Circular RNA SCMH1 promotes persistent brain repair via N6-methyladenosine methylation post stroke.

Circular RNA (circRNA)-based nucleic acid therapeutics exhibits distinct pharmacological advantages including sustained therapeutic effects from single-dose administration, but the molecular basis governing this persistence remains mechanistically unresolved. Using single-cell RNA sequencing (scRNA-seq), methylated RNA immunoprecipitation sequencing (MeRIP-seq), and genetic animal models, we demonstrated that a single dose of exogenous circSCMH1 sustained elevated endogenous circSCMH1 levels in the peri-infarct region. This persistence stems from a self-sustaining loop initiated by exogenous circSCMH1, as confirmed by experiments with a modified circSCMH1 variant (ΔcircSCMH1), which distinguishes endogenous from exogenous sources. Mechanistically, microglial overexpression of the m6A demethylase FTO enhances circSCMH1 biogenesis by suppressing m6A methylation, with YTHDC1 identified as the primary m6A reader protein facilitating this process. Furthermore, YTHDC1 collaborates with Exportin-4 to mediate m6A-dependent nuclear export of circSCMH1, a step critical for its therapeutic efficacy. In Exportin-4-deficient mice, impaired nuclear export abolishes the sustained brain repair induced by circSCMH1, as evidenced by diminished sensorimotor recovery in behavioural tests. These findings elucidate how a single dose of circSCMH1 improves brain repair through a self-sustaining loop that leverages endogenous circRNA biogenesis machinery. Unlike traditional therapies requiring repeated dosing, this approach achieves prolonged therapeutic efficacy, offering substantial translational advantages for stroke treatment.