ROLE OF MAST CELL PROTEASES IN AIRWAY INFLAMMATION

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The major stored and secreted proteins of mast cells are proteases. The most abundant of these in tryptase, a trypsin-like serine protease that is synthesized by virtually all lung and airway mast cells and resists inactivation by circulating antiproteases following release. Recent work deciphered the primary structure of dog and human tryptases, discovered the novel intron-exon organization of human tryptase genes, and established tryptase's destruction of bronchoactive peptides and potentiation of histamine-induced bronchoconstriction in vitro. A subset of airway mast cells contain a second major serine protease, chymase. Further studies solved the primary structure of dog and human chymase, localized the human gene to a cluster of hematopoietic serine protease genes, and established the close relationship of the human to the dog enzyme, which increase histamine-induced vascular leak in vivo an stimulates gland cell secretion in vitro. In human airway, chymase- containing mast cells were found to be particularly abundant near submucosal glands. Despite these advances and those of other groups in the field, the characteristics of these enzymes and their function in the airways are incompletely understood. The studies now proposed will use biochemical, morphological and physiological approaches to further explore the properties and roles of these and relative mast cell proteases in airway inflammation. One avenue of investigation is an exploration of the features and functions of a newly discovered relative of tryptase; known as dMCP-3, whose existence is predicted from an 'orphan' cDNA cloned from dog mastocytoma cells. The structure, secretion, catalytic properties and airway tissue expression of dMCP-3 and its putative human homolog will be examined. Additional studies will examine the participation of mast cell proteases in airway tissue growth and remodeling, focusing particularly on tryptases as growth factors for airway glands and smooth muscle, and will use an expression cloning strategy to identify and clone a putative receptor mediating the mitogenic effects of tryptase. Mast cells also will be examined as a source of matrix-degrading Zn++-metalloproteases distinct from serine proteases such as tryptase, chymase, and dMCP-3. Finally, the proposed studies will explore the modulation of vascular permeability by tryptase and chymase and their interactions with thrombin. These studies may reveal unsuspected roles for mast cell secretory proteases and may suggest a basis for developing new therapeutic approaches to the management of airway inflammation.