Urinary prostaglandin D synthase (beta-trace) excretion increases in the early stage of diabetes mellitus

Novel biomarkers for prognosticating diabetic kidney disease progression

The global burden of diabetic kidney disease (DKD) is escalating, and it remains as a predominant cause of the end-stage renal disease (ESRD). DKD is associated with increased cardiovascular disease and morbidity in all types of diabetes. Prediction of progression with albuminuria and eGFR is challenging in DKD, especially in non-proteinuric DKD patients. The pathogenesis of DKD is multifactorial characterized by injury to all components of the nephron, whereas albuminuria is an indicator of only glomerular injury. The limits in the diagnostic and prognostic value of urine albumin demonstrate the need for alternative and clinically significant early biomarkers, allowing more targeted and effective diabetic treatment, to reduce the burden of DKD and ESRD. Identification of biomarkers, based on multifactorial pathogenesis of DKD can be the crucial paradigm in the treatment algorithm of DKD patients. This review focuses on the potential biomarkers linked to DKD pathogenesis, particularly with the hope of broadening the diagnostic window to identify patients with different stages of DKD progression.

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.

A panel of urinary proteins predicts active lupus nephritis and response to rituximab treatment

OBJECTIVES

∼30% of patients with SLE develop LN. Presence and/or severity of LN are currently assessed by renal biopsy, but biomarkers in serum or urine samples may provide an avenue for non-invasive routine testing. We aimed to validate a urinary protein panel for its ability to predict active renal involvement in SLE.

METHODS

A total of 197 SLE patients and 48 healthy controls were recruited, and urine samples collected. Seventy-five of the SLE patients had active LN and 104 had no or inactive renal disease. Concentrations of lipocalin-like prostaglandin D synthase (LPGDS), transferrin, alpha-1-acid glycoprotein (AGP-1), ceruloplasmin, monocyte chemoattractant protein 1 (MCP-1) and soluble vascular cell adhesion molecule-1 (sVCAM-1) were quantified by MILLIPLEX® Assays using the MAGPIX Luminex platform. Binary logistic regression was conducted to examine whether proteins levels associate with active renal involvement and/or response to rituximab treatment.

RESULTS

Urine levels of transferrin (P <0.005), AGP-1 (P <0.0001), MCP-1 (P <0.001) and sVCAM-1 (P <0.005) were significantly higher in SLE patients when compared with healthy controls. Furthermore, levels of transferrin, AGP-1, ceruloplasmin, MCP-1 and sVCAM-1 (all P <0.0001) were higher in SLE patients with active LN when compared with patients without active LN. A combination of five urine proteins, namely LPGDS, transferrin, ceruloplasmin, MCP-1 and sVCAM-1 was a good predictor of active LN (AUC 0.898). A combined model of LPGDS, transferrin, AGP-1, ceruloplasmin, MCP-1 and sVCAM-1 predicted response to rituximab treatment at 12 months (AUC 0.818).

CONCLUSIONS

Findings support the use of a urinary protein panel to identify active LN and potentially predict response to treatment with rituximab in adult SLE patients. Prospective studies are required to confirm findings.

Prostaglandins as potential targets for the treatment of polycystic kidney disease

Polycystic kidney disease (PKD) is characterized by the proliferation of fluid-filled kidney cysts that enlarge over time, causing damage to the surrounding kidney and ultimately resulting in kidney failure. Both increased cell proliferation and fluid secretion are stimulated by increased cyclic adenosine monophosphate (cAMP) in PKD kidneys, so many treatments for the disease target cAMP lowering. Prostaglandins (PG) levels are elevated in multiple animal models of PKD and mediate many of their effects by elevating cAMP levels. Inhibiting the production of PG with cyclooxygenase 2 (COX2) inhibitors reduces PG levels and reduces disease progression. However, COX inhibitors also block beneficial PG and can cause nephrotoxicity. In an orthologous model of the main form of PKD, PGD₂ and PGI₂ were the two PG highest in kidneys and most affected by a COX2 inhibitor. Future studies are needed to determine whether specific blockage of PGD₂ and/or PGI₂ activity would lead to more targeted and effective treatments with fewer undesirable side-effects.

Biomarker panels may be superior over single molecules in prediction of renal flares in systemic lupus erythematosus: an exploratory study

Objective

Recent evidence suggests that some urinary biomarkers, namely Vascular Cell Adhesion Molecule-1 (VCAM-1), Intercellular Adhesion Molecule-1 (ICAM-1), Monocyte Chemoattractant Protein 1 (MCP-1), Neutrophil Gelatinase Associated Lipocalcin and Lipocalin-type Prostaglandin D-Synthetase (L-PGDS), might discriminate SLE patients with ongoing renal activity from those with stable disease. The objective of this study was to assess the role of these markers in predicting renal flares in comparison with conventional biomarkers and to derive a biomarker panel which may improve diagnostic accuracy.

Methods

Eligible participants were SLE patients prospectively followed at our clinic. Urinary biomarker levels were measured in urinary sample by ELISA assay and were compared by the unpaired Student’s t test or the Mann–Whitney U test as appropriate. Receiver operating characteristic analysis was used to calculate the area under the curve. Cox regression was used to identify independent factors associated with disease flares.

Results

Urine was collected from 61 patients. During 8 months’ follow-up, eight patients experienced a renal flare. Urinary L-PGDS, ICAM-1 and VCAM-1 levels were significantly increased in the patients who subsequently experienced a renal flare with respect to the remaining 53. At Cox regression analysis, L-PGDS, ICAM-1, VCAM-1, hypocomplementemia and anti-dsDNA antibodies were factors associated with renal flares. Based on receiver operating characteristic analysis, a combination of novel and conventional biomarkers demonstrated an excellent ability for accurately identifying a flare.

Conclusion

This study might suggest the usefulness of a novel biomarker panel in predicting a renal flare in SLE.

Prostaglandins in the pathogenesis of kidney diseases

Prostaglandins (PGs) are important lipid mediators produced from arachidonic acid via the sequential catalyzation of cyclooxygenases (COXs) and specific prostaglandin synthases. There are five subtypes of PGs, namely PGE2, PGI2, PGD2, PGF2α, and thromboxane A2 (TXA2). PGs exert distinct roles by combining to a diverse family of membrane-spanning G protein-coupled prostanoid receptors. The distribution of these PGs, their specific synthases and receptors vary a lot in the kidney. This review summarized the recent findings of PGs together with the COXs and their specific synthases and receptors in regulating renal function and highlighted the insights into their roles in the pathogenesis of various kidney diseases.

