Intermediate filament cytoskeleton of the liver in health and disease

ILDR2: an endoplasmic reticulum resident molecule mediating hepatic lipid homeostasis

Ildr2, a modifier of diabetes susceptibility in obese mice, is expressed in most organs, including islets and hypothalamus, with reduced levels in livers of diabetes-susceptible B6.DBA mice congenic for a 1.8 Mb interval of Chromosome 1. In hepatoma and neuronal cells, ILDR2 is primarily located in the endoplasmic reticulum membrane. We used adenovirus vectors that express shRNA or are driven by the CMV promoter, respectively, to knockdown or overexpress Ildr2 in livers of wild type and ob/ob mice. Livers in knockdown mice were steatotic, with increased hepatic and circulating triglycerides and total cholesterol. Increased circulating VLDL, without reduction in triglyceride clearance suggests an effect of reduced hepatic ILDR2 on hepatic cholesterol clearance. In animals that overexpress Ildr2, hepatic triglyceride and total cholesterol levels were reduced, and strikingly so in ob/ob mice. There were no significant changes in body weight, energy expenditure or glucose/insulin homeostasis in knockdown or overexpressing mice. Knockdown mice showed reduced expression of genes mediating synthesis and oxidation of hepatic lipids, suggesting secondary suppression in response to increased hepatic lipid content. In Ildr2-overexpressing ob/ob mice, in association with reduced liver fat content, levels of transcripts related to neutral lipid synthesis and cholesterol were increased, suggesting “relief” of the secondary suppression imposed by lipid accumulation. Considering the fixed location of ILDR2 in the endoplasmic reticulum, we investigated the possible participation of ILDR2 in ER stress responses. In general, Ildr2 overexpression was associated with increases, and knockdown with decreases in levels of expression of molecular components of canonical ER stress pathways. We conclude that manipulation of Ildr2 expression in liver affects both lipid homeostasis and ER stress pathways. Given these reciprocal interactions, and the relatively extended time-course over which these studies were conducted, we cannot assign causal primacy to either the effects on hepatic lipid homeostasis or ER stress responses.

Sorafenib enhances proteasome inhibitor-mediated cytotoxicity via inhibition of unfolded protein response and keratin phosphorylation

Hepatocellular carcinoma (HCC) is highly resistant to conventional systemic therapies and prognosis for advanced HCC patients remains poor. Recent studies of the molecular mechanisms responsible for tumor initiation and progression have identified several potential molecular targets in HCC. Sorafenib is a multi-kinase inhibitor shown to have survival benefits in advanced HCC. It acts by inhibiting the serine/threonine kinases and the receptor type tyrosine kinases. In preclinical experiments sorafenib had anti-proliferative activity in hepatoma cells and it reduced tumor angiogenesis and increased apoptosis. Here, we demonstrate for the first time that the cytotoxic mechanisms of sorafenib include its inhibitory effects on protein ubiquitination, unfolded protein response (UPR) and keratin phosphorylation in response to endoplasmic reticulum (ER) stress. Moreover, we show that combined treatment with sorafenib and proteasome inhibitors (PIs) synergistically induced a marked increase in cell death in hepatoma- and hepatocyte-derived cells. These observations may open the way to potentially interesting treatment combinations that may augment the effect of sorafenib, possibly including drugs that promote ER stress. Because sorafenib blocked the cellular defense mechanisms against hepatotoxic injury not only in hepatoma cells but also in hepatocyte-derived cells, we must be careful to avoid severe liver injury.

Brain region- and age-dependent dysregulation of p62 and NBR1 in a mouse model of Huntington's disease

Huntington's disease is characterized by the formation of protein aggregates, which can be degraded by macroautophagy. Here, we studied protein levels and intracellular distribution of p62 and NBR1, two macroautophagy cargo receptors, during disease progression. In R6/1 mice, p62 and NBR1 protein levels were decreased in all brain regions analyzed early in the disease, whereas at late stages they accumulated in the striatum and hippocampus, but not in the cortex. The accumulation of p62, but not NBR1, occurred in neuronal nuclei, where it co-localized with mutant huntingtin inclusions, both in R6/1 and Huntington's disease patients. Moreover, exportin-1 was selectively decreased in old R6/1 mice brain, and could worsen p62 nuclear accumulation. In conclusion, p62 interacts with mutant huntingtin and is retained in the nucleus along the progression of the disease, mostly in striatal and hippocampal neurons. Thus, cytoplasmic NBR1 might be important to maintain basal levels of selective macroautophagy in these neurons.

