Identification and localization of aquaporin water channels in human salivary glands

Sexual maturation and changes in water and salt transport components in the kidney and intestine of three-spined stickleback (Gasterosteus aculeatus L.)

Mature three-spined stickleback males use spiggin threads secreted from their kidney to glue together nest material. This requires strongly hypertrophied renal proximal tubular cells, which compromises renal osmoregulatory function during the breeding period. Experimental evidence suggests that the intestine takes over hypotonic fluid secretion at that stage but the mechanism is unexplored. To unravel the molecular mechanism we analyzed and compared transcript levels of several membrane proteins involved in water and salt transport in intestinal and renal tissues, in non-mature males (NM), mature males (MM), and mature females (MF). Aquaporin paralogs aqp1a, -3a, -8aa, -8ab, -10a, and -10b, two Na(+),K(+)-ATPase alpha-1 subunit isoforms (nka547, nka976), Na(+),K(+),2Cl(-)-, and Na(+),Cl(-)-cotransporters (nkcc1a, nkcc2, ncc), the cystic fibrosis transmembrane conductance regulator (cftr) and two claudin isoforms (cldn2, cldn15a) were expressed in the intestine and kidney in all groups. There were no differences in aqp and cldn expression between intestines of NM and MM; nkcc2 was lower and nka levels tended to be higher in intestines of MM than in NM. In the kidney, aqp1 and aqp8ab levels were lower in MM than in NM, whereas aqp3a, nkcc1a, cldn15a, and spiggin were markedly elevated. This was accompanied by marked hypertrophy of kidney tubules in MM. The data support an altered kidney function in terms of water handling in mature males, whereas there was no support for modified trans-epithelial water permeability or salt-secretory activity in the intestine of mature males. Salt-absorptive activity in the intestine may, however, be down-regulated during male maturation.

Calcium signaling and cell volume regulation are altered in Sjögren's Syndrome

OBJECTIVE

Sjögren's Syndrome (SS) is a chronic autoimmune disease, leading to deficient secretion from salivary and lacrimal glands. Saliva production is normally increased by cholinergic innervation, giving rise to intracellular calcium signaling and water transport through water channels (aquaporins, AQPs). The aim of this study was to investigate possible pathophysiological changes in cell volume regulation, AQP expression and localization, and intracellular calcium signaling in glandular cells from SS patients compared to controls.

MATERIALS AND METHODS

A total of 35 SS patients and 41 non-SS controls were included. Real time qPCR was combined with immunohistochemistry to analyze the mRNA expression and cellular distribution of AQP1, 3 and 5. Cell volume regulation and intracellular calcium signaling were examined in fresh acinar cells.

RESULTS

We show for the first time a reduced mRNA expression of AQP1 and 5 in SS compared to controls, accompanied by a decrease in staining intensity of AQP1, 3 and 5 in areas adjacent to local lymphocytic infiltration. Furthermore, we observed that the SS cells' capacity for volume regulation was abnormal. Similarly, the calcium response after parasympathetic agonist (carbachol) stimulation was markedly decreased in SS cells.

CONCLUSIONS

It is concluded that mRNA expression of AQP1 and 5, protein distribution of AQP1, 3 and 5, glandular cell volume regulation and intracellular calcium signaling are all altered in SS, pointing to possible pathophysiological mechanisms in SS.

Aquaporin expression profiles in normal sinonasal mucosa and chronic rhinosinusitis

BACKGROUND

Thickened secretions, mucosal edema, and polyp formation are pathological features in chronic rhinosinusitis (CRS) that could theoretically be caused by aberrant water flow through sinonasal mucosa. Aquaporins (AQPs) are a family of proteins with roles in water transport, with tissue-specific expression profiles. This study aims to determine if AQP expression in sinonasal mucosa is different between normal controls and patients with CRS, either with (CRSwNP) or without (CRSsNP) nasal polyps.

METHODS

During endoscopic sinus surgery or transsphenoidal surgery, sinonasal tissue was collected and classified as CRSwNP (n = 13), CRSsNP (n = 10), or normal (n = 10). Messenger RNA (mRNA) expression of human AQP0 to AQP12b was determined using quantitative real-time polymerase chain reaction (qRT-PCR). Cellular localization of AQP1, AQP3, AQP4, AQP5, AQP7, and AQP11 was determined by immunohistochemistry.

RESULTS

mRNA of AQP0 to AQP11 was identified in all samples. AQP12b mRNA was not detected. Significant differences in the mRNA expression levels of AQP4 and AQP11 were identified between normal and CRSwNP patients (p < 0.05). Differences in the cellular localization of AQPs were observed in both CRSsNP and CRSwNP patients vs normal controls. More intense localization to the cell cytoplasm was observed for AQP5 in glandular epithelium (CRSwNP; p < 0.05) and surface epithelium (CRSsNP; p < 0.05), and AQP4 in glandular epithelium (CRSsNP; p < 0.05).

CONCLUSION

This study characterized AQP mRNA expression and protein localization in normal human sinonasal tissue. Significant differences in mRNA expression were found for AQP4 and AQP11 in CRSwNP and differences in protein localization patterns of AQP4 and AQP5 were identified in both types of CRS.

Reciprocity in the developmental regulation of aquaporins 1, 3 and 5 during pregnancy and lactation in the rat

Milk secretion involves significant flux of water, driven largely by synthesis of lactose within the Golgi apparatus. It has not been determined whether this flux is simply a passive consequence of the osmotic potential between cytosol and Golgi, or whether it involves regulated flow. Aquaporins (AQPs) are membrane water channels that regulate water flux. AQP1, AQP3 and AQP5 have previously been detected in mammary tissue, but evidence of developmental regulation (altered expression according to the developmental and physiological state of the mammary gland) is lacking and their cellular/subcellular location is not well understood. In this paper we present evidence of developmental regulation of all three of these AQPs. Further, there was evidence of reciprocity since expression of the rather abundant AQP3 and less abundant AQP1 increased significantly from pregnancy into lactation, whereas expression of the least abundant AQP5 decreased. It would be tempting to suggest that AQP3 and AQP1 are involved in the secretion of water into milk. Paradoxically, however, it was AQP5 that demonstrated most evidence of expression located at the apical (secretory) membrane. The possibility is discussed that AQP5 is synthesized during pregnancy as a stable protein that functions to regulate water secretion during lactation. AQP3 was identified primarily at the basal and lateral membranes of the secretory cells, suggesting a possible involvement in regulated uptake of water and glycerol. AQP1 was identified primarily at the capillary and secretory cell cytoplasmic level and may again be more concerned with uptake and hence milk synthesis, rather than secretion. The fact that expression was developmentally regulated supports, but does not prove, a regulatory involvement of AQPs in water flux through the milk secretory cell.

