Uterine prostaglandin DP receptor induced upon implantation contributes to decidualization together with EP4 receptor.

To investigate the yet-unknown roles of prostaglandins (PGs) in the uterus, we analyzed the expression of various PG receptors in the uterus. We found that three types of Gs-coupled PG receptors, DP, EP2, and EP4 were expressed in luminal epithelial cells from the peri-implantation period to late pregnancy. DP expression was also induced in stromal cells within the mesometrial region, whereas EP4 was expressed in stromal cells within the anti-mesometrial region during the peri-implantation period. The timing of DP induction after embryo attachment correlated well with that of cyclooxygenase-2 (COX-2); however, COX-2-expressing stromal cells were located in the vicinity of the embryo, whereas DP-expressing stromal cells surrounded these cells on the mesometrial side. Specific [3H]PGD2-binding activity was detected in the decidua of uteri, with PGD2 synthesis comparable to that of PGE2 detected in the uteri during the peri-implantation period. Administration of the COX-2-specific inhibitor celecoxib caused adverse effects on decidualization, as demonstrated by the attenuated weight of the implantation sites, which was recovered by the simultaneous administration of a DP agonist. Such a rescuing effect of the DP agonist was mimicked by an EP4 agonist, but not an EP2 agonist. Whereas the importance of DP signaling was shown pharmacologically, DP/EP2 double deficiency did not affect implantation and decidualization, suggesting the contribution of EP4 to these processes. Indeed, administration of an EP4 antagonist substantially affected decidualization in DP/EP2-deficient mice. These results suggest that COX-2-derived PGD2 and PGE2 contribute to decidualization via a coordinated pathway of DP and EP4 receptors.

Prostaglandin F2α Affects the Cycle of Clock Gene Expression and Mouse Behavior.

Prostaglandins are bioactive compounds, and the activation of their receptors affects the expression of clock genes. However, the prostaglandin F receptor (Ptgfr) has no known relationship with biological rhythms. Here, we first measured the locomotor period lengths of Ptgfr-KO (B6.129-Ptgfrtm1Sna) mice and found that they were longer under constant dark conditions (DD) than those of wild-type (C57BL/6J) mice. We then investigated the clock gene patterns within the suprachiasmatic nucleus in Ptgfr-KO mice under DD and observed a decrease in the expression of the clock gene cryptochrome 1 (Cry1), which is related to the circadian cycle. Moreover, the expression of Cry1, Cry2, and Period2 (Per2) mRNA were significantly altered in the mouse liver in Ptgfr-KO mice under DD. In the wild-type mouse, the plasma prostaglandin F2α (PGF2α) levels showed a circadian rhythm under a 12 h cycle of light-dark conditions. In addition, in vitro experiments showed that the addition of PTGFR agonists altered the amplitude of Per2::luc activity, and this alteration differed with the timing of the agonist addition. These results lead us to hypothesize that the plasma rhythm of PGF2α is important for driving clock genes, thus suggesting the involvement of PGF2α- and Ptgfr-targeting drugs in the biological clock cycle.

Effects of an ω3 fatty acid-biased diet on luteolysis, parturition, and uterine prostanoid synthesis in pregnant mice.

The ω3 polyunsaturated fatty acids (PUFAs) are known to have beneficial effects on health and diseases, and hence their intake is encouraged. However, it remains unknown as to how ω3 PUFAs affect female reproduction processes, in which ω6 PUFA-derived prostaglandin (PG) E2 and PGF2α play crucial roles. We therefore compared female reproductive performance between ω3 PUFA-biased linseed oil diet-fed (Lin) mice and ω6 PUFA-biased soybean oil diet-fed (Soy) mice. In Lin mice, the uterine levels of arachidonic acid (AA) and eicosapentaenoic acid (EPA) were 0.42 fold and 16 fold of those in Soy mice, respectively, with the EPA/AA ratio being 0.7 (vs 0.02 in Soy mice). Lin mice showed no alterations in any of the fertility indexes, including luteolysis and parturition. The uterine PG synthesis profiles of Lin mice were similar to those of Soy mice, but the levels of PGF2α and PGE2 were 50% of those in Soy mice, as a result of the increased EPA/AA ratio. PGF3α and PGE3 were undetectable in the uterine tissues of Soy and Lin mice. Interestingly, in Lin mice, 'luteolytic' PGF2α synthesis was considerably maintained even in the ω6 PUFA-reduced condition. These results suggest the existence of an elaborate mechanism securing PGF2α synthesis to a level that is sufficient for triggering luteolysis and parturition, even under ω6 PUFA-reduced conditions.

