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Alzheimer’s disease (AD) is an age-associated neurodegenerative disease. As the population ages, the increasing prevalence of AD threatens massive healthcare costs in the coming decades. Unfortunately, traditional drug development efforts for AD have proven largely unsuccessful. A geroscience approach to AD suggests that since aging is the main driver of AD, targeting aging itself may be an effective way to prevent or treat AD. Here, we discuss the effectiveness of geroprotective interventions on AD pathology and cognition in the widely utilized triple-transgenic mouse model of AD (3xTg-AD) which develops both β-amyloid and tau pathologies characteristic of human AD, as well as cognitive deficits. We discuss the beneficial impacts of calorie restriction (CR), the gold standard for geroprotective interventions, and the effects of other dietary interventions including protein restriction. We also discuss the promising preclinical results of geroprotective pharmaceuticals, including rapamycin and medications for type 2 diabetes. Though these interventions and treatments have beneficial effects in the 3xTg-AD model, there is no guarantee that they will be as effective in humans, and we discuss the need to examine these interventions in additional animal models as well as the urgent need to test if some of these approaches can be translated from the lab to the bedside for the treatment of humans with AD.

Caloric restriction slows or prevents Alzheimer’s disease in animal models. Calorie restriction is typically implemented in rodents through feeding once per day; as the animals quickly consume their food, they are subject to a prolonged self-imposed fasting period between meals. Here, we examine the distinct contributions of fasting and reduced calories to the beneficial effects of calorie restriction on Alzheimer’s disease by placing male and female 3xTg and non-transgenic control mice on a series of diet regimens enabling us to dissect the effects of calories and fasting. We find that reducing calories alone improves body weight and glucose tolerance. However, a prolonged fast between meals is necessary for many of the benefits of calorie restriction, including improved insulin sensitivity, reduced Alzheimer’s pathology, improved neuroprotective signaling, and improved cognition. Overall, our results suggest that both when and how much we eat may influence the development and progression of Alzheimer’s disease. Caloric restriction improves Alzheimer’s Disease outcomes in mice, but this diet not only reduces calories, but imposes a prolonged fast between meals. Here, the authors show this fast is essential to improve Alzheimer’s pathology and cognition.

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. There is growing need for ways to slow or prevent Alzheimer’s disease (AD). Here, the authors demonstrate that a low protein diet can protect against metabolic dysfunction, slow AD progression, and preserve cognitive function in a mouse model of AD.

Calorie restriction (CR) promotes healthy ageing in diverse species. Recently, it has been shown that fasting for a portion of each day has metabolic benefits and promotes lifespan. These findings complicate the interpretation of rodent CR studies, in which animals typically eat only once per day and rapidly consume their food, which collaterally imposes fasting. Here we show that a prolonged fast is necessary for key metabolic, molecular and geroprotective effects of a CR diet. Using a series of feeding regimens, we dissect the effects of calories and fasting, and proceed to demonstrate that fasting alone recapitulates many of the physiological and molecular effects of CR. Our results shed new light on how both when and how much we eat regulate metabolic health and longevity, and demonstrate that daily prolonged fasting, and not solely reduced caloric intake, is likely responsible for the metabolic and geroprotective benefits of a CR diet. Pak et al. show that prolonged fasting is required for the effects of calorie restriction on insulin sensitivity, fuel utilization and ageing in mice.

Caloric restriction (CR) extends the health and lifespan of diverse species. When fed once daily, CR‐treated mice rapidly consume their food and endure a prolonged fast between meals. As fasting is associated with a rise in circulating ketone bodies, we investigated the role of ketogenesis in CR using mice with whole‐body ablation of Hmgcs2, the rate‐limiting enzyme producing the main ketone body β‐hydroxybutyrate (βHB). Here, we report that Hmgcs2 is largely dispensable for many metabolic benefits of CR, including CR‐driven changes in adiposity, glycemic control, liver autophagy, and energy balance. Although we observed sex‐specific effects of Hmgcs2 on insulin sensitivity, fuel selection, and adipocyte gene expression, the overall physiological response to CR remained robust in mice lacking Hmgcs2. To gain insight into why the deletion of Hmgcs2 does not disrupt CR, we measured fasting βHB levels as mice initiated a CR diet. Surprisingly, as mice adapt to CR, they no longer engage in high levels of ketogenesis during the daily fast. Our work suggests that the metabolic benefits of long‐term CR are not mediated by ketogenesis. In this study, we demonstrated that metabolic responses to a daily‐fed caloric restriction (CR) protocol remain robust in mice that cannot engage in canonical ketogenesis. This surprising finding is due to mice physiologically adapting to the daily bouts of fasting during CR by downregulating ketone production.

