Vasopressin increases expression of UT-A1, UT-A3, and ER chaperone GRP78 in the renal medulla of mice with a urinary concentrating defect

Abstract

Activation of V2 receptors (V2R) during antidiuresis increases the permeability of the inner medullary collecting duct to urea and water. Extracellular osmolality is elevated as the concentrating capacity of the kidney increases. Osmolality is known to contribute to the regulation of collecting duct water (aquaporin-2; AQP2) and urea transporter (UT-A1, UT-A3) regulation. AQP1KO mice are a concentrating mechanism knockout, a defect attributed to the loss of high interstitial osmolality. A V2R-specific agonist, deamino-8-D-arginine vasopressin (dDAVP), was infused into wild-type and AQP1KO mice for 7 days. UT-A1 mRNA and protein abundance were significantly increased in the medullas of wild-type and AQP1KO mice following dDAVP infusion. The mRNA and protein abundance of UT-A3, the basolateral urea transporter, was significantly increased by dDAVP in both wild-type and AQP1KO mice. Semiquantitative immunoblots revealed that dDAVP infusion induced a significant increase in the medullary expression of the endoplasmic reticulum (ER) chaperone GRP78. Immunofluorescence studies demonstrated that GRP78 expression colocalized with AQP2 in principal cells of the papillary tip of the renal medulla. Using immunohistochemistry and immunogold electron microscopy, we demonstrate that vasopressin induced a marked apical targeting of GRP78 in medullary principal cells. Urea-sensitive genes, GADD153 and ATF4 (components of the ER stress pathway), were significantly increased in AQP1KO mice by dDAVP infusion. These findings strongly support an important role of vasopressin in the activation of an ER stress response in renal collecting duct cells, in addition to its role in activating an increase in UT-A1 and UT-A3 abundance.

Phosphorylation of eIF2α via the general control kinase, GCN2, modulates the ability of renal medullary cells to survive high urea stress

“…Neither PERK nor ATF4 was activated by urea stress in our study. In vivo, we reported that ATF4 expression increases in the renal medulla of water-restricted mice (3) and in the renal medulla of dDAVP-infused, AQP1-null mice (5).…”

“…In a concentrating defect mouse model, we identified a potential role for urea in increasing the endoplasmic reticulum (ER) stress pathway genes glucose response protein 78 (GRP78) and ATF3 and ATF4 in renal collecting ducts (5). The aim of the current study was to determine whether high urea stress directly activated these stress response genes via the eIF2␣ phosphorylation pathway and we addressed this using a renal medullary cell line.…”

Morphological and functional characteristics of the kidney of cartilaginous fishes: with special reference to urea reabsorption

“…In the IMCD, urea is reabsorbed by UT-A1 and UT-A3 from the forming urine, in which urea is concentrated after the reabsorption of water, NaCl, and other useful substances. The urea reabsorption by UT-A1 and UT-A3 is regulated by vasopressin and other factors via PKA- and PKC-mediated pathways (15,32,65,100,123). This urea reabsorption is essential to maintain high urea concentration in the inner medullary interstitium and to set up the intrarenal osmotic gradient between the cortex and the inner medulla.…”

“…In mammals, it is well known that vasopressin controls the mRNA expression of UTs and the apical accumulation of UT-A1 via V2-type vasopressin receptor (12,14,15,64). In the houndshark, secretion of vasotocin, a nonmammalian ortholog of vasopressin, is enhanced in concentrated SW, whereas it is decreased in lowsalinity conditions (53).…”

Forskolin stimulation promotes urea transporter UT-A1 ubiquitination, endocytosis, and degradation in MDCK cells

“…In response to a reduction in plasma volume and an increase in the plasma osmolality, vasopressin is released from the posterior pituitary and causes an increased urea concentration in the papillary tip, which contributes to the efficiency of the urinary concentrating mechanism (2,21).…”