Cytoskeletal proteins: shaping progression of hepatitis C virus-induced liver disease

Hepatitis C virus (HCV) infection, which results in chronic hepatitis C (CHC) in most patients (70-85%), is a major cause of liver disease and remains a major therapeutic challenge. The mechanisms determining liver damage and the key factors that lead to a high rate of CHC remain imperfectly understood. The precise role of cytoskeletal (CS) proteins in HCV infection remains to be determined. Some studies including our recent study have demonstrated that changes occur in the expression of CS proteins in HCV-infected hepatocytes. A variety of host proteins interact with HCV proteins. Association between CS and HCV proteins may have implications in future design of CS protein-targeted therapy for the treatment for HCV infection. This chapter will focus on the interaction between host CS and viral proteins to signify the importance of this event in HCV entry, replication and transportation.

Sublethal dietary effects of microcystin producing Microcystis on threadfin shad, Dorosoma petenense

The presence of the toxic cyanobacterium Microcystis in the upper San Francisco Estuary (SFE) since 1999 is a potential but unquantified threat to the health and survival of aquatic organisms such as fish and zooplankton. The microcystins (MCs) predominantly in the LR-form (MC-LR) produced by Microcystis is hepatotoxic and a potential threat to the fishery. Concurrently, in the SFE significant declines in pelagic fish, known as the Pelagic Organism Decline (POD), has been recognized by state and federal agencies since 2000. In 2005, the presence of the toxic algal bloom, Microcystis has been hypothesized as a link to the POD by the Interagency Ecology Program Management Team. This study aims to characterize the toxic effects of Microcystis in one of the POD species, threadfin shad (Dorosoma petenense) by exposure to diets containing Microcystis harvested from the SFE. The diets contained Microcystis with 4.4 (D5) and 10.0 (D10) μg g⁻¹ MC-LR that was fed to threadfin shad for 57 days. The treatments were compared to the control diet, 0 μg g⁻¹ MC-LR (D0). Results showed that ingested Microcystis was localized in the gut by in situ hybridization and MCs were localized in the tissues of the gut, kidney and liver. Condition factor (CF) and liver and gonadal lesions were sensitive to MC exposure. There was a significant inverse relationship between CF and MC-LR with exposed fish exhibiting severe cachexia. Liver lesions of sinusoidal congestion and glycogen depletion significantly increased with increasing MC-LR concentrations, indicating hemorrhaging in the liver and poor nutritional status, respectively. In females, there was a significant increase in severe ovarian necrosis with increasing MC-LR concentration, indicating loss of reproductive potential. The results indicate that MC-LR from Microcystis significantly impairs the health and reproductive potential of threadfin shad has a potential negative effect on populations in the SFE.

Down-regulation of HtrA1 activates the epithelial-mesenchymal transition and ATM DNA damage response pathways

Expression of the serine protease HtrA1 is decreased or abrogated in a variety of human primary cancers, and higher levels of HtrA1 expression are directly related to better response to chemotherapeutics. However, the precise mechanisms leading to HtrA1 down regulation during malignant transformation are unclear. To investigate HtrA1 gene regulation in breast cancer, we characterized expression in primary breast tissues and seven human breast epithelial cell lines, including two non-tumorigenic cell lines. In human breast tissues, HtrA1 expression was prominent in normal ductal glands. In DCIS and in invasive cancers, HtrA1 expression was greatly reduced or lost entirely. HtrA1 staining was also reduced in all of the human breast cancer cell lines, compared with the normal tissue and non-tumorigenic cell line controls. Loss of HtrA1 gene expression was attributable primarily to epigenetic silencing mechanisms, with different mechanisms operative in the various cell lines. To mechanistically examine the functional consequences of HtrA1 loss, we stably reduced and/or overexpressed HtrA1 in the non-tumorigenic MCF10A cell line. Reduction of HtrA1 levels resulted in the epithelial-to-mesenchymal transition with acquisition of mesenchymal phenotypic characteristics, including increased growth rate, migration, and invasion, as well as expression of mesenchymal biomarkers. A concomitant decrease in expression of epithelial biomarkers and all microRNA 200 family members was also observed. Moreover, reduction of HtrA1 expression resulted in activation of the ATM and DNA damage response, whereas overexpression of HtrA1 prevented this activation. Collectively, these results suggest that HtrA1 may function as a tumor suppressor by controlling the epithelial-to-mesenchymal transition, and may function in chemotherapeutic responsiveness by mediating DNA damage response pathways.

