Benefits of calorie restriction in mice are mediated via energy imbalance, not absolute energy or protein intake.

Caloric restriction (CR) results in reduced energy and protein intake, raising questions about protein restriction's contribution to CR longevity benefits. We kept ad libitum (AL)-fed male C57BL/6J mice at 27°C (AL27) and pair-fed (PF) mice at 22°C (22(PF27)). The 22(PF27) group was fed to match AL27 while restricted for calories due to cold-induced metabolism. The 22(PF27) mice had significantly lower body weight, lean mass, fat mass, leptin, IGF-1, and TNF-α levels than AL27 mice (p<0.001 for all). Manipulations over ~11 weeks resulted in significant differences in body temperature, physical activity, and expression of key genes linked to hunger in the hypothalamus. Survival was significantly greater in 22(PF27) compared to AL27 overall (p<0.001). CR in the context of equivalent energy and protein intake resulted in hormonal, metabolic, and physiological benefits and extended longevity. Hence, energy imbalance, rather than low energy or protein intake per se, mediates the benefits of CR.

Not feeling the heat? Effects of dietary protein on satiation and satiety in mice are not due to its impact on body temperature.

Dietary protein modulates food intake (FI) via unclear mechanism(s). One possibility is that higher protein leads to greater post-ingestive heat production (Specific dynamic action: SDA) leading to earlier meal termination (increased satiation), and inhibition of further intake (increased satiety). The influence of dietary protein on feeding behaviour in C57BL/6J mice was tested using an automated FI monitoring system (BioDAQ), simultaneous to body temperature (Tb). Total FI, inter meal intervals (IMI, satiety) and meal size (MS, satiation) were related to changes in Tb after consuming low (5%, LP), moderate (15%, MP) and high (30%, HP) protein diets. Diets were tested over three conditions: 1) room temperature (RT, 21 ± 1 °C), 2) room temperature and running wheels (RTRW) and 3) low temperature (10 °C) and running wheels (LTRW). The differences between diets and conditions were also compared using mixed models. Mice housed at RT fed HP diet, reduced total FI compared with LP and MP due to earlier meal termination (satiation effect). FI was lowered in RTRW conditions with no differences between diets. FI significantly increased under LTRW conditions for all diets, with protein content leading to earlier meal termination (satiation) but not the intervals between feeding bouts (satiety). Tb fell immediately after feeding in all conditions. Despite a reduction in total FI in mice fed HP, mediated via increased satiation, this effect was not linked to increased Tb during meals. We conclude effects of dietary protein on intake are not mediated via SDA and Tb.

A step toward precision gerontology: Lifespan effects of calorie and protein restriction are consistent with predicted impacts on entropy generation.

Understanding aging is a key biological goal. Precision gerontology aims to predict how long individuals will live under different treatment scenarios. Calorie and protein restriction (CR and PR) extend lifespan in many species. Using data from C57BL/6 male mice under graded CR or PR, we introduce a computational thermodynamic model for entropy generation, which predicted the impact of the manipulations on lifespan. Daily entropy generation decreased significantly with increasing CR level, but not PR. Our predictions indicated the lifespan of CR mice should increase by 13 to 56% with 10 to 40% CR, relative to ad libitum-fed animals. This prediction was broadly consistent with the empirical observation of the lifespan impacts of CR in rodents. Modeling entropy fluxes may be a future strategy to identify antiaging interventions.

The Effects of Graded Levels of Calorie Restriction: XX. Impact of Long-Term Graded Calorie Restriction on Survival and Body Mass Dynamics in Male C57BL/6J Mice.

Calorie restriction (CR) typically promotes a reduction in body mass, which correlates with increased lifespan. We evaluated the overall changes in survival, body mass dynamics, and body composition following long-term graded CR (580 days/19 months) in male C57BL/6J mice. Control mice (0% restriction) were fed ad libitum in the dark phase only (12-hour ad libitum [12AL]). CR groups were restricted by 10%-40% of their baseline food intake (10CR, 20CR, 30CR, and 40CR). Body mass was recorded daily, and body composition was measured at 8 time points. At 728 days/24 months, all surviving mice were culled. A gradation in survival rate over the CR groups was found. The pattern of body mass loss differed over the graded CR groups. Whereas the lower CR groups rapidly resumed an energy balance with no significant loss of fat or fat-free mass, changes in the 30 and 40CR groups were attributed to higher fat-free mass loss and protection of fat mass. Day-to-day changes in body mass were less variable under CR than for the 12AL group. There was no indication that body mass was influenced by external factors. Partial autocorrelation analysis examined the relationship between daily changes in body masses. A negative correlation between mass on Day 0 and Day +1 declined with age in the 12AL but not the CR groups. A reduction in the correlation with age suggested body mass homeostasis is a marker of aging that declines at the end of life and is protected by CR.

