Short-term methionine deprivation improves metabolic health via sexually dimorphic, mTORC1-independent mechanisms

Non-canonical metabolic and molecular effects of calorie restriction are revealed by varying temporal conditions

Calorie restriction (CR) extends lifespan and healthspan in diverse species. Comparing ad libitum- and CR-fed mice is challenging due to their significantly different feeding patterns, with CR-fed mice consuming their daily meal in 2 h and then subjecting themselves to a prolonged daily fast. Here, we examine how ad libitum- and CR-fed mice respond to tests performed at various times and fasting durations and find that the effects of CR-insulin sensitivity, circulating metabolite levels, and mechanistic target of rapamycin 1 (mTORC1) activity-result from the specific temporal conditions chosen, with CR-induced improvements in insulin sensitivity observed only after a prolonged fast, and the observed differences in mTORC1 activity between ad libitum- and CR-fed mice dependent upon both fasting duration and the specific tissue examined. Our results demonstrate that much of our understanding of the effects of CR are related to when, relative to feeding, we choose to examine the mice.

Acarbose ameliorates Western diet-induced metabolic and cognitive impairments in the 3xTg mouse model of Alzheimer's disease

Age is the greatest risk factor for Alzheimer's disease (AD) as well as for other disorders that increase the risk of AD such as diabetes and obesity. There is growing interest in determining if interventions that promote metabolic health can prevent or delay AD. Acarbose is an anti-diabetic drug that not only improves glucose homeostasis, but also extends the lifespan of wild-type mice. Here, we test the hypothesis that acarbose will not only preserve metabolic health, but also slow or prevent AD pathology and cognitive deficits in 3xTg mice, a model of AD, fed either a Control diet or a high-fat, high-sucrose Western diet (WD). We find that acarbose decreases the body weight and adiposity of WD-fed 3xTg mice, increasing energy expenditure while also stimulating food consumption, and improves glycemic control. Both male and female WD-fed 3xTg mice have worsened cognitive deficits than Control-fed mice, and these deficits are ameliorated by acarbose treatment. Molecular and histological analysis of tau and amyloid pathology identified sex-specific effects of acarbose which are uncoupled from the dramatic improvements in cognition in females, suggesting that the benefits of acarbose on AD may be largely driven by improved metabolic health. In conclusion, our results suggest that acarbose may be a promising intervention to prevent, delay, or even treat AD, especially in individuals consuming a WD.

FGF21 mediating the Sex-dependent Response to Dietary Macronutrients

Sex is key variable influencing body composition and substrate utilization. At rest, females maintain greater adiposity than males and resist the mobilization of fat. Males maintain greater lean muscle mass and mobilize fat readily. Determining the mechanisms that direct these sex-dependent effects is important for both reproductive and metabolic health. Here, we highlight the fundamental importance of sex in shaping metabolic physiology and assess growing evidence that the hepatokine fibroblast growth factor-21 (FGF21) plays a mechanistic role to facilitate sex-dependent responses to a changing nutritional environment. First, we examine the importance of sex in modulating body composition and substrate utilization. We summarize new data that point toward sex-biased effects of pharmacologic FGF21 administration on these endpoints. When energy is not limited, metabolic responses to FGF21 mirror broader sex differences; FGF21-treated males conserve lean mass at the expense of increased lipid catabolism, whereas FGF21-treated females conserve fat mass at the expense of reduced lean mass. Next, we examine the importance of sex in modulating the endogenous secretion of FGF21 in response to changing macronutrient and energy availability. During the resting state when energy is not limited, macronutrient imbalance increases the secretion of FGF21 more so in males than females. When energy is limited, the effect of sex on both the secretion of FGF21 and its metabolic actions may be reversed. Altogether, we argue that a growing literature supports FGF21 as a plausible mechanism contributing to the sex-dependent mobilization vs preservation of lipid storage and highlight the need for further research.

Acarbose ameliorates Western diet-induced metabolic and cognitive impairments in the 3xTg mouse model of Alzheimer's disease

Age is the greatest risk factor for Alzheimer's disease (AD) as well as for other disorders that increase the risk of AD such as diabetes and obesity. There is growing interest in determining if interventions that promote metabolic health can prevent or delay AD. Acarbose is an anti-diabetic drug that not only improves glucose homeostasis, but also extends the lifespan of wild-type mice. Here, we test the hypothesis that acarbose will not only preserve metabolic health, but also slow or prevent AD pathology and cognitive deficits in 3xTg mice, a model of AD, fed either a Control diet or a high-fat, high-sucrose Western diet (WD). We find that acarbose decreases the body weight and adiposity of WD-fed 3xTg mice, increasing energy expenditure while also stimulating food consumption, and improves glycemic control. Both male and female WD-fed 3xTg mice have worsened cognitive deficits than Control-fed mice, and these deficits are ameliorated by acarbose treatment. Molecular and histological analysis of tau and amyloid pathology identified sex-specific effects of acarbose which are uncoupled from the dramatic improvements in cognition, suggesting that the benefits of acarbose on AD are largely driven by improved metabolic health. In conclusion, our results suggest that acarbose may be a promising intervention to prevent, delay, or even treat AD, especially in individuals consuming a Western diet.

Sulfur Amino Acid Restriction Enhances Exercise Capacity in Mice by Boosting Fat Oxidation in Muscle

Dietary restriction of the sulfur-containing amino acids methionine and cysteine (SAAR) improves body composition, enhances insulin sensitivity, and extends lifespan; benefits seen also with endurance exercise. Yet, the impact of SAAR on skeletal muscle remains largely unexplored. Here we demonstrate that one week of SAAR in sedentary, young, male mice increases endurance exercise capacity. Indirect calorimetry showed that SAAR increased lipid oxidation at rest and delayed the onset of carbohydrate utilization during exercise. Transcriptomic analysis revealed increased expression of genes involved in fatty acid catabolism especially in glycolytic muscle following SAAR. These findings were functionally supported by increased fatty acid circulatory turnover flux and muscle β-oxidation. Reducing lipid uptake from circulation through endothelial cell (EC)-specific CD36 deletion attenuated the running phenotype. Mechanistically, VEGF-signaling inhibition prevented exercise increases following SAAR, without affecting angiogenesis, implicating noncanonical VEGF signaling and EC CD36-dependent fatty acid transport in regulating exercise capacity by influencing muscle substrate availability.

Protein restriction slows the development and progression of pathology in a mouse model of Alzheimer's disease

Dietary protein is a critical regulator of metabolic health and aging. Low protein diets are associated with healthy aging in humans, and dietary protein restriction extends the lifespan and healthspan of mice. In this study, we examined the effect of protein restriction (PR) on metabolic health and the development and progression of Alzheimer's disease (AD) in the 3xTg mouse model of AD. Here, we show that PR promotes leanness and glycemic control in 3xTg mice, specifically rescuing the glucose intolerance of 3xTg females. PR induces sex-specific alterations in circulating and brain metabolites, downregulating sphingolipid subclasses in 3xTg females. PR also reduces AD pathology and mTORC1 activity, increases autophagy, and improves the cognition of 3xTg mice. Finally, PR improves the survival of 3xTg mice. Our results suggest that PR or pharmaceutical interventions that mimic the effects of this diet may hold promise as a treatment for AD.

