RESUMO
High density lipoprotein (HDL) has been proposed to be internalized and to promote reverse cholesterol transport in endothelial cells (ECs). However, the mechanism underlying these processes has not been studied. In this study, we aim to characterize HDL internalization and cholesterol efflux in ECs and regulatory mechanisms. We found mature HDL particles were reduced in patients with coronary artery disease (CAD), which was associated with an increase in CC-chemokine ligand 2 (CCL2). In cultured primary human coronary artery endothelial cells and human umbilical vein endothelial cells, we determined that CCL2 suppressed the binding (4 °C) and association (37 °C) of HDL to/with ECs and HDL cellular internalization. Furthermore, CCL2 inhibited [(3)H]cholesterol efflux to HDL/apoA1 in ECs. We further found that CCL2 induced CC-chemokine receptor 2 (CCR2) expression and siRNA-CCR2 reversed CCL2 suppression on HDL binding, association, internalization, and on cholesterol efflux in ECs. Moreover, CCL2 induced p42/44 mitogen-activated protein kinase (MAPK) phosphorylation via CCR2, and p42/44 MAPK inhibition reversed the suppression of CCL2 on HDL metabolism in ECs. Our study suggests that CCL2 was elevated in CAD patients. CCL2 suppressed HDL internalization and cholesterol efflux via CCR2 induction and p42/44 MAPK activation in ECs. CCL2 induction may contribute to impair HDL function and form atherosclerosis in CAD.
Assuntos
Quimiocina CCL2/metabolismo , Colesterol/metabolismo , Doença da Artéria Coronariana/metabolismo , Regulação da Expressão Gênica , Células Endoteliais da Veia Umbilical Humana/metabolismo , Lipoproteínas HDL/metabolismo , Sistema de Sinalização das MAP Quinases , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Receptores CCR2/metabolismo , Apolipoproteína A-I/metabolismo , Doença da Artéria Coronariana/patologia , Ativação Enzimática , Feminino , Células Endoteliais da Veia Umbilical Humana/patologia , Humanos , MasculinoRESUMO
Monocyte chemoattractant protein-1 (MCP-1) plays crucial roles at multiple stages of atherosclerosis. We hypothesized that MCP-1 might impair the reverse cholesterol transport (RCT) capacity of HepG2 cells by decreasing the cell-surface protein expression of ATP binding cassette A1 (ABCA1), ATP binding cassette G1 (ABCG1), and scavenger receptor class B type I (SR-BI). MCP-1 reduced the total protein and mRNA levels of ABCA1 and SR-BI, but not of ABCG1. MCP-1 decreased the cell-surface protein expression of ABCA1, ABCG1, and SR-BI in dose-dependent and time-dependent manners, as measured using cell-surface biotinylation. We further studied the phosphoinositide 3-kinase (PI3K)/serine/threonine protein kinase Akt pathway in regulating receptor trafficking. Both the translation and transcription of ABCA1, ABCG1, and SR-BI were not found to be regulated by the PI3K/Akt pathway. However, the cell-surface protein expression of ABCA1, ABCG1, and SR-BI could be regulated by PI3K activity, and PI3K activation corrected the MCP-1-induced decreases in the cell-surface protein expression of ABCA1, ABCG1, and SR-BI. Moreover, we found that MCP-1 decreased the lipid uptake by HepG2 cells and the ABCA1-mediated cholesterol efflux to apoA-I, which could be reversed by PI3K activation. Our data suggest that MCP-1 impairs RCT activity in HepG2 cells by a PI3K/Akt-mediated posttranslational regulation of ABCA1, ABCG1, and SR-BI cell-surface expression.
Assuntos
Transportadores de Cassetes de Ligação de ATP/genética , Aterosclerose/genética , Quimiocina CCL2/genética , Receptores Depuradores Classe B/genética , Transportador 1 de Cassete de Ligação de ATP , Membro 1 da Subfamília G de Transportadores de Cassetes de Ligação de ATP , Transportadores de Cassetes de Ligação de ATP/metabolismo , Aterosclerose/patologia , Quimiocina CCL2/metabolismo , Colesterol/metabolismo , Elafina/metabolismo , Regulação da Expressão Gênica , Células Hep G2 , Humanos , Proteína Oncogênica v-akt/metabolismo , Processamento de Proteína Pós-Traducional , Receptores Depuradores Classe B/metabolismo , Transdução de SinaisRESUMO
The ATP-binding cassette A1 (ABCA1) transporter plays a major role in the efflux of lipids by mediating the cellular transport of phospholipids and cholesterol to lipid-poor/lipid-free apolipoprotein A-I (apoA-I) particles and thereby exerting important anti-atherogenic effects. Although the mechanism whereby ABCA1 mediates cholesterol efflux is not completely understood, numerous studies have shown that, in addition to apoA-I, the expression level of the total or cell surface ABCA1 protein is a determining factor for the activity of ABCA1-mediated cholesterol efflux, and defects in ABCA1-mediated cholesterol efflux lead to various pathological conditions in different cells, including cardiovascular and metabolic disorders. It has been widely demonstrated that a growing list of natural and synthetic substances and metabolic regulators that modulate the expression of ABCA1 not only act directly on the ABCA1 gene promoter, but also occurs at the post-transcriptional level via micro-RNAs and post-translationally through the stabilization or localization of the protein. The complex regulatory network of ABCA1 results in promoting or suppressing cholesterol efflux from cells, therefore we speculate that the ABCA1 transporter is emerging as a novel therapeutic target for cardiovascular and metabolic disorders. Thus, ABCA1 is a key modulator of cellular cholesterol efflux and contributes to functional disorders in different types of cells.