研究者詳細 - 安井　正人

論文 - 安井　正人

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Analysis of aquaporin-mediated diffusional water permeability by coherent anti-Stokes Raman scattering microscopy

Ibata Keiji, Takimoto Shinichi, Morisaku Toshinori, Miyawaki Atsushi, Yasui Masato

Biophysical Journal 101 （ 9 ） 2277 - 2283 2011年

ISSN 0006-3495

Water can pass through biological membranes via two pathways: simple diffusion through the lipid bilayer, or water-selective facilitated diffusion through aquaporins (AQPs). Although AQPs play an important role in osmotic water permeability (P_f), the role of AQPs in diffusional water permeability remains unclear because of the difficulty of measuring diffusional water permeability (P_d). Here, we report an accurate and instantaneous method for measuring the P_d of a single HeLa S3 cell using coherent anti-Stokes Raman scattering (CARS) microscopy with a quick perfusion device for H₂O/D₂O exchange. Ultra-high-speed line-scan CARS images were obtained every 0.488 ms. The average decay time constant of CARS intensities (τ_CARS) for the external solution H₂O/D₂O exchange was 16.1 ms, whereas the intracellular H₂O/D₂O exchange was 100.7 ± 19.6 ms. To evaluate the roles of AQP in diffusional water permeability, AQP4 fused with enhanced green fluorescent protein (AQP4-EGFP) was transiently expressed in HeLa S3 cells. The average τ_CARS for the intracellular H ₂O/D₂O exchange in the AQP4-EGFP-HeLa S3 cells was 43.1 ± 15.8 ms. We also assessed the cell volume and the cell surface area to calculate P_d. The average P_d values for the AQP4-EGFP-HeLa S3 cells and the control EGFP-HeLa S3 cells were 2.7 ± 1.0 × 10^-3 and 8.3 ± 2.6 × 10^-4 cm/s, respectively. AQP4-mediated water diffusion was independent of the temperature but was dependent on the expression level of the protein at the plasma membrane. These results suggest the possibility of using CARS imaging to investigate the hydrodynamics of single mammalian cells as well as the regulation of AQPs. © 2011 Biophysical Society.

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Acid suppression by proton pump inhibitors enhances aquaporin-4 and KCNQ1 expression in gastric fundic parietal cells in mouse

Matsuzaki Juntaro, Suzuki Hidekazu, Minegishi Yuriko, Sugai Etsuko, Tsugawa Hitoshi, Yasui Masato, Hibi Toshifumi

Digestive Diseases and Sciences 55 （ 12 ） 3339 - 3348 2010年12月

ISSN 0163-2116

Background: The widespread use of proton pump inhibitors (PPIs) is known to cause sporadic gastric fundic gland polyps (FGPs). Altered expression and localization of the water or ion transport proteins might contribute to the excess fluid secretion into the cystic lumen for the development of FGPs. Aims: We investigated the alteration of the murine gastric fundic mucosa after PPI treatment, and examined the expression of water channel aquaporin-4 (AQP4) and potassium channel KCNQ1, which are expressed only in the parietal cells in the gastric mucosa. Methods: Male 5-week-old C57BL/6J mice were administered lansoprazole (LPZ) by subcutaneous injection for 8 weeks. The expression of AQP4 and KCNQ1 were investigated by Western blotting, quantitative RT-PCR, and immunohistochemistry. The expression of mucin-6 (Muc6), pepsinogen, and sonic hedgehog (Shh) were also investigated as mucosal cell lineage markers. Results: Gastric mucosal hyperplasia with multiple cystic dilatations, exhibiting similar histological findings to the FGPs, was observed in the LPZ-treated mice. An increase in the number of AQP4-positive parietal cells and KCNQ1-positive parietal cells was observed. The extension of the distribution of AQP4-positive cells toward the surface of the fundic glands was also observed. The expression levels of AQP4 mRNA and protein were significantly enhanced. The expression of KCNQ1 mRNA was correlated with that of AQP4 mRNA in the LPZ-treated mice. Mucous neck-to-zymogenic cell lineage differentiation was delayed in association with decreased expression of Shh in the LPZ-treated mice. Conclusions: PPI administration increased the number of parietal cells with enhanced expression of AQP4 and KCNQ1. © 2010 Springer Science+Business Media, LLC.

