Abstract 3707: A Novel Role of the Sympatho-Adrenergic System in Regulating Valve Calcification
Aortic valve Calcification has been shown to be a progressive process resembling ossification. Recent evidence has indicated that the sympathetic nervous system plays an important role in regulating bone deposition and resorption through the beta 2-adrenergic receptors (β2-AR). However, the role of the β2-AR in valve calcification is unknown. We aimed to determine the expression of β-ARs in human valve interstitial cells (ICs) and assess their influence on differentiation of the cells into an osteogenic cell phenotype. Using Real-time TaqMan PCR the expression of β1-AR and β2-AR genes was determined in primary cultures of human aortic valve ICs. Both genes were found to be expressed in human valve ICs. Immunohistochemical analysis also revealed the presence of both receptors in human valve cusps. In order to test the effect of β2-AR on changing the human valve ICs towards osteogenic phenotype, cells were treated with the selective β2-AR agonist, salmeterol, in the presence and absence of osteogenic media for 21 days. Using a colorimetric assay, alkaline phophatase (ALP) enzyme activity, an osteoblast marker, was measured in all samples. Salmeterol treatment in the presence of osteogenic media significantly reduced the ALP activity from 10.2±2.9 nmol/ min/mg protein in the osteogenic treated cells, to 4.7±1.9 nmol/min/mg protein (P<0.04, n=3).There was no increase in the ALP activity when human valve ICs were treated with salmeterol alone. Immunocytochemical staining of human valve ICs with osteocalcin (osteoblast marker) further confirmed our findings, whereby high levels of expression of osteocalcin was observed in cells treated with osteogeneic media and lower expression was seen in valve ICs treated with salmeterol, in the presence of osteogenic media. This study suggests an important novel role of the β2-AR in regulating valve calcification and may identify potential therapeutic targets.