The role of Rho-kinases in IL-1β release through phagocytosis of fibrous particles in human monocytes

Long fibers, such as asbestos and carbon nanotubes (CNTs), are more potent activators of inflammatory and genotoxicity than short or tangled fibers. Fibrous particles trigger interleukin (IL)-1 beta secretion and cause inflammatory diseases through NLRP3 inflammasomes in phagocytotic cells. However, the mechanism involved in fibrous particle-induced inflammation has not been well documented. In this study, we focused on GTPase effector Rho-kinases (ROCK1, and 2), which are known to be involved in a wide range of cellular functions such as adhesion, regulation of cytoskeleton, and phagocytosis. We examined whether ROCKs are associated with multi-walled CNT (MWCNT)- or asbestos-induced IL-1 beta secretion in human monocytic THP-1 cells using a selective inhibitor and small interfering RNA. THP-1 cells were differentiated to macrophages by PMA and were exposed to MWCNTs, crocidolite asbestos or lipopolysaccharide (LPS) in the presence or absence of Y27632 (ROCK inhibitor) or Z-YVAD (caspase-1 inhibitor). Exposure of the cells to MWCNTs or asbestos provoked IL-1 beta secretion, but this secretion was suppressed by both Y27632 and Z-YVAD, whereas LPS-induced IL-1 beta secretion was inhibited only by Z-YVAD and not by Y27632. siRNA designed for knockdown of both ROCK1 and ROCK2 suppressed MWCNT- and asbestos-induced IL-1 beta secretion, but did not change LPS-induced IL-1 beta secretion. Moreover, Y27632 suppressed pro-IL-1 beta protein levels and the release of activated-cathepsin B and activated-caspase-1 induced by MWCNTs or asbestos. In contrast, LPS-induced pro-IL-1 beta protein was not suppressed by Y27632. These results suggest that ROCKs are involved in fibrous particle-induced inflammasome responses in THP-1 cells.