OXIDATIVE-MECHANICAL SIGNALING ACTIVATES Wnt3a-Lrp5 MEDIATED AORTIC VALVE OSTEOGENESIS IN BICUSPID AORTIC VALVE DISEASE
Nalini M. Rajamannan, M.D., Northwestern University Feinberg School of Medicine, Chicago, IL, USA
Introduction: Calcific aortic valve disease (CAVD) is the most common indication for valve surgery in the USA. Cellular mechanisms are under intense investigation. This study hypothesizes that calcific aortic valve disease develops secondary to Wnt3a/Lrp5 activation via oxidative- mechanical stress via a tissue stem cell niche resident in the aortic valve.
Methods: eNOS-/- mice were tested with experimental diets including a control (n=20), cholesterol (n=20), cholesterol + Atorvastatin (n=20). After 23 weeks the mice were tested for the development of aortic stenosis by Echo, Histology, MicroCT and RTPCR for bone markers. In vitro studies measured Wnt3a secretion from aortic valve endothelial cells and confirmed oxidative stress via eNOS activity. Anion exchange chromatography was performed to isolate the mitogenic protein. Myofibroblast cells were tested to induce bone formation.
Results: Cholesterol treated eNOS mice develop severe stenosis with an increase in Wnt3a, Lrp5, Cbfa1, (3-fold increase (p<0.0001) in the bicuspid versus tricuspid aortic valves. Secretion of Wnt3a from aortic valve endothelium in the presence of abnormal oxidative stress was correlated with diminished eNOS enzymatic activity and tissue nitrite levels. Initial characterization of the architecture for a stem cell nice was determined by protein isolation using Anion-Exchange Chromatography and cell proliferation via thymidine incorporation. Osteoblastogenesis in the myofibroblast cell occurred via Lrp5 receptor upregulation in the presence of osteogenic media.
Conclusion: Targeting the Wnt3a/Lrp5 pathway in valve calcification and activation of osteogenesis is via an oxidative-mechanical stress in CAVD. These findings provide a foundation for treating this disease process by targeting the cross talk mechanism in a resident stem cell niche.