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Inflammatory stress increases unmodified LDL uptake via LDL receptor: an alternative pathway for macrophage foam-cell formation

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Abstract

Objective

To investigate if inflammatory stress increases intracellular accumulation of unmodified low-density lipoprotein (LDL) in human monocyte cell line (THP-1) macrophages by disrupting the sterol regulatory element binding proteins (SREBPs) cleavage-activating protein (SCAP)-SREBP2-mediated feedback regulation of LDL receptor.

Materials and methods

THP-1 macrophages were incubated in serum-free medium in the absence or presence of LDL alone, LDL plus lipopolysaccharide (LPS) and LPS alone, then intracellular cholesterol content, tumor necrosis factor alpha level in the supernatants, mRNA and protein expression of LDL receptor, and SREBP2 and SCAP in the treated cells were assessed by Oil Red O staining, cholesterol enzymatic assay, enzyme-linked immunosorbent assay, real-time quantitative polymerase chain reaction, and Western blotting analysis, respectively.

Results

We demonstrated that LPS enhanced transformation of THP-1 macrophages into foam cells by increased uptake of unmodified LDL as evidenced by Oil Red O staining and direct assay of intracellular cholesterol. In the absence of LPS, 25 μg/ml LDL decreased LDL receptor mRNA and protein expression (p < 0.05). However, LPS enhanced LDL receptor expression, overcoming the suppression of LDL receptor induced by 25 μg/ml LDL and inappropriately increasing LDL uptake (p < 0.05). Exposure to LPS also caused overexpression of mRNA and protein of SCAP and SREBP2 (p < 0.05). These observations indicate that LPS disrupts cholesterol-mediated LDL receptor feedback regulation, permitting intracellular accumulation of unmodified LDL and causing foam-cell formation.

Conclusion

The implication of these findings is that inflammatory stress may contribute to intracellular LDL accumulation in THP-1 macrophages without previous modification of LDL.

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Acknowledgements

We acknowledge the support of the National Nature Science Foundation of China (nos. 30670869 and 30772295; Key Program, no. 30530360), National Basic Research Program of China (973 Program, nos. 2006CB503907, 2008CB517309), and Natural Science Foundation Project of CQ CSTC (2008BA5016).

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Authors and Affiliations

  1. Centre for Lipid Research, Key Laboratory of Molecular Biology on Infectious Diseases, Ministry of Education, Chongqing Medical University, Chongqing, China

    Qiang Ye, Yaxi Chen, Han Lei & Xiong Z. Ruan

  2. Department of Cardiology, First Affiliated Hospital, Chongqing Medical University, Chongqing, China

    Qiang Ye & Han Lei

  3. Centre for Clinical Research, First Affiliated Hospital, Chongqing Medical University, Chongqing, China

    Qing Liu

  4. Centre for Nephrology, Royal Free and University College Medical School, UCL, London, UK

    John F. Moorhead, Zac Varghese & Xiong Z. Ruan

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  1. Qiang Ye
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  2. Yaxi Chen
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  3. Han Lei
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  7. Xiong Z. Ruan
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Correspondence to Han Lei or Xiong Z. Ruan.

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Responsible Editor: M. Katori.

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Ye, Q., Chen, Y., Lei, H. et al. Inflammatory stress increases unmodified LDL uptake via LDL receptor: an alternative pathway for macrophage foam-cell formation. Inflamm. Res. 58, 809–818 (2009). https://doi.org/10.1007/s00011-009-0052-4

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  • DOI: https://doi.org/10.1007/s00011-009-0052-4

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