Inflammation Research

, Volume 58, Issue 11, pp 809–818 | Cite as

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

  • Qiang Ye
  • Yaxi Chen
  • Han Lei
  • Qing Liu
  • John F. Moorhead
  • Zac Varghese
  • Xiong Z. Ruan
Original Research Paper



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.


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.


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


THP-1 macrophages Inflammation Atherosclerosis LDL receptor SREBP cleavage-activating protein 



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).


  1. 1.
    De Winther MP, Gijbels MJ, Van Dijk KW, Havekes LM, Hofker MH. Transgenic mouse models to study the role of the macrophage scavenger receptor class A in atherosclerosis. Int J Tissue React. 2000;22:85–91.PubMedGoogle Scholar
  2. 2.
    Nicholson AC, Febbraio M, Han J, Silverstein RL, Hajjar DP. CD36 in atherosclerosis. The role of a class B macrophage scavenger receptor. Ann N Y Acad Sci. 2000;902:128–31.PubMedCrossRefGoogle Scholar
  3. 3.
    Krieger M. Molecular flypaper and atherosclerosis: structure of the macrophage scavenger receptor. Trends Biochem Sci. 1992;17:141–6.PubMedCrossRefGoogle Scholar
  4. 4.
    Krieger M, Abrams JM, Lux A, Steller H. Molecular flypaper, atherosclerosis, and host defense: structure and function of the macrophage scavenger receptor. Cold Spring Harb Symp Quant Biol. 1992;57:605–9.PubMedGoogle Scholar
  5. 5.
    Liu B, Xie C, Richardson JA, Turley SD, Dietschy JM. Receptor-mediated and bulk-phase endocytosis cause macrophage and cholesterol accumulation in Niemann-Pick C disease. J Lipid Res. 2007;48:1710–23.PubMedCrossRefGoogle Scholar
  6. 6.
    Smith JR, Osborne TF, Goldstein JL, Brown MS. Identification of nucleotides responsible for enhancer activity of sterol regulatory element in low density lipoprotein receptor gene. J Biol Chem. 1990;265:2306–10.PubMedGoogle Scholar
  7. 7.
    Brown MS, Goldstein JL. A receptor-mediated pathway for cholesterol homeostasis. Science. 1986;232:34–47.PubMedCrossRefGoogle Scholar
  8. 8.
    Briggs MR, Yokoyama C, Wang X, Brown MS, Goldstein JL. Nuclear protein that binds sterol regulatory element of low density lipoprotein receptor promoter. I. Identification of the protein and delineation of its target nucleotide sequence. J Biol Chem. 1993;268:14490–6.PubMedGoogle Scholar
  9. 9.
    Goldstein JL, Brown MS. The LDL receptor and the regulation of cellular cholesterol metabolism. J Cell Sci Suppl. 1985;3:131–7.PubMedGoogle Scholar
  10. 10.
    Wang X, Sato R, Brown MS, Hua X, Goldstein JL. SREBP-1, a membrane-bound transcription factor released by sterol-regulated proteolysis. Cell. 1994;77:53–62.PubMedCrossRefGoogle Scholar
  11. 11.
    Yokoyama C, Wang X, Briggs MR, Admon A, Wu J, Hua X, et al. SREBP-1, a basic-helix-loop-helix-leucine zipper protein that controls transcription of the low density lipoprotein receptor gene. Cell. 1993;75:187–97.PubMedGoogle Scholar
  12. 12.
    Wang X, Briggs MR, Hua X, Yokoyama C, Goldstein JL, Brown MS. Nuclear protein that binds sterol regulatory element of low density lipoprotein receptor promoter. II. Purification and characterization. J Biol Chem. 1993;268:14497–504.PubMedGoogle Scholar
  13. 13.
    Sanchez HB, Yieh L, Osborne TF. Cooperation by sterol regulatory element-binding protein and Sp1 in sterol regulation of low density lipoprotein receptor gene. J Biol Chem. 1995;270:1161–9.PubMedCrossRefGoogle Scholar
  14. 14.
