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

<div><p>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.</p></div

Impact of LOX-1 overexpression on lipid uptake capability in TM-treated hepatic L02 cells.

<p>A: Flow cytometric analysis of DiI-ox-LDL uptake capability in L02 cells before (control) or after 24 h TM treatment. Mean fluorescence intensity is presented. B: Cells were transfected with pCMV6-XL5-LOX-1 plasmid (LOX-1 overexpression) or pCMV6-XL5 empty vector (N-T mock transfection control) for 24 h before treatment with TM (1 μg/mL). Untransfected cells in the absence of TM were used as a control. These data are representative of three independent experiments. **P < 0.01 vs. control; ## P < 0.01 vs. TM treatment alone. TM: tunicamycin.</p

Impacts on GRP78 and LOX-1 expression by TM treatment in hepatic L02 cells.

<p>A: Expression levels of GRP78 and LOX-1 in hepatic L02 cells exposed to different concentrations (0.1, 0.5, 1, 1.5, or 2 μg/mL) of TM. Cells were harvested at 24 h after exposure to TM, and the expression levels of GRP78, LOX-1, and β-actin were examined by western blot. B: Impact of the time course of TM treatment on expression. The cells were exposed to TM (1 μg/mL) for 6, 12, or 24 h. Expression levels of GRP78, LOX-1, and β-actin were examined by western blot. C: Immunostaining of GRP78 (red) and LOX-1 (green) in L02 cells before (control) and after TM treatment (1 μg/mL, 24 h). Nuclei were counterstained with DAPI (blue). These data are representative of three independent experiments. *<i>P</i> < 0.05; **<i>P</i> < 0.01, compared with the control. TM: tunicamycin.</p

Involvement of the IRE1/XBP-1 signaling pathway in TM-mediated downregulation of LOX-1 and lipid uptake function.

<p>A: The effects of IRE1 and XBP-1 siRNA on TM-induced IRE1, XBP-1, and LOX-1 protein expression. Cells were transfected with siRNA targeting IRE1 or XBP-1. Protein expression levels were examined by western blotting. B–D: The effects of IRE1 and XBP-1 siRNA on the TM-induced LOX-1 altered expression. Cells were transfected with siRNA targeting IRE1, XBP-1, or negative control (N-T). The mRNA expression of LOX-1 was examined by real-time PCR (B). The LOX-1 protein expression (C) and lipid uptake (D) in L02 cells were examined by immunocytochemistry and DiI-ox-LDL uptake assays, respectively. Nuclei were counterstained with DAPI (blue). These data are representative of the results of three separate experiments. **P < 0.01 vs. control (0 μg/mL TM), ## P < 0.01 vs. TM (1 μg/mL). TM: tunicamycin.</p

Proposed mechanism of HDL-mediated prevention of TM-induced downregulation of LOX-1 and lipid uptake function in hepatic cells.

<p>The ER stress inducer TM upregulates the expression of GRP78, thereby activating the IRE1/XBP-1 pathway. Activation of the IRE1/XBP-1 pathway leads to the downregulation of LOX-1 and lipid uptake function in hepatic L02 cells. HDL upregulates the TM-induced decrease of LOX-1 expression and hepatic lipid uptake, which is possibly mediated via inhibiting the IRE1/XBP-1 pathway.</p

The effect of LOX-1 expression and lipid uptake induced by HDL addition to TM-treated hepatic L02 cells.

<p>A: Hepatic L02 cells were exposed to different concentrations (1, 10, and 100 μg/mL) of HDL together with TM (1 μg/mL) for 24 h. Cells without drug treatment were used as a control. Expression levels of LOX-1 and β-actin under different treatments were examined by western blot. B: Immunostaining of LOX-1 (green) in cells treated with TM (1 μg/mL), TM (1 μg/mL) plus HDL (1 μg/mL), or TM (1 μg/mL) plus HDL (10 μg/mL) for 24 h. Cells without drug treatment were used as a control. Nuclei were counterstained with DAPI (blue). C: Flow cytometric analysis of DiI-ox-LDL uptake capability. Mean florescence intensity is presented. These data are representative of three independent experiments. **<i>P</i> < 0.01 vs. control; ^##<i>P</i> < 0.01 vs. TM treatment alone. TM: tunicamycin.</p

The impact of HDL on GRP78, IRE1, and XBP-1 expression levels in TM-treated cells.

<p>L02 cells were exposed to different concentrations (1, 10, and 100 μg/mL) of HDL together with TM (1 μg/mL) for 24 h. Cells treated with TM (1 μg/mL) alone were also included. Cells without drug treatment were used as a control. A: Expression levels of GRP78, IRE1, XBP-1, and β-actin were examined by western blot. B: Immunostaining of GRP78 (red) or IRE1 (red) in cells treated with TM (1 μg/mL), TM (1 μg/mL) plus HDL (1 μg/mL), or TM (1 μg/mL) plus HDL (10 μg/mL) for 24 h. Cells without drug treatment were used as a control. Nuclei were counterstained with DAPI (blue). Data are representative of three independent experiments. **<i>P</i> < 0.01 vs. control; ^##<i>P</i> < 0.01 vs. TM treatment alone. TM: tunicamycin.</p

A new neolignan from <i>Selaginella moellendorffii</i> Hieron

<p>A new neolignan, selamoellenin A (<b>1</b>), was isolated from the whole plants of <i>Selaginella moellendorffii</i> Hieron. The structure was elucidated on the basis of comprehensive spectroscopic methods (1D/2D NMR and HRMS). Compound <b>1</b> was evaluated for its protective effect against high glucose-induced human umbilical vein endothelial cells (HUVECs) damage <i>in vitro</i>.</p

Tailored Emission Properties of ZnTe/ZnTe:O/ZnO Core–Shell Nanowires Coupled with an Al Plasmonic Bowtie Antenna Array

The ability to manipulate light–matter interaction in semiconducting nanostructures is fascinating for implementing functionalities in advanced optoelectronic devices. Here, we report the tailoring of radiative emissions in a ZnTe/ZnTe:O/ZnO core–shell single nanowire coupled with a one-dimensional aluminum bowtie antenna array. The plasmonic antenna enables changes in the excitation and emission processes, leading to an obvious enhancement of near band edge emission (2.2 eV) and subgap excitonic emission (1.7 eV) bound to intermediate band states in a ZnTe/ZnTe:O/ZnO core–shell nanowire as well as surface-enhanced Raman scattering at room temperature. The increase of emission decay rate in the nanowire/antenna system, probed by time-resolved photoluminescence spectroscopy, yields an observable enhancement of quantum efficiency induced by local surface plasmon resonance. Electromagnetic simulations agree well with the experimental observations, revealing a combined effect of enhanced electric near-field intensity and the improvement of quantum efficiency in the ZnTe/ZnTe:O/ZnO nanowire/antenna system. The capability of tailoring light–matter interaction in low-efficient emitters may provide an alternative platform for designing advanced optoelectronic and sensing devices with precisely controlled response