A dietary supplement protects aging muscle: The oxidized form of cellular nicotinamide adenine dinucleotide (NAD ⁺ ) is critical for mitochondrial function, and its supplementation can lead to increased longevity. Zhang et al. found that feeding the NAD ⁺ precursor nicotinamide riboside (NR) to aging mice protected them from muscle degeneration (see the Perspective by Guarente). NR treatment enhanced muscle function and also protected mice from the loss of muscle stem cells. The treatment was similarly protective of neural and melanocyte stem cells, which may have contributed to the extended life span of the NR-treated animals. Science , this issue p. 1436 ; see also p. 1396

In recent years, tetracyclines, such as doxycycline, have become broadly used to control gene expression by virtue of the Tet-on/Tet-off systems. However, the wide range of direct effects of tetracycline use has not been fully appreciated. We show here that these antibiotics induce a mitonuclear protein imbalance through their effects on mitochondrial translation, an effect that likely reflects the evolutionary relationship between mitochondria and proteobacteria. Even at low concentrations, tetracyclines induce mitochondrial proteotoxic stress, leading to changes in nuclear gene expression and altered mitochondrial dynamics and function in commonly used cell types, as well as worms, flies, mice, and plants. Given that tetracyclines are so widely applied in research, scientists should be aware of their potentially confounding effects on experimental results. Furthermore, these results caution against extensive use of tetracyclines in livestock due to potential downstream impacts on the environment and human health.

With no approved pharmacological treatment, nonalcoholic fatty liver disease (NAFLD) is now the most common cause of chronic liver disease in Western countries and its worldwide prevalence continues to increase along with the growing obesity epidemic. Here, we show that a high‐fat high‐sucrose (HFHS) diet, eliciting chronic hepatosteatosis resembling human fatty liver, lowers hepatic nicotinamide adenine dinucleotide (NAD⁺) levels driving reductions in hepatic mitochondrial content, function, and adenosine triphosphate (ATP) levels, in conjunction with robust increases in hepatic weight, lipid content, and peroxidation in C57BL/6J mice. To assess the effect of NAD⁺ repletion on the development of steatosis in mice, nicotinamide riboside, a precursor of NAD⁺ biosynthesis, was added to the HFHS diet, either as a preventive strategy or as a therapeutic intervention. We demonstrate that NR prevents and reverts NAFLD by inducing a sirtuin (SIRT)1‐ and SIRT3‐dependent mitochondrial unfolded protein response, triggering an adaptive mitohormetic pathway to increase hepatic β‐oxidation and mitochondrial complex content and activity. The cell‐autonomous beneficial component of NR treatment was revealed in liver‐specific Sirt1 knockout mice (Sirt1hep−/− ), whereas apolipoprotein E‐deficient mice (Apoe ^−/−) challenged with a high‐fat high‐cholesterol diet affirmed the use of NR in other independent models of NAFLD. Conclusion: Our data warrant the future evaluation of NAD⁺ boosting strategies to manage the development or progression of NAFLD. (Hepatology 2016;63:1190–1204)

Mitochondria are cellular organelles that harvest energy in the form of ATP through a process termed oxidative phosphorylation (OXPHOS), which occurs via the protein complexes of the electron transport chain (ETC). In recent years it has become unequivocally clear that mitochondrial complexes of the ETC are not static entities in the inner mitochondrial membrane. These complexes are dynamic and in mammals they aggregate in different stoichiometric combinations to form supercomplexes (SCs) or respirasomes. It has been proposed that the net respiration is more efficient via SCs than via isolated complexes. However, it still needs to be determined whether the activity of a particular SC is associated with a disease etiology. Here we describe a simplified method to visualize and assess in‐gel activity of SCs and the individual complexes with good resolution using blue native polyacrylamide gel electrophoresis (BN‐PAGE). © 2016 by John Wiley & Sons, Inc.

NAD ⁺ treatment can reverse the functional decline in degenerating muscles.