in vivo derived apc-mp

Background-The endothelial protein C receptor (EPCR) plays an important role within the protein C (PC) pathway in regulating coagulation and inflammation. Recently, we described a novel mechanism of EPCR release from the surface of primary physiological cells. Induced by exogenous activated protein C (APC), EPCR is released in microparticulate form. Its bound APC retains proteolytic anticoagulant activity and we now hypothesise that this microparticulate EPCR-APC complex can also cleave endothelial protease activated receptor 1 (PAR1) to modulate inflammation and cytoprotection. Methods & Results-The gene profiling effect on human endothelial cells by 40nM APC, in free or microparticulate form, was assessed. Transcript profile results showed upregulation of anti-apoptotic and inflammatory genes by APC in either form, which were confirmed by RT-PCR. These translated into increased GM-CSF and interleukin 8 secretion and cytoprotection against staurosporine-induced apoptosis. PC or PAR1 antagonism reversed these results to demonstrate that induced effects by microparticles were APC specific and PAR1-dependent. Further analysis of human plasma from septic patients, by confocal microscopy and ELISA, showed evidence of circulating microparticle-associated EPCR during recombinant APC treatment. Functional coagulation and cellular studies demonstrate that these express APC-specific effects on anticoagulation with PAR1-mediated gene induction and anti-apoptotic function. Conclusions-APC induction of microparticle-associated EPCR release can occur in vivo. These microparticles could potentially disseminate the function of the EPCR-APC complex to PAR1 on different cells and vascular sites. Keywords: pre versus rhAPC-treatment mp in vivo MP were isolated from sepsis patients pre and during-rhAPC treatment. MP were counted by FACS using CD13 positivity and same number of mp was used in pre and during treatment comparisons. HUVEC were incubated with the in vivo mps according to mp number or apc content, and controls for both were done using non-treated patients or free-apc. The role of apc and par1 was analysed by including apc blocking antibody or par1 antaginist peptide respectively.