Endocannabinoid Signaling in Embryonic Neuronal Motility and Cell-Cell Contact - Role of mGluR5 and TRPC3 Channels

Cell-cell communication plays a central role in the guidance of migrating neuronal precursor cells during the development of the cerebral cortex. Endocannabinoids (eCBs) have previously been shown to be one of the central factors regulating neuronal migration. In this study the effects of eCBs on different parameters, expected to affect embryonic cortical neuronal motility have been analyzed in neurosphere-derived neuroblasts using time-lapse microscopy. Increased endogenous production of the endocannabinoid 2-arachidonyl glycerol (2-AG) causes bursts of neuroblast motility. The neuroblasts move longer distances and show a low frequency of turning, and the number of neuron-neuron contacts are reduced. Similar changes occur interfering with the function of the metabotropic glutamate receptor 5 (mGluR5) or its transducer canonical transient receptor potential channel 3 (TRPC3) or the neuregulin receptor ErbB4. Blocking of 2-AG production reverses these effects. The data suggest that eCB-regulated neuronal motility is controlled by mGluR5/TRPC3 activity possibly via NRG/ErbB4 signaling. (C) 2018 IBRO. Published by Elsevier Ltd. All rights reserved.Peer reviewe

Regulation of radial glial process growth by glutamate via mGluR5/TRPC3 and neuregulin/ErbB4

Radial glial cells play an essential role through their function as guides for neuronal migration during development. Disruption of metabotropic glutamate receptor 5 (mGluR5) function retards the growth of radial glial processes in vitro. Neuregulins (NRG) are activated by proteolytic cleavage and regulate (radial) glial maintenance via ErbB3/ErbB4 receptors. We show here that blocking ErbB4 disrupts radial process extension. Soluble NRG acting on ErbB4 receptors is able to promote radial process extension in particular where process elongation has been impeded by blockade of mGluR5, the nonselective cation channel canonical transient receptor potential 3 (TRPC3), or matrix metalloproteases (MMP). NRG does not restore retarded process growth caused by ErbB4 blockade. Stimulation of muscarinic receptors restores process elongation due to mGluR5 blockade but not that caused by TRPC3, MMP or ErbB4 blockade suggesting that muscarinic receptors can replace mGluR5 with respect to radial process extension. Additionally, NRG/ErbB4 causes Ca2+ mobilization in a population of cells through cooperation with ErbB1 receptors. Our results indicate that mGluR5 promotes radial process growth via NRG activation by a mechanism involving TRPC3 channels and MMPs. Thus neurotransmitters acting on G-protein coupled receptors could play a central role in the maintenance of the radial glial scaffold through activation of NRG/ErbB4 signaling.Peer reviewe

The Val66Met polymorphism in the BDNF gene is associated with epilepsy in fragile X syndrome

The Val66Met polymorphism in the brain-derived neurotrophic factor (BDNF) gene may modulate the epilepsy phenotype. We investigated the impact of polymorphisms in the BDNF gene on clinical features in fragile X syndrome (FXS). In our study sample, the Met66 allele associated with epilepsy of finnish FXS men. Abnormalities in BDNF-mediated plasticity are shown in FXS and the present data suggest that the Met66 allele might predispose FXS mates to epilepsy. (C) 2009 Published by Elsevier B.V.The Val66Met polymorphism in the brain-derived neurotrophic factor (BDNF) gene may modulate the epilepsy phenotype. We investigated the impact of polymorphisms in the BDNF gene on clinical features in fragile X syndrome (FXS). In our study sample, the Met66 allele associated with epilepsy of finnish FXS men. Abnormalities in BDNF-mediated plasticity are shown in FXS and the present data suggest that the Met66 allele might predispose FXS mates to epilepsy. (C) 2009 Published by Elsevier B.V.The Val66Met polymorphism in the brain-derived neurotrophic factor (BDNF) gene may modulate the epilepsy phenotype. We investigated the impact of polymorphisms in the BDNF gene on clinical features in fragile X syndrome (FXS). In our study sample, the Met66 allele associated with epilepsy of finnish FXS men. Abnormalities in BDNF-mediated plasticity are shown in FXS and the present data suggest that the Met66 allele might predispose FXS mates to epilepsy. (C) 2009 Published by Elsevier B.V.Peer reviewe

Reseptori signalointimekanismit hermoston kantasolujen erilaistumisessa ja fragiili-X-oireyhtymän hiirimallissa

