Circular RNA aptamers as superb sub-stoichiometric chaperones of TDP-43 condensation

Abstract

Pathological protein misfolding and aggregation underlie numerous human diseases, yet strategies that selectively antagonize pathological protein states while preserving normal protein function remain limited. Here, we identify two loosely structured circular RNA aptamers (Capts), circT3 and its minimized 116-nt derivative circT3-M3, as superb sub-stoichiometric RNA chaperones that suppress pathological condensation of TAR DNA-binding protein 43 (TDP-43), a hallmark of amyotrophic lateral sclerosis and frontotemporal dementia. Rather than acting through simple stoichiometric sequestration, these Capts engage TDP-43 reversibly and iteratively via binding the functionally and pathologically relevant residues within its RRM1 domain. Such interaction enables a single Capt to promote rapid and multiple RRM1-dependent homomeric assembly events, thereby stabilizing TDP-43 in a soluble oligomeric state to outcompete the C-terminal prion-like domain-driven condensation and supersaturation. Moreover, delivery of these Capts rescues TDP-43-dependent aberrant splicing in the cellular model and partially ameliorates TDP-43 proteinopathy-driven motor dysfunction in vivo. Together, our findings establish Capts as highly efficient subcellular RNA chaperones with exceptionally potent low-dose activity and highlight their promise as next-generation RNA therapeutics for TDP-43 proteinopathies.