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Rôle de la β1,3-Galactosyltransférase 6 (β3GalT6) dans la pathogénie d’une maladie génétique rare, les syndromes d’Ehlers-Danlos (SED)

Abstract : Proteoglycans (PGs) are major components of cell plasma membranes and extracellular matrix. These macromolecules play an important role in matrix organization of connective tissues and in cell signaling or embryonic and post-natal development. PGs are composed of glycosaminoglycan (GAG) chains covalently attached to a core protein through a tetrasaccharide linkage ßGlucuronic acid-ß1,3-Galactose-ß1,3-Galactose-ß1,4-Xylose-ß1-O-ß. The addition of the third residue (galactose) is catalyzed by the ß1,3-Galactosyltransferase 6 (ß3GalT6), a key glycosyltransferase in GAG initiation. Our group and others discovered that mutations of ß3GalT6 are associated to a spondylodysplastic form of Ehlers-Danlos Syndrome (spEDS), a severe connective tissue disorder characterized by skin and bone fragility, musculoskeletal malformations, delayed wound healing, joint hyperlaxity and intellectual disabilities. The objectives of this project is to understand the functional and structural consequences of ß3GalT6 mutations in the development of spEDS, (i) achieving the molecular and functional characterization of the recombinant human β3GalT6 and (ii) to develop cellular models (as ß3GalT6 KO cells) to study the impact of genetic deficiency on cells metabolism, precisely on GAGs synthesis. The first part of the project is dedicated to the determination of mutation impact on the ß3GalT6 function. For this, we produce and purify several truncated soluble forms of hß3GalT6 in fusion to Maltose Binding Protein. The enzymatic activity tests have determined a KM of 30 µM and a kcat of 0,05 min-1 on wild-type enzyme. ß3GalT6 mutants will be further analyzed using the same approach. The second part of the project is achieving to develop a ß3GalT6 deficient cell model using the CRISPR/Cas 9 technology. Deficient clones obtained present (i) a low level of RNA expression, (ii) an absence of galactosyltransferase activity and (iii) a defect on endogenous GAG synthesis or with exogenous substrate. We also analyze the capacity for WT β3GalT6 and two mutants (Asp207His and Gly217Ser) to restore GAGs synthesis in deficient cells. From this work, we better understand the implication of β3GalT6 in the pathology of spEDS and relationships between ß3GalT6 loss of function, cellular consequences of genetic defect. Those results linked with the severity of spEDS clinical symptoms observed in patients, would help clinicians with management and clinical monitoring of spEDS patients.
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Submitted on : Monday, October 12, 2020 - 3:27:55 PM
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Benjamin Jolivet. Rôle de la β1,3-Galactosyltransférase 6 (β3GalT6) dans la pathogénie d’une maladie génétique rare, les syndromes d’Ehlers-Danlos (SED). Biochimie, Biologie Moléculaire. Université de Lorraine, 2020. Français. ⟨NNT : 2020LORR0085⟩. ⟨tel-02964603⟩



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