Discussion of the promising effect of electroacupuncture on cognitive improvement in D-galactose-induced aging rats based on NLRP3-ASC-Caspase-1 signaling pathway

Objective To investigate the effect of electroacupuncture (EA) on cognitive function in D-galactose (D-gal)-induced aging rats, and the correlation between the effect and nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 (NLRP3)-ASC-Caspase-1 signaling pathway. Methods Forty-six male Sprague-Dawley (SD) rats were randomly divided into a control group ( n =10), a model group ( n =12), an EA-7 d group ( n =12) and an EA-21 d group ( n =12). Except the control group, the other three groups received 42 consecutive days of intraperitoneal injection of D-gal to establish aging rat models with cognitive dysfunction. The control group received the same amount of normal saline via intraperitoneal injection. Two EA groups were given EA therapy for 21 consecutive days (began from the 22nd day of modeling) or 7 consecutive days (began from the 36th day of modeling) accordingly at Dazhui (GV 14), Baihui (GV 20), Shenshu (BL 23) and Zusanli (ST 36). After modeling/intervention, all four groups received behavioral evaluations by Morris water maze (MWM) test, novel object recognition (NOR) test and step-down passive avoidance (SDPA) test followed by the Western blot (WB) detection of the expression levels of hippocampal NLRP3 inflammasome-associated proteins NLRP3, ASC and Caspase-1. Results MWM (place navigation test, PNT) results showed that the escape latency in the model group was significantly longer than that in the other three groups ( P <0.05), and there was no significant difference among the other three groups on the 1st day of the test ( P >0.05). From the 2nd day to the 4th day of the test, there was no significant difference between the EA-21 d group and the control group ( P >0.05) in the escape latency; the escape latency was significantly shorter in the EA-21 d group than in the model group and the EA-7 d group ( P <0.05). MWM (spatial probe test, SPT) results showed that the time spent in the target quadrant was significantly shorter and platform crossover number was significantly lower in the model group than in the other three groups ( P <0.05). The time spent in the target quadrant was longer in the EA-7 d group than in the model group ( P <0.05), but was shorter than that in the control group and the EA-21 d group ( P <0.05). There was no significant difference in the swimming speed among the four groups ( P >0.05). NOR results showed that there was no significant difference in the recognition ratio between the EA-7 d group and the EA-21 d group ( P >0.05), and the recognition ratio was significantly higher in the two EA groups than in the model group ( P <0.05), but was lower than in the control group ( P <0.05). SDPA results showed that the electric shock number was higher in the model group than in the other three groups ( P <0.05), and the differences among the other three groups were statistically insignificant ( P >0.05). The model group had the shortest step-down latency, followed by the EA-7 d group, the EA-21 d group and the control group in order ( P <0.05). The WB results indicated that the expression level of NLRP3 was significantly lower in the control group and the EA-21 d group than in the model group and the EA-7 d group ( P <0.05). The expression levels of ASC and Caspase-1 were significantly higher in the model group than in the other three groups ( P <0.05), and there was no significant difference among these three groups ( P >0.05). Conclusion NLRP3 inflammasome may be involved in the development of cognitive decline in aging rats; 7 consecutive days of EA intervention can partially improve the cognitive impairment in aging rats though the effect is rather limited; 21 consecutive days of EA intervention may improve the learning and memory abilities in aging rats via down-regulating the expression levels of NLRP3 inflammasome-associated proteins in hippocampus.