Lipocalin-type prostaglandin D synthase: a glymphopathy marker in idiopathic hydrocephalus.

Idiopathic normal pressure hydrocephalus in elderly people is considered a form of glymphopathy caused by malfunction of the waste clearance pathway, called the glymphatic system. Tau is a representative waste material similar to amyloid-ß. During neurodegeneration, lipocalin-type prostaglandin D synthase (L-PGDS), a major cerebrospinal fluid (CSF) protein, is reported to act as a chaperone that prevents the neurotoxic aggregation of amyloid-ß. L-PGDS is also a CSF biomarker in idiopathic normal pressure hydrocephalus and significantly correlates with tau concentration, age, and age-related brain white matter changes detected by magnetic resonance imaging. To investigate this glymphopathy, we aimed to analyze white matter changes and contributing factors in vivo and their interactions ex vivo. Cerebrospinal tap tests were performed in 60 patients referred for symptomatic ventriculomegaly. Patients were evaluated using an idiopathic normal pressure hydrocephalus grading scale, mini-mental state examination, frontal assessment battery, and timed up-and-go test. The typical morphological features of high convexity tightness and ventriculomegaly were measured using the callosal angle and Evans index, and parenchymal white matter properties were evaluated with diffusion tensor imaging followed by tract-based spatial statistics. Levels of CSF biomarkers, including tau, amyloid-ß, and L-PGDS, were determined by ELISA, and their interaction, and localization were determined using immunoprecipitation and immunohistochemical analyses. Tract-based spatial statistics for fractional anisotropy revealed clusters that positively correlated with mini-mental state examination, frontal assessment battery, and callosal angle, and clusters that negatively correlated with age, disease duration, idiopathic normal pressure hydrocephalus grading scale, Evans index, and L-PGDS. Other parameters also indicated clusters that correlated with symptoms, microstructural white matter changes, and L-PGDS. Tau co-precipitated with L-PGDS, and colocalization was confirmed in postmortem specimens of neurodegenerative disease obtained from the human Brain Bank. Our study supports the diagnostic value of L-PGDS as a surrogate marker for white matter integrity in idiopathic normal pressure hydrocephalus. These results increase our understanding of the molecular players in the glymphatic system. Moreover, this study indicates the potential utility of enhancing endogenous protective factors to maintain brain homeostasis.

Low-dose radiation induces unstable gene expression in developing human iPSC-derived retinal ganglion organoids.

The effects of low-dose radiation on undifferentiated cells carry important implications. However, the effects on developing retinal cells remain unclear. Here, we analyzed the gene expression characteristics of neuronal organoids containing immature human retinal cells under low-dose radiation and predicted their changes. Developing retinal cells generated from human induced pluripotent stem cells (iPSCs) were irradiated with either 30 or 180 mGy on days 4-5 of development for 24 h. Genome-wide gene expression was observed until day 35. A knowledge-based pathway analysis algorithm revealed fluctuations in Rho signaling and many other pathways. After a month, the levels of an essential transcription factor of eye development, the proportion of paired box 6 (PAX6)-positive cells, and the proportion of retinal ganglion cell (RGC)-specific transcription factor POU class 4 homeobox 2 (POU4F2)-positive cells increased with 30 mGy of irradiation. In contrast, they decreased after 180 mGy of irradiation. Activation of the "development of neurons" pathway after 180 mGy indicated the dedifferentiation and development of other neural cells. Fluctuating effects after low-dose radiation exposure suggest that developing retinal cells employ hormesis and dedifferentiation mechanisms in response to stress.

Attenuation of Laser-Induced Choroidal Neovascularization by Blockade of Prostaglandin D2 Receptor 2.

