Extracellular vesicle-mediated delivery of mitochondrial circRNA MTCO2 protects against cerebral ischemia by modulating mPTP-dependent ferroptosis.

Ischemic stroke remains a major cause of mortality and long-term disability, with few effective neuroprotective treatments currently available. Ferroptosis, an iron-dependent form of regulated cell death marked by lipid peroxidation, is increasingly recognized as a driver of neuronal damage. However, the mitochondrial mechanisms linking ischemia to ferroptosis remain poorly defined. Here, we identify circMTCO2, a mitochondria-encoded circular RNA, as a novel endogenous modulator of neuronal ferroptosis. CircMTCO2 expression is dynamically downregulated following cerebral ischemia/reperfusion both in vitro and in vivo. Mechanistically, circMTCO2 binds directly to adenine nucleotide translocase 1 (ANT1), a key component of the mitochondrial permeability transition pore (mPTP), thereby inhibiting mPTP opening and suppressing mitochondrial ROS (mtROS) release. Disruption of the binding site abolishes the circMTCO2-ANT1 interaction and eliminates the protective effects of circMTCO2. To restore and enhance this intrinsic defense mechanism, we developed a dual-targeting extracellular vesicle system (RVG-EV) capable of delivering circMTCO2 specifically to brain neuronal mitochondria. Systemic administration of RVG-EV attenuated mtROS production, reduced neuronal ferroptosis, decreased infarct volume, and improved neurological function in a mouse model of ischemic stroke, without inducing systemic toxicity. These findings establish circMTCO2 as a previously unrecognized mitochondrial circRNA that regulates ferroptosis by modulating mPTP activity, and provide proof of concept that organ-to-organelle circRNA delivery can be leveraged as a precision neuroprotective strategy for ischemic stroke.