No abstract

Regulation of synaptic neurotransmitter receptor content is a fundamental mechanism for tuning synaptic efficacy during experience-dependent plasticity and behavioral adaptation. However, experimental approaches to track and modify receptor movements in integrated experimental systems are limited. Exploiting AMPA-type glutamate receptors (AMPARs) as a model, we generated a knock-in mouse expressing the biotin acceptor peptide (AP) tag on the GluA2 extracellular N-terminal. Cell-specific introduction of biotin ligase allows the use of monovalent or tetravalent avidin variants to respectively monitor or manipulate the surface mobility of endogenous AMPAR containing biotinylated AP–GluA2 in neuronal subsets. AMPAR immobilization precluded the expression of long-term potentiation and formation of contextual fear memory, allowing target-specific control of the expression of synaptic plasticity and animal behavior. The AP tag knock-in model offers unprecedented access to resolve and control the spatiotemporal dynamics of endogenous receptors, and opens new avenues to study the molecular mechanisms of synaptic plasticity and learning.

Protein tyrosine phosphatase non‐receptor type 4 (PTPN4) encodes non‐receptor protein tyrosine phosphatase implicated in synaptic plasticity and innate immune response. The only report of PTPN4‐associated disease described a neurodevelopmental disorder associated with a whole gene deletion. We describe a child with developmental delay, autistic features, hypotonia, increased immunoglobulin E and dental problems with a novel mosaic de novo variant in PTPN4 (hg19 chr2:g.120620188 T > C, NM_002830.3:p.[Leu72Ser]/c.215T>C) located in domain that controls protein subcellular distribution. Studies in mouse hippocampal neurons transfected with non‐mutated or mutated human PTPN4 showed that despite their similar expression in neurons the mutated protein was absent from dendritic spines. Next, we studied patient's primary blood mononuclear cells' response to lipopolysaccharide stimulation and found no difference from control in phosphorylation of TBK1 and IRF3 (involved in Toll‐like receptor 4 signaling) and induction of cytokines' messenger RNA. We conclude that the PTPN4 p.(Leu72Ser) variant is a likely cause of neurodevelopmental symptoms of our proband whereas its role in immune dysfunction requires further studies.

is a major scaffolding protein of the post-synaptic density (PSD) of a glutamatergic synapse. PSD-95, via interactions with stargazin, anchors AMPA receptors at the synapse and regulates AMPAR currents. The expression of PSD-95 is regulated during synaptic plasticity. It is, however, unknown whether this regulation is required for induction of functional plasticity of glutamatergic synapses. Here, we show that NMDA-induced long-term depression of synaptic transmission (NMDA-LTD) is accompanied by downregulation of PSD-95 protein levels. Using pharmacologic and molecular manipulations, we further demonstrate that the NMDA-induced downregulation of PSD-95 depends on the activation of CaMKII and CaMKII-driven phosphorylation of PSD-95 serine 73. Surprisingly, neither CaMKII activity nor CaMKII-dependent phosphorylation of PSD-95 serine 73 are required for the expression of NMDA-LTD. These results support the hypothesis that synaptic plasticity of AMPARs may occur without dynamic regulation of PSD-95 protein levels. PSD-95 is the major scaffolding protein of a glutamatergic synapse 1 affecting its stability, activity-dependent modifications 2-5 and functional plasticity 6-9. PSD-95 interacts directly with NMDA receptors and with AMPA receptors through an auxiliary protein stargazin 10,11. Interaction of PSD-95 with stargazin regulates synaptic content of AMPARs 10,12,13. In agreement with these findings mice lacking functional PSD-95 protein have greatly enhanced hippocampal, NMDAR-dependent long-term potentiation (LTP), whereas NMDAR-dependent long-term depression (LTD) is absent 6. Conversely, overexpression of PSD-95 occludes LTP 7,8 and decreases the threshold for LTD induction 9. Importantly, PSD-95 is a highly dynamic protein. Upon stimulation, PSD-95 is phosphorylated at serine 73 and transiently removed from the dendritic spine in a CaMKII-dependent manner 2. However, inhibition of this process by mutation of serine 73 to alanine does not affect the propensity to induce LTP 2. Sturgill et al. have also shown that NMDA-LTD provokes rapid destabilization of PSD-95 in the spine head 4. It is yet unknown whether LTD-induced elimination of PSD-95 protein from the dendritic spine is necessary for the expression of LTD. Here, using organotypic hippocampal cultures (OHC) we confirmed that PSD-95 protein levels were downregulated in the stratum radiatum of CA1 hippocampal field after induction of NMDA-LTD 4. Since it has been shown that CaMKII-dependent phosphorylation of PSD-95 on serine 73 (PSD-95:Ser73) regulates the binding of PSD-95 to NMDAR 14 and translocation of PSD-95 from activated spines 2 , we checked if CaMKII contributes to LTD-induced downregulation of PSD-95. Using pharmacological manipulations and AAV transfection approach we found that NMDA-LTD-induced downregulation of PSD-95 levels is regulated by CaMKII activity and CaMKII-driven phosphorylation of PSD-95:Ser73. Surprisingly, we also observed that neither CaMKII activity nor CaMKII-dependent phosphorylation of PSD-95:Ser73 are necessary for the ex...

