Lead induces increased water permeability in astrocytes expressing aquaporin 4

The water channel aquaporin 4 (AQP4) is abundantly expressed in astrocytes. There is now compelling evidence that AQP4 may contribute to an unfavorable course in brain edema. Acute lead intoxication is a condition that causes brain damage preceded by brain edema. Here we report that lead increases AQP4 water permeability (P(f)) in astrocytes. A rat astrocyte cell line that does not express aquaporin 4 was transiently transfected with aquaporin 4 tagged with green fluorescent protein (GFP). Using confocal laser scanning microscopy we measured water permeability in these cells and in AQP4-negative cells located on the same plate. AQP4-expressing astrocytes had a three-fold higher water permeability than astrocytes not expressing AQP4. Lead exposure induced a significant, 40%, increase in water permeability in astrocytes expressing AQP4, but had no effect on P(f) in astrocytes not expressing AQP4. The increase in water permeability persisted after lead washout, while treatment with a lead chelator, meso-2,3-dimercaptosuccinic acid, abolished the lead-induced increase in P(f). The effect of lead was attenuated in the presence of a calcium (Ca(2+))/calmodulin-dependent protein kinase II (CaMKII) inhibitor, but not in the presence of a protein kinase C inhibitor. In cells expressing AQP4 where the consensus site for CaMKII phosphorylation was mutated, lead failed to increase water permeability. Lead exposure also increased P(f) in rat astroglial cells in primary culture, which express endogenous AQP4. Lead had no effect on P(f) in astrocytes transfected with aquaporin 3. In situ hybridization studies on rat brain after oral lead intake for three days showed no change in distribution of AQP4 mRNA. It is suggested that lead-triggered stimulation of water transport in AQP4-expressing astrocytes may contribute to the pathology of acute lead intoxication.     

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.     

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.     

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.     

Positive and negative regulation of water channel aquaporins in human small intestine by cholera toxin

Analysis of osmotic water permeability of aquaporin (AQP) 1, AQP3 and AQP4, which are expressed in human small intestine, in the presence or absence of cholera toxin (CT) was performed using a Xenopus oocyte expression system. When treated with CT, water permeability of AQP4 was facilitated while that of AQP3 was suppressed. AQP1 did not show any significant change of water permeability when treated with CT. An adenylyl cyclase accelerator forskolin showed similar effects as CT did, suggesting that changes of the water permeability of AQP4 and AQP3 were due to an increase of intracellular cAMP concentration. A possibility that these AQPs are responsible molecules for causing acute secretory diarrhoea as in cholera is considered.     

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.     

Missorting of the Aquaporin-2 mutant E258K to multivesicular bodies/lysosomes in dominant NDI is associated with its monoubiquitination and increased phosphorylation by PKC but is due to the loss of E258

To stimulate renal water reabsorption, vasopressin induces phosphorylation of Aquaporin-2 (AQP2) water channels at S256 and their redistribution from vesicles to the apical membrane, whereas vasopressin removal results in AQP2 ubiquitination at K270 and its internalization to multivesicular bodies (MVB). AQP2-E258K causes dominant nephrogenic diabetes insipidus (NDI), but its subcellular location is unclear, and the molecular reason for its involvement in dominant NDI is unknown. To unravel these, AQP2-E258K was studied in transfected polarized Madin–Darby canine kidney (MDCK) cells. In MDCK cells, AQP2-E258K mainly localized to MVB/lysosomes (Lys). Upon coexpression, wild-type (wt) AQP2 and AQP2-E258K formed multimers, which also localized to MVB/Lys, independent of forskolin stimulation. Orthophosphate labeling revealed that forskolin increased phosphorylation of wt-AQP2 and AQP2-E258K but not AQP2-S256A, indicating that the E258K mutation does not interfere with the AQP2 phosphorylation at S256. In contrast to wt-AQP2 but consistent with the introduced protein kinase C (PKC) consensus site, AQP2-E258K was phosphorylated by phorbol esters. Besides the 29-kDa band, however, an additional band of about 35 kDa was observed for AQP2-E258K only, which represented AQP2-E258K uniquely monoubiquitinated at K228 only. Analysis of several mutants interfering with AQP2-E258K phosphorylation, and/or ubiquitination, however, revealed that the MVB/lysosomal sorting of AQP2-E258K occurred independent of its monoubiquitination or phosphorylation by PKC. Instead, our data reveal that the loss of the E258 in AQP2-E258K is fundamental to its missorting to MVB/Lys and indicate that this amino acid has an important role in the proper structure formation of the C-terminal tail of AQP2.     

