研究者詳細 - 安井　正人

論文 - 安井　正人

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Roles of aquaporins in brain disorders

Yasui Masato

Brain and Nerve 67 （ 6 ） 733 - 738 2015年06月

ISSN 1881-6096

Aquaporin (AQP) is a water channel protein that is expressed in the cell membranes. AQPs are related to several kinds of human diseases such as cataract. In the mammalian central nervous system (CNS), AQP4 is specifically expressed in the astrocyte membranes lining the perivascular and periventricular structures. AQP4 plays a role in the development of brain edema associated with certain brain disorders. Neuromyelitis optica (NMO) is a demyelinating disorder, and patients with NMO develop autoimmune antibodies against AQP4 in their serum. Therefore, AQP4 is involved in NMO pathogenesis. A new concept referred to as "glymphatic pathway" has been recently proposed to explain the lymphatic system in the CNS. Dysfunction of the "glymphatic pathway" may cause several neurodegenerative diseases and mood disorders. Importantly, AQP4 may play a role in the "glymphatic pathway". Further investigation of AQP4 in CNS disorders is necessary, and a new drug against AQP4 is expected.

Origin of 1/f noise in hydration dynamics on lipid membrane surfaces

Yamamoto Eiji, Akimoto Takuma, Yasui Masato, Yasuoka Kenji

Scientific Reports 5 2015年03月

Water molecules on lipid membrane surfaces are known to contribute to membrane stability by connecting lipid molecules and acting as a water bridge. Although water structures and diffusivities near the membrane surfaces have been extensively studied, hydration dynamics on the surfaces has remained an open question. Here we investigate residence time statistics of water molecules on the surface of lipid membranes using all-atom molecular dynamics simulations. We show that hydration dynamics on the lipid membranes exhibits 1/f noise. Constructing a dichotomous process for the hydration dynamics, we find that residence times in each state follow a power-law with exponential cutoff and that the process can be regarded as a correlated renewal process where interoccurrence times are correlated. The results imply that the origin of the 1/f noise in hydration dynamics on the membrane surfaces is a combination of a power-law distribution with cutoff of interoccurrence times of switching events and a long-term correlation between the interoccurrence times. These results suggest that the 1/f noise attributed to the correlated renewal process may contribute to the stability of the hydration layers and lipid membranes.

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Dynamic subcellular localization of aquaporin-7 in white adipocytes

Miyauchi Takayuki, Yamamoto Hiroyuki, Abe Yoichiro, Yoshida Go J., Rojek Aleksandra, Sohara Eisei, Uchida Shinichi, Nielsen Søren, Yasui Masato

FEBS Letters 589 （ 5 ） 608 - 614 2015年02月

ISSN 0014-5793

Aquaporin-7 (AQP7) is expressed in adipose tissue, permeated by water and glycerol, and is involved in lipid metabolism. AQP7-null mice develop obesity, insulin resistance, and adipocyte hypertrophy. Here, we show that AQP7 is expressed in adipocyte plasma membranes, and is re-localized to intracellular membranes in response to catecholamine in mouse white adipose tissue. We found that internalization of AQP7 was induced by PKA activation and comparative gene identification 58 (CGI-58). This relocation was confirmed by functional studies in 3T3-L1 adipocytes. Collectively, these results suggest that AQP7 makes several contributions to adipocyte metabolism, in both cortical and intracellular membranes.

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Aquaporin 4-dependent expression of glial fibrillary acidic protein and tenascin-C in activated astrocytes in stab wound mouse brain and in primary culture