Potential serum biomarkers for early detection of diabetic nephropathy

AIM

Diabetic nephropathy (DN) is considered as one of the diabetic complications affecting up to 40% of patients with type 1 or type 2 diabetes. In clinical practice, the frequently used markers of renal disease and progression are serum creatinine, estimated glomerular filtration rate (eGFR) and albuminuria. The aim of this study is to determine new biomarkers in human serum which are promising for early detection of DN.

METHODS

This study included 50 patients with type 2 diabetes mellitus (T2DM) and 25 clinically healthy individuals. The patients were divided into two groups; group I included 25 T2DM patients with normoalbuminuria, and group II consisted of 25 T2DM patients with microalbuminuria. In all groups, neutrophil gelatinase-associated lipocalin (NGAL), β-trace protein (βTP) and microRNA- 130b (miR-130b) were estimated.

RESULTS

The serum levels of NGAL and βTP were significantly elevated in T2DM patients with microalbuminuria (group II) compared with T2DM patients with normoalbuminuria (group I) and control subjects but there was no significant difference between group I and control subjects. Serum miR-130b level was significantly decreased in patients with T2DM (groups I and II) compared with healthy control subjects, with a higher decrease in their levels in group II compared with group I.

CONCLUSION

Our results suggest that serum NGAL and βTP as tubular and glomerular markers respectively, together with serum miR-130b may be independent and reliable biomarkers for early detection of DN in patients with T2DM.

The therapeutic potential of CRTH2/DP2 beyond allergy and asthma

Prostaglandin (PG) D₂ has been in the focus of research for quite a long time, but its biological effects and its roles in human disease are still not fully characterized. When in 2001 a second major PGD₂ receptor termed chemoattractant receptor homologue expressed on Th2 cells (CRTH2; alternative name DP2) was discovered, diverse investigations started to shed more light on the complex and often controversial actions of the prostaglandin. With various immunomodulating effects, such as induction of migration, activation, and cytokine release of leukocytes observed both in vivo and in vitro, CRTH2 has emerged as a promising target for the treatment of allergic diseases. However, with more and more research being performed on CRTH2, it has also become clear that its biological actions are far more diverse than expected at the beginning. In this review, we aim to summarize the roles that PGD₂ - and CRTH2 in particular - might play in diseases of the central nervous system, kidney, intestine, lung, hair and skin, bone and cartilage, and in cancer. Based on current data we propose that blocking CRTH2 might be a potential therapeutic approach to numerous conditions beyond classical allergic diseases and asthma.

International validation of a urinary biomarker panel for identification of active lupus nephritis in children

BACKGROUND

Conventional markers of juvenile-onset systemic lupus erythematosus (JSLE) disease activity fail to adequately identify lupus nephritis (LN). While individual novel urine biomarkers are good at detecting LN flares, biomarker panels may improve diagnostic accuracy. The aim of this study was to assess the performance of a biomarker panel to identify active LN in two international JSLE cohorts.

METHODS

Novel urinary biomarkers, namely vascular cell adhesion molecule-1 (VCAM-1), monocyte chemoattractant protein 1 (MCP-1), lipocalin-like prostaglandin D synthase (LPGDS), transferrin (TF), ceruloplasmin, alpha-1-acid glycoprotein (AGP) and neutrophil gelatinase-associated lipocalin (NGAL), were quantified in a cross-sectional study that included participants of the UK JSLE Cohort Study (Cohort 1) and validated within the Einstein Lupus Cohort (Cohort 2). Binary logistic regression modelling and receiver operating characteristic curve analysis [area under the curve (AUC)] were used to identify and assess combinations of biomarkers for diagnostic accuracy.

RESULTS

A total of 91 JSLE patients were recruited across both cohorts, of whom 31 (34 %) had active LN and 60 (66 %) had no LN. Urinary AGP, ceruloplasmin, VCAM-1, MCP-1 and LPGDS levels were significantly higher in those patients with active LN than in non-LN patients [all corrected p values (p _c) < 0.05] across both cohorts. Urinary TF also differed between patient groups in Cohort 2 (p _c = 0.001). Within Cohort 1, the optimal biomarker panel included AGP, ceruloplasmin, LPGDS and TF (AUC 0.920 for active LN identification). These results were validated in Cohort 2, with the same markers resulting in the optimal urine biomarker panel (AUC 0.991).

CONCLUSION

In two international JSLE cohorts, urinary AGP, ceruloplasmin, LPGDS and TF demonstrate an 'excellent' ability for accurately identifying active LN in children.

Lipocalin-type prostaglandin D2 synthase reduces glucagon secretion in alpha TC-1 clone 6 cells via the DP1 receptor

Diabetes is associated with disturbances in the normal levels of both insulin and glucagon, both of which play critical roles in the regulation of glycemia. Recent studies have found lipocalin-type prostaglandin D₂ synthase (l-PGDS) to be an emerging target involved in the pathogenesis of type-2 diabetes. This study focused on the effect of l-PGDS on glucagon secretion from cultured pancreatic Alpha TC-1 Clone 6 cells. When cells were treated with various concentrations of l-PGDS (0, 10, 50, and 100 ug/ml) for 2 h in 1 mM glucose; glucagon secretion decreased to 670±45, 838±38, 479±11, and 437±45 pg/ml, respectively. In addition, pancreatic islets were isolated from C57BL/6 mice and stained for prostaglandin D₂ receptors, DP1 and DP2, using immunohistochemistry. Our results showed that these islets express only the DP1 receptor. Pancreatic islets were then stained for alpha and beta cells, as well as DP1, to find the primary location of the receptor within the islets using immunofluorescence. Interestingly, DP1 receptor density was found primarily in alpha cells rather than in beta cells. Our study is the first to report a correlation between l-PGDS and glucagon secretion in alpha cells. Based on our obtained results, it can be concluded that higher concentrations of l-PGDS significantly reduced the secretion of glucagon in alpha cells, which may contribute to the pathogenesis of diabetes as well as offer a novel therapeutic site for the treatment of diabetes.

