The Role of Local Protein Degradation in Neurotransmitter Release and Homeostatic Plasticity

Projektinformationen

SynDegrade

ID Finanzhilfevereinbarung: 679881

DOI

10.3030/679881

Projekt abgeschlossen

EK-Unterschriftsdatum 10 März 2016

Startdatum 1 Mai 2016

Enddatum 30 April 2022

Finanziert unter

• EXCELLENT SCIENCE - European Research Council (ERC)

Gesamtkosten

€ 1 489 340,95

EU-Beitrag

€ 1 489 340,95

Koordiniert durch

UNIVERSITAT ZURICH
Switzerland

Periodic Reporting for period 4 - SynDegrade (The Role of Local Protein Degradation in Neurotransmitter Release and Homeostatic Plasticity)

Berichtszeitraum: 2020-11-01 bis 2022-04-30

Zusammenfassung vom Kontext und den Gesamtzielen des Projekts

Background:
Robust animal behavior presupposes stable neural function. Chemical synapses are the major sites of information transfer in the nervous system. While many synapses reliably transmit information for decades, the proteins determining synaptic transmission have half-lives of hours to months. It is currently unclear how stable synaptic transmission can be achieved in the light of constant protein turnover.
Several neurological diseases, such autism spectrum disorder, have been linked to unstable neural function. Moreover, maladaptive protein turnover has been implicated in a number of neural pathologies. Synaptic protein abundance and synaptic transmission are stabilized by homeostatic mechanisms. Yet, the relationship between the homeostatic control of protein abundance, or proteostasis, and the homeostatic maintenance of synaptic transmission remains enigmatic.

General objectives:
The major goal of this project was to discover molecular links between the mechanisms controlling local protein turnover at synapses and the homeostatic stabilization of synaptic transmission. To this end, we focused on the role of a major protein degradation pathway – the Ubiquitin Proteasome System (UPS) – in regulating neurotransmitter release and homeostatic stabilization of synaptic transmission.

Relevance:
The results of our basic research are expected to advance our understanding of the role of homeostatic stabilization of neural activity. In this regard, the implication of neuropsychiatric disease-related genes in the homeostatic control of synaptic transmission and protein abundance may inform us about the relationship between these genes and the respective pathophysiology. The translation of aspects of our work from Drosophila into the mammalian CNS constitutes a first important step towards bridging the gap between homeostatic regulation of synaptic transmission and neural physiology, as well as pathology in humans. Finally, our discovery of rapid stabilization of synaptic transmission in the mammalian CNS may have implications for neural network simulations, because their stability requires fast compensatory processes with temporal dynamics similar to the form of homeostatic plasticity discovered in this project.

Arbeit, die ab Beginn des Projekts bis zum Ende des durch den Bericht erfassten Berichtszeitraums geleistet wurde, und die wichtigsten bis dahin erzielten Ergebnisse

To systematically investigate the molecular mechanisms mediating UPS-dependent stabilization of synaptic transmission, we combined genetic screens with detailed electrophysiological quantification of synaptic transmission. This approach, which is currently only feasible in Drosophila, established several new molecular links between UPS-mediated protein degradation and homeostatic stabilization of synaptic transmission. In particular, we realized the first systematic analysis of the roles of E3 ubiquitin ligases, a class of enzymes regulating protein degradation-mediated proteostasis, in synaptic transmission. This screen identified several genes encoding for evolutionarily conserved E3 ubiquitin ligases that are required for homeostatic control of neurotransmitter release. Among those genes was thin, the Drosophila homolog of human tripartite motif-containing 32 (TRIM32), a gene linked to several neurological disorders, including autism spectrum disorder and schizophrenia. Furthermore, we revealed that thin acts through dysbindin, a gene linked to homeostatic plasticity in Drosophila and schizophrenia in humans.

Additionally, we studied the nano-architecture of synapses during homeostatic stabilization of synaptic transmission employing super-resolution light microscopy. We discovered that glutamatergic neurotransmitter receptors are arranged in stereotypic ‘nano-rings’ at the Drosophila neuromuscular junction (NMJ). Interestingly, these receptor rings aligned with presynaptic rings formed by proteins located with the nerve terminal. Moreover, these transsynaptically-aligned rings were modulated during homeostatic plasticity, and we identified the first gene that is required for homeostatic regulation of transsynaptic nano-architecture and homeostatic plasticity.

Finally, we provided the first evidence for rapid homeostatic stabilization of synaptic transmission in the mammalian central nervous system (CNS). Studying synaptic transmission in acute brain slices of the mouse cerebellum, we discovered that cerebellar synapses homeostatically regulate synaptic efficacy within minutes upon activity perturbation, at least an order of magnitude faster than previously thought. This is achieved by specific mechanisms that regulate neurotransmitter release from the nerve terminals.

Fortschritte, die über den aktuellen Stand der Technik hinausgehen und voraussichtliche potenzielle Auswirkungen (einschließlich der bis dato erzielten sozioökonomischen Auswirkungen und weiter gefassten gesellschaftlichen Auswirkungen des Projekts)

We realized the first systematic investigation of E3 ubiquitin ligases in the context of synaptic transmission and homeostatic plasticity (Baccino-Calace et al., 2022). The results of this screen allow predicting the roles of those E3 ligases in synaptic function.

The discovery of rapid homeostatic compensation of synaptic transmission through neurotransmitter release regulation on the minute time scale in the mammalian CNS (Delvendahl et al. 2019, Kita et al., 2021) significantly advanced the field, because it was previously thought that (i) homeostatic mechanisms operate on a time scale of hours to days instead of minutes in the mammalian CNS, that (ii) homeostatic stabilization of synaptic transmission in the mammalian CNS is mainly expressed postsynaptically, and (iii) presynaptic homeostatic plasticity only acts in the peripheral nervous system, where it has been mainly studied in Drosophila (Delvendahl and Müller, 2019).

The unexpected discovery of transsynaptically aligned nano-rings and their homeostatic regulation is a major step, since it provides the first evidence for a stereotypic organization of transsynaptic nano-architecture, and because it links homeostatic release modulation to the regulation of transsynaptic nano-architecture (Muttathukunnel et al., https://doi.org/10.1101/2021.06.15.448550)

Cartoon summarizing the results of Baccino-Calace et al., 202