Purification and chemical characterization of beta-trace protein from human cerebrospinal fluid: its identification as prostaglandin D synthase

Prostaglandin D2 and sleep--a molecular genetic approach

Prostaglandin (PG) D2 is the major prostanoid in the mammalian brain, and is the endogenous sleep-promoting substance in mice, rats, and monkeys, and probably in humans as well. When PGD synthase (PGDS), the enzyme responsible for the biosynthesis of PGD2 in the brain, was inhibited in vivo by its selective inhibitors, tetravalent selenium compounds, both slow-wave sleep and rapid-eye-movement sleep were reduced almost completely but reversibly, indicating that PGDS is a key enzyme in sleep regulation. Experiments with transgenic mice also support this contention. In situ hybridization, immunoperoxidase staining, and direct enzyme assay of tissue samples revealed that PGDS is mainly, if not exclusively, localized in the arachnoid membrane and choroid plexus, from which it is secreted into the cerebrospinal fluid to become beta-trace protein. PGD2 exerts its somnogenic activity by binding with PGD2 receptors, exclusively localized at the ventro-rostral surface of the basal forebrain. CGS21680, an adenosine A2a agonist, mimicked the somnogenic activity of PGD2 when applied to the PGD2-sensitive zone. This effect was dose-dependently and selectively abolished by the prior i.p. application of the adenosine A2a antagonist KF17837. Furthermore, the somnogenic activity of PGD2 was also dose-dependently and selectively attenuated by KF17837, indicating the possibility that the sleep induction by PGD2 may be mediated by adenosine through A2a receptors under these conditions. When PGD2 was infused into the subarachnoid space below the rostral basal forebrain, concurrent with sleep induction, striking expression of Fos immunoreactivity was observed in the ventrolateral preoptic area. Fos expression in the ventrolateral preoptic area was positively correlated with the preceding amount of sleep and negatively correlated with Fos expression in the tuberomammillary nucleus. PGD2 also increased Fos IR in the basal leptomeninges and several regions implicated in autonomic regulation. These observations suggest that PGD2 may induce sleep via leptomeningeal PGD2 receptors with subsequent activation of the ventrolateral preoptic area neurons.

Seminal plasma biochemical markers and their association with semen analysis findings

OBJECTIVES

To examine the clinical value of six seminal plasma components in the evaluation of sperm quality and in the differential diagnosis of men with infertility.

METHODS

We analyzed 202 seminal plasmas for prostate-specific antigen, glucose, pepsinogen C, insulin-like growth factor binding protein-3, prostaglandin D synthase (PGDS), and BRCA1-like immunoreactive protein (BRCA1-LIP) using quantitative immunofluorometric procedures. The semen donors were categorized in four clinical groups: normal, oligospermic, azoospermic, and vasectomy patients. We then evaluated whether any of these biochemical markers were associated with other parameters of sperm quality, including patient age, total cell concentration, percentage of motility, and percentage of normal morphology.

RESULTS

We found that only PGDS concentration was significantly associated with other parameters of sperm quality. PGDS concentration correlated positively with total cell concentration (r = 0.55), percentage of motility (r = 0.31), and percentage of normal morphology (r = 0.31). Median PGDS concentration in seminal plasma decreased progressively from normal to oligospermic to azoospermic to vasectomy patients (P <0.001). There was no overlap between seminal plasma PGDS concentration of normal subjects versus vasectomy patients. The only other parameter that was moderately decreased in vasectomy patients was BRCA1-LIP. The source of PGDS in seminal plasma was determined with various techniques, including immunohistochemistry. This protein is produced and secreted by the Sertoli cells.

CONCLUSIONS

Our findings suggest that PGDS concentration in seminal plasma correlates with other known indicators of semen quality and is a new marker of post-testicular obstruction. This biochemical parameter could be used to aid in the differential diagnosis of obstructive and nonobstructive azoospermia in men with infertility.

Prostaglandin D synthase (beta-trace) in human arachnoid and meningioma cells: roles as a cell marker or in cerebrospinal fluid absorption, tumorigenesis, and calcification process

Glutathione-independent prostaglandin D synthase (PGDS) is an enzyme responsible for biosynthesis of prostaglandin D2 in the CNS and is identical to a major cerebrospinal fluid protein, beta-trace. Although PGDS has been identified recently in rat leptomeninges, little information is available about human meninges or meningiomas. Here, we report PGDS to be expressed consistently in 10 human arachnoid and arachnoid villi and in 21 meningiomas by immunohistochemistry, Western blot, and reverse transcription (RT)-PCR analyses. In arachnoid, PGDS immunoreactivity was seen in arachnoid barrier cells but was negligible in arachnoid trabecula and pia mater. In contrast, in arachnoid villi, PGDS was seen in core arachnoid cells rather than in the cap cell cluster or arachnoid cell layer. Meningioma cells also showed intense immunoreactivity in the perinuclear region, and it was often concentrated within meningocytic whorls and around calcifying psammoma bodies. Immunoelectron microscopic data, when compared with the ultrastructure, showed that PGDS was localized at rough endoplasmatic reticulum of arachnoid and meningioma cells. Western blot showed a 29 kDa immunoreactive band indicating PGDS, but the extent of expression was variable from case to case, which was compatible with immunohistochemical data. RT-PCR revealed PGDS gene expression in all meningiomas studied, regardless of histological subtypes, and also in human arachnoid villi. Because human arachnoid and meningioma cells exclusively express PGDS, it can be considered their specific cell marker. These results show functional differences in various types of meningeal cells attributable to differences in PGDS expression.