Metabolic Regulation in Adipocytes by Prostanoid Receptors.

Prostanoids are a group of typical lipid mediators that are biosynthesized from arachidonic acid by the actions of cyclooxygenases and their subsequent terminal synthases. Prostanoids exert a wide variety of actions through their specific membrane receptors on target cells. In addition to their classical actions, including fever, pain, and inflammation, prostanoids have been shown to play pivotal roles in various biological processes, such as female reproduction and the maintenance of vascular and gut homeostasis. Moreover, recent research using mice deficient in each of the prostanoid receptors, or using agonists/antagonists specific for each receptor clarified novel actions of prostanoids that had long been unknown, and the mechanisms therein. In this review, we introduce recent advances in the fields of metabolic control by prostanoid receptors such as in adipocyte differentiation, lipolysis, and adipocyte browning in adipose tissues, and discuss the potential of prostanoid receptors as a treatment target for metabolic disorders.

Ligand binding to human prostaglandin E receptor EP4 at the lipid-bilayer interface.

Prostaglandin E receptor EP4, a G-protein-coupled receptor, is involved in disorders such as cancer and autoimmune disease. Here, we report the crystal structure of human EP4 in complex with its antagonist ONO-AE3-208 and an inhibitory antibody at 3.2 Å resolution. The structure reveals that the extracellular surface is occluded by the extracellular loops and that the antagonist lies at the interface with the lipid bilayer, proximal to the highly conserved Arg316 residue in the seventh transmembrane domain. Functional and docking studies demonstrate that the natural agonist PGE2 binds in a similar manner. This structural information also provides insight into the ligand entry pathway from the membrane bilayer to the EP4 binding pocket. Furthermore, the structure reveals that the antibody allosterically affects the ligand binding of EP4. These results should facilitate the design of new therapeutic drugs targeting both orthosteric and allosteric sites in this receptor family.

Amakusamine from a Psammocinia sp. Sponge: Isolation, Synthesis, and SAR Study on the Inhibition of RANKL-Induced Formation of Multinuclear Osteoclasts.

A simple methylenedioxy dibromoindole alkaloid, amakusamine (1), was isolated from a marine sponge of the genus Psammocinia, and its structure was determined from spectroscopic data, time-dependent density-functional theory calculations, and synthesis. Compound 1 inhibited the receptor activator of nuclear factor-κB ligand (RANKL)-induced formation of multinuclear osteoclasts with an IC50 value of 10.5 µM in RAW264 cells. The structure-activity relationship of 1 was also investigated with synthetic derivatives.

Taichunins E-T, Isopimarane Diterpenes and a 20-nor-Isopimarane, from Aspergillus taichungensis (IBT 19404): Structures and Inhibitory Effects on RANKL-Induced Formation of Multinuclear Osteoclasts.

Fifteen new isopimarane-type diterpenes, taichunins E-S (1-15), and a new 20-nor-isopimarane, taichunin T (16), together with four known compounds were isolated from Aspergillus taichungensis (IBT 19404). The structures of these new compounds were determined by NMR and mass spectroscopy, and their absolute configurations were analyzed by NOESY and TDDFT calculations of ECD spectra. Taichunins G, K, and N (3, 7, and 10) completely inhibited the receptor activator of nuclear factor-κB ligand (RANKL)-induced formation of multinuclear osteoclasts in RAW264 cells at 5 µM, with 3 showing 92% inhibition at a concentration of 0.2 µM.

