The turnover of synaptic proteins: numbers, principles, and functional implications

• Applicants: Eugenio Fornasiero, Ph.D.; Professor Silvio-Olivier Rizzoli, Ph.D.
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells
• Term: since 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 273518920

Aged proteins need to be replaced by newly synthesized ones, to avoid the accumulation of old and damaged components that could lead to cellular dysfunction. This process, commonly known as protein turnover, is still poorly understood, especially in large and complex cells, as the neurons. In our recent funding period, we studied protein turnover in the context of brain aging, to clarify how defects in this pathway relate to brain dysfunction. We measured protein turnover in aged mice, comparing different brain regions and subcellular fractions, and we also analyzed protein amounts in 11 different mouse models of aging. We analyzed specific elements in dedicated experiments, as different myelin forms, synaptic vesicles and the extracellular matrix. Finally, we also compared protein ages with their own functionality, in different contexts. We will now focus on the question of how protein turnover in the presynapse relates to synaptic function. We aim to understand how individual proteins can be provided to synapses in a fashion that takes into account the local needs, from activity to plasticity. We have previously demonstrated that such a process takes place in synapses, but no mechanism is known. In brief, we found that several morphological features of the presynapse, and especially the size of the synaptic vesicle cluster (SVC, defined as the assembly of vesicles occupying the presynapse), correlate with protein turnover. This correlation can be explained by an influence of the SVC on synaptic mRNA organization and translation, or by direct regulation of these processes through a key SVC component. We already determined the identity of such a component, the elongation factor 1-alpha (eEF1A), which we propose to study in several objectives. We will investigate in detail how synapse functionality relates to the eEF1A dynamics, and whether this protein exerts a direct influence on fundamental parameters as local translation. We will connect SVC and synapse morphology to synapse function, and to eEF1A abundance. We will also test synapse and eEF1A behavior during aging, both in vivo and in more controlled in vitro environments. We will combine a series of advance methods, from ultra-resolution fluorescence imaging to multiplexing and advanced mass spectrometry approaches, both in solution and in an imaging context. Our results will provide a new understanding of synaptic turnover, and should finally clarify the link between this process and synaptic function, both in young adult and aging animals.

• DFG Programme: Research Grants