Roles of Glutamate Receptors and the Mammalian Target of Rapamycin (mTOR) Signaling Pathway in Activity-dependent Dendritic Protein Synthesis in Hippocampal Neurons

Ruomu Gong,Chang Sin Park,Nima Rezaei Abbassi,Shao-Jun Tang

doi:10.1074/jbc.m512524200

Abstract

Local protein synthesis in neuronal dendrites is critical for synaptic plasticity. However, the signaling cascades that couple synaptic activation to dendritic protein synthesis remain elusive. The purpose of this study is to determine the role of glutamate receptors and the mammalian target of rapamycin (mTOR) signaling in regulating dendritic protein synthesis in live neurons. We first characterized the involvement of various subtypes of glutamate receptors and the mTOR kinase in regulating dendritic synthesis of a green fluorescent protein (GFP) reporter controlled by alphaCaMKII 5' and 3' untranslated regions in cultured hippocampal neurons. Specific antagonists of N-methyl-d-aspartic acid (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and metabotropic glutamate receptors abolished glutamate-induced dendritic GFP synthesis, whereas agonists of NMDA and metabotropic but not AMPA glutamate receptors activated GFP synthesis in dendrites. Inhibitions of the mTOR signaling, as well as its upstream activators, phosphatidylinositol 3-kinase and AKT, blocked NMDA receptor-dependent dendritic GFP synthesis. Conversely, activation of mTOR signaling stimulated dendritic GFP synthesis. In addition, we also found that inhibition of the mTOR kinase blocked dendritic synthesis of the endogenous alphaCaMKII and MAP2 proteins induced by tetanic stimulations in hippocampal slices. These results identify critical roles of NMDA receptors and the mTOR signaling pathway for control of synaptic activity-induced dendritic protein synthesis in hippocampal neurons.

Highlights

Dependent long-term depression (LTD) [6], and serotonin-induced long-term facilitation of Aplysia neurons [7, 8]
We demonstrated that tetanus-induced dendritic synthesis of the ␣CaMKII protein in hippocampal slices required the activation of N-methyl-D-aspartic acid (NMDA) receptors and the mammalian target of rapamycin (mTOR) signaling
Several lines of evidence suggest that the activity-induced green fluorescent protein (GFP) recovery we observed in photobleached dendritic segments resulted from local protein synthesis rather than other cellular processes such as mRNA and protein transport from cell bodies

Summary

Introduction

Dependent long-term depression (LTD) [6], and serotonin-induced long-term facilitation of Aplysia neurons [7, 8]. The activation of NMDA receptors induced synthesis of ␣CaMKII protein in synaptosomes [19] and the activation of dopamine D1/D5 receptor in cultured neurons stimulates GluR1 synthesis in dendrites [20]. Despite these important observations, the role of glutamate receptors in regulating dendritic protein synthesis in live neurons has not been systematically investigated. Down-regulation of MAPK signaling impaired L-LTP and memory consolidation, which are protein synthesis-dependent, and activity-regulated phosphorylation of multiple translation initiation factors [37]. Glutamate Receptors and the mTOR Signaling in Dendritic Protein Synthesis synaptic activity-dependent dendritic proteins remains to be directly demonstrated

Objectives

Results

Conclusion