Involvement of Rho-kinase in contraction of guinea-pig aorta induced by prostanoid EP3 receptor agonists

EP3 Receptor Deficiency Improves Vascular Remodeling and Cognitive Impairment in Cerebral Small Vessel Disease

Aging and hypertension are major risk factors for cerebral small vessel disease (CSVD). Anti-hypertensive therapy has achieved effective; however, incomplete results in treating CSVD, suggesting the need for additional treatments. Targeting abnormal inflammatory responses has become a topic of research interest. Small artery remodeling is the main pathological feature of CSVD. Inhibition of the E-prostanoid 3 (EP3) receptor has been shown to attenuate vascular remodeling in peripheral organs; however, little is known about its role in CSVD. Therefore, we investigated whether the deletion of EP3 attenuates the development of CSVD in an animal model-- stroke-prone renovascular hypertensive rat (RHRsp). We found that the cerebral small arteries of RHRsp exhibited increased EP3 expression. Despite no alleviation of hypertension, the deletion of EP3 still attenuated the cerebral small artery remodeling of RHRsp, as evidenced by reduced overexpression of extracellular matrix (ECM) in the vessel. In vitro experiments indicated that EP3 deletion regulated the expression of ECM by downregulating TGF-β1/Smad signaling. Furthermore, the Morris water maze test and magnetic resonance test demonstrated that EP3 knockout attenuated cognitive impairment of the RHRsp, possibly through increased cerebral blood flow. Together, our results indicate that the deletion of EP3 attenuates vascular remodeling and vascular cognitive impairment induced by hypertension, and blockade of the EP3 receptor may be a promising strategy for the treatment of CSVD.

The deleterious role of the prostaglandin E2 EP3 receptor in angiotensin II hypertension

Angiotensin II (ANG II) plays a key role in regulating blood pressure and inflammation. Prostaglandin E₂ (PGE₂) signals through four different G protein-coupled receptors, eliciting a variety of effects. We reported that activation of the EP₃ receptor reduces cardiac contractility. More recently, we have shown that overexpression of the EP₄ receptor is protective in a mouse myocardial infarction model. We hypothesize in this study that the relative abundance of EP₃ and EP₄ receptors is a major determinant of end-organ damage in the diseased heart. Thus EP₃ is detrimental to cardiac function and promotes inflammation, whereas antagonism of the EP₃ receptor is protective in an ANG II hypertension (HTN) model. To test our hypothesis, male 10- to 12-wk-old C57BL/6 mice were anesthetized with isoflurane and osmotic minipumps containing ANG II were implanted subcutaneously for 2 wk. We found that antagonism of the EP₃ receptor using L798,106 significantly attenuated the increase in blood pressure with ANG II infusion. Moreover, antagonism of the EP₃ receptor prevented a decline in cardiac function after ANG II treatment. We also found that 10- to 12-wk-old EP₃-transgenic mice, which overexpress EP₃ in the cardiomyocytes, have worsened cardiac function. In conclusion, activation or overexpression of EP₃ exacerbates end-organ damage in ANG II HTN. In contrast, antagonism of the EP₃ receptor is beneficial and reduces cardiac dysfunction, inflammation, and HTN.NEW & NOTEWORTHY This study is the first to show that systemic treatment with an EP₃ receptor antagonist (L798,106) attenuates the angiotensin II-induced increase in blood pressure in mice. The results from this project could complement existing hypertension therapies by combining blockade of the EP₃ receptor with antihypertensive drugs.

PGE2-EP3 signaling exacerbates intracerebral hemorrhage outcomes in 24-mo-old mice

With the population aging at an accelerated rate, the prevalence of stroke and financial burden of stroke-related health care costs are expected to continue to increase. Intracerebral hemorrhage (ICH) is a devastating stroke subtype more commonly affecting the elderly population, who display increased mortality and worse functional outcomes compared with younger patients. This study aimed to investigate the contribution of the prostaglandin E2 (PGE2) E prostanoid (EP) receptor subtype 3 in modulating anatomical outcomes and functional recovery following ICH in 24-mo-old mice. EP3 is the most abundant EP receptor in the brain and we have previously shown that signaling through the PGE2-EP3 axis exacerbates ICH outcomes in young mice. Here, we show that EP3 receptor deletion results in 17.9 ± 6.1% less ICH-induced brain injury (P < 0.05) and improves neurological functional recovery (P < 0.01), as identified by lower neurological deficit scores, decreased resting time, and more gross and fine motor movements. Immunohistological staining was performed to investigate possible mechanisms of EP3-mediated neurotoxicity. Identified mechanisms include reduced blood accumulation and modulation of angiogenic and astroglial responses. Using this aged cohort of mice, we have confirmed and extended our previous results in young mice demonstrating the deleterious role of the PGE2-EP3 signaling axis in modulating brain injury and functional recovery after ICH, further supporting the notion of the EP3 receptor as a putative therapeutic avenue for the treatment of ICH.