Lack of tactile pain (allodynia) in lipocalin-type prostaglandin D synthase-deficient mice

Prostaglandin (PG) D2 is the most abundant prostanoid produced in the central nervous system of mammals and has been implicated in the modulation of neural functions such as sleep induction, nociception, regulation of body temperature, and odor responses. We generated gene-knockout mice for lipocalin-type PGD2 synthase (L-PGDS) and found that the intrathecal administration of PGE2, an endogenous pain-producing substance, failed to elicit allodynia (touch-evoked pain), which is one typical phenomenon of neuropathic pain, whereas it evoked thermal hyperalgesia, in L-PGDS-/- mice. We also found that the allodynic response induced by the gamma-aminobutyric acid (GABA)A receptor antagonist bicuculline was selectively abolished in the L-PGDS-/- mice, among excitatory and inhibitory agents that induced allodynia in wild-type mice. Interestingly, simultaneous injection of a femtogram amount of PGD2 with PGE2 or bicuculline induced allodynia in L-PGDS-/- mice to the same extent as in wild-type mice. The PGE2- or bicuculline-evoked allodynia in wild-type and in PGD2-supplemented L-PGDS-/- mice was blocked by a PGD2 receptor antagonist given in a femtogram amount. These results reveal that endogenous PGD2 is essential for both PGE2- and bicuculline-induced allodynia.

Prostaglandin D2 and sleep regulation

Prostaglandin (PG) D2 is recognized as the most potent endogenous sleep-promoting substance whose action mechanism is the best characterized among the various sleep-substances thus far reported. The PGD2 concentration in rat cerebrospinal fluid (CSF) shows a circadian change coupled to the sleep-wake cycle and elevates with an increase in sleep propensity during sleep deprivation. Lipocalin-type PGD synthase is dominantly produced in the arachnoid membrane and choroid plexus of the brain, and is secreted into the CSF to become beta-trace, a major protein component of the CSF. The PGD synthase as well as the PGD2 thus produced circulates in the ventricular system, subarachnoidal space, and extracellular space in the brain system. PGD2 then interacts with DP receptors in the chemosensory region of the ventro-medial surface of the rostral basal forebrain to initiate the signal to promote sleep probably via the activation of adenosine A2A receptive neurons. The activation of DP receptors in the PGD2-sensitive chemosensory region results in activation of a cluster of neurons within the ventrolateral preoptic area, which may promote sleep by inhibiting tuberomammillary nucleus, the source of the ascending histaminergic arousal system.

Highly elevated levels of prostaglandin D synthase in the serum of patients with renal failure

OBJECTIVES

To investigate whether prostaglandin D (PGD) synthase levels differ in the serum of patients with or without renal dysfunction. PGD synthase or beta-trace protein is a major constituent (approximately 3% of total protein) of human cerebrospinal fluid (CSF). We previously reported that PGD synthase levels in serum are approximately 40- to 60-fold lower than those in CSF.

METHODS

We measured the PGD synthase concentration in various sera with a highly sensitive and specific immunofluorometric assay along with the serum creatinine level. Analysis for PGD synthase and creatinine was performed in 30 sera from non-renal failure subjects, in 7 sera from patients treated with continuous ambulatory peritoneal dialysis, and in 34 sera that were before and after hemodialysis samples from 17 patients with renal failure.

RESULTS

Elevated creatinine concentration was observed in patients with renal insufficiency, as expected (Mann-Whitney P < 0.0001; chi-square P < 0.0001 ). We found that serum PGD synthase concentration from patients with renal failure is significantly elevated compared with the serum PGD synthase concentration from non-renal failure subjects (Mann-Whitney P < 0.0001; chi-square P < 0.0001). Approximately a 35-fold increase of serum PGD synthase is observed for patients with renal failure compared with non-renal failure subjects. Serum PGD synthase concentration is not affected by hemodialysis in acute renal failure patients (Mann-Whitney P = 0.918), unlike serum creatinine levels, which were decreased significantly after hemodialysis (Mann-Whitney P = 0.0001).

CONCLUSIONS

We conclude that renal impairment is highly associated with elevated serum PGD synthase levels. Measurement of PGD synthase in serum is a new biochemical marker of renal insufficiency.

Beta-trace protein in cerebrospinal fluid: a blood-CSF barrier-related evaluation in neurological diseases

Beta-trace protein concentrations in cerebrospinal fluid (CSF) and serum from 113 patients with various neurological diseases and 65 controls were determined with a sensitive and specific immunonephelometric assay. In adult control patients, beta-trace concentrations were 14.6+/-4.6 mg/L in CSF and 0.46+/-0.13 mg/L in serum, that is, 32-fold higher in CSF. beta-trace levels in CSF correlated with age as well as with the albumin CSF/serum ratio (Q(Alb)), which is considered a measure for blood-CSF barrier function. The relationship between CSF beta-trace levels and elevated Q(Alb) values was studied in various neurological diseases with CSF protein increase. In spinal canal stenosis, CSF beta-trace (mean=29.5+/-10.5 mg/L) correlated positively with increasing Q(Alb) values. In bacterial meningitis, CSF beta-trace (mean=8.7+/-3.9 mg/L) remained invariant to changes of Q(Alb) values. In Guillain-Barré syndrome, CSF beta-trace (mean=14.4+/-6.8 mg/L) was below the Q(Alb)-dependent reference range. In multiple sclerosis and viral meningoencephalitis, beta-trace levels were within the reference range. Beta-trace concentration in CSF can be used in conjunction with Q(AlB) to distinguish between different neurological pathologies associated with CSF protein increase.

