Adaptation of living organisms to constantly changing environments depends on the plasticity of the nervous system. Neuronal plasticity often requires activity-dependent translation to rapidly supply selected proteins, for example, through activation of Group 1 metabotropic glutamate receptors (Gp1 mGluRs). Gp1 mGluRs, including mGluR1 and mGluR5, mediate translation-dependent synaptic plasticity, including long-term synaptic depression (LTD). Dysregulated Gp1 mGluR signaling is observed with various neurological and mental disorders, including Fragile X Syndrome (FXS) and autism spectrum disorders (ASDs). Although pharmacological correction of Gp1 mGluR activity reverses many of the phenotypes in animal models of those diseases, the molecular and cellular mechanisms underlying Gp1 mGluR-mediated synaptic plasticity have been elusive. Our published and preliminary data introduce the ubiquitin E3 ligase Murine double minute-2 (Mdm2) as a novel translational repressor and a ?switch? that permits Gp1 mGluR-induced protein translation (Liu et al., Hum Mol Genet., 2017). In our proposed research, we aim to characterize the role of Mdm2 in Gp1 mGluR- dependent synaptic plasticity (Aim 1) and determine the mechanism by which Mdm2 mediates activity-dependent protein translation (Aim 2). Our new data also show that Mdm2 is molecularly altered and unresponsive to Gp1 mGluR activation in the Fmr1 knockout (KO) mouse, the commonly used animal model for studying FXS (Tsai et al., Hum Mol Genet., 2017).
In Aim 3 we will characterize the mechanism by which Fmr1 interconnects Gp1 mGluR signaling to permit translational activation through de-repressing Mdm2. Successful completion of this proposal will greatly facilitate the understanding of Gp1 mGluR-mediated synaptic plasticity through a novel mechanism of translational control. Building on the deep knowledge of Mdm2 in cancer biology, our research will also open a new avenue for the study of neurological disorders associated with abnormal Gp1 mGluR signaling.
Group 1 metabotropic glutamate receptors (Gp1 mGluR)-mediated synaptic plasticity requires rapid activation of protein translation but the precise mechanisms are still not fully understood. The proposed study aims to investigate a promising yet underdeveloped molecule, murine double minute-2 (Mdm2), in Gp1 mGluR- dependent protein translation and synaptic plasticity. Completion of this proposal will significantly expand our understanding of Gp1 mGluR-mediated synaptic plasticity and may introduce novel therapeutic targets into treating mGluR-associated neurological disorders.