The cytoplasmic hepatocyte inclusions, Mallory-Denk bodies (MDBs), are characteristic of several liver disorders, including alcoholic and nonalcoholic steatohepatitis. In mice, MDBs can be induced by long-term feeding with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) for 3 to 4 months or rapidly reformed in DDC-induced then recovered mice by DDC refeeding or exposure to a wide range of toxins for only 5 to 7 days. The molecular basis for such a rapid reinduction of MDBs is unknown. We hypothesized that protein changes retained after DDC priming contribute to the rapid MDB reappearance and associate with MDB formation in general terms. Two-dimensional differential-in-gel-electrophoresis coupled with mass spectrometry were used to characterize protein changes in livers from the various treatment groups. The alterations were assessed by real-time reverse-transcription polymerase chain reaction and confirmed by immunoblotting. DDC treatment led to pronounced charged isoform changes in several chaperone families, including Hsp25, 60, 70, GRP58, GRP75, and GRP78, which lasted at least for 1 month after discontinuation of DDC feeding, whereas changes in other proteins normalized during recovery. DDC feeding also resulted in altered expression of Hsp72, GRP75, and Hsp25 and in functional impairment of Hsp60 and Hsp70 as determined using a protein complex formation and release assay. The priming toward rapid MDB reinduction lasts for at least 3 months after DDC discontinuation, but becomes weaker after prolonged recovery. MDB reinduction parallels the rapid increase in p62 and Hsp25 levels as well as keratin 8 cross-linking that is normally associated with MDB formation.
Conclusion: Persistent posttranslational modifications in chaperone proteins, coupled with protein cross-linking and altered chaperone expression and function likely contribute to the "toxic memory" of DDC-primed mice. We hypothesize that similar changes are important contributors to inclusion body formation in several diseases.