful to improve the health and to cope with several behavioral changes observed in ASD subjects.

Targeted Manipulation of Brain Serotonin: RNAi-Mediated Knockdown of Tryptophan Hydroxylase 2 in Rats

Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the biosynthesis of the biogenic monoamine serotonin (5-hydroxytryptamine, 5-HT). Two existing TPH isoforms are responsible for the generation of two distinct serotonergic systems in vertebrates. TPH1, predominantly expressed in the gastrointestinal tract and pineal gland, mediates 5-HT biosynthesis in non-neuronal tissues, while TPH2, mainly found in the raphe nuclei of the brain stem, is accountable for the production of 5-HT in the brain. Neuronal 5-HT is a key regulator of mood and behavior and its deficiency has been implicated in a variety of neuropsychiatric disorders, e.g., depression and anxiety. To gain further insights into the complexity of central 5-HT modulations of physiological and pathophysiological processes, a new transgenic rat model, allowing an inducible gene knockdown of Tph2, was established based on doxycycline-inducible shRNA-expression. Biochemical phenotyping revealed a functional knockdown of Tph2 mRNA expression following oral doxycycline administration, with subsequent reductions in the corresponding levels of TPH2 enzyme expression and activity. Transgenic rats showed also significantly decreased tissue levels of 5-HT and its degradation product 5-Hydroxyindoleacetic acid (5-HIAA) in the raphe nuclei, hippocampus, hypothalamus, and cortex, while peripheral 5-HT concentrations in the blood remained unchanged. In summary, this novel transgenic rat model allows inducible manipulation of 5-HT biosynthesis specifically in the brain and may help to elucidate the role of 5-HT in the pathophysiology of affective disorders.

Homeobox genes in melatonin-producing pinealocytes: Otx2 and Crx act to promote hormone synthesis in the mature rat pineal gland

Homeobox genes encode transcription factors that regulate developmental processes; however, in the pineal gland, a neuroendocrine organ responsible for nocturnal melatonin synthesis, expression of the homeobox genes Otx2 (orthodenticle homeobox 2) and Crx (cone-rod homeobox) persists postnatally. We here show that OTX2 and CRX are exclusively present in melatonin-producing pinealocytes of the rat pineal gland. To understand the roles of Otx2 and Crx in the mature pineal gland, we used siRNA technology in cultured rat pinealocytes with the nocturnal situation mimicked by adding norepinephrine to the culture media. siRNA-induced knockdown of Otx2 was found to reduce expression levels of the enzymes involved in melatonin synthesis at both transcript and protein levels. Similar results were obtained when knocking down Crx. Knocking down Otx2 and Crx simultaneously produced an even larger reduction in both transcript and protein levels of the melatonin-producing enzymes and also reduced the levels of melatonin released to the culture media. These results suggest that Otx2 and Crx, both alone and in combination, act to control pineal melatonin synthesis.

Riding the Rhythm of Melatonin Through Pregnancy to Deliver on Time

Pregnancy is influenced by the circadian ("circa" or approximately; diēm or day) system, which coordinates physiology and behavior with predictable daily changes in the environment such as light/dark cycles. For example, most species deliver around a particular time of day. In mammals, circadian rhythms are controlled by the master circadian pacemaker, the suprachiasmatic nucleus. One key way that the suprachiasmatic nucleus coordinates circadian rhythms throughout the body is by regulating production of the sleep-promoting hormone melatonin. Serum melatonin concentration, which peaks at night and is suppressed during the day, is one of the best biological indicators of circadian timing. Circadian misalignment causes maternal disturbances in the temporal organization of many physiological processes including melatonin synthesis, and these disturbances of the circadian system have been linked to an increased risk for pregnancy complications. Here, we review evidence that melatonin helps regulate the maternal and fetal circadian systems and the timing of birth. Finally, we discuss the potential for melatonin-based therapeutic strategies to alleviate poor pregnancy outcomes such as preeclampsia and preterm birth.

Updates on the biology of serotonin and tryptophan hydroxylase

PURPOSE OF REVIEW

To summarize the most recent findings relevant to the biology of serotonin (5-hydroxytryptamine; 5-HT) and the enzyme tryptophan hydroxylase (TPH) in human gastrointestinal disease.

RECENT FINDINGS

Serotonin is synthesized in the central nervous system (CNS) and the gastrointestinal tract where it is secreted from enteroendocrine cells. Its biosynthesis is regulated by two isoforms of the enzyme TPH of which TPH1 is localized predominantly in gastrointestinal enteroendocrine cells. Serotonin activates the peristaltic reflexes, regulates gastrointestinal motility, and has a role in intestinal inflammation. Inhibition of TPH with novel molecules represents a new pharmacological tool in the successful management of carcinoid syndrome in patients with gastrointestinal neuroendocrine tumors (GI-NETs). Certain 5-HT receptor subtype agonists and antagonists are useful in the treatment of functional gastrointestinal disorders.

SUMMARY

The gastrointestinal tract is the largest storage organ for serotonin where its biosynthesis is regulated by TPH1. It has several important functions in gastrointestinal motility, secretion, and inflammation. Furthermore, TPH represents a target for inhibitory pharmacological therapy of serotonin access states such as the carcinoid syndrome.

