Role of PPAR-gamma in the Modulation of CD36 and FcgammaRII induced by LDL with Low and High Degrees of Oxidation During the Differentiation of the Monocytic THP-1 Cell Line

Abstract

Scavenger or Fcγ receptors are important for capture and clearance of modified LDL particles by monocytes/macrophages. Uptake via scavenger receptors is not regulated by intracellular levels of cholesterol and in consequence, macrophages develop into foam cells in the arterial intima. The levels of scavenger receptor CD36 are increased in atherosclerotic lesions and there is evidence that some components of oxLDL auto-regulate the expression of this receptor. Fcγ receptor expression is increased in cardiovascular diseases but it is not known weather their expression is regulated by oxLDL. The biological properties of oxLDLs vary depending on the degree of oxidation. In the present study we investigated the effect of LDL particles showing extensive or low oxidation (HoxLDL and LoxLDL) on the expression of CD36 and FcγRII in a human monocytic cell line (THP-1), differentiated or not to macrophage, and the involvement of PPARγ. It was found that both forms of oxLDL are able to increase the expression of CD36 and FcγRII and that this effect is dependent on the degree of oxidation and of the stage of cell differentiation (monocyte or macrophage). We also showed that the increased expression of FcγRII is dependent on PPARγ whereas that of the CD36 is independent of PPARγ.

High-Density Lipoprotein Inhibits the Uptake of Modified Low- Density Lipoprotein and the Expression of CD36 and FcγRI

“…Macrophage differentiation is a necessary step for atherosclerosis 13) and it is associated with the up-regulation of pattern recognition receptors for innate immunity, including scavenger receptors (SR) 1,2) . The formation of lipid-laden foam cells via the internalization of lipoproteins, especially LDL and its modified counterparts in the intima by scavenger receptors, represents a key event in the formation of an atherosclerotic lesion 2,10,42) .…”

“…The oxidation of LDL was achieved according to our standard protocol 8,13,14) . In short, 2 mg/mL LDL were dialyzed overnight against PBS without EDTA, and then incubated with 20 M CuSO4 for 18 hours at 37 .…”

“…The extent of LDL, oxLDL, enzLDL and HDL oxidation was evaluated by measuring two parameters: the production of thiobarbituric acid reactive substances (TBARS) 13,32) and the formation of conjugated dienes 33) . TBARS content is related to lipid peroxide levels.…”

“…The chromatographic profiles of LDL and mLDL conjugated or not with FITC were analyzed by anion exchange column (Resource-Q -FPLC; Amersham Biosciences), according to the previously established procedure 13) . Two solutions were used for elution: A, Tris-HCl 0.01 M, pH 7.4, and B, NaCl 1 M in buffer A.…”

“…In this study we decided to analyze the class B scavenger receptor CD36 that mediates the uptake of a broad variety of ligands, including oxidized LDL (oxLDL) and the Fc receptor, a known mediator of phagocytosis involved in the uptake of lipoproteins [10][11][12] . In the case of mLDL, the uptake and subsequent formation of foam cells can be either a rapid process involving already present receptors or a delayed process with the participation of mLDL-inducible receptors [13][14][15][16] . Modifications of LDL involve both oxidative modifications, caused by oxygen reactive radical species, and enzymatic alterations processed by serumor cell-associated proteolytic enzymes 4,[17][18][19][20] .…”