Fasting is required for many of the benefits of calorie restriction in the 3xTg mouse model of Alzheimer's disease.

Caloric restriction (CR) is a widely recognized geroprotective intervention that slows or prevents Alzheimer's disease (AD) in animal models. CR is typically implemented via feeding mice a single meal per day; as CR mice rapidly consume their food, they are subject to a prolonged fast between meals. While CR has been shown to improve metabolic and cognitive functions and suppress pathological markers in AD mouse models, the specific contributions of fasting versus calorie reduction remains unclear. Here, we investigated the contribution of fasting and energy restriction to the beneficial effects of CR on AD progression. To test this, we placed 6-month-old 3xTg mice on one of several diet regimens, allowing us to dissect the effects of calories and fasting on metabolism, AD pathology, and cognition. We find that energy restriction alone, without fasting, was sufficient to improve glucose tolerance and reduce adiposity in both sexes, and to reduce Aß plaques and improve aspects of cognitive performance in females. However, we find that a prolonged fast between meals is necessary for many of the benefits of CR, including improved insulin sensitivity, reduced phosphorylation of tau, decreased neuroinflammation, inhibition of mTORC1 signaling, and activation of autophagy, as well as for the full cognitive benefits of CR. Finally, we find that fasting is essential for the benefits of CR on survival in male 3xTg mice. Overall, our results demonstrate that fasting is required for the full benefits of a CR diet on the development and progression of AD in 3xTg mice, and suggest that both when and how much we eat influences the development and progress of AD.

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.

A nutrigeroscience approach: Dietary macronutrients and cellular senescence.

Cellular senescence, a process in which a cell exits the cell cycle in response to stressors, is one of the hallmarks of aging. Senescence and the senescence-associated secretory phenotype (SASP)-a heterogeneous set of secreted factors that disrupt tissue homeostasis and promote the accumulation of senescent cells-reprogram metabolism and can lead to metabolic dysfunction. Dietary interventions have long been studied as methods to combat age-associated metabolic dysfunction, promote health, and increase lifespan. A growing body of literature suggests that senescence is responsive to diet, both to calories and specific dietary macronutrients, and that the metabolic benefits of dietary interventions may arise in part through reducing senescence. Here, we review what is currently known about dietary macronutrients' effect on senescence and the SASP, the nutrient-responsive molecular mechanisms that may mediate these effects, and the potential for these findings to inform the development of a nutrigeroscience approach to healthy aging.

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.

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.

Late-life isoleucine restriction promotes physiological and molecular signatures of healthy aging.

In defiance of the paradigm that calories from all sources are equivalent, we and others have shown that dietary protein is a dominant regulator of healthy aging. The restriction of protein or the branched-chain amino acid isoleucine promotes healthspan and extends lifespan when initiated in young or adult mice. However, many interventions are less efficacious or even deleterious when initiated in aged animals. Here, we investigate the physiological, metabolic, and molecular consequences of consuming a diet with a 67% reduction of all amino acids (Low AA), or of isoleucine alone (Low Ile), in male and female C57BL/6J.Nia mice starting at 20 months of age. We find that both diet regimens effectively reduce adiposity and improve glucose tolerance, which were benefits that were not mediated by reduced calorie intake. Both diets improve specific aspects of frailty, slow multiple molecular indicators of aging rate, and rejuvenate the aging heart and liver at the molecular level. These results demonstrate that Low AA and Low Ile diets can drive youthful physiological and molecular signatures, and support the possibility that these dietary interventions could help to promote healthy aging in older adults.

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.

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

Over the last decade, it has become evident that dietary protein is a critical regulator of metabolic health and aging. Low protein diets are associated with healthy aging in humans, and we and others 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. We found that PR induces sex-specific alterations in circulating metabolites and in the brain 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.

Dual Regulation of Spine-Specific and Synapse-to-Nucleus Signaling by PKCδ during Plasticity.

