Quercetin modulates toll-like receptor-mediated protein kinase signaling pathways in oxLDL-challenged human PBMCs and regulates TLR-activated atherosclerotic inflammation in hypercholesterolemic rats
Authors: Shobha Bhaskar
A Helen
Journal: Molecular and Cellular Biochemistry (2016)
Discipline: MOLECULAR BIOLOGY & GENETICS
Keywords: Atherosclerosis; Cytokines; Inflammation; MAPK; NF-κB
Affiliations: Department of Biochemistry, University of Kerala, Thiruvananthapuram, Kerala, India., Department of Biochemistry, University of Kerala, Thiruvananthapuram, Kerala, India. .

Abstract:  Toll-like receptors (TLRs) are pattern recognition receptors that have a unique and essential function in innate immunity. The effect of quercetin on TLR-mediated downstream signaling mechanism and its effect on TLR-mediated MAP kinase and Akt pathways were studied in oxLDL-stimulated hPBMCs using specific inhibitors. The pretreatment of hPBMCs with specific TLR inhibitor, CLI-095, decreased the NF-κB nuclear translocation and TNF-α release by oxLDL. When the cells treated with inhibitor and quercetin together, the inhibition was more effective. The specific inhibitor for p38 MAPK, SB203580, reduced the phosphorylated p38 level and decreased the NF-κB activation and TNF-α release by oxLDL-challenged hPBMCs. This inhibitor showed enhanced inhibition when treated with quercetin together. The inhibitors for ERK1/2, PD98059, and for JNK, SP606125, also showed inhibitory effect on NF-κB activation and TNF-α release by oxLDL-simulated hPBMCs. Quercetin supplementation enhanced the inhibition of nuclear translocation of NF-κB and the release of cytokines. TLR4 inhibition study confirmed the downstream signaling mechanism mediated by NF-κB which is involved in the oxLDL-induced inflammatory response, and quercetin suppresses the cytokine, TNF-α release by modulating TLR-NF-κB signaling pathway. In addition to NF-κB signaling pathway, inflammation induced by oxLDL was also related to the activation of p38MAPK, ERK1/2 and JNK, and Akt pathways, and the protective effect of quercetin may be also related to the inhibition of activation of these pathways. Quercetin significantly downregulated the elevated mRNA expression of TLRs and cytokine TNF-α in HCD-fed atherosclerotic rats in vivo. As quercetin possesses inhibition on both TLR-NF-κB signaling pathway and TLR-mediated MAPK pathway, it is evident that it can be used as a therapeutic agent to ameliorate atherosclerotic inflammation. Since quercetin is the major flavonoid and forms the backbone of many other flavonoids and this study provides strong evidence that it has potent anti-inflammatory effect, quercetin may be a promising agent for the prevention and treatment of atherosclerosis and promote health by reducing harmful vascular inflammation. 

Retracted: No

PubPeer comments:
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 Figure 3G. The  Ctrlsh+TGF-B ligand and  MEG3sh panels appear to shown a large area of overlap, although they show a slightly tilted point of view. Could the authors please check? Shown with red boxes. ![file] , 
 #3 Dear Elisabeth Thank you very much for notifying us the mistake in figure 3G panel of our manuscript. After carefully going through the images we realised that images for the indicated panel that is Ctrlsh+TGF-u03b2 ligand and MEG3sh got duplicated during compilation of the figures, and we failed to identify this mistake during the manuscript preparation and subsequent revisions as well. We have now contacted the chief editor of Nature Communications with the correct image corresponding to figure 3g. We hope that the correction will be updated. Chandrasekhar Kanduri , 
 #4 Dr. Kanduri: Thank you for your reply. 1. Are you able to explain an assembly process that involves rotating images as appears to have occurred in this case? This is not simply the same image published twice. 2. Can you provide the correct image here and indicate which image is the incorrect one? , 
 #5 There are some exposure (could be from digital re-sampling however) artifact differences between the two images, and each image has information in it that is not present in the other one. Could certainly be possible that multiple images were taken of the same region on each plate and got mixed up. Trying to be charitable. , 
 #5 Both the images from the previous panel are from MEG3sh and were mistakenly included as Controlsh+ligand. We have not tilted the image and we included the image as is. Two images were taken from the same field and mistakenly included in the figure. If you look at the graph, the quantification of cells in Controlsh+ligand panel does not support the data in any way and it can easily noticed. Moreover, there are equal number of cells in the two images and that is wrong. Unfortunately, it was not noticed by reviewers.These older image Controlsh+ligand does not support our bar graph, located in the right panel (figure3g). I would like to emphasize that our observation that tumor suppressor role of MEG3 in breast cancer verified by several labs across the world (a few of many published articles: PMID- 28463794, 28635399, 30556250; 30389444, 27166155). ![file] , 
 November 2019 Correction: https: www.nature.com articles s41467-019-13200-7  This article contains an error in Fig. 3g. The image in the Ctrlsh+TGF-u03b2 ligand panel was inadvertently duplicated from the image in the MEG3sh panel. The correct version of this figure appears below as Fig. 1. ,