Protease-activated Receptor-1 Signaling by Activated Protein C in Cytokine-perturbed Endothelial Cells Is Distinct from Thrombin Signaling

Abstract

Activated protein C (APC) has anti-inflammatory and vascular protective effects independent of anticoagulation. We previously identified the prototypical thrombin receptor, protease-activated receptor-1 (PAR1), as part of a novel APC-endothelial cell protein C receptor (EPCR) signaling pathway in endothelial cells. Experiments in wild-type and PAR1؊/؊ mice demonstrated that intravenous injection of APC leads to PAR1-dependent gene induction in the lung. The vascular endothelium undergoes profound changes in severe sepsis, the approved therapeutic indication for APC. Similar to PAR1, APC activated PAR2 through canonical cleavage. Although PAR2 was up-regulated in cytokine-stimulated endothelial cells, APC signaling remained PAR1-dependent. Large scale gene expression profiling documented marked differences in both up-and down-regulated genes between APC and thrombin signaling in cytokine-stimulated cells. APC down-regulated transcripts for proapoptotic proteins including p53 and thrombospondin-1, but p53 was unchanged, and thrombospondin was even upregulated by thrombin. Concordant PAR1-dependent effects on protein levels were found. Thus, by signaling through the same receptor PAR1, APC, and thrombin can exert distinct biological effects in perturbed endothelium. These data may explain how APC can be therapeutically protective through the EPCR-PAR1 signaling despite ongoing thrombin generation due to disseminated intravascular coagulopathy.

The Endothelial Protein C Receptor Supports Tissue Factor Ternary Coagulation Initiation Complex Signaling through Protease-activated Receptors

“…The role of EPCR as a crucial co-receptor for PC activation and aPC-mediated cytoprotective signaling in vascular and immune cells is supported by in vitro and in vivo data (57)(58)(59)(60)(61)(62)(63). However, TF is normally not expressed in the vascular endothelium but co-expressed with EPCR in extravascular cells.…”

“…The presented data with SMCs raise the intriguing possibility that TF and EPCR expressed in the vessel wall regulate the cellular responses to low levels of coagulation proteases that are constitutively present or ectopically synthesized in the extravascular space. Intravascular EPCR-aPC-PAR1 signaling counteracts thrombin-PAR1 signaling (8,57,61,76). It is intriguing to speculate that EPCR-dependent ternary complex signaling may similarly regulate certain aspects of extravascular upstream coagulation signaling.…”

The Roles of Proteinase-Activated Receptors in the Vascular Physiology and Pathophysiology

“…2,[25][26][27][28] Plasmin either activates or disarms PAR1, 6,29,30 whereas it inactivates PAR2 and activates PAR4. 31,32 The activated protein C (APC) has been shown to activate PAR1 and PAR2, [33][34][35] although its functional role still remains controversial. 36 In the following sections, I would like to discuss the role of PARs in regulating the vascular functions and in the pathophysiology of vascular diseases, with some focus on thrombin and its major receptor PAR1.…”

Differential Effects of Activated Protein C on Synovial Fibroblasts in Response to Hypoxia and Normoxia

“…A previous study showed that under hypoxic conditions, p38 mitogen-activated protein kinase (p38MPAK) is essential for fibroblast proliferation and acts as a modulator of pro-inflammatory responses in rheumatological conditions (Mortimer et al 2007). Indeed, if protease-activated receptors (PARs) are activated, they signal via p38 to induce immune responses (Julovi et al 2011;Riewald & Ruf 2005). Thus, we expected that activation of p38 by APC under hypoxic conditions would be involved in the proliferation and anti-inflammatory response of RAFb.…”