Variations of human urinary proteome

The study on dynamic analysis of human urinary proteome is the foundation that we discriminate certain various urinary proteins as potential bio-marker derived from the disease itself or normal physiological change. In our results, based on RPLC-MS/MS and spectral count to study pooled and individual urine samples and other researchers' studies, it can be known that the content of many urinary proteins maintain relatively stable. We have reason to believe that the relatively stable urinary protein is a very valuable resource as biomarkers. Many similar proteins such as prostaglandin-H2 D-isomerase and apolipoprotein D proteins have been proved our hypothesis. The following field, the number, preservation and treatment methods of urine sample, the standardization of analysis method and data processing, and suitable quantitative method, is ought to the focus of future study.

β-Trace protein: a marker of GFR and other biological pathways

β-Trace protein (BTP), also known as lipocalin prostaglandin D2 synthase (L-PGDS; encoded by the PTGDS gene), is a low-molecular-weight glycoprotein and an emerging novel marker of glomerular filtration rate. BTP is an important constituent of cerebral spinal fluid and is found in much lower concentrations in blood. Its serum origin and renal handling remain poorly understood. Unlike serum creatinine, BTP is not physiologically inert. It possesses both ligand-binding and enzymatic properties. BTP catalyzes the conversion of prostaglandin H2 (PGH2) to PGD2. PGD2 is an eicosanoid involved in a variety of important physiologic processes, including platelet aggregation, vasodilation, inflammation, adipogenesis, and bone remodeling. Several studies now have documented BTP's strong association with glomerular filtration rate, end-stage renal disease, cardiovascular disease, and death in a variety of different patient populations. This review provides an overview of the biochemistry, physiology and metabolism, biological functions, and measurement of BTP; summarizes the evidence for BTP as a marker of both kidney function and cardiovascular disease; and then considers the interplay between its biological properties, serum concentration, and patient outcomes.

The role of lipocalins in airway disease

The pathogenesis of allergic airway inflammation and disease is complex and still not fully understood. Many cells, factors and mediators are involved in the different aspects of induction, maintenance and persistence of airway inflammation. The heterogeneity and redundancy of this system is one of the main reasons why novel therapeutic targets focusing on the pathogenesis of asthma only hesitantly reach the market and clinical application. Thus, it seems mandatory that we proceed in our efforts to better understand this micro cosmos to succeed in the development of safe and effective drugs for the treatment of more severe and refractory forms of asthma and chronic obstructive pulmonary disease. One of the more recently discovered mediators in the context of airway inflammation are the lipocalins (Lcns). They are a family of proteins that share functional and structural similarities and are involved in the transport of small hydrophobic molecules such as steroids and lipids into the cell. Lcns are found in many different cell types from plants and bacteria through invertebrate cells to cells of vertebrate origin. The purpose of this review is to summarize the role of Lcns in airway diseases, focusing on allergic and infectious inflammation. In particular, we will summarize the present knowledge about Lipocalin 1 and Lipocalin 2, where exciting new discoveries in the recent years have highlighted their role in pulmonary disease and infection. This new class of proteins is another putative candidate for the development of novel drugs against airway inflammation.

PGD2-CRTH2 pathway promotes tubulointerstitial fibrosis

Urinary excretion of lipocalin-type PGD(2) synthase (L-PGDS), which converts PG H(2) to PGD(2), increases in early diabetic nephropathy. In addition, L-PGDS expression in the tubular epithelium increases in adriamycin-induced nephropathy, suggesting that locally produced L-PGDS may promote the development of CKD. In this study, we found that L-PGDS-derived PGD(2) contributes to the progression of renal fibrosis via CRTH2-mediated activation of Th2 lymphocytes. In a mouse model, the tubular epithelium synthesized L-PGDS de novo after unilateral ureteral obstruction (UUO). L-PGDS-knockout mice and CRTH2-knockout mice both exhibited less renal fibrosis, reduced infiltration of Th2 lymphocytes into the cortex, and decreased production of the Th2 cytokines IL-4 and IL-13. Furthermore, oral administration of a CRTH2 antagonist, beginning 3 days after UUO, suppressed the progression of renal fibrosis. Ablation of IL-4 and IL-13 also ameliorated renal fibrosis in the UUO kidney. Taken together, these data suggest that blocking the activation of CRTH2 by PGD(2) might be a strategy to slow the progression of renal fibrosis in CKD.

Urinary markers of glomerular injury in diabetic nephropathy

Diabetic nephropathy, the leading cause of renal failure worldwide, affects approximately one-third of all people with diabetes. Microalbuminuria is considered the first sign and the best predictor of progression to renal failure and cardiovascular events. However, albuminuria has several limitations. Therefore, earlier, more sensitive and specific biomarkers with greater predictability are needed. The aim of this paper is to discuss the current literature on biomarkers of glomerular injury that have been implicated in diabetic kidney disease.

Serum and urinary markers of early impairment of GFR in chronic kidney disease patients: diagnostic accuracy of urinary β-trace protein

The screening for chronic kidney diseases (CKD) patients with impaired GFR needs the measurement of serum creatinine (SCr) or cystatin C (SCys). GFR can also be predicted from SCr or SCys with different formulas. The aim of this study, performed in a group of CKD patients with different levels of GFR, was to evaluate the possibility to select the patients with a GFR <90 ml·min(-1)·1.73 m(-2) by means of serum levels and urinary excretion of different low-molecular-weight proteins (LMWP), cystatin C (Cys), β2-microglobulin (β2M), retinol-binding protein (RBP), β-trace protein (BTP), and derived prediction equations for GFR. In the 295 CKD patients (137 women), at all stages of GFR impairment a very high correlation was found between GFR ((99m)Tc-DTPA) and serum Cr, Cys, β2M, and BTP. All these serum markers showed a similar accuracy as indicators of different GFR impairments. RBP had the lowest correlation with GFR and was also significantly less accurate. The different prediction formulas derived from gender, anthropometric data and SCr or S-LMWP had a diagnostic accuracy similar to that of serum Cr, Cys, β2M, and BTP. Urinary albumin was inadequate as an indicator of any level of GFR impairment. Urinary excretion of Cys and β2M increased significantly only in patients with a GFR <30 ml·min(-1)·1.73 m(-2), while urinary BTP increased already at GFR <90 ml·min(-1)·1.73 m(-2). In this selected group of CKD patients, the positive predictive value of urinary BTP for a GFR <90 ml·min(-1)·1.73 m(-2) was 85%, indicating that, in CKD patients, a urine-based test can predict a slight GFR impairment.