Purpose: The purpose of this study was to investigate the impact of prostaglandin D2 (PGD2) receptor 2 (DP2) on choroidal neovascularization (CNV) formation in mice. Methods: Using a laser-induced CNV model, the CNV size of wild-type (WT) mice treated with DP2 antagonist (CAY10471 or OC000459) was compared with that of untreated mice. Vascular endothelial growth factor (VEGF) and MCP-1 levels were also compared between the two groups. Similar experiments were performed comparing DP2 knockout (DP2KO) mice with WT mice (8 and 56 weeks old). The number of infiltrating macrophages to laser spots was also compared between the WT and DP2KO mice. We administered a DP2 antagonist to 15-methyl PGD2 (a DP2 agonist)-stimulated ARPE-19 cells and measured VEGF secretion by enzyme-linked immunosorbent assay. Tube formation assay was performed on human umbilical vein endothelial cells with or without a DP2 antagonist. Results: CNV sizes were significantly smaller in mice treated with CAY10471 or OC000459 than in those treated with vehicle. Similarly, the CNV size of DP2KO mice was significantly smaller than that of WT mice. The number of macrophages at laser spots in DP2KO mice was significantly lower than that in WT mice. The VEGF concentration of lasered DP2KO mice's eyes was significantly lower than that of lasered WT mice' eyes. DP2 antagonist treatment suppressed VEGF secretion in ARPE-19 cells under 15-methyl PGD2 stimulation. The tube formation assay suggested that lumen formation was inhibited by a DP2 antagonist. Conclusions: DP2 blockade attenuated choroidal neovascularization. Translational Relevance: Drugs targeting DP2 are potentially a novel treatment for age-related macular degeneration.

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

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

Hematopoietic Prostaglandin D2 Synthase Controls Tfh/Th2 Communication and Limits Tfh Antitumor Effects.

T follicular helper (Tfh) cells are a subset of CD4+ T cells essential in immunity and have a role in helping B cells produce antibodies against pathogens. However, their role during cancer progression remains unknown. The mechanism of action of Tfh cells remains elusive because contradictory data have been reported on their protumor or antitumor responses in human and murine tumors. Like Tfh cells, Th2 cells are also involved in humoral immunity and are regularly associated with tumor progression and poor prognosis, mainly through their secretion of IL4. Here, we showed that Tfh cells expressed hematopoietic prostaglandin D2 (PGD2) synthase in a pSTAT1/pSTAT3-dependent manner. Tfh cells produced PGD2, which led to recruitment of Th2 cells via the PGD2 receptor chemoattractant receptor homologous molecule expressed on Th type 2 cells (CRTH2) and increased their effector functions. This cross-talk between Tfh and Th2 cells promoted IL4-dependent tumor growth. Correlation between Th2 cells, Tfh cells, and hematopoietic PGD2 synthase was observed in different human cancers and associated with outcome. This study provides evidence that Tfh/Th2 cross-talk through PGD2 limits the antitumor effects of Tfh cells and, therefore, could serve as a therapeutic target.

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 ß-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 ß peptides, prevents their fibril formation, and disaggregates amyloid ß fibrils, acting as a major amyloid ß 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.

Inhibition of cardiac PERK signaling promotes peripartum cardiac dysfunction.

Peripartum cardiomyopathy (PPCM) is a life-threatening heart failure occurring in the peripartum period. Although mal-angiogenesis, induced by the 16-kDa N-terminal prolactin fragment (16 K PRL), is involved in the pathogenesis, the effect of full-length prolactin (23 K PRL) is poorly understood. We transfected neonate rat cardiomyocytes with plasmids containing 23 K PRL or 16 K PRL in vitro and found that 23 K PRL, but not 16 K PRL, upregulated protein kinase RNA-like endoplasmic reticulum kinase (PERK) signaling, and hypoxia promoted this effect. During the perinatal period, cardiomyocyte-specific PERK homogenous knockout (CM-KO) mice showed PPCM phenotypes after consecutive deliveries. Downregulation of PERK or JAK/STAT signaling and upregulation of apoptosis were observed in CM-KO mouse hearts. Moreover, in bromocriptine-treated CM-KO mice, cardiac function did not improve and cardiomyocyte apoptosis was not suppressed during the peripartum period. These results demonstrate that interaction between 23 K PRL and PERK signaling is cardioprotective during the peripartum term.

Substrate-induced product-release mechanism of lipocalin-type prostaglandin D synthase.

