EP4 emerges as a novel regulator of bile acid synthesis and its activation protects against hypercholesterolemia.

Prostaglandin E receptor subtype 4 (EP4) knockout mice develops spontaneous hypercholesterolemia but the detailed mechanisms by which EP4 affects cholesterol homeostasis remains unexplored. We sought to determine the cause of hypercholesterolemia in EP4 knockout mice, focusing on the role of EP4 in regulating the synthesis and elimination of cholesterol. Deficiency of EP4 significantly decreased total bile acid levels in the liver by 26.

Deletion of Rap1 disrupts redox balance and impairs endothelium-dependent relaxations.

Aims: Repressor activator protein 1 (Rap1) is conventionally known as a static structural component of the telomere, but recent evidence indicates that it exerts functions within and outside the nucleus taking part in metabolic regulation and promoting inflammatory responses. The present study investigated whether or not Rap1 deletion affects oxidative stress and nitric oxide (NO) bioavailability in the vascular wall, thus modulating endothelial function.

Methods And Results: Vascular responsiveness was studied in wire myographs in aortae from Rap1 wildtype and knockout mice.

Prostaglandin E receptor subtype 4 regulates lipid droplet size and mitochondrial activity in murine subcutaneous white adipose tissue.

The purpose of this study was to investigate whether genetic ablation of prostaglandin E receptor subtype 4 (EP4) affects white adipose tissue (WAT) remodeling mediated by β-adrenergic stimulation. The selective β-adrenergic agonist, CL316243 (1 mg/kg/d, i.p.

Cox-2 Inhibition Protects against Hypoxia/Reoxygenation-Induced Cardiomyocyte Apoptosis Akt-Dependent Enhancement of iNOS Expression.

The present study explored the potential causal link between ischemia-driven cyclooxygenase-2 (COX-2) expression and enhanced apoptosis during myocardial ischemia/reperfusion (I/R) by using H9C2 cardiomyocytes and primary rat cardiomyocytes subjected to hypoxia/reoxygenation (H/R). The results showed that H/R resulted in higher COX-2 expression than that of controls, which was prevented by pretreatment with Helenalin (NFB specific inhibitor). Furthermore, pretreatment with NS398 (COX-2 specific inhibitor) significantly attenuated H/R-induced cell injury [lower lactate dehydrogenase (LDH) leakage and enhanced cell viability] and apoptosis (higher Bcl2 expression and lower level of cleaved caspases-3 and TUNEL-positive cells) in cardiomyocytes.

Prostaglandin E Receptor Subtype 4 Signaling in the Heart: Role in Ischemia/Reperfusion Injury and Cardiac Hypertrophy.

Prostaglandin E2 (PGE2) is an endogenous lipid mediator, produced from the metabolism of arachidonic acids, upon the sequential actions of phospholipase A2, cyclooxygenases, and prostaglandin E synthases. The various biological functions governed by PGE2 are mediated through its four distinct prostaglandin E receptors (EPs), designated as EP1, EP2, EP3, and EP4, among which the EP4 receptor is the one most widely distributed in the heart. The availability of global or cardiac-specific EP4 knockout mice and the development of selective EP4 agonists/antagonists have provided substantial evidence to support the role of EP4 receptor in the heart.

Rap1 induces cytokine production in pro-inflammatory macrophages through NFκB signaling and is highly expressed in human atherosclerotic lesions.

Repressor activator protein 1 (Rap1) is essential for maintaining telomere length and structural integrity, but it also exerts other non-telomeric functions. The present study tested the hypothesis that Rap1 is released into the cytoplasm and induces production of pro-inflammatory cytokines via nuclear factor kappa B (NFκB) signaling in macrophages, a cell type involved in the development and progression of atherosclerotic lesions. Western blotting analysis confirmed that Rap1 was present in the cytoplasm of differentiated human monocytic leukemia cells (THP-1, a macrophage-like cell line).

Activation of prostaglandin E2-EP4 signaling reduces chemokine production in adipose tissue.

Inflammation of adipose tissue induces metabolic derangements associated with obesity. Thus, determining ways to control or inhibit inflammation in adipose tissue is of clinical interest. The present study tested the hypothesis that in mouse adipose tissue, endogenous prostaglandin E2 (PGE2) negatively regulates inflammation via activation of prostaglandin E receptor 4 (EP4).

