The effect of mast cell chymase on extracellular matrix: studies in autoimmune thyroiditis and in cultured thyroid cells.

In the first part of the study we analyzed the morphology of mast cells in autoimmune thyroiditis of BB/W rats. In the early stage of thyroiditis mast cells showed exocytosis of granules into the interstitium; this was associated with disorganization of the extracellular matrix and the appearance of a translucent ground substance in stroma. Mast cells were not seen in the mononuclear infiltrates in the later stages of thyroiditis. In order to further study the effect of mast cells on the extracellular matrix, we evaluated the effect of mast cell lysate and purified chymase on the matrix of cultured thyroid cells. Mast cells were obtained from peritoneal cavity; mast cell chymase was purified by anion exchange chromatography. After exposure to chymase there was a reduction of pericellular fibronectin in cultured thyroid cells, while laminin in matrix remained unchanged. Similarly, as found by gel electrophoresis, soluble fibronectin and vitronectin were digested by chymase in the reaction mixture. Cell attachment on both fibronectin and vitronectin was significantly decreased upon exposure of matrix proteins to chymase. The effects of chymase were abolished by enzyme inhibitor phenylmethane sulfonyl fluoride. These data suggest that mast cells possess proteolytic enzymes capable of digesting different host proteins which may have a role in the thyroid cell interaction with the surrounding matrix.