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.

Keratins: markers and modulators of liver disease

PURPOSE OF REVIEW

Keratins are a subgroup of intermediate filaments expressed in the epithelia. Keratins emerged as important tissue-protecting genes and keratin variants cause/predispose to development of more than 50 human disorders. Our review focuses on the importance of keratins in context of liver disease.

RECENT FINDINGS

K8/K18 variants are found in approximately 4% of white population and predispose to development and adverse outcome of multiple liver diseases. K8/K18 are major constituents of Mallory-Denk bodies, that is inclusions found in alcoholic and nonalcoholic steatohepatitis (NASH) and dysregulated keratin expression, K8 hyperphosphorylation, misfolding and crosslinking via transglutaminase 2 facilitate aggregate formation. Necrosis-generated and apoptosis-generated keratin serum fragments are emerging as important noninvasive markers of multiple liver diseases, particularly NASH. Keratins are established markers of tumor origin and in hepatocellular carcinoma, K19 expression is associated with poor prognosis.

SUMMARY

Keratins are established tumor markers and are widely used as noninvasive markers of liver injury. In addition, the data that have become available in recent years have greatly advanced our understanding of keratins as modifiers of liver disease development.

Sublethal dietary effects of Microcystis on Sacramento splittail, Pogonichthys macrolepidotus

The presence of the toxic cyanobacterium Microcystis in the upper San Francisco Estuary (SFE) since 1999 is a potential but to date an unquantified threat to the health and survival of aquatic organisms, such as fish and zooplankton. The microcystins (MCs) predominantly in the LR-form (MC-LR) contained in Microcystis is hepatotoxic and a potential threat to the fishery. This study was conducted to determine the effects of dietary exposure of the endemic Sacramento splittail, Pogonichthys macrolepidotus in SFE to Microcystis and its toxin, MC-LR. Juvenile splittail (12.59 ± 0.7 g fish(-1)) were exposed to five diets for 28 d with MC-LR obtained from: (1) Microcystis harvested from the SFE and (2) a synthetic purified form of MC-LR. Three of the test diets contained 3.55 (D5), 9.14 (D10) and 17.13 (D20)mg MC-LR kg(-1) from Microcystis. The other two diets contained either purified MC-LR at 3.89 mg MC-LR kg(-1) (D5R) or no MC-LR (D0). The RNA/DNA ratio of fish muscle was significantly lower for all treatments fed test diets containing MC-LR compared to the control diet D0, suggesting Microcystis adversely affected nutritional status. Protein phosphatase 2A expression in the fish from the D5, D10 and D20 treatments were inversely affected by increasing concentrations of MC-LR. Cytoplasmic inclusion bodies and single cell necrosis were more prevalent and greater in severity in the fish exposed to the diets D10 and D20 compared to fish from the D0 treatment and indicate severe liver toxicity in splittail exposed to MC-LR. The sublethal effects on splittail characterized by this study suggest cyanobacterial blooms have the potential to affect splittail nutritional status and health in SFE.

Canine liver transplantation model and the intermediate filaments of the cytoskeleton of the hepatocytes

Liver transplantation has been a successful therapy for liver failure. However, a significant number of recipients suffer from graft dysfunction. Considerably, ischemia and reperfusion (I/R) injury is the most important factor leading to organ dysfunction, although the pathogenesis has not been fully described. I/R injury have several established features that are accompanied by and/or linked to bile duct loss or ductopenia, cholestasis, and biliary ductular proliferations in the posttransplant liver biopsy. However, biliary marker levels increase usually only 5-7 days after transplantation. Intermediate filaments are one of the three cytoskeletal proteins that have a major role in liver protection and maintaining both cellular structure and integrity of eukaryotic cells. We reviewed the canine liver transplantation model as I/R injury model to delineate the intermediate filaments of the cytoskeleton that are probably the determinants in changing the phenotype of hepatocytes to cholangiocytes. Remarkably, this interesting feature seems to occur earlier than frank cholestasis. We speculate that I/R liver injury through a phenotypical switch of the hepatocytes may contribute to the poor outcome of the liver graft.

