Nuclear factor kappa B pathway down-regulates aquaporin 5 in the nasal mucosa of rats with allergic rhinitis

Nuclear factor kappa B (NF-κB) induces gene transcription by binding CREB-binding protein (CBP). The aim of the study was to detect the mechanisms by which NF-κB pathway regulated aquaporin 5 (AQP5) in the nasal mucosa of rats with allergic rhinitis (AR). Rats were divided into control (group C), model (group M), low-dose proline dithiocarbamate (PDTC) (group L) and high-dose PDTC (group H) groups. AR model was established by the sensitization with ovalbumin, then groups L and H were treated with PDTC (50 or 100 mg/kg/day) for 5 days. AQP5, interleukin-1β, NF-κBp65 and phosphorylated cAMP-response element binding protein (p-CREB) were detected by immunohistochemistry, Western blotting or real-time PCR. AQP5 expression in group M was lower than in group C, but in groups L and H it increased. NF-κBp65 expression in group M was higher than group C, but in groups L and H it reduced. p-CREB expression in group M was lower than group C, but in groups L and H it increased. Interleukin-1β gene level in group M was higher than group C, but in groups L and H it was lower. These data show that the NF-κB pathway could down-regulate AQP5 by interleukin-1β which inhibited CREB phosphorylation or by NF-κBp65 which competitively bound CBP.

[Expression and the correlation of AQP5, HIF-1alpha and VEGF in human nasal polyps]

OBJECTIVE

To detect the expression of AQP5, HIF-1alpha and VEGF in human nasal polyps, and to observe the relationship of AQP5 with HIF-1a and VEGF, and to investigate their role in the pathogenesis of nasal polyps.

METHOD

Using the techniques of Real-time Quantitative Polymerase chain Reaction and Western blot, the expressions of AQP5, HIF-1alpha, VEGF mRNA and protein were examined. The specimens were obtained from patients underwent endoscopic surgery at the same time, including eighteen nasal polyps and ten inferior turbinate tissues.

RESULT

(1) The result of RT-PCR showed that the expressions of the AQP5 mRNA were lower in nasal polyps than those in inferior turbinate tissue (P < 0.01); there was no significant difference between the expression of HIF-1alpha mRNA or VEGF mRNA in nasal polyps and inferior turbinate tissues (P > 0.05); (2) According to the Western blot, there was no significant difference between the expression of AQP5 in nasal polyps and inferior turbinate tissues (P > 0.05); the expression of HIF-la or VEGF were higher in nasal polyps than those in inferior turbinate tissues (P < 0.05); (3) According to the Western blot, there was a positive correlation between the expression of AQP5 and that of HIF-1alpha (r = 0.633, P < 0.05), and the correlation was also existed between AQP5 and that of VEGF (r = 0.611, P < 0.05).

CONCLUSION

AQP5, HIF-1alpha, VEGF are all involved in the edema formation of nasal polyps. The changes of AQP5's distribution can cause accumulation of water in nasal polyps, HIF-1alpha, VEGF can induce new blood vessels and increase vasopermeability in nasal polyps; they have separate regulatory mechanism in edema formation, but might have some relationships in some ways.

Expression of water and ion transporters in tracheal aspirates from neonates with respiratory distress

AIM

The aim of the study was to determine whether neonatal respiratory distress is related to changes in water and ion transporter expression in lung epithelium.

METHODS

The study included 32 neonates on mechanical ventilation: 6 patients with normal lung X-rays (control group), eight with respiratory distress syndrome (RDS), eight with transient tachypnea of the newborn (TTN), 10 with abnormal lung X-rays (mixed group). The protein abundance of water channel AQP5, epithelial sodium channel (ENaC; alpha-, beta- and gamma-ENaC) and Na(+), K(+)-ATPase alpha1 were examined in tracheal aspirates using semiquantitative immunoblotting.

RESULTS

beta-ENaC level was significantly lower in RDS group compared with infants with TTN and infants in the control group. AQP5 expression was significantly higher in TTN compared with the infants with RDS and all other infants with abnormal lung X-rays.

CONCLUSION

Neonatal respiratory distress is associated with changes in beta-ENaC and AQP5 expression. The lower beta-ENaC expression may be one of the factors that predispose to the development of RDS. The higher AQP5 expression may provide the possibility for reabsorption of postnatal lung liquid, which contributes to quick recovery of infants with TTN.

[Effect of intra nasally applied fluticasone propionate and levocabastine on the expression of aquaporin 5 in nasal mucosa of rat with experimental allergic rhinitis]

OBJECTIVE

To investigate the expression and distribution of aquaporin 5 (AQP5) in allergic rhinitis (AR) treated by fluticasone propionate and levocabastine.

METHOD

Forty Wistar rats were divided randomly into AR (n=30) and control groups (n=10). After AR models were established, the AR rats were divided evenly into F group, L group and AR control group. Three groups were treated respectively for 28 days, then the expression of AQP5 in nasal mucous membrane were detected by immunohistochemistry assay.

RESULT

The distribution of AQP5 was consistent in all groups. The expression of AQP5 in F group was significantly different from L group and AR group (P<0.05), while there was no significant difference between that of AR group and L group (P>0.05). The expression of AQP5 in L group was significantly different from that in control group (P<0.05).

CONCLUSION

High expressions of AQP5 in rat with AR indicated the positive correlation between AQP5 and AR. AQP5 might be one of pathological factors of AR concerned with glands excessive secretion and tissue edema. Glucocorticoid can down-regulate the expression of AQP5, but H1-receptor antagonist can not reduce the expression of AQP5.

[Effects of different fluid resuscitation regimes on lung injury and expression of pulmonary aquaporin 1 and aquaporin 5 in uncontrolled hemorrhagic shock in rats]

OBJECTIVE

To investigate the effects of different fluid resuscitation regimes on lung injury and expression of pulmonary aquaporin 1 (AQP1) and AQP5 in rats with uncontrolled hemorrhagic shock.

METHODS

Sixty Sprague-Dawley (SD) rats were randomly assigned to the following five groups: control group (C group), no fluid resuscitation group (NF group), lactated Ringer's solution group (LRS group), 7.5%NaCl group (HS group) and hydroxyethyl starch group (hydroxyethyl starch 130/0.4, HES group). A four-phased uncontrolled hemorrhagic shock model was reproduced. Uncontrolled hemorrhagic shock phase began with blood withdrawal extended over 15 minutes, in which animals were subjected to massive hemorrhage [mean arterial pressure (MAP)=40 mm Hg (1 mm Hg=0.133 kPa)] for 60 minutes and followed by intratracheal lipopolysaccharide 2 mg/kg and continuous bleeding with amputation of the tail. Then, animals were partially resuscitated with LRS of 3 times the volume of shed blood (LRS group), followed by a bolus dose of 4 ml/kg body weight of 7.5%NaCl (HS), or hydroxyethyl starch (a volume equal to that of the shed blood), respectively, during different fluid resuscitation regimes. After that, comprehensive resuscitation phase of 60 minutes began with hemostasis, and transfusion of all the shed blood plus same amount of normal saline. Observation phase was continued for 3.5 hours. At the end the experiment, the lung tissue was sampled to measure wet-to-dry lung weight ratio (W/D), and the expression of AQP1 and AQP5 were determined with immunohistochemistry. The paraffin-embedded lungs were stained with hematoxylin and eosin for pathological analysis.

RESULTS

When compared with NF and LRS groups, the lung W/D ratio was significantly decreased, and the shock induced decreased expression of AQP1 and AQP5 in lung tissue were attenuated in HES group, but these beneficial effects were blunted in the HS group.

CONCLUSION

Uncontrolled hemorrhagic shock may induce lung injury and pulmonary edema as well as down regulation of the expression of AQP1 and AQP5 in rats. Resuscitation with hypertonic fluids, especially with HES, can reduce lung damage and pulmonary edema in this kind of shock. The cause may be due in part to maintenance of the expression of AQP1 and/or AQP5 in the lung. Pulmonary AQP1 and AQP5 play an important role in fluid transportation.

