AQP1 Levels Research Articles

Reduced abundance of aquaporins in rats with bilateral ischemia-induced acute renal failure: prevention by alpha-MSH.

We examined the effect of temporary renal ischemia (30 min or 60 min) and reperfusion (1 day or 5 days) on the expression of renal aquaporins (AQPs) and urinary concentration in rats with bilateral ischemia-induced acute renal failure (ARF). Next, we tested whether reducing ischemia/reperfusion (I/R) injury by treatment with alpha-melanocyte stimulating hormone (alpha-MSH) affects the expression of AQPs and urine output. Rats with ARF showed significant renal insufficiency, and urinary concentration was markedly impaired. In rats with mild ischemic injury (30 min), urine output increased significantly to a maximum at 48 h, and then nearly normalized within 5 days. Consistent with this, semiquantitative immunoblotting revealed that kidney AQP1 and AQP2 abundance was significantly decreased after 24 h to 30 +/- 5% and 40 +/- 11% (n = 8) of controls (n = 9), respectively (P < 0.05). Five days after ischemia, AQP2 abundance was not significantly decreased and urine output was normalized. In contrast, severe ischemic injury (60 min) resulted in a marked reduction in urine output at 24 h, despite a significant decrease in urine osmolality and solute-free water reabsorption, T(c)H(2)O. AQP1 and AQP2 abundance was markedly decreased to 51 +/- 5% and 31 +/- 9% (n = 10) of controls (n = 8) at 24 h (P < 0.05). After 5 days, the rats developed gradually severe polyuria and had very low AQP2 and AQP1 levels [11 +/- 4% and 6 +/- 2% (n = 5) of controls (n = 8), respectively; P < 0.05]. A similar reduction was observed for AQP3. The reduction in AQP expression in the proximal tubule and inner medullary collecting duct was confirmed by immunocytochemistry. Next, we found that intravenous alpha-MSH treatment of rats with ARF significantly reduced the ischemia-induced downregulation of renal AQPs and reduced the polyuria. In conclusion, the I/R injury is associated with markedly reduced expression of the collecting duct and proximal tubule AQPs, in association with an impairment of urinary concentration. Moreover, alpha-MSH treatment significantly prevented the reduction in expression of AQPs and renal functional defects. Thus decreased AQP expression is likely to contribute to the impairment in urinary concentration in the postischemic period.

Low aquaporin-2 levels in polyuric DI +/+ severe mice with constitutively high cAMP-phosphodiesterase activity.

In the renal collecting duct, vasopressin acutely activates cAMP production, resulting in trafficking of aquaporin-2 water channels (AQP2) to the apical plasma membrane, thereby increasing water permeability. This acute response is modulated by long-term changes in AQP2 expression. Recently, a cAMP-responsive element has been identified in the AQP2 gene, raising the possibility that changes in cAMP levels may control AQP2 expression. To investigate this possibility, we determined AQP2 protein levels in a strain of mice, DI +/+ severe (DI), which have genetically high levels of cAMP-phosphodiesterase activity, and hence low cellular cAMP levels, and severe polyuria. Semiquantitative immunoblotting of membrane fractions prepared from whole kidneys revealed that AQP2 levels in DI mice were only 26 +/- 7% (+/-SE) of those in control mice (n = 10, P < 0.01). In addition, semiquantitative Northern blotting revealed a significantly lower AQP2 mRNA expression in kidneys from DI mice compared with control mice (43 +/- 6% vs. 100 +/- 10%; n = 6 in each group, P < 0.05). AQP3 levels were also reduced. The mice were polyuric and urine osmolalities were accordingly substantially lower in the DI mice than in controls (496 +/- 53 vs. 1,696 +/- 105 mosmol/kgH2O, respectively). Moreover, there was a linear correlation between urine osmolalities and AQP2 levels (P < 0.05). Immunoelectron microscopy confirmed the markedly lower expression of AQP2 in collecting duct principal cells in kidneys of DI mice and, furthermore, demonstrated that AQP2 was almost completely absent from the apical plasma membrane. Thus expression of AQP2 and AQP2 trafficking were severely impaired in DI mice. These results are consistent with the view that in vivo regulation of AQP2 expression by vasopressin is mediated by cAMP.

Transcript levels of aquaporin 1 and carbonic anhydrase IV as predictive indicators for prognosis of renal cell carcinoma patients after nephrectomy.

Since failure of differentiation has been suggested to be involved in the neoplastic process and progression of tumors, we evaluated whether the transcript levels of differentiation markers of proximal renal tubular cells, from which renal cell carcinoma (RCC) arises, could be used as prognostic markers. We used Northern blot analysis to study the expression of aquaporin 1 (aqp1) and carbonic anhydrase IV (ca4) genes in 66 paired samples of primary RCC and non-tumorous kidney tissues. Poor differentiation of tumor cells and non-clear cell-subtype RCC were significantly associated with low levels of aqp1 transcripts. When patients were divided into 2 groups according to level of aqpI transcript in RCC, a low level of aqp1 was significantly associated with unfavorable outcome. Among 18 patients with metastatic RCC and 40 patients with moderately differentiated RCC, those with RCC expressing low levels of aqpl mRNA demonstrated poorer survival than those with RCC expressing relatively high levels of aqp1. Similarly, decreased expression of ca4 mRNA in RCC was associated with poor survival. On multivariate analysis, transcript levels of aqpI and stage of the tumor were the independent factors predicting disease-specific survival. Transcript levels of aqp1 may serve as a new molecular prognostic marker in patients with RCC following nephrectomy.