Genetic deletion of the prostaglandin E2 E prostanoid receptor subtype 3 improves anatomical and functional outcomes after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a stroke subtype associated with high mortality and morbidity. Following ICH, excitotoxicity and inflammation significantly contribute to secondary brain injury and poor outcomes. Prostaglandin E2 (PGE2 ) levels rise locally with insult to the nervous system, and PGE2 is known to modulate these processes mainly through its E prostanoid (EP) receptors, EP1-4. EP receptor subtype 3 (EP3) is the most abundant EP receptor in the brain and we have previously shown that signaling through the PGE2 -EP3 axis exacerbates excitotoxicity and ischemic stroke outcomes. This study aimed to investigate the contribution of this pathway in modulating anatomical outcomes and functional recovery following ICH. Genetic deletion of EP3 resulted in 48.2 ± 7.3% less ICH-induced brain injury (P < 0.005) and improved functional recovery (P < 0.05), as identified by neurological deficit scoring. To start investigating the mechanisms involved in neuroprotection with impaired PGE2 -EP3 signaling, histological staining was performed to evaluate blood and ferric iron accumulation, neuroinflammation, blood-brain barrier dysfunction, and peripheral neutrophil infiltration. After ICH, EP3 knockout mice demonstrated 49.5 ± 8.8% and 42.8 ± 13.1% less blood (P < 0.01) and ferric iron (P < 0.05), respectively. Furthermore, EP3 knockout mice had significantly reduced astrogliosis, microglial activation, blood-brain barrier breakdown, and neutrophil infiltration. Collectively, these results suggest an injurious role for the PGE2 -EP3 signaling axis in modulating brain injury, inflammation, and neurological functional recovery after ICH. Modulation of the PGE2 -EP3 signaling axis may represent a putative therapeutic avenue for the treatment of ICH.

Rho-kinase as a therapeutic target in vascular diseases: striking nitric oxide signaling

Rho GTPases are a globular, monomeric group of small signaling G-protein molecules. Rho-associated protein kinase/Rho-kinase (ROCK) is a downstream effector protein of the Rho GTPase. Rho-kinases are the potential therapeutic targets in the treatment of cardiovascular diseases. Here, we have primarily discussed the intriguing roles of ROCK in cardiovascular health in relation to nitric oxide signaling. Further, we highlighted the biphasic effects of Y-27632, a ROCK inhibitor under shear stress, which acts as an agonist of nitric oxide production in endothelial cells. The biphasic effects of this inhibitor raised the question of safety of the drug usage in treating cardiovascular diseases.

ATP released via pannexin-1 hemichannels mediates bladder overactivity triggered by urothelial P2Y6 receptors

In contrast to the well-known signaling role of urothelial ATP to control bladder function, the hypothesis that uracil nucleotides (UTP and/or UDP) also exert autocrine/paracrine actions only recently gained experimental support. Urothelial cells express UDP-sensitive P2Y6 receptors, yet their role in the control of bladder activity has been mostly neglected. This study was designed to investigate the ability of PSB0474, a stable UDP analogue which exhibits selectivity for P2Y6 receptors, to modulate urodynamic responses in the anaesthetized rat in vivo. Instillation of PSB0474 into the bladder increased the voiding frequency (VF) without affecting the amplitude (A) and the duration (Δt) of bladder contractions. PSB0474-induced bladder overactivity was prevented by the selective P2Y6 antagonist, MRS2578. The increase in the VF produced by PSB0474 was also blocked by inhibitors of pannexin-1 hemichannels, (10)Panx or carbenoxolone, when these drugs were applied inside the bladder lumen but not when they were administered intravenously. Reduction of hemichannels pore permeability with H1152 also prevented PSB0474-induced bladder overactivity, but the exocytosis inhibitor, Exo-1, was inactive. PSB0474 increased by 3-fold the urinary ATP content. Implication of hemichannels permeability on PSB0474-induced ATP release was demonstrated by real-time fluorescence video-microscopy measuring the uptake of propidium iodide by intact urothelial cells in the absence and in the presence of MRS2578 or carbenoxolone. Confocal microscopy studies confirmed the co-localization of pannexin-1 and P2Y6 receptors in the rat urothelium. Data indicate that activation of P2Y6 receptors causes bladder overactivity in the anaesthetized rat indirectly by releasing ATP from the urothelium via pannexin-1 hemichannels.

Diverse effects of prostaglandin E₂ on vascular contractility

Prostaglandin E₂ (PGE₂) is a major prostanoid produced under inflammatory situations. There have been controversial reports showing contractile or relaxant effect of PGE₂ on vascular tone in various types of blood vessels. Thus, it is still elusive whether and how PGE₂ modulates vascular tone. We here assessed the effects of PGE₂ on vascular contractility using different types of vasculatures isolated form rat. In endothelium-denuded aortas and mesenteric arteries, PGE₂ (1 nM-10 μM) concentration-dependently enhanced the contraction elicited by K(+) (35.4 mM) or norepinephrine (10 nM). In pulmonary arteries, PGE₂ did not alter the both-induced contraction. Tail arteries were relaxed by a low dose of PGE₂ (1-100 nM), but this response shifted to contraction by the higher dose of PGE₂ (300 nM-10 μM). There are four types of PGE₂ receptors EP1-4. RT-PCR showed that aortas and mesenteric arteries abundantly expressed EP3, while tail arteries abundantly expressed EP4. We next revealed that selective EP3 agonism enhanced the contraction in mesenteric arteries, whereas EP4 agonism induced relaxation in tail arteries. Taken together, PGE₂ causes different contractile responses depending on the type of vascular bed. This phenomenon may be due to the difference in expression pattern and activity of EP receptors.

Inactivation of the E-prostanoid 3 receptor attenuates the angiotensin II pressor response via decreasing arterial contractility

OBJECTIVE

The present studies aimed at elucidating the role of prostaglandin E(2) receptor subtype 3 (E-prostanoid [EP] 3) in regulating blood pressure.

