p62 is involved in the mechanism of Mallory body formation

Defining the Nature and Clinicopathologic Significance of Mallory-Denk-like Inclusions in Ovarian Fibromas: A Potential Degenerative Phenomenon Associated With Torsion

Mallory-Denk bodies (MBD), described in alcoholic hepatitis, are composed of intermediate filaments admixed with other proteins. These cytoplasmic inclusions are irregularly shaped and eosinophilic as seen under the light microscope. MBD-like inclusions have rarely been described outside the hepatobiliary tree. Though rare, intracytoplasmic inclusions have been reported in ovarian fibromas. This study evaluates a series of torsed ovarian fibromas with intracytoplasmic inclusions resembling MDBs. Forty-three ovarian fibromas were retrieved from the pathology archives. The H&E slides were evaluated for the presence of MBD-like inclusions and histologic evidence of torsion. The cases with histologic features of torsion were included in the study group while the nontorsed fibromas formed the control group. Among the 15 cases of fibromas with torsion, MBD-like intracytoplasmic inclusions were seen in 5 cases, predominantly in the interface between necrotic areas and viable stroma. None of the cases from the control group showed any inclusions. There was no significant difference in the size of the fibroma or patient demographics between cases with and without inclusions. The inclusions were positive for cytokeratin and ubiquitin while being negative for per acidic Schiff and periodic acid-Schiff with diastase reaction, in the 3 cases selected for immunohistochemistry and special stains. Electron microscopy of the index case revealed a predominance of type 3 Mallory hyaline. This is the first report describing MDB-like inclusions in ovarian fibromas. These MDB-like inclusions appear to be limited to a fraction of ovarian fibromas that underwent torsion, suggesting that these inclusions likely result from subacute hypoxic damage to the cells.

The caspase-6-p62 axis modulates p62 droplets based autophagy in a dominant-negative manner

SQSTM1/p62, as a major autophagy receptor, forms droplets that are critical for cargo recognition, nucleation, and clearance. p62 droplets also function as liquid assembly platforms to allow the formation of autophagosomes at their surfaces. It is unknown how p62-droplet formation is regulated under physiological or pathological conditions. Here, we report that p62-droplet formation is selectively blocked by inflammatory toxicity, which induces cleavage of p62 by caspase-6 at a novel cleavage site D256, a conserved site across human, mouse, rat, and zebrafish. The N-terminal cleavage product is relatively stable, whereas the C-terminal product appears undetectable. Using a variety of cellular models, we show that the p62 N-terminal caspase-6 cleavage product (p62-N) plays a dominant-negative role to block p62-droplet formation. In vitro p62 phase separation assays confirm this observation. Dominant-negative regulation of p62-droplet formation by caspase-6 cleavage attenuates p62 droplets dependent autophagosome formation. Our study suggests a novel pathway to modulate autophagy through the caspase-6–p62 axis under certain stress stimuli.

Priming, Triggering, Adaptation and Senescence (PTAS): A Hypothesis for a Common Damage Mechanism of Steatohepatitis

Understanding the pathomechanism of steatohepatitis (SH) is hampered by the difficulty of distinguishing between causes and consequences, by the broad spectrum of aetiologies that can produce the phenotype, and by the long time-span during which SH develops, often without clinical symptoms. We propose that SH develops in four phases with transitions: (i) priming lowers stress defence; (ii) triggering leads to acute damage; (iii) adaptation, possibly associated with cellular senescence, mitigates tissue damage, leads to the phenotype, and preserves liver function at a lower level; (iv) finally, senescence prevents neoplastic transformation but favours fibrosis (cirrhosis) and inflammation and further reduction in liver function. Escape from senescence eventually leads to hepatocellular carcinoma. This hypothesis for a pathomechanism of SH is supported by clinical and experimental observations. It allows organizing the various findings to uncover remaining gaps in our knowledge and, finally, to provide possible diagnostic and intervention strategies for each stage of SH development.

Lipotoxicity reduces DDX58/Rig-1 expression and activity leading to impaired autophagy and cell death

Nonalcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease globally. NAFLD is a consequence of fat accumulation in the liver leading to lipotoxicity. Increasing evidence has demonstrated the critical role of autophagy in NAFLD. This study uncovers the unexpected role of immune surveillance protein DDX58/Rig-1 (DExD/H box helicase 58) in activating macroautophagy/autophagy and protecting from lipotoxicity associated with NAFLD. Here we show for the first time that DDX58 protein is significantly reduced in nonalcoholic steatohepatitis (NASH) mouse model, an aggressive form of NAFLD characterized by inflammation and fibrosis of the liver. In addition to decreased expression of DDX58, we found that DDX58 activity can be attenuated by treatments with palmitic acid (PA), a saturated fatty acid. To investigate whether PA inhibition of DDX58 is harmful to the cell, we characterized DDX58 function in hepatocytes when exposed to high doses of PA in the presence and/or absence of DDX58. We show that siRNA knockdown of DDX58 promotes apoptosis. Importantly, we show that stable overexpression of DDX58 is protective against toxic levels of PA and stimulates autophagy. This study begins to demonstrate the regulation of the autophagy receptor protein SQSTM1/p62 through DDX58. DDX58 expression directly influences SQSTM1 mRNA and protein levels. This work proposes a model in which activating DDX58 increases an autophagic response and this aids in clearing toxic lipid inclusion bodies, which leads to inflammation and apoptosis. Activating a DDX58-induced autophagy response may be a strategy for treating NAFLD.Abbreviations:5'pppdsRNA: 5' triphosphate double-stranded RNA; CDAHFD: choline-deficient, L-amino acid defined high-fat diet; CEBPB: CCAAT/enhancer binding protein (C/EBP), beta; CQ: chloroquine; DDX58/retinoic acid inducible gene 1/Rig-1: DExD/H box helicase 58; h: hours; IFIH1/MDA5: interferon induced with helicase C domain 1; IFNB/IFN-β: interferon beta 1, fibroblast; KO: knockout; MAVS: mitochondrial antiviral signaling protein; NAFLD: nonalcoholic fatty liver disease; NASH: nonalcoholic steatohepatitis; NFKB/NF-κB: nuclear factor of kappa light polypeptide gene enhancer in B cells; PA: palmitic acid; poly:IC: polyinosinic:polycytidylic acid; PRR: pattern recognition receptors; PSR: picrosirus red; RAP: rapamycin; RLR: RIG-I-like receptor; SQSTM1/p62: sequestosome 1; STING1: stimulator of interferon response cGAMP interactor 1; TBK1: TANK-binding kinase 1.

