Carbotoxicity-Noxious Effects of Carbohydrates.

Modern nutrition is often characterized by the excessive intake of different types of carbohydrates ranging from digestible polysaccharides to refined sugars that collectively mediate noxious effects on human health, a phenomenon that we refer to as "carbotoxicity." Epidemiological and experimental evidence combined with clinical intervention trials underscore the negative impact of excessive carbohydrate uptake, as well as the beneficial effects of reducing carbs in the diet. We discuss the molecular, cellular, and neuroendocrine mechanisms that link exaggerated carbohydrate intake to disease and accelerated aging as we outline dietary and pharmacologic strategies to combat carbotoxicity.

A hyper-quiescent chromatin state formed during aging is reversed by regeneration.

Epigenetic alterations are a key hallmark of aging but have been limitedly explored in tissues. Here, using naturally aged murine liver as a model and extending to other quiescent tissues, we find that aging is driven by temporal chromatin alterations that promote a refractory cellular state and compromise cellular identity. Using an integrated multi-omics approach and the first direct visualization of aged chromatin, we find that globally, old cells show H3K27me3-driven broad heterochromatinization and transcriptional suppression. At the local level, site-specific loss of H3K27me3 over promoters of genes encoding developmental transcription factors leads to expression of otherwise non-hepatocyte markers. Interestingly, liver regeneration reverses H3K27me3 patterns and rejuvenates multiple molecular and physiological aspects of the aged liver.

Reduced expression of MYC increases longevity and enhances healthspan.

MYC is a highly pleiotropic transcription factor whose deregulation promotes cancer. In contrast, we find that Myc haploinsufficient (Myc(+/-)) mice exhibit increased lifespan. They show resistance to several age-associated pathologies, including osteoporosis, cardiac fibrosis, and immunosenescence. They also appear to be more active, with a higher metabolic rate and healthier lipid metabolism. Transcriptomic analysis reveals a gene expression signature enriched for metabolic and immune processes. The ancestral role of MYC as a regulator of ribosome biogenesis is reflected in reduced protein translation, which is inversely correlated with longevity. We also observe changes in nutrient and energy sensing pathways, including reduced serum IGF-1, increased AMPK activity, and decreased AKT, TOR, and S6K activities. In contrast to observations in other longevity models, Myc(+/-) mice do not show improvements in stress management pathways. Our findings indicate that MYC activity has a significant impact on longevity and multiple aspects of mammalian healthspan.

The search for antiaging interventions: from elixirs to fasting regimens.

The phenomenon of aging is an intrinsic feature of life. Accordingly, the possibility to manipulate it has fascinated humans likely since time immemorial. Recent evidence is shaping a picture where low caloric regimes and exercise may improve healthy senescence, and several pharmacological strategies have been suggested to counteract aging. Surprisingly, the most effective interventions proposed to date converge on only a few cellular processes, in particular nutrient signaling, mitochondrial efficiency, proteostasis, and autophagy. Here, we critically examine drugs and behaviors to which life- or healthspan-extending properties have been ascribed and discuss the underlying molecular mechanisms.

Declining NAD(+) induces a pseudohypoxic state disrupting nuclear-mitochondrial communication during aging.

Ever since eukaryotes subsumed the bacterial ancestor of mitochondria, the nuclear and mitochondrial genomes have had to closely coordinate their activities, as each encode different subunits of the oxidative phosphorylation (OXPHOS) system. Mitochondrial dysfunction is a hallmark of aging, but its causes are debated. We show that, during aging, there is a specific loss of mitochondrial, but not nuclear, encoded OXPHOS subunits. We trace the cause to an alternate PGC-1α/ß-independent pathway of nuclear-mitochondrial communication that is induced by a decline in nuclear NAD(+) and the accumulation of HIF-1α under normoxic conditions, with parallels to Warburg reprogramming. Deleting SIRT1 accelerates this process, whereas raising NAD(+) levels in old mice restores mitochondrial function to that of a young mouse in a SIRT1-dependent manner. Thus, a pseudohypoxic state that disrupts PGC-1α/ß-independent nuclear-mitochondrial communication contributes to the decline in mitochondrial function with age, a process that is apparently reversible.

