F2R and acute respiratory distress syndrome: Indeed, PAR1 primary activator (thrombin) levels are found to be increased in chronic lung injury, participating not only in the coagulatory processes but also exerting a profibrotic cellular effect.45,54 In the inflammation of the respiratory airways, there is an overexpression of MMPs, which has been implicated in ARDS's pathogenesis, especially for its collagenolytic (MMP-1 and -8) and gelatinolytic (MMP-2 and -9) activities.55 MMP-1 triggers PAR1 via biased signaling and contributes to arterial thrombosis.