Upregulation of aquaporin expression in the salivary glands of heat-acclimated rats

It is known that aquaporin (AQP) 5 expression in the apical membrane of acinar cells in salivary glands is important for the secretion of saliva in rodents and humans. Although heat acclimation enhances saliva secretion in rodents, the molecular mechanism of how heat induces saliva secretion has not been determined. Here, we found that heat acclimation enhanced the expression of AQP5 and AQP1 in rat submandibular glands concomitant with the promotion of the HIF-1α pathway, leading to VEGF induction and CD31-positive angiogenesis. The apical membrane distribution of AQP5 in serous acinar cells enhanced after heat acclimation, while AQP1 expression was restricted to the endothelial cells in the submandibular glands. A network of AQPs may be involved in heat-acclimated regulation in saliva secretion. Because AQPs probably plays a crucial role in saliva secretion in humans, these findings may lead to a novel strategy for treating saliva hyposecretion.

Immunolocalization of AQP5 in resting and stimulated normal labial glands and in Sjögren's syndrome

OBJECTIVE

In our current work, in vivo examination of AQP5 distribution in labial salivary glands following stimulation of secretion has been carried out in normal individuals and in patients with Sjögren's syndrome.

SUBJECTS AND METHODS

For this study, we selected five patients with primary Sjögren's syndrome (mean age 62.4 ± 10.6 s.d. years) diagnosed in accordance with the European Cooperative Community classification criteria. There were five patients (mean age 27 ± 2.5 s.d. years) in the control group. The subcellular distribution of AQP5 in human labial gland biopsies was determined with light and immunoelectron microscopy before and 30 min after administration of oral pilocarpine.

RESULTS

In unstimulated control and Sjögren's labial glands, AQP5 is about 90% localized in the apical plasma membrane, with only rarely associated gold particles with intracellular membrane structures. We have found no evidence of pilocarpine-induced changes in localization of AQP5 in either healthy individuals or patients with Sjögren's syndrome.

CONCLUSIONS

Our studies indicate that neither Sjögren's syndrome itself, nor muscarinic cholinergic stimulation in vivo caused any significant changes in the distribution of AQP5 in the labial salivary gland cells.

Na(+)-K(+)-2Cl(-) cotransporter-mediated fluid secretion increases under hypotonic osmolarity in the mouse submandibular salivary gland

Water-handling epithelia are sensitive to the osmotic environment. In this study, the effects of a hypo-osmotic challenge on carbachol (CCh)-induced fluid secretion was investigated using an ex vivo submandibular gland perfusion technique and intracellular pH and Ca(2+) measurements. The osmolality of the perfusion solution was altered to examine the response of the gland to a hypotonic challenge. The flow rate was increased by 34% with a 30% hypotonic solution (225 mosmol/kgH2O), although the Ca(2+) response was unchanged. The lowering of the external Cl(-) by 50% abolished this increase in the 30% hypotonic solution. Furthermore, bumetanide, an inhibitor of the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1), completely inhibited the fluid secretion increase caused by the 30% hypotonic solution, and both the total amount of fluid and the flow rate were identical to those of the isotonic solution. This finding was confirmed by measuring the NKCC1 bumetanide-dependent NH4 (+) transport; Na(+)-K(+)-2Cl(-) transport was upregulated >40% by a 30% hypotonic challenge. Therefore, the increase in CCh-induced fluid secretion in response to hypotonic conditions can be attributed, to a large extent, to the specific activation of the NKCC1.

Quantitative analysis of protein and gene expression in salivary glands of Sjogren's-like disease NOD mice treated by bone marrow soup

Background

Bone marrow cell extract (termed as BM Soup) has been demonstrated to repair irradiated salivary glands (SGs) and restore saliva secretion in our previous study. In the present study, we aim to investigate if the function of damaged SGs in non-obese diabetic (NOD) mice can be restored by BM Soup treatment and the molecular alterations associated with the treatment.

Methods

Whole BM cells were lysed and soluble intracellular contents (“BM Soup”) were injected I.V. into NOD mice. Tandem mass tagging with 2-D liquid chromatography-mass spectrometry was used to quantify proteins in the submandibular glands (SMGs) between untreated and BM Soup-treated mice. Quantitative PCR was used to identify genes with altered expression in the treated mice.

Results BM Soup

restored salivary flow rates to normal levels and significantly reduced the focus scores of SMGs in NOD mice. More than 1800 proteins in SMG cells were quantified by the proteomic approach. Many SMG proteins involved in inflammation and apoptosis were found to be down-regulated whereas those involved in salivary gland biology and development/regeneration were up-regulated in the BM Soup-treated mice. qPCR analysis also revealed expression changes of growth factors and cytokines in the SMGs of the treated NOD mice.

Conclusion

BM Soup treatment is effective to restore the function of damaged SGs in NOD mice. Through gene/protein expression analysis, we have found that BM Soup treatment might effectuate via inhibiting apoptosis, focal adhesion and inflammation whereas promoting development, regeneration and differentiation of the SG cells in NOD mice. These findings provide important insights on the potential mechanisms underlying the BM Soup treatment for functional restoration of damaged SGs in NOD mice. Additional studies are needed to further confirm the identified target genes and their related signaling pathways that are responsible for the BM Soup treatment.