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Inflammatory mediators weaken the amniotic membrane barrier through disruption of tight junctions

Kobayashi Ken, Miwa Hideki, Yasui Masato

Journal of Physiology 588 （ 24 ） 4859 - 4869 2010年12月

ISSN 0022-3751

In chorioamnionitis, intra-amniotic infections render the amniotic fluid an adverse environment for the fetus and increase the risk of fetal mortality and morbidity. It remains unclear how infection crosses the amniotic barrier, which is made up of tight junctions (TJs). In this study, we investigated whether amniotic TJs are disrupted in inflammatory conditions such as chorioamnionitis. Amniotic TJs were disrupted by single applications of interleukin (IL)-1β, IL-6, tumour necrosis factor-α(TNF-α), and prostaglandin E2. In organ-cultured amniotic membranes, these inflammatory mediators decreased the claudin-3 and claudin-4 levels at the apical junction at different times. Injecting IL-6 into the amniotic cavity concurrently induced the disruption of amniotic TJs by decreasing the claudin-3 and claudin-4 levels at the apical junction, and the dysfunction of the amniotic barrier; in contrast, injecting TNF-α weakened the amniotic barrier by inducing apoptosis of the amniotic epithelial cells, with no decrease in claudin-3 and claudin-4 at the apical junction. Furthermore, inflammation in the amniotic membrane, which was induced by the administration of lipopolysaccharide to pregnant mice, concurrently caused dysfunction of the amniotic barrier and disruption of TJs, involving the decrease of claudin-3 and claudin-4 levels at the apical junction and apoptosis in the amniotic epithelium. These results indicate that the adverse effects of the inflammatory mediators on amniotic TJs cause severe dysfunction of the amniotic barrier.Chorioamnionitis increases the risk of mortality and morbidity in newborn infants because of amniotic fluid infection. However, the mechanism by which this infection crosses the amniotic barrier and spreads into the amniotic fluid remains unclear. In this study, we have shown that inflammation weakens the amniotic barrier and that this effect is induced by inflammatory mediators, such as interleukin-1β, interleukin-6, tumour necrosis factor-α, and prostaglandin E2, in distinctly different ways. Knowledge of the mechanism underlying the weakening of the amniotic barrier aids in increasing our understanding of the mechanism underlying antenatal infection. © 2010 The Authors. Journal compilation © 2010 The Physiological Society.

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Cellular and subcellular localization of aquaporins 1, 3, 8, and 9 in amniotic membranes during pregnancy in mice

Kobayashi Ken, Yasui Masato

Cell and Tissue Research 342 （ 2 ） 307 - 316 2010年11月

ISSN 0302-766X

The amniotic membrane encloses the amniotic fluid and plays roles in the regulation of amniotic fluid flux through the intramembranous pathway during pregnancy. Aquaporins (AQPs) 1, 3, 8, and 9 are expressed in amniotic membranes. AQPs are water channel proteins that facilitate the rapid flux of water or small molecules across the plasma membrane. Recently, additional roles of AQPs in facilitating cell migration, proliferation, and apoptosis have been suggested, with AQPs being distributed in the appropriate subcellular regions for their functions. The cellular and subcellular distributions of AQPs in the amniotic membrane however remain unclear. We have examined the cellular and subcellular localization of AQPs in amniotic membranes during pregnancy in mice. After embryonic day 12 (E12), AQP1 was distributed in the plasma membrane of finely branched cell processes in the amniotic fibroblasts. AQP3 was present in both epithelial cells and fibroblasts between E10 and E12. The distribution of AQP3 in the epithelial cells dynamically changed as follows: at E14 in the lateral membrane and apical junction; at E16 in the lateral membrane alone; at E17 in the lateral membrane and cytoplasm. AQP8 was expressed in the epithelial cells and complementarily localized in the apical junction and the lateral membrane. AQP9 was detected only in the apoptotic cells of the epithelium. These cellular and subcellular localizations of amniotic AQPs indicate that each AQP plays distinct functional roles, such as in water and urea transport, cell migration, cell proliferation, and apoptosis, for amniotic fluid homeostasis or tissue remodeling of amniotic membranes. © 2010 Springer-Verlag.