Vitamin D hormone regulates serotonin synthesis. Part 1: relevance for autism

Serotonin and vitamin D have been proposed to play a role in autism; however, no causal mechanism has been established. Here, we present evidence that vitamin D hormone (calcitriol) activates the transcription of the serotonin-synthesizing gene tryptophan hydroxylase 2 (TPH2) in the brain at a vitamin D response element (VDRE) and represses the transcription of TPH1 in tissues outside the blood-brain barrier at a distinct VDRE. The proposed mechanism explains 4 major characteristics associated with autism: the low concentrations of serotonin in the brain and its elevated concentrations in tissues outside the blood-brain barrier; the low concentrations of the vitamin D hormone precursor 25-hydroxyvitamin D [25(OH)D3]; the high male prevalence of autism; and the presence of maternal antibodies against fetal brain tissue. Two peptide hormones, oxytocin and vasopressin, are also associated with autism and genes encoding the oxytocin-neurophysin I preproprotein, the oxytocin receptor, and the arginine vasopressin receptor contain VDREs for activation. Supplementation with vitamin D and tryptophan is a practical and affordable solution to help prevent autism and possibly ameliorate some symptoms of the disorder.

Melatonin in the mammalian olfactory bulb

Melatonin is a neurohormone associated with circadian rhythms. A diurnal rhythm in olfactory sensitivity has been previously reported and melatonin receptor mRNAs have been observed in the olfactory bulb, but the effects of melatonin in the olfactory bulb have not been explored. First, we corroborated data from a previous study that identified melatonin receptor messenger RNAs in the olfactory bulb. We then investigated whether melatonin treatment would affect cells in the olfactory bulbs of rats. Using a combination of polymerase chain reaction (PCR), quantitative PCR (qPCR), cell culture, and electrophysiology, we discovered that melatonin receptors and melatonin synthesis enzymes were present in the olfactory bulb and we observed changes in connexin43 protein, GluR1 mRNA, GluR2 mRNA, Per1 mRNA, Cry2 mRNA, and K(+) currents in response to 2-iodomelatonin. Via qPCR, we observed that messenger RNAs encoding melatonin receptors and melatonin biosynthesis enzymes fluctuated in the olfactory bulb across 24h. Together, these data show that melatonin receptors are present in the olfactory bulb and likely affect olfactory function. Additionally, these data suggest that melatonin may be locally synthesized in the olfactory bulb.

IL-13-mediated immunological control of enterochromaffin cell hyperplasia and serotonin production in the gut

Enterochromaffin (EC) cells in the gastrointestinal (GI) mucosa are the main source of serotonin (5-hydroxytryptamine (5-HT)) in the body. 5-HT is implicated in the pathophysiology of many GI disorders including functional and inflammatory bowel disorders. Herein we studied the role of interleukin 13 (IL-13) in EC cell biology by utilizing IL-13-deficient (IL-13-/-) mice and BON cells (a model for human EC cells). The numbers of EC cells and 5-HT amount were significantly lower in enteric parasite, Trichuris muris-infected IL-13-/- mice compared with the wild-type mice. This was accompanied with increased parasite burden in IL-13-/- mice. Treatment of naive and infected IL-13-/- mice with IL-13 increased EC cell numbers and 5-HT amount. BON cells expressed IL-13 receptor and in response to IL-13 produced more 5-HT. These results provide novel information on IL-13-mediated immunological control of 5-HT in the gut, which may ultimately lead to improved therapeutic opportunities in various GI disorders.

Neuroimmune endocrine effects of antidepressants

Antidepressant pharmacotherapy is to date the most often used treatment for depression, but the exact mechanism of action underlying its therapeutic effect is still unclear. Many theories have been put forward to account for depression, as well as antidepressant activity, but none of them is exhaustive. Neuroimmune endocrine impairment is found in depressed patients; high levels of circulating corticosteroids along with hyperactivation of the immune system, high levels of proinflammatory cytokines, low levels of melatonin in plasma and urine, and disentrainment of circadian rhythms have been demonstrated. Moreover, antidepressant treatment seems to correct or at least to interfere with these alterations. In this review, we summarize the complex neuroimmune endocrine and chronobiological alterations found in patients with depression and how these systems interact with each other. We also explain how antidepressant therapy can modify these systems, along with some possible mechanisms of action shown in animal and human models.

Development by environment interactions controlling tryptophan hydroxylase expression

Tryptophan hydroxylase is the rate-limiting enzyme in the biosynthesis of serotonin (5-hydroxytryptamine; 5-HT). Two isoforms of tryptophan hydroxylase, derived from different genes, tph1 and tph2, have been identified. The tph1 isoform is expressed in peripheral tissues, whereas tph2 is brain and neuron-specific. Recent studies suggest that tph2 expression and brain serotonin turnover are upregulated in depressed suicide patients, and drug-free depressed patients, respectively. Increased tph2 expression could result from genetic influences, early life developmental influences, adverse experience during adulthood, or interactions among these factors. Studies in rodents support the hypothesis that interactions between early life developmental influences and adverse experience during adulthood play an important role in determining tph2 expression. In this review, we highlight the evidence for the effects of adverse early life experience and stressful experience during adulthood on both tph1 and tph2 expression.