Prostaglandin D2 (PGD2), an endogenous somnogen, is a unique PG that is secreted into the cerebrospinal fluid. PGD2 is a relatively fragile molecule and should be transported to receptors localized in the basal forebrain without degradation. However, it remains unclear how PGD2 is stably carried to such remote receptors. Here, we demonstrate that the PGD2-synthesizing enzyme, Lipocalin-type prostaglandin D synthase (L-PGDS), binds not only its substrate PGH2 but also its product PGD2 at two distinct binding sites for both ligands. This behaviour implys its PGD2 carrier function. Nevertheless, since the high affinity (Kd = âˆ¼0.6 µM) of PGD2 in the catalytic binding site is comparable to that of PGH2, it may act as a competitive inhibitor, while our binding assay exhibits only weak inhibition (Ki = 189 µM) of the catalytic reaction. To clarify this enigmatic behavior, we determined the solution structure of L-PGDS bound to one substrate analog by NMR and compared it with the two structures: one in the apo form and the other in substrate analogue complex with 1:2 stoichiometry. The structural comparisons showed clearly that open or closed forms of loops at the entrance of ligand binding cavity are regulated by substrate binding to two sites, and that the binding to a second non-catalytic binding site, which apparently substrate concentration dependent, induces opening of the cavity that releases the product. From these results, we propose that L-PGDS is a unique enzyme having a carrier function and a substrate-induced product-release mechanism.

Human U90926 orthologous long non-coding RNA as a novel biomarker for visual prognosis in herpes simplex virus type-1 induced acute retinal necrosis.

Acute retinal necrosis (ARN) is a form of infectious uveitis caused by alpha herpesviruses, including herpes simplex virus type 1 (HSV-1). We previously found that the long non-coding RNA (lncRNA) U90926 is upregulated in murine retinal photoreceptor cells following HSV-1 infection, leading to host cell death. However, to date, an orthologous transcript has not been identified in humans. We investigated U90926 orthologous transcript in humans and examined its utility as a prognostic marker for visual acuity in patients with ARN. We identified two human orthologous transcripts (1955 and 592 bases) of lncRNA U90926. The amount of the longer human U90926 transcript was approximately 30- and 40-fold higher in the vitreous fluid of patients with ARN than in those with sarcoidosis and intraocular lymphoma, respectively. Furthermore, the expression of the longer human U90926 transcript in the vitreous fluid was highly correlated with the final best-corrected logarithm of the minimum angle of resolution visual acuity in patients with ARN (r = 0.7671, p = 0.0079). This suggests higher expression of the longer human U90926 transcript in the vitreous fluid results in worse visual prognosis; therefore, expression of the longer human U90926 transcript is a potential negative prognostic marker for visual acuity in patients with ARN.

Induction of narcolepsy-like symptoms by orexin receptor antagonists in mice.

Orexins/hypocretins are hypothalamic neuropeptides that promote and stabilize wakefulness by binding to the orexin receptor type-1 (OX1R) and type-2 (OX2R). Disruption of orexinergic signaling results in the sleep disorder narcolepsy in mice, rats, dogs, and humans. The orexin receptor antagonist suvorexant promotes sleep by blocking both OX1R and OX2R. Whereas suvorexant has been clinically approved for the treatment of insomnia because it is well tolerated in experimental animals as well as in human patients, a logical question remains as to why orexin receptor antagonists do not induce overt narcolepsy-like symptoms. Here we show that acute and chronic suvorexant promotes both rapid eye movement (REM) and non-rapid eye movement (NREM) sleep without inducing cataplexy in mice. Interestingly, chronic suvorexant increases OX2R mRNA and decreases orexin mRNA and peptide levels, which remain low long after termination of suvorexant administration. When mice are chronically treated with suvorexant and then re-challenged with the antagonist after a 1-week washout, however, cataplexy and sleep-onset REM (SOREM) are observed, which are exacerbated by chocolate administration. Heterozygous orexin knockout mice, with lower brain orexin levels, show cataplexy and SOREM after acute suvorexant administration. Furthermore, we find that acute suvorexant can induce cataplexy and SOREM in wild-type mice when co-administered with chocolate under stress-free (temporally anesthetized) conditions. Taken together, these results suggest that suvorexant can inhibit orexin synthesis resulting in susceptibility to narcolepsy-like symptoms in mice under certain conditions.

