The current study indicates that EA facilitates the reduction of neuronal apoptosis and neurological impairment and the regulation of the expressing of inflammation factors through inhibiting the expressing level of P2X7R.
Given that the cerebrum is the most vulnerable organ, short periods of ischemia and hypoxia can cause irreversible functional and structural damage to the brain(Harutyunyan and Avitsian 2020), which is further exacerbated when blood flow is restored to the damaged area. Studies have shown that various excitatory neurotransmitters, a large amount of which can cause calcium overload and the generation of oxygen free radicals(Mattson 1996; Bak et al. 2018), including acetylcholine, aspartic acid, and glutamate, are closely related to cerebral ischemic injury(Liu et al. 2019; Caba et al. 2021). Therefore, if the release of these transmitters can be effectively controlled, the ischemic reperfusion injury to the brain tissue can be effectively alleviated.
Traditional Chinese Medicine has had a unique insight into “stroke” for millennia, while acupuncture and moxibustion are significant means of TCM treatment(Ifrim Chen et al. 2019). With the continuous development of science, the efficacy of acupuncture and moxibustion has been gradually recognized by the Western medical community, accompanied by clinical studies(Wang et al. 2021) which have confirmed that, through modern medicine, acupuncture and moxibustion treatments of patients with cerebral infarction have significantly improved the hemodynamic parameters and deposition indexes of red blood cells, and that acupuncture treatment also can contribute to the rehabilitation of stroke patients. 16 foreign scholars who acupunctured du meridian acupoints in rats in the cerebral infarction model found that neuron necrosis, cavitation, congestion, edema, and other ischemia-reperfusion injury were significantly reduced (Shiflett 2007) and functional magnetic resonance imaging (fMRI) was used to discover Zusanli point on the back in the brain's frontal activation(Li et al. 2008). In addition, it has been found that electroacupuncture stimulation of “Baihui point” in rats can induce cerebral ischemia tolerance(Kim and Bae 2010; Wu et al. 2015; Yao et al. 2018).
Hypoxic ischemia often leads to neuron death and inflammation which is mainly mediated by microglia(Hanisch and Kettenmann 2007). ATP, the precursor of adenosine, not only provides direct energy to cells but is also an important neurotransmitter in the central nervous system (CNS), while ATP(Giblett and Hoole 2017) and its related metabolites are involved in the purinergic signal transduction pathway by acting on the purinergic receptor (PR). There are two types of PR, P1 and P2, with the P1 receptor having the highest affinity for adenosine and the P2 receptor having the highest affinity for ATP. Studies have shown that electroacupuncture-induced cerebrum ischemia tolerance is closely related to the involvement of purinergic signals in neurons. P2X7R(Sluyter 2017), a purinergic receptor expressed on microglia, has been shown to be elevated in rats with peripheral nerval damage, whereas the antagonist of P2X7R (A804598) reduces phosphorylation of P38, glia cell stimulation, and the expressing level of IL-1B, coherent with less nerval impairment and improved neuron survival(Savio et al. 2017). Electroacupuncture inhibited SNL-triggered microglia cell stimulation under the medication of P38 MAPK(Liang et al. 2016; Liu et al. 2017). Assuming that the expressing levels of inflammation factors and the changes in neurobehavioral functions in post-stroke rats may be associated with the modulation of P2X7R and P38 MAPK. Herein, our team discovered that BzATP exacerbated neurological function and neuron injury in post-stroke rats, and facilitated the expressing levels of P2X7R, P-P38, IBA1, and pro-inflammation factors, which suggests that P2X7R may participate in the occurrence of cerebrum I/R damage.
This study also analyzed the relationship between EA and P2X7R, and the effect of electroacupuncture on cerebral ischemia tolerance as inhibited by the P2X7R agonist. The results of this study show that electroacupuncture can improve neuronal apoptosis and modulate the expressing levels of inflammation factors via suppressing the expressing level of P2X7R, whereas previously researches have revealed that the central causal link of electroacupuncture was anti-inflammatory may be associated with reduced expression of P-P38MAPK, thereby reducing microglial activation(Liang et al. 2016). Drawing on this, we hypothesized that electroacupuncture might repress the phosphonation of P38 via suppressing the activities of P2X7R in microglial cells, thereby reducing inflammatory events and producing ischemic tolerance.
In addition, this study has some limitations; firstly, the expressing level of P2X7R positive cells was identified without immune fluorescence staining and dual staining for P2X7R and IBA1 being performed. Secondly, we cannot reveal that the protective effect of electroacupuncture was achieved via suppressing the phosphorylation of P38 in microglial cells, a perspective that requires more investigation in the future. Thirdly, based on the current research, we can merely hypothesize that electroacupuncture is possible to be protective in the brain via decreasing the expressing level of P2X7R, a mechanism that should be further confirmed using P2X7R inhibitors or P2X7R siRNA.
In conclusion, this study shows that electroacupuncture may reduce the apoptosis and inflammatory response of nerve cells induced by cerebral ischemia reperfusion by down-regulating the expression of P2X7R, thus achieving cerebral ischemia tolerance, and therefore P2X7R can serve as a latent treatment target of electroacupuncture for brain protection. The results of this study reveal the mechanism of electroacupuncture-induced focal ischemic tolerance, complementing the theoretical and scientific basis for such preconditioning.