MicroRNA-34a suppresses neuronal apoptosis and alleviates microglia inflammation by negatively targeting the Notch pathway in spinal cord injury.

Objective: The purpose of this study was to investigate role of inhibition of microRNA-34a (miR-34a) in neural damage and repair after spinal cord injury, and to explore the underlying mechanism.
Materials and Methods: In BV2 microglia, we conducted classical activation using lipopolysaccharide (LPS) and pre-treatment using miR-34a mimics. The expressions of miR-34a, Notch 1, and Jagged 1 were detected by quantitative Real Time-Polymerase Chain Reaction (qRT-PCR). Moreover, the protein expressions of inflammatory microglia markers were evaluated by Western blotting. In vivo, SCI model was successfully established in rats. Subsequently, the expression levels of miR-34a, Notch 1, and Jagged 1 levels within 1 week were measured by qRT-PCR. Meanwhile, protein expressions of inflammatory mediators were determined by enzyme-linked immunosorbent assay (ELISA) assay. Immunofluorescence was conducted to display the activation degree of microglia and residual neural structure. Furthermore, locomotor function recovery was estimated using BBB rating scale.
Results: Compared with the only LPS-activated group, pre-treatment of miR-34a mimics significantly decreased the expressions of Notch 1 and Jagged 1. Similarly, the protein expressions of CD11b and iNOS were significantly down-regulated. In vivo, the levels of Notch 1 and Jagged 1 within 1 week increased significantly, while miR-34a was negatively regulated following spinal cord injury (SCI). Furthermore, the contents of interleukin-1 beta (IL-1β) and IL-6 were reduced with the treatment of miR-34a mimics when compared with SCI group. With the treatment of miR-34a, the number of inflammatory microglia decreased significantly, and the remaining neural structure was similarly improved. In addition, locomotor function recovery of hindlimbs in rats was significantly ameliorated after the administration of miR-34a mimics.
Conclusions: Increase of miR-34a suppresses neuronal apoptosis and alleviates microglia inflammation by negatively targeting the Notch pathway, thereby improving neural recovery and locomotor function.