Aquaporin-2 (AQP2) Antibody Review

 

 

 

Introduction

  • Aquaporins (AQPs) are membrane proteins serving in the transfer of water and small solutes across cellular membranes. At least 7 isoforms, namely AQP1, AQP2, AQP3, AQP4, AQP6, AQP7 and AQP11 are expressed in the kidney. Among them, AQP2 plays a pivotal role in the concentration of urine. AQP2 is expressed in the principal cells of the collecting ducts. It is localized in the intracellular compartment and is translocated to the cell surface upon anti-diuretic hormone stimulation. PMID: 17543219

  • an aquaporin water channel protein present at the apical membrane of kidney collecting duct cells and plays a key role in urine concentrating ability. PMID: 17565277

  • plays a key role in AVP-induced absorption of water, and its urinary excretion is related to its function. PMID: 17654319

  • plays an important, VP (vasopressin)-regulated role in water reabsorption by the kidney. PMID: 16563128, PMID: 16104839

  • the main target for antidiuretic action of arginine vasopressin (AVP), and the urinary excretion of this protein is believed to be an index of AVP signaling activity in the kidney. PMID: 16382324

  • Water channel aquaporin-2 (AQP2) strictly regulates body water homeostasis in mammals. PMID: 15336526

  • one of the water-channel proteins expressed in principal cells of kidney collecting ducts, where it is stored in the intracellular compartment. PMID: 15155571

  • translocated from intracellular vesicles to the apical membrane of collecting duct cells after vasopressin stimulation. PMID: 14561591

  • a water-channel protein, is known to increase water permeability due to vasopressin binding to V2 receptors at the renal collecting duct and is excreted into the urine. PMID: 12669273

  • a vasopressin regulated member of the aquaporin gene family. PMID: 12208541

  • AQP2 is a constitutive apical membrane protein in the vas deferens, and that it is not vasopressin-regulated in this tissue. PMID: 10751327

  • regulated by vasopressin by both short- and long-term mechanisms. PMID: 9822111

  • a vasopressin-regulated water channel in the kidney collecting duct, is selectively permeable to water molecule and is translocated between the apical membrane and subapical endosomes in response to vasopressin. PMID: 8617798

Normal Expression

  • Aquaporin-2 (AQP-2) proteins are mainly expressed at the apical region of the collecting duct cells. PMID: 16221200

  • We identified an aquaporin-2 (AQP2) homologue in apical/subapical regions of cortical and medullary collecting duct (CD) cells in kidneys of Japanese quail (q), Coturnix japonica. PMID: 17699563

  • Immunostaining of AQP2 is present in the luminal and glandular epithelium but not in the stroma. Some vessels stained positive for AQP2. When present, pinopodes stained positive, which was confirmed using confocal microscopy. A significant increase in staining intensity was seen in the glandular and luminal epithelium during the mid and late luteal phases of the cycle. The presence of AQP2 in human endometrium was also confirmed by RT-PCR. PMID: 16979638

  • Aquaporin-2 (AQP2) is one of the membrane water channel proteins expressed in principal cells of the kidney collecting ducts. In the basal state, AQP2 resides in the storage vesicles localized in the subapical cytoplasm. Upon stimulation with vasopressin, AQP2 is translocated to the apical plasma membrane by the exocytic fusion of the storage vesicles with the apical membrane. This translocation enables the transepithelial reabsorption of water from the lumen to the interstitium via AQP2 at the apical membrane and AQP3/AQP4 at the basolateral membrane. PMID: 15557733

  • Both AQP-2 mRNA and protein were detected in the epithelium of the endolymphatic sac. AQP-2 immunostaining was mainly cytoplasmic, suggesting that most AQP-2 was located in intracellular pools. PMID: 15224873

  • AQP2 is concentrated in clathrin-coated pits on the apical surface of collecting duct principal cells. PMID: 11997316

  • AQP-2 is expressed in apical membranes of rat distal colon epithelium, where it might be involved in a water-sparing mechanism. PMID: 11518698

  • we report that both AQP-2 and -3 are expressed during fetal life as early as embryonic d 18 in ureteric buds of rat kidneys, where each is localized to the apical and basolateral membranes of epithelial cells, respectively. PMID: 9621988

  • Aquaporin-2 is a vasopressin-regulated water channel located in the apical membrane, and aquaporin-3 is a constitutive water channel located in the basolateral membrane in the kidney collecting duct. PMID: 9558461

  • On immunoblots, the urine samples from healthy volunteers revealed clear aquaporin-1 and aquaporin-2 signals in antidiuretic but not diuretic states. PMID: 8793791

