Prostaglandin D synthase gene is involved in the regulation of non-rapid eye movement sleep

Microglia mediate the increase in slow-wave sleep associated with high ambient temperature

An increase in ambient temperature leads to an increase in sleep. However, the mechanisms behind this phenomenon remain unknown. This study aimed to investigate the role of microglia in the increase of sleep caused by high ambient temperature. We confirmed that at 35 °C, slow-wave sleep was significantly increased relative to those observed at 25 °C. Notably, this effect was abolished upon treatment with PLX3397, a CSF1R inhibitor that can deplete microglia, while sleep amount at 25 °C was unaffected. These observations suggest that microglia play a pivotal role in modulating the homeostatic regulation of sleep in response to the fluctuations in ambient temperature.

A novel method for measurements of sleep/wake states, feeding and drinking behaviors using the tracking technique of 3D positions in freely moving mice

We have previously developed a 3D video tracking system which enables us to analyze long-term quantitative analysis of gene expression in freely moving mice. In the present study, we improved 3D video tracking and developed a system that analyzes more detailed behavioral data. We succeeded in simultaneously analyzing sleep-wake, feeding, and drinking behavior rhythms in the same individual using our tracking system. This system will make it possible to measure gene expression in each tissue in vivo in real time in relation to the various behavioral rhythms mentioned above.

Oligodendrocyte-lineage cell exocytosis and L-type prostaglandin D synthase promote oligodendrocyte development and myelination

In the developing central nervous system, oligodendrocyte precursor cells (OPCs) differentiate into oligodendrocytes, which form myelin around axons. Oligodendrocytes and myelin are essential for the function of the central nervous system, as evidenced by the severe neurological symptoms that arise in demyelinating diseases such as multiple sclerosis and leukodystrophy. Although many cell-intrinsic mechanisms that regulate oligodendrocyte development and myelination have been reported, it remains unclear whether interactions among oligodendrocyte-lineage cells (OPCs and oligodendrocytes) affect oligodendrocyte development and myelination. Here, we show that blocking vesicle-associated membrane protein (VAMP) 1/2/3-dependent exocytosis from oligodendrocyte-lineage cells impairs oligodendrocyte development, myelination, and motor behavior in mice. Adding oligodendrocyte-lineage cell-secreted molecules to secretion-deficient OPC cultures partially restores the morphological maturation of oligodendrocytes. Moreover, we identified L-type prostaglandin D synthase as an oligodendrocyte-lineage cell-secreted protein that promotes oligodendrocyte development and myelination in vivo. These findings reveal a novel autocrine/paracrine loop model for the regulation of oligodendrocyte and myelin development.

Transcriptome Profiling Reveals Differential Expression of Circadian Behavior Genes in Peripheral Blood of Monozygotic Twins Discordant for Parkinson's Disease

Parkinson’s disease (PD) is one of the most common neurodegenerative diseases. Investigating individuals with the most identical genetic background is optimal for minimizing the genetic contribution to gene expression. These individuals include monozygotic twins discordant for PD. Monozygotic twins have the same genetic background, age, sex, and often similar environmental conditions. The aim of this study was to carry out a transcriptome analysis of the peripheral blood of three pairs of monozygotic twins discordant for PD. We identified the metabolic process “circadian behavior” as a priority process for further study. Different expression of genes included in the term “circadian behavior” confirms that this process is involved in PD pathogenesis. We found increased expression of three genes associated with circadian behavior, i.e., PTGDS, ADORA2A, and MTA1, in twins with PD. These genes can be considered as potential candidate genes for this disease.

Lipocalin-Type Prostaglandin D2 Synthase Protein- A Central Player in Metabolism

Lipocalin-type prostaglandin D synthase was previously known as β-trace protein (BTP), a low-molecular-weight glycoprotein that is heavily expressed in human cerebrospinal fluid. Nevertheless, it is also seen to be expressed in numerous other tissues including the kidney, liver, lung, heart, adipose, muscle, and pancreas. Functionally, L-PGDS behaves like a lipocalin type protein where it helps in binding and transportation of small lipophilic substances, such as steroids, retinoids, and other lipophilic ligands. Enzymatically, L-PGDS functions as a prostaglandin synthase where it helps in the production of PGD₂ by catalyzing the isomerization of PGH₂, a common precursor of the two series of prostaglandins. PGD₂ regulates its physiological function through two individual receptors named DP1 and DP2. L-PGDS has been a central player in many diseases, its role in metabolism including diabetes, fatty liver disease, and obesity has gathered a large attention. In this review, we summarize the current state of knowledge about L-PGDS and it's signaling in adipose, hepatic, skeletal muscle, and pancreas tissues, which are core targets for metabolic studies. Modulation of L-PGDS signaling can be considered as a potential future therapeutic target for the treatment of insulin resistance as well as fatty liver disease.

Biochemical and Structural Characteristics, Gene Regulation, Physiological, Pathological and Clinical Features of Lipocalin-Type Prostaglandin D2 Synthase as a Multifunctional Lipocalin

Lipocalin-type prostaglandin (PG) D₂ synthase (L-PGDS) catalyzes the isomerization of PGH₂, a common precursor of the two series of PGs, to produce PGD₂. PGD₂ stimulates three distinct types of G protein-coupled receptors: (1) D type of prostanoid (DP) receptors involved in the regulation of sleep, pain, food intake, and others; (2) chemoattractant receptor-homologous molecule expressed on T helper type 2 cells (CRTH2) receptors, in myelination of peripheral nervous system, adipocyte differentiation, inhibition of hair follicle neogenesis, and others; and (3) F type of prostanoid (FP) receptors, in dexamethasone-induced cardioprotection. L-PGDS is the same protein as β-trace, a major protein in human cerebrospinal fluid (CSF). L-PGDS exists in the central nervous system and male genital organs of various mammals, and human heart; and is secreted into the CSF, seminal plasma, and plasma, respectively. L-PGDS binds retinoic acids and retinal with high affinities (Kd < 100 nM) and diverse small lipophilic substances, such as thyroids, gangliosides, bilirubin and biliverdin, heme, NAD(P)H, and PGD₂, acting as an extracellular carrier of these substances. L-PGDS also binds amyloid β peptides, prevents their fibril formation, and disaggregates amyloid β fibrils, acting as a major amyloid β chaperone in human CSF. Here, I summarize the recent progress of the research on PGD₂ and L-PGDS, in terms of its “molecular properties,” “cell culture studies,” “animal experiments,” and “clinical studies,” all of which should help to understand the pathophysiological role of L-PGDS and inspire the future research of this multifunctional lipocalin.