Transient gastric irritation in the neonatal rats leads to changes in hypothalamic CRF expression, depression- and anxiety-like behavior as adults

AIMS

A disturbance of the brain-gut axis is a prominent feature in functional bowel disorders (such as irritable bowel syndrome and functional dyspepsia) and psychological abnormalities are often implicated in their pathogenesis. We hypothesized that psychological morbidity in these conditions may result from gastrointestinal problems, rather than causing them.

METHODS

Functional dyspepsia was induced by neonatal gastric irritation in male rats. 10-day old male Sprague-Dawley rats received 0.1% iodoacetamide (IA) or vehicle by oral gavage for 6 days. At 8-10 weeks of age, rats were tested with sucrose preference and forced-swimming tests to examine depression-like behavior. Elevated plus maze, open field and light-dark box tests were used to test anxiety-like behaviors. ACTH and corticosterone responses to a minor stressor, saline injection, and hypothalamic CRF expression were also measured.

RESULTS

Behavioral tests revealed changes of anxiety- and depression-like behaviors in IA-treated, but not control rats. As compared with controls, hypothalamic and amygdaloid CRF immunoreactivity, basal levels of plasma corticosterone and stress-induced ACTH were significantly higher in IA-treated rats. Gastric sensory ablation with resiniferatoxin had no effect on behaviors but treatment with CRF type 1 receptor antagonist, antalarmin, reversed the depression-like behavior in IA-treated rats

CONCLUSIONS

The present results suggest that transient gastric irritation in the neonatal period can induce a long lasting increase in depression- and anxiety-like behaviors, increased expression of CRF in the hypothalamus, and an increased sensitivity of HPA axis to stress. The depression-like behavior may be mediated by the CRF1 receptor. These findings have significant implications for the pathogenesis of psychological co-morbidity in patients with functional bowel disorders.

Association analysis of TPH2, 5-HT2A, and 5-HT6 with executive function in a young Chinese Han population

The 5-hydroxytryptamine (5-HT) system is widely distributed in the central nervous system. A growing body of evidence has suggested that the neurotransmitter system is implicated in the functions of the prefrontal cortex. So far, several studies have revealed that some functional genetic variants in TPH2, 5-HT2A, and 5-HT6 genes are possibly related to executive function. To investigate the potential influences of TPH2, 5-HT2A, and 5-HT6 on the components of executive function, the authors performed a population-based study with standard cognitive paradigms in a young Chinese Han group. The results indicated that -703 G/T polymorphism of TPH2 was associated with the performance of response inhibition (p = .002) and the T allele carriers (TT and GT) had fewer errors than the noncarriers (GG) did in the response inhibition test. Furthermore, there were no significant associations of the T102C in 5-HT2A and T267C in 5-HT6 with the components of executive function after correcting for multiple tests (p > .05). The present study suggests that TPH2 contributes distinctively to the inhibition domain of executive function, whereas 5-HT2A and 5-HT6 show no striking effects on executive function in the Chinese Han population.

Search for genetic markers and functional variants involved in the development of opiate and cocaine addiction and treatment

Addiction to opiates and illicit use of psychostimulants is a chronic, relapsing brain disease that, if left untreated, can cause major medical, social, and economic problems. This article reviews recent progress in studies of association of gene variants with vulnerability to develop opiate and cocaine addictions, focusing primarily on genes of the opioid and monoaminergic systems. In addition, we provide the first evidence of a cis-acting polymorphism and a functional haplotype in the PDYN gene, of significantly higher DNA methylation rate of the OPRM1 gene in the lymphocytes of heroin addicts, and significant differences in genotype frequencies of three single-nucleotide polymorphisms of the P-glycoprotein gene (ABCB1) between "higher" and "lower" methadone doses in methadone-maintained patients. In genomewide and multigene association studies, we found association of several new genes and new variants of known genes with heroin addiction. Finally, we describe the development and application of a novel technique: molecular haplotyping for studies in genetics of drug addiction.

Melatonin: a multitasking molecule

Melatonin (N-acetyl-5-methoxytryptamine) has revealed itself as an ubiquitously distributed and functionally diverse molecule. The mechanisms that control its synthesis within the pineal gland have been well characterized and the retinal and biological clock processes that modulate the circadian production of melatonin in the pineal gland are rapidly being unravelled. A feature that characterizes melatonin is the variety of mechanisms it employs to modulate the physiology and molecular biology of cells. While many of these actions are mediated by well-characterized, G-protein coupled melatonin receptors in cellular membranes, other actions of the indole seem to involve its interaction with orphan nuclear receptors and with molecules, for example calmodulin, in the cytosol. Additionally, by virtue of its ability to detoxify free radicals and related oxygen derivatives, melatonin influences the molecular physiology of cells via receptor-independent means. These uncommonly complex processes often make it difficult to determine specifically how melatonin functions to exert its obvious actions. What is apparent, however, is that the actions of melatonin contribute to improved cellular and organismal physiology. In view of this and its virtual absence of toxicity, melatonin may well find applications in both human and veterinary medicine.