In vivo specificity of human alpha1,3/4-fucosyltransferases III-VII in the biosynthesis of LewisX and Sialyl LewisX motifs on complex-type N-glycans. Coexpression studies from bhk-21 cells together with human beta-trace protein

Each of the five human alpha1,3/4-fucosyltransferases (FT3 to FT7) has been stably expressed in BHK-21 cells together with human beta-trace protein (beta-TP) as a secretory reporter glycoprotein. In order to study their in vivo properties for the transfer of peripheral Fuc onto N-linked complex-type glycans, detailed structural analysis was performed on the purified glycoprotein. All fucosyltransferases were found to peripherally fucosylate 19-52% of the diantennary beta-TP N-glycans, and all enzymes were capable of synthesizing the sialyl LewisX (sLex) motif. However, each enzyme produced its own characteristic ratio of sLex/Lex antennae as follows: FT7 (only sLex), FT3 (14:1), FT5 (3:1), FT6 (1.1:1), and FT4 (1:7). Fucose transfer onto beta-TP N-glycans was low in FT3 cells (11% of total antennae), whereas the values for FT7, FT5, FT4, and FT6 cells were 21, 25, 35, and 47%, respectively. FT3, FT4, FT5, and FT7 transfer preponderantly one Fuc per diantennary N-glycan. FT4 preferentially synthesizes di-Lex on asialo diantennary N-glycans and mono-Lex with monosialo chains. In contrast, FT6 forms mostly alpha1,3-difucosylated chains with no, one, or two NeuAc residues. FT3, FT4, and FT6 were proteolytically cleaved and released into the culture medium in significant amounts, whereas FT7 and FT5 were found to be largely resistant toward proteolysis. Studies on engineered soluble variants of FT6 indicate that these forms do not significantly contribute to the in vivo fucose transfer activity of the enzyme when expressed at activity levels comparable to those obtained for the wild-type Golgi form of FT6 in the recombinant host cells.

Cerebrospinal fluid prostaglandins and corticotropin releasing factor in schizophrenics and controls: relationship to sleep architecture

Sleep abnormalities have been consistently observed in patients with schizophrenia. Elevated levels of corticotropin releasing factor (CRF) and prostaglandins (PGs) in the cerebrospinal fluid (CSF) of patients with schizophrenia have been reported, and these neurochemical substances, known to modulate sleep in experimental animals, may play a role in these sleep abnormalities. In this study, we measured PGD2, PGE2, PGF2alpha and CRF levels in the CSF of 14 unmedicated schizophrenic patients and 14 age- and sex-matched control subjects. Polysomnographic recordings were also carried out for each subject. As expected, the sleep of the schizophrenic subjects significantly differed from that of the controls; schizophrenic subjects had a longer sleep onset latency, slept less, spent fewer minutes in stage 2 sleep and had a lower sleep efficiency. We could not, however, detect any differences in CSF CRF and PG levels between normal and schizophrenic subjects, nor could we find any correlation between CSF variables and sleep parameters in the schizophrenic subjects and the non-psychiatric controls. These results do not favor the hypothesis of a role for CRF or PGs in the pathophysiology of sleep disturbances in schizophrenia.

Sodium dodecyl sulfate-capillary gel electrophoretic analysis of molecular mass microheterogeneity of beta-trace protein in cerebrospinal fluid from patients with central nervous system diseases

Molecular mass (M(r)) microheterogeneity of beta-trace protein (beta TP) in cerebrospinal fluid (CSF) from patients with various neurological disorders was analyzed by sodium dodecyl sulfate capillary gel electrophoresis. Under the conditions employed, beta TP with a M(r) distribution of 23,000-30,000 was roughly separated into two subfractions containing the major peaks with M(r) of 26,000 and 28,500, respectively. The peak area ratios of the two subfractions of the electropherograms varied among the samples examined, and elevation in the total beta TP level in the CSF from patients with organic diseases in the central nervous system (CNS) was often accompanied by changes in the ratios of the subfractions. The quantitative changes in the subfraction level in CSF beta TP are considered to reflect the pathological alterations in the CNS.

Beta-trace protein concentration in cerebrospinal fluid is decreased in patients with bacterial meningitis

Although meninges represent a major site of biosynthesis, beta-trace protein (beta-trace) has not been studied in the cerebrospinal fluid (CSF) of meningitis patients. We measured beta-trace in lumbar CSF of normal controls (n = 27) and in patients with various neurological diseases (n = 92) by an immunonephelometric assay. The mean concentration of beta-trace in CSF of control patients was 16.6+/-3.6 mg/l. In bacterial meningitis (n = 41), CSF beta-trace was significantly decreased (8.7+/-3.9 mg/l; P< 0.001), whereas in spinal canal stenosis it was elevated (29.2+/-10.3 mg/l; P= 0.002). In viral meningoencephalitis (n = 12), beta-trace CSF concentrations were normal. Beta-trace concentrations remained below the normal range even after curing of bacterial meningitis, and normalisation of CSF leucocytes and blood-CSF barrier function. Beta-trace may be a useful tool for studying the pathophysiology of bacterial meningitis.

