Genetic Modeling of the Neurodegenerative Disease Spinocerebellar Ataxia Type 1 in Zebrafish

Dominant spinocerebellar ataxias (SCAs) are progredient neurodegenerative diseases commonly affecting the survival of Purkinje cells (PCs) in the human cerebellum. Spinocerebellar ataxia type 1 (SCA1) is caused by the mutated ataxin1 (Atx1) gene product, in which a polyglutamine stretch encoded by CAG repeats is extended in affected SCA1 patients. As a monogenetic disease with the Atx1-polyQ protein exerting a gain of function, SCA1 can be genetically modelled in animals by cell type-specific overexpression. We have established a transgenic PC-specific SCA1 model in zebrafish coexpressing the fluorescent reporter protein mScarlet together with either human wild type Atx1[30Q] as control or SCA1 patient-derived Atx1[82Q]. SCA1 zebrafish display an age-dependent PC degeneration starting at larval stages around six weeks postfertilization, which continuously progresses during further juvenile and young adult stages. Interestingly, PC degeneration is observed more severely in rostral than in caudal regions of the PC population. Although such a neuropathology resulted in no gross locomotor control deficits, SCA1-fish with advanced PC loss display a reduced exploratory behaviour. In vivo imaging in this SCA1 model may help to better understand such patterned PC death known from PC neurodegeneration diseases, to elucidate disease mechanisms and to provide access to neuroprotective compound characterization in vivo.

Complementary proteomics strategies capture an ataxin-1 interactome in Neuro-2a cells

Ataxin-1 mutation, arising from a polyglutamine (polyQ) tract expansion, is the underlying genetic cause of the late-onset neurodegenerative disease Spinocerebellar ataxia type 1 (SCA1). To identify protein partners of polyQ-ataxin-1 in neuronal cells under control or stress conditions, here we report our complementary proteomics strategies of proximity-dependent biotin identification (BioID) and affinity purification (via GFP-Trap pulldown) in Neuro-2a cells expressing epitope-tagged forms of ataxin-1[85Q]. These approaches allowed our enrichment of proximal proteins and interacting partners, respectively, with the subsequent protein identification performed by liquid chromatography-MS/MS. Background proteins, not dependent on the presence of the polyQ-ataxin-1 protein, were additionally defined by their endogenous biotinylation (for the BioID protocol) or by their non-specific interaction with GFP only (in the GFP-Trap protocol). All datasets were generated from biological replicates. Following the removal of the identified background proteins from the acquired protein lists, our experimental design has captured a comprehensive polyQ-ataxin-1 proximal and direct protein partners under normal and stress conditions. Data are available via ProteomeXchange, with identifier PXD010352.

Proliferation, differentiation and migration of SCA1-/CD31- cardiac side population cells in vitro and in vivo

BACKGROUND

Side-population (SP) cells, identified by their capacity to efflux Hoechst dye, are highly enriched for stem/progenitor cell activity. They are found in many mammalian tissues, including mouse heart. Studies suggest that cardiac SP (CSP) cells can be divided into SCA1⁺/CD31^-, SCA1⁺/CD31⁺ and SCA1^-/CD31^- CSP subpopulations. SCA1⁺/CD31^- were shown to be cardiac and endothelial stem/progenitors while SCA1⁺/CD31⁺ CSP cells are endothelial progenitors. SCA1^-/CD31^- CSP cells remain to be fully characterized. In this study, we characterized SCA1^-/CD31^- CSP cells in the adult mouse heart, and investigated their abilities to proliferate, differentiate and migrate in vitro and in vivo.

METHODS AND RESULTS

Using fluorescence-activated cell sorting, reverse transcriptase/polymerase chain reaction, assays of cell proliferation, differentiation and migration, and a murine model of myocardial infarction we show that SCA1^-/CD31^- CSP cells are located in the heart mesenchyme and express genes characteristic of stem cells and endothelial progenitors. These cells were capable of proliferation, differentiation, migration and vascularization in vitro and in vivo. Following experimental myocardial infarction, the SCA1^-/CD31^- CSP cells migrated from non-infarcted areas to the infarcted region within the myocardium where they differentiated into endothelial cells forming vascular (tube-like) structures. We further demonstrated that the SDF-1α/CXCR4 pathway may play an important role in migration of these cells after myocardial infarction.

CONCLUSIONS

Based on their gene expression profile, localization and ability to proliferate, differentiate, migrate and vascularize in vitro and in vivo, we conclude that SCA1^-/CD31^- CSP cells may serve as endothelial progenitor cells in the adult mouse heart.

Systematic analysis of fly models with multiple drivers reveals different effects of ataxin-1 and huntingtin in neuron subtype-specific expression

The fruit fly, Drosophila melanogaster, is a commonly used model organism for neurodegenerative diseases. Its major advantages include a short lifespan and its susceptibility to manipulation using sophisticated genetic techniques. Here, we report the systematic comparison of fly models of two polyglutamine (polyQ) diseases. We induced expression of the normal and mutant forms of full-length Ataxin-1 and Huntingtin exon 1 in cholinergic, dopaminergic, and motor neurons, and glial cells using cell type-specific drivers. We systematically analyzed their effects based on multiple phenotypes: eclosion rate, lifespan, motor performance, and circadian rhythms of spontaneous activity. This systematic assay system enabled us to quantitatively evaluate and compare the functional disabilities of different genotypes. The results suggest different effects of Ataxin-1 and Huntingtin on specific types of neural cells during development and in adulthood. In addition, we confirmed the therapeutic effects of LiCl and butyrate using representative models. These results support the usefulness of this assay system for screening candidate chemical compounds that modify the pathologies of polyQ diseases.