METHODS AND RESULTS

Mice bearing a genetic disruption of the EP3 gene (EP(3)(-/-)) exhibited reduced baseline mean arterial pressure monitored by both tail-cuff and carotid arterial catheterization. The pressor responses induced by EP3 agonists M&B28767 and sulprostone were markedly attenuated in EP3(-/-) mice, whereas the reduction of blood pressure induced by prostaglandin E(2) was comparable in both genotypes. Vasopressor effect of acute or chronic infusion of angiotensin II (Ang II) was attenuated in EP3(-/-) mice. Ang II-induced vasoconstriction in mesenteric arteries decreased in EP3(-/-) group. In mesenteric arteries from wild-type mice, Ang II-induced vasoconstriction was inhibited by EP3 selective antagonist DG-041 or L798106. The expression of Arhgef-1 is attenuated in EP3 deficient mesenteric arteries. EP3 antagonist DG-041 diminished Ang II-induced phosphorylation of myosin light chain 20 and myosin phosphatase target subunit 1 in isolated mesenteric arteries. Furthermore, in vascular smooth muscle cells, Ang II-induced intracellular Ca(2+) increase was potentiated by EP3 agonist sulprostone but inhibited by DG-041.

CONCLUSIONS

Activation of the EP3 receptor raises baseline blood pressure and contributes to Ang II-dependent hypertension at least partially via enhancing Ca(2+) sensitivity and intracellular calcium concentration in vascular smooth muscle cells. Selective targeting of the EP3 receptor may represent a potential therapeutic target for the treatment of hypertension.

Different effect of Rho kinase inhibition on calcium signaling in rat isolated large and small arteries

In addition to its role in the regulation of artery contraction, Rho kinase (ROCK) was reported to be involved in the cytosolic calcium response to vasoconstrictor agonists in rat aorta and superior mesenteric artery (SMA). However, it remains to be determined whether ROCK also contributes to calcium signaling in resistance arteries, which play a major role in blood pressure regulation. The investigation of the effect of ROCK inhibition on the calcium and contractile responses of rat resistance mesenteric artery (RMA), in comparison with aorta and SMA, indicated that the calcium response to noradrenaline was inhibited by the ROCK inhibitor Y-27632 in aorta and SMA but not in RMA. The effect of Y-27632 on the calcium signal was unaffected by cytochalasin-D. ROCK activation in noradrenaline-stimulated arteries was confirmed by the inhibition of myosin light chain phosphorylation by Y-27632. Moreover, noradrenaline-induced calcium signaling was similarly inhibited by nimodipine in aorta, SMA and RMA, but nimodipine sensitivity of the contraction increased from the aorta to the RMA, suggesting that the contraction was controlled by different sources of calcium. In pressurized RMA, Y-27632 and H-1152 depressed pressure-induced calcium responses and abolished myogenic contraction. These results stress the important differences in calcium signaling between conductance and resistance arteries.

Rho kinase regulation of vasopressin-induced calcium entry in vascular smooth muscle cell: comparison between rat isolated aorta and cultured aortic cells

In addition to its role in artery contraction, Rho kinase (ROCK) is reported to be involved in the Ca(2+) response to vasoconstrictor agonist in rat aorta. However the signaling pathway mediated by ROCK had not been investigated so far and it was not known whether ROCK also contributed to Ca(2+) signaling in cultured vascular smooth muscle cells (VSMC), which undergo profound phenotypic changes. Our results showed that in VSMC, ROCK inhibition by Y-27632 or H-1152 had no effect on the Ca(2+) response to vasopressin, while in aorta the vasopressin-induced Ca(2+) entry was significantly decreased. The inhibition of myosin light chain kinase (MLCK) by ML-7 depressed the vasopressin-induced Ca(2+) signal in aorta but not in VSMC. The difference in ROCK sensitivity of vasopressin-induced Ca(2+) entry between aorta and VSMC was not related to an alteration of the RhoA/ROCK pathway. However, MLCK expression and activity were depressed in cultured cells compared to aorta. We concluded that the regulation of vasopressin-induced Ca(2+) entry by ROCK in aorta could involve the myosin cytoskeleton and could be prevented by the downregulation of MLCK in VSMC. These results underline the important differences in Ca(2+) regulation between whole tissue and cultured cells.

Novel mechanism for negatively regulating Rho-kinase (ROCK) signaling through Coronin1B protein in neuregulin 1 (NRG-1)-induced tumor cell motility

Although many mechanisms that activate ROCK are known, corresponding negative regulatory mechanisms required for cytoskeletal plasticity are poorly understood. We have discovered that Coronin1B is a novel attenuator of ROCK signaling. We initially identified Coronin1A in a proteomics screen for ROCK2-binding proteins, and here we demonstrate that Coronin1A/B bind directly to ROCK2 through its PH (Pleckstrin Homology) domain. The consequence of the ROCK2-Coronin1B interaction was tested and revealed that increased expression of Coronin1B inhibited, whereas knockdown of Coronin1B stimulated, phosphorylation of the ROCK substrate myosin light chain phosphatase and subsequently, myosin light chain. Thus, Coronin1B is a previously unrecognized inhibitor of ROCK signaling to myosin. Furthermore, we found that the phosphatase Slingshot IL (SSH1L) was required for Coronin1B to inhibit ROCK signaling. To test the significance of this novel mechanism in tumor cell motility, we investigated its role in neuregulin 1 (NRG-1)-induced cell scattering. Importantly, we found that attenuation of the ROCK signaling by Coronin1B was required for NRG-1 stimulated scattering. Our data support a model in which Coronin1B fine-tunes ROCK signaling to modulate myosin activity, which is important for tumor cell motility.