The activity-dependent plasticity of synapses is believed to be the cellular basis of learning. These synaptic changes are mediated through the coordination of local biochemical reactions in synapses and changes in gene transcription in the nucleus to modulate neuronal circuits and behavior. The protein kinase C (PKC) family of isozymes has long been established as critical for synaptic plasticity. However, because of a lack of suitable isozyme-specific tools, the role of the novel subfamily of PKC isozymes is largely unknown. Here, through the development of fluorescence lifetime imaging-fluorescence resonance energy transfer activity sensors, we investigate novel PKC isozymes in synaptic plasticity in CA1 pyramidal neurons of mice of either sex. We find that PKCδ is activated downstream of TrkB and DAG production, and that the spatiotemporal nature of its activation depends on the plasticity stimulation. In response to single-spine plasticity, PKCδ is activated primarily in the stimulated spine and is required for local expression of plasticity. However, in response to multispine stimulation, a long-lasting and spreading activation of PKCδ scales with the number of spines stimulated and, by regulating cAMP response-element binding protein activity, couples spine plasticity to transcription in the nucleus. Thus, PKCδ plays a dual functional role in facilitating synaptic plasticity.SIGNIFICANCE STATEMENT Synaptic plasticity, or the ability to change the strength of the connections between neurons, underlies learning and memory and is critical for brain health. The protein kinase C (PKC) family is central to this process. However, understanding how these kinases work to mediate plasticity has been limited by a lack of tools to visualize and perturb their activity. Here, we introduce and use new tools to reveal a dual role for PKCδ in facilitating local synaptic plasticity and stabilizing this plasticity through spine-to-nucleus signaling to regulate transcription. This work provides new tools to overcome limitations in studying isozyme-specific PKC function and provides insight into molecular mechanisms of synaptic plasticity.

FGF21 has a sex-specific role in calorie-restriction-induced beiging of white adipose tissue in mice.

Calorie restriction (CR) promotes healthspan and extends the lifespan of diverse organisms, including mice, and there is intense interest in understanding the molecular mechanisms by which CR functions. Some studies have demonstrated that CR induces fibroblast growth factor 21 (FGF21), a hormone that regulates energy balance and that when overexpressed, promotes metabolic health and longevity in mice, but the role of FGF21 in the response to CR has not been fully investigated. We directly examined the role of FGF21 in the physiological and metabolic response to a CR diet by feeding Fgf21-/- and wild-type control mice either ad libitum (AL) diet or a 30% CR diet for 15 weeks. Here, we find that FGF21 is largely dispensable for CR-induced improvements in body composition and energy balance, but that lack of Fgf21 blunts CR-induced changes aspects of glucose regulation and insulin sensitivity in females. Surprisingly, despite not affecting CR-induced changes in energy expenditure, loss of Fgf21 significantly blunts CR-induced beiging of white adipose tissue in male but not female mice. Our results shed new light on the molecular mechanisms involved in the beneficial effects of a CR diet, clarify that FGF21 is largely dispensable for the metabolic effects of a CR diet, and highlight a sex-dependent role for FGF21 in the molecular adaptation of white adipose tissue to CR.

Tissue specificity of senescent cell accumulation during physiologic and accelerated aging of mice.

Senescent cells accumulate with age in vertebrates and promote aging largely through their senescence-associated secretory phenotype (SASP). Many types of stress induce senescence, including genotoxic stress. ERCC1-XPF is a DNA repair endonuclease required for multiple DNA repair mechanisms that protect the nuclear genome. Humans or mice with reduced expression of this enzyme age rapidly due to increased levels of spontaneous, genotoxic stress. Here, we asked whether this corresponds to an increased level of senescent cells. p16Ink4a and p21Cip1 mRNA were increased ~15-fold in peripheral lymphocytes from 4- to 5-month-old Ercc1-/∆ and 2.5-year-old wild-type (WT) mice, suggesting that these animals exhibit a similar biological age. p16Ink4a and p21Cip1 mRNA were elevated in 10 of 13 tissues analyzed from 4- to 5-month-old Ercc1-/∆ mice, indicating where endogenous DNA damage drives senescence in vivo. Aged WT mice had similar increases of p16Ink4a and p21Cip1 mRNA in the same 10 tissues as the mutant mice. Senescence-associated ß-galactosidase activity and p21Cip1 protein also were increased in tissues of the progeroid and aged mice, while Lamin B1 mRNA and protein levels were diminished. In Ercc1-/Δ mice with a p16Ink4a luciferase reporter, bioluminescence rose steadily with age, particularly in lung, thymus, and pancreas. These data illustrate where senescence occurs with natural and accelerated aging in mice and the relative extent of senescence among tissues. Interestingly, senescence was greater in male mice until the end of life. The similarities between Ercc1-/∆ and aged WT mice support the conclusion that the DNA repair-deficient mice accurately model the age-related accumulation of senescent cells, albeit six-times faster.