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A stable ATP binding to the nucleotide binding domain is important for reliable gating cycle in an ABC transporter CFTR

Shimizu Hiroyasu, Yu Ying Chun, Kono Koichi, Kubota Takahiro, Yasui Masato, Li Min, Hwang Tzyh Chang, Sohma Yoshiro

Journal of Physiological Sciences 60 （ 5 ） 353 - 362 2010年09月

ISSN 1880-6546

Cystic fibrosis transmembrane conductance regulator (CFTR) anion channel, a member of ABC transporter superfamily, gates following ATP-dependent conformational changes of the nucleotide binding domains (NBD). Reflecting the hundreds of milliseconds duration of the channel open state corresponding to the dimerization of two NBDs, macroscopic WT-CFTR currents usually showed a fast, single exponential relaxation upon removal of cytoplasmic ATP. Mutations of tyrosine1219, a residue critical for ATP binding in second NBD (NBD2), induced a significant slow phase in the current relaxation, suggesting that weakening ATP binding affinity at NBD2 increases the probability of the stable open state. The slow phase was effectively diminished by a higher affinity ATP analogue. These data suggest that a stable binding of ATP to NBD2 is required for normal CFTR gating cycle, andthat the instability of ATP binding frequently halts the gating cycle in the open state presumably through a failure of ATP hydrolysis at NBD2. © 2010 The Physiological Society of Japan and Springer.

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Regulation of water permeability through aquaporin-4

Yukutake Y., Yasui M.

Neuroscience 168 （ 4 ） 885 - 891 2010年07月

ISSN 0306-4522

Aquaporin-4 (AQP4) is a predominant water channel protein in mammalian brains that is distributed with the highest density in the perivascular and subpial astrocyte end-feet. AQP4 is a critical component of an integrated water and potassium homeostasis. Expression and regulation of AQP4 have been studied to understand the roles of AQP4 in physiology and several pathological conditions. Indeed, AQP4 has been implicated in several neurological conditions, such as brain edema and seizure. AQP4 is dynamically regulated at different levels: channel gating, subcellular distribution, phosphorylation, protein-protein interactions and orthogonal array formation. In this review, we focus on the short-term regulation of AQP4. Phosphorylation of AQP4 is important; AQP4 is inhibited when Ser180 is phosphorylated and activated when Ser111 is phosphorylated. AQP4 is also regulated by several metal ions. These metal ions inhibit AQP4 by interacting with the Cys178 residue located in the cytoplasmic loop D, suggesting that AQP4 is regulated by intracellular signaling pathways in response to extracellular stimuli. Recently, it was demonstrated that AQP4 may be inhibited by arylsulfonamides, antiepileptic drugs and other related chemical compounds. Structural analysis of AQP4 may guide a drug design for AQP4. © 2010 IBRO.

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Molecular mechanisms of how mercury inhibits water permeation through aquaporin-1

Hirano Yoshinori, Okimoto Noriaki, Kadohira Ikuko, Suematsu Makoto, Yasuoka Kenji, Yasui Masato

Biophysical Journal 98 （ 8 ） 1512 - 1519 2010年04月

ISSN 0006-3495

Aquaporin (AQP) functions as a water-conducting pore. Mercury inhibits the water permeation through AQP. Although site-directed mutagenesis has shown that mercury binds to Cys¹⁸⁹ during the inhibition process, it is not fully understood how this inhibits the water permeation through AQP1. We carried out 40 ns molecular dynamics simulations of bovine AQP1 tetramer with mercury (Hg-AQPI) or without mercury (Free AQP1). In Hg-AQPI, Cys¹⁹¹ (Cys¹⁸⁹ In human AQP1) is converted to CyS-SHg⁺ in each monomer. During each last 10 ns, we observed water permeation events occurred 23 times in Free AQP1 and never In Hg-AQPL Mercury binding did not influence the whole structure, but did induce a collapse in the orientation of several residues at the ar/R region. In Free AQP1, backbone oxygen atoms of Gly ¹⁹⁰, Cys¹⁹¹, and Gly¹⁹² lined, and were oriented to, the surface of the water pore channel. In Hg-AQP1, however, the SHg⁺ of Cys191-SHg⁺ was oriented toward the outside of the water pore. As a result, the backbone oxygen atoms of Gly¹⁹⁰, Cys¹⁹¹, and Gly¹⁹² became disorganized and the ar/R region collapsed, thereby obstructing the permeation of water. We suggest that mercury disrupts the water pore of AQP1 through local conformational changes in the ar/R region. © 2010 by the Biophysical Society.