p62 filaments capture and present ubiquitinated cargos for autophagy

The removal of misfolded, ubiquitinated proteins is an essential part of the protein quality control. The ubiquitin-proteasome system (UPS) and autophagy are two interconnected pathways that mediate the degradation of such proteins. During autophagy, ubiquitinated proteins are clustered in a p62-dependent manner and are subsequently engulfed by autophagosomes. However, the nature of the protein substrates targeted for autophagy is unclear. Here, we developed a reconstituted system using purified components and show that p62 and ubiquitinated proteins spontaneously coalesce into larger clusters. Efficient cluster formation requires substrates modified with at least two ubiquitin chains longer than three moieties and is based on p62 filaments cross-linked by the substrates. The reaction is inhibited by free ubiquitin, K48-, and K63-linked ubiquitin chains, as well as by the autophagosomal marker LC3B, suggesting a tight cross talk with general proteostasis and autophagosome formation. Our study provides mechanistic insights on how substrates are channeled into autophagy.

The mechanisms of Mallory-Denk body formation are similar to the formation of aggresomes in Alzheimer's disease and other neurodegenerative disorders

There is a possibility that the aggresomes that form in the brain in neurodegenerative diseases like Alzheimer's disease (AD) and in the liver where aggresomes like Mallory-Denk Bodies (MDB) form, share mechanisms. MDBs can be prevented by feeding mice sadenosylmethionine (SAMe) or betaine. Possibly these proteins could prevent AD. We compared the literature on MDBs and AD pathogenesis, which include roles played by p62, ubiquitin UBB +1, HSPs70, 90, 104, FAT10, NEDD8, VCP/97, and the protein quality control mechanisms including the 26s proteasome, the IPOD and JUNQ and autophagosome pathways.

Levels of metacaspase1 and chaperones related to protein quality control in alcoholic and nonalcoholic steatohepatitis

Efficient management of misfolded or aggregated proteins in ASH and NASH is crucial for continued hepatic viability. Cellular protein quality control systems play an important role in the pathogenesis and progression of ASH and NASH. In a recent study, elevated Mca1 expression counteracted aggregation and accumulation of misfolded proteins and extended the life span of the yeast Saccharomyces cerevisiae (Hill et al, 2014). Mca1 may also associate with Ssa1 and Hsp104 in disaggregation and fragmentation of aggregated proteins and their subsequent degradation through the ER-associated degradation (ERAD) pathway. If degradation is not available, protection of the cellular environment from a misfolded protein is accomplished by its sequestration into two distinct inclusion bodies (Kaganovich et al., 2008) called the JUNQ (JUxta Nuclear Quality control compartment) and the IPOD (Insoluble Protein Deposit). Mca1, Hsp104, Hsp40, Ydj1, Ssa1, VCP/p97, and p62 all play important roles in protein quality control systems. This study aims to measure the expression of Mca1 and related chaperones involved in protein quality control in alcoholic steatohepatitis (ASH), and nonalcoholic steatohepatitis (NASH) compared with normal control liver biopsies. Mca1, Hsp104, Hsp40, Ydj1, Ssa1, VCP/p97, and p62 expressions were measured in three to six formalin-fixed paraffin embedded ASH and NASH liver biopsies and control normal liver specimens by immunofluorescence staining and quantified by immunofluorescence intensity. Mca1, Hsp104, Ydj1 and p62 were significantly upregulated compared to control (p<0.05) in ASH specimens. Hsp40 and VCP/p97 were also uptrending in ASH. In NASH, the only significant difference was the increased expression of Hsp104 compared to control (p<0.05). Ssa1 levels were uptrending in both ASH and NASH specimens. The upregulation of Mca1, Hsp104, Ydj1 and p62 in ASH may be elicited as a response to the chronic exposure of the hepatocytes to the toxicity of alcohol. Recruitment of Mca1, Hsp104, Ydj1 and p62 may indicate that autophagy, the ERAD, JUNQ, and IPOD systems are active in ASH. Whereas in NASH, elevated Hsp104 and uptrending Ssa1 levels may indicate that autophagy and IPOD may be the only active protein quality control systems involved.

