Nickel and extracellular acidification inhibit the water permeability of human aquaporin-3 in lung epithelial cells.
(49/184)
Nickel is a common cause of pneumoconiosis. Here, we show that nickel inactivates aquaporin (AQP)-3, the water channel expressed apically in epithelial cells of human terminal airways. Human AQP3 was transiently transfected into human lung cells, and water permeability was measured in transfected and neighboring untransfected cells. Incubation with NiCl2 rapidly, dose-dependently, and reversibly decreased water permeability in AQP3-expressing cells. Acidification of the extracellular medium also caused rapid, dose-dependent, and reversible inhibition of AQP3. Sensitivity of AQP3 to nickel was lower at alkaline pH than at neutral and acidic pH. Cells transfected with human AQP4 and AQP5, which are also expressed in airway epithelia, were insensitive to nickel and extracellular acidification. Zinc and cadmium, other common causes of pneumoconiosis, had no effect on the water permeability of AQP3. Three extracellular residues, Trp128, Ser152, and His241, were responsible for the blocking effect of nickel on human AQP3. Ser152 was identified as a common site for nickel and pH sensitivity. His53, Tyr124, and His154 were also involved in regulation of AQP3 by extracellular pH. In addition, the aromatic side chain of His154 was shown to be important for the water permeability of AQP3. Our results imply that nickel and extracellular pH may modulate lung water clearance and that defective water clearance may be an early component of nickel-induced lung disease. (+info)
Increased renal ENaC subunit and sodium transporter abundances in streptozotocin-induced type 1 diabetes.
(50/184)
Uncontrolled diabetes mellitus (DM) is associated with copious water and sodium losses. We hypothesized that the kidney compensates for these losses by increasing the abundances of key sodium and water transporters and channels. Using targeted proteomic analysis via immunoblotting of kidney homogenates, we examined comprehensive regulation of transport proteins. In three studies, streptozotocin (STZ; 65 mg/kg) or vehicle was administered intraperitoneally to male Sprague-Dawley rats. In study 2, to control for potential renal toxicity of STZ, one group of STZ-treated rats was intensively treated with insulin to control diabetes. In another group, the reversibility of DM and related changes was assessed by treating animals with insulin for the final 4 days. In study 3, we correlated blood glucose to transporter changes by treating animals with different doses of insulin. In study 1, STZ treatment resulted in significantly increased band densities for the type 3 sodium/hydrogen exchanger (NHE3), the thiazide-sensitive Na-Cl cotransporter (NCC), and epithelial sodium channel (ENaC) subunits alpha, beta, and gamma (85- and 70-kDa bands) to 204, 125, 176, 132, 147, and 241% of vehicle mean, respectively. In study 2, aquaporin-2 (AQP2) and AQP3 were increased with DM, but not AQP1 or AQP4. Neither these changes, nor blood glucose itself, could be returned to normal by short-term intensive insulin treatment. Whole kidney abundance of AQP3, the bumetanide-sensitive Na-K-2Cl cotransporter (NKCC2), and gamma-ENaC (85-kDa band) correlated most strongly with blood glucose in study 3. These comprehensive changes would be expected to decrease volume contraction accompanying large-solute and water losses associated with DM. (+info)
Aquaporin expression in normal human kidney and in renal disease.
(51/184)
Aquaporins (AQPs), membrane-inserted water channel proteins, play a highly important role in the reabsorption of water from the renal tubular fluid. Experimentally, both in rats and mice, failure to insert functional AQP molecules into renal tubular membranes leads to nephrogenic diabetes insipidus. In humans, most forms of renal disease lead to a reduction in the water handling capacity of the kidney. AQP distribution in various forms of human renal disease has not been documented. Immunohistochemical studies of biopsy samples from a wide range of renal diseases revealed a substantial and striking upregulation of AQP-1 in the glomeruli of most diseased kidneys. AQP-1 expression remained prominent in proximal tubules in all lesions. In contrast, there was judged qualitatively to be a reduction in the amounts of AQP-2 and AQP-3 expression, especially in lesions with substantial interstitial fibrosis and nephron loss, as compared with a healthy region of normal kidneys. The results were quantitatively confirmed by real-time reverse transcriptase-PCR. This is the first documentation of altered AQP expression in human renal disease. The significance of the increased AQP-1 expression requires further studies. (+info)
Rosiglitazone activates renal sodium- and water-reabsorptive pathways and lowers blood pressure in normal rats.
