The free radical theory of aging posits oxidative damage to macromolecules as a primary determinant of lifespan. Recent studies challenge this theory by demonstrating that in some cases, longevity is enhanced by inactivation of oxidative stress defenses or is correlated with increased, rather than decreased reactive oxygen species and oxidative damage. Here we show that, in Saccharomyces cerevisiae, caloric restriction or inactivation of catalases extends chronological lifespan by inducing elevated levels of the reactive oxygen species hydrogen peroxide, which activate superoxide dismutases that inhibit the accumulation of superoxide anions. Increased hydrogen peroxide in catalase-deficient cells extends chronological lifespan despite parallel increases in oxidative damage. These findings establish a role for hormesis effects of hydrogen peroxide in promoting longevity that have broad implications for understanding aging and age-related diseases.aging | hydrogen peroxide | hormesis | antioxidant enzymes | oxidative damage T he longstanding free radical theory has guided investigations into the causes and consequences of aging for more than 50 y (1). However, the results of a number of recent studies have failed to provide support for the free radical theory or suggest that this theory is at best incomplete (2). Studies of naked mole rats, for example, demonstrated that this extremely long-lived rodent exhibits high levels of oxidative damage compared with mice or rats, whose lifespans are ≈1/10 that of naked mole rats (3). In addition, caloric restriction (CR), which extends the lifespans of a variety of eukaryotic organisms, promotes longevity in Caenorhabditis elegans by a mechanism that involves increased oxidative stress (4). In fact, in contrast to the destructive effects of reactive oxygen species (ROS), recent evidence indicates that in mammals, hydrogen peroxide (H 2 O 2 ) and other forms of ROS function as essential secondary messengers in the regulation of a variety of physiological processes (reviewed in ref. 5). For example, H 2 O 2 activates prosurvival signaling pathways mediated by p53, NF-κB, AP-1, and other molecules (6). Furthermore, increases in the intracellular steady-state production of H 2 O 2 by SOD2 overexpression can block the activation of cellular processes required for programmed cell death (7). However, a causal relationship between CR and effects on oxidative stress has been difficult to establish.To better understand how CR impacts oxidative stress and longevity in the model organism Saccharomyces cerevisiae, in this study we examined intracellular levels of H 2 O 2 and superoxide anions (O 2 − ), which are two forms of ROS implicated in aging in all eukaryotes, under CR and other conditions. Our findings indicate that CR or inactivation of catalases extends chronological lifespan (CLS) by inducing elevated levels of H 2 O 2 , which activate superoxide dismutases that inhibit the accumulation of O 2 − . These findings establish a role for hormesis effects of H 2 O 2 in promoting l...

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Nitric oxide (NO) is a small molecule with distinct roles in diverse physiological functions in biological systems, among them the control of the apoptotic signalling cascade. By combining proteomic, genetic and biochemical approaches we demonstrate that NO and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) are crucial mediators of yeast apoptosis. Using indirect methodologies and a NO-selective electrode, we present results showing that H2O2-induced apoptotic cells synthesize NO that is associated to a nitric oxide synthase (NOS)-like activity as demonstrated by the use of a classical NOS kit assay. Additionally, our results show that yeast GAPDH is a target of extensive proteolysis upon H2O2-induced apoptosis and undergoes S-nitrosation. Blockage of NO synthesis with Nω-nitro-L-arginine methyl ester leads to a decrease of GAPDH S-nitrosation and of intracellular reactive oxygen species (ROS) accumulation, increasing survival. These results indicate that NO signalling and GAPDH S-nitrosation are linked with H2O2-induced apoptotic cell death. Evidence is presented showing that NO and GAPDH S-nitrosation also mediate cell death during chronological life span pointing to a physiological role of NO in yeast apoptosis.

Amyloid fibrils and soluble oligomers are two types of protein aggregates associated with neurodegeneration. Classic therapeutic strategies try to prevent the nucleation and spread of amyloid fibrils, whilst diffusible oligomers have emerged as promising drug targets affecting downstream pathogenic processes. We developed a generic protein aggregation model and validate it against measured compositions of fibrillar and non-fibrillar assemblies of ataxin-3, a protein implicated in Machado-Joseph disease. The derived analytic rate-law equations can be used to 1) identify the presence of parallel aggregation pathways and 2) estimate the critical sizes of amyloid fibrils. The discretized population balance supporting our model is the first to quantitatively fit time-resolved measurements of size and composition of both amyloid-like and oligomeric species. The new theoretical framework can be used to screen a new class of drugs specifically targeting toxic oligomers.