Rnd2 differentially regulates oligodendrocyte myelination at different developmental periods.

In the CNS, oligodendrocyte precursor cells differentiate into oligodendrocytes to wrap their plasma membranes around neuronal axons, generating mature neural networks with myelin sheaths according to spatial and temporal patterns. While myelination is known to be one of the most dynamic cell morphological changes, the overall intrinsic and extrinsic molecular cues controlling myelination remain to be fully clarified. Here, we describe the biphasic roles of Rnd2, an atypical branch of the Rho family GTPase, in oligodendrocyte myelination during development and after maturation in mice. Compared with littermate controls, oligodendrocyte-specific Rnd2 knockout mice exhibit decreased myelin thickness at the onset of myelination but increased myelin thickness in the later period. Larger proportions of Rho kinase and its substrate Mbs, the signaling unit that negatively regulates oligodendrocyte myelination, are phosphorylated at the onset of myelination, while their smaller proportions are phosphorylated in the later period. In addition, we confirm the biphasic role of Rnd2 through experiments with oligodendrocyte-specific Rnd2 transgenic mice. We conclude that Rnd2 positively regulates myelination in the early myelinating period and negatively regulates myelination in the later period. This unique modulator thus plays different roles depending on the myelination period.

BIG1/Arfgef1 and Arf1 regulate the initiation of myelination by Schwann cells in mice.

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.

Complex formation between the vasopressin 1b receptor, ß-arrestin-2, and the µ-opioid receptor underlies morphine tolerance.

Chronic morphine exposure upregulates adenylate cyclase signaling and reduces analgesic efficacy, a condition known as opioid tolerance. Nonopioid neurotransmitters can enhance morphine tolerance, but the mechanism for this is poorly understood. We show that morphine tolerance was delayed in mice lacking vasopressin 1b receptors (V1bRs) or after administration of V1bR antagonist into the rostral ventromedial medulla, where transcripts for V1bRs and µ-opioid receptors are co-localized. Vasopressin increased morphine-binding affinity in cells expressing both V1bR and µ-opioid receptors. Complex formation among V1bR, ß-arrestin-2, and µ-opioid receptor resulted in vasopressin-mediated upregulation of ERK phosphorylation and adenylate cyclase sensitization. A leucine-rich segment in the V1bR C-terminus was necessary for the association with ß-arrestin-2. Deletion of this leucine-rich segment increased morphine analgesia and reduced vasopressin-mediated adenylate cyclase sensitization. These findings indicate that inhibition of µ-opioid-receptor-associated V1bR provides an approach for enhancing morphine analgesia without increasing analgesic tolerance.

Alternative plasticizer, 4-cyclohexene-1,2-dicarboxylic acid dinonyl ester, for blood containers with protective effects on red blood cells and improved cold resistance.

Di (2-ethylhexyl) phthalate (DEHP), a typical plasticizer used for polyvinyl chloride (PVC), is eluted from PVC-made blood containers and protects against red blood cell (RBC) hemolysis. However, concerns have arisen regarding the reproductive and developmental risks of DEHP in humans, and the use of alternative plasticizers for medical devices has been recommended worldwide. In this study, we propose that the use of a novel plasticizer, 4-cyclohexene-1,2-dicarboxylic acid dinonyl ester (DL9TH), could help produce more useful and safe blood containers. PVC sheet containing DL9TH and di (2-ethylhexyl) 4-cyclohexene-1,2-dicarboxylate (DOTH) provides comparable or superior protective effects to RBCs relative to PVC sheet containing DEHP or di-isononyl-cyclohexane-1,2-dicarboxylate (DINCH® , an alternative plasticizer that has been used in PVC sheets for blood containers). The total amount of plasticizer eluted from DOTH/DL9TH-PVC sheets is nearly the same as that eluted from DEHP-PVC sheets. In addition, DOTH/DL9TH-PVC has better cold resistance than DEHP- and DINCH® -PVC sheets. In vitro and in vivo tests for biological safety based on International Organization for Standardization guidelines (10993 series) suggest that the DOTH/DL9TH-PVC sheet can be used safely. Subchronic toxicity testing of DL9TH in male rats in accordance with the principles of Organisation for Economic Co-operation and Development Test Guideline 408 showed that DL9TH did not induce adverse effects up to the highest dose level tested (717 mg/kg body weight/day). There were no effects on testicular histopathology and sperm counts, and no indications of endocrine effects: testosterone, thyroid-stimulating hormone, follicle-stimulating hormone, and 17ß-estradiol were unchanged by the treatment, compared with the control group. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1052-1063, 2018.