Water permeability of the mammalian cochlea: functional features of an aquaporin-facilitated water shunt at the perilymph-endolymph barrier

The cochlear duct epithelium (CDE) constitutes a tight barrier that effectively separates the inner ear fluids, endolymph and perilymph, thereby maintaining distinct ionic and osmotic gradients that are essential for auditory function. However, in vivo experiments have demonstrated that the CDE allows for rapid water exchange between fluid compartments. The molecular mechanism governing water permeation across the CDE remains elusive. We computationally determined the diffusional (PD) and osmotic (Pf) water permeability coefficients for the mammalian CDE based on in silico simulations of cochlear water dynamics integrating previously derived in vivo experimental data on fluid flow with expression sites of molecular water channels (aquaporins, AQPs). The PD of the entire CDE (PD = 8.18 × 10(-5) cm s(-1)) and its individual partitions including Reissner's membrane (PD = 12.06 × 10(-5) cm s(-1)) and the organ of Corti (PD = 10.2 × 10(-5) cm s(-1)) were similar to other epithelia with AQP-facilitated water permeation. The Pf of the CDE (Pf = 6.15 × 10(-4) cm s(-1)) was also in the range of other epithelia while an exceptionally high Pf was determined for an epithelial subdomain of outer sulcus cells in the cochlear apex co-expressing AQP4 and AQP5 (OSCs; Pf = 156.90 × 10(-3) cm s(-1)). The Pf/PD ratios of the CDE (Pf/PD = 7.52) and OSCs (Pf/PD = 242.02) indicate an aqueous pore-facilitated water exchange and reveal a high-transfer region or "water shunt" in the cochlear apex. This "water shunt" explains experimentally determined phenomena of endolymphatic longitudinal flow towards the cochlear apex. The water permeability coefficients of the CDE emphasise the physiological and pathophysiological relevance of water dynamics in the cochlea in particular for endolymphatic hydrops and Ménière's disease.

Hypersensitive mAChRs are involved in the epiphora of transplanted glands

Autologous transplantation of the submandibular gland is an effective treatment for severe dry eye syndrome. However, more than 40% of patients experience epiphora 3 to 6 months after transplantation. The underlying mechanism of epiphora remains to be elucidated. To investigate the potential roles of muscarinic acetylcholine receptors (mAChRs) in the induction of epiphora in transplanted glands, we assessed and found elevated mRNA and protein expression of M1- and M3-mAChR in transplanted glands from epiphora patients. The content of inositol 1, 4, 5-trisphosphate was also elevated. Moreover, carbachol (5 and 10 µM) induced greater increase of [Ca(2+)]i in isolated epiphora submandibular cells than in controls. Although aquaporin-5 (AQP5) content and distribution in the apical and lateral plasma of epiphora glands did not change, AQP5 content was reduced in lipid microdomains (lipid rafts and caveolae) but increased in non-lipid microdomains compared with controls. Carbachol (10 µM) increased the ratio of non-lipid microdomain to total AQP5 in the cultured control submandibular gland tissue. Taken together, these results indicated that hypersensitive mAChRs might be involved in the epiphora of transplanted submandibular glands by modulating AQP5 trafficking.

Cerebrospinal Fluid Secretion by the Choroid Plexus

The choroid plexus epithelium is a cuboidal cell monolayer, which produces the majority of the cerebrospinal fluid. The concerted action of a variety of integral membrane proteins mediates the transepithelial movement of solutes and water across the epithelium. Secretion by the choroid plexus is characterized by an extremely high rate and by the unusual cellular polarization of well-known epithelial transport proteins. This review focuses on the specific ion and water transport by the choroid plexus cells, and then attempts to integrate the action of specific transport proteins to formulate a model of cerebrospinal fluid secretion. Significant emphasis is placed on the concept of isotonic fluid transport across epithelia, as there is still surprisingly little consensus on the basic biophysics of this phenomenon. The role of the choroid plexus in the regulation of fluid and electrolyte balance in the central nervous system is discussed, and choroid plexus dysfunctions are described in a very diverse set of clinical conditions such as aging, Alzheimer's disease, brain edema, neoplasms, and hydrocephalus. Although the choroid plexus may only have an indirect influence on the pathogenesis of these conditions, the ability to modify epithelial function may be an important component of future therapies.

Human aquaporins: regulators of transcellular water flow

BACKGROUND

Emerging evidence supports the view that (AQP) aquaporin water channels are regulators of transcellular water flow. Consistent with their expression in most tissues, AQPs are associated with diverse physiological and pathophysiological processes.

SCOPE OF REVIEW

AQP knockout studies suggest that the regulatory role of AQPs, rather than their action as passive channels, is their critical function. Transport through all AQPs occurs by a common passive mechanism, but their regulation and cellular distribution varies significantly depending on cell and tissue type; the role of AQPs in cell volume regulation (CVR) is particularly notable. This review examines the regulatory role of AQPs in transcellular water flow, especially in CVR. We focus on key systems of the human body, encompassing processes as diverse as urine concentration in the kidney to clearance of brain oedema.

MAJOR CONCLUSIONS

AQPs are crucial for the regulation of water homeostasis, providing selective pores for the rapid movement of water across diverse cell membranes and playing regulatory roles in CVR. Gating mechanisms have been proposed for human AQPs, but have only been reported for plant and microbial AQPs. Consequently, it is likely that the distribution and abundance of AQPs in a particular membrane is the determinant of membrane water permeability and a regulator of transcellular water flow.

GENERAL SIGNIFICANCE

Elucidating the mechanisms that regulate transcellular water flow will improve our understanding of the human body in health and disease. The central role of specific AQPs in regulating water homeostasis will provide routes to a range of novel therapies. This article is part of a Special Issue entitled Aquaporins.