High-fat diet triggers Mallory-Denk body formation through misfolding and crosslinking of excess keratin 8

Mallory-Denk bodies (MDBs) are protein aggregates consisting of ubiquitinated keratins 8/18 (K8/K18). MDBs are characteristic of alcoholic and nonalcoholic steatohepatitis (NASH) and discriminate between the relatively benign simple steatosis and the more aggressive NASH. Given the emerging evidence for a genetic predisposition to MDB formation and NASH development in general, we studied whether high-fat (HF) diet triggers MDB formation and liver injury in susceptible animals. Mice were fed a high-fat (HF) or low-fat (LF) diet plus a cofactor for MDB development, 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC). Additionally, we fed nontransgenic and K8 overexpressing mice (K8tg) with the HF diet. The presence of MDB and extent of liver injury was evaluated using biochemical markers, histological staining, and immunofluorescence microscopy. In DDC-fed animals, an HF diet resulted in greater liver injury and up-regulation of inflammation-related genes. As a potential mechanism, K8/K18 accumulation and increased ecto-5'-nucleotidase (CD73) levels were noted. In the genetically susceptible K8tg mice, HF diet triggered hepatocellular injury, ballooning, apoptosis, inflammation, and MDB development by way of 1) decreased expression of the major stress-inducible chaperone Hsp72 with appearance of misfolded keratins; 2) elevated levels of the transglutaminase 2 (TG2); 3) increased K8 phosphorylation at S74 with subsequent TG2-mediated crosslinking of phosphorylated K8; and 4) higher production of the MDB-modifier gene CD73.

CONCLUSION

Our data demonstrate that HF diet triggers aggregate formation and development of liver injury in susceptible individuals through misfolding and crosslinking of excess K8.

Genetic background effects of keratin 8 and 18 in a DDC-induced hepatotoxicity and Mallory-Denk body formation mouse model

Keratin 8 (K8) and keratin 18 (K18) form the major hepatocyte cytoskeleton. We investigated the impact of genetic loss of either K8 or K18 on liver homeostasis under toxic stress with the hypothesis that K8 and K18 exert different functions. krt8⁻/⁻ and krt18⁻/⁻ mice crossed into the same 129-ola genetic background were treated by acute and chronic administration of 3,5-diethoxy-carbonyl-1,4-dihydrocollidine (DDC). In acutely DDC-intoxicated mice, macrovesicular steatosis was more pronounced in krt8⁻/⁻ and krt18⁻/⁻ compared with wild-type (wt) animals. Mallory-Denk bodies (MDBs) appeared in krt18⁻/⁻ mice already at an early stage of intoxication in contrast to krt8⁻/⁻ mice that did not display MDB formation when fed with DDC. Keratin-deficient mice displayed significantly lower numbers of apoptotic hepatocytes than wt animals. krt8⁻/⁻, krt18⁻/⁻ and control mice displayed comparable cell proliferation rates. Chronically DDC-intoxicated krt18⁻/⁻ and wt mice showed a similarly increased degree of steatohepatitis with hepatocyte ballooning and MDB formation. In krt8⁻/⁻ mice, steatosis was less, ballooning, and MDBs were absent. krt18⁻/⁻ mice developed MDBs whereas krt8⁻/⁻ mice on the same genetic background did not, highlighting the significance of different structural properties of keratins. They are independent of the genetic background as an intrinsic factor. By contrast, toxicity effects may depend on the genetic background. krt8⁻/⁻ and krt18⁻/⁻ mice on the same genetic background show similar sensitivity to DDC intoxication and almost resemble wt animals regarding survival, degree of porphyria, liver-to-body weight ratio, serum bilirubin and liver enzyme levels. This stands in contrast to previous work where krt8⁻/⁻ and krt18⁻/⁻ mice on different genetic backgrounds were investigated.

[DNA mimics on the base of pyrrolidine and hydroxyproline]

In order to improve physicochemical and biological properties of natural oligonucleotides in particular increasing their affinity for nucleic acids, the selectivity of action and biological sustainability, several types of DNA mimics were designed. The survey collected data on the synthesis and properties of the DNA mimics - peptide-nucleic acids analogues, which are derivatives of pyrrolidine and hydroxyproline. We examine some physicochemical and biological properties of negatively charged mimics of this type, containing phosphonate residues, and possessing a high affinity for DNA and RNA, selective binding with nucleic acids and stability in various biological systems. Examples of the use of these mimics as tools for molecular biological research, particularly in functional genomics are given. The prospects for their use in diagnostics and medicine are discussed.

Ubiquitin/proteasome pathway impairment in neurodegeneration: therapeutic implications

The ubiquitin/proteasome pathway is the major proteolytic quality control system in cells. In this review we discuss the impact of a deregulation of this pathway on neuronal function and its causal relationship to the intracellular deposition of ubiquitin protein conjugates in pathological inclusion bodies in all the major chronic neurodegenerative disorders, such as Alzheimer's, Parkinson's and Huntington's diseases as well as amyotrophic lateral sclerosis. We describe the intricate nature of the ubiquitin/proteasome pathway and discuss the paradox of protein aggregation, i.e. its potential toxic/protective effect in neurodegeneration. The relations between some of the dysfunctional components of the pathway and neurodegeneration are presented. We highlight possible ubiquitin/proteasome pathway-targeting therapeutic approaches, such as activating the proteasome, enhancing ubiquitination and promoting SUMOylation that might be important to slow/treat the progression of neurodegeneration. Finally, a model time line is presented for neurodegeneration starting at the initial injurious events up to protein aggregation and cell death, with potential time points for therapeutic intervention.

