Impact of TLR 2, TLR 4-activation on the Expression of ABCA1 and ABCG1 in Raw Cells

Toll-like receptors (TLR) activation is thought to modulate the macrophage cholesterol efflux and contribute to the atherosclerosis progression; however, the precise pathophysiological mechanism remains unclear. We investigated the effects of TLR2- and TLR4-activation on the expression of the ATP-binding cassette (ABC) transporters ABCA1 and ABCG1 in a mouse macrophage cell line, Raw 264.7. Both TLR2- and TLR4-activation upregulated the expression of ABCA1 mRNA but downregulated that of ABCG1 mRNA. These alterations may be mainly regulated by the following 3 cascades: (1) the TLR/myeloid differentiation primary-response protein 88/Liver X receptor pathway, which upregulated the ABCA1 mRNA; (2) NF-κB pathway, which downregulated the ABCG1 mRNA, and (3) the p38 pathway, which upregulated and stabilized ABCA1 mRNA. These cascades are involved in a complex crosstalk and result in the upregulation of ABCA1 mRNA without a change in ABCA1 protein and the down-regulation of ABCG1 mRNA leading to the increase in ABCG1 protein. These alterations, especially the induction of ABCG1 protein, may be closely involved with the development of atherosclerosis.