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Regulation of Kv2.1 phosphorylation in an animal model of anoxia

Ito Takashi, Nuriya Mutsuo, Yasui Masato

Neurobiology of Disease 38 （ 1 ） 85 - 91 2010年04月

ISSN 0969-9961

Conditions such as hypoxia and anoxia inflict serious damage to the brain and continue to be major medical problems. However, the molecular mechanisms that give rise to such damage are not well understood. To elucidate these mechanisms, we established a clinically relevant rodent model of anoxia/recovery by monitoring blood gas levels after oxygen deprivation. Using this animal model, we examined the regulation of Kv2.1, a voltage-gated potassium channel that plays pivotal roles in the homeostasis and survival of neurons. We found that exposure to anoxia induces rapid dephosphorylation of Kv2.1 in the brain, which can be blocked by pre-administration of a NMDA-type glutamate receptor antagonist, memantine. Furthermore, this change is rapidly reversed as the animal recovers from anoxic stress. These results suggest that Kv2.1 is tightly regulated in a clinically relevant animal model of anoxia and further implicate its role in the homeostasis of neurons during anoxic stress. © 2010 Elsevier Inc. All rights reserved.

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Expression and Distribution of Tight Junction Proteins in Human Amnion During Late Pregnancy

Kobayashi K., Kadohira I., Tanaka M., Yoshimura Y., Ikeda K., Yasui M.

Placenta 31 （ 2 ） 158 - 162 2010年02月

ISSN 0143-4004

Amnion is the innermost layer of the fetal membrane and has been suggested to regulate the volume of amniotic fluid via the amniotic epithelium. The transepithelial pathway is generally restricted by tight junctions (TJs). Thus far, human amniotic TJs have not been identified. In this study, we determined whether the human amniotic epithelium contains TJs. Reverse transcription polymerase chain reaction (RT-PCR) and western blotting analyses showed that the human amniotic epithelium has TJ components, such as occludin, ZO-1, and at least 2 types of claudins, i.e., claudin-4 and claudin-7. The TJ components were found to localize in the lateral membranes and cytoplasm at 35 weeks of gestation; these components disappeared from the lateral membrane at 37 weeks of gestation. Organ culturing of the amnion at 37 weeks gestation induced the relocalization of the TJ proteins from the cytoplasm to the lateral membranes. Furthermore, in cultured amniotic epithelial cells, dexamethasone induced the downregulation of the protein expression of TJs. These findings suggest that the human amniotic epithelium has TJs that disrupt during late pregnancy. The disruption may be induced by several factors such as glucocorticoids present in the amniotic fluid during late pregnancy. © 2009 Elsevier Ltd. All rights reserved.

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Membrane potential dynamics of axons in cultured hippocampal neurons probed by second-harmonic-generation imaging

Nuriya Mutsuo, Yasui Masato

Journal of Biomedical Optics 15 （ 2 ） 2010年

ISSN 1083-3668

The electrical properties of axons critically influence the nature of communication between neurons. However, due to their small size, direct measurement of membrane potential dynamics in intact and complex mammalian axons has been a challenge. Furthermore, quantitative optical measurements of axonal membrane potential dynamics have not been available. To characterize the basic principles of somatic voltage signal propagation in intact axonal arbors, second-harmonic-generation (SHG) imaging is applied to cultured mouse hippocampal neurons. When FM4-64 is applied extracellularly to dissociated neurons, whole axonal arbors are visualized by SHG imaging. Upon action potential generation by somatic current injection, nonattenuating action potentials are recorded in intact axonal arbors. Interestingly, however, both current-and voltage-clamp recordings suggest that nonregenerative subthreshold somatic voltage changes at the soma are poorly conveyed to these axonal sites. These results reveal the nature of membrane potential dynamics of cultured hippocampal neurons, and further show the possibility of SHG imaging in physiological investigations of axons. © 2010 Society of Photo-Optical Instrumentation Engineers.

