Microvessel overexpression of aquaporin 1 parallels bone marrow angiogenesis in patients with active multiple myeloma

Aquaporins in colorectal cancer: exploring their role in tumorigenesis, metastasis, and drug response

Aquaporins (AQPs) are small, integral proteins facilitating water transport across plasma cell membranes in response to osmotic gradients. This family has 13 unique members (AQP0-12), which can also transport glycerol, urea, gases, and other salute small molecules. AQPs play a crucial role in the regulation of different cellular processes, including metabolism, migration, immunity, barrier function, and angiogenesis. These proteins are found to aberrantly overexpress in various cancers, including colorectal cancer (CRC). Growing evidence has explored AQPs as a potential diagnostic biomarker and therapeutic target in different cancers. However, there is no comprehensive review compiling the available information on the crucial role of AQPs in the context of colorectal cancer. This review highlights the significance of AQPs as the biomarker and regulator of tumor cells metabolism. In addition, the proliferation, angiogenesis, and metastasis of tumor cells related to AQPs expression as well as function are discussed. Understanding the AQPs prominent role in chemotherapy resistance is of great importance clinically.

Identification of key genes and validation of key gene aquaporin 1 on Wilms' tumor metastasis

Background

Wilms' tumor (WT) is one of the most common solid tumors in children with unsatisfactory prognosis, but few molecular prognostic markers have been discovered for it. Many genes are associated with the occurrence and prognosis of WT. This study aimed to explore the key genes and potential molecular mechanisms through bioinformatics and to verify the effects of aquaporin 1 (AQP1) on WT metastasis.

Methods

Differentially expressed genes (DEGs) were generated from WT gene expression data sets from the Gene Expression Omnibus (GEO) database. Gene functional enrichment analysis was carried out with the Database for Annotation, Visualization and Integrated Discovery (DAVID). A protein-protein interaction network (PPI) was constructed and visualized by the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database and Cytoscape software. Minimal Common Oncology Data Elements (MCODE) was used to detect the important modules in the PPI network, and the important nodes (genes) in the PPI module were sorted by CytoHubba. RT-qPCR was performed to validate the expression of the key genes in WT. Wound healing and Transwell assays were used to detect the cell migration and invasion abilities of AQP1-overexpressing cells. Phalloidin-iFlour 488 was used to stain the cytoskeleton to observe how AQP1 overexpression affects cytoskeletal microfilament structure.

Results

A total of 73 co-expressed DEGs were chosen for further investigation. The importance of homeostasis and transmembrane transport of ions and water were highlighted by functional analysis. Gene regulatory network and PPI network were predicted. MCODE plug identified two important modules. Finally, top five key genes were identified using CytoHubba, including Renin (REN), nephrosis 2 (NPHS2), Solute Carrier Family 12 Member 3 (SLC12A3), Solute Carrier Family 12 Member 1 (SLC12A1) and AQP1. The five key genes were mainly enriched in cell volume and ion homeostasis. RT-qPCR confirmed the expression of the five key genes in WT. AQP1 was validated to be expressed at significantly lower levels in WT than in normal tissue. AQP1 overexpression significantly reduced the migratory and invasive capacity of Wit-49 cells, as evidenced by reducing the scratch healing rate and the number of perforated control cells by Wit-49 cells. AQP1 overexpression also reduced the expression of biomarkers of epithelial-mesenchymal transformation, decreased levels of vimentin and N-cadherin and increased expression of E-cadherin, resulting in decreased formation of conspicuous lamellipodial protrusions, characteristic of diminished WT cell invasion and migration.

Conclusion

Our study reveals the key genes of WT. These key genes may provide novel insight for the mechanism and diagnosis of WT. AQP1 overexpression inhibited invasion, migration, EMT, and cytoskeletal rearrangement of WT cells, indicating that AQP1 plays a role in the pathogenesis of WT.

Aquaporins and Ion Channels as Dual Targets in the Design of Novel Glioblastoma Therapeutics to Limit Invasiveness

Current therapies for Glioblastoma multiforme (GBM) focus on eradicating primary tumors using radiotherapy, chemotherapy and surgical resection, but have limited success in controlling the invasive spread of glioma cells into a healthy brain, the major factor driving short survival times for patients post-diagnosis. Transcriptomic analyses of GBM biopsies reveal clusters of membrane signaling proteins that in combination serve as robust prognostic indicators, including aquaporins and ion channels, which are upregulated in GBM and implicated in enhanced glioblastoma motility. Accumulating evidence supports our proposal that the concurrent pharmacological targeting of selected subclasses of aquaporins and ion channels could impede glioblastoma invasiveness by impairing key cellular motility pathways. Optimal sets of channels to be selected as targets for combined therapies could be tailored to the GBM cancer subtype, taking advantage of differences in patterns of expression between channels that are characteristic of GBM subtypes, as well as distinguishing them from non-cancerous brain cells such as neurons and glia. Focusing agents on a unique channel fingerprint in GBM would further allow combined agents to be administered at near threshold doses, potentially reducing off-target toxicity. Adjunct therapies which confine GBM tumors to their primary sites during clinical treatments would offer profound advantages for treatment efficacy.

Assessing the Role of Aquaporin 4 in Skeletal Muscle Function

Water transport across the biological membranes is mediated by aquaporins (AQPs). AQP4 and AQP1 are the predominantly expressed AQPs in the skeletal muscle. Since the discovery of AQP4, several studies have highlighted reduced AQP4 levels in Duchenne muscular dystrophy (DMD) patients and mouse models, and other neuromuscular disorders (NMDs) such as sarcoglycanopathies and dysferlinopathies. AQP4 loss is attributed to the destabilizing dystrophin-associated protein complex (DAPC) in DMD leading to compromised water permeability in the skeletal muscle fibers. However, AQP4 knockout (KO) mice appear phenotypically normal. AQP4 ablation does not impair physical activity in mice but limits them from achieving the performance demonstrated by wild-type mice. AQP1 levels were found to be upregulated in DMD models and are thought to compensate for AQP4 loss. Several groups investigated the expression of other AQPs in the skeletal muscle; however, these findings remain controversial. In this review, we summarize the role of AQP4 with respect to skeletal muscle function and findings in NMDs as well as the implications from a clinical perspective.

Aquaporin 5 (AQP5) expression in breast cancer and its clinicopathological characteristics

The role of aquaporin water channels (AQPs) has become an area of great interest in human carcinogenesis. In this report, we have demonstrated the expression of AQP5 in breast cancer by analyzing 591 tissue samples with 7-year follow-ups. By immunochemistry analysis, AQP5 overexpression was observed in 36% (212/591 cases). Then, we have focused on the clinicopathologic variables among cancer tissue samples with strong AQP5 expression (3+ expression, 60/591 cases). The strong AQP5 expression was positively correlated with tumor grade in BCs (p<0.001) and was more frequent in ER/PR-negative BCs than positive ones (14.9% vs. 3.3% and 13.1% vs. 4.8%, respectively, both p<0.001), while Her2/neu-positive status was positively correlated with strong expression of AQP5 (p = 0.005). Of note, breast cancer patients with positive AQP expression (212/591 cases) showed a less favorable breast cancer specific survival rate over 7 years of follow and we further conclude that AQP5 expression is an independent molecular marker associated with worse clinical outcomes. By fluorescence in situ hybridization (FISH), we have identified evidence of gene amplification in 3 of 30 readable breast cancer and further conclude that, in breast cancer, at least some part of AQP5 overexpression is associated with an aberration in the genome level.