Neural stem cells and their arising progenitors create our central nervous system (CNS). The questions of how neural progenitor cells (NPCs) are determined to a certain neuronal fate, in that, how do they mature, migrate, and develop to take on their physiological roles, during the formation of functional networks in the brain, remain fundamentally unanswered. Despite the vast amount of information acquired and accumulated over the last centuries, the interplay between molecular mechanisms that drive brain development have only recently started to unravel. Studies have shown that early brain electrical activity, neurotransmitter-induced responses, and trophic factor signaling, acting through their respective receptors, are implicated as critical regulators of brain development. By elucidating the mechanisms governing progenitor cell behavior under normal and pathological conditions, such as fragile X syndrome (FXS), the most common cause of intellectual disability and leading genetic cause of autism, will further improve our understanding of brain development, and facilitate the development of CNS cell therapies. This thesis aims to shed light into the molecular and cellular mechanisms in the developing brain by utilizing in vitro neurosphere model to study the differentiation and migration of neural progenitors, by combining gene and protein expression analysis, and immunocytochemical stainings with intracellular calcium imaging and time-lapse video microscopy. In addition, in vivo immunohistological staining methodologies, in situ hybridization studies and in utero electroporation were utilized to study neocortical development in the absence of functional Fragile X mental retardation protein (FMRP), in a mouse model for FXS. Taken together, results presented in this thesis provide new information on the molecular mechanisms that guide neural progenitor cells and their interactions with radial glia (RG) cells. It sheds key insights into NPC functional responses as they mature and differentiate, identifying key molecular players as well as providing compelling evidence that neural-glia interaction during cortical formation plays an important role in brain development. Additionally, timing, and region-specific modulatory role of brain-derived neurotrophic factor (BDNF)-TrkB signaling during neocortical development and abnormalities particularly in glutamatergic neurogenesis in the absence of FMRP was demonstrated.Hermoston kantasolut ja niistä syntyvät esisolut (progenitors) luovat keskushermostomme. Miten solut löytävät oikeat paikkansa aivojen kehityksen aikana ja määrittyvät ja erilaistuvat fysiologisiin rooleihinsa, toiminnallisiksi hermoverkostoiksi, on keskeinen kysymys neurotieteessä. Tutkimukset ovat osoittaneet, että varhainen aivojen sähköinen aktiivisuus sekä välittäjäaineiden ja kasvutekijöiden aiheuttamat reseptori signalointivasteet ovat tärkeitä aivojen kehityksen säätelijöitä. Häiriöt näissä prosesseissa liittyvät autismin kirjon sairauksiin. Huolimatta tutkimustiedon jatkuvasta lisääntymisestä, aivojen kehitystä ohjaavien solu- ja molekyylimekanismien välinen vuorovaikutus on kuitenkin vielä monilta osin hämärän peitossa. Työssä selvitettiin eri solukuvantamistekniikoin ja molekulaarisin menetelmin mekanismeja, jotka ohjaavat hermoston kanta- ja esisolujen käyttäytymistä normaaleissa ja patologisissa olosuhteissa, kuten fragiili-X-oireyhtymässä (särö-X-oireyhtymä), joka on tavallisin perinnöllisen geenivian aiheuttama kehitysvammaisuuteen johtava tila ja johtava autismin kirjon sairausmalli. Tulokset selvittivät hermoston kanta- ja esisolujen erilaistumis- ja vaellusmekanismeja ja paljastivat glutamaatti-välittäjäaineen tärkeän roolin kehittyvien hermosolujen ja radiaali glia solujen välisessä vuorovaikutuksessa, solujen vaelluksen ja ulokkeiden kasvun säätelyssä. Lisäksi tulokset osoittivat häiriön glutamatergisten solujen erilaistumisessa ja poikkeavuuksia aivokuoren kehittymisessä fragiili-X-oireyhtymän hiirimallissa. Tämän lisäksi paljastimme aika- ja paikka riippuvaisen modulatorisen roolin aivoperäiselle hermokasvutekijälle (BDNF) eri aivorakenteissa sekä poikkeavuuksia Bdnf lähetti-RNA:n dendriittisessä kohdentamisessa fragiili-X-oireyhtymän hiirimallissa. Näiden tutkimusten avulla ymmärryksemme aivojen kehityksestä niin normaali kuin patofysiologisissa tiloissa syvenee ja lopulta tulevaisuudessa, ne voivat edesauttaa keskushermoston soluterapioiden hoitomuotojen kehittelyssä