α-linolenic acid prevents endoplasmic reticulum stress-mediated apoptosis of stearic acid lipotoxicity on primary rat hepatocytes
α-linolenic acid prevents endoplasmic reticulum stress-mediated apoptosis of stearic acid lipotoxicity on primary rat hepatocytes
Year: 2011
Authors: Zhang, Y. Dong, L. Yang, X. Shi, H. Zhang, L.
Publication Name: Lipids in Health and Disease
Publication Details: Volume 10; Pages 81 – 86.
Abstract:
Lipid 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. Cell 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. We have studied the ability of a-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. Alpha – linolenic acid (ALA) 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 ALA. These results suggest that a-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). (Authors abstract)
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. Hepatocyte death is a main feature of almost every liver disease. Thapsigargin (TG) has become widely used as selective inhibitor of the ubiquitous sarco-endoplasmic reticulum Ca2+-ATPases (SERCAs), which pump Ca2+ from the cytosol into the lumen of the endoplasmic reticulum (ER) in mammalian cells. Several studies have linked ER dysfunction and activation of the unfolded protein response (UPR) to impairments in glucose homeostasis and diabetes. Recent studies imply that long-chain saturated fatty acids may induce ER stress in breast cancer cells and liver cells. The present study had three aims: (1) To examine the characteristics of fatty acid-mediated ER stress and apoptosis in primary hepatocytes; (2) To determine whether ALA could provide protection against the cell death induced by stearic acid; (3) once the beneficial actions of ALA were confirmed, this study examined whether these effects were mediated via modification of the ER stress process with specific attention given to the role of GRP78, GRP94 expression and induction of CHOP.The delivery and accumulation of lipids in non-adipose tissues leads to cellular dysfunction and death. Disruption of ER homeostasis and activation of the UPR has been observed in murine models of obesity, cardiac dysfunction and NAFLD. Here it was observed that (1) stearic acid causes significant cell death in primary rat hepatocytes; (2) stearic acid causes a significant degree of ER stress in primary rat hepatocytes; (3) ALA protects primary rat hepatocytes against stearic acid lipotoxicity by reducing ER stress and apoptosis. ALA was also able to reduce cellular dysfunction and apoptosis caused by thapsigargin, a recognised inducer of ER stress. Thapsigargin causes apoptosis in many other cells such as neuronal cells, pancreatic beta-cells and cardiomyocytes. It is possible that by protecting cells against thapsigargin-induced apoptosis, ALA alleviated primary rat hepatocytes damaged. It was demonstrated for the first time that ER stress produced by stearic acid in primary rat hepatocytes can be significantly reduced by ALA, an unsaturated fatty acid and that the protection afforded by an unsaturated fatty acid involves a reduction of ER stress. To summarize, the results presented here suggest that unsaturated fatty acids such ALA may be able to offer protection of hepatocytes against the lipotoxicity of saturated fatty acids such as dietary stearic acid and nutrient overload associated with obesity and NAFLD. (Editors comments)
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. Hepatocyte death is a main feature of almost every liver disease. Thapsigargin (TG) has become widely used as selective inhibitor of the ubiquitous sarco-endoplasmic reticulum Ca2+-ATPases (SERCAs), which pump Ca2+ from the cytosol into the lumen of the endoplasmic reticulum (ER) in mammalian cells. Several studies have linked ER dysfunction and activation of the unfolded protein response (UPR) to impairments in glucose homeostasis and diabetes. Recent studies imply that long-chain saturated fatty acids may induce ER stress in breast cancer cells and liver cells. The present study had three aims: (1) To examine the characteristics of fatty acid-mediated ER stress and apoptosis in primary hepatocytes; (2) To determine whether ALA could provide protection against the cell death induced by stearic acid; (3) once the beneficial actions of ALA were confirmed, this study examined whether these effects were mediated via modification of the ER stress process with specific attention given to the role of GRP78, GRP94 expression and induction of CHOP.The delivery and accumulation of lipids in non-adipose tissues leads to cellular dysfunction and death. Disruption of ER homeostasis and activation of the UPR has been observed in murine models of obesity, cardiac dysfunction and NAFLD. Here it was observed that (1) stearic acid causes significant cell death in primary rat hepatocytes; (2) stearic acid causes a significant degree of ER stress in primary rat hepatocytes; (3) ALA protects primary rat hepatocytes against stearic acid lipotoxicity by reducing ER stress and apoptosis. ALA was also able to reduce cellular dysfunction and apoptosis caused by thapsigargin, a recognised inducer of ER stress. Thapsigargin causes apoptosis in many other cells such as neuronal cells, pancreatic beta-cells and cardiomyocytes. It is possible that by protecting cells against thapsigargin-induced apoptosis, ALA alleviated primary rat hepatocytes damaged. It was demonstrated for the first time that ER stress produced by stearic acid in primary rat hepatocytes can be significantly reduced by ALA, an unsaturated fatty acid and that the protection afforded by an unsaturated fatty acid involves a reduction of ER stress. To summarize, the results presented here suggest that unsaturated fatty acids such ALA may be able to offer protection of hepatocytes against the lipotoxicity of saturated fatty acids such as dietary stearic acid and nutrient overload associated with obesity and NAFLD. (Editors comments)
