MAST-CELL TRYPTASE STIMULATES THE SYNTHESIS OF TYPE-I COLLAGEN IN HUMAN LUNG FIBROBLASTS

Mast cell activation is a characteristic feature of chronic inflammati on, a condition that may lead to fibrosis as a result of increased col lagen synthesis by fibroblasts. We have investigated the potential of tryptase, the major protease of human mast cells, to stimulate collage n synthesis in the human lung fibroblast cell line MRC-5. Tryptase was isolated from human lung tissue by ion-exchange and affinity chromato graphy. At concentrations of 18 and 36 mU/ml, tryptase stimulated both an increase in cell numbers, and a fivefold increase in DNA synthesis as determined by methyl-[H-3]thymidine incorporation. Similar concent rations of tryptase resulted in a 2.5-fold increase in collagen synthe sis as determined both by incorporation of [H-3]proline into collagen, and by assay of hydroxyproline concentrations in the supernatants. Th ere was also a twofold increase in collagenolytic activity in the cult ure medium after tryptase treatment, indicating that the increase in c ollagen synthesis was not a consequence of decreased collagenase produ ction. All of these actions of tryptase were reduced in the presence o f the protease inhibitors leupeptin and benzamidine hydrochloride, ind icating a requirement for an active catalytic site. SDS-PAGE and autor adiographic analysis of the [H-3]collagen produced by the cells reveal ed it to be predominantly type I collagen. Our findings suggest that t he release of tryptase from activated mast cells may provide a signal for abnormal fibrosis in inflammatory disease.