[Effect of Electroacupuncture on Cognitive Impairment in APP/PS1 Mice Based on TLR4/NF-κB/NLRP3 Pathway]

Objective: To observe the effect of electroacupuncture (EA) on the expressions of tight junction related proteins Claudin-5, ZO-1 in the colon and hippocampus, Toll-like receptor 4/nuclear factor-kappa B/NOD-like receptor protein 3 (TLR4/NF-κB/NLRP3) pathway in the hippocampus of APP/PS1 mice, so as to explore its mechanisms underlying improvement of cognitive impairment.

Methods: Eighteen 5-month-old male APP/PS1 mice were equally randomized into model and EA groups,and nine 5-month-old male C57BL/6 mice were used as the normal control. EA(2 Hz, 1 mA) was applied to "Baihui" (GV20), "Dachangshu" (BL25) and "Zusanli" (ST36) for 15 min, once daily, 5 days a week for 5 weeks. The Morris water maze swimming test was used to evaluate the mice's cognitive impairment. Nissl staining was used to observe the pathological morphology of hippocampus. The expression of amyloid β-peptide (Aβ) in brain tissue was detect by immunohistochemistry; the contents of lipopolysaccharide (LPS) in colon, serum and hippocampus were detected by ELISA; the expression levels of Claudin-5, ZO-1 in colon and hippocampus, and TLR4/NF-κB/NLRP3 pathway related proteins in hippocampus were detected by Western blot.

Results: Compared with the normal group, the escape latency of the mice in the model group was prolonged from the 3 day (<0.05, <0.01), the number of crossing the platform and the percentage of target quadrant residence time were significantly decreased (<0.01), and the contents of LPS in colon, serum and hippocampus were significantly increased (<0.01), the expression levels of TLR4, NF-κB p65, NLRP3, Caspase-1, interleukin (IL)-1β and tumor necrosis factor (TNF)-α in hippocampus and Aβ in brain tissue were significantly increased (<0.01), while the expression levels of Claudin-5, ZO-1 in colon and hippocampus were significantly decreased (<0.01). Compared with the model group, the escape latency of mice in the EA group was shortened from the 4th day (<0.05, <0.01), the number of crossing the platform and the percentage of target quadrant residence time were increased (<0.01, <0.05), and the contents of LPS in serum and hippocampus were decreased (<0.05), and the expression levels of TLR4, NF-κB p65, Caspase-1, NLRP3, IL-1β, TNF-α in hippocampus and Aβ in brain tissue were significantly decreased (<0.05, <0.01), while the expression levels of Claudin-5, ZO-1 in colon and hippocampus were significantly increased (<0.05, <0.01). Outcomes of Nissl staining showed dispersed arrangement of neurons with nuclear pyknosis or hyperchromasia in the hippocampus, and a decreased number of cell layers in the model group, which was relatively milder in the EA group.

Conclusion: EA may improve the cognitive impairment of APP/PS1 mice by up-regulating the expression of Claudin-5 and ZO-1, reducing the transposition of gut-derived LPS to the central nervous system, inhibiting the over-activation of TLR4/NF-κB/NLRP3 pathway, and alleviating the inflammatory reaction of the central nervous system.