Inflammation in the central nervous system plays a crucial role in the occurrence and development of sepsis-associated encephalopathy. This study aims to explore the effects of maresin 1 (MaR1), an anti-inflammatory and pro-resolving lipid mediator, on sepsis-induced neuroinflammation and cognitive impairment. Mice were randomly assigned to 4 groups: A sham group (sham operation+vehicle), a cecal ligation and puncture (CLP) group (CLP operation+vehicle), a MaR1-LD group (CLP operation+1 ng MaR1), and a MaR1-HD group (CLP operation+10 ng MaR1). MaR1 or vehicle was intraperitoneally administered starting 1 h before CLP operation, then every other day for 7 days. Survival rates were monitored, and serum inflammatory cytokines [tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, and IL-6] were measured 24 h after operation using enzyme-linked immunosorbent assay (ELISA). Cognitive function was assessed 7 days after operation using the Morris water maze (MWM) test and novel object recognition (NOR) task. The mRNA expression of TNF-α, IL-1β, IL-6, inducible nitric oxide synthase (iNOS), IL-4, IL-10, and arginase 1 (Arg1) in cortical and hippocampal tissues was determined by real-time reverse transcription PCR (RT-PCR). Western blotting was used to determine the protein expression of iNOS, Arg1, signal transducer and activator of transcription 6 (STAT6), peroxisome proliferator-activated receptor gamma (PPARγ), and phosphorylated STAT6 (p-STAT6) in hippocampal tissue. Microglia activation was visualized via immunofluorescence. Mice were also treated with the PPARγ antagonist GW9662 to confirm the involvement of this pathway in MaR1's effects. CLP increased serum levels of TNF-α, IL-1β, and IL-6, and reduced body weight and survival rates (all P<0.05). Both 1 ng and 10 ng doses of MaR1 significantly reduced serum TNF-α, IL-1β, and IL-6 levels, improved body weight, and increased survival rates (all P<0.05). No significant difference in efficacy was observed between the 2 doses (all P>0.05). MWM test and NOR task indicated that CLP impaired spatial learning, which MaR1 mitigated. However, GW9662 partially reversed MaR1's protective effects. Real-time RT-PCR results demonstrated that, compared to the sham group, mRNA expression of TNF-α, IL-1β, and iNOS significantly increased in hippocampal tissues following CLP (all P<0.05), while IL-4, IL-10, and Arg1 showed a slight decrease, though the differences were not statistically significant (all P>0.05). Compared to the CLP group, both 1 ng and 10 ng MaR1 decreased TNF-α, IL-1β, and iNOS mRNA expression in hippocampal tissues and increased IL-4, IL-10, and Arg1 mRNA expression (all P<0.05). Immunofluorescence results indicated a significant increase in Iba1-positive microglia in the hippocampus after CLP compared to the sham group (P<0.05). Administration of 1 ng and 10 ng MaR1 reduced the percentage area of Iba1-positive cells in the hippocampus compared to the CLP group (both P<0.05). Western blotting results showed that, compared to the CLP group, both 1 ng and 10 ng MaR1 down-regulated the iNOS expression, while up-regulated the expression of Arg1, PPARγ, and p-STAT6 (all P<0.05). However, the inclusion of GW9662 counteracted the MaR1-induced upregulation of Arg1 and PPARγ compared to the MaR1-LD group (all P<0.05). MaR1 inhibits the classical activation of hippocampal microglia, promotes alternative activation, reduces sepsis-induced neuroinflammation, and improves cognitive decline.
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