Calorie restriction and calorie-restriction mimetics activate chaperone-mediated autophagy.

Chaperone-mediated autophagy (CMA) is part of the mammalian cellular proteostasis network that ensures protein quality control, maintenance of proteome homeostasis, and proteome changes required for the adaptation to stress. Loss of proteostasis is one of the hallmarks of aging. CMA decreases with age in multiple rodent tissues and human cell types. A decrease in lysosomal levels of the lysosome-associated membrane protein type 2A (LAMP2A), the CMA receptor, has been identified as a main reason for declined CMA in aging. Here, we report constitutive activation of CMA with calorie restriction (CR), an intervention that extends healthspan, in old rodent livers and in an in vitro model of CR with cultured fibroblasts. We found that CR-mediated upregulation of CMA is due to improved stability of LAMP2A at the lysosome membrane. We also explore the translational value of our observations using calorie-restriction mimetics (CRMs), pharmacologically active substances that reproduce the biochemical and functional effects of CR. We show that acute treatment of old mice with CRMs also robustly activates CMA in several tissues and that this activation is required for the higher resistance to lipid dietary challenges conferred by treatment with CRMs. We conclude that part of the beneficial effects associated with CR/CRMs could be a consequence of the constitutive activation of CMA mediated by these interventions.

Age-induced accumulation of methylmalonic acid promotes tumour progression.

The risk of cancer and associated mortality increases substantially in humans from the age of 65 years onwards1-6. Nonetheless, our understanding of the complex relationship between age and cancer is still in its infancy2,3,7,8. For decades, this link has largely been attributed to increased exposure time to mutagens in older individuals. However, this view does not account for the established role of diet, exercise and small molecules that target the pace of metabolic ageing9-12. Here we show that metabolic alterations that occur with age can produce a systemic environment that favours the progression and aggressiveness of tumours. Specifically, we show that methylmalonic acid (MMA), a by-product of propionate metabolism, is upregulated in the serum of older people and functions as a mediator of tumour progression. We traced this to the ability of MMA to induce SOX4 expression and consequently to elicit transcriptional reprogramming that can endow cancer cells with aggressive properties. Thus, the accumulation of MMA represents a link between ageing and cancer progression, suggesting that MMA is a promising therapeutic target for advanced carcinomas.

A specialized metabolic pathway partitions citrate in hydroxyapatite to impact mineralization of bones and teeth.

Citrate is a critical metabolic substrate and key regulator of energy metabolism in mammalian cells. It has been known for decades that the skeleton contains most (>85%) of the body's citrate, but the question of why and how this metabolite should be partitioned in bone has received singularly little attention. Here, we show that osteoblasts use a specialized metabolic pathway to regulate uptake, endogenous production, and the deposition of citrate into bone. Osteoblasts express high levels of the membranous Na+-dependent citrate transporter solute carrier family 13 member 5 (Slc13a5) gene. Inhibition or genetic disruption of Slc13a5 reduced osteogenic citrate uptake and disrupted mineral nodule formation. Bones from mice lacking Slc13a5 globally, or selectively in osteoblasts, showed equivalent reductions in cortical thickness, with similarly compromised mechanical strength. Surprisingly, citrate content in mineral from Slc13a5-/- osteoblasts was increased fourfold relative to controls, suggesting the engagement of compensatory mechanisms to augment endogenous citrate production. Indeed, through the coordinated functioning of the apical membrane citrate transporter SLC13A5 and a mitochondrial zinc transporter protein (ZIP1; encoded by Slc39a1), a mediator of citrate efflux from the tricarboxylic acid cycle, SLC13A5 mediates citrate entry from blood and its activity exerts homeostatic control of cytoplasmic citrate. Intriguingly, Slc13a5-deficient mice also exhibited defective tooth enamel and dentin formation, a clinical feature, which we show is recapitulated in primary teeth from children with SLC13A5 mutations. Together, our results reveal the components of an osteoblast metabolic pathway, which affects bone strength by regulating citrate deposition into mineral hydroxyapatite.

HuR and GRSF1 modulate the nuclear export and mitochondrial localization of the lncRNA RMRP.