Physiology and pharmacology of melatonin in relation to biological rhythms

Melatonin is an evolutionarily conserved molecule that serves a time-keeping function in various species. In vertebrates, melatonin is produced predominantly by the pineal gland with a marked circadian rhythm that is governed by the central circadian pacemaker (biological clock) in the suprachiasmatic nuclei of the hypothalamus. High levels of melatonin are normally found at night, and low levels are seen during daylight hours. As a consequence, melatonin has been called the "darkness hormone". This review surveys the current state of knowledge regarding the regulation of melatonin synthesis, receptor expression, and function. In particular, it addresses the physiological, pathological, and therapeutic aspects of melatonin in humans, with an emphasis on biological rhythms.

Serotonergic changes produced by repeated exposure to forced swimming: correlation with behavior

Repeated forced swim resulted in a decrease in the concentrations of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid in the hypothalamus and amygdala 24 h after the second swim session. This stressor also increased the mRNA levels for tryptophan hydroxylase-2, the rate-limiting enzyme in neuronal 5-HT synthesis, and 5-HT transporter in the midbrain as well as 5-HT1A receptor in the frontal cortex. Some of these serotonergic changes may be involved in the mechanisms of a depressive-like behavior induced by a stress of repeated swim in these animals.

Posttranslational regulation of TPH1 is responsible for the nightly surge of 5-HT output in the rat pineal gland

Serotonin (5-hydroxytryptamine, 5-HT), a precursor for melatonin production, is produced abundantly in the pineal gland of all vertebrate animals. The synthesis of 5-HT in the pineal gland is rate limited by tryptophan hydroxylase 1 (TPH1) whose activity displays a twofold increase at night. Earlier studies from our laboratory demonstrate that pineal 5-HT secretion exhibits dynamic circadian rhythms with elevated levels during the early night, and that the increase is controlled by adrenergic signaling at night. In this study, we report that (a) 5-HT total output from the pineal gland and TPH1 protein levels both display diurnal rhythms with a twofold increase at night; (b) stimulation of cAMP signaling elevates 5-HT output in vivo; (c) 5-HT total output and TPH1 protein content in rat pineal gland are both acutely inhibited by light exposure at night. Consistent with these findings, molecular analysis of TPH1 protein revealed that (a) TPH1 is phosphorylated at the serine 58 in vitro and in the night pineal gland; and (b) phosphorylation of TPH1 at this residue is required for cAMP-enhanced TPH1 protein stability. These data support the model that increased nocturnal 5-HT synthesis in the pineal gland is mediated by the phosphorylation of TPH1 at the serine 58, which elevates the TPH1 protein content and activity at night.

The existence of a local 5-hydroxytryptaminergic system in peripheral arteries

BACKGROUND AND PURPOSE

5-HT is a vasoconstrictor exhibiting enhanced effects in systemic arteries from subjects with cardiovascular disease. The effect of endogenous 5-HT on arteries is controversial, because the concentration of free circulating 5-HT is low and a 5-hydroxytryptaminergic system has not been identified in peripheral arteries. We hypothesized that a local 5-hydroxytryptaminergic system (including 5-HT synthesis, metabolism, uptake and release) with physiological function exists in peripheral arteries.

EXPERIMENTAL APPROACH

The presence of key components of a 5-hydroxytryptaminergic system in rat aorta and superior mesenteric artery was examined using western blot analyses, immunohistochemistry and immunocytochemistry. The function of the rate-limiting enzyme in 5-HT biosynthesis, tryptophan hydroxylase (TPH), and 5-HT transporter was tested by measuring enzyme activity and 5-HT uptake, respectively. Isometric contraction of arterial strips was used to demonstrate the function of released endogenous 5-HT in arterial tissues.

KEY RESULTS

mRNA for TPH-1 was present in arteries, with low levels of TPH protein and TPH activity. Expression and function of MAO A (5-HT metabolizing enzyme) was supported by immunohistochemistry, western analyses and the elevation of concentrations of 5-hydroxyindoleacetic acid (5-HT metabolite) after exposure to exogenous 5-HT. The 5-HT transporter was localized to the plasma membrane of freshly isolated aortic smooth muscle cells. Peripheral arteries actively took up 5-HT in a time-dependent and 5-HT transporter-dependent manner. The 5-HT transporter substrate, (+)-fenfluramine, released endogenous 5-HT from peripheral arteries, which potentiated noradrenaline-induced arterial contraction.

CONCLUSIONS AND IMPLICATIONS

This study revealed the existence of a local 5-hydroxytryptaminergic system in peripheral arteries.

Glucocorticoid modulation of tryptophan hydroxylase-2 protein in raphe nuclei and 5-hydroxytryptophan concentrations in frontal cortex of C57/Bl6 mice