Aquaporins in Cancer Biology

Aquaporins (AQPs) are a family of transmembrane water channel proteins, which were initially characterized as a novel protein family that plays a vital role in transcellular and transepithelial water movement. AQP1, AQP2, AQP4, AQP5, and AQP8 are primarily water selective, whereas AQP3, AQP7, AQP9, and AQP10 (called “aqua-glyceroporins”) also transport glycerol and other small solutes. Recently, multiple reports have suggested that AQPs have important roles in cancer cell growth, migration, invasion, and angiogenesis, each of which is important in human carcinogenesis. Here, we review recent data concerning the involvement of AQPs in tumor growth, angiogenesis, and metastasis and explore the expression profiles from various resected cancer samples to further dissect the underlying molecular mechanisms. Moreover, we discuss the potential role of AQPs during the development of genomic instability and performed modeling to describe the integration of binding between AQPs with various SH3 domain binning adaptor molecules. Throughout review and discussion of numerous reports, we have tried to provide key evidence that AQPs play key roles in tumor biology, which may provide a unique opportunity in designing a novel class of anti-tumor agents.

Identification of Two Exosomal miRNAs in Circulating Blood of Cancer Patients by Using Integrative Transcriptome and Network Analysis

Exosomes carry molecules of great biological and clinical interest, such as miRNAs. The contents of exosomes vary between healthy controls and cancer patients. Therefore, miRNAs and other molecules transported in exosomes are considered a potential source of diagnostic and prognostic biomarkers in cancer. Many miRNAs have been detected in recent years. Consequently, a substantial amount of miRNA-related data comparing patients and healthy individuals is available, which contributes to a better understanding of the initiation, development, malignancy, and metastasis of cancer using non-invasive sampling procedures. However, a re-analysis of available ncRNA data is rare. This study used available data about miRNAs in exosomes comparing healthy individuals and cancer patients to identify possible global changes related to the presence of cancer. A robust transcriptomic analysis identified two common miRNAs (miR-495-3p and miR-543) deregulated in five cancer datasets. They had already been implicated in different cancers but not reported in exosomes circulating in blood. The study also examined their target genes and the implications of these genes for functional processes.

Wall shear stress on vascular smooth muscle cells exerts angiogenic effects on extracranial arteriovenous malformations

Background

In addition to vascular endothelial cells, vascular smooth muscle cells (VSMCs) are subject to continuous shear stress because of blood circulation. The angiogenic properties of VSMCs in extracranial arteriovenous malformations (AVMs) may exceed those of normal blood vessels if the body responds more sensitively to mechanical stimuli. This study was performed to investigate the hypothesis that rapid angiogenesis may be achieved by mechanical shear stress.

Methods

VSMCs were obtained from six patients who had AVMs and six normal controls. The target genes were set to angiopoietin-2 (AGP2), aquaporin-1 (AQP1), and transforming growth factor-beta receptor 1 (TGFBR1). Reverse-transcriptase polymerase chain reaction (RT-PCR) and real-time PCR were implemented to identify the expression levels for target genes. Immunofluorescence was also conducted.

Results

Under the shear stress condition, mean relative quantity values of AGP2, AQP1, and TGFBR1 in AVM tissues were 1.927±0.528, 1.291±0.031, and 2.284±1.461 when compared with neutral conditions. The expression levels of all three genes in AVMs were higher than those in normal tissue except for AQP1 under shear stress conditions. Immunofluorescence also revealed increased staining of shear stress-induced genes in the normal tissue and in AVM tissue.

Conclusions

Shear stress made the VSMCs of AVMs more sensitive. Although the pathogenesis of AVMs remains unclear, our study showed that biomechanical stimulation imposed by shear stress may aggravate angiogenesis in AVMs.

Aquaporin ion conductance properties defined by membrane environment, protein structure, and cell physiology

Aquaporins (AQPs) are multifunctional transmembrane channel proteins permeable to water and an expanding array of solutes. AQP-mediated ion channel activity was first observed when purified AQP0 from bovine lens was incorporated into lipid bilayers. Electrophysiological properties of ion-conducting AQPs since discovered in plants, invertebrates, and mammals have been assessed using native, reconstituted, and heterologously expressed channels. Accumulating evidence is defining amino acid residues that govern differential solute permeability through intrasubunit and central pores of AQP tetramers. Rings of charged and hydrophobic residues around pores influence AQP selectivity, and are candidates for further work to define motifs that distinguish ion conduction capability, versus strict water and glycerol permeability. Similarities between AQP ion channels thus far include large single channel conductances and long open times, but differences in ionic selectivity, permeability to divalent cations, and mechanisms of gating (e.g., by voltage, pH, and cyclic nucleotides) are unique to subtypes. Effects of lipid environments in modulating parameters such as single channel amplitude could explain in part the variations in AQP ion channel properties observed across preparations. Physiological roles of the ion-conducting AQP classes span diverse processes including regulation of cell motility, organellar pH, neural development, signaling, and nutrient acquisition. Advances in computational methods can generate testable predictions of AQP structure-function relationships, which combined with innovative high-throughput assays could revolutionize the field in defining essential properties of ion-conducting AQPs, discovering new AQP ion channels, and understanding the effects of AQP interactions with proteins, signaling cascades, and membrane lipids.

Oscillatory shear stress promotes angiogenic effects in arteriovenous malformations endothelial cells

Background

Vascular endothelial cells (ECs) are subject to continuous shear stress due to blood circulation. Mechanical stress due to high shear flow can also cause arteriovenous malformation (AVM) when ECs respond hyper-sensitively to shear flow. This study was conducted to test the hypothesis that angiogenesis could be promoted in response to mechanical stress via regulation of pro-angiogenic factors in AVM cells.

Methods

ECs were extracted from the tissue samples from six AVM patients and six normal patients. Shear stress at 7 dynes/cm2 were applied for 24 h. Before and after application of shear stress to each group, RT-PCR was performed to access the expression levels of angiopoietin2(AGP2), aquaporin1(AQP1) and TGFβR1. Immunofluorescences was also performed to evaluate the level of protein expressions.

Results

In both normal and AVM tissues, AGP2 and TGFβR1 under the shear stress showed increased expression in the ECs compared to the non-sheared samples. When AVMs and normal arterial vasculature were compared, the expression levels of both AGP2 and TGFβR1 in AVMs were higher when compared to normal arterial vasculature with or without shear stress. Immunofluorescence-based protein analysis also confirmed shear-induced AGP2 and TGFβR1 in both samples of normal and AVM patients.

Conclusions

AVMs exhibited higher sensitivity to shear stress by producing higher expressions of some marked genes and proteins that regulate the endothelial functions upon exposure to shear stress. While the physiological mechanism for AVMs remain elusive, our study shows the plausibility of physical stress imposed by the shearing flow can cause the occurrence of AVMs.

Aquaporin 1 mediates early responses to osmotic stimuli in endothelial cells via the calmodulin pathway

The aquaporins (AQPs) are a family of integral membrane proteins which play critical roles in controlling transcellular water movement in various tissues throughout the body. AQP1 helps mediate the cellular response to osmotic stress and tissue water permeability. However, the mechanism by which AQP1 mediates changes in cell volume is not completely clear. Here, we investigated how AQP1 responds to and controls cell volume upon osmotic stimuli during the early phase after the immediate response. Cells overexpressing AQP1 were exposed to hypotonic or hypertonic medium in the presence or absence of staurosporine or W-7 hydrochloride, and fluorescence imaging was performed at 0, 5, 10, and 15 min later. Osmotic stimuli induced redistribution of AQP1 into the cell membrane, hypotonic stimuli caused cell enlargement, and hypertonic stimuli induced a reduction in cell size, which was blocked by T157A/T239A mutations. Changes in cell size induced by osmotic stimuli were blocked by an antagonist of calmodulin kinase, W-7 hydrochloride, but not by the PKC inhibitor staurosporine. These results suggest that calmodulin kinase regulates AQP1 activity during the early response to osmotic stimuli.