Abnormal Expression

  • The high expression of AQP-2 protein in nasal polyps may contribute to the genesis and development of nasal polyps. PMID: 14743636

  • AQP2 excretion, quantitated by immunoblotting, was eight times higher in cirrhosis patients than in controls. PMID: 12865281

  • The excretion of AQP-2 in urine is abnormal both in liver cirrhosis in which we find less suppression of u-AQP2 by an acute water load and in CHF in which we find a high baseline level and an exaggerated suppression of u-AQP2 by an acute water load. PMID: 12631357

  • After intraperitoneal administration of oxytocin (10 U), immunohistochemistry of IMCD revealed that AQP2 was shifted from diffuse cytoplasmic localization in controls to the apical and basolateral membrane domains in oxytocin-treated rats. PMID: 12411748

  • decreased urinary excretion of AQP-2 in diabetic nephropathy is due to the impaired cellular signaling of AVP in collecting duct cells, which may be partly involved in the urinary concentrating defect in renal failure. PMID: 12218327

Function

  • AQP2 can contribute to the urinary concentrating ability early in postnatal life. PMID: 16902321

  • In the kidney aquaporin-2 (AQP2) provides a target for hormonal regulation of water transport by vasopressin. PMID: 16150901

  • AVP and the AQP2 are involved in the pathogenesis of hypertension in spontaneously hypertensive rats (SHR). PMID: 15607625

  • regulation of AQP2 can attenuate cold-induced osmotic damage in rat kidney IMCD cells. PMID: 15311966

  • plays a pivotal role in the renal water regulation. PMID: 9486978

Diagnostic & Therapeutic Value

  • urinary excretion of AQP-2 is a potent marker for the diagnosis of water metabolism disorders dependent on AVP. PMID: 10766399

  • measurement of UAQP-2 is of value to diagnose central diabetes insipidus (CDI) in the 5%-NaCl infusion test. PMID: 9177390

  • Aquaporin-2 is detectable in the urine, and changes in the urinary excretion of this protein can be used as an index of the action of vasopressin on the kidney. PMID: 7537863

Review Articles

  • Routing of the aquaporin-2 water channel in health and disease. PMID: 11001488

Applications

 

Dot Blot

  • Urinary excretion of AQP2 was measured by dot immunoblotting technique. Studies were performed in the acute phase of pyelonephritis, in the same children after treatment, and in control patients. PMID: 16382324

ELISA

  • Recently, we have established an enzyme-linked immunosorbent assay (ELISA) for quantitation of urinary AQP2. The purpose of our current study was to compare three different immunoassay methods for measurement of urinary AQP2. The results indicate that the newly developed IB and ELISA methods are useful for measurement of urinary AQP2 and have an excellent correlation. PMID: 12427158

  • Double antibody sandwich ELISA was successfully established to detect urine AQP2 in CHF rats, which is more efficient and simpler than Western blot analysis. PMID: 12297463

  • Using an improved version of a fluorescence-based enzyme-linked immunosorbent assay (Y. Maeda, B. L. Smith, P. Agre, and M. A. Knepper. J. Clin. Invest. 95: 422-428, 1995), we quantified AQP-2 protein abundance in microdissected renal collecting ducts from normal Sprague-Dawley (SD) rats and vasopressin-deficient Brattleboro rats. PMID: 8760244

Immunoblotting (IB)

  • Aquaporin-1 and aquaporin-2 excretion was analyzed by immunoblotting. Urinary aquaporin-2 excretion was reduced in patients with cirrhosis compared to healthy subjects. PMID: 17133493

  • Northern blot and immunoblot were used to quantify mRNA and proteins for aquaporin-2 (AQP2) as well as urea transporters UT-A1, UT-A2 and UT-B1, in subzones of the renal medulla of rats with streptozotocin-induced diabetes. PMID: 11380083

  • Immunoblotting of rat urine samples revealed significant excretion of AQP2, whereas AQP3, being a basolateral aquaporin in the same cells, was undetectable. PMID: 10405197

  • Immunoblotting and densitometry of membrane fractions revealed a significant decrease in AQP2 expression in kidney inner medulla of hypercalcemic rats to 45.7 +/- 6.8% (n = 11) of control levels (100 +/- 12%, n = 9). PMID: 9848772

  • Quantitative immunoblotting of total kidney membrane fractions revealed a significant increase in AQP2 expression in animals with CHF (267 +/- 53%, n = 12) relative to sham-operated controls (100 +/- 13%, n = 14). PMID: 9144258