    Hua X, Yokoyama C, Wu J, Briggs MR, Brown MS, Goldstein JL, et al. SREBP-2, a second basic-helix-loop-helix-leucine zipper protein that stimulates transcription by binding to a sterol regulatory element. Proc Natl Acad Sci USA. 1993;90:11603–7.PubMedCrossRefGoogle Scholar
  15. 15.
    Nohturfft A, Bose-Boyd RA, Scheek S, Goldstein JL, Brown MS. Sterols regulate cycling of SREBP cleavage-activating protein (SCAP) between endoplasmic reticulum and Golgi. Proc Natl Acad Sci USA. 1999;96:11235–40.PubMedCrossRefGoogle Scholar
  16. 16.
    Brown MS, Goldstein JL. A proteolytic pathway that controls the cholesterol content of membranes, cells, and blood. Proc Natl Acad Sci USA. 1999;96:11041–8.PubMedCrossRefGoogle Scholar
  17. 17.
    Nohturfft A, Brown MS, Goldstein JL. Topology of SREBP cleavage-activating protein, a polytopic membrane protein with a sterol-sensing domain. J Biol Chem. 1998;273:17243–50.PubMedCrossRefGoogle Scholar
  18. 18.
    Hua X, Nohturfft A, Goldstein JL, Brown MS. Sterol resistance in CHO cells traced to point mutation in SREBP cleavage-activating protein. Cell. 1996;87:415–26.PubMedCrossRefGoogle Scholar
  19. 19.
    Goldstein JL, Rawson RB, Brown MS. Mutant mammalian cells as tools to delineate the sterol regulatory element-binding protein pathway for feedback regulation of lipid synthesis. Arch Biochem Biophys. 2002;397:139–48.PubMedCrossRefGoogle Scholar
  20. 20.
    Yang T, Goldstein JL, Brown MS. Overexpression of membrane domain of SCAP prevents sterols from inhibiting SCAP.SREBP exit from endoplasmic reticulum. J Biol Chem. 2000;275:29881–6.PubMedCrossRefGoogle Scholar
  21. 21.
    Sakai J, Rawson RB. The sterol regulatory element-binding protein pathway: control of lipid homeostasis through regulated intracellular transport. Curr Opin Lipidol. 2001;12:261–6.PubMedCrossRefGoogle Scholar
  22. 22.
    Fernando RL, Varghese Z, Moorhead JF. Oxidation of low-density lipoproteins by rat mesangial cells and the interaction of oxidized low-density lipoproteins with rat mesangial cells in vitro. Nephrol Dial Transplant. 1993;8:512–8.PubMedGoogle Scholar
  23. 23.
    Wheeler DC, Fernando RL, Gillett MP, Zaruba J, Persaud J, Kingstone D, et al. Characterisation of the binding of low-density lipoproteins to cultured rat mesangial cells. Nephrol Dial Transplant. 1991;6:701–8.PubMedGoogle Scholar
  24. 24.
    Moorhead JF, Chan MK, El-Nahas M, Varghese Z. Lipid nephrotoxicity in chronic progressive glomerular and tubulo-interstitial disease. Lancet. 1982;2:1309–11.PubMedCrossRefGoogle Scholar
  25. 25.
    Diamond JR. Analogous pathobiologic mechanisms in glomerulosclerosis and atherosclerosis. Kidney Int Suppl. 1991;31:S29–34.PubMedGoogle Scholar
  26. 26.
    Diamond JR, Karnovsky MJ. Focal and segmental glomerulosclerosis: analogies to atherosclerosis. Kidney Int. 1988;33:917–24.PubMedCrossRefGoogle Scholar
  27. 27.
    Salmon JE, Roman MJ. Subclinical atherosclerosis in rheumatoid arthritis and systemic lupus erythematosus. Am J Med. 2008;121:S3–8.PubMedCrossRefGoogle Scholar
  28. 28.
    Bongu A, Chang E, Ramsey-Goldman R. Can morbidity and mortality of SLE be improved? Best Pract Res Clin Rheumatol. 2002;16:313–32.PubMedCrossRefGoogle Scholar
  29. 29.
    Lowrie EG, Lew NL. Death risk in hemodialysis patients: the predictive value of commonly measured variables and an evaluation of death rate differences between facilities. Am J Kidney Dis. 1990;15:458–82.PubMedGoogle Scholar
  30. 30.
    Liu Y, Coresh J, Eustace JA, Longenecker JC, Jaar B, Fink NE, et al. Association between cholesterol level and mortality in dialysis patients: role of inflammation and malnutrition. JAMA. 2004;291:451–9.PubMedCrossRefGoogle Scholar
  31. 31.
