Acute spinal cord injury in rats should target activated autophagy

Abstract

Autophagy is a cellular mechanism of maintaining balance between protein synthesis and degradation; the latter can be induced by starvation and neurodegenerative disease. Spinal cord injury (SCI) induces necrosis and apoptosis. Autophagic flux has not yet been defined, especially the potential role of autophagy in relation to apoptosis in different tissue cells. The object of this study was to investigate the occurrence of autophagic flux and the potential role of autophagy and apoptosis post-SCI in rats. Following creation of SCI in rats, activation of autophagic flux was detected at the protein (LC3, beclin1, and p62) and mRNA (beclin1) levels and on electron microscopy images. Distribution of LC3, colocalization of activated caspase-3, and changes in expression levels of bcl-2 and Bax were assessed to investigate the potential role of autophagy and apoptosis. Sprague-Dawley rats were used, and T9-10 hemitransection was performed. Expression levels of LC3, beclin1, p62, bcl-2, and Bax were assessed by Western blot analysis, and beclin1 mRNA levels were assessed by reverse transcription-polymerase chain reaction. Distribution of LC3 and colocalization of activated caspase-3 were analyzed by immunohistochemistry. Autophagosome formation was investigated by electron microscopy. The authors found a dramatic elevation in LC3 and beclin1 levels near the scar region. Using double staining, they observed that upregulation of LC3 started at 4 hours in neurons and at 3 days in astrocytes after SCI. Confocal images indicated that the percentage of neurons with apoptosis was reduced, while the percentage of astrocytes with apoptosis was high at 4 hours, 8 hours, and 1 day post-SCI but decreased sharply at 3 days. Electron microscopy images provided evidence of autophagosome formation. Elimination of p62 indicated occurrence of autophagic flux. Expression levels of bcl-2 and Bax were increased and decreased, respectively, near the injury site. The results of this research demonstrated that autophagic flux is activated after SCI. Potentially, inhibition of apoptosis could be a target to promote neural recovery.