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High molecular weight components are main constituents of Mallory bodies isolated with a fluorescence activated cell
K Zatloukal1, G Böck, I Rainer
1Division of Molecular Pathology, University of Graz School of Medicine, Austria.
Abstract:
Mallory bodies (MBs) are cytoplasmic filamentous aggregates containing cytokeratin (CK) material. They occur in hepatocytes of patients with alcoholic liver disease (i.e., alcoholic hepatitis) and can also be induced experimentally in mice by chronic griseofulvin intoxication. To further investigate components and mechanisms involved in MB formation, a new method for MB purification was established. MBs present in a liver homogenate of griseofulvin-fed mice were labeled with a murine monoclonal antibody specific for MBs and a second fluorescein isothiocyanate-conjugated (anti-mouse IgG and IgM) antibody and subsequently isolated by two sequential sorting procedures using a fluorescence activated cell sorter (FACS). Purity of MB isolates was over 90% as revealed by computer analysis of sorting signals and fluorescence and electron microscopy. Electrophoretic separation on sodium dodecyl sulfate-polyacrylamide gels revealed three MB-related polypeptides with apparent molecular masses of 48, 55, and 65 kilodaltons but most of the highly purified MB material did not enter the gel or remained at the interphase between stacking and resolving gels. Western blotting with CK-specific antibodies showed the presence of CK epitopes in the high molecular weight MB material, which has a similar amino acid composition as normal liver CKs. These results establish that very high molecular weight material is the main constituent of MBs and suggest that a post-translational modification of CKs by covalent crosslinks is a principal mechanism of MB pathogenesis.
Insights
Mallory bodies, key indicators of alcoholic liver disease, are primarily composed of high molecular weight cytokeratin material. This study suggests covalent cross-linking of cytokeratins is crucial for their formation.
Area of Science:
- Hepatology
- Cell Biology
- Biochemistry
Background:
- Mallory bodies (MBs) are cytoplasmic inclusions found in hepatocytes, particularly in alcoholic liver disease.
- MBs contain cytokeratin (CK) and can be experimentally induced by griseofulvin.
- Understanding MB composition and formation is vital for liver disease research.
Purpose of the Study:
- To develop a novel purification method for Mallory bodies.
- To identify the molecular components of MBs.
- To elucidate the mechanisms underlying MB formation.
Main Methods:
- Purification of MBs from griseofulvin-intoxicated mouse liver homogenates using fluorescence-activated cell sorting (FACS).
- Characterization of purified MBs via fluorescence microscopy, electron microscopy, and SDS-PAGE.
- Western blotting with CK-specific antibodies to identify protein components.
Main Results:
- A highly purified MB fraction (>90%) was obtained.
- SDS-PAGE revealed three low-molecular-weight polypeptides (48, 55, 65 kDa), but the majority of MB material did not enter the gel.
- Western blotting confirmed the presence of CK epitopes in the high-molecular-weight fraction, with similar amino acid composition to normal CKs.
Conclusions:
- Very high molecular weight material, likely cross-linked CKs, constitutes the primary component of MBs.
- Post-translational modification of CKs through covalent cross-linking is a principal mechanism in MB pathogenesis.
- This research provides new insights into the molecular basis of alcoholic liver disease pathology.