Discovery of a potent small molecule inhibiting Huntington’s disease (HD) pathogenesis via targeting CAG repeats RNA and Poly Q protein

Abstract

CAG repeats RNA causes various fatal neurodegenerative diseases exemplified by Huntington’s disease (HD) and several spinocerebellar ataxias (SCAs). Although there are differences in the pathogenic mechanisms, these diseases share the common cause, i.e., expansion of CAG repeats. The shared cause of these diseases raises the possibility for the exploiting the common target as a potential therapeutic approach. Oligonucleotide-based therapeutics are designed earlier with the help of the base pairing rule but are not very promiscuous, considering the nonspecific stimulation of the immune system and the poor cellular delivery. Therefore, small molecules-based therapeutics are preferred for targeting the repeats expansion disorders. Here, we have used the chemical similarity search approach to discern the small molecules that selectively target toxic CAG RNA. The lead compounds showed the specificity towards AA mismatch in biophysical studies including CD, ITC, and NMR spectroscopy and thus aided to forestall the polyQ mediated pathogenicity. Furthermore, the lead compounds also explicitly alleviate the polyQ mediated toxicity in HD cell models and patient-derived cells. These findings suggest that the lead compound could act as a chemical probe for AA mismatch containing RNA as well as plays a neuroprotective role in fatal neurodegenerative diseases like HD and SCAs.

Flow cytometry allows rapid detection of protein aggregates in cellular and zebrafish models of spinocerebellar ataxia 3

“…Interestingly, we observed ataxin-3 protein aggregates predominately in the cell cytoplasm, contrasting with reports of intranuclear ataxin-3 + inclusions in SCA3 brain tissue ( Schmidt et al, 1998 ; Yamada et al, 2000 ; Paulson et al, 1997 ; Rüb et al, 2008 ). Our findings of predominately cytoplasmic ataxin-3 protein aggregates are consistent with existing evidence of cytoplasmic protein aggregates in cultured cells transiently expressing ataxin-3 constructs with EGFP fused to ataxin-3 at the N-terminus ( van Well et al, 2019 ; Joshi et al, 2019 ; Pavel et al, 2016 ; Khan et al, 2019 ; Rajamani et al, 2017 ; Chang et al, 2014 ; Upadhyay et al, 2018 ). In contrast, experiments utilising ataxin-3 constructs with EGFP fused to the C-terminus of the ataxin-3 protein produce ataxin-3 aggregates found within the cell nucleus ( Weishäupl et al, 2019 ).…”

“…Interestingly, we observed ataxin-3 protein aggregates predominately in the cell cytoplasm, contrasting with reports of intranuclear ataxin-3 positive inclusions in SCA3 brain tissue [11,13,42,45]. Our findings of predominately cytoplasmic ataxin-3 protein aggregates are consistent with existing evidence of cytoplasmic protein aggregates in cultured cells transiently expressing a EGFP fused to the N-terminus of the human ataxin-3 protein with 84 polyglutamines [44,[46][47][48][49][50][51]. In contrast, experiments involved mutant expanded ataxin-3 with EGFP fused to the C-terminus display predominately nuclear ataxin-3 aggregates [52].…”

CAG RNAs induce DNA damage and apoptosis by silencing NUDT16 expression in polyglutamine degeneration

“…An increasing number of small molecule compounds have been reported to target CAG repeat RNAs, some of which can reduce disease protein aggregation (e.g., ref. 19). It would be of interest to determine whether these compounds can also target CAG RNA toxicity.…”

Spinocerebellar ataxia clinical trials: opportunities and challenges

“… 16 , 17 , 18 Several high‐throughput small‐molecule screens have revealed promising candidates that may lower levels of the mutant protein. 3 , 19 , 20 But perhaps more exciting are recently developed approaches based on newer RNA depleting or DNA editing tools. 21 These include small‐interfering RNA (siRNA), micro‐RNA (miRNA), or antisense oligonucleotide (ASO)‐based approaches to target RNA species, as well as CRISPR‐based approaches to target RNA or DNA.…”