Sex-specific metabolic responses to 6 hours of fasting during the active phase in young mice.

KEY POINTS: Night time/active phase food restriction for 6 h impaired glucose intolerance in young male and female mice. Females displayed increased capacity for lipogenesis and triglyceride storage in response to a short daily fast. Females had lower fasting insulin levels and an increased potential for utilizing fat for energy through ß-oxidation compared to males. The need for the inclusion of both sexes, and the treatment of sex as an independent variable, is emphasized within the context of this fasting regime. ABSTRACT: There is growing interest in understanding the mechanistic significance and benefits of fasting physiology in combating obesity. Increasing the fasting phase of a normal day can promote restoration and repair mechanisms that occur during the post-absorptive period. Most studies exploring the effect of restricting food access on mitigating obesity have done so with a large bias towards the use of male mice. Here, we disentangle the roles of sex, food intake and food withdrawal in the response to a short-term daily fasting intervention, in which food was removed for 6 h in the dark/active phase of young, 8-week-old mice. We showed that the removal of food during the dark phase impaired glucose tolerance in males and females, possibly due to the circadian disruption induced by this feeding protocol. Although both sexes demonstrated similar patterns of food intake, body composition and various metabolic markers, there were clear sex differences in the magnitude and extent of these responses. While females displayed enhanced capacity for lipogenesis and triglyceride storage, they also had low fasting insulin levels and an increased potential for utilizing available energy sources such as fat for energy through ß-oxidation. Our results highlight the intrinsic biological and metabolic disparities between male and female mice, emphasizing the growing need for the inclusion of both sexes in scientific research. Furthermore, our results illustrate sex-specific metabolic pathways that regulate lipogenesis, obesity and overall metabolic health.

Maternal macronutrient intake effects on offspring macronutrient targets and metabolism.

OBJECTIVE: Exposure in utero to maternal diet can program offspring health and susceptibility to disease. Using C57BL6/JArc mice, we investigated how maternal dietary protein to carbohydrate balance influences male and female offspring appetite and metabolic health. METHODS: Dams were placed on either a low-protein (LP) or high-protein (HP) diet. Male and female offspring were placed on a food choice experiment post weaning and were then constrained to either a standard diet or Western diet. Food intake, body weight, and composition were measured, and various metabolic tests were performed at different timepoints. RESULTS: Offspring from mothers fed HP diets selected a higher protein intake and had increased body weight in early life relative to offspring from LP diet-fed dams. As predicted by protein leverage theory, higher protein intake targets led to increased food intake when offspring were placed on no-choice diets, resulting in greater body weight and fat mass. The combination of an HP maternal diet and a Western diet further exacerbated this obesity phenotype and led to long-term consequences for body composition and metabolism. CONCLUSIONS: This work could help explain the association between elevated protein intake in humans during early life and increased risk of obesity in childhood and later life.

The effects of paternal dietary fat versus sugar on offspring body composition and anxiety-related behavior.

Increasing evidence suggests that the pre-conception parental environment has long-term consequences for offspring health and disease susceptibility. Though much of the work in this field concentrates on maternal influences, there is growing understanding that fathers also play a significant role in affecting offspring phenotypes. In this study, we investigate effects of altering the proportion of dietary fats and carbohydrates on paternal and offspring body composition and anxiety-related behavior in C57Bl/6-JArc mice. We show that in an isocaloric context, greater dietary fat increased body fat and reduced anxiety-like behavior of studs, whereas increased dietary sucrose had no significant effect. These dietary effects were not reflected in offspring traits, rather, we found sex-specific effects that differed between offspring body composition and behavioral traits. This finding is consistent with past paternal effect studies, where transgenerational effects have been shown to be more prominent in one sex over the other. Here, male offspring of fathers fed high-fat diets were heavier at 10 weeks of age due to increased lean body mass, whereas paternal diet had no significant effect on female offspring body fat or lean mass. In contrast, paternal dietary sugar appeared to have the strongest effects on male offspring behavior, with male offspring of high-sucrose fathers spending less time in the closed arms of the elevated plus maze. Both high-fat and high-sugar paternal diets were found to reduce anxiety-like behavior of female offspring, although this effect was only evident when offspring were fed a control diet. This study provides new understanding of the ways in which diet can shape the behavior of fathers and their offspring and contribute to the development of dietary guidelines to improve obesity and mental health conditions, such as anxiety.

Toward reconciling the roles of FGF21 in protein appetite, sweet preference, and energy expenditure.

