Ischemic preconditioning protects motor neurons against ischemic injury by inducing endoplasmic reticulum stress, upregulating GRP78 and inhibiting caspase-12 activation

It has been established that ischemic preconditioning (IPC) via brief ischemia/reperfusion (I/R) induces resistance to the lethal cell ischemia. The aim of the present study was to elucidate the involvement of endoplasmic reticulum stress (ERS) in the IPC mediated protection against ischemic motor neuron injury. A rat model of spinal cord ischemia was established by clamping the infrarenal aorta. A total of 96 male Wistar rats were allocated at random into four groups: Sham, IPC, I/R and IPC+I/R. IPC consisted of 2 cycles of 5 min of ischemia and 5 min of reperfusion. In the I/R group, the aortic occlusion was continued for 45 min and then aorta patency was restored. The spinal cord was removed at 4, 8, 24 or 48 h, following 45 min of transient ischemia. Neurological function was evaluated prior to sacrifice, and histological changes were assessed using hematoxylin and eosin (HE) staining. A terminal deoxynucleotidyl transferase mediated dUTP nick end labeling assay was conducted to detect apoptotic cells. Immunohistochemistry (IHC) and western blot analysis were used to assess the expression of glucose regulated protein 78 (GRP78) and caspase 12. The results indicated that IPC markedly reduced motor neuron death during the subsequent ischemia. Elevated protein expression of GRP78 was observed, with a peak at 4 h of reperfusion in the IPC+I/R group, correlating with the ischemic tolerance time window. The results of the western blot and immunohistochemical analyses indicated that GRP78 expression was associated with the mitigation of caspase-12 activation. These results suggested that IPC induced ERS, upregulated GRP78 and inhibited the activation of caspase- 12 in motor neurons, thus protecting the spinal cord against I/R injury in rats.