Thyroid hormone affects both endothelial and vascular smooth muscle cells in rat arteries.

Hypothyroidism impairs endothelium-dependent dilatations, while hyperthyroidism augments the production of endothelial nitric oxide. Thus, experiments were designed to determine if thyroid hormone causes endothelium-dependent responses, or alleviates diabetic endothelial dysfunction. Isometric tension was measured in rings with or without endothelium of arteries from normal and diabetic Sprague-Dawley rats.

CXCR3 controls T-cell accumulation in fat inflammation.

Objective: Obesity associates with increased numbers of inflammatory cells in adipose tissue (AT), including T cells, but the mechanism of T-cell recruitment remains unknown. This study tested the hypothesis that the chemokine (C-X-C motif) receptor 3 (CXCR3) participates in T-cell accumulation in AT of obese mice and thus in the regulation of local inflammation and systemic metabolism.

Approach And Results: Obese wild-type mice exhibited higher mRNA expression of CXCR3 in periepididymal AT-derived stromal vascular cells compared with lean mice.

Anti-inflammation therapy by activation of prostaglandin EP4 receptor in cardiovascular and other inflammatory diseases.

Prostaglandin E2 constitutes a major cyclooxygenase-2-derived prostanoid produced at inflammatory sites. In vitro and in vivo data support its role as a modulator of inflammation. Prostaglandin E2 exerts anti-inflammatory effects by binding to one of its receptors, the prostaglandin E receptor 4 (EP4), thereby modulating macrophage and T lymphocyte functions that participate crucially in innate and adaptive immunity and tissue remodeling and repair.

Deletion of EP4 on bone marrow-derived cells enhances inflammation and angiotensin II-induced abdominal aortic aneurysm formation.

Objective: To examine whether a lack of prostaglandin E receptor 4 (EP4) on bone marrow-derived cells would increase local inflammation and enhance the formation of abdominal aortic aneurysm (AAA) in vivo.

Methods And Results: Prostaglandin E(2) (PGE(2)) through activation of EP4, can mute inflammation. Hypercholesterolemic low-density lipoprotein receptor knockout (LDLR(-/-)) mice transplanted with either EP4(+/+) (EP4(+/+)/LDLR(-/-)) or EP4(-/-) (EP4(-/-)/LDLR(-/-)) bone marrow received infusions of angiotensin II to induce AAA.

Lack of EP4 receptors on bone marrow-derived cells enhances inflammation in atherosclerotic lesions.

Aim: prostaglandin E(2), by ligation of its receptor EP4, suppresses the production of inflammatory cytokines and chemokines in macrophages in vitro. Thus, activation of EP4 may constitute an endogenous anti-inflammatory pathway. This study investigated the role of EP4 in atherosclerosis in vivo, and particularly its impact on inflammation.

Endothelial dysfunction: a strategic target in the treatment of hypertension?

Endothelial dysfunction is a common feature of hypertension, and it results from the imbalanced release of endothelium-derived relaxing factors (EDRFs; in particular, nitric oxide) and endothelium-derived contracting factors (EDCFs; angiotensin II, endothelins, uridine adenosine tetraphosphate, and cyclooxygenase-derived EDCFs). Thus, drugs that increase EDRFs (using direct nitric oxide releasing compounds, tetrahydrobiopterin, or L-arginine supplementation) or decrease EDCF release or actions (using cyclooxygenase inhibitor or thromboxane A2/prostanoid receptor antagonists) would prevent the dysfunction. Many conventional antihypertensive drugs, including angiotensin-converting enzyme inhibitors, calcium channel blockers, and third-generation beta-blockers, possess the ability to reverse endothelial dysfunction.

Prostanoids and reactive oxygen species: team players in endothelium-dependent contractions.

The endothelial cells control the tone of the underlying vascular smooth muscle by releasing vasoactive substances. Endothelium-derived relaxing factors (EDRF), in particular nitric oxide have received considerable attention, but much less is known about the ability of the endothelial cells to release endothelium-derived contracting factors (EDCF). The possible players of endothelium-dependent contractions and the underlying mechanisms leading to the release of EDCF will be discussed in the present review.

