The present study demonstrated that tolerance to focal cerebral ischemia induced by EA pretreatment is mediated by BDNF and SDF-1α. Our results showed that pretreatment with EA at Baihui (GV20) and Dazhui (GV14) for 20 min increased the brain tissue content of BDNF and upregulated the production of SDF-1α in the plasma. Moreover, EA preconditioning reduced infarct volume by 43.5% when compared to control mice 24 h after photothrombotic cortical ischemia. Consistent with a smaller infarct size, EA preconditioning showed prominent improvement of neurological function and motor function such as vestibule-motor function, sensori-motor function and asymmetry forelimb use. The expression of BDNF, colocalized within neurons, and SDF-1α, colocalized within the cerebral vascular endothelium, was observed throughout the ischemic cortex following EA. These findings provide valuable insight into BDNF and SDF-1α that elicited neuroprotective effects induced by EA preconditioning against focal cerebral ischemia.
Anticoagulation, thrombolysis and cellular protection have not been shown to fully improve stroke patients. EA is a novel therapy based on traditional acupuncture combined with modern electrotherapy. Clinically, acupuncture has shown significant therapeutic benefits for stroke patients
[1, 2, 24, 25]. A large number of animal studies have shown that EA could reduce neural apoptosis, promote cell proliferation, increase cerebral blood flow (CBF), and improve neurological function after stroke
[4–7]. However, the precise mechanism of EA function remains controversial. In addition, the type of stroke, its severity and the interval after the stroke and pretreatment might also significantly influence the results of EA studies
Preconditioning as a potent endogenous protective response, activates several endogenous signaling pathways that result in tolerance against ischemia
. In recent years, numerous studies have shown that EA also have pretreatment effects, including ischemic tolerance as well
[10, 11]. Since EA is economical, easily performed, and has few negative side effects, it is clinically applicable for prevention, and not just treatment of ischemic cerebral disease. Our study demonstrated that, similar to the ischemic tolerance induced by ischemic preconditioning, repeated EA pretreatment at Baihui (GV20) and Dazhui (GV14) for 20 min a day for three days before lethal ischemic insult could reduce infarct volumes and improve neurological function and motor function 24 h after occlusion. These findings indicate that EA pretreatment could induce tolerance to cerebral ischemic insult.
EA has been reported to increase neurotrophic factors such as insulin-like growth factor 1, basic fibroblast growth factor, glial derived neurotrophic factor or receptors, NMDA NR1 and TRPM7
[13, 28–30]. BDNF, SDF-1α and VEGF are hypoxia-inducible factor (HIF)-1 target proteins, which have been implicated in mediating neuroprotection after hypoxic preconditioning
[31, 32]. BDNF, SDF-1α and VEGF can affect both neuronal and vascular function in the ischemic brain. BDNF was originally discovered through its neuronal effects and then later found to also have vascular effects, whereas SDF-1α and VEGF were originally discovered through their angiogenic effects and then later found to also have neuroprotective activity
. BDNF is a potent growth factor involved in recovery following cerebral ischemia
[15, 16]. Altered BDNF plasma levels or association of BDNF genotypes indicate that this growth factor may be involved in the physiological response to stroke in humans
. SDF-1α, a CXC chemokine produced by bone marrow stromal cells, a potent chemo-attractant for hematopoietic stem cells, is constitutively expressed by all tissues
. Stumm et al. demonstrated that focal cerebral ischemia causes an increase in endothelial SDF-1α expression in regions adjacent to the infarcted area
. Recently, intracerebral administration of SDF-1α was reported to induce neuroprotection against neurotoxic insult, and induce increased bone marrow-derived cell targeting of the ischemic brain, thereby reducing the volume of cerebral infraction and improving neural plasticity
. VEGF is an angiogenic peptide that also exerts a large number of diverse neuronal effects in the central nervous system
. For these reasons, BDNF, SDF-1α and VEGF are potent candidates in ischemic preconditioning; however, little is known about the involvement of them in EA preconditioning in ischemic brains. Therefore, we examined whether BDNF, SDF-1α and VEGF were involved in neuroprotective effects of EA preconditioning in focal cerebral ischemia. We found that EA preconditioning increased the brain tissue content of BDNF and upregulated the production of SDF-1α in the plasma. In addition, a large number of BDNF- and SDF-1α-positive cells in the ischemic cortex were observed in the EA group. Moreover, the present immunofluorescence data showed that BDNF immunoreactivities were colocalized with NeuN immunoreactivities and SDF-1α immunoreactivities with CD31 immunoreactivities, indicating that the effect of EA pretreatment on BDNF expression was neuron-specific and SDF-1α was vessel-specific in the ischemic cortex. These current results strongly suggest that upregulation of neuronal BDNF and vascular SDF-1α after EA pretreatment might be an important protective mechanism of tolerance against ischemia. Interestingly, SDF-1α production was upregulated in a time-dependent manner following EA stimulation, while VEGF remained unchanged after EA pretreatment in the plasma. A few studies have shown that VEGF production was increased by EA
. These different results might be due to differences in the severity of cerebral ischemia or the use of different acupoints in this and previous studies.