  • Immunoblotting revealed that, compared with untreated controls, DDAVP treatment significantly increased the fraction of AQP2 protein associated with the plasma membrane fraction relative to intracellular vesicles. PMID: 7573395

Immunogold Electron Microscopy (IEM)

  • Immunogold electron microscopy and immunoblotting confirmed heavy AQP2 labeling of immunoisolated vesicles. PMID: 15905145

Immunofluorescence (IF)

  • Immunofluorescence revealed that AQP-2 was located on intracellular vesicles in nonstimulated cells but was relocated to the plasma membrane after vasopressin treatment, even in the presence of cycloheximide. PMID: 8780259

Immunohistochemistry (IHC)

  • Immunohistochemical studies revealed that AQP2 was localized in the collecting tubules/ducts of both species' renicules, as in terrestrial mammals. PMID: 17768629

  • Immunohistochemistry and Western blotting were utilized to detect the localization and expression of AQP2 in the endometrium. PMID: 16321251

  • Immunohistochemistry for aquaporin-1 and -2 was used in 11 explants, of which five had clinically and histologically confirmed CRAD. PMID: 15839941

  • Samples were immediately fixed in 10% formalin (24 h) and embedded in paraffin; in situ hybridization and immunohistochemistry were performed with an AQP-2-specific probe and a polyclonal antibody. PMID: 15224873

  • We immunohistochemically characterized the intracellular compartment harboring AQP2 in the rat kidney using antibodies to the endoplasmic reticulum, Golgi apparatus, trans-Golgi network, lysosome, and endosome. PMID: 12422412

  • A systematic immunohistochemical study of Aqp2 protein expression was performed on embryonic mouse inner ears ranging from embryonic day 10 (otocyst stage) to embryonic day 18 (just before birth). PMID: 11081612

  • We studied, by immunohistochemistry in the rabbit kidney cortex, the distributions of ENaC and AQP2, in conjunction with marker proteins for distal segments. PMID: 10751213

  • Immunohistochemistry revealed that AQP-2 was exclusively located in collecting duct principal cells both in infant and adult rats but that the signal was much weaker in infants. PMID: 8770180

Radioimmunoassay (RIA)

  • U-AQP2 and hormones were determined by radioimmunoassay. PMID: 16095054

  • This report describes the development of a radioimmunoassay for the measurement of U-AQP2 excretion in dogs. In addition, the localization of AQP2 in the canine kidney was investigated by immunohistochemistry. PMID: 15219933

  • To determine this, we measured urinary aquaporin-2 and vasopressin by radioimmunoassay in normonatremic or hyponatremic patients after cerebral infarction and in healthy controls. PMID: 12669273

  • Developed radioimmunoassay assay system suitable to measure AQP-2 in urine. PMID: 10196511

  • We measured urinary excretion of AQP-2 by radioimmunoassay in 15 term and 10 preterm infants on day 1 and day 4 of life to determine the molecular basis of water balance during the newborn period. AQP-2 was detectable in the urine of term and preterm newborns, but AQP-2 excretion was severalfold less than the reported level in normal adults. PMID: 9826210

  • We measured the urinary excretion of AQP-2 by radioimmunoassay in 14 term and 12 preterm infants aged 1 month. Excretion of AQP-2 was low compared with adults, and correlated significantly with urine osmolality in preterm infants. Our results demonstrate that AQP-2 water channels are expressed in the renal collecting duct of both term and preterm infants. PMID: 9570029

Western Blotting (WB)

  • Aquaporin-2 (AQP2) expression was measured by Western blot to evaluate water permeability in collecting ducts. PMID: 16675087

  • Western blot revealed a 29-kDa band that represented AQP2 in human endometrium. The expression of AQP2 in endometrium was confirmed by RT-PCR and immunohistochemical results. The immunohistochemical analysis demonstrated that AQP2 was prominent in luminal and glandular epithelial cells of endometrium. PMID: 16483614

  • Nine weeks after surgery, urinary AQP2 concentrations and renal AQP2 protein levels were measured by Western blot. The urinary concentration of AQP2 water channel protein increases significantly in chronic heart failure rats. PMID: 11780376

  • Detection of aquaporin-2 in the plasma membranes of oocytes: a novel isolation method with improved yield and purity. PMID: 11401515

  • AQP2 expression and trafficking were determined in the kidney by Western blot analysis and immunohistochemistry. PMID: 10760099

  • This study presents information about the development of an antibody to human AQP-2, and measures the urinary excretion of AQP-2 by quantitative Western analysis. PMID: 8704105