Lipocalin-type prostaglandin D synthase regulates light-induced phase advance of the central circadian rhythm in mice

We previously showed that mice lacking pituitary adenylate cyclase-activating polypeptide (PACAP) exhibit attenuated light-induced phase shift. To explore the underlying mechanisms, we performed gene expression analysis of laser capture microdissected suprachiasmatic nuclei (SCNs) and found that lipocalin-type prostaglandin (PG) D synthase (L-PGDS) is involved in the impaired response to light stimulation in the late subjective night in PACAP-deficient mice. L-PGDS-deficient mice also showed impaired light-induced phase advance, but normal phase delay and nonvisual light responses. Then, we examined the receptors involved in the response and observed that mice deficient for type 2 PGD₂ receptor DP2/CRTH2 (chemoattractant receptor homologous molecule expressed on Th2 cells) show impaired light-induced phase advance. Concordant results were observed using the selective DP2/CRTH2 antagonist CAY10471. These results indicate that L-PGDS is involved in a mechanism of light-induced phase advance via DP2/CRTH2 signaling.

Kawaguchi et al. show that mice deficient in lipocalin-type prostaglandin (PG) D synthase (L-PGDS) exhibit impaired light-induced phase advance, but normal phase delay and nonvisual light responses. This study suggests the role of L-PGDS for the light-induced phase advance possibly via a chemoattractant receptor DP2/CRTH2.

Role of the L-PGDS-PGD2-DP1 receptor axis in sleep regulation and neurologic outcomes

To meet the new challenges of modern lifestyles, we often compromise a good night's sleep. In preclinical models as well as in humans, a chronic lack of sleep is reported to be among the leading causes of various physiologic, psychologic, and neurocognitive deficits. Thus far, various endogenous mediators have been implicated in inter-regulatory networks that collectively influence the sleep-wake cycle. One such mediator is the lipocalin-type prostaglandin D2 synthase (L-PGDS)-Prostaglandin D2 (PGD2)-DP1 receptor (L-PGDS-PGD2-DP1R) axis. Findings in preclinical models confirm that DP1R are predominantly expressed in the sleep-regulating centers. This finding led to the discovery that the L-PGDS-PGD2-DP1R axis is involved in sleep regulation. Furthermore, we showed that the L-PGDS-PGD2-DP1R axis is beneficial in protecting the brain from ischemic stroke. Protein sequence homology was also performed, and it was found that L-PGDS and DP1R share a high degree of homology between humans and rodents. Based on the preclinical and clinical data thus far pertaining to the role of the L-PGDS-PGD2-DP1R axis in sleep regulation and neurologic conditions, there is optimism that this axis may have a high translational potential in human therapeutics. Therefore, here the focus is to review the regulation of the homeostatic component of the sleep process with a special focus on the L-PGDS-PGD2-DP1R axis and the consequences of sleep deprivation on health outcomes. Furthermore, we discuss whether the pharmacological regulation of this axis could represent a tool to prevent sleep disturbances and potentially improve outcomes, especially in patients with acute brain injuries.

Oral Delivery of Honokiol Microparticles for Nonrapid Eye Movement Sleep

Honokiol (HNK) is a small-molecule lignin extracted from Magnolia Officinalis, demonstrating high potency in promoting nonrapid eye movement (NREM) sleep by modulating the benzodiazepine site of the GABA_A receptor. However, the clinical use of HNK in the treatment of insomnia is restricted by its extremely low oral bioavailability. In the present work, enhanced oral bioavailability of HNK was achieved by loading it into poly lactide-glycolide acid microparticles (HNK-MP). After oral administration, HNK-MP demonstrated 15-fold increase of AUC_0-12 h in comparison to free HNK. The maximum blood concentration ( C_max) of HNK in HNK-MP-treated rats was 3.6 μg/mL at 2 h after oral administration, which was 6.5-fold of that in free HNK-treated rats. Oral administration of HNK-MP (20 mg/kg) efficiently increased NREM sleep by 60% by enhancing the transition from wakefulness to NREM sleep in rats. The biosafety of HNK-MP was assessed in vivo, and no damage occurred in the gastrointestinal tract. The present study provides a promising oral HNK formulation for the treatment of insomnia.

The Leptomeninges Produce Prostaglandin D2 Involved in Sleep Regulation in Mice

Injection of nanomolar amounts of prostaglandin D₂ (PGD₂) into the rat brain has dose and time-dependent somnogenic effects, and the PGD₂-induced sleep is indistinguishable from physiologic sleep. Sleep-inducing PGD₂ is produced in the brain by lipocalin-type PGD₂ synthase (LPGDS). Three potential intracranial sources of LPGDS have been identified: oligodendrocytes, choroid plexus, and leptomeninges. We aimed at the identification of the site of synthesis of somnogenic PGD₂ and therefore, generated a transgenic mouse line with the LPGDS gene amenable to conditional deletion using Cre recombinase (flox-LPGDS mouse). To identify the cell type responsible for producing somnogenic PGD₂, we engineered animals lacking LPGDS expression specifically in oligodendrocytes (OD-LPGDS KO), choroid plexus (CP-LPGDS KO), or leptomeninges (LM-LPGDS KO). We measured prostaglandins and LPGDS concentrations together with PGD synthase activity in the brain of these mice. While the LPGDS amount and PGD synthase activity were drastically reduced in the OD- and LM-LPGDS KO mice, they were unchanged in the CP-LPGDS KO mice compared with control animals. We then recorded electroencephalograms, electromyograms, and locomotor activity to measure sleep in 10-week-old mice with specific knockdown of LPGDS in each of the three targets. Using selenium tetrachloride, a specific PGDS inhibitor, we demonstrated that sleep is inhibited in OD-LPGDS and CP-LPGDS KO mice, but not in the LM-LPGDS KO mice. We concluded that somnogenic PGD₂ is produced primarily by the leptomeninges, and not by oligodendrocytes or choroid plexus.

