シンポジウム（Symposium）

Symposium Innovative researches for drug discovery and development ~ novel technologies have become clear throughout common functions between oligodendrocytes and Schwann cells シンポジウム新たな創薬研究領域の開拓~新技術から見えてきたオリゴデンドロサイトとシュワン細胞の共通性~

7月28日（日）10:50～11:14　第4会場（朱鷺メッセ　3F　301） 4S04a-1 シュワン細胞によるミエリン化に関与する新規シグナル分子BIG1とArf1 Junji Yamauchi（山内淳司）^1,2，Yuki Miyamoto（宮本幸）^1,2 ¹東京薬科大学・生命科学部・分子神経科学研究室 ²国立成育医療研究センター研究所・薬剤治療研究部 During development of the peripheral nervous system in mammals, Schwann cells wrap their plasma membranes around neuronal axons, forming multiple myelin sheaths. A mature myelin sheath insulates axons and increases nerve conduction velocity while protecting nerve fibers from various stresses such as physical ones. Despite this functional importance, the molecular units that underlie dynamic morphological changes in formation of myelin sheaths are not sufficiently understood. Arf1 is a small guanosine triphosphate-binding protein that plays multiple roles in intracellular trafficking and related signaling, both of which are processes involved in cell morphogenesis. We demonstrate that the Arf1 guanine nucleotide exchange factor, brefeldin A-inhibited guanine nucleotide-exchange protein 1 (BIG1)/Arfgef1, and the effector Arf1 regulate the initiation of myelination of axons by Schwann cells. Schwann cell-specific BIG1 conditional knockout mice, which have been generated here, exhibit reduced myelin thickness and decreased localization of myelin protein zero in the myelin membrane, compared with their littermate controls. BIG1 knockout mouse nerves specifically decrease the amounts of Arf1 in the AP1 clathrin adaptor protein subunits but not the Arf1 binding to GGA1 (Golgi-localized, gamma-adaptin ear-containing, Arf-binding protein 1) transporting proteins. The amounts of Arf1 in the COPI coatomer protein subunits were comparable in the knockout mice and controls. Similar results in myelin thickness are observed in Arf1 conditional knockout mice, which have also been generated here. Thus, the BIG1 and Arf1 unit plays a key role in Schwann cell myelination, newly adding it to the list of molecular units controlling myelination ( doi: 10.1126/sciadv.aar4471).		7月28日（日）11:14～11:38　第4会場（朱鷺メッセ　3F　301） 4S04a-2 アストロサイトCD38による髄鞘化と脱髄化のメカニズム Tsuyoshi Hattori（服部剛志）¹，Jureepon Roboon（Roboon Jureepon）¹，Hiroshi Ishii（石井宏史）¹，Mika Takarada（宝田美佳）¹，Dinh Thi Nguyen（Nguyen Thi Dinh）¹，Haruhiro Higashida（東田陽博）²，Osamu Hori（堀修）¹ ¹金沢大院医薬保健神経解剖 ²金沢大子どものこころの発達研究センター Glial cells such as astrocytes and oligodendrocytes have emerged as important players in brain function under both physiological and pathological conditions. CD38 is a multifunctional molecule with ADP-ribosyl cyclase activity. While critical roles of CD38 in the adult brain such as oxytocin release and social behavior have been reported, those in the developing brain remain largely unknown. Here we show CD38 is a novel regulator for glial development and activation. First, we demonstrate that deletion of Cd38 leads to impaired development of astrocytes and oligodendrocytes in mice. In situ hybridization analysis revealed that CD38 is expressed predominantly in astrocytes in the developing brain. Analyses of Cd38 knockout (Cd38KO) mice revealed delayed development of astrocytes and oligodendrocytes (OLs) at postnatal stages. In vitro experiments showed that astrocytic CD38 regulates the development of astrocytes in a cell-autonomous manner and the differentiation of OLs in a non-cell-autonomous manner. Further experiments revealed that increased levels of NAD+, caused by CD38 deficiency, are likely to be responsible for the suppression of astrocytic Cx43 expression and OL differentiation. Our data indicate that CD38 is a positive regulator of astrocyte and OL development. Next, to investigate the role of CD38 in pathological condition such as brain inflammation, we made a cuprizone(CPZ)-induced demyelination model of CD38KO mice. We found that CD38 expression was increased in CPZ-administrated WT mice. Interestingly, CPZ-induced demyelination was dramatically attenuated, and microglia and astrocytes were less activated in CD38KO mice. To study role of astrocytic CD38 for demyelination and glial activation, we generated astrocyte-specific conditional CD38 KO mouse (CD38 cKO). This CD38 cKO also showed attenuated CPZ-induced demyelination and glial activation. These results suggest that astrocytic CD38 promotes astrocytes and microglia activation.

