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

We recently characterized a heparin-deficient mouse strain generated by tar geting the gene for N-deacetylase/N-sulfotransferase-2 (NDST-2). The NDST-2 (-/-) mice show severe defects in their organization of mast cell (MC) secr etory granules, with an almost total absence of the various heparin-binding MC proteases. In the present report we have studied the consequences of he parin/MC protease deficiency for extravascular coagulation and fibrinolysis . Addition of prothrombin to peritoneal cells-a mixture of macrophages, lym phocytes, 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 activ ated 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. S ubsequent experiments with normal cells showed that cell surface-associated MC chymase, in a strongly heparin-dependent manner, was responsible for bo th the thrombinin-activating- and plasmin-inactivating activities. These re sults show that MC chymase-heparin complexes have the potential to regulate extravascular coagulation processes, as well as the plasminogen activator/ plasmin system.