Ikeshima-Kataoka Hiroko, Abe Yoichiro, Yasui Masato

Journal of Neuroscience Research 93 （ 1 ） 121 - 129 2015年01月

ISSN 0360-4012

We previously reported that aquaporin 4 (AQP4) has a neuroimmunological function via astrocytes and microglial cells involving osteopontin. AQP4 is a water channel localized in the endofoot of astrocytes in the brain, and its expression is upregulated after a stab wound to the mouse brain or the injection of methylmercury in common marmosets. In this study, the correlation between the expression of AQP4 and the expression of glial fibrillary acidic protein (GFAP) or tenascin-C (TN-C) in reactive astrocytes was examined in primary cultures and brain tissues of AQP4-deficient mice (AQP4/KO). In the absence of a stab wound to the brain or of any stimulation of the cells, the expressions of both GFAP and TN-C were lower in astrocytes from AQP4/KO mice than in those from wild-type (WT) mice. High levels of GFAP and TN-C expression were observed in activated astrocytes after a stab wound to the brain in WT mice; however, the expressions of GFAP and TN-C were insignificant in AQP4/KO mice. Furthermore, lipopolysaccharide (LPS) stimulation activated primary culture of astrocytes and upregulated GFAP and TN-C expression in cells from WT mice, whereas the expressions of GFAP and TN-C were slightly upregulated in cells from AQP4/KO mice. Moreover, the stimulation of primary culture of astrocytes with LPS also upregulated inflammatory cytokines in cells from WT mice, whereas modest increases were observed in cells from AQP4/KO mice. These results suggest that AQP4 expression accelerates GFAP and TN-C expression in activated astrocytes induced by a stab wound in the mouse brain and LPS-stimulated primary culture of astrocytes.

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Severely exacerbated neuromyelitis optica rat model with extensive astro cytopathy by high affinity anti-aquaporin-4 monoclonal antibody.

Kurosawa K, Misu T, Takai Y, Sato D K, Takahashi T, Abe Y, Iwanari H, Ogawa R, Nakashima I, Fujihara K, Hamakubo T, Yasui M and Aoki M.

Acta Neuropathol Com. 3 （ 1 ） 82 2015年

査読有り

The transmembrane transporter domain of glutamate transporters is a process tip localizer

Hayashi Mariko Kato, Yasui Masato

Scientific Reports 5 2015年

Glutamate transporters in the central nervous system remove glutamate released from neurons to terminate the signal. These transporters localize to astrocyte process tips approaching neuronal synapses. The mechanisms underlying the localization of glutamate transporters to these processes, however, are not known. In this study, we demonstrate that the trimeric transmembrane transporter domain fragment of glutamate transporters, lacking both N- and C-terminal cytoplasmic regions, localized to filopodia tips. This is a common property of trimeric transporters including a neutral amino acid transporter ASCT1. Astrocyte specific proteins are not required for the filopodia tip localization. An extracellular loop at the centre of the 4^th transmembrane helices, unique for metazoans, is required for the localization. Moreover, a C186S mutation at the 4^th transmembrane region of EAAT1, found in episodic ataxia patients, significantly decreased its process tip localization. The transmembrane transporter domain fragments of glutamate transporters also localized to astrocyte process tips in cultured hippocampal slice. These results indicate that the transmembrane transporter domain of glutamate transporters have an additional function as a sorting signal to process tips.

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Water confined in the local field of ions

Kojić Dušan, Tsenkova Roumiana, Tomobe Katsufumi, Yasuoka Kenji, Yasui Masato

ChemPhysChem 15 （ 18 ） 4077 - 4086 2014年12月

ISSN 1439-4235

Interionic distances are shorter in concentrated ionic solutions, thus instigating the interaction and overlap of hydration shells, as ions become separated by only one or two layers of water molecules. The simultaneous interaction of water with two oppositely charged ions has, so far, only been investigated by computer simulation studies, because the isolated vibrational spectroscopic signature of these molecules remains undetected. Our combined near-infrared spectroscopic and molecular dynamics simulation studies of alkali halide solutions present a distinct spectral feature, which is highly responsive to depletion of bulk water and merging of hydration shells. The analysis of this spectral feature demonstrates that absorption trends are in good agreement with the law of matching affinities, thus providing the first successful vibrational spectroscopic treatment of this topic. Combined with commonly observed near-infrared bands, this feature provides a spectral pattern that describes some relevant aspects of ionic hydration.

