FSL-1, a Toll-like Receptor 2/6 Agonist, Induces Expression of Interleukin-1α in the Presence of 27-hydroxycholesterol

We investigated the question of whether cholesterol catabolite can influence expression of inflammatory cytokines via Toll-like receptors (TLR) in monocytic cells. Treatment of THP-1 monocytic cells with 27-hydroxycholesterol (27OHChol) resulted in induction of gene transcription of TLR6 and elevated level of cell surface TLR6. Addition of FSL-1, a TLR6 agonist, to 27OHChol-treated cells resulted in transcription of the IL-1α gene and enhanced secretion of the corresponding gene product. However, cholesterol did not affect TLR6 expression, and addition of FSL-1 to cholesterol-treated cells did not induce expression of IL-1α. Using pharmacological inhibitors, we investigated molecular mechanisms underlying the expression of TLR6 and IL-1α. Treatment with Akt inhibitor IV or U0126 resulted in significantly attenuated expression of TLR6 and IL-1α induced by 27OHChol and 27OHChol plus FSL-1, respectively. In addition, treatment with LY294002, SB202190, or SP600125 resulted in significantly attenuated secretion of IL-1α. These results indicate that 27OHChol can induce inflammation by augmentation of TLR6-mediated production of IL-1α in monocytic cells via multiple signaling pathways.