It has previously been shown that mast cell chymase is the Ang II forming enzyme in the major non-ACE pathway in the heart (19
). Such pathways were later identified not only in the human heart, but also in the thoracic artery, saphenous vein (20
), radial artery (21
), gastroepiploic artery (22
), bleomycin-induced pulmonary fibrosis (4
) and cardiac fibrosis (6
In the present study, we used ketotifen, a mast cell membrane stabilizer, to investigate the production of Ang II in burn tissues in hamsters. The results showed that the production of Ang II in the ketotifen group was significantly decreased. This suggests that mast cell chymase has the same effects on the conversion of Ang I to Ang II in burn tissues as it does in other tissues or organs, including the heart (6
Ang II is the major effector peptide in the RAS. Besides being a physiological mediator restoring circulatory integrity (12
), Ang II is now recognized as a growth factor that regulates cell growth, angiogenesis, inflammation, tissue repair and remodeling (2
). Ang II contributes greatly to tissue fibrosis, including hepatic (24
), renal (25
) and cardiac fibrosis (26
). Ang II combines with Ang II type-1 receptor to increase the expression of TGF-β1 (27
). In addition, chymase also contributes to the release of TGF-β1 from its precursor (9
). TGF-β1 has been identified as the most significant profibrotic cytokine (29
), it induces an increase in collagen production and secretion and enhances the abundance of mRNA levels for collagen types I and III (30
). Ang II also activates collagen I gene expression, but would require activation of the MAPK/ERK and TGF-β signaling pathways (31
The present study showed that ketotifen treatment significantly reduced the production of TGF-β1 and collagens I and III. These results indicate that greatly decreased Ang II levels cannot induce excessive expression of TGF-β or collagen I and III genes due to the deficiency in activated mast cell chymase.
Ang II is able to stimulate not only cardiac fibroblast proliferation (32
) but also skin fibroblast proliferation (33
). Certain studies have indicated that mast cell chymase is able to induce smooth muscle cell and endothelial cell apoptosis (34
). However, no studies have reported whether or not Ang II and chymase are able to induce fibroblast apoptosis. The present study showed that there was no significant difference in fibro-blast apoptosis between the ketotifen group and the control group. This result indicates that mast cell chymase may have no effect on fibroblast apoptosis.
According to previous studies Ang II had no effect on the the activation of IL-1β. However, human mast cell chymase is able to induce the accumulation of neutrophils, eosinophils and other inflammatory cells in vivo
), as well as the rapid and specific conversion of precursor IL-1β to an active IL-1 species (39
). In the present study, in comparison to the control group, IL-1β was greatly reduced in the ketotifen group, suggesting that chymase may be involved in the activation of IL-1β in burn tissues.
Wound healing subsequent to burn injuries is an inevitable result of tissue repair involving the interaction of fibroblasts, the ECM and cytokines. Increased vascular permeability and inflammation following burn injury may cause an increase in mast cells and stimulate the release of mast cell chymase from secretory granules (1
). Results from the present study showed that in burn tissues, mast cell chymase contributed to the conversion of Ang II, the activation of TGF-β1 and the production of collagens I and III. Mast cell chymase is able to induce skin fibroblast proliferation (33
), but the present study showed that mast cell chymase had no effect on fibroblast apotosis. The study indicated that mast cell chymase is conducive to wound healing.
In conclusion, in a hamster model of burn injuries, ketotifen, a mast cell membrane stabilizer, decreased the local concentration of Ang II, the expression levels of TGF-β1 and collagens I and III and the concentration of inflammatory marker IL-1β. These results suggest that mast cell chymase contributes to burn wound healing. Thus, chymase activity provides a promising future therapeutic target to accelerate wound healing.