Improved cognitive morning performance in healthy older adults following blue-enriched light exposure on the previous evening

OBJECTIVES

Exposure to light can have acute alerting and circadian phase-shifting effects. This study investigated the effects of evening exposure to blue-enriched polychromatic white (BEL) vs. polychromatic white light (WL) on sleep inertia dissipation the following morning in older adults.

METHODS

Ten healthy older adults (average age = 63.3 yrs; 6F) participated in a 13-day study comprising three baseline days, an initial circadian phase assessment, four days with 2-h evening light exposures, a post light exposure circadian phase assessment and three recovery days. Participants were randomized to either BEL or WL of the same irradiance for the four evening light exposures. On the next mornings at 2, 12, 22 and 32 min after each wake time, the participants completed a 90-s digit-symbol substitution test (DSST) to assess working memory, and objective alertness was assessed using a wake EEG recording. DSST and power density from the wake EEG recordings were compared between the two groups.

RESULTS

DSST performance improved with time awake (p < 0.0001) and across study days in both light exposure groups (p < 0.0001). There was no main effect of group, although we observed a significant day x group interaction (p = 0.0004), whereby participants exposed to BEL performed significantly better on the first two mornings after light exposures than participants in WL (post-hoc, p < 0.05). On those days, the BEL group showed higher EEG activity in some of the frequency bins in the sigma and beta range (p < 0.05) on the wake EEG.

CONCLUSION

Exposure to blue-enriched white light in the evening significantly improved DSST performance the following morning when compared to polychromatic white light. This was associated with a higher level of objective alertness on the wake EEG, but not with changes in sleep or circadian timing.

Proteomic Analysis of the Peri-Infarct Area after Human Umbilical Cord Mesenchymal Stem Cell Transplantation in Experimental Stroke

Among various therapeutic approaches for stroke, treatment with human umbilical cord mesenchymal stem cells (hUC-MSCs) has acquired some promising results. However, the underlying mechanisms remain unclear. We analyzed the protein expression spectrum of the cortical peri-infarction region after ischemic stroke followed by treatment with hUC-MSCs, and found 16 proteins expressed differentially between groups treated with or without hUC-MSCs. These proteins were further determined by Gene Ontology term analysis and network with CD200-CD200R1, CCL21-CXCR3 and transcription factors. Three of them: Abca13, Grb2 and Ptgds were verified by qPCR and ELISA. We found the protein level of Abca13 and the mRNA level of Grb2 consistent with results from the proteomic analysis. Finally, the function of these proteins was described and the potential proteins that deserve to be further studied was also highlighted. Our data may provide possible underlying mechanisms for the treatment of stroke using hUC-MSCs.

Functions and Mechanisms of Sleep

Sleep is a complex physiological process that is regulated globally, regionally, and locally by both cellular and molecular mechanisms. It occurs to some extent in all animals, although sleep expression in lower animals may be co-extensive with rest. Sleep regulation plays an intrinsic part in many behavioral and physiological functions. Currently, all researchers agree there is no single physiological role sleep serves. Nevertheless, it is quite evident that sleep is essential for many vital functions including development, energy conservation, brain waste clearance, modulation of immune responses, cognition, performance, vigilance, disease, and psychological state. This review details the physiological processes involved in sleep regulation and the possible functions that sleep may serve. This description of the brain circuitry, cell types, and molecules involved in sleep regulation is intended to further the reader's understanding of the functions of sleep.

Intestinal tumor suppression in ApcMin/+ mice by prostaglandin D2 receptor PTGDR

Our earlier work showed that knockout of hematopoietic prostaglandin D synthase (HPGDS, an enzyme that produces prostaglandin D₂) caused more adenomas in Apc^Min/+ mice. Conversely, highly expressed transgenic HPGDS allowed fewer tumors. Prostaglandin D₂ (PGD₂) binds to the prostaglandin D₂ receptor known as PTGDR (or DP1). PGD₂ metabolites bind to peroxisome proliferator-activated receptor γ (PPARG). We hypothesized that Ptgdr or Pparg knockouts may raise numbers of tumors, if these receptors take part in tumor suppression by PGD₂. To assess, we produced Apc^Min/+ mice with and without Ptgdr knockouts (147 mice). In separate experiments, we produced Apc^Min/+ mice expressing transgenic lipocalin-type prostaglandin D synthase (PTGDS), with and without heterozygous Pparg knockouts (104 mice). Homozygous Ptgdr knockouts raised total numbers of tumors by 30–40% at 6 and 14 weeks. Colon tumors were not affected. Heterozygous Pparg knockouts alone did not affect tumor numbers in Apc^Min/+ mice. As mentioned above, our Pparg knockout assessment also included mice with highly expressed PTGDS transgenes. Apc^Min/+ mice with transgenic PTGDS had fewer large adenomas (63% of control) and lower levels of v-myc avian myelocytomatosis viral oncogene homolog (MYC) mRNA in the colon. Heterozygous Pparg knockouts appeared to blunt the tumor-suppressing effect of transgenic PTGDS. However, tumor suppression by PGD₂ was more clearly mediated by receptor PTGDR in our experiments. The suppression mechanism did not appear to involve changes in microvessel density or slower proliferation of tumor cells. The data support a role for PGD₂ signals acting through PTGDR in suppression of intestinal tumors.

Prostaglandin D(2) is crucial for seizure suppression and postictal sleep

Epilepsy is a neurological disorder with the occurrence of seizures, which are often accompanied by sleep. Prostaglandin (PG) D2 is produced by hematopoietic or lipocalin-type PGD synthase (H- or L-PGDS) and involved in the regulation of physiological sleep. Here, we show that H-PGDS, L/H-PGDS or DP1 receptor (DP1R) KO mice exhibited more intense pentylenetetrazole (PTZ)-induced seizures in terms of latency of seizure onset, duration of generalized tonic-clonic seizures, and number of seizure spikes. Seizures significantly increased the PGD2 content of the brain in wild-type mice. This PTZ-induced increase in PGD2 was attenuated in the brains of L- or H-PGDS KO and abolished in L/H-PGDS KO mice. Postictal non-rapid eye movement sleep was observed in the wild-type and H-PGDS or DP2R KO, but not in the L-, L/H-PGDS or DP1R KO, mice. These findings demonstrate that PGD2 produced by H-PGDS and acting on DP1R is essential for seizure suppression and that the L-PGDS/PGD2/DP1R system regulates sleep that follows seizures.

