Regulation of extravascular coagulation and fibrinolysis by heparin‐dependent mast cell chymase

We recently characterized a heparin‐deficient mouse strain generated by targeting the gene for N‐deacetylase/N‐sulfotransferase‐2 (NDST‐2). The NDST‐2 −/− mice show severe defects in their organization of mast cell (MC) secretory granules, with an almost total absence of the various heparin‐binding MC proteases. In the present report we have studied the consequences of heparin/MC protease deficiency for extravascular coagulation and fibrinolysis. Addition of prothrombin to peritoneal cells—a mixture of macrophages, lymphocytes, and MCs—resulted in formation of thrombin but the accumulation of thrombin occurred faster in the NDST‐2 −/− cells than in normal controls. Further, the generated thrombin was subsequently inactivated in the NDST‐2 +/+ cell cultures but not in the NDST‐2 −/− cells. Plasminogen was activated to plasmin at an apparently higher rate in peritoneal cells from NDST‐2 null mice than in the normal controls. Similar to thrombin, the generated plasmin was inactivated by NDST‐2 +/+ but not by the NDST‐2 −/− cells. Subsequent experiments with normal cells showed that cell surface‐associated MC chymase, in a strongly heparin‐dependent manner, was responsible for both the thrombin‐inactivating‐ and plasmin‐inactivating activities. These results show that MC chymase‐heparin complexes have the potential to regulate extravascular coagulation processes, as well as the plasminogen activator/plasmin system.