Keratin 18, Apoptosis, and Liver Disease in Children

Keratins, a major component of epithelial cell intermediate filaments, provide structural support to the cell and are important for the maintenance of structural integrity. Beyond its role of structural integrity in hepatocytes, keratin 18 (K18) is a known marker of apoptosis and has been proposed as an indicator of progression in chronic liver diseases such as nonalcoholic fatty liver disease (NAFLD). NAFLD is the most common cause of chronic liver disease in children and adolescents in the United States and throughout the world and comprises a wide spectrum of disease ranging from simple steatosis (fatty liver) to nonalcoholic steatohepatitis (NASH) and cirrhosis. While simple steatosis is typically benign in nature, NASH is a more serious condition that may progress to end-stage liver disease and liver failure. Currently, liver biopsy is considered the most reliable method of assessing the histological severity of disease and differentiating between simple steatosis and NASH. Because biopsy is invasive in nature, expensive, and subject to sampling error and/or variability in interpretation, it is not suitable as a screening test. Therefore, it is necessary to examine known mechanisms associated with the progression of liver disease, such as hepatocellular apoptosis, and identify potential biomarkers that could be used as a diagnostic tool in NASH. This review will focus on the role of apoptosis in pediatric liver disease and how K18, an early marker of apoptosis, can be utilized as a noninvasive biomarker to diagnose NASH.

The steatohepatitic variant of hepatocellular carcinoma and its association with underlying steatohepatitis

Steatohepatitis and metabolic syndrome are increasingly recognized as important risk factors for development of hepatocellular carcinoma. We have recently described a histologic subtype of hepatocellular carcinoma termed steatohepatitic hepatocellular carcinoma, which shows features resembling steatohepatitis in the nonneoplastic liver. The present study is undertaken to assess the association between the steatohepatitic hepatocellular carcinoma variant and underlying steatohepatitis and features of metabolic syndrome. We examined all hepatocellular carcinomas diagnosed on resections and explant specimens over a 3.5-year period at our institution. Tumors were classified as either conventional hepatocellular carcinoma or steatohepatitic hepatocellular carcinoma variant based on their predominant histopathologic pattern. The underlying chronic liver disease in each case was determined. The steatohepatitic hepatocellular carcinoma variant represented 13.5% (16/118) of cases. All but one case of steatohepatitic hepatocellular carcinoma occurred in patients with underlying steatohepatitis. Steatohepatitic hepatocellular carcinoma was diagnosed in 35.7% of patients with either nonalcoholic steatohepatitis or alcoholic liver disease compared with 1.3% of patient with other chronic liver diseases (P < .0001). The steatohepatitic hepatocellular carcinoma group had a significantly higher number of metabolic syndrome risk factors (2.44 versus 1.48, P = .01) and a higher percentage of patients with at least 3 metabolic syndrome components (50% versus 22.5%, P = .02). Immunohistochemically, there were diffuse loss of cytoplasmic CK8/18 and increased numbers of activated hepatic stellate cells within steatohepatitic hepatocellular carcinoma, in a pattern identical to that seen in steatohepatitis in nonneoplastic liver. Hepatocellular carcinomas showing a "steatohepatitic" histologic phenotype are strongly associated with underlying steatohepatitis and metabolic syndrome. This association further supports a possible role of steatohepatitis in human hepatocarcinogenesis.

Cross β-sheet conformation of keratin 8 is a specific feature of Mallory-Denk bodies compared with other hepatocyte inclusions

BACKGROUND & AIMS

Mallory-Denk bodies (MDBs) are cytoplasmic protein aggregates in hepatocytes in steatohepatitis and other liver diseases. We investigated the molecular structure of keratin 8 (K8) and 18 (K18), sequestosome 1/p62, and ubiquitin, which are the major constituents of MDBs, to investigate their formation and role in disease pathogenesis.

METHODS

Luminescent conjugated oligothiophenes (LCOs), h-HTAA, and p-FTAA are fluorescent amyloid ligands that specifically bind proteins with cross β-sheet conformation. We used LCOs to investigate conformational changes in MDBs in situ in human and murine livers as well as in transfection studies.

