Prostaglandin I2 signaling prevents angiotensin II-induced atrial remodeling and vulnerability to atrial fibrillation in mice.

Atrial fibrillation (AF) is the most common arrhythmia, and atrial fibrosis is a pathological hallmark of structural remodeling in AF. Prostaglandin I2 (PGI2) can prevent the process of fibrosis in various tissues via cell surface Prostaglandin I2 receptor (IP). However, the role of PGI2 in AF and atrial fibrosis remains unclear. The present study aimed to clarify the role of PGI2 in angiotensin II (Ang II)-induced AF and the underlying molecular mechanism. PGI2 content was decreased in both plasma and atrial tissue from patients with AF and mice treated with Ang II. Treatment with the PGI2 analog, iloprost, reduced Ang II-induced AF and atrial fibrosis. Iloprost prevented Ang II-induced atrial fibroblast collagen synthesis and differentiation. RNA-sequencing analysis revealed that iloprost significantly attenuated transcriptome changes in Ang II-treated atrial fibroblasts, especially mitogen-activated protein kinase (MAPK)-regulated genes. We demonstrated that iloprost elevated cAMP levels and then activated protein kinase A, resulting in a suppression of extracellular signal-regulated kinase1/2 and P38 activation, and ultimately inhibiting MAPK-dependent interleukin-6 transcription. In contrast, cardiac fibroblast-specific IP-knockdown mice had increased Ang II-induced AF inducibility and aggravated atrial fibrosis. Together, our study suggests that PGI2/IP system protects against atrial fibrosis and that PGI2 is a therapeutic target for treating AF.The prospectively registered trial was approved by the Chinese Clinical Trial Registry. The trial registration number is ChiCTR2200056733. Data of registration was 2022/02/12.

Prostacyclin receptor agonists induce DUSP1 to inhibit pulmonary artery smooth muscle cell proliferation.

AIMS: Upregulated p38MAPK signaling is implicated in the accelerated proliferation of pulmonary artery smooth muscle cells (PA-SMCs) and the pathogenesis of pulmonary artery remodeling observed in pulmonary arterial hypertension (PAH). Previously, we reported that after endothelin-1 (ET-1) pretreatment, bone morphogenetic protein 2 (BMP2) activates p38MAPK signaling and accelerates PA-SMC proliferation. The activity of p38MAPK signaling is tightly regulated by the inactivation of dual-specificity phosphatase 1 (DUSP1). Activated p38MAPK induces DUSP1 expression, forming a negative feedback loop. Prostacyclin IP receptor agonists (prostacyclin and selexipag) are used to treat PAH. In this study, we aimed to verify whether IP receptor agonists affect DUSP1 expression and accelerate the proliferation of PA-SMCs. MAIN METHODS: PA-SMCs were treated with BMP2, ET-1, prostacyclin, and MRE-269, an active metabolite of selexipag, either alone or in combination. We quantified mRNA expressions using real-time quantitative polymerase chain reaction. Pulmonary artery specimens and PA-SMCs were obtained during lung transplantation in patients with PAH. KEY FINDINGS: Both prostacyclin and MRE-269 increased DUSP1 expression. Combined treatment with BMP2 and ET-1 induced cyclin D1 and DUSP1 expression and increased PA-SMC proliferation. MRE-269 attenuated BMP2/ET-1-induced cell proliferation. ET-1 increased DUSP1 expression in PA-SMCs from control patients but not in PA-SMCs from patients with PAH. SIGNIFICANCE: This study showed that the p38MAPK/DUSP1 negative feedback loop is impaired in PAH, contributing to unregulated p38MAPK activation and PA-SMC hyperplasia. IP receptor agonist MRE-269 increases DUSP1 expression and inhibit p38MAPK-mediated PA-SMC proliferation. Future elucidation of the detailed mechanism underlying reduced DUSP1 expression would be informative for PAH treatment.

Electroacupuncture Treats Myocardial Infarction by Influencing the Regulation of Substance P in the Neurovascular to Modulate PGI2/TXA2 Metabolic Homeostasis via PI3K/AKT Pathway: A Bioinformatics-Based Multiomics and Experimental Study.