    Ruan XZ, Moorhead JF, Tao JL, Ma KL, Wheeler DC, Powis SH, et al. Mechanisms of dysregulation of low-density lipoprotein receptor expression in vascular smooth muscle cells by inflammatory cytokines. Arterioscler Thromb Vasc Biol. 2006;26:1150–5.PubMedCrossRefGoogle Scholar
  32. 32.
    Ruan XZ, Varghese Z, Powis SH, Moorhead JF. Dysregulation of LDL receptor under the influence of inflammatory cytokines: a new pathway for foam cell formation. Kidney Int. 2001;60:1716–25.PubMedCrossRefGoogle Scholar
  33. 33.
    Ruan XZ, Varghese Z, Fernando R, Moorhead JF. Cytokine regulation of low-density lipoprotein receptor gene transcription in human mesangial cells. Nephrol Dial Transplant. 1998;13:1391–7.PubMedCrossRefGoogle Scholar
  34. 34.
    Chen Y, Ruan XZ, Li Q, Huang A, Moorhead JF, Powis SH, et al. Inflammatory cytokines disrupt LDL-receptor feedback regulation and cause statin resistance: a comparative study in human hepatic cells and mesangial cells. Am J Physiol Renal Physiol. 2007;293:F680–7.PubMedCrossRefGoogle Scholar
  35. 35.
    Gallo LL, Atasoy R, Vahouny GV, Treadwell CR. Enzymatic assay for cholesterol ester hydrolase activity. J Lipid Res. 1978;19:913–6.PubMedGoogle Scholar
  36. 36.
    Gamble W, Vaughan M, Kruth HS, Avigan J. Procedure for determination of free and total cholesterol in micro- or nanogram amounts suitable for studies with cultured cells. J Lipid Res. 1978;19:1068–70.PubMedGoogle Scholar
  37. 37.
    Mikita T, Porter G, Lawn RM, Shiffman D. Oxidized low density lipoprotein exposure alters the transcriptional response of macrophages to inflammatory stimulus. J Biol Chem. 2001;276:45729–39.PubMedCrossRefGoogle Scholar
  38. 38.
    Umetani N, Kanayama Y, Okamura M, Negoro N, Takeda T. Lovastatin inhibits gene expression of type-I scavenger receptor in THP-1 human macrophages. Biochim Biophys Acta. 1996;1303:199–206.PubMedGoogle Scholar
  39. 39.
    Yang L, Yang JB, Chen J, Yu GY, Zhou P, Lei L, et al. Enhancement of human ACAT1 gene expression to promote the macrophage-derived foam cell formation by dexamethasone. Cell Res. 2004;14:315–23.PubMedCrossRefGoogle Scholar
  40. 40.
    Kruth HS, Huang W, Ishii I, Zhang WY. Macrophage foam cell formation with native low density lipoprotein. J Biol Chem. 2002;277:34573–80.PubMedCrossRefGoogle Scholar
  41. 41.
    Evensen SA, Galdal KS, Nilsen E. LDL-induced cytotoxicity and its inhibition by anti-oxidant treatment in cultured human endothelial cells and fibroblasts. Atherosclerosis. 1983;49:23–30.PubMedCrossRefGoogle Scholar
  42. 42.
    Sobal G, Menzel J, Sinzinger H. Why is glycated LDL more sensitive to oxidation than native LDL? A comparative study. Prostaglandins Leukot Essent Fatty Acids. 2000;63:177–86.PubMedCrossRefGoogle Scholar
  43. 43.
    Yang T, Espenshade PJ, Wright ME, Yabe D, Gong Y, Aebersold R, et al. Crucial step in cholesterol homeostasis: sterols promote binding of SCAP to INSIG-1, a membrane protein that facilitates retention of SREBPs in ER. Cell. 2002;110:489–500.PubMedCrossRefGoogle Scholar

Copyright information

© Birkhäuser Verlag, Basel/Switzerland 2009

Authors and Affiliations

  1. 1.Centre for Lipid Research, Key Laboratory of Molecular Biology on Infectious Diseases, Ministry of EducationChongqing Medical UniversityChongqingChina
  2. 2.Department of Cardiology, First Affiliated HospitalChongqing Medical UniversityChongqingChina
  3. 3.Centre for Clinical Research, First Affiliated HospitalChongqing Medical UniversityChongqingChina
  4. 4.Centre for NephrologyRoyal Free and University College Medical School, UCLLondonUK

Personalised recommendations