Urinary biomarkers involved in type 2 diabetes: a review

Diabetes mellitus is one of the most challenging health concerns of the 21st century. With at least 30% of the diabetic population remaining undiagnosed, effective and early diagnosis is of critical concern. Development of a diagnostic test, more convenient and reliable than those currently used, would therefore be highly beneficial. Urine as a diagnostic medium allows for non-invasive detection of biomarkers, including some associated with type 2 diabetes and its complications. This review provides a synopsis of those urinary biomarkers that potentially may provide a basis for the development of improved diagnostic tests. Three main pathways for the sourcing of potential makers are identified: kidney damage, oxidative stress and low-grade inflammation including atherosclerosis/vascular damage. This review briefly presents each pathway and some of the most relevant urinary biomarkers that may be used to monitor the development or progression of diabetes and its complications. In particular, biomarkers of renal dysfunction such as transferrin, type IV collagen and N-acetyl-beta-D-glucosaminidase might prove to be more sensitive than urinary albumin, the current gold standard, in the detection of incipient nephropathy and risk assessment of cardiovascular disease. Inflammatory markers including orosomucoid, tumour necrosis factor-alpha, transforming growth factor-beta, vascular endothelial growth factor and monocyte chemoattractant protein-1, as well as oxidative stress markers such as 8-hydroxy-2'deoxyguanosine may also be useful biomarkers for diagnosis or monitoring of diabetic complications, particularly kidney disease. However, the sensitivity of these markers compared with albumin requires further investigation.

Increased Concentrations of Prostaglandin D2 During Post-Fracture Bone Remodeling

Objective.

To test the hypothesis that increased concentrations of prostaglandin D2 (PGD2) correlate with bone remodeling. Studies using isolated bone cells indicate that PGD2 may be implicated in the regulation of bone homeostasis, with a positive influence on bone anabolism. We studied patients with traumatic fractures and age- and sex-matched healthy controls as an in vivo model of increased bone remodeling.

Methods.

Thirty-five patients with bone fracture and matched controls were recruited. Urine and sera samples were collected. Urinary 11ß-PGF2α, a PGD2 metabolite, and PGE2 metabolites (PGEM), serum lipocalin-type PGD2 synthase (L-PGDS), bone alkaline phosphatase (bone ALP), and crosslinked C-telopeptides of type I collagen (CTX) were measured.

Results.

At 5–6 weeks post-fracture, 11ß-PGF2α, L-PGDS, bone ALP, and CTX were significantly increased in the fracture patients compared to controls. PGEM levels were not different between groups. Levels of 11ß-PGF2α and bone ALP were positively correlated, suggesting that PGD2 may be implicated in fracture repair.

Conclusion.

These results support our working hypothesis that PGD2 could be implicated in the control of bone anabolism in humans.

Association of serum lipocalin-type prostaglandin D synthase levels with subclinical atherosclerosis in untreated asymptomatic subjects

Recent studies suggest that lipocalin-type prostaglandin (PG) D synthase (L-PGDS), which converts PGH2 to PGD2, is implicated in the pathogenesis of atherosclerosis. However, clinical evidence for the association between serum L-PGDS levels and atherosclerosis has not been reported. In this study, we measured the serum L-PGDS concentration using sandwich enzyme-linked immunosorbent assay (ELISA) and investigated the association with traditional cardiovascular risk factors and surrogate atherosclerotic indices, such as the maximum score of the intima-media complex thickness of the carotid artery (C-IMT(max)) and the brachial-ankle pulse wave velocity (ba-PWV), in 500 non-treated asymptomatic subjects. The serum concentration of L-PGDS was 0.56+/-0.01 (mean+/-SEM, range 0.25-1.27, median 0.54) mg/L. Serum L-PGDS levels increased with age and were higher in men than in women. Serum L-PGDS was higher in subjects with hypertension and increased with increasing numbers of the traditional atherosclerotic risk factors. When the subjects were divided into four groups according to the levels of serum L-PGDS, the age-adjusted values of C-IMT(max) and ba-PWV were significantly increased in subjects with higher serum L-PGDS levels (quartile 3 and quartile 4) compared to those in the lowest quartile (quartile 1), for both genders. Multiple regression analysis including risk factors revealed that serum L-PGDS was an independent determinant for ba-PWV (beta=0.130, p<0.001). Serum L-PGDS tended to associate with C-IMT(max) but was not statistically significant (beta=0.084, p=0.075). In conclusion, our results suggest that an increase in serum L-PGDS concentration is associated with the progression of atherosclerosis.

Increased expression of lipocalin-type prostaglandin D2 synthase in osteoarthritic cartilage

Introduction

Prostaglandin D synthase (PGDS) is responsible for the biosynthesis of PGD and J series, which have been shown to exhibit anti-inflammatory and anticatabolic effects. Two isoforms have been identified: hematopoietic- and lipocalin-type PGDS (H-PGDS and L-PGDS, respectively). The aims of this study were to investigate the expressions of H-PGDS and L-PGDS in cartilage from healthy donors and from patients with osteoarthritis (OA) and to characterize their regulation by interleukin-1-beta (IL-1β) in cultured OA chondrocytes.

Methods

The expressions of H-PGDS and L-PGDS mRNA and protein in cartilage were analyzed by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry, respectively. Chondrocytes were stimulated with IL-1β, and the expression of L-PGDS was evaluated by real-time RT-PCR and Western blotting. The roles of de novo protein synthesis and of the signalling pathways mitogen-activated protein kinases (MAPKs), nuclear factor-kappa-B (NF-κB), and Notch were evaluated using specific pharmacological inhibitors.

Results

L-PGDS and H-PGDS mRNAs were present in both healthy and OA cartilage, with higher levels of L-PGDS than H-PGDS (> 20-fold). The levels of L-PGDS mRNA and protein were increased in OA compared with healthy cartilage. Treatment of chondrocytes with IL-1β upregulated L-PGDS mRNA and protein expressions as well as PGD₂ production in a dose- and time-dependent manner. The upregulation of L-PGDS by IL-1β was blocked by the translational inhibitor cycloheximide, indicating that this effect is indirect, requiring de novo protein synthesis. Specific inhibitors of the MAPK p38 (SB 203580) and c-jun N-terminal kinase (JNK) (SP600125) and of the NF-κB (SN-50) and Notch (DAPT) signalling pathways suppressed IL-1β-induced upregulation of L-PGDS expression. In contrast, an inhibitor of the extracellular signal-regulated kinase (ERK/MAPK) (PD98059) demonstrated no significant influence. We also found that PGD₂ prevented IL-1β-induced upregulation of L-PGDS expression.