Protein kinase C delta contributes to increase in EP3 agonist-induced contraction in mesenteric arteries from type 2 diabetic Goto-Kakizaki rats

Prostaglandin E(2) (PGE(2)), an important and ubiquitously present vasoactive eicosanoid, may either constrict or dilate systemic vascular beds. However, little is known about the vascular contractile responsiveness to and signaling pathways for PGE(2) at the chronic stage of type 2 diabetes. We hypothesized that PGE(2)-induced arterial contraction is augmented in type 2 diabetic Goto-Kakizaki (GK) rats via the protein kinase Cδ (PKCδ) pathway. Here, we investigated the vasoconstrictor effects of PGE(2) and of sulprostone (EP1-/EP3-receptor agonist) in rings cut from superior mesenteric arteries isolated from GK rats (37-44 weeks old). In arteries from GK rats (vs. those from age-matched Wistar rats), examined in the presence of a nitric oxide synthase inhibitor: 1) the PGE(2)- and sulprostone-induced vasocontractions (which were not blocked by the selective EP1 receptor antagonist sc19220) were enhanced, and these enhancements were suppressed by rottlerin (selective PKCδ inhibitor) but not by Gö6976 (selective PKCα/β inhibitor); 2) the sulprostone-stimulated phosphorylation of PKCδ (at Thr(505)), which yields an active form, was increased and 3) sulprostone-stimulated caldesmon phosphorylations, which are related to isometric force generation in smooth muscle, were increased. The protein expression of EP3 receptor in superior mesenteric arteries was similar between the two groups of rats. Our data suggest that the diabetes-related enhancement of EP3 receptor-mediated vasocontraction results from activation of the PKCδ pathway. Alterations in EP3 receptor-mediated vasocontraction may be important factors in the pathophysiological influences over arterial tone that are present in diabetic states.

Differential reactivity of human mammary artery and saphenous vein to prostaglandin E(2) : implication for cardiovascular grafts

BACKGROUND AND PURPOSE

Human internal mammary arteries (IMA) and saphenous veins (SV) are frequently used for coronary artery bypass graft surgery. Intra- and postoperatively, the bypass grafts are exposed to inflammatory conditions, under which there is a striking increase in the synthesis of prostaglandin E(2) (PGE(2) ). In this context, the physiological response of these vascular grafts to PGE(2) is highly relevant. The aim of this study was thus to characterize the PGE(2) receptor subtypes (EP(1) , EP(2) , EP(3) or EP(4) ) involved in modulation of the vascular tone in these two vessels.

EXPERIMENTAL APPROACH

Rings of IMA and SV were prepared from 48 patients. The rings were mounted in organ baths for isometric recording of tension, and a pharmacological study was performed, together with associated reverse transcriptase PCR and immunohistochemistry experiments.

KEY RESULTS

PGE(2) induced contractions of IMA (E(max) = 1.43 ± 0.20 g; pEC(50) = 7.50 ± 0.10); contractions were also observed with the EP(3) receptor agonists, sulprostone, 17-phenyl-PGE(2) , misoprostol or ONO-AE-248. In contrast, PGE(2) induced relaxation of the precontracted SV (E(max) =-0.22 ± 0.02 g; pEC(50) = 7.14 ± 0.09), as did the EP(4) receptor agonist, ONO-AE1-329. These results were confirmed by the use of selective EP receptor antagonists (GW627368X, L-826266, ONO-8713, SC-51322) and by molecular biology and immunostaining.

CONCLUSIONS AND IMPLICATIONS

PGE(2) induced potent and opposite effects on the human vascular segments used for grafting, namely vasoconstriction of the IMA and vasodilatation of the SV via EP(3) and EP(4) receptors respectively. These observations suggest that EP(3) and EP(4) receptors could constitute therapeutic targets to increase vascular graft patency.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Roles of affinity and lipophilicity in the slow kinetics of prostanoid receptor antagonists on isolated smooth muscle preparations

BACKGROUND AND PURPOSE

The highly lipophilic acyl-sulphonamides L-798106 and L-826266 showed surprisingly slow antagonism of the prostanoid EP₃ receptor system in guinea-pig aorta. Roles of affinity and lipophilicity in the onset kinetics of these and other prostanoid ligands were investigated.

EXPERIMENTAL APPROACH

Antagonist selectivity was assessed using a panel of human recombinant prostanoid receptor-fluorimetric imaging plate reader assays. Potencies/affinities and onset half-times of agonists and antagonists were obtained on guinea-pig-isolated aorta and vas deferens. n-Octanol-water partition coefficients were predicted.

KEY RESULTS

L-798106, L-826266 and the less lipophilic congener (DG)-3ap appear to behave as selective, competitive-reversible EP₃ antagonists. For ligands of low to moderate lipophilicity, potency increments for EP₃ and TP (thromboxane-like) agonism on guinea-pig aorta (above pEC₅₀ of 8.0) were associated with progressively longer onset half-times; similar trends were found for TP and histamine H₁ antagonism above a pA₂ limit of 8.0. In contrast, L-798106 (EP₃), L-826266 (EP₃, TP) and the lipophilic H₁ antagonists astemizole and terfenadine exhibited very slow onset rates despite their moderate affinities; (DG)-3ap (EP₃) had a faster onset. Agonism and antagonism on the vas deferens EP₃ system were overall much faster, although trends were similar.

CONCLUSIONS AND IMPLICATIONS

High affinity and high liphophilicity may contribute to the slow onsets of prostanoid ligands in some isolated smooth muscle preparations. Both relationships are explicable by tissue disposition under the limited diffusion model. EP₃ antagonists used as research tools should have moderate lipophilicity. The influence of lipophilicity on the potential clinical use of EP₃ antagonists is discussed.

Microsomal prostaglandin E synthase-1 contributes to ischaemic excitotoxicity through prostaglandin E2 EP3 receptors

BACKGROUND AND PURPOSE

Although microsomal prostaglandin E synthase (mPGES)-1 is known to contribute to stroke injury, the underlying mechanisms remain poorly understood. This study examines the hypothesis that EP(3) receptors contribute to stroke injury as downstream effectors of mPGES-1 neurotoxicity through Rho kinase activation.

