Vascular endothelial growth factor-secreting mast cells and myofibroblasts: a novel self-perpetuating angiogenic pathway in aortic valve stenosis.

OBJECTIVE: To examine the proangiogenic potential of myofibroblasts and mast cells, 2 types of cells present in human aortic valves. METHODS AND
RESULTS: Aortic valve stenosis is an active atheroinflammatory disease, characterized by the accumulation of inflammatory cells and the neovascularization of the valves. A total of 85 stenotic valves and 20 control valves were obtained during valve replacement surgery. The results of immunohistochemistry analysis revealed stenotic aortic valves that contained 3 types of neovessels: small microvessels, medium microvessels, and organized arterioles. The distribution density of the neovessels was significantly higher in stenotic valves than in control valves (P<0.001) and correlated positively with valvular calcification gradus (r=0.26, P=0.02) and mast cell density (r=0.38, P<0.001). In the neovascularized areas of stenotic aortic valves, mast cells contained vascular endothelial growth factor and were degranulated, indicating their activation. The stimulation of cultured myofibroblasts derived from aortic valves with a mast cell-preconditioned medium, hypoxic culture conditions, or tobacco smoke all induced vascular endothelial growth factor secretion in the myofibroblasts. Finally, mast cell tryptase was able to degrade the antiangiogenic molecule endostatin in vitro.
CONCLUSIONS: Mast cells and myofibroblasts may accelerate the progression of aortic valve stenosis by altering the balance between angiogenic and antiangiogenic factors in the valves, thus promoting valvular neovascularization.