Augmented generation of protein fragments during wakefulness as the molecular cause of sleep: a hypothesis

Despite extensive understanding of sleep regulation, the molecular-level cause and function of sleep are unknown. I suggest that they originate in individual neurons and stem from increased production of protein fragments during wakefulness. These fragments are transient parts of protein complexes in which the fragments were generated. Neuronal Ca²⁺ fluxes are higher during wakefulness than during sleep. Subunits of transmembrane channels and other proteins are cleaved by Ca²⁺-activated calpains and by other nonprocessive proteases, including caspases and secretases. In the proposed concept, termed the fragment generation (FG) hypothesis, sleep is a state during which the production of fragments is decreased (owing to lower Ca²⁺ transients) while fragment-destroying pathways are upregulated. These changes facilitate the elimination of fragments and the remodeling of protein complexes in which the fragments resided. The FG hypothesis posits that a proteolytic cleavage, which produces two fragments, can have both deleterious effects and fitness-increasing functions. This (previously not considered) dichotomy can explain both the conservation of cleavage sites in proteins and the evolutionary persistence of sleep, because sleep would counteract deleterious aspects of protein fragments. The FG hypothesis leads to new explanations of sleep phenomena, including a longer sleep after sleep deprivation. Studies in the 1970s showed that ethanol-induced sleep in mice can be strikingly prolonged by intracerebroventricular injections of either Ca²⁺ alone or Ca²⁺ and its ionophore (Erickson et al., Science 1978;199:1219-1221; Harris, Pharmacol Biochem Behav 1979;10:527-534; Erickson et al., Pharmacol Biochem Behav 1980;12:651-656). These results, which were never interpreted in connection to protein fragments or the function of sleep, may be accounted for by the FG hypothesis about molecular causation of sleep.

Lipocalin prostaglandin D synthase and PPARγ2 coordinate to regulate carbohydrate and lipid metabolism in vivo

Mice lacking Peroxisome Proliferator-Activated Receptor γ2 (PPARγ2) have unexpectedly normal glucose tolerance and mild insulin resistance. Mice lacking PPARγ2 were found to have elevated levels of Lipocalin prostaglandin D synthase (L-PGDS) expression in BAT and subcutaneous white adipose tissue (WAT). To determine if induction of L-PGDS was compensating for a lack of PPARγ2, we crossed L-PGDS KO mice to PPARγ2 KO mice to generate Double Knock Out mice (DKO). Using DKO mice we demonstrated a requirement of L-PGDS for maintenance of subcutaneous WAT (scWAT) function. In scWAT, DKO mice had reduced expression of thermogenic genes, the de novo lipogenic program and the lipases ATGL and HSL. Despite the reduction in markers of lipolysis in scWAT, DKO mice had a normal metabolic rate and elevated serum FFA levels compared to L-PGDS KO alone. Analysis of intra-abdominal white adipose tissue (epididymal WAT) showed elevated expression of mRNA and protein markers of lipolysis in DKO mice, suggesting that DKO mice may become more reliant on intra-abdominal WAT to supply lipid for oxidation. This switch in depot utilisation from subcutaneous to epididymal white adipose tissue was associated with a worsening of whole organism metabolic function, with DKO mice being glucose intolerant, and having elevated serum triglyceride levels compared to any other genotype. Overall, L-PGDS and PPARγ2 coordinate to regulate carbohydrate and lipid metabolism.

Control of sleep and wakefulness

This review summarizes the brain mechanisms controlling sleep and wakefulness. Wakefulness promoting systems cause low-voltage, fast activity in the electroencephalogram (EEG). Multiple interacting neurotransmitter systems in the brain stem, hypothalamus, and basal forebrain converge onto common effector systems in the thalamus and cortex. Sleep results from the inhibition of wake-promoting systems by homeostatic sleep factors such as adenosine and nitric oxide and GABAergic neurons in the preoptic area of the hypothalamus, resulting in large-amplitude, slow EEG oscillations. Local, activity-dependent factors modulate the amplitude and frequency of cortical slow oscillations. Non-rapid-eye-movement (NREM) sleep results in conservation of brain energy and facilitates memory consolidation through the modulation of synaptic weights. Rapid-eye-movement (REM) sleep results from the interaction of brain stem cholinergic, aminergic, and GABAergic neurons which control the activity of glutamatergic reticular formation neurons leading to REM sleep phenomena such as muscle atonia, REMs, dreaming, and cortical activation. Strong activation of limbic regions during REM sleep suggests a role in regulation of emotion. Genetic studies suggest that brain mechanisms controlling waking and NREM sleep are strongly conserved throughout evolution, underscoring their enormous importance for brain function. Sleep disruption interferes with the normal restorative functions of NREM and REM sleep, resulting in disruptions of breathing and cardiovascular function, changes in emotional reactivity, and cognitive impairments in attention, memory, and decision making.

Prostaglandin D2 and sleep/wake regulation

Prostaglandin (PG) D2 is the most potent endogenous sleep-promoting substance. PGD2 is produced by lipocalin-type PGD synthase localized in the leptomeninges, choroid plexus, and oligodendrocytes in the brain, and is secreted into the cerebrospinal fluid as a sleep hormone. PGD2 stimulates DP1 receptors localized in the leptomeninges under the basal forebrain and the hypothalamus. As a consequence, adenosine is released as a paracrine sleep-promoting molecule to activate adenosine A2A receptor-expressing sleep-promoting neurons and to inhibit adenosine A1 receptor-possessing arousal neurons. PGD2 activates a center of non-rapid eye movement (NREM) sleep regulation in the ventrolateral preoptic area, probably mediated by adenosine signaling, which activation inhibits the histaminergic arousal center in the tuberomammillary nucleus via descending GABAergic and galaninergic projections. The administration of a lipocalin-type PGD synthase inhibitor (SeCl4), DP1 antagonist (ONO-4127Na) or adenosine A2A receptor antagonist (caffeine) suppresses both NREM and rapid eye movement (REM) sleep, indicating that the PGD2-adenosine system is crucial for the maintenance of physiological sleep.