Acute myocardial infarction (AMI) is the most severe form of coronary heart disease caused by ischemia and hypoxia. The study is aimed at investigating the role of neuropeptides and the mechanism of electroacupuncture (EA) in acute myocardial infarction (AMI) treatment. Compared with the normal population, a significant increase in substance P (SP) was observed in the serum of patients with AMI. PGI2 expression was increased in the SP-treated AMI mouse model, and TXA2 expression was decreased. And PI3K pathway-related genes, including Pik3ca, Akt, and Mtor, were upregulated in myocardial tissue of SP-treated AMI patients. Human cardiomyocyte cell lines (HCM) treated with SP increased mRNA and protein expression of PI3K pathway-related genes (Pik3ca, Pik3cb, Akt, and Mtor). Compared to MI control and EA-treated MI rat models, Myd88, MTOR, Akt1, Sp, and Irak1 were differentially expressed, consistent with in vivo and in vitro studies. EA treatment significantly enriched PI3K/AKT signaling pathway genes within MI-associated differentially expressed genes (DEGs) according to Kyoto Encyclopedia of Genes and Genomes (KEGG). Furthermore, it was confirmed by molecular docking analysis that PIK3CA, AKT1, and mTOR form stable dockings with neuropeptide SP. PI3K/AKT pathway activity may be affected directly or indirectly by EA via SP, which corrects the PGI2/TXA2 metabolic imbalance in AMI. MI treatment is now better understood as a result of this finding.

Sex-dependent compensatory mechanisms preserve blood pressure homeostasis in prostacyclin receptor-deficient mice.

Inhibitors of microsomal prostaglandin E synthase 1 (mPGES-1) are in the early phase of clinical development. Deletion of mPges-1 in mice confers analgesia, restrains atherogenesis, and fails to accelerate thrombogenesis, while suppressing prostaglandin E2 (PGE2), but increasing the biosynthesis of prostacyclin (PGI2). In low-density lipoprotein receptor-deficient (Ldlr-/-) mice, this last effect represents the dominant mechanism by which mPges-1 deletion restrains thrombogenesis, while suppression of PGE2 accounts for its antiatherogenic effect. However, the effect of mPges-1 depletion on blood pressure (BP) in this setting remains unknown. Here, we show that mPges-1 depletion significantly increased the BP response to salt loading in male Ldlr-/- mice, whereas, despite the direct vasodilator properties of PGI2, deletion of the I prostanoid receptor (Ipr) suppressed this response. Furthermore, combined deletion of the Ipr abrogated the exaggerated BP response in male mPges-1-/- mice. Interestingly, these unexpected BP phenotypes were not observed in female mice fed a high-salt diet (HSD). This is attributable to the protective effect of estrogen in Ldlr-/- mice and in Ipr-/- Ldlr-/- mice. Thus, estrogen compensates for a deficiency in PGI2 to maintain BP homeostasis in response to high salt in hyperlipidemic female mice. In male mice, by contrast, the augmented formation of atrial natriuretic peptide (ANP) plays a similar compensatory role, restraining hypertension and oxidant stress in the setting of Ipr depletion. Hence, men with hyperlipidemia on a HSD might be at risk of a hypertensive response to mPGES-1 inhibitors.

Low-dose Aspirin prevents hypertension and cardiac fibrosis when thromboxane A2 is unrestrained.

Enhanced platelet activation has been reported in patients with essential hypertension and heart failure. The possible contribution of platelet-derived thromboxane (TX)A2 in their pathophysiology remains unclear. We investigated the systemic TXA2 biosynthesis in vivo and gene expression of its receptor TP in 22 essential hypertension patients and a mouse model of salt-sensitive hypertension. The contribution of platelet TXA2 biosynthesis on enhanced blood pressure (BP) and overload-induced cardiac fibrosis was explored in mice by treating with low-dose Aspirin, resulting in selective inhibition of platelet cyclooxygenase (COX)-1-dependent TXA2 generation. In essential hypertensive patients, systemic biosynthesis of TXA2 [assessed by measuring its urinary metabolites (TXM) reflecting predominant platelet source] was enhanced together with higher gene expression of circulating leukocyte TP and TGF-ß, vs. normotensive controls. Similarly, in hypertensive mice with prostacyclin (PGI2) receptor (IP) deletion (IPKO) fed with a high-salt diet, enhanced urinary TXM, and left ventricular TP overexpression were detected vs. normotensive wildtype (WT) mice. Increased cardiac collagen deposition and profibrotic gene expression (including TGF-ß) was found. Low-dose Aspirin administration caused a selective inhibition of platelet TXA2 biosynthesis and mitigated enhanced blood pressure, cardiac fibrosis, and left ventricular profibrotic gene expression in IPKO but not WT mice. Moreover, the number of myofibroblasts and extravasated platelets in the heart was reduced. In cocultures of human platelets and myofibroblasts, platelet TXA2 induced profibrotic gene expression, including TGF-ß1. In conclusion, our results support tailoring low-dose Aspirin treatment in hypertensive patients with unconstrained TXA2/TP pathway to reduce blood pressure and prevent early cardiac fibrosis.

