Caloric restriction attenuates the age-associated increase of adipose-derived stem cells but further reduces their proliferative capacity

White adipose tissue is a promising source of mesenchymal stem cells. Currently, little is known about the effect of age and caloric restriction (CR) on adipose-derived stem cells (ASC). This is important for three reasons: firstly, age and CR cause extensive remodeling of WAT; it is currently unknown how this remodeling affects the resident stem cell population. Secondly, stem cell senescence has been theorized as one of the causes of aging and could reduce the utility of a stem cell as a reagent. Thirdly, the mechanism by which CR extends lifespan is currently not known, one theory postulates that CR maintains the resident stem cell population in youthful “fit” state. For the purpose of this study, we define ASC as lineage negative (lin⁻)/CD34^+(low)/CD31⁻. We show that aging increases the abundance of ASC and the expression of Cdkn2a 9.8-fold and Isl1 60.6-fold. This would suggest that aging causes an accumulation of non-replicative ASC. CR reduced the percentage of ASC in the lin⁻ SVF while also reducing colony forming ability. Therefore, CR appears to have anti-proliferative effects on ASC that may be advantageous from the perspective of cancer, but our data raises the possibility that it may be disadvantageous for regenerative medicine applications.     

Downregulation of plasma insulin levels and hepatic PPARgamma expression during the first week of caloric restriction in mice

Calorie restriction extends lifespan by decreasing the rate of tumor formation, an effect occurring within 8 weeks of initiating a restricted diet. Our goal was to define how the first weeks of a calorie restricted diet (60% of ad libitum calories) affects putative mediators of the calorie restriction phenotype, focusing on regulators of fatty acid biosynthesis. In C57Bl/6 mice, insulin decreased over 50% (p<0.05) during the first week of calorie restriction whereas IGF-1 was unaffected. In the liver, PPARgamma mRNA fell to 13% of baseline after 1 week of calorie restriction (p<0.05), whereas hepatic SREBP-1c and SIRT1 mRNA levels were unaffected. No changes in abdominal or subcutaneous adipose tissue were observed until after 4 weeks of caloric restriction. We conclude that calorie restriction-induced decreases in insulin and hepatic PPARgamma are rapid enough to support a role for these molecules in triggering the initial phase of the calorie restriction phenotype.     

Caloric restriction improves endothelial dysfunction during vascular aging: Effects on nitric oxide synthase isoforms and oxidative stress in rat aorta

Aging is characterized by activation of inducible over endothelial nitric oxide synthase (iNOS and eNOS), impaired antioxidant activity and increased oxidative stress, which reduces nitric oxide bioavailability and causes endothelial dysfunction. Caloric restriction (CR) blunts oxidative stress. We investigated whether CR impacts endothelial dysfunction in aging and the underlying mechanisms. Aortas from young (YC, 6 months of age) and old (OC, 24 months of age) rats ad-libitum fed and from old rats caloric-restricted for 3-weeks (OR, 26%) were investigated. Endothelium-dependent vasorelaxation was impaired in OC, associated with reduced eNOS and increased iNOS expression (P < 0.05). Aortic nitrite was similar in OC and YC, but the contribution of calcium-independent NOS to total NOS activity was increased whereas that of calcium-dependent NOS was reduced (p ≤ 0.0003). Plasma thiobarbituric acid-reactive substances (TBARS) were elevated in OC as well as aortic nitrotyrosine (P < 0.05). Expression of manganese superoxide dismutase (MnSOD) and total SOD activity were impaired in OC (P < 0.05 vs. YC), whereas copper-zinc (CuZn) SOD expression was similar in OC and YC. CR restored endothelial dysfunction in old rats, reduced iNOS expression, total nitrite and calcium-independent NOS activity in aorta (P < 0.05) without changes in eNOS expression and calcium-dependent NOS activity. Sirtuin-1 expression did not differ among groups. Plasma TBARS and aortic nitrotyrosine were reduced (P < 0.05) in OR compared with OC. In OR CuZnSOD protein and SOD activity increased (P < 0.05) without changes in MnSOD expression. Short-term CR improves age-related endothelial dysfunction. Reversal of altered iNOS/eNOS ratio, reduced oxidative stress and increased SOD enzyme activity rather than enhanced NO production appear to be involved in this effect.     

