DP2 receptor activity sensor suited for antagonist screening and measurement of receptor dynamics in real-time

The DP2 receptor is a G-protein coupled receptor involved in allergic inflammation and is the target of recently developed antagonists already being tested in clinics. To get insights into DP2 receptor dynamics and to study its pharmacology on the level of the receptor, we constructed a fluorescence resonance energy transfer-based conformation sensor. The sensor reflects the selectivity profile of the DP2 receptor-wt and is suited for screening of agonists and antagonists due to its robust response. Furthermore, the sensor enables the direct measurement of DP2 receptor dynamics in real-time and revealed markedly distinct on- and off-rates of prostaglandin D2 between DP2 and DP1 receptors, suggesting a different mechanism of ligand receptor interaction.

Prostaglandin 15d-PGJ2 inhibits proliferation of lung adenocarcinoma cells by inducing ROS production and activation of apoptosis via sirtuin-1

Lung adenocarcinoma (LUADC) belongs to the most prevalent and lethal cancer types. As 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) displays anti-oxidative, -inflammatory, and -cancer properties, we investigated whether this cyclopentenone PG, a stable degradation end-product of cyclooxygenase-generated PGD2, exerts beneficial effects in three LUADC cell lines (A549, H1299, H23). We here report that 15d-PGJ2 had substantial cytotoxic effects in all three LUADC cell lines by promoting early apoptosis and inhibiting the cell cycle, proliferation, and migration. As indicators of cell malignancy, scratch closure and colony formation were significantly inhibited by 15d-PGJ2. 15d-PGJ2 induced generation of ROS and subsequent activation of MAPKs. Expression of Nrf-2, a well-known tumor driver, was markedly diminished by 15d-PGJ2 treatment. Although PPARγ, DP1, and DP2 are expressed in LUADC cells, blocking these receptors with specific inhibitors (SR16832 and BW245C) did not reverse 15d-PGJ2-mediated cytotoxicity, suggesting receptor-independent effects. 15d-PGJ2 decreased SIRT1 expression in LUADC cells and the knockdown of SIRT1 diminished the cytotoxic effects of 15d-PGJ2. Importantly, 15d-PGJ2 significantly reduced tumor growth using the chorioallantoic membrane (CAM) assay. The structural analog of 15d- PGJ2, 9,10-dihydro-15d-PGJ2 (lacking the α,β-unsaturated ketone structural element), did not show any toxic effects in LUADC cells. Altogether, our findings suggest that 15d-PGJ2 led to significantly reduced tumor growth and cell proliferation in three LUADC cell lines. The CAM assay results suggest that 15d-PGJ2 is a suitable endogenous compound to interfere with LUADC tumor progression. We show that SIRT1 modulates the effects of 15d-PGJ2 and may be used as a therapeutic target for LUADC.

The vasoconstrictor activities of prostaglandin D2 via the thromboxane prostanoid receptor and E prostanoid receptor-3 outweigh its concurrent vasodepressor effect mainly through D prostanoid receptor-1 ex vivo and in vivo

Prostaglandin (PG) D2, a commonly considered vasodilator through D prostanoid receptor-1 (DP1), might also evoke vasoconstriction via acting on the thromboxane (Tx)-prostanoid receptor (the original receptor of TxA2; TP) and/or E prostanoid receptor-3 (one of the vasoconstrictor receptors of PGE2; EP3). This study aimed to test the above hypothesis in the mouse renal vascular bed (main renal arteries and perfused kidneys) and/or mesenteric resistance arteries and determine how the vasoconstrictor mechanism influences the overall PGD2 effect on systemic blood pressure under in vivo conditions. Experiments were performed on control wild-type (WT) mice and mice with deficiencies in TP (TP-/-) and/or EP3 (EP3-/-). Here we show that PGD2 indeed evoked vasoconstrictor responses in the above-mentioned tissues of WT mice, which were however not only reduced by TP-/- or EP3-/-, but also reversed by TP-/-/EP3-/- in some of the above tissues (mesenteric resistance arteries or perfused kidneys) to dilator reactions that were reduced by non-selective DP antagonism. A slight or mild pressor response was also observed with PGD2 under in vivo conditions, and this was again reversed to a depressor response in TP-/- or TP-/-/EP3-/- mice. Non-selective DP antagonism reduced the PGD2-evoked depressor response in TP-/-/EP3-/- mice as well. These results thus demonstrate that like other PGs, PGD2 activates TP and/or EP3 to evoke vasoconstrictor activities, which can outweigh its concurrent vasodepressor activity mediated mainly through DP1, and hence result in a pressor response, although the response might only be of a slight or mild extent.

15-deoxy-Δ12,14-prostaglandin J2 relieved acute liver injury by inhibiting macrophage migration inhibitory factor expression via PPARγ in hepatocyte

15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) exhibited potential to alleviate liver inflammation in chronic injury but was less studied in acute injury. Acute liver injury was associated with elevated macrophage migration inhibitory factor (MIF) levels in damaged hepatocytes. This study aimed to investigate the regulatory mechanism of hepatocyte-derived MIF by 15d-PGJ2 and its subsequent impact on acute liver injury. In vivo, mouse models were established by carbon tetrachloride (CCl4) intraperitoneal injection, with or without 15d-PGJ2 administration. 15d-PGJ2 treatment reduced the necrotic areas induced by CCl4. In the same mouse model constructed using enhanced green fluorescent protein (EGFP)-labeled bone marrow (BM) chimeric mice, 15d-PGJ2 reduced CCl4 induced BM-derived macrophage (BMM, EGFP+F4/80+) infiltration and inflammatory cytokine expression. Additionally, 15d-PGJ2 down-regulated liver and serum MIF levels; liver MIF expression was positively correlated with BMM percentage and inflammatory cytokine expression. In vitro, 15d-PGJ2 inhibited Mif expression in hepatocytes. In primary hepatocytes, reactive oxygen species inhibitor (NAC) showed no effect on MIF inhibition by 15d-PGJ2; PPARγ inhibitor (GW9662) abolished 15d-PGJ2 suppressed MIF expression and antagonists (troglitazone, ciglitazone) mimicked its function. In Pparg silenced AML12 cells, the suppression of MIF by 15d-PGJ2 was weakened; 15d-PGJ2 promoted PPARγ activation in AML 12 cells and primary hepatocytes. Furthermore, the conditioned medium of recombinant MIF- and lipopolysaccharide-treated AML12 respectively promoted BMM migration and inflammatory cytokine expression. Conditioned medium of 15d-PGJ2- or siMif-treated injured AML12 suppressed these effects. Collectively, 15d-PGJ2 activated PPARγ to suppress MIF expression in injured hepatocytes, reducing BMM infiltration and pro-inflammatory activation, ultimately alleviating acute liver injury.

Peroxisome proliferator-activated receptors alpha and beta mediate the anti-inflammatory effects of the cyclopentenone prostaglandin 15-deoxy-Δ12,14-PGJ2 in fish granulocytes

Prostaglandins (PGs) are highly reactive small lipophilic molecules derived from polyunsaturated fatty acids of the cell membrane and play a key role in the resolution of inflammation processes. 15-deoxy-Δ^12,14-PGJ₂ (15dPGJ₂) is a cyclopentenone PG (CyPG) of the J series with anti-inflammatory, anti-proliferative and pro-apoptotic effects. This CyPG can signal through: (i) the PGD₂ receptor (DP2) and peroxisome proliferator-activated receptor γ (PPARγ) or (ii) by covalent binding to protein nucleophiles, such as, thiols groups of cysteine, lysine or histidine via a Michael addition reaction, modifying its structure and function. In this work we show that acidophilic granulocytes (AGs) of gilthead seabream (Sparus aurata L.), the functional equivalent to mammalian neutrophils, constitutively expressed ppara, pparb and pparg genes, the latter showing the highest expression and up-regulation when stimulated by bacterial DNA. In addition, we tested the ability of 15dPGJ_2, and its biotinylated analog, as well as several PPARγ ligands, to modulate reactive oxygen species (ROS) and/or cytokines production during a Toll like receptor (TLR)-mediated granulocyte response. Thus, 15dPGJ₂ was able to significantly decrease bacterial DNA-induced ROS production and transcript levels of pparg, interleukin-1β (il1b) and prostaglandin-endoperoxide synthase 2 (ptgs2). In contrast, its biotinylated analog was less potent and a higher dose was required to elicit the same effects on ROS production and cytokine expression. In addition, different PPARγ agonists were able to mimic the effects of 15dPGJ₂. Conversely, the PPARγ antagonist T007097 abolished the effect of 15dPGJ₂ on DNA bacterial-induced ROS production. Surprisingly, transactivation assays revealed that both 15dPGJ₂ and its biotinylated analog signaled via Pparα and Pparβ, but not by Pparγ. These results were further confirmed by HPLC/MS analysis, where Pparβ was identified as an interactor of biotin-15dPGJ₂ in naïve and DNA-stimulated leukocytes. Taken together, our data show that 15dPGJ₂ acts both through Ppar activation and covalent binding to proteins in fish granulocytes and identify for the first time in vertebrates a role for Pparα and Pparβ in the resolution of inflammation mediated by 15dPGJ₂.

Timapiprant, a prostaglandin D2 receptor antagonist, ameliorates pathology in a rat Alzheimer's model

We investigated the relevance of the prostaglandin D2 pathway in Alzheimer's disease, because prostaglandin D2 is a major prostaglandin in the brain. Thus, its contribution to Alzheimer's disease merits attention, given the known impact of the prostaglandin E2 pathway in Alzheimer's disease. We used the TgF344-AD transgenic rat model because it exhibits age-dependent and progressive Alzheimer's disease pathology. Prostaglandin D2 levels in hippocampi of TgF344-AD and wild-type littermates were significantly higher than prostaglandin E2. Prostaglandin D2 signals through DP1 and DP2 receptors. Microglial DP1 receptors were more abundant and neuronal DP2 receptors were fewer in TgF344-AD than in wild-type rats. Expression of the major brain prostaglandin D2 synthase (lipocalin-type PGDS) was the highest among 33 genes involved in the prostaglandin D2 and prostaglandin E2 pathways. We treated a subset of rats (wild-type and TgF344-AD males) with timapiprant, a potent highly selective DP2 antagonist in development for allergic inflammation treatment. Timapiprant significantly mitigated Alzheimer's disease pathology and cognitive deficits in TgF344-AD males. Thus, selective DP2 antagonists have potential as therapeutics to treat Alzheimer's disease.

