EP(1) and EP(4) receptors mediate prostaglandin E(2) actions in the microcirculation of rat kidney

Immunosuppression with cyclosporine versus tacrolimus shows distinctive nephrotoxicity profiles within renal compartments

AIM

Calcineurin inhibitors (CNIs) are the backbone for immunosuppression after solid organ transplantation. Although successful in preventing kidney transplant rejection, their nephrotoxic side effects contribute to allograft injury. Renal parenchymal lesions occur for cyclosporine A (CsA) as well as for the currently favored tacrolimus (Tac). We aimed to study whether chronic CsA and Tac exposures, before reaching irreversible nephrotoxic damage, affect renal compartments differentially and whether related pathogenic mechanisms can be identified.

METHODS

CsA and Tac were administered chronically in wild type Wistar rats using osmotic minipumps over 4 weeks. Functional parameters were controlled. Electron microscopy, confocal, and 3D-structured illumination microscopy were used for histopathology. Clinical translatability was tested in human renal biopsies. Standard biochemical, RNA-seq, and proteomic technologies were applied to identify implicated molecular pathways.

RESULTS

Both drugs caused significant albeit differential damage in vasculature and nephron. The glomerular filtration barrier was more affected by Tac than by CsA, showing prominent deteriorations in endothelium and podocytes along with impaired VEGF/VEGFR2 signaling and podocyte-specific gene expression. By contrast, proximal tubule epithelia were more severely affected by CsA than by Tac, revealing lysosomal dysfunction, enhanced apoptosis, impaired proteostasis and oxidative stress. Lesion characteristics were confirmed in human renal biopsies.

CONCLUSION

We conclude that pathogenetic alterations in the renal compartments are specific for either treatment. Considering translation to the clinical setting, CNI choice should reflect individual risk factors for renal vasculature and tubular epithelia. As a step in this direction, we share protein signatures identified from multiomics with potential pathognomonic relevance.

The Natriuretic Peptide System: A Single Entity, Pleiotropic Effects

In the modern scientific landscape, natriuretic peptides are a complex and interesting network of molecules playing pleiotropic effects on many organs and tissues, ensuring the maintenance of homeostasis mainly in the cardiovascular system and regulating the water-salt balance. The characterization of their receptors, the understanding of the molecular mechanisms through which they exert their action, and the discovery of new peptides in the last period have made it possible to increasingly feature the physiological and pathophysiological role of the members of this family, also allowing to hypothesize the possible settings for using these molecules for therapeutic purposes. This literature review traces the history of the discovery and characterization of the key players among the natriuretic peptides, the scientific trials performed to ascertain their physiological role, and the applications of this knowledge in the clinical field, leaving a glimpse of new and exciting possibilities for their use in the treatment of diseases.

Neutrophil accumulation within tissues: A damage x healing dichotomy

The abundance of neutrophils in human circulation, their fast mobilization from blood to tissues, along with their alleged short life-span led to the image of neutrophils as a homogeneous cell type designed to fight infections and die in the process. Additionally, their granule content and capacity to produce molecules with considerable cytotoxic potential, lead to the general belief that neutrophil activation inexorably results in side effect of extensive tissue injury. Neutrophil activation in fact causes tissue injury as an adverse effect, but it seems that this is restricted to particular pathological situations and more of an "exception to the rule". Here we review evidences arising especially from intravital microscopy studies that demonstrate neutrophils as cells endowed with sophisticated mechanisms and able to engage in complex interactions as to minimize damage and optimize their effector functions. Moreover, neutrophil infiltration may even contribute to tissue healing and repair which may altogether demand a reexamination of current anti-inflammatory therapies that have neutrophil migration and activation as a target.

Atrial Natriuretic Peptide31-67: A Novel Therapeutic Factor for Cardiovascular Diseases

The characterization of the cardiac hormone atrial natriuretic peptide (ANP_99–126), synthesized and secreted predominantly by atrial myocytes under stimulation by mechanical stretch, has established the heart as an endocrine organ with potent natriuretic, diuretic, and vasodilating actions. Three additional distinct polypeptides resulting from proteolytic cleavage of proANP have been identified in the circulation in humans. The mid-sequence proANP fragment 31–67 (also known as proANP_31–67) has unique potent and prolonged diuretic and natriuretic properties. In this review, we report the main effects of this circulating hormone in different tissues and organs, and its mechanisms of actions. We further highlight recent evidence on the cardiorenal protective actions of chronic supplementation of synthetic proANP_31–67 in preclinical models of cardiorenal disease. Finally, we evaluate the use of proANP_31–67 as a new therapeutic strategy to repair end-organ damage secondary to hypertension, diabetes mellitus, renal diseases, obesity, heart failure, and other morbidities that can lead to impaired cardiac function and structure.

Local cyclic adenosine monophosphate signalling cascades-Roles and targets in chronic kidney disease

The molecular mechanisms underlying chronic kidney disease (CKD) are poorly understood and treatment options are limited, a situation underpinning the need for elucidating the causative molecular mechanisms and for identifying innovative treatment options. It is emerging that cyclic 3',5'-adenosine monophosphate (cAMP) signalling occurs in defined cellular compartments within nanometre dimensions in processes whose dysregulation is associated with CKD. cAMP compartmentalization is tightly controlled by a specific set of proteins, including A-kinase anchoring proteins (AKAPs) and phosphodiesterases (PDEs). AKAPs such as AKAP18, AKAP220, AKAP-Lbc and STUB1, and PDE4 coordinate arginine-vasopressin (AVP)-induced water reabsorption by collecting duct principal cells. However, hyperactivation of the AVP system is associated with kidney damage and CKD. Podocyte injury involves aberrant AKAP signalling. cAMP signalling in immune cells can be local and slow the progression of inflammatory processes typical for CKD. A major risk factor of CKD is hypertension. cAMP directs the release of the blood pressure regulator, renin, from juxtaglomerular cells, and plays a role in Na⁺ reabsorption through ENaC, NKCC2 and NCC in the kidney. Mutations in the cAMP hydrolysing PDE3A that cause lowering of cAMP lead to hypertension. Another major risk factor of CKD is diabetes mellitus. AKAP18 and AKAP150 and several PDEs are involved in insulin release. Despite the increasing amount of data, an understanding of functions of compartmentalized cAMP signalling with relevance for CKD is fragmentary. Uncovering functions will improve the understanding of physiological processes and identification of disease-relevant aberrations may guide towards new therapeutic concepts for the treatment of CKD.

International Union of Basic and Clinical Pharmacology. CIX. Differences and Similarities between Human and Rodent Prostaglandin E2 Receptors (EP1-4) and Prostacyclin Receptor (IP): Specific Roles in Pathophysiologic Conditions

Prostaglandins are derived from arachidonic acid metabolism through cyclooxygenase activities. Among prostaglandins (PGs), prostacyclin (PGI2) and PGE2 are strongly involved in the regulation of homeostasis and main physiologic functions. In addition, the synthesis of these two prostaglandins is significantly increased during inflammation. PGI2 and PGE2 exert their biologic actions by binding to their respective receptors, namely prostacyclin receptor (IP) and prostaglandin E2 receptor (EP) 1-4, which belong to the family of G-protein-coupled receptors. IP and EP1-4 receptors are widely distributed in the body and thus play various physiologic and pathophysiologic roles. In this review, we discuss the recent advances in studies using pharmacological approaches, genetically modified animals, and genome-wide association studies regarding the roles of IP and EP1-4 receptors in the immune, cardiovascular, nervous, gastrointestinal, respiratory, genitourinary, and musculoskeletal systems. In particular, we highlight similarities and differences between human and rodents in terms of the specific roles of IP and EP1-4 receptors and their downstream signaling pathways, functions, and activities for each biologic system. We also highlight the potential novel therapeutic benefit of targeting IP and EP1-4 receptors in several diseases based on the scientific advances, animal models, and human studies. SIGNIFICANCE STATEMENT: In this review, we present an update of the pathophysiologic role of the prostacyclin receptor, prostaglandin E2 receptor (EP) 1, EP2, EP3, and EP4 receptors when activated by the two main prostaglandins, namely prostacyclin and prostaglandin E2, produced during inflammatory conditions in human and rodents. In addition, this comparison of the published results in each tissue and/or pathology should facilitate the choice of the most appropriate model for the future studies.