Involvement of aquaporin-5 in differentiation of human gastric cancer cells

Litttle is known about the function of aquaporin (AQP) water channels in human gastric cancer. In the upper or middle part of human stomach, we found that expression level of AQP5 protein in intestinal type of adenocarcinoma was significantly higher than that in accompanying normal mucosa. AQP5 was localized in the apical membrane of the cancer cells. On the other hand, both AQP3 and AQP4 were not up-regulated in the adenocarcinoma. To elucidate the role of AQP5 in cancer cells, AQP5 was exogenously expressed in a cell line of poorly differentiated human gastric adenocarcinoma (MKN45). The AQP5 expression significantly increased the proportion of differentiated cells with a spindle shape, the activity of alkaline phosphatase, a marker for the intestinal epithelial cell type of cancer cells, and the expression level of laminin, an epithelial cell marker. Treatment of the MKN45 cells stably expressing AQP5 with HgCl(2), an inhibitor of aquaporins, significantly decreased the proportion of differentiated cells and the activity of alkaline phosphatase. Our results suggest that up-regulation of AQP5 may be involved in differentiation of human gastric cancer cells.

[Expression and its significance of aquaporin 5 in nasal polyps with or without allergic rhinitis]

OBJECTIVE

To confirm the expression and distribution of aquaporin 5 (AQP5) in nasal polyps.

METHOD

AQP5 were studied in 20 samples nasal polyp without AR (Group NAR) and 16 samples with AR (Group AR) with immunochemistric staging and its integrated light intensity and its grey step.

RESULT

(1) Hematoxylin and eosin staining showed that there was obvious inflammation reaction, a large quantity of glands hyperplasia and acidophils soaked in nasal polyps, especially those with allergic rhinitis. (2) Immunofluorescence technique showed that the distribution of AQP5 in the two groups was in accordance with that in nasal polyps on the whole. AQP5 expressed mainly in the membrane and cytoplasm of the epithelium of the glands, ducts and cilia. (3) The statistical analysis of the immunohistochemical staining showed that the integrated light intensity of AQP5 in Group AR (0.1675+/-0.006536) was obviously higher than that in the Group NARs nasal polyps (0.09343+/-0.001816). There was statistical significance between the two groups (t = -12.00, P<0.01). (4) The statistical analysis of the immunohistochemical staining showed that the grey step of AQP5 in Group AR (175.6+/-2.471) was obviously lower than that in the Group NAR's nasal polyps (206.2+/-0.9649). There was statistical significance between the two groups (t=12.46, P<0.01).

CONCLUSION

AQP5 is expressed in nasal polyp. Combined with the research before, it was conferred that the hypersecretion of glands and its character has a relationship with the high expression of AQP5 in nasal polyps, and nasal polyp with different symptom has different mechanism.

Human AQP5 plays a role in the progression of chronic myelogenous leukemia (CML)

Aquaporins (AQPs) have previously been associated with increased expression in solid tumors. However, its expression in hematologic malignancies including CML has not been described yet. Here, we report the expression of AQP5 in CML cells by RT-PCR and immunohistochemistry. While normal bone marrow biopsy samples (n = 5) showed no expression of AQP5, 32% of CML patient samples (n = 41) demonstrated AQP5 expression. In addition, AQP5 expression level increased with the emergence of imatinib mesylate resistance in paired samples (p = 0.047). We have found that the overexpression of AQP5 in K562 cells resulted in increased cell proliferation. In addition, small interfering RNA (siRNA) targeting AQP5 reduced the cell proliferation rate in both K562 and LAMA84 CML cells. Moreover, by immunoblotting and flow cytometry, we show that phosphorylation of BCR-ABL1 is increased in AQP5-overexpressing CML cells and decreased in AQP5 siRNA-treated CML cells. Interestingly, caspase9 activity increased in AQP5 siRNA-treated cells. Finally, FISH showed no evidence of AQP5 gene amplification in CML from bone marrow. In summary, we report for the first time that AQP5 is overexpressed in CML cells and plays a role in promoting cell proliferation and inhibiting apoptosis. Furthermore, our findings may provide the basis for a novel CML therapy targeting AQP5.

Effects of hyperoxia on the dynamic expression of Aquaporin5 in premature rats lung development

To explore the dynamic expression and role of Aquaporin5 (AQP5) in lung development and hyperoxia lung injury, gestation 21-day Sprague-Dawley (SD) rats (term=22 days) were randomly assigned to air group and hyperoxia group within 12-24 h after birth. The rats in hyperoxia group were continuously exposed to about 85% oxygen and those in air group to room air. After 1 to 14 days of exposure, total lung RNA was extracted and the expression of AQP5 mRNA was detected by reverse transcription polymerase chain reaction (RT-PCR). Immunohistochemistry and western-blot were used to detect the expression of AQP5 protein. The results showed that the expression of AQP5 in premature rats lung could be detected at various time points after birth, and the positive staining was restricted to the type I alveolar epithelial cells. In air group, the AQP5 expression was detected in a very low level at day 1, but exhibited a persistent increase after birth. Compared with the air group, the expression of AQP5 in hyperoxia group was increased at day 1, and had significant difference in mRNA level (P<0.05), but decreased significantly in mRNA and protein levels after 4 to 14 days (P<0.01 or P<0.05 respectively). It was concluded that AQP5 might play a key role in the alveolar period of premature rats by regulating the lung water balance. Hyperoxia exposure leads to a down-regulation of the AQP5 expression, which may be an important factor for the development of hyperoxia lung injury.

Expression of aquaporin 5 (AQP5) promotes tumor invasion in human non small cell lung cancer

The aquaporins (AQP) are water channel proteins playing a major role in transcellular and transepithelial water movement. Recently, the role of AQPs in human carcinogenesis has become an area of great interest. Here, by immunohistochemistry (IHC), we have found an expression of AQP5 protein in 35.3% (IHC-score: ≥1, 144/408) of the resected NSCLC tissue samples. Cases with AQP5-positive status (IHC-score: ≥2) displayed a higher rate of tumor recurrence than negative ones in NSCLC (54.7% vs. 35.1%, p = 0.005) and worse disease-free survival (p = 0.033; OR = 1.52; 95%CI:1.04−2.23). Further in vitro invasion assay using BEAS-2B and NIH3T3 cells stably transfected with overexpression constructs for full length wild-type AQP5 (AQP5) and its two mutants, N185D which blocks membrane trafficking and S156A which blocks phosphorylation on Ser156, showed that AQP5 induced cell invasions while both mutants did not. In BEAS-2B cells, the expression of AQP5 caused a spindle-like and fibroblastic morphologic change and losses of cell-cell contacts and cell polarity. Only cells with AQP5, not either of two mutants, exhibited a loss of epithelial cell markers and a gain of mesenchymal cell markers. In a human SH3-domains protein array, cellular extracts from BEAS-2B with AQP5 showed a robust binding activity to SH3-domains of the c-Src, Lyn, and Grap2 C-terminal. Furthermore, in immunoprecipitation assay, activated c-Src, phosphorylated on Tyr416, showed a stronger binding activity to cellular extracts from BEAS-2B with AQP5 compared with N185D or S156A mutant. Fluorescence in situ hybridization (FISH) analysis failed to show evidence of genomic amplification, suggesting AQP5 expression as a secondary event. Based on these clinical and molecular observations, we conclude that AQP5, through its phosphorylation on Ser156 and subsequent interaction with c-Src, plays an important role in NSCLC invasion and, therefore, may provide a unique opportunity for developing a novel therapeutic target as well as a prognostic marker in NSCLC.

Membrane trafficking of AQP5 and cAMP dependent phosphorylation in bronchial epithelium

Phosphorylation pathway has been identified as an important step in membrane trafficking for AQP5. We generated stably transfected BEAS-2B human bronchial epithelial cells with various over-expression constructs on permeable support. In stable cells with wild-type AQP5 and S156A (AQP5 mutant targeting PKA consensus sequence), AQP5 expression was predominantly polarized to the apical membrane, whereas stable cells with N185D (AQP5 mutant targeting second NPA motif), mainly localized to the cytoplasm. Treatment with H89 and/or chlorophenylthio-cAMP (cpt-cAMP) did not affect membrane expression of AQP5 in any of three stable cells. In cells with wild-type AQP5 and N185D, AQP5s were phosphorylated by PKA, while phosphorylation of AQP5 was not detected in cells with S156A. These results indicate that, in AQP5, serine156 may be phosphorylated by PKA, but membrane expression of AQP5 may not be regulated by PKA phosphorylation. We conclude that AQP5 membrane targeting can include more than one mechanism besides cAMP dependent phosphorylation.

Modified aquaporin 5 expression and distribution in submandibular glands from NOD mice displaying autoimmune exocrinopathy

OBJECTIVE

To investigate the expression and localization of aquaporin 5 (AQP5) in salivary glands and salivary gland function in the NOD mouse.

METHODS

All experiments were performed using NOD and BALB/c mice (ages 8 weeks and 24 weeks). Real-time reverse transcription-polymerase chain reaction, Western blotting, and immunohistochemical analysis were used to study the expression and distribution of AQP5 in salivary glands. In addition, salivary gland function was determined.