(52/184)
Synthetic agonists of the peroxisomal proliferator-activated receptor subtype gamma (PPAR-gamma) are highly beneficial in the treatment of type II diabetes. However, they are also associated with fluid retention and edema, potentially serious side effects of unknown origin. These studies were designed to test the hypothesis that rosiglitazone (RGZ, PPAR-gamma agonist) may activate sodium- and water-reabsorptive processes in the kidney, possibly in response to a drop in mean arterial blood pressure (MAP), as well as directly through PPAR-gamma. Targeted proteomics of the major renal sodium and water transporters and channel proteins was used to identify potentially regulated sites of renal sodium and water reabsorption. RGZ (47 or 94 mg/kg diet) was fed to male, Sprague-Dawley rats (approximately 270g) for 3 days. MAP, measured by radiotelemetry, was decreased significantly in rats fed either level of RGZ, relative to control rats. Delta MAP from baseline was -3.2 +/- 1.2 mm Hg in rats fed high-dose RGZ versus + 3.4 +/- 0.8 for rats fed control diet. RGZ did not affect feed or water intake, but rats treated with high-dose RGZ had decreased urine volume (by 22%), sodium excretion (44%), kidney weight (9%), and creatinine clearance (35%). RGZ increased whole kidney protein abundance of the alpha-1 subunit of Na-K-ATPase, the bumetanide-sensitive Na-K-2Cl cotransporter (NKCC2), the sodium hydrogen exchanger (NHE3), the aquaporins 2 and 3, and endothelial nitric-oxide synthase. We conclude that both increases in renal tubule transporter abundance and a decrease in glomerular filtration rate likely contribute to the RGZ-induced sodium retention. (+info)
Reduced renal expression of AQP2, p-AQP2 and AQP3 in haemorrhagic shock-induced acute renal failure.
(53/184)
BACKGROUND: The aims of this study were to investigate the changes in the expression levels of renal aquaporins (AQPs) in response to haemorrhagic shock (HS) in rats and whether a change in the expression of AQPs was associated with parallel changes in urinary concentration. METHODS: HS was induced by withdrawal of blood through the femoral artery in rats. A mean arterial blood pressure (MAP) of 40 mmHg was maintained for 1 h before blood was reinfused, and rats were kept in metabolic cages for urine measurements. Two days after HS, we examined the abundance of AQPs in kidney by semiquantitative immunoblotting. RESULTS: HS rats (n = 13) developed acute renal insufficiency (creatinine clearance was 5.5 +/- 0.4 vs 6.9 +/- 0.3 ml/min/kg in sham-operated rats, n = 13, P < 0.05) and decreased urine osmolality (888 +/- 88 vs 1799 +/- 110 mosmol/kg H(2)O, P < 0.05). Consistent with this, semiquantitative immunoblotting revealed that the abundance of AQP2, phosphorylated (Ser256) AQP2 (p-AQP2) and AQP3 in whole kidney was significantly decreased after 2 days to 33 +/- 4, 41 +/- 9 and 35 +/- 14% of sham levels, respectively (P < 0.05). Also, the abundance of AQP2, p-AQP2 and AQP3 in inner medulla was markedly decreased to 36 +/- 8, 39 +/- 10 and 34 +/- 16% of sham levels (P < 0.05). In contrast, the abundance of AQP1 was not significantly changed compared with sham levels. CONCLUSIONS: The expression of the collecting duct water channel AQP2, p-AQP2 and AQP3 was significantly downregulated after HS, which may play an important role in the impaired urinary concentrating ability in HS-induced acute renal failure. (+info)
Aquaporin 3 colocates with phospholipase d2 in caveolin-rich membrane microdomains and is downregulated upon keratinocyte differentiation.