Molecular mechanisms underlying prostaglandin E2-exacerbated inflammation and immune diseases.

Prostaglandins (PGs) are the major lipid mediators in animals and which are biosynthesized from arachidonic acid by the cyclooxygenases (COX-1 or COX-2) as the rate-limiting enzymes. Prostaglandin E2 (PGE2), which is the most abundantly detected PG in various tissues, exerts versatile physiological and pathological actions via four receptor subtypes (EP1-4). Non-steroidal anti-inflammatory drugs, such as aspirin and indomethacin, exert potent anti-inflammatory actions by the inhibition of COX activity and the resulting suppression of PG production. Therefore, PGE2 has been shown to exacerbate several inflammatory responses and immune diseases. Recently, studies using mice deficient in each PG receptor subtype have clarified the detailed mechanisms underlying PGE2-associated inflammation and autoimmune diseases involving each EP receptor. Here, we review the recent advances in our understanding of the roles of PGE2 receptors in the progression of acute and chronic inflammation and autoimmune diseases. PGE2 induces acute inflammation through mast cell activation via the EP3 receptor. PGE2 also induces chronic inflammation and various autoimmune diseases through T helper 1 (Th1)-cell differentiation, Th17-cell proliferation and IL-22 production from Th22 cells via the EP2 and EP4 receptors. The possibility of EP receptor-targeted drug development for the treatment of immune diseases is also discussed.

Induced Prostanoid Synthesis Regulates the Balance between Th1- and Th2-Producing Inflammatory Cytokines in the Thymus of Diet-Restricted Mice.

Multiple external and internal factors have been reported to induce thymic involution. Involution involves dramatic reduction in size and function of the thymus, leading to various immunodeficiency-related disorders. Therefore, clarifying and manipulating molecular mechanisms governing thymic involution are clinically important, although only a few studies have dealt with this issue. In the present study, we investigated the molecular mechanisms underlying thymic involution using a murine acute diet-restriction model. Gene expression analyses indicated that the expression of T helper 1 (Th1)-producing cytokines, namely interferon-γ and interleukin (IL)-2, was down-regulated, while that of Th2-producing IL-5, IL-6, IL-10 and IL-13 was up-regulated, suggesting that acute diet-restriction regulates the polarization of naïve T cells to a Th2-like phenotype during thymic involution. mRNAs for prostanoid biosynthetic enzymes were up-regulated by acute diet-restriction. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses detected the increased production of prostanoids, particularly prostaglandin D2 and thromboxane B2, a metabolite of thromboxane A2, in the diet-restricted thymus. Administration of non-steroidal anti-inflammatory drugs, namely aspirin and etodolac, to inhibit prostanoid synthesis suppressed the biased expression of Th1- and Th2-cytokines as well as molecular markers of Th1 and Th2 cells in the diet-restricted thymus, without affecting the reduction of thymus size. In vitro stimulation of thymocytes with phorbol myristate acetate (PMA)/ionomycin confirmed the polarization of thymocytes from diet-restricted mice toward Th2 cells. These results indicated that the induced production of prostanoids during diet-restriction-induced thymic involution is involved in the polarization of naïve T cells in the thymus.

An aromatic amino acid within intracellular loop 2 of the prostaglandin EP2 receptor is a prerequisite for selective association and activation of Gαs.

We previously demonstrated that the aromatic moiety of Tyr143 within the intracellular loop 2 (ICL2) region of the prostaglandin EP2 receptor plays a crucial role in Gs coupling. Here we investigated whether the ICL2 of the EP2 receptor directly binds to Gαs and whether an aromatic moiety affects this interaction. In Chinese hamster ovary cells, mutations of Tyr143 reduced the ability of the EP2 receptor to interact with G proteins as demonstrated by GTPγS sensitivity, as well as the ability of agonist-induced cAMP formation, with the rank order of Phe>Tyr (wild-type)=Trp>Leu>Ala (=0). We found that the wild-type ICL2 peptide (i2Y) and its mutant with Phe at Tyr143 (i2F) inhibited receptor-G protein complex formation of wild-type EP2 in membranes, whereas the Ala-substituted mutant (i2A) did not. Specific interactions between these peptides and the Gαs protein were detected by surface plasmon resonance, but Gαs showed different association rates, with a rank order of i2F>i2Y≫i2A, with similar dissociation rates. Moreover, i2F and i2Y, but not i2A activated membrane adenylyl cyclase. These results indicate that the ICL2 region of the EP2 receptor is its potential interaction site with Gαs, and that the aromatic side chain moiety at position 143 is a determinant for the accessibility of the ICL2 to the Gαs protein.

