Abstract 14933: Il-6 in Aortic Stenosis: Amplification Loop Between Inflammation and Calcification
BACKGROUND: Calcific aortic valve disease (CAVD) is the most common valvular heart disease and aortic valve replacement is the only available cure. CAVD is a disorder characterized by a calcification and a fibrosis of aortic valve. Inflammatory infiltrates mainly consists in macrophages, leukocytes and T cells. Our goal was to study the role of IL6 during calcification and explore molecular mechanism associated with its action.
METHODS AND RESULTS: A microarray analysis of IL6 gene expression profile in CAVD, compared with control valves, showed that IL6 is increased during mineralization. QPCR results confirmed that IL6 transcripts are increased by 8.9 fold in CAVD. Immunohistochemistry assays demonstrated that IL6 is present in vicinity of calcium nodules in CAVD. In vitro experiments, in human valve interstitial cells (VICs), revealed that exposure to a phosphate-rich medium (Pi) increased IL6 mRNA and protein. In addition, cells transfected with siRNA directed against IL6 have a reduced level of mineralization upon Pi treatment. Levels of several osteoblastic markers were also reduced by a siRNA against IL6. Moreover, a treatment of VIC with recombinant IL6 induced cell mineralization and overexpression of osteoblastic genes. ENPP1, a critical determinant of aortic calcification, is also increased by IL6 treatment and overexpression of ENPP1 significantly increased IL6 mRNA. Therefore, there seems to be a positive feedback loop between IL6 expression and calcification. Also, the consequence of Pi treatment on IkB phosphorylation was examined; with Pi, the ratio of phosphorylated IkB over total IkB was highly increased. This supports a role for the NF-kB transcription factor in regulating IL6 level during calcification. In addition, an agonist of P2Y2 purinergic receptors (P2Y2R), which prevents mineralization in vitro, reduced the ratio phospho IkB/total IkB. The same agonist impedes on the increase of IL6 mRNA induced by Pi. Noteworthy, in VICs isolated from P2Y2R-/- mice, IL6 expression was increased compared with VICs isolated from wild type mice.
CONCLUSION: Our results suggest that Pi-mediated activation of NF-kB regulates positively IL6, which entrain mineralization of VIC and that signalling through the P2Y2R hinders on this regulation.
- © 2013 by American Heart Association, Inc.