EXPERIMENTAL APPROACH

We used a glutamate-induced excitotoxicity model in cultured rat and mouse hippocampal slices and a mouse middle cerebral artery occlusion-reperfusion model. Effects of an EP(3) receptor antagonist on neuronal damage in mPGES-1 knockout (KO) mice was compared with that in wild-type (WT) mice.

KEY RESULTS

In cultures of rat hippocampal slices, the mRNAs of EP(1-4) receptors were constitutively expressed and only the EP(3) receptor antagonist ONO-AE3-240 attenuated and only the EP(3) receptor agonist ONO-AE-248 augmented glutamate-induced excitotoxicity in CA1 neurons. Hippocampal slices from mPGES-1 KO mice showed less excitotoxicity than those from WT mice and the EP(3) receptor antagonist did not attenuate the excitotoxicity. In transient focal ischaemia models, injection (i.p.) of an EP(3) antagonist reduced infarction, oedema and neurological dysfunction in WT mice, but not in mPGES-1 KO mice, which showed less injury than WT mice. EP(3) receptor agonist-induced augmentation of excitotoxicity in vitro was ameliorated by the Rho kinase inhibitor Y-27632 and Pertussis toxin. The Rho kinase inhibitor HA-1077 also ameliorated stroke injury in vivo.

CONCLUSION AND IMPLICATIONS

Activity of mPGES-1 exacerbated stroke injury through EP(3) receptors and activation of Rho kinase and/or G(i). Thus, mPGES-1 and EP(3) receptors may be valuable therapeutic targets for treatment of human stroke.

PGE2 inhibits basolateral 50 pS potassium channels in the thick ascending limb of the rat kidney

To study the inhibition of the inwardly rectifying basolateral 50 pS potassium channels by PGE(2) we performed patch-clamp studies on the basolateral membrane of the rat kidney thick ascending limb. PGE(2)'s effect was mimicked by the selective EP1- and EP3-receptor agonist, sulprostone, but was prevented by inhibiting protein kinase-C with calphostin-C. The mitogen-activated protein kinase inhibitor PD98059 (ERK) or SB203580 (p38) increased basal channel activity; however, while neither alone prevented the inhibitory effect of PGE(2), but using both of them together completely abolished PGE(2)'s effect on channel activity. Treatment with PGE(2) stimulated phosphorylation of both p38 and ERK in primary cultures of medullary thick ascending limb cells. The PGE(2)-mediated mitogen-activated protein kinase activation was not affected by indomethacin, but was completely blocked by calphostin-C. These studies show that inhibition of basolateral 50 pS potassium channels by PGE(2) is mediated by protein kinase-C, which in turn stimulates mitogen-activated protein kinases in the thick ascending limb of the rat kidney.

Prostaglandins mediate tonic contraction of the guinea pig and human gallbladder

The gallbladder (GB) maintains tonic contraction modulated by neurohormonal inputs but generated by myogenic mechanisms. The aim of these studies was to examine the role of prostaglandins in the genesis of GB myogenic tension. Muscle strips and cells were treated with prostaglandin agonists, antagonists, cyclooxygenase (COX) inhibitors, and small interference RNA (siRNA). The results show that PGE2, thromboxane A2 (TxA2), and PGF(2alpha) cause a dose-dependent contraction of muscle strips and cells. However, only TxA2 and PGE2 (E prostanoid 1 receptor type) antagonists induced a dose-dependent decrease in tonic tension. A COX-1 inhibitor decreased partially the tonic contraction and TxB2 (TxA2 stable metabolite) levels; a COX-2 inhibitor lowered the tonic contraction partially and reduced PGE2 levels. Both inhibitors and the nonselective COX inhibitor indomethacin abolished the tonic contraction. Transfection of human GB muscle strips with COX-1 siRNA partially lowered the tonic contraction and reduced COX-1 protein expression and TxB2 levels; COX-2 siRNA also partially reduced the tonic contraction, the protein expression of COX-2, and PGE2. Stretching muscle strips by 1, 2, 3, and 4 g increased the active tension, TxB2, and PGE2 levels; a COX-1 inhibitor prevented the increase in tension and TxB2; and a COX-2 inhibitor inhibited the expected rise in tonic contraction and PGE2. Indomethacin blocked the rise in tension and TxB2 and PGE2 levels. We conclude that PGE2 generated by COX-2 and TxA2 generated by COX-1 contributes to the maintenance of GB tonic contraction and that variations in tonic contraction are associated with concomitant changes in PGE2 and TxA2 levels.

RhoA Mediates Cyclooxygenase-2 Signaling to Disrupt the Formation of Adherens Junctions and Increase Cell Motility