Protein restriction slows the development and progression of Alzheimer's disease in mice

Dietary protein is a critical regulator of metabolic health and aging. Low protein diets are associated with healthy aging in humans, and many independent groups of researchers have shown that dietary protein restriction (PR) extends the lifespan and healthspan of mice. Here, we examined the effect of PR on metabolic health and the development and progression of Alzheimer's disease (AD) in the 3xTg mouse model of AD. We found that PR has metabolic benefits for 3xTg mice and non-transgenic controls of both sexes, promoting leanness and glycemic control in 3xTg mice and rescuing the glucose intolerance of 3xTg females. We found that PR induces sex-specific alterations in circulating metabolites and in the brain metabolome and lipidome, downregulating sphingolipid subclasses including ceramides, glucosylceramides, and sphingomyelins in 3xTg females. Consumption of a PR diet starting at 6 months of age reduced AD pathology in conjunction with reduced mTORC1 activity, increased autophagy, and had cognitive benefits for 3xTg mice. Finally, PR improved the survival of 3xTg mice. Our results demonstrate that PR slows the progression of AD at molecular and pathological levels, preserves cognition in this mouse model of AD, and suggests that PR or pharmaceutical interventions that mimic the effects of this diet may hold promise as a treatment for AD.

Dietary restriction of individual amino acids stimulates unique molecular responses in mouse liver

Dietary protein and essential amino acid (EAA) restriction promotes favorable metabolic reprogramming, ultimately resulting in improvements to both health and lifespan. However, as individual EAAs have distinct catabolites and engage diverse downstream signaling pathways, it remains unclear to what extent shared or AA-specific molecular mechanisms promote diet-associated phenotypes. Here, we investigated the physiological and molecular effects of restricting either dietary methionine, leucine, or isoleucine (Met-R, Leu-R, and Ile-R) for 3 weeks in C57BL/6J male mice. While all 3 AA-depleted diets promoted fat and lean mass loss and slightly improved glucose tolerance, the molecular responses were more diverse; while hepatic metabolites altered by Met-R and Leu-R were highly similar, Ile-R led to dramatic changes in metabolites, including a 3-fold reduction in the oncometabolite 2-hydroxyglutarate. Pathways regulated in an EAA-specific manner included glycolysis, the pentose phosphate pathway (PPP), nucleotide metabolism, the TCA cycle and amino acid metabolism. Transcriptiome analysis and global profiling of histone post-translational modifications (PTMs) revealed different patterns of responses to each diet, although Met-R and Leu-R again shared similar transcriptional responses. While the pattern of global histone PTMs were largely unique for each dietary intervention, Met-R and Ile-R had similar changes in histone-3 methylation/acetylation PTMs at lysine-9. Few similarities were observed between the physiological or molecular responses to EAA restriction and treatment with rapamycin, an inhibitor of the mTORC1 AA-responsive protein kinase, indicating the response to EAA restriction may be largely independent of mTORC1. Together, these results demonstrate that dietary restriction of individual EAAs has unique, EAA-specific effects on the hepatic metabolome, epigenome, and transcriptome, and suggests that the specific EAAs present in dietary protein may play a key role at regulating health at the molecular level.

Dietary protein restriction modulates 'dessert' intake after a meal, via fibroblast growth factor 21 (FGF21)

Pharmacological administration of fibroblast growth factor 21 (FGF21) alters food choice, including that it decreases the consumption of sucrose and other sweet tastants. Conversely, endogenous secretion of FGF21 by the liver is modulated by diet, such that plasma FGF21 is increased after eating foods that have a low dietary protein: total energy (P: E) ratio. Together, these findings suggest a strategy to promote healthy eating, in which the macronutrient content of a pre-load diet could reduce the consumption of sweet desserts in sated mice. Here, we tested the prediction that individuals maintained on a low P: E diet, and offered a highly palatable sweet 'dessert' following a pre-load meal, would eat less of the sugary snack compared to controls-due to increased FGF21 signaling. In addition to decreasing sweet intake, FGF21 increases the consumption of dietary protein. Thus, we predicted that individuals maintained on the low P: E diet, and offered a very high-protein pellet as 'dessert' or snack after a meal, would eat more of the high protein pellet compared to controls, and that this depends on FGF21. We tested this in C57Bl/6J, and liver-specific FGF21-null (FGF21ΔL) null male and female mice and littermate controls. Contrary to expectation, eating a low protein pre-load did not reduce the later consumption of a sweet solution in either males or females, despite robustly increasing plasma FGF21. Rather, eating the low protein pre-load increased later consumption of a high protein pellet. This was more apparent among males and was abrogated in the FGF21ΔL mice. We conclude that physiologic induction of hepatic FGF21 by a low protein pre-load diet is not sufficient to reduce the consumption of sweet desserts, though it effectively increases the subsequent intake of dietary protein in male mice.

Resistance exercise protects mice from protein-induced fat accretion

Low-protein (LP) diets extend the lifespan of diverse species and are associated with improved metabolic health in both rodents and humans. Paradoxically, many athletes and bodybuilders consume high-protein (HP) diets and protein supplements, yet are both fit and metabolically healthy. Here, we examine this paradox using weight pulling, a validated progressive resistance exercise training regimen, in mice fed either an LP diet or an isocaloric HP diet. We find that despite having lower food consumption than the LP group, HP-fed mice gain significantly more fat mass than LP-fed mice when not exercising, while weight pulling protected HP-fed mice from this excess fat accretion. The HP diet augmented exercise-induced hypertrophy of the forearm flexor complex, and weight pulling ability increased more rapidly in the exercised HP-fed mice. Surprisingly, exercise did not protect from HP-induced changes in glycemic control. Our results confirm that HP diets can augment muscle hypertrophy and accelerate strength gain induced by resistance exercise without negative effects on fat mass, and also demonstrate that LP diets may be advantageous in the sedentary. Our results highlight the need to consider both dietary composition and activity, not simply calories, when taking a precision nutrition approach to health.

Use of FGF21 analogs for the treatment of metabolic disorders: a systematic review and meta-analysis

FGF21 is a hormone produced primarily by the liver with several metabolic functions, such as induction of heat production, control of glucose homeostasis, and regulation of blood lipid levels. Due to these actions, several laboratories have developed FGF21 analogs to treat patients with metabolic disorders such as obesity and diabetes. Here, we performed a systematic review and meta-analysis of randomized controlled trials that used FGF21 analogs and analyzed metabolic outcomes. Our search yielded 236 articles, and we included eight randomized clinical trials in the meta-analysis. The use of FGF21 analogs exhibited no effect on fasting blood glucose, glycated hemoglobin, HOMA index, blood free fatty acids or systolic blood pressure. However, the treatment significantly reduced fasting insulinemia, body weight and total cholesterolemia. None of the included studies were at high risk of bias. The quality of the evidence ranged from moderate to very low, especially due to imprecision and indirection issues. These results indicate that FGF21 analogs can potentially treat metabolic syndrome. However, more clinical trials are needed to increase the quality of evidence and confirm the effects seen thus far.

