[Role of PI3K/Akt pathway in endoplasmic reticulum stress and apoptosis induced by saturated fatty acid in human steatotic hepatocytes].
OBJECTIVE
To investigate the roles of PI3K/Akt signaling in the unfolded protein response (UPR) and non-UPR signaling pathways of endoplasmic reticulum stress and apoptosis in hepatocytes under conditions of saturated fatty acid-induced steatosis.


METHODS
A steatosis model of hepatocytes (L02 cell and HepG2 cell line) was induced by palmitate sodium saturated fatty acids.The hepatocytes were divided into normal control group,experimental group (treated with palmitate sodium) and intervention group (treated with palmitate sodium and LY294002, a PI3K/Akt inhibitor). Cell apoptosis was detected by flow cytometry with Annexin V/PI double-staining.Western blot analysis was used to examine the protein expression of GRP78, PI3K, P-PI3K,Akt, P-Akt, CHOP and Bax.The F test and t-test were used in statistical analyses.


RESULTS
Flow cytometry showed that palmitate sodium induced cell apoptosis in steatotic hepatocytes;moreover, a significant increase in cell apoptosis was observed in the palmitate sodium-induced steatotic hepatocytes in the presence of LY294002.For the normal control group, the experimental group and the intervention group, the apoptosis ratios of L02 cells were 4.41 ± 0.78% vs. 6.01 ± 1.49% vs. 19.50 ± 2.53% after 24 hours of treatment,and 12.56 ± 2.78% vs. 29.72 ± 6.39% vs. 44.60 ± 4.17% after 48 hours of treatment in respectively (all P < 0.05),and of HepG2 cells were 11.16 ± 1.15% vs. 17.50 ± 6.83% vs. 30.41 ± 3.62% after 24 hours of treatment, and 22.37 ± 1.24% vs. 33.85 ± 5.79% vs. 48.56 ± 4.21% after 48 hours of treatment (all P < 0.05). Western blot analysis showed that expression of GRP78 was significantly upregulated in the palmitate sodium-induced steatosis hepatocytes, indicating activation of endoplasmic reticulum stress. In addition, the palmitate sodium treatment also activated the PI3K/Akt pathway,induced expression of CHOP and Bax of the UPR and non-UPR signaling pathways respectively. Moreover, Pretreatment with LY294002 inhibited the palmitate sodium induced-phosphorylation of PI3K and Akt, and promoted upregulation of CHOP and Bax induced by palmitate sodium.


CONCLUSIONS
The PI3K/Akt pathway may be involved in regulation of the UPR and non-UPR signaling pathways of endoplasmic reticulum stress and may promote apoptosis of hepatocytes by enhancing the expression of CHOP and Bax protein in saturated fatty acid-induced steatotic hepatocytes.
Department of Gastroenterology, the Second Affiliated Hospital of Chongqing Medical University, Chongqing 400010, China.
Mei
M
Qu
Wei
W
Shen
D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D000091342:Endoplasmic Reticulum Chaperone BiP; D059865:Endoplasmic Reticulum Stress; D005234:Fatty Liver; D006360:Heat-Shock Proteins; D022781:Hepatocytes; D006801:Humans; D019308:Palmitic Acid; D019869:Phosphatidylinositol 3-Kinases; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction; D056811:Unfolded Protein Response; D015854:Up-Regulation
D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D019308:Palmitic Acid; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; C000717247:HSPA5 protein, human