Conclusions

This is the first report demonstrating increased levels of L-PGDS in OA cartilage. IL-1β may be responsible for this upregulation through activation of the JNK and p38 MAPK and NF-κB signalling pathways. These data suggest that L-PGDS might have an important role in the pathophysiology of OA.

Lipocalin-type prostaglandin D(2) synthase stimulates glucose transport via enhanced GLUT4 translocation

Previously, we demonstrated that lipocalin-type prostaglandin D(2) synthase (L-PGDS) knockout mice become glucose intolerant and display signs of diabetic nephropathy and accelerated atherosclerosis. In the current study we sought to explain the link between L-PGDS and glucose tolerance. Using the insulin-sensitive rat skeletal muscle cell line, L6, we showed that L-PGDS could stimulate glucose transport approximately 2-fold as well as enhance insulin-stimulated glucose transport, as measured by 2-deoxy-[(3)H]-glucose uptake. The increased glucose transport was not attributed to increased GLUT4 production but rather the stimulation of GLUT4 translocation to the plasma membrane, a phenomenon that was lost when cells were cultured under hyperglycemic (20 mM) conditions or pretreated with wortmannin. There was however, an increase in GLUT1 expression as well as a 3-fold increase in hexokinase III expression, which was increased to nearly 5-fold in the presence of insulin, in response to L-PGDS at 20 mM glucose. In addition, adipocytes isolated from L-PGDS knockout mice were significantly less sensitive to insulin-stimulated glucose transport than wild-type. We conclude that L-PGDS, via production of prostaglandin D(2), is an important mediator of muscle and adipose glucose transport which is modulated by glycemic conditions and plays a significant role in the glucose intolerance associated with type 2 diabetes.

Urinary PGDS levels are associated with vascular injury in type 2 diabetes patients

BACKGROUND

The presence of metabolic syndrome has been shown to be predictors of cardiovascular morbidity and mortality in patients with type 2 diabetes. In a cross-sectional clinical study, we investigated the association of metabolic syndrome with asymptomatic lacunar strokes and cardiovascular disease (CVD) and we compared its significance with urinary protein markers.

METHODS

We studied Japanese type 2 diabetes patients (n=233, men=124, women=109). The diagnosis of metabolic syndrome was made according to WHO and International Diabetes Federation (IDF) criteria. Cardiovascular events were recorded and asymptomatic lacunar lesions were evaluated with magnetic resonance imaging (MRI). We also measured urinary levels of albumin, type IV collagen, beta2-microglobulin (beta2MG), N-acetyl-beta-d-glucosaminidase (NAG) and lipocalin-type prostaglandin D synthase (PGDS).

RESULTS

The prevalence of metabolic syndrome is 31.3% (IDF) and 52% (WHO) in 233 patients and microalbuminuria was present in 62 subjects (26.6%). Metabolic syndrome (WHO) significantly associated with asymptomatic lacunar lesions (p=0.035, OR=2.854, CI 1.075-7.579), while metabolic syndrome (IDF) or urinary markers failed to associate with presence of asymptomatic lacunar lesions. The presence of metabolic syndrome or microalbuminuria did not show significant association with CVD; however, the elevation of beta2MG, NAG and PGDS showed significant association with CVD. By a logistic regression analysis using urinary proteins as independent variables, the presence of higher PGDS excretion independently associated with history of CVD (p=0.025, OR=3.847, CI 1.180-12.545).

CONCLUSIONS

In type 2 diabetes patients, the elevation of urinary PGDS secretion closely associated with cardiovascular events and may be a supplemental or additional marker to the criteria of metabolic syndrome.

Post-translational modification regulates prostaglandin D2 synthase apoptotic activity: characterization by site-directed mutagenesis

Lipocalin-type prostaglandin D(2) synthase (L-PGDS) is a highly glycosylated protein found in several body fluids. Elevated L-PGDS levels have been observed in the serum of patients with renal impairment, diabetes mellitus, and hypertension. Recently, we demonstrated the ability of L-PGDS to induce apoptosis in a variety of cell types including epithelial cells, neuronal cells, and vascular smooth muscle cells (VSMCs). The aim of this study was to investigate the effect several site-directed mutations had on L-PGDS-induced apoptosis in order to identify potential sites of regulation. Point mutations created in a glycosylation site (Asn51), a protein kinase C phosphorylation site (Ser106), and the enzymatic active site (Cys65) all inhibited L-PGDS-induced apoptosis as determined by both terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end-labeling (TUNEL) and caspase3 activity. We also compared the L-PGDS isoforms present in GK rat serum to WKY control serum using two-dimensional gel electrophoresis and observed distinct differences which vanished after PNGase F glycolytic digestion. We conclude that post-translational modification of L-PGDS, by either glycosylation or phosphorylation, enhances its apoptotic activity and inhibits VSMC hyperproliferation and postulate that this process is altered in type 2 diabetes.

Positioning prostanoids of the D and J series in the immunopathogenic scheme

Prostaglandin D(2) (PGD(2)) is produced by a variety of immune and non-hematopoietic cells and appears to function in both an inflammatory and homeostatic capacity. Two genetically distinct PGD(2)-synthesizing enzymes have been identified to date, including hematopoietic- and lipocalin-type PGD synthases (H-PGDS and L-PGDS, respectively). Though the inter-species expression profiles of these two enzymes vary widely, H-PGDS is generally localized to the cytosolic aspect of immune and inflammatory cells, whereas L-PGDS is more resigned to tissue-based expression. PGD(2) activity is principally mediated through two unique G protein-coupled receptors (GPCR), designated DP(1) and DP(2). These receptors exhibit overlapping binding profiles, yet their respective agonists elicit generally distinctive responses. Additional to DP receptors, the PGD(2) metabolite 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) binds the nuclear peroxisome proliferator-activated receptor gamma (PPARgamma) and has the facility to initiate a variety of anti-inflammatory phenotypes either through or independent of PPARgamma association. This review highlights the collective relevance of PGD(2) and its respective synthases, receptors, and metabolites in immunopathologic responses.

Urinary excretions of lipocalin-type prostaglandin D2 synthase predict the development of proteinuria and renal injury in OLETF rats

BACKGROUND

Otsuka Long-Evans Tokushima Fatty (OLETF) rats genetically develop diabetes which is associated with hypertension. In preliminary studies, urinary excretions of L-PGDS (lipocaline-type prostaglandin D synthase) increase before diabetic nephropathy obviously develops, and this may predict progression of renal injury following diabetes. In the present study, we attempted to define whether urinary excretions of L-PGDS behave as the predictor of development of diabetic nephropathy in OLETF rats.

