Molecular Psychiatry An atypical antidepressant drug regulates - PDF document

4/9/2014 Molecular Psychiatry An atypical antidepressant drug regulates synaptic plasticity • Nature Publishing Group • Impact Factor: 14.897 (2012) – 1/135 Psychiatry – 7/251 Neuroscience – 5/290 Biochemistry & Zhang, H., Etherington, L. A., Hafner, A. S., Belelli, D., Ed Shi Molecular Biology Coussen, F., Delagrange, P., ... & Groc, L. (2013). April 7, 2014 Regulation of AMPA receptor surface trafficking and synaptic plasticity by a cognitive enhancer and “Molecular Psychiatry” (2014). Retreived April 5, 2014. antidepressant molecule. Molecular psychiatry, 18(4), 471- http://www.nature.com/mp/index.html 484. Laurent Groc Daniel Choquet • Research Director at • Research Director at French National Center for Research French National Center CNRS for Research (CNRS) • Director of the Institute of • Study of molecular Interdisciplinary Neuroscience – mechanisms of neural Bordeaux Segalin University • connection formation Director of Bordeaux Imaging Center • Principal Investigator at • Study of receptor trafficking via Bordeaux Segalin high resolution imaging Unversity techniques • Neuroscience PhD from • PhD in neuroscience from Pasteur Institute, France Wayne State University, Development and Adaptation of Neural Circuits. “Daniel Choquet Group” Retreived April 5, 2014. Michigan Retreived April 5, 2014. http://www.iins.u- http://www.iins.u-bordeaux2.fr/research-teams/daniel- bordeaux2.fr/research-teams/groc-team choquet-team Tianeptine is an unregulated legal substance with Others an unknown site of action • Honyu Zhang – • Not believed to directly Postdoc modulate monoamine • Anne-Sophie Hafner transmission – Postdoc • Action may involve • Francois Coussen – glutamate receptor Researcher (now transmission married to D. Choquet) “ Tianeptine Powder”(2014). Retreived March 25, 2014. http://nootropicsdepot.com/tianeptine-powder-99/ 1

4/9/2014 Ionotropic Glutamate Receptors Mechanism of long term potentiation (LTP) synaptic plasticity at a glutamate synapse (iGluRs) • 1. Depolarization of postsynaptic membrane Ligand gated (glutamate) ion channels responsible for 2. Relief of NMDAR Mg 2+ block excitatory synaptic transmission 3. Ca 2+ influx through NMDAR • AMPA Receptor (AMPAR) • Four subunits • GluA1-3 subunits 4. Activation of Ca 2+ Dependent Kinase • Excitatory • 5. Phosphorylation of AMPAR facilitating NMDA Receptor surface delivery (NMDAR) • V oltage 6. More excitatory AMPAR, more excitable dependent Mg 2+ block synapse • Kainate Receptor Kauer & Malenka 2007 AMPA receptor Tianeptine reverses stress induced Compromised synaptic plasticity decreases in LTP may underlie mood disorder • LTP dependent on high frequency activation • • 4 pulse of high freq. stim Alterations in plasticity seen in stress-induced animal models of results in subsequent higher depression fEPSP – Indicative of LTP • Synaptic plasticity mechanisms intimately related to denritic branching and brain region volume • Graph plot of fEPSP after LTP- • Regions affected include hippocampus, pre-frontal cortex, amygdala inducing stimulation, as % of control • Stress decreases magnitude of • All important in cognitive and affective function LTP • Effect reversed by • Tianeptine may exert its antidepressant effect by reversing tianeptine compromised plasticity Tianeptine decrease stimulation Tianeptine reduces stress induced threshold for LTP decrease in field EPSP • 3 pulse stimulation produces change in fEPSP in control (black trace) • Tianeptine administration results in significantly • Field EPSP greater potentiation – Extracellular recording of a population of neurons with 3 pulse – A measurement of basal synaptic transmission strength stimulation (red trace) 2

4/9/2014 GluA1 AMPA receptor subunit is important in LTP • Regulatory phosphorylation sites – Serine-831: receptor trafficking Tianeptine molecular mechanism – Serine-845: modulate how often receptor can open involves AMPA receptor lateral • AMPA receptors containing only GluA1 are diffusion trafficked to synapse in early LTP – Open “wider” – Permeability to Ca 2+ may play later role in LTP Tianeptine reduces stress induced Tianeptine increases GluA1 at the decrease of surface GluA1 AMPA synapse receptor subunit • Quantification of GluA1 at synapse by fluorescent intensity • Postsynaptic protein homer1c is tagged with • Fluorescent imaging of GluR1 :: superEcliptic pHluorin red fluorescent protein • Co-localization with (SEP) intensity tagged homer1c • pH sensitive fluorescent protein defines “synaptic” • Strong emission indicative of extracellular environment (~neutral pH) • Low emission in acidified intracellular vesicles GluA2 AMPA receptor subunit Tianeptine decreases GluA1 AMPAR surface diffusion quantum dot (QD) tracking • GluA1 :: SEP used to visualize • Light pulse is used • Antibody specific for N- to bleach SEP terminal domain of GluA2 • Unbleached tagged • QD secondary antibody GluA1 diffuse • Visualization using mercury laterally and florescence is lamp and regular CCD video recovered camera • High signal/noise ratio vs. • In (a) & (b) qualitative and fluorescent protein quantitative fluorescence recovery is faster with tianeptine • Indicates greater lateral mobility 3

4/9/2014 Tianeptine reduces glucocorticoid Tianeptine decreases GluA2-AMPAR surface incubation induced AMPAR diffusion movement • Yellow traces show path of a single GluA2 containing AMPA receptor • Glucocorticoid (GC) is a stress • Quantification of hormone diffusion revealed • Activation of glucocorticoid significant receptors in brain implicated in differences effects of stress • Figure shows trajectory of QD tagged GluA2 • GC induced mobility increase is reduced by tianeptine The molecular mechanism of tianeptine Further evidence for action is dependent on a CaMKII – affect on Stargazin Stargazin – PSD-95 interaction – PSD95 interaction • Energy emitted by GFP on • Dependent on CaMKII PSD95 is absorbed by red phosphorylation of Stargazin fluorophore on Stargazin if two protein that associates with are close together AMPARs • GFP will become dimmer • Phosphorylated Stargazin must • Measurement of GFP “lifetime” bind PSD-95 (a synaptic quantifies stargazin-PSD95 strutural protein) binding • Inhibition of either of these steps by drug or mutation • GFP lifetime is significantly prevented the effects of shorter in tianeptine tianeptine administration Summary • Tianeptine reduces stress induced LTP changes – Perhaps through reduction of LTP-inducing stimulation threshold • Tianeptine reduces lateral diffusion of AMPA receptors out of the synapse – No effect on endocytosis or exocytosis seen • A CaMKII – Stargazin – PSD-95 interaction is necessary for the effects of tianeptine 4