Article

Lipid peroxidation product 4-hydroxy-trans-2-nonenal causes endothelial activation by inducing endoplasmic reticulum stress

Diabetes and Obesity Center, University of Louisville, Louisville, Kentucky 40202, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 01/2012; 287(14):11398-409. DOI: 10.1074/jbc.M111.320416
Source: PubMed

ABSTRACT Lipid peroxidation products, such as 4-hydroxy-trans-2-nonenal (HNE), cause endothelial activation, and they increase the adhesion of the endothelium to circulating leukocytes. Nevertheless, the mechanisms underlying these effects remain unclear. We observed that in HNE-treated human umbilical vein endothelial cells, some of the protein-HNE adducts colocalize with the endoplasmic reticulum (ER) and that HNE forms covalent adducts with several ER chaperones that assist in protein folding. We also found that at concentrations that did not induce apoptosis or necrosis, HNE activated the unfolded protein response, leading to an increase in XBP-1 splicing, phosphorylation of protein kinase-like ER kinase and eukaryotic translation initiation factor 2α, and the induction of ATF3 and ATF4. This increase in eukaryotic translation initiation factor 2α phosphorylation was prevented by transfection with protein kinase-like ER kinase siRNA. Treatment with HNE increased the expression of the ER chaperones, GRP78 and HERP. Exposure to HNE led to a depletion of reduced glutathione and an increase in the production of reactive oxygen species (ROS); however, glutathione depletion and ROS production by tert-butyl-hydroperoxide did not trigger the unfolded protein response. Pretreatment with a chemical chaperone, phenylbutyric acid, or adenoviral transfection with ATF6 attenuated HNE-induced monocyte adhesion and IL-8 induction. Moreover, phenylbutyric acid and taurine-conjugated ursodeoxycholic acid attenuated HNE-induced leukocyte rolling and their firm adhesion to the endothelium in rat cremaster muscle. These data suggest that endothelial activation by HNE is mediated in part by ER stress, induced by mechanisms independent of ROS production or glutathione depletion. The induction of ER stress may be a significant cause of vascular inflammation induced by products of oxidized lipids.

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    • "In the negative labeling strategy, cells are exposed to oxidants or insults that promote oxidative stress (Fig. 2). These exposures often lead to mitochondrial damage [6] [32], activation of the autophagic program [6] [33], endoplasmic reticulum (ER) stress [34], and apoptosis [34] [35]. The proteins that could be involved with each of these processes can then be examined by postlabeling with BODIPY–iodoacetamide (BD-IAM), with the result being a decrease in (or negative) labeling under conditions of oxidative stress compared with control conditions. "
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    • "The selective activation of the PERK pathway in HNE-treated cells therefore appears to be an early adaptive response that stimulates autophagy to counter oxidative insults rather than a full-blown response which could lead to apoptosis. This differs from HNE-induced responses in endothelial cells, where, in addition to PERK, HNE increases XBP-1 splicing and induces Grp78 [43]. That the ER stress response in SMCs is adaptive rather than deleterious is further supported by the fact that HNE treatment did not result in appreciable cell death or the upregulation of the death effector, CHOP, but induced the cytoprotective protein HO- 1. "
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