The Effects of Graded Levels of Calorie Restriction: XIX. Impact of Graded Calorie Restriction on Protein Expression in the Liver.

Calorie restriction (CR) extends life span by modulating the mechanisms involved in aging. We quantified the hepatic proteome of male C57BL/6 mice exposed to graded levels of CR (0%-40% CR) for 3 months, and evaluated which signaling pathways were most affected. The metabolic pathways most significantly stimulated by the increase in CR, included the glycolysis/gluconeogenesis pathway, the pentose phosphate pathway, the fatty acid degradation pathway, the valine, leucine, and isoleucine degradation pathway, and the lysine degradation pathway. The metabolism of xenobiotics by cytochrome P450 pathway was activated and feminized by increased CR, while production in major urinary proteins (Mups) was strongly reduced, consistent with a reduced investment in reproduction as predicted by the disposable soma hypothesis. However, we found no evidence of increased somatic protection, and none of the 4 main pathways implied to be linked to the impact of CR on life span (insulin/insulin-like growth factor [IGF-1], nuclear factor-κB [NF-κB], mammalian Target of Rapamycin [mTOR], and sirtuins) as well as pathways in cancer, were significantly changed at the protein level in relation to the increase in CR level. This was despite previous work at the transcriptome level in the same individuals indicating such changes. On the other hand, we found Aldh2, Aldh3a2, and Aldh9a1 in carnitine biosynthesis and Acsl5 in carnitine shuttle system were up-regulated by increased CR, which are consistent with our previous work on metabolome of the same individuals. Overall, the patterns of protein expression were more consistent with a "clean cupboards" than a "disposable soma" interpretation.

Fur removal promotes an earlier expression of involution-related genes in mammary gland of lactating mice.

Peak lactation occurs when milk production is at its highest. The factors limiting peak lactation performance have been subject of intense debate. Milk production at peak lactation appears limited by the capacity of lactating females to dissipate body heat generated as a by-product of processing food and producing milk. As a result, manipulations that enhance capacity to dissipate body heat (such as fur removal) increase peak milk production. We investigated the potential correlates of shaving-induced increases in peak milk production in laboratory mice. By transcriptomic profiling of the mammary gland, we searched for the mechanisms underlying experimentally increased milk production and its consequences for mother-young conflict over weaning, manifested by advanced or delayed involution of mammary gland. We demonstrated that shaving-induced increases in milk production were paradoxically linked to reduced expression of some milk synthesis-related genes. Moreover, the mammary glands of shaved mice had a gene expression profile indicative of earlier involution relative to unshaved mice. Once provided with enhanced capacity to dissipate body heat, shaved mice were likely to rear their young to independence faster than unshaved mothers.

The Effects of Graded Levels of Calorie Restriction: XVIII.Tissue-Specific Changes in Cell Size and Number in Response to Calorie Restriction.

Calorie restriction (CR) without malnutrition increases the health and life span of diverse taxa. The mechanism(s) behind CR are debated but may be directly linked to body composition changes that maintain energy balance. During a deficit, energy is primarily obtained from white adipose tissue (WAT; utilized) while other tissues remain unchanged (protected) or grow (invested) relative to body mass. The changes in mass of 6 tissues from 48 male C57BL/6 mice following 3-month graded (10%, 20%, 30%, or 40%) CR or fed ad libitum for 12 or 24 hours a day were related to cell size (hypo/hypertrophy) and/or number (hypo/hyperplasia). Tissues studied were retroperitoneal and subcutaneous WAT, brown adipose tissue (BAT; utilized), lungs (protected), and stomach and cecum (invested). Methodology was based on number of nuclei/tissue equaling the number of cells. Extracted DNA was quantified and used to estimate cell numbers (total DNA/DNA per diploid nucleus) and size (tissue mass/nuclei number). WAT utilization was caused solely by hypotrophy whereas BAT utilization resulted from reduced cell number and size. WAT cell size positively correlated with circulating hormones related to energy balance, and BAT cell number and size positively correlated with body temperature. No changes were found in the lungs, consistent with their protected status, whereas hyperplasia appeared to be the dominant mechanism for invested alimentary-tract tissues. These findings indicate the pattern of change of cell size and number across increasing levels of short-term CR is tissue-specific.

