Characteristics of aquaporin 1, 3, and 5 expression during early murine salivary gland development

Aquaporins (AQPs) are essential to coordinate the transit of water and ions through the cell membrane. In salivary glands (SGs), AQPs have been associated with saliva formation, facilitating water absorption through the epithelium during the formation of hypotonic saliva, which is then secreted into the oral cavity. Different members of the AQP family have been suggested to play distinct roles during embryonic development, highlighted by their specific expression patterns. Here, we have investigated the expression patterns of AQP-1, AQP-3 and AQP-5 by immunofluorescence at key stages of salivary gland development, utilising cultured mouse embryonic submandibular (SMG) and sublingual (SLG) glands. The expression of AQPs was compared to a mitotic marker, phospho-histone 3 (PH3), a myoepithelial marker, smooth muscle actin (SMA), and a vascular marker, CD31. Qualitative analysis revealed that AQP-1 and AQP-3 were primarily expressed during the earlier phases of SG morphogenesis and were associated with cells undergoing mitotic processes (PH3-positive). AQP-5, in contrast, was not associated to mitotic figures, but was predominantly expressed during late stages of SG morphogenesis. Our results highlight that AQPs are expressed from early stages of SG morphogenesis and exhibit complimentary expression patterns that may contribute to the morphogenesis of salivary glands.     

Expression and localization of epithelial aquaporins in the adult human lung

Aquaporins (AQPs) facilitate water transport across epithelia and play an important role in normal physiology and disease in the human airways. We used in situ hybridization and immunofluorescence to determine the expression and cellular localization of AQPs 5, 4, and 3 in human airway sections. In nose and bronchial epithelia, AQP5 is expressed at the apical membrane of columnar cells of the superficial epithelium and submucosal gland acinar cells. AQP4 was detected in basolateral membranes in ciliated ducts and by in situ in gland acinar cells. AQP3 is present on basal cells of both superficial epithelium and gland acinus. In these regions AQPs 5, 4, and 3 are appropriately situated to permit transepithelial water permeability. In the small airways (proximal and terminal bronchioles) AQP3 distribution shifts from basal cell to surface expression (i.e., localized to the apical membrane of proximal and terminal bronchioles) and is the only AQP identified in this region of the human lung. The alveolar epithelium has all three AQPs represented, with AQP5 and AQP4 localized to type I pneumocytes and AQP3 to type II cells. This study describes an intricate network of AQP expression that mediates water transport across the human airway epithelium.     

Intracellular aquaporins: clues for intracellular water transport?

Aquaporins (AQPs) are usually present at the plasma membrane to regulate influx and outflow of water and small molecules. They are important for the regulation of water homeostasis for the cells and organisms. AQPs are also present inside the cell, at the membranes of intracellular organelles. The roles of such AQPs have not yet been established. They will be clues to clarify the mechanisms of water and small solutes movements inside the cell. Recently, a new AQP subfamily has been identified with highly deviated asparagine-proline-alanine boxes, signature sequences for AQP. With limited homology less than 20%, this subfamily will be a superfamily of AQPs. Accordingly, it was tentatively named "superaquaporin subfamily," which is so far only present in multicellular organisms including plants, insects, nematodes, and vertebrates. Some superaquaporins are functionally water channels and localized intracellularly. AQP11, one of the two superaquaporins in mammals, has been shown to be important for the development of the proximal tubule as its disruption produced neonatally fatal polycystic kidneys in mice. Hence, recent identification of intracellular AQPs will open new areas of research on cell biology and expand the scope of AQPs.     

Aquaporin 1 expression in cystic hemangioblastomas

Hemangioblastomas of the central nervous system (CNS) become clinically manifest through the development of huge associated cysts. The mechanism underlying these fluid collections is as yet largely unexplained. Aquaporins (AQPs) are cell proteins responsible for transmembrane water transport that have been extensively studied in the last 10 years. We analyzed AQP1 water channel expression by an immunostaining technique in ten specimens of operated cerebellar cystic hemangioblastomas, for which complete clinical and follow-up records were available. Tumour and associated cyst volumes were determined by neuroimaging and then compared with immunohistochemical scores. Stromal cancer cells showed surprisingly high AQP1 expression, and huge cyst volume development showed correlation with higher immunostaining scores. Heavy AQP1 expression in cystic hemangioblastomas could shed new light on the mechanisms of satellite cyst development.     