Combined Systematic Review and Transcriptomic Analyses of Mammalian Aquaporin Classes 1 to 10 as Biomarkers and Prognostic Indicators in Diverse Cancers

Aquaporin (AQP) channels enable regulated transport of water and solutes essential for fluid homeostasis, but they are gaining attention as targets for anticancer therapies. Patterns of AQP expression and survival rates for patients were evaluated by systematic review (PubMed and Embase) and transcriptomic analyses of RNAseq data (Human Protein Atlas database). Meta-analyses confirmed predominantly negative associations between AQP protein and RNA expression levels and patient survival times, most notably for AQP1 in lung, breast and prostate cancers; AQP3 in esophageal, liver and breast cancers; and AQP9 in liver cancer. Patterns of AQP expression were clustered for groups of cancers and associated with risk of death. A quantitative transcriptomic analysis of AQP1-10 in human cancer biopsies similarly showed that increased transcript levels of AQPs 1, 3, 5 and 9 were most frequently associated with poor survival. Unexpectedly, increased AQP7 and AQP8 levels were associated with better survival times in glioma, ovarian and endometrial cancers, and increased AQP11 with better survival in colorectal and breast cancers. Although molecular mechanisms of aquaporins in pathology or protection remain to be fully defined, results here support the hypothesis that overexpression of selected classes of AQPs differentially augments cancer progression. Beyond fluid homeostasis, potential roles for AQPs in cancers (suggested from an expanding appreciation of their functions in normal tissues) include cell motility, membrane process extension, transport of signaling molecules, control of proliferation and apoptosis, increased mechanical compliance, and gas exchange. AQP expression also has been linked to differences in sensitivity to chemotherapy treatments, suggesting possible roles as biomarkers for personalized treatments. Development of AQP pharmacological modulators, administered in cancer-specific combinations, might inspire new interventions for controlling malignant carcinomas.

Bone Marrow Stromal Cells-Induced Drug Resistance in Multiple Myeloma

Multiple myeloma is a B-cell lineage cancer in which neoplastic plasma cells expand in the bone marrow and pathophysiological interactions with components of microenvironment influence many biological aspects of the malignant phenotype, including apoptosis, survival, proliferation, and invasion. Despite the therapeutic progress achieved in the last two decades with the introduction of a more effective and safe new class of drugs (i.e., immunomodulators, proteasome inhibitors, monoclonal antibodies), there is improvement in patient survival, and multiple myeloma (MM) remains a non-curable disease. The bone marrow microenvironment is a complex structure composed of cells, extracellular matrix (ECM) proteins, and cytokines, in which tumor plasma cells home and expand. The role of the bone marrow (BM) microenvironment is fundamental during MM disease progression because modification induced by tumor plasma cells is crucial for composing a "permissive" environment that supports MM plasma cells proliferation, migration, survival, and drug resistance. The "activated phenotype" of the microenvironment of multiple myeloma is functional to plasma cell proliferation and spreading and to plasma cell drug resistance. Plasma cell drug resistance induced by bone marrow stromal cells is mediated by stress-managing pathways, autophagy, transcriptional rewiring, and non-coding RNAs dysregulation. These processes represent novel targets for the ever-increasing anti-MM therapeutic armamentarium.

MicroRNA-495 downregulates AQP1 and facilitates proliferation and differentiation of osteoblasts in mice with tibial fracture through activation of p38 MAPK signaling pathway

Osteoblasts are implicated in the building of the vertebrate skeleton. The current study aimed to investigate the role of microRNA-495 (miR-495) in the osteoblasts of mice with tibial fractures and the underlying mechanism involving in aquaporin-1 (AQP1) and the p38 mitogen-activated protein kinase (p38 MAPK) signaling pathway. Initially, a microarray-based analysis was performed to screen the differentially expressed genes and miRNAs associated with tibial fracture. Following the establishment of a tibial fracture mouse model, the positive rate of the AQP1 protein in the fracture tissue was detected by immunohistochemistry (IHC). Next, to verify the binding site between miR-495 on AQP1, bioinformatics data were employed in addition to the application of a dual-luciferase reporter gene assay. The osteoblast cell line MC3T3-E1 was treated with miR-495 mimic, miR-495 inhibitor and Anisomycin to explore the potent effects of miR-495 on proliferation and differentiation of osteoblasts in mice with tibial fracture. The expression of miR-495, AQP1, p38 MAPK, PCNA, Cyclin D1, OCN, and OPN was subsequently evaluated by RT-qPCR and Western blot analysis. Cell viability, the number of calcium nodules and alkaline phosphatase (ALP) activity were detected by MTT assay, alizarin red staining, and ALP activity assay, respectively. Our results revealed that miR-495 was down-regulated while AQP1 was up-regulated in the mice with tibial fractures. AQP1 was verified as a target gene of miR-495. When the cells were treated with overexpressed miR-495 or activated p38 MAPK signaling pathway, elevated expression of PCNA, Cyclin, D1, OCN, and OPN along with an increased amount of calcium nodules, higher cell viability, and enhanced ALP activity was detected, while the expression of AQP1 was reduced. Collectively, the key findings of the present study support the notion that overexpressed miR-495 may activate the p38 MAPK signaling pathway to inhibit AQP1 and to promote the proliferation and differentiation of osteoblasts in mice with tibial fracture.

Expression Pattern of Aquaporin 1 and Aquaporin 3 in Melanocytic and Nonmelanocytic Skin Tumors

OBJECTIVES

Study of aquaporin 1 (AQP1) and aquaporin 3 (AQP3) expression to understand its potential role in the pathophysiology of skin cancer.

METHODS

Analysis of AQP1 and AQP3 expression by immunohistochemistry of 72 skin biopsy specimens from melanocytic skin tumors, nonmelanocytic tumors, or healthy samples.

RESULTS

AQP1 showed strong labeling in 100% of benign common melanocytic nevi. Small blood vessels, stroma, and melanophages surrounding different types of melanomas tumors also were positive. Tumoral melanocytes in atypical nevi and melanomas were negative for AQP1. AQP3 showed strong labeling in 100% of melanocytic nevi, 100% of atypical melanocytic nevi, and 100% of melanomas. In all basal cell carcinomas and squamous cell carcinomas, staining for AQP3 was positive.

CONCLUSIONS

To our knowledge, this work represents the first demonstration of AQP1/AQP3 expression in human melanocytic skin tumors. More studies are needed to understand the underlying molecular mechanisms of expression of both AQPs in melanocytic tumors and their potential as molecular therapeutic targets.

