Lipopolysaccharide Down-regulate ABCA1 May Relate With TLR4-NF-κB Pathway In Foam Cells

Objective: When the primary receptor Toll-like receptor 4(TLR4) binds to Lip polysaccharide(LPS) can activate several signal transduction pathway including nucleus factor-κB(NF-κB) pathway in cells and associated with inflammatory activation in human atherosclerotic lesions. This study was to investigate the changes of cholesterol efflux, ATP-binding cassette transporter A1 (ABCA1) mRNA and protein expression in THP-1 macrophage derived foam cells after treated with LPS, and to discover whether those effections have relationship with TLR4-NF-κB pathway in LXRα-independent manner.Methods: We first induced THP-1 cells to become macrophages by phorbol. Then THP-1 macrophages were induced to be foam cells by ox-LDL. The foam cells were exposed to LPS with increasing levels(0, 0.2, 2, 20, 200ng/ml) for 24 hours or exposed to 20ng/ml LPS for increasing periods of time(0,6,12,24hours). Our experiment also used 20ng/ml LPS along or together with 20μM N-p-Tosyl-L-phenylalanine chloromethyl ketone (TPCK) to pretreat (2hours) THP-1 macrophage derived foam cells for 24 hours. Cellular lipid accumulation was determined by Oil Red O staining and high performance liquid chromatography analysis. Cholesterol efflux was determined by FJ-2107P type liquid scintillator. ABCA1, TLR4 and LXRαmRNA were measured by reverse transcriptase-polymerase chain reaction. Western blotting was used to determine protein levels for ABCA1, LXRαand intranuclear NF-κB p65.Results: Our experiments show that the lipid accumulation was increased but the cellular cholesterol efflux was decreased in THP-1 macrophage derived foam cells after exposured to LPS for 24 hours. LPS can decrease the expression of ABCA1 mRNA but increase TLR4 mRNA in dose- and time-dependent manner. ABCA1 protein levels were the same as the mRNA expression. Intranuclear NF-κB p65 were increased by LPS. But these changes can be reversed partly by TPCK pretreated. LPS and TPCK can not effect LXRαmRNA and protein expression.Conclusions: These findings suggest that LPS can down-regulate the expression of ABCA1 mRNA and protein, promote the accumulation of lipid and decrease cellular cholesterol efflux in THP-1 macrophage derived foam cells. The mechanism may have relationship with TLR4-NF-κB pathway in LXRα-independent manner.