Salivary gland cell differentiation and organization on micropatterned PLGA nanofiber craters

There is a need for an artificial salivary gland as a long-term remedy for patients suffering from salivary hypofunction, a leading cause of chronic xerostomia (dry mouth). Current salivary gland tissue engineering approaches are limited in that they either lack sufficient physical cues and surface area needed to facilitate epithelial cell differentiation, or they fail to provide a mechanism for assembling an interconnected branched network of cells. We have developed highly-ordered arrays of curved hemispherical "craters" in polydimethylsiloxane (PDMS) using wafer-level integrated circuit (IC) fabrication processes, and lined them with electrospun poly-lactic-co-glycolic acid (PLGA) nanofibers, designed to mimic the three-dimensional (3-D) in vivo architecture of the basement membrane surrounding spherical acini of salivary gland epithelial cells. These micropatterned scaffolds provide a method for engineering increased surface area and were additionally investigated for their ability to promote cell polarization. Two immortalized salivary gland cell lines (SIMS, ductal and Par-C10, acinar) were cultured on fibrous crater arrays of various radii and compared with those grown on flat PLGA nanofiber substrates, and in 3-D Matrigel. It was found that by increasing crater curvature, the average height of the cell monolayer of SIMS cells and to a lesser extent, Par-C10 cells, increased to a maximum similar to that seen in cells grown in 3-D Matrigel. Increasing curvature resulted in higher expression levels of tight junction protein occludin in both cell lines, but did not induce a change in expression of adherens junction protein E-cadherin. Additionally, increasing curvature promoted polarity of both cell lines, as a greater apical localization of occludin was seen in cells on substrates of higher curvature. Lastly, substrate curvature increased expression of the water channel protein aquaporin-5 (Aqp-5) in Par-C10 cells, suggesting that curved nanofiber substrates are more suitable for promoting differentiation of salivary gland cells.

An immunohistochemistry-based study on aquaporin (AQP)-1, 3, 4, 5 and 8 in the parotid glands, submandibular glands and sublingual glands of Sjögren's syndrome mouse models chronically administered cevimeline

Cevimeline is a muscarinic agonist that promotes saliva secretion and is used to treat Sjögren's syndrome (SS), an autoimmune disorder in which the exocrine glands that produce saliva are destroyed. Cevimeline is thought to affect the composition of saliva in part by regulating the localization of aquaporins (AQPs). In this study, we investigated the effects of chronic Cevimeline administration in the salivary glands of SS mice on the immunohistochemical localization of aquaporin (AQP)-1, 3, 4, 5 and 8. We used Cevimeline-untreated SS mice, treated SS mice, discontinued SS mice and untreated normal mice. AQP-5 was found in the apical and lateral membranes of acinar cells in the parotid and submandibular glands of cevimeline-treated SS mice and untreated normal mice. Saliva secretion and AQP-5 localization were sustained in SS mice who were chronically administered Cevimeline and at four weeks after discontinuation. Unlike AQP-5, the localization of AQP-1, 3, 4 and 8 were not affected by Cevimeline administration. Our findings demonstrated that administration of Cevimeline maintains the proper localization of AQP-5 in the acinar cells of the salivary gland, which may promote salivation in chronically treated SS mice. Clinically, this suggests that chronic Cevimeline administration may be useful therapeutically for SS patients suffering from a decrease in saliva secretion by improving the disordered AQP-5 localization.

The gating mechanism of the human aquaporin 5 revealed by molecular dynamics simulations

Aquaporins are protein channels located across the cell membrane with the role of conducting water or other small sugar alcohol molecules (aquaglyceroporins). The high-resolution X-ray structure of the human aquaporin 5 (HsAQP5) shows that HsAQP5, as all the other known aquaporins, exhibits tetrameric structure. By means of molecular dynamics simulations we analyzed the role of spontaneous fluctuations on the structural behavior of the human AQP5. We found that different conformations within the tetramer lead to a distribution of monomeric channel structures, which can be characterized as open or closed. The switch between the two states of a channel is a tap-like mechanism at the cytoplasmic end which regulates the water passage through the pore. The channel is closed by a translation of the His67 residue inside the pore. Moreover, water permeation rate calculations revealed that the selectivity filter, located at the other end of the channel, regulates the flow rate of water molecules when the channel is open, by locally modifying the orientation of His173. Furthermore, the calculated permeation rates of a fully open channel are in good agreement with the reported experimental value.

TNF-α inhibits aquaporin 5 expression in human salivary gland acinar cells via suppression of histone H4 acetylation

Sjögren's syndrome is a systemic autoimmune disease characterized by reductions in salivary and lacrimal secretions. The mechanisms underlying these reductions remain unclear. We have previously shown that TNF-α plays an important role in the destruction of acinar structures. Here we examined TNF-α's function in the expression of aquaporin (AQP) 5 in human salivary gland acinar cells. Immortalized human salivary gland acinar (NS-SV-AC) cells were treated with TNF-α, and then the expression levels of AQP5 mRNA and protein were analysed. In addition, the mechanisms underlying the reduction of AQP5 expression by TNF-α treatment were investigated. TNF-α-treatment of NS-SV-AC cells significantly suppressed the expression levels of AQP5 mRNA and protein, and reduced the net fluid secretion rate. We examined the expression and activation levels of DNA methyltransferases (Dnmts) in NS-SV-AC cells treated with TNF-α. However, no significant changes were observed in the expression or activation levels of Dnmt1, Dnmt3a or Dnmt3b. Although we also investigated the role of NF-κB activity in the TNF-α-induced suppression of AQP5 expression in NS-SV-AC cells, we detected similar TNF-α suppression of AQP5 expression in non-transfected cells and in a super-repressor form of IκBα cDNA-transfected cell clones. However, interestingly, chromatin immunoprecipitation analysis demonstrated a remarkable decrease in levels of acetylated histone H4 associated with the AQP5 gene promoter after treatment with TNF-α in NS-SV-AC cells. Therefore, our results may indicate that TNF-α inhibition of AQP5 expression in human salivary gland acinar cells is due to the epigenetic mechanism by suppression of acetylation of histone H4.

