Recombinant chitinase-3-like protein 1 alleviates learning and memory impairments via M2 microglia polarization in postoperative cognitive dysfunction mice.

Postoperative cognitive dysfunction is a severe complication of the central nervous system that occurs after anesthesia and surgery, and has received attention for its high incidence and effect on the quality of life of patients. To date, there are no viable treatment options for postoperative cognitive dysfunction. The identification of postoperative cognitive dysfunction hub genes could provide new research directions and therapeutic targets for future research. To identify the signaling mechanisms contributing to postoperative cognitive dysfunction, we first conducted Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses of the Gene Expression Omnibus GSE95426 dataset, which consists of mRNAs and long non-coding RNAs differentially expressed in mouse hippocampus 3 days after tibial fracture. The dataset was enriched in genes associated with the biological process "regulation of immune cells," of which Chill was identified as a hub gene. Therefore, we investigated the contribution of chitinase-3-like protein 1 protein expression changes to postoperative cognitive dysfunction in the mouse model of tibial fracture surgery. Mice were intraperitoneally injected with vehicle or recombinant chitinase-3-like protein 1 24 hours post-surgery, and the injection groups were compared with untreated control mice for learning and memory capacities using the Y-maze and fear conditioning tests. In addition, protein expression levels of proinflammatory factors (interleukin-1β and inducible nitric oxide synthase), M2-type macrophage markers (CD206 and arginase-1), and cognition-related proteins (brain-derived neurotropic factor and phosphorylated NMDA receptor subunit NR2B) were measured in hippocampus by western blotting. Treatment with recombinant chitinase-3-like protein 1 prevented surgery-induced cognitive impairment, downregulated interleukin-1β and nducible nitric oxide synthase expression, and upregulated CD206, arginase-1, pNR2B, and brain-derived neurotropic factor expression compared with vehicle treatment. Intraperitoneal administration of the specific ERK inhibitor PD98059 diminished the effects of recombinant chitinase-3-like protein 1. Collectively, our findings suggest that recombinant chitinase-3-like protein 1 ameliorates surgery-induced cognitive decline by attenuating neuroinflammation via M2 microglial polarization in the hippocampus. Therefore, recombinant chitinase-3-like protein 1 may have therapeutic potential for postoperative cognitive dysfunction.