Genetic basis of susceptibility to splenic lipofuscinosis in mice

Myocardial lipofuscin-laden lysosomes contain the apoptosis marker caspase-cleaved cytokeratin-18

BACKGROUND

Acute coronary syndrome is related to increased circulatory concentration of soluble apoptosis specific caspase-cleaved cytokeratin-18 (ccCK-18). Potential cardiac sources of this intermediate filament derivative have not been investigated to date.

MATERIALS AND METHODS

Paraffin embedded tissue of normal myocardium, and chronically damaged samples of ischaemic, congestive and hypertrophic cardiomyopathy were analysed by histology and by CK-8, CK-18, ccCK-18 immunohistochemistry (each group, n = 15). Antibody specificity of the ccCK-18 antibody M30 was checked by immunoblotting on lysed myocardium and enriched myocardial lysosomes.

RESULTS

ccCK-18 and CK-18 but not CK-8 were present in all forms of cardiomyopathy, most prominently in ischaemic cardiomyopathy while only traces were detectable immunohistochemically in normal myocardium. Weak CK-18 and strong ccCK-18 staining co-localized to lysosomes with cardiac age pigment lipofuscin. Weak staining of CK-18 was detected in the cytoplasm of coronary endothelia.

CONCLUSION

Our study reveals that cardiac lipofuscin-laden lysosomes contain ccCK-18, a marker of apoptosis and its precursor CK-18. This ccCK-18 pool might contribute to increased systemic levels of ccCK-18 in acute coronary syndrome thus monitoring myocardial damage.

Histochemical localization of autometallographically detectable mercury in tissues of the immune system from mice exposed to mercuric chloride

The distribution of mercury in the spleen, liver, lymph nodes, thymus and bone marrow was studied by autometallography in mice exposed to mercuric chloride intraperitoneally. Application of immunofluorescence histochemistry and an autometallographic silver amplification method was employed to the same tissue section. Mercury was not only detected in macrophages marked by the antibody M1/70 but also in macrophage-like cells, which were either autofluorescent or devoid of fluorescent signals. These two cell types were identified as macrophages at the electron microscopical level. Autometallographically stained macrophages were observed in the spleen, lymph nodes, thymus and in Kupffer cells of the liver. Furthermore, mercury was observed in endothelial cells. No obvious pathological disturbances were observed at light and electron microscopical level. At the subcellular level mercury was localized in lysosomes of macrophages and endothelial cells.

Involvement of the tyrosinase gene in the deposition of cardiac lipofuscin in mice. Association with aortic fatty streak development

Lipofuscin pigment, a terminal oxidation product, accumulates within cells during the normal aging process and under certain pathological conditions. We have analyzed a genetic cross between two inbred mouse strains, BALB/cJ and a subline of C57BL/6J, which differ in lipofuscin deposition. A comparison of the segregation pattern of cardiac lipofuscin with the albino locus (c) on mouse chromosome 7 revealed complete concordance. Analysis of spontaneous mutants of the tyrosinase gene, encoded by the albino locus, confirmed that the tyrosinase gene itself controls lipofuscin formation. Genetic analysis of other strains indicated that one or more additional genes cab contribute to the inheritance of lipofuscin. We also present evidence for an association between cardiac lipofuscin deposition and aortic fatty streak development in the mouse.