AQP1 expression analysis in human diseases: implications for proteomic characterization

Water channel protein AQP1 in cytoplasm is a critical factor in breast cancer local invasion

BACKGROUND

Metastasis of breast cancer grows from the local invasion to the distant colonization. Blocking the local invasion step would be promising for breast cancer treatment. Our present study demonstrated AQP1 was a crucial target in breast cancer local invasion.

METHODS

Mass spectrometry combined with bioinformatics analysis was used to identify AQP1 associated proteins ANXA2 and Rab1b. Co-immunoprecipitation, immunofluorescence assays and cell functional experiments were carried out to define the relationship among AQP1, ANXA2 and Rab1b and their re-localization in breast cancer cells. The Cox proportional hazards regression model was performed toward the identification of relevant prognostic factors. Survival curves were plotted by the Kaplan-Meier method and compared by the log-rank test.

RESULTS

Here, we show that the cytoplasmic water channel protein AQP1, a crucial target in breast cancer local invasion, recruited ANXA2 from the cellular membrane to the Golgi apparatus, promoted Golgi apparatus extension, and induced breast cancer cell migration and invasion. In addition, cytoplasmic AQP1 recruited cytosolic free Rab1b to the Golgi apparatus to form a ternary complex containing AQP1, ANXA2, and Rab1b, which induced cellular secretion of the pro-metastatic proteins ICAM1 and CTSS. Cellular secretion of ICAM1 and CTSS led to the migration and invasion of breast cancer cells. Both in vivo assay and clinical analysis data confirmed above results.

CONCLUSIONS

Our findings suggested a novel mechanism for AQP1-induced breast cancer local invasion. Therefore, targeting AQP1 offers promises in breast cancer treatment.

Changes in aquaporins expression due to acute water restriction in naturally aging mice

Aquaporins (AQPs) are water channels in the cell membrane that regulate osmosis in response to rapid changes in intracellular and extracellular fluid concentration caused by extrinsic factors. While there are so many studies on the association of AQPs with muscular atrophy, sarcopenia, and Duchenne muscular dystrophy (DMD), the expression of AQP has not been verified in naturally aging mice or humans. Notably, due to the characteristics of AQPs, the difference in function cannot be evaluated without extrinsic factors such as acute water restriction. The purpose of this study was to investigate the changes in AQPs expression and function due to natural aging under acute water restriction conditions in aging mice. The expression of AQP4 was shown to decrease with aging similar to previous studies. However, for the first time, this study results confirmed that AQP1 expression increased in aging mice. In addition, the expression of Aqp1 decreased in the acute water restricted group compared to the control group after acute water restriction in aging mice. These results suggest that although the expression of AQP1 increases with aging, its function is reduced. We also confirmed that overexpression of Aqp1 can inhibit myotube differentiation and that knockdown can promote myotube differentiation through in vitro experiments. In conclusion, based on our results, we suggest that the AQP1 is an important factor in sarcopenia caused by natural aging accompanied by chronic dehydration.

Aquaporins in Nervous System

Aquaporins (AQPs) mediate water flux between the four distinct water compartments in the central nervous system (CNS). In the present chapter, we mainly focus on the expression and function of the nine AQPs expressed in the CNS, which include five members of aquaporin subfamily: AQP1, AQP4, AQP5, AQP6, and AQP8; three members of aquaglyceroporin subfamily: AQP3, AQP7, and AQP9; and one member of superaquaporin subfamily: AQP11. In addition, AQP1, AQP2, and AQP4 expressed in the peripheral nervous system are also reviewed. AQP4, the predominant water channel in the CNS, is involved both in the astrocyte swelling of cytotoxic edema and the resolution of vasogenic edema and is of pivotal importance in the pathology of brain disorders such as neuromyelitis optica, brain tumors, and neurodegenerative disorders. Moreover, AQP4 has been demonstrated as a functional regulator of recently discovered glymphatic system that is a main contributor to clearance of toxic macromolecule from the brain. Other AQPs are also involved in a variety of important physiological and pathological process in the brain. It has been suggested that AQPs could represent an important target in treatment of brain disorders like cerebral edema. Future investigations are necessary to elucidate the pathological significance of AQPs in the CNS.