Time-Dependent Expression Patterns of Cardiac Aquaporins Following Myocardial Infarction

Aquaporins (AQPs) are expressed in myocardium and the implication of AQPs in myocardial water balance has been suggested. We investigated the expression patterns of AQP subtypes in normal myocardium and their changes in the process of edema formation and cardiac dysfunction following myocardial infarction (MI). Immunostaining demonstrated abundant expression of AQP1, AQP4, and AQP6 in normal mouse heart; AQP1 in blood vessels and cardiac myocytes, AQP4 exclusively on the intercalated discs between cardiac myocytes and AQP6 inside the myocytes. However, neither AQP7 nor AQP9 proteins were expressed in CD1 mouse myocardium. Echocardiography revealed that cardiac function was reduced at 1 week and recovered at 4 weeks after MI, whereas myocardial water content determined by wet-to-dry weight ratio increased at 1 week and rather reduced below the normal at 4 weeks. The expression of cardiac AQPs was up-regulated in MI-induced groups compared with sham-operated control group, but their time-dependent patterns were different. The time course of AQP4 expression coincided with that of myocardial edema and cardiac dysfunction following MI. However, expression of both AQP1 and AQP6 increased persistently up to 4 weeks. Our findings suggest a different role for cardiac AQPs in the formation and reabsorption of myocardial edema after MI.     

Vasopressin-dependent short-term regulation of aquaporin 4 expressed in Xenopus oocytes

Aquaporin 4 (AQP4) is abundantly expressed in the perivascular glial endfeet in the central nervous system (CNS), where it is involved in the exchange of fluids between blood and brain. At this location, AQP4 contributes to the formation and/or the absorption of the brain edema that may arise following pathologies such as brain injuries, brain tumours, and cerebral ischemia. As vasopressin and its G-protein-coupled receptor (V1_aR) have been shown to affect the outcome of brain edema, we have investigated the regulatory interaction between AQP4 and V1_aR by heterologous expression in Xenopus laevis oocytes. The water permeability of AQP4/V1_aR-expressing oocytes was reduced in a vasopressin-dependent manner, as a result of V1_aR-dependent internalization of AQP4. Vasopressin-dependent internalization was not observed in AQP9/V1_aR-expressing oocytes. The regulatory interaction between AQP4 and V1_aR involves protein kinase C (PKC) activation and is reduced upon mutation of Ser¹⁸⁰ on AQP4 to an alanine. Thus, the present study demonstrates at the molecular level a functional link between the vasopressin receptor V1_aR and AQP4. This functional interaction between AQP4 and V1_aR may prove to be a potential therapeutic target in the prevention and treatment of brain edema.     

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.     

Functional analysis of novel aquaporins from Fasciola gigantica

Fascioliasis, caused by liver flukes of the genus Fasciola, is an important disease of ruminants. In order to identify a potential new drug target we have studied aquaporin (AQP) in Fasciola gigantica. AQPs facilitate the transport of water, glycerol and other small solutes across biological membranes. The structure, function, and pathology of AQPs have been extensively studied in mammals but data for AQPs from trematodes is still limited. In the present study, we have functionally characterized two closely related AQP isoforms, FgAQP-1 and FgAQP-2, from the trematode F. gigantica. Immunohistochemical analysis located the FgAQPs in the tegumental cells, their processes and the tegument itself. In addition, they were present in the epithelial linings of testes and ovary. Expression in Xenopus oocytes of these FgAQPs increased osmotic water permeability 3-4-fold but failed to increase glycerol and urea permeability. AQPs have two highly conserved NPA motifs that are important for the function of the channel pore. In FgAQP-1 and FgAQP-2 the first NPA motif is changed to TAA. Substitution of Thr with Asn in the TAA motif of FgAQP-1 increased its water permeability twofold but did not affect urea and glycerol impermeability while the substitution at the pore mouth of Cys204 by Tyr caused loss of water permeability. In addition, the FgAQPs did not increase methylamine and ammonia permeability after expression in yeast. In comparison to rat AQP-1 the described FgAQPs showed low water permeability and further in vivo analyses are necessary to determine their contribution to osmoregulation in Fasciola.     