Role of vasopressin V1a receptor in ∆9-tetrahydrocannabinol-induced cataleptic immobilization in mice.

RATIONALE: Cannabis is a widely used illicit substance. ∆9-tetrahydrocannabinol (THC), the major psychoactive component of cannabis, is known to cause catalepsy in rodents. Recent studies have shown that vasopressin V1a and V1b receptors are widely distributed in the central nervous system and are capable of influencing a wide variety of brain functions such as social behavior, emotionality, and learning and memory. OBJECTIVES: The present study was designed to examine the possible involvement of V1a and V1b receptors in THC-induced catalepsy-like immobilization. METHODS: The induction of catalepsy following treatment with THC (10 mg/kg, i.p.) or haloperidol (1 mg/kg, i.p.) was evaluated in wild-type (WT), V1a receptor knockout (V1aRKO), and V1b receptor knockout (V1bRKO) mice. The effect of treatment with the selective 5-hydroxytryptamine1A receptor antagonist WAY100635 (0.1 mg/kg, i.p.) on THC-induced catalepsy was also evaluated in V1aRKO mice. Moreover, the effects of the V1a receptor antagonist VMAX-357 and the V1b receptor antagonist ORG-52186 on THC-induced catalepsy were evaluated in ddY mice. RESULTS: THC and haloperidol markedly caused catalepsy in V1bRKO mice as well as in WT mice. However, V1aRKO mice exhibited a reduction in catalepsy induced by THC but not by haloperidol. WAY100635 dramatically enhanced THC-induced catalepsy in V1aRKO mice. Although VMAX-357 (10 mg/kg, p.o.) but not ORG-52186 significantly attenuated THC-induced catalepsy, it had no significant effect on the enhancement of THC-induced catalepsy by WAY100635 in ddY mice. CONCLUSIONS: These findings suggest that V1a receptor regulates THC-induced catalepsy-like immobilization.

Data on the effect of hypomyelinating leukodystrophy 6 (HLD6)-associated mutations on the TUBB4A properties.

Hypomyelinating leukodystrophy (HLD) is genetic demyelinating or dysmyelinating disease and is associated with at least 13 responsible genes. The mutations seem likely cause the functional deficiency of their gene products. HLD4- and HLD5-associated HSPD1 and FAM126A mutations affect biochemical properties of the gene products (Miyamoto et al. (2015,2014) [[1], [2]]). Herein we provide the data regarding the effects of HLD6-associated tubulin beta 4A (TUBB4A) mutations on the properties.

Data supporting the role of Fyn in embryonic sciatic nerve fasciculation.

Fyn is the cytoplasmic tyrosine kinase that has critical roles in many aspects of biological functions. In the central [1] and peripheral nervous systems [2], [3], Fyn plays the key role in initiating myelination by myelin-forming glial cells (Schwann cells and oligodendrocytes). Herein we provide the data regarding the role of Fyn in fasciculation and branching of embryonic peripheral nerves.

Neuregulin-1 type III knockout mice exhibit delayed migration of Schwann cell precursors.

In an embryonic developmental stage of the peripheral nervous system (PNS), Schwann cell precursors migrate along neuronal axons to their final destinations. After birth, they eventually wrap around individual axons to form myelin sheaths, which insulate axons to increase the nerve conduction velocity. Some growth factors and adhesion molecules are known to control these developmental stages from in the fish to in the mammal. Neuregulin-1 (NRG1), which is composed of many alternative splicing variants, is such a growth factor. Among these variants, the type III isoform of NRG1, interacting with ErbB2 and ErbB3 receptors on Schwann cells, plays an essential role in myelination in the fish and the mammal. NRG1 type III is also known to promote migration of fish Schwann cell precursors; however, it still remains to be clarified whether mammalian type III isoform does it. We have therefore generated type III isoform-specific knockout mice in inbred strain. The mice result in delayed migration of the precursors from the dorsal to ventral root via a peripheral ganglion, comparing littermate controls. Similar results are observed in an in vitro migration assay using reaggregated Schwann cell precursors. Furthermore, the knockout mice exhibit reduced myelin thickness, consistent with the established role of NRG1 type III in myelination. These results indicate that in mice, NRG1 type III plays a key role not only in myelination but also in migration.

Zebularine upregulates expression of CYP genes through inhibition of DNMT1 and PKR in HepG2 cells.