Prostaglandin E2-induced inflammation: Relevance of prostaglandin E receptors.

Prostaglandin E2 (PGE2) is one of the most typical lipid mediators produced from arachidonic acid (AA) by cyclooxygenase (COX) as the rate-limiting enzyme, and acts on four kinds of receptor subtypes (EP1-EP4) to elicit its diverse actions including pyrexia, pain sensation, and inflammation. Recently, the molecular mechanisms underlying the PGE2 actions mediated by each EP subtype have been elucidated by studies using mice deficient in each EP subtype as well as several compounds highly selective to each EP subtype, and their findings now enable us to discuss how PGE2 initiates and exacerbates inflammation at the molecular level. Here, we review the recent advances in PGE2 receptor research by focusing on the activation of mast cells via the EP3 receptor and the control of helper T cells via the EP2/4 receptor, which are the molecular mechanisms involved in PGE2-induced inflammation that had been unknown for many years. We also discuss the roles of PGE2 in acute inflammation and inflammatory disorders, and the usefulness of anti-inflammatory therapies that target EP receptors. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Prostaglandin E2-EP3 signaling induces inflammatory swelling by mast cell activation.

PGE2 has long been known as a potentiator of acute inflammation, but its mechanisms of action still remain to be defined. In this study, we employed inflammatory swelling induced in mice by arachidonate and PGE2 as models and dissected the role and mechanisms of action of each EP receptor at the molecular level. Arachidonate- or PGE2-induced vascular permeability was significantly reduced in EP3-deficient mice. Intriguingly, the PGE2-induced response was suppressed by histamine H1 antagonist treatment, histidine decarboxylase deficiency, and mast cell deficiency. The impaired PGE2-induced response in mast cell-deficient mice was rescued upon reconstitution with wild-type mast cells but not with EP3-deficient mast cells. Although the number of mast cells, protease activity, and histamine contents in ear tissues in EP3-deficient mice were comparable to those in wild-type mice, the histamine contents in ear tissues were attenuated upon PGE2 treatment in wild-type but not in EP3-deficient mice. Consistently, PGE2-EP3 signaling elicited histamine release in mouse peritoneal and bone marrow-derived mast cells, and it exerted degranulation and IL-6 production in a manner sensitive to pertussis toxin and a PI3K inhibitor and dependent on extracellular Ca(2+) ions. These results demonstrate that PGE2 triggers mast cell activation via an EP3-Gi/o-Ca(2+) influx/PI3K pathway, and this mechanism underlies PGE2-induced vascular permeability and consequent edema formation.

Omega 3 Fatty Acids Attenuate the Acute Kidney Injury to CKD Transition and Renal Fibrosis: Identification of Antifibrotic Metabolites.

