シンポジウム
10 シナプスが担う可塑性と回路恒常性のバランス - 分子的基盤から生体への役割の理解
10 Balancing synapse plasticity and circuit homeostasis - from molecular mechanisms to physiological functions
座長：合田 裕紀子（理化学研究所 脳神経科学研究センター） |
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| 2022年7月1日 9:05～9:28 沖縄コンベンションセンター 劇場棟 第1会場
2S01m-01
Synapse-specific homeostatic responses in mouse cortex
*Tara Keck(1), Samuel J Barnes(2), Georg B Keller(3)
1. University College London, 2. UK Dementia Research Institute at Imperial College London, 3. Friedrich Miescher Institute for Biomedical Research
Keyword: synaptic plasticity, homeostasis, visual cortex, retrosplenial cortex
Homeostatic compensation of neuronal activity is necessary to prevent aberrantly high or low activity levels that could occur, for example, following a loss of peripheral input or recurrent plasticity. Compensatory mechanisms can take several forms, including synaptic adjustments that are anti-correlated with the changes in activity. Our previous work has shown that not all synapses undergo compensatory strengthening following deprivation in vivo, but the functional properties of the affected synapses have not been explored. Here we use repeated two-photon imaging of dendritic spines expressing a genetically encoded calcium indicator, which allows for the repeated measurements of dendritic spine signals before and after sensory deprivation in either the visual cortex or retrosplenial cortex of behaving mice. We show that the synapses that undergo compensatory increases in synaptic strength following sensory deprivation are more strongly correlated with the activity in the network prior to deprivation, whereas the spines that received the most sensory input prior to deprivation, show no change or a small relative decrease in synaptic response strength over the time course of homeostatic changes, independent of the sensory modality that is being deprived. These results suggest that a subset of synaptic homeostatic compensatory mechanisms in vivo may be implemented specifically in the subset dendritic spines whose inputs reflect network-correlated activity, but not just those inputs that have been spared by sensory deprivation. | | 2022年7月1日 9:28～9:51 沖縄コンベンションセンター 劇場棟 第1会場
2S01m-02
A Bidirectional Switch in the Shank3 Phosphorylation State Enables Synaptic Scaling Up or Down
*Gina Turrigiano(1)
1. Brandeis Univesity
Keyword: homeostatic plasticity, Shank3, autism spectrum disorders, synaptic scaling
Homeostatic synaptic plasticity requires widespread remodeling of synaptic signaling and scaffolding networks, but the role of posttranslational modifications in this process have not been systematically studied. Using deepscale, quantitative analysis of the phosphoproteome in mouse neocortical neurons, we found wide-spread and temporally complex changes during synaptic scaling up and down. We observed 424 bidirectionally modulated phosphosites that were strongly enriched for synapse-associated proteins, including S1539 in the ASD-associated synaptic scaffold protein Shank3. Using a parallel proteomic analysis performed on Shank3 isolated from rat neocortical neurons by immunoaffinity, we identified two sites that were hypo-phosphorylated during scaling up and hyper-phosphorylated during scaling down; one (rat S1615) that corresponded to S1539 in mouse, and a second highly conserved site, rat S1586. The phosphorylation status of these sites modified the synaptic localization of Shank3 during scaling protocols, and dephosphorylation of these sites via PP2A activity was essential for the maintenance of synaptic scaling up. Finally, phosphomimetic mutations at these sites prevented scaling up but not down, while phosphodeficient mutations prevented scaling down but not up. Thus, an activity-dependent switch between hypo- and hyperphosphorylation at S1586/ S1615 of Shank3 enables scaling up or down, respectively. Collectively our data show that activity-dependent phosphoproteome dynamics are important for the functional reconfiguration of synaptic scaffolds, and can bias synapses toward upward or downward homeostatic plasticity. | | 2022年7月1日 9:51～10:14 沖縄コンベンションセンター 劇場棟 第1会場
2S01m-03
Astrocytes in the hippocampus: Adding space to time for metaplasticity
*Wickliffe Abraham(1), Owen Jones(1), Shruthi Sateesh(1), Anurag Singh(2)
1. Dept Psych, Univ of Otago, Dunedin, New Zealand, 2. Dept Pharmacol, Univ of Otago, Dunedin, New Zealand
Keyword: Metaplasticity, Astrocytes, Tumor necrosis factor, NMDA receptors
The brain has evolved a large number of mechanisms for maintaining cellular and network homeostasis in the face of ongoing synaptic plasticity, including homeostatic plasticity and heterosynaptic plasticity. Metaplasticity entails a further family of mechanisms that can upregulate or downregulate plasticity capability, as the situation requires. We have been studying a form of heterodendritic metaplasticity in hippocampal area CA1, whereby priming stimulation of afferents in stratum oriens impairs future LTP while enhancing LTD in stratum radiatum. This long-range metaplasticity effect does not rely solely on neuronal mechanisms, but involves activation of at least astrocytes, as shown by its block by calcium-clamping of single patched astrocytes and its absence in IP3R2-KO mice. The whole effect entails a cascade of signalling including ATP, adenosine acting on adenosine A2BRs, tumour necrosis factor acting on TNFR1, inositol triphosphate acting on IP3R2s, and glutamate acting on GluN2B-containing NMDARs. Intriguingly, the effect in CA1 is selective for synapses in stratum radiatum compared to those in stratum oriens and stratum lacunosum-moleculare. More interestingly, the metaplasticity effect extends to medial perforant path synapses in the dentate gyrus both in vitro and in vivo, and in the case of slices, even in the absence of CA3. This effect in the dentate also requires the participation of astrocytes, as also revealed by the astrocyte calcium-clamp technique and IP3R2-KO mice. Taken together, these findings reveal a network-wide, yet pathway-specific, metaplasticity response to prior high-frequency activity. This transient regulation of future activity-dependent plasticity may contribute to the homeostasis of the wider network while also potentially serving an important role in information processing by the hippocampus.
