title: Glutamate transporter-dependent mTOR phosphorylation in Müller glia cells.
abstract: Glu (glutamate), the excitatory transmitter at the main signalling pathway in the retina, is critically involved in changes in the protein repertoire through the activation of signalling cascades, which regulate protein synthesis at transcriptional and translational levels. Activity-dependent differential gene expression by Glu is related to the activation of ionotropic and metabotropic Glu receptors; however, recent findings suggest the involvement of Na+-dependent Glu transporters in this process. Within the retina, Glu uptake is aimed at the replenishment of the releasable pool, and for the prevention of excitotoxicity and is carried mainly by the GLAST/EAAT-1 (Na+-dependent glutamate/aspartate transporter/excitatory amino acids transporter-1) located in Müller radial glia. Based on the previous work showing the alteration of GLAST expression induced by Glu, the present work investigates the involvement of GLAST signalling in the regulation of protein synthesis in Müller cells. To this end, we explored the effect of D-Asp (D-aspartate) on Ser-2448 mTOR (mammalian target of rapamycin) phosphorylation in primary cultures of chick Müller glia. The results showed that D-Asp transport induces the time- and dose-dependent phosphorylation of mTOR, mimicked by the transportable GLAST inhibitor THA (threo-β-hydroxyaspartate). Signalling leading to mTOR phosphorylation includes Ca2+ influx, the activation of p60src, phosphatidylinositol 3-kinase, protein kinase B, mTOR and p70S6K. Interestingly, GLAST activity promoted AP-1 (activator protein-1) binding to DNA, supporting a function for transporter signalling in retinal long-term responses. These results add a novel receptor-independent pathway for Glu signalling in Müller glia, and further strengthen the critical involvement of these cells in the regulation of glutamatergic transmission in the retina.
authors: *División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México D.F., México.
authors: Ana
authors: A
authors: María López-Colomé
authors: †Departamento de Genética y Biología Molecular, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Apartado Postal 14740, México D.F. 07000, México.
authors: Zila
authors: Z
authors: Martínez-Lozada
authors: †Departamento de Genética y Biología Molecular, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Apartado Postal 14740, México D.F. 07000, México.
authors: Alain M
authors: AM
authors: Guillem
authors: *División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, México D.F., México.
authors: Edith
authors: E
authors: López
authors: †Departamento de Genética y Biología Molecular, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Apartado Postal 14740, México D.F. 07000, México.
authors: Arturo
authors: A
authors: Ortega
mesh_terms: D027322:Amino Acid Transport System X-AG / Q000378:metabolism*; D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D026603:D-Aspartic Acid / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D024202:Electrophoretic Mobility Shift Assay; D063928:Ependymoglial Cells / Q000187:drug effects / Q000378:metabolism*; D018683:Excitatory Amino Acid Agents / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D018698:Glutamic Acid / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D012160:Retina / Q000166:cytology; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D027322:Amino Acid Transport System X-AG; D018683:Excitatory Amino Acid Agents; C120673:benzyloxyaspartate; D001224:Aspartic Acid; D000001:Calcimycin; D018698:Glutamic Acid; D012694:Serine; D026603:D-Aspartic Acid; D058570:TOR Serine-Threonine Kinases; D002118:Calcium