BACKGROUND: AKI is an established risk factor for developing CKD. Recently, the renoprotective effect of omega-3 polyunsaturated fatty acids (ω3PUFAs) has attracted attention. This study aimed to evaluate the effect of ω3PUFAs on the transition of AKI to CKD, and to identify fatty acid active metabolites in renal tissue. METHODS: Two mice models of AKI to CKD (7-week, male) and unilateral ureteral obstruction (UUO)-induced renal fibrosis (11-week, male) were fed linseed oil, rich in ω3PUFAs (Lin group), or with soybean oil, low in ω3PUFAs (Soy group). Renal fatty acids and metabolites composition in mice were measured by liquid chromatography-mass spectrometry. Rat renal fibroblast cells (NRK-49F cells) were used for in vitro study. RESULTS: At day 14 after 35 min bilateral renal ischemia reperfusion (IR), significant increase in survival was observed in the Lin group compared to the Soy group. Using the 30 min bilateral renal IR model (AKI to CKD model), the Lin group showed attenuated renal tissue damage and fibrosis. In addition, the antifibrotic effect of Lin group was also observed in UUO renal fibrosis model. In the two mice models, levels of eicosapentaenoic acid (EPA) and its metabolites were significantly elevated in renal tissue of mice fed with Lin. Cultured NRK-49F incubated with EPA and its metabolites 18-hydroxyeicosapentaenoic acid (18-HEPE), 17,18-epoxyeicosatetraenoic acid (17,18-EpETE) and 17,18-dihydroxyeicosatetraenoic acid (17,18-diHETE) displayed suppressed TGF-ß1-stimulated α-smooth muscle actin protein expression. These effects were suppressed in the presence of an inhibitor of a cytochrome P450 involved in EPA metabolism. This observation suggests that the EPA metabolites have antifibrotic effects. CONCLUSIONS: ω3PUFAs prevents AKI to CKD and renal fibrosis. Moreover, the EPA metabolites 18-HEPE, 17,18-EpETE and 17,18-diHETE were found to have antifibrotic effects.

Molecular and pharmacological characterization of zebrafish 'contractile' and 'inhibitory' prostanoid receptors.

Prostanoids comprising prostaglandins (PGs) and thromboxanes (TXs) have been shown to play physiological and pathological roles in zebrafish. However, the molecular basis of zebrafish prostanoid receptors has not been established. Here, we demonstrate that there exist at least five 'contractile' (Ca(2+)-mobilizing) and one 'inhibitory' (Gi-coupled) prostanoid receptors in zebrafish; five 'contractile' receptors consisting of two PGE2 receptors (EP1a and EP1b), two PGF2α receptors (FP1 and FP2), and one TXA2 receptor TP, and one 'inhibitory' receptor, the PGE2 receptor EP3. [(3)H]PGE2 specifically bound to the membranes of cells expressing zebrafish EP1a, EP1b and EP3 with a Kd of 4.8, 1.8 and 13.6nM, respectively, and [(3)H]PGF2α specifically bound to the membranes of cells expressing zebrafish FP1 and FP2, with a Kd of 6.5 and 1.6nM, respectively. U-46619, a stable agonist for human and mouse TP receptors, significantly increased the specific binding of [(35)S]GTPγS to membranes expressing the zebrafish TP receptor. Upon agonist stimulation, all six receptors showed an increase in intracellular Ca(2+) levels, although the increase was very weak in EP1b, and pertussis toxin abolished only the EP3-mediated response. Zebrafish EP3 receptor also suppressed forskolin-induced cAMP formation in a pertussis toxin-sensitive manner. In association with the low structural conservation with mammalian receptors, most agonists and antagonists specific for mammalian EP1, EP3 and TP failed to work on each corresponding zebrafish receptor. This work provides further insights into the diverse prostanoid actions mediated by their receptors in zebrafish.

Molecular and pharmacological characterization of zebrafish 'relaxant' prostanoid receptors.

Prostanoids comprising prostaglandins (PGs) and thromboxanes have been shown to play physiological and pathological roles in zebrafish. However, the molecular basis of zebrafish prostanoid receptors has not been characterized to date. Here, we demonstrate that there exist at least six 'relaxant' (Gs-coupled) prostanoid receptors in zebrafish; one PGI2 receptor IP and five PGE2 receptors comprising two EP2 (EP2a and EP2b), and three EP4 receptors (EP4a, EP4b and EP4c). In contrast, we failed to find a zebrafish PGD2 receptor with any structure and/or character similarities to the mammalian DP1 receptor. [(3)H]iloprost, a stable IP radioligand, specifically bound to the membrane of cells expressing zebrafish IP with a Kd of 42nM, and [(3)H]PGE2 specifically bound to the membranes of cells expressing zebrafish EP2a, EP2b, EP4a, EP4b and EP4c with a Kd of 6.9, 6.0, 1.4, 3.3 and 1.2nM, respectively. Upon agonist stimulation, the 'relaxant' prostanoid receptors showed intracellular cAMP accumulation. The responsiveness of these zebrafish receptors to subtype-specific agonists correlated with their structural conservation to the corresponding receptor in mammals. RT-PCR analysis revealed that the six zebrafish prostanoid receptors show unique tissue distribution patterns; each receptor gene may hence be under unique transcriptional regulation. This work provides further insights into the diverse functions of prostanoids in zebrafish.