15d-PGJ2 Promotes ROS-Dependent Activation of MAPK-Induced Early Apoptosis in Osteosarcoma Cell In Vitro and in an Ex Ovo CAM Assay

Osteosarcoma (OS) is the most common type of bone tumor, and has limited therapy options. 15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) has striking anti-tumor effects in various tumors. Here, we investigated molecular mechanisms that mediate anti-tumor effects of 15d-PGJ₂ in different OS cell lines. Human U2-OS and Saos-2 cells were treated with 15d-PGJ₂ and cell survival was measured by MTT assay. Cell proliferation and motility were investigated by scratch assay, the tumorigenic capacity by colony forming assay. Intracellular ROS was estimated by H₂DCFDA. Activation of MAPKs and cytoprotective proteins was detected by immunoblotting. Apoptosis was detected by immunoblotting and Annexin V/PI staining. The ex ovo CAM model was used to study growth capability of grafted 15d-PGJ₂-treated OS cells, followed by immunohistochemistry with hematoxylin/eosin and Ki-67. 15d-PGJ₂ substantially decreased cell viability, colony formation and wound closure capability of OS cells. Non-malignant human osteoblast was less affected by 15d-PGJ₂. 15d-PGJ₂ induced rapid intracellular ROS production and time-dependent activation of MAPKs (pERK1/2, pJNK and pp38). Tempol efficiently inhibited 15d-PGJ₂-induced ERK1/2 activation, while N-acetylcystein and pyrrolidine dithiocarbamate were less effective. Early but weak activation of cytoprotective proteins was overrun by induction of apoptosis. A structural analogue, 9,10-dihydro-15d-PGJ₂, did not show toxic effects in OS cells. In the CAM model, we grafted OS tumors with U2-OS, Saos-2 and MG-63 cells. 15d-PGJ₂ treatment resulted in significant growth inhibition, diminished tumor tissue density, and reduced tumor cell proliferation for all cell lines. Our in vitro and CAM data suggest 15d-PGJ₂ as a promising natural compound to interfere with OS tumor growth.

Prostaglandin D2 metabolites activate asthmatic patient-derived type 2 innate lymphoid cells and eosinophils via the DP2 receptor

BACKGROUND

Prostaglandin D2 (PGD2) signaling via prostaglandin D2 receptor 2 (DP2) contributes to atopic and non-atopic asthma. Inhibiting DP2 has shown therapeutic benefit in certain subsets of asthma patients, improving eosinophilic airway inflammation. PGD2 metabolites prolong the inflammatory response in asthmatic patients via DP2 signaling. The role of PGD2 metabolites on eosinophil and ILC2 activity is not fully understood.

METHODS

Eosinophils and ILC2s were isolated from peripheral blood of atopic asthmatic patients. Eosinophil shape change, ILC2 migration and IL-5/IL-13 cytokine secretion were measured after stimulation with seven PGD2 metabolites in presence or absence of the selective DP2 antagonist fevipiprant.

RESULTS

Selected metabolites induced eosinophil shape change with similar nanomolar potencies except for 9α,11β-PGF2. Maximal values in forward scatter of eosinophils were comparable between metabolites. ILC2s migrated dose-dependently in the presence of selected metabolites except for 9α,11β-PGF2 with EC50 values ranging from 17.4 to 91.7 nM. Compared to PGD2, the absolute cell migration was enhanced in the presence of Δ12-PGD2, 15-deoxy-Δ12,14-PGD2, PGJ2, Δ12-PGJ2 and 15-deoxy-Δ12,14-PGJ2. ILC2 cytokine production was dose dependent as well but with an average sixfold reduced potency compared to cell migration (IL-5 range 108.1 to 526.9 nM, IL-13 range: 125.2 to 788.3 nM). Compared to PGD2, the absolute cytokine secretion was reduced in the presence of most metabolites. Fevipiprant dose-dependently inhibited eosinophil shape change, ILC2 migration and ILC2 cytokine secretion with (sub)-nanomolar potencies.

CONCLUSION

Prostaglandin D2 metabolites initiate ILC2 migration and IL-5 and IL-13 cytokine secretion in a DP2 dependent manner. Our data indicate that metabolites may be important for in vivo eosinophil activation and ILC2 migration and to a lesser extent for ILC2 cytokine secretion.

Disease-Dependent Antiapoptotic Effects of Cannabidiol for Keratinocytes Observed upon UV Irradiation

Although apoptosis of keratinocytes has been relatively well studied, there is a lack of information comparing potentially proapoptotic treatments for healthy and diseased skin cells. Psoriasis is a chronic autoimmune-mediated skin disease manifested by patches of hyperproliferative keratinocytes that do not undergo apoptosis. UVB phototherapy is commonly used to treat psoriasis, although this has undesirable side effects, and is often combined with anti-inflammatory compounds. The aim of this study was to analyze if cannabidiol (CBD), a phytocannabinoid that has anti-inflammatory and antioxidant properties, may modify the proapoptotic effects of UVB irradiation in vitro by influencing apoptotic signaling pathways in donor psoriatic and healthy human keratinocytes obtained from the skin of five volunteers in each group. While CBD alone did not have any major effects on keratinocytes, the UVB treatment activated the extrinsic apoptotic pathway, with enhanced caspase 8 expression in both healthy and psoriatic keratinocytes. However, endoplasmic reticulum (ER) stress, characterized by increased expression of caspase 2, was observed in psoriatic cells after UVB irradiation. Furthermore, decreased p-AKT expression combined with increased 15-d-PGJ₂ level and p-p38 expression was observed in psoriatic keratinocytes, which may promote both apoptosis and necrosis. Application of CBD partially attenuated these effects of UVB irradiation both in healthy and psoriatic keratinocytes, reducing the levels of 15-d-PGJ₂, p-p38 and caspase 8 while increasing Bcl2 expression. However, CBD increased p-AKT only in UVB-treated healthy cells. Therefore, the reduction of apoptotic signaling pathways by CBD, observed mainly in healthy keratinocytes, suggests the need for further research into the possible beneficial effects of CBD.

Amplification by tramadol of PGD2-induced osteoprotegerin synthesis in osteoblasts: Involvement of μ-opioid receptor and 5-HT transporter

Tramadol, a weak μ-opioid receptor (MOR) agonist with inhibitory effects on the reuptake of serotonin (5-hydroxytryptamine; 5-HT) and norepinephrine, is an effective analgesic to chronic pains. Osteoprotegerin produced by osteoblasts is essential for bone remodeling to suppress osteoclastic bone resorption. We previously reported that prostaglandin D₂ (PGD₂) induces osteoprotegerin synthesis whereby p44/p42 mitogen-activated protein (MAP) kinase, p38 MAP kinase and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) are involved in osteoblast-like MC3T3-E1 cells. Herein, we investigated the mechanism underlying the effect of tramadol on the PGD₂-induced osteoprotegerin synthesis in these cells. Tramadol enhanced the PGD₂-induced release and mRNA expression of osteoprotegerin. Naloxone, a MOR antagonist, reduced the amplification by tramadol of the PGD₂-stimulated osteoprotegerin release. Not the selective norepinephrine reuptake inhibitor reboxetine but the selective serotonin reuptake inhibitors fluvoxamine and sertraline upregulated the PGD₂-induced osteoprotegerin release, which was further amplified by morphine. Tramadol enhanced PGD₂-stimulated phosphorylation of p38 MAP kinase and SAPK/JNK, but not p44/p42 MAP kinase. Both SB203580 and SP600125 suppressed the tramadol effect to enhance the PGD₂-stimulated osteoprotegerin release. Tramadol enhanced the PGE₂-induced osteoprotegerin release as well as PGD₂. These results suggest that tramadol amplifies the PGD₂-induced osteoprotegerin synthesis at the upstream of p38 MAP kinase and SAPK/JNK in the involvement of both MOR and 5-HT transporter in osteoblasts.

Deletion of Alox15 improves kidney dysfunction and inhibits fibrosis by increased PGD2 in the kidney

BACKGROUND

Lipid-metabolizing enzymes and their metabolites affect inflammation and fibrosis, but their roles in chronic kidney disease (CKD) have not been completely understood.

METHODS

To clarify their role in CKD, we measured the mRNA levels of major lipid-metabolizing enzymes in 5/6 nephrectomized (Nx) kidneys of C57BL/6 J mice. Mediator lipidomics was performed to reveal lipid profiles of CKD kidneys.

RESULTS

In 5/6 Nx kidneys, both mRNA and protein levels of Alox15 were higher when compared with those in sham kidneys. With respect to in situ hybridization, the mRNA level of Alox15 was higher in renal tubules of 5/6 Nx kidneys. To examine the role of Alox15 in CKD pathogenesis, we performed 5/6 Nx on Alox15-/- mice. Alox15-/- CKD mice exhibited better renal functions than wild-type mice. Interstitial fibrosis was also inhibited in Alox15-/- CKD mice. Mediator lipidomics revealed that Alox15-/- CKD mouse kidneys had significantly higher levels of PGD2 than the control. To investigate the effects of PGD2 on renal fibrosis, we administered PGD2 to TGF-β1-stimulated NRK-52E cells and HK-2 cells, which lead to a dose-dependent suppression of type I collagen and αSMA in both cell lines.

CONCLUSION

Increased PGD2 in Alox15-/- CKD mouse kidneys could inhibit fibrosis, thereby resulting in CKD improvement. Thus, Alox15 inhibition and PGD2 administration may be novel therapeutic targets for CKD.

Prostaglandin 15d-PGJ2 targets PPARγ and opioid receptors to prevent muscle hyperalgesia in rats

Pharmacological agents directed to either opioid receptors or peroxisome proliferator-activated receptor gamma (PPARγ) at peripheral tissues reduce behavioral signs of persistent pain. Both receptors are expressed in muscle tissue, but the contribution of PPARγ activation to muscle pain and its modulation by opioid receptors remains unknown. To address this question, we first tested whether the endogenous PPARγ ligand 15d-PGJ2 would decrease mechanical hyperalgesia induced by carrageenan administration into the gastrocnemius muscle of rats. Next, we used receptor antagonists to determine whether the antihyperalgesic effect of 15-deoxyΔ-12,14-prostaglandin J2 (15d-PGJ2) was PPARγ- or opioid receptor-dependent. Three hours after carrageenan, muscle hyperalgesia was quantified with the Randall-Selitto test. 15d-PGJ2 prevented carrageenan-induced muscle hyperalgesia in a dose-dependent manner. The antihyperalgesic effect of 15d-PGJ2 was dose-dependently inhibited by either the PPARγ antagonist, 2-chloro-5-nitro-N-phenylbenzamide, or by the opioid receptor antagonist, naloxone. We conclude that 15d-PGJ2 targets PPARγ and opioid receptors to prevent muscle hyperalgesia. We suggest that local PPARγ receptors are important pharmacological targets for inflammatory muscle pain.