7月28日（日）11:38～12:02　第4会場（朱鷺メッセ　3F　301） 4S04a-3 グリア機能のシグナルクロストーク制御と精神疾患 Yugo Ishino（石野雄吾）¹，Shoko Shimizu（清水尚子）¹，Masaya Tohyama（遠山正彌）^1,2，Shingo Miyata（宮田信吾）¹ ¹近畿大学東洋医学研究所分子脳科学研究部門 ²大阪府立病院機構 Glial cells are recently recognized as essential components with numerous key roles for the function within the nervous system. Among them, oligodendrocytes and Schwann cells have strong interaction with axons by wrapping them to form myelin sheath in the central nervous system and peripheral nervous system, respectively. Myelin provides support and insulation to the nervous system and is prerequisite for the smooth and high-speed nerve conduction. Therefore, defects and malfunctions of those glial cells have broad impacts within the nervous system. The most frequent diseases involving oligodendrocytes or Schwann cells, such as multiple sclerosis result from damaged myelin. In addition to demyelinating disorders, there are accumulating evidence indicating that some psychiatric status is also associated with glial malfunctions. Major depressive disorder (MDD) is one of the most common mental disorders and the number of people suffering from it is increasing tremendously. MDD is known to be a multifactorial disease related to genetic and environmental factors. Among several environmental factors, chronic stresses are thought to be attributable to the onset of MDD by the failure of the negative feedback of the hypothalamic-pituitary-adrenocortical (HPA) system, which results in higher levels of serum corticosterone. We have studied morphological and structural alterations of oligodendrocytes in the the corpus callosum induced by chronic stresses and found that the nodes and paranodes of Ranvier were narrower. Moreover, several molecules normally accumulating at the nodes and paranodes showed diffused distribution in the mice subjected to chronic stress. While these structural alterations of myelin forming oligodendrocytes in several pathological situation have been illustrated, genetical aspects that account for those defective events remain to be fully understood. Regarding molecular events, we have found that protein phosphorylation, one of the most major post-translational modifications, is enhanced in a certain signaling pathway in the mice subjected to a chronic stress. To understand more detail of the gene regulatory network acting for oligodendrocyte properties, we are now working on identifying novel molecules which regulate oligodendrocyte development, differentiation and maintenance in the central nervous system, which, we believe, leads to new approaches for screenings of drug seeds.		7月28日（日）12:02～12:26　第4会場（朱鷺メッセ　3F　301） 4S04a-4 軸索起始部：中枢神経疾患の機序に関わる重要な構造 Keiichiro Susuki（薄敬一郎） Dept Neurosci, Cell Biol&Physiol, Wright State Univ, Dayton, USA Among pathophysiologies implicated in neurodegenerative conditions, emerging evidence indicates the importance of alterations in excitable axonal domains, specifically the axon initial segment (AIS) and nodes of Ranvier. This is not surprising, as action potentials are generated at the AIS, regenerated at the nodes, and propagated along myelinated axons. The AIS is a 20-40 μm-long region between the neuronal soma and axon characterized by an accumulation of voltage-gated sodium channels. The structural characteristics of the AIS strongly affect the excitability and firing behavior of neurons. For example, shortening of AIS length has been shown to lower neuronal excitability, and is implicated in cognitive impairment during brain injury. Nodes of Ranvier are 1 μm-long gaps between adjacent myelin sheaths. Myelinating oligodendrocytes promote accumulation of sodium channels at the nodal axolemma. Disruption of nodes has been described in various neuropsychiatric disorders. Even slight elongation of nodal gaps causes nerve conduction slowing. Recently, we found that the AIS length is significantly decreased in prefrontal cortex and hippocampus in the type 2 diabetes model db/db mice. Nodes of Ranvier in corpus callosum were significantly elongated in db/db mice with prolonged diabetes burden. These structural changes in AIS and nodes might contribute to brain dysfunction in type 2 diabetes, such as impairment of executive function. The cellular and molecular mechanisms of how AIS and nodes are disrupted in disease conditions; however, remain poorly understood. Methylglyoxal, a highly reactive byproduct of glucose metabolism, is elevated in type 2 diabetes patients and in db/db mice. We reported that increased methylglyoxal leads to nodal elongation in the optic nerves. Furthermore, our data in neuronal culture show that an increase in methylglyoxal causes AIS shortening and decreased neuronal network activity without overt signs of neuronal damage. These observations suggest a mechanism in which elevation of methylglyoxal induced by diabetes mediates structural changes in AIS and nodes, leading to cognitive impairment. Our results identify methylglyoxal and AIS/nodes as therapeutic targets to mitigate neurological symptoms in type 2 diabetes and potentially in a wide variety of neurodegenerative conditions.

7月28日（日）12:26～12:50　第4会場（朱鷺メッセ　3F　301） 4S04a-5 電子顕微鏡による有髄神経線維の大容量ボリュームイメージング Nobuhiko Ohno（大野伸彦）^1,2，Tatsuhide Tanaka（田中達英）³ ¹自治医大医解剖 ²生理研分子神経生理 ³奈良医大第二解剖 Billions of neurons in the nervous system are connected physically through synaptic connections, and form numerous neural circuits in order to integrate sensory perception and motor program for brain functions. The interconnections of distant neurons are dependent on long neurite projections called axons, which are enriched in the white matter occupying nearly 40% of the brain volume. A number of these long axons in the white matter are ensheathed by myelin, which is multilamellar cell membrane formed by oligodendrocytes and Schwann cells in the central and peripheral nervous system, respectively. The myelin ensheathment divides axons into structurally and functionally distinct domains, and supports rapid salutatory nerve conduction and maintenance of axonal integrity. Recently, ultrastructural volume imaging of the myelinated nerve fibers started to provide evidences for the deeper understanding of physiology and pathology of the nervous system. For example, the distribution and morphology of axoplasmic organelles were modulated by electrical activities as well as myelin defects in the white matter, and current evidences support the concept that such modulations of organelle dynamics are beneficial for the functional integrity and survival of the axons. In addition, the functions of glial cells are also modulated by the alterations in their organelle dynamics, which could also have detrimental effects in the pathophysiology of myelin diseases. On the other hand, recent advancements in electron microscopy facilitated ultrastructural analyses from larger tissue volumes, and large-scale ultrastructural volume imaging has started to provide evidences suggesting that oligodendrocytes regulate nerve conductions of a group of distant axons by modulating structural properties of the myelinated axons at the whole cell level. This presentation will highlight recent advancements in the volume imaging studies of the white matter and discuss the perspective about the contribution of such advancements to elucidate the brain functions as well as pathophysiology of the neurological disorders.