Dietary restriction of isoleucine increases healthspan and lifespan of genetically heterogeneous mice

Low-protein diets promote health and longevity in diverse species. Restriction of the branched-chain amino acids (BCAAs) leucine, isoleucine, and valine recapitulates many of these benefits in young C57BL/6J mice. Restriction of dietary isoleucine (IleR) is sufficient to promote metabolic health and is required for many benefits of a low-protein diet in C57BL/6J males. Here, we test the hypothesis that IleR will promote healthy aging in genetically heterogeneous adult UM-HET3 mice. We find that IleR improves metabolic health in young and old HET3 mice, promoting leanness and glycemic control in both sexes, and reprograms hepatic metabolism in a sex-specific manner. IleR reduces frailty and extends the lifespan of male and female mice, but to a greater degree in males. Our results demonstrate that IleR increases healthspan and longevity in genetically diverse mice and suggests that IleR, or pharmaceuticals that mimic this effect, may have potential as a geroprotective intervention.

Short-term Pre-operative Methionine Restriction Induces Browning of Perivascular Adipose Tissue and Improves Vein Graft Remodeling in Mice

Short-term preoperative methionine restriction (MetR) shows promise as a translatable strategy to modulate the body's response to surgical injury. Its application, however, to improve post-interventional vascular remodeling remains underexplored. Here, we find that MetR protects from arterial intimal hyperplasia in a focal stenosis model and adverse vascular remodeling after vein graft surgery. RNA sequencing reveals that MetR enhances the brown adipose tissue phenotype in arterial perivascular adipose tissue (PVAT) and induces it in venous PVAT. Specifically, PPAR-α was highly upregulated in PVAT-adipocytes. Furthermore, MetR dampens the post-operative pro-inflammatory response to surgery in PVAT-macrophages in vivo and in vitro . This study shows for the first time that the detrimental effects of dysfunctional PVAT on vascular remodeling can be reversed by MetR, and identifies pathways involved in browning of PVAT. Furthermore, we demonstrate the potential of short-term pre-operative MetR as a simple intervention to ameliorate vascular remodeling after vascular surgery.

Genetic and molecular understanding for the development of methionine-rich maize: a holistic approach

Maize (Zea mays) is the most important coarse cereal utilized as a major energy source for animal feed and humans. However, maize grains are deficient in methionine, an essential amino acid required for proper growth and development. Synthetic methionine has been used in animal feed, which is costlier and leads to adverse health effects on end-users. Bio-fortification of maize for methionine is, therefore, the most sustainable and environmental friendly approach. The zein proteins are responsible for methionine deposition in the form of δ-zein, which are major seed storage proteins of maize kernel. The present review summarizes various aspects of methionine including its importance and requirement for different subjects, its role in animal growth and performance, regulation of methionine content in maize and its utilization in human food. This review gives insight into improvement strategies including the selection of natural high-methionine mutants, molecular modulation of maize seed storage proteins and target key enzymes for sulphur metabolism and its flux towards the methionine synthesis, expression of synthetic genes, modifying gene codon and promoters employing genetic engineering approaches to enhance its expression. The compiled information on methionine and essential amino acids linked Quantitative Trait Loci in maize and orthologs cereals will give insight into the hotspot-linked genomic regions across the diverse range of maize germplasm through meta-QTL studies. The detailed information about candidate genes will provide the opportunity to target specific regions for gene editing to enhance methionine content in maize. Overall, this review will be helpful for researchers to design appropriate strategies to develop high-methionine maize.

When a calorie is not just a calorie: Diet quality and timing as mediators of metabolism and healthy aging

An epidemic of obesity has affected large portions of the world, increasing the risk of developing many different age-associated diseases, including cancer, cardiovascular disease, and diabetes. In contrast with the prevailing notion that "a calorie is just a calorie," there are clear differences, within and between individuals, in the metabolic response to different macronutrient sources. Recent findings challenge this oversimplification; calories from different macronutrient sources or consumed at different times of day have metabolic effects beyond their value as fuel. Here, we summarize discussions conducted at a recent NIH workshop that brought together experts in calorie restriction, macronutrient composition, and time-restricted feeding to discuss how dietary composition and feeding schedule impact whole-body metabolism, longevity, and healthspan. These discussions may provide insights into the long-sought molecular mechanisms engaged by calorie restriction to extend lifespan, lead to novel therapies, and potentially inform the development of a personalized food-as-medicine approach to healthy aging.

Reduced insulin signaling in neurons induces sex-specific health benefits

Reduced activity of insulin/insulin-like growth factor signaling (IIS) extends health and life span in mammals. Loss of the insulin receptor substrate 1 (Irs1) gene increases survival in mice and causes tissue-specific changes in gene expression. However, the tissues underlying IIS-mediated longevity are currently unknown. Here, we measured survival and health span in mice lacking IRS1 specifically in liver, muscle, fat, and brain. Tissue-specific loss of IRS1 did not increase survival, suggesting that lack of IRS1 in more than one tissue is required for life-span extension. Loss of IRS1 in liver, muscle, and fat did not improve health. In contrast, loss of neuronal IRS1 increased energy expenditure, locomotion, and insulin sensitivity, specifically in old males. Neuronal loss of IRS1 also caused male-specific mitochondrial dysfunction, activation of Atf4, and metabolic adaptations consistent with an activated integrated stress response at old age. Thus, we identified a male-specific brain signature of aging in response to reduced IIS associated with improved health at old age.

A non-canonical sensing pathway mediates Plasmodium adaptation to amino acid deficiency

Eukaryotes have canonical pathways for responding to amino acid (AA) availability. Under AA-limiting conditions, the TOR complex is repressed, whereas the sensor kinase GCN2 is activated. While these pathways have been highly conserved throughout evolution, malaria parasites are a rare exception. Despite auxotrophic for most AA, Plasmodium does not have either a TOR complex nor the GCN2-downstream transcription factors. While Ile starvation has been shown to trigger eIF2α phosphorylation and a hibernation-like response, the overall mechanisms mediating detection and response to AA fluctuation in the absence of such pathways has remained elusive. Here we show that Plasmodium parasites rely on an efficient sensing pathway to respond to AA fluctuations. A phenotypic screen of kinase knockout mutant parasites identified nek4, eIK1 and eIK2-the last two clustering with the eukaryotic eIF2α kinases-as critical for Plasmodium to sense and respond to distinct AA-limiting conditions. Such AA-sensing pathway is temporally regulated at distinct life cycle stages, allowing parasites to actively fine-tune replication and development in response to AA availability. Collectively, our data disclose a set of heterogeneous responses to AA depletion in malaria parasites, mediated by a complex mechanism that is critical for modulating parasite growth and survival.

Effects of methionine intake on cognitive function in mild cognitive impairment patients and APP/PS1 Alzheimer's Disease model mice: Role of the cystathionine-β-synthase/H2S pathway

As a dietary intervention, methionine restriction (MR) has been reported to increase longevity and improve metabolism disorders. However, the effects of MR on alleviating neurodegenerative diseases such as Alzheimer's disease (AD) are largely unexplored. Here we sought to investigate the neuroprotective effects of low methionine intake in mild cognitive impairment (MCI) patients and APP/PS1 AD model mice, and to uncover the underlying mechanisms. In a cohort composed of 45 individuals diagnosed with MCI and 61 healthy controls without cognitive impairment, methionine intake was found to be positively associated with the increased risk of MCI, where no sex differences were observed. We further conducted a 16-week MR intervention (0.17% methionine, w/w) on APP/PS1 AD model mice. Although MR reduced Aβ accumulation in the brain of both male and female APP/PS1 mice, MR improved cognitive function only in male mice, as assessed by the Morris water maze test. Consistently, MR restored synapse ultrastructure and alleviated mitochondrial dysfunction by enhancing mitochondrial biogenesis in the brain of male APP/PS1 mice. Importantly, MR effectively balanced the redox status and activated cystathionine-β-synthase (CBS)/H₂S pathway in the brain of male APP/PS1 mice. Together, our study indicated that lower dietary methionine intake is associated with improved cognitive function, in which CBS/H₂S pathway plays an essential role. MR could be a promising nutritional intervention for preventing AD development.

