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      Free Fatty Acids Differentially Downregulate Chemokines in Liver Sinusoidal Endothelial Cells: Insights into Non-Alcoholic Fatty Liver Disease

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          Abstract

          Non-alcoholic fatty liver disease is a prevalent problem throughout the western world. Liver sinusoidal endothelial cells (LSEC) have been shown to play important roles in liver injury and repair, but their role in the underlying pathogenetic mechanisms of non-alcoholic fatty liver disease remains undefined. Here, we evaluated the effects of steatosis on LSEC gene expression in a murine model of non-alcoholic fatty liver disease and an immortalized LSEC line. Using microarray we identified distinct gene expression profiles following exposure to free fatty acids. Gene pathway analysis showed a number of differentially expressed genes including those involved in lipid metabolism and signaling and inflammation. Interestingly, in contrast to hepatocytes, fatty acids led to decreased expression of pro-inflammatory chemokines including CCL2 (MCP-1), CXCL10 and CXCL16 in both primary and LSEC cell lines. Chemokine downregulation translated into a significant inhibition of monocyte migration and LSECs isolated from steatotic livers demonstrated a similar shift towards an anti-inflammatory phenotype. Overall, these pathways may represent a compensatory mechanism to reverse the liver damage associated with non-alcoholic fatty liver disease.

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          Most cited references25

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          MCP-1 contributes to macrophage infiltration into adipose tissue, insulin resistance, and hepatic steatosis in obesity.

          Adipocytes secrete a variety of bioactive molecules that affect the insulin sensitivity of other tissues. We now show that the abundance of monocyte chemoattractant protein-1 (MCP-1) mRNA in adipose tissue and the plasma concentration of MCP-1 were increased both in genetically obese diabetic (db/db) mice and in WT mice with obesity induced by a high-fat diet. Mice engineered to express an MCP-1 transgene in adipose tissue under the control of the aP2 gene promoter exhibited insulin resistance, macrophage infiltration into adipose tissue, and increased hepatic triglyceride content. Furthermore, insulin resistance, hepatic steatosis, and macrophage accumulation in adipose tissue induced by a high-fat diet were reduced extensively in MCP-1 homozygous KO mice compared with WT animals. Finally, acute expression of a dominant-negative mutant of MCP-1 ameliorated insulin resistance in db/db mice and in WT mice fed a high-fat diet. These findings suggest that an increase in MCP-1 expression in adipose tissue contributes to the macrophage infiltration into this tissue, insulin resistance, and hepatic steatosis associated with obesity in mice.
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            A human hepatocellular in vitro model to investigate steatosis.

            The present study was designed to define an experimental model of hepatocellular steatosis with a fat overaccumulation profile in which the metabolic and cytotoxic/apoptotic effects could be separated. This was accomplished by defining the experimental conditions of lipid exposure that lead to significant intracellular fat accumulation in the absence of overt cytotoxicity, therefore allowing to differentiate between cytotoxic and apoptotic effects. Palmitic (C16:0) and oleic (C18:1) acids are the most abundant fatty acids (FFAs) in liver triglycerides in both normal subjects and patients with nonalcoholic fatty liver disease (NAFLD). Therefore, human hepatocytes and HepG2 cells were incubated with a mixture of different proportions of saturated (palmitate) and unsaturated (oleate) FFAs to induce fat-overloading. Similar intracellular levels of lipid accumulation as in the human steatotic liver were achieved. Individual FFAs have a distinct inherent toxic potential. Fat accumulation, cytotoxicity and apoptosis in cells exposed to the FFA mixtures were investigated. The FFA mixture containing a low proportion of palmitic acid (oleate/palmitate, 2:1 ratio) is associated with minor toxic and apoptotic effects, thus representing a cellular model of steatosis that mimics benign chronic steatosis. On the other hand, a high proportion of palmitic acid (oleate/palmitate, 0:3 ratio) might represent a cellular model of steatosis in which saturated FFAs promote an acute harmful effect of fat overaccumulation in the liver. These hepatic cellular models are apparently suitable to experimentally investigate the impact of fat overaccumulation in the liver excluding other factors that could influence hepatocyte behaviour.
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              Lipotoxicity in nonalcoholic fatty liver disease: not all lipids are created equal.

