Inhibition of apolipoprotein B100 secretion by lipid-induced hepatic endoplasmic reticulum stress in rodents
Tsuguhito Ota, … , Constance Gayet, Henry N. Ginsberg
Tsuguhito Ota, … , Constance Gayet, Henry N. Ginsberg
Published December 3, 2007
Citation Information: J Clin Invest. 2008;118(1):316-332. https://doi.org/10.1172/JCI32752.
View: Text | PDF
Research Article Cell biology

Inhibition of apolipoprotein B100 secretion by lipid-induced hepatic endoplasmic reticulum stress in rodents

Abstract

ER stress can cause hepatic insulin resistance and steatosis. Increased VLDL secretion could protect the liver from ER stress–induced steatosis, but the effect of lipid-induced ER stress on the secretion of VLDL is unknown. To determine the effect of lipids on hepatic ER stress and VLDL secretion, we treated McA-RH7777 liver cells with free fatty acids. Prolonged exposure increased cell triglycerides, induced steatosis, and increased ER stress. Effects on apoB100 secretion, which is required for VLDL assembly, were parabolic, with moderate free fatty acid exposure increasing apoB100 secretion, while greater lipid loading inhibited apoB100 secretion. This decreased secretion at higher lipid levels was due to increased protein degradation through both proteasomal and nonproteasomal pathways and was dependent on the induction of ER stress. These findings were supported in vivo, where intravenous infusion of oleic acid (OA) in mice increased ER stress in a duration-dependent manner. apoB secretion was again parabolic, stimulated by moderate, but not prolonged, OA infusion. Inhibition of ER stress was able to restore OA-stimulated apoB secretion after prolonged OA infusion. These results suggest that excessive ER stress in response to increased hepatic lipids may decrease the ability of the liver to secrete triglycerides by limiting apoB secretion, potentially worsening steatosis.

Authors

Tsuguhito Ota, Constance Gayet, Henry N. Ginsberg

×

Figure 7

Prolonged incubation of McA cells with high-dose OA reduces the accumulation of full-length apoB100; this is reversed by cotreatment with lactacystin.

Options: View larger image (or click on image) Download as PowerPoint
Prolonged incubation of McA cells with high-dose OA reduces the accumula...
McA cells were incubated for 16 hours with serum-free DMEM containing 1.5% BSA (lane 1), 1.5% BSA plus 0.4 mM OA (lane 2), 1.5% BSA plus 1.2 mM OA (lane 3); this was followed by an additional 10 minutes incubation, under the same 3 conditions, without (top left) or with 100 μM puromycin. The puromycin-treated cells were also incubated in the absence (top right) or presence (bottom right) of 10 μM lactacystin (Lacta). The cells were then put on ice and the puromycin removed. The cells were transferred to a 37°C water bath and labeled with serum-free, methionine/cysteine-free DMEM containing [35S]methionine for 15, 20, or 25 minutes. (The 2 latter steps were also performed with or without lactacystin.) 1.2 mM OA inhibited the accumulation of full-length apoB100; lactacystin treatment (bottom right) significantly increased the accumulation of full-length apoB100 after incubation with 1.2 mM OA for 16 hours (compare with top right). The data shown are representative of 2 experiments.