REGULATION OF GELATINASE ACTIVITY IN MICE WITH TARGETED INACTIVATION OF COMPONENTS OF THE PLASMINOGEN PLASMIN SYSTEM/

To investigate a potential physiological role of the plasminogen/ plas min system in activation of the matrix metalloproteinase (MMP), system , the distribution of latent and active MMP-2 (gelatinase A) or MMP-9 (gelatinase B) was monitored in aorta extracts and in serum-free condi tioned cell culture medium obtained from wild-type (WT) mice and from mice with deficiency of tissue-type plasminogen activator (t-PA(-/-)), urokinase-type plasminogen activator (u-PA(-/-)), plasminogen activat or inhibitor-1 (PAI-1(-/-)) or plasminogen (Plg(-/-)). In aorta extrac ts, the contribution of active MMP-2 to the total MMP-2 level ranged b etween 7 and 16% for the different genotypes, whereas active MMP-9 was not detected. The contribution of active 58 kDa MMP-2 to the total MM P-2 level (active plus latent) ranged between 14 and 29% (mean of 3 ex periments) for fibroblasts of the different genotypes, and between 18 and 32% for smooth muscle cells, and was relatively constant in time ( 7-72h). The contribution of active 83kDa MMP-9 to the total MMP-9 leve l ranged between 15 and 29% for fibroblasts of the different genotypes and was relatively constant in time (24-72 h); corresponding values w ere 17 to 57% for smooth muscle cells, with the exception of Pig(-/-) smooth muscle cells which had undetectable levels of active MMP-9. Add ition of plasmin(ogen) to the cell culture medium of fibroblasts did n ot significantly affect the distribution of active and latent MMP-2, b ut resulted in an approximately two-fold enhancement of the contributi on of active MMP-9. In macrophages of Plg(-/-) mice, active MMP-9 was detected only when the cells were cultured in the presence of plasmino gen. These data indicate that activation of proMMP-2 occurs independen tly of the physiological plasminogen activators and of plasmin(ogen) i n all the cell types evaluated. Activation of proMMP-9 was enhanced in the presence of plasmin(ogen), but active MMP-9 was also detected in fibroblasts of Plg(-/-) mice, indicating that in vivo activation may o ccur via plasmin(ogen)-independent mechanisms.