PGE(2) EP(3) receptor downregulates COX-2 expression in the medullary thick ascending limb induced by hypertonic NaCl

Inducible deletion of the prostaglandin EP3 receptor in kidney tubules of male and female mice has no major effect on water homeostasis

The prostaglandin E2 (PGE2) receptor EP3 has been detected in the thick ascending limb (TAL) and the collecting duct of the kidney, where its actions are proposed to inhibit water reabsorption. However, EP3 is also expressed in other cell types, including vascular endothelial cells. The aim here was to determine the contribution of EP3 in renal water handling in male and female adult mice by phenotyping a novel mouse model with doxycycline-dependent deletion of EP3 throughout the kidney tubule (EP3-/- mice). RNAscope demonstrated that EP3 was highly expressed in the cortical and medullary TAL of adult mice. Compared with controls EP3 mRNA expression was reduced by >80% in whole kidney (RT-qPCR) and nondetectable (RNAscope) in renal tubules of EP3-/- mice. Under basal conditions, there were no significant differences in control and EP3-/- mice of both sexes in food and water intake, body weight, urinary output, or clinical biochemistries. No differences were detectable between genotypes in handling of an acute water load or in their response to the vasopressin analog 1-deamino-8-d-arginine-vasopressin (dDAVP). No differences in water handling were observed when PGE2 production was enhanced using 1% NaCl load. Expression of proteins involved in kidney water handling was not different between genotypes. This study demonstrates that renal tubular EP3 is not essential for body fluid homeostasis in males or females, even when PGE2 levels are high. The mouse model is a novel tool for examining the role of EP3 in kidney function independently of potential developmental abnormalities or systemic effects.NEW & NOTEWORTHY The prostanoid EP3 receptor is proposed to play a key role in the kidney tubule and antagonize the effects of vasopressin on aquaporin-mediated water reabsorption. Here, we phenotyped a kidney tubule-specific inducible knockout mouse model of the EP3 receptor. Our major finding is that, even under physiological stress, tubular EP3 plays no detectable role in renal water or solute handling. This suggests that other EP receptors must be important for renal salt and water handling.

Dynamics of differentiated-renal epithelial cell monolayer after calcium oxalate injury: The role of cyclooxygenase-2

AIMS

Calcium oxalate (Oxa), constituent of most common kidney stones, damages renal tubular epithelial cells leading to kidney disease. Most in vitro studies designed to evaluate how Oxa exerts its harmful effects were performed in proliferative or confluent non-differentiated renal epithelial cultures; none of them considered physiological hyperosmolarity of renal medullary interstitium. Cyclooxygenase 2 (COX2) has been associated to Oxa deleterious actions; however, up to now, it is not clear how COX2 acts. In this work, we proposed an in vitro experimental system resembling renal differentiated-epithelial cells that compose medullary tubular structures which were grown and maintained in a physiological hyperosmolar environment and evaluated whether COX2 → PGE2 axis (COX2 considered a cytoprotective protein for renal cells) induces Oxa damage or epithelial restitution.

MAIN METHODS

MDCK cells were differentiated with NaCl hyperosmolar medium for 72 h where cells acquired the typical apical and basolateral membrane domains and a primary cilium. Then, cultures were treated with 1.5 mM Oxa for 24, 48, and 72 h to evaluate epithelial monolayer restitution dynamics and COX2-PGE2 effect.

KEY FINDINGS

Oxa completely turned the differentiated phenotype into mesenchymal one (epithelial-mesenchymal transition). Such effect was partially and totally reverted after 48 and 72 h, respectively. Oxa damage was even deeper when COX2 was blocked by NS398. PGE2 addition restituted the differentiated-epithelial phenotype in a time and concentration dependence.

SIGNIFICANCE

This work presents an experimental system that approaches in vitro to in vivo renal epithelial studies and, more important, warns about NSAIDS use in patients suffering from kidney stones.

Nephron-Specific Disruption of Polycystin-1 Induces Cyclooxygenase-2-Mediated Blood Pressure Reduction Independent of Cystogenesis

BACKGROUND

Hypertension often occurs before renal function deteriorates in autosomal dominant polycystic kidney disease (ADPKD). It is unknown whether the Pkd1 gene product polycystin-1-the predominant causal factor in ADPKD-itself contributes to ADPKD hypertension independent of cystogenesis.

METHODS

We induced nephron-specific disruption of the Pkd1 gene in 3-month-old mice and examined them at 4-5 months of age.