RESULTS

LCO analysis showed cross β-sheet conformation in human MDBs from patients with alcoholic and nonalcoholic steatohepatitis or hepatocellular carcinoma, but not in intracellular hyaline bodies, α₁-antitrypsin deficiency, or ground-glass inclusions. LCOs bound to MDBs induced by 3,5-diethoxycarbonyl-1,4-dihydrocollidine feeding of mice at all developmental stages. CHO-K1 cells transfected with various combinations of SQSTM1/p62, ubi, and Krt8/Krt18 showed that K8 was more likely to have cross β-sheet conformation than K18, whereas p62 never had cross β-sheet conformation. The different conformational properties of K8 and K18 were also shown by circular dichroism analysis.

CONCLUSIONS

K8 can undergo conformational changes from predominantly α-helical to cross β-sheet, which would allow it to form MDBs. These findings might account for the observation that krt8⁻/⁻ mice do not form MDBs, whereas its excess facilitates MDB formation. LCOs might be used in diagnosis of liver disorders; they can be applied to formalin-fixed, paraffin-embedded tissues to characterize protein aggregates in liver cells.

Synergistic effect of alcohol consumption and body mass on serum concentrations of cytokeratin-18

BACKGROUND

Cytokeratin-18 is an essential component of the cytoskeleton of epithelial cells (including hepatocytes). Serum concentrations of cytokeratin-18 (tissue polypeptide-specific antigen [TPS]) are used as a marker of epithelial neoplasms. Here, we investigated the potential interaction between alcohol and obesity in relation to serum TPS concentrations.

METHODS

Alcohol consumption, body mass index, and components of metabolic syndrome were measured in a random sample (n = 420) of the adult population (aged 18 to 92 years, 45% men) from a single municipality. Regular alcohol intake of >20 g/d (women) or >30 g/d (men) was considered risky drinking. Serum TPS was measured with a commercial immunoassay.

RESULTS

Risky drinking was associated with increased serum concentrations of TPS, which was particularly evident among obese individuals. Among individuals without risky drinking, TPS concentrations were similar for all levels of body mass. Conversely, among risky drinkers, serum TPS concentrations increased in parallel with body mass (p = 0.002). The odds ratio of a high (>100 U/l) TPS concentration for the combination of risky drinking and obesity was greater than the additive effect of the 2 separate factors, after adjusting for age and sex. A similar interaction was observed between risky drinking and abdominal adiposity, a major component of the metabolic syndrome. Serum TPS concentrations were correlated with markers of liver damage. Serum TPS was not superior to standard markers (gamma-glutamyl transferase and red blood cell mean volume) for the detection of risky drinking.

CONCLUSIONS

There is a synergism between risky alcohol consumption and common metabolic disorders (particularly obesity) in relation to serum concentrations of cytokeratin-18 (TPS), which probably reflect liver disease.

Hepatocellular ballooning in nonalcoholic steatohepatitis: the pathologist's perspective

Nonalcoholic fatty liver disease (NAFLD) is an important complication of the metabolic syndrome. The increasing prevalence of the metabolic syndrome is paralleled by an increasing prevalence of NAFLD, which has become one of the most common chronic liver diseases. NAFLD comprises a morphological spectrum ranging from nonalcoholic fatty liver (NAFL), characterized by accumulation of fat in hepatocytes, to nonalcoholic steatohepatitis (NASH). The key histological features of NASH accepted by most pathologists include steatosis, hepatocellular ballooning and lobular inflammation, whereas, like in other chronic liver diseases, the presence of fibrosis is not considered a requirement for the diagnosis. The diagnosis of NASH and the distinction from NAFL carries important prognostic and therapeutic implications because NASH, in contrast to NAFL, is associated with an increased risk of progression to cirrhosis and hepatocellular carcinoma. Hepatocellular ballooning is a key feature required for the diagnosis of NASH and a component of currently used histological grading and staging systems of NAFLD. However, it represents an ill-defined form of liver cell injury associated with cell swelling and rounding of the cytoplasm, the detection of which is prone to intra- as well as inter-observer variation. Some of the factors that may contribute to ballooning are the rearrangement of the intermediate filament cytoskeleton, accumulation of small-droplet fat in the cytoplasm and dilation of the endoplasmic reticulum. The rearrangement of the intermediate filament cytoskeleton can be demonstrated by the loss of keratin 8/18 immunostaining of the cytoplasm, and may thus be evaluated in the future as a marker for the more objective detection of hepatocellular ballooning in NASH.

