Adipocyte Fatty Acid-binding Protein Modulates Inflammatory Responses in Macrophages through a Positive Feedback Loop Involving c-Jun NH2-terminal Kinases and Activator Protein-1

Abstract

Adipocyte fatty acid-binding protein (A-FABP) has emerged as an important mediator of inflammation in macrophages. Macrophage-selective ablation of A-FABP alone is sufficient to prevent the development of high cholesterol diet-induced atherosclerosis in apoE-deficient mice. However, the precise mechanisms whereby A-FABP modulates inflammation remain elusive. Here, we report that A-FABP forms a finely tuned positive loop between JNK and activator protein-1 (AP-1) to exacerbate lipopolysaccharide (LPS)-induced inflammatory responses in macrophages. Real time PCR and luciferase reporter analysis showed that LPS induced A-FABP expression through transcriptional activation. This effect was mediated by JNK, which promoted the recruitment of c-Jun to a highly conserved AP-1 consensus binding motif located within the proximal region of the A-FABP promoter. LPS-induced transactivation of the A-FABP gene was diminished by either pharmacological inhibition of JNK or knocking down c-Jun or by mutating the AP-1 recognition site within the proximal region (-122 to -116 bp) of the A-FABP promoter. Conversely, the LPS-evoked phosphorylation of JNK, activation of AP-1, and production of pro-inflammatory cytokines were markedly attenuated by pharmacological or genetic suppression of A-FABP in macrophages. Furthermore, the LPS-induced elevation in A-FABP expression could also be prevented by the selective A-FABP inhibitor BMS309403. These findings support the notion that pharmacological inhibition of A-FABP represents a valid strategy for treating inflammation-related disorders such as atherosclerosis.