Selective degradation of p62 by autophagy

The autophagy-lysosome pathway is a highly conserved bulk degradation system in eukaryotes. During starvation, cytoplasmic constituents are non-selectively degraded by autophagy, and the resulting amino acids are utilized for cell survival. By taking advantage of mouse genetics, many physiological functions of mammalian autophagy have been uncovered. Growing lines of evidences have revealed the essential role of constitutive (or basal) autophagy in cellular homeostasis through its selectivity. p62, one of the selective substrates for autophagy, plays a key role in the formation of cytoplasmic proteinaceous inclusion, a hallmark of conformational diseases such as Alzheimer's disease, Parkinson's disease, and various chronic liver disorders. In this review, we discuss the physiological roles of the selective turnover of p62 by autophagy and their molecular mechanisms.

p62+ Hyaline inclusions in intrahepatic cholangiocarcinoma associated with viral hepatitis or alcoholic liver disease

Mallory bodies (MBs) and hyaline globules (HGs) are recognized as hepatocellular cytoplasmic inclusions in liver diseases. We reviewed 123 intrahepatic cholangiocarcinomas (ICCs) and encountered 16 cases (13.0%) in which cancer cells had MB-type inclusions and/or HG-type inclusions, both of which are positive for p62 and ubiquitin. The HG type was present in all 16 cases, and 5 cases contained the MB type. Of 16 patients, 12 had chronic liver disease that was related to alcoholic abuse in 4, hepatitis B surface antigen-positive in 3, and hepatitis C virus antibody-positive in 8. Viral infection and liver cirrhosis were more common in ICCs with p62+ inclusions (P = .0004 and P = .0199, respectively). Of 16 ICCs, 15 with hyaline inclusions had a peripheral tumor location (P = .0052). On ultrastructural examination, the MB type had an electron-dense fibrillar appearance, while the HG type appeared as rounded masses of granular materials. Our results suggest that intracytoplasmic hyaline bodies occasionally can be found in cholangiocarcinoma with chronic liver disease related to viral hepatitis or alcoholic intake.

Signaling, polyubiquitination, trafficking, and inclusions: sequestosome 1/p62's role in neurodegenerative disease

Aggregated misfolded proteins are hallmarks of most neurodegenerative diseases. In a chronic disease state, including pathologic situations of oxidative stress, these proteins are sequestered into inclusions. Accumulation of aggregated proteins can be prevented by chaperones, or by targeting their degradation to the UPS. If the accumulation of these proteins exceeds their degradation, they may impair the function of the proteasome. Alternatively, the function of the proteasome may be preserved by directing aggregated proteins to the autophagy-lysosome pathway for degradation. Sequestosome 1/p62 has recently been shown to interact with polyubiquitinated proteins through its UBA domain and may direct proteins to either the UPS or autophagosome. P62 is present in neuronal inclusions of individuals with Alzheimer's disease and other neurodegenerative diseases. Herein, we review p62's role in signaling, aggregation, and inclusion formation, and specifically as a possible contributor to Alzheimer's disease. The use of p62 as a potential target for the development of therapeutics and as a disease biomarker is also discussed.

The role of cytokines in UbD promoter regulation and Mallory-Denk body-like aggresomes

Mallory-Denk bodies (MDBs) are found in chronic liver diseases. Previous studies showed that diethyl-1,4-dihydro-2,4,6-trimethyl-3,5-pyridinedicarboxylate (DDC) induced formation of MDBs and the up regulation of UbD expression in mouse liver. UbD is a protein over expressed in hepatocellular carcinomas. It is a potential preneoplastic marker in the mouse. It is hypothesized that inflammatory cytokines play a critical role in UbD up regulation and MDB formation. TNFa and IFNg treatment of HCC cell line Hepa 1-6, induced the expression of UbD and the expression of genes coding for the immunoproteasome (LMP2, LMP7, and MECL-1 subunits). TNFa and IFNg induced the activity of the UbD promoter, using a luciferase assay. The cotreatment with TNFa and IFNg induced the activity of the UbD promoter through an Interferon Sequence Responsive Element (ISRE). In addition, long term treatment with TNFa and IFNg induced the formation of MDB-like aggresomes in Hepa 1-6 cells, which emphasizes the role of inflammation in the formation of MDBs leading to the formation of liver tumors, in the mouse. Identifying the mechanism that regulates gene expression of UbD supports the hypothesis that down regulation of UbD and the proinflammatory gene expression would prevent MDB and HCC formations. Previous studies indicate that S-adenosylmethionine or betaine prevented IFNg induced UbD and MDB formations.

Effects of ethanol on the proteasome interacting proteins

Proteasome dysfunction has been repeatedly reported in alcoholic liver disease. Ethanol metabolism end-products affect the structure of the proteasome, and, therefore, change the proteasome interaction with its regulatory complexes 19S and PA28, as well as its interacting proteins. Chronic ethanol feeding alters the ubiquitin-proteasome activity by altering the interaction between the 19S and the 20S proteasome interaction. The degradation of oxidized and damaged proteins is thus decreased and leads to accumulation of insoluble protein aggregates, such as Mallory-Denk bodies. Ethanol also affects the immunoproteasome formation. PA28a/b interactions with the 20S proteasome are decreased in the proteasome fraction isolated from the liver of rats fed ethanol chronically, thus affecting the cellular antigen presentation and defense against pathogenic agents. Recently, it has been shown that ethanol also affects the proteasome interacting proteins (PIPs). Interaction of the proteasome with Ecm29 and with deubiquitinating enzymes Rpn11, UCH37, and Usp14 has been found to decrease. However, the two UBL-ubiquitin-associated domain (UBA) PIPs p62 and valosin-containing protein are upregulated when the proteasome is inhibited. The increase of these UBL-UBA proteins, as well as the increase in Hsp70 and Hsp25 levels, compensated for the proteasome failure and helped in the unfolding/docking of misfolded proteins. Chronic alcohol feeding to rats causes a significant inhibition of the proteasome pathway and this inhibition results from a decreases of the interaction between the 20S proteasome and the regulatory complexes, PIPs, and the ubiquitin system components.

