Iron metabolism in Murine Macrophages: a proteomic insight.

Macrophages play a critical role at the crossroad between iron and immunity, being able to store and recycle iron derived from the phagocytosis of senescent erythrocytes. The way by which macrophages manage non-heme iron at physiological concentration is still not fully understood. We performed a 2-DE differential analysis to investigate the protein changes in Mouse Bone Marrow macrophages incubated with ferric ammonium citrate (FAC 10nM) for 24h in serum-free media. Differentially expressed spots were identified by nanoRP-HPLC-ESI-MS/MS. FAC induced the over-expression of ferritins, a family of iron storage proteins, and complex variations of several proteins of the cytoskeleton, which has been implicated in cytoplasmic distribution of ferritin molecules. Of note, FAC up-regulated the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) (↑ 2.36) at the membrane level, where it has been recently proposed to act as an alternative transferrin receptor for iron acquisition through internalization of the GAPDH-transferrin complex into the early endosomes. Among membrane associated proteins, FAC also up-regulated vimentin (↑ 4.54) and galectin-3 (↑ 1.97), both known to be involved in phagocytosis/internalization processes. Among cytosolic proteins, FAC induced de novo expression of macrophage inhibitory factor (MIF), a cytokine that plays a critical role in the inflammatory response. This proteomic study represents an example of the potential role of this methodology in the field of iron biology, especially for the elucidation of the molecular mechanisms controlling iron homeostasis in normal and disease conditions.