DNA demethylating agent decitabine increases AQP5 expression and restores salivary function

Xerostomia is the symptom of oral dryness resulting most frequently, but not exclusively, from salivary gland hypofunction. Because the prevalence of xerostomia may increase with age, it has multiple oral health consequences in aging populations. In the present study, we demonstrate that the in vivo administration of 5-aza-2'-deoxycytidine (5-Aza-CdR; decitabine), a DNA demethylating agent, to the murine aging model C57BL/6CrSlc mice (24 wks old) increased the volumes of salivary flow compared with those of control mice. Western blot analysis and immunohistochemical staining demonstrated the augmented expression of AQP5 protein in the salivary glands of 5-Aza-CdR-treated mice compared with those of control mice. In addition, AQP5 protein expression levels in 5-Aza-CdR-treated old mice (27 wks old) were much higher than those in untreated and young mice (6 wks old). Global methylation levels in the salivary glands were significantly lower in the 5-Aza-CdR-treated mice than in the untreated mice. Moreover, the induction of demethylation in the AQP5 promoter of 5-Aza-CdR-treated mice was stronger than in the control mice. Analysis of our data therefore suggests that a DNA demethylating agent may be a useful drug for restoring hyposalivation in elderly individuals, thereby leading to the resolution of xerostomia.

Vasculitis in Sjögren's Syndrome

Sjögren's syndrome is a chronic autoimmune disease that is commonly manifested by immune attack on the exocrine glands with resultant dry eyes and dry mouth. Sjögren's syndrome patients also have disease in other organs. One of the most common extraglandular manifestations is vasculitis. Skin vasculitis, with palpable purpura clinically and leukocytoclastic vasculitis on pathological examination, is common. Although half of those individuals with subcutaneous vasculitis have only a single episode, skin vasculitic involvement is associated with more severe disease. Necrotizing vasculitis of medium-sized vessels resembling polyarteritis nodosa can occur in Sjögren's syndrome patients. Experience in therapy for vasculitis is limited, but intravenous IgG may be effective. Recent data support a relationship between neuromyelitis optica (Devic disease) and Sjögren's syndrome. Sjögren's syndrome patients with optic neuritis or transverse myelitis have anti-aquaporin-4, which are characteristic of Devic disease. Devic disease patients have salivary lymphocytic infiltration similar to that found among Sjögren's syndrome patients.

Scientific frontiers: emerging technologies for salivary diagnostics

Saliva, a biofluid historically well-studied biochemically and physiologically, has entered the post-genomic 'omics' era, where its proteomic, genomic, and microbiome constituents have been comprehensively deciphered. The translational path of these salivary constituents has begun toward a variety of personalized individual medical applications, including early detection of cancer. Salivary diagnostics is a late-comer, but it is catching up where dedicated resources, like the Salivaomics Knowledge Base (SKB), now have taken center stage in the dissemination of the diagnostic potentials of salivary biomarkers and other translational and clinical utilities.

Aquaporin-5: a marker protein for proliferation and migration of human breast cancer cells

Aquaporin (AQP) is a family of transmembrane proteins for water transport. Recent studies revealed that AQPs are likely to play a role in tumor progression and invasion. We aimed to examine the potential role of AQP5 in the progression of human breast cancer cells. Expression of AQP5 mRNA and protein was seen in human breast cancer cell line (both MCF7 and MDA-MB-231) by RT-PCR and immunoblotting analysis. Immunoperoxidase labeling of AQP5 was observed at ductal epithelial cells of human breast tissues. In benign tumor, AQP5 labeling was mainly seen at the apical domains of ductal epithelial cells. In contrast, in invasive ductal carcinoma, prominent AQP5 labeling was associated with cancer cells, whereas some ducts were unlabeled and apical polarity of AQP5 in ducts was lost. Cell proliferation (BrdU incorporation assay) and migration of MCF7 cells were significantly attenuated by lentivirus-mediated AQP5-shRNA transduction. Hyperosmotic stress induced by sorbitol treatment (100 mM, 24 h) reduced AQP5 expression in MCF7 cells, which was also associated with a significant reduction in cell proliferation and migration. Taken together, prominent AQP5 expression in breast cancer cells with the loss of polarity of ductal epithelial cells was seen during the progression of breast carcinoma. shRNA- or hyperosmotic stress-induced reduction in AQP5 expression of MCF7 cells was associated with significantly reduced cell proliferation and migration. In conclusion, AQP5 overexpression is likely to play a role in cell growth and metastasis of human breast cancer and could be a novel target for anti-breast cancer treatment.

Morphological and biochemical evidence for the evolution of salt glands in snakes

Vertebrate salt glands have evolved independently multiple times, yet there are few hypotheses about the processes underlying the convergent evolution of salt glands across taxa. Here, we compare the morphology and molecular biology of specialized salt-secreting glands from a marine snake (Laticauda semifasciata) with the cephalic glands from semi-marine (Nerodia clarkii clarkii) and freshwater (N. fasciata) watersnakes to look for evidence of a salt gland in the former and to develop hypotheses about the evolution of snake salt glands. Like the salt gland of L. semifasciata, the nasal and anterior/posterior sublingual glands in both species of Nerodia exhibit a compound tubular shape, and express basolateral Na(+)/K(+)-ATPase (NKA) and Na(+)/K(+)/2Cl(-)cotransporter (NKCC); however, the abundance of NKA and NKCC in N. fasciata appears lower than in N. c. clarkii. Aquaporin 3 (AQP3) is also basolateral in the sublingual glands of both species of Nerodia, as is abundant neutral mucin; both AQP3 and mucin are absent from the salt gland in L. semifasciata. Thus, we propose that the evolution of the snake salt gland by co-option of an existing gland involved at least two steps: (i) an increase in the abundance of NKA and NKCC in the basolateral membranes of the secretory epithelia, and (ii) loss of AQP3/mucus secretion from these epithelia.

