Changes in the cytokeratin intermediate filament cytoskeleton associated with mallory body formation in mouse and human liver

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Abstract
Mouse and human extracted liver tissue were examined by indirect immunofluorescent staining and transmission electron microscopy in order to study the alteration of cytokeratin intermediate filaments associated with Mallory body formation. Frozen sections of griseofulvin-fed mouse liver and human liver of primary biliary cirrhosis and primary sclerosing cholangitis were extracted by Triton X-100 and nuclease. Indirect immunofluorescent staining was performed by using anticow hoof keratin antibody for mouse liver and anti-human epidermal keratin antibody (AE1 and AE3) for human liver. Transmission electron microscopy was also performed on extracted and critical point-dried samples. The griseofulvin-fed mouse hepatoma cells showed four different types of altered staining pattern based on the indirect immunofluorescent staining of the cytoplasm and Mallory bodies: Type I—cytoplasm(+), Mallory body(−); Type II—cytoplasm(+), Mallory body(+); Type III—cytoplasm(−), Mallory body(+), and Type IV—cytoplasm(−), Mallory body(−). Types I and III were predominant, however, some hepatoma cells which contain Mallory bodies revealed bright cytoplasmic staining (Type II). The nuclear rims were strongly stained. In human liver, AE1 stained Mallory bodies and the bile duct epithelium intensely, but did not stain normal hepatocytes. AE3 mainly stained Mallory bodies and normal hepatocytes, but also stained bile duct epithelium weakly. Indirect immunofluorescent staining for human liver showed the same staining patterns as found in mouse liver, except that Type IV was not observed. Although many hepatocytes which contained Mallory bodies did not react with either of these two antibodies (Type III), some of the hepatocytes were stained, not only with AE3, but also with AE1 (Type II). Transmission electron microscopy revealed that Mallory bodies were often surrounded by numerous intermediate filaments, which is equivalent to the Type II pattern in indirect immunofluorescent staining. This was true of mouse liver frozen sections and primary cultures, as well as human liver studied. The results clearly show that cells associated with Mallory bodies show changes in the expression of cytokeratins as well as rearrangement of intermediate filaments within the cell. Hepatocytes forming Mallory bodies often contain a variable density of intermediate filaments which fail to stain with cytokeratin antibodies, indicating that the antigenic determinants of the intermediate filaments were lost or masked.