METHODS

We investigated alterations of urinary L-PGDS excretions during the establishment of diabetes and assessed the relationship between the L-PGDS excretions and renal function in OLETF rats. Furthermore, we treated OLETF rats with troglitazone and analysed the effects on L-PGDS metabolisms. Urinary L-PGDS was measured by immunoenzyme assay and the occurrence of L-PGDS and its mRNA in the kidney was assessed by immunohistochemistry and a PCR method.

RESULTS

Urinary excretions of L-PGDS were significantly higher in OLETF rats than non-diabetic Long-Evans Tokushima Otsuka (LETO) rats. The excretions age-dependently increased in OLETF and this increase appeared to be due to increased glomerular permeability to L-PGDS. Messenger RNA and antigenicity of L-PGDS were demonstrated in renal tissue; however, the de novo synthesis of L-PGDS mRNA seemingly contributed to urinary L-PGDS excretions much less than glomerular filtration. Multiple regression analysis revealed that urinary L-PGDS was determined by urinary protein excretions, and not by high blood pressure per se. Conversely, urinary proteinuria in the established diabetic nephropathy was predicted by urinary L-PGDS excretions in the early stage of diabetes.

CONCLUSIONS

Urinary excretions of L-PGDS are likely to reflect the underlying increase in glomerular permeability. This property may be useful to predict forthcoming glomerular damage following diabetes in OLETF rats.

Accelerated glucose intolerance, nephropathy, and atherosclerosis in prostaglandin D2 synthase knock-out mice

Type 2 diabetics have an increased risk of developing atherosclerosis, suggesting the mechanisms that cause this disease are enhanced by insulin resistance. In this study we examined the effects of gene knock-out (KO) of lipocalin-type prostaglandin D(2) synthase (L-PGDS), a protein found at elevated levels in type 2 diabetics, on diet-induced glucose tolerance and atherosclerosis. Our results show that L-PGDS KO mice become glucose-in-tolerant and insulin-resistant at an accelerated rate when compared with the C57BL/6 control strain. Adipocytes were significantly larger in the L-PGDS KO mice compared with controls on the same diets. Cell culture data revealed significant differences between insulin-stimulated mitogen-activated protein kinase phosphatase-2, protein-tyrosine phosphatase-1D, and phosphorylated focal adhesion kinase expression levels in L-PGDS KO vascular smooth muscle cells and controls. In addition, only the L-PGDS KO mice developed nephropathy and an aortic thickening reminiscent to the early stages of atherosclerosis when fed a "diabetogenic" high fat diet. We conclude that L-PGDS plays an important role regulating insulin sensitivity and atherosclerosis in type 2 diabetes and may represent a novel model of insulin resistance, atherosclerosis, and diabetic nephropathy.

Inhibition of cell cycle progression and migration of vascular smooth muscle cells by prostaglandin D2 synthase: resistance in diabetic Goto-Kakizaki rats

The regulation of vascular smooth muscle cell (VSMC) proliferation, migration, and apoptosis plays a clear role in the atherosclerotic process. Recently, we reported on the inhibition of the exaggerated growth phenotype of VSMCs isolated from hypertensive rats by lipocalin-type prostaglandin D2 synthase (L-PGDS). In the present study, we report the differential effects of L-PGDS on VSMC cell cycle progression, migration, and apoptosis in wild-type VSMCs vs. those from a type 2 diabetic model. In wild-type VSMCs, exogenously added L-PGDS delayed serum-induced cell cycle progression from the G1 to S phase, as determined by gene array analysis and the decreased protein expressions of cyclin-dependent kinase-2, p21Cip1, and cyclin D1. Cyclin D3 protein expression was unaffected by L-PGDS, although its gene expression was stimulated by L-PGDS in wild-type cells. In addition, platelet-derived growth factor-induced VSMC migration was inhibited by L-PGDS in wild-type cells. Type 2 diabetic VSMCs, however, were resistant to the L-PGDS effects on cell cycle progression and migration. L-PGDS did suppress the hyperproliferation of diabetic cells, albeit through a different mechanism, presumably involving the 2.5-fold increase in apoptosis and the concomitant 10-fold increase of L-PGDS uptake we observed in these cells. We propose that in wild-type VSMCs, L-PGDS retards cell cycle progression and migration, precluding hyperplasia of the tunica media, and that diabetic cells appear resistant to the inhibitory effects of L-PGDS, which consequently may help explain the increased atherosclerosis observed in diabetes.

Lipocalin-type prostaglandin D synthase in urine in adriamycin-induced nephropathy of mice

BACKGROUND/AIMS

Lipocalin-type prostaglandin D synthase (L-PGDS), an enzyme converting prostaglandin H(2) to prostaglandin D(2), occurs particularly in the cardiovascular system. Urinary L-PGDS excretion is increased in diabetes prior to overt proteinuria, suggesting that it is a predictor of renal injury. In this study, we tested the hypothesis that L-PGDS excretion reflects renal injury in primary glomerular diseases using Adriamycin-induced nephropathy in mice.

METHODS

Twenty 6-week-old ICR female mice were intravenously given a dose of 25 mg Adriamycin/kg body weight through the tail vein. 24-hour urine was collected every day, and blood samples were obtained.

RESULTS

The mice developed significant albuminuria from day 3 onward (p < 0.05), which was followed by overt proteinuria from day 4 (p < 0.05). Histological examination revealed focal mesangial expansion with partial tubular atrophy. Urinary L-PGDS excretion significantly increased from day 1 onward (p < 0.05), and apparently preceded the increase in urinary albumin excretions. Either serum L-PGDS or creatinine levels were not changed by administration of Adriamycin. However, serum creatinine levels were inversely correlated to urinary L-PGDS excretions (r = -0.88, p < 0.05). Immunohistochemistry showed that L-PGDS occurred in the tubules, but not in the glomeruli in Adriamycin mice and L-PGDS mRNA paralleled urinary L-PGDS excretion.

CONCLUSION

Urinary L-PGDS excretion is increased in Adriamycin-induced nephropathy, and this precedes overt albuminuria.