Role of autophagy in liver physiology and pathophysiology

Autophagy is a highly conserved intracellular degradation pathway by which bulk cytoplasm and superfluous or damaged organelles are enveloped by double membrane structures termed autophagosomes. The autophagosomes then fuse with lysosomes for degradation of their contents, and the resulting amino acids can then recycle back to the cytosol. Autophagy is normally activated in response to nutrient deprivation and other stressors and occurs in all eukaryotes. In addition to maintaining energy and nutrient balance in the liver, it is now clear that autophagy plays a role in liver protein aggregates related diseases, hepatocyte cell death, steatohepatitis, hepatitis virus infection and hepatocellular carcinoma. In this review, I discuss the recent findings of autophagy with a focus on its role in liver pathophysiology.

Toward unraveling the complexity of simple epithelial keratins in human disease

Simple epithelial keratins (SEKs) are found primarily in single-layered simple epithelia and include keratin 7 (K7), K8, K18-K20, and K23. Genetically engineered mice that lack SEKs or overexpress mutant SEKs have helped illuminate several keratin functions and served as important disease models. Insight into the contribution of SEKs to human disease has indicated that K8 and K18 are the major constituents of Mallory-Denk bodies, hepatic inclusions associated with several liver diseases, and are essential for inclusion formation. Furthermore, mutations in the genes encoding K8, K18, and K19 predispose individuals to a variety of liver diseases. Hence, as we discuss here, the SEK cytoskeleton is involved in the orchestration of several important cellular functions and contributes to the pathogenesis of human liver disease.

Severe NAFLD with hepatic necroinflammatory changes in mice fed trans fats and a high-fructose corn syrup equivalent

The aims of this study were to determine whether combining features of a western lifestyle in mice with trans fats in a high-fat diet, high-fructose corn syrup in the water, and interventions designed to promote sedentary behavior would cause the hepatic histopathological and metabolic abnormalities that characterize nonalcoholic steatohepatitis (NASH). Male C57BL/6 mice fed ad libitum high-fat chow containing trans fats (partially hydrogenated vegetable oil) and relevant amounts of a high-fructose corn syrup (HFCS) equivalent for 1-16 wk were compared with mice fed standard chow or mice with trans fats or HFCS omitted. Cage racks were removed from western diet mice to promote sedentary behavior. By 16 wk, trans fat-fed mice became obese and developed severe hepatic steatosis with associated necroinflammatory changes. Plasma alanine aminotransferase levels increased, as did liver TNF-alpha and procollagen mRNA, indicating an inflammatory and profibrogenic response to injury. Glucose intolerance and impaired fasting glucose developed within 2 and 4 wk, respectively. Plasma insulin, resistin, and leptin levels increased in a profile similar to that seen in patients with NASH. The individual components of this diet contributed to the phenotype independently; isocaloric replacement of trans fats with lard established that trans fats played a major role in promoting hepatic steatosis and injury, whereas inclusion of HFCS promoted food consumption, obesity, and impaired insulin sensitivity. Combining risk factors for the metabolic syndrome by feeding mice trans fats and HFCS induced histological features of NASH in the context of a metabolic profile similar to patients with this disease. Because dietary trans fats promoted liver steatosis and injury, their role in the epidemic of NASH needs further evaluation.

Mallory-Denk-bodies: lessons from keratin-containing hepatic inclusion bodies

Inclusion bodies are characteristic morphological features of various neuronal, muscular and other human disorders. They share common molecular constituents such as p62, chaperones and proteasome subunits. The proteins within aggregates are misfolded with increased beta-sheet structure, they are heavily phosphorylated, ubiquitinylated and partially degraded. Furthermore, involvement of proteasomal system represents a common feature of virtually all inclusions. Multiple aggregates contain intermediate filament proteins as their major constituents. Among them, Mallory-Denk bodies (MDBs) are the best studied. MDBs represent hepatic inclusions observed in diverse chronic liver diseases such as alcoholic and non-alcoholic steatohepatitis, chronic cholestasis, metabolic disorders and hepatocellular neoplasms. MDBs are induced in mice fed griseofulvin or 3,5-diethoxycarbonyl-1,4-dihydrocollidine and resolve after discontinuation of toxin administration. The availability of a drug-induced model makes MDBs a unique tool for studying inclusion formation. Our review summarizes the recent advances gained from this model and shows how they relate to observations in other aggregates. The MDB formation-underlying mechanisms include protein misfolding, chaperone alterations, disproportional protein expression with keratin 8>keratin 18 levels and subsequent keratin 8 crosslinking via transglutaminase. p62 presence is crucial for MDB formation. Proteasome inhibitors precipitate MDB formation, whereas stimulation of autophagy with rapamycin attenuates their formation.

Parkin deletion causes cerebral and systemic amyloidosis in human mutated tau over-expressing mice

Deposition of proteins leading to amyloid takes place in some neurodegenerative diseases such as Alzheimer's disease and Huntington's disease. Mutations of tau and parkin proteins produce neurofibrillary abnormalities without deposition of amyloid. Here we report that mature, parkin null, over-expressing human mutated tau (PK(-/-)/Tau(VLW)) mice have altered behaviour and dopamine neurotransmission, tau pathology in brain and amyloid deposition in brain and peripheral organs. PK(-/-)/Tau(VLW) mice have abnormal behaviour and severe drop out of dopamine neurons in the ventral midbrain, up to 70%, at 12 months and abundant phosphorylated tau positive neuritic plaques, neuro-fibrillary tangles, astrogliosis, microgliosis and plaques of murine beta-amyloid in the hippocampus. PK(-/-)/Tau(VLW) mice have organomegaly of the liver, spleen and kidneys. The electron microscopy of the liver confirmed the presence of a fibrillary protein deposits with amyloid characteristics. There is also accumulation of mouse tau in hepatocytes. These mice have lower levels of CHIP-HSP70, involved in the proteosomal degradation of tau, increased oxidative stress, measured as depletion of glutathione which, added to lack of parkin, could trigger tau accumulation and amyloidogenesis. This model is the first that demonstrates beta-amyloid deposits caused by over-expression of tau and without modification of the amyloid precursor protein, presenilins or secretases. PK(-/-)/Tau(VLW) mice provide a link between the two proteins more important for the pathogenesis of Alzheimer disease.