肺脏的水孔蛋白家族

90年代以来 ,作为膜上水分子通道的水孔蛋白(ａｑｕａｐｏｒｉｎｓ ,ＡＱＰｓ)家族克隆成功[1,2 ] ,对自由水被动跨膜转运机制做出更加形象而深入的解释。肺脏的许多生理功能都有水分子运动的参与 ,同时许多肺脏疾病 ,如哮喘、肺水肿和急性呼吸窘迫综合征等也涉及肺内水运动平衡的紊乱。因此肺内水孔蛋白的分布及其病理生理意义日益受到重视。1　水孔蛋白的结构与功能特点水孔蛋白属于膜主体内在蛋白 (ｍａｊｏｒｉｎｔｅｒｎａｌｐｒｏｔｅｉｎ ,ＭＩＰ)家族的成员 ,目前在人类和哺乳动物身上共发现 10个亚型 ,广泛分布于多个组织器官 ,具…     

Upregulation of AQP3 and AQP5 induced by dexamethasone and ambroxol in A549 cells

Aquaporins (AQPs) are membrane channel proteins that play roles in the regulation of water permeability in many tissues. AQP1 and AQP5 expressed in lung provide the principal route for osmotically driven water transport. In the airways, AQP3 and AQP4 facilitate water transport. Dexamethasone and ambroxol are often used to treat patients with pulmonary diseases accompanied by airway hypersecretion. The role of AQPs in these effective treatments has not been addressed. In this study, we analyzed the expression of AQPs in a human airway epithelial cell line (A549 cells) and showed that AQP3 and 5, but not AQP1 and 4, were expressed in A549 cells. Both dexamethasone and ambroxol stimulated the expression of AQP3 and 5 at the mRNA and protein levels. The data suggest potential roles of AQP3 and 5 in the regulation of airway hypersecretion, perhaps ultimately providing a target for treating such diseases.     

Aquaporins—new players in cancer biology

The aquaporins (AQPs) are small, integral-membrane proteins that selectively transport water across cell plasma membranes. A subset of AQPs, the aquaglyceroporins, also transport glycerol. AQPs are strongly expressed in tumor cells of different origins, particularly aggressive tumors. Recent discoveries of AQP involvement in cell migration and proliferation suggest that AQPs play key roles in tumor biology. AQP1 is ubiquitously expressed in tumor vascular endothelium, and AQP1-null mice show defective tumor angiogenesis resulting from impaired endothelial cell migration. AQP-expressing cancer cells show enhanced migration in vitro and greater local tumor invasion, tumor cell extravasation, and metastases in vivo. AQP-dependent cell migration may involve AQP-facilitated water influx into lamellipodia at the front edge of migrating cells. The aquaglyceroporin AQP3, which is found in normal epidermis and becomes upregulated in basal cell carcinoma, facilitates cell proliferation in different cell types. Remarkably, AQP3-null mice are resistant to skin tumorigenesis by a mechanism that may involve reduced tumor cell glycerol metabolism and ATP generation. Together, the data suggest that AQP expression in tumor cells and tumor vessels facilitates tumor growth and spread, suggesting AQP inhibition as a novel antitumor therapy.     

Aquaporin-8 mediates human esophageal cancer Eca-109 cell migration via the EGFR-Erk1/2 pathway

Abnormal expression of aquaporins (AQPs) has been reported in several human cancers. Epidermal growth factor receptor (EGFR)-extracellular signal-regulated kinases1/2 (ERK1/2) are associated with tumorigenesis and cancer progression and may upregulate AQPs expression. In this study, we investigated acquaporin-8 expression and signaling via epidermal growth factor receptor-extracellular signal-regulated kinases1/2 in human esophageal cancer Eca-109 cells by western blot, immunofluorescence and wound healing (scratch) assays. Our results showed that epidermal growth factor (EGF) induced both Eca-109 migration and AQP8 expression. Wound healing results showed that cell migration was increased by 1.23-1.10-fold at 24 h and 48 h after EGF treatment. AQP8 expression was significantly increased (1.19-fold) at 48 h after EGF treatment in Eca-109. The EGFR kinase inhibitor, PD153035, blocked EGF-induced AQP8 expression and cell migration. AQP8 expression was decreased from 3.65-fold (EGF-treated) to 0.55-fold (PD153035-treated) in Eca-109. Furthermore, the MEK [MAPK (mitogen-activated protein kinase)/Erk1/2]/Erk1/2 inhibitor U0126 also inhibited EGF-induced AQP8 expression and cell migration. AQP8 expression was decreased from 3.92-fold (EGF-treated) to 1.38-fold (U0126-treated) in Eca-109. In conclusions, EGF induces AQP8 expression and cell migration in Eca-109 cells via the EGFR/Erk1/2 signal transduction pathway.     

