Saturated fatty acids activate TLR-mediated proinflammatory signaling pathways

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Saturated fatty acids (SFAs) have been implicated in activating Toll-like receptors (TLRs) 2 and 4.
• Concerns exist that SFA-induced TLR activation might be due to contaminants in bovine serum albumin (BSA) used for solubilization, casting doubt on their direct proinflammatory effects.

Purpose of the Study:

• To investigate whether SFAs directly activate TLRs without BSA, thereby clarifying their role in inflammation.
• To determine the specific TLRs and signaling pathways involved in SFA-mediated activation.

Main Methods:

• Culturing THP1 monocytes and RAW264.7 macrophages in low fetal bovine serum (FBS) medium.
• Treating cells with sodium palmitate (C16:0) or laurate (C12:0) with or without BSA.
• Assessing phosphorylation of key signaling molecules (IKKα, JNK, ERK, NF-κB p65) and TLR target gene expression.
• Utilizing polymyxin B and MyD88(-/-) macrophages to confirm specificity.

Main Results:

• Sodium palmitate and laurate induced TLR signaling pathway activation and target gene expression in monocytes and macrophages without BSA.
• C12:0 activated TLR2 (dimerized with TLR1 or TLR6) and TLR4.
• BSA-solubilized C16:0, not sodium C16:0, was required for activation in adherent RAW264.7 cells.
• SFAs specifically activate TLR2 and TLR4, independent of BSA or fatty acid preparation contaminants.

Conclusions:

• SFA-induced activation of TLR2 and TLR4 is a direct, fatty acid-specific effect.
• This activation is not attributable to contaminants in BSA or fatty acid preparations.
• SFAs play a direct role in initiating inflammatory responses through TLR signaling.