Differential expression of lumican and fatty acid binding protein-1: new insights into the histologic spectrum of nonalcoholic fatty liver disease

Advances in understanding the role of complement in the pathogenesis of fatty liver disease

Patients with fatty liver disease (FLD) exhibit various immunologic abnormalities in the adipose tissue and the liver. Complement plays an important role in the development of FLD. Innate immune dysfunction in the adipose tissue can lead to abnormal production of adipose-derived factors, some of which can activate complement. Complement can not only amplify the inflammatory response and lead to mitochondrial damage, but also inhibit hepatic fat disposal and promote lipid accumulation in hepatocytes. An exploration of the relationship between complement ant the liver can help us have a deep understanding of the mechanisms underlying the pathogenesis of FLD. The antagonists of the C5L2 receptor provide us potential new medicines for FLD. A further study of the role of complement in stress-induced liver remodeling can help clarify the role of complement in the development and progression of FLD.

Functional proteomic analysis of nonalcoholic fatty liver disease in rat models: enoyl-coenzyme a hydratase down-regulation exacerbates hepatic steatosis

Nonalcoholic fatty liver disease (NAFLD) has emerged as a common public health problem that can progress to end-stage liver disease. A high-fat diet (HFD) may promote the development of NAFLD through a mechanism that is poorly understood. We adopted a proteomic approach to examine the effect of HFD on the liver proteome during the progression of NAFLD. Male Sprague-Dawley rats fed an HFD for 4, 12, and 24 weeks replicated the progression of human NAFLD: steatosis, nonspecific inflammation, and steatohepatitis. Using two-dimensional difference gel electrophoresis (DIGE) combined with matrix-assisted laser desorption ionization time of flight/time of flight analysis, 95 proteins exhibiting significant changes (ratio > or = 1.5 or < or =-1.5, P < 0.05) during the development of NAFLD were identified. Biological functions for these proteins reflected phase-specific characteristics during the progression of the disease. The potential role of enoyl-coenzyme A hydratase (ECHS1), an enzyme that catalyzes the second step of mitochondrial fatty acid beta-oxidation, received further investigation. First, the reduced protein level of ECHS1 was validated both in rat models and in patients with biopsy-proven hepatic simple steatosis via immunoblotting or immunohistochemical analysis. Then the small interfering RNA (siRNA)-mediated knockdown of ECHS1 in the murine hepatocyte cell line alpha mouse liver 12 (AML12) demonstrated increased cellular lipid accumulation induced by free fatty acid (FFA) overload. Furthermore, using a hydradynamic transfection method, the in vivo silencing effect of siRNA duplexes targeting ECHS1 was further investigated in mice. Administering ECHS1 siRNA specifically reduced the expression of ECHS1 protein in mice liver, which significantly exacerbated the hepatic steatosis induced by an HFD.

CONCLUSION

Our results revealed that ECHS1 down-regulation contributed to HFD-induced hepatic steatosis, which may help clarify the pathogenesis of NAFLD and point to potential targets for therapeutic interventions.

Non-alcoholic fatty liver disease proteomics

PURPOSE

Non-alcoholic fatty liver disease (NAFLD) is an important cause of chronic liver injury that has gained concern in clinical hepatology. The principal aim of this study was to find differences in protein expression between patients with NAFLD and healthy controls.

EXPERIMENTAL DESIGN

Changes in protein expression of liver samples from each of the three groups of subjects, controls, non-alcoholic steatosis, and non-alcoholic steatohepatitis (NASH), were analyzed by DIGE combined with MALDI TOF/TOF analysis, a proteomic approach that allows to compare hundreds of proteins simultaneously.

RESULTS

Forty-three proteins exhibiting significant changes (ratio ≥1.5, p<0.05) were characterized, 22 comparing steatosis samples versus control samples and 21 comparing NASH versus control samples. Ten of these proteins were further analyzed by Western blot in tissue samples to confirm the observed changes of protein expression using DIGE. The proteins validated were further tested in serum samples of different cohorts of patients.

