Alterations in myocardial cytoskeletal and regulatory protein expression following a single doxorubicin injection

Immunochemical and ultrastructural studies of the rat heart after a single injection of doxorubicin (2.2 or 0.44 mg/kg) were performed. Ventricles were taken for the study 2 It and 3 weeks after injection. The light and electron microscopy and immunohistochemical determination of collagens of I, III, and IV types and fibronectin using specific antibodies were implied. Quantitive immunoblotting was used to analyze the expression levels of cytoskeletal and extracellular matrix proteins such as desmin, tubulin, vinculin, fibronectin, kinase-related protein (KRP or telokin), and smooth muscle/nonmuscle myosin light-chain kinase (MLCK). Doxorubicin (2.2 mg/kg) did not influence the relative volume and structure of collagen network but distinctly reduced the density of fibronectin distribution and decreased the content of tubulin, fibronectin, MLCK, and KRP. After 3 weeks, an increased density and extension of collagen network were observed, indicating the development of diffuse fibrosis whereas the content of tubulin and KRP increased above control level by 50+/-2.3% and 20+/-5.2%, correspondingly. Similar but less pronounced alterations were observed following the administration of 0.44 mg/kg doxorubicin. The content of MLCK after both doses consistently remained about 30% below its level in untreated animals. Isolated chick embryo cardiomyocytes subjected to doxorubicin responded by a 26% increase in KRP expression 4 days after whereas the level of tubulin expression remained unchanged. Thus, the damage of myocardium after a single injection of a therapeutic dose of doxorubicin was followed by an increased expression of selected cytoskeletal and extracellular matrix proteins, suggesting their involvement in cardiac reparation.