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Mucosal expression of aquaporin-4 in the stomach of histamine type 2 receptor knockout mice and Helicobacter pylori-infected mice

Fukuhara Seiichiro, Matsuzaki Juntaro, Tsugawa Hitoshi, Masaoka Tatsuhiro, Miyoshi Sawako, Mori Hideki, Fukushima Yasushi, Yasui Masato, Kanai Takanori, Suzuki Hidekazu

Journal of Gastroenterology and Hepatology (Australia) 29 （ S4 ） 53 - 59 2014年12月

ISSN 0815-9319

Background and Aim: Basolateral water channel, aquaporin-4 (AQP4), is known to be expressed in gastric parietal cells, especially in the basal side of gastric mucosa. However, the role of AQP4 in the stomach is still unknown. Histamine type 2 receptor (H₂R) knockout mice, which are characterized by suppressed gastric acid secretion, are known as formation of mucosal hyperplasia with cystic dilatation and spasmolytic polypeptide-expressing metaplasia (SPEM) in the stomach. The aim of the present study is to investigate whether the expression of AQP4 is changed by the condition of acid suppression and Helicobacter pylori infection. Methods: Male H₂R knockout mice and their controls (C57BL/6) were used. H.pylori was orally infected at the age of 5 weeks. The distributions of AQP4 and H⁺/K⁺-ATPase in the gastric mucosa were investigated by fluorescent immunohistochemistry. The mRNA expressions of AQP4, H⁺/K⁺- ATPase, sonic hedgehog (Shh), and trefoil factor-2 (TFF2) were investigated by quantitative reverse transcription polymerase chain reaction (RT-PCR). Results: In the H₂R knockout mice, the distribution of AQP4-positive parietal cells was extended toward the surface of the fundic glands. Although the mRNA expression levels of AQP4 and H⁺/K⁺ ATPase were elevated in H₂R knockout mice at the age of 20 weeks, the elevations were not maintained by aging or H.pylori infection. In H₂R knockout mice with H.pylori infection, the expression level of TFF2mRNA was elevated while the ratio between AQP4 and H⁺/K⁺ ATPase mRNA expression was decreased compared with the H₂R knockout mice without H.pylori infection. Conclusions: In the H₂R knockout mice, massive SPEM was induced by H.pylori colonization and the ratio between AQP4 and H⁺/K⁺ ATPase mRNA expression was decreased.

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Sustained down-regulation of β-dystroglycan and associated dysfunctions of astrocytic endfeet in epileptic cerebral cortex

Gondo Asako, Shinotsuka Takanori, Morita Ayaka, Abe Yoichiro, Yasui Masato, Nuriya Mutsuo

Journal of Biological Chemistry 289 （ 44 ） 30279 - 30288 2014年10月

ISSN 0021-9258

Epilepsy is characterized by the abnormal activation of neurons in the cerebral cortex, but the molecular and cellular mechanisms contributing to the development of recurrent seizures are largely unknown. Recently, the critical involvement of astrocytes in the pathophysiology of epilepsy has been proposed. However, the nature of plastic modulations of astrocytic proteins in the epileptic cortex remains poorly understood. In this study, we utilized the zero magnesium in vitro model of epilepsy and examined the potential molecular changes of cortical astrocytes, focusing specifically on endfeet, where specialized biochemical compartments exist. We find that the continuous epileptic activation of neurons for 1 h decreases the expression level of β-dystroglycan (βDG) in acute cortical brain slices prepared from mice. This change is completely abolished by the pharmacological blockade of NMDA-type glutamate receptors as well as by matrix metalloproteinase inhibitors. Consistent with the highly specialized localization of βDG at astrocytic endfeet, where it plays a pivotal role in anchoring endfeet-enriched proteins in astrocytes, the down-regulation of βDG is accompanied by a decrease in the expression of AQP4 but not laminin. Importantly, this down-regulation of βDG persists for at least 1 h, even after the apparent recovery of neuronal activation. Finally, we show that the down-regulation of βDG is associated with the dysfunction of the endfeet at the blood-brain interface as a diffusion barrier. These results suggest that the sustained downregulation of βDG leads to dysfunctions of astrocytic endfeet in the epileptic cerebral cortex and may contribute to the pathogenesis of epilepsy.