The Effects of Ginsenosides and Anserine on the Up-Regulation of Renal Aquaporins 1–4 in Hyperuricemic Mice

Hyperuricemia is a metabolic disease of the kidney that results in decreased uric acid excretion. Here, we aimed to investigate the effects of ginsenosides and anserine on hyperuricemia and the expression of aquaporin (AQP) 1–4, which are indicators of renal excretion. Ginsenosides and anserine were administered separately or together after the establishment of hyperuricemia with adenine in BALB/c mice. Renal function indexes such as serum uric acid, creatinine, and urea nitrogen were measured in each group of mice, and the expression of AQP1–4 in renal tissues was detected. Serum uric acid and urea nitrogen were decreased in the ginsenoside and the anserine +UA groups. Meanwhile, the uric acid excretion and clearance rate were clearly increased in the co-treatment +UA group ([Formula: see text].05). Moreover, ginsenosides or anserine ginsenosides or anserine alone and treatment with both increased the expression of AQP1–4; however, the synergistic effects were more significantly enhanced ([Formula: see text].01). We provide the first reported evidence that ginsenosides and anserine have synergistic effects on uric acid excretion. The improvement in renal function in hyperuricemic mice after treatment with ginsenosides and anserine may result from up-regulation of AQP1–4 expressions.

Sexual Dimorphic Pattern of Renal Transporters and Electrolyte Homeostasis

Compared with males, females have lower BP before age 60, blunted hypertensive response to angiotensin II, and a leftward shift in pressure natriuresis. This study tested the concept that this female advantage associates with a distinct sexual dimorphic pattern of transporters along the nephron. We applied quantitative immunoblotting to generate profiles of transporters, channels, claudins, and selected regulators in both sexes and assessed the physiologic consequences of the differences. In rats, females excreted a saline load more rapidly than males did. Compared with the proximal tubule of males, the proximal tubule of females had greater phosphorylation of Na+/H+ exchanger isoform 3 (NHE3), distribution of NHE3 at the base of the microvilli, and less abundant expression of Na+/Pi cotransporter 2, claudin-2, and aquaporin 1. These changes associated with less bicarbonate reabsorption and higher lithium clearance in females. The distal nephrons of females had a higher abundance of total and phosphorylated Na+/Cl- cotransporter (NCC), claudin-7, and cleaved forms of epithelial Na+ channel (ENaC) α and γ subunits, which associated with a lower baseline plasma K+ concentration. A K+-rich meal increased the urinary K+ concentration and decreased the level of renal phosphorylated NCC in females. Notably, we observed similar abundance profiles in female versus male C57BL/6 mice. These results define sexual dimorphic phenotypes along the nephron and suggest that lower proximal reabsorption in female rats expedites excretion of a saline load and enhances NCC and ENaC abundance and activation, which may facilitate K+ secretion and set plasma K+ at a lower level.

Reduced expression of aquaporins in human intestinal mucosa in early stage inflammatory bowel disease

Objectives

The aim of this study was to investigate the relationship between aquaporin (AQP) water channel expression and the pathological features of early untreated inflammatory bowel disease (IBD) in humans.

Methods

Patients suspected to have IBD on the basis of predefined symptoms, including abdominal pain, diarrhea, and/or blood in stool for more than 10 days, were examined at the local hospital. Colonoscopy with biopsies was performed and blood samples were taken. Patients who did not meet the diagnostic criteria for IBD and who displayed no evidence of infection or other pathology in the gut were included as symptomatic non-IBD controls. AQP1, 3, 4, 5, 7, 8, and 9 messenger RNA (mRNA) levels were quantified in biopsies from the distal ileum and colon by quantitative real-time polymerase chain reaction. Protein expression of selected AQPs was assessed by confocal microscopy. Through multiple alignments of the deduced amino acid sequences, the putative three-dimensional structures of AQP1, 3, 7, and 8 were modeled.

