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

Tissue lipidomic profiling supports a mechanistic role of the prostaglandin E2 pathway for albuminuria development in glomerular hyperfiltration

Background: Glomerular hyperfiltration (GH) is an important mechanism in the development of albuminuria in hypertension. The Munich Wistar Frömter (MWF) rat is a non-diabetic model of chronic kidney disease (CKD) with GH due to inherited low nephron number resulting in spontaneous albuminuria and podocyte injury. In MWF rats, we identified prostaglandin (PG) E2 (PGE2) signaling as a potential causative mechanism of albuminuria in GH. Method: For evaluation of the renal PGE2 metabolic pathway, time-course lipidomic analysis of PGE2 and its downstream metabolites 15-keto-PGE2 and 13-14-dihydro-15-keto-PGE2 was conducted in urine, plasma and kidney tissues of MWF rats and albuminuria-resistant spontaneously hypertensive rats (SHR) by liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS). Results: Lipidomic analysis revealed no dysregulation of plasma PGs over the time course of albuminuria development, while glomerular levels of PGE2 and 15-keto-PGE2 were significantly elevated in MWF compared to albuminuria-resistant SHR. Overall, averaged PGE2 levels in glomeruli were up to ×150 higher than the corresponding 15-keto-PGE2 levels. Glomerular metabolic ratios of 15-hydroxyprostaglandin dehydrogenase (15-PGDH) were significantly lower, while metabolic ratios of prostaglandin reductases (PTGRs) were significantly higher in MWF rats with manifested albuminuria compared to SHR, respectively. Conclusion: Our data reveal glomerular dysregulation of the PGE2 metabolism in the development of albuminuria in GH, resulting at least partly from reduced PGE2 degradation. This study provides first insights into dynamic changes of the PGE2 pathway that support a role of glomerular PGE2 metabolism and signaling for early albuminuria manifestation in GH.

Studies in Zebrafish and Rat Models Support Dual Blockade of EP2 and EP4 (Prostaglandin E2 Receptors Type 2 and 4) for Renoprotection in Glomerular Hyperfiltration and Albuminuria

BACKGROUND

Glomerular hyperfiltration (GH) is an important mechanism in the development of albuminuria in hypertension. Upregulation of COX2 (cyclooxygenase 2) and prostaglandin E₂ (PGE₂) was linked to podocyte damage in GH. We explored the potential renoprotective effects of either separate or combined pharmacological blockade of EP2 (PGE₂ receptor type 2) and EP4 (PGE₂ receptor type 4) in GH.

METHODS

We conducted in vivo studies in a transgenic zebrafish model (Tg[fabp10a:gc-EGFP]) suitable for analysis of glomerular filtration barrier function and a genetic rat model with GH, albuminuria, and upregulation of PGE₂. Similar pharmacological interventions and primary outcome analysis on albuminuria phenotype development were conducted in both model systems.

RESULTS

Stimulation of zebrafish embryos with PGE₂ induced an albuminuria-like phenotype, thus mimicking the suggested PGE₂ effects on glomerular filtration barrier dysfunction. Both separate and combined blockade of EP2 and EP4 reduced albuminuria phenotypes in zebrafish and rat models. A significant correlation between albuminuria and podocyte damage in electron microscopy imaging was identified in the rat model. Dual blockade of both receptors showed a pronounced synergistic suppression of albuminuria. Importantly, this occurred without changes in arterial blood pressure, glomerular filtration rate, or tissue oxygenation in magnetic resonance imaging, while RNA sequencing analysis implicated a potential role of circadian clock genes.

CONCLUSIONS

Our findings confirm a role of PGE₂ in the development of albuminuria in GH and support the renoprotective potential of combined pharmacological blockade of EP2 and EP4 receptors. These data support further translational research to explore this therapeutic option and a possible role of circadian clock genes.

