Objective: To derive neuronal lineages from patient’s peripheral blood mononuclear cells (PBMCs) and exploration of disease biology.

Background: Spinocerebellar ataxia type-12 (SCA-12) is a progressive cerebellar and purely neurodegenerative genetic disorder caused by  (CAG) expansion in 5’UTR of PPP2R2B gene. SCA12 is the second common genetic ataxia type and has unique prevalence in North Indian population. Transgenic or any other appropriate neuronal-cell/animal models are lacking to understand the underlying cellular perturbations in SCA12. Human-induced-pluripotent-stem cell based (HiPSC) based disease modeling overcomes the limitation of non-availability of specific cell type for studying such disorders. 

Methods: Lymphoblastoid-cell-lines (LCLs) derived from patient’s PBMCs were used to generate non-integrated iPSCs using episomal plasmids (Yamanaka-factors). These iPSCs were then de-differentiated into NSCs/Neuronal lineage. Appropriate cellular characterization was conducted for respective cell lines. A comprehensive candidate gene transcriptomic-profiling was conducted in cell lines and compared with appropriate controls

Results: PPP2R2B transcripts levels were found down-regulated in blood samples of patients compared to controls (N=10), however, in HiPSCs lines, we observed a significant variation of all the isoforms except brain-specific isoform-4. In neural progenitor cells (NSCs) and differentiated neurons, we observed the expression of brain-specific isoform-4. This suggest that these patient iPSC derived neuronal model are good for mechanistic analysis. We observed that CAG-containing non-coding PPP2R2B transcripts (isoform-12) significantly expressed (fc>30) lines compared to control in both NSCs and neurons.

Conclusions: We have generated patient derived HiPSCs and their differentiated derivatives to study SCA12 pathogenesis. Our preliminary data shows that HiPSC based model system can serve as model to study such adult onset complex disorders. We were able to identify  expression pattern  of  candidate gene PPP2R2B, mimicking brain-specific transcripts. Our preliminary data shows some trend towards disease relevant transcriptional signatures.

References:

1. Holmes SE, O’Hearn EE, McInnis MG, Gorelick-Feldman DA, Kleiderlein JJ, Callahan C, et al. Expansion of a novel CAG trinucleotide repeat in the 5′ region of PPP2R2B is associated with SCA12. Nat Genet. 1999; 23(4):391–2.
2. Takahashi K, Yamanaka S. Induction of Pluripotent Stem Cells from Mouse Embryonic and Adult Fibroblast Cultures by Defined Factors. Cell. 2006; 126(4):663–76.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/induced-pluripotent-stem-cells-based-in-vitro-modelling-of-spinocerebellar-ataxia-type-12-sca-12/