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Rapid and reversible inhibition of aquaporin-4 by zinc

Yukutake Yoshinori, Hirano Yoshinori, Suematsu Makoto, Yasui Masato

Biochemistry 48 （ 51 ） 12059 - 12061 2009年12月

ISSN 0006-2960

Aquaporin-4 (AQP4) is the predominant water channel in the brain. Although AQP4 plays an important role in brain water homeostasis, the molecular mechanisms of AQP4 regulation are not fully understood. In this report, we show how Zn²⁺ rapidly and reversibly decreases the water permeability of AQP4 when it is reconstituted into proteoliposomes. Mutagenesis analysis identified Cys178, located in cytoplasmic loop D, as a target residue of ZnCl₂ inhibition. Moreover, treatment with diamide enhanced the inhibitory effects of ZnCl₂. These results suggest that the water permeability of AQP4 may be regulated by dynamic changes in intracellular Zn²⁺ concentration linked to the cellular redox state. © 2009 American Chemical Society.

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教育講演5　中枢神経系におけるアクアポリン-4 (AQP4) の役割

安井正人

臨床神経学 49 （ 11 ） 786 - 788 2009年11月

Dynamic Changes in Amniotic Tight Junctions during Pregnancy

Kobayashi K., Inai T., Shibata Y., Yasui M.

Placenta 30 （ 10 ） 840 - 847 2009年10月

ISSN 0143-4004

The amniotic membrane encloses and retains amniotic fluid during pregnancy. In general, fluid flux is regulated by epithelial tissues, which have tight junctions (TJs). However, TJs have not yet been identified in the amniotic epithelium. In this study, we have determined whether the mouse amniotic epithelium contains TJs. Freeze-fracture electron microscopy revealed the presence of strand-like TJs in the amniotic epithelium. Amniotic TJs were composed of occludin; zona occludens (ZO)-1; and claudins 1, 3, 4, and 7. These claudins underwent developmental changes during pregnancy. The localization patterns of the claudins and their detergent solubility drastically changed between embryonic day (E) 16 and E17; the volume of the amniotic fluid also decreased sharply. Furthermore, in vitro assessment of amniotic membrane permeability showed that the amniotic membrane was more permeable on E17 than on E16. On E17, TJ components were sparsely distributed in parts of the amniotic epithelium. The results of Annexin V-fluorescein staining and Terminal dUTP nick-end labeling (TUNEL) assay revealed ongoing apoptosis in all the cells in such regions. The above findings suggest that TJs in the amniotic epithelium maintain amniotic fluid volume during pregnancy, while apoptosis of amniotic epithelial cells between E16 and E17 causes disruption of the TJs. © 2009 Elsevier Ltd. All rights reserved.

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Activity-dependent regulation of HCN1 protein in cortical neurons

Arimitsu Takeshi, Nuriya Mutsuo, Ikeda Kazushige, Takahashi Takao, Yasui Masato

Biochemical and Biophysical Research Communications 387 （ 1 ） 87 - 91 2009年09月

ISSN 0006-291X

Homeostasis of neuronal activity is crucial to neuronal physiology. In dendrites, hyperpolarization-activated cyclic nucleotide-gated channel (HCN) 1 is considered to play critical roles in this process. While electrophysiological studies have demonstrated the dynamic modulation of I_h current mediated by HCN1 proteins, little is known about the underlying molecular and cellular mechanisms. In this study, we utilized cortical cultured neurons and biochemical methods to identify molecular and cellular mechanisms that mediate the physiological regulation of HCN1 channel functions in cortical neurons. Pharmacological manipulations of neuronal activity resulted in changes in the expression level of HCN1. In addition, the surface expression of HCN1 was dynamically regulated by neuronal activity. Both of these changes led to functional modulations of HCN1 channels. Our study suggests that coordinated changes in protein expression and surface expression of HCN1 serve as the key regulatory mechanisms controlling the function of endogenous HCN1 protein in cortical neurons. © 2009 Elsevier Inc. All rights reserved.

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Drosophila big brain does not act as a water channel, but mediates cell adhesion

Tatsumi Kimiko, Tsuji Shoji, Miwa Hideki, Morisaku Toshinori, Nuriya Mutsuo, Orihara Minako, Kaneko Kazunari, Okano Hideyuki, Yasui Masato

FEBS Letters 583 （ 12 ） 2077 - 2082 2009年06月

ISSN 0014-5793

The neurogenic gene Drosophila big brain (bib) has a high sequence homology to aquaporin-4. However, its cellular functions in Drosophila neurogenesis have remained elusive. Here we investigated cell adhesion, and the ion and water permeability of Bib. The adhesive function was examined by a cell aggregation assay using L cells. Bib-transfected L cells formed aggregated clusters, while control-L cells remained as a single cell suspension. Ion permeation was not confirmed in L cells stably expressing Bib. When expressed in COS7 cells, Bib exhibited limited water permeability. This newly found cell adhesive function of Bib may be important for Drosophila neurogenesis. © 2009 Federation of European Biochemical Societies.