The effects of graded calorie restriction XVII: Multitissue metabolomics reveals synthesis of carnitine and NAD, and tRNA charging as key pathways.

The evolutionary context of why caloric restriction (CR) activates physiological mechanisms that slow the process of aging remains unclear. The main goal of this analysis was to identify, using metabolomics, the common pathways that are modulated across multiple tissues (brown adipose tissue, liver, plasma, and brain) to evaluate two alternative evolutionary models: the "disposable soma" and "clean cupboards" ideas. Across the four tissues, we identified more than 10,000 different metabolic features. CR altered the metabolome in a graded fashion. More restriction led to more changes. Most changes, however, were tissue specific, and in some cases, metabolites changed in opposite directions in different tissues. Only 38 common metabolic features responded to restriction in the same way across all four tissues. Fifty percent of the common altered metabolites were carboxylic acids and derivatives, as well as lipids and lipid-like molecules. The top five modulated canonical pathways were l-carnitine biosynthesis, NAD (nicotinamide adenine dinucleotide) biosynthesis from 2-amino-3-carboxymuconate semialdehyde, S-methyl-5'-thioadenosine degradation II, NAD biosynthesis II (from tryptophan), and transfer RNA (tRNA) charging. Although some pathways were modulated in common across tissues, none of these reflected somatic protection, and each tissue invoked its own idiosyncratic modulation of pathways to cope with the reduction in incoming energy. Consequently, this study provides greater support for the clean cupboards hypothesis than the disposable soma interpretation.

Protein quality and quantity influence the effect of dietary fat on weight gain and tissue partitioning via host-microbiota changes.

We investigated how protein quantity (10%-30%) and quality (casein and whey) interact with dietary fat (20%-55%) to affect metabolic health in adult mice. Although dietary fat was the main driver of body weight gain and individual tissue weight, high (30%) casein intake accentuated and high whey intake reduced the negative metabolic aspects of high fat. Jejunum and liver transcriptomics revealed increased intestinal permeability, low-grade inflammation, altered lipid metabolism, and liver dysfunction in casein-fed but not whey-fed animals. These differential effects were accompanied by altered gut size and microbial functions related to amino acid degradation and lipid metabolism. Fecal microbiota transfer confirmed that the casein microbiota increases and the whey microbiota impedes weight gain. These data show that the effects of dietary fat on weight gain and tissue partitioning are further influenced by the quantity and quality of the associated protein, primarily via effects on the microbiota.

Very-low-protein diets lead to reduced food intake and weight loss, linked to inhibition of hypothalamic mTOR signaling, in mice.

The protein leverage hypothesis predicts that low dietary protein should increase energy intake and cause adiposity. We designed 10 diets varying from 1% to 20% protein combined with either 60% or 20% fat. Contrasting the expectation, very low protein did not cause increased food intake. Although these mice had activated hunger signaling, they ate less food, resulting in decreased body weight and improved glucose tolerance but not increased frailty, even under 60% fat. Moreover, they did not show hyperphagia when returned to a 20% protein diet, which could be mimicked by treatment with rapamycin. Intracerebroventricular injection of AAV-S6K1 significantly blunted the decrease in both food intake and body weight in mice fed 1% protein, an effect not observed with inhibition of eIF2a, TRPML1, and Fgf21 signaling. Hence, the 1% protein diet induced decreased food intake and body weight via a mechanism partially dependent on hypothalamic mTOR signaling.

The Effects of Graded Levels of Calorie Restriction: XVI. Metabolomic Changes in the Cerebellum Indicate Activation of Hypothalamocerebellar Connections Driven by Hunger Responses.

