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Thesis defense – Yadaly Gassama

31 May 2022 / 13:30

Yadaly Gassama
Thoumine’s team, IINS

Thesis surpervisor:
Alexandre Favereaux.

Venue: Centre Broca Nouvelle-Aquitaine

Defense in french


Extracellular vesicles in the central nervous system: physiology, pathology and tool development


Extracellular vesicles (or EVs) are vesicular bodies used as a communication tool by a variety of cell types. They contain a multitude of bioactive molecules such as proteins, nucleic acid (DNA and RNA) as well as lipids. This enables them to have a direct action on the recipient cells they fuse with, by delivering their content directly into the cells. EVs are involved in numerous physiological but also pathological processes such as neuronal communication, metastasis formation or immune system evasion. In the last few years, the number of studies including EVs has grown exponentially, mainly due to the development of new tools and techniques to study them. However, technological progress is still needed in the EV field especially regarding the study of EVs depending on their cellular origin. Indeed, for now, it is impossible to collect EVs released by a specific cell type except from a pure in vitro culture that does not reflect the physiological environment the cell is usually in. The first part of my thesis work touched upon the technological development of such a tool: we designed a proximity labeling approach (APEX2) in extracellular vesicles using a fusion protein containing both the APEX2 enzyme and a protein present in extracellular vesicles. The creation of this tool allowed us to collect specifically proteins present in extracellular vesicles containing our construct of interest. This tool represents a big step forward to the purification of cell type specific EV content.

The other part of my work dealt with the study of the EVs’ microRNA (miRNA) content in both physiological and pathological context. We conducted a transcriptomic analysis on miRNAs purified from extracellular vesicles produced by astrocytes, a key cell type involved in the regulation of synaptic transmission. This transcriptomic study has been combined with an in silico study where we tried to analyze and predict the potential targets of the most
upregulated miRNAs in the EVs after stimulating astrocytes with ATP. This allowed us to gain good insight on the different potential downregulated genes as well as the implicated signaling pathways/cellular processes. The last part of my work consisted in working on a cellular model of glioblastoma, a type of brain cancer which currently does not have any therapeutic solution. The main goal was to understand the underlying mechanisms regarding
cancer invasion and the role of EVs in this invasion. Similarly to the previous study, we combined a transcriptomic approach with an in silico study on miRNAs extracted from EVs produced by U87 cell, a glioblastoma cell line. This allowed us to identify a list of upregulated miRNAs in our condition of interest, and put together a putative target genes list and highlight potential pathways, signaling pathways as well as cellular processes that could be affected
by the presence of thoses EVs, and could explain the increased tumor invasion. To conclude, this thesis has been focusing on extracellular vesicles, where we worked on both technological development with the creation of tools that will allow in the future a better understanding of EVs, but also on the specific study of EVs in the CNS in both physiological (astrocytes) and pathological (glioblastoma) context to try and specifically decipher the role of EVs in certain pathologies like cancer.

Keywords: extracellular vesicles, exosomes, technological development, central nervous system, astrocyte, glioblastoma

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31 May 2022
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