(54/184)
Aquaporin 3 is a channel that transports both water and glycerol. Aquaporin 3-deficient mice exhibit skin defects, including decreased glycerol content and impairment of water holding capacity, barrier recovery, and wound healing. Whether aquaporin 3 and its glycerol transporting capacity are involved in regulating keratinocyte function, we have previously shown that phospholipase D2 can metabolize phospholipids in the presence of glycerol to yield phosphatidylglycerol. We hypothesized that aquaporin 3 is involved in the regulation of keratinocyte function by a mechanism involving the interaction between aquaporin 3 and phospholipase D. Using sucrose gradient centrifugation, immunoprecipitation analysis, and confocal microscopy, we found that aquaporin 3 and phospholipase D2 colocalized in caveolin-rich membrane microdomains. In addition, aquaporin 3 expression was downregulated at the transcriptional level and glycerol uptake was reduced upon primary mouse keratinocytes to differentiation in response to an elevated extracellular calcium concentration or 1,25-dihydroxyvitamin D3. Our results suggest that aquaporin 3 and phospholipase D2 form a signaling module in lipid rafts, where aquaporin 3 transports glycerol to phospholipase D2 for the synthesis of phosphatidylglycerol. Phosphatidylglycerol, as a bioactive lipid, could potentially mediate the effects of the aquaporin 3-phospholipase D2 signaling module, with aquaporin 3 as a modulatory unit, in the regulation of keratinocyte function. (+info)
Upregulation of urea transporter UT-A2 and water channels AQP2 and AQP3 in mice lacking urea transporter UT-B.
(55/184)
The UT-B urea transporter is the major urea transporter in red blood cells and kidney descending vasa recta. Humans and mice that lack UT-B have a mild urine-concentrating defect. Whether deletion of UT-B altered the expression of other transporter proteins involved in urinary concentration was tested. Fluorescence-based real-time reverse transcription-PCR and Northern blot analysis showed upregulation of the UT-A2 urea transporter and the aquaporin 2 (AQP2) and AQP3 water channel transcripts but no change in other urea transporters or AQP. Western blot analysis showed that UT-A2 protein abundance in the outer medulla of UT-B null mice increased to 122 +/- 6% of wild-type control. AQP2 protein abundance increased to 177 +/- 32% and 127 +/- 7% in the outer and inner medulla, respectively, of UT-B null versus wild-type mice. The abundance of UT-A1, AQP1, renal outer medullary potassium channel, and NKCC2/BSC1 proteins were not significantly different between UT-B null and wild-type mice. The increases in AQP2 and AQP3 would reduce water loss and improve concentrating ability. The lack of UT-B does not result in a change in expression of urea transporters involved in urea reabsorption from the inner medullary collecting duct (UT-A1 and UT-A3). However, UT-B null mice have a selective increase in UT-A2 protein abundance. This may be an adaptive response to the loss of UT-B, because UT-B and UT-A2 are involved in different intrarenal urea recycling pathways. (+info)
Characterization of the sensitizing potential of chemicals by in vitro analysis of dendritic cell activation and skin penetration.
(56/184)
Development of in vitro models to identify sensitizing chemicals receives public interest since animal testing should be avoided whenever possible. In this article we analyze two essential properties of sensitizing chemicals: skin penetration and dendritic cell (DC) activation. Activation of immature DC derived from peripheral blood monocytes was evaluated by flow cytometric analysis of CD86 positive cells and quantitative measurement of interleukin-1beta and aquaporin P3 gene expression. The sensitizer 2,4,6-trinitrobenzenesulfonic acid induced a concentration-dependent response for all parameters, whereas the irritant sodium lauryl sulfate did not. When two related aromatic amines, p-toluylenediamine (PTD) and hydroxyethyl-p-phenylenediamine (HE-PPD) were tested, both induced substantial DC activation indicating their potential sensitizing properties. These findings contrasted with in vivo results: in murine local lymph node assays (LLNA) PTD, but not HE-PPD, was sensitizing using acetone/aqua/olive oil as vehicle. Skin penetration measurement revealed that this was due to bioavailability differences. On retesting HE-PPD in the LLNA using the penetration enhancer dimethylsulfoxide as vehicle, it induced a specific response. We conclude that in vitro analysis of DC activation capability of the two selected chemicals demonstrates that prediction of skin sensitization potential is possible provided that skin penetration data indicate sufficient bioavailability of the test compound. (+info)