The cytoskeleton in nonalcoholic steatohepatitis: 100 years old but still youthful

The hepatocellular cytoskeleton consists of three filamentous systems: microfilaments, microtubules and keratins (Ks). While the alterations in microfilaments and microtubules during nonalcoholic steatohepatitis (NASH) are largely unexplored, K8/K18 reorganization into Mallory-Denk bodies (MDBs) represents a NASH hallmark, and serological K18 fragments constitute an established tool to monitor NASH severity. To commemorate the 100th anniversary of the first description of MDBs, this article summarizes the composition and function of the hepatocellular cytoskeleton, as well as the importance of cytoskeletal alterations in NASH. The significance of MDBs in clinical routine is illustrated, as are the findings from MDB mouse models, which shape our current view of MDB pathogenesis. Even after 100 years, the cytoskeleton represents a fascinating but greatly understudied area of NASH biology.

Autophagy regulates keratin 8 homeostasis in mammary epithelial cells and in breast tumors

Autophagy is activated in response to cellular stressors and mediates lysosomal degradation and recycling of cytoplasmic material and organelles as a temporary cell survival mechanism. Defective autophagy is implicated in human pathology, as disruption of protein and organelle homeostasis enables disease-promoting mechanisms such as toxic protein aggregation, oxidative stress, genomic damage, and inflammation. We previously showed that autophagy-defective immortalized mouse mammary epithelial cells are susceptible to metabolic stress, DNA damage, and genomic instability. We now report that autophagy deficiency is associated with endoplasmic reticulum (ER) and oxidative stress, and with deregulation of p62-mediated keratin homeostasis in mammary cells, allograft tumors, and mammary tissues from genetically engineered mice. In human breast tumors, high phospho(Ser73)-K8 levels are inversely correlated with Beclin 1 expression. Thus, autophagy preserves cellular fitness by limiting ER and oxidative stress, a function potentially important in autophagy-mediated suppression of mammary tumorigenesis. Furthermore, autophagy regulates keratin homeostasis in the mammary gland via a p62-dependent mechanism. High phospho(Ser73)-K8 expression may be a marker of autophagy functional status in breast tumors and, as such, could have therapeutic implications for breast cancer patients.

Lack of glycoprotein 130/signal transducer and activator of transcription 3-mediated signaling in hepatocytes enhances chronic liver injury and fibrosis progression in a model of sclerosing cholangitis

The 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) model leads to chronic cholestatic liver injury and therefore resembles human diseases such as sclerosing cholangitis and forms of metabolic liver diseases. The role of the interleukin-6/glycoprotein 130 (gp130) system in this context is still undefined. Therefore, conditional gp130 knockout and knockin mice were used to achieve hepatocyte-specific deletions of gp130 (gp130(Deltahepa)), gp130-dependent ras (gp130(DeltahepaRas)), and signal transducer and activator of transcription (STAT) (gp130(DeltahepaSTAT)) activation. These mice were treated with a DDC-containing diet and analyzed over time. Mice deficient in hepatic gp130 and STAT signaling showed increased and earlier mortality than wild-type and gp130(DeltahepaRas) animals. Over time, significantly more apoptosis and cholestasis became evident in gp130(Deltahepa) and gp130(DeltahepaSTAT) mice. These mice also displayed increased tumor necrosis factor-alpha expression, a diminished acute-phase response (lack of STAT3 and serum amyloid A activation), and enhanced immune cell infiltration in the liver. These were associated with stronger periportal oval cell activation. In addition, DDC treatment in gp130(Deltahepa) and gp130(DeltahepaSTAT) mice resulted in significantly stronger hepatic stellate cell activation. Long-term analysis revealed the development of severe liver fibrosis in gp130(Deltahepa) and gp130(DeltahepaSTAT) animals, as evidenced by increased collagen accumulation. Here we demonstrate that gp130/STAT signaling in hepatocytes provides protection in a cholestatic hepatitis mouse model. STAT3-dependent signaling pathways in hepatocytes protect from apoptosis and tissue injury, which subsequently reduce oval cell activation and prevent fibrosis progression.