CD248 induces a maladaptive unfolded protein response in diabetic kidney disease

Dysfunction of mesangial cells plays a major role in the pathogenesis of diabetic kidney disease (DKD), the leading cause of kidney failure. However, the underlying molecular mechanisms are incompletely understood. By unbiased gene expression analysis of glucose-exposed mesangial cells, we identified the transmembrane receptor CD248 as the most upregulated gene, and the maladaptive unfolded protein response (UPR) as one of the most stimulated pathways. Upregulation of CD248 was further confirmed in glucose-stressed mesangial cells in vitro, in kidney glomeruli isolated from diabetic mice (streptozotocin; STZ and db/db models, representing type 1 and type 2 diabetes mellitus, respectively) in vivo, and in glomerular kidney sections from patients with DKD. Time course analysis revealed that glomerular CD248 induction precedes the onset of albuminuria, mesangial matrix expansion and maladaptive UPR activation (hallmarked by transcription factor C/EBP homologous protein (CHOP) induction) but is paralleled by loss of the adaptive UPR regulator spliced X box binding protein (XBP1). Mechanistically, CD248 promoted maladaptive UPR signaling via inhibition of the inositol requiring enzyme 1α (IRE1α)-mediated transcription factor XBP1 splicing in vivo and in vitro. CD248 induced a multiprotein complex comprising heat shock protein 90, BH3 interacting domain death agonist (BID) and IRE1α, in which BID impedes IRE1α-mediated XBP1 splicing and induced CHOP mediated maladaptive UPR signaling. While CD248 knockout ameliorated DKD-associated glomerular dysfunction and reverses maladaptive unfolded protein response signaling, concomitant XBP1 deficiency abolished the protective effect in diabetic CD248 knockout mice, supporting a functional interaction of CD248 and XBP1 in vivo. Hence, CD248 is a novel mesangial cell receptor inducing maladaptive UPR signaling in DKD.

Intact prostaglandin signaling through EP2 and EP4 receptors in stromal progenitor cells is required for normal development of the renal cortex in mice

Cyclooxygenase (Cox) inhibitors are known to have severe side effects during renal development. These consist of reduced renal function, underdeveloped subcapsular glomeruli, interstitial fibrosis, and thinner cortical tissue. Global genetic deletion of Cox-2 mimics the phenotype observed after application of Cox inhibitors. This study aimed to investigate which cell types express Cox-2 and prostaglandin E2 receptors and what functions are mediated through this pathway during renal development. Expression of EP2 and EP4 mRNA was detected by RNAscope mainly in descendants of FoxD1+ stromal progenitors; EP1 and EP3, on the other hand, were expressed in tubules. Cox-2 mRNA was detected in medullary interstitial cells and macula densa cells. Functional investigations were performed with a cell-specific approach to delete Cox-2, EP2, and EP4 in FoxD1+ stromal progenitor cells. Our data show that Cox-2 expression in macula densa cells is sufficient to drive renal development. Deletion of EP2 or EP4 in FoxD1+ cells had no functional effect on renal development. Codeletion of EP2 and EP4 in FoxD1+ stromal cells, however, led to severe glomerular defects and a strong decline of glomerular filtration rate (1.316 ± 69.7 µL/min/100 g body wt in controls vs. 644.1 ± 64.58 µL/min/100 g body wt in FoxD1+/Cre EP2-/- EP4ff mice), similar to global deletion of Cox-2. Furthermore, EP2/EP4-deficient mice showed a significant increase in collagen production with a strong downregulation of renal renin expression. This study shows the distinct localization of EP receptors in mice. Functionally, we could identify EP2 and EP4 receptors in stromal FoxD1+ progenitor cells as essential receptor subtypes for normal renal development.NEW & NOTEWORTHY Cyclooxygenase-2 (Cox-2) produces prostaglandins that are essential for normal renal development. It is unclear in which cells Cox-2 and the receptors for prostaglandin E2 (EP receptors) are expressed during late nephrogenesis. This study identified the expression sites for EP subtypes and Cox-2 in neonatal mouse kidneys. Furthermore, it shows that stromal progenitor cells may require intact prostaglandin E2 signaling through EP2 and EP4 receptors for normal renal development.