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Expression and localization of aquaporin-4 in sensory ganglia

Kato Jungo, Takai Yoshiki, Hayashi Mariko Kato, Kato Yasuhiro, Tanaka Manami, Sohma Yoshiro, Abe Yoichiro, Yasui Masato

Biochemical and Biophysical Research Communications 451 （ 4 ） 562 - 567 2014年09月

ISSN 0006-291X

Aquaporin-4 (AQP4) is a water channel protein that is predominantly expressed in astrocytes in the CNS. The rapid water flux through AQP4 may contribute to electrolyte/water homeostasis and may support neuronal activities in the CNS. On the other hand, little is known about the expression of AQP4 in the peripheral nervous system (PNS). Using AQP4^-/- mice as a negative control, we demonstrated that AQP4 is also expressed in sensory ganglia, such as trigeminal ganglia and dorsal root ganglia in the PNS. Immunohistochemistry revealed that AQP4 is exclusively localized to satellite glial cells (SGCs) surrounding the cell bodies of the primary afferent sensory neurons in the sensory ganglia. Biochemical analyses revealed that the expression levels of AQP4 in sensory ganglia were considerably lower than those in astrocytes in the CNS. Consistently, behavioral analyses did not show any significant difference in terms of mechanical and cold sensitivity between wild type and AQP4^-/- mice. Overall, although the pathophysiological relevance of AQP4 in somatosensory perception remains unclear, our findings provide new insight into the involvement of water homeostasis in the peripheral sensory system.

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Origin of subdiffusion of water molecules on cell membrane surfaces

Yamamoto Eiji, Akimoto Takuma, Yasui Masato, Yasuoka Kenji

Scientific Reports 4 2014年04月

Water molecules play an important role in providing unique environments for biological reactions on cell membranes. It is widely believed that water molecules form bridges that connect lipid molecules and stabilize cell membranes. Using all-atom molecular dynamics simulations, we show that translational and rotational diffusion of water molecules on lipid membrane surfaces exhibit subdiffusion and aging. Moreover, we provide evidence that both divergent mean trapping time (continuous-time random walk) and long-correlated noise (fractional Brownian motion) contribute to this subdiffusion. These results suggest that subdiffusion on cell membranes causes the water retardation, an enhancement of cell membrane stability, and a higher reaction efficiency.

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1 / f fluctuations of amino acids regulate water transportation in aquaporin 1

Yamamoto Eiji, Akimoto Takuma, Hirano Yoshinori, Yasui Masato, Yasuoka Kenji

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 89 （ 2 ） 2014年02月

ISSN 1539-3755

Aquaporins (AQPs), which transport water molecules across cell membranes, are involved in many physiological processes. Recently, it is reported that the water-water interactions within the channel are broken at the aromatic/arginine selectivity filter (ar/R region), which prevents proton transportation [U. K. Eriksson, Science 340, 1346 (2013)SCIEAS0036-807510.1126/science.1234306]. However, the effects of the conformational fluctuations of amino acids on water transportation remain unclear. Using all-atom molecular dynamics simulations, we analyze water transportation and fluctuations of amino acids within AQP1. The amino acids exhibit 1/f fluctuations, indicating possession of long-term memory. Moreover, we find that water molecules crossing the ar/R region obey a non-Poisson process. To investigate the effect of 1/f fluctuations on water transportation, we perform restrained molecular dynamics simulations of AQP1 and simple Langevin stochastic simulations. As a result, we confirm that 1/f fluctuations of amino acids contribute to water transportation in AQP1. These findings appreciably enhance our understanding of AQPs and suggest possibilities for developing biomimetic nanopores. © 2014 American Physical Society.

