microRNA‐9‐5p alleviates blood–brain barrier damage and neuroinflammation after traumatic brain injury

The level of microRNA‐9‐5p (miRNA‐9‐5p) in brain tissues is significantly changed after traumatic brain injury (TBI). However, the effect of miRNA‐9‐5p for brain function in TBI has not been elucidated. In this study, a controlled cortical impact model was used to induce TBI in Sprague–Dawley rats, and an oxygen glucose deprivation model was used to mimic the pathological state in vitro. Brain microvascular endothelial cells (BMECs) and astrocytes were extracted from immature Sprague–Dawley rats and cocultured to reconstruct blood–brain barrier (BBB) in vitro. The results show that the level of miRNA‐9‐5p was significantly increased in brain tissues after TBI, and up‐regulation of miRNA9‐5p contributed to the recovery of neurological function. Up‐regulation of miRNA‐9‐5p with miRNA agomir may significantly alleviate apoptosis, neuroinflammation, and BBB damage in rats after TBI. Moreover, a dual luciferase reporter assay confirmed that miRNA‐9‐5p is a post‐transcriptional modulator of Ptch‐1. In in vitro experiments, the results confirmed that up‐regulation of miRNA‐9‐5p with miRNA mimic alleviates cellular apoptosis, inflammatory response, and BBB damage mainly by inhibiting Ptch‐1. In addition, we found that the activation of Hedgehog pathway was accompanied by inhibition of NF‐κB/MMP‐9 pathway in the BMECs treated with miRNA‐9‐5p mimic. Taken together, these results indicate that up‐regulation of miRNA‐9‐5p alleviates BBB damage and neuroinflammatory responses by activating the Hedgehog pathway and inhibiting NF‐κB/MMP‐9 pathway, which promotes the recovery of neurological function after TBI.
Hedgehog pathway and NF‐κB proteins play important roles in cellular apoptosis and inflammatory responses. Using bioinformatics techniques, we find that Ptch‐1, which is an inhibitor of Hedgehog pathway, and NF‐κB are potential targets for microRNA‐9‐5p. We propose the following cascade for microRNA‐9‐5p that alleviates the damage of blood–brain barrier and neuroinflammation after traumatic brain injury: over‐expression of microRNA‐9‐5p activates Hedgehog pathway and blocks NF‐κB/MMP‐9 pathway by inhibiting Ptch‐1 and NF‐κB, which inhibit cellular apoptosis and inflammatory responses of brain microvascular endothelial cells. We think these findings may provide a new target for the treatment of traumatic brain injury.