Hematopoietic prostaglandin D synthase (HPGDS): a high stability, Val187Ile isoenzyme common among African Americans and its relationship to risk for colorectal cancer

Intestinal tumors in Apc(Min/+) mice are suppressed by over-production of HPGDS, which is a glutathione transferase that forms prostaglandin D(2) (PGD(2)). We characterized naturally occurring HPGDS isoenzymes, to see if HPGDS variation is associated with human colorectal cancer risk. We used DNA heteroduplex analysis and sequencing to identify HPGDS variants among healthy individuals. HPGDS isoenzymes were produced in bacteria, and their catalytic activities were tested. To determine in vivo effects, we conducted pooled case-control analyses to assess whether there is an association of the isoenzyme with colorectal cancer. Roughly 8% of African Americans and 2% of Caucasians had a highly stable Val187lle isoenzyme (with isoleucine instead of valine at position 187). At 37°C, the wild-type enzyme lost 15% of its activity in 1h, whereas the Val187Ile form remained >95% active. At 50°C, the half life of native HPGDS was 9min, compared to 42 min for Val187Ile. The odds ratio for colorectal cancer among African Americans with Val187Ile was 1.10 (95% CI, 0.75-1.62; 533 cases, 795 controls). Thus, the Val187Ile HPGDS isoenzyme common among African Americans is not associated with colorectal cancer risk. Other approaches will be needed to establish a role for HPGDS in occurrence of human intestinal tumors, as indicated by a mouse model.

The light responsive transcriptome of the zebrafish: function and regulation

Most organisms possess circadian clocks that are able to anticipate the day/night cycle and are reset or “entrained” by the ambient light. In the zebrafish, many organs and even cultured cell lines are directly light responsive, allowing for direct entrainment of the clock by light. Here, we have characterized light induced gene transcription in the zebrafish at several organizational levels. Larvae, heart organ cultures and cell cultures were exposed to 1- or 3-hour light pulses, and changes in gene expression were compared with controls kept in the dark. We identified 117 light regulated genes, with the majority being induced and some repressed by light. Cluster analysis groups the genes into five major classes that show regulation at all levels of organization or in different subset combinations. The regulated genes cover a variety of functions, and the analysis of gene ontology categories reveals an enrichment of genes involved in circadian rhythms, stress response and DNA repair, consistent with the exposure to visible wavelengths of light priming cells for UV-induced damage repair. Promoter analysis of the induced genes shows an enrichment of various short sequence motifs, including E- and D-box enhancers that have previously been implicated in light regulation of the zebrafish period2 gene. Heterologous reporter constructs with sequences matching these motifs reveal light regulation of D-box elements in both cells and larvae. Morpholino-mediated knock-down studies of two homologues of the D-box binding factor Tef indicate that these are differentially involved in the cell autonomous light induction in a gene-specific manner. These findings suggest that the mechanisms involved in period2 regulation might represent a more general pathway leading to light induced gene expression.

Crucial role of prostaglandin D2 and adenosine in sleep regulation: experimental evidence from pharmacological approaches to gene-knockout mice

Prostaglandin (PG) D2 is the most potent endogenous sleep-promoting substance reported thus far. Its mechanism of action has been extensively studied at the molecular level. PGD2 is produced by lipocalin-type PGD synthase, which is predominantly localized in the leptomeninges, choroid plexus and oligodendrocytes in the brain; it is secreted into the cerebrospinal fluid and stimulates DP1 receptors localized in the arachnoid membrane of the ventral surface from the basal forebrain to the hypothalamus, increasing the extracellular concentration of adenosine as a paracrine sleep-promoting molecule. Adenosine diffuses into the brain parenchyma, suppresses cholinergic arousal neurons in the basal forebrain via adenosine A1 receptors, activates sleep-active neurons in the ventrolateral preoptic area via adenosine A2A receptors and concomitantly suppresses the histaminergic arousal center in the tuberomammillary nucleus through GABAergic and galaninergic inhibitory projections. Administration of an inhibitor of lipocalin-type PGD synthase (SeCl4), an antagonist of DP1 receptors (ONO-4127Na) or an antagonist of adenosine A2A receptors (caffeine) results in sleep inhibition in rats and mice. These results indicate that the PGD2–adenosine system is crucial for the maintenance of physiological sleep.

Pronounced adipogenesis and increased insulin sensitivity caused by overproduction of prostaglandin D2 in vivo

Lipocalin-type prostaglandin (PG) D synthase is expressed in adipose tissues and involved in the regulation of glucose tolerance and atherosclerosis in type 2 diabetes. However, the physiological roles of PGD(2) in adipogenesis in vivo are not clear, as lipocalin-type prostaglandin D synthase can also act as a transporter for lipophilic molecules, such as retinoids. We generated transgenic (TG) mice overexpressing human hematopoietic PGDS (H-PGDS) and investigated the in vivo functions of PGD(2) in adipogenesis. PGD(2) production in white adipose tissue of H-PGDS TG mice was increased approximately seven-fold as compared with that in wild-type (WT) mice. With a high-fat diet, H-PGDS TG mice gained more body weight than WT mice. Serum leptin and insulin levels were increased in H-PGDS TG mice, and the triglyceride level was decreased by about 50% as compared with WT mice. Furthermore, in the white adipose tissue of H-PGDS TG mice, transcription levels of peroxisome proliferator-activated receptor gamma, fatty acid binding protein 4 and lipoprotein lipase were increased approximately two-fold to five-fold as compared with those of WT mice. Finally, H-PGDS TG mice showed clear hypoglycemia after insulin clamp. These results indicate that TG mice overexpressing H-PGDS abundantly produced PGD(2) in adipose tissues, resulting in pronounced adipogenesis and increased insulin sensitivity. The present study provides the first evidence that PGD(2) participates in the differentiation of adipocytes and in insulin sensitivity in vivo, and the H-PGDS TG mice could constitute a novel model mouse for diabetes studies.