[PGD(2)/L-PGDS system in hypertension and renal injury]

Prostaglandin D(2) (PGD(2)) and its metabolites bind to the intracellular PPARs to regulate vasoactive substances involved in vascular remodeling through regulation of mRNAs transcription as well as through receptor-mediated mechanisms. PGD(2) decreases inducible NO, PAI-1, endothelin, and VCAM expression through inhibition to NF kappa B, STAT, or AP-1 transcription factors, which are regulated by cytokines/immune system. Moreover, transfer of L-PGDS (PGD(2) synthase) into the intracellular space of EC or SMC increases intracellular PGD(2), thereby decreasing these substances. PGD(2) attenuates in vivo organ injury mediated by cytokines and the immune system. The pretreatment with PGD(2) attenuates the liver damage and hemodynamic collapse following LPS. Dahl salt-sensitive rats, with decreased PGD(2) in the outer medulla of the kidney, are prone to hypertensive kidney injury. Serum L-PGDS level is increased in renal dysfunction through a decrease in glomerular filtration. L-PGDS in urine may be derived from a failure of tubular reabsorption or from in situ synthesis. Urinary L-PGDS excretion markedly increases in the early stage of kidney injury, and urinary L-PGDS is a useful predictor of the forthcoming renal injury. Indeed, urinary L-PGDS precedes clinically overt proteinuria or other parameters indicating renal dysfunction in hypertension, primary renal diseases, and diabetes in humans. PGD(2)/L-PGDS system is a Cinderella of vascular biology.

[Functional analyses of lipocalin-type and hematopoietic prostaglandin D synthases]

Prostaglandin (PG) D synthase (PGDS) catalyzes the isomerization of PGH(2) to PGD(2), which acts as an endogenous somnogen and an allergic mediator. There are two distinct types of PGDS: one is lipocalin-type PGDS (L-PGDS) localized in the central nervous system, male genitals, and heart; and the other is hematopoietic PGDS (H-PGDS) in mast cells and Th2 lymphocytes. L-PGDS is the same as beta-trace, a major protein in human cerebrospinal fluid, and is also secreted into the seminal plasma and plasma. The L-PGDS concentration in various body fluids is useful as a marker for various diseases such as renal failure and coronary atherosclerosis. H-PGDS is a cytosolic enzyme and is a member of the Sigma class of glutathione S-transferase. We determined the X-ray crystallographic structures of H-PGDS and L-PGDS. We also generated the gene-knockout (KO) mice and the human enzyme-overexpressing transgenic mice for each PGDS. L-PGDS-KO mice lacked PGE(2)-induced tactile allodynia and rebound of non-rapid eye movement sleep after sleep deprivation. Human L-PGDS-overexpressing transgenic mice showed an increase in non-rapid eye movement sleep due to accumulation of PGD(2) in the brain after tail clipping. H-PGDS-KO mice showed an allergic reaction weaker than that of the wild-type mice.

Specific regulation of lipocalin-type prostaglandin D synthase in mouse heart by estrogen receptor beta

Estrogens have important physiological roles in the cardiovascular system. We use DNA microarray technology to study the molecular mechanism of estrogen action in the heart and to identify novel estrogen-regulated genes. In this investigation we identify genes that are regulated by chronic estrogen treatment of mouse heart. We present our detailed characterization of one of these genes, lipocalin-type prostaglandin D synthase (L-PGDS). Northern and Western blot analysis revealed that L-PGDS was induced both by acute and chronic estrogen treatment. Northern blot analysis, using estrogen receptor (ER)-disrupted mice, suggests that L-PGDS is specifically induced by ERbeta in vivo. In further support of ERbeta-selective regulation, we identify a functional estrogen-responsive element in the L-PGDS promoter, the activity of which is up-regulated by ERbeta, but not by ERalpha. We demonstrate that a one-nucleotide change (A to C) in the L-PGDS estrogen-responsive element affects receptor selectivity.

Prostaglandin D2 synthase inhibits the exaggerated growth phenotype of spontaneously hypertensive rat vascular smooth muscle cells

Lipocalin-type prostaglandin D2 synthase (L-PGDS) has recently been linked to a variety of pathophysiological cardiovascular conditions including hypertension and diabetes. In this study, we report on the 50% increase in L-PGDS protein expression observed in vascular smooth muscle cells (VSMC) isolated from spontaneously hypertensive rats (SHR). L-PGDS expression also increased 50% upon the differentiation of normotensive control cells (WKY, from Wistar-Kyoto rats). In addition, we demonstrate differential effects of L-PGDS treatment on cell proliferation and apoptosis in VSMCs isolated from SHR versus WKY controls. L-PGDS (50 microg/ml) was able to significantly inhibit VSMC proliferation and DNA synthesis and induce the apoptotic genes bax, bcl-x, and ei24 in SHR but had no effect on WKY cells. Hyperglycemic conditions also had opposite effects, in which increased glucose concentrations (20 mm) resulted in decreased L-PGDS expression in control cells but actually stimulated L-PGDS expression in SHR. Furthermore, we examined the effect of L-PGDS incubation on insulin-stimulated Akt, glycogen synthase kinase-3beta (GSK-3beta), and ERK phosphorylation. Unexpectedly, we found that when WKY cells were pretreated with L-PGDS, insulin could actually induce apoptosis and failed to stimulate Akt/GSK-3beta phosphorylation. Insulin-stimulated ERK phosphorylation was unaffected by L-PGDS pretreatment in both cell lines. We propose that L-PGDS is involved in the balance of VSMC proliferation and apoptosis and in the increased expression observed in the hypertensive state is an attempt to maintain a proper equilibrium between the two processes via the induction of apoptosis and inhibition of cell proliferation.

Blood sugar control reverses the increase in urinary excretion of prostaglandin D synthase in diabetic patients

BACKGROUND/AIMS

We investigated basal levels of serum and urinary lipocalin-type prostaglandin D synthase/beta-trace (L-PGDS) in type-2 diabetic patients and explored whether glycemic control affects L-PGDS status in another 55 diabetic inpatients with normoalbuminuria.

METHODS

Fifty-five type-2 diabetic outpatients (HbA1c, 9.14 +/- 0.20%; creatinine (Cr), 85.1 +/- 2.4 micromol/l), and 55 age-matched healthy control subjects were recruited. Serum and urinary levels of L-PGDS were determined with respect to the stage of diabetic nephropathy. The L-PGDS was localized by immunohistochemistry.