Drug-induced hepatotoxicity is one of the major reasons cited for drug withdrawal. Therefore, it is of extreme importance to detect human hepatotoxic candidates as early as possible during the drug development process. In this study, we aimed to enhance hepatocyte functions such as CYP gene expression in HepG2 cells, one of the most extensively used cell lines in evaluating hepatotoxicity of chemicals and drugs. We found that zebularine, a potent inhibitor of DNA methylation, remarkably upregulates the expression of CYP genes in HepG2 cells. In addition, we revealed that the upregulation of CYP gene expression by zebularine was mediated through the inhibition of both DNA methyltransferase 1 (DNMT1) and double-stranded RNA-dependent protein kinase (PKR). Furthermore, HepG2 cells treated with zebularine were more sensitive than control cells to drug toxicity. Taken together, our results show that zebularine may make HepG2 cells high-functioning and thus could be useful for evaluating the hepatotoxicity of chemicals and drugs speedily and accurately in in-vitro systems. The finding that zebularine upregulates CYP gene expression through DNMT1 and PKR modulation sheds light on the mechanisms controlling hepatocyte function and thus may aid in the development of new in-vitro systems using high-functioning hepatocytes.

VCAM1 acts in parallel with CD69 and is required for the initiation of oligodendrocyte myelination.

Oligodendrocytes differentiate to wrap their plasma membranes around axons, forming the myelin sheath. A neuronal cue is one of the regulator elements controlling this process. Here, we demonstrate that VCAM1, which plays a key role throughout the immune system, is also expressed in oligodendrocytes, where it regulates the initiation of myelination. VCAM1 knockout mice exhibit reduced myelin thickness. Decreased myelin thickness is also observed in mutant mice of α4 integrin, which is a neuronal VCAM1 ligand. Furthermore, CD69 is identified as one of the transcripts downregulated when VCAM1 is knocked down in oligodendrocytes. Knockdown of CD69 in mice indicates its role in myelination. Therefore, VCAM1 contributes not only to the initiation of myelination but also to its regulation through controlling the abundance of CD69, demonstrating that an intercellular molecule whose primary role is in the immune system can also play an unexpected role in the CNS.

Prenatal Exposure to Arsenic Impairs Behavioral Flexibility and Cortical Structure in Mice.

Exposure to arsenic from well water in developing countries is suspected to cause developmental neurotoxicity. Although, it has been demonstrated that exposure to sodium arsenite (NaAsO2) suppresses neurite outgrowth of cortical neurons in vitro, it is largely unknown how developmental exposure to NaAsO2 impairs higher brain function and affects cortical histology. Here, we investigated the effect of prenatal NaAsO2 exposure on the behavior of mice in adulthood, and evaluated histological changes in the prelimbic cortex (PrL), which is a part of the medial prefrontal cortex that is critically involved in cognition. Drinking water with or without NaAsO2 (85 ppm) was provided to pregnant C3H mice from gestational days 8 to 18, and offspring of both sexes were subjected to cognitive behavioral analyses at 60 weeks of age. The brains of female offspring were subsequently harvested and used for morphometrical analyses. We found that both male and female mice prenatally exposed to NaAsO2 displayed an impaired adaptation to repetitive reversal tasks. In morphometrical analyses of Nissl- or Golgi-stained tissue sections, we found that NaAsO2 exposure was associated with a significant increase in the number of pyramidal neurons in layers V and VI of the PrL, but not other layers of the PrL. More strikingly, prenatal NaAsO2 exposure was associated with a significant decrease in neurite length but not dendrite spine density in all layers of the PrL. Taken together, our results indicate that prenatal exposure to NaAsO2 leads to behavioral inflexibility in adulthood and cortical disarrangement in the PrL might contribute to this behavioral impairment.

Data supporting the role of Fyn in initiating myelination in the peripheral nervous system.

Transgenic mice, which express active Fyn tyrosine kinase under the control of a glial fibrillary acidic protein promoter, have been produced. This promoter induces protein expression in the initiation stage of myelination in the peripheral nervous system (PNS) "Phosphorylation of cytohesin-1 by Fyn is required for initiation of myelination and the extent of myelination during development (Yamauchi et al., 2015 [1])". Herein we provide the data regarding myelination-related protein markers and myelin ultrastructure in transgenic mice.

Data supporting mitochondrial morphological changes by SPG13-associated HSPD1 mutants.