Expression of lipocalin-type prostaglandin D synthase (beta-trace) in human heart and its accumulation in the coronary circulation of angina patients

Lipocalin-type prostaglandin D synthase (L-PGDS) is localized in the central nervous system and male genital organs of various mammals and is secreted as beta-trace into the closed compartment of these tissues separated from the systemic circulation. In this study, we found that the mRNA for the human enzyme was expressed most intensely in the heart among various tissues examined. In human autopsy specimens, the enzyme was localized immunocytochemically in myocardial cells, atrial endocardial cells, and a synthetic phenotype of smooth muscle cells in the arteriosclerotic intima, and accumulated in the atherosclerotic plaque of coronary arteries with severe stenosis. In patients with stable angina (75-99% stenosis), the plasma level of L-PGDS was significantly (P < 0.05) higher in the great cardiac vein (0.694 +/- 0.054 microg/ml, n = 7) than in the coronary artery (0.545 +/- 0.034 microg/ml), as determined by a sandwich enzyme immunoassay. However, the veno-arterial difference in the plasma L-PGDS concentration was not observed in normal subjects without stenosis. After a percutaneous transluminal coronary angioplasty was performed to compress the stenotic atherosclerotic plaques, the L-PGDS concentration in the cardiac vein decreased significantly (P < 0.05) to 0.610 +/- 0.051 microg/ml at 20 min and reached the arterial level within 1 h. These findings suggest that L-PGDS is present in both endocardium and myocardium of normal subjects and the stenotic site of patients with stable angina and is secreted into the coronary circulation.

Prostaglandin D synthase in human megakaryoblastic cells

The cytosol fraction of human platelets did not convert prostaglandin (PG) H2 to PGD2. However, a homogenate of human megakaryoblastic CMK cells (precursor cells of platelets) produced PGD2 from PGH2. The PGD synthase activity was localized in the cytosol of CMK cells, and absolutely required glutathione. The catalytic properties and Western and Northern blottings indicated that the enzyme was PGD synthase of the hematopoietic type rather than the lipocalin type. When CMK cells were differentiated to megakaryocytes with phorbol ester along with induction of cyclooxygenase-1, the PGD synthase activity increased about 2-fold for 2 days and then decreased. In another human megakaryoblastic cell line, Dami, the PGD synthase increased about 10-fold by the addition of phorbol ester. Thus, the PGD synthase, which was undetectable in platelets, appeared during differentiation of megakaryoblasts to megakaryocytes.

Analysis of low-molecular-mass proteins in cerebrospinal fluid by sodium dodecyl sulfate capillary gel electrophoresis

Proteins of low molecular (M(r)) in human cerebrospinal fluid (CSF) were analyzed by capillary electrophoresis in a sodium dodecyl sulfate-containing polymer solution. Under the conditions employed, peaks of beta 2-microglobulin (beta MG) (M(r): 11,700), gamma-trace protein (12,300), myelin basic protein (18,000), beta-trace protein (beta TP) (23,000 to 30,000) and alpha 1-acid glycoprotein (42,000) were detected on the electropherograms. The concentrations of beta MG and beta TP were determined based on the peak area relative to that of an internal standard, Orange G, which was added at a constant amount as the front marker. It was demonstrated that their levels in CSF change under various pathological conditions in the central nervous system.

Prostaglandin D synthase concentration in cerebrospinal fluid and serum of patients with neurological disorders

Prostaglandin D synthase (PGD synthase) or beta-trace protein is a major constituent of human cerebrospinal fluid (CSF) representing-3% of the total CSF protein. We have recently developed a highly specific immunofluorometric assay for PGD synthase, which enabled us to quantify the presence of PGD synthase in fluids and tissues not associated with the CNS. In this report we provide quantitative data of the presence of PGD synthase in CSF and serum from 302 subjects with various neurological diseases and symptoms. PGD synthase levels in CSF are approximately 35-fold higher than those of serum, with a median concentration of 11,299 micrograms/L. A statistically significant association of PGD synthase concentration in CSF was observed with both patient age and gender. There was no correlation between PGD synthase concentration in serum and patient age or gender. To evaluate the clinical utility of PGD synthase in diagnosing neurological diseases, the distribution pattern of PGD synthase in CSF and serum was examined for each neuropathology of 268 patients whose diagnosis was known. No statistical difference was observed between PGD synthase concentration in the CSF (129 cases) or the serum (94 cases) of multiple sclerosis afflicted subjects in comparison to all other patients studied. The distribution pattern was also not different for PGD synthase levels in CSF of patients with HIV/AIDS related neuropathies, viral meningitis and fibromyalgia. We conclude that PGD synthase measurement presents no clinical utility in diagnosing neurological disorders in adulthood. PGD synthase may have a physiological and/or pathological role in the developing brain and in neurodegenerative diseases.

Lipocalin-type prostaglandin D synthase (beta-trace) is a newly recognized type of retinoid transporter

Lipocalin-type prostaglandin D synthase is responsible for the biosynthesis of prostaglandin D2 in the central nervous system and the genital organs and is secreted into the cerebrospinal fluid and the seminal plasma as beta-trace. Here we analyzed retinoids binding of the enzyme by monitoring the fluorescence quenching of an intrinsic tryptophan residue, and appearance of circular dichroism around 330 nm, and a red shift of the UV absorption spectra of retinoids. We found that the enzyme binds all-trans- or 9-cis-retinoic acid and all-trans- or 13-cis-retinal, but not all-trans-retinol, with affinities (Kd of 70-80 nM) sufficient for function as a retinoid transporter. All-trans-retinoic acid inhibited the enzyme activity in a noncompetitive manner, suggesting that it binds to the same hydrophobic pocket as prostaglandin H2, the substrate for prostaglandin D synthase, but at a different site in this pocket. It is likely that this enzyme is a bifunctional protein that acts as both retinoid transporter and prostaglandin D2-producing enzyme.

