title: Microglial Heparan Sulfate Proteoglycans Facilitate the Cluster-of-Differentiation 14 (CD14)/Toll-like Receptor 4 (TLR4)-Dependent Inflammatory Response.
abstract: Microglia rapidly mount an inflammatory response to pathogens in the central nervous system (CNS). Heparan sulfate proteoglycans (HSPGs) have been attributed various roles in inflammation. To elucidate the relevance of microglial HSPGs in a pro-inflammatory response we isolated microglia from mice overexpressing heparanase (Hpa-tg), the HS-degrading endoglucuronidase, and challenged them with lipopolysaccharide (LPS), a bacterial endotoxin. Prior to LPS-stimulation, the LPS-receptor cluster-of-differentiation 14 (CD14) and Toll-like receptor 4 (TLR4; essential for the LPS response) were similarly expressed in Ctrl and Hpa-tg microglia. However, compared with Ctrl microglia, Hpa-tg cells released significantly less tumor necrosis factor-α (TNFα), essentially failed to up-regulate interleukin-1β (IL1β) and did not initiate synthesis of proCD14. Isolated primary astroyctes expressed TLR4, but notably lacked CD14 and in contrast to microglia, LPS challenge induced a similar TNFα response in Ctrl and Hpa-tg astrocytes, while neither released IL1β. The astrocyte TNFα-induction was thus attributed to CD14-independent TLR4 activation and was unaffected by the cells HS status. Equally, the suppressed LPS-response in Hpa-tg microglia indicated a loss of CD14-dependent TLR4 activation, suggesting that microglial HSPGs facilitate this process. Indeed, confocal microscopy confirmed interactions between microglial HS and CD14 in LPS-stimulated microglia and a potential HS-binding motif in CD14 was identified. We conclude that microglial HSPGs facilitate CD14-dependent TLR4 activation and that heparanase can modulate this mechanism.
authors: From the Departments of Medical Cell Biology, Medical Biochemistry and Microbiology, Science for Life Laboratory, and paul.ocallaghan@mcb.uu.se.
authors: Paul
authors: http://orcid.org/0000-0003-3117-5367
authors: P
authors: O'Callaghan
authors: Medical Biochemistry and Microbiology, Science for Life Laboratory, and.
authors: Jin-Ping
authors: JP
authors: Li
authors: Department of Public Health and Caring Sciences, Molecular Geriatrics, Rudbeck Laboratory C11, Uppsala University, Dag Hammarskjölds väg 20, 751 85 Uppsala, Sweden.
authors: Lars
authors: L
authors: Lannfelt
authors: Medical Biochemistry and Microbiology, Science for Life Laboratory, and.
authors: Ulf
authors: U
authors: Lindahl
authors: Neuroscience, Uppsala University Biomedical Center, Husargatan 3, 751 23, Uppsala, Sweden and xiao.zhang@neuro.uu.se.
authors: Xiao
authors: X
authors: Zhang
mesh_terms: D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D017931:DNA Primers; D004797:Enzyme-Linked Immunosorbent Assay; D005966:Glucuronidase / Q000378:metabolism; D019812:Heparan Sulfate Proteoglycans / Q000378:metabolism / Q000502:physiology*; D007249:Inflammation / Q000503:physiopathology*; D053583:Interleukin-1beta / Q000378:metabolism; D018950:Lipopolysaccharide Receptors / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic; D017628:Microglia / Q000201:enzymology / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D051197:Toll-Like Receptor 4 / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D000099175:Heparanase
chemical_list: D017931:DNA Primers; D005966:Glucuronidase; D019812:Heparan Sulfate Proteoglycans; D053583:Interleukin-1beta; D018950:Lipopolysaccharide Receptors; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; D000099175:Heparanase; C493487:Tlr4 protein, mouse
keywords: Toll-like receptor 4 (TLR4); astrocyte; cluster of differentiation 14 (CD14); heparan sulfate; lipopolysaccharide (LPS); lymphocyte antigen 96 (MD2); microglia; neuroinflammation; proteoglycan