title: Importance of Shank3 protein in regulating metabotropic glutamate receptor 5 (mGluR5) expression and signaling at synapses.
abstract: Shank3/PROSAP2 gene mutations are associated with cognitive impairment ranging from mental retardation to autism. Shank3 is a large scaffold postsynaptic density protein implicated in dendritic spines and synapse formation; however, its specific functions have not been clearly demonstrated. We have used RNAi to knockdown Shank3 expression in neuronal cultures and showed that this treatment specifically reduced the synaptic expression of the metabotropic glutamate receptor 5 (mGluR5), but did not affect the expression of other major synaptic proteins. The functional consequence of Shank3 RNAi knockdown was impaired signaling via mGluR5, as shown by reduction in ERK1/2 and CREB phosphorylation induced by stimulation with (S)-3,5-dihydroxyphenylglycine (DHPG) as the agonist of mGluR5 receptors, impaired mGluR5-dependent synaptic plasticity (DHPG-induced long-term depression), and impaired mGluR5-dependent modulation of neural network activity. We also found morphological abnormalities in the structure of synapses (spine number, width, and length) and impaired glutamatergic synaptic transmission, as shown by reduction in the frequency of miniature excitatory postsynaptic currents (mEPSC). Notably, pharmacological augmentation of mGluR5 activity using 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)-benzamide as the positive allosteric modulator of these receptors restored mGluR5-dependent signaling (DHPG-induced phosphorylation of ERK1/2) and normalized the frequency of mEPSCs in Shank3-knocked down neurons. These data demonstrate that a deficit in mGluR5-mediated intracellular signaling in Shank3 knockdown neurons can be compensated by 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)-benzamide; this raises the possibility that pharmacological augmentation of mGluR5 activity represents a possible new therapeutic approach for patients with Shank3 mutations.
authors.affiliation: Department of Pharmacology, CNR Institute of Neuroscience, University of Milan, Milan 20129, Italy.
authors.forename: Chiara
authors.initials: C
authors.lastname: Verpelli
authors.forename: Elena
authors.initials: E
authors.lastname: Dvoretskova
authors.forename: Cinzia
authors.initials: C
authors.lastname: Vicidomini
authors.forename: Francesca
authors.initials: F
authors.lastname: Rossi
authors.forename: Michela
authors.initials: M
authors.lastname: Chiappalone
authors.forename: Michael
authors.initials: M
authors.lastname: Schoen
authors.forename: Bruno
authors.initials: B
authors.lastname: Di Stefano
authors.forename: Renato
authors.initials: R
authors.lastname: Mantegazza
authors.forename: Vania
authors.initials: V
authors.lastname: Broccoli
authors.forename: Tobias M
authors.initials: TM
authors.lastname: Böckers
authors.forename: Alexander
authors.initials: A
authors.lastname: Dityatev
authors.forename: Carlo
authors.initials: C
authors.lastname: Sala
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D049229:Dendritic Spines / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D009419:Nerve Tissue Proteins; D009474:Neurons / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D064529:Receptor, Metabotropic Glutamate 5; D018091:Receptors, AMPA / Q000378:metabolism; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D015398:Signal Transduction; D013569:Synapses / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C578936:Grm5 protein, mouse; C578937:Grm5 protein, rat; D009419:Nerve Tissue Proteins; D064529:Receptor, Metabotropic Glutamate 5; D018091:Receptors, AMPA; D018094:Receptors, Metabotropic Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; C120532:Shank3 protein, rat