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Unprecedented cell-selection using ultra-quick freezing combined with aquaporin expression

Kato Yasuhiro, Miyauchi Takayuki, Abe Youichiro, Kojić Dušan, Tanaka Manami, Chikazawa Nana, Nakatake Yuhki, Ko Shigeru B H, Kobayashi Daisuke, Hazama Akihiro, Fujiwara Shoko, Uchida Tatsuya, Yasui Masato

PLoS ONE 9 （ 2 ） 2014年02月

Freezing is usually used for preservation and storage of biological samples; however, this process may have some adverse effects such as cell membrane damage. Aquaporin (AQP), a water channel protein, has been suggested to play some roles for cryopreservation although its molecular mechanism remains unclear. Here we show that membrane damage caused by ultra-quick freezing is rescued by the expression of AQP4. We next examine if the expression of AQP combined with ultra-quick freezing can be used to select cells efficiently under freezing conditions where most cells are died. CHO cells stably expressing AQP4 were exclusively selected from mixed cell cultures. Having identified the increased expression of AQP4 during ES cell differentiation into neuro-ectoderm using bioinformatics, we confirmed the improved survival of differentiated ES cells with AQP4 expression. Finally we show that CHO cells transiently transfected with Endothelin receptor A and Aqp4 were also selected and concentrated by multiple cycles of freezing/thawing, which was confirmed with calcium imaging in response to endothelin. Furthermore, we found that the expression of AQP enables a reduction in the amount of cryoprotectants for freezing, thereby decreasing osmotic stress and cellular toxicity. Taken together, we propose that this simple but efficient and safe method may be applicable to the selection of mammalian cells for applications in regenerative medicine as well as cell-based functional assays or drug screening protocols. © 2014 Kato et al.

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Astrocytic gap junctional networks suppress cellular damage in an in vitro model of ischemia

Shinotsuka Takanori, Yasui Masato, Nuriya Mutsuo

Biochemical and Biophysical Research Communications 444 （ 2 ） 171 - 176 2014年02月

ISSN 0006-291X

Astrocytes play pivotal roles in both the physiology and the pathophysiology of the brain. They communicate with each other via extracellular messengers as well as through gap junctions, which may exacerbate or protect against pathological processes in the brain. However, their roles during the acute phase of ischemia and the underlying cellular mechanisms remain largely unknown. To address this issue, we imaged changes in the intracellular calcium concentration ([Ca²⁺]_i) in astrocytes in mouse cortical slices under oxygen/glucose deprivation (OGD) condition using two-photon microscopy. Under OGD, astrocytes showed [Ca²⁺]_i oscillations followed by larger and sustained [Ca²⁺]_i increases. While the pharmacological blockades of astrocytic receptors for glutamate and ATP had no effect, the inhibitions of gap junctional intercellular coupling between astrocytes significantly advanced the onset of the sustained [Ca²⁺]_i increase after OGD exposure. Interestingly, the simultaneous recording of the neuronal membrane potential revealed that the onset of the sustained [Ca²⁺]_i increase in astrocytes was synchronized with the appearance of neuronal anoxic depolarization. Furthermore, the blockade of gap junctional coupling resulted in a concurrent faster appearance of neuronal depolarizations, which remain synchronized with the sustained [Ca²⁺]_i increase in astrocytes. These results indicate that astrocytes delay the appearance of the pathological responses of astrocytes and neurons through their gap junction-mediated intercellular network under OGD. Thus, astrocytic gap junctional networks provide protection against tissue damage during the acute phase of ischemia. © 2014 Elsevier Inc. All rights reserved.

