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Les astrocytes réactifs, des partenaires anti-agrégants dans la maladie de Huntington : identification des mécanismes impliqués dans le dialogue neurone-astrocyte

Laurene Abjean 1
1 LMN - Laboratoire des Maladies Neurodégénératives - UMR 9199
MIRCEN - Service MIRCEN : DRF/JACOB, CNRS - Centre National de la Recherche Scientifique : UMR 9199
Abstract : Huntington’s disease (HD) is a hereditary neurodegenerative disease caused by an expansion of CAG codons in the Huntingtin gene. It is characterized by the death of striatal neurons and the presence of mutant Huntingtin (mHtt) aggregates. In pathological conditions, as in HD, astrocytes change and become reactive. Astrocyte reactivity is characterized by morphological and significant transcriptomic changes. Astrocytes are essential for the proper functioning of neurons but the functional changes associated with reactivity are still unclear.To better understand the roles played by reactive astrocytes in HD, we took advantage of our recently developed viral vectors that infect selectively astrocytes in vivo and either block or induce reactivity, through manipulation of the JAK2-STAT3 pathway. We used these vectors in two complementary mouse models of HD and found that reactive astrocytes decrease the number and the size of mHtt aggregates that mainly form in neurons. Reduced mHtt aggregation was associated with improvement of neuronal alterations observed in our mouse models of HD. A genome-wide transcriptomic analysis was performed on acutely sorted reactive astrocytes and revealed an enrichment in genes linked to proteolysis. Lysosomal and proteosomal activities were also increased in reactive astrocytes in HD mice. Moreover, we show that reactive astrocytes degrade more efficiently their own mHtt aggregates, suggesting that these cells could siphon mHtt away from neurons. Alternatively, several chaperones were induced in reactive astrocytes. In particular, the co-chaperone DNAJB1/Hsp40 was upregulated in reactive astrocytes and was present in exosomal fraction from HD mouse striatum. Loss and gain of function experiments suggest that this chaperone is involved in the beneficial effects of reactive astrocytes on mHtt aggregation and neuronal status. Therefore, reactive astrocytes could release anti-aggregation proteins that could promote mHtt clearance in neurons.Overall, our data show that astrocytes, by becoming reactive in HD, develop a protective response that involves complex bidirectional signaling with neurons to reduce mHtt aggregation.
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Laurene Abjean. Les astrocytes réactifs, des partenaires anti-agrégants dans la maladie de Huntington : identification des mécanismes impliqués dans le dialogue neurone-astrocyte. Neurosciences [q-bio.NC]. Université Paris Saclay (COmUE), 2019. Français. ⟨NNT : 2019SACLS088⟩. ⟨tel-02562821⟩

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