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Astro- versus microglia-enriched transcriptomes from aged Atxn2-CAG100-knockin mice suggest underlying pathology of RNA processing at ribosomes, and possibly at U-bodies [panRNAseq]

ABSTRACT: Spinocerebellar Ataxia type 2 (SCA2) and Amyotrophic Lateral Sclerosis type 13 (ALS13) are triggered by polyglutamine expansion in Ataxin-2 (ATXN2). To understand these neurodegenerative disorders at the molecular level, the brains of 10-month-old Atxn2-CAG100-knockin mice were analyzed either as a whole or as microglial, astroglial (and neuronal) fractions via global RNA sequencing. Data was validated by comparison with spinal cord oligonucleotide microarray profile. Here, glial fractions showed upregulation of Gpnmb (to 2082%), Cst7, Clec7a, Axl, Csf1, Lgals3, Lgals3bp, Slc11a1, and Usp18 as an unspecific neuroinflammatory signature, versus downregulation of the Nefh (to <19%), Scn4b, Camk2b, Rab15, and Grin1 synaptic mRNAs correlating with circuit disconnection. In all fractions, reductions of Kif5a, Rph3a, and Cplx1 were noted, versus disease-specific inductions of ribosomal subunits, presumably mirroring the partial loss-of-function of ATXN2 as RNA translation modulator. Glial tRNAs were also consistently upregulated. Selective accumulation of embryonic factors Rnu1b2 (8-fold) and Eef1a1 versus downregulation of adult Eef1a2, specify mutation impact on splicing and translation elongation. As a potential underpinning of toxic gain-of-functions, proteostasis factor Rnf213 was increased in all fractions. These transcriptome data suggest altered spliceosome and ribosomal machinery, with massive microgliosis versus mild astrogliosis, at the core of SCA2 and ALS13. The quantity and quality of rRNA and U1 snRNA should be assessed next.

ORGANISM(S): Mus musculus

PROVIDER: GSE319875 | GEO | 2026/05/15

REPOSITORIES: GEO

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Project description:Spinocerebellar Ataxia Type 2 (SCA2) is caused by expansion of a polyglutamine encoding triplet repeat in the human ATXN2 gene beyond (CAG)31. This is thought to mediate toxic gain-of-function by protein aggregation, and affect RNA processing, resulting in degenerative processes affecting preferentially cerebellar neurons. As a faithful animal model, we generated a knock-in mouse replacing the single CAG of murine Atxn2 with CAG42, a frequent patient genotype. This expansion size was inherited stably. The mice showed phenotypes with reduced weight and later motor incoordination. Although brain Atxn2 mRNA became elevated, soluble ATXN2 protein levels diminished over time, which might explain partial loss-of-function effects. Deficits in soluble ATXN2 protein correlated with the appearance of insoluble ATXN2, a progressive feature in cerebellum possibly reflecting toxic gains-of-function. Since in vitro ATXN2 overexpression was known to reduce levels of its protein interactor PABPC1, we studied expansion effects on PABPC1. In cortex, PABPC1 transcript, soluble and insoluble protein levels were increased. In more vulnerable cerebellum the progressive insolubility of PABPC1 was accompanied by decreased soluble protein levels, with PABPC1 mRNA showing no compensatory increase. The sequestration of PABPC1 into insolubility by ATXN2 function gains was validated in human cell culture. To understand consequences on mRNA processing, transcriptome profiles at medium and old age in three different tissues were studied and demonstrated selective induction of Fbxw8 in old cerebellum. Fbxw8 is encoded next to the Atxn2 locus and was shown in vitro to decrease the level of expanded insoluble ATXN2 protein. In conclusion, our data support the concept that expanded ATXN2 undergoes progressive insolubility and affects PABPC1 by a toxic gain-of-function mechanism with tissue-specific effects, which may be partially alleviated by the induction of FBXW8. Factorial design comparing Atxn2 knock-in mice with wild type littermates in three different tissues (brainstem, cerebellum, liver)

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Astro- versus microglia-enriched transcriptomes from aged Atxn2-CAG100-knockin mice suggest underlying pathology of RNA processing at ribosomes, and possibly at U-bodies [panRNAseq]

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