Rare loss-of-function mutations of PTGIR are enriched in fibromuscular dysplasia.

AIMS: Fibromuscular dysplasia (FMD) and spontaneous coronary artery dissection (SCAD) are related, non-atherosclerotic arterial diseases mainly affecting middle-aged women. Little is known about their physiopathological mechanisms. We aimed to identify rare genetic causes to elucidate molecular mechanisms implicated in FMD and SCAD. METHODS AND RESULTS: We analysed 29 exomes that included familial and sporadic FMD. We identified one rare loss-of-function variant (LoF) (frequencygnomAD = 0.000075) shared by two FMD sisters in the prostaglandin I2 receptor gene (PTGIR), a key player in vascular remodelling. Follow-up was conducted by targeted or Sanger sequencing (1071 FMD and 363 SCAD patients) or lookups in exome (264 FMD) or genome sequences (480 SCAD), all independent and unrelated. It revealed four additional LoF allele carriers, in addition to several rare missense variants, among FMD patients, and two LoF allele carriers among SCAD patients, including one carrying a rare splicing mutation (c.768 + 1C>G). We used burden test to test for enrichment in patients compared to gnomAD controls, which detected a putative enrichment in FMD (PTRAPD = 8 × 10-4), but not a significant enrichment (PTRAPD = 0.12) in SCAD. The biological effects of variants on human prostaclycin receptor (hIP) signalling and protein expression were characterized using transient overexpression in human cells. We confirmed the LoFs (Q163X and P17RfsX6) and one missense (L67P), identified in one FMD and one SCAD patient, to severely impair hIP function in vitro. CONCLUSIONS: Our study shows that rare genetic mutations in PTGIR are enriched among FMD patients and found in SCAD patients, suggesting a role for prostacyclin signalling in non-atherosclerotic stenosis and dissection.

Prostaglandin I2 (PGI2) inhibits Brucella abortus internalization in macrophages via PGI2 receptor signaling, and its analogue affects immune response and disease outcome in mice.

To date, the implications of prostaglandin I2 (PGI2), a prominent lipid mediator for modulation of immune responses, has not been clearly understood in Brucella infection. In this study, we found that cyclooxygenase-2 (COX-2) was significantly expressed in both infected bone marrow-derived macrophages (BMMs) and RAW 264.7 cells. Prostaglandin I2 synthase (PTGIS) expression was not significantly changed, and PGI2receptor (PTGIR) expression was downregulated in BMMs but upregulated in RAW 264.7 macrophages at late infection. Here, we presented that PGI2, a COX-derived metabolite, was produced by macrophages during Brucella infection and its production was regulated by COX-2 and IL-10. We suggested that PGI2 and selexipag, a potent PGI2 analogue, inhibited Brucella internalization through IP signaling which led to down-regulation of F-actin polymerization and p38α MAPK activity. Administration with selexipag suppressed immune responses and resulted in a notable reduction in bacterial burden in spleen of Brucella-challenged mice. Taken together, our study is the first to characterize PGI2 synthesis and its effect in evasion strategy of macrophages against Brucella infection.

Targeted Drugs for Treatment of Pulmonary Arterial Hypertension: Past, Present, and Future Perspectives.

Pulmonary arterial hypertension (PAH) is a devastating disease that can lead to right ventricular failure and premature death. Although approved drugs have been shown to be safe and effective, PAH remains a severe clinical condition, and the long-term survival of patients with PAH is still suboptimal. Thus, potential therapeutic targets and new agents to treat PAH are urgently needed. In recent years, a variety of related pathways and potential therapeutic targets have been found, which brings new hope for PAH therapy. In this perspective, not only are the marketed drugs used to treat PAH summarized but also the recently developed novel pharmaceutical therapies currently in clinical trials are discussed. Furthermore, the advances in natural products as potential treatment for PAH are also updated.