Glomerular Biomechanical Stress and Lipid Mediators during Cellular Changes Leading to Chronic Kidney Disease

Hyperfiltration is an important underlying cause of glomerular dysfunction associated with several systemic and intrinsic glomerular conditions leading to chronic kidney disease (CKD). These include obesity, diabetes, hypertension, focal segmental glomerulosclerosis (FSGS), congenital abnormalities and reduced renal mass (low nephron number). Hyperfiltration-associated biomechanical forces directly impact the cell membrane, generating tensile and fluid flow shear stresses in multiple segments of the nephron. Ongoing research suggests these biomechanical forces as the initial mediators of hyperfiltration-induced deterioration of podocyte structure and function leading to their detachment and irreplaceable loss from the glomerular filtration barrier. Membrane lipid-derived polyunsaturated fatty acids (PUFA) and their metabolites are potent transducers of biomechanical stress from the cell surface to intracellular compartments. Omega-6 and ω-3 long-chain PUFA from membrane phospholipids generate many versatile and autacoid oxylipins that modulate pro-inflammatory as well as anti-inflammatory autocrine and paracrine signaling. We advance the idea that lipid signaling molecules, related enzymes, metabolites and receptors are not just mediators of cellular stress but also potential targets for developing novel interventions. With the growing emphasis on lifestyle changes for wellness, dietary fatty acids are potential adjunct-therapeutics to minimize/treat hyperfiltration-induced progressive glomerular damage and CKD.

Changing prostaglandin E2 (PGE2) signaling during lesional progression and exacerbation of endometriosis by inhibition of PGE2 receptor EP2 and EP4

Purpose

We investigated the change, if any, in prostaglandin E2 (PGE₂) signaling in endometriotic lesions of different developmental stages in mouse. In addition, we evaluated the effect of treatment of mice with induced deep endometriosis (DE) with inhibitors of PGE₂ receptor subtypes EP2 and EP4 and metformin.

Methods

Three mouse experimentations were conducted. In Experiment 1, female Balb/C mice were induced with endometriosis or DE and were serially sacrificed after induction. Experiments 2 and 3 evaluated the effect of treatment with EP2 and EP4 inhibitors and metformin, respectively, in mice with induced DE. Immunohistochemistry analysis of COX-2, EP2, and EP4, along with the extent of lesional fibrosis, was evaluated.

Results

The immunostaining of COX-2, EP2, and EP4 turned from activation to a stall as lesions progressed. Treatment with EP2/EP4 inhibitors in DE mice exacerbated endometriosis-associated hyperalgesia and promoted fibrogenesis in lesions even though it suppressed the PGE₂ signaling dose-dependently. In contrast, treatment with metformin resulted in increased PGE₂ signaling, concomitant with improved hyperalgesia, and retarded lesional fibrogenesis.

Conclusions

The PGE₂ signaling diminishes as endometriotic lesions progress. Treatment with EP2/EP4 inhibitors in DE mice exacerbates endometriosis, but metformin appears to be promising seemingly through the induction of the PGE₂ signaling.

Diabetic Kidney Disease Alters the Transcriptome and Function of Human Adipose-Derived Mesenchymal Stromal Cells but Maintains Immunomodulatory and Paracrine Activities Important for Renal Repair

Mesenchymal stem/stromal cells (MSCs) facilitate repair in experimental diabetic kidney disease (DKD). However, the hyperglycemic and uremic milieu may diminish regenerative capacity of patient-derived therapy. We hypothesized that DKD reduces human MSC paracrine function. Adipose-derived MSC from 38 participants with DKD and 16 control subjects were assessed for cell surface markers, trilineage differentiation, RNA sequencing (RNA-seq), in vitro function (coculture or conditioned medium experiments with T cells and human kidney cells [HK-2]), secretome profile, and cellular senescence abundance. The direction of association between MSC function and patient characteristics were also tested. RNA-seq analysis identified 353 differentially expressed genes and downregulation of several immunomodulatory genes/pathways in DKD-MSC versus Control-MSC. DKD-MSC phenotype, differentiation, and tube formation capacity were preserved, but migration was reduced. DKD-MSC with and without interferon-γ priming inhibited T-cell proliferation greater than Control-MSC. DKD-MSC medium contained higher levels of anti-inflammatory cytokines (indoleamine 2,3-deoxygenase 1 and prostaglandin-E2) and prorepair factors (hepatocyte growth factor and stromal cell-derived factor 1) but lower IL-6 versus control-MSC medium. DKD-MSC medium protected high glucose plus transforming growth factor-β-exposed HK-2 cells by reducing apoptotic, fibrotic, and inflammatory marker expression. Few DKD-MSC functions were affected by patient characteristics, including age, sex, BMI, hemoglobin A_1c, kidney function, and urine albumin excretion. However, senescence-associated β-galactosidase activity was lower in DKD-MSC from participants on metformin therapy. Therefore, while DKD altered the transcriptome and migratory function of culture-expanded MSCs, DKD-MSC functionality, trophic factor secretion, and immunomodulatory activities contributing to repair remained intact. These observations support testing of patient-derived MSC therapy and may inform preconditioning regimens in DKD clinical trials.