Considerable attention has focused on regulation of central tryptophan hydroxylase (TPH) activity and protein expression. At the time of these earlier studies, it was thought that there was a single central TPH isoform. However, with the recent identification of TPH2, it becomes important to distinguish between regulatory effects on the protein expression and activity of the two isoforms. We have generated a TPH2-specific polyclonal antiserum (TPH2-6361) to study regulation of TPH2 at the protein level and to examine the distribution of TPH2 expression in rodent and human brain. TPH2 immunoreactivity (IR) was detected throughout the raphe nuclei, in lateral hypothalamic nuclei and in the pineal body of rodent and human brain. In addition, a prominent TPH2-IR fiber network was found in the human median eminence. We recently reported that glucocorticoid treatment of C57/Bl6 mice for 4 days markedly decreased TPH2 messenger RNA levels in the raphe nuclei, whereas TPH1 mRNA was unaffected. The glucocorticoid-elicited inhibition of TPH2 gene expression was blocked by co-administration of the glucocorticoid receptor antagonist mifepristone (RU-486). Using TPH2-6361, we have extended these findings to show a dose-dependent decrease in raphe TPH2 protein levels in response to 4 days of treatment with dexamethasone; this effect was blocked by co-administration of mifepristone. Moreover, the glucocorticoid-elicited inhibition of TPH2 was functionally significant: serotonin synthesis was significantly reduced in the frontal cortex of glucocorticoid-treated mice, an effect that was blocked by mifepristone co-administration. This study provides further evidence for the glucocorticoid regulation of serotonin biosynthesis via inhibition of TPH2 expression, and suggest that elevated glucocorticoid levels may be relevant to the etiology of psychiatric diseases, such as depression, where hypothalamic-pituitary-adrenal axis dysregulation has been documented.

TPH2 and TPH1: association of variants and interactions with heroin addiction

The tryptophan hydroxylase 2 gene (TPH2) was resequenced at the 5' upstream, coding, and 3' downstream regions, including all 11 exons in 185 subjects. Twenty-three novel and 14 known variants were identified. In a cohort of 583 consecutively ascertained subjects, including normal volunteers and those with specific addictive diseases, six common TPH2 and one TPH1 variant were genotyped. Allele frequencies of three TPH2 variants and the TPH1 variant varied significantly among the four ethnic groups within the control subjects. Of these subjects, 385 who met heroin addiction or control criteria and were of Caucasian, African-American, or Hispanic ethnicity were examined for potential association with vulnerability to develop heroin addiction. At the two locus genotype level in Hispanics, the TPH1 rs1799913 variant was found to significantly interact with the TPH2 rs7963720 variant and heroin addiction (P=0.022), and with the TPH2 rs4290270 variant and heroin addiction (P=0.011). In the African-American group, a significant association of a specific TPH2 haplotype with heroin addiction also was found (SNPHAP, P=0.004; PHASE P=0.036).

Anterior thalamic lesions produce chronic and profuse transcriptional de-regulation in retrosplenial cortex: A model of retrosplenial hypoactivity and covert pathology

Anterior thalamic lesions are thought to produce 'covert pathology' in retrosplenial cortex, but the causes are unknown. Microarray analyses tested the hypothesis that thalamic damage causes a chronic, hypo-function of metabolic and plasticity-related pathways (Experiment 1). Rats with unilateral, anterior thalamic lesions were exposed to a novel environment for 20 minutes, and granular retrosplenial tissue sampled from both hemispheres 30 minutes, 2h, or 8h later. Complementary statistical approaches (analyses of variance, predictive patterning and gene set enrichment analysis) revealed pervasive gene expression differences between retrosplenial cortex ipsilateral to the thalamic lesion and contralateral to the lesion. Selected gene differences were validated by QPCR, immunohistochemistry (Experiment 1), and in situ hybridisation (Experiment 2). Following thalamic lesions, the retrosplenial cortex undergoes profuse cellular transcriptome changes including lower relative levels of specific mRNAs involved in energy metabolism and neuronal plasticity. These changes in functional gene expression may be largely driven by decreases in the expression of multiple transcription factors, including brd8, c-fos, fra-2, klf5, nfix, nr4a1, smad3, smarcc2, and zfp9, with a much smaller number (nfat5, neuroD1, RXRγ) showing increases. These findings have implications for conditions such as diencephalic amnesia and Alzheimer's disease, where both anterior thalamic pathology and retrosplenial cortex hypometabolism are prominent.

Tryptophan hydroxylase is modulated by L-type calcium channels in the rat pineal gland

Calcium is an important second messenger in the rat pineal gland, as well as cAMP. They both contribute to melatonin synthesis mediated by the three main enzymes of the melatonin synthesis pathway: tryptophan hydroxylase, arylalkylamine N-acetyltransferase and hydroxyindole-O-methyltransferase. The cytosolic calcium is elevated in pinealocytes following alpha(1)-adrenergic stimulation, through IP(3)-and membrane calcium channels activation. Nifedipine, an L-type calcium channel blocker, reduces melatonin synthesis in rat pineal glands in vitro. With the purpose of investigating the mechanisms involved in melatonin synthesis regulation by the L-type calcium channel, we studied the effects of nifedipine on noradrenergic stimulated cultured rat pineal glands. Tryptophan hydroxylase, arylalkylamine N-acetyltransferase and hydroxyindole-O-methyltransferase activities were quantified by radiometric assays and 5-hydroxytryptophan, serotonin, N-acetylserotonin and melatonin contents were quantified by HPLC with electrochemical detection. The data showed that calcium influx blockaded by nifedipine caused a decrease in tryptophan hydroxylase activity, but did not change either arylalkylamine N-acetyltransferase or hydroxyindole-O-methyltransferase activities. Moreover, there was a reduction of 5-hydroxytryptophan, serotonin, N-acetylserotonin and melatonin intracellular content, as well as a reduction of serotonin and melatonin secretion. Thus, it seems that the calcium influx through L-type high voltage-activated calcium channels is essential for the full activation of tryptophan hydroxylase leading to melatonin synthesis in the pineal gland.