Some mitochondrial long noncoding RNAs (lncRNAs) are encoded by nuclear DNA, but the mechanisms that mediate their transport to mitochondria are poorly characterized. Using affinity RNA pull-down followed by mass spectrometry analysis, we found two RNA-binding proteins (RBPs), HuR (human antigen R) and GRSF1 (G-rich RNA sequence-binding factor 1), that associated with the nuclear DNA-encoded lncRNA RMRP and mobilized it to mitochondria. In cultured human cells, HuR bound RMRP in the nucleus and mediated its CRM1 (chromosome region maintenance 1)-dependent export to the cytosol. After RMRP was imported into mitochondria, GRSF1 bound RMRP and increased its abundance in the matrix. Loss of GRSF1 lowered the mitochondrial levels of RMRP, in turn suppressing oxygen consumption rates and modestly reducing mitochondrial DNA replication priming. Our findings indicate that RBPs HuR and GRSF1 govern the cytoplasmic and mitochondrial localization of the lncRNA RMRP, which is encoded by nuclear DNA but has key functions in mitochondria.

Preclinical and translational models for delirium: Recommendations for future research from the NIDUS delirium network.

Delirium is a common, morbid, and costly syndrome that is closely linked to Alzheimer's disease (AD) and AD-related dementias (ADRD) as a risk factor and outcome. Human studies of delirium have advanced our knowledge of delirium incidence and prevalence, risk factors, biomarkers, outcomes, prevention, and management. However, understanding of delirium neurobiology remains limited. Preclinical and translational models for delirium, while challenging to develop, could advance our knowledge of delirium neurobiology and inform the development of new prevention and treatment approaches. We discuss the use of preclinical and translational animal models in delirium, focusing on (1) a review of current animal models, (2) challenges and strategies for replicating elements of human delirium in animals, and (3) the utility of biofluid, neurophysiology, and neuroimaging translational markers in animals. We conclude with recommendations for the development and validation of preclinical and translational models for delirium, with the goal of advancing awareness in this important field.

Does diet influence aging? Evidence from animal studies.

Nutrition profoundly influences the risk for many age-related diseases. Whether nutrition influences human aging biology directly is less clear. Studies in different animal species indicate that reducing food intake ("caloric restriction" [CR]) can increase lifespan and delay the onset of diseases and the biological hallmarks of aging. Obesity has been described as "accelerated aging" and therefore the lifespan and health benefits generated by CR in both aging and obesity may occur via similar mechanisms. Beyond calorie intake, studies based on nutritional geometry have shown that protein intake and the interaction between dietary protein and carbohydrates influence age-related health and lifespan. Studies where animals are calorically restricted by providing free access to diluted diets have had less impact on lifespan than those studies where animals are given a reduced aliquot of food each day and are fasting between meals. This has drawn attention to the role of fasting in health and aging, and exploration of the health effects of various fasting regimes. Although definitive human clinical trials of nutrition and aging would need to be unfeasibly long and unrealistically controlled, there is good evidence from animal experiments that some nutritional interventions based on CR, manipulating dietary macronutrients, and fasting can influence aging biology and lifespan.

Metabolic remodelling of glucose, fatty acid and redox pathways in the heart of type 2 diabetic mice.