Phospholipase C-beta4 is essential for the progression of the normal sleep sequence and ultradian body temperature rhythms in mice

Background

The sleep sequence: i) non-REM sleep, ii) REM sleep, and iii) wakefulness, is stable and widely preserved in mammals, but the underlying mechanisms are unknown. It has been shown that this sequence is disrupted by sudden REM sleep onset during active wakefulness (i.e., narcolepsy) in orexin-deficient mutant animals. Phospholipase C (PLC) mediates the signaling of numerous metabotropic receptors, including orexin receptors. Among the several PLC subtypes, the β4 subtype is uniquely localized in the geniculate nucleus of thalamus which is hypothesized to have a critical role in the transition and maintenance of sleep stages. In fact, we have reported irregular theta wave frequency during REM sleep in PLC-β4-deficient mutant (PLC-β4−/−) mice. Daily behavioral phenotypes and metabotropic receptors involved have not been analyzed in detail in PLC-β4−/− mice, however.

Methodology/Principal Findings

Therefore, we analyzed 24-h sleep electroencephalogram in PLC-β4−/− mice. PLC-β4−/− mice exhibited normal non-REM sleep both during the day and nighttime. PLC-β4−/− mice, however, exhibited increased REM sleep during the night, their active period. Also, their sleep was fragmented with unusual wake-to-REM sleep transitions, both during the day and nighttime. In addition, PLC-β4−/− mice reduced ultradian body temperature rhythms and elevated body temperatures during the daytime, but had normal homeothermal response to acute shifts in ambient temperatures (22°C–4°C). Within the most likely brain areas to produce these behavioral phenotypes, we found that, not orexin, but group-1 metabotropic glutamate receptor (mGluR)-mediated Ca²⁺ mobilization was significantly reduced in the dorsal lateral geniculate nucleus (LGNd) of PLC-β4−/− mice. Voltage clamp recordings revealed that group-1 mGluR-mediated currents in LGNd relay neurons (inward in wild-type mice) were outward in PLC-β4−/− mice.

Conclusions/Significance

These lines of evidence indicate that impaired LGNd relay, possibly mediated via group-1 mGluR, may underlie irregular sleep sequences and ultradian body temperature rhythms in PLC-β4−/− mice.

Identification and characterisation of new inhibitors for the human hematopoietic prostaglandin D2 synthase

Prostaglandin D(2) synthesised by the hematopoietic prostaglandin D(2) synthase has a pro-inflammatory effect in allergic asthma, regulating many hallmark characteristics of the disease. Here we describe identification of hematopoietic prostaglandin D(2) synthase inhibitors including cibacron blue, bromosulfophthalein and ethacrynic acid. Expansion around the drug-like ethacrynic acid identified a novel inhibitor, nocodazole, and a fragment representing its aromatic core. Nocodazole binding was further characterised by docking calculations in combination with conformational strain analysis. The benzyl thiophene core was predicted to be buried in the active site, binding in the putative prostaglandin binding site, and a likely hydrogen bond donor site identified. X-ray crystallographic studies supported the predicted binding mode.

Structural basis of the catalytic mechanism operating in open-closed conformers of lipocalin type prostaglandin D synthase

Lipocalin type prostaglandin D synthase (L-PGDS) is a multifunctional protein acting as a somnogen (PGD2)-producing enzyme, an extracellular transporter of various lipophilic ligands, and an amyloid-beta chaperone in human cerebrospinal fluid. In this study, we determined the crystal structures of two different conformers of mouse L-PGDS, one with an open cavity of the beta-barrel and the other with a closed cavity due to the movement of the flexible E-F loop. The upper compartment of the central large cavity contains the catalytically essential Cys65 residue and its network of hydrogen bonds with the polar residues Ser45, Thr67, and Ser81, whereas the lower compartment is composed of hydrophobic amino acid residues that are highly conserved among other lipocalins. SH titration analysis combined with site-directed mutagenesis revealed that the Cys65 residue is activated by its interaction with Ser45 and Thr67 and that the S45A/T67A/S81A mutant showed less than 10% of the L-PGDS activity. The conformational change between the open and closed states of the cavity indicates that the mobile calyx contributes to the multiligand binding ability of L-PGDS.

Biochemical, functional, and pharmacological characterization of AT-56, an orally active and selective inhibitor of lipocalin-type prostaglandin D synthase

We report here that 4-dibenzo[a,d]cyclohepten-5-ylidene-1-[4-(2H-tetrazol-5-yl)-butyl]-piperidine (AT-56) is an orally active and selective inhibitor of lipocalin-type prostaglandin (PG) D synthase (L-PGDS). AT-56 inhibited human and mouse L-PGDSs in a concentration (3–250 μm)-dependent manner but did not affect the activities of hematopoietic PGD synthase (H-PGDS), cyclooxygenase-1 and -2, and microsomal PGE synthase-1. AT-56 inhibited the L-PGDS activity in a competitive manner against the substrate PGH₂ (K_m = 14 μm) with a K_i value of 75 μm but did not inhibit the binding of 13-cis-retinoic acid, a nonsubstrate lipophilic ligand, to L-PGDS. NMR titration analysis revealed that AT-56 occupied the catalytic pocket, but not the retinoid-binding pocket, of L-PGDS. AT-56 inhibited the production of PGD₂ by L-PGDS-expressing human TE-671 cells after stimulation with Ca²⁺ ionophore (5 μm A23187) with an IC₅₀ value of about 3 μm without affecting their production of PGE₂ and PGF_2α but had no effect on the PGD₂ production by H-PGDS-expressing human megakaryocytes. Orally administered AT-56 (<30 mg/kg body weight) decreased the PGD₂ production to 40% in the brain of H-PGDS-deficient mice after a stab wound injury in a dose-dependent manner without affecting the production of PGE₂ and PGF_2α and also suppressed the accumulation of eosinophils and monocytes in the bronco-alveolar lavage fluid from the antigen-induced lung inflammation model of human L-PGDS-transgenic mice.

