Relationships between melanocytes, mechanical properties and extracellular matrix composition in mouse heart valves.

Heart valves are complex structures composed of organized layers of extracellular matrix, and interstitial and overlying endothelial cells. In this article, we present the specific localization of a population of melanocytes within the murine heart valves at ages important for their post-natal development. In all stages analyzed in our study, melanocytes were found in high numbers populating the atrial aspect of the tricuspid and mitral leaflets. The pulmonary valve did not present melanocytes. To characterize a putative role for the valve melanocytes, the dynamic nanomechanical properties of tricuspid leaftets containing large numbers or no melanocytes were measured. The stiffness coefficient of hyperpigmented leaflets was higher (11.5 GPa) than the ones from wild-type (7.5 GPa) and hypopigmented (5.5 GPa) leaflets. These results suggest that melanocytes may contribute to the mechanical properties of the heart valves. The arrangement of extracellular matrix molecules such as Collagen I and Versican B is responsible for the mechanical characteristics of the leaflets. Melanocytes were found to reside primarily in areas of Versican B expression. The patterns of expression of Collagen I and Versican B were not, however, disrupted in hyper or hypopigmented leaflets. Melanocytes may affect other extracellular matrix molecules to alter the valves' microenvironment.