No abstract

Inflammasome activation has been implicated in various inflammatory diseases including post-ischaemic inflammation after stroke. Inflammasomes mediate activation of caspase-1, which subsequently induces secretion of pro-inflammatory cytokines such as IL-1β and IL-18, as well as a form of cell death called pyroptosis. In this study, we report that Bruton's tyrosine kinase (BTK) is an essential component of the NLRP3 inflammasome, in which BTK physically interacts with ASC and NLRP3. Inhibition of BTK by pharmacological or genetic means severely impairs activation of the NLRP3 inflammasome. The FDA-approved BTK inhibitor ibrutinib (PCI-32765) efficiently suppresses infarct volume growth and neurological damage in a brain ischaemia/reperfusion model in mice. Ibrutinib inhibits maturation of IL-1β by suppressing caspase-1 activation in infiltrating macrophages and neutrophils in the infarcted area of ischaemic brain. Our study indicates that BTK is essential for NLRP3 inflammasome activation and could be a potent therapeutic target in ischaemic stroke.

Damage-associated molecular patterns (DAMPs) trigger sterile inflammation after tissue injury, but the mechanisms underlying the resolution of inflammation remain unclear. In this study, we demonstrate that common DAMPs, such as high-mobility-group box 1 (HMGB1), peroxiredoxins (PRXs), and S100A8 and S100A9, were internalized through the class A scavenger receptors MSR1 and MARCO in vitro. In ischemic murine brain, DAMP internalization was largely mediated by MSR1. An elevation of MSR1 levels in infiltrating myeloid cells observed 3 d after experimental stroke was dependent on the transcription factor Mafb. Combined deficiency for Msr1 and Marco, or for Mafb alone, in infiltrating myeloid cells caused impaired clearance of DAMPs, more severe inflammation, and exacerbated neuronal injury in a murine model of ischemic stroke. The retinoic acid receptor (RAR) agonist Am80 increased the expression of Mafb, thereby enhancing MSR1 expression. Am80 exhibited therapeutic efficacy when administered, even at 24 h after the onset of experimental stroke. Our findings uncover cellular mechanisms contributing to DAMP clearance in resolution of the sterile inflammation triggered by tissue injury.