Mutant γPKC found in spinocerebellar ataxia type 14 induces aggregate-independent maldevelopment of dendrites in primary cultured Purkinje cells

Abstract

Missense mutations in protein kinase Cγ ( γPKC) gene have been found in spinocerebellar ataxia type 14 (SCA14), an autosomal dominant neurodegenerative disease. We previously demonstrated that mutant γPKC found in SCA14 is susceptible to aggregation and induces apoptosis in cultured cell lines. In the present study, we investigated whether mutant γPKC formed aggregates and how mutant γPKC affects the morphology and survival of cerebellar Purkinje cells (PCs), which are degenerated in SCA14 patients. Adenovirus-transfected primary cultured PCs expressing mutant γPKC-GFP also had aggregates and underwent apoptosis. Long-term time-lapse observation revealed that PCs have a potential to eliminate aggregates of mutant γPKC-GFP. Mutant γPKC-GFP disturbed the development of PC dendrites and reduced synapse formation, regardless of the presence or absence of its aggregates. In PCs without aggregates, mutant γPKC-GFP formed soluble oligomers, resulting in reduced mobility and attenuated translocation of mutant γPKC-GFP upon stimulation. These molecular properties of mutant γPKC might affect the dendritic morphology in PCs, and be involved in the pathogenesis of SCA14.