Downregulation of oar-miR-125b Drives Blood–Brain Barrier Breakdown Through the TNFSF4–NF-κB Inflammatory Axis in Enterococcus Faecalis Meningitis

Bacterial meningitis involves complex molecular networks, including microRNA-mediated regulation of inflammatory responses; however, the specific role of Ovis aries microRNA-125b (oar-miR-125b) in this process remains poorly understood. In this study, using a lamb model of Enterococcus faecalis-induced meningitis, we observed significant downregulation of oar-miR-125b, which inversely correlated with its newly identified target, Tumor Necrosis Factor Superfamily Member 4 (TNFSF4). Dual-luciferase reporter assays confirmed that oar-miR-125b directly binds to the 3' Untranslated Region (3'UTR) of TNFSF4 but not to the 3'UTRs of Kelch Like Family Member 31 (KLHL31) or NF-κB Inhibitor Interacting Ras Like 2 (NKIRAS2). Mechanistically, decreased oar-miR-125b expression relieves its repression of TNFSF4, leading to NF-κB pathway activation and blood-brain barrier disruption. Collectively, our results demonstrate that oar-miR-125b serves as a key anti-inflammatory regulator in bacterial meningitis by targeting TNFSF4 and constraining NF-κB signaling, highlighting its potential as a therapeutic target for attenuating neuroinflammation in meningitis.