Role of human aquaporin 5 in colorectal carcinogenesis

While overexpression of several aquaporins (AQPs) has been reported in different types of human cancer, the role of AQPs in carcinogenesis has not been clearly defined. Here, by immunochemistry, we have found expression of AQP5 protein in 62.8% (59/94) of resected colon cancer tissue samples as well as association of AQP5 with liver metastasis. We then demonstrated that overexpression of human AQP5 (hAQP5) induces cell proliferation in colon cancer cells. Overexpression of wild-type hAQP5 increased proliferation and phosphorylation of extracellular signal-regulated kinase-1/2 in HCT116 colon cancer cells whereas these phenomena in hAQP5 mutants (N185D and S156A) were diminished, indicating that both membrane association and serine/threonine phosphorylation of AQP5 are required for proper function. Interestingly, overexpression of AQP1 and AQP3 showed no differences in extracellular signal-regulated kinase-1/2 phosphorylation, suggesting that AQP5, unlike AQP1, may be involved in signal transduction. Moreover, hAQP5-overexpressing cells showed an increase in retinoblastoma protein phosphorylation through the formation of a nuclear complex with cyclin D1 and CDK4. Small interfering RNA analysis confirmed that hAQP5 activates the Ras signaling pathway. These data not only describe the induction of hAQP5 expression during colorectal carcinogenesis but also provide a molecular mechanism for colon cancer development through the interaction of hAQP5 with the Ras/extracellular signal-regulated kinase/retinoblastoma protein signaling pathway, identifying hAQP5 as a novel therapeutic target.     

AQP1 expression in human gingiva and its correlation with periodontal and peri-implant tissue alterations

Aquaporins (AQPs) are a family of hydrophobic integral membrane proteins that function as transmembrane channels and play an important role in tissue homeostasis. Aquaporin-1 (AQP1), in particular, has been reported to be involved in several biological processes including inflammation, angiogenesis, wound healing and others. Periodontitis and peri-implantitis can be defined as inflammatory processes that affect the tissues surrounding a tooth or an osseointegrated implant, respectively. To date, there are limited data about the involvement of AQPs in these diseases. The aim of this study was to evaluate the possible link between the histomorphological alterations and the expression of AQP1 in healthy, pathological and healed periodontal and peri-implant gingival tissues. The results obtained showed that changes in organization of collagen fibers were observed in periodontitis and peri-implantitis, together with an increase in the percentage of area occupied by inflammatory cell infiltration and an increase of AQP1 immunostaining, which was located in the endothelial cells of the vessels within the lamina propria. Moreover, in healed periodontal and peri-implant mucosa a restoration of histomorphological alterations was observed together with a concomitant decrease of AQP1 immunostaining. These data suggested a possible link between the degree of inflammatory state and the presence of AQP1, where the latter could be involved in the chain of inflammatory reactions triggered at periodontal and peri-implant levels.     

Water permeability through aquaporin-4 is regulated by protein kinase C and becomes rate-limiting for glioma invasion

Glial-derived tumors, gliomas, are highly invasive cancers that invade normal brain through the extracellular space. To navigate the tortuous extracellular spaces, cells undergo dynamic changes in cell volume, which entails water flux across the membrane through aquaporins (AQPs). Two members of this family, AQP1 and AQP4 are highly expressed in primary brain tumor biopsies and both have a consensus phosphorylation site for protein kinase C (PKC), which is a known regulator of glioma cell invasion. AQP4 colocalizes with PKC to the leading edge of invading processes and clustered with chloride channel (ClC2) and K⁺–Cl⁻ cotransporter 1 (KCC1), believed to provide the pathways for Cl⁻ and K⁺ secretion to accomplish volume changes. Using D54MG glioma cells stably transfected with either AQP1 or AQP4, we show that PKC activity regulates water permeability through phosphorylation of AQP4. Activation of PKC with either phorbol 12-myristate 13-acetate or thrombin enhanced AQP4 phosphorylation, reduced water permeability and significantly decreased cell invasion. Conversely, inhibition of PKC activity with chelerythrine reduced AQP4 phosphorylation, enhanced water permeability and significantly enhanced tumor invasion. PKC regulation of AQP4 was lost after mutational inactivation of the consensus PKC phosphorylation site S180A. Interestingly, AQP1 expressing glioma cells, by contrast, were completely unaffected by changes in PKC activity. To demonstrate a role for AQPs in glioma invasion in vivo, cells selectively expressing AQP1, AQP4 or the mutated S180A-AQP4 were implanted intracranially into SCID mice. AQP4 expressing glioma cells showed significantly reduced invasion compared to AQP1 and S180 expressing tumors as determined by quantitative stereology, consistent with a differential role for AQP1 and AQP4 in this process.     

