G9a Targeting by miR-122 Ameliorates Ischemic Brain Injury via Enhanced Microglial Autophagy and Suppressed Ferroptosis.

Microglia are crucial in ischemic brain injury (IBI). Modulating microglial autophagy and inhibiting ferroptosis via miR-122 targeting G9a may mitigate disease progression. This study investigated whether miR-122 attenuates IBI progression by targeting G9a to promote microglial autophagy and inhibit ferroptosis. In vivo, a transient middle cerebral artery occlusion (tMCAO) rat model received intracerebroventricular injections of agomiR-122 for miR-122 overexpression or AAV-G9a for G9a overexpression to assess miR-122/G9a roles in autophagy and ferroptosis. In vitro, oxygen-glucose deprivation/reperfusion (OGD/R)-treated BV2 cells were transfected with miR-122 mimic, oe-G9a, and treated with rapamycin (RA) or ferrostatin-1 (Fer-1) to delineate the miR-122/G9a-autophagy-ferroptosis axis. A microglia-hippocampal neuronal cell transwell co-culture system assessed HT22 viability to confirm miR-122-mediated neuroprotection via G9a inhibition. In vivo, miR-122 ameliorated neurological deficits and attenuated brain injury in tMCAO rats by negatively regulating G9a. This was accompanied by enhanced autophagy (e.g., increased LC3-II/I ratio) and suppression of ferroptosis (e.g., upregulation of GPX4) and inflammatory responses. In vitro, agomiR-122 in OGD/R-injured BV2 cells promoted cell viability and autophagy, while inhibiting ferroptosis. These effects were reversed by AAV-G9a but rescued upon treatment with RA or Fer-1. Moreover, in a BV2-HT22 co-culture system, agomiR-122 in microglia conferred neuroprotection, an effect that was abolished by G9a upregulation. MiR-122 ameliorates IBI by targeting G9a to enhance microglial autophagy and suppress ferroptosis, offering mechanistic insights and novel therapeutic targets.