Role For Mast Cell Chymase In Intestinal Epithelial Permeability

Employing mast cell (MC) neutralizing antibodies and stabilizing agents, we have previously demonstrated a critical role for MCs in the regulation of intestinal epithelial permeability in mice. We hypothesize that a MC-derived serine protease, chymase, is an important mediator of intestinal epithelial permeability. Jejunal levels of mouse mast cell protease-4 (mMCP-4), the murine functional homologue to human chymase, were analyzed by quantitative real-time PCR and immunohistochemistry in wild-type BALB/c (WT) mice and in a murine model of intestinal mastocytosis using intestinal IL-9 Tg (iIL-9 Tg) mice. To examine the effect of chymase on intestinal epithelial permeability, confluent colonic adenocarcinoma Caco2-bbe cells were exposed to 0, 2.5 or 5U of human skin-derived chymase basolaterally for 24 hours and intestinal epithelial permeability measured in Ussing Chambers by monitoring the mucosal to serosal flux of FITC-dextran and the inversely correlating transepithelial resistance (TER). Intestinal mastocytosis was associated with a significant increase in jejunal mMCP-4 mRNA levels (10.1 ± 1.0 fold; p < 0.0001) in iIL-9 Tg mice compared to WT. Furthermore, jejunum from iIL-9 Tg mice displayed strong and diffuse mMCP-4 positive immunohistochemical staining in comparison to very low levels of punctate staining in jejunum from WT mice. Exposure of Caco2-bbe monolayers to chymase induced a significant decrease in the TER (2.5U: 125.9 ± 47.6, p < 0.05; 5U: 192.4 ± 19.9, p < 0.005; vs control: 297.5 ± 15.9 Ω/cm2) and increase in FITC-dextran permeability (2.5U: 12926 ± 2277, p < 0.05; 5U: 11752 ± 2063, p < 0.01; vs control: 3474 ± 457 ng/ml) compared to controls. Collectively, these data suggest that MC-derived chymase may play an important role in MC-mediated intestinal epithelial permeability.