RNA-binding protein RCAN1.1L modulates ATF2 mRNA stability to promote mitochondrial fission in acute ischemic stroke

Regulator of calcineurin 1 (RCAN1) is an RNA-binding protein with diverse functions, the regulatory mechanisms underlying mitochondrial function in ischemic neuronal injury remain only partially understood. This study identified significantly elevated plasma RCAN1.1 levels in acute ischemic stroke (AIS) patients and demonstrated that mitochondrial translocation of RCAN1.1L ‌within the ischemic penumbra‌ aggravates cerebral infarction ‌by promoting pathological mitochondrial fission and neuronal apoptosis‌. Mechanistically, in AIS cell and mouse models, multi-omics screening identified activating transcription factor 2 (ATF2) mRNA as a critical downstream target of RCAN1.1L. RCAN1.1L binds to the 2915-2935 nucleotide in the 3'-untranslated region (UTR) of ATF2 mRNA, stabilizing its expression and promoting the accumulation of mitochondrial ATF2 (mtATF2) protein. MtATF2, in turn, binds to and upregulates mitochondrial fission 1 (FIS1) protein, thereby enhancing mitochondrial fission and driving intrinsic apoptosis. Notably, the RNA aptamer R1SR13 competitively binds to RCAN1.1L protein with ATF2 mRNA, exerting neuroprotective effects by disrupting the RCAN1.1L-mtATF2-FIS1 axis. These findings identify RCAN1.1L as an upstream regulator of ATF2 mRNA stability-mediated mitochondrial fission and apoptosis in ischemic penumbra neurons and highlight R1SR13 as a promising therapeutic candidate for preserving neuronal mitochondrial integrity.