Alcohol-induced alterations of the hepatocyte cytoskeleton

The hepatocyte cytoskeleton consists of three filamentous networks: microtubules, actin microfilaments and keratin intermediate filaments. Because of the abundance of the proteins that comprise each system and the central role each network plays in a variety of cellular processes, the three filament systems have been the focus of a host of studies aimed at understanding the progression of alcohol-induced liver injury. In this review, we will briefly discuss the hepatic organization of each cytoskeletal network and highlight some components of each system. We will also describe what is known about ethanol-induced changes in the dynamics and distributions of each cytoskeletal system and discuss what is known about changes in protein expression levels and post-translational modifications. Finally, we will describe the possible consequences of these cytoskeletal alterations on hepatocyte function and how they might contribute to the progression of liver disease.

Differential patterns of liver proteins in experimental murine hepatosplenic schistosomiasis

Schistosoma mansoni eggs produced by adult worms in the mesenteric vasculature become trapped in the liver, where they induce granulomatous lesions and strong immune responses. Infected individuals suffer from intestinal schistosomiasis (INT) in 90% of cases, whereas the remaining 10% present with severe hepatosplenic schistosomiasis (HS). The CBA/J mouse model mimics human disease, with 20% of infected mice developing hypersplenomegaly syndrome (HSS) that resembles HS and 80% developing moderate splenomegaly syndrome (MSS) similar to INT. We studied differential patterns of protein expression in livers of 20-week-infected CBA/J mice with MSS or HSS to understand the molecular changes that underlie these two disease forms. Using differential in-gel electrophoresis to identify differentially expressed protein spots, we found 80 protein spots significantly changed with infection and 35 changes specific to severe disease. In particular, the abundances of prohibitin 2, transferrin isoforms, and major urinary protein isoforms were significantly altered in HSS mice. Furthermore, annexin 5, glutathione S-transferase pi class, and S. mansoni phosphoenolpyruvate carboxykinase expression levels changed significantly with schistosome infection. Additionally, levels of major urinary protein decreased and levels of transferrin increased significantly in the sera of HSS mice compared to levels in sera of MSS or control mice, and these differences correlated to the degree of splenomegaly. These findings indicate that the liver protein abundances differ between MSS and HSS mice and may be used for the development of diagnostic markers for the early detection of hepatosplenic schistosomiasis.

Proteomic analysis of regenerating mouse liver following 50% partial hepatectomy

Background

Although 70% (or 2/3) partial hepatectomy (PH) is the most studied model for liver regeneration, the hepatic protein expression profile associated with lower volume liver resection (such as 50% PH) has not yet been reported. Therefore, the aim of this study was to determine the global protein expression profile of the regenerating mouse liver following 50% PH by differential proteomics, and thereby gaining some insights into the hepatic regeneration mechanism(s) under this milder but clinically more relevant condition.

Results

Proteins from sham-operated mouse livers and livers regenerating for 24 h after 50% PH were separated by SDS-PAGE and analyzed by nanoUPLC-Q-Tof mass spectrometry. Compared to sham-operated group, there were totally 87 differentially expressed proteins (with 50 up-regulated and 37 down-regulated ones) identified in the regenerating mouse livers, most of which have not been previously related to liver regeneration. Remarkably, over 25 differentially expressed proteins were located at mitochondria. Several of the mitochondria-resident proteins which play important roles in citric acid cycle, oxidative phosphorylation and ATP production were found to be down-regulated, consistent with the recently-proposed model in which the reduction of ATP content in the remnant liver gives rise to early stress signals that contribute to the onset of liver regeneration. Pathway analysis revealed a central role of c-Myc in the regulation of liver regeneration.

Conclusions

Our study provides novel evidence for mitochondria as a pivotal organelle that is connected to liver regeneration, and lays the foundation for further studies on key factors and pathways involved in liver regeneration following 50% PH, a condition frequently used for partial liver transplantation and conservative liver resection.

