Protein aggregation occurs in association with a variety of liver diseases and is typically cytoplasmic. A common form of protein aggregates are Mallory-Denk bodies (MDBs) that are found in association with steatohepatitis, viral hepatitis and other forms of liver disease. Recent findings indicate that the presence of MDBs provides an independent poor clinical and histological outcome in patients with hepatitis C. The propensity to form MDBs is linked to the genetic background as supported by higher predisposition to their formation in specific mouse (C57BL > C3H strain) and human (Hispanic > White) genotypes. Among the molecular alterations that positively associate with experimental MDB formation are hypersumoylation and hypoacetylation of keratins (the major protein constituents of MDBs). Also, the overall liver sumoylation is impaired in the C57BL MDB-susceptible strain. Another potential genetic modifier we identified is the ecto-5'- nucleotidase, CD73, whereby a novel and hitherto unknown spliced variant is modulated differently in the MDB formation-prone versus formation-resistant strains. Aside from the cytoplasmic MDBs, a novel type of nuclear protein aggregation that we recently observed in cell culture, in mouse liver injury models undergoing oxidative stress, and in some human chronic liver disease explants involves the nuclear lamins. Formation of lamin- containing aggregates is rapid and is noted within days of exposure to the insult; and is observed prior to MDB formation, which requires weeks. Lamin aggregation could interfere with one or more nuclear functions, and its rapid onset may serve as an early marker of specific types of oxidative injury. Our hypothesis is that genetic variations unmask differences in hepatocyte responses to oxidative injury which manifest as nuclear and cytoplasmic protein aggregation. This hypothesis will be tested using 3 specific aims: (i) Characterize the role of CD73 in strain-selective MDB formation and liver injury; (ii) Characterize keratin acetylation and its relationship to keratin sumoylation and aggregation during oxidative stress; and (iii) Define the biochemical and functional alterations that associate with nuclear lamin disorganization in response to liver injury. Completion of our aims should provide fundamental knowledge regarding genetic modifiers and posttranslational regulation involved in MDB formation. In addition, the exciting finding of a novel CD73 isoform and its genetic background-related differences in response to liver injury may unfold a new paradigm for the role of CD73 in liver and other cell responses to injury. Furthermore, the newly appreciated aggregation of nuclear lamins in response to liver injury provides a potential novel mechanism for direct nuclear involvement that may protect from or promote liver injury, with consequent possible therapeutic, prognostic and diagnostic targets and approaches.
The overarching goal of this proposal is to identify genetic influences on the predisposition to protein aggregation in response to oxidative liver injury. Understanding the role of genetic factors is highly beneficial and relevant since it provides potential diagnostic, prognostic and therapeutic targets in human liver disease, in addition to providing possible molecular explanations to the observed differences in susceptibility to a range of liver diseases in humans.
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