Emerging role of epigenetics in the actions of alcohol

This review deals with the recent developments on the epigenetic effects of ethanol. A large body of data have come from studies in liver and in neuronal systems and involve post-translational modifications in histones and methylations in DNA. Ethanol causes site selective acetylation, methylation, and phosphorylation in histone. With respect to methylations the methyl group donating system involving S-adenosyl methionine appears to play a central role. There is contrasting effect of acetylation versus methylation on the same site of histone, as it relates to the transcriptional activation. Epigenetic memory also appears to correlate with liver pathology and Mallory body formation. Experimental evidence supports transcriptional regulation of genes in the CNS by DNA methylations. These studies are contributing towards a better understanding of a novel epigenetic regulation of gene expression in the context of alcohol. The critical steps and the enzymes (e.g., histone acetyltransferase, histone deacetylase, DNA methyltransferase) responsible for the epigenetic modifications are prime targets for intense investigation. The emerging data are also beginning to offer novel insight towards defining the molecular actions of ethanol and may contribute to potential therapeutic targets at the nucleosomal level. These epigenetic studies have opened up a new avenue of investigation in the alcohol field.

Autophagy modulates keratin-containing inclusion formation and apoptosis in cell culture in a context-dependent fashion

The major pathways for protein degradation are the proteasomal and lysosomal systems. Derangement of protein degradation causes the formation of intracellular inclusions, and apoptosis and is associated with several diseases. We utilized hepatocyte-derived cell lines to examine the consequences of the cytoplasmic hepatocyte Mallory-Denk body-like inclusions on organelle organization, autophagy and apoptosis, and tested the hypothesis that autophagy affects inclusion turnover. Proteasome inhibitors (PIs) generate keratin-containing Mallory-Denk body-like inclusions in cultured cells and cause reorganization of mitochondria and other organelles, autophagy and apoptosis. In cultured hepatoma cells, caspase inhibition blocks PI-induced apoptosis but not inclusion formation or autophagy activation. Autophagy induction by rapamycin decreases the extent of PI-induced inclusions and apoptosis in Huh7 and OUMS29 cells. Surprisingly, blocking of autophagy sequestration by 3 methyl adenine or beclin 1 siRNA, but not bafilomycin A1 inhibition of autophagic degradation, also inhibits inclusion formation in the tested cells. Therefore, autophagy can be upstream of apoptosis and may promote or alleviate inclusion formation in cell culture in a context-dependent manner via putative autophagy-associated molecular triggers. Manipulation of autophagy may offer a strategy to address the importance of inclusion formation and its significance in inclusion-associated diseases.

S-adenosylmethionine prevents Mallory Denk body formation in drug-primed mice by inhibiting the epigenetic memory

In previous studies, microarray analysis of livers from mice fed diethyl-1,4-dihydro-2,4,6-trimethyl-3,5-pyridine decarboxylate (DDC) for 10 weeks followed by 1 month of drug withdrawal (drug-primed mice) and then 7 days of drug refeeding showed an increase in the expression of numerous genes referred to here as the molecular cellular memory. This memory predisposes the liver to Mallory Denk body formation in response to drug refeeding. In the current study, drug-primed mice were refed DDC with or without a daily dose of S-adenosylmethionine (SAMe; 4 g/kg of body weight). The livers were studied for evidence of oxidative stress and changes in gene expression with microarray analysis. SAMe prevented Mallory Denk body formation in vivo. The molecular cellular memory induced by DDC refeeding lasted for 4 months after drug withdrawal and was not manifest when SAMe was added to the diet in the in vivo experiment. Liver cells from drug-primed mice spontaneously formed Mallory Denk bodies in primary tissue cultures. SAMe prevented Mallory Denk bodies when it was added to the culture medium.

CONCLUSION

SAMe treatment prevented Mallory Denk body formation in vivo and in vitro by preventing the expression of a molecular cellular memory induced by prior DDC feeding. No evidence for the involvement of oxidative stress in induction of the memory was found. The molecular memory included the up-regulation of the expression of genes associated with the development of liver cell preneoplasia.