RESULTS

The urinary L-PGDS index increased in diabetic patients, compared with the controls (234.8 +/- 27.4 vs. 73.8 +/- 7.8 microg/mmol Cr, p < 0.001). Even in normoalbuminuric patients as well as in microalbuminuric patients, urinary L-PGDS indexes were higher than the controls (166.0 +/- 21.1, p < 0.0001 and 338.6 +/- 62.5 microg/mmol Cr, p < 0.0001, respectively), although the serum L-PGDS level was equal to that in the control subjects. Multiple regression analysis revealed that the urinary L-PGDS index was predicted solely by glucose levels and type-IV collagen index, whereas the serum L-PGDS was determined mainly by age and serum Cr. Glycemic control reduced the urinary L-PGDS index towards the normal range in diabetic patients with normoalbuminuria (172.3 +/- 6.6 vs. 118.1 +/- 2.6 (SE) microg/mmol Cr, p < 0.0001). Immunohistochemistry showed that L-PGDS was uniquely present in the renal tubules in diabetes while in nondiabetics, L-PGDS occurred solely in the peritubular interstitium, not in the tubular cells.

CONCLUSION

Inadequate glycemic control is responsible for urinary L-PGDS excretion in the diabetic patients. Urinary L-PGDS is useful to predict subclinical renal injury associated with type-2 diabetes.

Development and Evaluation of a Practical ELISA for Human Urinary Lipocalin-Type Prostaglandin D Synthase

Background: Urinary excretion of lipocalin-type prostaglandin D synthase (L-PGDS) is significantly increased in patients with chronic renal failure, but its diagnostic potential in less advanced stages of renal diseases remains to be elucidated.

Methods: Six mouse monoclonal antibodies (MAbs) were raised against recombinant human L-PGDS. We constructed a sandwich ELISA with two MAbs that recognized different epitopes with high affinities and assessed its assay performance and clinical utility with urine samples from healthy controls, diabetic patients, and patients with various renal diseases.

Results: Western blot analyses with NH2-terminus-truncated L-PGDS mapped the epitopes to Ala23–Val28 (MAb-7F5 and -10A3), Ser52–Ala73 (MAb-9A6), Tyr107–Val120 (MAb-1B7 and -6F5), and Gly140–Pro155 (MAb-6B9). A sandwich ELISA was constructed with MAb-1B7 and -7F5, the Kd values of which were 3.6 and 3.9 nmol/L, respectively, for native L-PGDS. Recoveries were 91–111%, and intra- and interassay CVs were &lt;6% and &lt;9%, respectively. The ELISA showed parallelism of standard and urine samples and no significant interference by a variety of urinary constituents. Urinary L-PGDS excretion was significantly increased in patients with diabetic nephropathy, IgA nephropathy, and chronic glomerulonephritis even when serum creatinine was not increased. In patients with renal diseases, urinary L-PGDS was correlated with urinary albumin (r = 0.64; P &lt;0.0001), N-acetyl-β-d-glucosaminidase (r = 0.43; P &lt;0.001), and serum creatinine (r = 0.66; P &lt;0.0001). At a cutoff value of 284 mg/mol creatinine, the assay had sensitivities of 74% for diabetic nephropathy and 83% for chronic glomerulonephritis and a specificity of 93%.

Conclusions: This ELISA system is suitable for measurement of urinary L-PGDS in a routine clinical assay and may be useful to detect less advanced stages of renal diseases.

Pronounced eosinophilic lung inflammation and Th2 cytokine release in human lipocalin-type prostaglandin D synthase transgenic mice

PGD(2) is a major lipid mediator released from mast cells, but little is known about its role in the development of allergic reactions. We used transgenic (TG) mice overexpressing human lipocalin-type PGD synthase to examine the effect of overproduction of PGD(2) in an OVA-induced murine asthma model. The sensitization of wild-type (WT) and TG mice was similar as judged by the content of OVA-specific IgE. After OVA challenge, PGD(2), but not PGE(2), substantially increased in the lungs of WT and TG mice with greater PGD(2) increment in TG mice compared with WT mice. The numbers of eosinophils and lymphocytes in the bronchoalveolar lavage (BAL) fluid were significantly greater in TG mice than in WT mice on days 1 and 3 post-OVA challenge, whereas the numbers of macrophages and neutrophils were the same in both WT and TG mice. The levels of IL-4, IL-5, and eotaxin in BAL fluid were also significantly higher in TG mice than in WT mice, although the level of IFN-gamma in the BAL fluid of TG mice was decreased compared with that in WT mice. Furthermore, lymphocytes isolated from the lungs of TG mice secreted less IFN-gamma than those from WT mice, whereas IL-4 production was unchanged between WT and TG mice. Thus, overproduction of PGD(2) caused an increase in the levels of Th2 cytokines and a chemokine, accompanied by the enhanced accumulation of eosinophils and lymphocytes in the lung. These results indicate that PGD(2) plays an important role in late phase allergic reactions in the pathophysiology of bronchial asthma.

Biochemical, structural, genetic, physiological, and pathophysiological features of lipocalin-type prostaglandin D synthase

Lipocalin-type prostaglandin (PG) D synthase (PGDS) catalyzes the isomerization of PGH(2), a common precursor of various prostanoids, to produce PGD(2), a potent endogenous somnogen and nociceptive modulator, in the presence of sulfhydryl compounds. PGDS is an N-glycosylated monomeric protein with an M(r) of 20000-31000 depending on the size of the glycosyl moiety. PGDS is localized in the central nervous system and male genital organs of various mammals and in the human heart and is secreted into the cerebrospinal fluid, seminal plasma, and plasma, respectively, as beta-trace. The PGDS concentrations in these body fluids are useful for the diagnosis of several neurological disorders, dysfunction of sperm formation, and cardiovascular and renal diseases. The cDNA and gene for PGDS have been isolated from several animal species, and the tissue distribution and cellular localization have also been determined. This enzyme is considered to be a dual functional protein; i.e. it acts as a PGD(2)-producing enzyme and also as a lipophilic ligand-binding protein, because the enzyme binds biliverdin, bilirubin (K(d)=30 nM), retinaldehyde, retinoic acid (K(d)=80 nM) with high affinities. X-ray crystallographic analyses revealed that PGDS possesses a beta-barrel structure with a hydrophobic pocket in which an active thiol, Cys(65), the active center for the catalytic reaction, was located facing to the inside of the pocket. Gene-knockout and transgenic mice for PGDS were generated and found to have abnormalities in the regulation of nociception and sleep.