Expression of collagenase and IL‐1α in developing rat hearts

During development, extracellular matrix (ECM) molecules are thought to play a major role in regulating the formation of the heart. The change in the heart from a simple tube to a complex, four‐chambered organ requires the modification of both the cellular components as well as the surrounding ECM. Matrix metalloproteinases (MMP), which include collagenases, are enzymes present in the ECM that have the potential to modify the existing ECM during the development of the heart. Using both monoclonal and polyclonal antisera against collagenase, specific temporal and spatial patterns have been documented during critial periods of heart development. The cytokine interleukin 1α (IL‐1α), a potent inducer of the MMP expression, was also shown to have a similar staining pattern in the developing heart. The monoclonal anti‐rat collagenase (Mab) intensely stained the surfaces of the myocytes in the trabeculae and the ventricular and atrial walls of the 11.5 or 12.5 embryonic day (ED) rat hearts. In contrast, the polyclonal anti‐human collagenase (Pab) stained not only the cardiomyocytes but also the hypertrophic endocardial cells. Pab appeared to stain the leading edge of the mesenchymal cells that migrate into the cardiac jelly of the 11.5 or 12.5 ED hearts. Immunohistochemical staining showed IL‐1α on the endocardial endothelium and the surface of cardiomyocytes near the cardiac jelly just before or coincident with the appearance of migrating cells. IL‐1α was detected on the endocardial endothelium, cardiomyocytes in the trabeculae, and the ventricular and atrial walls, as well as in the myocardial basement membrane of the truncal or atrioventricular region. However, no staining could be detected on the migrating cells in the cardiac cushions. These results indicate the presence of collagenase and IL‐1α on the surface of cardiomyocytes and mesenchymal cells at times when the heart is undergoing acute remodeling during septation and trabeculation. These data suggest a role for collagenase/cytokine interaction in tissue remodeling during critical stages of cardiac embryogenesis where modification of the ECM is essential to cardiac morphogenesis. © 1992 Wiley Liss, Inc.