Effects of prostaglandin E2 and D2 on cell proliferation and osteogenic capacity of human mesenchymal stem cells

The manifestation of periodontitis-related inflammatory reaction is inevitably bound to the production of prostaglandins E₂ and D₂ which have been suggested to mediate osteoclastic and osteogenic effects within the affected tissue. We demonstrated the presence of PGE₂ and PGD₂ receptors on hMSCs on RNA level and with immunofluorescence. For each Prostaglandin, three concentrations were studied: 0.1; 0.5 or 1.0 µg/ml. A lower expression of EP1 and EP4 (PGE₂ receptors 1 and 4) after stimulation with PGE₂ was shown, thus a tendency to compromise osteogenic differentiation and metabolism. PGE₂ induced a higher growth-rate during the first week, while a continuous inflammatory challenge determined a decrease of the proliferation of hMSCs. PGD₂ inhibited cell growth irrespective of the duration of the stimulation. PGE₂ and PGD₂ have also negative effects on calcium deposition osteogenic, thus on differentiation of hMSCs. PGE₂ and PGD₂ seem to induce bone resorption also having indirectly a negative impact on the osteogenic differentiation of hMSCs. Thus, inhibitors of PGE₂ and PGD₂ can be used as adjunct to mechanical periodontal treatment.

15-deoxy-Δ12,14-Prostaglandin J2 inhibits human soluble epoxide hydrolase by a dual orthosteric and allosteric mechanism

Human soluble epoxide hydrolase (hsEH) is an enzyme responsible for the inactivation of bioactive epoxy fatty acids, and its inhibition is emerging as a promising therapeutical strategy to target hypertension, cardiovascular disease, pain and insulin sensitivity. Here, we uncover the molecular bases of hsEH inhibition mediated by the endogenous 15-deoxy-Δ12,14-Prostaglandin J2 (15d-PGJ2). Our data reveal a dual inhibitory mechanism, whereby hsEH can be inhibited by reversible docking of 15d-PGJ2 in the catalytic pocket, as well as by covalent locking of the same compound onto cysteine residues C423 and C522, remote to the active site. Biophysical characterisations allied with in silico investigations indicate that the covalent modification of the reactive cysteines may be part of a hitherto undiscovered allosteric regulatory mechanism of the enzyme. This study provides insights into the molecular modes of inhibition of hsEH epoxy-hydrolytic activity and paves the way for the development of new allosteric inhibitors.

Effects of Flavored Nonalcoholic Beverages on Transcriptional Activities of Nuclear and Steroid Hormone Receptors: Proof of Concept for Novel Reporter Cell Line PAZ-PPARg

We developed and characterized a novel human luciferase reporter cell line for the assessment of peroxisome proliferator-activated receptor γ (PPARγ) transcriptional activity, PAZ-PPARg. The luciferase activity induced by PPARγ endogenous agonist 15d-PGJ2 and prostaglandin PGD2 reached mean values of (87.9 ± 14.0)-fold and (89.6 ± 19.7)-fold after 24 h of exposure to 40 μM 15d-PGJ2 and 70 μM PGD2, respectively. A concentration-dependent inhibition of 15d-PGJ2- and PGD2-induced luciferase activity was observed after the application of T0070907, a selective antagonist of PPARγ, which confirms the specificity of response to both agonists. The PAZ-PPARg cell line, along with the reporter cell lines for the assessment of transcriptional activities of thyroid receptor (TR), vitamin D3 receptor (VDR), androgen receptor (AR), and glucocorticoid receptor (GR), were used for the screening of 27 commonly marketed flavored nonalcoholic beverages for their possible disrupting effects. Our findings indicate that some of the examined beverages have the potential to modulate the transcriptional activities of PPARγ, VDR, and AR.

Prostaglandin D2 evokes potent uterine contraction via the F prostanoid receptor in postpartum rats

Prostaglandin (PG) D₂, a prostanoid known to have hypotensive effect, can evoke increased in vitro prepartum myometrial contraction resulting from up-regulation of the F prostanoid (FP) receptor. The present study further determined postpartum rat uterine responses to PGD₂ to evaluate the possibility of the prostanoid becoming a therapeutic for postpartum uterine atony, a major cause of postpartum hemorrhage that can lead to maternal morbidity. In vitro and in vivo postpartum uterine responses to PGD₂ were determined and compared to those of prepartum rats. Here we show that in postpartum myometrial strips PGD₂ did evoke a contraction sensitive to FP receptor antagonism. Interestingly, this response was not only to a greater extent than that of prepartum rats, but also comparable with the contraction obtained with PGF_2α, a therapeutic for postpartum uterine atony but contradicted in conditions including hypertension. Indeed, PGD₂ was also found to cause increases of basal uterine contraction under in vivo conditions. Western blots revealed that the expression of FP receptors in postpartum myometrium was higher than that of prepartum rats. Moreover, we noted that the amount of PGD₂ produced in postpartum uteri, although lower than that of prepartum rats, was increased compared to non-pregnant conditions. These results thus demonstrate that due to a further up-regulation or high expression of myometrial FP receptors, PGD₂ can evoke potent uterine contraction postpartum, and hence the prostanoid, which is naturally synthesized in uterine tissues, could be a potential therapeutic for postpartum uterine atony, especially in settings, such as hypertension.

A gain-of-function study of amelioration of pentylenetetrazole-induced seizures by endogenous prostaglandin D2

We previously showed that knockout mice of hematopoietic prostaglandin (PG) D synthase (H-PGDS) produce less PGD₂ to exacerbate pentylenetetrazole (PTZ)-induced seizures. Here, we adopted a gain-of-function strategy and used transgenic mice that over-express human H-PGDS enzyme, to elucidate the role of overproduction of endogenous PGD₂ in PTZ-induced seizures. H-PGDS-transgenic mice showed the elevated level of a urinary metabolite of PGD₂, tetranor-PGDM, 3.3- and 2.8-fold higher than the wild-type littermates under the basal condition and after the PTZ administration, respectively, without significantly changing the urinary concentration of a PGE₂-metabolite, tetranor-PGE₂. The intensity of PTZ-induced seizures was decreased in H-PGDS-transgenic mice as evident by the increased seizure onset latency, and a decrease in total duration of generalized tonic-clonic seizures and a total number of EEG seizure spikes during the postictal period (84 s, 17 s, and 5.3/min, respectively), as compared to wild-type mice (53 s, 24 s, and 12.6/min, respectively). These results indicate that overproduction of endogenous PGD₂ decreased PTZ-induces seizures.

Activation of Th2 cells downregulates CRTh2 through an NFAT1 mediated mechanism

CRTh2 (encoded by PTGDR2) is a G-protein coupled receptor expressed by Th2 cells as well as eosinophils, basophils and innate lymphoid cells (ILC)2s. Activation of CRTh2, by its ligand prostaglandin (PG)D2, mediates production of type 2 cytokines (IL-4, IL-5 and IL-13), chemotaxis and inhibition of apoptosis. As such, the PGD2-CRTh2 pathway is considered important to the development and maintenance of allergic inflammation. Expression of CRTh2 is mediated by the transcription factor GATA3 during Th2 cell differentiation and within ILC2s. Other than this, relatively little is known regarding the cellular and molecular mechanisms regulating expression of CRTh2. Here, we show using primary human Th2 cells that activation (24hrs) through TCR crosslinking (αCD3/αCD28) reduced expression of both mRNA and surface levels of CRTh2 assessed by flow cytometry and qRT-PCR. This effect took more than 4 hours and expression was recovered following removal of activation. EMSA analysis revealed that GATA3 and NFAT1 can bind independently to overlapping sites within a CRTh2 promoter probe. NFAT1 over-expression resulted in loss of GATA3-mediated CRTh2 promoter activity, while inhibition of NFAT using a peptide inhibitor (VIVIT) coincided with recovery of CRTh2 expression. Collectively these data indicate that expression of CRTh2 is regulated through the competitive action of GATA3 and NFAT1. Though prolonged activation led to NFAT1-mediated downregulation, CRTh2 was re-expressed when stimulus was removed suggesting this is a dynamic mechanism and may play a role in PGD2-CRTh2 mediated allergic inflammation.

Prostaglandin D2 Uses Components of ROS Signaling to Enhance Testosterone Production in Keratinocytes

Elevated levels of prostaglandin D2 (PGD2) have been shown to be present in the bald scalp of androgenic alopecia (AGA) patients and to functionally inhibit hair growth. However, its precise mechanism in AGA has yet to be clearly defined. Although testosterone plays a critical role in the initiation and progression of AGA, the existence of a possible link between PGD2 and testosterone in skin has not been investigated. Here we show that human keratinocytes treated with PGD2 show enhanced capacity to convert the weak androgen, androstenedione, to testosterone. At the same time, treatment with PGD2 induced reactive oxygen species as indicated by generation of the lipid peroxidation product, 4-hydroxynonenal. To determine whether these two events are linked, we used the reactive oxygen species scavenger N-acetyl-cysteine, which blocked the enhanced testosterone production from PGD2-treated keratinocytes. Our study suggests the existence of a possible crosstalk between the PGD2-reactive oxygen species axis and testosterone metabolism in keratinocytes. Thus, we propose that AGA patients might benefit from the use of N-acetyl-cysteine or other antioxidants as a supplement to currently available or emerging AGA therapies such as finasteride, minoxidil, and PGD2 receptor blockers.

Inhibition of indoleamine 2,3-dioxygenase activity by fatty acids and prostaglandins: A structure function analysis

Indoleamine 2,3-dioxygenase-1 (IDO-1) catalyses the first and rate-limiting step in the metabolism of L-tryptophan. Degradation of L-Trp leads to the production of several immunosuppressive metabolites, including N-formyl kynurenine and kynurenine (Kyn). Apart from a normal physiological role, IDO-1 has also been identified to play a crucial role in immune suppression and tumour induced tolerance. Indeed, many primary tumours express high levels of IDO-1 compared to normal cells of the same stroma. IDO-1 is accepted as being an inducible negative regulator of T cell viability, proliferation and activation. As such, IDO-1 has become a target of intense interest for pharmacological inhibition, for the treatment of cancer. We have previously demonstrated that AA and the prostaglandin metabolite, PGD₂, repressed the IFNγ mediated activity of IDO-1 in THP-1 cells and human monocytes. In this study, we characterise the structure-function relationship of fatty acids and eicosanoids towards inhibition of IDO-1 activity in THP-1 cells and human monocytes. Using a commercial library of fatty acids, 55% of fatty acids inhibited IDO-1 activity. The activity of individual FAs was affected by chain length, number of double bonds and bond configuration. Interrogation of an AA derived eicosanoid library identified 13 PGs with significant inhibitory activity. A structure-function analysis revealed that the γ position of the cyclopentenone ring, double bond in the α-β position of the cyclopentenone ring, the presence of multiple OH groups in the side arm and the addition of an ethanolamide group, significantly increased the inhibitory activity of the PGs. Based on this data we have identified the structure of two possible compounds that may be even more potent pharmacological repressors of IDO-1.