Methionine and total homocysteine in hypertensive patients with renal excretory dysfunction

The role of the kidneys in the metabolism and homeostasis of sulfur-containing amino acids is great, so the levels of methionine (Met), total homocysteine (tHcy) and their ratios can be of diagnostic value in chronic kidney disease (CKD), in a course of the arterial hypertension (AH). The aim of the study was to evaluate the Met/tHcy ratio in hypertensive patients with CKD. We used blood plasma of 76 patients aged 40-75 years with AH and the excretory dysfunction of the kidneys; subgroups: 1 - with proteinuria (n=37); 2 - without proteinuria with glomerular filtration rate (GFR) < 90 ml/min/1.73 m2 (n=39) and comparison group 3 - patients with AH without renal excretory dysfunction (n=28). Significantly lower Met levels were in subgroup 1. THcy levels were higher in subgroups 1 and 2 than in group 3. The Met/tHcy ratio revealed differences in subgroups 1 and 2 vs group 3. No differences were found in Arg and Lys levels. Positive correlations of the Met/tHcy ratio with the number of erythrocytes, but not with the level of hemoglobin, were revealed. In the ROC analysis, the cut-off points for the Met/tHcy ratio compared to group 3 were 3.08 for subgroup 1 and 3.36 for subgroup 2. With the progression of CKD, there is an increase in the levels of tHcy in the blood, and a decrease in the content of Met. A decrease in GFR, especially in a case with proteinuria, is accompanied by a decrease in the level of Met. The Met/tHcy ratio above 3.36 can be considered as the minimum of the balance between these sulfur-containing amino acids contents in a blood necessary for hypertensive patients with CKD.

Methionine restriction - Association with redox homeostasis and implications on aging and diseases

Methionine is an essential amino acid, involved in the promotion of growth, immunity, and regulation of energy metabolism. Over the decades, research has long focused on the beneficial effects of methionine supplementation, while data on positive effects of methionine restriction (MR) were first published in 1993. MR is a low-methionine dietary intervention that has been reported to ameliorate aging and aging-related health concomitants and diseases, such as obesity, type 2 diabetes, and cognitive disorders. In addition, MR seems to be an approach to prolong lifespan which has been validated extensively in various animal models, such as Caenorhabditis elegans, Drosophila, yeast, and murine models. MR appears to be associated with a reduction in oxidative stress via so far mainly undiscovered mechanisms, and these changes in redox status appear to be one of the underlying mechanisms for lifespan extension and beneficial health effects. In the present review, the association of methionine metabolism pathways with redox homeostasis is described. In addition, the effects of MR on lifespan, age-related implications, comorbidities, and diseases are discussed.

ERα-Dependent Regulation of Adropin Predicts Sex Differences in Liver Homeostasis during High-Fat Diet

Non-alcoholic fatty liver disease (NAFLD) represents a public health issue, due to its prevalence and association with other cardiometabolic diseases. Growing evidence suggests that NAFLD alters the production of hepatokines, which, in turn, influence several metabolic processes. Despite accumulating evidence on the major role of estrogen signaling in the sexually dimorphic nature of NAFLD, dependency of hepatokine expression on sex and estrogens has been poorly investigated. Through in vitro and in vivo analysis, we determined the extent to which hepatokines, known to be altered in NAFLD, can be regulated, in a sex-specific fashion, under different hormonal and nutritional conditions. Our study identified four hepatokines that better recapitulate sex and estrogen dependency. Among them, adropin resulted as one that displays a sex-specific and estrogen receptor alpha (ERα)-dependent regulation in the liver of mice under an excess of dietary lipids (high-fat diet, HFD). Under HFD conditions, the hepatic induction of adropin negatively correlates with the expression of lipogenic genes and with fatty liver in female mice, an effect that depends upon hepatic ERα. Our findings support the idea that ERα-mediated induction of adropin might represent a potential approach to limit or prevent NAFLD.

Activation and execution of the hepatic integrated stress response by dietary essential amino acid deprivation is amino acid specific

Dietary removal of an essential amino acid (EAA) triggers the integrated stress response (ISR) in liver. Herein, we explored the mechanisms that activate the ISR and execute changes in transcription and translation according to the missing EAA. Wild‐type mice and mice lacking general control nonderepressible 2 (Gcn2) were fed an amino acid complete diet or a diet devoid of either leucine or sulfur amino acids (methionine and cysteine). Serum and liver leucine concentrations were significantly reduced within the first 6 h of feeding a diet lacking leucine, corresponding with modest, GCN2‐dependent increases in Atf4 mRNA translation and induction of selected ISR target genes (Fgf21, Slc7a5, Slc7a11). In contrast, dietary removal of the sulfur amino acids lowered serum methionine, but not intracellular methionine, and yet hepatic mRNA abundance of Atf4, Fgf21, Slc7a5, Slc7a11 substantially increased regardless of GCN2 status. Liver tRNA charging levels did not correlate with intracellular EAA concentrations or GCN2 status and remained similar to mice fed a complete diet. Furthermore, loss of Gcn2 increased the occurrence of ribosome collisions in liver and derepressed mechanistic target of rapamycin complex 1 signal transduction, but these changes did not influence execution of the ISR. We conclude that ISR activation is directed by intracellular EAA concentrations, but ISR execution is not. Furthermore, a diet devoid of sulfur amino acids does not require GCN2 for the ISR to execute changes to the transcriptome.

Intermittent methionine restriction reduces IGF-1 levels and produces similar healthspan benefits to continuous methionine restriction

A sustained state of methionine restriction (MR) dramatically extends the healthspan of several model organisms. For example, continuously methionine‐restricted rodents have less age‐related pathology and are up to 45% longer‐lived than controls. Promisingly, MR is feasible for humans, and studies have suggested that methionine‐restricted individuals may receive similar benefits to rodents. However, long‐term adherence to a methionine‐restricted diet is likely to be challenging for many individuals. Prompted by this, and the fact that intermittent variants of other healthspan‐extending interventions (i.e., intermittent fasting and the cyclic ketogenic diet) are just as effective, if not more, than their continuous counterparts, we hypothesized that an intermittent form of MR might produce similar healthspan benefits to continuous MR. Accordingly, we developed two increasingly stringent forms of intermittent MR (IMR) and assessed whether mice maintained on these diets demonstrate the beneficial metabolic changes typically observed for continuous MR. To the best of our knowledge, we show for the first time that IMR produces similar beneficial metabolic effects to continuous MR, including improved glucose homeostasis and protection against diet‐induced obesity and hepatosteatosis. In addition, like continuous MR, IMR confers beneficial changes in the plasma levels of the hormones IGF‐1, FGF‐21, leptin, and adiponectin. Together, our findings demonstrate that the more practicable intermittent form of MR produces similar healthspan benefits to continuous MR, and thus may represent a more appealing alternative to the classical intervention.

