Localization of type IV collagen alpha chain in the myocardium of dilated and hypertrophic cardiomyopathy.

A total of 6 alpha chains [alpha 1 (IV) to alpha 6 (IV)] have been identified in type IV collagen. We examined the localization of these chains in the myocardium of patients with dilated (DCM) and hypertrophic (HCM) cardiomyopathy. The localization of alpha 1 (IV)-alpha 6 (IV) in biopsy specimens of 5 patients with DCM and 4 with HCM was examined using immunohistochemistry with monoclonal antibodies. Both alpha 1 (IV) and alpha 2 (IV) immunostaining formed thin homogeneous outlines around myocytes in control hearts. In the DCM specimens, alpha 1 (IV) and alpha 2 (IV) immunostaining formed thick and irregular patterns around myocytes. Staining for alpha 1(IV) and alpha 2 (IV) was also observed in some enlarged intercellular spaces. In 3 DCM hearts, moderate staining for alpha 1 (IV) and alpha 2 (IV) was observed in small replacement fibrotic lesions. In large replacement fibrotic lesions, no alpha 1 (IV) or alpha 2 (IV) staining was observed. In the HCM specimens, alpha 1 (IV) and alpha 2 (IV) staining formed thick homogeneous patterns around myocytes. In the enlarged intercellular spaces, no alpha 1 (IV) or alpha 2 (IV) staining was observed. No labeling for alpha 3 (IV)-alpha 6 (IV) was observed in any heart examined. In conclusion, the present results demonstrate that type IV collagen consisting of alpha 1 and alpha 2 chains appears in the fibrotic lesions of DCM, indicating its contribution to the development of fibrotic changes in the myocardium of DCM patients. In contrast, type IV collagen was restricted to the myocyte membrane in the HCM hearts. Fibrotic processes in the intercellular spaces may differ between DCM and HCM hearts.