Prostaglandin E2 sequentially activates E-prostanoid receptor-3 and thromboxane prostanoid receptor to evoke contraction and increase in resistance of the mouse renal vasculature

Although recognized to have an in vivo vasodepressor effect blunted by the vasoconstrictor effect of E-prostanoid receptor-3 (EP3), prostaglandin E₂ (PGE₂ ) evokes contractions of many vascular beds that are sensitive to antagonizing the thromboxane prostanoid receptor (TP). This study aimed to determine the direct effect of PGE₂ on renal arteries and/or the whole renal vasculature and how each of these two receptors is involved in the responses. Experiments were performed on isolated vessels and perfused kidneys of wild-type mice and/or mice with deficiency in TP (TP^-/- ), EP3 (EP3^-/- ), or both TP and EP3 (TP^-/- /EP3^-/- ). Here we show that PGE₂ (0.001-30 μM) evoked not only contraction of main renal arteries, but also a decrease of flow in perfused kidneys. EP3^-/- diminished the response to 0.001-0.3 μM PGE₂ , while TP^-/- reduced that to the prostanoid of higher concentrations. In TP^-/- /EP3^-/- vessels and perfused kidneys, PGE₂ did not evoke contraction but instead resulted in vasodilator responses. These results demonstrate that PGE₂ functions as an overall direct vasoconstrictor of the mouse renal vasculature with an effect reflecting the vasoconstrictor activities outweighing that of dilation. Also, our results suggest that EP3 dominates the vasoconstrictor effect of PGE₂ of low concentrations (≤0.001-0.3 μM), but its effect is further added by that of TP, which has a higher efficacy, although activated by higher concentrations (from 0.01 μM) of the same prostanoid PGE₂ .

Renoprotective effects of the novel prostaglandin EP4 receptor-selective antagonist ASP7657 in 5/6 nephrectomized chronic kidney disease rats

Prostaglandins (PGs) are important lipid mediators of numerous physiologic and pathophysiologic processes in the kidney. PGE₂, the most abundant renal PG, plays a major role in renal physiology, including renin release and glomerular hemodynamics. We investigated the renoprotective properties of the novel PGE₂ EP4 receptor-selective antagonist ASP7657 in 5/6 nephrectomized rats, a chronic kidney disease (CKD) model. Eight weeks of repeated administration of ASP7657 (0.001-0.1 mg/kg) dose-dependently and significantly reduced urinary protein excretion and attenuated the development of glomerulosclerosis and tubulointerstitial damage, including fibrosis and inflammatory cell infiltration, without affecting blood pressure. Additionally, ASP7657 tended to have beneficial effects on renal function, as indicated by the decrease in plasma creatinine and blood urea nitrogen levels and attenuation of the decline in creatinine clearance (Ccr). The angiotensin II receptor blocker losartan (10 mg/kg) also showed these renoprotective effects while significantly reducing blood pressure. ASP7657 dose-dependently and significantly reduced the EP4 receptor agonist-induced increase in plasma renin activity, as assessed by angiotensin I release in normal rats. Additionally, ASP7657 attenuated hyperfiltration assessed by Ccr without changing the renal blood flow or blood pressure in diabetic rats. These results suggest that ASP7657 suppresses the progression of chronic renal failure by modulating renin release and improving renal hemodynamics, and may therefore be a promising therapeutic option for inhibiting the progression of CKD.

Pharmacological properties of ASP7657, a novel, potent, and selective prostaglandin EP4 receptor antagonist

We determined the pharmacologic profile of ASP7657, trans-4-[({[1-(quinolin-2-ylmethyl)-5-(trifluoromethyl)-1H-indol-7 yl] carbonyl} amino) methyl] cyclohexanecarboxylic acid methanesulfonate (1:1), a newly synthesized selective E-type prostaglandin (EP)4 receptor antagonist using several in vitro and in vivo experiments. ASP7657 exhibited high affinity for rat and human EP4 receptors, with K_i values of 6.02 nM and 2.21 nM, respectively. In addition, ASP7657 potently inhibited the PGE₂-induced cyclic adenosine monophosphate (cAMP) increase in Chinese hamster ovary (CHO) cells expressing rat EP4 receptors and human lymphoblastoid T (Jurkat) cells, with IC₅₀ values of 0.86 nM and 0.29 nM, respectively. In contrast, ASP7657 did not inhibit the PGE₂-induced intracellular calcium increase in HEK293 cells expressing rat EP1 and EP3 receptors, or cAMP increase in CHO cells expressing rat EP2 receptors. ASP7657 showed good pharmacokinetic properties following oral dosing and dose-dependently antagonized the prostaglandin (PG)E₂-mediated inhibition of lipopolysaccharide-induced tumor necrosis factor-α release from rat whole blood culture. In addition, 4 weeks repeated oral administration of ASP7657 dose-dependently attenuated albuminuria in type 2 diabetic mice; these effects were significant at doses of 0.01 mg/kg or higher. These results demonstrate that ASP7657 is a potent and selective EP4 receptor antagonist that may be useful in future studies to help clarify the physiological and pathophysiological roles of PG.

GPCRs in context: sexual dimorphism in the cardiovascular system

Cardiovascular disease (CVD) remains the largest cause of mortality worldwide, and there is a clear gender gap in disease occurrence, with men being predisposed to earlier onset of CVD, including atherosclerosis and hypertension, relative to women. Oestrogen may be a driving factor for female-specific cardioprotection, though androgens and sex chromosomes are also likely to contribute to sexual dimorphism in the cardiovascular system (CVS). Many GPCR-mediated processes are involved in cardiovascular homeostasis, and some exhibit clear sex divergence. Here, we focus on the G protein-coupled oestrogen receptor, endothelin receptors ET_A and ET_B and the eicosanoid G protein-coupled receptors (GPCRs), discussing the evidence and potential mechanisms leading to gender dimorphic responses in the vasculature. The use of animal models and pharmacological tools has been essential to understanding the role of these receptors in the CVS and will be key to further delineating their sex-specific effects. Ultimately, this may illuminate wider sex differences in cardiovascular pathology and physiology.

LINKED ARTICLES

This article is part of a themed section on Molecular Pharmacology of GPCRs. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.21/issuetoc.

EP4 inhibition attenuates the development of diabetic and non-diabetic experimental kidney disease

The therapeutic targeting of prostanoid subtype receptors may slow the development of chronic kidney disease (CKD) through mechanisms that are distinct from those of upstream COX inhibition. Here, employing multiple experimental models of CKD, we studied the effects of inhibition of the EP4 receptor, one of four receptor subtypes for the prostanoid prostaglandin E₂. In streptozotocin-diabetic endothelial nitric oxide synthase knockout mice, EP4 inhibition attenuated the development of albuminuria, whereas the COX inhibitor indomethacin did not. In Type 2 diabetic db/db mice, EP4 inhibition lowered albuminuria to a level comparable with that of the ACE inhibitor captopril. However, unlike captopril, EP4 inhibition had no effect on blood pressure or hyperfiltration although it did attenuate mesangial matrix accumulation. Indicating a glucose-independent mechanism of action, EP4 inhibition also attenuated proteinuria development and glomerular scarring in non-diabetic rats subjected to surgical renal mass ablation. Finally, in vitro, EP4 inhibition prevented transforming growth factor-ß1 induced dedifferentiation of glomerular podocytes. In rodent models of diabetic and non-diabetic CKD, EP4 inhibition attenuated renal injury through mechanisms that were distinct from either broadspectrum COX inhibition or “standard of care” renin angiotensin system blockade. EP4 inhibition may represent a viable repurposing opportunity for the treatment of CKD.

Vascular Smooth Muscle-Specific EP4 Receptor Deletion in Mice Exacerbates Angiotensin II-Induced Renal Injury

AIMS

Cyclooxygenase inhibition by non-steroidal anti-inflammatory drugs is contraindicated in hypertension, as it may reduce glomerular filtration rate (GFR) and renal blood flow. However, the identity of the specific eicosanoid and receptor underlying these effects is not known. We hypothesized that vascular smooth muscle prostaglandin E2 (PGE2) E-prostanoid 4 (EP4) receptor deletion predisposes to renal injury via unchecked vasoconstrictive actions of angiotensin II (AngII) in a hypertension model. Mice with inducible vascular smooth muscle cell (VSMC)-specific EP4 receptor deletion were generated and subjected to AngII-induced hypertension.

RESULTS

EP4 deletion was verified by PCR of aorta and renal vessels, as well as functionally by loss of PGE2-mediated mesenteric artery relaxation. Both AngII-treated groups became similarly hypertensive, whereas albuminuria, foot process effacement, and renal hypertrophy were exacerbated in AngII-treated EP4^VSMC-/- but not in EP4^VSMC+/+ mice and were associated with glomerular scarring, tubulointerstitial injury, and reduced GFR. AngII-treated EP4^VSMC-/- mice exhibited capillary damage and reduced renal perfusion as measured by fluorescent bead microangiography and magnetic resonance imaging, respectively. NADPH oxidase 2 (Nox2) expression was significantly elevated in AngII-treated EP4^-/- mice. EP4-receptor silencing in primary VSMCs abolished PGE2 inhibition of AngII-induced Nox2 mRNA and superoxide production.

INNOVATION

These data suggest that vascular EP4 receptors buffer the actions of AngII on renal hemodynamics and oxidative injury.