Delayed blockage of prostaglandin EP4 receptors can reduce dedifferentiation, epithelial-to-mesenchymal transition and fibrosis following acute kidney injury

Dedifferentiation of tubular epithelial cells is involved in both regeneration and fibrosis following acute kidney injury (AKI). Prostaglandin E2 receptor 4 (EP4 ) antagonist can inhibit the dedifferentiation of renal tubular cells. The present study investigated whether the time of blockage of EP4 receptors, using grapiprant, could affect the tubular regeneration or interstitial fibrosis in AKI. Cisplatin was used to induce AKI in 72 C57BL/6 adult female mice. Animals were assigned to four groups; control, cisplatin-treated, cisplatin-treated with early grapiprant intervention and cisplatin-treated with late grapiprant intervention. AKI was assessed by kidney function tests and histopathology. Fibrosis was evaluated by Masson's trichrome and alpha smooth muscle actin (α-SMA) expression. Markers of dedifferentiation, CD133, and epithelial to mesenchymal transition (EMT), vimentin were assessed. Early intervention with grapiprant significantly ameliorated AKI more efficiently than late intervention. However, even late intervention was useful in reducing the overall fibrosis as demonstrated by Masson's trichrome and α-SMA expression. In both grapiprant-treated groups, a parallel reduction of dedifferentiation (CD133) and EMT (vimentin) was evident. It seems that the progressive fibrotic changes that follow AKI could still be reduced possibly by targeting dedifferentiation and/or EMT.

Agonism of Prostaglandin E2 Receptor 4 Ameliorates Tubulointerstitial Injury in Nephrotoxic Serum Nephritis in Mice

Selectively targeting the E-type prostanoid receptor 4 (EP4) might be a new therapeutic option in the treatment of glomerulonephritis (GN), since the EP4 receptor is expressed on different immune cells, resident kidney cells, and endothelial cells, which are all involved in the pathogenesis of immune-complex GN. This study aimed to evaluate the therapeutic potential and to understand the mode of action of EP4 agonist in immune-complex GN using the murine model of nephrotoxic serum nephritis (NTS). In vivo, NTS mice were treated two times daily with two different doses of an EP4 agonist ONO AE1-329 or vehicle for 14 days total. The effect of PGE2 and EP4 agonism and antagonism was tested on murine distal convoluted tubular epithelial cells (DCT) in vitro. In vivo, the higher dose of the EP4 agonist led to an improved NTS phenotype, including a reduced tubular injury score and reduced neutrophil gelatinase-associated lipocalin (NGAL) and blood urea nitrogen (BUN) levels. EP4 agonist treatment caused decreased CD4+ T cell infiltration into the kidney and increased proliferative capacity of tubular cells. Injection of the EP4 agonist resulted in dose-dependent vasodilation and hypotensive episodes. The low-dose EP4 agonist treatment resulted in less pronounced episodes of hypotension. In vitro, EP4 agonism resulted in cAMP production and increased distal convoluted tubular (DCT) proliferation. Taken together, EP4 agonism improved the NTS phenotype by various mechanisms, including reduced blood pressure, decreased CD4+ T cell infiltration, and a direct effect on tubular cells leading to increased proliferation probably by increasing cAMP levels.

