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

Abstract

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.

Downregulation of microRNA-9-5p promotes synaptic remodeling in the chronic phase after traumatic brain injury

“…1I ). These results are partly consistent with those from our previous research 20 . Unexpectedly, however, we found that when the miRNA-9-5p oligomers were injected only at 14 days after CCI, although the level of miRNA-9-5p in injured brain tissues was similar to that observed with DI (Fig.…”

“…Therefore, clarifying the role of miRNAs after TBI may be helpful for formulating treatment strategies in the future. Our previous studies also verified that upregulation of miR-9-5p in the acute phase after TBI can reduce the inflammatory response and BBB destruction, thus promoting neurological function recovery 20 . However, whether the upregulation of miR-9-5p has the same neuroprotective role in the chronic phase after TBI remains unknown.…”

“…All steps were performed according to the manufacturers’ instructions. The changing level of miRNA-9-5p was calculated using the comparative threshold cycle (Ct) method and 2 −ΔΔCt as previously described 20 .…”

“…Briefly, the immunofluorescence staining was performed as previously reported 20 . The tissue slices or cells were treated with the primary antibody overnight at 4 °C and then incubated with secondary antibody for 1 h at room temperature.…”

“…miRNA-9 is highly expressed in the central nervous system and plays an important role in the differentiation and synaptic formation of neural stem cells 19 . Our previous studies have shown that continuous upregulation of miRNA-9 in the acute phase after TBI can inhibit the apoptosis of neurons, alleviate the inflammatory response, reduce BBB destruction, and promote neurological function recovery 20 . However, whether continuous upregulation of miRNA-9 only in the chronic convalescence phase can also promote neurological function recovery after TBI remains unknown.…”