Le dynamisme du phénoptype microglial dans la pathogénèse de la sclérose latérale amyotrophique

Authors: Béland, Louis-Charles
Advisor: Kriz, Jasna
Other Title(s): Dynamisme du phénotype microglial dans la pathogénèse de la sclérose latérale amyotrophique
Abstract: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder that leads to motoneuron loss, progressive paralysis and death a few years after the first symptoms. As every other neurodegenerative disorder, inflammation is a main component of ALS pathogenesis. One of the cell type implicated in this inflammation, the microglia, is the central subject of this thesis. With the emergence of the symptoms, microglia transforms from an anti-inflammatory and neuroprotective phenotype to an aberrant and neurotoxic phenotype. It is necessary to elucidate the cellular mechanisms underlying this phenotypic change and the factors maintaining these phenotypes to allow the development of effective inflammation-targeting therapies. In this thesis we seek to identify, using multiple molecular tools and animal models, the microglial signature at the different stage of the disease. During the symptomatic stage, we identified the immunosuppressive cytokine IL-10 to be responsible for maintaining the anti-inflammatory phenotype. This cytokine is at the same time produced and recognized by microglial cells. Blocking IL-10 receptor accelerated disease progression and shortened survival in a mouse model. Moreover, the augmentation of the expression of IL-10, using a viral vector, slowed disease progression and lengthened lifespan in the same mouse model. In order to understand the cellular mechanisms implicated in the microglial phenotypic change in ALS, we used a system-model for the microglia-specific molecular profiling. This tool, EDTA-TRAP, consists in the microglial poly-ribosome immunopurification and the subsequent identification of in-translation mRNAs and proteins sequestered on these ribosomes. It was possible to identify a strong mismatch in the nature of the most regulated mRNAs and proteins. The transcriptomic profile of symptomatic microglia denotes a phagocytic and possible neuroprotective function for microglia while its proteomic profile is proliferative and potentially neurotoxic. The discrepancy between these two profiles is explained by the repression of immune gene mRNA translation by a mechanism implicating the interaction of their 3'UTR and the RNA-binding protein SRSF3. The phosphorylated form of SRSF3 specifically accumulates in microglia cytoplasm proportionally with disease progression. The decrease of SRSF3 expression by an interfering oligonucleotide restores immune mRNA translation and the microglial phagocytic function. This leads to and slower disease progression and a longer survival in a mouse model. Hence, the use of an interfering oligonucleotide against SRSF3 could be a new therapeutic avenue in ALS treatment. The understanding of the diverse cellular mechanisms implicating SRSF3 is important in elucidating its dynamic function in ALS. SRSF3 is the shortest protein from the SR family. This family can be distinguished by their structure : one or two N-terminal RNA recognition motif and a C-terminal highly phosphorylatable arginine and serine rich domain. SRSF3 can be phosphorylated in the nucleus by the CLK1 kinase or in the nucleus and the cytoplasm by the SRPK kinases. SRSF3 is implicated in splicing, nucleocytoplasmic transport and translation, among others. The deregulation of the expression level or the phosphorylation of SRSF3 can drastically change its role in the cell. Hence, SRSF3 is implicated in many diseases such as cancer, viral infection and ALS. The cellular mechanisms governing SRSF3 dynamism should then by well understood in order to make the interfering oligonucleotide against SRSF3 an efficient therapy to treat ALS.
Document Type: Thèse de doctorat
Issue Date: 2021
Open Access Date: 5 July 2021
Permalink: http://hdl.handle.net/20.500.11794/69506
Grantor: Université Laval
Collection:Thèses et mémoires

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