Le rôle des isoformes de TSPO sur l'érythropoïèse terminale humaine en relation avec le métabolisme du cholestérol

Erythropoiesis is the process of producing mature red blood cells in the bone marrow. It is a long process characterised by successive cell divisions towards the red lineage and a large number of cell changes. During erythroid differentiation, erythroblasts progressively lose their organelles, in particular their mitochondria and nucleus, to become mature red blood cells. This mecanism is highly regulated and involve a lot large number of proteins. Our team has published results showing that transcriptional repression of TSPO1 leads to a defect in enucleation and a delay in the elimination of mitochondria in cord blood cells. TSPO1 is a protein present on the outer membrane of mitochondria. Depending on the cell type, TSPO1 can perform various functions, such as transport of protoporphyrin IX (PPIX) or cholesterol translocation. TSPO2 is an isoform of TSPO that is specific to the erythroid lineage. Loss of function of TSPO2 induces a change in cholesterol localisation and a defect in enucleation. The key objective of this thesis was therefore to gain a better understanding of the modulation of TSPO function and its effects on human terminal erythropoiesis, with a particular focus on cholesterol and its impact on enucleation. To achieve this, we modulated TSPO function using a ligand: NCS1026, which is known to regulate cholesterol import into mature red blood cells and neuroblastoma cells, impacting both TSPO1 and TSPO2. The NCS1026 ligand increases enucleation, without impacting cell proliferation or differentiation kinetics. This phenotype was accompanied by mitochondrial retention and vesicle accumulation at day 14 of differentiation. NCS1026 treatment also induced a change in intracellular cholesterol repair where it exacerbated the decrease in cholesterol content (free and storage forms) during erythroid differentiation. This change in intracellular distribution is not due to a change in cholesterol import. This change in cholesterol levels in cells treated with NCS1026 is also visible in cholesterol-enriched regions. In fact, the treated cells had a greater number of contact points between the mitochondria and the endoplasmic reticulum (MAM).