Dr. Lisette Leyton is a Biochemist from the Faculty of Chemical and Pharmaceutical Sciences, University of Chile. Dr. Leyton obtained her PhD in Sciences in the Faculty of Basic Sciences, University of Chile. She is currently a Professor of the Faculty of Medicine, University of Chile and also the Academic Secretary of the Committee of the Postgraduate Program in Biomedical Sciences of the same Faculty.
Signal transduction pathways triggered by cell-cell and cell-matrix interactions. Rho GTPases involved in cell adhesion and migration. Our model includes neuron-astrocyte interaction, its function in astrocyte activation (morphological changes, adhesion and migration) and neuronal cell death under pro-inflammatory stimuli.
Astrocytes are ubiquitously present throughout the brain and intimately associated with neurons. Upon injury or in response to inflammation, astrocytes are activated, migrate, increase in size and participate in the formation of the glial scar. In doing so, the glial scar generates a non-permissive environment for neuronal regeneration. Molecular mechanisms responsible for the lack of neuronal regeneration in the adult CNS are still unclear, possibly due to the participation of multiple inhibitory cell-cell, as well as cell-matrix interactions. Our interest focuses on an interaction described initially by our group, between Thy-1, an abundantly expressed neuronal surface molecule, and its reported astrocyte ligand/receptor, (aVb3) integrin. Our initial data provided evidence indicating that Thy-1 clusters a β3-containing integrin in astrocytes to induce tyrosine phosphorylation of focal adhesion proteins (Leyton et al., 2001), RhoA activation (Ávalos et al., 2002, 2004) and the formation of focal adhesion and stress fibers. Focal adhesions anchor stress fibers to the plasma membrane, contain multiple structural, signalling and adaptor molecules and are implicated in cell migration, growth and differentiation. Results obtained indicate that αv integrin forms an αvβ3 heterodimer in astrocytes and both integrin subunits are required for its association with Thy-1. Using the Surface Plasmon Resonance technique, the interaction was shown to be direct and although there are many molecules that mediate neuron-astrocyte association, we demonstrated the requirement of Thy-1-integrin interaction to induce astrocyte adhesion to the extracellular matrix (Hermosilla et al., 2008). Additionally, we have shown that Thy-1-induced RhoA activation, as well as focal adhesion and stress fiber formation require an additional interaction with the proteoglycan syndecan-4, as evidenced by silencing syndecan-4 expression. Furthermore, lack of RhoA activation and astrocyte responses in the presence of a PKC inhibitor or a dominant negative form of PKCα, implicated PKCα and RhoA activation in these events. Therefore, Thy-1 requires both αvβ3 integrin and syndecan-4 engagement to stimulate astrocytes via PKCα and RhoA-dependent pathways (Ávalos, et al., 2009). In addition, the Thy-1 heparin-binding site has been identified and mutated. Interestingly, the mutant neither binds to heparin, nor induces RhoA activation, nor induces FA formation in astrocytes (Ávalos, et al., 2009). Finally, since PKCα activation is calcium-dependent, we studied whether calcium elevation was due to extracellular calcium influx via ATP-activated P2X7 receptors. We documented that αvβ3 integrin engagement in astrocytes by neuronal Thy-1, triggers ATP release that activates P2X7 pore-forming channels, permits calcium entry and increases intracellular calcium levels. All these events are required for FA formation in astrocytes. These results uncover a new finding concerning Thy-1 action by identifying a functional link between αvβ3 integrin and P2X7 receptors in cellular adhesion (Henríquez, et al., 2011). All these signaling events are temporally regulated and the prolonged stimulation with Thy-1 leads to disassembly-assembly of focal adhesions in a dynamic process that induces astrocyte migration in a PI3K and Rac1-dependent manner (Kong, et al., 2013).
Our most recent data indicates that αVβ3 integrin acts as a ligand for Thy-1 that upon binding not only restricts the growth of neurites, but also induces retraction of already existing processes by inducing Thy-1 clustering and recruitment of Src (Herrera-Molina, et al., 2012). These observations argue that Thy-1 functions in a bimodal fashion, as a receptor on neuronal cells and as a ligand for aVb3 integrin on astrocytes. Since Thy-1 is implicated in the inhibition of neurite outgrowth, signaling events in astrocytes are likely to play an important role in this process. Understanding such mechanisms should yield insights to astrogliosis, a process triggered in astrocytes following brain injury that precludes neuronal regeneration. These studies are expected to yield a better understanding of molecular mechanisms controlling neurite outgrowth and astrocyte function. Such insights are of fundamental interest to brain physiology in general and nerve regeneration in particular.
A Cárdenas, et al., Signaling pathways involved in neuron-astrocyte adhesion and migration. Current Molecular Medicine 14(2):275-290 (2014).