CUL5 is required for thalidomide-dependent inhibition of cellular proliferation

Angiogenesis is essential for cancer metastasis, thus the discovery and characterization of molecules that inhibit this process is important. Thalidomide is a teratogenic drug which is known to inhibit angiogenesis and effectively inhibit cancer metastasis, yet the specific cellular targets for its effect are not well known. We discovered that CUL5 (previously identified as VACM-1), a scaffold protein in E3 ligase complexes, is involved in thalidomide-dependent inhibition of endothelial cell growth. Our results show that in human endothelial cells (HUVEC), thalidomide-dependent decrease in cell growth was associated with decreased nuclear localization of CUL5. In HUVEC transfected with anti-VACM-1 siRNA, thalidomide failed to decrease cell growth. Previously it was established that the antiproliferative effect of CUL5 is inhibited in rat endothelial cells (RAMEC) transfected with mutated CUL5 which is constitutively modified by NEDD8, a ubiquitin-like protein. In this study, the antiproliferative response to thalidomide was compromised in RAMEC expressing mutated CUL5. These results suggest that CUL5 protein is involved in the thalidomide-dependent regulation of cellular proliferation in vitro. Consequently, CUL5 may be an important part of the mechanism for thalidomide-dependent inhibition of cellular proliferation, as well as a novel biomarker for predicting a response to thalidomide for the treatment of disorders such as multiple myeloma and HIV infection.

Mechanisms of Aquaporin-Facilitated Cancer Invasion and Metastasis

Cancer is a leading cause of death worldwide, and its incidence is rising with numbers expected to increase 70% in the next two decades. The fact that current mainline treatments for cancer patients are accompanied by debilitating side effects prompts a growing demand for new therapies that not only inhibit growth and proliferation of cancer cells, but also control invasion and metastasis. One class of targets gaining international attention is the aquaporins, a family of membrane-spanning water channels with diverse physiological functions and extensive tissue-specific distributions in humans. Aquaporins−1,−2,−3,−4,−5,−8, and−9 have been linked to roles in cancer invasion, and metastasis, but their mechanisms of action remain to be fully defined. Aquaporins are implicated in the metastatic cascade in processes of angiogenesis, cellular dissociation, migration, and invasion. Cancer invasion and metastasis are proposed to be potentiated by aquaporins in boosting tumor angiogenesis, enhancing cell volume regulation, regulating cell-cell and cell-matrix adhesions, interacting with actin cytoskeleton, regulating proteases and extracellular-matrix degrading molecules, contributing to the regulation of epithelial-mesenchymal transitions, and interacting with signaling pathways enabling motility and invasion. Pharmacological modulators of aquaporin channels are being identified and tested for therapeutic potential, including compounds derived from loop diuretics, metal-containing organic compounds, plant natural products, and other small molecules. Further studies on aquaporin-dependent functions in cancer metastasis are needed to define the differential contributions of different classes of aquaporin channels to regulation of fluid balance, cell volume, small solute transport, signal transduction, their possible relevance as rate limiting steps, and potential values as therapeutic targets for invasion and metastasis.

Aquaporin-1 inhibition reduces metastatic formation in a mouse model of melanoma

Aquaporin-1 (AQP1) is a proangiogenic water channel protein promoting endothelial cell migration. We previously reported that AQP1 silencing by RNA interference reduces angiogenesis-dependent primary tumour growth in a mouse model of melanoma. In this study, we tested the hypothesis that AQP1 inhibition also affects animal survival and lung nodule formation. Melanoma was induced by injecting B16F10 cells into the back of C57BL6J mice. Intratumoural injection of AQP1 siRNA and CTRL siRNA was performed 10 days after tumour cell implantation. Lung nodule formation was analysed after the death of the mice. Western blot was used to quantify HIF-1α, caspase-3 (CASP3) and metalloproteinase-2 (MMP2) protein levels. We found that AQP1 knock-down (KD) strongly inhibited metastatic lung nodule formation. Moreover, AQP1 siRNA-treated mice showed a twofold survival advantage compared to mice receiving CTRL siRNAs. The reduced AQP1-dependent tumour angiogenesis caused a hypoxic condition, evaluated by HIF-1α significant increase, in turn causing an increased level of apoptosis in AQP1 KD tumours, assessed by CASP3 quantification and DNA fragmentation. Importantly, a decreased level of MMP2 after AQP1 KD indicated a decreased activity against extracellular matrix associated with reduced vascularization and metastatic formation. In conclusion, these findings highlight an additional role for AQP1 as an important determinant of tumour dissemination by facilitating tumour cell extravasation and metastatic formation. This study adds knowledge on the role played by AQP1 in tumour biology and supports the view of AQP1 as a potential drug target for cancer therapy.

The association between aquaporin-1 expression, microvessel density and the clinicopathological features of hepatocellular carcinoma

The present study aimed to evaluate the effects of aquaporin-1 (AQP1) level and intratumoral microvessel density (IMD) on the clinicopathological features of patients with hepatocellular carcinoma (HCC). The AQP1 expression levels, IMD and AQP1/IMD ratios in patients with HCC were measured using a semi-quantitative immunohistochemical technique. The association between these features and clinicopathological variables were evaluated. The prognostic impact of AQP1 and IMD on overall survival (OS), and 5-year disease-free survival (DFS) of HCC patients was investigated retrospectively. P<0.05 was considered to indicate a statistically significant difference. A total of 90 cases of HCC were included in the present study. AQP1 was markedly expressed in the membranes of microvessels and small vessels, but seldom in hepatocellular carcinoma cells. Blood vessels in the tumors were markedly stained by anti-cluster of differentiation 34 antibody. AQP1 expression and IMD was significantly correlated with tumor size, histologic grade, Child-Pugh classification, microvascular invasion and tumor-node-metastasis (TNM) stage (P<0.05). Concurrently, for the 5-year DFS and OS, a larger tumor size, poorly differentiated histological grade, B and C Child-Pugh classification, presence of microvascular invasion, high TNM stage, a high AQP1 expression and a high IMD were significant risk factors for mortality. Multivariate analysis revealed that TNM stage and IMD were independent unfavorable prognostic markers for 5-year DFS (P=0.049 and P=0.025, respectively) and OS (P=0.043 and P=0.042, respectively). These data suggest that high AQP1 expression and IMD are associated with tumor progression and prognosis in HCC. The IMD level may serve as an independent indicator for the 5-year DFS and OS.

Multiple Myeloma as the Underlying Cause of Thrombotic Microangiopathy Leading to Acute Kidney Injury: Revisiting a Very Rare Entity

Thrombotic microangiopathy (TMA) describes a pathological process of microvascular thrombosis, consumptive thrombocytopenia, and microangiopathic hemolytic anemia, leading to end-organ ischemia and infarction, affecting particularly the kidney and brain. TMA is a pathological feature of a number of clinical disorders including thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, and atypical hemolytic uremic syndrome. Rare but important, TMA may also occur in malignancy, connective tissue disease, malignant hypertension, and renal transplantation (rejection or drug toxicity). We present a very rare case where the patient developed acute kidney injury from TMA but found to have multiple myeloma as the possible underlying etiology.

Aquaporins: Novel Targets for Age-Related Ocular Disorders

Aquaporins (AQPs), a large family of membrane protein channels that facilitate transport of water and other small solutes, play important roles in physiological functions and human diseases. Up till now, 13 types of AQPs, numbered 0 through 12, have been identified in various mammalian tissues. Homologous genes for AQPs in amphibians, insects, and bacteria highlight the evolutionary conservation and, thus, the importance of these membrane channels. Many members of the AQP family are expressed in the eye. AQP1, which is a water-selective channel, is expressed in the anterior chamber (cornea, ciliary body, trabecular meshwork) and posterior chamber (retina and microvessels in choroid), controlling the fluid homeostasis in the eye. Mice knockout studies have indicated that AQP1 plays an important function in the eye by suggesting its role in aqueous humor dynamics and retina angiogenesis. This review will focus on the role of AQP1 as a novel target for ocular disorders such as glaucoma and age-related macular degeneration, and it will discuss challenges and advances in identifying modulators of AQP1 function that could be useful in clinical applications.