RESULTS

Compared with the levels in BALB/c mice, relative AQP5 messenger RNA levels were not significantly modified in the parotid glands from NOD mice of both ages but were significantly increased in the submandibular glands from NOD mice of both ages. Western blot analyses of both salivary gland membranes revealed that the level of AQP5 protein was increased in 24-week-old NOD mice. Important inflammatory infiltrates were observed in the submandibular glands, but not in the parotid glands, from 24-week-old NOD mice. The 8-week-old and 24-week-old BALB/c mice and the 8-week-old NOD mice showed AQP5 primarily at the apical membrane of the salivary gland acinus. In contrast, in acini from the submandibular glands (but not the parotid glands) from 24-week-old NOD mice, AQP5 staining was reduced at the apical membrane but was increased at the basal membrane. A moderately statistically significant decrease in pilocarpine-stimulated salivary flow was observed in 24-week-old NOD mice compared with that in age-matched BALB/c mice.

CONCLUSION

Submandibular glands from 24-week-old NOD mice displayed inflammatory infiltrates, increased AQP5 protein expression, and impaired AQP5 distribution. However, the moderately statistically significant decrease in the salivary flow rate in these mice did not match the extent of AQP5 misdistribution.

Topiramate reduced sweat secretion and aquaporin-5 expression in sweat glands of mice

Decreased sweat secretion is a primary side effect of topiramate in pediatric patients, but the mechanism underlying this effect remains unclear. This study aimed to better understand how topiramate decreases sweat secretion by examining its effect on the expression of carbonic anhydrase (CA) II and aquaporin-5 (AQP5), total CA activity, as well as on tissue morphology of sweat glands in mice. Both developing and mature mice were treated with a low (20 mg/kg/day) and high dose (80 mg/kg/day) of topiramate for 4 weeks. Sweat secretion was investigated by an established technique of examining mold impressions of hind paws. CA II and AQP5 expression levels were determined by immunofluorescence and immunoblotting and CA activity by a colorimetric assay. In mature mice, topiramate treatment decreased the number of pilocarpine reactive sweat glands from baseline in both the low and high dose groups by 83% and 75%, respectively. A similar decrease was seen in developing mice. Mature mice with reactive sweat glands that declined more than 25% compared to baseline were defined as anhidrotic mice. These mice did not differ from controls in average secretory coil diameter, CA II expression and CA activity. In contrast, anhidrotic mice did show a reduction in membrane AQP5 expression in sweat glands after topiramate delivery. Thus, sweat secretion and membrane AQP5 expression in mouse sweat glands decreased following topiramate administration. These results suggest dysregulation of AQP5 may be involved in topiramate-induced hypohidrosis and topiramate may serve as a novel therapy for hyperhidrosis.

[Study of mucus secretion and aquaporin-5 expression of bronchial epithelium cultured in hypotonic medium]

OBJECTIVE

To study mucus secretion and aquaporin-5 (AQP5) expression of bronchial epithelium cultured at the air-liquid interface of hypotonic medium, and to elucidate the role of AQP5 and osmotic pressure in airway mucus hypersecretion process.

METHODS

With the air-liquid interface culture model, rabbit tracheal epithelium was cultured at the air-liquid interface. One week after culture, media of 235, 255 and 270 mmol/L were used for experimental groups, and that of 282 mmol/L for culture in control group. Twelve hours after the culture, reverse transcriptase polymerase chain reaction (RT-PCR) was used to detect AQP5 mRNA in each experimental group, and Western blotting to determine mucin5AC (MUC5AC) in the supernatant. The same procedures were done in control group.

RESULTS

Multilayers of cultured cells were observed with inverted microscope in each group. MUC5AC expressions in experimental groups were significantly higher, whereas AQP5 mRNA levels were obviously lower compared with those in control group (all P<0.001), the changes in 235 mmol/L group were most obvious. Moreover, AQP5 mRNA and MUC5AC in experimental groups were notably negatively correlated (r=-0.77, P<0.001).

CONCLUSION

The model of air-liquid interface culture could increase MUC5AC expression, which provides an environment closely resembles that in the body is an ideal framework for the research of mucus hypersecretion of chronic obstructive pulmonary disease (COPD). Expressions of AQP5 mRNA and MUC5AC are negatively correlated. Hypotonicity and reduction of AQP5 mRNA may play critical roles in airway mucus secretion process in COPD.

Interleukin-13 interferes with CFTR and AQP5 expression and localization during human airway epithelial cell differentiation

Interleukin-13 (IL-13) is a central regulator of Th2-dominated respiratory disorders such as asthma. Lesions of the airway epithelial barrier frequently observed in chronic respiratory inflammatory diseases are repaired through proliferation, migration and differentiation of epithelial cells. Our work is focused on the effects of IL-13 in human cellular models of airway epithelial cell regeneration. We have previously shown that IL-13 altered epithelial cell polarity during mucociliary differentiation of human nasal epithelial cells. In particular, the cytokine inhibited ezrin expression and interfered with its apical localization during epithelial cell differentiation in vitro. Here we show that CFTR expression is enhanced in the presence of the cytokine, that two additional CFTR protein isoforms are expressed in IL-13-treated cells and that part of the protein is retained within the endoplasmic reticulum. We further show that aquaporin 5 expression, a water channel localized within the apical membrane of epithelial cells, is completely abolished in the presence of the cytokine. These results show that IL-13 interferes with ion and water channel expression and localization during epithelial regeneration and may thereby influence mucus composition and hydration.

Interaction between transcellular and paracellular water transport pathways through Aquaporin 5 and the tight junction complex

To investigate potential physiological interactions between the transcellular and paracellular pathways of water transport, we asked whether targeted deletion of Aquaporin 5 (AQP5), the major transcellular water transporter in salivary acinar cells, affected paracellular transport of 4-kDa FITC-labeled dextran (FITC-D), which is transported through the paracellular but not the transcellular route. After i.v. injection of FITC-D into either AQP5 wild-type or AQP5-/- mice and saliva collection for fixed time intervals, we show that the relative amount of FITC-D transported in the saliva of AQP5-/- mice is half that in matched AQP5+/+ mice, indicating a 2-fold decrease in permeability of the paracellular barrier in mice lacking AQP5. We also found a significant difference in the proportion of transcellular vs. paracellular transport between male and female mice. Freeze-fracture electron microscopy revealed an increase in the number of tight junction strands of both AQP5+/+ and AQP5-/- male mice after pilocarpine stimulation but no change in strand number in female mice. Average acinar cell volume was increased by approximately 1.4-fold in glands from AQP5-/- mice, suggesting an alteration in the volume-sensing machinery of the cell. Western blots revealed that expression of Claudin-7, Claudin-3, and Occludin, critical proteins that regulate the permeability of the tight junction barrier, were significantly decreased in AQP5-/- compared with AQP5+/+ salivary glands. These findings reveal the existence of a gender-influenced molecular mechanism involving AQP5 that allows transcellular and paracellular routes of water transport to act in conjunction.

Reduced expression of aquaporin 5 water channel in nitrofen-induced hypoplastic lung with congenital diaphragmatic hernia rat model

PURPOSE

Pulmonary hypoplasia remains the principal cause of high morbidity and mortality in patients with congenital diaphragmatic hernia (CDH). The precise mechanisms causing lung hypoplasia remains unclear. Aquaporins (AQPs) are reported to constitute a family of water channels that facilitate membrane water permeability in various tissues of animals. Aquaporin 5 has been reported to be an important marker expressed in type I alveolar epithelial cells in late gestation and mediates water transport across the human airway epithelium. We hypothesized that AQP5 is reduced in hypoplastic lungs and therefore designed this study to determine AQP5 expression in normal and hypoplastic lungs.

METHODS

Fetal rat lungs of control (n=23) and nitrofen-treated (n=37) dams were harvested on embryonic day (E) 15, E17, E19, and E21. The expression of the AQP5 was analyzed in each lung by real-time reverse transcriptase-polymerase chain reaction. Immunohistochemical studies were performed to evaluate the protein expression level of AQP5.

RESULTS

Aquaporin 5 messenger RNA levels on E21 were significantly reduced in lungs from the nitrofen with CDH group (11.8 +/- 2.3) compared with normal controls (23.5 +/- 11.8) and nitrofen without CDH group (26.9 +/- 13.0) (P < .05). Aquaporin 5 immunohistochemistry demonstrated AQP5 strongly expressed at the apical membrane of type I alveolar epithelial cells in the normal and nitrofen without CDH groups. By contrast, the AQP5-positive cells were markedly reduced in hypoplastic lungs in the nitrofen with CDH group.