Capillary electrophoretic analyses of beta-trace protein and other low molecular weight proteins in cerebrospinal fluid from patients with central nervous system diseases

Ordinary capillary-zone electrophoresis (CZE), as well as CZE in a sodium dodecylsulfate-containing polymer solution (SDS-CZE) and capillary isoelectrofocusing (CIEF), was applied to the analysis of low molecular weight proteins in cerebrospinal fluid (CSF) from patients with various neuropsychiatric disorders. Under the CZE conditions employed, a peaks of beta-trace protein (beta TP), which is the most abundant low MW protein in CSF, was clearly detected on the electropherograms of all the samples examined, and the CSF beta TP level could be tentatively determined using allylamine added at a constant concentration as the internal standard. The results revealed that beta TP in CSF was non-specifically increased in organic disease in the central nervous system (CNS), especially in ones giving severe physical damage to the brain tissues. On the other hand, SDS-CZE allowed us to determine simultaneously the CSF minor low MW proteins other than beta TP, such as beta 2-microglobulin, gamma-trace protein, myelin basic protein, etc., while the CIEF electropherograms suggested that beta TP were separated into several fractions with the different PI values. These capillary electrophoresis systems seem to be powerful as aids in the biochemical examinations of beta TP and other low molecular weight proteins in CSF from patients with CNS diseases.

Beta-trace gene expression is regulated by a core promoter and a distal thyroid hormone response element

We isolated and characterized the human beta-Trace protein (betaTP) gene promoter. betaTP, also known as prostaglandin D2 synthase, is a lipocalin secreted from the choroid plexus and meninges into cerebrospinal fluid. Basal transcription of the betaTP gene is directed from a core promoter found within the first 325 bases of the 5'-flanking sequence. The betaTP gene promoter is responsive to thyroid hormone (3,3',5-triiodothyronine, T3) and efficiently repressed by unliganded human thyroid hormone receptor beta (TRbeta). Functional analysis of the betaTP promoter in TE671 cells revealed that responsiveness to T3 occurs in sequences 2.5 kilobase pairs 5' of the start site. Within the hormone-responsive region we identified a thyroid hormone response element (TRE) located from -2576 to -2562 base pairs relative to the transcription start site. The betaTP TRE is composed of two directly repeated consensus half-sites separated by a 3-base pair space (DR3). The betaTP TRE forms specific complexes with TRbeta. We have shown that a gene active in the choroid plexus and meninges is responsive to T3. T3 may play a role in the regulated transport of substances into the cerebrospinal fluid and ultimately the brain.

Prostaglandin D synthase (beta-trace protein): a molecular clock to trace the origin of REM sleep?

In 1965, Zuckerkandl and Pauling proposed a novel concept that some important molecules termed semantides, which carry the information of the genes or a transcript thereof, can be used as molecular clocks to trace evolutionary history. According to this concept, enzymes are designated as tertiary semantides, following genes (primary semantides) and the mRNA (secondary semantides). Based on this idea, I propose that prostaglandin D synthase (which has been demonstrated recently as identical to the beta-trace protein present in the cerebrospinal fluid of mammals) may serve as a molecular clock to trace the origin and evolution of rapid eye movement sleep in the vertebrates.

CSF levels of prostaglandins, especially the level of prostaglandin D2, are correlated with increasing propensity towards sleep in rats

The concentration of PGD2, PGE2, and of PGF2 alpha was measured in the cerebrospinal fluid (CSF) collected from the cisterna magna of conscious rats (n = 29), which, chronically implanted with a catheter for the CSF sampling, underwent deprivation of daytime sleep. Significant elevation of the CSF level of PGD2 was observed following 2.5-h sleep deprivation (SD), and the elevation became more marked following 5- and 10-h SD, apparently reaching the maximum at 5-h SD (703 +/- 140 pg/ml (mean +/- S.E.M.) for baseline vs. 1734 +/- 363 pg/ml for SD, n = 10). The levels of PGE2, and PGF2 alpha also significantly increased following 5- and 10-h SD, but not following 2.5-h SD. It is unlikely that these changes were simply caused by some responses of the animals to stress stimuli, because stress stimuli derived from restraint of the animal at the supine position to a board for 1 h did not produce any acute responses in the CSF levels of prostaglandins (n = 13). In a different group of animals (n = 11) implanted with electrodes for recording electroencephalogram (EEG) and electromyogram (EMG) in addition to the catheter, the levels of the prostaglandins in CSF were determined for slow-wave sleep (SWS) and wakefulness in the day and for SWS and wakefulness in the night. The highest PGD2 value was obtained at daytime SWS, whereas the lowest was at night wakefulness; furthermore, a significant difference was observed between SWS and wakefulness rather than between day and night. The CSF level of PGE2 also showed a similar tendency. In an additional group of animals (n = 6), not only PGD2 but also PGE2 and PGF2 alpha significantly increased the sleeping time of the animal when applied into the subarachnoid space underlying the ventral surface area of the rostral basal forebrain, the previously defined site of action for the sleep-promoting effect of PGD2. The promotion of sleep by PGE2 applied to the subarachnoid space was an effect completely opposite to the well-established awaking effect of the same prostaglandin demonstrated in the hypothalamic region in a series of previous studies. Based on these results, we conclude that increases in CSF levels of prostaglandins, especially that of PGD2, are correlated in rats with heightened propensity towards sleep and further with the depth of sleep under normal as well as SD conditions.