Molecular species of prostaglandins involved in modulating luteinising hormone pulses of female rats under infectious stress conditions

Mammalian reproductive function is controlled by the hypothalamic-pituitary-gonadal (HPG) axis, which is suppressed under infectious stress conditions. By analysing the pulsatility of luteinising hormone (LH), we have previously demonstrated that prostaglandins (PGs) in the central nervous system mediate infectious stress to suppress the activity of the HPG axis. The present study aimed to characterise the types of PGs responsible for suppression of the HPG axis. We focused on three major types of PGs: PGE₂ , PGD₂ and PGF_2α . We used female rats overiectomised bilaterally 1 week before the experiments. Lipopolysaccharide (100 μg kg^-1 ) suppressed LH pulses at the same time as enhancing the concentration of all three PGs in the cerebrospinal fluid, which was restored by indomethacin (10 mg kg^-1 ). Subsequently, we observed LH pulsatility after a single injection of each PG and after co-injection of PGE₂ with PGF_2α into the third cerebral ventricle. A single injection of PGE₂ dose-dependently induced a transient increase in mean LH concentration and LH pulse amplitude, and PGD₂ significantly increased the amplitude of LH pulses, wereas PGF_2α did not affect LH pulsatility. On the other hand, co-injection of PGE₂ and PGF_2α induced a significant suppression of both the frequency and amplitude of LH pulses. These results suggest that PGE₂ and PGF_2α can represent two of the mediators that suppress the HPG axis in situations of infectious stress. Moreover, the results imply that there are two contradictory effects of PGE₂ on LH pulsatility: (i) enhancive when working alone and (ii) suppressive when working together with PGF_2α .

Reactive oxygen species (ROS) production triggered by prostaglandin D2 (PGD2) regulates lactate dehydrogenase (LDH) expression/activity in TM4 Sertoli cells

Reactive oxygen species (ROS) regulate testicular function in health and disease. We previously described a prostaglandin D2 (PGD2) system in Sertoli cells. Now, we found that PGD2 increases ROS and hydrogen peroxide (H2O2) generation in murine TM4 Sertoli cells, and also induces antioxidant enzymes expression suggesting that defense systems are triggered as an adaptive stress mechanism that guarantees cell survival. ROS and specially H2O2 may act as second messengers regulating signal transduction pathways and gene expression. We describe a stimulatory effect of PGD2 on lactate dehydrogenase (LDH) expression via DP1/DP2 receptors, which is prevented by the antioxidant N-acetyl-L-cysteine and the PI3K/Akt pathway inhibitor LY 294002. PGD2 also enhances Akt and CREB/ATF-1 phosphorylation. Our results provide evidence for a role of PGD2 in the regulation of the oxidant/antioxidant status in Sertoli cells and, more importantly, in the modulation of LDH expression which takes place through ROS generation and the Akt-CREB/ATF-1 pathway.

Effect of prostaglandin D2 on VEGF release by nasal polyp fibroblasts

BACKGROUND

Vascular endothelial growth factor (VEGF) is known to be associated with the pathogenesis of chronic rhinosinusitis with nasal polyps (CRSwNP). VEGF is produced by a variety of cells including fibroblasts. It was recently reported that prostaglandin (PG) E₂ induces VEGF release by nasal polyp fibroblasts. However, little is known regarding possible regulation of VEGF by other PGs. We have reported that molecules that regulate PGD₂ metabolism play roles in the pathogenesis of CRS including in local eosinophilia and type 2 cytokine production. In the present study, we sought to determine whether PGD₂ regulates VEGF release by nasal polyp fibroblasts.

METHODS

Nasal polyp fibroblasts were established from nasal polyps. These fibroblasts were stimulated with serial dilutions of PGD₂ or PGD₂ receptor (DP/CRTH2)-selective agonists in the presence or absence of receptor-selective antagonists. The concentration of VEGF in the culture supernatants was determined using ELISA.

RESULTS

5 μM of PGD₂ significantly induced VEGF release by nasal polyp fibroblasts. VEGF release was also obtained by stimulation with a DP receptor-selective, but not with a CRTH2 receptor-selective agonist. In addition, PGD₂-induced VEGF release was significantly inhibited by pre-treatment with DP receptor-selective antagonists. In contrast, pre-treatment with a CRTH2 receptor-selective antagonist significantly enhanced PGD₂-induced VEGF release.

CONCLUSIONS

PGD₂ stimulates VEGF production via DP but not CRTH2 receptors in nasal polyp fibroblasts.

The role of endogenous opioid peptides in the antinociceptive effect of 15-deoxy(Δ12,14)-prostaglandin J2 in the temporomandibular joint

We have previously demonstrated that peripheral administration of 15d-PGJ2 in the Temporomandibular joint (TMJ) of rats can prevent nociceptor sensitization, mediated by peroxisome proliferator activated receptor-γ (PPAR-γ), and κ- and δ- opioid receptors. However, the mechanism that underlies the signaling of PPAR-γ (upon activation by 15d-PGJ2) to induce antinociception, and how the opioid receptors are activated via 15d-PGJ2 are not fully understood. This study demonstrates that peripheral antinociceptive effect of 15d-PGJ2 is mediated by PPAR-γ expressed in the inflammatory cells of TMJ tissues. Once activated by 15d-PGJ2, PPAR-γ induces the release of β-endorphin and dynorphin, which activates κ- and δ-opioid receptors in primary sensory neurons to induce the antinociceptive effect.

Prostaglandin D2 is a novel repressor of IFNγ induced indoleamine-2,3-dioxygenase via the DP1 receptor and cAMP pathway

Expression of elevated levels of Indoleamine 2,3-dioxygenase (IDO) is well established as a mechanism of cancer induced immunosuppression. Pharmacological inhibition of IDO activity is thus a promising alternative in the treatment of cancer. Previously we demonstrated that cyclooxygenase derived metabolites of arachidonic acid inhibited the interferon-gamma mediated induction of IDO in both THP-1 cells and human monocytes. Here we identified that of the five primary prostanoids produced by COX-1/COX-2, only PGD2 displayed significant repressor activity. PGD2 inhibited IDO activity with an IC50 of 7.2µM in THP-1 cells and 5.2µM in monocytes. PGD2 caused a significant decrease in both IDO mRNA and protein. Using receptor specific agonists, PGD2 was found to act via the DP1 receptor, while the CRTH2 receptor was not involved. A DP1 antagonist significantly reduced the activity of PGD2, while CRTH2 agonists were ineffective. PGD2 increased intracellular cAMP levels and exogenous N(6)-cAMP was also found to be highly inhibitory. The effects of PGD2 via cAMP were blocked by Rp-cAMP indicating involvement of PKA. PGD2 also stimulated CREB phosphorylation, a PKA dependent transcription factor. This is the first report demonstrating that PGD2, a prostanoid typically associated with allergy, can inhibit IDO activity via the DP1/cAMP/PKA/CREB pathway. Our findings suggest that PGD2 and its derivatives may form the basis of novel repressors of IFNγ-mediated IDO expression.

Nrf2 Activation Inhibits Effects of Thrombin in Human Amnion Cells and Thrombin-Induced Preterm Birth in Mice

CONTEXT

Nrf2 is a key transcription factor that modulates cell defense mechanisms against endogenous and exogenous stress. Previously, we reported that thrombin increased matrix metalloproteinases and prostaglandin synthesis in human amnion mesenchymal cells.

OBJECTIVE

We sought to determine whether activation of Nrf2 alters the effect of thrombin on prostaglandin synthesis, protease activation, and cytokine release in human amnion. Furthermore, we analyzed the effect of Nrf2 activation on thrombin-induced preterm labor in mice.

DESIGN

Primary human amnion mesenchymal cells and pregnant mice were employed to investigate the effect of Nrf2 on thrombin-induced inflammation and preterm birth.

SETTING

This was a laboratory-based study using cells and mice.

RESULTS

As expected, thrombin increased cyclooxygenase-2, IL-1β, IL-6, IL-8, and matrix metalloproteinase-1 in amnion mesenchymal cells. Preincubation with Nrf2 activators, diethyl maleate or 15-deoxy-Δ12, 14-prostaglandin J2 (15d-PGJ2), profoundly repressed thrombin-induced gene expression. In addition, Nrf2 activation inhibited thrombin-induced cyclooxygenase-2 protein levels and secretion of prostaglandin E2, IL-1β, IL-6, IL-8, TNFα, and granulocyte-macrophage colony-stimulating factor in the media. Whereas vehicle and 15d-PGJ2 did not alter gestational length, all pregnant mice treated with thrombin delivered preterm. 15d-PGJ2 delayed thrombin-induced preterm birth significantly.

CONCLUSIONS

The results indicate that Nrf2 activation represents a key stress response in amnion mesenchyme cells and in pregnant mice to mitigate the adverse proinflammatory effects of thrombin on the fetal membranes. We suggest, therefore, that pharmacological activation of Nrf2 may prevent the increased risk of preterm premature rupture of the membranes associated with thrombin activation that accompanies subchorionic hemorrhage or bleeding during pregnancy.

PPARγ-induced upregulation of CD36 enhances hematoma resolution and attenuates long-term neurological deficits after germinal matrix hemorrhage in neonatal rats

Germinal matrix hemorrhage remains the leading cause of morbidity and mortality in preterm infants in the United States with little progress made in its clinical management. Survivors are often afflicted with long-term neurological sequelae, including cerebral palsy, mental retardation, hydrocephalus, and psychiatric disorders. Blood clots disrupting normal cerebrospinal fluid circulation and absorption after germinal matrix hemorrhage are thought to be important contributors towards post-hemorrhagic hydrocephalus development. We evaluated if upregulating CD36 scavenger receptor expression in microglia and macrophages through PPARγ stimulation, which was effective in experimental adult cerebral hemorrhage models and is being evaluated clinically, will enhance hematoma resolution and ameliorate long-term brain sequelae using a neonatal rat germinal matrix hemorrhage model. PPARγ stimulation (15d-PGJ2) increased short-term PPARγ and CD36 expression levels as well as enhanced hematoma resolution, which was reversed by a PPARγ antagonist (GW9662) and CD36 siRNA. PPARγ stimulation (15d-PGJ2) also reduced long-term white matter loss and post-hemorrhagic ventricular dilation as well as improved neurofunctional outcomes, which were reversed by a PPARγ antagonist (GW9662). PPARγ-induced upregulation of CD36 in macrophages and microglia is, therefore, critical for enhancing hematoma resolution and ameliorating long-term brain sequelae.

