High-Density Lipoprotein Prevents Endoplasmic Reticulum Stress-Induced Downregulation of Liver LOX-1 Expression.

Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is a specific cell-surface receptor for oxidized-low-density lipoprotein (ox-LDL). The impact of high-density lipoprotein (HDL) on endoplasmic reticulum (ER) stress-mediated alteration of the LOX-1 level in hepatocytes remains unclear. We aimed to investigate the impact on LOX-1 expression by tunicamycin (TM)-induced ER stress and to determine the effect of HDL on TM-affected LOX-1 expression in hepatic L02 cells. Overexpression or silencing of related cellular genes was conducted in TM-treated cells. mRNA expression was evaluated using real-time polymerase chain reaction (PCR). Protein expression was analyzed by western blot and immunocytochemistry. Lipid uptake was examined by DiI-ox-LDL, followed by flow cytometric analysis. The results showed that TM induced the upregulation of ER chaperone GRP78, downregulation of LOX-1 expression, and lipid uptake. Knock down of IRE1 or XBP-1 effectively restored LOX-1 expression and improved lipid uptake in TM-treated cells. HDL treatment prevented the negative impact on LOX-1 expression and lipid uptake induced by TM. Additionally, 1-10 µg/mL HDL significantly reduced the GRP78, IRE1, and XBP-1 expression levels in TM-treated cells. Our findings reveal that HDL could prevent the TM-induced reduction of LOX-1 expression via inhibiting the IRE1/XBP-1 pathway, suggesting a new mechanism for beneficial roles of HDL in improving lipid metabolism.

Asymmetric dimethylarginine triggers macrophage apoptosis via the endoplasmic reticulum stress pathway.

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), is emerging as a key contributing factor in atherogenesis, a process in turn known to involve macrophage apoptosis. The aim of this study was to determine the effect of ADMA on macrophage apoptosis, with specific reference to the endoplasmic reticulum (ER) stress pathway. Macrophage apoptosis was evaluated by Annexin V- Propidium iodide (PI) and Hoechst 33258 staining assays. Levels of the ER stress marker glucose regulated protein 78 (GRP78) were characterized by western blot. Levels of the proapoptotic C/EBP-homologous protein (CHOP) were evaluated by western blot and reverse transcription polymerase chain reaction (RT-PCR), and caspase-4 activity was measured using a colorimetric protease assay kit. We observed ADMA dose- and time-dependent increases in macrophage levels of GRP78. Similar ADMA dose- and time-dependent increases were detected in intracellular caspase-4 activity and macrophage apoptosis, all of which were sensitive to treatment with siRNAs for protein kinase RNA-like ER kinase and inositol-requiring protein-1 (IRE1), the ADMA antagonist L-arginine, as well as inhibitors of eukaryotic translation initiation factor-2 (salubrinal), IRE1 (irestatin 9389), and c-Jun N-terminal kinase (SP600125). Our results indicate that ADMA triggers macrophage apoptosis via the ER stress pathway.

Ox-LDL induces endothelial cell apoptosis via the LOX-1-dependent endoplasmic reticulum stress pathway.