KEY POINTS: Hearts from type 2 diabetic animals display perturbations in excitation-contraction coupling, impairing myocyte contractility and delaying relaxation, along with altered substrate consumption patterns. Under high glucose and ß-adrenergic stimulation conditions, palmitate can, at least in part, offset left ventricle (LV) dysfunction in hearts from diabetic mice, improving contractility and relaxation while restoring coronary perfusion pressure. Fluxome calculations of central catabolism in diabetic hearts show that, in the presence of palmitate, there is a metabolic remodelling involving tricarboxylic acid cycle, polyol and pentose phosphate pathways, leading to improved redox balance in cytoplasmic and mitochondrial compartments. Under high glucose and increased energy demand, the metabolic/fluxomic redirection leading to restored redox balance imparted by palmitate helps explain maintained LV function and may contribute to designing novel therapeutic approaches to prevent cardiac dysfunction in diabetic patients. ABSTRACT: Type-2 diabetes (T2DM) leads to reduced myocardial performance, and eventually heart failure. Excessive accumulation of lipids and glucose is central to T2DM cardiomyopathy. Previous data showed that palmitate (Palm) or glutathione preserved heart mitochondrial energy/redox balance under excess glucose, rescuing ß-adrenergic-stimulated cardiac excitation-contraction coupling. However, the mechanisms underlying the accompanying improved contractile performance have been largely ignored. Herein we explore in intact heart under substrate excess the metabolic remodelling associated with cardiac function in diabetic db/db mice subjected to stress given by ß-adrenergic stimulation with isoproterenol and high glucose compared to their non-diabetic controls (+/+, WT) under euglycaemic conditions. When perfused with Palm, T2DM hearts exhibited improved contractility/relaxation compared to WT, accompanied by extensive metabolic remodelling as demonstrated by metabolomics-fluxomics combined with bioinformatics and computational modelling. The T2DM heart metabolome showed significant differences in the abundance of metabolites in pathways related to glucose, lipids and redox metabolism. Using a validated computational model of heart's central catabolism, comprising glucose and fatty acid (FA) oxidation in cytoplasmic and mitochondrial compartments, we estimated that fluxes through glucose degradation pathways are ∼2-fold lower in heart from T2DM vs. WT under all conditions studied. Palm addition elicits improvement of the redox status via enhanced ß-oxidation and decreased glucose uptake, leading to flux-redirection away from redox-consuming pathways (e.g. polyol) while maintaining the flux through redox-generating pathways together with glucose-FA 'shared fuelling' of oxidative phosphorylation. Thus, available FAs such as Palm may help improve function via enhanced redox balance in T2DM hearts during peaks of hyperglycaemia and increased workload.

Sirt1 protects from K-Ras-driven lung carcinogenesis.

The NAD+-dependent deacetylase SIRT1 can be oncogenic or tumor suppressive depending on the tissue. Little is known about the role of SIRT1 in non-small cell lung carcinoma (NSCLC), one of the deadliest cancers, that is frequently associated with mutated K-RAS Therefore, we investigated the effect of SIRT1 on K-RAS-driven lung carcinogenesis. We report that SIRT1 protein levels are downregulated by oncogenic K-RAS in a MEK and PI3K-dependent manner in mouse embryo fibroblasts (MEFs), and in human lung adenocarcinoma cell lines. Furthermore, Sirt1 overexpression in mice delays the appearance of K-RasG12V-driven lung adenocarcinomas, reducing the number and size of carcinomas at the time of death and extending survival. Consistently, lower levels of SIRT1 are associated with worse prognosis in human NSCLCs. Mechanistically, analysis of mouse Sirt1-Tg pneumocytes, isolated shortly after K-RasG12V activation, reveals that Sirt1 overexpression alters pathways involved in tumor development: proliferation, apoptosis, or extracellular matrix organization. Our work demonstrates a tumor suppressive role of SIRT1 in the development of K-RAS-driven lung adenocarcinomas in mice and humans, suggesting that the SIRT1-K-RAS axis could be a therapeutic target for NSCLCs.

RNA-binding protein HuD controls insulin translation.

Although expression of the mammalian RNA-binding protein HuD was considered to be restricted to neurons, we report that HuD is present in pancreatic ß cells, where its levels are controlled by the insulin receptor pathway. We found that HuD associated with a 22-nucleotide segment of the 5' untranslated region (UTR) of preproinsulin (Ins2) mRNA. Modulating HuD abundance did not alter Ins2 mRNA levels, but HuD overexpression decreased Ins2 mRNA translation and insulin production, and conversely, HuD silencing enhanced Ins2 mRNA translation and insulin production. Following treatment with glucose, HuD rapidly dissociated from Ins2 mRNA and enabled insulin biosynthesis. Importantly, HuD-knockout mice displayed higher insulin levels in pancreatic islets, while HuD-overexpressing mice exhibited lower insulin levels in islets and in plasma. In sum, our results identify HuD as a pivotal regulator of insulin translation in pancreatic ß cells.

