INTERACTION OF OSTEOBLASTS WITH EXTRACELLULAR-MATRIX - EFFECT OF MAST-CELL CHYMASE

We studied the effect of mast cell chymase on the interaction between osteoblasts and extracellular matrix. Chymase was purified from mast c ell lysate by anion exchange chromatography. Osteoblasts were isolated from rat calvarias by collagenase digestion. Incubation of osteoblast s with mast cell lysate (40-170 mug/ml) or purified chymase (8-32 mug/ ml) resulted in changes in cell-matrix interaction and cell morphology . Osteoblasts treated with chymase also showed a gradual detachment fr om the artificial substrata and from the biomatrix (collagen-digested rib fragment). A similar effect of mast cell chymase on the osteoblast s was found in vitro on endosteum of an intact parietal bone. Neutral protease inhibitors abolished the effect of both crude and purified en zyme preparations on the cell-matrix interaction. Mast cell chymase ha d no effect on osteoblast viability. The effect of enzyme on osteoblas t proliferation was studied with lower concentrations of enzyme (0.2 m ug/ml) in order to avoid cell detachment; there was no effect on eithe r the metaphase index or on the number of cells after 5 days of incuba tion with chymase. Osteoblast attachment and cell spreading on differe nt matrix proteins (fibronectin, vitronectin, extract of noncollagenou s matrix proteins from rat bone) were significantly altered by their p retreatment with chymase. Matrix fibronectin of osteoblasts in culture as well as soluble vitronectin and fibronectin were digested by rat m ast cell chymase. Our data suggest that mast cells through action of n eutral protease chymase may alter molecules in extracellular matrix th at are important in osteoblast adhesion, cell spreading, maintenance o f cell morphology, and, most likely, cell function.