After traumatic spinal cord injury (SCI), endoplasmic reticulum (ER) stress exacerbates secondary injury, leading to expansion of demyelination and reduced remyelination due to oligodendrocyte precursor cell (OPC) apoptosis. Although recent studies have revealed that amiloride controls ER stress and leads to improvement in several neurological disorders including SCI, its mechanism is not completely understood. Here, we used a rat SCI model to assess the effects of amiloride on functional recovery, secondary damage expansion, ER stress-induced cell death and OPC survival. Hindlimb function in rats with spinal cord contusion significantly improved after amiloride administration. Amiloride significantly decreased the expression of the pro-apoptotic transcription factor CHOP in the injured spinal cord and significantly increased the expression of the ER chaperone GRP78, which protects cells against ER stress. In addition, amiloride treatment led to a significant decrease in ER stress-induced apoptosis and a significant increase of NG2-positive OPCs in the injured spinal cord. Furthermore, in vitro experiments performed to investigate the direct effect of amiloride on OPCs revealed that amiloride reduced CHOP expression in OPCs cultured under ER stress. These results suggest that amiloride controls ER stress in SCI and inhibits cellular apoptosis, contributing to OPC survival. The present study suggests that amiloride may be an effective treatment to reduce ER stress-induced cell death in the acute phase of SCI.
Endoplasmic reticulum (ER) stress induces apoptotic cell death by causing the accumulation of structurally abnormal proteins. The 78-kDa glucose-regulated protein (GRP78) is an ER chaperone that regulates protein folding in the ER and has been suggested to contribute to cell survival. Using the rat C6 glioma cell line and flow cytometry, we assessed GRP78 expression following tunicamycin- and glutamate-induced ER stress. The results showed that GRP78 expression is upregulated following ER stress and has protective effects on injured glial cells. Annexin V and propidium iodide labeling revealed cells transiently expressing GRP78 prior to injury were protected against high-concentrations of tunicamycin and glutamate within 72 h. Our findings support the hypothesis that GRP78 inhibits cell death associated with ER stress.
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