Sulfate glycosaminoglycan from swim bladder exerts immunomodulatory potential on macrophages via toll-like receptor 4 mediated NF-κB signaling pathways.

This study explored the immunomodulatory impact and potential mechanisms on macrophages RAW264.7 using a purified macromolecular sulfate glycosaminoglycan (SBSG) from the swim bladder, whose structure was similar to chondroitin sulfate A. The results showed that SBSG at 0.25-1 mg/mL increased the viability and phagocytosis of RAW264.7 cells. Meanwhile, SBSG promoted the secretion of tumor necrosis factor α (TNF-α), interleukin 10 (IL-10), and nitric oxide (NO), as well as the production of reactive oxygen species (ROS). According to the RT-PCR and Western blot data, SBSG activated TLR4-nuclear factor kappa B (NF-κB) signaling pathways, which decreased the relative mRNA and protein levels of Toll-like receptor 4 (TLR4), IκB kinase β (IKKβ), NF-κB p65, and p-NF-κB p65. The molecular docking and molecular dynamic simulation findings revealed that the main binding force between TLR4 and SBSG was conventional hydrogen bond interaction, resulting in more stable ligand receptor complexes. In summary, SBSG exhibits significant immunomodulatory potential, similar to chondroitin sulfate C. The underlying molecular mechanism involved the binding of SBSG through hydrogen bonding to TLR4 receptors, triggering the NF-κB signaling pathway to downregulate the expression of related genes and proteins. This, in turn, regulated the secretion of various cytokines that were mediated by macrophages to exert the immunity of the body.