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      Redox Signaling and Its Impact on Skeletal and Vascular Responses to Spaceflight

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          Abstract

          Spaceflight entails exposure to numerous environmental challenges with the potential to contribute to both musculoskeletal and vascular dysfunction. The purpose of this review is to describe current understanding of microgravity and radiation impacts on the mammalian skeleton and associated vasculature at the level of the whole organism. Recent experiments from spaceflight and ground-based models have provided fresh insights into how these environmental stresses influence mechanisms that are related to redox signaling, oxidative stress, and tissue dysfunction. Emerging mechanistic knowledge on cellular defenses to radiation and other environmental stressors, including microgravity, are useful for both screening and developing interventions against spaceflight-induced deficits in bone and vascular function.

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          Most cited references136

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          Superoxide dismutases: role in redox signaling, vascular function, and diseases.

          Excessive reactive oxygen species Revised abstract, especially superoxide anion (O₂•-), play important roles in the pathogenesis of many cardiovascular diseases, including hypertension and atherosclerosis. Superoxide dismutases (SODs) are the major antioxidant defense systems against (O₂•-), which consist of three isoforms of SOD in mammals: the cytoplasmic Cu/ZnSOD (SOD1), the mitochondrial MnSOD (SOD2), and the extracellular Cu/ZnSOD (SOD3), all of which require catalytic metal (Cu or Mn) for their activation. Recent evidence suggests that in each subcellular location, SODs catalyze the conversion of (O₂•-), H2O2, which may participate in cell signaling. In addition, SODs play a critical role in inhibiting oxidative inactivation of nitric oxide, thereby preventing peroxynitrite formation and endothelial and mitochondrial dysfunction. The importance of each SOD isoform is further illustrated by studies from the use of genetically altered mice and viral-mediated gene transfer. Given the essential role of SODs in cardiovascular disease, the concept of antioxidant therapies, that is, reinforcement of endogenous antioxidant defenses to more effectively protect against oxidative stress, is of substantial interest. However, the clinical evidence remains controversial. In this review, we will update the role of each SOD in vascular biologies, physiologies, and pathophysiologies such as atherosclerosis, hypertension, and angiogenesis. Because of the importance of metal cofactors in the activity of SODs, we will also discuss how each SOD obtains catalytic metal in the active sites. Finally, we will discuss the development of future SOD-dependent therapeutic strategies.
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            Isolation of NF-E2-related factor 2 (Nrf2), a NF-E2-like basic leucine zipper transcriptional activator that binds to the tandem NF-E2/AP1 repeat of the beta-globin locus control region.

            Hypersensitive site 2 located in the beta-globin locus control region confers high levels of expression to the genes of the beta-globin cluster. A tandem repeat of the consensus sequence for the transcription factors AP1 and NF-E2 (activating protein 1 and nuclear factor erythroid 2, respectively) is present within hypersensitive site 2 and is absolutely required for strong enhancer activity. This sequence binds, in vitro and in vivo, to ubiquitous proteins of the AP1 family and to the recently cloned erythroid-specific transcription factor NF-E2. Using the tandem repeat as a recognition site probe to screen a lambda gt11 cDNA expression library from K562 cells, we isolated several DNA binding proteins. Here, we report the characterization of one of the clones isolated. The gene, which we named Nrf2 (NF-E2-related factor 2), is encoded within a 2.2-kb transcript and predicts a 66-kDa protein with a basic leucine zipper DNA binding domain highly homologous to that of NF-E2. Although Nrf2 is expressed ubiquitously, a role of this protein in mediating enhancer activity of hypersensitive site 2 in erythroid cells cannot be excluded. In this respect, Nrf2 contains a powerful acidic activation domain that may participate in the transcriptional stimulation of beta-globin genes.
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              Hypertension in mice lacking the gene for endothelial nitric oxide synthase.

              Nitric oxide (NO), a potent vasodilator produced by endothelial cells, is thought to be the endothelium-dependent relaxing factor (EDRF) which mediates vascular relaxation in response to acetylcholine, bradykinin and substance P in many vascular beds. NO has been implicated in the regulation of blood pressure and regional blood flow, and also affects vascular smooth-muscle proliferation and inhibits platelet aggregation and leukocyte adhesion. Abnormalities in endothelial production of NO occur in atherosclerosis, diabetes and hypertension. Pharmacological blockade of NO production with arginine analogues such as L-nitroarginine (L-NA) or L-N-arginine methyl ester affects multiple isoforms of nitric oxide synthase (NOS), and so cannot distinguish their physiological roles. To study the role of endothelial NOS (eNOS) in vascular function, we disrupted the gene encoding eNOS in mice. Endothelium-derived relaxing factor activity, as assayed by acetylcholine-induced relaxation, is absent, and the eNOS mutant mice are hypertensive. Thus eNOS mediates basal vasodilation. Responses to NOS blockade in the mutant mice suggest that non-endothelial isoforms of NOS may be involved in maintaining blood pressure.
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                Author and article information

                Journal
                Int J Mol Sci
                Int J Mol Sci
                ijms
                International Journal of Molecular Sciences
                MDPI
                1422-0067
                16 October 2017
                October 2017
                : 18
                : 10
                : 2153
                Affiliations
                [1 ]Space Biosciences Division, NASA Ames Research Center, Moffett Field, CA 94035, USA; candiceginn.t.tahimic@ 123456nasa.gov
                [2 ]KBRWyle, Moffett Field, CA 94035, USA
                Author notes
                [* ]Correspondence: Ruth.K.Globus@ 123456nasa.gov ; Tel.: +1-650-604-1743
                Article
                ijms-18-02153
                10.3390/ijms18102153
                5666834
                29035346
                e36e9f83-41d0-4d84-96ec-90922a7f5bad
                © 2017 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 02 September 2017
                : 10 October 2017
                Categories
                Review

                Molecular biology
                spaceflight,bone,vasculature,oxidative stress,microgravity,hindlimb unloading,radiation,reactive oxygen species,antioxidant

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