The selective PGI2 receptor agonist selexipag ameliorates Sugen 5416/hypoxia-induced pulmonary arterial hypertension in rats.

Pulmonary arterial hypertension (PAH) is a lethal disease characterized by a progressive increase in pulmonary artery pressure due to an increase in vessel tone and occlusion of vessels. The endogenous vasodilator prostacyclin and its analogs are used as therapeutic agents for PAH. However, their pharmacological effects on occlusive vascular remodeling have not been elucidated yet. Selexipag is a recently approved, orally available and selective prostacyclin receptor agonist with a non-prostanoid structure. In this study, we investigated the pharmacological effects of selexipag on the pathology of chronic severe PAH in Sprague-Dawley and Fischer rat models in which PAH was induced by a combination of injection with the vascular endothelial growth factor receptor antagonist Sugen 5416 and exposure to hypoxia (SuHx). Oral administration of selexipag for three weeks significantly improved right ventricular systolic pressure and right ventricular (RV) hypertrophy in Sprague-Dawley SuHx rats. Selexipag attenuated the proportion of lung vessels with occlusive lesions and the medial wall thickness of lung arteries, corresponding to decreased numbers of Ki-67-positive cells and a reduced expression of collagen type 1 in remodeled vessels. Administration of selexipag to Fischer rats with SuHx-induced PAH reduced RV hypertrophy and mortality caused by RV failure. These effects were probably based on the potent prostacyclin receptor agonistic effect of selexipag on pulmonary vessels. Selexipag has been approved and is used in the clinical treatment of PAH worldwide. It is thought that these beneficial effects of prostacyclin receptor agonists on multiple aspects of PAH pathology contribute to the clinical outcomes in patients with PAH.

Voltage Dependence of Prostanoid Receptors.

G protein-coupled receptors (GPCRs) are the largest class of transmembrane receptors and serve as signal mediators to transduce information from extracellular signals such as neurotransmitters, hormones, or drugs to cellular responses. They are exposed to the strong electrical field of the plasma membrane. In the last decade voltage modulation of ligand-induced GPCR activity has been reported for several GPCRs. Using Foerster resonance energy transfer-based biosensors in patch clamp experiments, we discovered a robust voltage dependence of the thromboxane receptor (TP receptor) on the receptor level as well as on downstream signaling. TP receptor activity doubled upon depolarization from -90 to +60 mV in the presence of U46619, a stable analog of prostaglandin H2 Half-maximal effective potential (V0.5) determined for TP receptor was -46 mV, which is within the physiologic range. We identified that depolarization affected the agonist affinity for the TP receptor. Depolarization enhanced responses of several structural analogs of U46619 with modifications to a similar extent all around the molecule, indicating that voltage modulates the general conformation of TP receptor. By means of site direct mutagenesis, we identified TP receptor R2957.40, which showed alteration of voltage sensitivity of TP receptor upon mutation. Voltage sensitivity was not limited to TP receptor because prostaglandin F receptor activated with U46619 and prostaglandin E2 receptor subtype 3 activated with iloprost showed a similar reaction to depolarization as TP receptor. However, prostacyclin receptor activated with iloprost showed no detectable voltage dependence. SIGNIFICANCE STATEMENT: Prostanoids mediate many of their physiological effects via transmembrane receptors expressed in the plasma membrane of excitable cells. We found that agonist-mediated activation of prostaglandin F receptors and prostaglandin E2 receptors as well as thromboxane receptors are activated upon depolarization, whereas prostacyclin receptors are not. The voltage-induced modulation of thromboxane receptor activity was observed on the level of receptor conformation and downstream signaling. The range of voltage dependence was restricted by R2957.40 in the agonist-binding pocket.

The omega-3 lipid 17,18-EEQ sensitizes TRPV1 and TRPA1 in sensory neurons through the prostacyclin receptor (IP).

