Vasopressin-independent targeting of aquaporin-2 by selective E-prostanoid receptor agonists alleviates nephrogenic diabetes insipidus

Abstract

In the kidney, the actions of vasopressin on its type-2 receptor (V2R) induce increased water reabsorption alongside polyphosphorylation and membrane targeting of the water channel aquaporin-2 (AQP2). Loss-of-function mutations in the V2R cause Xlinked nephrogenic diabetes insipidus. Treatment of this condition would require bypassing the V2R to increase AQP2 membrane targeting, but currently no specific pharmacological therapy is available. The present study examined specific E-prostanoid receptors for this purpose. In vitro, prostaglandin E2 (PGE2) and selective agonists for the E-prostanoid receptors EP2 (butaprost) or EP4 (CAY10580) all increased trafficking and ser-264 phosphorylation of AQP2 in Madin-Darby canine kidney cells. Only PGE2 and butaprost increased cAMP and ser-269 phosphorylation of AQP2. Ex vivo, PGE2, butaprost, or CAY10580 increased AQP2 phosphorylation in isolated cortical tubules, whereas PGE2 and butaprost selectively increased AQP2 membrane accumulation in kidney slices. In vivo, a V2R antagonist caused a severe urinary concentrating defect in rats, which was greatly alleviated by treatment with butaprost. In conclusion, EP2 and EP4 agonists increase AQP2 phosphorylation and trafficking, likely through different signaling pathways. Furthermore, EP2 selective agonists can partially compensate for a nonfunctional V2R, providing a rationale for new treatment strategies for hereditary nephrogenic diabetes insipidus.T he anti-diuretic hormone vasopressin (VP) controls wholebody water balance mainly by regulating the water permeability of the kidney collecting duct. VP binds to the Gs-proteincoupled VP type 2 receptor (V2R) in collecting duct principal cells, stimulating the accumulation of aquaporin-2 (AQP2) in the apical plasma membrane (1). This process increases the water permeability of the epithelium, allowing water to be reabsorbed from the collecting-duct lumen and increasing the concentration of the urine. The intracellular signaling cascades of VP in the collecting duct involve increased cAMP and protein kinasedependent phosphorylation of AQP2 at ser-256, ser-264, and ser-269. The ser-256 and ser-269 sites appear to be essential for apical membrane accumulation of AQP2 (2). Although VP's role is well characterized, there is evidence that alternative mechanisms may also regulate water permeability. For example, functional studies on collecting ducts have shown an EC 50 of 10 −11 M for VP-induced increases in water permeability and a requirement of 10 −8 M for maximal effect (3). Water restriction does not increase plasma VP to these levels (4-6). This leaves room for additional mechanisms to be involved in modulating collecting-duct water permeability, supported by evidence that the urinary concentrating ability of the kidney can increase in the presence of a V2R antagonist during water restriction (7).Prostanoids are a family of arachidonic acid derivatives produced in most cell types. The biological actions of one class of prostanoids, prostaglandin E2 (PGE2), are diverse. This may...

Is There a Role for PGE2 in Urinary Concentration?

“…16,18 EP2 has also been localized to mouse CCD cells, 14 the rabbit CCD, 33 and the human connecting tubule, 20 but kidney EP2 localization in mouse, rabbit, and human CDs is not consistently found. 13,14,21,22,33 EP2 is also expressed in renomedullary interstitial cells.…”

Diabetes Insipidus: A Review

“…This is a potential mechanism by which prostaglandin inhibitors such as nonsteroidal anti-inflammatory agents may cause fluid retention. Recent studies done in Madin-Darby canine kidney cells show that AQP-2 phosphorylation and apical insertion are increased by prostaglandin EP2 and EP4 receptors activation [23]. It has also been shown in rats that butaprost, a EP2 agonist can increase urinary concentration in rats with the V2R blocked.…”

Urinary concentration: different ways to open and close the tap

“…Conversely, inhibition of prostaglandine synthesis by indomethacine enhances the effect of vasopressin [31,32]. Recently, data for the role of PGE2 in urinary concentration were published that conflict with the earlier results of an antagonism between PGE2 and vasopressin [33]: these data show a vasopressin-independent direct increase in cAMP and consequent Aqp2 phosphorylation and membrane insertion after treatment with PGE2 or related agonists for the E-prostanoid receptors EP2 or EP4. Indeed, rats treated with a blocker of Avpr2 develop a pharmacologically induced NDI and the phenotype could be significantly alleviated by treatment with an EP2 agonist [33].…”

“…The recent data on AVPR2-independent activation by agonists for the EP2 and EP4 receptors raises the intriguing possibility of a new therapeutic pathway for patients with X-linked NDI [33]. However, at this point it is unclear how to resolve the contradiction between giving prostaglandins to reduce urine output, when the blockade of their synthesis by indomethacine has actually proven clinical efficacy.…”