The updating of contextual memories is essential for survival in a changing environment. Accumulating data indicate that the dorsal CA1 area (dCA1) contributes to this process. However, the cellular and molecular mechanisms of contextual fear memory updating remain poorly understood. Postsynaptic density protein 95 (PSD-95) regulates the structure and function of glutamatergic synapses. Here, using dCA1-targeted genetic manipulations in vivo, combined with ex vivo 3D electron microscopy and electrophysiology, we identify a novel, synaptic mechanism that is induced during attenuation of contextual fear memories and involves phosphorylation of PSD-95 at Serine 73 in dCA1. Our data provide the proof that PSD-95–dependent synaptic plasticity in dCA1 is required for updating of contextual fear memory.

The updating of contextual memories is essential for survival in a changing environment. Accumulating data indicate that the dorsal CA1 area (dCA1) contributes to this process. However, the cellular and molecular mechanisms of contextual fear memory updating remain poorly understood. Postsynaptic density protein 95 (PSD-95) regulates the structure and function of glutamatergic synapses. Here, using dCA1-targeted genetic manipulations in vivo, combined with ex vivo 3D electron microscopy and electrophysiology, we identify a novel, synaptic mechanism that is induced during attenuation of contextual fear memories and involves phosphorylation of PSD-95 at Serine 73 in dCA1. Our data provide the proof that PSD-95-dependent synaptic plasticity in dCA1 is required for updating of contextual fear memory.

Regulation of synaptic neurotransmitter receptor content is a fundamental mechanism for tuning synaptic efficacy during experience-dependent plasticity and behavioral adaptation. However, experimental approaches to track and modify receptor movements in integrated experimental systems are limited. Exploiting AMPA-type glutamate receptors (AMPAR) as a model, we generated a knock-in mouse expressing the biotin acceptor peptide (AP) tag on the GluA2 extracellular N-terminus. Cell-specific introduction of biotin ligase allows the use of monovalent or tetravalent avidin variants to respectively monitor or manipulate the surface mobility of endogenous AMPAR containing biotinylated AP-GluA2 in neuronal subsets. AMPAR immobilization precluded the expression of long-term potentiation and formation of contextual fear memory, allowing for target-specific control of the expression of synaptic plasticity and animal behavior. The AP tag knock-in model offers unprecedented access to resolve and control the spatiotemporal dynamics of endogenous receptors, and opens new avenues to study the molecular mechanisms of synaptic plasticity and learning.

As microRNAs have emerged to be important regulators of molecular events occurring at the synapses, the new questions about their regulatory effect on the behavior have araised. In the present study, we show for the first time that the dysregulated specific targeting of miR132 to Mmp9 mRNA in the mouse brain results in the increased level of Mmp9 protein, which affects synaptic plasticity and has an effect on memory formation. Our data points at the importance of complex and precise regulation of the Mmp9 level by miR132 in the brain.