15d-PGJ2 Induces Apoptosis of MCF-7 and MDA-MB-231 Cells via Increased Intracellular Calcium and Activation of Caspases, Independent of ERα and ERβ

Reports indicate that 15deoxydelta12,14prostaglandinJ2 (15dPGJ2) has anticancer activities, but its mechanisms of action have yet to be fully elucidated. We therefore investigated the effects of 15dPGJ2 on the human breast cancer cell lines, MCF7 (estrogen receptor ERα+/ERβ+) and MDAMB231 (ERα/ERβ+). Cellular proliferation and cytotoxicity were determined using the 3(4,5dimethylthiazol2yl)2,5diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays while apoptosis was determined by fluorescence microscopy and flow cytometry using annexin Vpropidium iodide (PI) staining. ER expression was determined by Western blotting. Intracellular calcium was stained with Fluo4 AM while intracellular caspase activities were detected with CaspaseFLICA® and measured by flow cytometry. We showed that 15dPGJ2 caused a significant increase in apoptosis in MCF7 and MDAMB231 cells. ERα protein expression was reduced in treated MCF7 cells but preincubation with the ERα inhibitor' ICI 182 780' did not affect the percentage of apoptotic cells. The expression of ERβ was unchanged in both cell lines. In addition, 15dPGJ2 increased intracellular calcium (Ca²+) staining and caspase 8, 9 and3/7 activities. We therefore conclude that 15dPGJ2 induces caspasedependent apoptosis that is associated with an influx of intracellular Ca²+ with no involvement of ER signaling.

[Effect of peroxisome proliferator-activated receptor-γ on endothelial cells oxidative stress induced by Porphyromonas gingivalis]

OBJECTIVE

To detect the degree of oxidative stress in the process when Porphyromonas gingivalis (P. gingivalis) stimulates human vascular endothelium, And to investigate the effect of peroxisome proliferator-activated receptor(PPAR)γ on oxidative stress during this process.

METHODS

Human vascular endothelial cells (HVECs) line EA.hy926 (American Type Culture Collection ,United States) was cultured in high glucose Dulbecco's modified eagle medium (DMEM). Four groups were designed: control group, P. gingivalis infected group, PPARγ activated group and PPARγ blocked group. In control group HVECs were cultured with only DMEM. In P. gingivalis infected group, HVECs were time-dependently stimulated by P. gingivalis W83 from 0 to 12 h. In PPARγ activated group or PPARγ blocked group, PPARγ was pre-activated or blocked by a representative PPARγ agonist(15d-PGJ2 10 μmol/L) or antagonist (GW966210 μmol/L) 30 minutes before the cells were stimulated by P. gingivalis. At 0, 0.5, 1, 1.5, 2, 4, 8, and 12 h, the culture medium was collected individually and centrifuged, and the supernatant was stored for assay. Glutathione peroxidase (GSH-PX) and malondialdehyde (MDA) were analysed by enzyme-linked immunosorbent assay. Cellular reactive oxygen species (ROS) were detected through 2',7'-dichlorofluorescin diacetate (DCFA-DA) fluorescent probe at various time points of the different groups.

RESULTS

In P. gingivalis infected group, the levels of GSH-PX [(5.56±0.97) μmol/L] and MDA [(0.84±0.18) nmol/L] were significantly higher than those in control group [GSH-PX(4.71±0.64) μmol/L, MDA (0.59±0.18) nmol/L)]. The levels of GSH-PX and MDA in PPARγ activated group [GSH-PX (5.38±0.84) μmol/L, MDA (0.84±0.22) nmol/L] and in PPARγ blocked group [GSH-PX (5.37±0.76) μmol/L, MDA (0.85±0.14) nmol/L] were significantly higher than those in control group (P<0.05). In the PPARγ activated group, the levels of GSH-PX at 0.5 and 8 h were significantly higher than those from 1.5 h to 4 h (P<0.05), while no difference was observed on the MDA levels at different time points. There was no significant difference at various time points for the levels of GSH-PX and MDA in PPARγ blocked group. The level of cellular ROS detected by DCFH-DA in P. gingivalis infected group was significantly higher than that in control group (10 108.65 ± 1 805.18 vs. 6 049.06 ± 1 199.19,P<0.05). No difference was observed between PPARγ activated group (7 120.94±1 447.30) or PPARγ blocked group (6 727.35±1 483.68) and control group.

CONCLUSION

Oxidative stress happens when P. gingivalis stimulates human vascular endothelium. PPARγ may involve in modulating oxidative stress during this process.

PGD2 stimulates osteoprotegerin synthesis via AMP-activated protein kinase in osteoblasts: Regulation of ERK and SAPK/JNK

AMP-activated protein kinase (AMPK), a key enzyme sensing cellular energy metabolism, is currently known to regulate multiple metabolic pathways. Osteoprotegerin plays a pivotal role in the regulation of bone metabolism by inhibiting osteoclast activation. We have previously reported that prostaglandin D2 (PGD2) stimulates the synthesis of osteoprotegerin through the activation of p38 mitogen-activated protein (MAP) kinase, p44/p42 MAP kinase and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) in osteoblast-like MC3T3-E1 cells. On the basis of these findings, we herein investigated the implication of AMPK in PGD2-stimulated osteoprotegerin synthesis in these cells. PGD2 induced the phosphorylation of AMPKα (Thr-172) and AMPKβ (Ser-108), and the phosphorylation of acetyl-coenzyme A carboxylase, a direct AMPK substrate. Compound C, an AMPK inhibitor, which suppressed the phosphorylation of acetyl-coenzyme A carboxylase, significantly attenuated both the release and the mRNA levels of osteoprotegerin stimulated by PGD2. The PGD2-induced phosphorylation of p44/p42 MAP kinase and SAPK/JNK but not p38 MAP kinase were markedly inhibited by compound C. These results strongly suggest that AMPK regulates the PGD2-stimulated osteoprotegerin synthesis at a point upstream of p44/p42 MAP kinase and SAPK/JNK in osteoblasts.

15-deoxy-δ12,14-prostaglandin j2 inhibits osteolytic breast cancer bone metastasis and estrogen deficiency-induced bone loss

Breast cancer is the major cause of cancer death in women worldwide. The most common site of metastasis is bone. Bone metastases obstruct the normal bone remodeling process and aberrantly enhance osteoclast-mediated bone resorption, which results in osteolytic lesions. 15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) is an endogenous ligand of peroxisome proliferator-activated receptor gamma (PPARγ) that has anti-inflammatory and antitumor activity at micromolar concentrations through PPARγ-dependent and/or PPARγ-independent pathways. We investigated the inhibitory activity of 15d-PGJ₂ on the bone loss that is associated with breast cancer bone metastasis and estrogen deficiency caused by cancer treatment. 15d-PGJ₂ dose-dependently inhibited viability, migration, invasion, and parathyroid hormone-related protein (PTHrP) production in MDA-MB-231 breast cancer cells. 15d-PGJ₂ suppressed receptor activator of nuclear factor kappa-B ligand (RANKL) mRNA levels and normalized osteoprotegerin (OPG) mRNA levels in hFOB1.19 osteoblastic cells treated with culture medium from MDA-MB-231 cells or PTHrP, which decreased the RANKL/OPG ratio. 15d-PGJ₂ blocked RANKL-induced osteoclastogenesis and inhibited the formation of resorption pits by decreasing the activities of cathepsin K and matrix metalloproteinases, which are secreted by mature osteoclasts. 15d-PGJ₂ exerted its effects on breast cancer and bone cells via PPARγ-independent pathways. In Balb/c nu/nu mice that received an intracardiac injection of MDA-MB-231 cells, subcutaneously injected 15d-PGJ₂ substantially decreased metastatic progression, cancer cell-mediated bone destruction in femora, tibiae, and mandibles, and serum PTHrP levels. 15d-PGJ₂ prevented the destruction of femoral trabecular structures in estrogen-deprived ICR mice as measured by bone morphometric parameters and serum biochemical data. Therefore, 15d-PGJ₂ may be beneficial for the prevention and treatment of breast cancer-associated bone diseases.

[Delta12-prostaglandinJ2-nano capsule up-regulates growth factor expression and enhances bone regeneration in rats]

OBJECTIVE

To investigate the effect of local delivery of delta12-prostaglandinJ2-loaded poly (lactic-co-glycolic acid) (Δ(12)-PGJ2-NC) on growth factors expression and bone formation.

METHODS

Δ(12)-PGJ2-NC was prepared by the emulsion solvent diffusion method. The physical and chemical properties of the nanoparticles were evaluated by particle size analysis, transmission electron microscopy, drug-loading ratio and the in vitro release study. Then standardized transcortical defect (5.0 mm × 1.5 mm) was conducted in the femur of 48 male Wistar rats which were randomly divided into four groups (n = 12), S, K, F, and N. Thirty microliter of saline (S), unloaded nanoparticles (K), Δ(12)-PGJ2 (F) and Δ(12)-PGJ2-NC(N) in a collagen vehicle were delivered inside a titanium chamber fixed over the defect. Then, four subgroups were randomly divided in each group named as D3, D7, D14, and D28 (n = 3) according to the days 3, 7, 14, and 28 after the surgery. At days 3, 7, 14, and 28, the mRNA expression of the bone morphogenetic protein-6 (BMP-6), platelet-derived growth factor-B (PDGF-B) in defect aera was analyzed by real time quantitive-polymerase blotting. HE staining was employed to reveal new bone formation in weeks 2 and 4.

