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 β ₂-adrenergic receptors (β₂-ARs). The aim of this study is to determine the level and pattern of expression of β₂-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 β₂-ARs, β₁-ARs, β₃-AR,s and receptor activator of nuclear factor-κB (RANK) in calcified aortic valves. The expression of β₂-ARs and β₁-ARs mRNA was assessed by real-time TaqMan PCR in cultures of human aortic valve ICs. Human valve ICs treated with the selective β₂-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 β₂-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 β₂-ARs in regulating valve calcification and may identify potential therapeutic targets.