Low-level caloric restriction rescues proteasome activity and Hsc70 level in liver of aged rats

Proteasome activity is known to decrease with aging in ad libitum (AL) fed rats. Severe caloric restriction (CR) significantly extends the maximum life-span of rats, and counteracts the age-associated decrease in liver proteasome activities. Since few investigations have explored whether lower CR diets might positively counteract the age associated decrease in proteasome activity, we then investigated the effects of a mild CR regimen on animal life-span, proteasome content and function. In addition, we addressed the question whether both CR regimens might also affect the expression of Hsc70 protein, a constitutive chaperone reported to share a role in the function of proteasome complex and in the repair of proteotoxic damage, and whose level decreased during aging. In contrast to severe CR, mild CR had a poor effect on life-span; however, it better counteracted the decrease of proteasome activities. Both regimens, however, maintain Hsc70 in liver of old rats at level comparable to that of young rats. Interestingly, the effects of aging and CRs on liver proteasome enzyme activities did not appear to be associated with parallel changes in the amount of proteasome proteins suggesting that the quality (molecular activity of the enzymes) rather than the quantity are likely to be modified with age. In conclusion, the results presented in this work show that a mild CR can have beneficial effects on liver function of aging rats because is adequate to counteract the decrease of proteasome function and Hsc70 chaperone level.     

Caloric restriction attenuates aging-induced cardiac insulin resistance in male Wistar rats through activation of PI3K/Akt pathway

Background and Aim

Caloric restriction (CR) improves insulin sensitivity and is one of the dietetic strategies most commonly used to enlarge life and to prevent aging-induced cardiovascular alterations. The aim of this study was to analyze the possible beneficial effects of caloric restriction (CR) preventing the aging-induced insulin resistance in the heart of male Wistar rats.

Facts and controversies in our understanding of how caloric restriction impacts the mitochondrion

Caloric restriction (CR) has pronounced benefits in promoting healthy aging. Amongst the most frequently implicated physiological mechanisms implicated in this benefit is altered mitochondrial function. Whereas a reduction in mitochondrial reactive oxygen species (ROS) production is a widely consistent effect of CR, an increase in mitochondrial biogenesis, which is accepted by many as fact, is contradicted on several levels, most critically by a lack of increase in mitochondrial protein synthesis rate in vivo. Furthermore, an increase in PGC-1α protein and markers of mitochondrial content with CR is a highly variable observation between studies. On the other hand, deacetylation of several mitochondrial proteins by the sirtuin, Sirt3, is an increasingly reported observation and at least so far, this observation is consistent between studies. Notwithstanding this point, the controversies evident in the published literature underscore the significant questions that remain in our understanding of how CR impacts the mitochondrion and suggest we have yet to fully understand the complexities herein.     

Comparing the effects of food restriction and overeating on brain reward systems

Both caloric restriction and overeating have been shown to affect neural processes associated with reinforcement. Both preclinical and some clinical studies have provided evidence that food restriction may increase reward sensitivity, and while there are mixed findings regarding the effects of overeating on reward sensitivity, there is strong evidence linking this behavior with changes in reward-related brain regions. Evidence of these changes comes in part from findings that show that such eating patterns are associated with increased drug use. The data discussed here regarding the differential effects of various eating patterns on reward systems may be particularly relevant to the aging population, as this population has been shown to exhibit altered reward sensitivity and decreased caloric consumption. Moreover, members of this population appear to be increasingly affected by the current obesity epidemic. Food, like alcohol or drugs, can stimulate its own consumption and produce similar neurochemical changes in the brain. Age-related loss of appetite, decreased eating, and caloric restriction are hypothesized to be associated with changes in the prevalence of substance misuse, abuse, and dependence seen in this cohort.     

Caloric restriction promotes the reproductive capacity of female rats via modulating the level of insulin-like growth factor-1 (IGF-1)

The insulin-like growth factor-1 (IGF-1) plays an important role in the regulation of reproductive function. In the present study, we examined the effects of caloric restriction (CR) on the reproductive lifespan in rats and investigated the potential role of IGF-1. After 10 weeks of treatment, we determined the distribution of the ovarian follicles at various stages and measured the plasma level of IGF-1, luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estrogen (ESG). Our results show that IGF-1 level was decreased after CR and correlated with the decrease in the levels of LH, FSH and ESG. Moreover, a higher percentage of primordial follicles and surviving follicles was observed in CR rats than in control rats (P < 0.05). Immunohistochemical analysis showed that IGF-1 was extensively expressed in the cytoplasm of granulosa cells in the surviving follicles at different stages but not in the atretic follicles. Taken together, these results suggest that caloric restriction promotes the reproductive capacity of female rats via modulating the level of IGF-1, which then regulate pituitary gonadotrope cells to reduce the release of LH, FSH and ESG, and modulate follicular development.     

