Bovine mitral valve organ culture: role of interstitial cells in repair of valvular injury.

The atrial and ventricular surfaces of the mitral valve are lined by endothelial cells termed endocardial cells, while the valve stroma contains interstitial cells. Bovine mitral valve organ cultures were immunoperoxidase-stained for Factor VIII RAg, alpha smooth muscle actin, and PCNA/cyclin in order to identify the cell types involved in mitral valve wound repair. Factor VIII RAg is a well-characterized endothelial cell marker, alpha smooth muscle actin is an indicator of smooth muscle differentiation and PCNA/cyclin is a marker for S phase. Bovine mitral valve endocardium was Factor VIII RAg positive and remained positive after culturing for 6 days (n = 7). Mitral valve interstitial cells were Factor VIII RAg negative and positive for alpha smooth muscle actin. By 6 days in culture, the lateral edges of the preparations, where the tissue was originally dissected from the mitral valve leaflet, were covered by multiple layers of cells. These cells were Factor VIII RAg negative (n = 7), and hence not endocardial, but were alpha smooth muscle actin positive like interstitial cells. Interstitial cells subjacent to the lateral edges were negative for PCNA/cyclin in uncultured preparations (n = 5), but positive in 12 out of 15 specimens cultured for 6 days. The results suggest that mitral valve interstitial cells are responsible for the repair process seen in the lateral edges of mitral valve organ cultures.