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Aquaporin 6 binds calmodulin in a calcium-dependent manner

Rabaud Nicole E., Song Linhua, Wang Yiding, Agre Peter, Yasui Masato, Carbrey Jennifer M.

Biochemical and Biophysical Research Communications 383 （ 1 ） 54 - 57 2009年05月

ISSN 0006-291X

Aquaporin 6 (AQP6) is an anion channel that is expressed primarily in acid secreting α-intercalated cells of the kidney collecting duct. In addition, AQP6 anion channel permeability is gated by low pH. Inspection of the N-terminus of AQP6 revealed a putative calmodulin binding site. AQP6-expressing CHO-K1 cell lysates were mixed with calmodulin beads and AQP6 was pulled down in the presence of calcium. Mutagenesis of the N-terminal calmodulin binding site in full length mouse AQP6 resulted in a loss of calmodulin binding activity. Mouse and human AQP6 calmodulin binding site peptides bound dansyl-calmodulin with a dissociation constant of approximately 1 μM. The binding of AQP6 to calmodulin may be an important key to determining the physiological role of AQP6 in the kidney. © 2009 Elsevier Inc. All rights reserved.

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TSHR mutations as a cause of congenital hypothyroidism in Japan

Narumi Satoshi, Muroya Koji, Abe Yoichiro, Yasui Masato, Asakura Yumi, Adachi Masanori, Hasegawa Tomonobu

Journal of Clinical Endocrinology and Metabolism 94 （ 4 ） 1317 - 1323 2009年04月

ISSN 0021-972X

Context: The prevalence of congenital hypothyroidism (CH) associated with mutations in the TSH receptor gene (TSHR) has not been established. Objective: We examined the frequency of TSHR mutations among patients with permanent primary CH and in the general population in Japan. Subjects and Methods: We enrolled 102 patients with permanent primary CH [70 with "moderate to severe CH" (TSH, >10 mU/liter) and 32 with "mild CH" (TSH, 5-10 mU/liter)], who were identified through newborn screening among 353,000 newborns born in Kanagawa prefecture from October 1979 to June 2006. These subjects were tested for TSHR mutations by PCR-based direct sequencing. We further characterized molecular functions of identified mutant TSHRs in vitro. Results: We found three patients with moderate to severe CH who had biallelic mutations in TSHR and three patients with mild CH who had monoallelic mutations. Observed mutations included one previously characterized mutation (p.R450H) and three uncharacterized mutations (p.G132R, p.A204V, and p.D403N). In vitro experiments confirmed loss of functions of these four mutants. Among four mutations, p.R450H was particularly frequent: six of nine mutant alleles harbored p.R450H. All six alleles with p.R450H commonly carried a minor single nucleotide polymorphism, suggesting a founder effect. We estimated the prevalence of biallelic TSHR mutations to be 4.3% (three in 70) in Japanese patients with moderate to severe CH, and 1 in 118,000 (three in 353,000) in the general Japanese population. Conclusions: In Japan, TSHR mutations are relatively common among patients with CH, and a founder mutation (p.R450H) accounts for about 70% of mutants. Copyright © 2009 by The Endocrine Society.

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PH regulated anion permeability of aquaporin-6