Aquaporins in Brain Edema and Neuropathological Conditions

The aquaporin (AQP) family of water channels are a group of small, membrane-spanning proteins that are vital for the rapid transport of water across the plasma membrane. These proteins are widely expressed, from tissues such as the renal epithelium and erythrocytes to the various cells of the central nervous system. This review will elucidate the basic structure and distribution of aquaporins and discuss the role of aquaporins in various neuropathologies. AQP1 and AQP4, the two primary aquaporin molecules of the central nervous system, regulate brain water and CSF movement and contribute to cytotoxic and vasogenic edema, where they control the size of the intracellular and extracellular fluid volumes, respectively. AQP4 expression is vital to the cellular migration and angiogenesis at the heart of tumor growth; AQP4 is central to dysfunctions in glutamate metabolism, synaptogenesis, and memory consolidation; and AQP1 and AQP4 adaptations have been seen in obstructive and non-obstructive hydrocephalus and may be therapeutic targets.

Diabetes mitigates the recovery following intracranial hemorrhage in rats

Intracranial hemorrhage (ICH) is a common subtype of stroke with high morbidity and mortality. However, few studies have examined the effects of diabetes on the recovery from ICH-induced brain injury. Therefore, we examined the effects of diabetes on protein levels of aquaporins, neuronal loss, angiogenesis, blood brain barrier (BBB) integrity, and neurological deficits following intra-DH collagenase-induced ICH in the hippocampus. We found that diabetic rats exhibited enhanced AQP9 expression in the hippocampus relative to non-diabetic rats, which was associated with increased behavioral deficits. Additionally, ICH induced neovascularization, proliferation of brain microvascular endothelial cells, and hippocampal neuronal loss. However, ICH-induced neovascularization and proliferation of brain microvascular endothelial cells was severely impaired in diabetic rats. Furthermore, ICH-induced hippocampal neuronal loss was exaggerated in diabetic rats. Finally, ICH impaired BBB integrity in the ipsilateral hemisphere, which was increased in diabetic rats. Taken together, the attenuated brain angiogenesis, increased hippocampal neuronal loss, and impaired BBB integrity in diabetic rats after ICH were associated with enhanced AQP9 expression. This may suggest that AQP9 is one of the underlying mechanisms that can mitigate the recovery from ICH in diabetic populations.

Aquaporin 1 protein expression is associated with BRAF V600 mutation and adverse prognosis in cutaneous melanoma

Despite experimental findings suggesting the prognostic significance of Aquaporin 1 (AQP1) in human melanoma, no published clinical data are available. We studied the expression of AQP1 protein in cutaneous melanoma, correlated our findings with standard histological and genetic markers, and long-term clinical follow-up. Our study evaluated the AQP1 protein expression in 78 melanoma patients, representing two predefined risk cohorts using the immune labeling technique with commercially available anti-AQP1 antibodies on routinely formalin-fixed and paraffin-embedded tumor tissue samples. BRAF V600E mutation analyses were carried out successfully in 70 patients using PCR and restriction fragment length polymorphism analyses, followed by confirmatory analysis with the Sanger sequencing technique. AQP1-expressing melanoma cells were found in 52 cases (66.7%, median H-score=124.24). Significantly higher AQP1 H-scores (P=0.047) were found in the 'high-risk' patients. No correlations were found with the established histological markers, such as mitotic index (P=0.42), Clark level (P=0.95), and Breslow thickness (P=0.51). BRAF V600 mutation analyses were successful in 89%, and showed a two times higher mutation frequency in the 'high-risk' group. The BRAF V600 mutations were significantly associated with AQP1 expression (P=0.014). Long-term follow-up indicated a reduced progression-free survival (P=0.036) and overall survival (P=0.017) for the AQP1-positive cutaneous melanoma patients. AQP1 expression is likely to be associated with an adverse prognosis in cutaneous melanoma.

Aquaporin 9 is down-regulated in hepatocellular carcinoma and its over-expression suppresses hepatoma cell invasion through inhibiting epithelial-to-mesenchymal transition

Aquaporin 9 (AQP9) is the main aquaglyceroporin in the liver. Few studies have been performed regarding the role of AQP9 in hepatocellular carcinoma (HCC). Here, we report the expression and function of AQP9 in HCC tissues and cell lines. We found that AQP9 mRNA and protein levels were down-regulated in HCC tissues and human hepatoma cell lines compared to the para-cancer normal liver tissues and normal hepatocyte line, respectively. In a human HCC SMMC-7721 cell line, over-expression of AQP9 suppressed cell invasion in vitro and xenograft tumor growth in vivo. AQP9 over-expression increased the expression of E-cadherin and decreased the expression of N-cadherin in SMMC-7721 cells and xenografted tumors, which was correlated with decreased levels of phosphoinositide 3-kinase (PI3K) and p-Akt. Conversely, using siRNA to knock down AQP9 over-expression could reverse the phenotype caused by AQP9 over-expression. Our findings suggest that AQP9 is down-regulated in hepatocellular carcinoma and its over-expression suppresses hepatoma cell invasion through inhibiting epithelial-to-mesenchymal transition.

Fragment Screening of Human Aquaporin 1

Aquaporins (AQPs) are membrane proteins that enable water transport across cellular plasma membranes in response to osmotic gradients. Phenotypic analyses have revealed important physiological roles for AQPs, and the potential for AQP water channel modulators in various disease states has been proposed. For example, AQP1 is overexpressed in tumor microvessels, and this correlates with higher metastatic potential and aggressiveness of the malignancy. Chemical modulators would help in identifying the precise contribution of water channel activity in these disease states. These inhibitors would also be important therapeutically, e.g., in anti-cancer treatment. This perceived importance contrasts with the lack of success of high-throughput screens (HTS) to identify effective and specific inhibitors of aquaporins. In this paper, we have screened a library of 1500 "fragments", i.e., smaller than molecules used in HTS, against human aquaporin (hAQP1) using a thermal shift assay and surface plasmon resonance. Although these fragments may not inhibit their protein target, they bound to and stabilized hAQP1 (sub mM binding affinities (KD), with an temperature of aggregation shift ΔTagg of +4 to +50 °C) in a concentration-dependent fashion. Chemically expanded versions of these fragments should follow the determination of their binding site on the aquaporin surface.

Prognostic Significance of Aquaporin 5 Expression in Non-small Cell Lung Cancer

BACKGROUND

Aquaporins are water channel proteins that play a major role in the movement of water in various human tissues. Recently, it has been found that aquaporins have influence in the carcinogenesis of human malignancies. We analyzed the prognostic impact of aquaporin 5 (AQP5) in non-small lung cancer (NSCLC).

METHODS

Seventy-six cases of NSCLC were studied, including 44 cases of adenocarcinoma (ADC) and 32 cases of squamous cell carcinoma (SQCC). Tissue microarray was constructed and immunohistochemical staining for AQP5 was performed.