Oxidized lipids play an important role in pain processing by modulation of the activity of sensory neurons. However, the role of many signalling lipids that do not belong to the classical group of eicosanoids, especially of oxidized omega-3 lipids in pain processing is unclear. Here we investigated the role of the endogenously produced omega-3 lipids 17,18-EEQ and 19,20-EDP in modulating the activity of sensory neurons. We found that 17,18-EEQ but not 19,20-EDP can sensitize the transient receptor potential vanilloid 1 and ankyrin 1 ion channels (TRPV1 and TRPA1) in sensory neurons, which depends on activation of a Gs-coupled receptor and PKA activation. Screening of different Gs-coupled lipid receptor-deficient mice, identified the prostacyclin receptor IP as putative receptor for 17,18-EEQ. Since 17,18-EEQ is synthesized by the Cytochrome-P450-Epoxygenase CYP2J2, we established a cellular mass spectrometry-based screening assay to identify substances that can suppress 17,18-EEQ concentrations. Using this assay, we identify the antidepressant venlafaxine and the antihypertensive drug telmisartan as potent inhibitors of CYP2J2-dependent 17,18-EEQ synthesis. These findings identify 17,18-EEQ as first omega-3-derived lipid mediator that acts via the IP receptor and sensitizes the TRPV1 channel in sensory neurons. Moreover, the results give a mechanistic explanation for the antinociceptive effects of venlafaxine, which are still not well understood. Like telmisartan, venlafaxine may reduce neuronal activity by blocking CYP2J2 and 17,18-EEQ synthesis and by inhibiting the IP receptor-PKA-TRPV1 axis in sensory neurons.

Mechanistic definition of the cardiovascular mPGES-1/COX-2/ADMA axis.

AIMS: Cardiovascular side effects caused by non-steroidal anti-inflammatory drugs (NSAIDs), which all inhibit cyclooxygenase (COX)-2, have prevented development of new drugs that target prostaglandins to treat inflammation and cancer. Microsomal prostaglandin E synthase-1 (mPGES-1) inhibitors have efficacy in the NSAID arena but their cardiovascular safety is not known. Our previous work identified asymmetric dimethylarginine (ADMA), an inhibitor of endothelial nitric oxide synthase, as a potential biomarker of cardiovascular toxicity associated with blockade of COX-2. Here, we have used pharmacological tools and genetically modified mice to delineate mPGES-1 and COX-2 in the regulation of ADMA. METHODS AND RESULTS: Inhibition of COX-2 but not mPGES-1 deletion resulted in increased plasma ADMA levels. mPGES-1 deletion but not COX-2 inhibition resulted in increased plasma prostacyclin levels. These differences were explained by distinct compartmentalization of COX-2 and mPGES-1 in the kidney. Data from prostanoid synthase/receptor knockout mice showed that the COX-2/ADMA axis is controlled by prostacyclin receptors (IP and PPARß/δ) and the inhibitory PGE2 receptor EP4, but not other PGE2 receptors. CONCLUSION: These data demonstrate that inhibition of mPGES-1 spares the renal COX-2/ADMA pathway and define mechanistically how COX-2 regulates ADMA.

Mannitol triggers mast cell-dependent contractions of human small bronchi and prostacyclin bronchoprotection.

BACKGROUND: Clinical research supports that exercise-induced bronchoconstriction (EIB) is caused by hyperosmolar triggering of mast cells. The reaction can be mimicked by inhalation of mannitol, but it has paradoxically previously not been possible to replicate this mode of action of mannitol in isolated airways. OBJECTIVE: We sought to establish an ex vivo model of EIB in human small bronchi. METHODS: Small bronchi (inner diameter, 0.5-2 mm) from macroscopically healthy human lung tissue were obtained from 48 patients and mounted in organ baths. Contractions and mediator release were analyzed after challenge with hyperosmolar mannitol (850 mOsm). RESULTS: Ten minutes of exposure to mannitol caused a small initial contraction (12% ± 1% of maximum) that was followed by a second and much larger contraction (maximum effect [Emax], 47% ± 5%) when mannitol was washed out. The mast cell stabilizer cromolyn reduced the second contraction (Emax, 27% ± 3%). Furthermore, this main contraction was abolished by the combination of antagonists of histamine and cysteinyl leukotrienes in the presence of indomethacin. Mannitol increased the release of the mast cell mediators histamine (9.0-fold), cysteinyl leukotrienes (4.5-fold), and prostaglandin (PG) D2 (5.4-fold), as well as PGE2 (6.3-fold) and the prostacyclin metabolite 6-keto PGF1α (5.7-fold). In contrast, indomethacin alone enhanced the bronchoconstriction (Emax, 68% ± 6%). Likewise, receptor antagonists for PGE2 (EP2 and EP4) and prostacyclin (IP) also enhanced the mannitol-induced bronchoconstriction (Emax, 67% ± 5%, 66% ± 4%, and 68% ± 3%, respectively). In bronchi precontracted by carbachol, the IP receptor agonist cicaprost induced profound relaxation. CONCLUSION: This new protocol established an in vitro model for studies of EIB in isolated human bronchi. The IP receptor might be a new target for asthma treatment.