The Effect of Interleukin-4 and Dexamethasone on RNA-Seq-Based Transcriptomic Profiling of Human Podocytes: A Potential Role in Minimal Change Nephrotic Syndrome

Interleukin-4 (IL-4) expression is implicated in the pathogenesis of nephrotic syndrome (NS). This study aimed to investigate the changes in the transcriptomes of human podocytes induced by IL-4 treatment and to analyze whether these changes could be affected by simultaneous steroid treatment. Three groups of human podocytes were treated with control, IL-4, and IL-4 plus dexamethasone (DEX), respectively. We performed whole-transcriptome sequencing to identify differentially expressed genes (DEGs) between the groups. We investigated relevant biological pathways using Gene Ontology (GO) enrichment analyses. We also attempted to compare and validate the DEGs with the genes listed in PodNet, a literature-based database on mouse podocyte genes. A total of 176 genes were differentially expressed among the three groups. GO analyses showed that pathways related to cytoskeleton organization and cell signaling were significantly enriched. Among them, 24 genes were listed in PodNet, and 12 of them were previously reported to be associated with IL-4-induced changes in human podocytes. Of the 12 genes, the expression levels of BMP4, RARB, and PLCE1 were reversed when podocytes were simultaneously treated with DEX. In conclusion, this study explored changes in the transcriptome profiles of human podocytes treated with IL-4. Few genes were reported in previous studies and were previously validated in experiments with human podocytes. We speculate that IL-4 may exert pathogenic effects on the transcriptome of human podocytes, and a few genes may be involved in the pathogenesis.

Inhibition of 15-PGDH prevents ischemic renal injury by the PGE2/EP4 signaling pathway mediating vasodilation, increased renal blood flow, and increased adenosine/A2A receptors

In the present study, we demonstrated the marked activity of SW033291, an inhibitor of 15-hydoxyprostaglandin dehydrogenase (15-PGDH), in preventing acute kidney injury (AKI) in a murine model of ischemia-reperfusion injury. AKI due to ischemic injury represents a significant clinical problem. PGE₂ is vasodilatory in the kidney, but it is rapidly degraded in vivo due to catabolism by 15-PGDH. We investigated the potential of SW033291, a potent and specific 15-PGDH inhibitor, as prophylactic treatment for ischemic AKI. Prophylactic administration of SW033291 significantly increased renal tissue PGE₂ levels and increased post-AKI renal blood flow and renal arteriole area. In parallel, prophylactic SW033291 decreased post-AKI renal morphology injury scores and tubular apoptosis and markedly reduced biomarkers of renal injury that included blood urea nitrogen, creatinine, neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1. Prophylactic SW033291 also reduced post-AKI induction of proinflammatory cytokines, high-mobility group box 1, and malondialdehyde. Protective effects of SW033291 were mediated by PGE₂ signaling, as they could be blocked by pharmacological inhibition of PGE₂ synthesis. Consistent with activation of PGE₂ signaling, SW033291 induced renal levels of both EP₄ receptors and cAMP, along with other vasodilatory effectors, including AMP, adenosine, and the adenosine A_2A receptor. The protective effects of SW0333291 could largely be achieved with a single prophylactic dose of the drug. Inhibition of 15-PGDH may thus represent a novel strategy for prophylaxis of ischemic AKI in multiple clinical settings, including renal transplantation and cardiovascular surgery.

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.

Effect of selective inhibition or activation of PGE2 EP1 receptor on glomerulosclerosis

