中島 昭

The gene encoding 5'-nucleotidase domain-containing protein 2 (NT5DC2) has been associated with neuropsychiatric disorders related to the abnormality of dopamine activity in the brain. However, its physiological functions remain unclear. In this study, we analyzed the features of NT5DC2 that influence its binding with tyrosine hydroxylase (TH) and its effects on dihydroxyphenylalanine (DOPA) synthesis, using NT5DC2 overexpressed in PC12D cells by the pCMV vector. Western blot analysis revealed that the purified NT5DC2-DYKDDDDK-tag (NT5DC2-tag) protein can bind with the phosphorylated form of recombinant human TH type 1 (rhTH1), apart from the endogenous TH in PC12D cells. Proteomic analysis by mass spectrometry revealed that the purified NT5DC2-tag protein has the potential to bind to 41 proteins with multiple phosphorylation sites in PC12D cells (NT5DC2 binding proteins: positive, 391 sites/41 proteins; and negative, 85 sites/27 proteins). Overexpression of NT5DC2 in PC12D cells decreased DOPA levels in the medium. When the lysate of PC12D cells overexpressing NT5DC2 was incubated at 37 °C, the phosphorylated form of endogenous TH in PC12D cells decreased. This decrease was also detected when phosphorylated rhTH1 was incubated with purified NT5DC2-tag. Overall, our results suggest that NT5DC2 regulates DOPA synthesis by promoting the dephosphorylation of TH, similar to a phosphatase. Therefore, our study provides useful information for understanding various disorders associated with abnormalities in dopamine levels in the brain.

Abstract The dark pigment neuromelanin (NM) is abundant in cell bodies of dopamine (DA) neurons in the substantia nigra (SN) and norepinephrine (NE) neurons in the locus coeruleus (LC) in the human brain. During the progression of Parkinson’s disease (PD), together with the degeneration of the respective catecholamine (CA) neurons, the NM levels in the SN and LC markedly decrease. However, questions remain among others on how NM is associated with PD and how it is synthesized. The biosynthesis pathway of NM in the human brain has been controversial because the presence of tyrosinase in CA neurons in the SN and LC has been elusive. We propose the following NM synthesis pathway in these CA neurons: (1) Tyrosine is converted by tyrosine hydroxylase (TH) to L-3,4-dihydroxyphenylalanine (L-DOPA), which is converted by aromatic L-amino acid decarboxylase to DA, which in LC neurons is converted by dopamine β-hydroxylase to NE; (2) DA or NE is autoxidized to dopamine quinone (DAQ) or norepinephrine quinone (NEQ); and (3) DAQ or NEQ is converted to eumelanic NM (euNM) and pheomelanic NM (pheoNM) in the absence and presence of cysteine, respectively. This process involves proteins as cysteine source and iron. We also discuss whether the NM amounts per neuromelanin-positive (NM⁺) CA neuron are higher in PD brain, whether NM quantitatively correlates with neurodegeneration, and whether an active lifestyle may reduce NM formation.

Human stem cell-derived organoid culture enables the in vitro analysis of the cellular function in three-dimensional aggregates mimicking native organs, and also provides a valuable source of specific cell types in the human body. We previously established organoid models of the hypothalamic-pituitary (HP) complex using human pluripotent stem cells. Although the models are suitable for investigating developmental and functional HP interactions, we consider that isolated pituitary cells are also useful for basic and translational research on the pituitary gland, such as stem cell biology and regenerative medicine. To develop a method for the purification of pituitary cells in HP organoids, we performed surface marker profiling of organoid cells derived from human induced pluripotent stem cells (iPSCs). Screening of 332 human cell surface markers and a subsequent immunohistochemical analysis identified epithelial cell adhesion molecule (EpCAM) as a surface marker of anterior pituitary cells, as well as their ectodermal precursors. EpCAM was not expressed on hypothalamic lineages; thus, anterior pituitary cells were successfully enriched by magnetic separation of EpCAM⁺ cells from iPSC-derived HP organoids. The enriched pituitary population contained functional corticotrophs and their progenitors; the former responded normally to a corticotropin-releasing hormone stimulus. Our findings would extend the applicability of organoid culture as a novel source of human anterior pituitary cells, including stem/progenitor cells and their endocrine descendants.