Aquaporin and vascular diseases

Aquaporins (AQP) are family of water channels found in several epithelial and endothelial cells, whose recent identification has provided insights into water transport in several tissues, including the central nervous system (CNS). Since brain edema continues to be the main cause of death from several CNS diseases, such as stroke, much of the interest in AQPs and their functional contribution to the water balance is due to their possible role in clearing edema water from the brain and in managing hydrocephalus and benign intracranial hypertension, suggesting that they could be targets for future treatments of various brain conditions, particularly vascular diseases. AQPs also seem to be involved in cell migration, and a mechanism of AQP-facilitated cell migration has been proposed where local osmotic gradients created at the tip of the lamellipodium drive water influx, facilitating lamellipodial extension and cell migration. AQP-facilitated cell migration was also detected in tumour cells, suggesting that it may have an important role in tumour angiogenesis and spread, and accounting for AQP expression in many tumour cell types and for correlations found between AQP expression and tumour stage in some tumours.

Rat parotid gland cell differentiation in three-dimensional culture

The use of polarized salivary gland cell monolayers has contributed to our understanding of salivary gland physiology. However, these cell models are not representative of glandular epithelium in vivo, and, therefore, are not ideal for investigating salivary epithelial functions. The current study has developed a three-dimensional (3D) cell culture model for rat Par-C10 parotid gland cells that forms differentiated acinar-like spheres on Matrigel. These 3D Par-C10 acinar-like spheres display characteristics similar to differentiated acini in salivary glands, including cell polarization, tight junction (TJ) formation required to maintain transepithelial potential difference, basolateral expression of aquaporin-3 and Na+/K+/2Cl- cotransporter-1, and responsiveness to the muscarinic receptor agonist carbachol that is decreased by the anion channel blocker diphenylamine-2-carboxylic acid or chloride replacement with gluconate. Incubation of the spheres in the hypertonic medium increased the expression level of the water channel aquaporin-5. Further, the proinflammatory cytokines tumor necrosis factor-alpha and interferon-gamma induced alterations in TJ integrity in the acinar-like spheres without affecting individual cell viability, suggesting that cytokines may affect salivary gland function by altering TJ integrity. Thus, 3D Par-C10 acinar-like spheres represent a novel in vitro model to study physiological and pathophysiological functions of differentiated acini.

Localization of AQP5 during development of the mouse submandibular salivary gland

Aquaporin 5 (AQP5) is known to be central for salivary fluid secretion. A study of the temporal-spatial distribution of AQP5 during submandibular gland (SMG) development and in adult tissues might offer further clues to its unknown role during development. In the present work, SMGs from embryonic day (E) 14.5-18.5 and postnatal days (P) 0, 2, 5, 25, and 60 were immunostained for AQP5 and analyzed using light microscopy. Additional confocal and transmission electron microscopy were performed on P60 glands. Our results show that AQP5 expression first occurs in a scattered pattern in the late canalicular stage and becomes more prominent and organized in the terminal tubuli/pro-acinar cells towards birth. Additional apical membrane staining in the entire intralobular duct is found just prior to birth. During postnatal development, AQP5 is expressed in both the luminal and lateral membrane of pro-acinar/acinar cells. AQP5 is also detected in the basal membrane of acinar cells at P25 and P60. In the intercalated ducts at P60, the male glands show apical staining in the entire segment, while only the proximal region is positive in the female glands. These results demonstrate an evolving distribution of AQP5 during pre- and postnatal development in the mouse SMGs.

Channels and transporters in salivary glands

According to the two-stage hypothesis, primary saliva, a NaCl-rich plasma-like isotonic fluid is secreted by salivary acinar cells and its ionic composition becomes modified in the duct system. The ducts secrete K(+) and HCO (3) (-) and reabsorb Na(+) and Cl(-) without any water movement, thus establishing a hypotonic final saliva. Salivary secretion depends on the coordinated action of several channels and transporters localized in the apical and basolateral membrane of acinar and duct cells. Early functional studies in perfused glands, followed by the molecular cloning of several transport proteins and the subsequent analysis of mutant mice, have greatly contributed to our understanding of salivary fluid and the electrolyte secretion process. With a few exceptions, most of the key channels and transporters involved in salivary secretion have now been identified and characterized. However, the picture that has emerged from all these studies is one of a complex molecular network characterized by redundancy for several transport proteins, compensatory mechanisms, and adaptive changes in health and disease. Current research is directed to the molecular interactions between the determinants and the ways in which they are regulated by extracellular signals and intracellular mediators. This review focuses on the functionally and molecularly best-characterized channels and transporters that are considered to be involved in transepithelial fluid and electrolyte transport in salivary glands.

Effect of cell swelling on ER/PM junctional interactions and channel assembly involved in SOCE

Store-operated calcium entry (SOCE) regulates critical cellular functions and is determined by precise ER/plasma membrane (PM) junctional interactions. Here we have assessed the effect of hypotonic cell volume increase on SOCE in a salivary gland epithelial cell line (HSG). Thapsigargin (Tg) activated a 2APB- and 1microM Gd(3+)-sensitive, inwardly rectifying, cation current, I(SOC), while hypotonic solution (150mOsm) induced cell swelling and activated an outwardly rectifying cation current that was blocked by 100microM Gd(3+) but not by 2APB. HTS addition before or after Tg attenuated the sensitivity of Ca(2+) influx to 2APB and 1microM Gd(3+). After HTS-induced volume increase, while stimulation of cells with Tg resulted in intracellular Ca(2+) release without Ca(2+) influx, stimulation with CCh caused neither internal Ca(2+) release nor Ca(2+) influx. Importantly, HTS caused the ER to recede from the plasma membrane which prevented Tg-stimulated clustering of STIM1 in the ER/PM region and association of STIM1 with TRPC1 and Orai1. Disruption of SOCE was dependent on the level of hypotonic stress as 225mOsm HTS induced relatively less cell swelling or disruption of SOCE. These results demonstrate that epithelial cells can tolerate small increases (up to 5%) in cell volume while larger increases lead to disruption of ER-PM interactions that are critical for activation of SOCE. We suggest that loss of SOCE could impact cell function and contribute to the deleterious effects of severe hypotonic stress.