CONCLUSION

Our results show that the expression of AQP5 is down-regulated in hypoplastic lungs with CDH. Down-regulation of AQP5 may result in abnormal pulmonary fluid metabolism in perinatal period and may be one of the mechanisms disturbing the pulmonary development in late stage in the CDH model.

[Expression of alpha1-adrenoceptor and promoting secretory response by phenylephrine in rabbit submandibular gland]

OBJECTIVE

To investigate the expression and distribution of alpha1-adrenoceptor subtypes in rabbit submandibular gland and the effect of phenylephrine on salivary secretion.

METHODS

The expressions of alpha1A-, alpha1B-, and alpha1D-adrenoceptor mRNA and protein were investigated by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot in rabbit submandibular gland. Immunohistochemical assay was applied to detect the distribution of alpha1A-, alpha1B-, and alpha1D-adrenoceptor and localization of aquaporin 5 in rabbit submandibular gland. Different concentrations of phenylephrine (1 x 10(-8))-(1 x 10(-6)) mol/L were administrated through a polyethylene tube, which was intubated into Wharton's duct of submandibular gland. Heart rate and blood pressure of rabbits were observed during phenylephrine administration. Salivary flow was measured by the length of moist filter paper (35 mm x 5 mm) within 5 min.

RESULTS

Alpha1A-, alpha1B-, and alpha1D-adrenoceptor mRNA and protein were expressed in rabbit submandibular gland. Three alpha1-adrenoceptor subtypes were widely distributed in the membrane and cytoplasma of both acinar and ductal cells. Phenylephrine (1 x 10(-7) mol/L, 100 microl) stimulated effectively salivary secretion without inducing significant alteration of blood pressure and heart rate in rabbit. Immunohistochemical assay showed that aquaporin 5 was mainly localized in the apical and lateral plasma membrane in both acinar and ductal cells in unstimulated condition, while the expression of aquaporin 5 was increased after administration of phenylephrine.

CONCLUSIONS

Expression of alpha1A-, alpha1B-, and alpha1D-adrenoceptor mRNA and protein was existed in rabbit submandibular gland. Phenylephrine safely and effectively promoted salivary secretion when it was administrated through Wharton's duct of submandibular gland. The mechanism of phenylephrine on salivary secretion may involve in the increase of expression of aquaporin 5 in the apical and lateral plasma membrane in rabbit submandibular gland. This study will hopefully lead to a novel strategy for clinical treatment of dysfunction of submandibular gland.

Downregulation of aquaporins 1 and 5 in nasal gland by osmotic stress in ducklings, Anas platyrhynchos: implications for the production of hypertonic fluid

Using primers against highly conserved regions of mammalian and bird aquaporins in RT-PCR experiments, we amplified products derived from duck (Anas platyrhynchos) nasal gland RNA that were identified as homologues of mammalian and chicken aquaporin 1 and aquaporin 5 cDNAs by sequencing. Using digoxigenin-labelled probes derived from these PCR products in northern blot analyses of mRNA isolated from nasal glands of untreated (naïve) or osmotically stressed ducklings (replacement of drinking water with a 1% NaCl solution), we observed a decrease in aquaporin 1 (AQP1) and aquaporin 5 (AQP5) mRNA abundance (by approximately 40%) during saline adaptation in the animals. Western blot analysis of AQP1 and AQP5 expression in the glands revealed that protein abundance decreased in a similar fashion. Immunohistochemical analysis of AQP1 distribution in cryosections of nasal gland indicated that AQP1 is mainly expressed in endothelial cells of the capillaries, but definitely not in the secretory or ductal cells of the gland. AQP5 distribution in the gland, however, seems to be different, since staining was exclusively observed in apical and basolateral plasma membranes of individual epithelial cells of the primary and central ducts, which collect fluid from the secretory tubules. The observations are consistent with the hypothesis that strongly hyperosmotic fluid is produced by the secretory cells at very low (unstimulated gland) or high (activated gland) rates. In the unstimulated gland, secretions may be diluted by aquaporin-mediated transcellular water flux while passing through the ductal system flushing the glandular ducts, thereby potentially preventing ascending infections. In the activated gland, however, downregulation of aquaporins in capillaries and duct cells may prevent dilution of the initially secreted fluid, enabling the animals to excrete large volumes of a highly concentrated salt solution.

The role of CpG methylation in cell type-specific expression of the aquaporin-5 gene

Aquaporin-5 (AQP5) is expressed in a cell type-specific manner. Here, we show that the AQP5 gene is regulated by CpG methylation. The AQP5 promoter containing a putative CpG island was highly methylated in NIH-3T3 or freshly isolated alveolar epithelial cells, correlating with the repression of this gene in these cells. In contrast, the AQP5 promoter was hypo-methylated in MLE-12 or cultured alveolar epithelial cells, which express high levels of AQP5. Repression of AQP5 transcription in NIH-3T3 cells could be relieved with 5-azacytidine, and in vitro methylation of the AQP5 promoter resulted in inhibition of transcription of the reporter gene in MLE-12 cells. Chromatin immunoprecipitation assays showed that endogenous Sp1 bound to the hypo-methylated, but not highly methylated, AQP5 promoter region. These results demonstrate that the hypo-methylated state of the AQP5 promoter leading to increased Sp1 binding may play a role in regulation of cell type-specific expression of the AQP5 gene.

Radioprotective effect of heat shock protein 25 on submandibular glands of rats

Irradiation (IR) is a fundamental treatment modality for head and neck malignancies. However, a significant drawback of IR treatment is irreversible damage of salivary gland in the IR field. In the present study, we investigated whether heat shock protein (HSP) 25 could be used as a radioprotective molecule for radiation-induced salivary gland damage in rats. HSP25 as well as inducible HSP70 (HSP70i) that were delivered to the salivary gland via an adenoviral vector significantly ameliorated radiation-induced salivary fluid loss. Radiation-induced apoptosis, caspase-3 activation, and poly(ADP-ribose) polymerase cleavage in acinar cells, granular convoluted cells, and intercalated ductal cells were also inhibited by HSP25 or HSP70i transfer. The alteration of salivary contents, including amylase, protein, Ca+, Cl-, and Na+, was also attenuated by HSP25 transfer. Histological analysis revealed almost no radiation-induced damage in salivary gland when HSP25 was transferred. Aquaporin 5 expression in salivary gland was inhibited by radiation; and HSP25 transfer to salivary gland prevented this alteration. The protective effect of HSP70i on radiation-induced salivary gland damage was less or delayed than that of HSP25. These results indicate that HSP25 is a good candidate molecule to protect salivary gland from the toxicity of IR.

A naturally occurring point mutation in the rat aquaporin 5 gene, influencing its protein production by and secretion of water from salivary glands

A greater than twofold diversity in the expression level of aquaporin 5 (AQP5) has been observed in the membrane fraction of the submandibular gland (SMG) in Sprague-Dawley rats (Murdiastuti K, Miki O, Yao C, Parvin MN, Kosugi-Tanaka C, Akamatsu T, Kanamori N, and Hosoi K. Pflügers Arch 445: 405-412, 2002). In the present study, breeding between brother and sister rats was repeated within high AQP5 producers and low ones to obtain inbred offspring. High- and low-producer rats from 3rd to 18th generations were used for experiments. By Western blotting, levels of AQP5 proteins in the parotid and lacrimal glands, and lungs were all low in low producers, whereas they were all high in high producers, implying genetic variations of the gene for this water channel. Despite this implication, AQP5 mRNA levels were almost the same between the two groups by Northern blotting, suggesting the irrelevance of transcriptional regulation for this diversity. AQP5 cDNAs from the SMGs of the two groups were sequenced. The nucleotide sequence of AQP5 cDNA from low producers indicated the existence of a point mutation at nt 308 (G308A), leading to a replacement of (103)Gly with (103)Asp in the third transmembrane domain, but no alteration was detected in the Kozak area. The existence of such a mutation was confirmed by the assessment of genomic DNA also. This mutation may have resulted in an abnormal membrane insertion or ineffective trafficking of AQP5, since the rats having this mutation showed extremely low membrane expression of AQP5 in the SMG acinar cells and decreased water secretion from their salivary glands.