Prostaglandin E2 receptor Ptger4b regulates female-specific peptidergic neurons and female sexual receptivity in medaka.

In vertebrates, female receptivity to male courtship is highly dependent on ovarian secretion of estrogens and prostaglandins. We recently identified female-specific neurons in the medaka (Oryzias latipes) preoptic area that express Npba, a neuropeptide mediating female sexual receptivity, in response to ovarian estrogens. Here we show by transcriptomic analysis that these neurons express a multitude of neuropeptides, in addition to Npba, in an ovarian-dependent manner, and we thus termed them female-specific, sex steroid-responsive peptidergic (FeSP) neurons. Our results further revealed that FeSP neurons express a prostaglandin E2 receptor gene, ptger4b, in an ovarian estrogen-dependent manner. Behavioral and physiological examination of ptger4b-deficient female medaka found that they exhibit increased sexual receptivity while retaining normal ovarian function and that their FeSP neurons have reduced firing activity and impaired neuropeptide release. Collectively, this work provides evidence that prostaglandin E2/Ptger4b signaling mediates the estrogenic regulation of FeSP neuron activity and female sexual receptivity.

Prostaglandin E2-EP4 signaling suppresses adipocyte differentiation in mouse embryonic fibroblasts via an autocrine mechanism.

The prostaglandin (PG) receptors EP4 and FP have the potential to exert negative effects on adipogenesis, but the exact contribution of endogenous PG-driven receptor signaling to this process is not fully understood. In this study, we employed an adipocyte differentiation system from mouse embryonic fibroblasts (MEF) and compared the effects of each PG receptor-deficiency on adipocyte differentiation. In wild-type (WT) MEF cells, inhibition of endogenous PG synthesis by indomethacin augmented the differentiation, whereas exogenous PGE2, as well as an FP agonist, reversed the effect of indomethacin. In EP4-deficient cells, basal differentiation was upregulated to the levels in indomethacin-treated WT cells, and indomethacin did not further enhance differentiation. Differentiation in FP-deficient cells was equivalent to WT and was still sensitive to indomethacin. PGE2 or indomethacin treatment of WT MEF cells for the first two days was enough to suppress or enhance transcription of the Pparg2 gene as well as the subsequent differentiation, respectively. Differentiation stimuli induced COX-2 gene and protein expression, as well as PGE2 production, in WT MEF cells. These results suggest that PGE2-EP4 signaling suppresses adipocyte differentiation by affecting Pparg2 expression in an autocrine manner and that FP-mediated inhibition is not directly involved in adipocyte differentiation in the MEF system.

Effects of the Selective EP2 Receptor Agonist Omidenepag on Adipocyte Differentiation in 3T3-L1 Cells.