Physiology and pathophysiology of prostanoid receptors

Prostanoids, consisting of prostaglandins (PGs) and thromboxanes (TXs), are oxygenated products of C20 unsaturated fatty acids. They include PGD2, PGE2, PGF2 α , PGI2, and TXA2. Given that aspirin-like nonsteroidal anti-inflammatory drugs exert their actions by suppressing prostanoid production, prostanoids have been implicated in processes inhibited by these drugs, including inflammation, fever, and pain. Prostanoids also contribute to vascular homeostasis, reproduction, and regulation of kidney and gastrointestinal functions. How prostanoids exert such a variety of actions had remained unclear, however. Prostanoids are released outside of cells immediately after their synthesis and exert their actions by binding to receptors on target cells. We have identified a family of eight types or subtypes of G protein-coupled receptors that mediate prostanoid actions. Another G protein-coupled receptor was also identified as an additional receptor for PGD2. Genes for these receptors have been individually disrupted in mice, and analyses of these knockout mice have not only elucidated the molecular and cellular mechanisms of known prostanoid actions but also revealed previously unknown actions. In this article, I review the physiological and pathophysiological roles of prostanoids and their receptors revealed by these studies.

Induction and function of lipocalin prostaglandin D synthase in host immunity

Although mainly expressed in neuronal cells, lipocalin-type PGD synthase (L-PGDS) is detected in the macrophages infiltrated to atherosclerotic plaques. However, the regulation and significance of L-PGDS expression in macrophages are unknown. Here, we found that treatment of macrophages with bacterial endotoxin (LPS) or Pseudomonas induced L-PGDS expression. Epigenetic suppression of L-PGDS expression in macrophages blunted a majority of PGD(2) produced after LPS treatment. Chromatin immunoprecipitation assays show that L-PGDS induction was regulated positively by AP-1, but negatively by p53. L-PGDS expression was detected in whole lung and alveolar macrophages treated with LPS or Pseudomonas. L-PGDS overexpressing transgenic mice improved clearance of Pseudomonas from the lung compared with nontransgenic mice. Similarly, intratracheal instillation of PGD(2) enhanced removal of Pseudomonas from the lung in mice. In contrast, L-PGDS knockout mice were impaired in their ability to remove Pseudomonas from the lung. Together, our results identify induction of L-PGDS expression by inflammatory stimuli or bacterial infection, the regulatory mechanism of L-PGDS induction, and the protective role of L-PGDS expression in host immune response. Our study suggests a potential therapeutic usage of L-PGDS or PGD(2) against Pseudomonas pneumonia.

Neuroendocrine functions of melanocytes: beyond the skin-deep melanin maker

The skin is armored with "dead cells", the stratum corneum, and is continuously exposed to external stressful environments, such as atmospheric oxygen, solar radiations, and thermal and chemical insults. Melanocytes of neural crest origin are located in the skin, eye, inner ear, and leptomeninges. Melanin pigment in the skin is produced by melanocytes under the influence of various endogenous factors, derived from neighboring keratinocytes and underlying fibroblasts. The differentiation and functions of melanocytes are regulated at multiple processes, including transcription, RNA editing, melanin synthesis, and the transport of melanosomes to keratinocytes. Impairment at each step causes the pigmentary disorders in humans, with the historical example of oculocutaneous albinism. Moreover, heterozygous mutations in the gene coding for microphthalmia-associated transcription factor, a key regulator for melanocyte development, are associated with Waardenburg syndrome type 2, an auditory-pigmentary disorder. Sun tanning, melasma, aging spots (lentigo senilis), hair graying, and melanoma are well-known melanocyte-related pathologies. Melanocytes therefore have attracted much attention of many ladies, makeup artists and molecular biologists. More recently, we have shown that lipocalin-type prostaglandin D synthase (L-PGDS) is expressed in melanocytes but not in other skin cell types. L-PGDS generates prostaglandin D2 and also functions as an inter-cellular carrier protein for lipophilic ligands, such as bilirubin and thyroid hormones. Thus, melanocytes may exert hitherto unknown functions through L-PGDS and prostaglandin D2. Here we update the neuroendocrine functions of melanocytes and discuss the possible involvement of melanocytes in the control of the central chemosensor that generates respiratory rhythm.

Beta-trace protein--a marker of kidney function in children: "Original research communication-clinical investigation"

OBJECTIVES

To determine the pediatric reference interval for serum beta-trace protein (beta-TP) and to compare beta-TP with established LMW markers of GFR, i.e., cystatin C (CysC) and beta(2)-microglobulin (beta(2)-M).

DESIGN AND METHODS

All three LMW markers were measured immunonephelometrically. In 106 children above the age of 2 years without evidence of kidney disease, non-parametric reference intervals were calculated. The relative rise of the GFR marker concentrations above the upper reference was studied in 107 samples from 96 patients covering the entire GFR range.

RESULTS

Above 2 years, the reference range of beta-TP was constant at 0.43-1.04 mg/L. With decreasing Schwartz-GFR, there was a comparable rise in beta-TP and beta(2)-M, while CysC rose less in the group with GFR below 30 mL/min/1.73 m(2) (278+/-49% [CysC] versus 336+/-65% [beta-TP] and 342+/-76% [beta(2)-M]; p=0.043 and 0.027, respectively).

CONCLUSIONS

These data confirm the potential of ss-TP as an endogenous GFR marker in children.

Cooperative activation of lipocalin-type prostaglandin D synthase gene expression by activator protein-2beta in proximal promoter and upstream stimulatory factor 1 within intron 4 in human brain-derived TE671 cells

We investigated the activation mechanism of gene expression of lipocalin-type prostaglandin D synthase (L-PGDS) in human brain-derived TE671 cells. Reporter analyses of constructs carrying various lengths of the promoter region and intron 1 to 6, or 3'-untranslated region of the human L-PGDS gene demonstrated that one atypical E-box (aE-box) at +2569 in intron 4 was critical for transactivation of the gene. The aE-box inside the intron 4 functioned as an enhancer element in both directions and in a cell-type specific manner in TE671 cells. Yeast one-hybrid screening revealed that upstream stimulatory factor (USF) 1 bound to the aE-box. Expression of exogenous USF1 induced the endogenous L-PGDS expression in TE671 cells, whereas administration of USF1 siRNA suppressed L-PGDS expression. Binding of USF1 to the aE-box was confirmed by performing electrophoretic mobility shift assay and chromatin immunoprecipitation assay. Furthermore, USF1-mediated transcriptional activation was dependent upon activator protein (AP)-2beta binding to the AP-2 element at position -98 in the proximal promoter region of human L-PGDS gene. These results indicate that L-PGDS gene expression in TE671 cells was activated by USF1 through the aE-box within intron 4 and cooperatively by AP-2beta in the promoter in a cell-type-specific manner.

