Summary
Despite the success of the anti-coagulant protease protein C (PC) in treating septic
shock in humans, the signaling pathways used are still unclear. To explore the effects
of treatment with PC zymogen and its activated form aPC in a setting of sepsis, we
employed a piglet model of endotoxic shock. In the aPC group, we observed a 65%-90%
reduction in plasmaTNF-alpha levels and a concomitant clinical improvement. Unexpectedly,
administration of aPC also resulted in stabilization of the plasma pH above 7.2. Moreover,
phosphorylated p38 mitogen-activated protein kinase (p38MAPK) was virtually absent
in the livers of those piglets receiving aPC. In cultured human umbilical vein endothelial
cells, we observed that nanomolar concentrations of PC and aPC inhibited the phosphorylation
of p38MAPK. Furthermore, we showed that the regulation of the pro-apoptotic cell cycle
regulator p53 by PC and aPC is dependent on the reduction of p38MAPK activation. The
transduction of these effects involves all three receptors associated with protein
C signaling, namely endothelial protein C receptor, protease-activated receptor 1,
and sphingosine 1-phosphate receptor 1. Ultimately, this study elucidates novel signaling
pathways regulated by protein C and emphasises the pivotal importance of its multiple
modes of action beyond anticoagulation. APC’s clinical success may, in part, be due
to p38MAPK inhibition.
Keywords
Protein C - sepsis - signal transduction - p38MAPK - apoptosis