Aerobic Training Inhibits Hippocampal Inflammation by Activating the Hippocampus TLR4/miR223/NLRP3 Signaling Pathway Axis in Mice with CUMS Depression

Objective: The purpose of this study was to explore the effects of aerobic training on the hippocampal inflammation by activating the hippocampal TLR4/miR-223/NLRP3 signal pathway in mice with chronic unpredictable mild stress depression(CUMS). Methods: Sixty 8-week-old male C57 BL/6 mice were divided into control group(CG), CUMS model group(MG), CUMS model plus exercise group(ME), TLR4 inhibitor group(TG) and TLR4 inhibitor plus exercise group(TE)(n =12).Except CG, the CUMS was molded in mice of the other four groups by suffering from chronic stress for 28 days. Both ME group and TE group were trained for 8 weeks by running on a treadmill in moderate-intensity. TG group and TE group were received intraperitoneal injection of TAK-242, which was an inhibitor of TLR4, for 4 weeks. The neurobehavioral scores were tested after the 8-week training for all mice. Then, the samples were collected the day after their last training. The level of blood IL-1β and IL-10 were measuredby ELISA kit, the morphology of Nissl body in hippocampus were detected by Nissl staining, the positive expression areasof TLR4, IL-1β, IL-10 and NF-κB protein weredetected by immunohistochemistry, the gene expression levels of hippocampus NLRP3, TLR4, IL-1β, IL-10, NF-κB and miR-223 were examined by RT-PCR, and the protein expression levels of hippocampus TLR4, IL-1β and IL-10 were tested by Western Blot. Results: The neurobehavioral function of CUMS mice was significantly decreased, the inflammatory factors such as IL-1β in blood were significantly increased, and the Nissl body nuclear pyknosis were observed. 8-week aerobic training improved the hippocampus function in CUMS micesignificantly, it also reduced the level of IL-1β in blood and Nissl body nuclear pyknosis the desperate behaviorswere reduced and thedesire to survive was increased in the mice. High-throughput sequencing and correlation analysis of miRNA and mRNA showed that there was targeting regulatory relations between miR-223 and NLRP3, which was influencedby exercise intervention. The expressions of inflammatory factors such as NLRP3, TLR4, IL-1β and NF-κBweredecreased and the anti-inflammatory cytokines IL-10 was enhanced in ME mice. The expressions of NF-κB and NLRP3 were down-regulated and the miR-223 was over-expression in TG mice, while the anti-inflammatory effects was increased. The consistent anti-inflammatory effects were also found in TE mice. Conclusion: Aerobic training significantly reduced the expression of TLR4 in the hippocampus of CUMS depression mice, while the TLR4/miR-223/NLRP3 pathway axis was activated, thusthe hippocampus functionwas improved in depressed mice,and the inflammation was reduced and the repair of hippocampal inflammatory injury was enhanced as well.