Neuritogenesis Induced by Thyroid Hormone-treated Astrocytes Is Mediated by Epidermal Growth Factor/Mitogen-activated Protein Kinase-Phosphatidylinositol 3-Kinase Pathways and Involves Modulation of Extracellular Matrix Proteins*
- From the Instituto de Ciências Biomédicas, Departamento de Anatomia, Universidade Federal do Rio de Janeiro, 21941-590, Rio de Janeiro, RJ, Brazil
Abstract
Thyroid hormone (T3) plays a crucial role in several steps of cerebellar ontogenesis. By using a neuron-astrocyte coculture model, we have investigated the effects of T3-treated astrocytes on cerebellar neuronal differentiation in vitro. Neurons plated onto T3-astrocytes presented a 40–60% increase on the total neurite length and an increment in the number of neurites. Treatment of astrocytes with epidermal growth factor (EGF) yielded similar results, suggesting that this growth factor might mediate T3-induced neuritogenesis. EGF and T3 treatment increased fibronectin and laminin expression by astrocytes, suggesting that astrocyte neurite permissiveness induced by these treatments is mostly due to modulation of extracellular matrix (ECM) components. Such increase in ECM protein expression as well as astrocyte permissiveness to neurite outgrowth was reversed by the specific EGF receptor tyrosine kinase inhibitor, tyrphostin. Moreover, studies using selective inhibitors of several transduction-signaling cascades indicated that modulation of ECM proteins by EGF is mainly through a synergistic activation of mitogen-activated protein kinase and phosphatidylinositol 3-kinase pathways. In this work, we provide evidence of a novel role of EGF as an intermediary factor of T3 action on cerebellar ontogenesis. By modulating the content of ECM proteins, EGF increases neurite outgrowth. Our data reveal an important role of astrocytes as mediators of T3-induced cerebellar development and partially elucidate the role of EGF and mitogen-activated protein kinase/phosphatidylinositol 3-kinase pathways on this process.
Footnotes
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↵* This work was supported by grants from Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq), Coordenação de Aperfeiçoamento de Pessoal de Nı́vel Superior-Comité Francais d'Evaluation de la Coopération Universitaire avec le Brésil (CAPES-COFECUB), Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), Conselho de Ensino para Graduados e Pesquisa-Universidade Federal do Rio de Janeiro (CEPG-UFRJ), and Programa de Apoio a Núcleos de Excelência2-Ministério de Ciência e Tecnologia (PRONEX2-MCT).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed: Instituto de Ciências Biomédicas, Departamento de Anatomia, Universidade Federal do Rio de Janeiro, Centro de Ciências da Saúde, Bloco F, Ilha do Fundão 21941-590, Rio de Janeiro, RJ, Brazil. Tel.: 55-21-2562-6460; E-mail: fgomes@anato.ufrj.br.
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Published, JBC Papers in Press, September 27, 2002, DOI 10.1074/jbc.M209284200
- Abbreviations:
- T3
-
triiodothyronine
- NS
-
nervous system
- CNS
-
central nervous system
- ECM
-
extracellular matrix protein
- EGF
-
epidermal growth factor
- EGFR
-
EGF receptor
- EGL
-
external granular layer
- MAPK
-
mitogen-activated protein (MAP) kinase
- MEK
-
MAPK/extracellular signal regulated kinase kinase
- PI3K
-
phosphatidylinositol 3-kinase
- DMEM
-
Dulbecco's modified Eagle's medium
- CM
-
conditioned medium
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- Received September 10, 2002.
- The American Society for Biochemistry and Molecular Biology, Inc.