Skeletal effects of long-term caloric restriction in rhesus monkeys

Age-related bone loss is well established in humans and is known to occur in nonhuman primates. There is little information, however, on the effect of dietary interventions, such as caloric restriction (CR), on age-related bone loss. This study examined the effects of long-term, moderate CR on skeletal parameters in rhesus monkeys. Thirty adult male rhesus monkeys were subjected to either a restricted (R, n = 15) or control (C, n = 15) diet for 20 years and examined throughout for body composition and biochemical markers of bone turnover. Total body, spine, and radius bone mass and density were assessed by dual-energy X-ray absorptiometry. Assessment of biochemical markers of bone turnover included circulating serum levels of osteocalcin, carboxyterminal telopeptide of type I collagen, cross-linked aminoterminal telopeptide of type I collagen, parathyroid hormone, and 25(OH)vitamin D. Overall, we found that bone mass and density declined over time with generally higher levels in C compared to R animals. Circulating serum markers of bone turnover were not different between C and R with nonsignficant diet-by-time interactions. We believe the lower bone mass in R animals reflects the smaller body size and not pathological osteopenia.     

Effects of life-long caloric restriction and voluntary exercise on age-related changes in levels of catecholamine biosynthetic enzymes and angiotensin II receptors in the rat adrenal medulla and hypothalamus

We examined if life-long mild caloric restriction (CR) alone or with voluntary exercise prevents the age-related changes in catecholamine biosynthetic enzyme levels in the adrenal medulla and hypothalamus. Ten-week-old Fisher-344 rats were assigned to: sedentary; sedentary+8% CR; or 8% CR+wheel running. Rats were euthanized at 6 or 24 months of age. Tyrosine hydroxylase (TH) mRNA expression was 4.4-fold higher in the adrenal medullae and 60% lower in the hypothalamus of old sedentary rats compared to young (p<0.01). Life-long CR reduced the age-related increase in adrenomedullary TH by 50% (p<0.05), and completely reversed the changes in hypothalamic TH. Voluntary exercise, however, had no additional effect over CR. Since angiotensin II is involved in the regulation of catecholamine biosynthesis, we examined the expressions of angiotensin II receptor subtypes in the adrenal medulla. AT(1) protein levels were 2.8-fold higher in the old animals compared to young (p<0.01), and while AT(1) levels were unaffected by CR alone, CR+wheel running decreased AT(1) levels by 50% (p<0.01). AT(2) levels did not change with age, however CR+wheel running increased its level by 42% (p<0.05). These data indicate that a small decrease in daily food intake can avert age-related changes in catecholamine biosynthetic enzyme levels in the adrenal medulla and hypothalamus, possibly through affecting angiotensin II signaling.     

Age-specific effects of short- and long-term caloric restriction on the expression of adiponectin and adiponectin receptors: influence of intensity of food restriction

Hormonal signals from adipose tissue regulate energy homeostasis and may be involved in anti-aging effects of caloric restriction (CR). The adipokine adiponectin is abundantly expressed in adipose tissue and directly sensitizes the body to insulin. The purpose of the current study was to investigate age-dependent effects of different levels of CR (16%, 2 months or 40%, 6 months) on adiponectin and on its receptors AdipoR1 and AdipoR2 in the left ventricle (LV). In young and senescent rats, 2 months of moderate CR reduced serum leptin. The same diet was sufficient to enhance serum adiponectin, adiponectin expression (visceral fat) and left ventricular AdipoR1 expression in young but not in senescent rats. The higher degree of CR, however, resulted in a mild induction of adiponectin expression in adipose tissue and release into plasma together with increased LV AdipoR1 also in old rats, while these effects were more pronounced in young rats. These changes in adiponectin activation were associated with reduced LV triglyceride content, suggesting an adiponectin-mediated reduced ectopic lipid deposition in nonadipose tissues. Thus, aging is associated with a loss of adiponectin inducibility by moderate CR. This reduction can only partially be overcome by increasing the degree and duration of CR.     

