Effect of electroacupuncture of "Jiaji" (EX-B2) on NOD-like receptor protein 3 mediated pyroptosis in spinal cord tissue of rats with acute spinal cord injury.

Abstract

To observe the effect of electroacupuncture (EA) stimulation of "Jiaji"(EX-B2) on motor function, histomorphology, and expression of NOD-like receptor protein 3 (NLRP3) and N-terminal domain of gasdermin D (GSDMD-N) in the spinal cord tissue of rats with spinal cord injury (SCI), so as to explore its mechanism underlying improvement of SCI. Forty eight female SD rats were randomly divided into sham surgery (sham), SCI model (model), EA, and NLRP3 agonist (monosodium urate, MSU) combined with Jiaji EA (MSU+EA) groups, with 12 rats in each group which were further divided into 3 d and 7 d subgroups, with 6 rats at each time point. Two EA groups received EA stimulation of EX-B2 with a frequency of 100 Hz, electrical current of 1-2 mA for 30 min, once a day for 3 or 7 days. After 5 min, 6 h, and 24 h of modeling, rats of the MSU+EA group received intraperitoneal injection of MSU (200 μg/kg, 200 μg/mL) . The motor function was evaluated using Basso-Beattie-Bresnahan (BBB) scale, the morphological structure of rat spinal cord tissue was observed by H.E. staining. The expression of pyroptosis related factors NLRP3, cleaved Caspase-1 and GSDMD-N of the spinal cord was observed by using immunohistochemistry and Western blot separately, the expression and localization of Iba-1 and GSDMD-N in the spinal cord tissue were observed using immunofluorescence double staining method. Compared with the sham group, the BBB scores after modeling and on day 3 and 7 were decreased (P<0.05), while the average OD values (immunoactivity) and expression levels of NLRP3, cleaved Caspase-1 and GSDMD-N proteins, and the immunofluorescence intensity of Iba-1/GSDMD-N (co-expression) of the spinal cord tissues on day 3 and 7 were significantly increased in the model group (P<0.05). In comparison with the model group, the BBB scores on day 3 and 7 were obviously increased (P<0.05), while the immunoactivity and expression levels of NLRP3, cleaved Caspase-1 and GSDMD proteins, and the immunofluorescence intensity of Iba-1/GSDMD-N on day 3 and 7 significantly down-regulated in the EA group (P<0.05) but not in the MSU+EA group (P>0.05), suggesting an elimination of the effects of EA after administration of NLRP3 agonist (MSU). H.E. staining showed obvious bleeding area in the spinal cord tissue, loose tissue and inflammatory cell infiltration on day 3 after modeling, and basic absorption of the bleeding, loose tissue, obvious vacuolar changes of the white matter area, loss and contraction of neurons with infiltration of a large number of inflammatory cells, which was milder in the EA group but not in the MSU+EA group. EA of EX-B2 can improve the motor function of SCI rats, which may be related to its functions in inhibiting pyroptosis of microglia mediated by NLRP3/Caspase-1 signaling pathway.