Restoring Glutamate receptosome dynamics at synapses rescues Autism-like deficits in Shank3-deficient mice

Abstract

Shank3 monogenic mutations lead to Autism Spectrum Disorders (ASD). Shank3 is part of the glutamate receptosome that physically links ionotropic NMDA receptors to metabotropic mGlu5 receptors through interactions with scaffolding proteins PSD95-GKAP-Shank3-Homer. A main physiological function of the glutamate receptosome is to control NMDA synaptic function that is required for plasticity induction. Intact glutamate receptosome supports glutamate receptors activation and plasticity induction, while glutamate receptosome disruption blocks receptors activity, preventing the induction of subsequent plasticity. Despite possible impact on metaplasticity and cognitive behaviors, scaffold interaction dynamics and their consequences are poorly defined. Here we used mGlu5-Homer interaction as a biosensor of glutamate receptosome integrity to report changes of NMDA synaptic function. Combining BRET imaging and electrophysiology, we show that a transient neuronal depolarization inducing NMDA-dependent plasticity disrupts glutamate receptosome in a long-lasting manner at synapses and induces signaling required for the expression of the initiated neuronal plasticity such as ERK and mTOR pathways. Glutamate receptosome disruption also decreases NMDA/AMPA currents ratio, freezing the sensitivity of the synapse to subsequent changes of neuronal activity. These data show the importance of a fine-tuning of protein-protein interactions within glutamate receptosome, driven by changes of neuronal activity, to control plasticity. In a mouse model of ASD, a truncated mutant form of Shank3 prevents the integrity of the glutamate receptosome. These mice display altered plasticity, anxiety-like and stereotyped behaviors. Interestingly, repairing the integrity of glutamate receptosome and its sensitivity to the neuronal activity rescued synaptic transmission, plasticity and some behavioral traits of Shank3∆C mice. Altogether, our findings characterize mechanisms by which Shank3 mutations cause ASD and highlight scaffold dynamics as new therapeutic target.

Activity dependent dissociation of the Homer1 interactome

“…We next turned our attention to the activity-dependence of these interactions. We 20 , 21 and others 11 , 15 have previously reported that Homer1 dissociates from mGlu5 (and other interactors) following KCl treatment of cultured neurons or acute cortical slices stimulated in vitro. We compared peptides IP’d from WT-KCL treated mouse brain slices with those IP’d from KO-KCL-treated slices using identical methods as above.…”

“…Release from the Homer scaffold can have profound effects on the activity of the Homer binding partner. By binding to the Shank–Homer scaffold, mGlu5 is spatially segregated from NMDARs, which is important for downstream signaling through ERK and mTOR pathways 15 . When mGlu5 releases from the Homer scaffold, it physically associates with NMDARs, and prevents NMDAR-mediated activation of these pathways 15 – 17 .…”

“…By binding to the Shank–Homer scaffold, mGlu5 is spatially segregated from NMDARs, which is important for downstream signaling through ERK and mTOR pathways 15 . When mGlu5 releases from the Homer scaffold, it physically associates with NMDARs, and prevents NMDAR-mediated activation of these pathways 15 – 17 . This may shut synapses “off” following activity, so that plasticity in response to a strong input can proceed without interference from subsequent incoming stimuli.…”

“…This may shut synapses “off” following activity, so that plasticity in response to a strong input can proceed without interference from subsequent incoming stimuli. In Shank3 KO mice, the regulation of NMDA signaling and synaptic plasticity is disrupted, and can be rescued by the expression of an artificial scaffold linking mGlu5 to the PSD 15 . Similarly, in Fragile X syndrome, mGlu5-Homer disruption seems play an active role in disease pathogenesis 11 , 18 , 19 .…”

Targeting Shank3 deficiency and paresthesia in autism spectrum disorder: A brief review

“…Many human SHANK3 mutations map to exon 21 and are associated with moderate to severe intellectual disability (D'Antoni et al, 2014;Mossa et al, 2021;Purushotham et al, 2022). Mutations in the pro-domain region of exon 21 were not associated with altered pathophysiology (Shi et al, 2017;Moutin et al, 2021). One possible explanation is that exon 21 is present in most SHANK3 isotype surrogates (Moutin et al, 2021).…”