Role of endoplasmic reticulum stress in acrolein-induced endothelial activation

Abstract

Acrolein is a ubiquitous environmental pollutant and an endogenous product of lipid peroxidation. It is also generated during the metabolism of several drugs and amino acids. In this study, we examined the effects of acrolein on endothelial cells. Treatment of human umbilical vein endothelial cells (HUVECs) with 2 to 10 μM acrolein led to an increase in the phosphorylation of eIF-2α within 10 to 30 min of exposure. This was followed by alternate splicing of XBP-1 mRNA and an increase in the expression of the endoplasmic reticulum (ER) chaperone genes Grp78 and Herp. Within 2–4 h of treatment, acrolein also increased the abundance and the nuclear transport of the transcription factors ATF3, AFT4, and CHOP. Acrolein-induced increase in ATF3 was prevented by treating the cells with the chemical chaperone – phenylbutryic acid (PBA). Treatment with acrolein increased phosphorylation of ERK1/2, p38, and JNK. The increase in JNK phosphorylation was prevented by PBA. Acrolein treatment led to the activation and nuclear translocation of the transcription factor NF-κB and an increase in TNF-α, IL-6 and IL-8, but not MCP-1, mRNA. Increased synthesis of cytokine genes and NF-κB activation were not observed in cells treated with PBA. These findings suggest that exposure to acrolein induces ER stress and triggers the unfolded protein response and that NF-κB activation and stimulation of cytokine production by acrolein could be attributed, in part, to ER stress. Chemical chaperones of protein-folding may be useful in treating toxicological and pathological states associated with excessive acrolein exposure or production.

Phosphatidylethanolamines Modified by γ-Ketoaldehyde (γKA) Induce Endoplasmic Reticulum Stress and Endothelial Activation

“…OxPC induces mRNA for ATF4 and the spliced (active) version of XBP1, which are important downstream mediators of ER stress signaling (50), and silencing these two genes dramatically reduces oxPC induced IL-8 and MCP-1 expression (32). Treatment of human endothelial cells with acrolein and HNE also induces ER stress as indicated by spliced XBP-1, ATF4 nuclear localization, and increased levels of CHOP mRNA (33,51). Furthermore, inhibition of ER stress blocks acrolein-induced increases in mRNA levels of the proinflammatory cytokines TNF␣, IL-6, and IL-8 (33).…”

“…Treatment of human endothelial cells with acrolein and HNE also induces ER stress as indicated by spliced XBP-1, ATF4 nuclear localization, and increased levels of CHOP mRNA (33,51). Furthermore, inhibition of ER stress blocks acrolein-induced increases in mRNA levels of the proinflammatory cytokines TNF␣, IL-6, and IL-8 (33). As ␥KA, HNE, and acrolein all modify PE (8,11,13,(15)(16)(17)(18), our finding that ␥KA-PE induces CHOP, IL-8, and MCP-1 expression raises the possibility that these other aldehydes also mediate their inflammatory effects by forming modified PE, which induce ER stress responses.…”

Molecular Biology of Atherosclerosis

“…One of these sensors is inositol-requiring enzyme 1 (IRE1) which, in the face of ER stress, binds and activates TRAF2 thereby triggering canonical NF-B signaling. ER stress and subsequent NF-B activation was seen in endothelial cells exposed to acrolein and a number of other reactive aldehydes (687).…”

“…Somewhat lower doses can irreversibly deactivate key antioxidant enzymes such as Trx and initiate inflammatory signaling (624). ER stress is promoted by degradation of alkylated proteins by the p20 proteosome (which recognizes misfolded proteins with external lipophilic groups) and degradation of ubiquitinated proteins by the p26 proteosome (659,687). Some electrophilic adducts can cause proteosomal degradation of GTP cyclohydrolase I (the rate-limiting enzyme for synthesis of the essential eNOS cofactor tetrahydrobiopterin) as well as HSP90, causing eNOS uncoupling and increased superoxide production (1956).…”

The chemical chaperone 4-phenylbutyrate inhibits adipogenesis by modulating the unfolded protein response

“…Many recent reports demonstrate that 4-PBA has chaperone properties and by stabilizing protein conformation in the ER, it can repress ER stress/UPR activation in vitro and in vivo ( 14,19,(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40). 4-PBA was found to restore glucose homeostasis, enhance insulin sensitivity, and decrease fatty liver disease in the diabetic ob/ob mouse model ( 14 ).…”