OBJECTIVE: To investigate the effect of lectin-like ox-LDL receptor-1 (LOX-1) on oxidized low-density lipoprotein (ox-LDL)-induced apoptosis and the involvement of the endoplasmic reticulum (ER) stress response pathway. METHODS AND RESULTS: Human umbilical vein endothelial cells were treated with 50, 100, or 200 µg/ml ox-LDL and cultured for 12, 24, or 48 h for concentration- and time-dependent studies. Cells were transfected with LOX-1 or Nox-4 shRNAs, and target proteins were inhibited with the corresponding antibodies for mechanistic studies. Active proteins and mRNAs were analyzed by Western blotting and RT-PCR, respectively. Cell apoptosis was analyzed by Annexin and Hoechst staining assays. Ox-LDL induced both apoptosis and protein expression of LOX-1 and Nox-4 through activation of ER stress sensors IRE1 and PERK, and nuclear translocation of ATF6 and their subsequent pathways were indicated by JNK, eukaryotic initiation factor 2 phosphorylation, XBP-1, and chaperone GRP78 expression; up-regulation of proapoptotic proteins CHOP and Bcl-2; and caspase-12 activity. LOX-1 gene silencing and treatment with an anti-LOX-1 antibody attenuated the effects of ox-LDL. Pretreatment with irestatin 9389, salubrinal, or AEBSF also blocked ox-LDL-induced expression of CHOP and Bcl-2 and activation of caspase-12 activity, leading to an attenuation of endothelial cell apoptosis. Furthermore, Nox-4 siRNA attenuated the up-regulated expression of GRP78, PERK, IRE1, and XBP-1 to reduce ox-LDL-induced endothelial cell apoptosis. CONCLUSIONS: LOX-1 plays a critical role in ox-LDL-induced endothelial cell apoptosis via the ER stress pathway.

Ang II induces capillary formation from endothelial cells via the AT1R-dependent inositol requiring enzyme 1 pathway.

Previous studies have demonstrated an important interaction between angiotension II type 1 receptor (AT1R) and angiotension II (Ang II) -induced capillary formation from endothelial cells and vascular endothelial growth factor (VEGF). However, the underlying mechanism remains elusive. Recent studies revealed that the unfolded protein response regulates an angiogenic response by the kidney epithelium during ischemic stress. Therefore, in the present study, we investigated the effects of Ang II on AT1R-mediated capillary formation from endothelial cells and the possible involvement of the IRE1/JNK/p38 MAPK pathway. Our results show that Ang II (1 nmol/L) induced the expression of VEGF and enhanced capillary formation from endothelial cells in the Matrigel assay. This effect was significantly depressed by the AT1R blocker losartan and different inhibitors (irestatin, IRE1 specific inhibitor; SP600125, JNK specific inhibitor; SB203580, p38 MAPK specific inhibitor) but not by the AT2R blocker PD123319. Next, we investigated the effect of Ang II on the IRE1/JNK/p38 MAPK pathway and the 78kDA glucose regulated protein 78 (GRP78) activity in HUVECs and the role of the AT1 Receptor. The results show that Ang II activated both the IRE1/JNK/p38 MAPK pathway and GRP78 binding activity. These effects were markedly inhibited by the AT1R blocker losartan. The IRE1 specific inhibitor irestatin, the JNK specific inhibitor SP600125, and the p38 MAPK specific inhibitor SB203580 significantly inhibited Ang II-induced capillary formation from endothelial cells and VEGF expression but had no effect on GRP78. Collectively, these findings suggest for the first time that Ang II promotes capillary formation by inducing the expression of VEGF via Ang II type 1 receptor-mediated stimulation of the IRE1/JNK/p38 MAPK pathway.

[Compatible low target feature coatings].

Indium tin oxide (ITO) film has low reflectance in near infrared band while high reflectance in infrared band, and its dielectric constant can be described by Drude free-electron model. SiO film has very strong absorption at certain infrared wavelength By combining them, certain spectral selectivity can be realized. In the present paper, the authors investigated SiO/ITO films in terms of spectrum selectivity, and discussed the influence of film structure on reflection spectrum. By means of the computation of reflection spectrum with characteristic matrix, the authors found that SiO/ITO film can be used as a compatible infrared low target feature coating by properly adjusting film arrangement and selecting suitable film parameters.

[A novel material with low infrared target features].

As the working mode of modem detecting system is changing from single mode to compound one, materials with certain spectral characteristics are required to meet low observable demands. In the present paper, the authors designed a novel material with low target features in infrared band based on one dimensional doped photonic crystal, and investigated the influence of the composite structure on reflection spectrum. It was found that under certain conditions, a local narrow low-reflectivity region can be formed within a wide high-reflectivity band in reflection spectrum, providing a reference for the development of a new type of infrared functional materials.