Upregulation of miR-128 inhibits neuronal cell apoptosis following spinal cord injury via FasL downregulation by repressing ULK1

Spinal cord injury (SCI) is characterized by permanent motor deficits followed by inflammation and oxidative stress, causing neuronal cell death. The present study aimed to investigate the role of microRNA (miR)-128 in neuronal cell apoptosis and its underlying mechanism. Targeting relationships among miR-128 and Unc-51 like autophagy activating kinase 1 (ULK1) and Fas ligand (FasL) were verified using dual-luciferase reporter assay and ChIP assays. Loss- and gain-of-function assays were conducted in rat models of SCI to determine the roles of miR-128 and ULK1 in neuronal cell apoptosis, inflammation, and motor function. Apoptosis, motor function and expression of inflammatory factors were respectively determined by Terminal deoxynucleotidyl transferase-mediated dUTp nick end-labeling, Basso, Beattie and Bresnahan (BBB) score and enzyme-linked immunosorbent assay. Hematoxylin and eosin staining, Nissl staining and immunofluorescence were respectively performed to observe morphological changes and number of neurons and nestin-positive cells. The neuronal cells were isolated from neuron injury models and cultured in vitro. MTT and flow cytometry was conducted to determine the neuronal cell viability and apoptosis respectively. miR-128 was downregulated whereas ULK1 was upregulated in rats with SCI. Overexpression of miR-128 or downregulation of ULK1 inhibited neuronal cell apoptosis and inflammation as evidenced by an increased BBB score and more neurons and nestin-positive cells, but reduced expression of inflammatory and apoptosis-related factors. ULK1 was negatively regulated by miR-128, whereas FasL was positively regulated by ULK1. In vitro experiments validated the roles of miR-128 and ULK1 in neuronal cell differentiation and apoptosis. In conclusion, the upregulation of miR-128 depresses neuronal cell apoptosis by downregulating ULK1, thereby attenuating SCI via the downregulation of FasL.