'Role reversal' for the receptor PAR1 in sepsis-induced vascular damage

Abstract

Sepsis is a deadly disease characterized by considerable derangement of the proinflammatory, anti-inflammatory and coagulation responses. Protease-activated receptor 1 (PAR1), an important regulator of endothelial barrier function and blood coagulation, has been proposed to be involved in the lethal sequelae of sepsis, but it is unknown whether activation of PAR1 is beneficial or harmful. Using a cell-penetrating peptide (pepducin) approach, we provide evidence that PAR1 switched from being a vascular-disruptive receptor to a vascular-protective receptor during the progression of sepsis in mice. Unexpectedly, we found that the protective effects of PAR1 required transactivation of PAR2 signaling pathways. Our results suggest therapeutics that selectively activate PAR1-PAR2 complexes may be beneficial in the treatment of sepsis.Sepsis remains the leading cause of mortality of patients in intensive care units, causing at least 210,000 deaths annually in the United States1. Much of the pathology of sepsis has been attributed to a hyper-reaction of the inflammatory system to the invading pathogens, a condition called 'systemic inflammatory response syndrome' 2 . During the early phases of sepsis, systemic concentrations of inflammatory cytokines and chemokines rapidly increase and the endothelium is activated to cause vascular leakage and septic shock. In late-stage sepsis, the clotting cascade is triggered by the damaged endothelium, leading to disseminated intravascular coagulation (DIC) and multiorgan failure 3, 4. The vascular damage is caused by many sepsis-related factors, including bacterial endotoxin, tumor

Targeting Protease-Activated Receptor-1 with Cell-Penetrating Pepducins in Lung Cancer

“…Multiple studies have been performed to determine the specificity of pepducins to their cognate receptors. 22,[31][32][33][34] We found that PAR1 pepducins based on the i1 and i3 loops had comparable efficacy in inhibiting migration and Ca 2ϩ signaling. In contrast, i3-targeted pepducins also could block PAR1-dependent ERK1/2 activity and VEGF secretion.…”

“…Pepducins are lipidated peptides that are specifically targeted to the intracellular surface of their cognate GPCR, resulting in modulation of signal transduction. 21,22,31,32,50,51 Pepducins targeting the PAR1 i3 loop completely inhibited cell motility, calcium mobilization, and ERK1/2 activation. In contrast, the i1-targeted PAR1 pepducin inhibited cell motility, but did not have any effect on ERK1/2 activation and only partially suppressed calcium mobilization.…”

“…21,22,38 Pepducins based on the i1 and i3 loops have proven to be potent inhibitors of chemokine receptors 32 and PAR4. 21,35 To guide in the design of i1 and i3 pepducins, a model of PAR1 based on the X-ray structure of rhodopsin 39 was generated 40 as shown in Figure 1A.…”

“…PAR1 and PAR3 can serve as co-factors for PAR4, 13,21 and PAR1 can transactivate PAR2. 22 Each PAR couples to a distinct subset of G proteins. For instance, PAR1 couples with G␣-subunits G q , G i , and G 12/ 13, which are activated differentially by different proteases.…”

“…We previously have shown that a switch in G-protein signaling from G 12/13 to G i occurs in the context of PAR1-PAR2 heterodimers and is involved in the maintenance of endothelial barrier function. 22 G i is involved in activation of rac and inhibition of adenylate cyclase and suppression of cAMP. It is still not understood how PAR1 regulates the mitogen-activated protein kinase cascade members such as ERK1/2.…”