肝窦内皮细胞与肝窦毛细血管化研究进展

肝窦内皮细胞具有开放的、没有横膈膜的窗孔,内皮下没有基底膜。这种结构有利于调控肝细胞与肝窦血液的物质交换。肝窦内皮细胞能分泌内皮素-1和一氧化氮,并通过窗孔的变化,对肝脏微循环进行调节,同时可分泌大量的形成基底膜的成分,在肝窦毛细血管化的过程中起主导作用。肝窦内皮细胞表型标志发生变化,Ⅷ因子相关抗原、CD44等表达增强,也是肝窦毛细血管化的重要标志。笔者对肝窦内皮细胞的结构及其在肝窦毛细血管化中的功能和表型变化进行综述。     

Dietary restriction reduces age-related degeneration of stria vascularis in the inner ear of the rat

We report here beneficial effects of life-long dietary restriction on the progression of age-associated cochlear degeneration in female Sprague–Dawley rats. Thirty-month old rats on a 70% dietary restriction were compared to ad libitum fed age-matched rats, and three-month old adult rats. As expected, aged dietary restricted rats displayed about 20% higher survival rate than age-matched rats fed ad libitum. This difference was reflected also in the auditory system. In the dietary restricted group, 73% of the subjects had preserved auditory reflexes (Preyer), and only modest degeneration of the stria vascularis of the inner ear was observed. In contrast, aged ad libitum fed animals, of which only 15% had detectable Preyer reflexes, showed a marked thinning, cellular degeneration and loss of cell processes in the stria vascularis. The extent of loss of sensory hair cells (~ 24%) was similar in both the aged groups, and neither group showed a significant reduction in the number of spiral ganglion neurons across adult life-span. The observations thus demonstrate that dietary restriction delays age-related degradation of the auditory system. The results provide further insights into the mechanisms of strial presbycusis.     

The hydrogen sulfide signaling system: changes during aging and the benefits of caloric restriction

Hydrogen sulfide gas (H₂S) is a putative signaling molecule that causes diverse effects in mammalian tissues including relaxation of blood vessels and regulation of perfusion in the liver, but the effects of aging on H₂S signaling are unknown. Aging has negative impacts on the cardiovascular system. However, the liver is more resilient with age. Caloric restriction (CR) attenuates affects of age in many tissues. We hypothesized that the H₂S signaling system is negatively affected by age in the vasculature but not in the liver, which is typically more resilient to age, and that a CR diet minimizes the age affect in the vasculature. To investigate this, we determined protein and mRNA expression of the H₂S-producing enzymes cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS), H₂S production rates in the aorta and liver, and the contractile response of aortic rings to exogenous H₂S. Tissue was collected from Fisher 344 × Brown Norway rats from 8–38 months of age, which had been maintained on an ad libitum (AL) or CR diet. The results demonstrate that age and diet have differential effects on the H₂S signaling system in aorta and liver. The aorta showed a sizeable effect of both age and diet, whereas the liver only showed a sizeable effect of diet. Aortic rings showed increased contractile sensitivity to H₂S and increased protein expression of CSE and CBS with age, consistent with a decrease in H₂S concentration with age. CR appears to benefit CSE and CBS protein in both aorta and liver, potentially by reducing oxidative stress and ameliorating the negative effect of age on H₂S concentration. Therefore, CR may help maintain the H₂S signaling system during aging.     

Effects of caloric restriction are species-specific

This article addresses two questions: (1) ‘can caloric restriction (CR) extend the life spans of all species of experimental animals’, and (2) ‘is CR likely to slow the human aging process and/or extend the human life span?’ The answer to the first question is clearly ‘no’, because CR decreases the life span of the housefly, Musca domestica, and fails to extend the life span of at least one mouse strain. The answer to the second question is unknown, because human CR has not yet been shown either to increase or curtail the human life span. However, recent efforts to develop insect models of CR have been unsuccessful and/or relatively uninformative, so any insights regarding the relationship between CR and human aging are more likely to arise from studies of established, mammalian models of CR.     

Lifelong exercise and mild (8%) caloric restriction attenuate age-induced alterations in plantaris muscle morphology, oxidative stress and IGF-1 in the Fischer-344 rat

