IRAK regulates macrophage foam cell formation by modulating genes involved in cholesterol uptake and efflux.

Interleukin-1 receptor-associated kinase-1 (IRAK1) is linked to the pathogenesis of atherosclerosis; however, its role in macrophage foam cell formation is not known. Therefore, the present study investigated the role of IRAK1 in lipid uptake, biosynthesis, and efflux in THP-1 derived macrophages and human monocyte-derived macrophages (HMDMs). Ox-LDL (40 mu g/mL, 15 minutes-48 hours) treatment induced time-dependent increase in IRAK1, IRAK4, and Stat1 activation in THP-1 derived macrophages. IRAK1/4 inhibitor (INH) or IRAK1 siRNA significantly attenuated cholesterol accumulation, DiI-Ox-LDL binding, and uptake while cholesterol efflux to apoAI and HDL was enhanced in THP-1 derived macrophages and HMDMs. Ox-LDL treatment significantly increased the mRNA expression of CD36, LOX-1, SR-A, ABCA1, ABCG1, Caveolin-1, CYP27A1 while that of SR-BI was decreased. IRAK1/4 inhibition or IRAK1 knockdown, however, attenuated Ox-LDL-induced CD36 expression; augmented ABCA1 and ABCG1 expression while expression of others was unaffected in THP-1 derived macrophages and HMDMs. Moreover, IRAK1/4 inhibition had no significant effect on genes involved in lipid biosynthesis. In IRAK1/4 INH pre-treated THP-1 derived macrophages Ox-LDL-induced Stat1 phosphorylation and its binding to CD36 promoter was significantly attenuated while LXR alpha expression and its binding to the ABCA1/ABCG1 locus, NFATc2 activation and its binding to ABCA1 locus was enhanced. The present study thus demonstrates that IRAK regulates lipid accumulation by modulating CD36-mediated uptake and ABCA1-, ABCG1-dependent cholesterol efflux. Therefore, IRAK1 can be a potential target for preventing macrophage foam cell formation.