RESULTS

AQP5 was positive in 59.2% of the total enrolled NSCLCs (63.7% in ADC and 53.1% in SQCC). The difference in expression of AQP5 according to the histologic grade of the tumor was significant (p<.047), but not in a serial order. When ADC and SQCC were separately evaluated, no significant difference was observed according to the histologic grade of the tumor (p=.076 in ADC and p=.631 in SQCC). No difference was observed between AQP5 expression and other demographic data and tumor characteristics. Disease-free survival (DFS) was higher in AQP5 negative cases than positive cases in ADC (p=.047), but no significance was found in SQCC (p=.068). We were unable to find a significance between AQP5 overexpression and overall survival in either ADC (p=.210) or SQCC (p=.533).

CONCLUSIONS

AQP5 expression is associated with DFS in ADC of the lung and tumor grade of NSCLC. The present study suggests that AQP5 can be a prognostic factor of NSCLC.

The Trafficking of the Water Channel Aquaporin-2 in Renal Principal Cells-a Potential Target for Pharmacological Intervention in Cardiovascular Diseases

Arginine-vasopressin (AVP) stimulates the redistribution of water channels, aquaporin-2 (AQP2) from intracellular vesicles into the plasma membrane of renal collecting duct principal cells. By this AVP directs 10% of the water reabsorption from the 170 L of primary urine that the human kidneys produce each day. This review discusses molecular mechanisms underlying the AVP-induced redistribution of AQP2; in particular, it provides an overview over the proteins participating in the control of its localization. Defects preventing the insertion of AQP2 into the plasma membrane cause diabetes insipidus. The disease can be acquired or inherited, and is characterized by polyuria and polydipsia. Vice versa, up-regulation of the system causing a predominant localization of AQP2 in the plasma membrane leads to excessive water retention and hyponatremia as in the syndrome of inappropriate antidiuretic hormone secretion (SIADH), late stage heart failure or liver cirrhosis. This article briefly summarizes the currently available pharmacotherapies for the treatment of such water balance disorders, and discusses the value of newly identified mechanisms controlling AQP2 for developing novel pharmacological strategies. Innovative concepts for the therapy of water balance disorders are required as there is a medical need due to the lack of causal treatments.

Role of aquaporins in cell proliferation: What else beyond water permeability?

In addition to the extensive data demonstrating the importance of mammalian AQPs for the movement of water and some small solutes across the cell membrane, there is now a growing body of evidence indicating the involvement of these proteins in numerous cellular processes seemingly unrelated, at least some of them in a direct way, to their canonical function of water permeation. Here, we have presented a broad range of evidence demonstrating that these proteins have a role in cell proliferation by various different mechanisms, namely, by allowing fast cell volume regulation during cell division; by affecting progression of cell cycle and helping maintain the balance between proliferation and apoptosis, and by crosstalk with other cell membrane proteins or transcription factors that, in turn, modulate progression of the cell cycle or regulate biosynthesis pathways of cell structural components. In the end, however, after discussing all these data that strongly support a role for AQPs in the cell proliferation process, it remains impossible to conclude that all these other functions attributed to AQPs occur completely independently of their water permeability, and there is a need for new experiments designed specifically to address this interesting issue.

Challenges and achievements in the therapeutic modulation of aquaporin functionality

Aquaporin (AQP) water and solute channels have basic physiological functions throughout the human body. AQP-facilitated water permeability across cell membranes is required for rapid reabsorption of water from pre-urine in the kidneys and for sustained near isosmolar water fluxes e.g. in the brain, eyes, inner ear, and lungs. Cellular water permeability is further connected to cell motility. AQPs of the aquaglyceroporin subfamily are necessary for lipid degradation in adipocytes and glycerol uptake into the liver, as well as for skin moistening. Modulation of AQP function is desirable in several pathophysiological situations, such as nephrogenic diabetes insipidus, Sjögren's syndrome, Menière's disease, heart failure, or tumors to name a few. Attempts to design or to find effective small molecule AQP inhibitors have yielded only a few hits. Challenges reside in the high copy number of AQP proteins in the cell membranes, and spatial restrictions in the protein structure. This review gives an overview on selected physiological and pathophysiological conditions in which modulation of AQP functions appears beneficial and discusses first achievements in the search of drug-like AQP inhibitors.

The over-expression of aquaporin-1 alters erythroid gene expression in human erythroleukemia K562 cells

Aquaporin genes are differentially expressed in primitive versus definitive erythropoiesis. Our previous research results showed that over-expression of aquaporin-1 (AQP1) gene greatly promotes the erythroid differentiation of erythroleukemia K562 cells, using benzidine staining and quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) analysis for representative erythroid-related genes, including γ-globin. But the molecular mechanisms underlying erythroid-specific gene regulation remain unknown. In this study, we demonstrated that AQP1 induced hemoglobins expression and altered erythroid gene expression by microarray analysis in K562 cells. The retroviral expression vector of AQP1 (pBABE-puro-AQP1) was constructed and infected K562 cells to establish a stable AQP1 over-expression cell line (K562-AQP1). AQP1 over-expression effectively inhibited cell proliferation and induced cell growth arrest in G1 phase of K562 cells. Then microarray profile was applied to analyze the differentially expressed genes which involved the mechanism of AQP1 in erythroid differentiation induction. The DAVID functional annotation clustering tool was used to identify biological functions enriched with the differentially expressed genes (n = 466 genes) and to group genes into clusters based on their functional similarity. Significant enrichment of genes involved in "oxygen transporter activity" (p = 3.8E-7) including hemoglobins (HBD, HBG, HBB, HBE1, and HBQ1), HEMGN, and EBP42 were validated by qRT-PCR. Moreover, silencing of HEMGN by RNA interference in K562-AQP1 cells resulted in down-regulation of these genes. These data provide a better understanding of the role of AQP1 in erythroid differentiation, by promoting HEMGN induction and other potential signaling pathways associated with hemoglobin induction.

Functional properties of ion channels and transporters in tumour vascularization

Vascularization is crucial for solid tumour growth and invasion, providing metabolic support and sustaining metastatic dissemination. It is now accepted that ion channels and transporters play a significant role in driving the cancer growth at all stages. They may represent novel therapeutic, diagnostic and prognostic targets for anti-cancer therapies. On the other hand, although the expression and role of ion channels and transporters in the vascular endothelium is well recognized and subject of recent reviews, only recently has their involvement in tumour vascularization been recognized. Here, we review the current literature on ion channels and transporters directly involved in the angiogenic process. Particular interest will be focused on tumour angiogenesis in vivo as well as in the different steps that drive this process in vitro, such as endothelial cell proliferation, migration, adhesion and tubulogenesis. Moreover, we compare the 'transportome' system of tumour vascular network with the physiological one.

New insights into the mechanism for VACM-1/cul5 expression in vascular tissue in vivo

Vasopressin-activated calcium-mobilizing (VACM-1)/cul5 is the least conserved member of a cullin protein family involved in the formation of E3-specific ligase complexes that are responsible for delivering the ubiquitin protein to their target substrate proteins selected for ubiquitin-dependent degradation. This chapter summarizes work to date that has focused on VACM-1/cul5's tissue-specific expression in vivo and on its potential role in the control of specific cellular signaling pathways in those structures. As mammalian cells may contain hundreds of E3 ligases, identification VACM-1/cul5 as a specific subunit of the system that is expressed in the endothelium and in collecting tubules, structures known for their control of cellular permeability, may have significant implications when designing studies to elucidate the mechanism of water conservation. For example, VACM-1/cul5 expression is affected by water deprivation in some tissues and there is a potential relationship between neddylated VACM-1/cul5 and aquaporins.