Results

AQP1, 3, 7, and 8 mRNAs were detected in all parts of the intestinal mucosa. Notably, AQP1 and AQP3 mRNA levels were reduced in the ileum of patients with Crohn’s disease, and AQP7 and AQP8 mRNA levels were reduced in the ileum and the colon of patients with ulcerative colitis. Immunofluorescence confocal microscopy showed localization of AQP3, 7, and 8 at the mucosal epithelium, whereas the expression of AQP1 was mainly confined to the endothelial cells and erythrocytes. The reduction in the level of AQP3, 7, and 8 mRNA was confirmed by immunofluorescence, which also indicated a reduction of apical immunolabeling for AQP8 in the colonic surface epithelium and crypts of the IBD samples. This could indicate loss of epithelial polarity in IBD, leading to disrupted barrier function.

Conclusion

AQPs 1 and 8 and the aquaglyceroporins AQPs 3 and 7 are the AQPs predominantly expressed in the lower intestinal tract of humans. Their expression is significantly reduced in patients with IBD, and they are differentially expressed in specific bowel segments in patients with Crohn’s disease and ulcerative colitis. The data present a link between gut inflammation and water/solute homeostasis, suggesting that AQPs may play a significant role in IBD pathophysiology.

Ontogeny of the mammalian kidney: expression of aquaporins 1, 2, 3, and 4

BACKGROUND

Determining the expression and functions of aquaporins (AQPs) in the adult kidney has generated important information about the roles of this protein family in the renal regulation of water homeostasis. However, limited information describes the expression of AQPs in fetal kidneys, and most reports on fetal renal AQPs originate from animal studies. Although there are the maturation and regulation of the renal-concentrating mechanism, the ways in which changes in the expression of AQPs contribute to the formation of urine during the perinatal period remain unclear.

DATA SOURCES

This review summarizes current knowledge about the spatial and temporal expression patterns of AQP1, AQP2, AQP3, and AQP4 in the fetal and postnatal kidneys in different animal species and in human beings.

RESULTS

AQP1 and AQP2 expression can be detected earlier in gestation in human beings and sheep compared with mice and rats. AQP1 expression is detected earlier in the proximal tubules than the expression of AQP2, AQP3, and AQP4 in the collecting ducts.

CONCLUSION

Further studies investigating the regulation of AQPs during kidney development may provide insights into normal water-handling mechanisms and the pathophysiology of fetal kidneys, which may determine new directions for the clinical treatment of kidney diseases.

Urinary concentrations of aquaporin-1 and perilipin-2 in patients with renal cell carcinoma correlate with tumor size and stage but not grade

OBJECTIVE

To evaluate the trends in urine aquaporin-1 (AQP1) and perilipin 2 (PLIN2) concentrations in patients with clear cell and papillary renal cell carcinoma (RCC), we determined the relationship between the urine concentration of these biomarkers and tumor size, grade, and stage.

MATERIALS AND METHODS

The biomarker concentrations were determined by sensitive and specific Western blot procedures normalized to the urine creatinine excretion. The analysis included 61 patients undergoing partial or radical nephrectomy for clear cell or papillary RCC and 43 age- and sex-matched control patients. Relationships between urine biomarker concentrations and tumor size, stage, and grade were assessed.

RESULTS

Patients with RCC had 35-fold and 9-fold higher median urinary AQP1 and PLIN2 concentrations, respectively, compared with controls. Both tumor markers decreased after tumor resection to concentrations equivalent to those of controls. The sensitivity and specificity were both 100% for AQP1 and 92% and 100%, respectively, for PLIN2. A significant linear correlation was found between the tumor size and the prenephrectomy AQP1 (Spearman coefficient 0.78, P <.001) and PLIN2 (Spearman coefficient 0.69, P <.001) concentrations. A correlation was found for both markers with tumor stage (overall P = .030), when the stage was dependent primarily on the tumor size (stages T1 and T2), but not with stage T3, which reflected extrarenal spread. Neither marker showed a significant correlation with tumor grade.