Purpose: We aimed at comparing the effects of omidenepag (OMD) with those of prostaglandin F (FP) receptor agonists (FP agonists) on adipogenesis in mouse 3T3-L1 cells. Methods: To evaluate the agonistic activities of OMD against the mouse EP2 (mEP2) receptor, we determined cAMP contents in mEP2 receptor-expressing CHO cells by using radioimmunoassays. Overall, 3T3-L1 cells were cultured in differentiation medium for 10 days and adipocyte differentiation was assessed according to Oil Red O-stained cell areas. Changes in expression levels of the adipogenic transcription factors Pparg, Cebpa, and Cebpb were determined by using real-time polymerase chain reaction (PCR). OMD at 0.1, 1, 10, and 40 µmol/L, latanoprost free acid (LAT-A) at 0.1 µmol/L, or prostaglandin F2α (PGF2α), at 0.1 µmol/L were added to cell culture media during adipogenesis. Oil Red O-stained areas and expression patterns of transcription factor targets of OMD or FP agonists were compared with those of untreated controls. Results: The 50% effective concentration (EC50) of OMD against the mEP2 receptor was 3.9 nmol/L. Accumulations of Oil Red O-stained lipid droplets were observed inside control cells on day 10. LAT-A and PGF2α significantly inhibited the accumulation of lipid droplets; however, OMD had no effect on this process even at concentrations up to 40 µmol/L. LAT-A and PGF2α significantly suppressed Pparg, Cebpa, and Cebpb gene expression levels during adipocyte differentiation. Conversely, OMD had no obvious effects on the expression levels of these genes. Conclusions: A selective EP2 receptor agonist, OMD, did not affect the adipocyte differentiation in 3T3-L1 cells, whereas FP agonists significantly inhibited this process.

Prostaglandin E2-EP4 Axis Promotes Lipolysis and Fibrosis in Adipose Tissue Leading to Ectopic Fat Deposition and Insulin Resistance.

Lipolysis, the breakdown of triglyceride storage in white adipose tissue, supplies fatty acids to other tissues as a fuel under fasting conditions. In morbid obesity, fibrosis limits adipocyte expandability, resulting in enforced lipolysis, ectopic fat distribution, and ultimately insulin resistance. Although basal levels of lipolysis persist even after feeding, the regulatory mechanisms of basal lipolysis remain unclear. Here, we show the important role of adipocyte prostaglandin (PG) E2-EP4 receptor signaling in controlling basal lipolysis, fat distribution, and collagen deposition during feeding-fasting cycles. The PGE2-synthesis pathway in adipocytes, which is coupled with lipolysis, is activated by insulin during feeding. By regulating the lipolytic key players, the PGE2-EP4 pathway sustains basal lipolysis as a negative feedback loop of insulin action, and perturbation of this process leads to "metabolically healthy obesity." The potential role of the human EP4 receptor in lipid regulation was also suggested through genotype-phenotype association analyses.

Advanced Oxidation Protein Products Contribute to Renal Tubulopathy via Perturbation of Renal Fatty Acids.

Background: Renal proximal tubulopathy plays a crucial role in kidney disease, but its molecular mechanism is incompletely understood. Because proximal tubular cells consume a lot of energy during reabsorption, the relationship between fatty acids (FAs) and proximal tubulopathy has been attracting attention. The purpose of this study is to investigate the association between change in renal FA composition and tubulopathy. Methods: Mice with cisplatin-induced nephrotoxicity were used as a model of AKI and 5/6-nephrectomized mice were used as a model of CKD. Renal FA composition in mice was measured by GC-MS. Human tubular epithelial cells (HK-2 cells) were used for in vitro studies. Results: In kidneys of AKI mice, increased stearic acid (C18:0) and decreased palmitic acid (C16:0) were observed, accompanied by increased expression of the long-chain FA elongase Elovl6. Similar results were also obtained in CKD mice. We show that C18:0 has higher tubular toxicity than C16:0 via induction of ER stress. Using adenovirus-expressing Elovl6 or siRNA for Elovl6 in HK-2 cells, we demonstrated that increased Elovl6 expression contributes to tubulopathy via increasing C18:0. Elovl6 knockout suppressed the increased serum creatinine levels, renal ER stress, and inflammation that would usually result after 5/6 nephrectomy. Advanced oxidation protein products (AOPPs), specifically an oxidized albumin, was found to induce Elovl6 via the mTORC1/SREBP1 pathway. Conclusions: AOPPs may contribute to renal tubulopathy via perturbation of renal FAs through induction of Elovl6. The perturbation of renal FAs induced by the AOPPs-Elovl6 system could be a potential target for the treatment of tubulopathy.