Aquaporins in cancer

BACKGROUND

The aquaporins (AQPs) are a family of 13 small hydrophobic integral transmembrane water channel proteins involved in transcellular and transepithelial water movement, transport of fluid and cell migration.

SCOPE OF THE REVIEW

This review article summarizes our knowledge concerning the involvement of AQPs in tumor growth, angiogenesis and metastatic process.

MAJOR CONCLUSIONS

Tumor cells types express AQPs and a positive correlation exists between histological tumor grade and the AQP expression. Moreover, AQPs are involved also in tumor edema formation and angiogenesis in several solid and hematological tumors.

GENERAL SIGNIFICANCE

AQPs inhibition in endothelial and tumor cells might limit tumor growth and spread, suggesting a potential therapeutic use in the treatment of tumors. This article is part of a Special Issue entitled Aquaporins.

siRNA-chitosan complexes in poly(lactic-co-glycolic acid) nanoparticles for the silencing of aquaporin-1 in cancer cells

A large number of studies document the strong expression of aquaporin-1 (AQP1) in tumor microvessels and correlate this aberrant expression with higher metastatic potential and aggressiveness of the malignancy. Although small animal experiments have shown that the modulation of AQP1 expression can halt angiogenesis and induce tumor regression, effective and safe strategies for the tissue specific inhibition of AQP1 are still missing. Here, small interference RNA-chitosan complexes encapsulated in poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) are proposed for the intracellular delivery of siRNA molecules against AQP1. These NPs are coated with poly(vinyl alcohol) (PVA), to improve stability under physiological conditions, and demonstrate a diameter of 160 nm. The partial neutralization of the negatively charged siRNA molecules with the cationic chitosan enhances the loading by 5-fold, as compared to that of the free siRNA molecules, and allows one to modulate the release kinetics in the pH-dependent manner. At pH = 7.4, mimicking the conditions found in the systemic circulation, only the 40% of siRNA is released at 24 h post incubation; whereas at pH = 5.0, recreating the cell endosomal environment, all siRNA molecules are released in about 3 h. These NPs show no cytotoxicity on HeLa cells up to 72 h of incubation. In the same cells, transfected to overexpress AQP1, a silencing efficiency of 70% is achieved at 24 h post treatment with siRNA-loaded NPs. Confocal microscopy analysis of NP uptake demonstrates that siRNA molecules accumulate perinuclearly and in the nucleus. Given the stability, preferential release behavior, and well-known biocompatibility properties of PLGA nanostructures, these siRNA-loaded NPs hold potential for the efficient and safe in vivo silencing of AQPs via systemic administration.

Aquaporin-1 plays a crucial role in estrogen-induced tubulogenesis of vascular endothelial cells

CONTEXT

Aquaporin-1 (AQP1) has been proposed as a mediator of estrogen-induced angiogenesis in human breast cancer and endometrial cancer. Elucidation of the molecular mechanisms governing AQP1-mediated, estrogen-induced angiogenesis may contribute to an improved understanding of tumor development.

OBJECTIVE

Our objective was to identify the estrogen-response element (ERE) in the promoter of the Aqp1 gene and investigate the effects and mechanisms of AQP1 on estrogen-induced tubulogenesis of vascular endothelial cells.

SETTING

The study was conducted in a university hospital in eastern China.

MAIN OUTCOME MEASURES

Immunohistological, real-time PCR and Western blot analyses were used to determine the expression AQP1 mRNA and protein in vascular endothelial cells. Chromatin immunoprecipitation analyses and luciferase reporter assays identified ERE-like motif in the promoter of the Aqp1 gene.

RESULTS

Expression of AQP1 in blood vessels of human breast and endometrial carcinoma tissues were significantly higher than controls. Estradiol (E2) dose-dependently increased the expression levels of AQP1 mRNA and protein in human umbilical vein endothelial cells (HUVECs). A functional ERE-like motif was identified in the promoter of the Aqp1 gene. AQP1 colocalized with ezrin, a component of the ezrin/radixin/moesin protein complex, and, ezrin colocalized with filamentous actin in HUVECs. Knockdown of AQP1 or ezrin with specific small interfering RNA significantly attenuated the formation of transcytoplasmic filamentous actin stress fibers induced by E2 and inhibited E2-enhanced cell proliferation, migration, invasion, and tubule formation of HUVECs.

CONCLUSIONS

Estrogen induces AQP1 expression by activating ERE in the promoter of the Aqp1 gene, resulting in tubulogenesis of vascular endothelial cells. These results provide new insights into the molecular mechanisms underpinning the angiogenic effects of estrogen.

Molecular basis of the inner blood-retinal barrier and its breakdown in diabetic macular edema and other pathological conditions

Breakdown of the inner endothelial blood-retinal barrier (BRB), as occurs in diabetic retinopathy, age-related macular degeneration, retinal vein occlusions, uveitis and other chronic retinal diseases, results in vasogenic edema and neural tissue damage, causing loss of vision. The central mechanism of altered BRB function is a change in the permeability characteristics of retinal endothelial cells caused by elevated levels of growth factors, cytokines, advanced glycation end products, inflammation, hyperglycemia and loss of pericytes. Subsequently, paracellular but also transcellular transport across the retinal vascular wall increases via opening of endothelial intercellular junctions and qualitative and quantitative changes in endothelial caveolar transcellular transport, respectively. Functional changes in pericytes and astrocytes, as well as structural changes in the composition of the endothelial glycocalyx and the basal lamina around BRB endothelium further facilitate BRB leakage. As Starling's rules apply, active transcellular transport of plasma proteins by the BRB endothelial cells causing increased interstitial osmotic pressure is probably the main factor in the formation of macular edema. The understanding of the complex cellular and molecular processes involved in BRB leakage has grown rapidly in recent years. Although appropriate animal models for human conditions like diabetic macular edema are lacking, these insights have provided tools for rational design of drugs aimed at restoring the BRB as well as for design of effective transport of drugs across the BRB, to treat the chronic retinal diseases such as diabetic macular edema that affect the quality-of-life of millions of patients.

Discovery of novel human aquaporin-1 blockers

Human aquaporin-1 (hAQP1) is a water channel found in many tissues and potentially involved in several human pathologies. Selective inhibitors of hAQP1 are discussed as novel treatment opportunities for glaucoma, brain edema, inflammatory pain, and certain types of cancer. However, only very few potent and chemically attractive blockers have been reported to date. In this study we present three novel hAQP1 blockers that have been identified by virtual screening and inhibit water flux through hAQP1 in Xenopus laevis oocyte swelling assays at low micromolar concentrations. The newly discovered compounds display no chemical similarity to hitherto known hAQP1 blockers and bind at the extracellular entrance of the channel, close to the ar/R selectivity filter. Furthermore, mutagenesis studies showed that Lys36, which is not conserved among the hAQP family, is crucially involved in binding and renders the discovered compounds suitable as leads for the development of selective hAQP1 inhibitors.

