Oxidative stress has been widely implicated as an important factor in the aging process. Because mitochondrial respiration is the principal source of reactive oxygen within cells, the mitochondrially localized superoxide dismutase (SOD) 2 is thought to play an important front-line defensive role against aging-related oxidative stress. Although genetic studies with mutants deficient in SOD1, the predominantly cytosolic isoform of SOD, have been instrumental in elucidating the role of reactive oxygen metabolism in aging in Drosophila, the lack of available mutations in the Sod2 gene has hampered an equivalent analysis of the participation of this important antioxidant enzyme in the Drosophila aging model. Here we report that ablation of mitochondrial SOD2 through expression of a GAL4-regulated, inverted-repeat Sod2 RNA-interference transgene in an otherwise normal animal causes increased endogenous oxidative stress, resulting in loss of essential enzymatic components of the mitochondrial respiratory chain and the tricarboxylic acid cycle, enhances sensitivity to applied oxidative stress, and causes early-onset mortality in young adults. In sharp contrast, ablation of SOD2 has no overt effect on the development of larvae and pupae, which may reflect a fundamental transition in oxygen utilization and͞or reactive oxygen metabolism that occurs during metamorphosis from larval to adult life.
Iron and oxygen are essential but potentially toxic constituents of most organisms, and their transport is meticulously regulated both at the cellular and systemic levels. Compartmentalization may be a homeostatic mechanism for isolating these biological reactants in cells. To investigate this hypothesis, we have undertaken a genetic analysis of the interaction between iron and oxygen metabolism in Drosophila. We show that Drosophila iron regulatory protein-1 (IRP1) registers cytosolic iron and oxidative stress through its labile iron sulfur cluster by switching between cytosolic aconitase and RNA-binding functions. IRP1 is strongly activated by silencing and genetic mutation of the cytosolic superoxide dismutase (Sod1), but is unaffected by silencing of mitochondrial Sod2. Conversely, mitochondrial aconitase activity is relatively insensitive to loss of Sod1 function, but drops dramatically if Sod2 activity is impaired. This strongly suggests that the mitochondrial boundary limits the range of superoxide reactivity in vivo. We also find that exposure of adults to paraquat converts cytosolic aconitase to IRP1 but has no affect on mitochondrial aconitase, indicating that paraquat generates superoxide in the cytosol but not in mitochondria. Accordingly, we find that transgene-mediated overexpression of Sod2 neither enhances paraquat resistance in Sod1 ؉ flies nor compensates for lack of SOD1 activity in Sod1-null mutants. We conclude that in vivo, superoxide is confined to the subcellular compartment in which it is formed, and that the mitochondrial and cytosolic SODs provide independent protection to compartment-specific protein iron-sulfur clusters against attack by superoxide generated under oxidative stress within those compartments.Iron and oxygen are indispensable but potentially harmful elements of aerobic life. Individually, their reactivity has been harnessed through association with a variety of proteins and the regulation of iron and oxygen metabolism constitutes one of the major triumphs of molecular evolution (1). Iron sulfur cluster proteins function in electron transport during oxidative phosphorylation and metabolism, but can also serve as iron and oxygen sensors (2). For instance, iron regulatory protein-1 (IRP1) 1 exerts its dual activities through the reciprocal use or dissasembly of its cubane iron sulfur [4Fe-4S] cluster; the holoprotein functions as a cytosolic aconitase, whereas the apoprotein is an RNA-binding translational regulator (1, 3). The stability and functionality of IRP1 as a translation regulator is affected not only by iron levels, but also by oxidative stress, which induces IRP1 to bind iron responsive elements (IREs) located on the 5Ј and 3Ј untranslated regions of target genes (4, 5). Although it is established that [4Fe-4S] cluster proteins can be specifically inactivated by superoxide (O 2 . ) (6 -8), the questions of whether the IRP1 [4Fe-4S] cluster reacts with O 2
Regeneration deficiency is one of the main obstacles limiting the effectiveness of tissue-engineered scaffolds. To develop scaffolds that are capable of accelerating regeneration, we created a heparin/chitosan nanoparticle-immobilized decellularized bovine jugular vein scaffold to increase the loading capacity and allow for controlled release of vascular endothelial growth factor (VEGF). The vascularization of the scaffold was evaluated in vitro and in vivo. The functional nanoparticles were prepared by physical self-assembly with a diameter of 67–132 nm, positive charge, and a zeta potential of ∼30 mV and then the nanoparticles were successfully immobilized to the nanofibers of scaffolds by ethylcarbodiimide hydrochloride/hydroxysulfosuccinimide modification. The scaffolds immobilized with heparin/chitosan nanoparticles exhibited highly effective localization and sustained release of VEGF for several weeks in vitro. This modified scaffold significantly stimulated endothelial cells’ proliferation in vitro. Importantly, utilization of heparin/chitosan nanoparticles to localize VEGF significantly increased fibroblast infiltration, extracellular matrix production, and accelerated vascularization in mouse subcutaneous implantation model in vivo. This study provided a novel and promising system for accelerated regeneration of tissue-engineering scaffolds.
Benzo[4,5]imidazo[2,1-a]isoquinolin-6(5H)-one derivatives are prevalent in many synthetic intermediates, pharmaceuticals, and organic materials. Herein, we develop a Mn-catalyzed electrochemical radical cascade cyclization reaction that uses electricity as the primary energy input to promote the reaction, leading to a series of benzo[4,5]imidazo[2,1-a]isoquinolin-6(5H)-one derivatives under exogenous-oxidant-free conditions. It is worth noting that this electrochemical method can not only realize the synthesis of benzo[4,5]imidazo[2,1-a]isoquinolin-6(5H)-one derivatives but also provides a new strategy for generating alkyl radicals from alkylboronic acids.
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