THE PRODUCTION OF TISSUE INHIBITORS OF METALLOPROTEINASES (TIMP) IN MEGAKARYOPOIESIS - POSSIBLE ROLE OF PLATELET-DERIVED AND MEGAKARYOCYTE-DERIVED TIMPS IN BONE-MARROW FIBROSIS

We quantified tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP- 2 in serum and plasma in normal control subjects and patients with a l ow or high platelet count, using one-step sandwich enzyme immunoassays . The serum levels of TIMP-1 and TIMP-2 were 101.1 +/- 13.3 ng/ml, and 82.7 +/- 26.3 ng/ml, respectively in normal subjects. In patients wit h an elevated platelet count, such as in essential thrombocytosis, pol ycythaemia vera, and myelofibrosis, serum levels of TIMP-1 and TIMP-2 were 351.6 +/- 200.9 ng/ml and 148.9 +/- 84.0 ng/ml, respectively. Ser um levels of TIMP-1 and TIMP-2 in patients with a low platelet count, such as in aplastic anaemia and idiopathic thrombocytopenic purpura, w ere 57.2 +/- 25.8 ng/ml and 19.7 +/- 7.68 ng/ml, respectively The seru m level of TIMP-1 was significantly correlated with the platelet count in all subjects. The correlation between the serum level of TIMP-2 an d the platelet count was not as strong. The level of TIMP-1 in platele t-depleted plasma was not correlated with the platelet count, Immunohi stochemical staining using monoclonal antibodies against TIMP-1 and TI MP-2 showed that megakaryocytes and platelets were positive for both T IMP-1 and TIMP-2, confirming that they are rich sources of TIMPs. TIMP -1 and TIMP-2 stimulated the proliferation of bone marrow fibroblasts, although their effect was less potent than that of TGF-beta and PDGF. Erythroleukaemia and megakaryoblastic cell lines showed the highest s ecretion of TIMP-1 among the leukaemia cell lines examined. There was no lineage specificity for TIMP-2 secretion. These results suggest tha t TIMPs released from megakaryocytes or from local platelet coagulatio n may be important in the development of bone marrow fibrosis.