Abstract

Mast cells (MCs) are immune cells that release preformed mediators from granules when activated by e.g. bacteria, viruses and allergens. Among the granule components are proteoglycans, histamine and proteases (chymase, tryptase and carboxypeptidase A). The proteases are bound to serglycin proteoglycans in the granules, and some remain attached to the proteoglycans after expulsion from the secretory granules. The importance of the interaction between proteases and proteoglycans is exemplified by MCs lacking an enzyme essential for heparin biosynthesis, N-deactylase/Nsulfotransferase-2 (NDST-2). Mice with this deficit display impaired storage of many MC granule components, e.g. proteases and histamine. We could show that polycationic compounds inhibited chymase (mMCP-4/rMCP-1) by disrupting its interaction with heparin. Furthermore, these polycations inhibited human tryptase (recombinant βI-tryptase) and made the otherwise resilient enzyme susceptible to macromolecular inhibitors. Our findings may be of therapeutic interest when treating pathologies associated with these enzymes. Mast cells may take part in regulation of blood pressure and angiogenesis, and this could occur through metabolism of the peptide angiotensin I (AngI). We confirmed the MC involvement in AngI processing using the NDST-2 deficient mice. We subsequently elucidated that the responsible proteases were chymase (mMCP-4) and carboxypeptidase A (CPA), and that they acted in concert on AngI, producing both blood pressure elevating peptides and blood pressure reducing peptides. Mast cells are implicated in connective tissue regulation, and a suggested pathway is through activation of matrix degrading enzymes, e.g. the matrix metalloproteases (MMPs). We could show that activation of proMMP-9 is dependent on MCs, and especially the chymase mMCP-4, as shown by impaired processing of proMMP-9 in peritoneal cell cultures from mice lacking NDST-2 or mMCP-4. Investigation of tissues from mMCP-4-/- revealed increased deposits of extracellular matrix components and reduced levels MMP-9. Additionally, we could show that proMMP-2 processing was completely abolished in peritoneal cell cultures from mice lacking serglycin. Furthermore, we showed that the formation of MMP-2 was abrogated in the presence of serine protease inhibitors and when cell cultures were depleted of MCs. The latter study reveals a novel pathway for proMMP-2 processing, which could be of relevance in connection with MMP2-associated pathological conditions such as cancer.