Transcriptomic Dynamics of a non-coding trinucleotide repeat expansion disorder SCA12 in iPSC derived neuronal cells: signatures of interferon induced response

Abstract

Spinocerebellar ataxia type-12 (SCA12) is a neurological disorder that exhibits a unique progressive tremor/ataxia syndrome induced by triplet (CAG) repeat expansion in 5 UTR of PPP2R2B. SCA12 is one of the most prominent SCA-subtype in India and till date no appropriate disease models have been described. Our aim was to establish human iPSC derived neuronal cell lines of SCA12 and study transcriptomic level alterations induced by CAG expansion. For translational application, peripheral blood transcriptomics of SCA12 patients was also performed. Lymphoblastoid cell lines of three SCA12 patients were reprogrammed to iPSCs and then re-differentiated into pan-neuronal lineage. RNA-sequencing based comparative transcriptomics was performed for disease and control cell lineages. Microarray based transcriptomic profiling of peripheral blood of SCA12 patients was performed in a case/control (n=15/9) design. We have successfully created human neuronal cell lines of SCA12 patient as exhibited by their molecular profiling. Differential expression analysis of RNA-Seq data has shown enrichment for type-I interferon signaling and other relevant cellular processes in SCA12-neurons. At the splice-isoform level, we observed an upregulation of expanded CAG containing non-coding transcript of PPP2R2B. Peripheral blood transcriptomics analysis and targeted validation of RNA-Seq data has allowed us to identify inflammatory signatures as potential markers of molecular pathology in SCA12. Our study has allowed us to establish first iPSC based neuronal cell lines of SCA12. We have identified pro-inflammatory signatures in SCA12-neurons suggestive of a dsRNA mediated activation of interferon signaling and that corroborates with the emerging evidence of neuronal atrophy due to neuro-inflammation in common neurodegenerative diseases. This study involved development of an iPSCs derived neuronal cells of SCA12 and look through signatures of neurodegeneration by whole RNA sequencing. This model sheds light upon key role of RNA mediated induced response in Interferon signaling for neurodegeneration.