Pumilio1 Haploinsufficiency Leads to SCA1-like Neurodegeneration by Increasing Wild-Type Ataxin1 Levels

• The RNA-binding protein PUMILIO1 regulates levels of ATAXIN1 protein and mRNA
• A modest increase in wild-type Ataxin1 levels is enough to cause neurodegeneration
• Pumilio1 haploinsufficiency accelerates SCA1 disease progression
• Ataxin1 haploinsufficiency rescues Pumilio1+/− phenotypes

SummarySpinocerebellar ataxia type 1 (SCA1) is a paradigmatic neurodegenerative proteinopathy, in which a mutant protein (in this case, ATAXIN1) accumulates in neurons and exerts toxicity; in SCA1, this process causes progressive deterioration of motor coordination. Seeking to understand how post-translational modification of ATAXIN1 levels influences disease, we discovered that the RNA-binding protein PUMILIO1 (PUM1) not only directly regulates ATAXIN1 but also plays an unexpectedly important role in neuronal function. Loss of Pum1 caused progressive motor dysfunction and SCA1-like neurodegeneration with motor impairment, primarily by increasing Ataxin1 levels. Breeding Pum1+/− mice to SCA1 mice (Atxn1154Q/+) exacerbated disease progression, whereas breeding them to Atxn1+/− mice normalized Ataxin1 levels and largely rescued the Pum1+/− phenotype. Thus, both increased wild-type ATAXIN1 levels and PUM1 haploinsufficiency could contribute to human neurodegeneration. These results demonstrate the importance of studying post-transcriptional regulation of disease-driving proteins to reveal factors underlying neurodegenerative disease.

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