Calorie restriction (CR) remains the most robust intervention to extend life span and improve healthspan. Though the cerebellum is more commonly associated with motor control, it has strong links with the hypothalamus and is thought to be associated with nutritional regulation and adiposity. Using a global mass spectrometry-based metabolomics approach, we identified 756 metabolites that were significantly differentially expressed in the cerebellar region of the brain of C57BL/6J mice, fed graded levels of CR (10, 20, 30, and 40 CR) compared to mice fed ad libitum for 12 hours a day. Pathway enrichment indicated changes in the pathways of adenosine and guanine (which are precursors of DNA production), aromatic amino acids (tyrosine, phenylalanine, and tryptophan) and the sulfur-containing amino acid methionine. We also saw increases in the tricarboxylic acid cycle (TCA) cycle, electron donor, and dopamine and histamine pathways. In particular, changes in l-histidine and homocarnosine correlated positively with the level of CR and food anticipatory activity and negatively with insulin and body temperature. Several metabolic and pathway changes acted against changes seen in age-associated neurodegenerative disorders, including increases in the TCA cycle and reduced l-proline. Carnitine metabolites contributed to discrimination between CR groups, which corroborates previous work in the liver and plasma. These results indicate the conservation of certain aspects of metabolism across tissues with CR. Moreover, this is the first study to indicate CR alters the cerebellar metabolome, and does so in a graded fashion, after only a short period of restriction.

The Effects of Graded Levels of Calorie Restriction XV: Phase Space Attractors Reveal Distinct Behavioral Phenotypes.

Calorie restriction (CR) has a positive impact on health and life span. Previous work, however, does not reveal the whole underlying mechanism of behavioral phenotypes under CR. We propose a new approach based on phase space reconstruction (PSR) to analyze the behavioral responses of mice to graded CR. This involved reconstructing high-dimensional attractors which topologically represent the intrinsic dynamics of mice based on low-dimensional time series of movement counts observed during the 90-day time course of restriction. PSR together with correlation dimensions (CD), Kolmogorov entropy (KE), and multifractal spectra builds a map from internal attractors to the phenotype of mice and reveals the mice with increasing CR levels undergo significant changes from a normal to a new state. Features of the attractors (CD and KE) were significantly associated with gene expression profiles in the hypothalamus of the same individuals.

The Effects of Graded Levels of Calorie Restriction: XIV. Global Metabolomics Screen Reveals Brown Adipose Tissue Changes in Amino Acids, Catecholamines, and Antioxidants After Short-Term Restriction in C57BL/6 Mice.

Animals undergoing calorie restriction (CR) often lower their body temperature to conserve energy. Brown adipose tissue (BAT) is stimulated through norepinephrine when rapid heat production is needed, as it is highly metabolically active due to the uncoupling of the electron transport chain from ATP synthesis. To better understand how BAT metabolism changes with CR, we used metabolomics to identify 883 metabolites that were significantly differentially expressed in the BAT of C57BL/6 mice, fed graded CR (10%, 20%, 30%, and 40% CR relative to their individual baseline intake), compared with mice fed ad libitum (AL) for 12 hours a day. Pathway analysis revealed that graded CR had an impact on the TCA cycle and fatty acid degradation. In addition, an increase in nucleic acids and catecholamine pathways was seen with graded CR in the BAT metabolome. We saw increases in antioxidants with CR, suggesting a beneficial effect of mitochondrial uncoupling. Importantly, the instigator of BAT activation, norepinephrine, was increased with CR, whereas its precursors l-tyrosine and dopamine were decreased, indicating a shift of metabolites through the activation pathway. Several of these key changes were correlated with food anticipatory activity and body temperature, indicating BAT activation may be driven by responses to hunger.

Ablation of Bscl2/seipin in hepatocytes does not cause metabolic dysfunction in congenital generalised lipodystrophy.

