Possible role for mast cell-derived cathepsin G in the adverse remodelling of stenotic aortic valves

Aims Aortic stenosis (AS) is characterized by extensive remodelling of the valves, including infiltration of inflammatory cells, extracellular matrix degradation, and fibrosis. The molecular mechanisms behind this adverse remodelling have remained obscure. In this article, we study whether cathepsin G, an angiotensin II (Ang II)-forming elastolytic enzyme, contributes to progression of AS. Methods and results Stenotic aortic valves (n = 86) and control valves (n = 17) were analysed for cathepsin G, transforming growth factor-beta 1 (TGF-beta 1), and collagens I and III with RT-PCR and immunohistochemistry. Valvular collagen/elastin ratio was quantified by histochemistry. In stenotic valves, cathepsin G was present in mast cells and showed increased expression (P < 0.001), which correlated positively (P < 0.001) with the expression levels of TGF-beta 1 and collagens I and III. TGF-beta 1 was also present in mast cell-rich areas and cathepsin G induced losartan-sensitive TGF-beta 1 expression in cultured fibroblasts. Collagen/elastin ratio was increased in stenotic valves (P < 0.001) and correlated positively with smoking (P = 0.02). Nicotine in cigarette smoke activated mast cells and induced TGF-beta 1 expression in cultured fibroblasts. Fragmented elastin was observed in stenotic valves containing activated cathepsin G-secreting mast cells and in normal valves treated with cathepsin G. Conclusion In stenotic aortic valves, mast cell-derived cathepsin G may cause adverse valve remodelling and AS progression.