The aims of this project are to assess the effects of aging and caloric restriction (CR) at a cellular and biochemical level of analysis, to identify physiological mechanisms associated with these effects, and to evaluate interventions/molecular pathways that might alter age-related declines in function. Laboratory studies consistently demonstrate extended lifespan in animals on calorie restriction (CR), where total caloric intake is reduced by 10-40% but adequate nutrition is otherwise maintained. CR has been further shown to delay the onset and severity of chronic diseases associated with aging such as cancer, and to extend the functional health span of important faculties like cognition. Less understood are the underlying mechanisms through which CR might act to induce such alterations. One theory postulates that CR's beneficial effects are intimately tied to the neuroendocrine response to low energy availability, of which the arcuate nucleus in the hypothalamus plays a pivotal role. CR induces measurable changes on circulating levels of several hormones and growth factors that regulate cell growth and proliferation. Serum obtained from CR animals alters growth, proliferation and stress responses of cells in culture. We have demonstrated that it is possible to investigate certain aspects of CR using this in vitro approach. This approach lends itself to a more rapid investigation of possible mechanisms and, perhaps more importantly to the research, development and rapid evaluation of interventions that would be able to induce or promote a phenotype similar to that seen with CR, essentially a CR mimetic. Below is the description of two of the most prominent lines of work in my laboratory associated with this project. Mitochondrial Biogenesis and Caloric Restriction. CR is hypothesized to decrease mitochondrial electron flow and proton leaks to attenuate damage due to reactive oxygen species (ROS). We have focused our research on a related, but different anti-aging mechanism of CR. Specifically, using both in vivo and in vitro analyses, we reported that CR reduces oxidative stress by stimulating the proliferation of mitochondria through a PGC1a signaling pathway. These mitochondria under CR conditions show less oxygen consumption, reduced membrane potential and generate less ROS than controls but remarkably are able to maintain their critical ATP production. Thus, CR can induce a PGC1a-dependent increase in mitochondria capable of efficient and balanced bioenergetics to reduce oxidative stress and attenuate age-dependent endogenous oxidative damage. In mammals, the regulation of mitochondrial biogenesis is complex, and it is not known whether the effects of CR on mitochondrial biogenesis are tissue-specific. Mitochondrial biogenesis is a highly regulated process that coordinates the activity of the approximately 1000 genes involved in mitochondrial function. This process requires coordination of the nuclear and mitochondrial genomes. Under CR, PGC-1αis expressed and activated, leading to an increase of mitochondrial mass. PGC-1αgene expression has been shown to be maintained with aging in CR models. In addition to PGC-1αthere are other master regulators that are expressed under CR conditions like Peroxisome Proliferator Activated Receptor (PPAR) family and liver X receptor, which control fatty acid metabolism. PGC-1αseems to be a crucial factor in activation of cellular respiration. Its physiological importance has been demonstrated since repression of PGC-1αby a mutant form of the huntingtin protein leads to mitochondrial dysfunction whereas its over-expression rescues cells from the deleterious effect of huntingtin. PGC-1αspecifically modulates the activity of several transcription factors and co-activators involved in mitochondrial respiration and biogenesis such as Nuclear Respiratory Factor 1 (NRF-1), NRF -2, PPARα, steroid receptor coactivator-1 and mitochondrial transcriptor factor A. NRF1 and NRF2 coordinate the expression of nuclear and mitochondrial genes that encode most of the subunits of mitochondrial complexes. Furthermore, PGC1-αactivates the shift of substrate utilization from carbohydrates to fatty acids through co-regulation of PPARα. Although it has been reported that CR enhances mitochondrial performance, the mechanism remains controversial as reports conflict about the extent to which CR changes expression of genes involved in nutrient sensing, mitochondrial biogenesis, and other key mitochondrial enzymes involved in the Krebs cycle, β-oxidation, and electron transport chain activities in humans. Carcinogenesis and Caloric Restriction. Almost a century ago Moreschi and Rous published their separate observations on the impact of caloric restriction (CR) on transplanted and induced tumors. Years later, McCay and colleagues first observed lifespan extension in laboratory rats maintained on a CR diet. Since then, CR has been studied intensively with consistent results showing its beneficial