Activated macrophages utilize glycolytic ATP to maintain mitochondrial membrane potential and prevent apoptotic cell death.

This corrects the article DOI: 10.1038/cdd.2010.27.

Activated macrophages utilize glycolytic ATP to maintain mitochondrial membrane potential and prevent apoptotic cell death.

We have previously analysed the bioenergetic consequences of activating J774.A1 macrophages (MΦ) with interferon-γ (IFN-γ) and lipopolysaccharide (LPS) and found that there is a nitric oxide (NO)-dependent mitochondrial impairment and stabilization of hypoxia-inducible factor (HIF)-1α, which synergize to activate glycolysis and generate large quantities of ATP. We now show, using tetramethylrhodamine methyl ester (TMRM) fluorescence and time-lapse confocal microscopy, that these cells maintain a high mitochondrial membrane potential (ΔΨ(m)) despite the complete inhibition of respiration. The maintenance of high ΔΨ(m) is due to the use of a significant proportion of glycolytically generated ATP as a defence mechanism against cell death. This is achieved by the reverse functioning of F(o)F(1)-ATP synthase and adenine nucleotide translocase (ANT). Treatment of activated MΦ with inhibitors of either of these enzymes, but not with inhibitors of the respiratory chain complexes I to IV, led to a collapse in ΔΨ(m) and to an immediate increase in intracellular [ATP], due to the prevention of ATP hydrolysis by the F(o)F(1)-ATP synthase. This collapse in ΔΨ(m) was followed by translocation of Bax from cytosol to the mitochondria, release of cytochrome c into the cytosol, activation of caspases 3 and 9 and subsequent apoptotic cell death. Our results indicate that during inflammatory activation 'glycolytically competent cells' such as MΦ use significant amounts of the glycolytically generated ATP to maintain ΔΨ(m) and thereby prevent apoptosis.

High-resolution respirometry--a modern tool in aging research.

Alterations in mitochondrial function are believed to play a major role in aging processes in many species, including fungi and animals, and increased oxidative stress is considered a major consequence of altered mitochondrial function. In support of this theory, a lot of correlative evidence has been collected, suggesting that changes in mitochondrial DNA accumulate with age in certain tissues. Furthermore, genetic experiments from lower eukaryotic model organisms, indicate a strong correlative link between increased resistance to oxidative stress and an extended lifespan; in addition, limited experimental evidence suggests that the inhibition of mitochondrial function by selected pharmacologically active compounds can extend lifespan in certain species. However, changes in mitochondrial function may affect aging in a different way in various tissues, and a clear statement about the role of mitochondrial deterioration during physiological aging is missing for most if not all species. At this point, respirometric analyses of mitochondrial function provide a tool to study age-associated changes in mitochondrial respiratory chain function and mitochondrial ATP production within living cells and isolated mitochondria. In the recent years, new instruments have been developed, which allow for an unprecedented high-resolution respirometry, which enables us to determine many parameters of mitochondrial function in routine assays using small samples of biological material. It is conceivable that this technology will become an important tool for all those, who are interested in experimentally addressing the mitochondrial theory of aging. In this article, we provide a synopsis of traditional respirometry and the advances of modern high-resolution respirometry, and discuss how future applications of this technology to recently established experimental models in aging research may provide exciting new insights into the role of mitochondria in the aging process.