Cooperation between Mast Cell Carboxypeptidase A and the Chymase Mouse Mast Cell Protease 4 in the Formation and Degradation of Angiotensin II*

The octapeptide angiotensin II (Ang II) exerts a wide range of effects on the cardiovascular system but has also been implicated in the regulation of cell proliferation, fibrosis, and apoptosis. Ang II is formed by cleavage of Ang I by angiotensin-converting enzyme, but there is also evidence for non-angiotensin-converting enzyme-dependent conversion of Ang I to Ang II. Here we address the role of mast cell proteases in Ang II production by using two different mouse strains lacking mast cell heparin or mouse mast cell protease 4 (mMCP-4), the chymase that may be the functional homologue to human chymase. Ang I was added to ex vivo cultures of peritoneal cells, and the generation of Ang II and other metabolites was analyzed. Activation of mast cells resulted in marked increases in both the formation and subsequent degradation of Ang II, and both of these processes were strongly reduced in heparin-deficient peritoneal cells. In the mMCP-4–/– cell cultures no reduction in the rate of Ang II generation was seen, but the formation of Ang-(5–10) was completely abrogated. Addition of a carboxypeptidase A (CPA) inhibitor to wild type cells caused complete inhibition of the formation of Ang-(1–9) and Ang-(1–7) but did not inhibit Ang II formation. However, when the CPA inhibitor was added to the mMCP-4–/– cultures, essentially complete inhibition of Ang II formation was obtained. Taken together, the results of this study indicate that mast cell chymase and CPA have key roles in both the generation and degradation of Ang II