A systematic analysis of diet-induced nephroprotection reveals overlapping changes in cysteine catabolism

Caloric Restriction (CR) extends lifespan and augments cellular stress-resistance from yeast to primates, making CR an attractive strategy for organ protection in the clinic. Translation of CR to patients is complex, due to problems regarding adherence, feasibility, and safety concerns in frail patients. Novel tailored dietary regimens, which modulate the dietary composition of macro- and micronutrients rather than reducing calorie intake promise similar protective effects and increased translatability. However, a direct head-to-head comparison to identify the most potent approach for organ protection, as well as overlapping metabolic consequences have not been performed. We systematically analyzed six dietary preconditioning protocols - fasting mimicking diet (FMD), ketogenic diet (KD), dietary restriction of branched chained amino acids (BCAA), two dietary regimens restricting sulfur-containing amino acids (SR80/100) and CR - in a rodent model of renal ischemia-reperfusion injury (IRI) to quantify diet-induced resilience in kidneys. Of the administered diets, FMD, SR80/100 and CR efficiently protect from kidney damage after IRI. Interestingly, these approaches show overlapping changes in oxidative and hydrogen sulfide (H₂S)-dependent cysteine catabolism as a potential common mechanism of organ protection.

Methionine adenosyltransferase 1a antisense oligonucleotides activate the liver-brown adipose tissue axis preventing obesity and associated hepatosteatosis

Altered methionine metabolism is associated with weight gain in obesity. The methionine adenosyltransferase (MAT), catalyzing the first reaction of the methionine cycle, plays an important role regulating lipid metabolism. However, its role in obesity, when a plethora of metabolic diseases occurs, is still unknown. By using antisense oligonucleotides (ASO) and genetic depletion of Mat1a, here, we demonstrate that Mat1a deficiency in diet-induce obese or genetically obese mice prevented and reversed obesity and obesity-associated insulin resistance and hepatosteatosis by increasing energy expenditure in a hepatocyte FGF21 dependent fashion. The increased NRF2-mediated FGF21 secretion induced by targeting Mat1a, mobilized plasma lipids towards the BAT to be catabolized, induced thermogenesis and reduced body weight, inhibiting hepatic de novo lipogenesis. The beneficial effects of Mat1a ASO were abolished following FGF21 depletion in hepatocytes. Thus, targeting Mat1a activates the liver-BAT axis by increasing NRF2-mediated FGF21 secretion, which prevents obesity, insulin resistance and hepatosteatosis.

Impacts of essential amino acids on energy balance

BACKGROUND

Obesity develops due to an imbalance in energy homeostasis, wherein energy intake exceeds energy expenditure. Accumulating evidence shows that manipulations of dietary protein and their component amino acids affect the energy balance, resulting in changes in fat mass and body weight. Amino acids are not only the building blocks of proteins but also serve as signals regulating multiple biological pathways.

SCOPE OF REVIEW

We present the currently available evidence regarding the effects of dietary alterations of a single essential amino acid (EAA) on energy balance and relevant signaling mechanisms at both central and peripheral levels. We summarize the association between EAAs and obesity in humans and the clinical use of modifying the dietary EAA composition for therapeutic intervention in obesity. Finally, similar mechanisms underlying diets varying in protein levels and diets altered of a single EAA are described. The current review would expand our understanding of the contribution of protein and amino acids to energy balance control, thus helping discover novel therapeutic approaches for obesity and related diseases.

MAJOR CONCLUSIONS

Changes in circulating EAA levels, particularly increased branched-chain amino acids (BCAAs), have been reported in obese human and animal models. Alterations in dietary EAA intake result in improvements in fat and weight loss in rodents, and each has its distinct mechanism. For example, leucine deprivation increases energy expenditure, reduces food intake and fat mass, primarily through regulation of the general control nonderepressible 2 (GCN2) and mammalian target of rapamycin (mTOR) signaling. Methionine restriction by 80% decreases fat mass and body weight while developing hyperphagia, primarily through fibroblast growth factor 21 (FGF-21) signaling. Some effects of diets with different protein levels on energy homeostasis are mediated by similar mechanisms. However, reports on the effects and underlying mechanisms of dietary EAA imbalances on human body weight are few, and more investigations are needed in future.

Sex and genetic background define the metabolic, physiologic, and molecular response to protein restriction

Low-protein diets promote metabolic health in humans and rodents. Despite evidence that sex and genetic background are key factors in the response to diet, most protein intake studies examine only a single strain and sex of mice. Using multiple strains and both sexes of mice, we find that improvements in metabolic health in response to reduced dietary protein strongly depend on sex and strain. While some phenotypes were conserved across strains and sexes, including increased glucose tolerance and energy expenditure, we observed high variability in adiposity, insulin sensitivity, and circulating hormones. Using a multi-omics approach, we identified mega-clusters of differentially expressed hepatic genes, metabolites, and lipids associated with each phenotype, providing molecular insight into the differential response to protein restriction. Our results highlight the importance of sex and genetic background in the response to dietary protein level, and the potential importance of a personalized medicine approach to dietary interventions.

Fibroblast Growth Factor 21 Facilitates the Homeostatic Control of Feeding Behavior

Fibroblast growth factor 21 (FGF21) is a stress hormone that is released from the liver in response to nutritional and metabolic challenges. In addition to its well-described effects on systemic metabolism, a growing body of literature now supports the notion that FGF21 also acts via the central nervous system to control feeding behavior. Here we review the current understanding of FGF21 as a hormone regulating feeding behavior in rodents, non-human primates, and humans. First, we examine the nutritional contexts that induce FGF21 secretion. Initial reports describing FGF21 as a 'starvation hormone' have now been further refined. FGF21 is now better understood as an endocrine mediator of the intracellular stress response to various nutritional manipulations, including excess sugars and alcohol, caloric deficits, a ketogenic diet, and amino acid restriction. We discuss FGF21's effects on energy intake and macronutrient choice, together with our current understanding of the underlying neural mechanisms. We argue that the behavioral effects of FGF21 function primarily to maintain systemic macronutrient homeostasis, and in particular to maintain an adequate supply of protein and amino acids for use by the cells.

Molecular mechanisms of dietary restriction promoting health and longevity

Dietary restriction with adequate nutrition is the gold standard for delaying ageing and extending healthspan and lifespan in diverse species, including rodents and non-human primates. In this Review, we discuss the effects of dietary restriction in these mammalian model organisms and discuss accumulating data that suggest that dietary restriction results in many of the same physiological, metabolic and molecular changes responsible for the prevention of multiple ageing-associated diseases in humans. We further discuss how different forms of fasting, protein restriction and specific reductions in the levels of essential amino acids such as methionine and the branched-chain amino acids selectively impact the activity of AKT, FOXO, mTOR, nicotinamide adenine dinucleotide (NAD+), AMP-activated protein kinase (AMPK) and fibroblast growth factor 21 (FGF21), which are key components of some of the most important nutrient-sensing geroprotective signalling pathways that promote healthy longevity.