Lipocalin-type prostaglandin D synthase/beta-trace is a major amyloid beta-chaperone in human cerebrospinal fluid

The conformational change in amyloid beta (Abeta) peptide from its monomeric form to aggregates is crucial in the pathogenesis of Alzheimer's disease (AD). In the healthy brain, some unidentified chaperones appear to prevent the aggregation of Abeta. Here we reported that lipocalin-type prostaglandin D synthase (L-PGDS)/beta-trace, the most abundant cerebrospinal fluid (CSF) protein produced in the brain, was localized in amyloid plaques in both AD patients and AD-model Tg2576 mice. Surface plasmon resonance analysis revealed that L-PGDS/beta-trace tightly bound to Abeta monomers and fibrils with high affinity (K(D) = 18-50 nM) and that L-PGDS/beta-trace recognized residues 25-28 in Abeta, which is the key region for its conformational change to a beta-sheet structure. The results of a thioflavin T fluorescence assay to monitor Abeta aggregation disclosed that L-PGDS/beta-trace inhibited the spontaneous aggregation of Abeta (1-40) and Abeta (1-42) within its physiological range (1-5 microM) in CSF. L-PGDS/beta-trace also prevented the seed-dependent aggregation of 50 microM Abeta with K(i) of 0.75 microM. Moreover, the inhibitory activity toward Abeta (1-40) aggregation in human CSF was decreased by 60% when L-PGDS/beta-trace was removed from the CSF by immunoaffinity chromatography. The deposition of Abeta after intraventricular infusion of Abeta (1-42) was 3.5-fold higher in L-PGDS-deficient mice and reduced to 23% in L-PGDS-overexpressing mice as compared with their wild-type levels. These data indicate that L-PGDS/beta-trace is a major endogenous Abeta-chaperone in the brain and suggest that the disturbance of this function may be involved in the onset and progression of AD. Our findings may provide a diagnostic and therapeutic approach for AD.

Hematopoietic prostaglandin D synthase suppresses intestinal adenomas in ApcMin/+ mice

Aspirin and other nonsteroidal anti-inflammatory drugs prevent some cases of colon cancer by inhibiting prostaglandin (PG) synthesis. PGE(2) promotes colon neoplasia, as shown by knockout mouse studies on enzymes and receptors in the PG cascade. A few experiments 20 to 30 years ago suggested that PGD(2) may suppress tumors, but a role for biosynthetic enzymes for PGD(2) in tumor development has not been studied. We report here that disruption of the gene for hematopoietic PGD synthase in Apc(Min/+) mice led to approximately 50% more intestinal adenomas compared with controls. Tumor size was not affected. By immunohistochemistry, we detected hematopoietic PGD synthase mainly in macrophages and monocytes of the gut mucosa. The mean number of tumors did not increase with knockout of the gene for the lipocalin type of the enzyme, which is not produced in the intestine. On the other hand, Apc(Min/+) mice with transgenic human hematopoietic PGD synthase tended to have 80% fewer intestinal adenomas. The transgene produced high mRNA levels (375-fold over endogenous). There was a suggestion of higher urinary excretion of 11beta-PGF(2alpha) and a lower excretion of a PGE(2) metabolite in transgenic mice, but differences (30-40%) were not statistically significant. The results support an interpretation that hematopoietic PGD synthase controls an inhibitory effect on intestinal tumors. Further studies will be needed to prove possible mechanisms, such as routing of PG production away from protumorigenic PGE(2) or inhibition of the nuclear factor-kappaB cascade by PGD(2) metabolites.

Mast cell mediators in allergic inflammation and mastocytosis

Mast cells possess an array of potent inflammatory mediators capable of inducing acute symptoms after cell activation, including urticaria, angioedema, bronchoconstriction, diarrhea, vomiting, hypotension, cardiovascular collapse, and death in few minutes. In contrast, mast cells can provide an array of beneficial mediators in the setting of acute infections, cardiovascular diseases, and cancer. The balance between the detrimental and beneficial roles of mast cells is not completely understood. Although the symptoms of acute mast cell mediator release can be reversed with epinephrine, adrenergic agonists, and mediator blockers, the continued release of histamine, proteases, prostaglandins, leukotrienes, cytokines, and chemokines leads to chronic and debilitating disease, such as mastocytosis. Identification of the molecular factors and mechanisms that control the synthesis and release of mast cell mediators should benefit all patients with mast cell activation syndromes and mastocytosis.

Lipocalin-type prostaglandin D synthase produces prostaglandin D2 involved in regulation of physiological sleep

Prostaglandin (PG) D2 has been proposed to be essential for the initiation and maintenance of the physiological sleep of rats because intracerebroventricular administration of selenium tetrachloride (SeCl4), a selective inhibitor of PGD synthase (PGDS), was shown to reduce promptly and effectively the amounts of sleep during the period of infusion. However, gene knockout (KO) mice of PGDS and prostaglandin D receptor (DP1R) showed essentially the same circadian profiles and daily amounts of sleep as wild-type (WT) mice, raising questions about the involvement of PGD2 in regulating physiological sleep. Here we examined the effect of SeCl4 on the sleep of WT and KO mice for PGDS and DP1R and that of a DP1R antagonist, ONO-4127Na, on the sleep of rats. The i.p. injection of SeCl4 into WT mice decreased the PGD2 content in the brain without affecting the amounts of PGE2 and PGF(2alpha). It inhibited sleep dose-dependently and immediately after the administration during the light period when mice normally sleep, increasing the wake time; and the treatment with this compound resulted in a distinct sleep rebound during the following dark period. The SeCl4-induced insomnia was observed in hematopoietic PGDS KO mice but not at all in lipocalin-type PGDS KO, hematopoietic and lipocalin-type PGDS double KO or DP1R KO mice. Furthermore, the DP1R antagonist ONO-4127Na reduced sleep of rats by 30% during infusion into the subarachnoid space under the rostral basal forebrain at 200 pmol/min. These results clearly show that the lipocalin-type PGDS/PGD2/DP1R system plays pivotal roles in the regulation of physiological sleep.