Rôle de la cholestérol hydroxylase CYP46A1 dans le métabolisme du cholestérol et les mécanismes de neuroprotection dans la maladie de Huntington

Huntington’s disease (HD) is an autosomal dominant neurodegenerative disease caused by abnormal CAG expansion on huntingtin’s gene. Recently, altered brain cholesterol homeostasis has been implicated in HD. Particularly, the expression of CYP46A1, the rate-limiting enzyme for cholesterol degradation in the brain, is decreased in patients’ putamen and in the striatum of HD mouse models. We restored CYP46A1 expression into the striatum of the zQ175 mice. Behavioral, neuropathological and molecular tests were performed and showed an improvement of locomotor activity and histological landmarks. Cholesterol homeostasis was restored with an increase of cholesterol degradation and synthesis. CYP46A1 induced a new transcriptional signature, with restoration of pathways involved in autophagy, proteasome, synaptic communication and axonal transport, which are known to be dysfunctional in HD. CYP46A1 improved synaptic transmission and spine density in the striatum of the zQ175 mice. Aggregate clearance mediated by autophagy and proteasome was increased after CYP46A1 expression. Finally, BDNF and TrkB transport were enhanced by CY46A1 in HD in vitro models. Overall, CYP46A1 restoration alleviates the zQ175 pathological phenotype through a global compensation. To gain further insights into CYP46A1 neuroprotection, a cell sorting strategy was set up to study the transcriptomic and lipidomic signature in purified neurons and astrocytes. This method will lead to a greater understanding of cell-type-specific regulations and cell communication. Altogether, this project gave new insights into the potential application of CYP46A1 restoration as a therapeutic strategy in HD.La maladie de Huntington (MH) est une maladie génétique autosomique dominante, causée par une augmentation du nombre de CAG sur le gène de la huntingtin. L’homéostasie du cholestérol cérébral est altérée dans la MH. L’expression de CYP46A1, enzyme neuronale catabolisant le cholestérol dans le cerveau, est diminuée dans le putamen des patients et dans le striatum de souris modèles de la MH. Après restauration de l’expression de CYP46A1 dans le striatum des souris Knock-In zQ175, les capacités locomotrices sont améliorées, l’agrégation de la huntingtine mutée est diminuée, l’atrophie neuronale est limitée et le métabolisme du cholestérol est stimulé. Une nouvelle signature transcriptionnelle est induite par CYP46A1, avec une restauration des voies impliquées dans l'autophagie, le protéasome, la communication synaptique et le transport axonal, connues pour leur dysfonctionnement dans la MH. CYP46A1 améliore la transmission synaptique et augmente la densité en épines synaptiques. L'élimination des agrégats par autophagie et par le protéasome est augmentée avec CYP46A1. Enfin, le transport de BDNF et de TrkB est amélioré par CYP46A1 dans un modèle in vitro de la MH. Ces résultats révèlent l'effet pléiotrope et bénéfique de la régulation du métabolisme du cholestérol dans la MH. Pour approfondir cette étude, une technique de tri cellulaire a été mise au point, afin de séparer les neurones et les astrocytes à partir de striatum de souris, pour étudier les régulations transcriptomique et lipidomique de ces deux populations. Cette étude permettra d’identifier de nouvelles cibles impliquées dans la neuroprotection par CYP46A1 et présentant un intérêt thérapeutique dans la MH

Altered Cholesterol Homeostasis in Huntington’s Disease

International audienceHuntington's disease (HD) is an autosomal dominant genetic disorder caused by an expansion of the CAG repeat in the first exon of Huntingtin's gene. The associated neurodegeneration mainly affects the striatum and the cortex at early stages and progressively spreads to other brain structures. Targeting HD at its earlier stages is under intense investigation. Numerous drugs were tested, with a rate of success of only 3.5% approved molecules used as symptomatic treatment. The restoration of cholesterol metabolism, which is central to the brain homeostasis and strongly altered in HD, could be an interesting disease-modifying strategy. Cholesterol is an essential membrane component in the central nervous system (CNS); alterations of its homeostasis have deleterious consequences on neuronal functions. The levels of several sterols, upstream of cholesterol, are markedly decreased within the striatum of HD mouse model. Transcription of cholesterol biosynthetic genes is reduced in HD cell and mouse models as well as post-mortem striatal and cortical tissues from HD patients. Since the dynamic of brain cholesterol metabolism is complex, it is essential to establish the best method to target it in HD. Cholesterol, which does not cross the blood-brainbarrier, is locally synthesized and renewed within the brain. All cell types in the CNS synthesize cholesterol during development but as they progress through adulthood, neurons down-regulate their cholesterol synthesis and turn to astrocytes for their full supply. Cellular levels of cholesterol reflect the dynamic balance between synthesis, uptake and export, all integrated into the context of the cross talk between neurons and glial cells. In this review, we describe the latest advances regarding the role of cholesterol deregulation in neuronal functions and how this could be a determinant factor in neuronal degeneration and HD progression. The pathways and major mechanisms by which cholesterol and sterols are regulated in the CNS will be described. From this overview, we discuss the main clinical strategies for manipulating cholesterol metabolism in the CNS, and how to reinstate a proper balance in HD

Propensity for somatic expansion increases over the course of life in Huntington disease

International audienceRecent work on Huntington disease (HD) suggests that somatic instability of CAG repeat tracts, which can expand into the hundreds in neurons, explains clinical outcomes better than the length of the inherited allele. Here, we measured somatic expansion in blood samples collected from the same 50 HD mutation carriers over a twenty-year period, along with post-mortem tissue from 15 adults and 7 fetal mutation carriers, to examine somatic expansions at different stages of life. Post-mortem brains, as previously reported, had the greatest expansions, but fetal cortex had virtually none. Somatic instability in blood increased with age, despite blood cells being short-lived compared to neurons, and was driven mostly by CAG repeat length, then by age at sampling and by interaction between these two variables. Expansion rates were higher in symptomatic subjects. These data lend support to a previously proposed computational model of somatic instability-driven disease

CYP46A1 protects against NMDA-mediated excitotoxicity in Huntington's disease: Analysis of lipid raft content

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CYP46A1 gene therapy deciphers the role of brain cholesterol metabolism in Huntington’s disease

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Structural and Functional Characterization of the Interaction of Snapin with the Dopamine Transporter: Differential Modulation of Psychostimulant Actions

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