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CAG repeat-selective compunds reduce abundance of expanded CAG RNAs in patient and murine models of SCAs I

ABSTRACT: Spinocerebellar ataxias (SCAs) are a genetically heterogenous group of >40 devastating neurodegenerative conditions for which clinical care currently focuses on managing symptoms. Across these diseases there is a large unmet need for therapies that address underlying disease mechanisms. In this study, we utilised the shared CAG repeat expansion mutation causative for a large subgroup of SCAs, to develop a novel disease-independent and mechanism agnostic small molecule screening approach to identify compounds with therapeutic potential across CAG SCAs. Using this screening approach, we identified the FDA approved microtubule inhibitor Colchicine and a novel CAG-repeat binding compound that reduce expression of disease associated transcripts across SCA1, 3 and 7 patient derived fibroblast lines and the Atxn1154Q/2Q SCA1 mouse model in a repeat selective manner. Furthermore, we demonstrate that our lead candidate rescues dysregulated alternative splicing in Atxn1154Q/2Q mice. This work provides the first example of small molecules capable of targeting the underlying mechanism of disease across multiple CAG SCAs.

ORGANISM(S): Homo sapiens

PROVIDER: GSE249555 | GEO | 2025/12/04

REPOSITORIES: GEO

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Project description:Spinocerebellar ataxia type 6 (SCA6) is a dominantly inherited neurodegenerative disease caused by an expansion of a CAG repeat encoding a polyglutamine (PolyQ) tract in the Cav2.1 voltage-gated calcium channel. Pathologically, it is characterized by selective degeneration of cerebellar Purkinje cells (PCs), which are a common target for PolyQ-induced toxicity among several different SCAs. Mutant Cav2.1 confers toxicity mainly through a toxic gain-of-function mechanism, but subcellular site of expanded Cav2.1 toxicity is controversial and it remains elusive whether SCA6 shares pathogenic cascades with other SCAs. To gain insight into these problems, we studied the cerebellar gene expression patterns of young Sca6 MPI 118Q/118Q knockin (KI) mice, which express mutant Cav2.1 from endogenous locus and faithfully models human SCA6. Comparison of transcriptional changes with those of Sca1 154Q/2Q mice, a faithful KI mouse model of SCA1, revealed that transcriptional signatures in the MPI 118Q/118Q were distinct from those of Sca1 154Q/2Q. Examination of temporal profiles of candidate genes showed that upregulation of those associated with microglial activation was initiated before PC degeneration was apparent and augmented as the disease progressed. Histological analysis of the MPI 118Q/118Q cerebellum confirmed the presence of Iba-1 positive activated microglia. Moreover, predominance of M1-like pro-inflammatory microglia was observed and was concomitant with the increased expression of pro-inflammatory cytokines. These results suggest that the unique transcriptional response, which highlights upregulation of neuroinflammatory genes possibly associated with lysosomal involvement, may play a pivotal role in the pathogenesis. Modulation of innate immune system could pave the way for slowing the progression of SCA6. We used MPI 118Q/118Q and MPI 11Q/11Q mice for Sca6 KI model at six weeks old. Statistical analysis of differently expressed genes was performed using the Linear Models for Microarray Data (limma) package in R/Bioconductor.

Project description:In Huntington’s disease (HD), expanded HTT CAG repeat length correlates strongly with age at motor onset, indicating that it determines the rate of the disease process leading to diagnostic clinical manifestations. Similarly, in normal individuals, HTT CAG repeat length is correlated with biochemical differences that reveal it as a functional polymorphism. Here, we tested the hypothesis that gene expression signatures can capture continuous, length-dependent effects of the HTT CAG repeat. Using gene expression datasets for 107 HD and control lymphoblastoid cell lines, we constructed mathematical models in an iterative manner, based upon CAG correlated gene expression patterns in randomly chosen training samples, and tested their predictive power in test samples. Predicted CAG repeat lengths were significantly correlated with experimentally determined CAG repeat lengths, whereas models based upon randomly permuted CAGs were not at all predictive. Predictions from different batches of mRNA for the same cell lines were significantly correlated, implying that CAG length-correlated gene expression is reproducible. Notably, HTT expression was not itself correlated with HTT CAG repeat length. Taken together, these findings confirm the concept of a gene expression signature representing the continuous effect of HTT CAG length and not primarily dependent on the level of huntingtin expression. Such global and unbiased approaches, applied to additional cell types and tissues, may facilitate the discovery of therapies for HD by providing a comprehensive view of molecular changes triggered by HTT CAG repeat length for use in screening for and testing compounds that reverse effects of the HTT CAG expansion. To evaluate the continuous analytical approach as a strategy to discover the molecular consequences of the HTT CAG repeat, genome-wide gene expression datasets were generated from a panel of 107 human lymphoblastoid cell lines with HTT CAGs spanning the entire spectrum of allele sizes.

Project description:Spinocerebellar ataxia type 3 (SCA3) is one of the polyglutamine (polyQ) diseases, which are caused by a CAG repeat expansion within the coding region of the associated genes. The CAG repeat specifies glutamine, and the expanded polyQ domain with mutation confers dominant toxicity on the protein. Traditionally, studies have focused on protein toxicity in polyQ disease mechanisms. Recent findings, however, demonstrate that the CAG repeat RNA, which encodes the toxic polyQ protein, also contributes to the disease in Drosophila. To provide insight into the nature of the RNA toxicity, we extracted brain-enriched RNA from flies expressing a toxic CAG repeat mRNA (CAG100) and a non-toxic interrupted CAA/G mRNA repeat (CAA/G105) for microarray analysis. This approach identified a set of genes that are differentially expressed specifically in CAG100 flies. Four independent replicates of flies expressing CAG0, CAG100, or CAA/G105 by elav-GAL4 were collected at 3 days. The transgenes are DsRed with either (CAG0) no CAG repeat in the 3'UTR, (CAG100) a CAG repeat of 100 CAGs in the 3'UTR, or (CAA/G105) an interrupted CAA CAG repeat in the 3'UTR (ref: Li et al., Nature 453:1107) The transgenes were adjusted to match in mRNA expression such that CAG0 flies had one copy of the transgene, CAG100 flies had 5 copies, and CAA/G105 had two copies. Fly brain tissue (about 20 brains per sample, dissected from head capsule, eyes, lamina and outer medulla removed) was dissected in cold phosphate buffered saline (PBS) and stored in Trizol reagent (Invitrogen Corporation, Carlsbad, CA) at -80Ë?C. Total brain RNA was extracted and purified using TRIzol reagent (Invitrogen) and the RNeasy Mini system (Qiagen), and treated with RNase-free DNase I (Qiagen). To define genes whose expression is altered in response to a toxic CAG repeat RNA, we compared CAG100 flies with age-matched flies expressing CAG0. To exclude transcriptional changes in response to a non-toxic trinucleotide repeat, a second gene list was generated by comparing CAA/G105 flies with age-matched CAG0 flies.

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CAG repeat-selective compunds reduce abundance of expanded CAG RNAs in patient and murine models of SCAs I

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