Calcific Aortic Valve Disease: Osteoblast Differentiation in a Stem Cell Niche.

Calcific aortic valve disease is the most common indication for heart valve surgery. Until the past decade the cellular mechanisms for this disease were not known. It was thought to be a passive degenerative process for decades and now is considered an active cellular process, which evolves into an end-stage calcific bone phenotype. The cells involved in this phenotype are the critical link towards the understanding of bone formation. The studies in this field have now defined two types of cardiac stem cells, first, the innate interstitial mesenchymal cell that contains the embryologic ability to form bone in the presence of oxidative stress. The second cell is the circulating osteoprogeniter cell, which also has the ability to "home" to the site of calcifying tissues and form bone. This review article will discuss both cell types and the contributions of this science towards the understanding of how calcific aortic valve disease develops.