CONCLUSION

EP4 agonists may, therefore, protect against hypertension-associated kidney damage. Antioxid. Redox Signal. 25, 642-656.

Heme Oxygenases in Cardiovascular Health and Disease

Heme oxygenases are composed of two isozymes, Hmox1 and Hmox2, that catalyze the degradation of heme to carbon monoxide (CO), ferrous iron, and biliverdin, the latter of which is subsequently converted to bilirubin. While initially considered to be waste products, CO and biliverdin/bilirubin have been shown over the last 20 years to modulate key cellular processes, such as inflammation, cell proliferation, and apoptosis, as well as antioxidant defense. This shift in paradigm has led to the importance of heme oxygenases and their products in cell physiology now being well accepted. The identification of the two human cases thus far of heme oxygenase deficiency and the generation of mice deficient in Hmox1 or Hmox2 have reiterated a role for these enzymes in both normal cell function and disease pathogenesis, especially in the context of cardiovascular disease. This review covers the current knowledge on the function of both Hmox1 and Hmox2 at both a cellular and tissue level in the cardiovascular system. Initially, the roles of heme oxygenases in vascular health and the regulation of processes central to vascular diseases are outlined, followed by an evaluation of the role(s) of Hmox1 and Hmox2 in various diseases such as atherosclerosis, intimal hyperplasia, myocardial infarction, and angiogenesis. Finally, the therapeutic potential of heme oxygenases and their products are examined in a cardiovascular disease context, with a focus on how the knowledge we have gained on these enzymes may be capitalized in future clinical studies.

PGE2, Kidney Disease, and Cardiovascular Risk: Beyond Hypertension and Diabetes

An important measure of cardiovascular health is obtained by evaluating the global cardiovascular risk, which comprises a number of factors, including hypertension and type 2 diabetes, the leading causes of illness and death in the world, as well as the metabolic syndrome. Altered immunity, inflammation, and oxidative stress underlie many of the changes associated with cardiovascular disease, diabetes, and the metabolic syndrome, and recent efforts have begun to elucidate the contribution of PGE2 in these events. This review summarizes the role of PGE2 in kidney disease outcomes that accelerate cardiovascular disease, highlights the role of cyclooxygenase-2/microsomal PGE synthase 1/PGE2 signaling in hypertension and diabetes, and outlines the contribution of PGE2 to other aspects of the metabolic syndrome, particularly abdominal adiposity, dyslipidemia, and atherogenesis. A clearer understanding of the role of PGE2 could lead to new avenues to improve therapeutic options and disease management strategies.

Cardiohemodynamic and electrophysiological effects of a selective EP4 receptor agonist ONO--AE1--329 in the halothane-anesthetized dogs

Cardiovascular effects of a highly selective prostaglandin E2 type 4 (EP4) receptor agonist ONO-AE1-329 were assessed with the halothane-anesthetized dogs (n=6). ONO-AE1-329 was intravenously infused in three escalating doses of 0.3, 1 and 3ng/kg/min for 10min with a pause of 20min between the doses. The low dose of 0.3ng/kg/min significantly increased maximum upstroke velocity of left ventricular pressure by 18% at 20min, indicating increase of ventricular contractility. The middle dose of 1ng/kg/min significantly decreased total peripheral resistance by 24% and left ventricular end-diastolic pressure by 32% at 10min, indicating dilation of arteriolar resistance vessels and venous capacitance ones, respectively; and increased cardiac output by 25% at 10min in addition to the change induced by the low dose. The high dose of 3ng/kg/min increased heart rate by 34% at 10min; decreased mean blood pressure by 14% at 10min and atrioventricular nodal conduction time by 13% at 5min; and shortened left ventricular systolic period by 8% at 10min and electromechanical coupling defined as an interval from completion of repolarization to the start of ventricular diastole by 39% at 10min in addition to the changes induced by the middle dose. No significant change was detected in a ventricular repolarization period. These results indicate that ONO-AE1-329 may possess a similar cardiovascular profile to typical phosphodiesterase 3 inhibitors as an inodilator, and suggest that EP4 receptor stimulation can become an alternative strategy for the treatment of congestive heart failure.

Prostaglandin I 2 and Prostaglandin E 2 Modulate Human Intrarenal Artery Contractility Through Prostaglandin E2-EP4, Prostacyclin-IP, and Thromboxane A2-TP Receptors

Cyclooxygenase inhibitors decrease renal blood flow in settings with decreased effective circulating volume. The present study examined the hypothesis that prostaglandins, prostaglandin E 2 (PGE 2 ) and prostacyclin (PGI 2 ), induce relaxation of human intrarenal arteries through PGE 2 -EP and PGI 2 -IP receptors. Intrarenal arteries were microdissected from human nephrectomy samples (n=53, median diameter ≈362 μm, 88% viable, 76% relaxed in response to acetylcholine). Rings were suspended in myographs to record force development. In vessels with K + -induced tension (EC 70 : –log [mol/L]=1.36±0.03), PGE 2 and PGI 2 induced concentration-dependent relaxation (–log EC 50 : PGE 2 =7.1±0.3 and PGI 2 =7.7). The response to PGE 2 displayed endothelium dependence and desensitization. Relaxation by PGE 2 was mimicked by an EP4 receptor agonist (CAY10598, EC 50 =6.7±0.2). The relaxation after PGI 2 was abolished by an IP receptor antagonist (BR5064, 10 –8 mol/L). Pretreatment of quiescent arteries with PGE 2 for 5 minutes (10 –6 mol/L) led to a significant right shift of the concentration–response to norepinephrine (EC 50 from 6.6±0.1–5.9±0.1). In intrarenal arteries with K + -induced tone, PGE 2 and PGI 2 at 10 –5 mol/L elicited increased tension. This was abolished by thromboxane receptor (TP) antagonist (S18886, 10 –6 mol/L). A TP agonist (U46619, n=6) evoked tension (EC 50 =8.1±0.2) that was inhibited by S18886. Polymerase chain reaction and immunoblotting showed EP4, IP, and TP receptors in intrarenal arteries. In conclusion, PGE 2 and PGI 2 may protect renal perfusion by activating cognate IP and EP4 receptors associated with smooth muscle cells and endothelium in human intrarenal arteries and contribute to increased renal vascular resistance at high pathological concentrations mediated by noncognate TP receptor.

Antagonism of the prostaglandin E2 EP1 receptor in MDCK cells increases growth through activation of Akt and the epidermal growth factor receptor

The actions of prostaglandin E2 (PGE2) in the kidney are mediated by G protein-coupled E-prostanoid (EP) receptors, which affect renal growth and function. This report examines the role of EP receptors in mediating the effects of PGE2 on Madin-Darby canine kidney (MDCK) cell growth. The results indicate that activation of Gs-coupled EP2 and EP4 by PGE2 results in increased growth, while EP1 activation is growth inhibitory. Indeed, two EP1 antagonists (ONO-8711 and SC51089) stimulate, rather than inhibit, MDCK cell growth, an effect that is lost following an EP1 knockdown. Similar observations were made with M1 collecting duct and rabbit kidney proximal tubule cells. ONO-8711 even stimulates growth in the absence of exogenous PGE2, an effect that is prevented by ibuprofen (indicating a dependence upon endogenous PGE2). The involvement of Akt was indicated by the observation that 1) ONO-8711 and SC51089 increase Akt phosphorylation, and 2) MK2206, an Akt inhibitor, prevents the increased growth caused by ONO-8711. The involvement of the EGF receptor (EGFR) was indicated by 1) the increased phosphorylation of the EGFR caused by SC51089 and 2) the loss of the growth-stimulatory effect of ONO-8711 and SC51089 caused by the EGFR kinase inhibitor AG1478. The growth-stimulatory effect of ONO-8711 was lost following an EGFR knockdown, and transduction of MDCK cells with a dominant negative EGFR. These results support the hypothesis that 1) signaling via the EP1 receptor involves Akt as well as the EGFR, and 2), EP1 receptor pharmacology may be employed to prevent the aberrant growth associated with a number of renal diseases.

Chronic kidney disease: targeting prostaglandin E2 receptors

Chronic kidney disease is a leading cause of morbidity and mortality in the world. A better understanding of disease mechanisms has been gained in recent years, but the current management strategies are ineffective at preventing disease progression. A widespread focus of research is placed on elucidating the specific processes implicated to find more effective therapeutic options. PGE2, acting on its four EP receptors, regulates many renal disease processes; thus EP receptors could prove to be important targets for kidney disease intervention strategies. This review summarizes the major pathogenic mechanisms contributing to initiation and progression of chronic kidney disease, emphasizing the role of hyperglycemia, hypertension, inflammation, and oxidative stress. We have long recognized the multifaceted role of PGs in both the initiation and progression of chronic kidney disease, yet studies are only now seriously contemplating specific EP receptors as targets for therapy. Given the plethora of renal complications attributed to PG involvement in the kidney, this review highlights these pathogenic events and emphasizes the PGE2 receptor targets as options available to complement current therapeutic strategies.