Acetylation of histone H3 and adrenergic-regulated gene transcription in rat pinealocytes

In this study we investigated the effect of histone acetylation on the transcription of adrenergic-induced genes in rat pinealocytes. We found that treatment of pinealocytes with trichostatin A (TSA), a histone deacetylase inhibitor, caused hyperacetylation of histone H3 (H3) Lys14 at nanomolar concentrations. Hyperacetylation of H3 was also observed after treatment with scriptaid, a structurally unrelated histone deacetylase inhibitor. The effects of TSA and scriptaid were inhibitory on the adrenergic induction of arylalkylamine-n-acetyltransferase (aa-nat) mRNA, protein, and enzyme activity, and on melatonin production. TSA at higher concentrations also inhibited the adrenergic induction of mapk phosphatase-1 (mkp-1) and inducible cAMP early repressor mRNAs. In contrast, the effect of TSA on the norepinephrine induction of the c-fos mRNA was stimulatory. Moreover, the effect of TSA on adrenergic-induced gene transcription was dependent on the time of its addition; its effect was only observed during the active phase of transcription. Chromatin immunoprecipitation with antibodies against acetylated Lys14 of H3 showed an increase in DNA recovery of the promoter regions of aa-nat, mkp-1, and c-fos after treatment with TSA. Together, our results demonstrate that histone acetylation differentially influences the transcription of adrenergic-induced genes, an enhancing effect for c-fos but inhibitory for aa-nat, mkp-1, and inducible cAMP early repressor. Moreover, both inhibitory and enhancing effects appear to be mediated through specific modification of promoter-bound histones during gene transcription.

Up-regulation of tryptophan hydroxylase-2 mRNA in the rat brain by chronic fluoxetine treatment correlates with its antidepressant effect

Tryptophan hydroxylase-2 (TPH2), the rate-limiting enzyme in 5-HT synthesis in the brain, is a candidate for participation in a mechanism mediating the antidepressant effect of selective 5-HT reuptake inhibitors such as fluoxetine. Using real-time reverse transcription-polymerase chain reaction (RT-PCR) and semi-quantitative RT-PCR techniques, we have examined the effects of fluoxetine administration with drinking water (7.5 mg/kg/day) for 2, 4 and 8 weeks on TPH2 mRNA expression in the midbrain part of the dorsal raphe nucleus (DRN) and in the brainstem containing the rest of the raphe complex. Fluoxetine treatment for 4 and 8 weeks significantly increased basal TPH2 mRNA levels in the midbrain, an effect that was correlated with the appearance of antidepressant-like effects in the forced swim test. A significant induction of TPH2 and 5-HT transporter (5-HTT) mRNAs was detected in the midbrain of untreated rats 24 h after the swim test. In these animals, the swim test also produced a marked decrease in 5-HT metabolite (5-hydroxyindoleacetic acid (5-HIAA)) content in the amygdala. Fluoxetine treatment for 4 and 8, but not for 2 weeks, abolished these swim-induced changes in TPH2 and 5-HTT mRNAs levels in the midbrain and 5-HIAA content in the amygdala. The results of the present study suggest that TPH2 gene expression in the midbrain part of the DRN is implicated in depression and stress response, as well as in the antidepressant fluoxetine action.

Neural adrenergic/cyclic AMP regulation of the immunoglobulin E receptor alpha-subunit expression in the mammalian pinealocyte: a neuroendocrine/immune response link?

The high affinity immunoglobulin E receptor (FcepsilonRI) complex is dedicated to immunoglobulin E-mediated allergic responses. Expression of the FcepsilonRI receptor is thought to be relatively stable and limited to mast cells, basophils, eosinophils, monocytes, Langerhans cells, platelets, and neutrophils. We now report that the FcepsilonRIalpha and FcepsilonRIgamma polypeptides are expressed in the pinealocyte, the melatonin-secreting cell of the pineal gland. Moreover, Fcer1a mRNA levels increased approximately 100-fold at night to levels that were higher than in other tissues examined. Pineal FcepsilonRIalpha protein also increased markedly at night from nearly undetectable daytime levels. Our studies indicate that pineal Fcer1a mRNA levels are controlled by a well described neural pathway that controls pineal function. This pathway includes the master circadian oscillator in the suprachiasmatic nucleus and passes through central and peripheral structures. The circadian expression of FcepsilonRIalpha in the pineal gland is driven by this neural circuit via an adrenergic/cyclic AMP mechanism. Pineal FcepsilonRIalpha and FcepsilonRIgamma may represent a previously unrealized molecular link between the neuroendocrine and immune systems.

The mammalian pineal gland: known facts, unknown facets

In the mammalian pineal gland, information on environmental lighting conditions that is neuronally encoded by the retina is converted into nocturnally elevated synthesis of the hormone melatonin. Evolutionary pressure has changed the morphology of vertebrate pinealocytes, eliminating direct photoreception and the endogenous clock function. Despite these changes, nocturnally elevated melatonin synthesis has remained a reliable indicator of time throughout evolution. In the photo-insensitive mammalian pineal gland this message of darkness depends on the master circadian pacemaker in the hypothalamic suprachiasmatic nuclei. The dramatic change in vertebrate pinealocytes has received little attention; here, we therefore link the known evolutionary morphodynamics and well-investigated biochemical details responsible for rhythmic synthesis of melatonin with recently characterized patterns of gene expression in the pineal gland. We also address the enigmatic function of clockwork molecules in mammalian pinealocytes.

