Lymphangiogenesis in aortic valve stenosis--novel regulatory roles for valvular myofibroblasts and mast cells

Abstract

Objective: To investigate mechanisms of lymphangiogenesis in aortic valve stenosis (AS).

Methods: Lymphatic vessels were visualized with LYVE-1 staining in 20 control, 5 sclerotic, and 40 stenotic human aortic valves. Vascular endothelial growth factors (VEGFs) VEGF-C and VEGF-D, and their lymphangiogenic receptor VEGFR-3, and the angiogenic VEGFR-2 were analysed by quantitative real-time PCR and immunohistochemistry. Cultured myofibroblasts derived from human stenotic aortic valves, and cultured human mast cells were used to study VEGF-C regulation, and VEGF-C and VEGF-A were quantified from cell culture media by enzyme immunoassays.

Results: Lymphatic vessels, VEGF-C, VEGF-D, VEGFR-3 and VEGFR-2 all were present in the aortic valves. In AS, the number of lymphatic vessels and the expression of VEGF-D, VEGFR-3, and VEGFR-2 were increased. Moreover, the numbers of lymphatic vessels correlated positively with those of neovessels (r = 0.525, p = 0.001) and mast cells (r = 0.374, p = 0.017). Cultured valvular myofibroblasts produced VEGF-C, and addition of tumour necrosis factor alpha (TNF-α) to the cells augmented its secretion. In contrast, proteases released by activated human mast cells degraded VEGF-C.

Conclusion: These results show that lymphangiogenesis is induced in advancing AS. Furthermore, valvular myofibroblasts and activated mast cells were identified as novel regulators of lymphangiogenesis in aortic valves.