In vitro production of Mallory bodies and intracellular hyaline bodies: the central role of sequestosome 1/p62

Mallory bodies (MBs) and intracellular hyaline bodies (IHBs) are characteristic hepatocellular inclusions. MBs are hallmarks of steatohepatitis, whereas IHBs have first been detected in hepatocellular carcinoma. MBs and IHBs contain ubiquitin and sequestosome 1/p62 (p62), a stress-inducible adapter protein with affinity to polyubiquitinated proteins. MBs differ from IHBs by their keratin content and morphology. In vitro transfections were undertaken to study under defined conditions MB and IHB formation, their pathogenesis, and relationship. CHO-K1, TIB73, and HeLa cells were transfected with keratin 8, keratin 18, ubiquitin, p62, and p62 lacking the ubiquitin binding domain (p62DeltaUBA) and analyzed by immunofluorescence, immunoelectron microscopy, and immunoblotting. Transfection of p62 complementary deoxyribonucleic acid (cDNA) alone led to cytoplasmic aggregates consisting of filaments mostly arranged in parallel arrays resembling amyloid and type 1 MBs. Transfection of p62 and ubiquitin resulted in globular cytoplasmic aggregates with indistinct fibrillar ultrastructure resembling IHBs. Cotransfection of p62, keratin 8, and ubiquitin was necessary to produce in vitro type 2 MBs-like aggregates consisting of randomly oriented 10- to 15-nm filaments. A similar result was obtained when keratin 8 was replaced by keratin 18. After cotransfection of p62DeltaUBA, keratin 8, and ubiquitin, keratin formed irregular aggregates with electron-dense granular-amorphous ultrastructure (resembling type 3 MBs), whereas p62DeltaUBA remained in diffuse cytoplasmic distribution.

CONCLUSION

Our studies show that in vitro development of classical type 2 MBs requires overexpression of keratin 8 (or keratin 18), ubiquitin, and p62 containing the ubiquitin binding domain, whereas IHBs result from overexpression of p62 together with ubiquitin without keratin involvement.

From Mallory to Mallory–Denk bodies: What, how and why?

Frank B. Mallory described cytoplasmic hyaline inclusions in hepatocytes of patients with alcoholic hepatitis in 1911. These inclusions became known as Mallory bodies (MBs) and have since been associated with a variety of other liver diseases including non-alcoholic fatty liver disease. Helmut Denk and colleagues described the first animal model of MBs in 1975 that involves feeding mice griseofulvin. Since then, mouse models have been instrumental in helping understand the pathogenesis of MBs. Given the tremendous contributions made by Denk to the field, we propose renaming MBs as Mallory-Denk bodies (MDBs). The major constituents of MDBs include keratins 8 and 18 (K8/18), ubiquitin, and p62. The relevant proteins and cellular processes that contribute to MDB formation and accumulation include the type of chronic stress, the extent of stress-induced protein misfolding and consequent proteasome overload, a K8-greater-than-K18 ratio, transamidation of K8 and other proteins, presence of p62 and autophagy. Although it remains unclear whether MDBs serve a bystander, protective or injury promoting function, they do serve an important role as histological and potential progression markers in several liver diseases.

Mallory body (cytokeratin aggresomes) formation is prevented in vitro by p38 inhibitor

Microarray analysis of livers from mice fed diethyl-1,4-dihydro-2,4,6-trimethyl-3,5-pyridinedicarboxylate (DDC) to induce Mallory body (MB) cytokeratin aggresome formation showed that gene expression for cellular adhesion molecules, cytokeratins, kinases and aggresome forming proteins were upregulated, when MBs were formed in vivo. This response was enhanced when the DDC was refed (mice fed DDC for 10 weeks followed by DDC withdrawal for 1 month, then refed DDC for 7 days). Immunofluorescent antibody staining of the MBs that formed showed that MAPK p38 was colocalized with ubiquitin and p62 in the MBs. To investigate further the mechanisms of MB formation, primary cultures derived from DDC primed mice and their controls were incubated for 6 days. Liver cells cultured for 3 h and 6 days were used for microarray analysis. At 3 h, there were no MBs formed, but MBs were numerous after 6 days of culture. At 3 h, the expression of a large number of genes was different when the control, and the DDC primed hepatocytes were compared, which indicates that the primed hepatocytes were phenotypically changed. The gene expression of many kinases including p38 was upregulated after 6 days where the gene expression of cytokeratins, adhesion molecules and aggresome forming proteins were upregulated when MBs formed. An inhibitor of p38 phosphorylation (SB202190) completely prevented MB formation. Western blot showed that phosphorylated p38 MAPK and total p38 were absent in vitro after the p38 inhibitor treatment. Immunostaining of 6-day DDC-primed hepatocyte cultures stained with antibodies to p62 and phospho-p38 MAPK showed that phosphorylated p38 MAPK was concentrated within the MBs. Antibodies to specific serine phosphorylated sites 73 and 431, located in cytokeratin 8, localized to Mallory bodies in vivo, indicating that cytokeratin 8 was hyperphosphorylated. The data supported the concept that MBs form as the result of hyperphosphorylation of cytokeratin 8 by p38.

Synthesis and application of negatively charged PNA analogues

Negatively charged DNA mimics containing phosphonate analogoues of peptide nucleic acids were designed, and their physicochemical and biological properties were evaluated in the comparison with natural oligonucleotides, classical peptide nucleic acids, and morpholino phosphorodiamidate oligonucleotide analogues. The results obtained revealed a high potential of phosphonate-containing PNA derivatives for a number of biological applications, such as diagnostic, nucleic acids analysis, and inhibition of gene expression.

Modifications in P62 occur due to proteasome inhibition in alcoholic liver disease

P62 is capable of binding the polyubiquitin chain that targets proteins for degradation by the proteasome through its ubiquitin associated domain (UBA). Immunostaining of hepatocytes from human liver with alcoholic hepatitis showed colocalization of ubiquitin and P62 in Mallory bodies. Rats fed ethanol chronically and their controls showed that P62 is colocalized with the proteasome in hepatocytes as shown by confocal microscopy. P62 cosedimented with 26S proteasomes isolated from livers of control and alcohol fed rats. P62 was increased in the 26S proteasome fraction when the proteasome chymotrypsin-like (ChT-L) activity decreased in rats fed ethanol. PS-341, a potent proteasome inhibitor was used to compare the inhibition of the proteasome with the inhibition which occurs with ethanol feeding. P62 protein levels were also increased in the purified proteasome fraction of rats given PS-341. This data indicates that modifications in P62 occur due to proteasome inhibition in experimental alcoholic liver disease.