Development and characterization of a novel human in vitro blood-nerve barrier model using primary endoneurial endothelial cells

There are phenotypic and functional differences between vascular endothelium from different tissues and between microvascular and macrovascular endothelial cells (ECs) from the same tissue. Relatively little is known about the human blood-nerve barrier (BNB). We report the development of an in vitro BNB model using primary human endoneurial ECs freshly isolated and purified from decedent sciatic nerves via endoneurial stripping, connective tissue enzymatic digestion, and density centrifugation. Primary human endoneurial ECs are spindle shaped and contact inhibited. They rapidly differentiate to form capillary-like networks and microvessels, bind Ulex Europaeus Agglutinin 1 lectin, express von Willebrand factor, and endocytose acetylated low-density lipoprotein. They also express specific transport and cellular adhesion molecules and tight junction proteins, consistent with cells that form a highly restrictive endothelial barrier similar to the blood-brain barrier. When cultured on collagen-coated transwell inserts, the primary human endoneurial ECs develop an in vitro BNB with high transendothelial electrical resistances (160 Omega x cm(2); maximal 12 days after seeding) and low solute permeability coefficient to fluoresceinated high-molecular weight (70 kDa) dextran (2.75 x 10(-3) cm/minute). This in vitro BNB model retains essential known or expected characteristics of the human BNB and has many potential applications for studies of solute, macromolecule, microbial, virus, and leukocyte interactions with this highly specialized endothelial barrier.

Localization of aquaporins, water channel proteins, in the mouse eustachian tube

CONCLUSION

Immunolocalization of the subtypes of water channel proteins, aquaporins (AQPs), was detected in the mouse eustachian tube (ET). AQPs are located continuously from the serous glands and the capillary vessels to the luminal side in the ET epithelium and may play an important role in the transportation of water to the surface of the ET lumen through the epithelium.

OBJECTIVES

Although the water supply to the surface of the ET lumen is considered to be essential for closing of the ET, the pathway of the water in the ET is not fully understood. Since AQPs, a group of water transport proteins, have been reported to regulate water homeostasis, we examined the location of AQPs in the mouse ET.

MATERIALS AND METHODS

Nine subtypes of AQPs were examined in paraffin embedded ETs of adult mice using the avidin-biotin peroxidase complex method of immunohistochemistry.

RESULTS

Four subtypes of AQPs were detected in the mouse ET. AQP-1 was detected in fibroblasts, endothelial cells of capillary vessels and cartilage cells. AQP-3 was distinctly detected in the basal membrane of epithelial cells. AQP-4 was detected in the basal membrane of epithelial cells. AQP-5 was expressed in the luminal side of the ET epithelial cells and also in the apical surface of the cells of the serous glands.

Aquaporins in secretory glands and their role in Sjögren's syndrome

Salivary, lacrimal and pancreatic secretions are known to account for multiple physiological functions. These exocrine secretions are watery fluids containing electrolytes, and a mixture of proteins, and can be stimulated by a number of agonists. Since water movement is involved in exocrine secretion, aquaporins (AQPs) have been hypothesised to contribute to fluid production in exocrine glands. This chapter will focus on the expression, localisation and function of AQPs in salivary and lacrimal glands and pancreas. The role of multiple water and ion transporters and channels in exocrine fluid secretion will also be reviewed. Finally, this chapter will address the potential role of AQPs in Sjögren's syndrome.

Increased expression of c-fos protein associated with increased matrix metalloproteinase-9 protein expression in the endometrium of endometriotic patients

OBJECTIVE

To investigate c-fos and matrix metalloproteinase-9 (MMP-9) expression in the endometrium from women with or without endometriosis throughout the menstrual cycle, and to explore the correlation of c-fos expression with MMP-9 expression and 17beta-E(2) levels in serum.

DESIGN

Molecular studies in human tissue.

SETTING

A women's hospital in China.

PATIENT(S)

Fifty-five premenopausal women (25 with endometriosis and 30 without endometriosis) undergoing laparoscopic surgery or hysterectomy.

INTERVENTION(S)

Eutopic and ectopic endometrium tissue were obtained at the time of surgery. Peripheral sera were also collected on the same day.

MAIN OUTCOME MEASURE(S)

Immunohistochemical localization of c-fos in the endometrium, c-fos and MMP-9 protein levels in the endometrium, and 17beta-E(2) levels in the serum.

RESULT(S)

c-fos protein was predominantly located in the nuclei of glandular epithelial cells and stromal cells. c-fos and MMP-9 protein levels in paired eutopic and ectopic endometria from women with endometriosis were significantly higher than those in the endometrium from women without endometriosis. No significant difference in c-fos or MMP-9 protein levels was observed between paired eutopic and ectopic endometria. c-fos protein levels in endometrium positively correlated with endometrial MMP-9 levels and serum 17beta-E(2) levels.

CONCLUSION(S)

Expression of c-fos in the human endometrium may be regulated by 17beta-E(2), and c-fos may be involved in development of endometriosis by promoting MMP-9 gene expression and subsequently the invasive potential of endometrial explants.

Immunolocalization of a mammalian aquaporin 3 homolog in water-transporting epithelial cells in several organs of the clawed toad Xenopus laevis

Nucleotide sequences of cDNA were used to construct antibodies against an aquaporin (AQP) expressed in the clawed toad, Xenopus laevis, viz., Xenopus AQP3, a homolog of mammalian AQP3. Xenopus AQP3 was immunolocalized in the basolateral membrane of the principal cells of the ventral skin, the urinary bladder, the collecting duct and late distal tubule of the kidney, the absorptive epithelial cells of the large intestine, and the ciliated epithelial cells of the oviducts. Therefore, we designated this AQP as basolateral Xenopus AQP3 (AQP-x3BL). The intensity of labeling for AQP-x3BL differed between the ventral and dorsal skin, with the basolateral membrane of the principal cells in the ventral skin showing intense labeling, whereas that in the dorsal skin was lightly labeled. AQP-x3BL was also immunolocalized in the basolateral membrane of secretory cells in the small granular and mucous glands of the skin. As AQP-x5, a homolog of mammalian AQP5, is localized in the apical membrane of these same cells, this provides a pathway for fluid secretion by the glands. Although Hyla AQP-h2 is translocated from the cytoplasm to the apical membrane of the Hyla urinary bladder in response to arginine vasotocin (AVT), AQP-h2 immunoreactivity in Xenopus bladder remains in the cytoplasm and barely moves to the apical membrane, regardless of AVT stimulation. AQP-x3 is localized in the basolateral membrane, even though the AVT-stimulated AQP-h2 does not translocate to the apical membrane. These findings provide new insights into AQP function in aquatic anurans.