Altered aquaporin expression in glaucoma eyes

Aquaporins (AQP) are channels in the cell membrane that mainly facilitate a passive transport of water. In the eye, AQPs are expressed in the ciliary body and retina and may contribute to the pathogenesis of glaucoma and optic neuropathy. We investigated the expression of AQP1, AQP3, AQP4, AQP5, AQP7 and AQP9 in human glaucoma eyes compared with normal eyes. Nine glaucoma eyes were examined. Of these, three eyes were diagnosed with primary open angle glaucoma; three eyes had neovascular glaucoma; and three eyes had chronic angle‐closure glaucoma. Six eyes with normal intraocular pressure and without glaucoma were used as control. Immunohistochemistry was performed using antibodies against AQP1, AQP3, AQP4, AQP5, AQP7 and AQP9. For each specimen, optical densities of immunoprecipitates were measured using Photoshop and the staining intensities were calculated. Immunostaining showed labelling of AQP7 and AQP9 in the nonpigmented ciliary epithelium and the staining intensities were significantly decreased in glaucoma eyes (p = 0.003; p = 0.018). AQP7 expression in the Müller cell endfeet was increased (p = 0.046), and AQP9 labelling of the retinal ganglion cells (RGC) showed decreased intensity (p = 0.037). No difference in AQP1, AQP4 and AQP9 expression was found in the optic nerve fibres. This study is the first investigating AQPs in human glaucoma eyes. We found a reduced expression of AQP9 in the retinal ganglion cells of glaucoma eyes. Glaucoma also induced increased AQP7 expression in the Müller cell endfeet. In the ciliary body of glaucoma eyes, the expression of AQP7 and AQP9 was reduced. Therefore, the expression of AQPs seems to play a role in glaucoma.     

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.     

Immunolocalization of water channel aquaporins in the nasal olfactory mucosa

Aquaporins (AQPs), membrane water channel proteins expressed in various tissues and organs, serve in the transfer of water and small solutes across the membrane. We raised antibodies to AQPs using isoform-specific synthetic peptides and surveyed their expression in the rat nasal olfactory and respiratory mucosae. AQP1, AQP3, AQP4, and AQP5 were detected by immunohistochemical and immunoblotting analyses. AQP1 was expressed in the endothelial cells of blood vessels and the surrounding connective tissue cells in the olfactory and respiratory mucosae. AQP1 may be involved in water transfer across the blood vessel wall. In the olfactory epithelium, no AQP was detected in the olfactory sensory cells. Instead, AQP3 was abundant in the olfactory epithelium, where it was localized in the supporting cells and basal cells. Expression of AQP3 was mostly restricted to the basal cells in the respiratory epithelium. In marked contrast, AQP4 was abundant in the respiratory epithelium, but its abundance was limited to the basal cells in the olfactory epithelium. In the Bowman's gland, AQP5 was localized in the apical membrane in the secretory acinar cells, whereas AQP3 and AQP4 were found in the basolateral membrane. Similar localization was seen in its duct cells. These results showed a distinct localization pattern for AQPs in the olfactory epithelium. AQP3 and AQP4 in the supporting cells and basal cells may play an important role in generating and maintaining the specific microenvironment around the olfactory sensory cells. AQP3, AQP4, and AQP5 in the Bowman's gland may serve in the secretion to generate the microenvironment at the apical surface of the olfactory dendrites for odorant reception.     

Decreases in rat brain aquaporin-4 expression following intracerebroventricular administration of an endothelin ETB receptor agonist

Aquaporins (AQPs) comprise a family of water channel proteins, some of which are expressed in brain. Expressions of brain AQPs are altered after brain insults, such as ischemia and head trauma. However, little is known about the regulation of brain AQP expression. Endothelins (ETs), vasoconstrictor peptides, regulate several pathophysiolgical responses of damaged nerve tissues via ET_B receptors. To show possible roles of ET_B receptors in the regulation of brain AQP expression, the effects of intracerebroventricular administration of an ET_B agonist were examined in rat brain. In the cerebrum, the copy numbers of AQP4 mRNAs were highest among AQP1, 3, 4, 5 and 9. Continuous administration of 500 pmol/day Ala^1,3,11,15-ET-1, an ET_B selective agonist, into rat brain for 7 days decreased the level of AQP4 mRNA in the cerebrum, but had no effect on AQP1, 3, 5 and 9 mRNA levels. The level of AQP4 protein in the cerebrum decreased by the administration of Ala^1,3,11,15-ET-1. Immunohistochemical observations of Ala^1,3,11,15-ET-1-infused rats showed that GFAP-positive astrocytes, but not neurons, activated microglia or brain capillary endothelial cells, had immunoreactivity for AQP4. These findings indicate that activation of brain ET_B receptors causes a decrease in AQP4 expression, suggesting that ET down-regulates brain AQP4 via ET_B receptors.     