PERK inhibition attenuates vascular remodeling in pulmonary arterial hypertension caused by BMPR2 mutation.

Pulmonary arterial hypertension (PAH) is a fatal disease characterized by excessive pulmonary vascular remodeling. However, despite advances in therapeutic strategies, patients with PAH bearing mutations in the bone morphogenetic protein receptor type 2 (BMPR2)-encoding gene present severe phenotypes and outcomes. We sought to investigate the effect of PER-like kinase (PERK), which participates in one of three major pathways associated with the unfolded protein response (UPR), on PAH pathophysiology in BMPR2 heterozygous mice. BMPR2 heterozygosity in pulmonary artery smooth muscle cells (PASMCs) decreased the abundance of the antiapoptotic microRNA miR124-3p through the arm of the UPR mediated by PERK. Hypoxia promoted the accumulation of unfolded proteins in BMPR2 heterozygous PASMCs, resulting in increased PERK signaling, cell viability, cellular proliferation, and glycolysis. Proteomic analyses revealed that PERK ablation suppressed PDGFRß-STAT1 signaling and glycolysis in hypoxic BMPR2 heterozygous PASMCs. Furthermore, PERK ablation or PERK inhibition ameliorated pulmonary vascular remodeling in the Sugen/chronic hypoxia model of PAH, irrespective of BMPR2 status. Hence, these findings suggest that PERK inhibition is a promising therapeutic strategy for patients with PAH with or without BMPR2 mutation.

Steroids Inhibit Eosinophil Accumulation and Downregulate Hematopoietic Chemotaxic Prostaglandin D2 Receptor in Aspirin-Exacerbated Respiratory Disease.

BACKGROUND: Aspirin-exacerbated respiratory disease (AERD) is characterized by eosinophilic rhinosinusitis, nasal polyposis, aspirin sensitivity, and asthma. Aims/Objectives: This study aims to identify a mechanism to target for the future treatment of AERD via the elucidation of the effect of systemic steroids on the expression of hematopoietic prostaglandin D2 synthase (HPGDS) and chemotaxic prostaglandin D2 (DP2) receptor relative to eosinophil activation in the nasal polyps of patients with AERD. MATERIALS AND METHODS: Among 37 patients undergoing endoscopic sinus surgery, 28 received systemic steroids preoperatively. Nasal polyps were harvested from all 37 patients. After routine processing of paraffin sections, immunohistochemistry was performed using specific antibodies for HPGDS, eosinophil peroxidase (EPX), and DP2. RESULTS: Expression of HPGDS, DP2, and EPX by eosinophils was higher and more frequent in patients with non-preoperative steroid therapy. Likewise, HPGDS and DP2 were highly expressed in activated eosinophils in the nasal polyps, but not in normal eosinophils. CONCLUSION AND SIGNIFICANCE: This study provides clear evidence that systemic steroid therapy inhibits eosinophil activation and decreases HPGDS and DP2 expression in patients with AERD, indicating a reduction in prostaglandin D2 production and hence control hyperplasia of nasal polyps.

Preventing Dementia Using Saffron, The Kampo Medicine, Kamiuntanto, and Their Combination, Kamiuntantokabankoka.

The objective of this review is to evaluate the anti-dementia activities of saffron and its combination with Kampo medicine. The Kampo formula Kamiuntanto composed of 13 crude drugs is well known for its anti-dementia activity. A significant increase in choline acetyltransferase activity and mRNA levels were observed. Polygala radix was identified as the most essential component drug in Kamiuntanto, probably due to the saponins, tenuifolin, and sinapinic acid. Ginseng was also identified as an essential Kamiuntanto component in terms of its synergistic functions with Polygala radix. Saffron, which was recommended in the Bencao Gangmu for memory and dementia, and is used as an anti-spasmodic, anti-catarrhal, and sedative herbal drug. Saffron and its major constituent, crocin were shown to enhance learning-memory, non-rapid eye movement (rem) sleep, and inhibit depression and neuronal cell death due to strong anti-oxidant and anti-inflammation activities. In addition based on the epidemiological studies such as the treatment of sleeping disorders and the clinical trials of saffron for Alzheimer patients, we demonstrated the indirect and direct anti-dementia activities of crocin and saffron.