Evidence for p62 aggregate formation: Role in cell survival

The polyubiquitin-binding protein p62 has been shown to localize in aggregates common to several types of diseases. Here, we report that p62 forms independent fibrillar aggregates in vitro in a time- and concentration-dependent manner. FTIR spectra and ThT fluorescence assay of p62 reveals increased beta-sheet content as aggregates form compared to the native protein. The fibrillar nature of the aggregates was observed by transmission electron microscopy. Overexpression of p62 in HEK cells results in aggregate formation that may protect cells from apoptosis. Altogether, these results suggest that p62 fibrils may influence cell viability and indicates an important role for p62 in aggresome formation.

The role of laminin–integrin signaling in triggering MB formation. An in vivo and in vitro study

It is still unclear as to how hepatocytes perceive external factors and transduce the signals which initiate MB formation. To investigate this phenomenon, the model of MB formation in liver in vivo and in primary culture of hepatocytes derived from drug-primed mice was used. Control mice were fed the control diet (group 1). MBs were induced in the livers of mice fed diethyl-1, 4-dihydro-2, 4, 6-trimethyl-3, 5-pyridinedicarboxylate (DDC) for 10 weeks (group 2). The induced MBs completely disappeared after the withdrawal of DDC for 4 weeks (group 3). Newly formed MBs were numerous after DDC was refed for 1 week (group 4). Relative mRNA abundance was determined by quantitative real-time RT-PCR in the liver from the mice. The expression of integrin alpha(6) and beta(2) was significantly increased in the livers of DDC-treated (group 2) and drug refed mice (group 4), when compared with the livers from controls (group 1) and DDC-withdrawn (group 3) mice. The increased mRNA of these two integrin genes was associated with the increased expression of laminin (a ligand for integrin alpha(6)beta(1) and alpha(6)beta(4)), Icam1 (a ligand of alphaLbeta2), Src, MEKK1, and ERK1. Primary cultures of isolated DDC-primed hepatocytes (group 4 mice were withdrawn from DDC-CMZ for 4-6 weeks) produced significantly more MBs on laminin-coated coverslips compared with plastic uncoated, fibronectin-, collagen-, or fibrinogen-coated coverslips. U0126, an inhibitor of MEK1 protein, significantly reduced the phosphorylated forms of ERK1/2 and MB formation in vitro. In conclusion, the current study revealed an association between MB formation and integrin-mediated signaling in vivo. The data indicate that laminin-integrin signaling which activates ERK, triggered MB formation in vitro, and an inhibitor of the signaling cascade reduced MB formation.

The p105/50 NF-kappaB pathway is essential for Mallory body formation

To determine if nuclear factor-kappaB (NF-kB) plays a role in Mallory body (MB) formation, quantitative real-time RT-PCR assay was used to measure liver NF-kappaB1/p105 mRNA levels in 4 different groups of mice. Group 1: mice given IP saline for 15 weeks; group 2: mice fed diethyl 1,4-dihydro-2,4,6,-trimethyl-3,5-pyridinedicarboxylate (DDC) for 10 weeks when MBs were formed; group3: mice fed DDC 10 weeks, then withdrawn 5 weeks when MBs disappeared; group 4: mice fed DDC 10 weeks, withdrawn 4 weeks, then fed DDC+chlormethiazole (CMZ) for 1 week when MBs again formed. The mRNA for p105 NF-kappaB expression was significantly increased in the livers of mice treated with DDC (group 2) and DDC+CMZ (group 4) compared with the control livers (group 1) as well as the drug-withdrawal livers (group 3). Primary cultures of hepatocytes from drug-primed mice (the group 4 mice were withdrawn for another 4 weeks when the MBs had disappeared) were studied. The hepatocytes from drug-primed mice were MB free when isolated and used for primary culture. MBs began to form spontaneously within their cytoplasm after 2-3 days of culture. The NF-kappaB inhibitor (NF-kappaBi), a cell-permeable quinazoline compound that acts as a potent inhibitor of NF-kappaB transcriptional activation, was added to the medium 3 h after planting the cultures of liver cells. No MBs formed in the cells treated with 10 microM, 1 microM, and 0.1 microM NF-kappaBi for 6 days. MBs still formed in the cells treated with 10 nM NF-kappaBi for 6 days. Both DDC-primed and normal control liver cells began to enlarge and elongate after a few hours of culture. In contrast, the cells treated with NF-kappaBi stayed polyhedral in shape just as they appeared prior to culturing. The level of NF-kappaB1/p105 mRNA significantly increased in DDC-primed hepatocytes after 24 h of culture and in normal control hepatocytes after 48 h of culture. In DDC-primed hepatocytes, NF-kappaBi 0.1 muM treatment for 6 days significantly decreased mRNA expression of Src, p105/NF-kappaB1, ERK1, MEKK1, and JNK1/2. In normal control liver cells, NF-kappaBi treatment decreased mRNA expression of Src and JNK1 and stimulated the mRNA expression of p105/NF-kappaB1 and Junk2. NF-kappaBi treatment significantly decreased the total ERK1/2 protein and further decreased the phosphorylated (activated) form of ERK1/2 in the cultured hepatocytes. The results indicate that the p105 NF-kappaB pathway which putatively regulates ERK at both the transcriptional and post-translational levels regulates MB formation by way of changes in gene expression.