Role of VEGF Receptors in the Degeneration Process of Aortic Valves

Objectives: Calcific aortic valve disease (CAVD) has been identified as an active process involving lipoprotein accumulation, inflammation and creation of calcium nodules as well as valvular angiogenesis. The formation of new blood vessels has been frequently observed in degenerated aortic valve leaflets but its mechanistic role in CAVD is barely understood. The aim of this study was to investigate the role of the vascular endothelial growth factor receptors (VEGFR) in the degeneration process of the aortic valve (AV).

Methods: Expression of mRNA was analyzed in human unaltered, fibrotic and calcified AV (each n = 20) by semiquantitative RT-PCR. Ovine aortic heart valves (n = 6–8) were cultivated in vitro under pro-degenerative conditions (10% FBS, 10 mM β-glycerolphosphate, 3 mM CaCl2) for 7d to 28d before gene expression was measured. Calcium deposition of AV was evaluated by alizarin red and von Kossa staining.

Results: Expression of VEGFR2 (p < 0.001), neuropilin-1 (NRP-1; p < 0.001)), histon-deacetylase 1 (HDAC1; p < 0.05), HDAC3 (p < 0.001), collagen (COL) 1A1 (p < 0.001), COL3A1 (p < 0.001), COL5A1 (p < 0.001) and α-actin-2 (ACTA2; p < 0.01)) was increased in human fibrotic and calcified AV. Expression of VEGFR2 was increased in calcified AV (p < 0.05). In vitro mRNA expression of VEGFR1 was upregulated in leaflets of ovine AV after 7d (p < 0.01) and at the same level after 14d and 28d. VEGFR2 and VEGFR3 were decreased after 7d and 14d (p < 0.05) before upregulated after 28d. NRP-1 was downregulated after 7d and 14d (p < 0.05) and increased after 28d (p < 0.05). Osteopontin (OPN; p < 0.05 after 14d), Osteoprotegerin (OPG; p < 0.01 after 28d) and VEGF-A (p < 0.05 after 14d) were upregulated at all time points. HDAC3 expression was increased after 28d (p < 0.01). Col1A1, Col3A1, Col5A1, ACTA-2 and osteocalcin (OCAL) were decreased after 7d and 14d and increased after 28d (p < 0.01). Histological staining confirmed progression of AV degeneration during cultivation time.

Conclusions: Key molecular components of valvular angiogenesis are activated in human CAVD as well as in a simplified experimental model using ovine aortic valves, where angiogenesis is first triggered after calcium accumulation. Further studies are required to clarify the role of angiogenesis in the degeneration process of AV.