It is now generally accepted that calcific aortic valve disease is an atherosclerotic-like process. Recent studies in an experimental model of aortic valve sclerosis demonstrated the presence of tissue factor (TF), the main contributor to atherosclerotic plaque thrombogenicity, in diseased valve leaflets. We assessed the hypothesis that human aortic valve disease is an atherosclerotic-like process in which TF plays an important role and evaluated the valvular expression and localization of TF and other components of atherosclerosis.
Calcified aortic valves (n=52) were obtained from patients undergoing aortic valve replacement. Leaflet structure, cellular and lipid infiltration and expression of TF, its inhibitors, VEGF and other components of atherosclerosis were evaluated by histological and immunohistochemical staining. TF, TFPI, osteopontin, MMP- 9, TIMP-1 and VEGF antigen were measured by ELISA and TF and alkaline phosphatase activity were determined using chromogenic assays. Finally, we performed semi-quantification of TF transcripts by RT- PCR and further analyzed protein expression by Western blot.
Histological and immunohistochemical staining of the valve leaflets revealed neovascularisation at the centre of the lesions, overall macrophage and myofibroblast infiltration and the abundant presence of MMP-9. On the other hand, TF and TFPI were associated with calcification and extracellular lipid deposits in the fibrosa and the subendothelial layer of the aortic side of the leaflets. Correspondingly, TF antigen and activity were found to be higher in calcified regions of the valve leaflets (733.29±70.49pg/mgvs 429.40±73.17pg/mg and 144.75±14.65pg/mgvs 40.15±6.19pg/mg respectively (p<0.0001)). Similar results were found for osteopontin, MMP-9, TIMP-1 and VEGF. In contrast, TFPI antigen was found to be much lower in these calcified regions (722.54±153.92pg/mgvs 2459.28±285.36pg/mg (p<0.0001)).
These results demonstrate that aortic valve lesions display several characteristics of atherosclerosis, including TF expression. In addition, we showed that TF is colocalized with calcification and lipid deposition. Further studies are now set up to evaluate the role of TF in aortic valve disease and its association with other components of the atherosclerotic process.Le texte complet de cet article est disponible en PDF.