Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
Hepatology. 2012 Jul;56(1):322-31. doi: 10.1002/hep.25664. Epub 2012 Apr 25.
Mallory-Denk bodies (MDBs) are hepatocyte inclusions commonly seen in steatohepatitis. They are induced in mice by feeding 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) for 12 weeks, which also causes porphyrin accumulation. Erythropoietic protoporphyria (EPP) is caused by mutations in ferrochelatase (fch), and a fraction of EPP patients develop liver disease that is phenocopied in Fech(m1Pas) mutant (fch/fch) mice, which have an inactivating fch mutation. fch/fch mice develop spontaneous MDBs, but the molecular factors involved in their formation and whether they relate to DDC-induced MDBs are unknown. We tested the hypothesis that fch mutation creates a molecular milieu that mimics experimental drug-induced MDBs. In 13- and 20-week-old fch/fch mice, serum alkaline phosphatase, alanine aminotransferase, and bile acids were increased. The 13-week-old fch/fch mice did not develop histologically evident MDBs but manifested biochemical alterations required for MDB formation, including increased transglutaminase-2 and keratin overexpression, with a greater keratin 8 (K8)-to-keratin 18 (K18) ratio, which are critical for drug-induced MDB formation. In 20-week-old fch/fch mice, spontaneous MDBs were readily detected histologically and biochemically. Short-term (3-week) DDC feeding markedly induced MDB formation in 20-week-old fch/fch mice. Under basal conditions, old fch/fch mice had significant alterations in mitochondrial oxidative-stress markers, including increased protein oxidation, decreased proteasomal activity, reduced adenosine triphosphate content, and Nrf2 (redox sensitive transcription factor) up-regulation. Nrf2 knockdown in HepG2 cells down-regulated K8, but not K18.
Fch/fch mice develop age-associated spontaneous MDBs, with a marked propensity for rapid MDB formation upon exposure to DDC, and therefore provide a genetic model for MDB formation. Inclusion formation in the fch/fch mice involves oxidative stress which, together with Nrf2-mediated increase in K8, promotes MDB formation.
Mallory-Denk 体（MDBs）是常见于脂肪性肝炎的肝细胞内含物。用 3,5-二乙氧羰基-1,4-二氢吡啶（DDC）喂养 12 周可诱导小鼠产生 MDBs，同时还会导致卟啉积累。原卟啉症（EPP）是由亚铁螯合酶（fch）突变引起的，一部分 EPP 患者会发展为肝疾病，这种疾病在 Fech(m1Pas)突变（fch/fch）小鼠中是表型模拟的，fch/fch 小鼠有一个失活的 fch 突变。fch/fch 小鼠会自发产生 MDBs，但形成 MDB 的分子因素以及它们是否与 DDC 诱导的 MDBs 有关尚不清楚。我们测试了这样一个假设，即 fch 突变创造了一个分子环境，模拟了实验性药物诱导的 MDBs。在 13 周和 20 周龄的 fch/fch 小鼠中，血清碱性磷酸酶、丙氨酸氨基转移酶和胆汁酸升高。13 周龄的 fch/fch 小鼠没有表现出组织学上明显的 MDBs，但表现出 MDB 形成所需的生化改变，包括转谷氨酰胺酶-2 和角蛋白过度表达，角蛋白 8（K8）与角蛋白 18（K18）的比值增加，这对于药物诱导的 MDB 形成至关重要。在 20 周龄的 fch/fch 小鼠中，自发 MDBs 很容易在组织学和生化上被检测到。短期（3 周）DDC 喂养显著诱导 20 周龄 fch/fch 小鼠的 MDB 形成。在基础条件下，老年 fch/fch 小鼠的线粒体氧化应激标志物发生显著改变，包括蛋白质氧化增加、蛋白酶体活性降低、三磷酸腺苷含量减少和 Nrf2（氧化还原敏感转录因子）上调。HepG2 细胞中的 Nrf2 敲低下调了 K8，但没有下调 K18。
fch/fch 小鼠会随着年龄的增长而自发产生 MDBs，并且在接触 DDC 后会迅速形成 MDBs，因此为 MDBs 的形成提供了一个遗传模型。fch/fch 小鼠中的包涵体形成涉及氧化应激，Nrf2 介导的 K8 增加共同促进 MDB 形成。