Application of prostaglandin E2 improves ileal blood flow in NEC

PURPOSE

Indomethacin, a nonselective prostaglandin inhibitor used to treat patent ductus arteriosus, is associated with intestinal perforation inducing an NEC-like illness. We sought to define the contribution of prostaglandin E2 (PG E2) and its receptor EP4 to intestinal blood flow regulation in premature neonates with NEC.

METHODS

Newborn Sprague-Dawley rats were randomized by litter to undergo experimental NEC induction or to serve as a CONTROL. At 48hours of age, intestinal laser Doppler blood flow was assessed at baseline and after intraperitoneal administration of indomethacin, PG E2, EP4 antagonist, or EP4 agonist. Data were analyzed using a 2-way ANOVA with post hoc Tukey-Kramer correction.

RESULTS

At baseline, NEC animals had lower intestinal blood flow than controls. Indomethacin, PG E2 and EP4 agonist all increased ileal blood flow, but PG E2 and EP4 agonist increased blood flow the most in NEC pups. EP4 antagonist decreased intestinal perfusion in both groups.

CONCLUSION

The above evidence suggests the importance of PG E2 and EP4 in regulation of neonatal intestinal blood flow. Since indomethacin treatment of patent ductus arteriosus in the premature infant is associated with an increased risk of intestinal perforation owing to compromised blood flow, PG E2 supplementation might provide intestinal protection if administered simultaneously with indomethacin.

The renoprotective effects of berberine via the EP4-Gαs-cAMP signaling pathway in different stages of diabetes in rats

AIMS

To investigate the renoprotective roles of berberine (BBR) in different stages of diabetic nephropathy (DN) in streptozotocin (STZ)-induced diabetic rats fed a high-sugar and high-fat diet.

METHODS

Diabetes was induced in mice by intraperitoneal injection of STZ, and the mice were then randomly divided into groups: normal, diabetes, high-sugar and high-fat and BBR (high, median and low dose) groups. The body weight (BW), kidney weight to body weight (KW/BW), blood urea nitrogen, urine total protein to urine creatinine ratio and serum creatinine were measured on different weeks throughout the study. The protein levels of E prostanoid receptor 4 (EP4), Gαs and content of cAMP in the kidney were, respectively, detected by western blot analysis and RIA analysis.

RESULTS

In the DN rats, there was remarkable renal damage. BBR restored renal functional parameters, suppressed alterations in histological and ultrastructural changes in the kidney tissues and increased EP4, Gαs and cAMP levels compared with those of the DN model group. In addition, BBR has different therapeutic effects during the different stages of the development of DN, and it works best in the sixth week.

CONCLUSION

These studies demonstrate, for the first time, that BBR exerts renoprotective effects in different stages of DN via EP4- Gαs- AC-cAMP signaling pathway in STZ-induced DN rats fed a high-sugar and high-fat diet.

Cyclooxygenase metabolites in the kidney

In the mammalian kidney, prostaglandins (PGs) are important mediators of physiologic processes, including modulation of vascular tone and salt and water. PGs arise from enzymatic metabolism of free arachidonic acid (AA), which is cleaved from membrane phospholipids by phospholipase A2 activity. The cyclooxygenase (COX) enzyme system is a major pathway for metabolism of AA in the kidney. COX are the enzymes responsible for the initial conversion of AA to PGG2 and subsequently to PGH2, which serves as the precursor for subsequent metabolism by PG and thromboxane synthases. In addition to high levels of expression of the "constitutive" rate-limiting enzyme responsible for prostanoid production, COX-1, the "inducible" isoform of cyclooxygenase, COX-2, is also constitutively expressed in the kidney and is highly regulated in response to alterations in intravascular volume. PGs and thromboxane A2 exert their biological functions predominantly through activation of specific 7-transmembrane G-protein-coupled receptors. COX metabolites have been shown to exert important physiologic functions in maintenance of renal blood flow, mediation of renin release and regulation of sodium excretion. In addition to physiologic regulation of prostanoid production in the kidney, increases in prostanoid production are also seen in a variety of inflammatory renal injuries, and COX metabolites may serve as mediators of inflammatory injury in renal disease.

Prostaglandin E2 mediates connecting tubule glomerular feedback

Connecting tubule glomerular feedback (CTGF) is a mechanism in which Na reabsorption in the connecting tubule (CNT) causes afferent arteriole (Af-Art) dilation. CTGF is mediated by eicosanoids, including prostaglandins and epoxyeicosatrienoic acids; however, their exact nature and source remain unknown. We hypothesized that during CTGF, the CNT releases prostaglandin E2, which binds its type 4 receptor (EP4) and dilates the Af-Art. Rabbit Af-Arts with the adherent CNT intact were microdissected, perfused, and preconstricted with norepinephrine. CTGF was elicited by increasing luminal NaCl in the CNT from 10 to 80 mmol/L. We induced CTGF with or without the EP4 receptor blocker ONO-AE3-208 added to the bath in the presence of the epoxyeicosatrienoic acid synthesis inhibitor MS-PPOH. ONO-AE3-208 abolished CTGF (control, 9.4 ± 0.5; MS-PPOH+ONO-AE3-208, -0.6 ± 0.2 μm; P<0.001; n=6). To confirm these results, we used a different, specific EP4 blocker, L161982 (10(-5) mol/L), that also abolished CTGF (control, 8.5 ± 0.9; MS-PPOH+L161982, 0.8 ± 0.4 μm; P<0.001; n=6). To confirm that the eicosanoids that mediate CTGF are released from the CNT rather than the Af-Art, we first disrupted the Af-Art endothelium with an antibody and complement. Endothelial disruption did not affect CTGF (7.9 ± 0.9 versus 8.6 ± 0.6 μm; P=NS; n=7). We then added arachidonic acid to the lumen of the CNT while maintaining zero NaCl in the perfusate. Arachidonic acid caused dose-dependent dilation of the attached Af-Art (from 8.6 ± 1.2 to 15.3 ± 0.7 μm; P<0.001; n=6), and this effect was blocked by ONO-AE3-208 (10(-7) mol/L). We conclude that during CTGF, the CNT releases prostaglandin E2, which acts on EP4 on the Af-Art inducing endothelium-independent dilation.

E-type prostanoid receptor 4 (EP4) in disease and therapy

The large variety of biological functions governed by prostaglandin (PG) E2 is mediated by signaling through four distinct E-type prostanoid (EP) receptors. The availability of mouse strains with genetic ablation of each EP receptor subtype and the development of selective EP agonists and antagonists have tremendously advanced our understanding of PGE2 as a physiologically and clinically relevant mediator. Moreover, studies using disease models revealed numerous conditions in which distinct EP receptors might be exploited therapeutically. In this context, the EP4 receptor is currently emerging as most versatile and promising among PGE2 receptors. Anti-inflammatory, anti-thrombotic and vasoprotective effects have been proposed for the EP4 receptor, along with its recently described unfavorable tumor-promoting and pro-angiogenic roles. A possible explanation for the diverse biological functions of EP4 might be the multiple signaling pathways switched on upon EP4 activation. The present review attempts to summarize the EP4 receptor-triggered signaling modules and the possible therapeutic applications of EP4-selective agonists and antagonists.

Do prostaglandins modulate renal haemodynamic effects of endothelin-1 in conscious lambs?

To test the hypothesis that vasodilatory prostaglandins buffer the renal vasoconstrictor effects of endothelin-1 (ET-1) early in life, renal haemodynamic responses to ET-1 were measured in 2 groups of conscious, chronically instrumented lambs at 1-2 weeks of age (group I, n = 11) and 6 weeks of age (group II, n = 10). Lambs were pretreated with vehicle or 1 mg x kg(-1) indomethacin, a nonselective cyclooxygenase inhibitor, and renal haemodynamic effects were measured continuously for 1 min before (control) and 5 min after intra-arterial injection of 250 ng x kg(-1) ET-1. In group II lambs, there was a marked decrease in renal blood flow (RBF) and renal vascular conductance (RVC) elicited by ET-1 administration, as we have previously described. This response was not altered by vehicle or indomethacin pretreatment. In group I lambs, there was an initial increase but no decrease in RBF and RVC elicited by ET-1 administration, as we have previously described, and this response was also not altered by either vehicle or indomethacin. These results suggest that endogenously produced prostaglandins do not appear to modulate the renal haemodynamic effects of ET-1 in conscious lambs during postnatal maturation.