              Nonalcoholic fatty liver disease (NAFLD) is currently the most common form of chronic liver disease affecting both adults and children in the USA and many other parts of the world. NAFLD encompasses a wide spectrum of conditions associated with the overaccumulation of lipids in the liver, ranging from steatosis to nonalcoholic steatohepatitis, to cirrhosis and its feared complications of portal hypertension, liver failure and hepatocellular carcinoma. In this article, we will focus on the growing evidence linking changes in hepatic lipid metabolism and accumulation of specific lipid types in the liver with hepatocellular damage, inflammation and apoptosis, resulting in disease progression to the more serious forms of this condition.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                25 July 2016
                2016
                : 11
                : 7
                : e0159217
                Affiliations
                [1 ]Department of Medicine, Division of Gastroenterology and Hepatology, University of Colorado Denver, Aurora, Colorado, United States of America
                [2 ]Department of Medicine, Division of Pulmonary Sciences and Critical Care Medicine, University of Colorado Denver, Aurora, Colorado, United States of America
                [3 ]Department of Microbiology and Immunology, University of Colorado Denver, Aurora, Colorado, United States of America
                [4 ]Denver Veteran’s Affairs Medical Center, Denver, Colorado, United States of America
                INRA, FRANCE
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: RHM HRR. Performed the experiments: RHM CEP. Analyzed the data: RHM CEP MGE. Contributed reagents/materials/analysis tools: RHM HRR MGE. Wrote the paper: RHM HRR.

                Article
                PONE-D-16-14212
                10.1371/journal.pone.0159217
                4959750
                27454769
                a5c4df3c-5648-411a-aefe-981f35038541
                © 2016 McMahan et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 7 April 2016
                : 28 June 2016
                Page count
                Figures: 5, Tables: 0, Pages: 14
                Funding
                Funded by: funder-id http://dx.doi.org/10.13039/100000062, National Institute of Diabetes and Digestive and Kidney Diseases;
                Award ID: K01 DKO96025
                Award Recipient :
                Funded by: VA Merit Review Grant
                Award Recipient :
                RHM was funded by NIH/NIDDK K01DKO96025. HRR was funded by a VA Merit Review Grant. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Biology and Life Sciences
                Cell Biology
                Cell Motility
                Chemotaxis
                Chemokines
                Medicine and Health Sciences
                Gastroenterology and Hepatology
                Liver Diseases
                Fatty Liver
                Biology and Life Sciences
                Cell Biology
                Cellular Types
                Animal Cells
                Blood Cells
                White Blood Cells
                Monocytes
                Biology and Life Sciences
                Cell Biology
                Cellular Types
                Animal Cells
                Immune Cells
                White Blood Cells
                Monocytes
                Biology and Life Sciences
                Immunology
                Immune Cells
                White Blood Cells
                Monocytes
                Medicine and Health Sciences
                Immunology
                Immune Cells
                White Blood Cells
                Monocytes
                Biology and Life Sciences
                Genetics
                Gene Expression
                Biology and Life Sciences
                Cell Biology
                Cellular Types
                Animal Cells
                Hepatocytes
                Biology and Life Sciences
                Anatomy
                Liver
                Hepatocytes
                Medicine and Health Sciences
                Anatomy
                Liver
                Hepatocytes
                Biology and Life Sciences
                Biochemistry
                Lipids
                Fatty Acids
                Biology and Life Sciences
                Nutrition
                Diet
                Medicine and Health Sciences
                Nutrition
                Diet
                Biology and life sciences
                Cell biology
                Signal transduction
                Cell signaling
                Signaling cascades
                MAPK signaling cascades
                Custom metadata
                Microarray data is available in the Gene Expression Omnibus (GEO) repository (NCBI) under the accession # GSE67651. All other data is within the paper and its Supporting Information files.

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                Uncategorized

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