Role of galectin-3 in the pathogenesis of bladder transitional cell carcinoma

Galectins constitute an evolutionary conserved family that binds to β-galactosides. There is growing evidence that galectins are implicated in essential biological processes such as cellular communication, inflammation, differentiation and apoptosis. Galectin-3 is one of the best-known galectins, which is found in vertebrates. Galectin-3 has been shown to be expressed in some cell lines and plays important roles in several physiological and pathological processes, including cell adhesion, cell activation and chemoattraction, cell cycle, apoptosis, cell growth, and differentiation. Moreover, this galectin is of interest due to its involvement in regulation of cancer. Changes in galectin-3 expression are commonly seen in cancerous and pre-cancerous conditions and galectin-3 may be involved in the regulation of cancer cell activities that contribute to tumourigenesis, cancer progression and metastasis. Finally, galectin-3 seems to be involved in cell events in tumor microenvironment, and therefore it could be considered as a target in transitional cell carcinoma therapies. This review aims to describe recent progress in understanding the role of galectin-3 in cancer biology, with emphasis on bladder tumor progression and metastasis.     

Aquaporins and cell migration

Aquaporin (AQP) water channels are expressed primarily in cell plasma membranes. In this paper, we review recent evidence that AQPs facilitate cell migration. AQP-dependent cell migration has been found in a variety of cell types in vitro and in mice in vivo. AQP1 deletion reduces endothelial cell migration, limiting tumor angiogenesis and growth. AQP4 deletion slows the migration of reactive astrocytes, impairing glial scarring after brain stab injury. AQP1-expressing tumor cells have enhanced metastatic potential and local infiltration. Impaired cell migration has also been seen in AQP1-deficient proximal tubule epithelial cells, and AQP3-deficient corneal epithelial cells, enterocytes, and skin keratinocytes. The mechanisms by which AQPs enhance cell migration are under investigation. We propose that, as a consequence of actin polymerization/depolymerization and transmembrane ionic fluxes, the cytoplasm adjacent to the leading edge of migrating cells undergoes rapid changes in osmolality. AQPs could thus facilitate osmotic water flow across the plasma membrane in cell protrusions that form during migration. AQP-dependent cell migration has potentially broad implications in angiogenesis, tumor metastasis, wound healing, glial scarring, and other events requiring rapid, directed cell movement. AQP inhibitors may thus have therapeutic potential in modulating these events, such as slowing tumor growth and spread, and reducing glial scarring after injury to allow neuronal regeneration.     

肾上腺皮质激素对水通道蛋白表达的调节

肾上腺皮质激素参与水盐代谢的调节,盐皮质激素和糖皮质激素调节上皮细胞水通道蛋白 (Aquaporins,AQPs)的表达。盐皮质激素可使肾脏AQP3表达上调,对肾脏的AQP2表达依据刺激的时间不 同而表达不同,但对AQP1没有影响。糖皮质激素对不同组织器官AQPs的影响不尽相同。肾上腺皮质激素 对AQPs的调节作用在某些水代谢紊乱疾病的诊断与治疗方面可能有着广阔的应用前景。     

AQP1 mediates water transport in the carotid body

In this study, we explored the presence of aquaporins (AQPs), a family of membrane water channel proteins, in carotid body (CB) type I chemoreceptor cells. The CB is a polymodal chemoreceptor whose major function is to detect changes in arterial O₂ tension to elicit hyperventilation during hypoxia. The CB has also been proposed to function as a systemic osmoreceptor, thus we hypothesized that the presence of AQPs in type I cell membrane may confer higher sensitivity to osmolarity changes and hence accelerate the activation of chemoreceptor cells. We detected the expression of AQP1, AQP7, and AQP8 in the CB and confirmed the location of AQP1 in type I cells. We have also shown that inhibition of AQP1 expression clearly reduced type I cell swelling after a hyposmotic shock, demonstrating that AQP1 has a major contribution in transmembrane water movement in these chemoreceptor cells. Interestingly, CB AQP1 expression levels change during postnatal development, increasing during the first postnatal weeks as the organ matures. In conclusion, in this study, we report the novel observation that AQPs are expressed in the CB. We also show that AQP1 mediates water transport across the cell membrane of type I cells, supporting the contribution of this protein to the osmoreception function of the CB.     