All-trans retinoic acid increases expression of aquaporin-5 and plasma membrane water permeability via transactivation of Sp1 in mouse lung epithelial cells

Aquaporin-5 (AQP5) is a water-selective channel protein that is expressed in lacrimal glands, salivary glands, and distal lung. Several studies using AQP5 knockout mice have revealed that AQP5 plays an important role in maintaining water homeostasis in the lung. We report here that all-trans retinoic acid (atRA) increases plasma membrane water permeability, AQP5 mRNA and protein expression, and AQP5 promoter activity in MLE-12 cells. The promoter activation induced by atRA was diminished by mutation at the Sp1/Sp3 binding element (SBE), suggesting that the SBE mediates the effects of atRA. In addition, atRA increased the binding of Sp1 to the SBE without changing the levels of Sp1 in the nucleus. Taken together, our data indicate that atRA increases AQP5 expression through transactivation of Sp1, leading to an increase in plasma membrane water permeability.

Specific aquaporins facilitate the diffusion of hydrogen peroxide across membranes

The metabolism of aerobic organisms continuously produces reactive oxygen species. Although potentially toxic, these compounds also function in signaling. One important feature of signaling compounds is their ability to move between different compartments, e.g. to cross membranes. Here we present evidence that aquaporins can channel hydrogen peroxide (H2O2). Twenty-four aquaporins from plants and mammals were screened in five yeast strains differing in sensitivity toward oxidative stress. Expression of human AQP8 and plant Arabidopsis TIP1;1 and TIP1;2 in yeast decreased growth and survival in the presence of H2O2. Further evidence for aquaporin-mediated H2O2 diffusion was obtained by a fluorescence assay with intact yeast cells using an intracellular reactive oxygen species-sensitive fluorescent dye. Application of silver ions (Ag+), which block aquaporin-mediated water diffusion in a fast kinetics swelling assay, also reversed both the aquaporin-dependent growth repression and the H2O2-induced fluorescence. Our results present the first molecular genetic evidence for the diffusion of H2O2 through specific members of the aquaporin family.

Effects of pilocarpine on the secretory acinar cells in human submandibular glands

Pilocarpine has been used as a choice of drugs for treatment of impaired salivary flow. Although considerable data are available as to the stimulatory effect of pilocarpine on the salivary secretion in human, its underlying mechanism, at the cellular level, has not been rigorously studied. In this experiment, we studied the effect of pilocarpine on the ion channel activity, cytoplasmic free Ca(2+) concentration ([Ca(2+)](i)) and aquaporin (AQP)-5 expression, which play key roles in the secretary process and determine the capacity of fluid secretion. In human submandibular gland (SMG) acinar cells, 10(-5) M pilocarpine activated the outward rectifying-current, which was predominantly K(+) selective in the whole cell patch clamp study. The pilocarpine increased [Ca(2+)](i) in a concentration-dependent manner in the range of 10(-6) M to 10(-4) M. We found that both increases of [Ca(2+)](i) and outward rectifying- K(+) current were inhibited by 10(-5) M U-73122, a specific phospholipase C inhibitor. The magnitudes of pilocarpine-induced [Ca(2+)](i) transients were approximately 55% lower than those with the same concentration of carbachol (CCh). Pilocarpine also increased the amount of AQP-5 protein in the apical membrane (APM) in human SMG acinar cells. Our results suggest that pilocarpine induce salivary secretions in human by activating K(+) channels, increasing [Ca(2+)](i) via phospholipase C dependent pathway, and increasing AQP-5 protein expression in the APM of SMG acinar cells.

Stimulation of aquaporin-5 and transepithelial water permeability in human airway epithelium by hyperosmotic stress

Osmotic water permeability (P(f )) was measured in spheroid-shaped human nasal airway epithelial explants pre-exposed to increasing levels of hyperosmotic stress. The fluid-filled spheroids, derived from nasal polyps, were lined by a single cell layer with the ciliated apical cell membrane facing the outside. The P(f ) was determined from diameter changes of the spheroids in response to changes in bathing medium osmolarity forth and back between 300 and 225 mOsm x l(-1). Continuous diameter measurements also allowed determination of spontaneous fluid absorption. Hyperosmotic pretreatment (increase from 300 up to 600 mOsm x l(-1)) caused a time- and osmolarity-dependent increase (up to approximately 1.5 times) in epithelial P(f ) which was of similar magnitude in cystic fibrosis (CF) and non-CF spheroids. The effect saturated at approximately 450 mOsm x l(-1) and at approximately 24 h. Expression of aquaporin-5 (AQP5), studied by immunofluorescence and confocal microscopy, showed an increase in parallel with the increase in P(f ) following hyperosmotic stress. The AQP5 was localized both in cytoplasmic vesicles and in apical cell membranes. Spontaneous fluid absorption rates were equal in CF and non-CF spheroids and were not significantly influenced by hyperosmotic stress. The results suggest that hyperosmotic stress is an important activator of AQP-5 in human airway epithelium, leading to significantly increased transepithelial water permeability.

Aquaporin expression and cell volume regulation in the SV40 immortalized rat submandibular acinar cell line

The amount of aquaporins present and the cellular ability to perform regulatory volume changes are likely to be important for fluid secretions from exocrine glands. In this work these phenomena were studied in an SV40 immortalized rat submandibular acinar cell line. The regulatory cell volume characteristics have not previously been determined in these cells. Cell volume regulation following hyposmotic exposure and aquaporin induction was examined with Coulter counter methodology, radioactive efflux studies, fura-2 fluorescence, and polymerase chain reaction and Western blot techniques. Cell volume regulation was inhibited by the K(+) channel antagonists quinine and BaCl(2) and the Cl(-) channel blocker 5-nitro-2-(3-phenypropylamino)benzoic acid. A concomitant increase in cellular (3)H-taurine release and Ca(2+) concentration was also observed. Chelation of both intra- and extracellular Ca(2+) with EGTA and the Ca(2+) ionophore A23187 did not, however, affect cell volume regulation. Aquaporin 5 (AQP5) mRNA and protein levels were upregulated in hyperosmotic conditions and downregulated upon return to isosmotic solutions, but were reduced by the mitogen-activated ERK-activating kinase (MEK) inhibitor U0126. A 24-h MEK inhibition also diminished hyposmotically induced cell swelling and cell volume regulation. In conclusion, it was determined that regulatory volume changes in this immortalized cell line are due to KCl and taurine efflux. In conditions that increased AQP5 levels, the cells showed a faster cell swelling and a more complete volume recovery following hyposmotic exposure. This response could be overturned by MEK inhibition.

Molecular and cellular characterization of a new aquaporin, AQP-x5,specifically expressed in the small granular glands of Xenopusskin

A new toad aquaporin (AQP) cDNA was cloned from a cDNA library constructed from the ventral skin of Xenopus laevis. This AQP (XenopusAQP-x5) consisted of 273 amino acid residues with a high sequence homology to mammalian AQP5. The predicted amino acid sequence contained the two conserved Asn-Pro-Ala motifs found in all major intrinsic protein (MIP) family members and six putative transmembrane domains. The sequence also contained a mercurial-sensitive cysteine and a putative phosphorylation motif site for protein kinase A at Ser-257. The swelling assay using Xenopus oocytes revealed that AQP-x5 facilitated water permeability. Expression of AQP-x5 mRNA was restricted to the skin, brain, lungs and testes. Immunofluorescence and immunoelectron microscopical studies using an anti-peptide antibody (ST-156)against the C-terminal region of the AQP-x5 protein revealed the presence of immunopositive cells in the skin, with the label predominately localized in the apical plasma membrane of the secretory cells of the small granular glands. These glands are unique both in being close to the epidermal layer of the skin and in containing mitochondria-rich cells with vacuolar H+-ATPase dispersed among its secretory cells. Results from immunohistochemical experiments on the mucous or seromucous glands of several other anurans verified this result. We conclude that the presence of AQP-x5 in the apical plasma membrane of the small granular glands suggests its involvement in water secretion from the skins. The physiological roles of the AQP-x5 protein in the small or mucous glands are discussed.

[Expression and modulation of aquaporin 5 in hyperoxia induced lung injury]

OBJECTIVE

To explore the expression and the modulation of aquaporin 5(AQP5) in hyperoxia induced lung injury.

METHODS

Sixty four Wistar rats of 2 weeks old, were randomly assigned to following groups (n=8): air group, hyperoxia 3, 7, 14 days groups, air + dexamethasone (Dex), hyperoxia 3, 7, 14 days + Dex groups. The rats were kept in oxygen chamber at normal pressure (O(2)> or =95%) in hyperoxia groups, and in normal pressure air (O(2)=21%) in room-air group, and the rats in Dex groups were injected with Dex (5 mg.kg(-1).d(-1)) intraperitoneally for 3 consecutive days in room-air or hyperoxia exposure. The expression of AQP5 mRNA level and the location were detected by reverse transcription-polymerase chain reaction and immunohistochemistry respectively.