Water and Glycerol Permeabilities of Aquaporins 1–5 and MIP Determined Quantitatively by Expression of Epitope-tagged Constructs inXenopus Oocytes

The goal of this study was to compare single channel water and glycerol permeabilities of mammalian aquaporins (AQP) 1-5 and the major intrinsic protein of lens fiber (MIP). Each of the six cloned cDNAs from rat was left untagged or was epitope-tagged with c-Myc or FLAG at either the N or C terminus so that results would not depend on epitope identity or location. The constructs were expressed in Xenopus oocytes for measurement of osmotic water permeability (Pf), [3H]glycerol uptake, and protein expression. Each of the 30 epitope-tagged constructs was expressed strongly at the oocyte plasma membrane. The 10-min uptake of [3H]glycerol was increased significantly (range of 4.5-8-fold over control) in oocytes expressing untagged AQP3 (GLIP) and each of the four tagged AQP3 constructs; [3H]glycerol uptake was not increased in oocytes expressing AQP1, AQP2, AQP4, AQP5, or MIP. In oocytes microinjected with 5 ng of cRNA, average Pf values (in cm/s x 10(-3)) were 0.67 +/- 0.06 (control), 19 +/- 2 (AQP1), 10 +/- 1 (AQP2), 8 +/- 2 (AQP3), 29 +/- 1 (AQP4), 10 +/- 1 (AQP5), and 1.3 +/- 0.2 (MIP), and they were relatively insensitive to the presence, identity, or location of the epitope tag. Pf values were not affected by protein kinase A or C activation. After normalization for plasma membrane expression by immunoprecipitation of microdissected plasma membranes, single channel water permeabilities (pf, referenced to the AQP1 pf of 6 x 10(-14) cm3/s) were (in cm3/s x 10(-14)) 3.3 +/- 0.2 (AQP2), 2.1 +/- 0.3 (AQP3), 24 +/- 0.6 (AQP4), 5.0 +/- 0.4 (AQP5), and 0.25 +/- 0.05 (MIP); pf values were insensitive to epitope identity and location. These results indicate very different intrinsic water permeabilities for the mammalian aquaporin homologs, with the pf value for AQP4 remarkably higher than those for the others. The pf values establish limits on aquaporin tissue densities required for physiological function and suggest significant structural and functional differences among the aquaporins.

Expression of Aquaporins in the Rat Ocular Tissue

The aquaporins (AQPs) are a rapid growing family of water channel proteins found in animals, plants and microorganisms that raise plasma membrane water permeability required for efficient isosmotic fluid transport. Five homologs of aquaporins (AQP1, AQP2, AQP3, AQP4 and AQP5) have been identified from various mammalian tissues; the expression of these aquaporins in ocular tissues was studied. Semiquantitative expression levels of these aquaporins were determined in ciliary body, cornea, lens, retina, iris and choroid using RT-PCR. Expression levels of AQP1 are highest among the known aquaporins in each rat ocular tissue examined. In cornea, AQP1 is expressed approximately three-fold higher than AQP3 and 2.5 fold higher than AQP5. However, the highest intraocular expressions of AQP3 and AQP5 are in the cornea. In the iris, expression levels of AQP1 are approximately 600–700 fold higher than AQP4 and AQP5. In the ciliary body, the expression levels of AQP1 are approximately ten-fold higher than AQP4, the only other aquaporin expressed. In the lens, the major water channel is AQP1 with detectable levels of AQP4 and AQP5 that are approximately 1000-fold lower than AQP1. In choroid, AQP1 is the only water channel expressed. In retina, AQP1 is expressed approximately six-fold higher than AQP4, the only other aquaporin expressed. However, the highest ocular expression of AQP4 is in retina. AQP2 is not detected in the eye. Finally, the possible physiological roles of aquaporins in maintaining and regulating the aqueous flow, and corneal and lens transparency are discussed.

Plants used in traditional medicine in lower Zambesia

Ziziphora clinopodioides has been frequently used as an anti asthmatic plant in traditional medication. Recent work explores the anti-asthmatic activity of Z. clinopodioides in allergen-induced asthmatic mice. Intraperitoneal sensitization followed by intranasal challenge were given with ovalbumin (allergen) to develop allergic asthma. Investigational groups of animals were administered with drug methylprednisolone (MP) (15 mg/kg body weight), n-hexane fraction, ethylacetate fraction, and methanolic extract of Z. clinopodioides extract (500 mg/kg b.w.) for successive 07 days. Hematoxyline and eosin (H&E) and periodic acid-Schiff (PAS) stains were used to evaluate histopathological parameters on lung tissues. As an index of lungs tissues edema, wet/dry weight ratio of lungs was determined. Evaluation of expression levels of AQP1, AQP5, IL4, and IL5 was conducted by using RT-PCR. The data exhibited that both Z. clinopodioides and MP attenuated differential and total leukocyte counts in hematological examination i.e. in BALF and blood. Treatment with Z. clinopodioides also caused suppression of inflammatory cell infiltration and expression levels of IL4 and IL5, the later could have caused attenuation of pulmonary inflammation. The study also found decline in lung wet/dry ratio and goblet cellh hyperplasia in treated groups which indicates amelioration of lung edema. Treatment with Z. clinopodioides significantly increased the expression levels of aquaporin-1 and -5, which could have led to reduction in lung edema. The treatment with MP showed comparable results to Z. clinopodioides. Current investigation revealed that Z. clinopodioides possessed anti-asthmatic property which might be accredited to upregulagted AQP1 and AQP5 levels and downregulated IL4 and IL5 levels.