AK106-001616, a Potent and Selective Inhibitor of Cytosolic Phospholipase A2: In Vivo Efficacy for Inflammation, Neuropathic Pain, and Pulmonary Fibrosis.

3-[3-Amino-4-(indan-2-yloxy)-5-(1-methyl-1H-indazol-5-yl)-phenyl]-propionic acid (AK106-001616) is a novel, potent, and selective inhibitor of the cytosolic phospholipase A2 (cPLA2) enzyme. Unlike traditional nonsteroidal anti-inflammatory drugs and selective cyclooxygenase-2 inhibitors, AK106-001616 reduced prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) production by stimulated cells. The suppression of PGE2 and LTB4 production was also confirmed using an air pouch model in rats administered a single oral dose of AK106-001616. AK106-001616 alleviated paw swelling in a rat adjuvant-induced arthritis (AIA) model. The maximum effect of the inhibitory effect of AK106-001616 was comparable with that of naproxen on paw swelling in a rat AIA model. Meanwhile, the inhibitory effect of AK106-001616 was more effective than that of naproxen in the mouse collagen antibody-induced arthritis model with leukotrienes contributing to the pathogenesis. AK106-001616 dose dependently reversed the decrease in paw withdrawal threshold not only in rat carrageenan-induced hyperalgesia, but also in a rat neuropathic pain model induced by sciatic nerve chronic constriction injury (CCI). However, naproxen and celecoxib did not reverse the decrease in the paw withdrawal threshold in the CCI model. Furthermore, AK106-001616 reduced the disease score of bleomycin-induced lung fibrosis in rats. In addition, AK106-001616 did not enhance aspirin-induced gastric damage in fasted rats, increase blood pressure, or increase the thromboxane A2/ prostaglandin I2 ratio that is thought to be an underlying mechanism of thrombotic cardiovascular events increased by selective cyclooxygenase-2 inhibitors. Taken together, these data demonstrate that oral AK106-001616 may provide valuable effects for wide indications without attendant gastrointestinal and cardiovascular risks.

Prostacyclin synthesis and prostacyclin receptor expression in the porcine corpus luteum: evidence for a luteotropic role in vitro.

The prostacyclin (prostaglandin I2) signaling system is an essential regulator of vascular homeostasis. Since the corpus luteum is a highly vascularized gland, prostacyclin seems to be crucial for luteal development and function. Although progress has been made in understanding the luteotropic action of prostacyclin in mammals, its role in the porcine corpus luteum remains to be determined. Therefore, studies were conducted to (1) determine profiles of prostacyclin synthase expression and prostacyclin metabolite concentration, as well as prostacyclin G-protein-coupled receptor expression in porcine luteal tissue on days 2 to 16 of the estrous cycle and days 10 to 30 of pregnancy using real-time PCR, western blot, or enzyme immunoassay; and (2) examine the effect of prostacyclin on progesterone synthesis in vitro. To accomplish the second aim, luteal cells were treated with prostacyclin analogs, iloprost and carbaprostacyclin, in the presence or absence of prostacyclin receptor antagonists. The mRNA expression of cytochrome P450 family 11 subfamily A member 1 and hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 1 was analyzed using real-time PCR, while progesterone concentration in culture medium was assessed by radioimmunoassay.Dynamic changes of prostacyclin synthase and prostacyclin receptor expression were observed in porcine luteal tissue during the estrous cycle and early pregnancy. Moreover, prostacyclin stimulated progesterone production and this effect was abolished by the addition of prostacyclin receptor antagonists. Our findings provide strong evidence that prostacyclin and its signaling system are present in corpus luteum of the pig and may directly promote luteotropic activity through upregulation of progesterone synthesis.

Prostacyclin: A major prostaglandin in the regulation of adipose tissue development.