The difference of aquaporin 5 distribution in acinar and ductal cells in lacrimal and parotid glands

PURPOSE

This study was designed to clarify the physiological function and tissue distribution of aquaporin 5 (AQP5) in the lacrimal and parotid glands.

METHODS

Saliva and tear volumes were compared in AQP5 knockout (AQP5-/-) mice and wild-type mice. Immunohistochemistry and immunoblot analysis were performed in wild-type and AQP5-/- mice.

RESULTS

Immunofluorescence of AQP5 staining showed that AQP5 was localized mainly in the ductal cells rather than in the acinar cells of the lacrimal gland. In contrast, in the parotid gland, AQP5 was observed abundantly in acinar cells with undetectable staining in ductal cells. Tear secretion was not changed in AQP5-/- mouse, although saliva secretion was significantly reduced.

CONCLUSIONS

AQP5 distribution in acinar cells and ductal cells was completely opposite in the lacrimal and parotid glands. The physiological role of AQP5 might be dependent on the characteristic tissue distribution of the protein in the lacrimal and parotid glands.

Expression and localization of aquaporins in the kidney of the musk shrew (Suncus murinus)

Expression and localization of members of the aquaporin (AQP) family (AQP1, 2, 3, 4, and 5) in the kidney of the musk shrew (Suncus murinus) was examined by immunohistochemistry. AQP1 was expressed in the proximal tubules and in the thin limb of the loops of Henle. AQP1 was the only water channel expressed in the proximal nephron examined, indicating that AQP1 may be an independent water transporter in the proximal nephron. AQP2 and AQP5 were localized to the apical cytoplasm of the cortical to medullary collecting duct (CD) cells and AQP3 and AQP4 were localized to the basal aspect of the cortical to medullary CD cells. AQP3 expression was weaker in the cortical cells compared with the medullary cells, whereas AQP4 was strongly positive throughout the CD. These indicate that the CD is the main water reabsorption segment of the nephron and is regulated by AQPs. Indeed, apical water transport of CD cells of the musk shrew may be controlled by both AQP2 and AQP5. The characteristic expression pattern of the AQPs in this animal provides a novel animal model for elucidating the regulation of water reabsorption by AQPs in the mammalian kidney.

Deregulation of tumor angiogenesis and blockade of tumor growth in PPARbeta-deficient mice

The peroxisome proliferator-activated receptor-beta (PPARbeta) has been implicated in tumorigenesis, but its precise role remains unclear. Here, we show that the growth of syngeneic Pparb wild-type tumors is impaired in Pparb(-/-) mice, concomitant with a diminished blood flow and an abundance of hyperplastic microvascular structures. Matrigel plugs containing pro-angiogenic growth factors harbor increased numbers of morphologically immature, proliferating endothelial cells in Pparb(-/-) mice, and retroviral transduction of Pparb triggers microvessel maturation. We have identified the Cdkn1c gene encoding the cell cycle inhibitor p57(Kip2) as a PPARbeta target gene and a mediator of the PPARbeta-mediated inhibition of cell proliferation, which provides a possible mechanistic explanation for the observed tumor endothelial hyperplasia and deregulation of tumor angiogenesis in Pparb(-/-) mice. Our data point to an unexpected essential role for PPARbeta in constraining tumor endothelial cell proliferation to allow for the formation of functional tumor microvessels.

Functional and molecular characterization of the fluid secretion mechanism in human parotid acinar cells

The strategies available for treating salivary gland hypofunction are limited because relatively little is known about the secretion process in humans. An initial microarray screen detected ion transport proteins generally accepted to be critically involved in salivation. We tested for the activity of some of these proteins, as well as for specific cell properties required to support fluid secretion. The resting membrane potential of human acinar cells was near -51 mV, while the intracellular [Cl-] was approximately 62 mM, about fourfold higher than expected if Cl ions were passively distributed. Active Cl- uptake mechanisms included a bumetanide-sensitive Na+ -K+ -2Cl- cotransporter and paired DIDS-sensitive Cl-/HCO3- and EIPA-sensitive Na+/H+ exchangers that correlated with expression of NKCC1, AE2, and NHE1 transcripts, respectively. Intracellular Ca2+ stimulated a niflumic acid-sensitive Cl- current with properties similar to the Ca2+ -gated Cl channel BEST2. In addition, intracellular Ca2+ stimulated a paxilline-sensitive and voltage-dependent, large-conductance K channel and a clotrimazole-sensitive, intermediate-conductance K channel, consistent with the detection of transcripts for KCNMA1 and KCNN4, respectively. Our results demonstrate that the ion transport mechanisms in human parotid glands are equivalent to those in the mouse, confirming that animal models provide valuable systems for testing therapies to prevent salivary gland dysfunction.

Proteomic knowledge of human aquaporins

Aquaporins (AQPs) are an ubiquitous family of proteins characterized by sequence similarity and the presence of two NPA (Asp-Pro-Ala) motifs. At present, 13 human AQPs are known and they are divided into two subgroups according to their ability to transport only water molecules (AQP0, AQP1, AQP2, AQP4, AQP5, AQP6, and AQP8), or also glycerol and other small solutes (AQP3, AQP7, AQP9, AQP10, AQP12). The genomic, structural, and functional aspects of this family are briefly described. In particular, proteomic approaches to identify and characterize the most studied AQPs, mainly through SDS-PAGE followed by MS analysis, are discussed. Moreover, the clinical importance of the best studied aquaporin (AQP1) in human diseases is also provided.