Characterization of cell motility in single heart valve interstitial cells in vitro

Valve interstitial cells (VIC) are the most prevalent cells in the heart valve, regulating to a large extent the normal biology of the valve and its pathobiological response to disease. In the process of valve tissue repair by VICs, single cell motility is likely to be important, as it is in wound repair by most mesenchymal type cells. We designed in vitro experiments using low density monolayer cultures to study the association of morphology and motility in single VICs which expressed alpha-smooth muscle actin. We observed that the morphology of single VICs can be categorized into six types which are reminiscent of the shape of VICs seen in vivo during valve repair. Of these morphologies, round, rhomboid, tailed and spindled shaped VICs were the most common. VICs did change their morphology over time. Rhomboid cells could become tailed or spindle-shaped and vice versa. Using time-lapse imaging and immunofluorescent microscopy, we showed that VIC morphologies reflect differences in cell motility and cell-matrix interactions. Tailed and spindle-shaped VICs were the predominant motile types and were associated with few extracellular fibronectin fibrils and less focal adhesions, as demonstrated by vinculin staining. Round and rhomboid shaped VICs were less motile and were associated with prominent vinculin and extracellular fibronectin fibrils. We found that cell mitosis is an important determinant of VIC migration. Many of the motile VICs were associated with mitosis as the daughter cells separated by migrating as tailed and spindle shaped cells. Thus cell morphology is an important determinant of VIC motility.