Expression of bone sialoprotein and bone morphogenetic protein-2 in calcific aortic stenosis

Calcific aortic stenosis, the major heart valve disease encountered in the elderly, leads to massive calcium deposition in the valve leaflets that morphologically resembles bone formation. Recent studies have demonstrated the expression of various bone-associated proteins in stenotic valves, suggesting that valvular calcification may be an actively regulated process. Bone sialoprotein (BSP), a non-collagenous bone matrix protein, and bone morphogenetic protein-2 (BMP-2), a member of the transforming growth factor cytokine superfamily, are known to participate in the regulation of bone development and maturation. Their pathogenetic role in calcific aortic stenosis is unknown.

Using an immunoperoxidase technique and antibodies against BSP and BMP-2, the expression of BSP and BMP-2 was examined in 16 human aortic valves with calcific aortic stenosis obtained at valve replacement, and in seven normal autopsy controls without signs of aortic stenosis.

By semiquantitative scoring, stenotic valves showed a significantly increased staining of BSP in cells and extracellular matrix as compared to control valves (2.7 +/- 0.1 versus 0.6 +/- 0.2 score units, p <0.001). Marked BMP-2 expression was detected in stenotic valves, mostly in cell-rich areas associated with focal calcium deposits, but no specific staining for BMP-2 was detected in control valves (1.5 +/- 0.2 versus 0.0 +/- 0.0 score units, p <0.001).

These results demonstrate for the first time that BSP and BMP-2 are differentially expressed in normal aortic valves and in aortic stenosis, thereby supporting the concept that valvular calcification might be based on an actively regulated process involving BSP and BMP-2.