title: High molecular weight hyaluronan reduces lipopolysaccharide mediated microglial activation.
abstract: Toll-like receptor-4 (TLR4) signaling has been implicated in microglial activation and propagation of inflammation following spinal cord injury (SCI). As such, modulating microglial activation through TLR4 represents an attractive therapeutic approach to treat SCI. High molecular weight hyaluronan (HMW-HA), a polymer with multiple therapeutic uses, has been previously shown to modulate TLR4 activation in macrophages and has shown early promise as a therapeutic agent in SCI. However, the mechanism associated with HMW-HA has not been fully elucidated or tested in microglia, a similar cell type. In the current study, we sought to determine the effects of HMW-HA on TLR4 activation in microglia and to gain insights into the mechanism of action. Rat primary microglial cultures were exposed to lipopolysaccharides (LPS) and HMW-HA, and the extent and mechanisms of inflammation were studied. HMW-HA decreased LPS mediated IL-1β, IL-6, and Tumor necrosis factor-α gene expression and IL-6 and nitric oxide production. This decrease was associated with a reduction in ERK 1/2 and p38 phosphorylation, was dependent on the continued presence of HMW-HA, and activation of Akt and A20 protein expression was reduced by HMW-HA. Together, our results show that HMW-HA can reduce LPS-mediated inflammatory signaling in microglia. We suggest that HA possibly mediates its effects by blocking the induction of inflammatory signaling through an extracellular mechanism.
authors.affiliation: Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada.
authors.forename: James W
authors.initials: JW
authors.lastname: Austin
authors.forename: Chris
authors.initials: C
authors.lastname: Gilchrist
authors.forename: Michael G
authors.initials: MG
authors.lastname: Fehlings
mesh_terms: D000818:Animals; D000893:Anti-Inflammatory Agents; D015153:Blotting, Western; D002478:Cells, Cultured; D004247:DNA / Q000032:analysis; D004268:DNA-Binding Proteins / Q000502:physiology; D004797:Enzyme-Linked Immunosorbent Assay; D006820:Hyaluronic Acid / Q000494:pharmacology*; D007150:Immunohistochemistry; D007249:Inflammation / Q000473:pathology; D015850:Interleukin-6 / Q000378:metabolism; D008070:Lipopolysaccharides / Q000037:antagonists & inhibitors* / Q000494:pharmacology*; D008262:Macrophage Activation / Q000187:drug effects*; D017628:Microglia / Q000187:drug effects*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008970:Molecular Weight; D009569:Nitric Oxide / Q000378:metabolism; D051058:Oncogene Protein v-akt / Q000502:physiology; D010766:Phosphorylation; D051381:Rats; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D051197:Toll-Like Receptor 4 / Q000187:drug effects; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3
chemical_list: D000893:Anti-Inflammatory Agents; D004268:DNA-Binding Proteins; D015850:Interleukin-6; D008070:Lipopolysaccharides; D051197:Toll-Like Receptor 4; D009569:Nitric Oxide; D006820:Hyaluronic Acid; D004247:DNA; D051058:Oncogene Protein v-akt; D020928:Mitogen-Activated Protein Kinases; C000602677:TNFAIP3 protein, rat; D000072598:Tumor Necrosis Factor alpha-Induced Protein 3