α-Linolenic acid prevents endoplasmic reticulum stress-mediated apoptosis of stearic acid lipotoxicity on primary rat hepatocytes

Yong Zhang,Hongyang Shi,Xia Yang,Lei Dong,Li Zhang

doi:10.1186/1476-511x-10-81

Abstract

AimsLipid accumulation in non-adipose tissues leads to cell dysfunction and apoptosis, a phenomenon known as lipotoxicity. Unsaturated fatty acids may offset the lipotoxicity associated with saturated fatty acids. Stearic acid induced endoplasmic reticulum (ER) stress and caused apoptotic and necrotic cell death in the primary rat hepatocytes.MethodsCell viability was investigated using MTT assay, and apoptosis was evaluated with Hoechst 33342 staining. Western blot analysis was used to examine the changes in the expression levels of glucose regulated protein 78 (GRP78), glucose regulated protein 94 (GRP94), and C/EBP homologous protein (CHOP). Caspase-3 activity was evaluated using a Caspase-3 substrate kit.ResultsWe have studied the ability of α-linolenic acid to prevent endoplasmic reticulum stress-mediated apoptosis of rat hepatocytes elicited by stearic acid and thapsigargin. Incubation of primary rat hepatocytes for 16 h with stearic acid produced a significant increase in cell death. Stearic acid also increased levels of three indicators of ER stress -- GRP78, CHOP, and GRP94. α-Linolenic acid distinctly reduced cell death and levels of all three indicators of ER stress brought about by stearic acid. Thapsigargin, which induces ER stress produced similar effects to those obtained using stearic acid; its effects were partly reversed by α-linolenic acid.ConclusionThese results suggest that α-linolenic acid prevents ER stress-mediated apoptosis of stearic acid lipotoxicity on primary rat hepatocytes might become a target to develop new antiapoptotic compounds in nonalcoholic fatty liver disease (NAFLD).

Highlights

The endoplasmic reticulum (ER) is a subcellular organelle where the vast majority of secreted and membrane proteins are folded
The mode of cell death observed at this concentration of stearic acid was a combination of apoptosis and necrosis as determined using a combination of Hoechst 33342-propidium iodide (HPI) staining (Figure 1B)
Co-incubation of primary rat hepatocytes with 250 μmol/l stearic acid and 150 or 250 μmol/l a-linolenic acid restored cell viability to levels observed in untreated cells (Figure 1A)

Summary

Introduction

The endoplasmic reticulum (ER) is a subcellular organelle where the vast majority of secreted and membrane proteins are folded. Many kinds of cellular perturbations, such as imbalances in calcium, loss of the luminal oxidizing environment and/or nutrient homeostasis, can lead to the accumulation of unfolded proteins and apoptosis[1,2]. The apoptosis is involved in the pathogenesis of many diseases and conditions including ischemiareperfusion injury, diabetes and nonalcoholic fatty liver disease (NAFLD) [3,4]. Hepatocyte death is a main feature of almost every liver disease, with apoptosis characterized by biochemical and morphological features being one of its modes. It has long been known that elevation of intracellular free calcium ([Ca2+]i) has cytotoxic consequence in many cells including hepatocytes [9]. ER function is mediated, in part, by intraluminal Ca2+-binding proteins, which include the glucose-regulated proteins GRP78 and GRP94 [10,11]

Methods

Results

Conclusion