Regulation of 3',5'-cAMP in preglomerular smooth muscle and endothelial cells from genetically hypertensive rats

Our previous studies show that inhibition of phosphodiesterase 4 (PDE4) augments agonist-induced renovascular 3',5'-cAMP secretion more in isolated, perfused kidneys from spontaneously hypertensive rats (SHR) versus Wistar-Kyoto normotensive rats (WKY); however, whether this is because of PDE4 inhibition in renovascular smooth muscle cells or endothelial cells is unknown. Therefore, we examined the effects of 3-isobutyl-1-methylxanthine (broad-spectrum PDE inhibitor) and RO 20-1724 (selective PDE4 inhibitor) on isoproterenol-induced 3',5'-cAMP levels in cultured WKY and SHR preglomerular vascular smooth muscle and endothelial cells. 3-Isobutyl-1-methylxanthine and RO 20-1724 augmented isoproterenol-induced 3',5'-cAMP levels similarly in WKY versus SHR endothelial cells. In contrast, 3-isobutyl-1-methylxanthine and RO 20-1724 augmented isoproterenol-induced 3',5'-cAMP levels significantly more in SHR, compared to WKY, smooth muscle cells (P<0.0001). In both cell types from both rat strains, mRNA levels for the PDE4B subtype exceeded levels for the PDE4A, PDE4C, and PDE4D subtypes, and small interfering RNA knockdown of PDE4B mRNA in SHR smooth muscle cells increased isoproterenol-induced 3',5'-cAMP. mRNA levels for the PDE4B2 variant exceeded levels for the PDE4B1, PDE4B3, PDE4B4, and PDE4B5 variants. In vivo, infusions of RO 20-1724 increased the urinary excretion of 3',5'-cAMP more in SHR than WKY (P=0.0211). We conclude that (1) the greater effect of PDE4 inhibition on renovascular 3',5'-cAMP is mediated by inhibition of PDE4 in renovascular smooth muscle cells, not endothelial cells; (2) the major PDE4 subtype in both renovascular smooth muscle and endothelial cells is PDE4B with variant PDE4B2 likely being dominant; and (3) inhibition of PDE4 in vivo increases renal 3',5'-cAMP levels more in genetically hypertensive rats.

Functional and molecular characterization of prostaglandin E2 dilatory receptors in the rat craniovascular system in relevance to migraine

Introduction: Migraine pain is thought to involve an increase in trigeminal nerve terminal activity around large cerebral and meningeal arteries, leading to vasodilatation. Because prostaglandin E2 (PGE2) is elevated in cephalic venous blood during migraine attacks, and is also capable of inducing headache in healthy volunteers, we hypothesize that PGE2 dilatory receptors, EP2 and EP4, mediate the response.

Materials and methods: By the use of specific agonists and antagonists, the dilatory effect of PGE2 was characterized in rat cranial arteries by use of in vivo and in vitro methods. Furthermore, EP2 and EP4 quantitative messenger RNA (mRNA) receptor expression was studied in the rat craniovascular system.

Results: Our results suggest that EP4, and to a lesser degree EP2, receptors mediate the dilatory effect of PGE2 in the craniovascular system in rats. Thus, antagonism of these receptors might be of therapeutic relevance in migraine.

A selective EP4 PGE2 receptor agonist alleviates disease in a new mouse model of X-linked nephrogenic diabetes insipidus

X-linked nephrogenic diabetes insipidus (XNDI) is a severe kidney disease caused by inactivating mutations in the V2 vasopressin receptor (V2R) gene that result in the loss of renal urine-concentrating ability. At present,no specific pharmacological therapy has been developed for XNDI, primarily due to the lack of suitable animal models. To develop what we believe to be the first viable animal model of XNDI, we generated mice in which the V2R gene could be conditionally deleted during adulthood by administration of 4-OH-tamoxifen.Radioligand-binding studies confirmed the lack of V2R-binding sites in kidneys following 4-OH-tamoxifen treatment, and further analysis indicated that upon V2R deletion, adult mice displayed all characteristic symptoms of XNDI, including polyuria, polydipsia, and resistance to the antidiuretic actions of vasopressin. Gene expression analysis suggested that activation of renal EP4 PGE2 receptors might compensate for the lack of renal V2R activity in XNDI mice. Strikingly, both acute and chronic treatment of the mutant mice with a selective EP4 receptor agonist greatly reduced all major manifestations of XNDI, including changes in renal morphology.These physiological improvements were most likely due to a direct action on EP4 receptors expressed on collecting duct cells. These findings illustrate the usefulness of the newly generated V2R mutant mice for elucidating and testing new strategies for the potential treatment of humans with XNDI.

The impact of microsomal prostaglandin e synthase 1 on blood pressure is determined by genetic background

Prostaglandin (PG)E(2) has multiple actions that may affect blood pressure. It is synthesized from arachidonic acid by the sequential actions of phospholipases, cyclooxygenases, and PGE synthases. Although microsomal PGE synthase (mPGES)1 is the only genetically verified PGE synthase, results of previous studies examining the consequences of mPGES1 deficiency on blood pressure (BP) are conflicting. To determine whether genetic background modifies the impact of mPGES1 on BP, we generated mPGES1(-/-) mice on 2 distinct inbred backgrounds, DBA/1lacJ and 129/SvEv. On the DBA/1 background, baseline BP was similar between wild-type (WT) and mPGES1(-/-) mice. By contrast, on the 129 background, baseline BPs were significantly higher in mPGES1(-/-) animals than WT controls. During angiotensin II infusion, the DBA/1 mPGES1(-/-) and WT mice developed mild hypertension of similar magnitude, whereas 129-mPGES1(-/-) mice developed more severe hypertension than WT controls. DBA/1 animals developed only minimal albuminuria in response to angiotensin II infusion. By contrast, WT 129 mice had significantly higher levels of albumin excretion than WT DBA/1 and the extent of albuminuria was further augmented in 129 mPGES1(-/-) animals. In WT mice of both strains, the increase in urinary excretion of PGE(2) with angiotensin II was attenuated in mPGES1(-/-) animals. Urinary excretion of thromboxane was unaffected by angiotensin II in the DBA/1 lines but increased more than 4-fold in 129 mPGES1(-/-) mice. These data indicate that genetic background significantly modifies the BP response to mPGES1 deficiency. Exaggerated production of thromboxane may contribute to the robust hypertension and albuminuria in 129 mPGES1-deficient mice.

Regulation of renovascular adenosine 3',5'-cyclic monophosphate in spontaneously hypertensive rats

This study tested the hypothesis that regulation of 3',5'-cAMP levels in the kidney vasculature is abnormal in spontaneously hypertensive rats. In isolated, perfused kidneys from adult rats (16 weeks of age), isoproterenol similarly increased renal venous 3',5'-cAMP secretion from kidneys of hypertensive versus normotensive Wistar-Kyoto rats. However, a broad-spectrum phosphodiesterase inhibitor (isobutyl-1-methylxanthine) augmented isoproterenol (3 mumol/L)-induced increases in renal venous 3',5'-cAMP secretion more so in kidneys from adult hypertensive versus age-matched normotensive rats (31-fold and 5-fold, respectively; P<0.0001). In contrast to isoproterenol, broad-spectrum phosphodiesterase inhibition augmented forskolin-induced increases in renal venous 3',5'-cAMP secretion similarly in kidneys from adult hypertensive versus age-matched normotensive rats. In kidneys from adults of both strains, the effects of isobutyl-1-methylxanthine on isoproterenol-induced 3',5'-cAMP responses were mimicked by the inhibition of phosphodiesterase 4 (RO 20-1724) but not by the inhibition of phosphodiesterase 1 (3,8-methoxymethyl-3-isobutyl-1-methylxanthine) or phosphodiesterase 3 (milrinone). In kidneys from young (5 weeks of age), adult, and old (39 weeks of age) rats, RO 20-1724 augmented isoproterenol-induced renal 3',5'-cAMP secretion more so in kidneys from hypertensive rats. In adult hypertensive rats, arterial blood pressure and renal vascular resistance were elevated compared with age-matched normotensive rats, and intravenous infusions of RO 20-1724 reduced blood pressure and renal vascular resistance in hypertensive rats but had little effect on these variables in normotensive rats. We conclude that, in the renal vasculature of spontaneously hypertensive rats (young, adult, and old), there is increased activity of a compartment of phosphodiesterase 4. Selective inhibition of renal vascular phosphodiesterase 4 may represent a new strategy for improving renal hemodynamics in genetic hypertension.

