Mast cells limit extracellular levels of IL-13 via a serglycin proteoglycan-serine protease axis

Abstract

: Mast cell (MC) granules contain large amounts of proteases of the chymase, tryptase and carboxypeptidase A (MC-CPA) type that are stored in complex with serglycin, a proteoglycan with heparin side chains. Hence, serglycinprotease complexes are released upon MC degranulation and may influence local inflammation. Here we explored the possibility that a serglycin-protease axis may regulate levels of IL-13, a cytokine involved in allergic asthma. Indeed, we found that wild-type MCs efficiently degraded exogenous or endogenously produced IL-13 upon degranulation, whereas serglycin −/− MCs completely lacked this ability. Moreover, MC-mediated IL-13 degradation was blocked both by a serine protease inhibitor and by a heparin antagonist, which suggests that IL-13 degradation is catalyzed by serglycin-dependent serine proteases and that optimal IL-13 degradation is dependent on both the serglycin and the protease component of the serglycin-protease complex. Moreover, IL-13 degradation was abrogated in MC-CPA −/− MC cultures, but was normal in cultures of MCs with an inactivating mutation of MC-CPA, which suggests that the IL-13-degrading serine proteases rely on MC-CPA protein. Together, our data implicate a serglycin-serine protease axis in the regulation of extracellular levels of IL-13. Reduction of IL-13 levels through this mechanism possibly can provide a protective function in the context of allergic inflammation.

Granzyme D Is a Novel Murine Mast Cell Protease That Is Highly Induced by Multiple Pathways of Mast Cell Activation

“…Peritoneal cell-derived mast cells (PCMCs) were established according to a protocol described previously by Malbec et al (24). The PCMC population was of a homogenous mast cell phenotype, as judged by morphological criteria, expression of cell surface c-kit and high-affinity IgE receptor, and expression of mast cell granule proteases (25).…”

IL‐6 and IL‐17A degradation by mast cells is mediated by a serglycin:serine protease axis

“…Previous phenotypic characterizations of PCMCs have demonstrated the presence of large amounts of preformed granule mediators (including mMCP4, ‐5, ‐6, and CPA3) and potent proteolytic activity has been confirmed in supernatants collected from degranulated PCMCs 6, 11, 23. In contrast to WT counterparts, serglycin‐deficient PCMCs did not contain any detectable amounts of mMCP4, ‐5, ‐6, or CPA3, and serglycin‐deficient peritoneal extracts were virtually depleted of trypsin‐, chymotrypsin‐, and CPA‐like activity 11, 22. To confirm the phenotype of WT and serglycin −/− PCMCs, we measured protease activity in supernatants collected 1 h after activation with either 2 μM calcium ionophore A23187 (Sigma–Adrich, St Louis, MO) or with FcϵRI cross‐linking (described in a later section).…”

“…Accordingly, this finding indicates a role for any of the serine proteases that are known to be stored in a serglycin‐dependent manner. These include the mast cell‐restricted serine proteases of chymase (mMCP4, ‐5) and tryptase (mMCP6) type, but there are also indications that additional, unidentified serine proteases can be stored in complex with serglycin and be of biological significance in regulating cytokine levels 11. We are at present not able to identify which of the various serglycin‐dependent serine proteases that is mainly responsible for the degradation of IL‐6 and IL‐17A by peritoneal mast cells.…”

“…We recently showed that a murine chymase, mouse mast cell protease 4 (mMCP4), is protective in a house dust mite‐induced asthma model, possibly by regulating the levels of the pro‐inflammatory cytokine interleukin 33 (IL‐33) 6 and, similarly, mMCP4 was shown to be protective in an ovalbumin (OVA) model of allergic airway inflammation 7. It has also been demonstrated that serglycin‐associated mast cell proteases can regulate levels of tumor necrosis factor α (TNF‐α), and various venom‐derived toxins 8, 9, 10, and there are indications that serglycin‐dependent proteases can regulate the levels of IL‐13 11. Interestingly, regulation of both external and endogenously produced IL‐6 and IL‐13 by human mast cells has been shown to involve proteolytic degradation by chymase and cathepsin G 12.…”

“…Interestingly, regulation of both external and endogenously produced IL‐6 and IL‐13 by human mast cells has been shown to involve proteolytic degradation by chymase and cathepsin G 12. In contrast, murine chymase mMCP4 and murine cathepsin G were unable to degrade IL‐13 11, and degradation of IL‐6 was exerted by the tryptase mMCP6 and not by mMCP4 13. Despite these species differences, studies of both human and mouse mast cells support a role for the serglycin:protease axis in the down‐regulation of inflammatory cytokines.…”