Differential Effects of Wnt-β-catenin Signaling in Purkinje Cells and Bergmann Glia in Spinocerebellar Ataxia Type 1

Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited neurodegenerative disease characterized by progressive ataxia and degeneration of specific neuronal populations, including Purkinje cells (PCs) in the cerebellum. Previous studies have demonstrated a critical role for various evolutionarily conserved signaling pathways in cerebellar patterning, such as the Wnt-β-catenin pathway; however, the roles of these pathways in adult cerebellar function and cerebellar neurodegeneration are largely unknown. In this study, we found that Wnt-β-catenin signaling activity was progressively enhanced in multiple cell types in the adult SCA1 mouse cerebellum, and that activation of this signaling occurs in an ataxin-1 polyglutamine (polyQ) expansion-dependent manner. Genetic manipulation of the Wnt-β-catenin signaling pathway in specific cerebellar cell populations revealed that activation of Wnt-β-catenin signaling in PCs alone was not sufficient to induce SCA1-like phenotypes, while its activation in astrocytes, including Bergmann glia (BG), resulted in gliosis and disrupted BG localization, which was replicated in SCA1 mouse models. Our studies identify a mechanism in which polyQ-expanded ataxin-1 positively regulates Wnt-β-catenin signaling and demonstrate that different cell types have distinct responses to the enhanced Wnt-β-catenin signaling in the SCA1 cerebellum, underscoring an important role of BG in SCA1 pathogenesis.