Lipocalin-type prostaglandin D synthase (beta-trace) is located in pigment epithelial cells of rat retina and accumulates within interphotoreceptor matrix

Glutathione-Independent prostaglandin D synthase, identical to beta-trace, (a major CSF protein), is localized in the CNS. This enzyme, lipocalin-type prostaglandin D synthase, is a member of the lipocalin family of secretory proteins that transport small lipophilic substances. This enzyme's activity in adult rat retina was enriched sixfold in retinal pigment epithelium (RPE) and even more in interphotoreceptor matrix (IPM), all higher than brain. Western blots with anti-lipocalin-type prostaglandin D synthase showed three distinct immunoreactive bands. In the retinal cytosolic fraction, only one band was observed (M(r) 25,000); in IPM, the larger component occurred (M(r), 26,000). The RPE membrane-bound fraction showed two bands (M(r) 20,000 and 23,000), indicating synthesis, and the cytosolic fraction contained two bands (M(r) 23,000 and 26,000), indicating modification for release into IPM. At least two glycosylation sites occurred on the prostaglandin D synthase moiety, explaining the three immunoreactive bands in Western blots. Immunohistochemistry with polyclonal antibodies against this lipocalin-type enzyme showed intense localization in RPE, but less in photoreceptor outer and inner segments. In situ hybridization showed mRNA specifically expressed in RPE. Thus, lipocalin-type prostaglandin D synthase is predominantly expressed in RPE and actively accumulated in IPM. This may demonstrate gene sharing because, while catalyzing prostaglandin D2 synthesis, it may perform an additional, unrelated role in IPM. This enzyme is secreted from the RPE into IPM from which it is then taken up by photoreceptors. However, the nature of its ligand(s) is not known; they may be retinoids and/or docosahexanoic acid.

Developmental expression of murine Beta-trace in embryos and adult animals suggests a function in maturation and maintenance of blood-tissue barriers

The complete cDNA for murine Beta-trace protein was isolated by RT-PCR using degenerate primers designed according to amino acid sequences derived from tryptic peptides. It encodes a protein of 165 amino acids (calculated molecular weight 18,472 Da) with a predicted 24-amino-acid leader peptide. In situ analyses during mouse embryonic development and in adult animals revealed a specific temporal expression pattern of Beta-trace. Beta-Trace mRNA was initially detected at 14.5 days postconception in mesenchymal cells destined to become leptomeninges and in the developing testis. Later in development, a lower level of expression was additionally observed in choroid plexus epithelium, in strictly confined regions of the eye (pigment and ciliary epithelium), in the ear (cochlear duct), and within single cells in the brain. Expression was also found in epithelia of the epididymis and the testis Leydig cells of postpubertal animals. The highly specific expression at blood-tissue barriers such as the blood-cerebrospinal fluid, blood-retina blood-aqueous humor, and blood-testis barriers indicates a potential role for this lipocalin in transport and/or in maturation and maintenance of these barriers.

Constitutive secretion of beta-trace protein by cultivated porcine choroid plexus epithelial cells: elucidation of its complete amino acid and cDNA sequences

Primary porcine choroid plexus epithelial cells cultivated in chemically defined medium maintain their epithelial characteristics and form confluent monolayers. They produce a fluid the composition of which resembles cerebrospinal fluid. The present study demonstrates constitutive secretion of large amounts of beta-trace protein. This intrathecally synthesized protein is a prominent polypeptide constituent of natural cerebrospinal fluid. According to the identity of amino acid sequences it has previously been tentatively identified as a prostaglandin-D synthase and as a member of the lipocalin protein family. beta-Trace was purified from cell culture supernatants and was subjected to tryptic digestion and amino acid sequencing of the resulting peptides. The complete primary structure of the protein was obtained by additional isolation of the cDNA from cultured epithelial cells. The porcine 163-amino acid polypeptide showed 69% identity with the human beta-trace and contained two N-glycosylation sites occupied by complex-type oligosaccharides as is the case for the human protein. The amino acid sequences around the N-glycosylation sites of mammalian beta-trace proteins (porcine, human, murine, and rat) were highly conserved. The nucleotide sequence was found to be less conserved; the porcine cDNA had a strikingly high GC-content (67%). The constitutive secretion of beta-trace protein from the in vitro cultivated porcine choroid plexus epithelial cells demonstrates that the cells have retained their major in vivo physiological properties: secretion of cerebrospinal fluid proteins. Therefore, this in vitro culture system may be used as a versatile tool for studying the regulation of the formation of cerebrospinal fluid.

Molecular mechanism of sleep regulation by prostaglandin D2

Recent biochemical, molecular biological, and pharmacological experiments revealed that prostaglandin D synthase as well as prostaglandin D2 circulated in the ventricular system, subarachnoidal space, and extracellular space in the brain. Prostaglandin D2 then interacts with chemosensors or receptors on the ventro-medial surface of the rostral basal forebrain to initiate the signal to promote sleep. Prostaglandin D2 is, therefore, not a typical neurotransmitter but rather a 'neurohormone' or an 'informational substance' that circulates through the cerebrospinal fluid and transmits certain chemical messages to promote sleep. The mode of communication through the cerebrospinal fluid in the ventricular system and the extracellular space has advantages for global regulation of the brain to induce sleep.