Hypothalamic melanin-concentrating hormone (MCH) neurons are important regulators of multiple physiological processes, such as sleep, feeding, and memory. Despite the increasing interest in their neuronal functions, the molecular mechanism underlying MCH neuron development remains poorly understood. We report that a three-dimensional culture of mouse embryonic stem cells (mESCs) can generate hypothalamic-like tissues containing MCH-positive neurons, which reproduce morphologic maturation, neuronal connectivity, and neuropeptide/neurotransmitter phenotype of native MCH neurons. Using this in vitro system, we demonstrate that Hedgehog (Hh) signaling serves to produce major neurochemical subtypes of MCH neurons characterized by the presence or absence of cocaine- and amphetamine-regulated transcript (CART). Without exogenous Hh signals, mESCs initially differentiated into dorsal hypothalamic/prethalamic progenitors and finally into MCH+CART+ neurons through a specific intermediate progenitor state. Conversely, activation of the Hh pathway specified ventral hypothalamic progenitors that generate both MCH+CART- and MCH+CART+ neurons. These results suggest that in vivo MCH neurons may originate from multiple cell lineages that arise through early dorsoventral patterning of the hypothalamus. Additionally, we found that Hh signaling supports the differentiation of mESCs into orexin/hypocretin neurons, a well-defined cell group intermingled with MCH neurons in the lateral hypothalamic area (LHA). The present study highlights and improves the utility of mESC culture in the analysis of the developmental programs of specific hypothalamic cell types.Significance StatementA growing body of literature has revealed the importance of hypothalamic melanin-concentrating hormone (MCH) neurons in energy homeostasis and the cognitive function, but their developmental biology remains relatively unknown. To establish a new approach for addressing this issue, we tested the ability of an in vitro differentiation system of mouse embryonic stem cells (mESCs) to recapitulate the development of MCH neurons. The mESC culture robustly generated MCH-positive neurons resembling native neurons in several aspects and provided evidence that Hedgehog (Hh) signaling is a key factor to produce neurochemical subtypes of MCH neurons. Our results demonstrate the suitability of mESC culture as a platform to study the molecular mechanisms underlying the development of MCH neurons and possibly of other hypothalamic cell types.

The hypothalamus is comprised of heterogenous cell populations and includes highly complex neural circuits that regulate the autonomic nerve system. Its dysfunction therefore results in severe endocrine disorders. Although recent experiments have been conducted for in vitro organogenesis of hypothalamic neurons from embryonic stem (ES) or induced pluripotent stem (iPS) cells, whether these stem cell-derived hypothalamic neurons can be useful for regenerative medicine remains unclear. We therefore performed orthotopic transplantation of mouse ES cell (mESC)-derived hypothalamic neurons into adult mouse brains. We generated electrophysiologically functional hypothalamic neurons from mESCs and transplanted them into the supraoptic nucleus of mice. Grafts extended their axons along hypothalamic nerve bundles in host brain, and some of them even projected into the posterior pituitary (PPit), which consists of distal axons of the magnocellular neurons located in hypothalamic supraoptic and paraventricular nuclei. The axonal projections to the PPit were not observed when the mESC-derived hypothalamic neurons were ectopically transplanted into the substantia nigra reticular part. These findings suggest that our stem cell-based orthotopic transplantation approach might contribute to the establishment of regenerative medicine for hypothalamic and pituitary disorders.