RESULTS

AQP5 was strongly labeled in alveolar epithelial type I cells, and was also expressed in the secretory epithelium plasma membrane in the airway. The location of AQP5 in hyperoxia groups was not changed, but the expression of AQP5 mRNA had a notable gradual decline when the time of hyperoxia exposure was prolonged, compared to control group (all P<0.05). There was no difference in AQP5 mRNA level between hyperoxia groups and hyperoxia + Dex groups at different time points (all P<0.05).

CONCLUSION

The significant decrease in AQP5 may be an important factor of pulmonary edema formation in hyperoxia-induced lung injury. Dex does not have effect on modulating the AQP5 expression in acute lung injury.

Decreased saliva secretion and down-regulation of AQP5 in submandibular gland in irradiated rats

The molecular mechanisms of radiation-induced xerostomia remain unclear. The purpose of this study was to investigate the alterations of aquaporins (AQPs) and Na(+)/K(+)-ATPase in irradiated rat submandibular glands and to test the hypothesis that down-regulation of AQP5 expression in irradiated salivary glands is one of the mechanisms of radiation-induced xerostomia. Saliva from control and irradiated rat submandibular glands was analyzed. The mRNA level of AQP5 in the submandibular glands was assessed by semi-quantitative RT-PCR and in situ hybridization. The protein expression of AQP5, AQP1 and Na(+)/K(+)-ATPase was determined by Western blotting and immunohistochemistry. The body weight, submandibular gland weight, and saliva secretion of irradiated rats significantly decreased by 12, 24 and 32% on day 3 and 24, 16 and 38% on day 30 postirradiation, respectively. There was a significant increase in the protein concentration and osmolality of saliva in irradiated rats on days 3 and 30 postirradiation. However, there was no significant difference between irradiated and control rats in total saliva protein secretion. RT-PCR analysis showed that mRNA expression of AQP5 was significantly down-regulated by 37 and 51% in irradiated rats on days 3 and 30 postirradiation, respectively. Immunoblotting showed that the AQP5 protein level was decreased by 40 and 60% in irradiated glands, in contrast to the slight reductions of AQP1 and Na(+)/K(+)-ATPase proteins. Immunohistochemical analysis demonstrated that loss of AQP5 protein occurred throughout the irradiated glands, while no significant reduction was detected in AQP1 and Na(+)/ K(+)-ATPase labeling density. These results suggest that the preferential down-regulation of AQP5 with minor effects on AQP1 and Na(+)/K(+)-ATPase may contribute to radiation-induced salivary dysfunction.

AQP and the control of fluid transport in a salivary gland

Experiments were performed with the perfused rat submandibular gland in vitro to investigate the nature of the coupling between transported salt and water by varying the osmolarity of the source bath and observing the changes in secretory volume flow. Glands were submitted to hypertonic step changes by changing the saline perfusate to one containing different levels of sucrose. The flow rate responded by falling to a lower value, establishing a new steady-state flow. The rate changes did not correspond to those expected from a system in which fluid production is due to simple osmotic equilibration, but were much larger. The changes were fitted to a model in which fluid production is largely paracellular, the rate of which is controlled by an osmosensor system in the basal membrane. The same experiments were done with glands from rats that had been bred to have very low levels of AQP5 (the principal aquaporin of the salivary acinar cell) in which little AQP5 is expressed at the basal membrane. In these rats, salivary secretion rates after hypertonic challenges were small and best modelled by simple osmotic equilibration. In rats which had intermediate AQP5 levels the changes in flow rate were similar to those of normal rats although their AQP5 levels were reduced.Finally, perfused normal glands were subject to retrograde ductal injection of salines containing different levels of Hg(2+) ions (0, 10 and 100 microM: ) which would act as inhibitors of AQP5 at the apical acinar membrane. The overall flow rates were progressively diminished with rising Hg(2+) concentration, but after hypertonic challenge the changes in flow rates were unchanged and similar to those of normal rats. All these results are difficult to explain by a cellular osmotic model but can be explained by a model in which paracellular flow is controlled by an osmosensor (presumably AQP5) present on the basal membrane.

Estrogen-induced proliferation of uterine epithelial cells is independent of estrogen receptor alpha binding to classical estrogen response elements

Acting via the estrogen receptor (ER), estradiol exerts pleomorphic effects on the uterus, producing cyclical waves of cellular proliferation and differentiation in preparation for embryo implantation. In the classical pathway, the ER binds directly to an estrogen response element to activate or repress gene expression. However, emerging evidence supports the existence of nonclassical pathways in which the activated ER alters gene expression through protein-protein tethering with transcription factors such as c-Fos/c-Jun B (AP-1) and Sp1. In this report, we examined the relative roles of classical and nonclassical ER signaling in vivo by comparing the estrogen-dependent uterine response in mice that express wild-type ERalpha, a mutant ERalpha (E207A/G208A) that selectively lacks ERE binding, or ERalpha null. In the compound heterozygote (AA/-) female, the nonclassical allele (AA) was insufficient to mediate an acute uterotrophic response to 17beta-estradiol (E2). The uterine epithelial proliferative response to E2 and 4-hydroxytamoxifen was retained in the AA/-females, and uterine luminal epithelial height increased commensurate with the extent of ERalpha signaling. This proliferative response was confirmed by 5-bromo-2'-deoxyuridine incorporation. Microarray experiments identified cyclin-dependent kinase inhibitor 1A as a nonclassical pathway-responsive gene, and transient expression experiments using the cyclin-dependent kinase inhibitor 1A promoter confirmed transcriptional responses to the ERalpha (E207A/G208A) mutant. These results indicate that nonclassical ERalpha signaling is sufficient to restore luminal epithelial proliferation but not other estrogen-responsive events, such as fluid accumulation and hyperemia. We conclude that nonclassical pathway signaling via ERalpha plays a critical physiologic role in the uterine response to estrogen.

Heparin and fibroblast growth factors affect surfactant protein gene expression in type II cells

The stimulation and maintenance of the pulmonary alveolar type II cell's capacity to biosynthesize, store, and secrete surfactant proteins (SPs) are modulated to a great extent by growth factors, extracellular matrix (ECM) components, and hormones. It is possible that differences in ECM composition, as exist between type I and II cells normally or as might occur with excessive cell surface shedding during inflammation or injury states, may specifically alter SP expression. Here, isolated type II cells were exposed to the model sulfated ECM heparin; desulfated heparin; and/or fibroblast growth factor (FGF)-1, -2, or -7 for 24 h to examine by quantitative real-time polymerase chain reaction their effects on SP gene expression. Aquaporin 5 (AQP-5) gene expression was also examined as a phenotypic marker for the type I cell. SP-B mRNA abundance was increased 4- to 8-fold by all three FGFs. Heparin at low concentrations (5 microg/ml) or desulfated heparin at high concentrations (500 microg/ml) enhanced the effects of FGF-2 and -7, while high heparin concentrations (500 microg/ml) were inhibitory. In contrast, SP-B mRNA abundance was increased by heparin in a dose- and sulfation-dependent manner when used in combination with FGF-1. SP-C and AQP-5 mRNA levels were increased by heparin alone in a dose- and sulfation-dependent manner, while all FGFs lacked effect on SP-C or AQP-5 mRNA levels. These data indicate that heparin can be stimulatory to SP gene expression depending on concentration, degree of sulfation, and surrounding FGF environment, and that heparin plays a significant role in modulating alveolar epithelial cell phenotype in vitro.

Downregulation of aquaporin 5 induced by vector-based short hairpin RNA and its effect on MUC5AC gene expression in human airway submucosal gland cells

The aquaporins (AQPs) are a family of homologous water channels expressed in many epithelial and endothelial cells, however no reliable and non-toxic inhibitors of AQPs have been reported yet. Our researchers have analyzed the changes of AQP5 expression induced by vector-based short hairpin RNA (shRNA) in the human airway submucosal gland cell line (SPC-A1) and observed its regulation on the expression of MUC5AC gene. Localizations of AQP5 and MUC5AC in SPC-A1cells were detected by Immunofluorescence. AQP5 mRNA was significantly reduced by 75.1% one day after transfection with specific shRNA, named shAQP5. However, the significant suppression of AQP5 protein did not appear until day 5 after transfection. MUC5AC mRNA was remarkably increased by 119.9% On day 3 after shAQP5 transfection, while comparable MUC5AC protein changes were not found in SPC-A1 cells with flow cytometry analysis. These results indicate that vector-based shRNA could be used as a potential tool to inhibit the expression of AQP5. This is the first investigation providing evidence demonstrating the regulation of the mucin gene by AQP5 gene silencing.

