Angiopoietin like protein 4 expression is decreased in activated macrophages

Angiopoietin like protein 4 (ANGPTL4) inhibits lipoprotein lipase (LPL) activity. Previous studies have shown that Toll-like Receptor (TLR) activation increases serum levels of ANGPTL4 and expression of ANGPTL4 in liver, heart, muscle, and adipose tissue in mice. ANGPTL4 is expressed in macrophages and is induced by inflammatory saturated fatty acids. The absence of ANGPTL4 leads to the increased uptake of pro-inflammatory saturated fatty acids by macrophages in the mesentery lymph nodes due to the failure of ANGPTL4 to inhibit LPL activity, resulting in peritonitis, intestinal fibrosis, weight loss, and death. Here we determined the effect of TLR activation on the expression of macrophage ANGPTL4. LPS treatment resulted in a 70% decrease in ANGPTL4 expression in mouse spleen, a tissue enriched in macrophages. In mouse peritoneal macrophages, LPS treatment also markedly decreased ANGPTL4 expression. In RAW cells, a macrophage cell line, LPS, zymosan, poly I:C, and imiquimod all inhibited ANGPTL4 expression. In contrast, neither TNF, IL-1, nor IL-6 altered ANGPTL4 expression. Finally, in cholesterol loaded macrophages, LPS treatment still decreased ANGPTL4 expression. Thus, while in most tissues ANGPTL4 expression is stimulated by inflammatory stimuli, in macrophages TLR activators inhibit ANGPTL4 expression, which could lead to a variety of down-stream effects important in host defense and wound repair.