Cellular and subcellular localization of catalase in the heart of transgenic mice

Previous studies have described a cardiac-specific, catalase-overexpressing transgenic mouse model that was used to study myocardial oxidative injury. This study was undertaken to demonstrate cellular and subcellular localization of catalase in the hearts of transgenic mice. By the light microscopic immunoperoxidase method, we found that the overexpressed catalase was exclusively localized in cardiomyocytes. The ratios of immunoreactive cardiomyocytes in the heart were quite different among three transgenic lines examined but agreed with the elevated levels of catalase activity. In the cardiac blood vessels, positive cells were found in the walls of pulmonary veins and the vena cava, which consist of cardiomyocytes, but not in the pulmonary arteries, aorta, or cardiac valves. The electron microscopic immunogold method revealed that the elevated catalase was in sarcoplasm, nucleus, and peroxisomes, but not in mitochondria. In contrast to these distributions, catalase in the non-transgenic cardiomyocytes was in peroxisomes only. In addition, the number and size of peroxisomes in the transgenic cardiomyocytes were markedly increased, but no other ultrastructural changes were observed in comparison with those of non-transgenic mice. These results demonstrated that the elevated catalase in transgenic mouse heart is localized in cardiomyocytes and is distributed to peroxisomal and extraperoxisomal, but not mitochondrial, compartments.