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.

Aquaporin-5 water channel in lipid rafts of rat parotid glands

Aquaporin-5 (AQP5), an apical plasma membrane (APM) water channel in salivary glands, lacrimal glands, and airway epithelium, has an important role in fluid secretion. The activation of M3 muscarinic acetylcholine receptors (mAChRs) or alpha1-adrenoceptors on the salivary glands induces salivary fluid secretion. AQP5 localizes in lipid rafts and activation of the M3 mAChRs or alpha1-adrenoceptors induced its translocation together with the lipid rafts to the APM in the interlobular ducts of rat parotid glands. This review focuses on the mechanisms of AQP5 translocation together with lipid rafts to the APM in the interlobular duct cells of parotid glands of normal rats and the impairment of AQP5 translocation in diabetes and senescence.

A role for AQP5 in activation of TRPV4 by hypotonicity: concerted involvement of AQP5 and TRPV4 in regulation of cell volume recovery

Regulation of cell volume in response to changes in osmolarity is critical for cell function and survival. However, the molecular basis of osmosensation and regulation of cell volume are not clearly understood. We have examined the mechanism of regulatory volume decrease (RVD) in salivary gland cells and report a novel association between osmosensing TRPV4 (transient receptor potential vanalloid 4) and AQP5 (aquaporin 5), which is required for regulating water permeability and cell volume. Exposure of salivary gland cells and acini to hypotonicity elicited an increase in cell volume and activation of RVD. Hypotonicity also activated Ca2+ entry, which was required for subsequent RVD. Ca2+ entry was associated with a distinct nonselective cation current that was activated by 4alphaPDD and inhibited by ruthenium red, suggesting involvement of TRPV4. Consistent with this, endogenous TRPV4 was detected in cells and in the apical region of acini along AQP5. Importantly, acinar cells from mice lacking either TRPV4 or AQP5 displayed greatly reduced Ca2+ entry and loss of RVD in response to hypotonicity, although the extent of cell swelling was similar. Expression of N terminus-deleted AQP5 suppressed TRPV4 activation and RVD but not cell swelling. Furthermore, hypotonicity increased the association and surface expression of AQP5 and TRPV4. Both these effects and RVD were reduced by actin depolymerization. These data demonstrate that (i) activation of TRPV4 by hypotonicity depends on AQP5, not on cell swelling per se, and (ii) TRPV4 and AQP5 concertedly control regulatory volume decrease. These data suggest a potentially important role for TRPV4 in salivary gland function.

Transient receptor potential vanilloid 4 regulates aquaporin-5 abundance under hypotonic conditions

Aquaporin-5 (AQP5) is expressed in epithelia of lung, cornea, and various secretory glands, sites where extracellular osmolality is known to fluctuate. Hypertonic aquaporin (AQP) induction has been described, but little is known about the effects of a hypotonic environment on AQP abundance. We report that, when mouse lung epithelial cells were exposed to hypotonic medium, a dose-responsive decrease in AQP5 abundance was observed. Hypotonic reduction of AQP5 was blocked by ruthenium red, methanandamide, and miconazole, agents that inhibit the cation channel transient receptor potential vanilloid (TRPV) 4 present in lung epithelial cells. Several observations indicate that TRPV4 participates in hypotonic reduction of AQP5, including a requirement for extracellular calcium to achieve AQP5 reduction; an increase in intracellular calcium in mouse lung epithelial (MLE) cells after hypotonic stimulation; and reduction of AQP5 abundance after addition of the TRPV4 agonist 4alpha-Phorbol-12,13-didecanoate (4alpha-PDD). Similarly, addition of hypotonic PBS to mouse trachea in vivo decreased AQP5 within 1 h, an effect blocked by ruthenium red. To confirm a functional interaction, AQP5 was expressed in control or TRPV4-expressing human embryonic kidney (HEK) cells. Hypotonic reduction of AQP5 was observed only in the presence of TRPV4 and was blocked by ruthenium red. Combined with earlier studies, these observations indicate that AQP5 abundance is tightly regulated along a range of osmolalities and that AQP5 reduction by extracellular hypotonicity can be mediated by TRPV4. These findings have direct relevance to regulation of membrane water permeability and water homeostasis in epithelia of the lung and other organs.

Protein kinase A-regulated membrane trafficking of a green fluorescent protein-aquaporin 5 chimera in MDCK cells

The green fluorescent protein (GFP) of the jellyfish, Aeqorea victoria, was used as an autofluorescent tag to track the trafficking of aquaporin 5 (AQP5), an exocrine gland-type water channel. Two groups of chimeric proteins were constructed; one in which GFP was fused to the amino-terminus of AQP5 (GFP-AQP5) and the other, in which it was fused to the carboxyl terminus of it (AQP5-GFP). In each group, 2 chimeras were produced, a wild-type AQP5 with its normal sequence and a mutant AQP5 having a mutated amino acid at 259, i.e., GFP-AQP5-T259A and AQP5-GFP-T259A. They were used to transfect Madin-Darby canine kidney (MDCK) cells. The GFP-AQP5 chimera was localized in the intracellular vesicles, which trafficked to the plasma membrane in response to N(6), 2'-O-dibutyryladenosine 3', 5'-cyclic monophosphate (dbcAMP). Membrane trafficking was inhibited by N-[2-(p-bromocinnamylamino)ethyl]-5-isoquimolinesulfonamide (H-89) but not by palmitoyl-dl-carnitine chloride (PCC). In contrast, the AQP5-GFP chimera expressed in MDCK cells was localized constitutively on the plasma membrane. The cellular localization of the latter chimera was not affected by stimulation with dbcAMP in the presence or absence of H-89 or PCC. Replacement of Thr-259 with Ala-259 did not affect the dbcAMP-induced translocation of the chimeric protein, suggesting that phosphorylation of Thr-259 was not necessary for AQP5 trafficking under the present experimental conditions. Thus, the GFP-AQP5 chimera will be a useful tool to study AQP5 trafficking in vitro, whereas the constitutive membrane localization of the AQP5-GFP chimera suggests the importance of the carboxyl terminus of the AQP5 protein for its sorting, whether it is translocated to intracellular vesicles or to the plasma membrane.

Distribution and roles of aquaporins in salivary glands

Salivary glands are involved in secretion of saliva, which is known to participate in the protection and hydratation of mucosal structures within the oral cavity, oropharynx and oesophagus, the initiation of digestion, some antimicrobial defence, and the protection from chemical and mechanical stress. Saliva secretion is a watery fluid containing electrolytes and a mixture of proteins and can be stimulated by muscarinic and adrenergic agonists. Since water movement is involved in saliva secretion, the expression, localization and function of aquaporins (AQPs) have been studied in salivary glands. This review will focus on the expression, localization and functional roles of the AQPs identified in salivary glands. The presence of AQP1, AQP5 and AQP8 has been generally accepted by many, while the presence of AQP3, AQP4, AQP6 and AQP7 still remains controversial. Functionally, AQP5 seems to be the only AQP thus far to be clearly playing a major role in the salivary secretion process. Modifications in AQPs expression and/or distribution have been reported in xerostomic conditions.

Aquaporins in chicken: Localization of ck-AQP5 along the small and large intestine

Aquaporins (AQPS) are transmembrane water channels poorly investigated in birds. Using degenerated primers and RT-PCR, we identified in kidney and gastrointestinal tract of Hubbard chickens (Gallus gallus) three fragments, corresponding to ck-AQP2, ck-AQP4, and ck-AQP5 mRNAs. Comparison of nucleotide ck-AQPs sequences to their rat and human orthologues revealed an overall identity of 75-90%. Expression in the renal and gastrointestinal systems of the three ck-AQPs mRNA was analysed by Northern assays. Transcript of ck-AQP2 was only identified in kidney. ck-AQP4 mRNA was highly expressed in brain, and to a lesser extent in kidney and stomach. ck-AQP5 mRNA was found in jejunum and ileum, and to a lesser extent in colon and lung. In situ hybridisation showed ck-AQP5 mRNA in the crypt cells of jejunum, ileum and colon, whereas it was absent from the cells lining the villi. Levels of ck-AQP5 mRNA (analyzed by Northern and in situ hybridisation assays) and protein (analysed by immunohistochemistry) decreased from the jejunum to the colon. This work confirmed the presence of AQPs in chicken, and showed that chicken and mammalian AQPs share a high degree of similarity in nucleotide sequence and tissue distribution.