Role of TPH-2 in brain function: News from behavioral and pharmacologic studies

The recent discovery of TPH-2, a new isoform of tryptophan hydroxylase, the enzyme that catalyses the transformation of tryptophan into 5-hydroxytryptophan and the rate-limiting step in brain serotonin (5-HT) biosynthesis, has boosted new interest in the many functions of 5-HT in the brain and non-nervous tissues. Recent studies on TPH-2 are reviewed with particular attention to the role of this enzyme in behavior and in response to drugs as assessed by comparing strains of mice carrying a functional polymorphism of TPH-2. Most studies concur to indicate that 5-HT synthesis through TPH-2 influence nervous tissues whereas TPH-1 is responsible for the synthesis and action of 5-HT in peripheral organs. Partial impairment of brain 5-HT synthesis caused by polymorphism of the gene encoding TPH-2 causes reduced release of the neurotransmitter, increased aggressiveness, and alters the response to drugs inhibiting the reuptake of 5-HT. Strain comparison might be a useful strategy to investigate the genotype-dependent alterations of TPH-2.

Differential tissue distribution of tryptophan hydroxylase isoforms 1 and 2 as revealed with monospecific antibodies

Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the synthesis of the neurotransmitter serotonin. Once thought to be a single-gene product, TPH is now known to exist in two isoforms-TPH1 is found in the pineal and gut, and TPH2 is selectively expressed in brain. Heretofore, probes used for localization of TPH protein or mRNA could not distinguish between the TPH isoforms because of extensive homology shared by them at the nucleotide and amino acid level. We have produced monospecific polyclonal antibodies against TPH1 and TPH2 using peptide antigens from nonoverlapping sequences in the respective proteins. These antibodies allow the differentiation of TPH1 and TPH2 upon immunoblotting, immunoprecipitation, and immunocytochemical staining of tissue sections from brain and gut. TPH1 and TPH2 antibodies do not cross-react with either tyrosine hydroxylase or phenylalanine hydroxylase. Analysis of mouse tissues confirms that TPH1 is the predominant form expressed in pineal gland and in P815 mastocytoma cells with a molecular weight of 51 kDa. TPH2 is the predominant enzyme form expressed in brain extracts from mesencephalic tegmentum, striatum, and hippocampus with a molecular weight of 56 kDa. Antibody specificity against TPH1 and TPH2 is retained across mouse, rat, rabbit, primate, and human tissues. Antibodies that distinguish between the isoforms of TPH will allow studies of the differential regulation of their expression in brain and periphery.

Tissue-specific expression of tryptophan hydroxylase mRNAs in the rat midbrain: anatomical evidence and daily profiles

Serotonin (5-HT) is involved in both photic and non-photic synchronization of the mammalian biological clock located in the suprachiasmatic nuclei (SCN). We have previously demonstrated that tryptophan hydroxylase protein (TPH), the rate-limiting enzyme of 5-HT synthesis, shows circadian rhythmicity in the pathways projecting from the raphe nuclei to the intergeniculate leaflets of the thalamus on one hand, and to the SCN on the other hand. In this study, we investigate whether the circadian rhythmicity in TPH protein could result from the rhythmic expression of tph gene in the raphe nuclei. We thus cloned specific tph1 and tph2 partial cDNAs and assessed the daily profiles of TPH mRNA levels by in situ hybridization in the rat raphe nuclei. Our results demonstrate that: (i) tph2 gene is exclusively expressed in the raphe nuclei, whereas tph1 gene is expressed in the pineal gland; (ii) under light-dark cycle (LD), TPH2 mRNA levels present daily variation within both median and dorsal raphe nuclei; (iii) under constant darkness TPH2 mRNA levels in both nuclei exhibit the same variation reported under LD cycle. These data show that the circadian 5-HT synthesis within the serotonergic neurons projecting to the circadian system might be explained by the rhythmic transcription of the tph2 gene in raphe nuclei. Taking our result with previous data into consideration, we further suggest that 5-HT synthesis and release within the circadian system could be directly or indirectly under the control of the SCN.

Different properties of the central and peripheral forms of human tryptophan hydroxylase

Tryptophan hydroxylase (TPH) catalyses the rate-limiting reaction in the biosynthesis of serotonin. In humans, two different TPH genes exist, located on chromosomes 11 and 12, respectively, and encoding two enzymes (TPH1 and TPH2) with an overall sequence identity of 71%. We have expressed both enzymes as various fusion proteins in Escherichia coli and using an in vitro transcription/translation system, and compared their solubility and kinetic properties. TPH2 is more soluble than TPH1, has a higher molecular weight and different kinetic properties, including a lower catalytic efficiency towards phenylalanine than TPH1. Both enzymes are phosphorylated by cAMP-dependent protein kinase A. TPH2 was phosphorylated at Ser19, a phosphorylation site not present in TPH1. The differences between TPH1 and TPH2 have important implications for the regulation of serotonin production in the brain and the periphery and may provide an explanation for some of the diverging results reported for TPH from different sources in the past.

