Differential Regulation of IL-1 beta and IL-6 Release in Murine Macrophages

摘要

Asbestos and silica (exogenous danger) and adenosine triphosphate (ATP, endogenous danger-signaling molecule) synergistically increase IL-1 beta release from endotoxin-primed macrophage, which is mediated by NOD-like receptor protein 3 (NLRP3) inflammasome. However, the conversion of pro-IL-1 beta to its active form seems to depend on the macrophage cell types. In the present study, bone marrow-derived macrophages (BMM) and three murine macrophage cell lines, J774.1, J774A.1, and RAW264.7 were exposed to ATP or fibrous titanium dioxide (FTiO2) in the presence or absence of lipopolysaccharide (LPS), and the concentrations of IL-1 beta and IL-6 in both cell lysates and in the culture media were measured by immunoblotting to differentiate active form of IL-1 beta from pro-IL-1 beta. IL-1 beta release was synergistically increased when the cells were exposed to both LPS and ATP or FTiO2, while IL-6 was readily released by LPS alone. IL-1 beta released into the culture medium was pro-IL-1 beta in J774.1 and RAW264.7, and most of the pro-IL-1 beta remained inside the cells. In contrast, the active form of IL-1 beta was released together with pro-IL-1 beta from J774A.1 and BMM after the co-stimulation. J774A.1 and BMM express apoptosis-associated speck-like protein contains a carboxyl-terminal CARD (ASC) while J774.1 and RAW264.7 do not or only faintly express ASC, and accordingly, caspase-1, which converts pro-IL-1 beta to its active form, is activated only in J774A.1 and BMM. Collectively, the canonical inflammasome pathway is not activated in J774.1 and RAW264.7, and the apparent synergistical increase of IL-1 beta in the culture medium mostly reflects the leakage of pro-IL-1 beta from these cells.