Dietary protein is a key regulator of healthy aging in both mice and humans. In mice, reducing dietary levels of the branched‐chain amino acids (BCAAs) recapitulates many of the benefits of a low protein diet; BCAA‐restricted diets extend lifespan, reduce frailty, and improve metabolic health, while BCAA supplementation shortens lifespan, promotes obesity, and impairs glycemic control. Recently, high protein diets have been shown to promote cellular senescence, a hallmark of aging implicated in many age‐related diseases, in the liver of mice. Here, we test the hypothesis that the effects of high protein diets on metabolic health and on cellular senescence are mediated by BCAAs. We find that reducing dietary levels of BCAAs protects male mice from the negative metabolic consequences of both normal and high protein diets. Further, we identify tissue‐specific effects of BCAAs on cellular senescence, with restriction of all three BCAAs—but not individual BCAAs—protecting from hepatic cellular senescence while potentiating cellular senescence in white adipose tissue. We also find that these effects are sex‐specific. We find that the effects of BCAAs on hepatic cellular senescence are cell‐autonomous, with lower levels of BCAAs protecting cultured cells from antimycin‐A induced senescence. Our results demonstrate a direct effect of a specific dietary component on a hallmark of aging and suggest that cellular senescence may be highly susceptible to dietary interventions. Restriction of dietary BCAAs protects male mice from the metabolic consequences of both normal‐ and high‐protein diets. BCAA restriction also protects from hepatic cellular senescence in vivo and in vitro, especially in the context of mitochondrial stress.

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.

Objective Alexander disease (AxD) is a severe neurodegenerative disorder caused by gain‐of‐function mutations in the gene for GFAP, which lead to protein aggregation and a primary astrocytopathy. Symptoms vary, but failure to thrive (FTT) and frequent emesis are common and cause significant morbidity. Here we investigate GDF15, a member of the TGFβ superfamily, which regulates energy balance and appetite, as a potential mediator of FTT in AxD. Methods In this study, we use the Gfap+/R237H rat model (R237H), in which pups fail to gain weight after weaning and become frail and impaired as they mature, to assess muscle atrophy, energy expenditure, and feeding behavior in AxD. We measure GDF15 in brain and cerebrospinal fluid (CSF), assess activation of its receptor GFRAL in area postrema neurons, and use GFAP suppression to correlate FTT phenotypes with GDF15 expression. Finally, we measure GDF15 in patients with AxD. Results R237H rats show reduced lean and fat mass and muscle atrophy despite reduced energy expenditure, and at an early age exhibit pica and anorexia. GDF15 is expressed by R237H rat astrocytes and is elevated in brainstem and CSF, but not in plasma. Neurons expressing GFRAL, a mediator of GDF15‐induced appetite suppression, are activated in the area postrema. Suppression of GFAP using antisense oligonucleotides normalizes weight gain and GDF15 levels in brainstem and CSF. In human AxD, GDF15 is elevated in CSF, but not in blood. Interpretation GDF15 is associated with FTT in AxD and provides both a target and useful biomarker for the development of future therapeutics.

Background Thirteen-lined ground squirrels ( Ictidomys tridecemlineatus ) are obligate hibernators and are only active 4–5 months annually. During this period, squirrels rapidly acquire fat for use during hibernation. We investigated how the gut microbiome changed over the active season in the mucosa and lumen of two gut sections: the cecum and ileum. We sequenced the 16S rRNA gene to assess diversity and composition of the squirrel gut microbiome and used differential abundance and network analyses to identify relationships among gut sections. Results Microbial composition significantly differed between the cecum and ileum, and within the ileum between the mucosa and lumen. Cecum mucosa and lumen samples did not differ in alpha diversity and composition, and clustered by individual squirrel. Ileum mucosa and lumen samples differed in community composition, which can likely be attributed to the transient nature of food-associated bacteria in the lumen. We did not detect a shift in microbiome diversity and overall composition over the duration of the active season, indicating that the squirrel microbiome may be relatively robust to changes in physiology. Conclusions Overall, we found that the 13-lined ground squirrel microbiome is shaped by microenvironment during the active season. Our results provide baseline data for new avenues of research, such as investigating potential differences in microbial function among these physiologically unique gut environments.

Obesity is a worldwide pandemic with significant comorbidities. It is often accompanied by mild inflammation of the intestine followed by inflammation of metabolic tissues such as liver, adipose tissue, and skeletal muscle. Several laboratory models of obesity exist, but seasonal models like hibernators may be valuable for understanding the pathogenesis of obesity independent of genetic or high-fat diet-induced changes. As part of their annual cycle, obligate hibernators, like the 13-lined ground squirrel (Ictidomys tridecemlineatus), undergo a rapid shift from a lean to an obese state to store energy in the form of fat for their prolonged winter fast. Here, we show that ground squirrels gained mass steadily throughout the active season despite a drop in energy intake starting around 9 weeks post-hibernation. Glucose tolerance tests revealed a significant decrease in tolerance late in the active season. In visceral adipose, we found increases in adipocyte size, tumor necrosis factor (TNF)-α and interleukin (IL)-6 levels. IL-6 levels also increased in liver and muscle and TNF-α increased in the ileum late in the active season. Levels of the anti-inflammatory cytokine, IL-10, decreased in visceral adipose and colon tissues around the same time. These data suggest metabolic inflammation develops along with adiposity late in the squirrels’ active season.