Prostaglandins (PGs) belong to the group lipid mediators and can act as local hormones. They contain 20 carbon atoms, including a 5-carbon ring, and are biosynthesized from membrane phospholipid derived arachidonic acid through the arachidonate cyclooxygenase (COX) pathway with the help of various terminal synthase enzymes. Prostacyclin (prostaglandin I2 ) is one of the major prostanoids produced with the help of prostacyclin synthase (prostaglandin I2 synthase) enzyme and rapidly hydrolyzed into 6-keto-PGF1α in biological fluids. Obesity indicates an excess of body adiposity, which is globally considered as one of the major health disasters responsible for developing complex pathological situations in the human body. Adipose tissues can produce various PGs, and thus, the level and the molecular activity of these endogenously synthesized PGs are considered critical for the development of obesity. In this regard, the involvement of prostacyclin in adipogenesis has been studied in the last few decades. The current review, along with the background of other related PGs, presents the several molecular aspects of endogenous prostaglandin I2 in adipose tissue development. Especially, the regulation of life cycle of adipocytes, impact on terminal differentiation, activity through prostacyclin receptor (IP), autocrine-paracrine manner, thermogenic adipose tissue remodeling and some future experimental aspects of prostacyclin have been focused upon in this study. This discussion might assist to develop new drug molecules acting on the signaling pathways of prostacyclin and devise therapeutic strategies for treating obesity.

The Antifibrotic Activity of Prostacyclin Receptor Agonism Is Mediated through Inhibition of YAP/TAZ.

Idiopathic pulmonary fibrosis is a life-threatening progressive disease characterized by loss of alveolar epithelial cells, inflammation, and aberrant fibroblast activation. The two currently approved therapies do not halt or reverse tissue remodeling, and therefore novel disease-modifying mechanisms are needed. Our results describe YAP/TAZ inhibition through prostacyclin (IP) receptor activation as a novel mechanism that suppresses profibrotic (myo)fibroblast activity. We investigated the antifibrotic properties of the selective IP receptor agonist ACT-333679 using primary human lung fibroblasts. ACT-333679 prevented transforming growth factor ß1-induced fibroblast-to-myofibroblast transition, proliferation, extracellular matrix synthesis, and IL-6 and PAI-1 secretion, and exerted relaxant effects in cell contraction assays. ACT-333679 treatment also reverted an established myofibroblast phenotype. Unbiased analysis of ACT-333679-induced whole-genome expression changes in transforming growth factor ß1-treated fibroblasts identified significant attenuation of genes regulated by YAP/TAZ, two transcriptional cofactors that are essential for fibrosis. We then demonstrated that ACT-333679, via elevation of cAMP, caused YAP/TAZ nuclear exclusion and subsequent suppression of YAP/TAZ-dependent profibrotic gene transcription. In summary, we offer a rationale for further exploring the potential of IP receptor agonists for the treatment of idiopathic pulmonary fibrosis.

Protective Role of mPGES-1 (Microsomal Prostaglandin E Synthase-1)-Derived PGE2 (Prostaglandin E2) and the Endothelial EP4 (Prostaglandin E Receptor) in Vascular Responses to Injury.

OBJECTIVE: Deletion of mPGES-1 (microsomal prostaglandin E synthase-1)-an anti-inflammatory target alternative to COX (cyclooxygenase)-2-attenuates injury-induced neointima formation in mice. This is attributable to the augmented levels of PGI2 (prostacyclin)-a known restraint of the vascular response to injury, acting via IP (I prostanoid receptor). To examine the role of mPGES-1-derived PGE2 (prostaglandin E2) in vascular remodeling without the IP. APPROACH AND RESULTS: Mice deficient in both IP and mPGES-1 (DKO [double knockout] and littermate controls [IP KO (knockout)]) were subjected to angioplasty wire injury. Compared with the deletion of IP alone, coincident deletion of IP and mPGES-1 increased neointima formation, without affecting media area. Early pathological changes include impaired reendothelialization and increased leukocyte invasion in neointima. Endothelial cells (ECs), but not vascular smooth muscle cells, isolated from DKOs exhibited impaired cell proliferation. Activation of EP (E prostanoid receptor) 4 (and EP2, to a lesser extent), but not of EP1 or EP3, promoted EC proliferation. EP4 antagonism inhibited proliferation of mPGES-1-competent ECs, but not of mPGES-1-deficient ECs, which showed suppressed PGE2 production. EP4 activation inhibited leukocyte adhesion to ECs in vitro, promoted reendothelialization, and limited neointima formation post-injury in the mouse. Endothelium-restricted deletion of EP4 in mice suppressed reendothelialization, increased neointimal leukocytes, and exacerbated neointimal formation. CONCLUSIONS: Removal of the IP receptors unmasks a protective role of mPGES-1-derived PGE2 in limiting injury-induced vascular hyperplasia. EP4, in the endothelial compartment, is essential to promote reendothelialization and restrain neointimal formation after injury. Activating EP4 bears therapeutic potential to prevent restenosis after percutaneous coronary intervention.