Choroid plexus: the major site of mRNA expression for the beta-trace protein (prostaglandin D synthase) in human brain

Expression of beta-trace protein (beta-trace), recently identified as glutathion-independent prostaglandin D synthase (prostaglandin-H2 D-isomerase; EC 5.3.99.2), was localized in paraffin sections of the human brain by in situ hybridization using digoxigenin-labeled antisense cRNA probes. The mRNA for beta-trace was predominantly found in the epithelial cells of the choroid plexus. Hybridization signals were also obtained in some oligodendrocytes, particularly in the white matter. In the leptomeninges, specific signals were found in meningeal macrophages and in single cells of the arachnoid barrier layer. The cells exhibiting hybridization signals with the antisense cRNA probes for beta-trace were identified by counterstaining with antibodies directed against specific cell markers. Additionally, beta-trace mRNA was localized in tubular epithelial and basal cells of the human epididymis and in different cell types within the seminiferous epithelium of the testis.

Astrocytes synthesize and secrete prostaglandin D synthetase in vitro

Prostaglandin D synthetase [PGD-S, prostaglandin-H2 D-isomerase, (5Z, 13E)-(15S)-9alpha, 11 alpha-epidioxy-15-hyrdroxyprosta-5,13-dienoate D-isomerase, EC 5,3,99,2], an enzyme that catalyzes the formation of prostaglandin D2, was originally isolated from homogenates of rat brain and spleen and is known to be a membrane-bound enzyme. Subsequent immunohistochemical studies have shown that PGD-S is associated with neurons in the brain of immature rats, whereas in adult rats it is associated with oligodendrocytes. Several recent studies have shown that the beta-trace protein isolated from human cerebrospinal fluid (CSF), the second most abundant protein in human CSF after albumin, is equivalent to PGD-S. In this paper, we report the preparation of a monospecific polyclonal antibody against purified PGD-S isolated from human CSF and the establishment of a specific radioimmunoassay for this protein. Using this radioimmunoassay in conjunction with immunoblot analysis, PGD-S was detected in various biological fluids including serum, aqueous humor, and rete testis fluid. In addition, an antibody prepared against human PGD-S partially cross-reacted with the PGD-S in the rat and ram. Using a monospecific polyclonal antibody prepared against purified rat PGD-S isolated from rat CSF in conjunction with [35S]methionine incorporation and immunoprecipitation techniques, it was shown for the first time that PGD-S is actively synthesized and secreted by astrocytes cultured in vitro, suggesting the astrocyte is the cellular origin of PGD-S in the CSF. The identification of the astrocyte as the cellular origin of this unique enzyme will allow the use of an in vitro system to study its regulation.

Intercellular communication in the brain: wiring versus volume transmission

During the past two decades several revisions of the concepts underlying interneuronal communication in the central nervous system have been advanced. We propose here to classify communicational phenomena between cells of the central neural tissue under two general frames: "wiring" and "volume" transmission. "Wiring" transmission is defined as intercellular communication occurring through a well-defined connecting structure. Thus, wiring transmission is characterized by the presence of physically identifiable communication channels within the neuronal and/or glial cell network. It includes synaptic transmission but also other types of intercellular communication through a connecting structure (e.g., gap junctions). "Volume" transmission is characterized by signal diffusion in a three-dimensional fashion within the brain extracellular fluid. Thus, multiple, structurally often not well characterized extracellular pathways connect intercommunicating cells. Volume transmission includes short- (but larger than synaptic cleft, i.e. about 20 nm) and long-distance diffusion of signals through the extracellular and cerebrospinal fluid. It must be underlined that the definitions of wiring and volume transmission focus on the modality of transmission and are neutral with respect to the source and target of the transmission, as well as type of informational substance transmitted. Therefore, any cell present in the neural tissue (neurons, astroglia, microglia, ependyma, tanycytes, etc.) can be a source or a target of wiring and volume transmission. In this paper we discuss the basic definitions and some distinctive characteristics of the two types of transmission. In addition, we review the evidence for different types of intercellular communication besides synaptic transmission in the central nervous system during phylogeny, and in vertebrates in physiological and pathological conditions.

Construction of stable BHK-21 cells coexpressing human secretory glycoproteins and human Gal(beta 1-4)GlcNAc-R alpha 2,6-sialyltransferase alpha 2,6-linked NeuAc is preferentially attached to the Gal(beta 1-4)GlcNAc(beta 1-2)Man(alpha 1-3)-branch of diantennary oligosaccharides from secreted recombinant beta-trace protein

The human beta-trace protein has been cloned and has been expressed for the first time in a mammalian host cell line. Stable BHK-21 cell lines exhibiting altered terminal sialylation properties were constructed by cotransfection of cells with the plasmids pMT-beta TP or pAB3-1 which contain the cDNAs encoding the human secretory glycoproteins beta-trace protein or antithrombin III and pABSial containing the human Golgi enzyme CMP-NeuAc:Gal(beta 1-4)GlcNAc-R alpha 2,6-sialyltransferase (ST6N) gene. The beta-trace protein was purified by immunoaffinity chromatography and N-linked oligosaccharides were subjected to carbohydrate structural analysis. The enzymically liberated oligosaccharides were found to consist of 90% of diantennary chains as is the case for natural beta-trace protein from human cerebrospinal fluid. About 90% of the total oligosaccharides were recovered in the monosialo and disialo fractions in a ratio of 1:5. The monosialylated oligosaccharides of beta-trace protein coexpressed with human ST6N were found to contain NeuAc in alpha 2,6- or alpha 2,3-linkage in the same ratio. From 1H-NMR analysis as well as calculations of peak areas obtained by HPLC, 60% of the molecules of the disialo fraction were found to contain NeuAc in both alpha 2,3- and alpha 2,6-linkage to Gal beta(1-4)GlcNAc-R, whereas 40% of the molecules of this fraction contained NeuAc in only alpha 2,3-linkage to Gal(beta 1-4)GlcNAc-R. The alpha 2,6-linked NeuAc was shown to be attached preferentially to the Gal(beta 1-4)GlcNAc(beta 1-2)Man(alpha 1-3) branch of the diantennary structure. Therefore the in vivo specificity of the newly introduced recombinant human ST6N observed in this study supports the previously reported in vitro branch specificity of the bovine colostrum ST6N activity. Furthermore, these studies demonstrate the suitability of genetically engineered mammalian host cell lines with novel glycosylation properties for the production of human-type glycosylated secretory recombinant polypeptides.