The human longevity gene homolog INDY and interleukin-6 interact in hepatic lipid metabolism.

Reduced expression of the Indy ("I am Not Dead, Yet") gene in lower organisms promotes longevity in a manner akin to caloric restriction. Deletion of the mammalian homolog of Indy (mIndy, Slc13a5) encoding for a plasma membrane-associated citrate transporter expressed highly in the liver, protects mice from high-fat diet-induced and aging-induced obesity and hepatic fat accumulation through a mechanism resembling caloric restriction. We studied a possible role of mIndy in human hepatic fat metabolism. In obese, insulin-resistant patients with nonalcoholic fatty liver disease, hepatic mIndy expression was increased and mIndy expression was also independently associated with hepatic steatosis. In nonhuman primates, a 2-year high-fat, high-sucrose diet increased hepatic mIndy expression. Liver microarray analysis showed that high mIndy expression was associated with pathways involved in hepatic lipid metabolism and immunological processes. Interleukin-6 (IL-6) was identified as a regulator of mIndy by binding to its cognate receptor. Studies in human primary hepatocytes confirmed that IL-6 markedly induced mIndy transcription through the IL-6 receptor and activation of the transcription factor signal transducer and activator of transcription 3, and a putative start site of the human mIndy promoter was determined. Activation of the IL-6-signal transducer and activator of transcription 3 pathway stimulated mIndy expression, enhanced cytoplasmic citrate influx, and augmented hepatic lipogenesis in vivo. In contrast, deletion of mIndy completely prevented the stimulating effect of IL-6 on citrate uptake and reduced hepatic lipogenesis. These data show that mIndy is increased in liver of obese humans and nonhuman primates with NALFD. Moreover, our data identify mIndy as a target gene of IL-6 and determine novel functions of IL-6 through mINDY. CONCLUSION: Targeting human mINDY may have therapeutic potential in obese patients with nonalcoholic fatty liver disease. German Clinical Trials Register: DRKS00005450. (Hepatology 2017;66:616-630).

Pharmacological Strategies to Retard Cardiovascular Aging.

Aging is the major risk factor for cardiovascular diseases, which are the leading cause of death in the United States. Traditionally, the effort to prevent cardiovascular disease has been focused on addressing the conventional risk factors, including hypertension, hyperglycemia, hypercholesterolemia, and high circulating levels of triglycerides. However, recent preclinical studies have identified new approaches to combat cardiovascular disease. Calorie restriction has been reproducibly shown to prolong lifespan in various experimental model animals. This has led to the development of calorie restriction mimetics and other pharmacological interventions capable to delay age-related diseases. In this review, we will address the mechanistic effects of aging per se on the cardiovascular system and focus on the prolongevity benefits of various therapeutic strategies that support cardiovascular health.

Impact of caloric restriction on health and survival in rhesus monkeys from the NIA study.

Calorie restriction (CR), a reduction of 10­40% in intake of a nutritious diet, is often reported as the most robust non-genetic mechanism to extend lifespan and healthspan. CR is frequently used as a tool to understand mechanisms behind ageing and age-associated diseases. In addition to and independently of increasing lifespan, CR has been reported to delay or prevent the occurrence of many chronic diseases in a variety of animals. Beneficial effects of CR on outcomes such as immune function, motor coordination and resistance to sarcopenia in rhesus monkeys have recently been reported. We report here that a CR regimen implemented in young and older age rhesus monkeys at the National Institute on Aging (NIA) has not improved survival outcomes. Our findings contrast with an ongoing study at the Wisconsin National Primate Research Center (WNPRC), which reported improved survival associated with 30% CR initiated in adult rhesus monkeys (7­14 years) and a preliminary report with a small number of CR monkeys. Over the years, both NIA and WNPRC have extensively documented beneficial health effects of CR in these two apparently parallel studies. The implications of the WNPRC findings were important as they extended CR findings beyond the laboratory rodent and to a long-lived primate. Our study suggests a separation between health effects, morbidity and mortality, and similar to what has been shown in rodents, study design, husbandry and diet composition may strongly affect the life-prolonging effect of CR in a long-lived nonhuman primate.