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Poisson property of the occurrence of flip-flops in a model membrane

Arai Noriyoshi, Akimoto Takuma, Yamamoto Eiji, Yasui Masato, Yasuoka Kenji

Journal of Chemical Physics 140 （ 6 ） 2014年

ISSN 0021-9606

How do lipid molecules in membranes perform a flip-flop? The flip-flops of lipid molecules play a crucial role in the formation and flexibility of membranes. However, little has been determined about the behavior of flip-flops, either experimentally, or in molecular dynamics simulations. Here, we provide numerical results of the flip-flops of model lipid molecules in a model membrane and investigate the statistical properties, using millisecond-order coarse-grained molecular simulations (dissipative particle dynamics). We find that there are three different ways of flip-flops, which can be clearly characterized by their paths on the free energy surface. Furthermore, we found that the probability of the number of the flip-flops is well fitted by the Poisson distribution, and the probability density function for the inter-occurrence times of flip-flops coincides with that of the forward recurrence times. These results indicate that the occurrence of flip-flops is a Poisson process, which will play an important role in the flexibilities of membranes. © 2014 AIP Publishing LLC.

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A general anaesthetic propofol inhibits aquaporin-4 in the presence of Zn²⁺

Kato Jungo, Hayashi Mariko Kato, Aizu Shinnosuke, Yukutake Yoshinori, Takeda Junzo, Yasui Masato

Biochemical Journal 454 （ 2 ） 275 - 282 2013年09月

ISSN 0264-6021

AQP4 (aquaporin-4), a water channel protein that is predominantly expressed in astrocyte end-feet, plays an important role in the brain oedema formation, and is thereby considered to be a potential therapeutic target. Using a stopped-flow analysis, we showed that propofol (2,6-diisopropylphenol), a general anaesthetic drug, profoundly inhibited the osmotic water permeability of AQP4 proteoliposomes in the presence of Zn2+ . This propofol inhibition was not observed in AQP1, suggesting the specificity for AQP4. In addition, the inhibitory effects of propofol could be reversed by the removal of Zn2+ . Other lipid membrane fluidizers also similarly inhibited AQP4, suggesting that themodulation of protein-lipid interactions plays an essential role in the propofol-induced inhibition of AQP4. Accordingly, we used Blue native PAGE and showed that the profound inhibition caused by propofol in the presence of Zn2+ is coupled with the reversible clustering of AQP4 tetramers. Site-directed mutagenesis identified that Cys253, located at the membrane interface connecting to the C-terminal tail, is responsible for Zn2+ -mediated propofol inhibition. Overall, we discovered that propofol specifically and reversibly inhibits AQP4 through the interaction between Zn2+ and Cys253. The findings provide new insight into the functional regulation of AQP4 and may facilitate the identification of novel AQP4-specific inhibitors. © 2013 Biochemical Society.

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Immunological function of aquaporin-4 in stab-wounded mouse brain in concert with a pro-inflammatory cytokine inducer, osteopontin

Ikeshima-Kataoka Hiroko, Abe Yoichiro, Abe Takaya, Yasui Masato

Molecular and Cellular Neuroscience 56 65 - 75 2013年09月

ISSN 1044-7431

During injury to the central nervous system (CNS), astrocytes and microglia proliferate and migrate around the lesion sites. Recently, it has been reported that one of the water channels, aquaporin-4 (AQP4) is seemed to have a role in astroglial migration and glial scar formation caused by brain injury, although its molecular mechanism is largely unknown. In the present study, we examined the expression profiles in wild-type (WT) and AQP4-deficient (AQP4/KO) mice after a stab wound to the cerebral cortex. Three days after the stab wound, AQP4 expression was observed in activated microglia around the lesion site as well as in astrocytes. A microarray analysis revealed that 444 genes around the lesion site were upregulated 3. days after the wounding in WT mice. Surprisingly, most of these up-regulations were significantly attenuated in AQP4/KO mice. Real-time RT-PCR and immunofluorescence showed that osteopontin (OPN) expression around the lesion site was much lower in AQP4/KO mice than in WT mice. Moreover, the up-regulation of pro-inflammatory cytokines was significantly attenuated in AQP4/KO mice. Taken together, these results suggest that AQP4 plays an important role in immunological function in concert with OPN under pathological conditions in the CNS. © 2013 Elsevier Inc.

