Hemin Induces the Activation of NLRP3 Inflammasome in N9 Microglial Cells

Background: Hemin is an important sterile component that induces a neuroinflammatory response after intracerebral hemorrhage, in which NLRP3 inflammasome activation has also proved to be involved. Although microglial activation acts as a key contributor in the neuroinflammatory response, the relationship between hemin and NLRP3 in microglia remains poorly understood. Objective: To investigate whether or not hemin regulates microglia-mediated secondary injury through activating the NLRP3/caspase-1 signaling pathway in microglia. Methods: In this study, N9 microglial cells were treated with hemin, and subsequently used to detect the production of caspase-1 p10 and NLRP3 inflammasome assembly. An ELISA was subsequently performed to measure the secretion of IL-1β. Results: It was found that the production of activated caspase-1 was dose- and time-dependent with regards to hemin. Moreover, hemin was observed to be capable of inducing the assembly of the NLRP3 inflammasome without any increase in IL-1β. Similarly, the supernatant of hemintreated primary microglial cells did not increase in IL-1β secretion. Furthermore, hemininduced NLRP3 inflammasome activation did not significantly affect pyroptosis. Conclusion: Hemin is a potential sterile danger signal molecule that can induce inflammasome activation without directly mediating inflammation damage on microglia.