Iron overload results in an accumulation of electron-dense iron-containing particles (IPs) such as ferritin and hemosiderin within the lysosomes of rat liver cells. In order to evaluate the effect or iron overload on lysosomal function, efforts were made to isolate lysosomes with different iron contents by means of ultracentrifugation in Percoll and Metrizamide gradients.
Lysosomes isolated on the Percoll gradient were characterized ultrastructurally by a uniform matrix consisting mainly of IPs and these lysosomes contained a high iron concentration and showed a very low proteolytic activity. They may, therefore, constitute, or be equated, with a special type of residual bodies. They were also fragile, as judged by their significant release of enzymes during incubation in vitro.
Lysosomes isolated in the Metrizamide gradient contained remnants of sequestered organelles and some IPs. These organelles displayed a somewhat impeded proteolytic activity compared with control lysosomes, as well as preserved membrane stability during incubation in vitro. We suggest that these may be precursors of the heavily iron-laden lysosomes recovered in the Percoll gradient.
Our findings demonstrate that different populations of lysosomes exist in iron-overloaded rat liver cells, which show specific characteristics with regard to ultrastructural appearance, iron content and proteolytic activity. Differing iron contents is the most likely reason for their diverging densities and membrane integrities, whereas the difference in proteolytic activity could be a result of varying amounts of degradable substrate.
Iron overload Lysosomes Proteolysis
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Abok K, Hirt T, Ericsson JLE, Brunk U (1983) Effect of iron on the stability of macrophage lysosomes. Virchows Arch [Cell Pathol] 43:85–101Google Scholar
Ahlberg J, Marzella L, Glaumann H (1982) Uptake and degratation of proteins by isolated rat liver lysosomes. Suggestion of a microautophagic pathway of proteolysis. Lab Invest 47:523–532PubMedGoogle Scholar
Arborgh B, Glaumann H, Ericsson JLE (1974) Studies on iron loading of rat liver lysosomes. Effects on the liver and distribution and fate of iron. Lab Invest 30:664–673PubMedGoogle Scholar
Glaumann H, Ericsson JLE, Marzella L (1981) Mechanisms of intralysosomal degradation with special reference to autophagocytosis and heterophagocytosis of cell organelles. Int Rev Cytology 73:149–182Google Scholar
Henell F, Glaumann H (1984) Effect of leupeptin on the autophagic vacuolar system of rat hepatocytes. Correlation between ultrastructure and degradation of membrane and cytosolic proteins. Lab InvestGoogle Scholar
Hultcrantz R (1983) Studies on the rat liver following iron overload. Morphometrical investigation of parenchymal and Kupffer cells. Acta Pathol Microbiol Scand [Sect A] 91:125–132Google Scholar
Hultcrantz R, Glaumann H (1982) Studies on the rat liver following iron overload. Biochemical analysis after iron mobilization. Lab Invest 46:383–393PubMedGoogle Scholar
Hultcrantz R, Arborgh B, Wroblewski R, Ericsson JLE (1979) Studies on the rat liver following iron overload. Electron probe X-ray microanalysis of acid phosphatase and iron. Am J Pathol 96:625–640PubMedGoogle Scholar
Hultcrantz R, Arborgh B, Wroblewski R, Ericsson JLE (1980) Studies on the rat liver following iron overload. Electron microscopical and histochemical depletion after iron depletion. Acta Pathol Microbiol Scand A 88:341–353PubMedGoogle Scholar
Hultcrantz R, Ericsson JLE, Hirt T (1984) Levels of malondialdehydeproduction in rat liver following loading and unloading of iron. Virchows Arch [Cell Pathol] 45:139–146CrossRefGoogle Scholar
Lowry OH, Rosebrough NJ, Farr AL, Randall RL (1951) Protein measurement with the Folin phenol reagent. J Biol Chem 193:265–272PubMedGoogle Scholar
Marzella L, Glaumann H (1983) Biogenesis, translocation and function of lysosomal enzymes. Int Rev Expl Pathol 25:239–278Google Scholar
Marzella L, Sandberg PO, Glaumann H (1980) Autophagic degradation in rat liver after vinblastine treatment. Expt Cell Res 128:291–301CrossRefGoogle Scholar
Marzella L, Ahlberg J, Glaumann H (1982) Isolation of autophagic vacuoles from rat liver. Morphological and biochemical characterization. J Cell Biol 93:144–154PubMedCrossRefGoogle Scholar
Neff NT, de Martino GN, Goldberg AL (1979) The effect of protease inhibitors and decreased temperature on the degradation of different classes of proteins in cultured hepatocytes. J Cell Physiol 101:439–458PubMedCrossRefGoogle Scholar
Pfeifer U, Werder E, Bergeest H (1978) Inhibition by insulin of the formation of autophagic vacuoles in rat liver. A morphometric approach to the kinetics of intracellular degradation by autophagy. J Cell Biol 78:152–167PubMedCrossRefGoogle Scholar
Roy AB (1958) Comparative studies on the liver sulphatases. Biochem J 68:519–528PubMedGoogle Scholar
Seglen PO, Grinde B, Solheim AE (1979) Inhibition of the lysosomal pathway of protein degradation in isolated rat hepatocytes by ammonia, methylamine, chloroquine and leupeptin. Eur J Biochem 95:215–225PubMedCrossRefGoogle Scholar
Seymor CA, Peters TJ (1978) Organelle pathology in primary and secondary hemochromatosis with special reference to lysosomal changes. Br J Haematol 40:239–253CrossRefGoogle Scholar
Sheldon JH (1935) Hemochromatosis. Oxford University Press, LondonGoogle Scholar
Wattiaux R, Wattiaux-de Coninck S, Ronveaux-Dupal MF, Dubois F (1978) Isolation of rat liver lysosomes by isopycnic centrifugation in a metrizamide gradient. J Cell Biol 78:349–368PubMedCrossRefGoogle Scholar
Wills ED (1972) Effects of iron overload on lipid peroxide formation and oxidative demethylation by the liver endoplasmic reticulum. Biochem Pharmacol 21:239–247PubMedCrossRefGoogle Scholar