Emerging roles of PGE2 receptors in models of neurological disease

This review presents an overview of the emerging field of prostaglandin signaling in neurological diseases, focusing on PGE(2) signaling through its four E-prostanoid (EP) receptors. A large number of studies have demonstrated a neurotoxic function of the inducible cyclooxygenase COX-2 in a broad spectrum of neurological disease models in the central nervous system (CNS), from models of cerebral ischemia to models of neurodegeneration and inflammation. Since COX-1 and COX-2 catalyze the first committed step in prostaglandin synthesis, an effort is underway to identify the downstream prostaglandin signaling pathways that mediate the toxic effect of COX-2. Recent epidemiologic studies demonstrate that chronic COX-2 inhibition can produce adverse cerebrovascular and cardiovascular effects, indicating that some prostaglandin signaling pathways are beneficial. Consistent with this concept, recent studies demonstrate that in the CNS, specific prostaglandin receptor signaling pathways mediate toxic effects in brain but a larger number appear to mediate paradoxically protective effects. Further complexity is emerging, as exemplified by the PGE(2) EP2 receptor, where cerebroprotective or toxic effects of a particular prostaglandin signaling pathway can differ depending on the context of cerebral injury, for example, in excitotoxicity/hypoxia paradigms versus inflammatory-mediated secondary neurotoxicity. The divergent effects of prostaglandin receptor signaling will likely depend on distinct patterns and dynamics of receptor expression in neurons, endothelial cells, and glia and the specific ways in which these cell types participate in particular models of neurological injury.

Cellular mediators of renal vascular dysfunction in hypertension

The renal vasculature plays a major role in the regulation of renal blood flow and the ability of the kidney to control the plasma volume and blood pressure. Renal vascular dysfunction is associated with renal vasoconstriction, decreased renal blood flow, and consequent increase in plasma volume and has been demonstrated in several forms of hypertension (HTN), including genetic and salt-sensitive HTN. Several predisposing factors and cellular mediators have been implicated, but the relationship between their actions on the renal vasculature and the consequent effects on renal tubular function in the setting of HTN is not clearly defined. Gene mutations/defects in an ion channel, a membrane ion transporter, and/or a regulatory enzyme in the nephron and renal vasculature may be a primary cause of renal vascular dysfunction. Environmental risk factors, such as high dietary salt intake, vascular inflammation, and oxidative stress further promote renal vascular dysfunction. Renal endothelial cell dysfunction is manifested as a decrease in the release of vasodilatory mediators, such as nitric oxide, prostacyclin, and hyperpolarizing factors, and/or an increase in vasoconstrictive mediators, such as endothelin, angiotensin II, and thromboxane A(2). Also, an increase in the amount/activity of intracellular Ca(2+) concentration, protein kinase C, Rho kinase, and mitogen-activated protein kinase in vascular smooth muscle promotes renal vasoconstriction. Matrix metalloproteinases and their inhibitors could also modify the composition of the extracellular matrix and lead to renal vascular remodeling. Synergistic interactions between the genetic and environmental risk factors on the cellular mediators of renal vascular dysfunction cause persistent renal vasoconstriction, increased renal vascular resistance, and decreased renal blood flow, and, consequently, lead to a disturbance in the renal control mechanisms of water and electrolyte balance, increased plasma volume, and HTN. Targeting the underlying genetic defects, environmental risk factors, and the aberrant renal vascular mediators involved should provide complementary strategies in the management of HTN.

Preglomerular and postglomerular basal diameter changes and reactivity to angiotensin II in obese rats

AIM AND METHODS

Obesity in humans is associated with proteinuria and an increased glomerular filtration, possibly related to an increase in glomerular capillary pressure. We investigated in obese and lean Zucker rats (10-12 weeks old) whether this might be related to alterations in the diameter of preglomerular and postglomerular microvessels and their reactivity to the resistance regulator angiotensin II (AngII), using the hydronephrotic kidney model.

RESULTS

The obese rats exhibited a hyperinsulinaemic, euglycaemic state and hypertension. Urinary protein concentration and fluid intake were both increased threefold. Basal diameters of distal interlobular arteries (ILAs) and afferent arterioles (AAs) were larger in the obese rat than in the lean rat (ILA: 25.7 +/- 0.3 vs. 23.0 +/- 0.4 microm and AA: 18.8 +/- 0.3 vs. 16.7 +/- 0.5 microm, respectively; p </= 0.01), while diameters of efferent arterioles (EAs) were smaller in obese animals (14.2 +/- 1.1 vs. 18.2 +/- 1.2 microm; p </= 0.05). AngII induced a concentration-dependent constriction in ILA, AA and EA with an augmented response in the obese compared with the lean rats. Thus, at higher concentrations, AngII abolished the diameter difference between obese and lean animals in preglomerular microvessels while exaggerating that in postglomerular arterioles.

CONCLUSIONS

Our data indicate that in obese rats, a vasodilated state in small preglomerular microvessels and a vasoconstricted state in the postglomerular arterioles exist. Although AngII cancelled the former, the latter remained. Therefore, these data reveal periglomerular vascular changes that may play a role in glomerular dysfunction and renal pathology associated with obesity.

Prostaglandins in the kidney: developments since Y2K

There are five major PGs (prostaglandins/prostanoids) produced from arachidonic acid via the COX (cyclo-oxygenase) pathway: PGE(2), PGI(2) (prostacyclin), PGD(2), PGF(2alpha) and TXA(2) (thromboxane A(2)). They exert many biological effects through specific G-protein-coupled membrane receptors, namely EP (PGE(2) receptor), IP (PGI(2) receptor), DP (PGD(2) receptor), FP (PGF(2alpha) receptor) and TP (TXA(2) receptor) respectively. PGs are implicated in physiological and pathological processes in all major organ systems, including cardiovascular function, gastrointestinal responses, reproductive processes, renal effects etc. This review highlights recent insights into the role of each prostanoid in regulating various aspects of renal function, including haemodynamics, renin secretion, growth responses, tubular transport processes and cell fate. A thorough review of the literature since Y2K (year 2000) is provided, with a general overview of PGs and their synthesis enzymes, and then specific considerations of each PG/prostanoid receptor system in the kidney.

Intrarenal renin-angiotensin system and counteracting protective mechanisms in angiotensin II-dependent hypertension

It is now well accepted that alterations in kidney function, due either to primary renal disease or to inappropriate hormonal influences on the kidney, are a cardinal characteristic in all forms of hypertension, and lead to a reduced ability of the kidneys to excrete sodium and the consequent development of elevated arterial pressures. However, it is also apparent that many extrarenal factors are important contributors to altered kidney function and hypertension. Central to many hypertensinogenic processes is the inappropriate activation of the renin-angiotensin system (RAS) and its downstream consequences by various pathophysiologic mechanisms. There may also be derangements in arachidonic acid metabolites, endothelium derived factors such as nitric oxide and carbon monoxide, and various paracrine and neural systems that normally interact with or provide a counteracting balance to the actions of the RAS. Thus, when the capacity of the kidneys to maintain sodium balance and extracellular fluid volume within appropriate ranges is compromised, increases in arterial pressure become necessary to re-establish normal balance.

Direct vasoconstrictor effect of prostaglandin E2on renal interlobular arteries: role of the EP3 receptor

Evidence indicates that prostaglandin E2(PGE2) preferentially affects preglomerular renal vessels. However, whether this is limited to small-caliber arterioles or whether larger vessels farther upstream also respond to PGE2is currently unclear. In the present study, we first investigated the effects of PGE2along the preglomerular vascular tree and subsequently focused on proximal interlobular arteries (ILAs). Proximal ILAs in hydronephrotic rat kidneys as well as isolated vessels from normal kidneys constricted in response to PGE2, both under basal conditions and after the induction of vascular tone. By contrast, smaller vessels, i.e., distal ILAs and afferent arterioles, exhibited PGE2-induced vasodilation. Endothelium removal and pretreatment of single, isolated proximal ILAs with an EP1 receptor blocker (SC51322, 1 μmol/l) or a thromboxane A2receptor blocker (SQ29548, 1 μmol/l) did not prevent vasoconstriction to PGE2. Furthermore, in the presence of SC51322, responses of these vessels to PGE2and the EP1/EP3 agonist sulprostone were superimposable, indicating that PGE2-induced vasoconstriction is mediated by EP3 receptors on smooth muscle cells. Immunohistochemical staining of proximal ILAs confirmed the presence of EP3 receptor protein on these cells and the endothelium. Adding PGE2to normal isolated kidneys induced a biphasic flow response, i.e., an initial flow increase at PGE2concentrations ≤0.1 μmol/l followed by a flow decrease at 1 μmol/l PGE2. Thus our results demonstrate that PGE2affects multiple segments of the preglomerular vascular tree in a different way. At the level of the proximal ILAs, PGE2had a direct vasoconstrictor action mediated by EP3 receptors.