The data is related to the research article entitled "Hypomyelinating leukodystrophy-associated missense mutation in HSPD1 blunts mitochondrial dynamics" [1]. In addition to hypomyelinating leukodystrophy (HLD) 4 (OMIM no. 612233), it is known that spastic paraplegia (SPG) 13 (OMIM no. 605280) is caused by HSPD1's amino acid mutation. Two amino acid mutations Val-98-to-Ile (V98I) and Gln-461-to-Glu (Q461E) are associated with SPG13 [2]. In order to investigate the effects of HSPD1's V98I or Q461E mutant on mitochondrial morphological changes, we transfected each of the respective mutant-encoding genes into Cos-7 cells. Either of V98I or Q461E mutant exhibited increased number of mitochondria and short length mitochondrial morphologies. Using MitoTracker dye-incorporating assay, decreased mitochondrial membrane potential was also observed in both cases. The data described here supports that SPG13-associated HSPD1 mutant participates in causing aberrant mitochondrial morphological changes with decreased activities.

Dock8 interacts with Nck1 in mediating Schwann cell precursor migration.

During embryonic development of the peripheral nervous system (PNS), Schwann cell precursors migrate along neuronal axons to their final destinations, where they will myelinate the axons after birth. While the intercellular signals controlling Schwann cell precursor migration are well studied, the intracellular signals controlling Schwann cell precursor migration remain elusive. Here, using a rat primary cell culture system, we show that Dock8, an atypical Dock180-related guanine-nucleotide exchange factor (GEF) for small GTPases of the Rho family, specifically interacts with Nck1, an adaptor protein composed only of Src homology (SH) domains, to promote Schwann cell precursor migration induced by platelet-derived growth factor (PDGF). Knockdown of Dock8 or Nck1 with its respective siRNA markedly decreases PDGF-induced cell migration, as well as Rho GTPase activation, in precursors. Dock8, through its unique N-terminal proline-rich motif, interacts with the SH3 domain of Nck1, but not with other adaptor proteins composed only of SH domains, e.g. Grb2 and CrkII, and not with the adaptor protein Elmo1. Reintroduction of the proline-rich motif mutant of Dock8 in Dock8 siRNA-transfected Schwann cell precursors fails to restore their migratory abilities, whereas that of wild-type Dock8 does restore these abilities. These results suggest that Nck1 interaction with Dock8 mediates PDGF-induced Schwann cell precursor migration, demonstrating not only that Nck1 and Dock8 are previously unanticipated intracellular signaling molecules involved in the regulation of Schwann cell precursor migration but also that Dock8 is among the genetically-conservative common interaction subset of Dock family proteins consisting only of SH domain adaptor proteins.

Arf6 mediates Schwann cell differentiation and myelination.

During development of the peripheral nervous system (PNS), Schwann cells wrap neuronal axons, becoming the myelin sheaths that help axonal functions. While the intercellular signals controlling the myelination process between Schwann cells and peripheral neurons are well studied, the transduction of these signals in Schwann cells still remains elusive. Here, we show that Arf6, an Arf protein of the small GTPase family, is involved in promoting the myelination process. Knockdown of Arf6 with the small-interfering (si)RNA in primary Schwann cells markedly decreases dibutyl-cyclic AMP-induced myelin marker protein expression, indicating that Arf6 plays a role in differentiation-like phenotypic changes. To obtain in vivo evidence, we generated small-hairpin (sh)RNA transgenic mice targeting Arf6 for Schwann cells. Transgenic mice exhibited reduced myelin thickness compared to littermate controls, consistent with the defective myelin formation observed in the transgenic mouse-derived Schwann cell and neuronal culture system. Transgenic mice also exhibited decreased phosphorylation of myelination-related signaling molecules such as Akt kinase cascade proteins as well as downregulation of myelin marker proteins. These results suggest that signaling through Arf6 is required for Schwann cell myelination, adding Arf6 to the list of intracellular signaling molecules involved in the myelination process.

Role of Environmental Chemical Insult in Neuronal Cell Death and Cytoskeleton Damage.

Environmental influences, such as chemical exposure, have long been considered potential risk factors for neurodegenerative disorders, including neuromuscular diseases. However, no definitive links between environmental chemical exposure and a pathogenic mechanism of neurodegenerative disease has yet been established. In this study, we describe that exposure to arsenic, an environmental pollutant naturally found in drinking water, induces neuronal cell death and alteration of morphology, particularly neurite outgrowth and in the cytoskeleton of neurons. Since progressive cell loss accompanied by the alteration of neuronal structures and cytoskeleton is considered the major pathologic feature of neurodegenerative disorders, arsenic-induced neurotoxicity might contribute to an etiologic mechanism of some neurodegenerative diseases. Further, we discuss the importance of in vitro assay, particularly an embryonic toxicity test, for assessing the neurotoxicity of chemicals, because most of chemicals found in our environment remain to be evaluated regarding their neurotoxicity risk for neurodegenerative diseases.