Cyclooxygenase-2 (COX-2) represents an important target for treatment and prevention of colorectal cancer. Although COX-2 signaling is implicated in promoting tumor cell growth and invasion, the molecular mechanisms that mediate these processes are largely unknown. In this study, we show that the RhoA pathway mediates COX-2 signaling to disrupt the formation of adherens junctions and increase cell motility. Disruption of adherens junctions promotes tumor cell invasion and metastasis and is often associated with tumor progression. We detected high levels of RhoA activity in HCA-7 colon carcinoma cells that constitutively express COX-2. Inhibition of COX-2 significantly reduced the levels of RhoA activity in HCA-7 cells, suggesting that constitutive expression of COX-2 stimulates RhoA activity. Interestingly, inhibition of COX-2 or silencing of COX-2 expression with small interfering RNA (siRNA) stimulated the formation of adherens junctions, concomitant with increased protein levels of E-cadherin and alpha-catenin. Furthermore, inhibition of RhoA or silencing of RhoA expression with siRNA increased the levels of E-cadherin and alpha-catenin. Inhibition of Rho kinases (ROCK), the RhoA effector proteins, also increased levels of E-cadherin and alpha-catenin and stimulated formation of adherens junctions. The motility of HCA-7 cells was significantly decreased when COX-2 or RhoA was inhibited. Therefore, our data reveal a novel molecular mechanism that links COX-2 signaling to disrupt the formation of adherens junctions; COX-2 stimulates the RhoA/ROCK pathway, which reduces levels of E-cadherin and alpha-catenin leading to disruption of adherens junction formation and increased motility. Understanding of COX-2 downstream signaling pathways that promote tumor progression is crucial for the development of novel therapeutic strategies.

Investigation of the prostacyclin (IP) receptor antagonist RO1138452 on isolated blood vessel and platelet preparations

BACKGROUND AND PURPOSE

The current study examined the utility of the recently described prostacyclin (prostanoid IP) receptor antagonist RO1138452 (2-(4-(4-isopropoxybenzyl)-phenylamino) imidazoline) as a tool for classifying prostanoid receptors.

EXPERIMENTAL APPROACH

pA(2) values were determined on isolated smooth muscle and platelet preparations.

KEY RESULTS

RO1138452 antagonized relaxation of human pulmonary artery, guinea-pig aorta and rabbit mesenteric artery induced by the selective IP agonist cicaprost. Schild plots had slopes close to unity, generating pA(2) values of 8.20, 8.39 and 8.12 respectively. Non-surmountable antagonism was sometimes found with the higher concentrations of RO1138452, attributable to the EP(3) contractile action of cicaprost. RO1138452 did not block relaxation of guinea-pig trachea induced by the EP(2)-selective agonist butaprost. In contrast, there was a modest inhibition of butaprost-induced relaxation of human pulmonary artery by RO1138452, implying activation of both EP(2) and IP receptors by butaprost. RO1138452 did not affect relaxation induced by PGE(2) (EP(4) agonist) and substance P (NK(1)/endothelium-dependent agonist) in rabbit mesenteric artery. In human and rat platelet-rich plasmas, RO1138452 antagonized cicaprost-induced inhibition of platelet aggregation in a surmountable manner; pA(2) values may have been affected by binding of RO1138452 to plasma protein. RO1138452 did not affect the inhibitory actions of PGD(2) (DP(1) agonist) and NECA (adenosine A(2A) agonist) in human platelets.

CONCLUSIONS AND IMPLICATIONS

The data indicate that RO1138452 is a potent and selective IP receptor antagonist. RO1138452 represents an important addition to our armoury of prostanoid receptor antagonists and a potential clinical agent in situations where prostacyclin has a pathophysiological function.

Rho-kinase inhibitor, Y-27632, has an antinociceptive effect in mice

The possible antinociceptive effect of a Rho-kinase inhibitor, (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate (Y-27632), was investigated in mice by using the hot-plate and abdominal constriction response (writhing) tests. In addition, the expression of Rho-kinase protein (ROCK-2) was studied in the mouse brain and spinal cord by Western blotting. Male balb/c mice (n=8, for each group) were used in the experiment. Hot-plate latency and the number of writhes were recorded in control and in Y-27632-treated (1-5 mg/kg, i.p.) groups. Y-27632 (1 mg/kg) did not affect hot-plate latency; however, it considerably diminished the number of writhes, from 89+/-12 in control to 30+/-6 in the mice treated with 1 mg/kg Y-27632 (P=0.001). At a higher dose (5 mg/kg), Y-27632 prolonged the hot-plate latency from 8.7+/-1.0 s to 14.4+/-1.7 s (P=0.005) and decreased the number of writhes from 80+/-8 to 24+/-7 (P=0.002). Western blot analysis revealed that mouse spinal cord and brain homogenates expressed ROCK-2 protein. These results indicate that Rho-kinase may be involved in nociception and that its inhibitors, such as Y-27632, may represent a new type of antinociceptive drug.

Investigation of the pronounced synergism between prostaglandin E2 and other constrictor agents on rat femoral artery

This study investigates the pronounced synergism between the weak contractile action of prostaglandin E(2) (PGE(2)) and strong actions of phenylephrine, U-46619 and K(+) on rat isolated femoral artery. The potency ranking for synergism was SC-46275 (prostanoid receptor agonist selectivity: EP(3)>>EP(1))=sulprostone (EP(3)>EP(1))>17-phenyl PGE(2) (EP(1)>EP(3)). The novel EP(3) antagonist L-798106 (0.2-1microM) blocked the enhanced action of sulprostone (pA(2)=7.35-8.10), while the EP(1) antagonist SC-51322 (1microM) did not (pA(2)<6.0). Matching responses to priming agent and priming agent/sulprostone were similarly suppressed by nifedipine (300nM) and the selective Rho-kinase inhibitors H-1152 (0.1-1microM) and Y-27632 (1-10microM). Our findings implicate an EP(3) receptor in the prostanoid component of contractile synergism. While the synergism predominantly operates through a Ca(2+) influx-Rho-kinase pathway, the EP(3) receptor does not necessarily transduce via Rho-kinase.

