Regulation of iron metabolism in murine J774 macrophages: Role of nitric oxide-dependent and independent pathways following activation with gamma interferon and lipopolysaccharide

To elucidate the pathways by which nitric oxide (NO) influences macrophage iron metabolism, the uptake, release, and intracellular distribution of iro n in the murine macrophage cell line J774 has been investigated, together w ith transferrin receptor (TfR) expression and iron-regulatory protein (IRP1 and IRP2) activity. Stimulation of macrophages with interferon-gamma (IFN- gamma) and/or lipopolysaccharide (LPS) decreased Fe uptake from transferrin (Tf), and there was a concomitant downregulation of TfR expression. These effects were mediated by NO-dependent and NO-independent mechanisms, Additi on of the NO synthase (NOS) inhibitor N-monomethyl arginine (NMMA) partiall y restored Fe uptake but either had no effect on or downregulated TfR expre ssion, which suggests that NO by itself is able to affect iron availability . Analysis of the intracellular distribution of incorporated iron revealed that in IFN-gamma/LPS-activated macrophages there was a decreased amount an d proportion of ferritin-bound iron and a compensatory increase in insolubl e iron, which probably consists mainly of iron bound to intracellular organ elles. Finally, although NO released by IFN-gamma/LPS-activated macrophages increased the iron-responsive element (IRE)-binding activity of both IRP1 and IRP2, lFN-gamma treatment decreased IRP2 activity in an NO-independent manner. This study demonstrates that the effect of IFN-gamma and/or LPS on macrophage iron metabolism is complex, and is not entirely due to either NO -or to IRP-mediated mechanisms. The overall effect is to decrease iron upta ke, but not its utilization. (C) 1999 by The American Society of Hematology .