Modest rescue of RBFOX1 splicing function attenuates Huntington's disease features
Background: RNA mis-splicing underlies a growing number of neurological disorders and, consequently, splicing correction therapies have been developed for some monogenic forms, like spinal muscular atrophy or neuronal ceroid lipofuscinosis. In Huntington's disease (HD), alternative splicing alteration emerged as a molecular mechanism in view of individually reported mis-splicing events in neurodegeneration-linked genes such as HTT itself, MAPT and TAF1. Later, more systematic genome-wide RNA-seq analyses of HD brains revealed mis-splicing signatures involving additional neurodegeneration-linked genes. Individual correction of each of the potentially pathogenic mis-spliced genes would be unapproachable. However, the identification of upstream pivotal splicing factors altered in HD may be useful to design pleiotropic therapeutic strategies. We previously performed motif-enrichment analyses of the sequences flanking exons that are mis-spliced in HD and identified RBFOX splicing factors as underlying candidates. Methods: We performed RT-PCR and Western blot analyses of RBFOX in post-mortem brain samples from HD patients and mice. We generated transgenic mouse lines overexpressing RBFOX1 in forebrain neurons and performed RNA-seq to analyze its impact on HD-associated mis-splicing. In addition, we combined HD mice with RBFOX1-overexpressing mice to verify correction of Rbfox1 levels and mis-splicing of RBFOX target genes, and performed histopathological and motor behavioral analyses. Results: We observed that decreased expression of Rbfox1 in striatum of HD mice at early stages of disease progression correlates with a reduction of Rbfox1 immunostaining particularly in the nucleus. This prompted us to generate transgenic mouse lines overexpressing the nuclear isoform of RBFOX1. The overexpression of RBFOX1 in this new transgenic mouse line induced widespread alternative splicing changes that significantly overlapped with genes mis-spliced in brains of both HD patients and mouse models. We found that moderate neuronal RBFOX1 overexpression in HD mice results in correction of several HD-associated mis-splicing events and in attenuation of neurodegeneration and motor symptoms. Conclusions: These results demonstrate that the observed decrease of RBFOX1 levels in brains of HD patients and mice contributes to HD pathogenesis and suggest therapeutic potential of RBFOX-increasing strategies for HD.