American journal of physiology. Renal physiology
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Am. J. Physiol. Renal Physiol. · Jun 2012
Disruption of cyclooxygenase-2 prevents downregulation of cortical AQP2 and AQP3 in response to bilateral ureteral obstruction in the mouse.
Bilateral ureteral obstruction (BUO) in rats is associated with increased cyclooxygenase type 2 (COX-2) expression, and selective COX-2 inhibition prevents downregulation of aquaporins (AQPs) in response to BUO. It was hypothesized that a murine model would display similar changes in renal COX-2 and AQPs upon BUO and that targeted disruption of COX-2 protects against BUO-induced suppression of collecting duct AQPs. COX-2(-/-) and wild-type littermates (C57BL/6) were employed to determine COX-1, -2, AQP2, and AQP3 protein abundances and localization after BUO. ⋯ In parallel, inhibition of COX-2 by parecoxib rescued C+OM AQP3 and IM AQP2 protein level in wild-type mice subjected to BUO. In summary, 1) In C57BL/6 mice, ureteral obstruction increases renal COX-2 expression in interstitial cells and lowers AQP2/-3 abundance and 2) inhibition of COX-2 activity by targeted disruption or pharmacological blockade attenuates obstruction-induced AQP downregulation. In conclusion, COX-2-derived prostaglandins contribute to downregulation of transcellular water transporters in the collecting duct and likely to postobstruction diureses in the mouse.
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Am. J. Physiol. Renal Physiol. · Jun 2012
In mpkCCD cells, long-term regulation of aquaporin-2 by vasopressin occurs independent of protein kinase A and CREB but may involve Epac.
Urine concentration involves the hormone vasopressin (AVP), which stimulates cAMP production in renal principal cells, resulting in translocation and transcription of aquaporin-2 (AQP2) water channels, greatly increasing the water permeability, leading to a concentrated urine. As cAMP levels decrease shortly after AVP addition, whereas AQP2 levels still increase and are maintained for days, we investigated in the present study the mechanism responsible for the AQP2 increase after long-term 1-desamino-8-d-arginine vasopressin (dDAVP) application using mouse collecting duct (mpkCCD) cells. While 30 min of dDAVP incubation strongly increased cAMP, cAMP was lower with 1 day and was even further reduced with 4 days of dDAVP, although still significantly higher than in control cells. ⋯ Incubation with a specific Epac activator after dDAVP pretreatment increased both AQP2 abundance and transcription compared with cells left unstimulated the last day. In conclusion, the PKA-CRE pathway is involved in the initial rise in AQP2 levels after dDAVP stimulation but not in the long-term effect of dDAVP. Instead, long-term regulation of AQP2 may involve the activation of Epac.
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Am. J. Physiol. Renal Physiol. · May 2012
Angiotensin AT1 receptor-associated protein Arap1 in the kidney vasculature is suppressed by angiotensin II.
Arap1 is a protein that interacts with angiotensin II type 1 (AT(1)) receptors and facilitates increased AT(1) receptor surface expression in vitro. In the present study, we assessed the tissue localization and regulation of Arap1 in vivo. Arap1 was found in various mouse organs, with the highest expression in the heart, kidney, aorta, and adrenal gland. ⋯ Similar to in vivo, Arap1 mRNA and protein were suppressed by angiotensin II in a time- and dose-dependent manner in cultured mesangial cells. In summary, Arap1 is highly expressed in the renal vasculature, and its expression is suppressed by angiotensin II. Thus Arap1 may serve as a local modulator of vascular AT(1) receptor function in vivo.
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Am. J. Physiol. Renal Physiol. · May 2012
Cytokine elevation and transaminitis after laparoscopic donor nephrectomy.
Acute kidney injury frequently occurs in the critically ill and often progresses into multiorgan dysfunction syndrome, resulting in high mortality. We previously showed that nephrectomized mice had increased interleukin (IL)-6 and tumor necrosis factor (TNF)-α that directly contributed to systemic inflammation and hepatic injury. In this study, we examined whether patients undergoing laparoscopic donor nephrectomy have increased postoperative cytokine levels with injury to the liver and whether the remaining kidney sustains injury. ⋯ Finally, the donor nephrectomy group showed increased urinary NGAL but not KIM-1 at 24 h. Taken together, our findings of increased serum IL-6, MCP-1, and AST after donor nephrectomy suggest that an acute reduction of kidney function induces systemic inflammation and may have distant effects on the liver. Further studies are needed to correlate increased urinary NGAL after donor nephrectomy both as a potential marker for renal tubular stress and/or hypertrophy in the contralateral kidney.
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Am. J. Physiol. Renal Physiol. · Apr 2012
Inducible kidney-specific Sgk1 knockout mice show a salt-losing phenotype.
The expression of the serum- and glucocorticoid-regulated kinase 1 (Sgk1) is induced by mineralocorticoids and, in turn, upregulates the renal epithelial Na(+) channel (ENaC). Total inactivation of Sgk1 has been associated with transient urinary Na(+) wasting with a low-Na(+) diet, while the aldosterone-mediated ENaC channel activation was unchanged in the collecting duct. Since Sgk1 is ubiquitously expressed, we aimed to study the role of renal Sgk1 and generated an inducible kidney-specific knockout (KO) mouse. ⋯ On a low-Na(+) diet, the Sgk1 KO mice were also hyperkaliuric and lost body weight. This phenotype was accompanied by a decrease in systolic and diastolic blood pressure. At the protein level, we observed a reduction in phosphorylation of the ubiquitin protein-ligase Nedd4-2 and a decrease in the expression of the Na(+)-Cl(-)-cotransporter (NCC) and to a lesser extent of ENaC.