Urinary tract obstruction induces transient accumulation of COX-2-derived prostanoids in kidney tissue

Inhibitors of cyclooxygenase (COX)-2 prevent suppression of aquaporin-2 and reduce polyuria in the acute phase after release of bilateral ureteral obstruction (BUO). We hypothesized that BUO leads to COX-2-mediated local accumulation of prostanoids in inner medulla (IM) tissue. To test this, rats were subjected to BUO and treated with selective COX-1 or COX-2 inhibitors. Tissue was examined at 2, 6, 12, and 24 h after BUO. COX-2 protein abundance increased in IM 12 and 24 h after onset of BUO but did not change in cortex. COX-1 did not change at any time points in any region. A full profile of all five primary prostanoids was obtained by mass spectrometric determination of PGE(2), PGF(2α), 6-keto-PGF(1α), PGD(2), and thromboxane (Tx) B(2) concentrations in kidney cortex/outer medulla and IM fractions. IM concentration of PGE(2), 6-keto-PGF(1α), and PGF(2α) was increased at 6 h BUO, and PGE(2) and PGF(2α) increased further at 12 h BUO. TxB(2) increased after 12 h BUO. 6-keto-PGF(1α) remained significantly increased after 24 h BUO. The COX-2 inhibitor parecoxib lowered IM PGE(2,) TxB(2), 6-keto-PGF(1α), and PGF(2α) below vehicle-treated BUO and sham rats at 6, 12 and, 24 h BUO. The COX-1 inhibitor SC-560 lowered PGE(2), PGF(2α), and PGD(2) in IM compared with untreated 12 h BUO, but levels remained significantly above sham. In cortex tissue, PGE(2) and 6-keto-PGF(1α) concentrations were elevated at 6 h only. In conclusion, COX-2 activity contributes to the transient increase in prostacyclin metabolite 6-keto-PGF(1α) and TxB(2) concentration in the kidney IM, and COX-2 is the predominant isoform that is responsible for accumulation of PGE(2) and PGF(2α) with minor, but significant, contributions from COX-1. PGD(2) synthesis is mediated exclusively by COX-1. In BUO, therapeutic interventions aimed at the COX-prostanoid pathway should target primarily COX-2

Aldosterone-mediated apical targeting of ENaC subunits is blunted in rats with streptozotocin-induced diabetes mellitus.

BACKGROUND: Diabetes mellitus (DM) is associated with a significant polyuria and natriuesis as well as increased plasma aldosterone and anti-diuretic hormone arginine vasopressin (AVP). This study aimed to determine whether diabetic kidneys compensate for the urinary sodium and water losses by increasing apical targeting of epithelial sodium channel (ENaC) subunits and aquaporin-2 (AQP2) in the collecting duct, in addition to the previously observed changes in ENaC subunit protein expression in different kidney zones. METHODS: Female rats were investigated 2 weeks after induction of DM by streptozotocin administration. Kidneys were examined by immunohistochemisty and semiquantitative immunoblotting. RESULTS: We demonstrated that the protein expression of renal AQP2, Ser-256 phosphorylated AQP2, AQP3, beta- and gamma-ENaC (but not alpha-ENaC) increased consistently with an increased AVP response. In contrast, there were no significant changes in the relative apical targeting of beta-, gamma- and alpha-ENaC, and the shift in the molecular weight of gamma-ENaC from 85 kDa to 70 kDa was not observed despite increased plasma aldosterone levels. These results were supported by changes in the functional data showing increased solute-free water reabsorption, increased fractional excretion of sodium and an unchanged ratio of potassium to sodium in the urine. CONCLUSIONS: The data demonstrate that diabetic kidneys have a reduced sensitivity to the anti-natriuretic action of elevated plasma aldosterone levels with no relative increase in ENaC subunit apical targeting, whereas there is increased expression of beta- and gamma-ENaC, which alone may play a role in the increased sodium reabsorption in the kidney in DM

Tankyrase-mediated β-catenin activity regulates vasopressin-induced AQP2 expression in kidney collecting duct mpkCCDc14 cells

Aquaporin-2 (AQP2) mediates arginine vasopressin (AVP)-induced water reabsorption in the kidney collecting duct. AVP regulates AQP2 expression primarily via Gsα/cAMP/PKA signaling. Tankyrase, a member of the poly(ADP-ribose) polymerase family, is known to mediate Wnt/β-catenin signaling-induced gene expression. We examined whether tankyrase plays a role in AVP-induced AQP2 regulation via ADP-ribosylation of G protein-α (Gα) and/or β-catenin-mediated transcription of AQP2. RT-PCR and immunoblotting analysis revealed the mRNA and protein expression of tankyrase in mouse kidney and mouse collecting duct mpkCCDc14 cells. dDAVP-induced AQP2 upregulation was attenuated in mpkCCDc14 cells under the tankyrase inhibition by XAV939 treatment or small interfering (si) RNA knockdown. Fluorescence resonance energy transfer image analysis, however, revealed that XAV939 treatment did not affect dDAVP- or forskolin-induced PKA activation. Inhibition of tankyrase decreased dDAVP-induced phosphorylation of β-catenin (S552) and nuclear translocation of phospho-β-catenin. siRNA-mediated knockdown of β-catenin decreased forskolin-induced AQP2 transcription and dDAVP-induced AQP2 expression. Moreover, inhibition of phosphoinositide 3-kinase/Akt, which was associated with decreased nuclear translocation of β-catenin, diminished dDAVP-induced AQP2 upregulation, further indicating that β-catenin mediates AQP2 expression. Taken together, tankyrase plays a role in AVP-induced AQP2 regulation, which is likely via β-catenin-mediated transcription of AQP2, but not ADP-ribosylation of Gα. The results provide novel insights into vasopressin-mediated urine concentration and homeostasis of body water metabolism.</jats:p