0374 Leptin and its receptor in human calcific aortic valve: expression and functional implications

Abstract

Calcific aortic valve disease (CAVD) affects 2% to 6% of population over 65 years in industrialized countries. CAVD, assimilated to an “atherosclerosis-like” disease, results from dysregulated mechanisms such as fibrosis, inflammation and calcification. These mechanisms could be enhanced by the osteoblastic differentiation of the valvular interstitial cells (VIC), the most prevalent cell type in the human aortic valves. Leptin, known as the product of obesity gene, has recently been linked to aortic valve calcification in ApoE -/- mice. Our hypothesis is that leptin could play an important role in the calcifying processes implicated in CAVD via direct effects on VIC phenotype in humans. Expression of leptin and its receptor was analysed by RT-qPCR, immunohistochemistry and ELISA in 74 human calcific aortic valves and in 10 normal valves. VIC isolated from calcific and normal aortic valves were also analysed. The effects of leptin on the expression of osteoblastic markers such as osteopontin, osteonectin, alkaline phosphatase, BMP-2 and BMP-7 in cultured VIC were investigated. The presence of leptin and its long, functional, receptor isoform (ObR-L) was observed in human aortic valves with an overexpression of leptin in calcified vs non-calcified valvular zones (114.52 pg/mg (47.96- 234.55) vs 66.95 pg/mg (42.76-137.15), p<0.05). Moreover, ObR-L and leptin were constitutively expressed in VIC with a higher ObR-L expression in VIC isolated from pathological vs normal valves (p<0.05). Finally, stimulation of VIC by leptin at physiological concentrations (20 to 100 ng/mL) significantly increased osteonectin (pro-calcifying) and decreased BMP-7 (anti-calcifying) expression levels. Taken together, these novel findings suggest that leptin could be involved in the process of human valve calcification by modifying VIC phenotype.