RESULTS

Kidneys from the Pkd1 knockout mice showed no apparent renal cysts, tubule dilation, or increased cell proliferation. Compared with control mice, Pkd1 knockout mice exhibited reduced arterial pressure during high salt intake; this associated with an increased natriuretic, diuretic, and kaliuretic response during the first 2-3 days of salt loading. The lower arterial pressure and enhanced natriuresis during high salt loading in Pkd1 knockout mice were associated with lower urinary nitrite/nitrate excretion and markedly increased urinary PGE₂ excretion, whereas GFR, plasma renin concentration, and urinary endothelin-1 excretion were similar between knockout and control mice. Kidney cyclooxygenase-2 protein levels were increased in Pkd1 knockout mice during high salt intake; administration of NS-398, a selective cyclooxygenase-2 inhibitor, abolished the arterial pressure difference between the knockout and control mice during high salt intake. Total kidney Na⁺/K⁺/2Cl^- cotransporter isoform 2 (NKCC2) levels were greatly reduced in Pkd1 knockout mice fed a high salt diet compared with controls.

CONCLUSIONS

These studies suggest that nephron polycystin-1 deficiency does not itself contribute to ADPKD hypertension and that it may, in fact, exert a relative salt-wasting effect. The work seems to comprise the first in vivo studies to describe a potential physiologic role for nephron polycystin-1 in the absence of cysts, tubule dilation, or enhanced cell proliferation.

PGE2 EP1 receptor inhibits vasopressin-dependent water reabsorption and sodium transport in mouse collecting duct

PGE2 regulates glomerular hemodynamics, renin secretion, and tubular transport. This study examined the contribution of PGE2 EP1 receptors to sodium and water homeostasis. Male EP1-/- mice were bred with hypertensive TTRhRen mice (Htn) to evaluate blood pressure and kidney function at 8 weeks of age in four groups: wildtype (WT), EP1-/-, Htn, HtnEP1-/-. Blood pressure and water balance were unaffected by EP1 deletion. COX1 and mPGE2 synthase were increased and COX2 was decreased in mice lacking EP1, with increases in EP3 and reductions in EP2 and EP4 mRNA throughout the nephron. Microdissected proximal tubule sglt1, NHE3, and AQP1 were increased in HtnEP1-/-, but sglt2 was increased in EP1-/- mice. Thick ascending limb NKCC2 was reduced in the cortex but increased in the medulla. Inner medullary collecting duct (IMCD) AQP1 and ENaC were increased, but AVP V2 receptors and urea transporter-1 were reduced in all mice compared to WT. In WT and Htn mice, PGE2 inhibited AVP-water transport and increased calcium in the IMCD, and inhibited sodium transport in cortical collecting ducts, but not in EP1-/- or HtnEP1-/- mice. Amiloride (ENaC) and hydrochlorothiazide (pendrin inhibitor) equally attenuated the effect of PGE2 on sodium transport. Taken together, the data suggest that EP1 regulates renal aquaporins and sodium transporters, attenuates AVP-water transport and inhibits sodium transport in the mouse collecting duct, which is mediated by both ENaC and pendrin-dependent pathways.

Two Sulfur Glycoside Compounds Isolated from Lepidium apetalum Willd Protect NRK52e Cells against Hypertonic-Induced Adhesion and Inflammation by Suppressing the MAPK Signaling Pathway and RAAS

Lepidium apetalum Willd has been used to reduce edema and promote urination. Cis-desulfoglucotropaeolin (cis-DG) and trans-desulfoglucotropaeolin (trans-DG) were isolated from Lepidium apetalum Willd, and caused a significant increase in cell viability in a hypertonic model in NRK52e cells. In the hypertonic model, cis-DG and trans-DG significantly promoted the cell viability of NRK52e cells and inhibited the elevation of Na⁺ in the supernatant, inhibited the renin-angiotensin-aldosterone (RAAS) system, significantly reduced the levels of angiotensin II (Ang II) and aldosterone (ALD), and lowered aquaporin-2 (AQP2) and Na⁺–K⁺ ATP content in renal medulla. After treatment with cis-DG and trans-DG, expression of calcineurin (CAN) and Ca/calmodulin-dependent protein kinase II (CaMK II) was decreased in renal tissue and Ca²⁺ influx was inhibited, thereby reducing the secretion of transforming growth factor-β (TGFβ), reversing the increase in adhesion and inflammatory factor E-selectin and monocyte chemotactic protein 1 (MCP-1) induced by high NaCl, while reducing oxidative stress status and decreasing the expression of cyclooxygenase-2 (COX2). Furthermore, inhibition of protein kinase C (PKC) expression also contributed to these improvements. The cis-DG and trans-DG reduced the expression of p-p44/42 MAPK, p-JNK and p-p38, inhibited the phosphorylation of the MAPK signaling pathway in NRN52e cells induced by high salt, decreased the overexpression of p-p38 and p-HSP27, and inhibited the overactivation of the p38-MAPK signaling pathway, suggesting that the p38-MAPK pathway may play a vital role in the hypertonic-induced adhesion and inflammatory response. From the results of this study, it can be concluded that the mechanism of cis-DG and trans-DG may mainly be through inhibiting the p38-MAPK signaling pathway, inhibiting the excessive activation of the RAAS system, and thereby reducing adhesion and inflammatory factors.

