Mucopolysaccharidosis type IIIB (MPSIIIB) is a lysosomal storage disease (LSD) characterized by accumulation of heparan sulfate oligosaccharides (HSO), which results in progressive mental retardation, neurodegeneration and premature death in children. The underlying mechanisms are poorly understood. Coming to a better understanding of the pathophysiology of MPSIIIB has become a necessity to assess the efficacy of gene therapy treatment regarding loss of neuronal plasticity, and to define the best conditions for treatment. To address the link between HSO accumulation and downstream pathological events, new cell models of MPSIIIB were created. First, induced pluripotent stem cells (iPSc) were generated from fibroblasts of affected children, followed by differentiation of patient-derived iPSc into a neuronal progeny. Second, a HeLa cell model was created in which expression of shRNAs directed against a-N-acetylglucosaminidase (NAGLU), the deficient enzyme in MPSIIIB, is induced by tetracycline. Success in the isolation of these different models was pointed by the presence of cardinal features of MPSIIIB cell pathology. Studies in these models showed that: I) HSO excreted in the extracellular matrix modifies cell perception of environmental cues, affecting downstream signalling pathways with consequences on the Golgi morphology. II) Accumulation of intracellular storage vesicles, a hallmark of LSDs is due to overexpression of the cis-Golgi protein GM130 and subsequent Golgi alterations. It is likely that these vesicles are abnormal lysosomes formed in the cis- and medial-Golgi which are misrouted at an early step of lysosome biogenesis, giving rise to a dead-end compartment. III) Other cell functions controlled by GM130 are affected, including centrosome morphology and microtubule nucleation. These data point to possible consequences on cell polarization, cell migration and neuritogenesis.

La mucopolysaccharidose IIIB (MPSIIIB) est une maladie de surcharge lysosomale (MSL) causée par une accumulation d’oligosaccharides d’héparane sulphate (OHS), induisant chez les enfants atteints un retard mental progressif, une neurodégénérescence et une mort prématurée. Les mécanismes physiopathologiques impliqués sont mal compris. Il est nécessaire d’élucider ces mécanismes, afin d’évaluer l’efficacité d’un traitement par thérapie génique en regard de la perte de la plasticité neuronale, et pour définir les meilleures conditions de traitement. Pour cela, de nouveaux modèles cellulaires de la maladie ont été créés. Des cellules souches pluripotentes induites ont été générées à partir de fibroblastes de patients, lesquelles ont ensuite été différenciées en une lignée neuronale. Un modèle HeLa a également été créé dans lequel l’expression de shRNAs dirigés contre la a-N-acétylglucosaminidase (NAGLU), l’enzyme manquante dans la MPSIIIB, est induite par la tétracycline. Ces modèles ont été isolés avec succès, et présentent les caractéristiques pathologiques fondamentales de la MPSIIIB. L’étude de ces modèles a montré que : I) Les OHS excrétés dans la matrice extracellulaire modifient la perception cellulaire des signaux environnementaux, affectant les voies de signalisation en aval avec des conséquences sur la morphologie du Golgi. II) L’accumulation de vésicules de stockage intracellulaires qui caractérisent les MSLs est due à la surexpression de la protéine cis-golgienne GM130 et aux altérations du Golgi qui en résultent. Ces vésicules sont possiblement des lysosomes anormaux formés dans le Golgi cis et médian qui sont déroutés à une étape précoce de la biogenèse du lysosome, donnant naissance à un compartiment « cul-de-sac ». III) D’autres fonctions cellulaires contrôlées par GM130 sont affectées dont la morphologie du centrosome ou la nucléation des microtubules. Ces données suggèrent de possibles conséquences sur la polarisation et la migration cellulaire, et la neuritogenèse. / Mucopolysaccharidosis type IIIB (MPSIIIB) is a lysosomal storage disease (LSD) characterized by accumulation of heparan sulfate oligosaccharides (HSO), which results in progressive mental retardation, neurodegeneration and premature death in children. The underlying mechanisms are poorly understood. Coming to a better understanding of the pathophysiology of MPSIIIB has become a necessity to assess the efficacy of gene therapy treatment regarding loss of neuronal plasticity, and to define the best conditions for treatment. To address the link between HSO accumulation and downstream pathological events, new cell models of MPSIIIB were created. First, induced pluripotent stem cells (iPSc) were generated from fibroblasts of affected children, followed by differentiation of patient-derived iPSc into a neuronal progeny. Second, a HeLa cell model was created in which expression of shRNAs directed against a-N-acetylglucosaminidase (NAGLU), the deficient enzyme in MPSIIIB, is induced by tetracycline. Success in the isolation of these different models was pointed by the presence of cardinal features of MPSIIIB cell pathology. Studies in these models showed that: I) HSO excreted in the extracellular matrix modifies cell perception of environmental cues, affecting downstream signalling pathways with consequences on the Golgi morphology. II) Accumulation of intracellular storage vesicles, a hallmark of LSDs is due to overexpression of the cis-Golgi protein GM130 and subsequent Golgi alterations. It is likely that these vesicles are abnormal lysosomes formed in the cis- and medial-Golgi which are misrouted at an early step of lysosome biogenesis, giving rise to a dead-end compartment. III) Other cell functions controlled by GM130 are affected, including centrosome morphology and microtubule nucleation. These data point to possible consequences on cell polarization, cell migration and neuritogenesis.