Palmitic and linoleic acids induce ER stress and apoptosis in hepatoma cells.
OBJECTIVE
Hepatic inflammation and degeneration induced by lipid depositions may be the major cause of nonalcoholic fatty liver disease. In this study, we tried to investigate the effects of saturated and unsaturated fatty acids on hepatoma cell apoptosis.


METHODS
H4IIE liver cells were treated with palmitic acid, linoleic acid, or both with or without the calcium-specific chelator BAPTA-AM after which the expression of proteins associated with endoplasmic reticulum (ER) stress, apoptosis, caspase-3 levels, and calcium flux were measured.


RESULTS
Palmitic or linoleic acid (250 μM) induced H4IIE cell apoptosis, which required calcium flux but not caspase-3. Apoptosis was not observed when cells were co-treated with linoleic acid (125 μM) and palmitic acid (250 μM). Importantly, the release of cytochrome C from mitochondria into cytoplasm during cell apoptosis was specifically detected only when linoleic acid (125 μM), but not palmitic acid (250 μM), was added to the cells. Depletion of intracellular calcium flux by the calcium-specific chelator, BAPTA-AM, abolished linoleic acid-induced apoptosis. Moreover, in the presence of BAPTA-AM, expression of the unfolded protein response (UPR)-associated genes, CHOP, GRP78, and GRP94, was induced by linoleic acid, but not palmitic acid.


CONCLUSIONS
The results suggest that linoleic acid promotes cell apoptosis through the release of cytochrome C, only if the intracellular calcium flux is unperturbed and intact. These results confirm that ER stress contributes to fatty acid-induced liver cell apoptosis.
Anesthesia Department, the Second Affiliated Hospital of Xi'an Jiaotong University, No, 157, West 5th Road, Xi'an, Shaanxi Province-710004, China.
Yong
Y
Zhang
Rongliang
R
Xue
Zhenni
Z
Zhang
Xia
X
Yang
Hongyang
H
Shi
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D020013:Calcium Signaling; D006528:Carcinoma, Hepatocellular; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D045304:Cytochromes c / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D005234:Fatty Liver / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D008041:Linoleic Acids / Q000494:pharmacology*; D008113:Liver Neoplasms; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D065626:Non-alcoholic Fatty Liver Disease; D010169:Palmitic Acids / Q000494:pharmacology*; D051381:Rats; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D056811:Unfolded Protein Response / Q000235:genetics; D000091342:Endoplasmic Reticulum Chaperone BiP
D053148:Caspase 3; D045304:Cytochromes c; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D008041:Linoleic Acids; D008565:Membrane Proteins; D010169:Palmitic Acids; D051742:Transcription Factor CHOP; C497251:Ddit3 protein, rat; C051684:GRP78 protein, rat; D000091342:Endoplasmic Reticulum Chaperone BiP; C018551:glucose-regulated proteins; C505410:Casp3 protein, rat