Disruption of prostaglandin E2 receptor EP4 impairs urinary concentration via decreasing aquaporin 2 in renal collecting ducts

Abstract

The antidiuretic hormone arginine vasopressin is a systemic effector in urinary concentration. However, increasing evidence suggests that other locally produced factors may also play an important role in the regulation of water reabsorption in renal collecting ducts. Recently, prostaglandin E2 (PGE2) receptor EP4 has emerged as a potential therapeutic target for the treatment of nephrogenic diabetes insipidus, but the underlying mechanism is unknown. To evaluate the role of EP4 in regulating water homeostasis, mice with renal tubule-specific knockout of EP4 (Ksp-EP4 −/−) and collecting duct-specific knockout of EP4 (AQP2-EP4 −/− ) were generated using the Cre-loxP recombination system. Urine concentrating defect was observed in both Ksp-EP4−/− and AQP2-EP4 −/− mice. Decreased aquaporin 2 (AQP2) abundance and apical membrane targeting in renal collecting ducts were evident in Ksp-EP4 −/− mice. In vitro studies demonstrated that AQP2 mRNA and protein levels were significantly up-regulated in mouse primary inner medullary collecting duct (IMCD) cells after pharmacological activation or adenovirusmediated overexpression of EP4 in a cAMP/cAMP-response element binding protein-dependent manner. In addition, EP4 activation or overexpression also increased AQP2 membrane accumulation in a mouse IMCD cell line (IMCD3) stably transfected with the AQP2 gene, mainly through the cAMP/protein kinase A and extracellular signal-regulated kinase pathways. In summary, the EP4 receptor in renal collecting ducts plays an important role in regulating urinary concentration under physiological conditions. The ability of EP4 to promote AQP2 membrane targeting and increase AQP2 abundance makes it a potential therapeutic target for the treatment of clinical disorders including acquired and congenital diabetes insipidus.arachidonic acid | cyclooxygenase | antidiuretic hormone | gene targeting | water homeostasis U rinary concentration is a key process for maintaining body water homeostasis, which is primarily regulated by the antidiuretic hormone arginine vasopressin (AVP). AVP is produced in the hypothalamus and stored in and released from the posterior pituitary, either in response to increased plasma osmolality or decreased blood volume. It binds to its type 2 receptor (V2R) on the basolateral membrane of the principal cells of renal collecting ducts (CDs), triggering the redistribution of aquaporin 2 (AQP2) from intracellular vesicles into the apical membrane. The prolonged activation of V2R can also increase AQP2 expression in CDs, which is essential for urinary concentration (1). AVP thus increases water permeability of the CDs, resulting in enhanced water reabsorption from the tubule lumens and concentrated urine output (1, 2). In some cases, however, urinary concentration is altered independent of AVP, a phenomenon called vasopressin escape, suggesting additional mechanisms may participate in the process of water reabsorption in renal collecting ducts (3-5).Among many identified factors affecting urine output, prostaglandin E2 (PGE2...

Unraveling the Physiology of (Pro)Renin Receptor in the Distal Nephron

“…In microdissected nephron segments, EP 4 mRNA was abundantly detected in the cortical collecting duct 70 where PGE 2 stimulated cAMP production 71 . Following 24-hour water deprivation, EP 4 protein expression is remarkably upregulated contrasting to unchanged expression of the other 3 EP subtypes 72 , indicating a unique role of EP 4 receptors in regulation of water homeostasis. This notion has been confirmed by generation of nephron- (Ksp-EP 4 -/-) and CD (AQP2-EP 4 -/-) -specific deletion of EP 4 , both of which impair urine concentrating capability 72 .…”

“…Following 24-hour water deprivation, EP 4 protein expression is remarkably upregulated contrasting to unchanged expression of the other 3 EP subtypes 72 , indicating a unique role of EP 4 receptors in regulation of water homeostasis. This notion has been confirmed by generation of nephron- (Ksp-EP 4 -/-) and CD (AQP2-EP 4 -/-) -specific deletion of EP 4 , both of which impair urine concentrating capability 72 . An earlier study from our group showed that EP 4 acting downstream of COX-2 mediates upregulation of renal medullary PRR and the intrarenal RAS during AngII-induced hypertension 73, 74 .…”

Prorenin Receptor, a Necessary Component in Urine Concentration Mechanism

“…[11][12][13] Although first observations in mice with global EP 4 receptor deletion showed a mild diuresis only after low salt intake, no electrolyte disturbances, and impaired renin release from juxtaglomerular cells, 14,15 the 2015 data indicated that EP 4 receptors were physiologically stimulated by water deprivation in renal medulla. 10 Moreover, renal tubule-and CD-specific EP 4 receptor deletion resulted in increased baseline diuresis, normal electrolyte excretion, impaired urine concentrating ability with attenuated AQP2 protein abundance, and impaired cAMP formation but intact circulating levels of AVP. 10 Thus, similar to CD-specific PRR deletion, the CD EP 4 -deleted phenotype exhibited nephrogenic insipidus.…”

“…10 Moreover, renal tubule-and CD-specific EP 4 receptor deletion resulted in increased baseline diuresis, normal electrolyte excretion, impaired urine concentrating ability with attenuated AQP2 protein abundance, and impaired cAMP formation but intact circulating levels of AVP. 10 Thus, similar to CD-specific PRR deletion, the CD EP 4 -deleted phenotype exhibited nephrogenic insipidus. This observation provided a mechanistic clue to the previous observations that, in experimental nephrogenic diabetes insipidus models in rats and mice, EP 4 receptor agonists alleviated increased diuresis 16,17 Similar to the PRR, EP 4 receptor seems necessary for baseline renal water conservation and urine concentration ability through an intrarenal mechanism.…”

“…9 An unequivocal function for the PGE 2 EP 4 receptor in renal water handling was shown in 2015. 10 The EP 4 receptor couples to a G s protein, leading to adenylate cyclase stimulation and formation of cAMP. In the kidney, the EP 4 receptor is associated with CDs, glomeruli, and renal resistance vessels.…”