RESULTS

Δ(12)-PGJ2-NC appeared opalescent white and remained relatively stable, with an average particle size of (135.2 ± 0.85) nm. The images from transmission electron microscopy showed that Δ(12)-PGJ2-NC was spherical in shape and homogeneously distributed. The encapsulation efficiency of Δ(12)-PGJ2 with the poly (lactic-co-glycolic acid) (PLGA) nanocapsules was about 92%. The in vitro release of Δ(12)-PGJ2-NC at 37 °C showed a sustained fashion and the average accumulated amount was 30%, 52%, 77%, 91%, and 98% respectively, at 0.5, 1, 2, 4 and 6 h. Compared with the animals treated with saline, after dose of 100 mg/L Δ(12)-PGJ2 and Δ(12)-PGJ2-NC apllication, the mRNA expression level of BMP-6, PDGF-B increased significantly (P < 0.05, P < 0.001). The protein expression of BMP-6, Ephrin-B2 also was up-regulated. Histomorphometry revealed that new bone formation increased at the same dose of 100 mg/L. But the unloaded nanoparticles did not have the same effect (P > 0.05).

CONCLUSIONS

A stable Δ(12)-PGJ2 loaded nanoparticle was successfully prepared. Δ(12)-PGJ2-NC may upregulate the expression of BMP-6, PDGF-B and Ephrin-B2, and promote new bone formation in bone defect area.

The role of peroxisome-proliferator-activating receptor gamma agonists: rosiglitazone and 15-deoxy-delta12,14-prostaglandin J2 in chronic experimental cyclosporine A-induced nephrotoxicity

Cyclosporine A(CsA) is an immunosuppressor frequently used in the transplant surgery and in the treatment of autoimmune diseases. The therapeutic benefits of CsA are often limited by it's main side effect-nephrotoxicity. Mechanisms of chronic CsA- induced renal damage include: activation of renin-angiotensin-aldosterone system, upregulation of transforming growth factor beta (TGF-β), oxidative stress. This study was undertaken to investigate the protective effect of the peroxisome-proliferator-activated receptors gamma (PPARs-γ) agonists: rosiglitazone and 15-deoxy-Δ12,14-prostaglandin J2 (PGDJ2), against CsA-induced kidney injury in male Wistar rats. CsA was administered subcutaneously at a dose of 15 mg/kg/day for 28 days. Both PPAR-γ agonists were given for 28 days 0.5 hour before the administration of CsA. Rosiglitazone was administered orally at a dose of 8 mg/kg/day and PGDJ2 was given intraperitoneally at a dose of 30 μg/kg/day. CsA induced renal failure was evidenced by increased serum levels of urea, uric acid and creatinine. Serum concentrations of GSH and GSSG, lipid peroxidation products as well as NAD+/NADH, NADP+/NADPH and ADP/ATP ratios showed, that CsA induced oxidative stress and evoked an imbalanced red-ox state in the kidney. Light and electron microscope studies showed degenerative changes within renal tubules with damage to their mitochondria, interstitial fibrosis and arteriolopathy. Immunohistochemical expression of profibrotic TGF-β was assessed. The biochemical and morphological changes induced by CsA were limited by administration of both rosiglitazone and PGDJ2. Ultrastructural examination of renal tubular epithelial cells showed marked improvement within mitochondria. Our results indicate that both PPAR-γ agonists used in the experiment may play an important role in protecting against CsA-induced damage in the kidney.

Oxidative stress-induced expression of HSP70 contributes to the inhibitory effect of 15d-PGJ2 on inducible prostaglandin pathway in chondrocytes

The inhibitory effect of 15-deoxy-Δ(12,14)-prostaglandin J2 (15d-PGJ2) on proinflammatory gene expression has been extensively documented and frequently ascribed to its ability to prevent NF-κB pathway activation. We and others have previously demonstrated that it was frequently independent of the peroxisome proliferator activated receptor (PPAR)γ activation. Here, we provide evidence that induction of intracellular heat shock protein (HSP)70 by oxidative stress is an additional regulatory loop supporting the anti-inflammatory effect of 15d-PGJ2 in chondrocytes. Using real-time quantitative PCR and Western blotting, we showed that 15d-PGJ2 stimulated HSP70, but not HSP27 expression while increasing oxidative stress as measured by spectrofluorimetry and confocal spectral imaging. Using N-acetylcysteine (NAC) as an antioxidant, we demonstrated further that oxidative stress was thoroughly responsible for the increased expression of HSP70. Finally, using an HSP70 antisense strategy, we showed that the inhibitory effect of 15d-PGJ2 on IL-1-induced activation of the NF-κB pathway, COX-2 and mPGES-1 expression, and PGE2 synthesis was partly supported by HSP70. These data provide a new anti-inflammatory mechanism to support the PPARγ-independent effect of 15d-PGJ2 in chondrocyte and suggest a possible feedback regulatory loop between oxidative stress and inflammation via intracellular HSP70 up-regulation. This cross talk is consistent with 15d-PGJ2 as a putative negative regulator of the inflammatory reaction.

Peroxisome proliferator activated receptor ligands affect progesterone and 17β-estradiol secretion by porcine corpus luteum during early pregnancy

In the present study we investigated the effect of peroxisome proliferator activated receptor (PPAR) ligands on progesterone (P4) and 17β-estradiol (E2) secretion and 3b-hydroxysteroid dehydrogenase/Δ(5)-Δ(4) isomerase (3β-HSD) mRNA abundance in porcine corpora lutea (CL) collected on days 10-12 and 14-16 of the estrous cycle or pregnancy. The PPAR agonists reduced P4 secretion by the CL during pregnancy whereas they were ineffective during the estrous cycle. An inhibitory effect of WY-14643 (PPARα agonist) on P4 release was noted on days 14-16 of pregnancy. The treatment of the CL with L-165,045 (PPARβ agonist) diminished P4 release by the tissue during both stages of pregnancy. A natural PPARγ agonist, PGJ2, reduced P4 release on days 14-16 or days 10-12 of pregnancy, respectively. Rosiglitazone (PPARγ agonist) inhibited P4 secretion by the CL on days 10-12 of pregnancy. In turn, PPARα ligands effect on E2 release was differential. While PPARγ activator diminished E2 secretion by the CL explants during all tested stages of the estrous cycle and pregnancy, PPARβ ligands did not induce any change in E2 level. In turn, PPARβ agonist reduced E2 release by the tissue during both stages of pregnancy but did not affect the secretion during the estrous cycle. In the present study there was a lack of PPAR ligands effect on 3β-HSD mRNA abundance. In summary, the results suggest that PPARs are involved in the regulation of progesterone and 17β-estradiol release by porcine CL. Porcine CL indicates a different receptivity to PPAR ligands depending on the reproductive status of animals.

Expression of DP2 (CRTh2), a prostaglandin D₂ receptor, in human mast cells

PGD₂ has long been implicated in allergic diseases. Recent cloning of a second PGD₂ receptor, DP2 (also known as CRTh2), led to a greater understanding of the physiological and pathophysiological implications of PGD₂. PGD₂ signaling through DP1 and DP2 mediates different and often opposite effects in many cell types of the immune system. Although mast cells (MC) are the largest source of PGD₂ in the body, there is little information about their potential expression of DP2 and its functional significance. In this study, we show that tissue MC in human nasal polyps express DP2 protein, and that human MC lines and primary cultured human MC express mRNA as well as protein of DP2. By immunohistochemistry, we detected that 34% of MC in human nasal polyps expressed DP2. In addition, flow cytometry showed that 87% of the LAD2 human MC line and 98% of primary cultured human MC contained intracellular DP2. However, we could not detect surface expression of DP2 on human MC by single cell analysis using imaging flow cytometry. Blocking of endogenous PGD2 production with aspirin did not induce surface expression of DP2 in human MC. Two DP2 selective agonists, DK-PGD₂ and 15R-15-methyl PGD₂ induced dose-dependent intracellular calcium mobilization that was abrogated by pertussis toxin, but not by three DP2 selective antagonists. MC mediator release including degranulation was not affected by DP2 selective agonists. Thus, human MC express DP2 intracellularly rather than on their surface, and the function of DP2 in human MC is different than in other immune cells such as Th2 cells, eosinophils and basophils where it is expressed on the cell surface and induces Th2 cytokine and/or granule associated mediator release. Further studies to elucidate the role of intracellular DP2 in human MC may expand our understanding of this molecule and provide novel therapeutic opportunities.

Suppression by resveratrol of prostaglandin D2-stimulated osteoprotegerin synthesis in osteoblasts

Resveratrol, a natural polyphenol with health-related properties mainly existing in grape skins and red wine, possesses beneficial effects on human being. We have previously reported that prostaglandin D2 (PGD2) stimulates heat shock protein 27 (HSP27) induction via activation of p44/p42 mitogen-activated protein (MAP) kinase, p38 MAP kinase and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) in osteoblast-like MC3T3-E1 cells. In the present study, we investigated the mechanism behind the effect of PGD2 on osteoprotegerin (OPG) synthesis and the effect of resveratrol on the OPG synthesis in MC3T3-E1 cells. PGD2 significantly stimulated both the OPG release and the expression levels of OPG mRNA. Resveratrol and SRT1720, an activator of SIRT1, markedly suppressed the PGD2-induced OPG release and the mRNA levels of OPG. PD98059, a specific MEK inhibitor, SB203580, a specific p38 MAP kinase inhibitor, and SP600125, a specific SAPK/JNK inhibitor suppressed the PGD2-stimulated OPG release. PGD2-induced phosphorylation of p38 MAP kinase and SAPK/JNK was attenuated by resveratrol or SRT1720. However, resveratrol or SRT1720 failed to affect the phosphorylation of myosin phosphatase-targeting subunit-1 (MYPT-1), a downstream substrate of Rho-kinase and p44/p42 MAP kinase. These results strongly suggest that resveratrol suppresses PGD2-stimulated OPG synthesis through inhibiting p38 MAP kinase and SAPK/JNK in osteoblasts, and that the suppressive effect is exerted at the point downstream of Rho-kinase but upstream of p38 MAP kinase or SAPK/JNK.

[PPAR-γ agonist inhibits the expressions of chemokines induced by IFN-γ and TNF-α in renal tubular epithelial cells]

OBJECTIVE

To investigate the effect of peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist 15d-PGJ2 on the expressions of CXCL9, CXCL10 and CXCL11 in renal tubular epithelial cells (HK-2) stimulated by interferon-γ (IFN-γ) plus tumor necrosis factor-α (TNF-α).

METHODS

HK-2 cells were stimulated with IFN-γ plus TNF-α only, or incubated with 15d-PGJ2 for 48 hours. CXCL9, CXCL10 and CXCL11 expressions were determined by real-time quantitative PCR (qRT-PCR) and ELISA.