PGE2 upregulates renin through E-prostanoid receptor 1 via PKC/cAMP/CREB pathway in M-1 cells

During the early phase of ANG II-dependent hypertension, tubular PGE₂ is increased. Renin synthesis and secretion in the collecting duct (CD) are upregulated by ANG II, contributing to further intratubular ANG II formation. However, what happens first and whether the triggering mechanism is independent of tubular ANG II remain unknown. PGE₂ stimulates renin synthesis in juxtaglomerular cells via E-prostanoid (EP) receptors through the cAMP/cAMP-responsive element-binding (CREB) pathway. EP receptors are also expressed in the CD. Here, we tested the hypothesis that renin is upregulated by PGE₂ in CD cells. The M-1 CD cell line expressed EP1, EP3, and EP4 but not EP2. Dose-response experiments, in the presence of ANG II type 1 receptor blockade with candesartan, demonstrated that 10^-6 M PGE₂ maximally increases renin mRNA (approximately 4-fold) and prorenin/renin protein levels (approximately 2-fold). This response was prevented by micromolar doses of SC-19220 (EP1 antagonist), attenuated by the EP4 antagonist, L-161982, and exacerbated by the highly selective EP3 antagonist, L-798106 (~10-fold increase). To evaluate further the signaling pathway involved, we used the PKC inhibitor calphostin C and transfections with PKCα dominant negative. Both strategies blunted the PGE₂-induced increases in cAMP levels, CREB phosphorylation, and augmentation of renin. Knockdown of the EP1 receptor and CREB also prevented renin upregulation. These results indicate that PGE₂ increases CD renin expression through the EP1 receptor via the PKC/cAMP/CREB pathway. Therefore, we conclude that during the early stages of ANG II-dependent hypertension, there is augmentation of PGE₂ that stimulates renin in the CD, resulting in increased tubular ANG II formation and further stimulation of renin.

Prostaglandin E2 Induces Prorenin-Dependent Activation of (Pro)renin Receptor and Upregulation of Cyclooxygenase-2 in Collecting Duct Cells

BACKGROUND

Prostaglandin E2 (PGE₂) regulates renin expression in renal juxtaglomerular cells. PGE₂ acts through E-prostanoid (EP) receptors in the renal collecting duct (CD) to regulate sodium and water balance. CD cells express EP1 and EP4, which are linked to protein kinase C (PKC) and PKA downstream pathways, respectively. Previous studies showed that the presence of renin in the CD, and that of PKC and PKA pathways, activate its expression. The (pro)renin receptor (PRR) is also expressed in CD cells, and its activation enhances cyclooxygenase-2 (COX-2) through extracellular signal-regulated kinase (ERK). We hypothesized that PGE₂ stimulates prorenin and renin synthesis leading to subsequent activation of PRR and upregulation of COX-2.

METHODS

We used a mouse M-1 CD cell line that expresses EP1, EP3 and EP4 but not EP2.

RESULTS

PGE₂ (10^-6M) treatment increased prorenin and renin protein levels at 4 and 8 hours. No differences were found at 12-hour after PGE₂ treatment. Phospho-ERK was significantly augmented after 12 hours. COX-2 expression was decreased after 4 hours of PGE₂ treatment, but increased after 12 hours. Interestingly, the full-length form of the PRR was upregulated only at 12 hours. PGE₂-mediated phospho-ERK and COX-2 upregulation was suppressed by PRR silencing.

CONCLUSIONS

Our results suggest that PGE₂ induces biphasic regulation of COX-2 through renin-dependent PRR activation via EP1 and EP4 receptors. PRR-mediated increases in COX-2 expression may enhance PGE₂ synthesis in CD cells serving as a buffer mechanism in conditions of activated renin-angiotensin system.