5'-Nucleotidase domain-containing protein 2 (NT5DC2) has been revealed by genome-wide association studies (GWAS) as a gene implicated in neuropsychiatric disorders related to the abnormality of dopamine (DA) activity in the brain. Based on its amino acid sequence, NT5DC2 is assumed to be a member of the family of haloacid dehalogenase-type phosphatases; although there is no information about its function and structural conformation. We recently reported that NT5DC2 binds to tyrosine hydroxylase (TH) and that the down-regulation of NT5DC2 tended to increase DA synthesis. In this study, we investigated whether NT5DC2 could regulate the catalytic activity of TH, which converts tyrosine to DOPA, because the phosphorylation level of TH, controlled by protein kinases and phosphatases, is well known to regulate its catalytic activity. The down-regulation of NT5DC2 by siRNA increased mainly DOPA synthesis by TH in PC12D cells, although this down-regulation tended to increase the conversion of DOPA to DA by aromatic L-amino acid decarboxylase. The increased DOPA synthesis should be attributed to the catalytic activity of TH controlled by its phosphorylation, because Western blot analysis revealed that the down-regulation of NT5DC2 tended to increase the level of TH phosphorylated at its Ser residues, but not that of the TH protein. Moreover, the induction of kinase activity by forskolin markedly potentiated the phosphorylation of TH at its Ser40 in PC12D cells having down-regulated NT5DC2. Immunocytochemical analysis of PC12D cells demonstrated that NT5DC2, TH protein, and TH phosphorylated at its Ser40 were predominantly localized in the cytoplasm and that the localization of NT5DC2 and TH proteins partially overlapped. Collectively, our results indicate that NT5DC2 could work to inhibit the DOPA synthesis by decreasing the phosphorylation of TH at its Ser40. We propose that NT5DC2 might decrease this phosphorylation of TH by promoting dephosphorylation or by inhibiting kinase activity.

Objectives: According to our previous work, aripiprazole exerted a protective effect on hydrogen peroxide (H2O2)-treated PC12 cells; haloperidol did not. Because aripiprazole has distinct affinities to a set of neurotransmitter receptor subtypes, this study aimed to clarify which subtype is responsible for rescuing cells from 0.25 mM H2O2 exposure.Methods: A set of compounds, which are more specific to each subset of G-protein coupled receptors, wereexamined for their ability to mimic the pharmacological effects of aripiprazole or haloperidol, including their Ki values.The viability of PC12 cells cultured with test compounds with or without H2O2 was assessed using WST-8 reagent.Results: Results from in vitro studies using PC12 cells showed that agonism at serotonin 5-HT2C-receptors based on the antagonism against 5-HT2B-receptors played a significant role in resistingH2O2-induced cell death. However, the use of a specific 5-HT2B-receptor agonist instead of a 5-HT2B-receptor antagonist completely negated the effect of a specific 5-HT2C-receptor agonist. Furthermore, unlike the dopamine D1-receptor specific antagonist, none of the agonists of dopamine D2-, D3-, and D4-receptors ameliorated the cytopathic effects of H2O2.Conclusion: Antagonism at 5-HT2B-receptors is fundamental for the protection of PC12 cells against the cytopathiceffects caused by 0.25 mM H2O2. However, the role of negatively regulated cyclic adenosine monophosphate in this phenomenon requires further investigation.

1）新研修医が研修開始直後に必要となる手技を習得できることを目標としたスキルスラボを利用したトレーニングをオリエンテーション期間内に導入した．<br>2）新2年目研修医がトレーニングの内容を計画し，新研修医を指導し，3年目以上の上級医は，新2年目研修医の指導を支援する「屋根瓦方式」の指導体制の構築を目指した．<br>3）本トレーニングを開催したことにより研修医間の関係が良好なものとなり，新研修医に安心感を与えるといった波及効果がみられた．

藤田保健衛生大学医学部入試では, 全入学者の約30%を推薦入試により選抜している.推薦入試入学者の入学後の成績が適正であるかどうかを検証するために, 入学直後に実施した基礎学力を測定するプレースメントテストの成績と, 入学後の1, 2年次の欠席状況と成績との関連性を比較検討した.<BR>1) 平成14年から17年までの入学生398名を, 推薦入試入学者 (126名), および, 一般入試の成績の上位1/2入学者 (137名) と下位1/2入学者 (135名) の3群に分類して解析した.<BR>2) 入学時のプレースメントテストの成績 (基礎学力) は, 一般上位>一般下位>推薦の順であったが, 入学後の成績は1, 2年次共に, 一般上位>推薦>一般下位となった.<BR>3) 推薦入試入学者の1, 2年次欠席コマ数は, 一般入試上位・下位入学者よりも少ない傾向にあった.<BR>4) 2年次の成績は1年次の成績とよく相関し, また, 2年次の欠席コマ数は1年次の欠席コマ数とも強く相関した.<BR>5) 入学時の基礎学力だけでなく, 1年次での勉強の取り組み方が, その後の成績に影響する重要な要因であることが示唆された.