Extracellular cystine influences human preadipocyte differentiation and correlates with fat mass in healthy adults

Plasma cysteine is associated with human obesity, but it is unknown whether this is mediated by reduced, disulfide (cystine and mixed-disulfides) or protein-bound (bCys) fractions. We investigated which cysteine fractions are associated with adiposity in vivo and if a relevant fraction influences human adipogenesis in vitro. In the current study, plasma cysteine fractions were correlated with body fat mass in 35 adults. Strong positive correlations with fat mass were observed for cystine and mixed disulfides (r ≥ 0.61, P < 0.001), but not the quantitatively major form, bCys. Primary human preadipocytes were differentiated in media containing cystine concentrations varying from 10-50 μM, a range similar to that in plasma. Increasing extracellular cystine (10-50 μM) enhanced mRNA expression of PPARG2 (to sixfold), PPARG1, PLIN1, SCD1 and CDO1 (P = 0.042- < 0.001). Adipocyte lipid accumulation and lipid-droplet size showed dose-dependent increases from lowest to highest cystine concentrations (P < 0.001), and the malonedialdehyde/total antioxidant capacity increased, suggesting increased oxidative stress. In conclusion, increased cystine concentrations, within the physiological range, are positively associated with both fat mass in healthy adults and human adipogenic differentiation in vitro. The potential role of cystine as a modifiable factor regulating human adipocyte turnover and metabolism deserves further study.

Dysregulated Metabolites Serve as Novel Biomarkers for Metabolic Diseases Caused by E-Cigarette Vaping and Cigarette Smoking

Metabolites are essential intermediate products in metabolism, and metabolism dysregulation indicates different types of diseases. Previous studies have shown that cigarette smoke dysregulated metabolites; however, limited information is available with electronic cigarette (e-cig) vaping. We hypothesized that e-cig vaping and cigarette smoking alters systemic metabolites, and we propose to understand the specific metabolic signature between e-cig users and cigarette smokers. Plasma from non-smoker controls, cigarette smokers, and e-cig users was collected, and metabolites were identified by UPLC-MS (ultra-performance liquid chromatography mass spectrometer). Nicotine degradation was activated by e-cig vaping and cigarette smoking with increased concentrations of cotinine, cotinine N-oxide, (S)-nicotine, and (R)-6-hydroxynicotine. Additionally, we found significantly decreased concentrations in metabolites associated with tricarboxylic acid (TCA) cycle pathways in e-cig users versus cigarette smokers, such as d-glucose, (2R,3S)-2,3-dimethylmalate, (R)-2-hydroxyglutarate, O-phosphoethanolamine, malathion, d-threo-isocitrate, malic acid, and 4-acetamidobutanoic acid. Cigarette smoking significant upregulated sphingolipid metabolites, such as d-sphingosine, ceramide, N-(octadecanoyl)-sphing-4-enine, N-(9Z-octadecenoyl)-sphing-4-enine, and N-[(13Z)-docosenoyl]-sphingosine, versus e-cig vaping. Overall, e-cig vaping dysregulated TCA cycle-related metabolites while cigarette smoking altered sphingolipid metabolites. Both e-cig and cigarette smoke increased nicotinic metabolites. Therefore, specific metabolic signatures altered by e-cig vaping and cigarette smoking could serve as potential systemic biomarkers for early pathogenesis of cardiopulmonary diseases.

The regulation of healthspan and lifespan by dietary amino acids

As a key macronutrient and source of essential macromolecules, dietary protein plays a significant role in health. For many years, protein-rich diets have been recommended as healthy due to the satiety-inducing and muscle-building effects of protein, as well as the ability of protein calories to displace allegedly unhealthy calories from fats and carbohydrates. However, clinical studies find that consumption of dietary protein is associated with an increased risk of multiple diseases, especially diabetes, while studies in rodents have demonstrated that protein restriction can promote metabolic health and even lifespan. Emerging evidence suggests that the effects of dietary protein on health and longevity are not mediated simply by protein quantity but are instead mediated by protein quality - the specific amino acid composition of the diet. Here, we discuss how dietary protein and specific amino acids including methionine, the branched chain amino acids (leucine, isoleucine, and valine), tryptophan and glycine regulate metabolic health, healthspan, and aging, with attention to the specific molecular mechanisms that may participate in these effects. Finally, we discuss the potential applicability of these findings to promoting healthy aging in humans.

The adverse metabolic effects of branched-chain amino acids are mediated by isoleucine and valine

Low-protein diets promote metabolic health in rodents and humans, and the benefits of low-protein diets are recapitulated by specifically reducing dietary levels of the three branched-chain amino acids (BCAAs), leucine, isoleucine, and valine. Here, we demonstrate that each BCAA has distinct metabolic effects. A low isoleucine diet reprograms liver and adipose metabolism, increasing hepatic insulin sensitivity and ketogenesis and increasing energy expenditure, activating the FGF21-UCP1 axis. Reducing valine induces similar but more modest metabolic effects, whereas these effects are absent with low leucine. Reducing isoleucine or valine rapidly restores metabolic health to diet-induced obese mice. Finally, we demonstrate that variation in dietary isoleucine levels helps explain body mass index differences in humans. Our results reveal isoleucine as a key regulator of metabolic health and the adverse metabolic response to dietary BCAAs and suggest reducing dietary isoleucine as a new approach to treating and preventing obesity and diabetes.

Dietary Essential Amino Acid Restriction Promotes Hyperdipsia via Hepatic FGF21

Prior studies have reported that dietary protein dilution (DPD) or amino acid dilution promotes heightened water intake (i.e., hyperdipsia) however, the exact dietary requirements and the mechanism responsible for this effect are still unknown. Here, we show that dietary amino acid (AA) restriction is sufficient and required to drive hyperdipsia during DPD. Our studies demonstrate that particularly dietary essential AA (EAA) restriction, but not non-EAA, is responsible for the hyperdipsic effect of total dietary AA restriction (DAR). Additionally, by using diets with varying amounts of individual EAA under constant total AA supply, we demonstrate that restriction of threonine (Thr) or tryptophan (Trp) is mandatory and sufficient for the effects of DAR on hyperdipsia and that liver-derived fibroblast growth factor 21 (FGF21) is required for this hyperdipsic effect. Strikingly, artificially introducing Thr de novo biosynthesis in hepatocytes reversed hyperdipsia during DAR. In summary, our results show that the DPD effects on hyperdipsia are induced by the deprivation of Thr and Trp, and in turn, via liver/hepatocyte-derived FGF21.

Physiologic Responses to Dietary Sulfur Amino Acid Restriction in Mice Are Influenced by Atf4 Status and Biological Sex

BACKGROUND

Dietary sulfur amino acid restriction (SAAR) improves body composition and metabolic health across several model organisms in part through induction of the integrated stress response (ISR).

OBJECTIVE

We investigate the hypothesis that activating transcription factor 4 (ATF4) acts as a converging point in the ISR during SAAR.

METHODS

Using liver-specific or global gene ablation strategies, in both female and male mice, we address the role of ATF4 during dietary SAAR.

RESULTS

We show that ATF4 is dispensable in the chronic induction of the hepatokine fibroblast growth factor 21 while being essential for the sustained production of endogenous hydrogen sulfide. We also affirm that biological sex, independent of ATF4 status, is a determinant of the response to dietary SAAR.

