Abstract
Emerging evidence indicates that microRNAs play a pivotal role in neural remodeling after spinal cord injury (SCI). This study aimed to investigate the mechanisms of miR-135a-5p in regulating the functional recovery of SCI by impacting its target genes and downstream signaling. The gene transfection assay and luciferase reporter assay confirmed the target relationship between miR-135a-5p and its target genes (specificity protein 1 [SP1] and Rho-associated kinase [ROCK]1/2). By establishing the H2O2-induced injury model, miR-135a-5p transfection was found to inhibit the apoptosis of PC12 cells by downregulating the SP1 gene, which subsequently induced downregulation of pro-apoptotic proteins (Bax, cleaved caspase-3) and upregulation of anti-apoptotic protein Bcl-2. By measuring the neurite lengths of PC12 cells, miR-135a-5p transfection was found to promote axon outgrowth by downregulating the ROCK1/2 gene, which subsequently caused upregulation of phosphate protein kinase B (AKT) and phosphate glycogen synthase kinase 3β (GSK3β). Use of the rat SCI models showed that miR-135a-5p could increase the Basso, Beattie, and Bresnahan (BBB) scores, indicating neurological function recovery. In conclusion, the miR-135a-5p-SP1-Bax/Bcl-2/caspase-3 and miR-135a-5p-ROCK-AKT/GSK3β axes are involved in functional recovery of SCI by regulating neural apoptosis and axon regeneration, respectively, and thus can be promising effective therapeutic strategies in SCI.