Muscle atrophy is a highly prevalent condition among older adults, and results from reduced muscle mass and fiber cross-sectional area. Resistive exercise training and moderate (30-40%) caloric restriction may reduce the rate of sarcopenia in animal models. We tested the hypothesis that lifelong, voluntary exercise combined with mild (8%) caloric restriction would attenuate the reduction of muscle fiber cross-sectional area in the rat plantaris. Fischer-344 rats were divided into: young adults (6 mo) fed ad libitum (YAL); 24 mo old fed ad libitum (OAL); 24 mo old on 8% caloric restriction (OCR); lifelong wheel running with 8% CR (OExCR). Plantaris fiber cross-sectional area was significantly lower in OAL than YAL (-27%), but protected in OCR and OExCR, while mass/body mass ratio was preserved in OExCR only. Furthermore, 8% CR and lifelong wheel running attenuated the age-induced increases in extramyocyte space and connective tissue. Citrate synthase activity decreased with age, but was not significantly protected in OCR and OExCR. Total hydroperoxides were higher in OAL than YAL, but were not elevated in OExCR, with out a change in MnSOD. IGF-1 levels were lower in OAL (-57%) than YAL, but partially protected in the OExCR group (+51%).     

Short-term caloric restriction improves ischemic tolerance independent of opening of ATP-sensitive K+ channels in both young and aged hearts

Ischemic tolerance decreases with aging and the cardioprotective effect of ischemic preconditioning (IPC) is impaired in aged animals. Although lifelong caloric restriction (CR) profoundly affects the physiological and pathophysiological modifications induced by aging and markedly increases life span in several species, it is unclear whether short-term CR affects ischemic tolerance and IPC in aged hearts. Six-month-old (Y) and 24-month-old (O) Fischer 344 male rats were randomly divided into two groups; AL rats were fed ad libitum, whereas CR rats were fed 90% of the caloric intake of AL for 2 weeks followed by 65% of the caloric intake for 2 weeks. Isolated perfused hearts were subjected to 25 min of ischemia followed by 30 min of reperfusion with or without IPC. The recovery of LV function after reperfusion improved with IPC in ALY but not in ALO. CR improved the recovery of LV function in both CRY and CRO but the cardioprotective effect of IPC was not additive to that of CR. Neither 5-hydroxydecanoate nor glibenclamide abrogated the protective effect of CR in either CRY or CRO. The recovery of myocardial high-energy phosphates after reperfusion was better with CR in both generations. There was no difference in myocardial expression levels of AMP-activated kinase (AMPK) but AMPK-alpha phosphorylated at Thr172 increased with CR in both Y and O. In conclusion, short-term CR improves myocardial ischemic tolerance independent of the opening of KATP channels in both Y and O. CR-induced cardioprotection is associated with an increase in activated AMPK.     

Caloric Restriction Increases Longevity Substantially only When the Reaction Norm is Steep

Evolutionary theory leads to the general expectation that dietary restriction will often result in increased survival probabilities, and thus increased lifespan. The reaction norm is a basic tool of evolutionary analysis that quantifies the relationship between environmental parameters and functional characters, including reproduction and longevity. In rodents, the reaction norm connecting adult longevity to caloric intake is fairly steep; small changes in intake lead to large changes in longevity. If this strong quantitative relationship were evolutionarily conserved among all mammals, then the prospects for a substantial increase in human lifespan from caloric restriction would be very good. In theory, however, reaction norms are expected to evolve for fitness related characters such as reproduction and survival. It has been shown experimentally in Drosophila that dietary reaction norms readily evolve in the laboratory, suggesting that they can do so among mammals as well, particularly over the millions of years since contemporary rodents and primates last shared a common ancestor. Our previous work crudely estimates that the dietary reaction norms of rodents and humans have diverged substantially, with a very flat dietary reaction norm for human longevity. These general principles and our specific results suggest that the benefits from human caloric restriction would be minor.     

Dietary restriction by bacterial deprivation increases life span in wild-derived nematodes

Dietary restriction is known to promote longevity in a variety of eukaryotic organisms. Most studies of dietary restriction have been performed on animals bred for many generations under conditions that differ substantially from their natural environment, raising the possibility that some apparent beneficial effects of dietary restriction are due to adaptation to laboratory conditions. To address this question in an invertebrate model, we determined the effect of dietary restriction by bacterial deprivation on life span in five different wild-derived Caenorhabditis elegans strains and two strains of the related species Caenorhabditis remanei. Longevity was enhanced in each of the wild-derived C. elegans strains, in most cases to a degree similar to that observed in N2, the standard laboratory strain. Both strains of C. remanei were substantially longer lived any of the C. elegans isolates, produced larger brood sizes, and retained the ability to produce offspring for a longer period of time. Dietary restriction failed to increase mean life span in one C. remanei isolate, but significantly increased the maximum life span of both C. remanei strains. Thus, we find no evidence that adaptation to laboratory conditions has significantly altered the aging process in C. elegans under either standard or food-restricted conditions.