RESULTS

IFN-γ plus TNF-α increased mRNA and protein expressions of CXCL9, CXCL10 and CXCL11 in HK-2 cells. PPAR-γ agonist 15d-PGJ2 inhibited the expressions of CXCL9, CXCL10 and CXCL11 in IFN-γ combined with TNF-α-induced HK-2 cells. Compared with the IFN-γ plus TNF-α group (untreated with 15d-PGJ2), the CXCL9, CXCL10 and CXCL11 were depressed by 76.8%, 78.7% and 81.9% at mRNA level and 66.9%, 86.6% and 39.9% at protein level in 2.0 ng/mL 15d-PGJ2-treated HK-2 cells, respectively (P<0.05).

CONCLUSION

PPAR-γ agonist 15d-PGJ2 could inhibit CXCL9, CXCL10 and CXCL11 production induced by IFN-γ combined with TNF-α in HK-2 cells.

15-Deoxy-Δ12,14-prostaglandin J2 induces PPARγ- and p53-independent apoptosis in rabbit synovial cells

A ligand of peroxisome proliferator-activated receptor γ (PPARγ), 15-deoxy-Δ(12,14)-prostaglandin J2 (15d-PGJ2) induces apoptosis in various cells. However, the mechanism appears to be complex and cell-type specific. We investigated the mechanism of 15d-PGJ2-induced apoptosis of rabbit synovial cells. Exposure to 15d-PGJ2 resulted in DNA fragmentation accompanied by caspase-3 and -9 activations in the cells, suggesting occurrence of mitochondria-mediated apoptosis. Although the exposure also induced remarkable increase in p53 protein, its transcriptional activity was rather reduced, suggesting non-necessity of p53 in 15d-PGJ2-induced apoptosis. Covalent binding of 15d-PGJ2 to cellular proteins including p53 resulted in their insolubilization. N-acetylcysteine inhibited not only the 15d-PGJ2-induced apoptotic events but also the protein insolubilizations via its interaction with 15d-PGJ2. The studies using a PPARγ-agonist and -antagonist showed noninvolvement of PPARγ in 15d-PGJ2-induced apoptosis. The pre-exposure to pro-inflammatory cytokines did not affect the cytotoxicity of 15d-PGJ2 in synovial cells. Taken together, these results show that 15d-PGJ2 induces a mitochondria-mediated apoptotic pathway in p53- and PPARγ-independent manners.

Inhibitory effects of PPARγ ligands on TGF-β1-induced corneal myofibroblast transformation

Corneal scarring, whether caused by trauma, laser refractive surgery, or infection, remains a significant problem for humans. Certain ligands for peroxisome proliferator-activated receptor gamma (PPARγ) have shown promise as antiscarring agents in a variety of body tissues. In the cornea, their relative effectiveness and mechanisms of action are still poorly understood. Here, we contrasted the antifibrotic effects of three different PPARγ ligands (15-deoxy-Δ12,14-prostaglandin J2, troglitazone, and rosiglitazone) in cat corneal fibroblasts. Western blot analyses revealed that all three compounds reduced transforming growth factor (TGF)-β1-driven myofibroblast differentiation and up-regulation of α-smooth muscle actin, type I collagen, and fibronectin expression. Because these effects were independent of PPARγ, we ascertained whether they occurred by altering phosphorylation of Smads 2/3, p38 mitogen-activated protein kinase, stress-activated protein kinase, protein kinase B, extracellular signal-regulated kinase, and/or myosin light chain 2. Only p38 mitogen-activated protein kinase phosphorylation was significantly inhibited by all three PPARγ ligands. Finally, we tested the antifibrotic potential of troglitazone in a cat model of photorefractive keratectomy-induced corneal injury. Topical application of troglitazone significantly reduced α-smooth muscle actin expression and haze in the stromal ablation zone. Thus, the PPARγ ligands tested here showed great promise as antifibrotics, both in vitro and in vivo. Our results also provided new evidence for the signaling pathways that may underlie these antifibrotic actions in corneal fibroblasts.

Prostaglandin D(2) induces apoptosis of human osteoclasts through ERK1/2 and Akt signaling pathways

In a recent study we have shown that prostaglandin D2 (PGD2) induces human osteoclast (OC) apoptosis through the activation of the chemoattractant receptor homologous molecule expressed on T-helper type 2 cell (CRTH2) receptor and the intrinsic apoptotic pathway. However, the molecular mechanisms underlying this response remain elusive. The objective of this study is to investigate the intracellular signaling pathways mediating PGD2-induced OC apoptosis. OCs were generated by in vitro differentiation of human peripheral blood mononuclear cells (PBMCs), and then treated with or without the selective inhibitors of mitogen-activated protein kinase-extracellular signal-regulated kinase (ERK) kinase, (MEK)-1/2, phosphatidylinositol3-kinase (PI3K) and NF-κB/IκB kinase-2 (IKK2) prior to the treatments of PGD2 as well as its agonists and antagonists. Fluorogenic substrate assay and immunoblotting were performed to determine the caspase-3 activity and key proteins involved in Akt, ERK1/2 and NF-κB signaling pathways. Treatments with both PGD2 and a CRTH2 agonist decreased ERK1/2 (Thr202/Tyr204) and Akt (Ser473) phosphorylation, whereas both treatments increased β-arrestin-1 phosphorylation (Ser412) in the presence of naproxen, which was used to eliminate endogenous prostaglandin production. In the absence of naproxen, treatment with a CRTH2 antagonist increased both ERK1/2 and Akt phosphorylations, and reduced the phosphorylation of β-arrestin-1. Treatment of OCs with a selective MEK-1/2 inhibitor increased caspase-3 activity and OC apoptosis induced by both PGD2 and a CRTH2 agonist. Moreover, a CRTH2 antagonist diminished the selective MEK-1/2 inhibitor-induced increase in caspase-3 activity in the presence of endogenous prostaglandins. In addition, treatment of OCs with a selective PI3K inhibitor decreased ERK1/2 (Thr202/Tyr204) phosphorylation caused by PGD2, whereas increased ERK1/2 (Thr202/Tyr204) phosphorylation by a CRTH2 antagonist was attenuated with a PI3K inhibitor treatment. The DP receptor was not implicated in any of the parameters evaluated. Treatment of OCs with PGD2 as well as its receptor agonists and antagonists did not alter the phosphorylation of RelA/p65 (Ser536). Moreover, the caspase-3 activity was not altered in OCs treated with a selective IKK2/NF-κB inhibitor. In conclusion, endogenous or exogenous PGD2 induces CRTH2-dependent apoptosis in human differentiated OCs; β-arrestin-1, ERK1/2, and Akt, but not IKK2/NF-κB are probably implicated in the signaling pathways of this receptor in the model studied.

Cytotoxic effects of 15d-PGJ2 against osteosarcoma through ROS-mediated AKT and cell cycle inhibition

Polo-like kinase 1 (PLK1), a critical cell cycle regulator, has been identified as a potential target in osteosarcoma (OS). 15-deoxy-Δ12, 14-prostaglandin J2 (15d-PGJ2), a prostaglandin derivative, has shown its anti-tumor activity by inducing apoptosis through reactive oxygen species (ROS)-mediated inactivation of v-akt, a murine thymoma viral oncogene homolog, (AKT) in cancer cells. In the study analyzing its effects on arthritis, 15d-PGJ2 mediated shear-induced chondrocyte apoptosis via protein kinase A (PKA)-dependent regulation of PLK1. In this study, the cytotoxic effect and mechanism underlying 15d-PGJ2 effects against OS were explored using OS cell lines. 15d-PGJ2 induced significant G2/M arrest, and exerted time- and dose-dependent cytotoxic effects against all OS cell lines. Western blot analysis showed that both AKT and PKA-PLK1 were down-regulated in OS cell lines after treatment with 15d-PGJ2. In addition, transfection of constitutively active AKT or PLK1 partially rescued cells from 15d-PGJ2-induced apoptosis, suggesting crucial roles for both pathways in the anti-cancer effects of 15d-PGJ2. Moreover, ROS generation was found treatment with 15d-PGJ2, and its cytotoxic effect could be reversed with N-acetyl-l-cysteine. Furthermore, inhibition of JNK partially rescued 15d-PGJ2 cytotoxicity. Thus, ROS-mediated JNK activation may contribute to apoptosis through down-regulation of the p-Akt and PKA-PLK1 pathways. 15d-PGJ2 is a potential therapeutic agent for OS, exerting cytotoxicity mediated through both AKT and PKA-PLK1 inhibition, and these results form the basis for further analysis of its role in animal studies and clinical applications.

Nrf2 is essential for the expression of lipocalin-prostaglandin D synthase induced by prostaglandin D2

Nrf2 is a transcription factor that protects against inflammatory diseases, but the underlying mechanism of this effect remains unclear. Here, we report that Nrf2 uses lipocalin-prostaglandin D synthase (L-PGDS) as a mechanism for suppressing inflammation. Exogenously added prostaglandin D2 (PGD2) induced L-PGDS expression in bone-marrow-derived macrophages (BMDMs), suggesting a positive feedback loop between L-PGDS expression and PGD2. Unlike lipopolysaccharide (LPS)-induced L-PGDS expression, PGD2-mediated expression was independent of MAPK, PU.1, or TLR4. Sequence analysis located a putative Nrf2 binding site in the murine L-PGDS promoter, to which Nrf2 bound when treated with PGD2. Chemical activation, or overexpression, of Nrf2 was sufficient to induce L-PGDS expression in macrophages, BMDMs, or lungs of Nrf2-knockout (KO) mice, but treatment with PGD2 failed to do so, suggesting a pivotal role for Nrf2 in the expression of L-PGDS. Consistent with this, expression of Nrf2 in the lungs of Nrf2-KO mice was sufficient to induce the expression of L-PGDS and to reduce neutrophilic lung inflammation elicited by LPS. Furthermore, expression of L-PGDS in mouse lungs decreased neutrophilic infiltration, ameliorating lung inflammation in mice. Together, our results show that Nrf2, activated by PGD2, induced L-PGDS expression, resulting in decreased inflammation. We suggest that the positive feedback induction of L-PGDS by PGD2 is part of the mechanism by which Nrf2 regulates inflammation.