Yasui Masato

Handbook of Experimental Pharmacology 190 299 - 308 2009年

ISSN 0171-2004

The kidney is a model organ for transport physiology (Nielsen 1996). AQPs are well-characterized in mammalian kidneys, where they facilitate transep-ithelial water reabsorption. Most renal AQPs are expressed either in proximal tubule cells or in collecting duct principal cells, which are known as sites for water reab-sorption. AQP1 is present in both apical and basolateral membranes of proximal tubules, and in descending limbs of Henle's loop where 70% of filtrated water is isoosmotically reabsorbed (King and Agre 1996). AQP2 is expressed in principal cells of the collecting duct; in response to vasopressin, AQP2 translocates from in-tracellular vesicles to the apical plasma membranes, thereby increasing water permeability to concentrate urine (Nielsen et al. 1993, 1995; Knepper 1997; Schrier 2006). AQP3 and AQP4 reside in the basolateral membranes of collecting duct principal cells, where they may provide the exit pathways for urine. AQP7, AQP8, and AQP11 are also present in the proximal tubules (Nielsen et al. 1998). A rat cDNA clone encoding AQP6 was isolated by PCR-based homologous cloning from a rat kidney cDNA library (Ma et al. 1993; Yasui et al. 1999). AQP6 has high sequence homology to AQP0, AQP2, and AQP5. A human AQP6 was also cloned (Ma et al. 1996). Interestingly, the genes encoding AQP2, AQP5, and AQP6 are mapped to chromosome band 12q13 as a family gene cluster at this locus (Ma et al. 1997). Nevertheless, AQP6 is distinct from AQP0, AQP2, and AQP5 in terms of function. Among the renal aquaporins mentioned above, AQP6 has a unique distribution and a distinct function. © 2009 Springer Berlin Heidelberg.

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Regulation, structure and function of brain aquaporin

Yasui Masato

Clinical Neurology 49 （ 11 ） 786 - 788 2009年

ISSN 0009-918X

Discovery of aquaporin water channel proteins has provided insight into the molecular mechanism of membrane water permeability. In mammalian brain, Aquaporin-4 (AQP4) is the main water channel and is distributed with highest density in the perivascular and subpial astrocyte end-feet. AQP4 is a critical component of an integrated water and potassium homeostasis. Indeed, AQP4 has been implicated in several neurologic conditions, such as brain edema, seizure and even mood disorders. Expression and regulation of AQP4 have been studied to understand the roles of AQP4 in physiological and pathological conditions. Here we discuss about the mechanisms how AQP4 is dynamically regulated at different levels; channel gating, subcellular distribution, phosphorylation, protein-protein interactions and orthogonal array formation. Interestingly, AQP4 has been identified as a target antigen of autoimmune attack in neuromyelitis optica (NMO). We have evaluated putative epitopes on AQP4 for NMO-IgG binding. We have also studied Drosophila Big Brain (Bib), since Bib has high sequence homology to AQP-4, and play an important role for Drosophila neurogenesis. AQP4 may be a potential therapeutic target in several neurologic conditions. Further studies from different aspects are required to develop new drugs against AQP4.

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Aquaporin-6 is expressed along the rat gastrointestinal tract and upregulated by feeding in the small intestine

Laforenza Umberto, Gastaldi Giulia, Polimeni Mariarosa, Tritto Simona, Tosco Marisa, Ventura Ulderico, Scaffino Manuela F., Yasui Masato

BMC Physiology 9 （ 1 ） 2009年

Background. Several aquaporins (a family of integral membrane proteins) have been recently identified in the mammalian gastrointestinal tract, and their involvement in the movement of fluid and small solutes has been suggested. In this direction we investigated, in some regions of the rat gastrointestinal tract, the presence and localization of aquaporin-6, given its peculiar function as an ion selective channel. Results. RT-PCR and immunoblotting experiments showed that aquaporin-6 was expressed in all the investigated portions of the rat gastrointestinal tract. The RT-PCR experiments showed that aquaporin-6 transcript was highly expressed in small intestine and rectum, and less in stomach, caecum and colon. In addition, jejunal mRNA expression was specifically stimulated by feeding. Immunoblotting analysis showed a major band with a molecular weight of about 55 kDa corresponding to the aquaporin-6 protein dimer; this band was stronger in the stomach and large intestine than in the small intestine. Immunoblotting analysis of brush border membrane vesicle preparations showed an intense signal for aquaporin-6 protein. The results of in situ hybridization experiments demonstrate that aquaporin-6 transcript is present in the isthmus, neck and basal regions of the stomach lining, and throughout the crypt-villus axis in both small and large intestine. In the latter regions, immunohistochemistry revealed strong aquaporin-6 labelling in the apical membrane of the surface epithelial cells, while weak or no labelling was observed in the crypt cells. In the stomach, an intense staining was observed in mucous neck cells and lower signal in principal cells and some parietal cells. Conclusion. The results indicate that aquaporin-6 is distributed throughout the gastrointestinal tract. Aquaporin-6 localization at the apical pole of the superficial epithelial cells and its upregulation by feeding suggest that it may be involved in movements of water and anions through the epithelium of the villi. © 2009 Laforenza et al.

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