Expression and localization of aquaporin-5 in the epithelial ovarian tumors

OBJECTIVE

To investigate the expression and localization of aquaporin-5 (AQP5) in epithelial ovarian tumors and its clinic significance.

METHODS

The expression of AQP5 protein and mRNA in 65 cases epithelial ovarian tumors and 13 cases normal tissue were measured by immunohistochemical technique, Western blotting and RT-PCR, respectively.

RESULTS

AQP5 is mainly localized in the basolateral membranes of benign tumor cells, the apical and basolateral membrane of borderline cells and scattered in the membrane of malignant cells and almost no or weak staining in normal ovarian epithelium. The AQP5 expression in ovarian malignant and borderline tumors was significantly higher than that of benign tumors (P < 0.05) and normal tissue (P < 0.05). Of all the epithelial ovarian malignant tumors, the AQP5 expression in cases with ascites volume more than 1000 ml was higher than that of ascites volume less than 500 ml (P < 0.05). Increased AQP5 protein level was associated with lymph node metastasis (P < 0.05). There is a positive correlation between ascites amount and the expression of AQP5 protein and mRNA (P < 0.05), as well as lymph node metastasis and the expression of AQP5 protein and mRNA (P < 0.05). The AQP5 expression was not related with FIGO stage, grade and histological type (P > 0.05).

CONCLUSION

The data suggest that overexpression of AQP5 play an important role in tumorigenesis of epithelial ovarian tumors, which may be related to the ascites formation of ovarian carcinoma.

Immunolocalization of aquaporin-5 expression in sweat gland cells from normal and anhidrotic horses

Western blot analysis showed that sweat gland cells from freely sweating horses expressed the water channel aquaporin-5 (AQP-5). Immunohistochemistry revealed a strong AQP-5-like activity reaction at the apical membrane of the glandular secretory cells, which was absent from the surrounding myoepithelium and all other skin structures. In anhidrotic horses, AQP-5 was also found at the apical membrane of the luminal sweat gland cells, but the level of expression reduced with the length of time that the animal had displayed anhidrosis. The level of AQP-5 expression was substantially reduced in animals with long-term anhidrosis, hence implicating water channel impairment as a possible factor in the development of this disorder.

Successful treatment of a patient with primary Sjögren's syndrome with Rituximab

We report the course of a 55-year-old woman, the first patient with primary Sjögren's syndrome and distal renal tubular acidosis but without lymphoma to be treated with B-cell depletion using Rituximab. Rapidly after B-cell depletion, remarkable improvement in xerostomia occurred, while serological findings and tubular acidosis have been unchanged. In labial salivary gland biopsy, lymphocyte infiltration and particularly CD20-positive cells decreased strikingly. Aquaporin 1 (AQP-1) expression in myoepithelial cells was very low before treatment and increased noticeably. Apical AQP-5 in acinus cells likewise increased following Rituximab. In contrast, basolateral NKCC1 was expressed at unchanged intensity before and following Rituximab. The improvement has been sustained and still is most gratifying 10 months after treatment. B-cell depletion may be effective treatment in Sjögren's syndrome. Likewise, it may now be possible to separate the immunologic phenomena in Sjögren's syndrome from the consequences of prolonged hyposalivation when studying the pathophysiology of xerostomia.

Modifying the NH2 and COOH Termini of Aquaporin-5: Effects on Localization in Polarized Epithelial Cells

To reengineer polarized epithelial cell functions directly in situ, or ex vivo in the fabrication of an artificial organ, it is necessary to understand mechanisms that account for polarized membrane sorting. We have used the aquaporins (AQPs), a family of homotetrameric water channel proteins, as model membrane proteins for this purpose. AQP monomers contain six transmembrane-spanning domains linked by five interconnecting loops, with the NH2 and COOH termini residing in the cytosol. AQP5 is localized in the apical membranes of several different epithelia in vivo, and in stably transfected MDCK-II cells grown as a polarized monolayer. We wished to identify a structural region(s) within rat AQP5 (rAQP5) important for apical localization, and to study the MDCK-II cell localization of rAQP5s modified in either their NH2 or COOH terminus. We show that the NH2- terminal region does not play a major role in apical localization as deletion of the NH2 terminus produced a modified rAQP5 construct (AQP5-NT(del)) that was stably expressed and localized primarily to the apical membranes of MDCK-II cells. Attachment of a FLAG epitope to the NH2 terminus of AQP5 (AQP5(flag) construct) also did not perturb apical localization. In addition, we found that the exchange of NH2-terminal regions between rAQP5 and human AQP1 (hAQP1; a nonpolarized AQP isoform) produced a modified rAQP5 construct (AQP5-1NT) and a modified hAQP1 construct (AQP1-5NT), each of which localized as the parental AQP (apically, and to both apical and basolateral membranes, respectively). In contrast, we found that deletion of the COOH terminus resulted in a modified rAQP5 construct (AQP5-CT(del)) that was unstably expressed and localized to intracellular site(s) in MDCK-II cells. Substitution of the COOH terminus of AQP1 with the COOH terminus of AQP5 also produced a construct (AQP1-5CT) transiently expressed in intracellular compartment(s). However, substitution of the COOH terminus of rAQP5 with the COOH terminus of hAQP1 produced a modified rAQP5 construct (AQP5-1CT) that was stably expressed and localized to basolateral membranes, suggesting the loss of an apical targeting/retention signal from rAQP5, the gain of a basolateral targeting/retention signal from hAQP1, or a combination of these two possibilities.

[Experimental study on the expression and function of aquaporin-1 and aquaporin-5 in rats with acute lung injury induced by lipopolysaccharide]

OBJECTIVE

To investigate whether the expression and function of aquaporin-1 (AQP-1) is altered by tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) in primary rat lung microvessel endothelial cells (LMECs) after exposure to lipopolysaccharide (LPS), and to study the expressions of AQP-1 and AQP-5 in lung tissue of rats with acute lung injury (ALI) induced by LPS. The aim is to further clarify the pathogenesis of ALI/acute respiratory distress syndrome (ARDS).

METHODS

(1) In vitro: The third passage LMECs were randomly divided into LPS group, TNF-alpha group, IL-1beta group and DMEM control group, and the experimental groups were exposed to LPS, TNF-alpha and IL-1beta respectively. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to quantify AQP-1 mRNA changes and an immunocytochemistry method was used for determining AQP-1 protein changes in cultured rat LMECs. Isotope tracer technique was applied for the assay of the intra-cellular tritium water ((3)H2O) signal intensity in rat LMECs. (2) In vivo: Forty male Wistar rats were randomly divided into five groups: LPS 2 h group, LPS 4 h group, LPS 6 h group, LPS 8 h group and a control group, eight rats per group; The LPS treated groups served as the ALI models. RT-PCR was used to observe the changes of AQP-1 and AQP-5 mRNA and the immunohistochemistry method was used for determining AQP-1 and AQP-5 protein changes in ALI rats.

RESULTS

(1) In vitro: The expression of AQP-1 mRNA and protein in LMECs were decreased significantly in the LPS group (0.428 +/- 0.026, 0.366 +/- 0.009), the TNF-alpha group (0.446 +/- 0.029, 0.374 +/- 0.014) and IL-1beta group (0.454 +/- 0.023, 0.377 +/- 0.007) as compared to the DMEM control group (0.793 +/- 0.035, 0.660 +/- 0.013, respectively; all P < 0.01). The quantities of tritium water's permeability in the LPS group, the TNF-alpha group and the IL-1beta group [(726 +/- 58), (738 +/- 45), (774 +/- 44) counts per minute] were significantly less than that in the DMEM control group [(1 148 +/- 70) counts per minute, P < 0.01]. (2) In vivo: The expression levels of AQP-1 and AQP-5 mRNA in ALI rats (LPS 2 h group 0.409 +/- 0.018, 0.421 +/- 0.020; LPS 4 h group 0.421 +/- 0.023, 0.412 +/- 0.023; LPS 6 h group 0.435 +/- 0.020, 0.388 +/- 0.031; LPS 8 h group 0.438 +/- 0.016, 0.386 +/- 0.019, respectively) were significantly lower than that in the control group (0.794 +/- 0.015, 0.787 +/- 0.022; all P < 0.01).

CONCLUSION

AQP-1 and AQP-5 may play a role in abnormal fluid transportation and probably involve in the formation of pulmonary edema in ALI/ARDS.