This research has been supported by grants from the Health Research Council of New Zealand and a New Zealand International Doctoral Scholarship. | | 2022年7月1日 10:14～10:37 沖縄コンベンションセンター 劇場棟 第1会場
2S01m-04
生体脳内１細胞でのシナプス活動と分子ダイナミクスのイメージング
Imaging synaptic activity and molecular dynamics in single neurons in vivo
*三國 貴康(1)
1. 新潟大学脳研究所
*Takayasu Mikuni(1)
1. Brain Res Ins, Niigata Univ, Niigata, Japan
Keyword: Synapse, Protein, Imaging, CRISPR-Cas9
A neuron in the brain receives thousands of synaptic inputs, and integrates the input signals to ultimately induce gene expression and molecular trafficking at the appropriate subcellular location and timing. Thus, monitoring synaptic activity and molecular dynamics in a whole single neuron in vivo will give us good information to understand the neuronal computation in the context of various behavioral paradigms in animals. In this talk, we will show our new tools for large-scale monitoring of synaptic activity and molecular dynamics in single neurons in vivo. To monitor synaptic activity, we developed a synaptic calcium sensor and performed two-photon volumetric imaging of calcium activity in hundreds of excitatory synapses in a single neuron in the mouse brain. To monitor molecular dynamics, we combined chemical labeling techniques with CRISPR-Cas9-based genome editing technologies, enabling multi-color labeling of endogenous proteins in spatially and temporally different subcellular pools. Since proteins in spatially and temporally different pools can play different roles in neuronal function, this strategy would provide a valuable readout of the behavior and function of distinct proteins. Using this strategy, we selectively imaged spatially and temporally different pools of various endogenous proteins such as 1) cell-surface and intracellular reserve pools of AMPA-type glutamate receptors, 2) cell-surface AMPA- and NMDA-type glutamate receptors to visualize “silent synapses”, which contain NMDA- but no AMPA-type receptors, 3) pre-existing and newly synthesized CaMKII in 2 hours, and so on. We also achieved quantitative imaging of AMPA-type glutamate receptors in combination with a brain clearing method, detecting thousands of excitatory synapses in a single neuron in the cerebral cortex. Thus, our toolkit will provide a powerful means to monitor how a neuron in the brain receives synaptic inputs and responds at the molecular level. | | 2022年7月1日 10:37～11:00 沖縄コンベンションセンター 劇場棟 第1会場
2S01m-05
Intrinsic synaptic dynamics and distribution scaling of synaptic sizes
*Noam Ziv(1)
1. Technion, Israel Institute of Technology
Keyword: synapse, intrinsic dynamics, synaptic scaling, long-term imaging
Imaging studies reveal that synapses are not truly structures and are better thought of as dynamic assemblies of molecules that move in, out and between synaptic sites. These innate dynamics, combined with continual turnover of synaptic molecules, drive spontaneous changes in synaptic sizes in manners that do not depend on particular activity histories, or for that matter, on activity at all. These inherent dynamics, referred to as intrinsic dynamics, are not without effect. In fact, imaging studies from our lab as well as others show that these intrinsic dynamics are sufficient to produce the full gamut of synaptic sizes, even in networks that have never experienced any spiking activity whatsoever. Importantly, intrinsic dynamics seem to be governed by well characterized stochastic processes which can be fully described by a small number of parameters. These stochastic processes continuously confine synaptic sizes and size distributions, effectively normalizing these in face of continuous change. Moreover, these processes give rise to the typical skewed shape of synaptic size distributions, while their parameters define the scale of these distributions. Consequently, small alterations to these parameters, related to changes in actively levels or neuromodulatory influences for example, result in the scaling of these distributions. Of note, this scaling is not matched by scaling at the individual synapse level and emerges only as a population-level phenomenon. | | | |
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