Evidence of Macrophage Foam Cell Formation by Very Low-Density Lipoprotein Receptor

Abstract

Background-Expression of the VLDL receptor, primarily in macrophages, has been confirmed in human and rabbit atherosclerotic lesions. The high binding affinity of the VLDL receptor for remnant particles implicates the VLDL receptor pathway in the foam cell formation mechanism in macrophages. This study investigates the effect of interferon (IFN)-␥ on VLDL receptor expression in phorbol-12-myristate-13-acetate (PMA)-treated THP-1, HL-60 macrophages, and human monocyte-derived macrophages. Methods and Results-THP-1 cells were induced to differentiate into macrophages by PMA treatment. IFN-␥ was added to the medium, and expression of the VLDL receptor was determined. 125 I-␤-VLDL degradation study and oil red O staining were examined. In THP-1 macrophages, VLDL receptor protein expression decreased at 2 days after PMA treatment but increased at 3 days and increased up to 5 days. Scavenger receptor proteins, which were not originally present, appeared at 3 days after PMA treatment. IFN-␥ inhibited VLDL receptor expression in a dose-and time-dependent manner in macrophages. However, no inhibitory effect was observed in monocytes. Moreover, IFN-␥ receptor mRNA increased during differentiation to macrophages.125 I-␤-VLDL degradation study and oil red O staining showed that IFN-␥ significantly inhibited foam cell formation after the uptake of ␤-VLDL. LDL receptor-related protein (LRP) and LDL receptor mRNAs were not expressed in macrophages. In PMA-treated HL-60 macrophages and human monocyte-derived macrophages, IFN-␥ also inhibited VLDL receptor expression and foam cell formation by ␤-VLDL. Conclusions-VLDL receptor expression is upregulated during monocyte-macrophage differentiation. IFN-␥ inhibits VLDL receptor expression and foam cell formation only in macrophages. Remnant particles induce macrophage foam cell formation through the VLDL receptor pathway.

Functional Protein Delivery into Neurons Using Polymeric Nanoparticles

“…Incorporation of the NPs is also saturable and dose-dependent, findings consistent with a receptor-mediated endocytic pathway (51). In all cells tested here (primary neurons, PC12 cells, and CHO cells) uptake was specifically dependent on LDL receptor, because pre-treatment of cells with an LDL receptor-specific blocking antibody (17,18) Several observations suggest that the NP cargo proteins are somehow delivered to the cytosolic compartment. The pattern of ␤-gal staining is diffuse, unlike the punctate pattern typical of the endolysosomal system.…”

“…We tested whether uptake into cultured neurons might require LDL receptor by blocking the receptor prior to treatment with nanoparticles and examining the effects on FITC-NP uptake. Pre-treatment of primary neuron cultures with a monoclonal blocking antibody against LDL receptor (17,18) inhibited incorporation of fluorescence, whereas treatment with a blocking antibody against the EGF receptor, which is also known to be specifically endocytosed (21,22), resulted in no change ( Fig. 2A).…”

“…For cells pre-treated with IgG-8H6 (generous gift of Dr. Hiroaki Hattori and Dr. Tadao Iawaki, BML Inc., Saitama, Japan), a monoclonal blocking antibody against LDL receptor (17,18), antibody was added directly to the cell medium at a concentration of 100 g/ml, and the samples were incubated for 2 h then washed three times with PBS prior to addition of the nanoparticles plus fresh medium. Anti-EGF receptor antibody 151-8AE4 (Developmental Studies Hybridoma Bank, University of Iowa) was utilized at a concentration of 250 g/ml (19) as above.…”

Interferon-γ Stimulates the Expression of the Inducible cAMP Early Repressor in Macrophages through the Activation of Casein Kinase 2

“…Further studies are required, especially in the light of the potential biological importance of such regulation. For example, IFN-␥ has been shown to inhibit macrophage foam cell formation, a critical early event in atherogenesis, at least in part by suppressing the expression of several genes that are involved in the uptake of lipoproteins, including lipoprotein lipase (LPL), very low density lipoprotein receptor, low density lipoprotein receptor-related protein, and the scavenger receptors A and CD136 (12,(23)(24)(25)(26)(27).…”

Functional impairment of two novel mutations detected in lipoprotein-associated phospholipase A2 (Lp-PLA2) deficiency patients

“…After mononuclear cells were isolated by centrifugation with Separate L (Muto Pure Chemicals Co., Osaka, Japan), monocyte-derived macrophages were cultured as previously described (Kosaka et al 2001). On day 7, the medium was replaced with RPMI supplemented with 10% bovine serum albumin, 100 U/ ml penicillin, and 100 lg/ml streptomycin.…”