Targeting PAR1 biased signaling with parmodulin reduces thromboinflammation and acute lung injury in sickle cell disease.

Protease activated receptor 1 (PAR1) is expressed by numerous cell types, including endothelial cells. Thrombin cleaves PAR1 at Arg41 and activates proinflammatory and barrier disruptive signaling. Alternatively, PAR1 is cleaved at Arg46 by activated protein C (APC) that is bound to endothelial protein C receptor (ECPR), which induces anti-inflammatory and barrier protective signaling. In sickle cell disease (SCD), we showed that thrombin-PAR1 signaling contributes to vascular stasis and, more recently, that PAR1-R41-biased signaling enhances inflammation, whereas PAR1-R46 signaling reduces thrombo-inflammation. We hypothesized that ECPR-PAR1-R46-biased signaling protects sickle mice from thrombo-inflammation. To test this hypothesis, Townes sickle mice were treated with parmodulin (parmodulin 2 [PM2, aka ML161] or NRD-21) to promote protective, anti-inflammatory PAR1-biased signaling. We found that PM2 significantly attenuated thrombin generation, inflammation, and endothelial activation and protected sickle mice from a model of lethal acute chest syndrome. These results suggest that using PM2 to block thrombin-PAR1 signaling while inducing APC-like signaling can promote cytoprotective, anti-inflammatory effects in mouse models of SCD.