Aconitase Regulation of Erythropoiesis Correlates with a Novel Licensing Function in Erythropoietin-Induced ERK Signaling

Erythroid development requires the action of erythropoietin (EPO) on committed progenitors to match red cell output to demand. In this process, iron acts as a critical cofactor, with iron deficiency blunting EPO-responsiveness of erythroid progenitors. Aconitase enzymes have recently been identified as possible signal integration elements that couple erythropoiesis with iron availability. In the current study, a regulatory role for aconitase during erythropoiesis was ascertained using a direct inhibitory strategy.In C57BL/6 mice, infusion of an aconitase active-site inhibitor caused a hypoplastic anemia and suppressed responsiveness to hemolytic challenge. In a murine model of polycythemia vera, aconitase inhibition rapidly normalized red cell counts, but did not perturb other lineages. In primary erythroid progenitor cultures, aconitase inhibition impaired proliferation and maturation but had no effect on viability or ATP levels. This inhibition correlated with a blockade in EPO signal transmission specifically via ERK, with preservation of JAK2-STAT5 and Akt activation. Correspondingly, a physical interaction between ERK and mitochondrial aconitase was identified and found to be sensitive to aconitase inhibition.Direct aconitase inhibition interferes with erythropoiesis in vivo and in vitro, confirming a lineage-selective regulatory role involving its enzymatic activity. This inhibition spares metabolic function but impedes EPO-induced ERK signaling and disturbs a newly identified ERK-aconitase physical interaction. We propose a model in which aconitase functions as a licensing factor in ERK-dependent proliferation and differentiation, thereby providing a regulatory input for iron in EPO-dependent erythropoiesis. Directly targeting aconitase may provide an alternative to phlebotomy in the treatment of polycythemia vera

Cerium oxide nanoparticles accelerate the decay of peroxynitrite (ONOO−)

Cerium oxide nanoparticles (CeO(2) NPs) have been shown to possess a substantial oxygen storage capacity via the interchangeable surface reduction and oxidation of cerium atoms, cycling between the Ce(4+) and Ce(3+) redox states. It has been well established in many studies that depending on their reactivity and surface chemistry, CeO(2) NPs can effectively convert both reactive oxygen species (superoxide, O(2)(•−), and hydrogen peroxide) into more inert species and scavenge reactive nitrogen species (RNS)(nitric oxide, •NO), both in vitro and in vivo. Since much of damage attributed to •NO and O(2)(•−) is actually the result of oxidation or nitration by peroxynitrite or its breakdown products and due to the multiple species that these nanoparticles target in vivo, it was logical to test their interaction with the highly reactive molecule peroxynitrite (ONOO(−)). Here, we report that CeO(2) NPs significantly accelerated the decay of ONOO(−) by three independent methods. Additionally, our data suggest the ability of CeO(2) NPs to interact with ONOO(−) is independent of the Ce(3+)/Ce(4+) ratio on the surface of the CeO(2) NPs. The accelerated decay was not observed when reactions were carried out in an inert gas (argon), suggesting strongly that the decay of peroxynitrite is being accelerated due to a reaction of CeNPs with the carbonate radical anion. These results suggest that one of the protective effects of CeO(2) NPs during RNS is likely due to reduction in peroxynitrite or its reactive breakdown products

New rhodamine nitroxide based fluorescent probes for intracellular hydroxyl radical identification in living cells

The synthesis, characteristics, and biological applications of a series of new rhodamine nitroxide fluorescent probes that enable imaging of hydroxyl radicals (•OH) in living cells are described. These probes are highly selective for •OH in aqueous solution, avoiding interference from other reactive oxygen species (ROS), and they facilitate •OH imaging in biologically active samples. The robust nature of these probes (high specificity and selectivity, and facile synthesis) offer distinct advantages over previous methods for •OH detection. © 2011 American Chemical Society