Experimental Arthritis Is Dependent on Mouse Mast Cell Protease-5
Richard L Stevens1,2, H Patrick McNeil3, Lislaine A Wensing4,5
1From the Department of Infectious Diseases, Immunology, and Sexual Health, St. George Hospital, and the St. George and Sutherland Clinical School, Faculty of Medicine, University of New South Wales, Sydney, New South Wales 2217, Australia, rstevens@richardstevensphd.org.
Abstract:
The constitutive heparin+ (HP) mast cells (MCs) in mice express mouse MC protease (mMCP)-5 and carboxypeptidase A (mMC-CPA). The amino acid sequence of mMCP-5 is most similar to that of human chymase-1, as are the nucleotide sequences of their genes and transcripts. Using a homologous recombination approach, a C57BL/6 mouse line was created that possessed a disrupted mMCP-5 gene. The resulting mice were fertile and had no obvious developmental abnormality. Lack of mMCP-5 protein did not alter the granulation of the IL-3/IL-9-dependent mMCP-2+ MCs in the jejunal mucosa of Trichinella spiralis-infected mice. In contrast, the constitutive HP+ MCs in the tongues of mMCP-5-null mice were poorly granulated and lacked mMC-CPA protein. Bone marrow-derived MCs were readily developed from the transgenic mice using IL-3. Although these MCs contained high levels of mMC-CPA mRNA, they also lacked the latter exopeptidase. mMCP-5 protein is therefore needed to target translated mMC-CPA to the secretory granule along with HP-containing serglycin proteoglycans. Alternately, mMCP-5 is needed to protect mMC-CPA from autolysis in the cell's granules. Fibronectin was identified as a target of mMCP-5, and the exocytosis of mMCP-5 from the MCs in the mouse's peritoneal cavity resulted in the expression of metalloproteinase protease-9, which has been implicated in arthritis. In support of the latter finding, experimental arthritis was markedly reduced in mMCP-5-null mice relative to wild-type mice in two disease models.
Insights
Mouse mast cells (MCs) lacking mouse mast cell protease-5 (mMCP-5) show impaired granulation and reduced carboxypeptidase A (mCPA) levels. This protease is crucial for targeting mCPA and impacts arthritis development.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Constitutive heparin+ (HP) mast cells (MCs) in mice express mouse MC protease-5 (mMCP-5) and carboxypeptidase A (mCPA).
- mMCP-5 shares sequence similarity with human chymase-1, suggesting conserved functions.
Purpose of the Study:
- To investigate the role of mMCP-5 in mast cell function and development.
- To determine the impact of mMCP-5 deficiency on mast cell granulation and protease localization.
- To explore the involvement of mMCP-5 in inflammatory conditions like arthritis.
Main Methods:
- Generation of mMCP-5-null mice using homologous recombination.
- Analysis of mast cell granulation and protease content in wild-type and mMCP-5-null mice.
- Culture of bone marrow-derived mast cells (BMCs) from transgenic mice.
- Identification of mMCP-5 substrates and assessment of its role in protease-9 expression.
Main Results:
- mMCP-5-null mice exhibited poorly granulated constitutive HP+ MCs lacking mCPA in the tongue.
- Bone marrow-derived MCs from mMCP-5-null mice lacked mCPA protein despite high mRNA levels, indicating mMCP-5's role in mCPA targeting or stability.
- mMCP-5 targets fibronectin, and its exocytosis induces matrix metalloproteinase-9 (MMP-9) expression, a factor implicated in arthritis.
- Experimental arthritis was significantly reduced in mMCP-5-null mice compared to wild-type controls.
Conclusions:
- mMCP-5 is essential for the proper targeting and/or stability of mCPA within mast cell secretory granules.
- mMCP-5 plays a critical role in regulating matrix metalloproteinase-9 expression, influencing inflammatory processes.
- Deficiency in mMCP-5 confers protection against experimental arthritis, highlighting its therapeutic potential.
