Ox-LDL Upregulates IL-6 Expression by Enhancing NF-κB in an IGF2-Dependent Manner in THP-1 Macrophages

Interleukin 6 (IL-6) is a pro-inflammatory cytokine that is well established as a vital factor in determining the risk of coronary heart disease and pathogenesis of atherosclerosis. Moreover, accumulating evidences have shown that oxidized low-density lipoprotein (ox-LDL) can promote IL-6 expression in macrophages. Nevertheless, the underlying mechanism of how ox-LDL upregulates IL-6 expression remains largely unexplained. We found that the expression of insulin-like growth factor 2 (IGF2), nuclear factor kappa B (NF-κB), and IL-6 was upregulated at both the messenger RNA (mRNA) and protein levels in a dose-dependent manner when treated with 0, 25, 50, or 100 μg/mL of ox-LDL for 48 h in THP-1 macrophages. Moreover, overexpression of IGF2 significantly upregulated NF-κB and IL-6 expressions in THP-1 macrophages. However, the upregulation of NF-κB and IL-6 expressions induced by ox-LDL were significantly abolished by IGF2 small interfering RNA (siRNA) in THP-1 macrophages. Further studies indicated the upregulation of IL-6 induced by ox-LDL could be abolished when treated with NF-κB siRNA in THP-1 macrophages. Ox-LDL might upregulate IL-6 in the cell and its secretion via enhancing NF-κB in an IGF2-dependent manner in THP-1 macrophages.