The AUUUC repeat RNA aggregates sequester RNA-binding proteins like NOVA2 and lead to iron dyshomeostasis in spinocerebellar ataxia type 37

Abstract

Transcribed nucleotide repeat expansions can contribute to disease by altering RNA structure and function. Spinocerebellar ataxia type 37 (SCA37) is a neurodegenerative disorder caused by a pathogenic ATTTC repeat insertion within a non-pathogenic ATTTT repeat in the 5 untranslated region of DAB1. We have shown that the AUUUC repeat RNA forms aberrant nuclear aggregates in cells, subsequently confirmed by others in neurons from subjects with familial adult myoclonic epilepsy carrying a similar ATTTC repeat insertion. However, the mechanism by which these RNA aggregates cause neuropathology remains unknown. Here, we show that overexpression of the ATTTC repeat in human neural stem cells leads to the formation of abnormal nuclear RNA aggregates, supporting an AUUUC repeat-mediated mechanism of pathology through the sequestration of RNA-binding proteins (RBP). We identified 12 AUUUC repeat-interacting RBPs with specific neuronal functions, including NOVA2, which we demonstrate to colocalize with the AUUUC repeat aggregates. Moreover, we further investigated the accumulation of iron in these aggregates and observed a significant colocalization of iron and NOVA2 hotspots in ATTTC repeat-expressing cells, a pattern absent in control cells. Together, these findings uncover a novel RNA-mediated mechanism of pathology involving both RBPs and iron, expanding the current understanding of RNA repeat toxicity.