Mutations affecting the BSCL2 gene cause the most severe form of congenital generalised lipodystrophy (CGL). Affected individuals develop severe metabolic complications including diabetes and hepatic steatosis. Bscl2-deficient mice almost entirely reproduce the CGL phenotype. Adipose tissue-specific loss of Bscl2 is also sufficient to cause early-onset generalised lipodystrophy in mice. However, these mice do not show severe metabolic dysfunction, even when challenged with a high-fat diet. Germline Bscl2 loss in mice and BSCL2 disruption in humans causes severe hepatic steatosis, and the encoded protein, seipin, has acknowledged roles in lipid accumulation. Given the critical role of the liver in glucose regulation, we speculated that intact hepatic Bscl2 expression may protect adipose tissue-specific Bscl2-deficient mice from metabolic disease. To investigate this, we generated a novel mouse model in which Bscl2 has been deleted in both adipose tissue and hepatocytes simultaneously using an adeno-associated viral vector. Despite achieving efficient disruption of Bscl2 in the liver, hepatic lipid accumulation and metabolic homeostasis was unaffected in mice fed a high-fat diet for 4 weeks. We also investigated the consequences of BSCL2 ablation in the human hepatocyte HepG2 cell line using CRISPR/Cas9 genome editing. No significant increases in lipid accumulation were observed in BSCL2 knockout cell lines. Overall, we reveal that Bscl2/BSCL2 does not appear to play a cell-autonomous role in the regulation of lipid accumulation in the liver. Loss of hepatic BSCL2 is therefore unlikely to contribute significantly to the development of hepatic steatosis or metabolic dysfunction in this form of CGL.

The Effects of Graded Levels of Calorie Restriction: XIII. Global Metabolomics Screen Reveals Graded Changes in Circulating Amino Acids, Vitamins, and Bile Acids in the Plasma of C57BL/6 Mice.

Calorie restriction (CR) remains the most robust intervention to extend life span and improve health span. Using a global mass spectrometry-based metabolomics approach, we identified metabolites that were significantly differentially expressed in the plasma of C57BL/6 mice, fed graded levels of calorie restriction (10% CR, 20% CR, 30% CR, and 40% CR) compared with mice fed ad libitum for 12 hours a day. The differential expression of metabolites increased with the severity of CR. Pathway analysis revealed that graded CR had an impact on vitamin E and vitamin B levels, branched chain amino acids, aromatic amino acids, and fatty acid pathways. The majority of amino acids correlated positively with fat-free mass and visceral fat mass, indicating a strong relationship with body composition and vitamin E metabolites correlated with stomach and colon size, which may allude to the beneficial effects of investing in gastrointestinal organs with CR. In addition, metabolites that showed a graded effect, such as the sphinganines, carnitines, and bile acids, match our previous study on liver, which suggests not only that CR remodels the metabolome in a way that promotes energy efficiency, but also that some changes are conserved across tissues.

GPR55 deficiency is associated with increased adiposity and impaired insulin signaling in peripheral metabolic tissues.

Emerging evidence indicates that G-protein coupled receptor 55 (GPR55), a nonclassic receptor of the endocannabinoid system that is activated by L-α-lysophosphatidylinositol and various cannabinoid ligands, may regulate endocrine function and energy metabolism. We examined how GPR55 deficiency and modulation affects insulin signaling in skeletal muscle, adipose tissue, and liver alongside expression analysis of proteins implicated in insulin action and energy metabolism. We show that GPR55-null mice display decreased insulin sensitivity in these tissues, as evidenced by reduced phosphorylation of PKB/Akt and its downstream targets, concomitant with increased adiposity and reduced physical activity relative to wild-type counterparts. Impaired tissue insulin sensitivity coincided with reduced insulin receptor substrate-1 abundance in skeletal muscle, whereas in liver and epididymal fat it was associated with increased expression of the 3-phosphoinoistide lipid phosphatase, phosphatase and tensin homolog. In contrast, GPR55 activation enhanced insulin signaling in cultured skeletal muscle cells, adipocytes, and hepatocytes; this response was negated by receptor antagonists and GPR55 gene silencing in L6 myotubes. Sustained GPR55 antagonism in 3T3-L1 adipocytes enhanced expression of proteins implicated in lipogenesis and promoted triglyceride accumulation. Our findings identify GPR55 as a positive regulator of insulin action and adipogenesis and as a potential therapeutic target for countering obesity-induced metabolic dysfunction and insulin resistance.-Lipina, C., Walsh, S. K., Mitchell, S. E., Speakman, J. R., Wainwright, C. L., Hundal, H. S. GPR55 deficiency is associated with increased adiposity and impaired insulin signaling in peripheral metabolic tissues.