The role of aquaporin-4 in the blood-brain barrier development and integrity: studies in animal and cell culture models

Aquaporin-4 (AQP4) is the major water channel expressed in brain perivascular astrocyte processes. Although the role of AQP4 in brain edema has been extensively investigated, little information exists regarding its functional role at the blood-brain barrier (BBB). The purpose of this work is to integrate previous and recent data regarding AQP4 expression during BBB formation and depending on BBB integrity, using several experimental models. Results from studies on the chick optic tectum, a well-established model of BBB development, and the effect of lipopolysaccharide on the BBB integrity and on perivascular AQP4 expression have been analyzed and discussed. Moreover, data on the BBB structure and AQP4 expression in murine models of Duchenne muscular dystrophy are reviewed. In particular, published results obtained from mdx(3cv) mice have been analyzed together with new data obtained from mdx mice in which all the dystrophin isoforms including DP71 are strongly reduced. Finally, the role of the endothelial component on AQP4 cellular expression and distribution has been investigated using rat primary astrocytes and brain capillary endothelial cell co-cultures as an in vitro model of BBB.     

CXCR4 and cancer

The chemokine receptor CXCR4 belongs to the large superfamily of G protein‐coupled receptors and has been identified to play a crucial role in a number of biological processes, including the trafficking and homeostasis of immune cells such as T lymphocytes. CXCR4 has also been found to be a prognostic marker in various types of cancer, including leukemia and breast cancer, and recent evidence has highlighted the role of CXCR4 in prostate cancer. Furthermore, CXCR4 expression is upregulated in cancer metastasis, leading to enhanced signaling. These observations suggest that CXCR4 is important for the progression of cancer. The CXCR4‐CXCL12 (stromal cell‐derived factor 1 (SDF‐1)) axis has additionally been identified to have a role in normal stem cell homing. Interestingly, cancer stem cells also express CXCR4, indicating that the CXCR4‐SDF‐1 axis may direct the trafficking and metastasis of these cells to organs that express high levels of SDF‐1, such as the lymph nodes, lungs, liver, and bone. This review focuses on the current knowledge of CXCR4 regulation and how deregulation of this protein may contribute to the progression of cancer.     

胎儿发育中水通道蛋白的免疫组化观察

目的观察胎儿器官和组织发育过程中水通道蛋白(AQPs)的表达特征,初步探讨AQPs对胎儿发育进程的生物意义。方法14～38周胎儿共12例,取用肾脏、肺脏、唾液腺、甲状腺和胃等器官,常规固定、石蜡包埋和切片;用免疫组化S-P法,检测AQPs(AQP1、AQP2和AQP4)在胎儿不同胎龄器官组织中的表达。结果胎儿肾脏中AQPs定位于近端小管和集合管系统;胎肺中AQPs的表达随肺泡发育分化而迁移,始终定位于肺泡上皮;晚期胎肺中AQPs于肺泡及呼吸道上皮均有表达;胎16周起检出AQPs反应于唾液腺、胃腺和胰腺等消化腺,同时甲状腺中AQPs在滤泡上皮也有活跃表达。结论胎肾中AQPs的表达与肾的重吸收功能直接相关;胎肺内AQPs的表达反映肺泡上皮分化的轨迹,其调节水分的作用为肺泡发育提供空间;AQPs介导细胞内外水分的转运不但调节消化腺的分泌还参与调节甲状腺滤泡的激素合成和分泌过程。表明AQPs在胎儿发育过程,对各器官中水转运功能的成熟起重要作用。     

Role of aquaporins in lung liquid physiology

Aquaporins (AQPs) are small, integral membrane proteins that facilitate water transport across cell membranes in response to osmotic gradients. Water transport across epithelia and endothelia in the peripheral lung and airways occurs during airway hydration, alveolar fluid transport and submucosal gland secretion. Several AQPs are expressed in the lung and airways: AQP1 in microvascular endothelia, AQP3 and AQP4 in airway epithelia, and AQP5 in type I alveolar epithelial cells, submucosal gland acini, and a subset of airway epithelial cells. Phenotype analysis of transgenic knockout mice lacking AQPs has defined their roles in the lung and airways. AQP1 and AQP5 provide the principal route for osmotically driven water transport between airspace and capillary compartments; however, alveolar fluid clearance in the neonatal and adult lung is not affected by their deletion, nor is lung fluid accumulation in experimental models of lung injury. In the airways, though AQP3 and AQP4 facilitate osmotic water transport, their deletion does not impair airway hydration, regulation of airway surface liquid, or fluid absorption. In contrast to these negative findings, AQP5 deletion in submucosal glands reduced fluid secretion by >50%. The substantially slower fluid transport in the lung compared to renal and secretory epithelia probably accounts for the lack of functional significance of AQPs in the lung and airways. Recent data outside of the lung implicating the involvement of AQPs in cell migration and proliferation suggests possible new roles for lung AQPs to be explored.