Regulation of synapse development, function and plasticity by the extracellular matrix of the central nervous system
Final Report Abstract
Chemical synapses represent key structures for the communication between neurons of the nervous system, consist of a pre- and a post-synapse and mediate the rapid and efficient signal transmission between neurons. Astrocytes surround synapses and affect synaptic strength and plasticity, whereby astrocytes and neurons form the so-called tripartite synapse. Astrocytes release nutrients, neurotrophins, cytokines, neurotransmitters and glycoproteins and chondroitinsulfate proteoglycans (CSPGs) of the extracellular matrix (ECM). In a project funded within the SPP "Neuroglia and Synapse" the laboratory began to explore functions of the neural ECM for synapse formation. To this end, a culture system for primary embryonic hippocampal neurons was developed that allows for the analysis of synapse formation in vitro. Using this system, we have been able to demonstrate that CSPGs regulate synapse density on neuronal surfaces and influence the amplitude of miniature excitatory postsynaptic currents (mEPSCs) of hippocampal neurons. The analysis of a quadruple knockout mouse mutant that misses the CSPGs neurocan and brevican as well as the glycoproteins tenascin-C and tenascin-R revealed that the neural ECM regulates synapse density within the first two weeks of culture and is required for synapse stabilization and the formation of ECM superstructures designated as perineuronal nets (PNNs) in medium term. Quadruple knockout neurons displayed a deficit of synaptic transmission that manifested in reduced mIPSCS and mEPSC frequencies. Based on these results we have developed three hypotheses that were investigated in the present proposal. The first hypothesis posits that the ECM environment regulates the expression of genes that are relevant for synapse formation and function and was confirmed by transcriptome analyses in combination with multielectrode array (MEA) analysis in vitro and in vivo recordings using implanted electrodes. The second hypothesis claims that PNN structures are modified in the quadruppel knockout tissue. This assumption could be confirmed by immunocytochemistry and was elaborated further using high-resolution standard emission depletion (STED) as well as structured illumination (SIM) microscopy. In particular, the fine structure of PNNs appeared sensitive to pathophysiological alterations in a stroke model. Thereby, plastic reorganization of synapses in lesion territories after ischemia may be explained. The third hypothesis proposes that the genetic changes of the quadruple mutant neurons and PNNs modify the activity patterns of neuronal networks. Using the multi electrode array (MEA) technology the network activities of wild type and mutant neurons were compared. A significant shift of the ratio of excitation to inhibition could be detected that resulted in enhanced activity in neural networks in vitro. Thus, the ECM intervenes in the balance of excitatory and inhibitory synapses. This proved an exciting observation because the excitation versus inhibition ratio is altered in neuropsychiatric diseases. Consistent with this, recent genetic and neuropathological investigations have evidenced an association of ECM genes, for example of the CSPG Neurocan, with neuropsychiatric diseases. We used our in vitro model to test the effects of first and second generation antipsychotics on the biology of neurons. We could show that the treatment with neuropharmacological drugs impacts synapse formation and the ratio of excitation versus inhibition in neuronal networks. In conclusion, the model of the quadruple knockout mouse offers a unique opportunity to investigate the biological effects of the ECM and PNN structures in the context of synaptic functions within neuronal networks and to develop concepts relating to the significance of ECM changes in the realm of psychiatric diseases.
Publications
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(2016) First and second generation antipsychotics differentially affect structural and functional properties of rat hippocampal neuron synapses. Neuroscience 337:117-130
Gottschling C, Geissler M, Springer G, Wolf R, Juckel G, Faissner A
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(2016) Neuron-Glia Interactions in Neural Plasticity: Contributions of Neural Extracellular Matrix and Perineuronal Nets. Neural Plast 2016:5214961
Dzyubenko E, Gottschling C, Faissner A
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(2016) The Indirect Neuron-astrocyte Coculture Assay: An In Vitro Set-up for the Detailed Investigation of Neuron-glia Interactions. Journal of visualized experiments : JoVE
Gottschling C, Dzyubenko E, Geissler M, Faissner A
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(2017) Intrinsic cellular and molecular properties of in vivo hippocampal synaptic plasticity are altered in the absence of key synaptic matrix molecules. Hippocampus 27:920-933
Jansen S, Gottschling C, Faissner A, Manahan-Vaughan D
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(2017) The antipsychotic drugs olanzapine and haloperidol modify network connectivity and spontaneous activity of neural networks in vitro. Sci Rep 7:11609
Dzyubenko E, Juckel G, Faissner A
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(2018) Topological remodeling of cortical perineuronal nets in focal cerebral ischemia and mild hypoperfusion. Matrix Biol 74:121-132
Dzyubenko E, Manrique-Castano D, Kleinschnitz C, Faissner A, Hermann DM
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(2019) Elimination of the four extracellular matrix molecules tenascin-C, tenascin-R, brevican and neurocan alters the ratio of excitatory and inhibitory synapses. Sci Rep 9:13939
Gottschling C, Wegrzyn D, Denecke B, Faissner A
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(2020) Deletion of the Nucleotide Exchange Factor Vav3 Enhances Axonal Complexity and Synapse Formation but Tampers Activity of Hippocampal Neuronal Networks In Vitro. Int J Mol Sci: 21
Wegrzyn D, Wegrzyn C, Tedford K, Fischer KD, Faissner A