Involvement of COX-2/PGE2 signalling in hypoxia-induced angiogenic response in endothelial cells

To evaluate the impact of hypoxia on the angiogenic capability of endothelial cells (ECs), and further investigate whether the cyclooxygenase-2 (COX-2)/prostaglandin E(2) (PGE(2)) signalling is involved in the angiogenic response of ECs to hypoxia. We explored the impact of various periods (1, 3, 6, 12, 24 hrs) of hypoxia (2% O(2)) on human umbilical vein endothelial cells (HUVECs) in vitro. We observed cell viability, migration, tube formation, analysed COX-2, vascular endothelial growth factor (VEGF), AQP1 mRNA transcription, protein expression and measured PGE(2), VEGF protein concentration in cell supernatants. Then we treated HUVECs with COX-2 selective inhibitor NS398, EP1/2 combined antagonist AH6809 and exogenous PGE(2) to investigate the role of COX-2/PGE(2) signalling in the angiogenic response of ECs to hypoxia. The results demonstrated that short-term hypoxic treatment enhanced HUVECs proliferation, migration, tube formation, significantly up-regulated COX-2, VEGF, AQP1 mRNA level, protein expression and promoted PGE(2) , VEGF release. The pharmacological inhibition study revealed that exposure of HUVEC to NS398 and AH6809 under hypoxia impaired the biological responses of ECs to hypoxia. Exogenous PGE(2) augments the effects of hypoxia on HUVECs, and partially reversed the inhibitory effects of NS398 on HUVECs proliferation and angiogenic capability. Short-term hypoxic treatment enhanced angiogenic capability of ECs, and COX-2/PGE(2) signalling may play a critical role in the biological response of ECs to hypoxia.

Cell culture models and animal models for studying the patho-physiological role of renal aquaporins

Aquaporins (AQPs) are key players regulating urinary-concentrating ability. To date, eight aquaporins have been characterized and localized along the nephron, namely, AQP1 located in the proximal tubule, thin descending limb of Henle, and vasa recta; AQP2, AQP3 and AQP4 in collecting duct principal cells; AQP5 in intercalated cell type B; AQP6 in intercalated cells type A in the papilla; AQP7, AQP8 and AQP11 in the proximal tubule. AQP2, whose expression and cellular distribution is dependent on vasopressin stimulation, is involved in hereditary and acquired diseases affecting urine-concentrating mechanisms. Due to the lack of selective aquaporin inhibitors, the patho-physiological role of renal aquaporins has not yet been completely clarified, and despite extensive studies, several questions remain unanswered. Until the recent and large-scale development of genetic manipulation technology, which has led to the generation of transgenic mice models, our knowledge on renal aquaporin regulation was mainly based on in vitro studies with suitable renal cell models. Transgenic and knockout technology approaches are providing pivotal information on the role of aquaporins in health and disease. The main goal of this review is to update and summarize what we can learn from cell and animal models that will shed more light on our understanding of aquaporin-dependent renal water regulation.

VACM-1/cul5 expression in vascular tissue in vivo is induced by water deprivation and its expression in vitro regulates aquaporin-1 concentrations

VACM-1, a cul5 gene product, when overexpressed in vitro, has an antiproliferative effect. In vivo, VACM-1/cul5 is present in tissues involved in the regulation of water balance. Neither proteins targeted for VACM-1/cul5-specific degradation nor factors that may regulate its expression in those tissues have been studied. To identify genes that may be misregulated by VACM-1 cDNA, we performed microarray analysis. Our results indicate that in cos-1 cells transfected with VACM-1 cDNA, mRNA levels for several genes, including AQP1, were decreased when compared to the control group. Our results also indicate that in cos-1 cells transfected with VACM-1 cDNA, endogenous AQP1 protein was decreased about 6-fold when compared to the controls. To test the hypothesis that VACM-1/cul5 may be regulated by conditions that compromise water homeostasis in vivo, we determined if 24 h of water deprivation affects VACM-1/cul5 levels or the effect of VACM-1/cul5 on AQP1. VACM-1 mRNA and protein levels were significantly higher in rat mesenteric arteries, skeletal muscle and the heart ventricle but not in the heart atrium from 24-h water-deprived rats when compared to the controls. Interestingly, 24 h of water deprivation increased modification of VACM-1 by an ubiquitin-like protein, Nedd8, essential for cullin-dependent E3 ligase activity. Although water deprivation did not significantly change AQP1 levels in the mesenteric arteries, AQP1 protein concentrations were inversely correlated with the ratio of the VACM-1 to Nedd8-modified VACM-1. These results suggest that VACM-1/cul5 may regulate endothelial AQP1 concentration both in vivo and in vitro.

Functional and transcriptional induction of aquaporin-1 gene by hypoxia; analysis of promoter and role of Hif-1α

Aquaporin-1 (AQP1) is a water channel that is highly expressed in tissues with rapid O₂ transport. It has been reported that this protein contributes to gas permeation (CO₂, NO and O₂) through the plasma membrane. We show that hypoxia increases Aqp1 mRNA and protein levels in tissues, namely mouse brain and lung, and in cultured cells, the 9L glioma cell line. Stopped-flow light-scattering experiments confirmed an increase in the water permeability of 9L cells exposed to hypoxia, supporting the view that hypoxic Aqp1 up-regulation has a functional role. To investigate the molecular mechanisms underlying this regulatory process, transcriptional regulation was studied by transient transfections of mouse endothelial cells with a 1297 bp 5′ proximal Aqp1 promoter-luciferase construct. Incubation in hypoxia produced a dose- and time-dependent induction of luciferase activity that was also obtained after treatments with hypoxia mimetics (DMOG and CoCl₂) and by overexpressing stabilized mutated forms of HIF-1α. Single mutations or full deletions of the three putative HIF binding domains present in the Aqp1 promoter partially reduced its responsiveness to hypoxia, and transfection with Hif-1α siRNA decreased the in vitro hypoxia induction of Aqp1 mRNA and protein levels. Our results indicate that HIF-1α participates in the hypoxic induction of AQP1. However, we also demonstrate that the activation of Aqp1 promoter by hypoxia is complex and multifactorial and suggest that besides HIF-1α other transcription factors might contribute to this regulatory process. These data provide a conceptual framework to support future research on the involvement of AQP1 in a range of pathophysiological conditions, including edema, tumor growth, and respiratory diseases.

Aquaporin-1 associated with hepatic arterial capillary proliferation on hepatic sinusoid in human cirrhotic liver

BACKGROUND

Aquaporins (AQPs) are key regulators not only of water transport in the cytoplasm but also of angiogenesis. Although AQPs in the normal hepatobiliary system have been studied in mammals, little is known about the localization and changes of AQPs in the hepatic microvascular system including sinusoids in cirrhotic liver, which might contribute to portal hypertension.

AIMS

We designed this study to examine the localization of AQP1 in human cirrhotic liver.

METHODS

Surgical wedge biopsy specimens were obtained from non-cirrhotic portions of human livers (normal control) and from cirrhotic livers (LC) (Child A-LC and Child C-LC). Immunostaining, Western blotting, in situ hybridization (ISH) and laser-captured microdissection (LCM) were conducted.

RESULTS

In control liver tissue, AQP1 was localized mainly in the portal venules, hepatic arterioles and bile ducts in the portal tract, although AQP1 was detected only slightly in the sinusoids. In cirrhotic liver tissue, AQP1 expression was evident, aberrantly observed on periportal sinusoidal endothelial cells corresponding to the capillarized sinusoids, on the proliferated arterial capillaries opening into the sinusoid in the generating hepatic nodule and on proliferated bile ductules at the peripheral edge of nodules and fibrotic septa. In cirrhotic liver, overexpression of AQP1 at protein and mRNA levels was demonstrated, respectively, using Western blot and ISH. AQP-1 of mRNA level in sinusoid was confirmed using LCM.

CONCLUSIONS

Aberrant expressions of AQP1 in periportal sinusoidal regions in human cirrhotic liver indicate the proliferation of arterial capillaries directly connected to the sinusoids, contributing to microvascular resistance in cirrhosis.