The EP3 receptor regulates water excretion in response to high salt intake

The mechanisms by which prostanoids contribute to the maintenance of whole body water homeostasis are complex and not fully understood. The present study demonstrates that an EP3-dependent feedback mechanism contributes to the regulation of water homeostasis under high-salt conditions. Rats on a normal diet and tap water were placed in metabolic cages and given either sulprostone (20 μg·kg^-1·day^-1) or vehicle for 3 days to activate EP3 receptors in the thick ascending limb (TAL). Treatment was continued for another 3 days in rats given either 1% NaCl in the drinking water or tap water. Sulprostone decreased expression of cyclooxygenase 2 (COX-2) expression by ∼75% in TAL tubules from rats given 1% NaCl concomitant with a ∼60% inhibition of COX-2-dependent PGE₂ levels in the kidney. Urine volume increased after ingestion of 1% NaCl but was reduced ∼40% by sulprostone. In contrast, the highly selective EP3 receptor antagonist L-798106 (100 μg·kg^-1·day^-1), which increased COX-2 expression and renal PGE₂ production, increased urine volume in rats given 1% NaCl. Sulprostone increased expression of aquaporin-2 (AQP2) in the inner medullary collecting duct plasma membrane in association with an increase in phosphorylation at Ser269 and decrease in Ser261 phosphorylation; antagonism of EP3 with L-798106 reduced AQP2 expression. Thus, although acute activation of EP3 by PGE₂ in the TAL and collecting duct inhibits the Na-K-2Cl cotransporter and AQP2 activity, respectively, chronic activation of EP3 in vivo limits the extent of COX-2-derived PGE₂ synthesis, thereby mitigating the inhibitory effects of PGE₂ on these transporters and decreasing urine volume.

PGE2 released by primary sensory neurons modulates Toll-like receptor 4 activities through an EP4 receptor-dependent process

Exogenous prostaglandin E2 (PGE2) displays mixed regulatory properties with regard to inflammatory gene expression in dorsal root ganglion (DRG) cells. We show here that endogenously-produced nanomolar concentrations of PGE2, such as that generated in response to Toll-like receptor 4 (TLR4) stimulation, inhibits both cyclooxygenase-2 (COX-2) and tumour necrosis factor alpha (TNFα) mRNA expression in DRG cells in an EP4 receptor-dependent manner. DRG neurons appear to be the major source of PGE2 in the DRG and likely serve as both an autocrine and paracrine system for limiting over-activation of both DRG neurons and glial cells in response to TLR4 stimulation.

Regulation of PGE2 signaling pathways and TNF-alpha signaling pathways on the function of bone marrow-derived dendritic cells and the effects of CP-25

This study was to investigate PGE2 and TNF-alpha signaling pathway involving in the maturation and activation of bone marrow dendritic cells (DCs) and the effect of CP-25. Bone marrow DCs were isolated and stimulated by PGE2 and TNF-alpha respectively. The markers of maturation and activation expressed on DCs, such as CD40, CD80, CD83, CD86, MHC-II, and the ability of antigen uptake of DCs were analyzed by flow cytometry. The proliferation of T cells co-cultured with DCs, the signaling pathways of PGE2-EP4-cAMP and TNF-alpha-TRADD-TRAF2-NF-κB in DCs were analyzed. The results showed that both PGE2 and TNF-alpha up-regulated the expressions of CD40, CD80, CD83, CD86, and MHC-II, decreased the antigen uptake of DCs, and DCs stimulated by PGE2 or TNF-alpha could increase T cell proliferation. CP-25 (10(-5), 10(-6), and 10(-7)mol/l) decreased significantly the expressions of CD40, CD80, CD83, CD86 and MHC-II, increased the antigen uptake of DCs, and suppressed T cell proliferation induced by DCs. PGE2 increased the expressions of EP4, NF-κB and down-regulated cAMP level of DCs. TNF-alpha could also up-regulate TNFR1, TRADD, TRAF2, and NF-κB expression of DCs. CP-25 (10(-5), 10(-6), and 10(-7)mol/l) decreased the expressions of EP4 and NF-κB, increased cAMP level in DCs stimulated by PGE2. CP-25 (10(-5), 10(-6), and 10(-7)mol/l) also could down-regulate significantly TNFR1, TRADD, TRAF2, and NF-κB expression in DCs stimulated by TNF-alpha. These results demonstrate that PGE2 and TNF-alpha could enhance DCs functions by mediating PGE2-EP4-cAMP pathway, TNF-alpha-TNFR1-TRADD-TRAF2-NF-κB pathway respectively. CP-25 might inhibit the function of DCs through regulating PGE2-EP4-cAMP and TNF-alpha-TNFR1-TRADD-TRAF2-NF-κB pathways.