Localization of changes in β-actin expression in remodeled canine myocardium

β-actin is a cytoskeletal protein that has been implicated as a potentially important mediator of the growth, signaling, migration, and remodeling of cells. Beta-actin is upregulated in remodeling myocardium in response to either pressure or volume overload. The cellular localization of this response has, however, not been determined and is a necessary first step to begin to clarify the role of β-actin in myocardial remodeling. Here we demonstrate that β-actin protein was confined primarily to the cardiac interstitium using immunofluorescent and immunohistochemical staining. Furthermore, both staining and immunoblotting showed markedly increased β-actin protein in myocardium within 24 h of either regional left ventricular damage or chronic volume overload. More importantly, this increase persisted up to 90 days in both models. Double staining showed co-localization of β-actin protein and von Willebrand factor, a specific endothelial cell marker. These results suggest that increased β-actin expression predominantly localized in cardiac interstitial cells, including endothelial cells. The increased β-actin could be due to either proliferation of the interstitial cells or upregulation of the β-actin gene.