Prostaglandin E2 (PGE2) is involved in numerous physiological and pathological processes of the kidney via its four receptors. A previous study has suggested that a defect in the PGE2 receptor 1 (EP1) gene markedly suppressed the transforming growth factor-β1 (TGF-β1)-induced mesangial cell (MC) proliferation and extracellular matrix aggregation. Therefore, the present study aimed to adopt a pharmacological method of specifically suppressing or activating the EP1 receptor to further verify and demonstrate these results. The EP1 receptor antagonist SC-19220 and EP1 receptor agonist 17-phenyl-trinor-PGE2 ethyl amide (17-pt-PGE2) were selectively used to treat five-sixths nephrectomy renal fibrosis model mice and TGF-β1-stimulated MCs. An Alpha screen PGE2 assay kit, flow cytometry, western blotting and immunohistochemical techniques were adopted to perform in vivo and in vitro experiments. The present results suggested that compared with the control group, the selective EP1 receptor antagonist SC-19220 improved renal function, markedly reduced the plasma blood urea nitrogen and creatinine levels (P<0.05) and alleviated glomerulosclerosis (P<0.05). By contrast, the EP1 receptor agonist 17-pt-PGE2 aggravated renal dysfunction and glomerulosclerosis (P<0.05). To verify the renal protection mechanisms mediated by suppression of the EP1 receptor, the expression levels of endoplasmic reticulum stress (ERS)-related proteins, including chaperone glucose-regulated protein 78 (GRP78), transient receptor potential channel 1 (TRPC1) and protein kinase R-like endoplasmic reticulum kinase (PERK), were further evaluated histologically. The expression of GRP78, TRPC1 and PERK in the antagonist treatment group were markedly downregulated (P<0.05), whereas those in the agonist treatment group were upregulated (P<0.05). The present in vitro experiments demonstrated that, compared with the control group, the EP1 receptor antagonist suppressed the expression of GRP78, TRPC1 and PERK (P<0.05), reduced the production of PGE2 (P<0.05) and decreased the MC apoptosis rate (P<0.05), thus alleviating TGF-β1-stimulated MC injury. Consequently, consistent with previous results, selectively antagonizing the EP1 receptor improved renal function and mitigated glomerulosclerosis, and its potential mechanism might be associated with the suppression of ERS.

Concerted EP2 and EP4 Receptor Signaling Stimulates Autocrine Prostaglandin E2 Activation in Human Podocytes

Glomerular hyperfiltration is an important mechanism in the development of albuminuria. During hyperfiltration, podocytes are exposed to increased fluid flow shear stress (FFSS) in Bowman’s space. Elevated Prostaglandin E2 (PGE₂) synthesis and upregulated cyclooxygenase 2 (Cox2) are associated with podocyte injury by FFSS. We aimed to elucidate a PGE₂ autocrine/paracrine pathway in human podocytes (hPC). We developed a modified liquid chromatography tandem mass spectrometry (LC/ESI-MS/MS) protocol to quantify cellular PGE₂, 15-keto-PGE₂, and 13,14-dihydro-15-keto-PGE₂ levels. hPC were treated with PGE₂ with or without separate or combined blockade of prostaglandin E receptors (EP), EP2, and EP4. Furthermore, the effect of FFSS on COX2, PTGER2, and PTGER4 expression in hPC was quantified. In hPC, stimulation with PGE₂ led to an EP2- and EP4-dependent increase in cyclic adenosine monophosphate (cAMP) and COX2, and induced cellular PGE₂. PTGER4 was downregulated after PGE₂ stimulation in hPC. In the corresponding LC/ESI-MS/MS in vivo analysis at the tissue level, increased PGE₂ and 15-keto-PGE₂ levels were observed in isolated glomeruli obtained from a well-established rat model with glomerular hyperfiltration, the Munich Wistar Frömter rat. COX2 and PTGER2 were upregulated by FFSS. Our data thus support an autocrine/paracrine COX2/PGE₂ pathway in hPC linked to concerted EP2 and EP4 signaling.

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.

Histone H3 Serine 10 Phosphorylation Facilitates Endothelial Activation in Diabetic Kidney Disease

The posttranslational histone modifications that epigenetically affect gene transcription extend beyond conventionally studied methylation and acetylation patterns. By examining the means by which podocytes influence the glomerular endothelial phenotype, we identified a role for phosphorylation of histone H3 on serine residue 10 (phospho-histone H3Ser10) in mediating endothelial activation in diabetes. Culture media conditioned by podocytes exposed to high glucose caused glomerular endothelial vascular cell adhesion protein 1 (VCAM-1) upregulation and was enriched for the chemokine CCL2. A neutralizing anti-CCL2 antibody prevented VCAM-1 upregulation in cultured glomerular endothelial cells, and knockout of the CCL2 receptor CCR2 diminished glomerular VCAM-1 upregulation in diabetic mice. CCL2/CCR2 signaling induced glomerular endothelial VCAM-1 upregulation through a pathway regulated by p38 mitogen-activated protein kinase, mitogen- and stress-activated protein kinases 1/2 (MSK1/2), and phosphorylation of H3Ser10, whereas MSK1/2 inhibition decreased H3Ser10 phosphorylation at the VCAM1 promoter. Finally, increased phospho-histone H3Ser10 levels were observed in the kidneys of diabetic endothelial nitric oxide synthase knockout mice and in the glomeruli of humans with diabetic kidney disease. These findings demonstrate the influence that histone protein phosphorylation may have on gene activation in diabetic kidney disease. Histone protein phosphorylation should be borne in mind when considering epigenetic targets amenable to therapeutic manipulation in diabetes.

