Autophagy is involved in the elimination of intracellular inclusions, Mallory-Denk bodies, in hepatocytes

Abstract

Several human liver diseases are associated with formation of hepatocyte Mallory-Denk bodies (MDB) composed of keratins and ubiquitin. Similar inclusions are found in various other diseases, neurodegenerative and muscle disorders. However, the mechanisms of MDB formation have been unclear. Autophagy is a degradation process of intracellular proteins and organelles. In the present study we examined the association of autophagy with the formation of MDB. We fed wild-type and keratin 8-transgenic mice with a 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-containing diet for 9 days. The livers were analyzed by immunohistochemistry and conventional and immune electron microscopy. Short-term DDC feeding induced MDB in keratin 8-transgenic but not in nontransgenic mouse livers. Electron microscopy revealed inclusions composed of electron-dense materials and filaments in hepatocyte cytoplasm and many autophagolysosomes in hepatocytes. Inclusions were positive for keratin 8/18 and ubiquitin examined by immunoelectron microscopy. Gold particles for keratin 8/18 or ubiquitin were found in the autophagic vacuoles near or in the inclusions. Keratin 8 overexpression accelerates MDB formation, and the keratin 8-transgenic mouse is a useful tool for the study of MDB formation. Autophagy apparently participates in the elimination of components of MDB. Manipulation of autophagy may be a possible therapeutic strategy for various inclusion-associated diseases.