Fibroblast growth factor 21 (FGF21), an endocrine signal robustly increased by protein restriction independently of an animal's energy status, exerts profound effects on feeding behavior and metabolism. Here, we demonstrate that considering the nutritional contexts within which FGF21 is elevated can help reconcile current controversies over its roles in mediating macronutrient preference, food intake, and energy expenditure. We show that FGF21 is primarily a driver of increased protein intake in mice and that the effect of FGF21 on sweet preference depends on the carbohydrate balance of the animal. Under no-choice feeding, FGF21 infusion either increased or decreased energy expenditure depending on whether the animal was fed a high- or low-energy diet, respectively. We show that while the role of FGF21 in mediating feeding behavior is complex, its role in promoting protein appetite is robust and that the effects on sweet preference and energy expenditure are macronutrient-state-dependent effects of FGF21.

The Effects of Metformin on Age-Related Changes in the Liver Sinusoidal Endothelial Cell.

Age-related changes in the liver sinusoidal endothelium, particularly the reduction in fenestrations, contribute to insulin resistance in old age. Metformin impacts on the aging process and improves insulin resistance. Therefore, the effects of metformin on the liver sinusoidal endothelium were studied. Metformin increased fenestrations in liver sinusoidal endothelial cells isolated from both young and old mice. Mice administered metformin in the diet for 12 months had increased fenestrations and this was associated with lower insulin levels. The effect of metformin on fenestrations was blocked by inhibitors of AMP-activated protein kinase (AMPK), endothelial nitric oxide synthase, and myosin light chain kinase phosphorylation. Metformin led to increased transgelin expression and structural changes in the actin cytoskeleton but had no effect on lactate production. Metformin also generated fenestration-like structures in SK-Hep1 cells, a liver endothelial cell line, and this was associated with increased ATP, cGMP, and mitochondrial activity. In conclusion, metformin ameliorates age-related changes in the liver sinusoidal endothelial cell via AMPK and endothelial nitric oxide pathways, which might promote insulin sensitivity in the liver, particularly in old age.

Of Older Mice and Men: Branched-Chain Amino Acids and Body Composition.

Protein and branched-chain amino acid (BCAA) intake are associated with changes in circulating BCAAs and influence metabolic health in humans and rodents. However, the relationship between BCAAs and body composition in both species is unclear, with many studies questioning the translatability of preclinical findings to humans. Here, we assessed and directly compared the relationship between circulating BCAAs, body composition, and intake in older mice and men. Body weight and body fat were positively associated with circulating BCAA levels in both mouse and human, which remained significant after adjustments for age, physical activity, number of morbidities, smoking status, and source of income in the human cohort. Macronutrient intakes were similarly associated with circulating BCAA levels; however, the relationship between protein intake and BCAAs were more pronounced in the mice. These findings indicate that the relationship between circulating BCAAs, body composition, and intakes are comparable in both species, suggesting that the mouse is an effective model for examining the effects of BCAAs on body composition in older humans.

Branched chain amino acids impact health and lifespan indirectly via amino acid balance and appetite control.

Elevated branched chain amino acids (BCAAs) are associated with obesity and insulin resistance. How long-term dietary BCAAs impact late-life health and lifespan is unknown. Here, we show that when dietary BCAAs are varied against a fixed, isocaloric macronutrient background, long-term exposure to high BCAA diets leads to hyperphagia, obesity and reduced lifespan. These effects are not due to elevated BCAA per se or hepatic mTOR activation, but rather due to a shift in the relative quantity of dietary BCAAs and other AAs, notably tryptophan and threonine. Increasing the ratio of BCAAs to these AAs resulted in hyperphagia and is associated with central serotonin depletion. Preventing hyperphagia by calorie restriction or pair-feeding averts the health costs of a high BCAA diet. Our data highlight a role for amino acid quality in energy balance and show that health costs of chronic high BCAA intakes need not be due to intrinsic toxicity but, rather, a consequence of hyperphagia driven by AA imbalance.

Comparing the Effects of Low-Protein and High-Carbohydrate Diets and Caloric Restriction on Brain Aging in Mice.

Calorie restriction (CR) increases lifespan and improves brain health in mice. Ad libitum low-protein, high-carbohydrate (LPHC) diets also extend lifespan, but it is not known whether they are beneficial for brain health. We compared hippocampus biology and memory in mice subjected to 20% CR or provided ad libitum access to one of three LPHC diets or to a control diet. Patterns of RNA expression in the hippocampus of 15-month-old mice were similar between mice fed CR and LPHC diets when we looked at genes associated with longevity, cytokines, and dendrite morphogenesis. Nutrient-sensing proteins, including SIRT1, mTOR, and PGC1α, were also influenced by diet; however, the effects varied by sex. CR and LPHC diets were associated with increased dendritic spines in dentate gyrus neurons. Mice fed CR and LPHC diets had modest improvements in the Barnes maze and novel object recognition. LPHC diets recapitulate some of the benefits of CR on brain aging.