CONCLUSION

AQP1 and PLIN2 were significantly increased in patients with clear cell and papillary RCC compared with controls. The preoperative urinary concentrations of these markers reflected the tumor size and stage.

Urinary biomarkers for the early diagnosis of kidney cancer

OBJECTIVE

To test the hypothesis that increased tumor expression of proteins such as aquaporin-1 (AQP1) and adipophilin (ADFP) in patients with renal cancer would result in increased urine AQP1 and ADFP excretion.

PATIENTS AND METHODS

Prenephrectomy and postnephrectomy (pseudocontrol) urine samples were collected from 42 patients with an incidental radiographically discovered renal mass and presurgical presumptive diagnosis of kidney cancer from July 8, 2008, through March 10, 2009. Also enrolled were 15 control patients who underwent nonrenal surgery and 19 healthy volunteers. Urine AQP1 and ADFP concentrations normalized to urine creatinine were determined by sensitive and specific Western blot assays.

RESULTS

Mean +/- SD preexcision urine AQP1 and ADFP concentrations (76+/-29 and 117+/-74 arbitrary units, respectively) in patients with a pathologic diagnosis of clear cell (n=22) or papillary (n=10) cancer were significantly greater than in patients with renal cancer of nonproximal tubule origin, control surgical patients, and healthy volunteers (combined values of 0.1+/-0.1 and 1.0+/-1.6 arbitrary units, respectively; n=44; P<.001). The AQP1 and ADFP concentrations decreased 88% to 97% in the 25 patients with clear cell or papillary cancer who provided postnephrectomy follow-up urine samples. In patients with clear cell and papillary carcinoma, a linear correlation (Spearman) was found between tumor size and preexcision urine AQP1 or ADFP concentration (r=0.82 and 0.76, respectively; P<.001 for each).

CONCLUSION

Urine AQP1 and ADFP concentrations appear to be sensitive and specific biomarkers of kidney cancers of proximal tubule origin. These biomarkers may be useful to diagnose an imaged renal mass and screen for kidney cancer at an early stage.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00851994.

Close association of water channel AQP1 with amyloid-beta deposition in Alzheimer disease brains

Aquaporin-1 (AQP1), a membrane water channel protein, is expressed exclusively in the choroid plexus epithelium in the central nervous system under physiological conditions. However, AQP1 expression is enhanced in reactive astrocytes, accumulating in brain lesions of Creutzfeldt-Jakob disease and multiple sclerosis, suggesting a role of AQP1-expressing astrocytes in brain water homeostasis under pathological conditions. To clarify a pathological implication of AQP1 in Alzheimer disease (AD), we investigated the possible relationship between amyloid-beta (Aβ) deposition and astrocytic AQP1 expression in the motor cortex and hippocampus of 11 AD patients and 16 age-matched other neurological disease cases. In all cases, AQP1 was expressed exclusively in a subpopulation of multipolar fibrillary astrocytes. The great majority of AQP1-expressing astrocytes were located either on the top of or in close proximity to Aβ plaques in AD brains but not in non-AD cases, whereas those independent of Aβ deposition were found predominantly in non-AD brains. By Western blot, cultured human astrocytes constitutively expressed AQP1, and the levels of AQP1 protein expression were not affected by exposure to Aβ_1-42 peptide, but were elevated by hypertonic sodium chloride. By immunoprecipitation, the C-terminal fragment-beta (CTFβ) of amyloid precursor protein interacted with the N-terminal half of AQP1 spanning the transmembrane helices H1, H2 and H3. These observations suggest the possible association of astrocytic AQP1 with Aβ deposition in AD brains.