The presence of elevated numbers of activated mast cells (MCs) in the joints of patients with rheumatoid arthritis (RA) raised the possibility in the 1980s that MCs participate in the inflammation, proteolytic damage, and/or remodeling of the arthritic joint. Using MC-deficient mice, we and others subsequently demonstrated that these immune cells do indeed contribute substantially to experimental inflammatory arthritis. Nevertheless, the relevant mediators produced by the Fc3RIII- and C5a-activated MCs in the synovium that adversely affect the joint had not been identified. Mouse MC protease (mMCP) 6 and mMCP-7 are members of the chromosome 17A3.3 family of tryptic proteases that are preferentially stored in the secretory granules of MCs as homotypic and heterotypic tetramers ionically bound to heparin-containing serglycin proteoglycans. The human ortholog of mMCP-6 is hTryptase-21. We generated enzymatically active mMCP-6, mMCP-7, and hTryptase-21. We also recently created inbred transgenic C57BL/6 mouse strains that differ in their expression of mMCP-6, mMCP-7, and heparin. Using the latter mice, we showed that C57BL/6 mice that lack tryptase7heparin complexes have reduced inflammation and diminished loss of aggrecan proteoglycans from their cartilage in two different mouse models of inflammatory arthritis. The overall objectives of the proposed studies are to use complementary approaches to determine at the molecular level the roles of mouse and human tetramer-forming tryptases in RA and mouse models of this autoimmune disorder. Our genetically modified mouse strains, recombinant tryptases, and other key protease-specific reagents will be used in the proposed studies to determine how MC-restricted tetramer-forming human and mouse tryptases affect fibroblast-like synoviocytes (FLS) and chondrocytes at multiple levels in varied in vitro and in vivo studies, as well as how these mesenchymal cells affect MCs. Additional studies will be carried out to determine how exocytosed mMCP-6 and hTryptase-21 are negatively regulated in the arthritic joint, and even in MCs themselves. The factors and mechanisms that control the expression of enzymatically active tryptases inside MCs have not been identified. To this end, we recently discovered that FLS-derived IL-33 induces MCs to increase their expression of tryptases at the mRNA and protein levels. Thus, additional mechanistic studies are proposed to understand how IL-33 controls the transcription of the mMCP-6 and hTryptase-21 genes in MCs and/or the stability of their transcripts. In combination, these studies promise to provide novel insights into both MC and synovial physiology, as well as elucidate novel disease mechanisms in human inflammatory arthritis.

Public Health Relevance

We have discovered that a cell lineage called the mast cell can contribute to inflammation in rheumatoid arthritis (RA) by studying mouse models of disease. Now, we have found that a protein made by mast cells, called tryptase, is among the means by which mast cells impact disease. We are working out the mechanisms that tryptase impacts to understand better how to target this novel pathway in treating people with RA.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
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Hypersensitivity, Autoimmune, and Immune-mediated Diseases Study Section (HAI)
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Peyman, John A
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Brigham and Women's Hospital
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Stevens, Richard L; McNeil, H Patrick; Wensing, Lislaine A et al. (2017) Experimental Arthritis Is Dependent on Mouse Mast Cell Protease-5. J Biol Chem 292:5392-5404
Douaiher, Jeffrey; Succar, Julien; Lancerotto, Luca et al. (2014) Development of mast cells and importance of their tryptase and chymase serine proteases in inflammation and wound healing. Adv Immunol 122:211-52
Hamilton, Matthew J; Frei, Sandra M; Stevens, Richard L (2014) The multifaceted mast cell in inflammatory bowel disease. Inflamm Bowel Dis 20:2364-78
Prieto-García, A; Castells, M C; Stevens, R L (2014) Mast cell-derived htryptase-beta functions as a potent anticoagulant by proteolytically damaging fibrinogen. J Investig Allergol Clin Immunol 24:286-7
Prieto-García, Alicia; Castells, Mariana C; Hansbro, Philip M et al. (2014) Mast cell-restricted tetramer-forming tryptases and their beneficial roles in hemostasis and blood coagulation. Immunol Allergy Clin North Am 34:263-81
Hansbro, Philip M; Hamilton, Matthew J; Fricker, Michael et al. (2014) Importance of mast cell Prss31/transmembrane tryptase/tryptase-? in lung function and experimental chronic obstructive pulmonary disease and colitis. J Biol Chem 289:18214-27
Beckett, Emma L; Stevens, Richard L; Jarnicki, Andrew G et al. (2013) A new short-term mouse model of chronic obstructive pulmonary disease identifies a role for mast cell tryptase in pathogenesis. J Allergy Clin Immunol 131:752-62
Magarinos, Natalia J; Bryant, Katherine J; Fosang, Amanda J et al. (2013) Mast cell-restricted, tetramer-forming tryptases induce aggrecanolysis in articular cartilage by activating matrix metalloproteinase-3 and -13 zymogens. J Immunol 191:1404-12
Adachi, Roberto; Krilis, Steven A; Nigrovic, Peter A et al. (2012) Ras guanine nucleotide-releasing protein-4 (RasGRP4) involvement in experimental arthritis and colitis. J Biol Chem 287:20047-55
Kaieda, Shinjiro; Wang, Jun-Xia; Shnayder, Ruslan et al. (2012) Interleukin-33 primes mast cells for activation by IgG immune complexes. PLoS One 7:e47252

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