Female adipose tissue-specific Bscl2 knockout mice develop only moderate metabolic dysfunction when housed at thermoneutrality and fed a high-fat diet.

Mutations affecting the BSCL2 gene cause the most severe form of congenital generalised lipodystrophy. Affected individuals almost completely lack adipose tissue and suffer from severe diabetes and metabolic complications. Likewise, mice lacking Bscl2 in all tissues have dramatically reduced adipose mass, glucose intolerance and hyperinsulinaemia. However, male adipose tissue-specific Bscl2 knockout mice fail to develop the metabolic dysfunction observed in Bscl2 null mice and BSCL2 deficient patients, despite a similar generalised lack of adipose tissues. Clinical reports indicate gender differences frequently exist in cases of lipodystrophy, with female patients more adversely affected than male patients. We therefore generated and characterised female mice lacking Bscl2 specifically in adipose tissue (Ad-B2(-/-)). We show that female Ad-B2(-/-) mice also develop early-onset lipodystrophy when fed a chow diet and are maintained under standard housing conditions (21 °C) or thermoneutrality (30 °C). Despite this, female Ad-B2(-/-) mice fail to develop severe metabolic dysfunction. Only when female Ad-B2(-/-) mice are maintained at thermoneutrality and fed a high-fat diet do subtle alterations to metabolic homeostasis manifest. This is despite a striking inability to expand adipose mass. Our findings provide further evidence that loss of Bscl2 in non-adipose tissues may contribute to the severity of metabolic dysfunction in this condition.

Limits to sustained energy intake. XXVIII. Beneficial effects of high dietary fat on lactation performance in mice.

Maximal animal performance may be limited by the ability of an animal to dissipate heat: the heat dissipation limitation (HDL) theory. Because the incidental heat produced during digestion [specific dynamic action (SDA)] varies among diets, the HDL theory predicts that lactating female mice consuming diets with lower SDA should have increased reproductive performance. Dietary fat has a lower SDA than dietary carbohydrate. Female mice were fed low (LF), medium (MF) or high (HF) fat diets (10, 45 and 60% energy from fat, respectively) from days 4-18 of lactation. HF- and MF-fed mice weaned significantly heavier litters than LF mice. This was because they not only consumed more energy [metabolisable energy intake (Emei); HF: 306.5±25.0, MF: 340.5±13.5 kJ day-1] at peak lactation, but also delivered more milk energy to their pups [milk energy output (Emilk); HF: 203.2±49.9, MF 229.3±42.2 kJ day-1] than the LF-fed mice (Emei=266.7±4.5, Emilk=164.60±30.59 kJ day-1). A mathematical model based on the predictions from the HDL theory showed that this effect was greater than predicted from differences in SDA between the diets. Fatty acid profiles of the diets, milk and pups showed significant correlations between the profiles. Besides reduced SDA, HF- and MF-fed mice were probably able to directly transfer absorbed dietary fat into milk, reducing the heat production of lactogenesis and enabling them to perform better than expected from the HDL model. In summary, HF and MF diets had beneficial effects on reproductive performance compared with the LF diet because they enabled mice to generate milk more efficiently with less incidental heat production.

The effects of graded caloric restriction: XII. Comparison of mouse to human impact on cellular senescence in the colon.

Calorie restriction (CR) is an effective strategy to delay the onset and progression of aging phenotypes in a variety of organisms. Several molecular players are involved in the anti-aging effects of CR, but mechanisms of regulation are poorly understood. Cellular senescence-a cellular state of irreversible growth arrest-is considered a basic mechanism of aging. Senescent cells accumulate with age and promote a number of age-related pathologies. Whether environmental conditions such as diet affect the accumulation of cellular senescence with age is still unclear. Here, we show that a number of classical transcriptomic markers of senescent cells are reduced in adult but relatively young mice under CR. Moreover, we demonstrate that such senescence markers are not induced in the colon of middle-age human volunteers under CR in comparison with age-matched volunteers consuming normal Western diets. Our data support the idea that the improvement in health span observed in different organisms under CR might be partly due to a reduction in the number of senescent cells.