MMP13 and heart failure: MMP1 is able to cleave and activate the thrombin receptor protease activated receptor-1 (PAR-1), which is expressed on nearly all cells in the blood, leading to signaling in the platelets in a form distinct from thrombin induced signaling.[15] MMP13 can cleave and activate PAR-1, resulting in pathologic activation of downstream signaling events that contribute to platelet thrombosis and heart failure.[16] Recent studies have demonstrated that MMP2 regulates the shedding of CD40 ligand from the surface of activated human platelets, suggesting MMP2 plays an important role in thrombosis.[17]