CONCLUSIONS

Our results suggest that auxiliary components of the ISR, which are independent of ATF4, are critical for SAAR-mediated improvements in metabolic health in mice.

Selenium supplementation inhibits IGF-1 signaling and confers methionine restriction-like healthspan benefits to mice

Methionine restriction (MR) dramatically extends the healthspan of several organisms. Methionine-restricted rodents have less age-related pathology and increased longevity as compared with controls, and recent studies suggest that humans might benefit similarly. Mechanistically, it is likely that the decreased IGF-1 signaling that results from MR underlies the benefits of this regimen. Thus, we hypothesized that interventions that decrease IGF-1 signaling would also produce MR-like healthspan benefits. Selenium supplementation inhibits IGF-1 signaling in rats and has been studied for its putative healthspan benefits. Indeed, we show that feeding mice a diet supplemented with sodium selenite results in an MR-like phenotype, marked by protection against diet-induced obesity, as well as altered plasma levels of IGF-1, FGF-21, adiponectin, and leptin. Selenomethionine supplementation results in a similar, albeit less robust response, and also extends budding yeast lifespan. Our results indicate that selenium supplementation is sufficient to produce MR-like healthspan benefits for yeast and mammals.

How Far Are We from Prescribing Fasting as Anticancer Medicine?

(1) Background: the present review provides a comprehensive and up-to date overview of the potential exploitation of fasting as an anticancer strategy. The rationale for this concept is that fasting elicits a differential stress response in the setting of unfavorable conditions, empowering the survival of normal cells, while killing cancer cells. (2) Methods: the present narrative review presents the basic aspects of the hormonal, molecular, and cellular response to fasting, focusing on the interrelationship of fasting with oxidative stress. It also presents nonclinical and clinical evidence concerning the implementation of fasting as adjuvant to chemotherapy, highlighting current challenges and future perspectives. (3) Results: there is ample nonclinical evidence indicating that fasting can mitigate the toxicity of chemotherapy and/or increase the efficacy of chemotherapy. The relevant clinical research is encouraging, albeit still in its infancy. The path forward for implementing fasting in oncology is a personalized approach, entailing counteraction of current challenges, including: (i) patient selection; (ii) fasting patterns; (iii) timeline of fasting and refeeding; (iv) validation of biomarkers for assessment of fasting; and (v) establishment of protocols for patients’ monitoring. (4) Conclusion: prescribing fasting as anticancer medicine may not be far away if large randomized clinical trials consolidate its safety and efficacy.

Sestrin is a key regulator of stem cell function and lifespan in response to dietary amino acids

Dietary restriction (DR) promotes healthy aging in diverse species. Essential amino acids play a key role, but the molecular mechanisms are unknown. The evolutionarily conserved Sestrin protein, an inhibitor of activity of the target of rapamycin complex 1 (TORC1), has recently been discovered as a sensor of amino acids in vitro. Here, we show that Sestrin null mutant flies have a blunted response of lifespan to DR. A mutant Sestrin fly line, with blocked amino acid binding and TORC1 activation, showed delayed development, reduced fecundity, extended lifespan and protection against lifespan-shortening, high-protein diets. Sestrin mediated reduced intestinal stem cell activity and gut cell turnover from DR, and stem cell proliferation in response to dietary amino acids, by regulating the TOR pathway and autophagy. Sestrin expression in intestinal stem cells was sufficient to maintain gut homeostasis and extend lifespan. Sestrin is thus a molecular link between dietary amino acids, stem cell function and longevity.

Effects of dietary restriction on metabolic and cognitive health

Life expectancy in most developed countries has been rising over the past century. In the UK alone, there are about 12 million people over 65 years old and centenarians have increased by 85% in the past 15 years. As a result of the ageing population, which is due mainly to improvements in medical treatments, public health, improved housing and lifestyle choices, there is an associated increase in the prevalence of pathological conditions, such as metabolic disorders, type 2 diabetes, cardiovascular and neurodegenerative diseases, many types of cancer and others. Statistics suggest that nearly 54% of elderly people in the UK live with at least two chronic conditions, revealing the urgency for identifying interventions that can prevent and/or treat such disorders. Non-pharmacological, dietary interventions such as energetic restriction (ER) and methionine restriction (MR) have revealed promising outcomes in increasing longevity and preventing and/or reversing the development of ageing-associated disorders. In this review, we discuss the evidence and mechanisms that are involved in these processes. Fibroblast growth factor 1 and hydrogen sulphide are important molecules involved in the effects of ER and MR in the extension of life span. Their role is also associated with the prevention of metabolic and cognitive disorders, highlighting these interventions as promising modulators for improvement of health span.

Next Generation Strategies for Geroprotection via mTORC1 Inhibition

Inhibition of mTORC1 (mechanistic Target Of Rapamycin Complex 1) with the pharmaceutical rapamycin prolongs the lifespan and healthspan of model organisms including rodents, with evidence now emerging that rapamycin and its analogs may also have rejuvenative effects in dogs and humans. However, the side effects associated with long-term rapamycin treatment, many of which are due to inhibition of a second mTOR complex, mTORC2, have seemed to preclude the routine use of rapamycin as a therapy for age-related diseases. Here, we discuss recent findings suggesting that strong, chronic inhibition of both mTOR complexes may not be necessary to realize the geroprotective effects of rapamycin. Instead, modestly but specifically inhibiting mTORC1 via a variety of emerging techniques, including intermittent or transient treatment with rapamycin derivatives, or specific dietary regimens, may be sufficient to promote health and longevity with reduced side effects. We will also discuss prospects for the development of new molecules that, by harnessing the detailed molecular understanding of mTORC1 signaling developed over the last decade, will provide new routes to the selective inhibition of mTORC1. We conclude that therapies based on the selective inhibition of mTORC1 may soon permit the safer treatment of diseases of aging.

Restriction of essential amino acids dictates the systemic metabolic response to dietary protein dilution

Dietary protein dilution (DPD) promotes metabolic-remodelling and -health but the precise nutritional components driving this response remain elusive. Here, by mimicking amino acid (AA) supply from a casein-based diet, we demonstrate that restriction of dietary essential AA (EAA), but not non-EAA, drives the systemic metabolic response to total AA deprivation; independent from dietary carbohydrate supply. Furthermore, systemic deprivation of threonine and tryptophan, independent of total AA supply, are both adequate and necessary to confer the systemic metabolic response to both diet, and genetic AA-transport loss, driven AA restriction. Dietary threonine restriction (DTR) retards the development of obesity-associated metabolic dysfunction. Liver-derived fibroblast growth factor 21 is required for the metabolic remodelling with DTR. Strikingly, hepatocyte-selective establishment of threonine biosynthetic capacity reverses the systemic metabolic response to DTR. Taken together, our studies of mice demonstrate that the restriction of EAA are sufficient and necessary to confer the systemic metabolic effects of DPD.

Dietary protein dilution, where protein is reduced and replaced by other nutrient sources without caloric restriction, promotes metabolic health via the hepatokine Fgf21. Here, the authors show that essential amino acids threonine and tryptophan are necessary and sufficient to induce these effects.