Lipocalin-type prostaglandin D synthase levels increase in patients with narcolepsy and idiopathic hypersomnia.

STUDY OBJECTIVES: Excessive daytime sleepiness (EDS) is a frequent cause for consultation and a defining symptom of narcolepsy and idiopathic hypersomnia (IH). The associated mechanisms remain unclear. Lipocalin-type prostaglandin D synthase (LPGDS) is a plausible sleep-inducing candidate. This study is to compare cerebral spinal fluid (CSF) and serum LPGDS levels in patients group with hypersomnia of central origin, including those with narcolepsy type 1 (NT1) and type 2 (NT2) and IH, to those in healthy controls (Con). METHODS: Serum LPGDS, CSF LPGDS, and CSF hypocretin-1(Hcrt-1) levels were measured by ELISA in 122 narcolepsy patients (106 NT1 and 16 NT2), 27 IH, and 51Con. RESULTS: LPGDS levels in CSF (p = 0.02) and serum (p < 0.001) were 22%-25% lower in control subjects than in patients with EDS complaints, including NT1, NT2, and IH. In contrast to significant differences in CSF Hcrt-1 levels, CSF L-PGDS levels and serum L-PGDS were comparable among NT1, NT2, and IH (p > 0.05), except for slightly lower serum LPGDS in IH than in NT1 (p = 0.01). Serum L-PGDS correlated modestly and negatively to sleep latency on MSLT (r = -0.227, p = 0.007) in hypersomnia subjects. CONCLUSIONS: As a somnogen-producing enzyme, CSF/serum LPGDS may serve as a new biomarker for EDS of central origin and imply a common pathogenetic association, but would complement rather than replaces orexin markers.

L-PGDS deficiency accelerated the development of naturally occurring age-related osteoarthritis.

Osteoarthritis (OA) is the most common musculoskeletal disorder among the elderly. It is characterized by progressive cartilage degradation, synovial inflammation, subchondral bone remodeling and pain. Lipocalin prostaglandin D synthase (L-PGDS) is responsible for the biosynthesis of PGD2, which has been implicated in the regulation of inflammation and cartilage biology. This study aimed to evaluate the effect of L-PGDS deficiency on the development of naturally occurring age-related OA in mice. OA-like structural changes were assessed by histology, immunohistochemistry, and micro-computed tomography. Pain related behaviours were assessed using the von Frey and the open-field assays. L-PGDS deletion promoted cartilage degradation during aging, which was associated with enhanced expression of extracellular matrix degrading enzymes, matrix metalloprotease 13 (MMP-13) and a disintegrin and metalloproteinase with thrombospondin motifs 5 (ADAMTS-5), and their breakdown products, C1,2C, VDIPEN and NITEG. Moreover, L-PGDS deletion enhanced subchondral bone changes, but had no effect on its angiogenesis. Additionally, L-PGDS deletion increased mechanical sensitivity and reduced spontaneous locomotor activity. Finally, we showed that the expression of L-PGDS was elevated in aged mice. Together, these findings indicate an important role for L-PGDS in naturally occurring age-related OA. They also suggest that L-PGDS may constitute a new efficient therapeutic target in OA.

PERK participates in cardiac valve development via fatty acid oxidation and endocardial-mesenchymal transformation.