Iloprost, a prostacyclin analog, inhibits the invasion of ovarian cancer cells by downregulating matrix metallopeptidase-2 (MMP-2) through the IP-dependent pathway.

Recent studies have shown that a bioactive lipid prostacyclin (PGI2) plays a role in various cancers, including lung cancer. However, the specific function of PGI2 in ovarian cancer progression has not been determined. This study investigated the effects of PGI2 on cell growth, migration, and invasion in ovarian cancer cells using iloprost, a stable PGI2 analog. Iloprost significantly inhibited migration and invasion, but not cell growth, in a dose-dependent manner in human ovarian cancer cells (A2780 and SKOV3). Interestingly, the cell surface Gs protein-coupled PGI2 receptor IP was enhanced in human ovarian cancer cells. The inhibitory effect of iloprost on migration and invasion was entirely reversed by an IP antagonist (CAY10449) and IP siRNA, whereas the knockdown of peroxisome proliferator-activated receptor δ (PPARδ), a nuclear receptor of PGI2, did not rescue the effect of iloprost. Additionally, iloprost markedly decreased the expression of matrix metallopeptidase-2 and -9 (MMP-2 and MMP-9), which may be induced in the process of ovarian cancer metastasis. IP siRNA inhibited iloprost-reduced MMP-2 expression but not MMP-9 expression. Moreover, inhibition of protein kinase A (PKA) and overexpression of Akt and p38 rescued the inhibition of invasion and the reduction of MMP-2 expression by iloprost. Furthermore, iloprost-induced activation of PKA was associated with PKA-mediated Akt and p38 inactivation in ovarian cancer cells. Taken together, these results demonstrate that iloprost inhibits ovarian cancer cell invasion by downregulating MMP-2 expression via the IP-mediated PKA pathway. This study is the first to reveal a novel role for iloprost and to clarify its underlying mechanism in human ovarian cancer cells.

Prostaglandin I2 suppresses the development of diet-induced nonalcoholic steatohepatitis in mice.

Nonalcoholic steatohepatitis (NASH) is a hepatic manifestation of metabolic syndrome. Although the prostaglandin (PG)I2 receptor IP is expressed broadly in the liver, the role of PGI2-IP signaling in the development of NASH remains to be determined. Here, we investigated the role of the PGI2-IP system in the development of steatohepatitis using mice lacking the PGI2 receptor IP [IP-knockout (IP-KO) mice] and beraprost (BPS), a specific IP agonist. IP-KO and wild-type (WT) mice were fed a methionine- and choline-deficient diet (MCDD) for 2, 5, or 10 wk. BPS was administered orally to mice every day during the experimental periods. The effect of BPS on the expression of chemokine and inflammatory cytokines was examined also in cultured Kupffer cells. WT mice fed MCDD developed steatohepatitis at 10 wk. IP-KO mice developed steatohepatitis at 5 wk with augmented histologic derangements accompanied by increased hepatic monocyte chemoattractant protein-1 (MCP-1) and TNF-α concentrations. After 10 wk of MCDD, IP-KO mice had greater hepatic iron deposition with prominent oxidative stress, resulting in hepatocyte damage. In WT mice, BPS improved histologic and biochemical parameters of steatohepatitis, accompanied by reduced hepatic concentration of MCP-1 and TNF-α. Accordingly, BPS suppressed the LPS-stimulated Mcp-1 and Tnf-α mRNA expression in cultured Kupffer cells prepared from WT mice. PGI2-IP signaling plays a crucial role in the development and progression of steatohepatitis by modulating the inflammatory response, leading to augmented oxidative stress. We suggest that the PGI2-IP system is an attractive therapeutic target for treating patients with NASH.-Kumei, S., Yuhki, K.-I., Kojima, F., Kashiwagi, H., Imamichi, Y., Okumura, T., Narumiya, S., Ushikubi, F. Prostaglandin I2 suppresses the development of diet-induced nonalcoholic steatohepatitis in mice.