CONCLUSIONS AND CLINICAL RELEVANCE

Following this approach we identified two candidate markers, carbamoyl phosphate synthase 1 and 78  kDa glucose-regulated protein, differentially expressed between control and NASH. This proteomics approach demonstrates that DIGE combined with MALDI TOF/TOF and Western blot analysis of tissue and serum samples is a useful approach to identify candidate markers associated with NAFLD, resulting in proteins whose level of expression can be correlated to a disease state.

Non-alcoholic fatty liver disease: the hepatic consequence of obesity and the metabolic syndrome

Non-alcoholic fatty liver disease (NAFLD) is now the most common liver disease in both adults and children worldwide. As a disease spectrum, NAFLD may progress from simple steatosis to steatohepatitis, advanced fibrosis and cirrhosis. An estimated 20–35% of the general population has steatosis, 10% of whom will develop the more progressive non-alcoholic steatohepatitis associated with markedly increased risk of cardiovascular- and liver-related mortality. Development of NAFLD is strongly linked to components of the metabolic syndrome including obesity, insulin resistance, dyslipidaemia and type 2 diabetes. The recognition that NAFLD is an independent risk factor for CVD is a major public health concern. There is a great need for a sensitive non-invasive test for the early detection and assessment of the stage of NAFLD that could also be used to monitor response to treatment. The cellular and molecular aetiology of NAFLD is multi-factorial; genetic polymorphisms influencing NAFLD have been identified and nutrition is a modifiable environmental factor influencing NAFLD progression. Weight loss through diet and exercise is the primary recommendation in the clinical management of NAFLD. The application of systems biology to the identification of NAFLD biomarkers and factors involved in NAFLD progression is an area of promising research.

Mechanisms and clinical implications of hepatocyte lipoapoptosis

Nonalcoholic fatty liver disease (NAFLD) is characterized by insulin resistance, elevated serum levels of free fatty acids (FFAs) and fatty infiltration of the liver. Accumulation of triglycerides in the hepatocyte results from the uptake and esterification of circulating FFAs by the liver. Contrary to current theory, hepatic steatosis appears to be a detoxification process, as FFAs are directly cytotoxic for the hepatocyte and inhibition of triglyceride formation enhances FFAs toxicity. Hepatocyte apoptosis is a key feature of NAFLD and correlates with disease severity. Since FFA-induced toxicity, or lipoapoptosis, represents a mechanism for the pathogenesis of NAFLD, this article will highlight the cellular pathways contributing to hepatocyte lipoapoptosis. To date, there is no proven effective therapy for patients with NAFLD and insights into the molecular mediators of lipoapoptosis should help promote effective therapeutic strategies for this disease.

Serum proteomics and biomarker discovery across the spectrum of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), ranging from relatively benign simple steatosis to progressive nonalcoholic steatohepatitis (NASH) and fibrosis, is an increasingly common chronic liver disease. Liver biopsy is currently the only reliable tool for staging the subtypes of NAFLD; therefore, noninvasive serum biomarkers for evaluation of liver disease and fibrosis are urgently needed. We performed this study to describe changes in the serum proteome and identify biomarker candidates in serum samples from 69 patients with varying stages of NAFLD (simple steatosis, NASH, and NASH with advanced bridging [F3/F4] fibrosis) and 16 obese controls. Using a label-free mass spectrometry-based approach we identified over 1,700 serum proteins with a peptide identification (ID) confidence level of >75%, 605 of which changed significantly between any two patient groups (false discovery rate <5%). Importantly, expression levels of 55 and 15 proteins changed significantly between the simple steatosis and NASH F3/F4 group and the NASH and NASH F3/F4 group, respectively. Classification of proteins with significant changes showed involvement in immune system regulation and inflammation, coagulation, cellular and extracellular matrix structure and function, and roles as carrier proteins in the blood. Further, many of these proteins are synthesized exclusively by the liver and could potentially serve as diagnostic biomarkers for identifying and staging NAFLD.

CONCLUSION

This proteomic analysis reveals important information regarding the pathogenesis/progression of NAFLD and NASH and demonstrates key changes in serum protein expression levels between control subjects and patients with different stages of fatty liver. Future validation of these potential biomarkers is needed such that these proteins may be used in place of liver biopsy to facilitate diagnosis and treatment of patients with NAFLD.