Protein kinase R-like endoplasmic reticulum kinase (PERK) is one of the endoplasmic reticulum (ER) stress sensors. PERK loss-of-function mutations are known to cause Wolcott-Rallison syndrome. This disease is characterized by early-onset diabetes mellitus, skeletal dysplasia, and cardiac valve malformation. To understand the role of PERK in valve formation in vivo, we used an endothelial-specific PERK conditional knockout mice as well as in vitro PERK inhibition assays. We used ProteoStat dyes to visualize the accumulation of misfolded proteins in the endocardial cushion and valve mesenchymal cells (VMCs). Then, VMCs were isolated from E12.5 fetal mice, by fluorescence assisted cell sorting. Proteomic analysis of PERK-deleted VMCs identified the suppression of proteins related to fatty acid oxidation (FAO), especially carnitine palmitoyltransferase II (CPT2). CPT2 is a critical regulator of endocardial-mesenchymal transformation (EndoMT); however how TGF-ß downstream signaling controls CPT2 expression remains unclear. Here, we showed that PERK inhibition suppressed, not only EndoMT but also CPT2 protein expression in human umbilical vein endothelial cells (HUVECs) under TGF-ß1 stimulation. As a result, PERK inhibition suppressed mitochondrial metabolic activity. Taken together, these results demonstrate that PERK signaling is required for cardiac valve formation via FAO and EndoMT.

Long noncoding RNA U90926 is crucial for herpes simplex virus type 1 proliferation in murine retinal photoreceptor cells.

Long non-coding RNAs (lncRNAs) play vital roles in the pathogenesis of infectious diseases, but the role of lncRNAs in herpes simplex virus 1 (HSV-1) infection remains unknown. Using RNA sequencing analysis, we explored lncRNAs that were highly expressed in murine retinal photoreceptor cell-derived 661W cells infected with HSV-1. U90926 RNA (522 nucleotides) was the most upregulated lncRNA detected post HSV-1 infection. The level of U90926 RNA was continuously increased post HSV-1 infection, reaching a 100-fold increase at 24 h. Cellular fractionation showed that U90926 RNA was located in the nucleus post HSV-1 infection. Downregulation of U90926 expression by RNA interference markedly suppressed HSV-1 DNA replication (80% reduction at 12 h post infection) and HSV-1 proliferation (93% reduction at 12 h post infection) in 661W cells. The survival rates of U90926-knockdown cells were significantly increased compared to those of control cells (81% and 21%, respectively; p < 0.0001). Thus, lncRNA U90926 is crucial for HSV-1 proliferation in retinal photoreceptor cells and consequently leads to host cell death by promoting HSV-1 proliferation.

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

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

Niacin Attenuates Pulmonary Hypertension Through H-PGDS in Macrophages.

RATIONALE: Pulmonary arterial hypertension (PAH) is characterized by progressive pulmonary vascular remodeling, accompanied by varying degrees of perivascular inflammation. Niacin, a commonly used lipid-lowering drug, possesses vasodilating and proresolution effects by promoting the release of prostaglandin D2 (PGD2). However, whether or not niacin confers protection against PAH pathogenesis is still unknown. OBJECTIVE: This study aimed to determine whether or not niacin attenuates the development of PAH and, if so, to elucidate the molecular mechanisms underlying its effects. METHODS AND RESULTS: Vascular endothelial growth factor receptor inhibitor SU5416 and hypoxic exposure were used to induce pulmonary hypertension (PH) in rodents. We found that niacin attenuated the development of this hypoxia/SU5416-induced PH in mice and suppressed progression of monocrotaline-induced and hypoxia/SU5416-induced PH in rats through the reduction of pulmonary artery remodeling. Niacin boosted PGD2 generation in lung tissue, mainly through H-PGDS (hematopoietic PGD2 synthases). Deletion of H-PGDS, but not lipocalin-type PGDS, exacerbated the hypoxia/SU5416-induced PH in mice and abolished the protective effects of niacin against PAH. Moreover, H-PGDS was expressed dominantly in infiltrated macrophages in lungs of PH mice and patients with idiopathic PAH. Macrophage-specific deletion of H-PGDS markedly decreased PGD2 generation in lungs, aggravated hypoxia/SU5416-induced PH in mice, and attenuated the therapeutic effect of niacin on PAH. CONCLUSIONS: Niacin treatment ameliorates the progression of PAH through the suppression of vascular remodeling by stimulating H-PGDS-derived PGD2 release from macrophages.