title: Inflammasome activation and IL-1β/IL-18 processing are influenced by distinct pathways in microglia.
abstract: Microglia are important innate immune effectors against invading CNS pathogens, such as Staphylococcus aureus (S. aureus), a common etiological agent of brain abscesses typified by widespread inflammation and necrosis. The NLRP3 inflammasome is a protein complex involved in IL-1β and IL-18 processing following exposure to both pathogen- and danger-associated molecular patterns. Although previous studies from our laboratory have established that IL-1β is a major cytokine product of S. aureus-activated microglia and is pivotal for eliciting protective anti-bacterial immunity during brain abscess development, the molecular machinery responsible for cytokine release remains to be determined. Therefore, the functional role of the NLRP3 inflammasome and its adaptor protein apoptosis-associated speck-like protein (ASC) in eliciting IL-1β and IL-18 release was examined in primary microglia. Interestingly, we found that IL-1β, but not IL-18 production, was significantly attenuated in both NLRP3 and ASC knockout microglia following exposure to live S. aureus. NLRP3 inflammasome activation was partially dependent on autocrine/paracrine ATP release and α- and γ-hemolysins produced by live bacteria. A cathepsin B inhibitor attenuated IL-β release from NLRP3 and ASC knockout microglia, demonstrating the existence of alternative inflammasome-independent mechanisms for IL-1β processing. In contrast, microglial IL-18 secretion occurred independently of cathepsin B and inflammasome action. Collectively, these results demonstrate that microglial IL-1β processing is regulated by multiple pathways and diverges from mechanisms utilized for IL-18 cleavage. Understanding the molecular events that regulate IL-1β production is important for modulating this potent proinflammatory cytokine during CNS disease.
authors.affiliation: Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska 68198, USA.
authors.forename: Richa
authors.initials: R
authors.lastname: Hanamsagar
authors.forename: Victor
authors.initials: V
authors.lastname: Torres
authors.forename: Tammy
authors.initials: T
authors.lastname: Kielian
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D051017:Apoptosis Regulatory Proteins; D001426:Bacterial Proteins / Q000494:pharmacology; D001427:Bacterial Toxins / Q000494:pharmacology; D053468:CARD Signaling Adaptor Proteins; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D003598:Cytoskeletal Proteins / Q000172:deficiency / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D006460:Hemolysin Proteins / Q000494:pharmacology; D020382:Interleukin-18 / Q000378:metabolism*; D053583:Interleukin-1beta / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000187:drug effects / Q000276:immunology / Q000378:metabolism* / Q000382:microbiology; D008954:Models, Biological; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D058919:Purinergic P2 Receptor Antagonists / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics*; D013211:Staphylococcus aureus / Q000472:pathogenicity / Q000502:physiology; D013844:Thiazoles / Q000494:pharmacology; D013997:Time Factors
chemical_list: C516674:AZ 11645373; D051017:Apoptosis Regulatory Proteins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D053468:CARD Signaling Adaptor Proteins; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D004791:Enzyme Inhibitors; D006460:Hemolysin Proteins; D020382:Interleukin-18; D053583:Interleukin-1beta; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C492716:Nlrp3 protein, mouse; D058919:Purinergic P2 Receptor Antagonists; C498534:Pycard protein, mouse; D013844:Thiazoles; C037956:gamma-hemolysin, Staphylococcus aureus; C021091:staphylococcal alpha-toxin; D000255:Adenosine Triphosphate