Leyton, L., Schneider, P., Labra, C.V., Rüegg, C., Hetz, C.A., Quest, A.F.G. and C. Bron. “Thy-1 binds to integrin ß3 on astrocytes and triggers formation of focal contact sites”. Current Biology. 11:1028-38 (2001). PubMed Link
Ávalos, A.M., Labra, C., Quest, A.F.G., and Leyton, L. “Signaling triggered by Thy-1 interaction with ß3 integrin on astrocytes is an essential step towards unraveling neuronal Thy-1 function” Biol. Res. 35: 231-238 (2002). PubMed Link
Avalos AM, Arthur WT, Schneider P, Quest AF, Burridge K, Leyton L. “Aggregation of integrins and RhoA activation are required for Thy-1-induced morphological changes in astrocytes”. J Biol Chem. Sep 10;279(37):39139-45. Epub 2004 Jun 25 (2004) Abstract. . PubMed Link
Hermosilla, T., Muñoz, D, Herrera-Molina, R., Valdivia, A., Nham, S.-U., Schneider, P., Burridge, K., Quest, A.F.G., Leyton, L.“Direct Thy-1/integrin αvβ3 interaction mediates neuron to astrocyte communication” BBA Mol Cell Biol, 1783: 1111-1120 (2008). PubMed Link
Avalos, A.M., Valdivia, A.D., Muñoz, N., Herrera-Molina, R., Tapia, J.C., Lavandero, S., Chiong, M., Burridge, K., Schneider, P., Quest, A.F.G., and Leyton, L. “Neuronal Thy-1 induces astrocyte adhesion by engaging syndecan-4 in a cooperative interaction with αvβ3 integrin that activates PKCα and RhoA” J. Cell Sci. 122:3462-3471 (2009). PubMed Link
Henríquez, M, Herrera-Molina, R., Valdivia, A., Alvarez, A., Kong, M., Muñoz, N., Eisner, V., Jaimovich, E., Schneider, P., Quest, A.F.G.,*Leyton, L,*“ATP release due to Thy-1-integrin binding induces P2X7-mediated calcium entry required for focal adhesion formation” J. Cell Sci.124: 1581-1588 (2011) *equal contribution as corresponding authors. PubMed Link
Herrera-Molina, R., Frischknecht, R., Maldonado, H., Seidenbecher, C.I., Gundelfinger, E.D., Hetz, C., Aylwin, M.L., Quest, A.F.G., and Leyton, L. “Astrocytic αVβ3 Integrin Inhibits Neurite Outgrowth and Promotes Retraction of Neuronal Processes by Clustering Thy-1”. PLoS One. 7(3):e34295. Epub 2012 Mar 30 (2012). PubMed Link
Herrera-Molina, R., Valdivia, A., Kong, M., Alvarez, A., Cárdenas, A., Quest, A. F. G. and Leyton L. “Thy-1-interacting molecules and cellular signaling in both Cis and Trans”. International Reviews of Cell and Molecular Biology. 305: 163-216 (2013). PubMed Link
Kong, M., Muñoz, N., Valdivia, A., Alvarez, A., Herrera-Molina, R., Cárdenas, A., Schneider, P., Burridge, K., Quest, A.F.G., and Leyton, L. “Thy-1-mediated Cell -Cell Contact Induces Astrocyte Migration through the Engagement of αVβ3 Integrin and Syndecan-4”. BBA-Mol Cell Res. 1833:1409-1420 (2013). PubMed Link
Leyton, L., Torres, V.A., Quest A.F.G. Editorial (Thematic Issue: Signaling in Cell Migration and Disease). Curr. Mol. Med. 14: 197-198 (2014). PubMed Link
Cárdenas, C., Kong, M., Alvarez, A., Maldonado, H., Leyton, L. “Signaling pathways involved in neuron-astrocyte adhesion and migration”. Current Molecular Medicine 14(2):275-290 (2014). PubMed Link
Alvarez, A., Lagos-Cabré, R., Kong, M., Cárdenas, A., Burgos-Bravo, F., Schneider, P., Quest, A.F.G., Leyton L. “Integrin-mediated transactivation of P2X7R via hemichannel-dependent ATP release stimulates astrocyte migration”. BBA-Mol Cell Res. 1863: 2175–2188 (2016). PubMed Link
Maldonado, H., Calderon, C., Burgos-Bravo, F., Kobler, O., Zuschratter, W., Ramirez, O., Härtel, S., Schneider, P., Quest, A.F.G., Herrera-Molina, R.*, Leyton, L.*. “Astrocyte-to-neuron communication through integrin-engaged Thy-1/CBP/Csk/Src complex triggers neurite retraction via the RhoA/ROCK pathway”. BBA-Mol Cell Res. 1864:243-254 (2016). *Corresponding authors (equal contribution). PubMed Link