'Brain-type' N-glycosylation of asialo-transferrin from human cerebrospinal fluid

Asialo-transferrin from human cerebrospinal fluid was purified to homogeneity. Investigation of the structural characteristics of its oligosaccharides support our hypothesis of 'brain-type' glycosylation of intrathecally synthesized cerebrospinal fluid proteins. For carbohydrate structural analysis, high-pH anion-exchange chromatography, methylation analysis, liquid secondary ion- and matrix-assisted laser desorption/ ionization mass spectrometry of the permethylated derivatives were used. The major structure turned out to be a complex-type agalactodiantennary oligosaccharide with bisecting N-acetylglucosamine and proximal fucose. Analysis of a second transferrin preparation containing both asialo- and sialo-transferrin revealed another major glycan species derived from the sialylated transferrin variant which is galactosylated and lacks bisecting N-acetylglucosamine and fucose.

Structural and functional significance of cysteine residues of glutathione-independent prostaglandin D synthase. Identification of Cys65 as an essential thiol

Glutathione-independent prostaglandin D synthase in rat brain is composed of 189 amino acid residues and catalyzes the isomerization of prostaglandin H2 to prostaglandin D2, an endogenous sleep-promoting substance. This enzyme is the only enzyme among members of the lipocalin superfamily composed of various secretory lipophilic ligand-carrier proteins and is recently identified to be a beta-trace protein, a major constituent of human cerebrospinal fluid. We expressed the active enzyme in Escherichia coli and then systematically substituted all cysteine residues of the delta 1-29 enzyme at positions of 65, 89, and 186 with alanine or serine. The parent and mutant enzymes were purified to apparent homogeneity with a recovery of approximately 30% by chromatography with Sephadex G-50 and S-Sepharose, by which all the enzymes showed identical elution profiles. The purified enzymes, irrespective of the mutation, showed almost the same circular dichroism spectral characteristics as displayed by a highly ordered beta-structure. The recombinant enzymes containing Cys65 showed the activity comparable with that of the enzyme purified from rat brain (approximately 3 mumol/min/mg of protein) in the presence, but not in the absence, of sulfhydryl compounds. However, all of the single, double, and triple mutants without Cys65 lost the enzyme activity. The purified delta 1-29 Ala89,186 enzyme was inactivated reversibly by conjugation with glutathione at Cys65 and irreversibly by the stoichiometric chemical modification with N-ethylmaleimide. These results indicate that Cys65 is an essential thiol of the enzyme and that both the intrinsic and extrinsic sulfhydryl groups are necessary for nonoxidative rearrangement of 9,11-endoperoxide of prostaglandin H2 to produce prostaglandin D2 catalyzed by the enzyme.

Prostaglandins and sleep

The concept of humoral regulation of sleep was initially proposed by a French neuroscientist, Henri Piéron of Paris, in the first decade of this century. He and his associate Legendre were the first to show the presence of a sleep-inducing substance in the cerebrospinal fluid (CSF) of sleep-deprived dogs. Concurrently and independently, Kuniomi Ishimori of Nagoya University, Nagoya, Japan, employing a similar experimental approach, also demonstrated a sleep-inducing substance in the CSF of sleep-deprived dogs. During the next 80 years or so, more than 30 so-called endogenous sleep substances have been reported to exist in the brain by numerous investigators, CSF, and other organs and tissues of mammals. However, their physiological relevance has remained uncertain in most instances. In this review, we shall focus upon our own work concerning the molecular mechanisms of sleep-wake regulation by prostaglandins (PGs) D2 and E2, with special emphasis on the recent developments during the last several years.

Dominant expression of mRNA for prostaglandin D synthase in leptomeninges, choroid plexus, and oligodendrocytes of the adult rat brain

Glutathione-independent prostaglandin D synthase [prostaglandin-H2 D-isomerase; (5Z,13E)-(15S)-9 alpha,11 alpha-epidioxy-15-hydroxyprosta-5,13-dienoate D-isomerase, EC 5.3.99.2] is an enzyme responsible for biosynthesis of prostaglandin D2 in the central nervous system. In situ hybridization with antisense RNA for the enzyme indicated that mRNA for the enzyme was predominantly expressed in the leptomeninges, choroid plexus, and oligodendrocytes of the adult rat brain. The findings agree with those obtained by immunohistochemical staining with antibodies against the enzyme. It was further revealed that prostaglandin D synthase activity was considerably greater in the isolated leptomeninges (14.2 nmol per min per mg of protein) and choroid plexus (7.0 nmol per min per mg of protein) than the activity in the whole brain (2.0 nmol per min per mg of protein). These results, taken together, indicate that the enzyme is mainly synthesized and located in the leptomeninges, choroid plexus, and oligodendrocytes in the brain.