A novel Ataxin-3 knock-in mouse model mimics the human SCA3 disease phenotype including neuropathological, behavioral, and transcriptional abnormalities

Abstract

Background: Spinocerebellar ataxia type 3 is the most common autosomal dominant inherited ataxia worldwide and is caused by a CAG repeat expansion in the Ataxin-3 gene resulting in a polyQ expansion in the corresponding protein. The disease is characterized by neuropathological (aggregate formation, cell loss), phenotypical (gait instability, body weight reduction), and specific transcriptional changes in affected brain regions. So far, there is no mouse model available representing all the different aspects of the disease, yet highly needed to gain a better understanding of the disease pathomechanism.Methods: Here, we characterized a novel Ataxin-3 knock-in mouse model, expressing either a heterozygous or homozygous expansion of 304 CAG/CAAs in the murine Ataxin-3 locus using biochemical, behavioral, and transcriptomic approaches. Further, we compared the transcriptional changes of the knock-in mice to those found in human SCA3 patients, to evaluate the comparability of our model. Results:The novel Ataxin-3 knock-in mouse is characterized by the expression of a polyQ-expansion in the murine Ataxin-3 protein, leading to massive aggregate formation, especially in brain regions known to be vulnerable in SCA3 patients, and impairment of Purkinje cells. Along these neuropathological changes, mice showed a reduction in body weight accompanied by gait and balance instability. Transcriptomic analysis of cerebellar tissue revealed age-dependent differential expression, enriched for genes attributed to myelinating oligodendrocytes. Comparing these transcriptional changes with those found in cerebellar tissue of SCA3 patients, we discovered an overlap of differentially expressed genes pointing towards similar gene expression perturbances in several genes linked to myelin sheaths and myelinating oligodendrocytes. Conclusion:The novel Ataxin-3 knock-in model shares neuropathological, behavioral, and transcriptomic features with human SCA3 patients and, therefore, represents an ideal model to investigate early-onset developments, therapy studies, or longitudinal biomarker alterations.

Neurofilaments in spinocerebellar ataxia type 3: blood biomarkers at the preataxic and ataxic stage in humans and mice

“…We used the 304Q SCA3 knock‐in mouse model containing a 304 trinucleotide repeat expansion in the murine ATXN3 homolog, which was generated on the background of C5BL/6N mice (Charles River) by zinc finger technology (Carbery et al , ), as described in detail elsewhere (preprint: Haas et al , ; Martier et al , ). In short, this method resulted in a double‐strand break within the murine (CAACAGCAG) 2 region and the introduction of a specific expansion of the CAACAGCAG region accomplished by homologous recombination using a donor vector with (CAACAGCAG) 48 repeats, flanked by 800 bp up‐ and downstream of ATXN3 (for a more detailed description of the mouse model, see preprint: Haas et al ()). More repeats than contained in the donor vector were introduced, resulting in the expression of 304 glutamines in the ataxin‐3 protein under control of all endogenous regulatory elements.…”

“…We expected the blood Nf increases in human SCA3 to be paralleled by blood Nf increases in SCA3 animal models, also starting already in the presymptomatic stage and at the earliest stages of SCA3 neurodegeneration. We therefore assessed plasma NfL and pNfH also in a SCA3 knock‐in mouse model (preprint: Haas et al , ; Martier et al , ) across presymptomatic and symptomatic disease stages, correlating plasma concentrations of both Nfs with the temporal course of phenotypic and neuropathological disease features, including brain ataxin‐3 protein levels and aggregation.…”