A Key Role for Mast Cell Chymase in the Activation of Pro-matrix Metalloprotease-9 and Pro-matrix Metalloprotease-2

Abstract

Chymases, serine proteases exclusively expressed by mast cells, have been implicated in various pathological conditions. However, the basis for these activities is not known, i.e. the in vivo substrate(s) for mast cell chymase has not been identified. In this study we show that mice lacking the chymase mouse mast cell protease 4 (mMCP-4) fail to process pro-matrix metalloprotease 9 (pro-MMP-9) to its active form in vivo, whereas both the pro and active form of MMP-9 was found in tissues of wild type mice. Moreover, the processing of pro-MMP-2 into active enzyme was markedly defective in mMCP-4 null animals. Histological analysis revealed an increase in collagen in the ear tissue of mMCP-4-deficient animals accompanied by increased ear thickness and a higher content of hydroxyproline. Furthermore, both lung and ear tissue from the knock-out animals showed a markedly increased staining for fibronectin. MMP-9 and MMP-2 are known to have a range of important activities, but the mechanisms for their activation in vivo have not been clarified previously. The present study thus indicates a key role for mast cell chymase in the regulation of pro-MMP-2 and -9 activities. Moreover, the results suggest an important role for mast cell chymase in regulating connective tissue homeostasis. When mast cells (MCs)1 are activated, they degranulate and thereby release a panel of powerful preformed inflammatory mediators, including histamine, cytokines such as tumor necrosis factor-␣, proteoglycans, and various MC-specific proteases (1, 2). The MC proteases are divided into three main subclasses, tryptases, chymases, and carboxypeptidase A (3-5), all of which are stored in the MC granule in complex with heparin proteoglycan (6, 7). Chymases, serine proteases with chymotrypsin-like substrate specificities, have potent pro-inflammatory properties (8) and have been implicated in a variety of pathophysiological conditions, e.g. angiogenesis (9), heart failure (10), and fibrosis (11). However, it has not been possible to determine the mechanism by which chymases influences these processes, i.e. the physiological substrate(s) for chymase has not been identified.Matrix metalloproteases (MMPs) are known to be involved in a variety of physiological and pathological processes and are currently attracting a large clinical interest as potential drug targets in therapeutic intervention with various diseases (12-16). The MMPs, similar to most proteolytic enzymes, are synthesized with an N-terminal propeptide that needs to be removed to achieve proteolytic activity. Thus, the physiological processes that lead to propeptide cleavage are imperative in terms of regulating the activity of most proteases (17). The MMP family currently comprises Ͼ20 members (18). The members all share common structural features but differ in regard to substrate specificities, although overlapping substrate specificities between certain members of the MMP family occur. Thus, MMP-2 and -9 share the ability to degrade denatured collagen (gelatin) and are therefore also den...

Control of matrix metalloproteinase catalytic activity

“…One group of serine proteases that do seem to activate proMMPs in vivo are mast cell chymases (Fang et al, 1997;Fang et al, 1999). Mice lacking mast cell chymase-4 (MCP-4) have diminished activation of proMMP-2 and proMMP-9 (Tchougounova et al, 2005). However, the absence of mMCP-4 does not completely abolish the activation of these two MMPs by mast cells.…”

Emerging roles of serine proteinases in tissue turnover in arthritis

“…Tryptase can process prothrombin (74), generate C3a from complement C3 (75), and degrade ECM components including fibrinogen (76,77), denatured type I collagen (78), and fibronectin (79). Tryptase and chymase can further promote ECM degradation by activating proMMPs (80)(81)(82)(83)(84) and pro-uPA (85). Mast cell tryptase is important in activating PAR-2 on synovial fibroblasts and inducing proinflammatory cytokine release (86,87).…”

ACE inhibitors to block MMP-9 activity: New functions for old inhibitors

“…[21] Chymase has been shown to process MMP-9 to its active form [22], indicating that the connection between angiotensin II and MMP-9 is further complicated. Studies evaluating ACE and MMP-9 connections will also need to take into account chymase activity.…”

“…This effort is complicated by the fact that chymase also increases in the infarct region, chymase generates angiotensin II, and chymase inhibition also improves post-MI outcomes. [17,18] Chymase-dependent angiotensin II formation has been reported to account for over 90% of total myocardial levels, although chymase levels do vary among species.[19] Chymase from human, dog, and hamster all hydrolyze the Phe 8 -His 9 bond of angiotensin I to efficiently produce angiotensin II.[20] In contrast, rodent chymase cleaves angiotensin I at the Tyr 4 -Ile 5 bond to generate inactive angiotensin fragments.[20] Also, mast cells are the major source of chymase, and the fact that rodents have very few mast cells in the left ventricle further defines species differences.[21] Chymase has been shown to process MMP-9 to its active form [22], indicating that the connection between angiotensin II and MMP-9 is further complicated. Studies evaluating ACE and MMP-9 connections will also need to take into account chymase activity.…”

“…[20] Also, mast cells are the major source of chymase, and the fact that rodents have very few mast cells in the left ventricle further defines species differences. [21] Chymase has been shown to process MMP-9 to its active form [22], indicating that the connection between angiotensin II and MMP-9 is further complicated. Studies evaluating ACE and MMP-9 connections will also need to take into account chymase activity.…”