Background: Aortic valve calcification is a progressive process resembling ossification. Recent evidence indicates that the sympathetic nervous system plays an important role in regulating bone deposition and resorption through the beta2-adrenergic receptors (beta2-ARs). The aim of this study is to determine the level and pattern of expression of beta2-ARs in human valve interstitial cells (ICs) and assess their influence on differentiation of the cells into an osteoblast-like phenotype.
Methods and results: Immunohistochemical analysis demonstrated a high expression of beta2-ARs, beta1-ARs, beta3-AR,s and receptor activator of nuclear factor-kappaB (RANK) in calcified aortic valves. The expression of beta2-ARs and beta1-ARs mRNA was assessed by real-time TaqMan PCR in cultures of human aortic valve ICs. Human valve ICs treated with the selective beta2-AR agonist, salmeterol, in the presence of osteogenic medium showed a significant 5-fold decrease in the alkaline phosphatase (ALP) activity in comparison to cells treated with osteogenic medium only (P<0.05). Immunocytochemical staining of the valve ICs showed a concomitant reduction in osteocalcin expression. In addition, other beta2-AR agonists caused a reduction in the protein expression of bone markers including ALP, Cbfa-1, and periostin. Human valve ICs treated with norepinephrine, in the presence of osteogenic medium, did not show a significant reduction in the ALP activity.
Conclusions: These findings suggest an important role of the beta2-ARs in regulating valve calcification and may identify potential therapeutic targets.