Involvement of the Tyro3 receptor and its intracellular partner Fyn signaling in Schwann cell myelination.

During early development of the peripheral nervous system, Schwann cell precursors proliferate, migrate, and differentiate into premyelinating Schwann cells. After birth, Schwann cells envelop neuronal axons with myelin sheaths. Although some molecular mechanisms underlying myelination by Schwann cells have been identified, the whole picture remains unclear. Here we show that signaling through Tyro3 receptor tyrosine kinase and its binding partner, Fyn nonreceptor cytoplasmic tyrosine kinase, is involved in myelination by Schwann cells. Impaired formation of myelin segments is observed in Schwann cell neuronal cultures established from Tyro3-knockout mouse dorsal root ganglia (DRG). Indeed, Tyro3-knockout mice exhibit reduced myelin thickness. By affinity chromatography, Fyn was identified as the binding partner of the Tyro3 intracellular domain, and activity of Fyn is down-regulated in Tyro3-knockout mice, suggesting that Tyro3, acting through Fyn, regulates myelination. Ablating Fyn in mice results in reduced myelin thickness. Decreased myelin formation is observed in cultures established from Fyn-knockout mouse DRG. Furthermore, decreased kinase activity levels and altered expression of myelination-associated transcription factors are observed in these knockout mice. These results suggest the involvement of Tyro3 receptor and its binding partner Fyn in Schwann cell myelination. This constitutes a newly recognized receptor-linked signaling mechanism that can control Schwann cell myelination.

Hypomyelinating leukodystrophy-associated missense mutation in HSPD1 blunts mitochondrial dynamics.

Myelin-forming glial cells undergo dynamic morphological changes in order to produce mature myelin sheaths with multiple layers. In the central nervous system (CNS), oligodendrocytes differentiate to insulate neuronal axons with myelin sheaths. Myelin sheaths play a key role in homeostasis of the nervous system, but their related disorders lead not only to dismyelination and repeated demyelination but also to severe neuropathies. Hereditary hypomyelinating leukodystrophies (HLDs) are a group of such diseases affecting oligodendrocytes and are often caused by missense mutations of the respective responsible genes. Despite increasing identification of gene mutations through advanced nucleotide sequencing technology, studies on the relationships between gene mutations and their effects on cellular and subcellular aberrance have not followed at the same rapid pace. In this study, we report that an HLD4-associated (Asp-29-to-Gly) mutant of mitochondrial heat shock 60-kDa protein 1 (HSPD1) causes short-length morphologies and increases the numbers of mitochondria due to their aberrant fission and fusion cycles. In experiments using a fluorescent dye probe, this mutation decreases the mitochondrial membrane potential. Also, mitochondria accumulate in perinuclear regions. HLD4-associated HSPD1 mutant blunts mitochondrial dynamics, probably resulting in oligodendrocyte malfunction. This study constitutes a first finding concerning the relationship between disease-associated HSPD1 mutation and mitochondrial dynamics, which may be similar to the relationship between another disease-associated HSPD1 mutation (MitCHAP-60 disease) and aberrant mitochondrial dynamics.

Arf6 guanine-nucleotide exchange factor cytohesin-2 regulates myelination in nerves.

In postnatal development of the peripheral nervous system (PNS), Schwann cells differentiate to insulate neuronal axons with myelin sheaths, increasing the nerve conduction velocity. To produce the mature myelin sheath with its multiple layers, Schwann cells undergo dynamic morphological changes. While extracellular molecules such as growth factors and cell adhesion ligands are known to regulate the myelination process, the intracellular molecular mechanism underlying myelination remains unclear. In this study, we have produced Schwann cell-specific conditional knockout mice for cytohesin-2, a guanine-nucleotide exchange factor (GEF) specifically activating Arf6. Arf6, a member of the Ras-like protein family, participates in various cellular functions including cell morphological changes. Cytohesin-2 knockout mice exhibit decreased Arf6 activity and reduced myelin thickness in the sciatic nerves, with decreased expression levels of myelin protein zero (MPZ), the major myelin marker protein. These results are consistent with those of experiments in which Schwann cell-neuronal cultures were treated with pan-cytohesin inhibitor SecinH3. On the other hand, the numbers of Ki67-positive cells in knockout mice and controls are comparable, indicating that cytohesin-2 does not have a positive effect on cell numbers. Thus, signaling through cytohesin-2 is required for myelination by Schwann cells, and cytohesin-2 is added to the list of molecules known to underlie PNS myelination.