Endothelium-dependent contractions: when a good guy turns bad!

Endothelial cells can induce contractions of the underlying vascular smooth muscle by generating vasoconstrictor prostanoids (endothelium-dependent contracting factor; EDCF). The endothelial COX-1 isoform of cyclooxygenase appears to play the dominant role in the phenomenon. Its activation requires an increase in intracellular Ca(2+) concentration.

Gap junction inhibitors reduce endothelium-dependent contractions in the aorta of spontaneously hypertensive rats.

Experiments were designed to determine the effect of gap junction inhibitors on endothelium-dependent contractions. Isolated aortic rings of spontaneously hypertensive rats (SHR) were suspended in vitro for isometric force recording. The nonselective gap junction inhibitor, carbenoxolone, reduced endothelium-dependent contractions to acetylcholine and the calcium ionophore A23187 [5-methylamino-2-(2S,3R,5R,8S,9S)-3,5,9-trimethyl-2-(1-oxo-(1H-pyrrol-2-yl)propan-2-yl)-1,7-dioxaspiro-(5,5)undecan-8-yl)methyl)benzooxazole-4-carboxylic acid].

Nitric oxide the gatekeeper of endothelial vasomotor control.

The endothelium can elicit relaxations and contractions of the underlying smooth muscle cells. It does so by releasing vasodilator (EDRF) and vasoconstrictor (EDCF) mediators. Among the diffusible endothelial factors nitric oxide (NO) plays a key role, particularly in large blood vessels.

The role of prostaglandin E and thromboxane-prostanoid receptors in the response to prostaglandin E2 in the aorta of Wistar Kyoto rats and spontaneously hypertensive rats.

Aims: The present study examined the hypothesis that prostaglandin E2 (PGE2) through activation of prostaglandin E (EP) receptor contributes to endothelium-dependent contractions.

Methods And Results: Western blotting revealed that the protein expression of EP1 receptor was significantly down-regulated in the aorta of the spontaneously hypertensive rat (SHR), but there was no significant difference in the expression of EP2, EP4, and total EP3 receptors between preparations of Wistar Kyoto rats (WKY) and SHR. Isometric tension studies showed that low concentrations of PGE2 caused endothelium-dependent relaxations in WKY but not in aortas of the SHR.

Gene expression changes of prostanoid synthases in endothelial cells and prostanoid receptors in vascular smooth muscle cells caused by aging and hypertension.

The present study was designed to assess whether or not changes in genomic expression of cyclooxygenases (COX-1, COX-2), endothelial nitric oxide synthase (eNOS), and prostanoid synthases in the endothelium and of prostanoid receptors in vascular smooth muscle contribute to the occurrence of endothelium-dependent contractions during aging and hypertension. Gene expression was quantified by real-time PCR using isolated endothelial cells and smooth muscle cells (SMC) from the aorta of Wistar-Kyoto and spontaneously hypertensive rats. Genes for all known prostanoid synthases and receptors were present in endothelial cells and SMC, respectively.

Endothelium-dependent contractions occur in the aorta of wild-type and COX2-/- knockout but not COX1-/- knockout mice.

The present experiments were designed to determine whether or not endothelium-dependent contractions can be evoked in the aorta of the mouse, and if so, whether or not deleting the COX1 gene affects the response. Sex differences in the response were also examined. Rings of murine aorta were suspended in a Halpern-Mulvany myograph for recording of isometric force.

Acetylcholine and sodium nitroprusside cause long-term inhibition of EDCF-mediated contractions.

Preliminary studies suggested that previous exposure to acetylcholine (ACh) exerts a delayed inhibition of subsequent contractions mediated by endothelium-derived contracting factor (EDCF). To confirm this long-term inhibitory effect of ACh and to determine whether nitric oxide (NO) mediates the phenomenon, we suspended rings of spontaneously hypertensive rat (SHR) aortas in organ chambers for the recording of isometric force. The rings were incubated in the absence or presence of Nomega-nitro-L-arginine methyl ester (L-NAME; inhibitor of NO synthases) or 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ; inhibitor of soluble guanylyl cyclase) before exposure to increasing concentrations of ACh or sodium nitroprusside (SNP) during contractions to phenylephrine.