A novel indole compound, AWT-489, inhibits prostaglandin D2-induced CD55 expression by acting on DP prostanoid receptors as an antagonist in LS174T human colon cancer cells

Indoles are composed of a common core structure, the indole ring, and are widely used as pharmaceuticals and their precursors. In this study, a newly composed relatively small indole compound, AWT-489 was examined to find a novel specific antagonist for DP receptors; the cognate receptors for prostaglandin D2 (PGD2), to prevent colon cancer malignancy. Here we showed that AWT-489 antagonized DP receptor-mediated cyclic AMP formation, and expression of CD55, an inhibitor of the complement system that correlates with poor survival in patients with colorectal cancer, in LS174T human colon cancer cells. Interestingly, unlike a popular indole compound, indomethacin, AWT-489 did not act on the cyclooxygenases as a non-steroidal anti-inflammatory drug. Moreover, AWT-489 exhibited a better inhibitory effect than that of the well-used DP receptor antagonist, BWA868C when a dose close to the physiological concentration of PGD2 was used. These results suggest that AWT-489 can act as a novel human DP receptor antagonist to reduce the expression of CD55 in LS174T human colon cancer cells. We believe that AWT-489 has potential as a lead compound for designing a new DP receptor antagonist that may help improve PGD2-related diseases, especially colon cancer in the near future.

Amplified inhibition of stellate cell activation pathways by PPAR-γ, RAR and RXR agonists

Peroxisome proliferator activator receptors (PPAR) ligands such as 15-Δ12,13-prostaglandin L(2) [PJ] and all trans retinoic acid (ATRA) have been shown to inhibit the development of liver fibrosis. The role of ligands of retinoic X receptor (RXR) and its ligand, 9-cis, is less clear. The purpose of this study was to investigate the effects of combined treatment of the three ligends, PJ, ATRA and 9-cis, on key events during liver fibrosis in rat primary hepatic stellate cells (HSCs). We found that the anti-proliferative effect of the combined treatment of PJ, ATRA and 9-cis on HSCs was additive. Further experiments revealed that this inhibition was due to cell cycle arrest at the G0/G1 phase as demonstrated by FACS analysis. In addition, the combined treatment reduced cyclin D1 expression and increased p21 and p27 protein levels. Furthermore, we found that the three ligands down regulated the phosphorylation of mTOR and p70(S6K). The activation of HSCs was also inhibited by the three ligands as shown by inhibition of vitamin A lipid droplets depletion from HSCs. Studies using real time PCR and western blot analysis showed marked inhibition of collagen Iα1 and αSMA by the combination of the three ligands. These findings suggest that the combined use of PJ, ATRA and 9-cis causes inhibition of cell proliferation by cell cycle arrest and down-regulation of fibrotic markers to a greater extent compared to each of the ligands alone.

Identification of 15d-PGJ2 as an antagonist of farnesoid X receptor: molecular modeling with biological evaluation

15-Deoxy-Δ(12,14)-PGJ2 (15d-PGJ2) is one of the major metabolites from prostaglandin D2 in arachidonic acid (AA) metabolic pathway. It was determined as a ligand of peroxisome proliferator-activated receptor γ (PPARγ) functioning potently in adipocyte development. However, the fact that 15d-PGJ2 exerts also PPARγ-independent biological actions has highly addressed its multi-target behavior. Here, we identified that 15d-PGJ2 was an antagonist of farnesoid X receptor (FXR), as investigated by surface plasmon resonance, fluorescence quenching and homo time-resolved fluorescence based analyses, and the coactivator-recruitment and luciferase-reporter related investigation. Assay of 15d-PGJ2 regulation on hFXRα target genes revealed that treatment of HepG2 cells with 15d-PGJ2 resulted in the stimulation of mRNA expressions of bile-salt export pump (BSEP), and the decrease of cholesterol 7a-hydroxylase (CYP7a1). In addition, functional assays indicated that 15d-PGJ2 promoted the conversion of cholesterol to bile acids in HepG2 cells. Moreover, molecular docking combined with molecular dynamics simulation was applied to develop the possible model of 15d-PGJ2 binding to hFXRα ligand binding domain (LBD) at atomic level, and the responsible residues for 15d-PGJ2/hFXRα-LBD interaction were thereby determined, which were further confirmed by SPR assays against hFXRα-LBD site-directed mutations. Given that hFXRα functions potently in the regulation of hepatic bile acid metabolism and lipid/glucose homeostasis, our current work is expected to help better understand the multi-target features of this PGD2 metabolite in biological pathways, and 15d-PGJ2 as a new discovered FXR antagonist might find its potential application in further anti-hypercholesterol research.

Inhibition of oxidative stress-elicited AKT activation facilitates PPARγ agonist-mediated inhibition of stem cell character and tumor growth of liver cancer cells

Emerging evidence suggests that tumor-initiating cells (TICs) are the most malignant cell subpopulation in tumors because of their resistance to chemotherapy or radiation treatment. Targeting TICs may be a key innovation for cancer treatment. In this study, we found that PPARγ agonists inhibited the cancer stem cell-like phenotype and attenuated tumor growth of human hepatocellular carcinoma (HCC) cells. Reactive oxygen species (ROS) initiated by NOX2 upregulation were partially responsible for the inhibitory effects mediated by PPARγ agonists. However, PPARγ agonist-mediated ROS production significantly activated AKT, which in turn promoted TIC survival by limiting ROS generation. Inhibition of AKT, by either pharmacological inhibitors or AKT siRNA, significantly enhanced PPARγ agonist-mediated inhibition of cell proliferation and stem cell-like properties in HCC cells. Importantly, in nude mice inoculated with HCC Huh7 cells, we demonstrated a synergistic inhibitory effect of the PPARγ agonist rosiglitazone and the AKT inhibitor triciribine on tumor growth. In conclusion, we observed a negative feedback loop between oxidative stress and AKT hyperactivation in PPARγ agonist-mediated suppressive effects on HCCs. Combinatory application of an AKT inhibitor and a PPARγ agonist may provide a new strategy for inhibition of stem cell-like properties in HCCs and treatment of liver cancer.

Prostaglandin D2 toxicity in primary neurons is mediated through its bioactive cyclopentenone metabolites

Prostaglandin D2 (PGD2) is the most abundant prostaglandin in brain but its effect on neuronal cell death is complex and not completely understood. PGD2 may modulate neuronal cell death via activation of DP receptors or its metabolism to the cyclopentenone prostaglandins (CyPGs) PGJ2, Δ(12)-PGJ2 and 15-deoxy-Δ(12,14)-PGJ2, inducing cell death independently of prostaglandin receptors. This study aims to elucidate the effect of PGD2 on neuronal cell death and its underlying mechanisms. PGD2 dose-dependently induced cell death in rat primary neuron-enriched cultures in concentrations of ≥10μM, and this effect was not reversed by treatment with either DP1 or DP2 receptor antagonists. Antioxidants N-acetylcysteine (NAC) and glutathione which contain sulfhydryl groups that can bind to CyPGs, but not ascorbate or tocopherol, attenuated PGD2-induced cell death. Conversion of PGD2 to CyPGs was detected in neuronal culture medium; treatment with these CyPG metabolites alone exhibited effects similar to those of PGD2, including apoptotic neuronal cell death and accumulation of ubiquitinated proteins. Disruption of lipocalin-type prostaglandin D synthase (L-PGDS) protected neurons against hypoxia. These results support the hypothesis that PGD2 elicits its cytotoxic effects through its bioactive CyPG metabolites rather than DP receptor activation in primary neuronal culture.

15-Deoxy-Δ12,14-prostaglandin J2 inhibits macrophage colonization by Salmonella enterica serovar Typhimurium

15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) is an anti-inflammatory downstream product of the cyclooxygenase enzymes. It has been implicated to play a protective role in a variety of inflammatory mediated diseases, including rheumatoid arthritis, neural damage, and myocardial infarctions. Here we show that 15d-PGJ₂ also plays a role in Salmonella infection. Salmonella enterica Typhimurium is a Gram-negative facultative intracellular pathogen that is able to survive and replicate inside phagocytic immune cells, allowing for bacterial dissemination to systemic sites. Salmonella species cause a wide range of morbidity and mortality due to gastroenteritis and typhoid fever. Previously we have shown that in mouse models of typhoid fever, Salmonella infection causes a major perturbation in the prostaglandin pathway. Specifically, we saw that 15d-PGJ₂ production was significantly increased in both liver and feces. In this work we show that 15d-PGJ₂ production is also significantly increased in macrophages infected with Salmonella. Furthermore, we show that the addition of 15d-PGJ₂ to Salmonella infected RAW264.7, J774, and bone marrow derived macrophages is sufficient to significantly reduce bacterial colonization. We also show evidence that 15d-PGJ₂ is reducing bacterial uptake by macrophages. 15d-PGJ₂ reduces the inflammatory response of these infected macrophages, as evidenced by a reduction in the production of cytokines and reactive nitrogen species. The inflammatory response of the macrophage is important for full Salmonella virulence, as it can give the bacteria cues for virulence. The reduction in bacterial colonization is independent of the expression of Salmonella virulence genes SPI1 and SPI2, and is independent of the 15d-PGJ₂ ligand PPAR-γ. 15d-PGJ₂ also causes an increase in ERK1/2 phosphorylation in infected macrophages. In conclusion, we show here that 15d-PGJ₂ mediates the outcome of bacterial infection, a previously unidentified role for this prostaglandin.

Mitochondrial dynamics associated with oxygen-glucose deprivation in rat primary neuronal cultures

Our objective was to investigate the mitochondrial dynamics following oxygen-glucose deprivation (OGD) in cultured rat cortical neurons. We documented changes in morphology, protein expression, and DNA levels in mitochondria following OGD and examined the roles of mitochondrial fission [dynamin-related protein 1 (Drp1), fission protein-1 (Fis1)] and fusion [mitofusin-1 (Mfn1), mitofusin-2 (Mfn2), and optic atrophy-1 protein (OPA1)] proteins on mitochondrial biogenesis and morphogenesis. We tested the effects of two Drp1 blockers [15-deoxy-Δ12,14-Prostaglandin J2 (PGJ2) and Mitochondrial Division Inhibitor (Mdivi-1)] on mitochondrial dynamics and cell survival. One hour of OGD had minimal effects on neuronal viability but mitochondria appeared condensed. Three hours of OGD caused a 60% decrease in neuronal viability accompanied by a transition from primarily normal/tubular and lesser number of rounded mitochondria during normoxia to either poorly labeled or small and large rounded mitochondria. The percentage of rounded mitochondria remained the same. The mitochondrial voltage-dependent anion channel, Complex V, and mitoDNA levels increased after OGD associated with a dramatic reduction in Drp1 expression, less reduction in Mfn2 expression, an increase in Mfn1 expression, with no changes in either OPA1 or Fis1. Although PGJ2 increased polymerization of Drp1, it did not reduce cell death or alter mitochondrial morphology following OGD and Mdivi-1 did not protect neurons against OGD. In summary, mitochondrial biogenesis and maintained fusion occurred in neurons along with mitochondrial fission following OGD; thus Mfn1 but not Drp1 may be a major regulator of these processes.