Cytoprotection by activated
protein C (aPC) after
ischemia-reperfusion injury (IRI) is associated with apoptosis inhibition. However, IRI is hallmarked by
inflammation, and hence, cell-death forms disjunct from immunologically silent apoptosis are, in theory, more likely to be relevant. Because pyroptosis (ie, cell death resulting from
inflammasome activation) is typically observed in IRI, we speculated that aPC ameliorates IRI by inhibiting
inflammasome activation. Here we analyzed the impact of aPC on
inflammasome activity in myocardial and renal IRIs. aPC treatment before or after myocardial IRI reduced
infarct size and Nlrp3
inflammasome activation in mice. Kinetic in vivo analyses revealed that Nlrp3
inflammasome activation preceded myocardial injury and apoptosis, corroborating a pathogenic role of the Nlrp3
inflammasome. The constitutively active Nlrp3A350V mutation abolished the protective effect of aPC, demonstrating that Nlrp3 suppression is required for aPC-mediated protection from IRI. In vitro aPC inhibited
inflammasome activation in macrophages, cardiomyocytes, and cardiac fibroblasts via
proteinase-activated receptor 1 (PAR-1) and
mammalian target of rapamycin complex 1 (
mTORC1) signaling. Accordingly, inhibiting PAR-1 signaling, but not the
anticoagulant properties of aPC, abolished the ability of aPC to restrict Nlrp3
inflammasome activity and tissue damage in myocardial IRI. Targeting biased PAR-1 signaling via
parmodulin-2 restricted
mTORC1 and Nlrp3
inflammasome activation and limited myocardial IRI as efficiently as aPC. The relevance of aPC-mediated Nlrp3
inflammasome suppression after IRI was corroborated in renal IRI, where the tissue protective effect of aPC was likewise dependent on Nlrp3
inflammasome suppression. These studies reveal that aPC protects from IRI by restricting mTORC1-dependent
inflammasome activation and that mimicking biased aPC PAR-1 signaling using parmodulins may be a feasible therapeutic approach to combat IRI.