Atorvastatin reduces the expression of prostaglandin E2 receptors in human carotid atherosclerotic plaques and monocytic cells: potential implications for plaque stabilization

Prostaglandin E2 (PGE2), the product of cyclooxygenase-2 (COX-2) and prostaglandin E synthase-1 (mPGES-1), acts through its receptors (EPs) and induces matrix metalloproteinase (MMP) expression, which may favor the instability of atherosclerotic plaques. The effect of statins on EPs expression has not been previously studied. The aim of this study was to investigate the effect of atorvastatin (ATV, 80 mg/d, for one month) on EP expression in plaques and peripheral blood mononuclear cells (PBMC) of patients with carotid atherosclerosis. In addition, we studied the mechanisms by which statins could modulate EPs expression on cultured monocytic cells (THP-1) stimulated with proinflammatory cytokines (IL-1beta and TNF-alpha). Patients treated with atorvastatin showed reduced EP-1 (14 +/- 1.8% versus 26 +/- 2%; P < 0.01), EP-3 (10 +/- 1.5% versus 26 +/- 1.5%; P < 0.05), and EP-4 expression (10 +/- 4.1% versus 26.6 +/- 4.9%; P < 0.05) in atherosclerotic plaques (immunohistochemistry), and EP-3 and EP-4 mRNA expression in PBMC (real time PCR) in relation to non-treated patients. In cultured monocytic cells, atorvastatin (10 micromol/L) reduced EP-1/-3/-4 expression, along with COX-2, mPGES-1, MMP-9, and PGE2 levels elicited by IL-1beta and TNF-alpha. Similar results were noted with aspirin (100 micromol/L), dexamethasone (1 micromol/L), and the Rho kinase inhibitors Y-27632 and fasudil (10 micromol/L both). The effect of atorvastatin was reversed by mevalonate, farnesyl pyrophosphate, and geranylgeranyl pyrophosphate. On the whole, we have shown that atorvastatin reduces EPs expression in atherosclerotic plaques and blood mononuclear cells of patients with carotid stenosis and in cultured monocytic cells. The inhibition of EP receptors could explain, at least in part, some of the mechanisms by which statins could modulate the COX-2/mPGES-1 proinflammatory pathway and favor plaque stabilization in humans.

Role of contractile prostaglandins and Rho-kinase in growth factor-induced airway smooth muscle contraction

Background

In addition to their proliferative and differentiating effects, several growth factors are capable of inducing a sustained airway smooth muscle (ASM) contraction. These contractile effects were previously found to be dependent on Rho-kinase and have also been associated with the production of eicosanoids. However, the precise mechanisms underlying growth factor-induced contraction are still unknown. In this study we investigated the role of contractile prostaglandins and Rho-kinase in growth factor-induced ASM contraction.

Methods

Growth factor-induced contractions of guinea pig open-ring tracheal preparations were studied by isometric tension measurements. The contribution of Rho-kinase, mitogen-activated protein kinase (MAPK) and cyclooxygenase (COX) to these reponses was established, using the inhibitors Y-27632 (1 μM), U-0126 (3 μM) and indomethacin (3 μM), respectively. The Rho-kinase dependency of contractions induced by exogenously applied prostaglandin F_2α (PGF_2α) and prostaglandin E₂ (PGE₂) was also studied. In addition, the effects of the selective FP-receptor antagonist AL-8810 (10 μM) and the selective EP₁-antagonist AH-6809 (10 μM) on growth factor-induced contractions were investigated, both in intact and epithelium-denuded preparations. Growth factor-induced PGF_2α-and PGE₂-release in the absence and presence of Y-27632, U-0126 and indomethacin, was assessed by an ELISA-assay.

Results

Epidermal growth factor (EGF)-and platelet-derived growth factor (PDGF)-induced contractions of guinea pig tracheal smooth muscle preparations were dependent on Rho-kinase, MAPK and COX. Interestingly, growth factor-induced PGF_2α-and PGE₂-release from tracheal rings was significantly reduced by U-0126 and indomethacin, but not by Y-27632. Also, PGF_2α-and PGE₂-induced ASM contractions were largely dependent on Rho-kinase, in contrast to other contractile agonists like histamine. The FP-receptor antagonist AL-8810 (10 μM) significantly reduced (approximately 50 %) and the EP₁-antagonist AH-6809 (10 μM) abrogated growth factor-induced contractions, similarly in intact and epithelium-denuded preparations.

Conclusion

The results indicate that growth factors induce ASM contraction through contractile prostaglandins – not derived from the epithelium – which in turn rely on Rho-kinase for their contractile effects.

Cardiospecific Overexpression of the Prostaglandin EP 3 Receptor Attenuates Ischemia-Induced Myocardial Injury

Background— The generation of prostaglandin E 2 (PGE 2 ) is significantly increased in acute myocardial ischemia and reperfusion. PGE 2 , in addition to other prostaglandins, protects the reperfused ischemic myocardium. It has been hypothesized that this cardioprotection is mediated by E-type prostaglandin receptors of the G i -coupled EP 3 subtype.

Methods and Results— We tested this hypothesis by generating transgenic (tg) mice with cardiospecific overexpression of the EP 3 receptor. According to ligand binding, a 40-fold overexpression of the EP 3 receptor was achieved in membranes prepared from tg hearts compared with wild-type (wt) littermates. In isolated cardiomyocytes from tg mice, the forskolin-induced rise in cAMP was markedly attenuated, indicating coupling of the overexpressed EP 3 receptor to inhibitory G proteins (G i ) with constitutive receptor activity. There was no evidence for EP 3 receptor coupling to G q -mediated protein kinase C signaling. Isolated hearts from tg and wt mice were subjected to 60 minutes of no-flow ischemia and 45 minutes of reperfusion. In tg hearts, ischemic contracture was markedly delayed compared with wt hearts, and the ischemia-induced increase in left ventricular end-diastolic pressure was reduced by 55%. Creatine kinase and lactate dehydrogenase release was significantly decreased by 85% and 73%, respectively, compared with wt hearts.