Blockade of prostaglandin E2 receptor 4 ameliorates nephrotoxic serum nephritis

Prostaglandin E₂ (PGE₂) signaling is known to modulate inflammation and vascular resistance. Receptors of PGE₂ [E-type prostanoid receptors (EP)] might be an attractive pharmacological target in immune-mediated diseases such as glomerulonephritis. We hypothesized that selective EP4 antagonism improves nephrotoxic serum nephritis (NTS) by its anti-inflammatory properties. Mice were subjected to NTS and treated with the EP4 antagonist ONO AE3-208 (10 mg·kg body wt^-1·day^-1] or vehicle starting from disease initiation. In one set of experiments, treatment was started 4 days after NTS induction. Tubular epithelial cells were evaluated in vitro under starving conditions. EP4 antagonist treatment significantly improved the NTS phenotype without affecting blood pressure levels. Remarkably, the improved NTS phenotype was also observed when treatment was started 4 days after NTS induction. EP4 antagonism decreased tubular chemokine (C-X-C motif) ligand ( Cxcl) 1 and Cxcl-5 expression and thereby subsequently reduced interstitial neutrophil infiltration into the kidney. In vitro, tubular epithelial cells increasingly expressed Cxcl-5 mRNA and Cxcl-5 protein when treated with PGE₂ or an EP4 agonist under starving conditions, which was blunted by EP4 antagonist treatment. Together, EP4 antagonism improves the NTS phenotype, probably by decreasing mainly Cxcl-5 production in tubular cells, thereby reducing renal neutrophil infiltration.

EP4 knockdown alleviates glomerulosclerosis through Smad and MAPK pathways in mesangial cells

Prostaglandin E2 has exhibited pleiotropic effects in the regulation of glomerulosclerosis progression through its four receptors. The current study aimed to evaluate the effect of prostaglandin receptor EP4 on mesangial cell proliferation. In vivo, 5/6 nephrectomy was introduced into EP4+/‑ and wild‑type (WT) mice. Clinical parameters were monitored post‑surgery. At 8 weeks post‑surgery, glomerular fibrosis‑associated indicators were measured by immunohistochemical staining and trichrome staining. In vitro, mesangial cells in different groups (transfected with green fluorescent protein, AD‑EF4 or AD‑CRE) were exposed to transforming growth factor (TGF)‑β1 for 24 h to detect the level of downstream signaling. Corresponding signaling inhibitors were also used to validate the signaling effects. Following surgery, EP4+/‑ mice presented a higher survival rate and normal urine volume compared with the WT group, and serum creatinine level and 24 h urine protein were lower in the EP4+/‑ mice. Furthermore, associated profibrotic indicators were identified to have decreased at 8 weeks post‑surgery along with less tubule‑interstitial fibrosis. In vivo, the inhibition of extracellular signal‑regulated kinase and P38 phosphorylation alleviated the accumulation of mesangial matrix, and these signals were enhanced when EP4 was overexpressed. EP4 enhancement aggravated imbalanced mesangial cell proliferation stimulated by TGF‑β1 and GS of mice treated with 5/6 nephrectomy through the Smad and mitogen‑activated protein kinase pathways.

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.

Prostaglandins in the pathogenesis of kidney diseases

Prostaglandins (PGs) are important lipid mediators produced from arachidonic acid via the sequential catalyzation of cyclooxygenases (COXs) and specific prostaglandin synthases. There are five subtypes of PGs, namely PGE2, PGI2, PGD2, PGF2α, and thromboxane A2 (TXA2). PGs exert distinct roles by combining to a diverse family of membrane-spanning G protein-coupled prostanoid receptors. The distribution of these PGs, their specific synthases and receptors vary a lot in the kidney. This review summarized the recent findings of PGs together with the COXs and their specific synthases and receptors in regulating renal function and highlighted the insights into their roles in the pathogenesis of various kidney diseases.