Tanshinone IIA ameliorates seawater exposure-induced lung injury by inhibiting aquaporins (AQP) 1 and AQP5 expression in lung

Aquaporins (AQPs), a family of transmembrane water channels, mediate physiological response to changes of fluid volume and osmolarity. It is still unknown what role of AQPs plays in seawater drowning-induced acute lung injury (ALI) and whether pharmacologic modulation of AQPs could alleviate the severity of ALI caused by seawater aspiration. In our study, the results from RT-PCR and Western blotting showed that intratracheal installation of seawater up-regulated the mRNA and protein levels of AQP1 and AQP5 in lung tissues. Furthermore, we found that treatment of tanshinone IIA (TIIA, one of the main active components from Chinese herb Danshen) significantly reduced the elevation of AQP1 and AQP5 expression induced by seawater in rats, A549 cells and primary alveolar type II cells. Treatment of TIIA also improved lung histopathologic changes and blood-gas indices, and reduced lung edema and vascular leakage. These findings demonstrated that AQP1 and AQP5 might play an important role in the development of lung edema and lung injury, and that treatment with TIIA could significantly alleviate seawater exposure-induced ALI, which was probably through the inhibition of AQP1 and AQP5 over-expression in lungs.     

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…     

Phosphorylation of protein kinase C sites in NBD1 and the R domain control CFTR channel activation by PKA

Activation of the cystic fibrosis transmembrane conductance regulator (CFTR) channel by protein kinase A (PKA) is enhanced by protein kinase C (PKC). However, the mechanism of modulation is not known and it remains uncertain whether PKC acts directly on CFTR or through phosphorylation of an ancillary protein. Using excised patches that had been pre-treated with phosphatases, we found that PKC exposure results in much larger PKA-activated currents and shifts the PKA concentration dependence. To examine if these effects are mediated by direct PKC phosphorylation of CFTR, a mutant was constructed in which serines or threonines at nine PKC consensus sequences on CFTR were replaced by alanines (i.e. the '9CA' mutant T582A/T604A/S641A/T682A/S686A/S707A/S790A/T791A/S809A). In excised patches, 9CA channels had greatly reduced responses to PKA (i.e. 5–10 % that of wild-type), which were not enhanced by PKC pre-treatment, although the mutant channels were still functional according to iodide efflux assays. Stimulation of iodide efflux by chlorophenylthio-cAMP (cpt-cAMP) was delayed in cells expressing 9CA channels, and a similar delay was observed when cells expressing wild-type CFTR were treated with the PKC inhibitor chelerythrine. This suggests that weak activation by PKA in excised patches and slow stimulation of iodide efflux from intact cells are specifically due to the loss of PKC phosphorylation. Finally, PKC caused a slight activation of wild-type channels when added to excised patches after phosphatase pre-treatment but had no effect on the mutant. We conclude that direct phosphorylation of CFTR at one or more of the nine sites mutated in 9CA is required for both the partial activation by PKC and for its modulation of CFTR responses to PKA.     

Immunolocalization of water channel aquaporins in human knee articular cartilage with intact and early degenerative regions

Aquaporins (AQPs), a family of water channel proteins expressed in various cells and tissues, serve as physiological pathways of water and small solute transport. Articular cartilage is avascular tissue with unique biomechanical structure, a major component of which is “water”. Our objective is to investigate the immunolocalization and expression pattern changes of AQPs in articular cartilage with normal and early degenerative regions in the human knee joint, which is the joint most commonly involved in osteoarthritis (OA). Two isoforms (AQPs 1 and 3) of AQPs were examined by immunohistochemical analyses using isoform-specific antibodies with cartilage samples from OA patients undergoing total knee arthroplasty. AQP 1 and AQP 3 were expressed in human knee articular cartilage and were localized in chondrocytes, both in the intact and early degenerative cartilage regions. Compared to the intact cartilage, both AQP 1 and AQP 3 immunopositive cells were observed at the damaged surface area in the degenerative region. These findings suggest that these AQPs play roles in metabolic water regulation in articular cartilage of load bearing joints and that they are responsible for OA onset.