effects on longevity, age-associated diseases, attenuation of functional declines, and carcinogenesis across a variety of species and diet formulations. However, the mechanism(s) underlying the effects of CR protection still remain unknown. Nevertheless, it is safe to say that the three most extensively studied hallmarks of CR are enhanced protection against induced and spontaneous carcinogenesis, reduced insulin/IGF-1 signaling, and increased median and maximum lifespan. Even if CR was shown to benefit human health, confer cancer protection, and increase longevity, it would be extremely difficult to achieve adherence to such a stringent diet that might require a reduction of 20-40% in caloric intake. To this end, considerable investment has been focused on dissecting the pathways that regulate CR benefits that could spur development of pharmacological agents potentially acting as CR mimetics. Several of the currently proposed CR mimetics are phytochemicals (resveratrol, quercetin, and curcumin) that act, at least in part, through the activation of the NF-E2-related factor 2 (Nrf2) pathway. Nrf2 is a transcription factor that binds to the antioxidant response element (ARE) of target genes as an adaptive response to oxidative stress and increases the transcription of a variety of anti-oxidative and carcinogen detoxification enzymes. Stress can result from a variety of causes including fasting, overfeeding, endogenous compounds, exposure to chemicals or environmental agents but generally leads to the production of ROS. As a result of ROS exposure, Nrf2, which is typically bound to Keap1 in the cytoplasm, where it undergoes proteolytic degradation and rapid turnover, is phosphorylated and translocates to the nucleus where it binds to ARE sequences to induce expression of multiple cytoprotective enzymes including NAD(P)H-quinone oxidoreductase 1 (NQO1), glutathione S-transferases (GSTs), and heme oxygenase-1. We have now shown that Nrf2 is responsible for the protection of CR against carcinogenesis. However, the lack of Nrf2 did not attenuate lifespan extension or alter the CR improvement on insulin sensitivity in the Nrf2 KO mice. Similar to our findings with induced carcinogenesis, Van Remmen et al. were the first to show that reduction of an antioxidant enzyme could markedly increase DNA damage and spontaneous cancer incidence without affecting survival and lifespan. However, this study is the first to demonstrate that distinct pathways exert beneficial effects of CR and suggests that many mechanisms are involved in its protection. Recent data from invertebrates suggested that Nrf2 or at least some of its downstream effectors could hold the key to caloric restriction and longevity

National Institute of Health (NIH)
National Institute on Aging (NIA)
Investigator-Initiated Intramural Research Projects (ZIA)
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Cai, Huan; Daimon, Caitlin M; Cong, Wei-Na et al. (2014) Longitudinal analysis of calorie restriction on rat taste bud morphology and expression of sweet taste modulators. J Gerontol A Biol Sci Med Sci 69:532-44
Khraiwesh, Husam; López-Domínguez, José A; Fernández del Río, Lucía et al. (2014) Mitochondrial ultrastructure and markers of dynamics in hepatocytes from aged, calorie restricted mice fed with different dietary fats. Exp Gerontol 56:77-88
Mitchell, Sarah J; Martin-Montalvo, Alejandro; Mercken, Evi M et al. (2014) The SIRT1 activator SRT1720 extends lifespan and improves health of mice fed a standard diet. Cell Rep 6:836-43
Siendones, Emilio; Santacruz-Calvo, Sara; Martin-Montalvo, Alejandro et al. (2014) Membrane-Bound CYB5R3 Is a Common Effector of Nutritional and Oxidative Stress Response Through FOXO3a and Nrf2. Antioxid Redox Signal :
Mercken, Evi M; Hu, Jia; Krzysik-Walker, Susan et al. (2014) SIRT1 but not its increased expression is essential for lifespan extension in caloric-restricted mice. Aging Cell 13:193-6
de Cabo, Rafael; Carmona-Gutierrez, Didac; Bernier, Michel et al. (2014) The search for antiaging interventions: from elixirs to fasting regimens. Cell 157:1515-26
Samuel, Melanie A; Voinescu, P Emanuela; Lilley, Brendan N et al. (2014) LKB1 and AMPK regulate synaptic remodeling in old age. Nat Neurosci 17:1190-7
Scheibye-Knudsen, Morten; Mitchell, Sarah J; Fang, Evandro F et al. (2014) A high-fat diet and NAD(+) activate Sirt1 to rescue premature aging in cockayne syndrome. Cell Metab 20:840-55
Lopez-Dominguez, Jose Alberto; Khraiwesh, Husam; Gonzalez-Reyes, Jose Antonio et al. (2014) Dietary Fat and Aging Modulate Apoptotic Signaling in Liver of Calorie-Restricted Mice. J Gerontol A Biol Sci Med Sci :
Khraiwesh, Husam; Lopez-Dominguez, Jose A; Lopez-Lluch, Guillermo et al. (2013) Alterations of ultrastructural and fission/fusion markers in hepatocyte mitochondria from mice following calorie restriction with different dietary fats. J Gerontol A Biol Sci Med Sci 68:1023-34

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