The mammalian brain is highly vulnerable to oxygen deprivation, yet the mechanism underlying the brain’s sensitivity to hypoxia is incompletely understood. Hypoxia induces accumulation of hydrogen sulfide, a gas that inhibits mitochondrial respiration. Here, we show that, in mice, rats, and naturally hypoxia-tolerant ground squirrels, the sensitivity of the brain to hypoxia is inversely related to the levels of sulfide:quinone oxidoreductase (SQOR) and the capacity to catabolize sulfide. Silencing SQOR increased the sensitivity of the brain to hypoxia, whereas neuron-specific SQOR expression prevented hypoxia-induced sulfide accumulation, bioenergetic failure, and ischemic brain injury. Excluding SQOR from mitochondria increased sensitivity to hypoxia not only in the brain but also in heart and liver. Pharmacological scavenging of sulfide maintained mitochondrial respiration in hypoxic neurons and made mice resistant to hypoxia. These results illuminate the critical role of sulfide catabolism in energy homeostasis during hypoxia and identify a therapeutic target for ischemic brain injury.

Objective— Inflammatory stimuli enhance the progression of atherosclerotic disease. Inflammation also increases the expression of hepcidin, a hormonal regulator of iron homeostasis, which decreases intestinal iron absorption, reduces serum iron levels and traps iron within macrophages. The role of macrophage iron in the development of atherosclerosis remains incompletely understood. The objective of this study was to investigate the effects of hepcidin deficiency and decreased macrophage iron on the development of atherosclerosis. Approach and Results— Hepcidin- and LDL (low-density lipoprotein) receptor-deficient ( Hamp −/− / Ldlr −/− ) mice and Hamp +/+ / Ldlr −/− control mice were fed a high-fat diet for 21 weeks. Compared with control mice, Hamp −/− / Ldlr −/− mice had decreased aortic macrophage activity and atherosclerosis. Because hepcidin deficiency is associated with both increased serum iron and decreased macrophage iron, the possibility that increased serum iron was responsible for decreased atherosclerosis in Hamp −/− / Ldlr −/− mice was considered. Hamp +/+ / Ldlr −/− mice were treated with iron dextran so as to produce a 2-fold increase in serum iron. Increased serum iron did not decrease atherosclerosis in Hamp +/+ / Ldlr −/− mice. Aortic macrophages from Hamp −/− / Ldlr −/− mice had less labile free iron and exhibited a reduced proinflammatory (M1) phenotype compared with macrophages from Hamp +/+ / Ldlr −/− mice. THP1 human macrophages treated with an iron chelator were used to model hepcidin deficiency in vitro. Treatment with an iron chelator reduced LPS (lipopolysaccharide)-induced M1 phenotypic expression and decreased uptake of oxidized LDL. Conclusions— In summary, in a hyperlipidemic mouse model, hepcidin deficiency was associated with decreased macrophage iron, a reduced aortic macrophage inflammatory phenotype and protection from atherosclerosis. The results indicate that decreasing hepcidin activity, with the resulting decrease in macrophage iron, may prove to be a novel strategy for the treatment of atherosclerosis.

Messenger RNA processing bodies (P-bodies) are cytoplasmic membrane-free organelles that contain proteins involved in mRNA silencing, storage and decay. The mechanism by which P-body components interact and the factors that regulate the stability of these structures are incompletely understood. In this study, we used a fluorescence-based, two-hybrid assay to investigate interactions between P-body components that occur inside the cell. LSm14a, PATL1, XRN1, and NBDY were found to interact with the N-terminal, WD40-domain-containing portion of EDC4. The N-terminus of full-length PATL1 was required to mediate the interaction between EDC4 and DDX6. The C-terminal, alpha helix-domain- containing portion of EDC4 was sufficient to mediate interaction with DCP1a and CCHCR1. In the absence of endogenous P-bodies, caused by depletion of LSm14a or DDX6, expression of the portion of EDC4 that lacked the N-terminus retained the ability to form cytoplasmic dots that were indistinguishable from P-bodies at the level of UV light microscopy. Despite the absence of endogenous P-bodies, this portion of EDC4 was able to recruit DCP1a, CCHCR1 and EDC3 to cytoplasmic dots. The results of this study permit the development of a new model of P-body formation and suggest that the N-terminus of EDC4 regulates the stability of these structures.