A functional polymorphism in the promoter region of the tryptophan hydroxylase gene is associated with alcohol dependence in one aboriginal group in Taiwan

BACKGROUND

Polymorphisms within intron 7 of the tryptophan hydroxylase (TPH1) gene were found to be associated with alcohol dependence in different ethnic groups, including the aboriginal Bunun group in Taiwan. This study aimed to identify genetic variants at the TPH1 locus and to examine their associations with alcoholism. We hypothesized that the polymorphism of TPH1 gene is functional and influences the human circadian rhythm to contribute to the pathophysiology of alcohol dependence.

METHODS

DNA from the Taiwanese Han and Bunun was subjected to sequence for screening genetic variation in the coding and promoter regions of the TPH1 locus. Polymorphisms among individuals with alcohol dependence and control subjects in two ethnic groups in Taiwan were investigated.

RESULTS

Three variants in the TPH1 promoter region were identified, and the markers are in complete linkage disequilibrium in both populations. Positive associations at both allelic and genotypic levels were obtained between case and control groups in the Bunun. Expression studies demonstrated that the variants indeed affected reporter gene activity in human choriocarcinoma and colon adenocarcinoma cell lines.

CONCLUSIONS

Polymorphisms in the promoter region may influence the function of the TPH1 gene and further influence the proclivity of alcohol dependence in one ethnic group in Taiwan. The associations between TPH1 genotypes and alcoholism may deserve further investigation.

Monoamine Oxidase A and Tryptophan Hydroxylase Gene Polymorphisms

Most of the candidate gene studies in bipolar disorder have focused on the major neurotransmitter systems that are influenced by drugs used in the treatment of this disorder. The monoamine oxidase A (MAOA) and the tryptophan hydroxylase (TPH1, TPH2) genes are two of the candidates that have been tested in a series of association studies using unrelated or family-based controls. This review summarizes the existing association studies regarding these genes. Most of these studies were based on the unrelated case-control design with samples of 50 to 600 subjects. Regarding MAOA, three meta-analyses with partially overlapping samples supported a modest effect of this gene in bipolar disorder in female Caucasians. However, as several studies could not replicate these findings, more work is necessary to demonstrate unequivocally the involvement of MAOA in bipolar disorder and establish the biological mechanism underlying the genetic association. With respect to TPH1 and TPH2, the majority of studies did not provide evidence for an association between these genes and bipolar disorder. The genes are more likely to be related to suicidal behavior than to bipolar disorder.

The circadian rhythm of 5-HT biosynthetic and degradative enzymes in immortalized mouse neuroendocrine pineal cell line--a model for studying circadian rhythm

Serotonin (5-HT) plays an important role in circadian rhythm and its level decreases at night and increases during day time in pineal gland. This study investigates the role of 5-HT biosynthetic and metabolic genes in the circadian rhythm using the mouse neuroendocrine pineal cell line (PT811). We first determined which type of monoamine oxdiase (MAO) was present in PT811 cells. Our results showed that only MAO A, a key which enzyme degrades 5-HT, was present in these cells because both 5-HT (the MAO A preferred substrate) and PEA (the MAO B preferred substrate) oxidation were sensitive to clorgyline but insensitive to deprenyl inhibition. This finding was supported by Northern blot analysis in which MAO A, but not MAO B, transcript was detectable. More sensitive quantitative RT-PCR showed the presence of both MAO A and MAO B, however there was no difference between day and night time. In contrast, the expression of tryptophan hydroxylase (TPH, the 5-HT synthetic enzyme), arylalklamine N-acetyltransferase (AANAT) and Arc (activity regulated, cytoskeleton associated protein) genes showed diurnal cycle. AANAT converts 5-HT to N-acetylserotonin, leading to the synthesis of melatonin. The Arc gene is an effector early immediate gene, regulated by 5-HT. This study suggested that the 5-HT circadian rhythm is regulated by TPH and AANAT but not the MAO A gene in this cell line. This cell line will be a valuable model for studying the molecular mechanisms of circadian rhythm.

Diurnal rhythms of tryptophan hydroxylase 1 and 2 mRNA expression in the rat retina

Tryptophan hydroxylase is the first of four enzymes in the melatonin biosynthetic pathway. Recent studies have shown that there are two genes, Tph1 and Tph2, that encode tryptophan hydroxylase in mammals. In this study, we investigated which of the two genes is expressed in the rat retina. To that end, we measured Tph1 (classical Tph) and Tph2 mRNA levels using real-time quantitative RT-PCR in the retina. Our data demonstrate that Tph1 mRNA is the prevalent form expressed in the retina; Tph2 mRNA is also present but the level is very low. We also measured Tph1 expression levels in the outer nuclear layer, inner nuclear layer, and ganglion cell layer by combining laser capture microdissection and real-time RT-PCR. Tph1 mRNA is more abundant in the photoreceptors of the outer nuclear layer than in the inner nuclear layer or ganglion cell layer. Tph1 and Tph2 transcripts showed robust diurnal rhythms of abundance, with highest levels at night. Our results support the hypothesis that Tph1 is involved in melatonin synthesis in retinal photoreceptor cells.