Cardiac valve interstitial cells secrete fibronectin and form fibrillar adhesions in response to injury

BackgroundFibronectin, an extracellular matrix protein, is associated with the general process of tissue repair and is present in heart valves. In order to understand the cellular mechanisms of heart valve repair, we hypothesized that fibronectin is produced and secreted by valvular interstitial cells (VICs), and when up-regulated in VICs involved in active repair, it is associated with prominent fibrillar adhesions composed of tensin and α5β1 integrin. We investigated the interaction of porcine mitral VICs with the underlying fibronectin matrix and the formation and localization of focal and fibrillar adhesion complexes in an in vitro wound model.MethodsConfluent monolayers of VICs were wounded with a 1-mm-wide cell scraper, maintained in standard media and 10% fetal bovine serum, and fixed at various time points after wounding. Immunohistochemistry was used to localize fibronectin, paxillin, tensin, and α5β1 integrin. F-actin was localized with an Alexa-Fluor-568-labeled phalloidin. Cells were examined with a scanning confocal laser microscope.ResultsIn response to in vitro mechanical wounding, migrating VICs at the wound edge expressed cytoplasmic fibronectin compared to nonwounded confluent monolayers. Over 24 to 48 h, fibrils were deposited into the subcellular space. Coincident with this, staining for α5β1 appeared, and tensin redistributed from focal adhesions to fibrillar adhesions, which colocalized with α5β1.ConclusionsFibronectin in association with fibrillar adhesions is a component of the matrix that may be secreted by migrating VICs to regulate repair at sites of valve injury.