Extending the knowledge in histochemistry and cell biology

Central to modern Histochemistry and Cell Biology stands the need for visualization of cellular and molecular processes. In the past several years, a variety of techniques has been achieved bridging traditional light microscopy, fluorescence microscopy and electron microscopy with powerful software-based post-processing and computer modeling. Researchers now have various tools available to investigate problems of interest from bird's- up to worm's-eye of view, focusing on tissues, cells, proteins or finally single molecules. Applications of new approaches in combination with well-established traditional techniques of mRNA, DNA or protein analysis have led to enlightening and prudent studies which have paved the way toward a better understanding of not only physiological but also pathological processes in the field of cell biology. This review is intended to summarize articles standing for the progress made in "histo-biochemical" techniques and their manifold applications.

Keratin 18 provides resistance to Fas-mediated liver failure in mice

BACKGROUND

Keratins are intermediate filament proteins of epithelial cells with pivotal functions for cell integrity. They comprise keratins 18 [K18] and 8 [K8] in hepatocytes. Keratins are of major importance for an intact cellular microarchitecture and have protective functions in human liver diseases. In mice, K8 has been demonstrated to protect against Fas-antibody-induced liver failure by direct interaction with apoptotic regulators, while the role of K18 remains unresolved.

MATERIALS AND METHODS

We analysed effects of K18 deficiency on Fas-induced liver failure in mice. We determined survival and analysed induction of apoptosis after injection of the agonistic Fas antibody Jo2 into K18(-/-) and wild-type control mice by TUNEL assay and fluorometrically analysed caspase-3, -8 and -9 activities 1, 2 and 3 h after Jo2 injection.

RESULTS

In K18(-/-) mice, survival of Fas-antibody treated mice was significantly shorter than that of wild-type controls (P = 0.02). However, shortened survival of K18(-/-) mice was caused by increased hepatic damage but was not correlated to enhanced induction of apoptotic pathways, as neither numbers of TUNEL positive apoptotic cells nor activities of caspases-3, -8 and -9 differed between K18(-/-) and K18(+/+) mice at any point of time.

CONCLUSION

K18(-/-) mice are significantly more susceptible to Fas-antibody-induced liver failure. The cytoprotective effect of K18 is not explained by a differential activation of caspases-3, -8 and -9, suggesting that K18 does not directly interfere with apoptotic regulators. Importantly, however, K18 exerts significant protective functions by other mechanisms.

Proteomic identification of LASP-1 down-regulation after RNAi urokinase silencing in human hepatocellular carcinoma cells

In human hepatocellular carcinoma (HCC), the high expression of urokinase-type plasminogen activator (uPA) is an unfavorable prognostic factor and a therapeutic target. To identify the downstream effects of uPA silencing by RNA interference, we studied proteome modifications of uPA-inhibited SKHep1C3 cells, an HCC-derived cell line. The study with two-dimensional difference gel electrophoresis and matrix-assisted laser desorption/ionization-time of flight-mass spectrometry showed Lim and SH3 protein 1 (LASP-1), cytokeratin 1 (CK-1), cytokeratin 10 (CK-10), and heterogeneous nuclear ribonucleoprotein H1 down-modulation after uPA inhibition. LASP-1, CK-1, and CK-10 are involved in cytoskeleton dynamics as heterogeneous nuclear ribonucleoprotein H1 takes part in the mRNA processing and stability. We first confirmed the proteomic data by Western blot and immunoflorescence and then explored the link between uPA and LASP-1. The ectopic expression of uPA and LASP-1 supported the proteomic results and showed that uPA up-regulation increased LASP-1 expression and that both were implicated in SKHep1C3 motility. siRNA LASP-1 inhibition showed that LASP-1 was involved in actin microfilaments organization of SKHep1C3 cells. The disruption of the actin microfilaments after LASP-1 depletion increased uPA secretion and SKHep1C3 motility. Our results would suggest the hypothesis that uPA and LASP-1 expression may be coordinated in HCC-derived cells. In summary, the proteomic identification of a set of uPA downstream proteins provides new insight into the function of uPA in HCC cells.

State-of-the-art technologies, current opinions and developments, and novel findings: news from the field of histochemistry and cell biology

Investigations of cell and tissue structure and function using innovative methods and approaches have again yielded numerous exciting findings in recent months and have added important data to current knowledge, inspiring new ideas and hypotheses in various fields of modern life sciences. Topics and contents of comprehensive expert reviews covering different aspects in methodological advances, cell biology, tissue function and morphology, and novel findings reported in original papers are summarized in the present review.

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.