Differential Lipotoxic Effects of Palmitate and Oleate in Activated Human Hepatic Stellate Cells and Epithelial Hepatoma Cells.
OBJECTIVE
Nonalcoholic fatty liver disease (NAFLD) progression to fibrosis, cirrhosis and hepatocellular carcinoma, alters the cellular composition of this organ. During late-stage NAFLD, fibrotic and possibly cancerous cells can proliferate and, like normal hepatocytes, are exposed to high concentrations of fatty acids from both surrounding tissue and circulating lipid sources. We hypothesized that primary human activated hepatic stellate cells and epithelial hepatoma (HepG2) cells respond differently to lipotoxic conditions, and investigated the mechanisms involved.


METHODS
Primary activated hepatic stellate cells and HepG2 cells were exposed to pathophysiological concentrations of fatty acids and comparative studies of lipid metabolic and stress response pathways were performed.


RESULTS
Both cell types remained proliferative during exposure to a combination of palmitate plus oleate reflective of the general saturated versus unsaturated fatty acid composition of western diets. However, exposure to either high palmitate or high oleate alone induced cytotoxicity in activated stellate cells, while only palmitate caused cytotoxicity in HepG2 cells. mRNA microarray and biochemical comparisons revealed that stellate cells stored markedly less fatty acids as neutral lipids, and had reduced capacity for beta-oxidation. Similar to previous observations in HepG2 cells, palmitate, but not oleate, induced ER stress and actin stress fiber formation in activated stellate cells. In contrast, oleate, but not palmitate, induced the inflammatory signal TXNIP, decreased cytoskeleton proteins, and decreased cell polarity preceding cell death in activated stellate cells.


CONCLUSIONS
Palmitate-induced lipotoxicity was associated with ER stress pathways in both primary activated hepatic stellate cells and epithelial hepatoma cells, whereas high oleate caused lipotoxicity only in activated stellate cells, possibly through a distinct mechanism involving disruption of cytoskeleton components. This may have implications for optimal dietary fatty acid compositions during various stages of NAFLD.
Department of Physiology and Pharmacology, Western University, London, Ontario, Canada.
Alexandra M
AM
Hetherington
Cynthia G
CG
Sawyez
Emma
E
Zilberman
Alexandra M
AM
Stoianov
Debra L
DL
Robson
Nica M
NM
Borradaile
D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D016764:Cell Polarity / Q000187:drug effects; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects / Q000235:genetics; D005786:Gene Expression Regulation; D056945:Hep G2 Cells; D055166:Hepatic Stellate Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D050356:Lipid Metabolism / Q000187:drug effects* / Q000235:genetics; D019301:Oleic Acid / Q000633:toxicity*; D020411:Oligonucleotide Array Sequence Analysis; D009928:Organ Specificity; D010084:Oxidation-Reduction; D019308:Palmitic Acid / Q000633:toxicity*; D061251:Primary Cell Culture; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological / Q000187:drug effects* / Q000235:genetics; D059467:Transcriptome
D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D012333:RNA, Messenger; C486715:TXNIP protein, human; D019301:Oleic Acid; D019308:Palmitic Acid