Sunday, 22nd October 2017

 Molecular Neuropathology

    Molecular bases of glutamatergic synapses





Cecilio Giménez /
Francisco Zafra









Research summary:



For years, a primary focus of our laboratory has been the understanding the basic regulatory mechanisms of glial and neuronal glutamate and glycine transporters in CNS, and how dysregulation of these proteins, or their associated regulatory proteins, could contribute to neurological disorders such as schizophrenia, amyotrophic lateral sclerosis, or ischemic insults to the brain. Neurotransporters for glutamate (GLT1, GLAST, EAAT3) and glycine (GLYT1) control the levels of these neurotransmitters in glutamatergic synapses thereby regulating the activity of NMDA receptors that requires both ligands as obligatory coagonists. While overstimulation of these receptors drives neurodegenerative processes, the hypofunction has been associated to schizophrenia. Thus, the activity of these transporters has a profound impact on the activity of the glutamatergic pathways, and its modulation is considered of great interest in the treatment of dysfunctions that affect to the glutamatergic system. The glycine and the glutamate transporters are subjected to intracellular trafficking processes, which in turn, are regulated by various signal transduction pathways and interactions with cellular proteins and determining finally the concentration and the location of these carriers in glutamatergic synapses.

More specifically, our work has intended a better understanding the biogenesis mechanisms: exit from the endoplasmic reticulum, transit through the Golgi complex, and asymmetric distribution to different subdomains of the plasma membrane, its anchoring to scaffolding proteins and, finally, the endocytosis either for degradation or recycling. Our studies have contributed to the fine localization of these proteins in the brain as well as to the identification of several associated proteins (PDZ proteins, exocytst) and to the identification of structural motifs involved in the asymmetric distribution of these transporters in polarized cells. Also, we have defined regulatory mechanisms based in posttranscriptional modifications on the transporters such as phosphorylation and ubiquitination / deubiquitination. In addition, we keep interest in the function of glycine as an inhibitory neurotransmitter, and the associated transporter GLYT2, involved in the genetic disease hyperekplexia. These studies, especially those related with trafficking of GLYT2, have been performed in the last few years in collaboration with the group of Dr. C. Aragón.
The main focus for the next few years is the identification of additional regulatory mechanisms, the identification of novel partners in the interactome of these transporters, taking advantage of new proteomic strategies, and how these mechanisms might be modified in animal models of diseases, more precisely in model of schizophrenia (mice deficient in the vesicular glutamate transporter vGLUT2) and in a rat models of cerebral ischemia (MCAO).


Relevant publications:

1 - Zafra, F.*, Aragón, C., Olivares, L., Danbolt, N.C, Giménez, C., Storm-Mathisen, J. (1995) "Glycine transporters are differentially expressed among CNS cells". J. Neurosci. 15, 3952-3969. IF7.5 Number of citations: 289

2 - Casado, M., Bendahan, A., Zafra, F., Danbolt, N.C., Aragón, C., Giménez, C. Kanner, B.I.* (1993) "Phosphorylation and modulation of brain glutamate transporters by protein kinase C". J. Biol. Chem. 268, 27313-27317. IF5.6 Number of citations: 242

3 - Zafra, F., Gomeza, J., Olivares, L., Aragón, C., Giménez. C.* (1995) "Regional distribution and developmental changes of glycine transporters (GLYT1 and GLYT2) in rat brain". Eur. J. Neurosci. 7, 1342-1352. IF3.7 Number of citations: 149

4 - Cubelos, B., Giménez, C., Zafra F.* (2005) Localization at glutamatergic synapses of the glycine transporter GLYT1. Cerebral Cortex 15(4):448-459. IF6.5 Number of citations: 111

5 - Casado, M., Zafra, F., Aragón, M.C., Giménez, C.* (1990) "Activation of high-affinity uptake of glutamate by phorbol esters in primary glial cell cultures." J. Neurochem. 57, 1185-1190. IF4.6 Number of citations: 98


Others by F. Zafra

Zafra, F., Hengerer, B., Leibrock, J., Thoenen, H., Lindholm,D. (1990) "Activity dependent regulation of BDNF and NGF mRNAs in the rat hippocampus is mediated by non-NMDA glutamate receptors." EMBO. J. 9, 3545-3550. IF8.7 Number of citations: 723

Zafra, F., Castrén, E., Thoenen, H., Lindholm, D. (1991) "Interplay between glutamate and γ-aminobutyric acid transmitter systems in the physiological regulation of brain-derived neurotrophic factor and nerve growth factor synthesis in hippocampal neurons." Proc. Natl. Acad. Sci. USA 88, 10037-10041. IF9.6 Number of citations: 424