PGE2 amplifies the effects of IL-1beta on vascular smooth muscle cell de-differentiation: a consequence of the versatility of PGE2 receptors 3 due to the emerging expression of adenylyl cyclase 8

Transition of vascular smooth muscle cells from a contractile/quiescent to a secretory/proliferative phenotype is one of the critical steps in atherosclerosis and is instigated by pro-inflammatory cytokines released from macrophages that have infiltrated into the vascular wall. In most inflammatory diseases, cell activation induced by these compounds leads to a massive production of type E2 prostaglandin (PGE2) which often takes over and even potentiates the pro-inflammatory cytokine-related effects. To evaluate PGE2 incidence on atheroma plaque development, we investigated whether and how this compound could enhance the dedifferentiation of smooth muscle cells initially induced by interleukin-1beta (IL-1beta). To address this issue, we took advantage of vascular smooth muscle cells in primary culture and tracked two markers: PLA2 secretion and alpha-actin filament disorganization. In such a context, we found that PGE2 synergizes with IL-1beta to further enhance the phenotype transition of smooth muscle cells, through cAMP-protein kinase A. As indicated by pharmacological studies, the full PGE2-dependent potentiation of IL-1beta induced PLA2 secretion is associated with a change of regulation exerted by the subtypes 3 G(i)-coupled PGE2 receptors toward adenylyl cyclase(s) activated by the subtype 4 G(s)-linked PGE2 receptor. Whereas on contractile cells, stimulated subtypes 3 inhibit type 4-dependent PLA2 secretion, this negative regulation is switched to positive on IL-1beta-treated cells. Using real time PCR, pharmacological tools and small interfering RNA (siRNA), we demonstrated that the different integration of PGE2 signals depends on the upregulation of calcium/calmodulin stimulable adenylyl cyclase 8.

Cyclooxygenase-2 inhibition normalizes arterial blood pressure in CYP1A1-REN2 transgenic rats with inducible ANG II-dependent malignant hypertension

The present study was performed to determine the effects of cyclooxygenase (COX)-1 and COX-2 inhibition on blood pressure and renal hemodynamics in transgenic rats with inducible malignant hypertension [strain name: TGR(Cyp1a1Ren2)]. Male Cyp1a1-Ren2 rats ( n = 7) were fed a normal diet containing the aryl hydrocarbon, indole-3-carbinol (I3C; 0.3%), for 6–9 days to induce malignant hypertension. Mean arterial pressure (MAP) and renal hemodynamics were measured in pentobarbital sodium-anesthetized Cyp1a1-Ren2 rats during control conditions, following administration of the COX-2 inhibitor nimesulide (3 mg/kg iv), and following administration of the nonspecific COX inhibitor meclofenamate (5 mg/kg iv). Rats induced with I3C had higher MAP than noninduced rats ( n = 7; 188 ± 6 vs. 136 ± 4 mmHg, P < 0.01). There was no difference in renal plasma flow (RPF) or glomerular filtration rate (GFR) between induced and noninduced rats. Nimesulide elicited a larger decrease in MAP in hypertensive rats (188 ± 6 to 140 ± 8 mmHg, P < 0.01) than in normotensive rats (136 ± 4 to 113 ± 8 mmHg, P < 0.01). Additionally, nimesulide decreased GFR (0.9 ± 0.13 to 0.44 ± 0.05 ml·min−1·g−1, P < 0.05) and RPF (2.79 ± 0.27 to 1.35 ± 0.14 ml·min−1·g−1, P < 0.05) in hypertensive rats but did not alter GFR or RPF in normotensive rats. Meclofenamate further decreased MAP in hypertensive rats (to 115 ± 10 mmHg, P < 0.05) but did not decrease MAP in normotensive rats. Meclofenamate did not alter GFR or RPF in either group. These findings demonstrate that COX-1- and COX-2-derived prostanoids contribute importantly to the development of malignant hypertension in Cyp1a1-Ren2 transgenic rats. The data also indicate that COX-2-derived vasodilatory metabolites play an important role in the maintenance of RPF and GFR following induction of malignant hypertension in Cyp1a1-Ren2 transgenic rats.

Up-regulation of glomerular COX-2 by angiotensin II: role of reactive oxygen species

BACKGROUND

Prostaglandins such as prostaglandin E(2) (PGE(2)) and prostaglandin I(2) (PGI(2)) counteract the angiotensin II (Ang II)-induced vasoconstriction in the glomerular microcirculation. We have shown that Ang II promotes mesangial cell hypertrophy via reactive oxygen species (ROS), which originate from nicotinamide adenine dinucleotide phosphate and its reduced form (NADH/NADPH) oxidase. It has been reported that conditions associated with activation of the renin-angiotensin system result in increased glomerular cyclooxygenase-2 (COX-2) expression and activity.

METHODS

We designed studies to determine (1) whether Ang II induces COX-2 in the glomerulus in vivo in the glomerulus as well as in vitro in mesangial cells, (2) whether ROS originated from Ang II are involved, and (3) whether COX-2-derived prostaglandins modulate the growth promoting effects of Ang II in mesangial cells. Rats were infused with Ang II (0.7 mg/kg/day) for 5 days and glomerular COX-2 expression and activity assessed in isolated glomeruli.

RESULTS

Ang II increased glomerular PGE(2) production (100%) accompanied by a concomitant increase in glomerular COX-2 expression at the mRNA (1.7-fold) and protein level (sixfold). In mesangial cells, Ang II significantly increased mesangial cell PGE(2) (200%) and PGI(2) (100%) production as well as COX-2 mRNA that was prevented by the angiotensin type 1 (AT1) receptor blocker irbesartan and the COX-2 inhibitor NS-398. The NADPH oxidase inhibitor diphenyleneiodonium (DPI), the ROS scavenger tiron as well as catalase, inhibited Ang II-induced PGE(2) production suggesting that Ang II-induced ROS mediate COX-2 up-regulation. Strikingly, COX-2 inhibition as well as blockade of the type 1 PGE(2) receptor (EP1) prevented Ang II-induced mesangial cell hypertrophy suggesting that COX-2-derived prostaglandins, and specifically PGE(2), importantly contribute to the growth promoting effects of Ang II.

CONCLUSION

These studies suggest that blockade of specific PGE(2) receptors may be a novel strategy to modulate the pathologic effects of COX-2-derived prostaglandins without simultaneously affecting protective vasodilatory mechanisms.

Dominant role of prostaglandin E2 EP4 receptor in furosemide-induced salt-losing tubulopathy: a model for hyperprostaglandin E syndrome/antenatal Bartter syndrome

Increased formation of prostaglandin E2 (PGE2) is a key part of hyperprostaglandin E syndrome/antenatal Bartter syndrome (HPS/aBS), a renal disease characterized by NaCl wasting, water loss, and hyperreninism. Inhibition of PGE2 formation by cyclo-oxygenase inhibitors significantly lowers patient mortality and morbidity. However, the pathogenic role of PGE2 in HPS/aBS awaits clarification. Chronic blockade of the Na-K-2Cl co-transporter NKCC2 by diuretics causes symptoms similar to HPS/aBS and provides a useful animal model. In wild-type (WT) mice and in mice lacking distinct PGE2 receptors (EP1-/-, EP2-/-, EP3-/-, and EP4-/-), the effect of chronic furosemide administration (7 d) on urine output, sodium and potassium excretion, and renin secretion was determined. Furthermore, furosemide-induced diuresis and renin activity were analyzed in mice with defective PGI2 receptors (IP-/-). In all animals studied, furosemide stimulated a rise in diuresis and electrolyte excretion. However, this effect was blunted in EP1-/-, EP3-/-, and EP4-/- mice. Compared with WT mice, no difference was observed in EP2-/- and IP-/- mice. The furosemide-induced increase in plasma renin concentration was significantly decreased in EP4-/- mice and to a lesser degree also in IP-/- mice. Pharmacologic inhibition of EP4 receptors in furosemide-treated WT mice with the specific antagonist ONO-AE3-208 mimicked the changes in renin mRNA expression, plasma renin concentration, diuresis, and sodium excretion seen in EP4-/- mice. The GFR in EP4-/- mice was not changed compared with that in WT mice, which indicated that blunted diuresis and salt loss seen in EP4-/- mice were not a consequence of lower GFR. In summary, these findings demonstrate that the EP4 receptor mediates PGE2-induced renin secretion and that EP1, EP3, and EP4 receptors all contribute to enhanced PGE2-mediated salt and water excretion in the HPS/aBS model.

Prostaglandin E2 EP2 and EP4 receptor activation mediates cAMP-dependent hyperpolarization and exocytosis of renin in juxtaglomerular cells

PGE(2) and PGI(2) stimulate renin secretion and cAMP accumulation in juxtaglomerular granular (JG) cells. We addressed, at the single-cell level, the receptor subtypes and intracellular transduction mechanisms involved. Patch clamp was used to determine cell capacitance (C(m)), current, and membrane voltage in response to PGE(2), EP2 and EP4 receptor agonists, and an IP receptor agonist. PGE(2) (0.1 micromol/l) increased C(m) significantly, and the increase was abolished by intracellular application of the protein kinase A antagonist Rp-8-CPT-cAMPS. EP2-selective ligands butaprost (1 micromol/l), AE1-259-01 (1 nmol/l), EP4-selective agonist AE1-329 (1 nmol/l), and IP agonist iloprost (1 micromol/l) significantly increased C(m) mediated by PKA. The EP4 antagonist AE3-208 (10 nmol/l) blocked the effect of EP4 agonist but did not alter the response to PGE(2). Application of both EP4 antagonist and EP2-antagonist AH-6809 abolished the effects of PGE(2) on C(m) and current. EP2 and EP4 ligands stimulated cAMP formation in JG cells. PGE(2) rapidly stimulated renin secretion from superfused JG cells and diminished the membrane-adjacent granule pool as determined by confocal microscopy. The membrane potential hyperpolarized significantly after PGE(2), butaprost, AE1-329 and AE1-259 and outward current was augmented in a PKA-dependent fashion. PGE(2)-stimulated outward current, but not C(m) change, was abolished by the BK(Ca) channel inhibitor iberiotoxin (300 nmol/l). EP2 and EP4 mRNA was detected in sampled JG cells, and the preglomerular and glomerular vasculature was immunopositive for EP4. Thus IP, EP2, and EP4 receptors are associated with JG cells, and their activation leads to rapid PKA-mediated exocytotic fusion and release of renin granules.