Methyl-Metabolite Depletion Elicits Adaptive Responses to Support Heterochromatin Stability and Epigenetic Persistence

S-adenosylmethionine (SAM) is the methyl-donor substrate for DNA and histone methyltransferases that regulate epigenetic states and subsequent gene expression. This metabolism-epigenome link sensitizes chromatin methylation to altered SAM abundance, yet the mechanisms that allow organisms to adapt and protect epigenetic information during life-experienced fluctuations in SAM availability are unknown. We identified a robust response to SAM depletion that is highlighted by preferential cytoplasmic and nuclear mono-methylation of H3 Lys 9 (H3K9) at the expense of broad losses in histone di- and tri-methylation. Under SAM-depleted conditions, H3K9 mono-methylation preserves heterochromatin stability and supports global epigenetic persistence upon metabolic recovery. This unique chromatin response was robust across the mouse lifespan and correlated with improved metabolic health, supporting a significant role for epigenetic adaptation to SAM depletion in vivo. Together, these studies provide evidence for an adaptive response that enables epigenetic persistence to metabolic stress.

Effects of inhaled fluticasone propionate on extrinsic tongue muscles in rats

Obstructive sleep apnea (OSA) is more common in patients with asthma, and inhaled corticosteroids may contribute to OSA pathogenesis in these patients. This study tested the effects of orally inhaled fluticasone propionate (FP) on extrinsic tongue muscles. Unanesthetized rats were treated with FP or placebo for 28 days. On day 29, tongue retrusive and protrusive functions were tested via hypoglossal nerve stimulation under a state of anesthesia, followed by genioglossus (GG), styloglossus (SG) and hyoglossus (HG) muscle extraction, after euthanasia, for histology [myosin heavy chain (MHC) fibers and laminin content reflecting extracellular matrix (ECM)]. On protrusive testing, FP increased percent maximum tetanic force at 40 Hz (P = 0.03 vs. placebo) and endurance index (P = 0.029 vs. placebo). On retrusive testing, FP increased maximum twitch (P = 0.026 vs. placebo) and tetanic forces (P = 0.02 vs. placebo) with no effect on endurance index. On histology, FP increased GG cross-sectional area of MHC type IIa (P = 0.036 vs. placebo) and tended to increase type IIb (P = 0.057 vs. placebo) fibers and HG MHC IIx fibers (P = 0.065). The FP group had significantly increased laminin-stained areas, of greatest magnitude in the HG muscle. FP affects tongue protrusive and retrusive functions differently, concurrent with a shift in MHC fibers and increased ECM accumulation. These differential alterations may destabilize the tongue's "muscle hydrostat" during sleep and promote collapse.NEW & NOTEWORTHY The effects of inhaled corticosteroid on upper airway may contribute to OSA pathogenesis in asthma. In this study, we tested the effects of orally inhaled fluticasone propionate on tongue protrusive and retrusive functions and on tongue extrinsic muscle fiber composition and molecular properties. We found that fluticasone treatment: 1) increased protrusive endurance and retrusive maximum twitch and tetanic force; and 2) on histology, increased cross-sectional area of myosin heavy chain (MHC) type IIa fibers and tended to increase cross-sectional area of MHC type IIb fibers in the protrusive muscle and of MHC IIx fibers in the retrusors. It also increased laminin-stained areas, across extrinsic tongue muscles, of greatest magnitude in the retrusors; and 3) reduced protein degradation and activated pathways associated with increased protein synthesis in the protrusor. These differential effects on the protrusors and retrusors may destabilize the tongue's "muscle hydrostat" properties during sleep and promote collapse.

Widespread sex dimorphism in aging and age-related diseases

Although aging is a conserved phenomenon across evolutionary distant species, aspects of the aging process have been found to differ between males and females of the same species. Indeed, observations across mammalian studies have revealed the existence of longevity and health disparities between sexes, including in humans (i.e. with a female or male advantage). However, the underlying mechanisms for these sex differences in health and lifespan remain poorly understood, and it is unclear which aspects of this dimorphism stem from hormonal differences (i.e. predominance of estrogens vs. androgens) or from karyotypic differences (i.e. XX vs. XY sex chromosome complement). In this review, we discuss the state of the knowledge in terms of sex dimorphism in various aspects of aging and in human age-related diseases. Where the interplay between sex differences and age-related differences has not been explored fully, we present the state of the field to highlight important future research directions. We also discuss various dietary, drug or genetic interventions that were shown to improve longevity in a sex-dimorphic fashion. Finally, emerging tools and models that can be leveraged to decipher the mechanisms underlying sex differences in aging are also briefly discussed.

Sexually Dimorphic Effects of Dietary Methionine Restriction are Dependent on Age when the Diet is Introduced

OBJECTIVE

Restricting dietary methionine to 0.17% in male mice increases energy expenditure, reduces fat deposition, and improves metabolic health. The goal of this work was to compare each of these responses in postweaning male and female mice and in physically mature male and female mice.

METHODS

Methionine-restricted (MR) diets were fed to age-matched cohorts of male and female mice for 8 to 10 weeks beginning at 8 weeks of age or beginning at 4 months of age. The physiological and transcriptional responses to MR were compared in the respective cohorts.

RESULTS

Dietary MR produced sexually dimorphic changes in body composition in young growing animals, with males preserving lean at the expense of fat and females preserving fat at the expense of lean. The effects of MR on energy balance were comparable between sexes when the diet was initiated after attainment of physical maturity (4 months), and metabolic and endocrine responses were also comparable between males and females after 8 weeks on the MR diet.

CONCLUSIONS

The sexually dimorphic effects of MR are limited to nutrient partitioning between lean and fat tissue deposition in young, growing mice. Introduction of the diet after physical maturity produced comparable effects on growth and metabolic responses in male and female mice.

A toolbox for the longitudinal assessment of healthspan in aging mice

The number of people aged over 65 is expected to double in the next 30 years. For many, living longer will mean spending more years with the burdens of chronic diseases such as Alzheimer's disease, cardiovascular disease, and diabetes. Although researchers have made rapid progress in developing geroprotective interventions that target mechanisms of aging and delay or prevent the onset of multiple concurrent age-related diseases, a lack of standardized techniques to assess healthspan in preclinical murine studies has resulted in reduced reproducibility and slow progress. To overcome this, major centers in Europe and the United States skilled in healthspan analysis came together to agree on a toolbox of techniques that can be used to consistently assess the healthspan of mice. Here, we describe the agreed toolbox, which contains protocols for echocardiography, novel object recognition, grip strength, rotarod, glucose tolerance test (GTT) and insulin tolerance test (ITT), body composition, and energy expenditure. The protocols can be performed longitudinally in the same mouse over a period of 4-6 weeks to test how candidate geroprotectors affect cardiac, cognitive, neuromuscular, and metabolic health.

Methionine metabolism in health and cancer: a nexus of diet and precision medicine

Methionine uptake and metabolism is involved in a host of cellular functions including methylation reactions, redox maintenance, polyamine synthesis and coupling to folate metabolism, thus coordinating nucleotide and redox status. Each of these functions has been shown in many contexts to be relevant for cancer pathogenesis. Intriguingly, the levels of methionine obtained from the diet can have a large effect on cellular methionine metabolism. This establishes a link between nutrition and tumour cell metabolism that may allow for tumour-specific metabolic vulnerabilities that can be influenced by diet. Recently, a number of studies have begun to investigate the molecular and cellular mechanisms that underlie the interaction between nutrition, methionine metabolism and effects on health and cancer.