The fine regulation of mitochondrial function has proved to be an essential metabolic adaptation to fluctuations in oxygen availability. During hypoxia, cells activate an anaerobic switch that favors glycolysis and attenuates the mitochondrial activity. This switch involves the hypoxia-inducible transcription factor-1 (HIF-1). We have identified a HIF-1 target gene, the mitochondrial NDUFA4L2 (NADH dehydrogenase [ubiquinone] 1 alpha subcomplex, 4-like 2). Our results, obtained employing NDUFA4L2-silenced cells and NDUFA4L2 knockout murine embryonic fibroblasts, indicate that hypoxia-induced NDUFA4L2 attenuates mitochondrial oxygen consumption involving inhibition of Complex I activity, which limits the intracellular ROS production under low-oxygen conditions. Thus, reducing mitochondrial Complex I activity via NDUFA4L2 appears to be an essential element in the mitochondrial reprogramming induced by HIF-1.

The European Cooperation in Science and Technology (COST) provides an ideal framework to establish multi-disciplinary research networks. COST Action BM1203 (EU-ROS) represents a consortium of researchers from different disciplines who are dedicated to providing new insights and tools for better understanding redox biology and medicine and, in the long run, to finding new therapeutic strategies to target dysregulated redox processes in various diseases. This report highlights the major achievements of EU-ROS as well as research updates and new perspectives arising from its members. The EU-ROS consortium comprised more than 140 active members who worked together for four years on the topics briefly described below. The formation of reactive oxygen and nitrogen species (RONS) is an established hallmark of our aerobic environment and metabolism but RONS also act as messengers via redox regulation of essential cellular processes. The fact that many diseases have been found to be associated with oxidative stress established the theory of oxidative stress as a trigger of diseases that can be corrected by antioxidant therapy. However, while experimental studies support this thesis, clinical studies still generate controversial results, due to complex pathophysiology of oxidative stress in humans. For future improvement of antioxidant therapy and better understanding of redox-associated disease progression detailed knowledge on the sources and targets of RONS formation and discrimination of their detrimental or beneficial roles is required. In order to advance this important area of biology and medicine, highly synergistic approaches combining a variety of diverse and contrasting disciplines are needed.

Within the last twenty years the view on reactive oxygen species (ROS) has changed; they are no longer only considered to be harmful but also necessary for cellular communication and homeostasis in different organisms ranging from bacteria to mammals. In the latter, ROS were shown to modulate diverse physiological processes including the regulation of growth factor signaling, the hypoxic response, inflammation and the immune response. During the last 60–100 years the life style, at least in the Western world, has changed enormously. This became obvious with an increase in caloric intake, decreased energy expenditure as well as the appearance of alcoholism and smoking; These changes were shown to contribute to generation of ROS which are, at least in part, associated with the occurrence of several chronic diseases like adiposity, atherosclerosis, type II diabetes, and cancer. In this review we discuss aspects and problems on the role of intracellular ROS formation and nutrition with the link to diseases and their problematic therapeutical issues.

Nitric oxide is implicated in a variety of signaling pathways in different systems, notably in endothelial cells. Some of its effects can be exerted through covalent modifications of proteins and, among these modifications, increasing attention is being paid to S-nitrosylation as a signaling mechanism. In this work, we show by a variety of methods (ozone chemiluminescence, biotin switch, and mass spectrometry) that the molecular chaperone Hsp90 is a target of S-nitrosylation and identify a susceptible cysteine residue in the region of the C-terminal domain that interacts with endothelial nitric oxide synthase (eNOS). We also show that the modification occurs in endothelial cells when they are treated with S-nitroso-L-cysteine and when they are exposed to eNOS activators. Hsp90 ATPase activity and its positive effect on eNOS activity are both inhibited by S-nitrosylation. Together, these data suggest that S-nitrosylation may functionally regulate the general activities of Hsp90 and provide a feedback mechanism for limiting eNOS activation.atherosclerosis ͉ nitrosation ͉ vascular wall ͉ chaperone R ecent years have witnessed an increasing interest in the roles of nitric oxide (NO) in signal transduction pathways other than its activation of the cGMP pathway. Many of these roles rely on NO's ability to alter protein function through posttranslational modifications. Among these modifications, S-nitrosylation has emerged as a potential and fundamental regulator of protein function. S-nitrosylation is a covalent modification of thiol groups by formation of a thionitrite (-S-NϭO) group, facilitated by the formation of higher nitrogen oxides (1, 2). To date, several dozens of proteins have been shown to become S-nitrosylated and, in many cases, this modification was accompanied by altered function (see table S1 of ref. 1 for review).Nitric oxide, synthesized in the endothelium by endothelial nitric oxide synthase (eNOS), plays crucial roles in the vascular wall, including the maintenance of vascular tone. The possibility that NO might modify eNOS, or elements of the complex system involved in its activation, is an attractive hypothesis, suggesting a potential autoregulatory feedback mechanism. The eNOS enzyme is regulated by several posttranslational modifications including myristoylation, palmitoylation, and phosphorylation (3). This enzyme is also tightly regulated by specific interactions with inhibitory proteins such as caveolin-1 and by positive modulation by the scaffolding protein Hsp90. These interactions have been described in detail, and a relatively complete picture is beginning to emerge (4).We have previously used a proteomic approach to identify several proteins that were S-nitrosylated after exposure of vascular endothelial cells to the physiological nitrosothiol, Snitroso-L-cysteine (CSNO) (5). Further work led to the identification of Hsp90 as a protein susceptible to S-nitrosylation. This chaperone protein, known for its functions in protein folding, degradation, and scaffolding, has attracted renewed ...