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Diffusion properties of molecules at the blood-brain interface

Nuriya Mutsuo, Shinotsuka Takanori, Yasui Masato

Cerebral Cortex 23 （ 9 ） 2118 - 2126 2013年09月

ISSN 1047-3211

Molecular diffusion in the extracellular space (ECS) plays a key role in determining tissue physiology and pharmacology. The blood-brain barrier regulates the exchange of substances between the brain and the blood, but the diffusion properties of molecules at this blood-brain interface, particularly around the astrocyte endfeet, are poorly characterized. In this study, we used 2-photon microscopy and acute brain slices of mouse neocortex and directly assessed the diffusion patterns of fluorescent molecules. By observing the diffusion of unconjugated and 10-kDa dextran-conjugated Alexa Fluor 488 from the ECS of the brain parenchyma to the blood vessels, we find various degrees of diffusion barriers at the endfeet: Some allow the invasion of dye inside the endfoot network while others completely block it. Detailed analyses of the time course for dye clearance support the existence of a tight endfoot network capable of acting as a diffusion barrier. Finally, we show that this diffusion pattern collapses under pathological conditions. These data demonstrate the heterogeneous nature of molecular diffusion dynamics around the endfeet and suggest that these structures can serve as the diffusion barrier. Therefore, astrocyte endfeet may add another layer of regulation to the exchange of molecules between blood vessels and brain parenchyma. © 2012 The Author.

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A novel monoclonal antibody against the c-terminal region of aquaporin-4

Ramadhanti Julia, Huang Ping, Kusano-Arai Osamu, Iwanari Hiroko, Sakihama Toshiko, Misu Tasturo, Fujihara Kazuo, Hamakubo Takao, Yasui Masato, Abe Yoichiro

Monoclonal Antibodies in Immunodiagnosis and Immunotherapy 32 （ 4 ） 270 - 276 2013年08月

Aquaporin-4 (AQP4), the most abundant water channel in the brain, plays a central role in water homeostasis, neuronal activity, and migration of astrocytes in the central nervous system. Recent studies have demonstrated that AQP4 is a target of an autoantibody specifically detected in an autoimmune neurologic disease called neuromyelitis optica. Here we have generated a monoclonal antibody (MAb) against the C-terminal region of AQP4 using a baculovirus expressing mouse AQP4 as an immunogen. This antibody (clone E5206) recognized both human and mouse AQP4s in a denaturing condition and was able to precipitate AQP4 from cell lysates of CHO cells stably expressing AQP4. Western blot analysis using deletion mutants revealed that the epitope was located within a region between Asp³⁰³ and Leu³²⁰ in the C-terminal tail of AQP4. Although clone E5206 could not be used for immunostaining when cells or tissues were fixed with 4% paraformaldehyde or 10% formalin, it could be used when cells were fixed with 10% trichloroacetic acid and when a formalin-fixed tissue section was pretreated with antigen-retrieval reagents. This MAb can be a valuable tool for analysis of AQP4 in a variety of physiological and pathophysiological contexts, in human tissues and organs as well as in rodent models, both in vitro and in vivo. © Copyright 2013, Mary Ann Liebert, Inc. 2013.

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Power-law trapping of water molecules on the lipid-membrane surface induces water retardation

Yamamoto Eiji, Akimoto Takuma, Hirano Yoshinori, Yasui Masato, Yasuoka Kenji

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 87 （ 5 ） 2013年05月

ISSN 1539-3755

Cell membranes provide unique local environments for biological reactions, where the diffusion of biomolecules as well as water molecules plays critical roles. Translational and rotational motions of water molecules near membranes are known to be slower than those in bulk. Using all-atom molecular dynamics simulations of a membrane, we show that the temperature dependence of the water molecular motions on the membrane surface is different from that in bulk. Decreasing temperature enhances the water retardation on the membrane surface, and the lateral motions of water molecules are correlated with the vertical motions. We find that trapping times of water molecules onto membrane surfaces are distributed according to a power-law distribution and that the power-law exponents depend linearly on temperature, suggesting a random energy landscape picture. Moreover, we find that water molecules on the membrane surfaces exhibit subdiffusions in translational motions. © 2013 American Physical Society.

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