Conclusions— Constitutive prostaglandin EP 3 receptor signaling exerts a protective effect on cardiomyocytes, which is probably G i mediated and results in a remarkable attenuation of myocardial injury during ischemia and reperfusion. Cardioprotective actions of E-type prostaglandins may be mediated by this receptor subtype.

Prostacyclin attenuates oxidative damage of myocytes by opening mitochondrial ATP-sensitive K+ channels via the EP3 receptor

Prostacyclin (PGI2) and the PGE family alleviate myocardial ischemia-reperfusion injury and limit oxidative damage. The cardioprotective effects of PGI2 have been traditionally ascribed to activation of IP receptors. Recent advances in prostanoid research have revealed that PGI2 can bind not only to IP, but also to EP, receptors, suggesting cross talk between PGI2 and PGEs. The mechanism(s) whereby PGI2 protects myocytes from oxidative damage and the specific receptors involved remain unknown. Thus fresh isolated adult rat myocytes were exposed to 200 microM H2O2 with or without carbaprostacyclin (cPGI2), IP-selective agonists, and ONO-AE-248 (an EP3-selective agonist). Cell viability was assessed by trypan blue exclusion after 30 min of H2O2 superfusion. cPGI2 and ONO-AE-248 significantly improved cell survival during H2O2 superfusion; IP-selective agonists did not. The protective effect of cPGI2 and ONO-AE-248 was completely abrogated by pretreatment with 5-hydroxydecanoate or glibenclamide. In the second series of experiments, the mitochondrial ATP-sensitive K+ (K(ATP)) channel opener diazoxide (Dx) reversibly oxidized flavoproteins in control myocytes. Exposure to prostanoid analogs alone had no effect on flavoprotein fluorescence. A second application of Dx in the presence of cPGI2 or ONO-AE-248 significantly increased flavoprotein fluorescence compared with Dx alone, but IP-selective agonists did not. This study demonstrates that PGI2 analogs protect cardiac myocytes from oxidative stress mainly via activation of EP3. The data also indicate that activation of EP3 receptors primes the opening of mitochondrial K(ATP) channels and that this mechanism is essential for EP3-dependent protection.

L-type Voltage-Gated Ca 2+ Channels Modulate Expression of Smooth Muscle Differentiation Marker Genes via a Rho Kinase/Myocardin/SRF–Dependent Mechanism

Vascular smooth muscle cell (SMC) contraction is mediated in part by calcium influx through L-type voltage-gated Ca 2+ channels (VGCC) and activation of the RhoA/Rho kinase (ROK) signaling cascade. We tested the hypothesis that Ca 2+ influx through VGCCs regulates SMC differentiation marker expression and that these effects are dependent on RhoA/ROK signaling. Depolarization-induced activation of VGCCs resulted in a nifedipine-sensitive increase in endogenous smooth muscle myosin heavy chain (SMMHC) and SM α-actin expression and CArG-dependent promoter activity, as well as c-fos promoter activity. The ROK inhibitor, Y-27632, prevented depolarization-induced increase in SMMHC/SM α-actin but had no effect on c-fos expression. Conversely, the Ca 2+ /calmodulin-dependent kinase inhibitor, KN93, prevented depolarization-induced increases in c-fos expression with no effect on SMMHC/SM α-actin. Depolarization increased expression of myocardin, a coactivator of SRF that mediates CArG-dependent transcription of SMC marker gene promoters containing paired CArG cis regulatory elements (SMMHC/SM α-actin). Both nifedipine and Y-27632 prevented the depolarization-induced increase in myocardin expression. Moreover, short interfering RNA (siRNA) specific for myocardin attenuated depolarization-induced SMMHC/SM α-actin transcription. Chromatin immunoprecipitation (ChIP) assays revealed that depolarization increased SRF enrichment of the CArG regions in the SMMHC, SM α-actin, and c-fos promoters in intact chromatin. Whereas Y-27632 decreased basal and depolarization-induced SRF enrichment in the SMMHC/SM α-actin promoter regions, it had no effect of SRF enrichment of c-fos. Taken together, these results provide evidence for a novel mechanism whereby Ca 2+ influx via VGCCs stimulates expression of SMC differentiation marker genes through mechanisms that are dependent on ROK, myocardin, and increased binding of SRF to CArG cis regulatory elements.

Mechanisms of ADRF release from rat aortic adventitial adipose tissue

Blood vessels are surrounded by variable amounts of adipose tissue. We showed earlier that adventitial adipose tissue inhibits rat aortic contraction by release of a transferable factor, adventitium-derived relaxing factor (ADRF), which activates smooth muscle K(+) channels. However, little is known about the mechanisms of ADRF release. Using isolated rat aortic rings and isometric contraction measurements, we show that ADRF release depends on extracellular [Ca(2+)] (EC(50) approximately 4.7 mM). ADRF effects do not involve neuronal presynaptic N-type Ca(2+) and Na(+) channels or vanilloid, cannabinoid, and CGRP receptors. ADRF release is strongly inhibited by the protein tyrosine kinase inhibitors genistein and tyrphostin A25. In contrast, daidzein, an inactive genistein analog, and the protein tyrosine kinase inhibitor ST638 had no effect. Protein kinase A inhibition by H89 also inhibited ADRF release, whereas the protein kinase G inhibitor KT-5823 had no effect. We propose that ADRF release is Ca(2+) dependent and is regulated by intracellular signaling pathways involving tyrosine kinase and protein kinase A. Furthermore, ADRF release does not depend on perivascular nerve endings.