Nicotinamide (NAM), a form of vitamin B, is a byproduct and noncompetitive inhibitor of the deacetylation reaction catalyzed by Sirtuins. These represent a family of evolutionarily conserved NAD-dependent deacetylases that are well-known critical regulators of metabolism and aging and whose founding member is Sir2 of Saccharomyces cerevisiae. Here, we investigated the effects of NAM supplementation in the context of yeast chronological aging, the established model for studying aging of postmitotic quiescent mammalian cells. Our data show that NAM supplementation at the diauxic shift results in a phenocopy of chronologically aging sir2Δ cells. In fact, NAM-supplemented cells display the same chronological lifespan extension both in expired medium and extreme Calorie Restriction. Furthermore, NAM allows the cells to push their metabolism toward the same outcomes of sir2Δ cells by elevating the level of the acetylated Pck1. Both these cells have the same metabolic changes that concern not only anabolic pathways such as an increased gluconeogenesis but also respiratory activity in terms both of respiratory rate and state of respiration. In particular, they have a higher respiratory reserve capacity and a lower non-phosphorylating respiration that in concert with a low burden of superoxide anions can affect positively chronological aging.

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During growth on fermentable substrates, such as glucose, pyruvate, which is the end-product of glycolysis, can be used to generate acetyl-CoA in the cytosol via acetaldehyde and acetate, or in mitochondria by direct oxidative decarboxylation. In the latter case, the mitochondrial pyruvate carrier (MPC) is responsible for pyruvate transport into mitochondrial matrix space. During chronological aging, yeast cells which lack the major structural subunit Mpc1 display a reduced lifespan accompanied by an age-dependent loss of autophagy. Here, we show that the impairment of pyruvate import into mitochondria linked to Mpc1 loss is compensated by a flux redirection of TCA cycle intermediates through the malic enzyme-dependent alternative route. In such a way, the TCA cycle operates in a “branched” fashion to generate pyruvate and is depleted of intermediates. Mutant cells cope with this depletion by increasing the activity of glyoxylate cycle and of the pathway which provides the nucleocytosolic acetyl-CoA. Moreover, cellular respiration decreases and ROS accumulate in the mitochondria which, in turn, undergo severe damage. These acquired traits in concert with the reduced autophagy restrict cell survival of the mpc1∆ mutant during chronological aging. Conversely, the activation of the carnitine shuttle by supplying acetyl-CoA to the mitochondria is sufficient to abrogate the short-lived phenotype of the mutant.

16Background 17Aging is a multifactorial process that affects multiple tissues and is characterized by changes in 18 homeostasis over time, leading to increased morbidity. Whole blood gene expression signatures have 19 been associated with aging and have been used to gain information on its biological mechanisms, which 20 are still not fully understood. However, blood is composed of many cell types whose proportions in 21 blood vary with age. As a result, previously observed associations between gene expression levels and 22 aging might be driven by cell type composition rather than intracellular aging mechanisms. To 23 overcome this, previous aging studies already accounted for major cell types, but the possibility that the 24 reported associations are false positives driven by less prevalent cell subtypes remains. 25 Results 26Here, we compared the regression model from our previous work to an extended model that corrects 27 for 33 additional white blood cell subtypes. Both models were applied to whole blood gene expression 28 2 data from 3165 individuals belonging to the general population (age range of 18-81 years). We 29 evaluated that the new model is a better fit for the data and it identified fewer genes associated with 30 aging (625, compared to the 2808 of the initial model; P ≤ 2.5⨯10 -6 ). Moreover, 511 genes (~18% of 31 the 2,808 genes identified by the initial model) were found using both models, indicating that the other 32 previously reported genes could be proxies for less abundant cell types. In particular, functional 33 enrichment of the genes identified by the new model highlighted pathways and GO terms specifically 34 associated with platelet activity. 35 Conclusions 36We conclude that gene expression analyses in blood strongly benefit from correction for both common 37 and rare blood cell types, and recommend using blood-cell count estimates as standard covariates when 38 studying whole blood gene expression. 39 40