Similar Effects of Humoral or Mechanical Stress on Cell-Cell Contacts in Cultured Cardiomyocytes

Abstract

We have previously characterised the specific changes that occur at the cell-cell contacts (intercalated discs) of cardiomyocytes in dilated cardiomyopathy. These include increased membrane convolution and increased presence of actin-associated proteins as well as signalling molecules such as PKCalpha at these sites. Aim of the current project is to study these alterations as they happen during humoral (excessive beta-adrenergic stimulation) or mechanical (substrates that are mimicking a fibrotic environment) stress on neonatal rat cardiomyocytes in culture. After only three days exposure to stress, we already observed increased membrane convolution at the cell-cell contacts, as suggested by a broader signal for e.g. beta-catenin and also increased total beta-catenin expression levels as analysed by immunoblotting. The signal for phosphorylated FHOD1, the active form of a formin that is located at the intercalated disc, was also increased at cell-cell contacts of stressed compared to control cardiomyocytes. These changes in cytoarchitecture were accompanied by increased targeting of phosphorylated PKCalpha to the cell-cell contacts. These data suggest that the cardiomyocytes respond very rapidly to humoral or mechanical stress in the 2D environment in vitro and that mainly the myofibril anchorage sites at the cell-cell contacts are reinforced following stress induced by arrhythmic contractions. This may be a useful model system to study the time course of events that lead to changes in cytoarchitecture during cardiomyopathy.