Furosemide-induced renal medullary hypoperfusion in the rat: role of tissue tonicity, prostaglandins and angiotensin II

Furosemide (frusemide)-induced renal medullary hypoperfusion provides a model for studies of the dependence of local circulation on tissue tonicity. We examined the role of medullary prostaglandins (PG) and adenosine (Ado) as possible mediators of the response to furosemide. Furosemide was infused i.v. at 0.25 mg kg(-1) h(-1) in anaesthetized rats, untreated or treated with intramedullary indomethacin (Indo) or Ado. An integrated set-up was used to measure renal medullary laser-Doppler flux (MBF) and medullary ionic tonicity (electrical admittance, Y), and to infuse Indo and Ado directly into the medulla. The cortical flux was measured on kidney surface. The excretion of water, sodium and total solute was also determined. Intramedullary Indo (1 mg kg(-1) h(-1)) decreased MBF 18 +/- 5% and increased tissue Y 14 +/- 3% (both significant); the treatment abolished the post-furosemide decrease in MBF (-22% in untreated group) and enhanced slightly the increase in renal excretion. Intramedullary Ado (5 mg kg(-1) h(-1)) did not change baseline MBF or Y; the post-furosemide decreases in MBF (-22%) and Y, and the increase in renal excretion were preserved. We conclude that a decrease in intramedullary PG activity secondary to decreased medullary hypertonicity mediates the fall in medullary perfusion in response to furosemide; the hypoperfusion may help restore the initial tonicity. Together with the earlier evidence on the dependence of post-furosemide medullary hypoperfusion on angiotensin II, the study exposes its interaction with PG in the control of medullary circulation. Adenosine is not involved in medullary vascular responses to decreased tissue hypertonicity.

PGE2 exerts its effect on the LPS-induced release of TNF-alpha, ET-1, IL-1alpha, IL-6 and IL-10 via the EP2 and EP4 receptor in rat liver macrophages

Lipopolysaccharide (LPS) induces a release of tumor necrosis factor (TNF)-alpha, endothelin (ET)-1, interleukin (IL)-1alpha, IL-6 and IL-10 in rat liver macrophages (Kupffer cells). Prostaglandin (PG)E2 inhibits the release of the fibrogenic mediators TNF-alpha, ET-1 and IL-1alpha, and enhances the release of the anti-fibrogenic mediators IL-6 and IL-10. This effect of PGE2 is mimicked by specific agonists for the PGE2 receptors EP2 and EP4; whereas, agonists for the PGE2 receptors EP1 and EP3 are inactive. Rat liver macrophages express mRNA encoding the PGE2 receptors EP2 and EP4 but not the PGE2 receptors EP1 and EP3. These data suggest that PGE2 exerts its anti-fibrogenic effect through the EP2 and EP4 receptor by inhibiting the release of the fibrogenic mediators TNF-alpha, ET-1 and IL-1alpha, and by enhancing the release of the anti-fibrogenic mediators IL-6 and IL-10 in liver macrophages.

Vasoconstriction induced by activation of EP1 and EP3 receptors in human lung: effects of ONO-AE-248, ONO-DI-004, ONO-8711 or ONO-8713

This study investigated the effects and selectivity of ONO-AE-248, ONO-DI-004, ONO-8711 and ONO-8713 on EP1 and EP3 receptors in human pulmonary vessels. The prostanoid receptors involved in the vasoconstriction of human pulmonary arteries (HPA) are TP and EP3 whereas in pulmonary veins (HPV), this response is associated with TP and EP1. The experiments were performed in presence of BAY u3405 (TP antagonist). ONO-DI-004 (EP1 agonist) and ONO-AE-248 (EP3 agonist), exhibited little or no activity in HPV whereas contractions were induced in HPA with ONO-AE-248. In HPV, the contractions produced with sulprostone (EP1,3 agonist) were blocked in a non competitive manner by both EP1 antagonists (ONO-8711, 30 microM; ONO-8713, 10 microM). The involvement of EP1 mediated contraction in HPV was also observed during the vasorelaxations induced with PGE1 and 5-cis-carba-PGI2. In pre-contracted HPV treated with AH6809 (30 microM; EP1 antagonist) the PGE1 vasorelaxations were potentiated, while unchanged in HPA. These results demonstrate the selectivity of ONO-AE-248 for the EP3 receptor in HPA, ONO-DI-004 was ineffective on the EP1 receptor present in HPV while ONO-8713 was the more potent EP1 antagonist used in this tissue.

Stimulation of renin release by prostaglandin E2is mediated by EP2and EP4receptors in mouse kidneys

PGE2is a potent stimulator of renin release. So far, the contribution of each of the four PGE2receptor subtypes (EP1–EP4) in the regulation of renin release has not been characterized. Therefore, we investigated the effects PGE2on renin secretion rates (RSR) from isolated, perfused kidneys of EP1−/−, EP2−/−, EP3−/−, EP4−/−, and wild-type mice. PGE2concentration dependently stimulated RSR from kidneys of all four knockout strains with a threshold concentration of 1 nM in EP1−/−, EP2−/−, EP3−/−, and wild-type mice, whereas the threshold concentration was shifted to 10 nM in EP4−/− mice. Moreover, the maximum stimulation of RSR by PGE2at 1 μM was significantly reduced in EP4−/− (12.8-fold of control) and EP2−/− (15.9-fold) compared with wild-type (20.7-fold), EP1−/− (23.8-fold), and EP3−/− (20.1-fold). In contrast, stimulation of RSR by either the loop diuretic bumetanide or the β-adrenoceptor agonist isoproterenol was similar in all strains. PGE2exerted a dual effect on renal vascular tone, inducing vasodilatation at low concentrations (1 nmol/) and vasoconstriction at higher concentrations (100 nmol/) in kidneys of wild-type mice. In kidneys of EP2−/− as well as EP4−/− mice, vasodilatation at low PGE2concentrations was prevented, whereas vasoconstriction at higher concentrations was augmented. In contrast, the vasodilatatory component was pronounced in kidneys of EP1and EP3knockout mice, whereas in both genotypes the vasoconstriction at higher PGE2concentrations was markedly blunted. Our data provide evidence that PGE2stimulates renin release via activation of EP2and EP4receptors, whereas EP1and EP3receptors appear to be without functional relevance in juxtaglomerular cells. In contrast, all four receptor subtypes are involved in the control of renal vascular tone, EP1and EP3receptors increasing, and EP2as well as EP4receptors, decreasing it.

Role of prostaglandin E receptor EP1 subtype in the development of renal injury in genetically hypertensive rats

One of the major causes of end-stage renal diseases is hypertensive renal disease, in which enhanced renal prostaglandin (PG) E2 production has been shown. PGE2, a major arachidonic acid metabolite produced in the kidney, acts on 4 receptor subtypes, EP1 through EP4, but the pathophysiological importance of the PGE2/EP subtypes in the development of hypertensive renal injury remains to be elucidated. In this study, we investigated whether an orally active EP1-selective antagonist (EP1A) prevents the progression of renal damage in stroke-prone spontaneously hypertensive rats (SHRSP), a model of human malignant hypertension. Ten-week-old SHRSP, with established hypertension but with minimal renal damage, were given EP1A or vehicle for 5 weeks. After the treatment period, vehicle-treated SHRSP showed prominent proliferative lesions in arterioles, characterized by decreased alpha-smooth muscle actin expression in multilayered vascular smooth muscle cells. Upregulation of transforming growth factor-beta expression and tubulointerstitial fibrosis were also observed in vehicle-treated SHRSP. All these changes were dramatically attenuated in EP1A-treated SHRSP. Moreover, EP1A treatment significantly inhibited both increase in urinary protein excretion and decrease in creatinine clearance but had little effect on systemic blood pressure. These findings indicate that the PGE2/EP1 signaling pathway plays a crucial role in the development of renal injury in SHRSP. This study opens a novel therapeutic potential of selective blockade of EP1 for the treatment of hypertensive renal disease.