Bip overexpression, but not CHOP inhibition, attenuates fatty-acid-induced endoplasmic reticulum stress and apoptosis in HepG2 liver cells.
OBJECTIVE
In this study we investigated whether attenuation of endoplasmic reticulum stress (ER stress) could protect HepG2 cells from free fatty acid (FFA)-induced apoptosis.


METHODS
Human liver cell line HepG2 cells were exposed to Sodium Palmitate (Pa) or Sodium Oleate (Ol). Apoptosis and ER stress of HepG2 cells were analyzed with flow cytometry, real-time RT-PCR and Western Blotting. An expression plasmid encoding for the ER chaperone immunoglobulin heavy chain-binding protein (Bip) was transfected into HepG2 cells to attenuate ER stress. Small interfering RNA siCHOP was used to knockdown the expression of C/EBP Homologous Protein (CHOP) in HepG2.


RESULTS
Pa led to cytotoxicity and apoptosis in HepG2 cells in a dose-dependent pattern and also induced ER stress indicated by increased phosphorylation of eIF2α, upregulation of IRE1α and CHOP. Bip expression levels were slightly down regulated after Pa treatment. The unsaturated fatty acid, Ol, induced neither apoptosis nor ER stress in HepG2 cells. Overexpression of Bip attenuated Pa-induced ER stress and led to a significant reduction in Pa-mediated apoptosis, indicating a requirement of ER stress for lipotoxicity in liver cells. siRNA-mediated reduction of CHOP did not protect against Pa-induced apoptosis.


CONCLUSIONS
While ER stress makes a necessary contribution to palmitate cytotoxicity, inhibition of CHOP alone is not sufficient to prevent palmitate-induced apoptosis. Our findings could advance the detailed understanding on the mechanism of high fatty acid (FFA)-induced apoptosis.
Department of Medicine and Therapeutics, The Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong, China.
Xuemei
X
Gu
Kwan
K
Li
D Ross
DR
Laybutt
Ming-liang
ML
He
Hai-Lu
HL
Zhao
Juliana C N
JC
Chan
Gang
G
Xu
D017209:Apoptosis / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000473:pathology; D000091342:Endoplasmic Reticulum Chaperone BiP; D055785:Gene Knockdown Techniques; D006360:Heat-Shock Proteins / Q000187:drug effects* / Q000235:genetics; D056945:Hep G2 Cells; D006801:Humans; D008099:Liver / Q000187:drug effects / Q000473:pathology; D019301:Oleic Acid / Q000008:administration & dosage / Q000633:toxicity*; D019308:Palmitic Acid / Q000008:administration & dosage / Q000633:toxicity*; D010766:Phosphorylation / Q000187:drug effects; D034741:RNA, Small Interfering / Q000008:administration & dosage; D051742:Transcription Factor CHOP / Q000037:antagonists & inhibitors*
D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D034741:RNA, Small Interfering; D051742:Transcription Factor CHOP; D019301:Oleic Acid; D019308:Palmitic Acid; C013173:osteum