Early-life nutrition influences thymic growth in male mice that may be related to the regulation of longevity

Characterization of Different Commercial Dietary Supplements in the Peri-Weaning Period on Consumption and Growth Performance in C57Bl/6J Mice

Simple Summary

The current study compares two different commercially available nutritional supplements promoted as caloric support for weanlings for acceptability and effect on weight and survival in mouse pups and lactating dams in the peri-weaning phase with standard diet mash or no supplementation. Our aim was to provide an independent characterization of nutritional supplementation on survival and weight gain in a commonly used mouse strain. These factors influence animal welfare and are essential for the success of a general breeding program. Similarly, supplementation in the peri-weaning phase can alter early nutrition depending on type, which can introduce unintentional confounding that affects the reliability of subsequent experimental outcomes. This study was also designed to consider pragmatic aspects including timing, cost-effectiveness, diet composition, and practicality in an effort to identify supplements capable of optimally supporting pup growth and survival for various research applications in diverse animal use programs.

Abstract

This experiment was conducted to investigate the effects of common commercially available dietary supplementation in the peri-weaning period on feed intake, growth, and survival in C57Bl/6J mouse pups and lactating dams. A total of 96 pups and their dams were randomized to the control group or one of three nutritional supplement treatment groups: (i) control group without supplementation, or (ii) weanling-targeted Clear H₂O gel (Gel), (iii) transgenic-targeted Bio-Serv dough (Dough), or (iv) dam diet as a mash (Chow), in the peri-weaning period (from 11 to 28 days). Stool was observed daily for a dye marker indicating supplement consumption. Pups were weaned at 21 days and followed for a total of 42 days. No pup morbidity or mortality was observed. There was a higher proportion of pups consuming dough and gel earlier than chow (p = 0.0091). The majority of treated pups (>95%) were consuming the supplement by day 23 (range 15–23), suggesting interplay between organoleptic properties of the supplement and pup maturity. All groups gained weight, with typical sexual dimorphism observed in the growth curves. Dough treatment led to significantly higher average daily gain in male pups (0.64 ± 0.03 g/d) as compared with controls (0.58 ± 0.03 g/d). The highest average daily gain in all groups was observed pre-weaning between days 21 and 28. Compared with controls, the weight gain slope was significantly higher in the Dough and Chow treatment groups and lower in Gel treatment groups, with a more pronounced effect in males. In this study, the composition of nutritional supplementation was the dominant factor in increasing the growth trend as opposed to energy density. Peri-weaning supplementation with Dough and Chow treatments improved pre- and post-growth performance in a comparable way and was more effective than Gel treatment during adaptation to solid feeding. Proper application of supplements to support weanlings can directly improve welfare and limit unintended experimental variability.

The Good, the Bad, and the Ugly of Pregnancy Nutrients and Developmental Programming of Adult Disease

Maternal nutrition plays a decisive role in developmental programming of many non-communicable diseases (NCDs). A variety of nutritional insults during gestation can cause programming and contribute to the development of adult-onset diseases. Nutritional interventions during pregnancy may serve as reprogramming strategies to reverse programming processes and prevent NCDs. In this review, firstly we summarize epidemiological evidence for nutritional programming of human disease. It will also discuss evidence from animal models, for the common mechanisms underlying nutritional programming, and potential nutritional interventions used as reprogramming strategies.

A suboptimal maternal diet combined with accelerated postnatal growth results in an altered aging profile in the thymus of male rats

Reduced fetal nutrition and rapid postnatal growth accelerates the aging phenotype in many organ systems; however, effects on the immune system are unclear. We addressed this by studying the thymus from a rat model of developmental programming. The recuperated group was generated by in utero protein restriction, followed by cross-fostering to control-fed mothers, and were then compared with controls. Fat infiltration and adipocyte size increased with age ( P < 0.001) and in recuperated thymi ( P < 0.05). Cortex/medulla ratio decreased with age ( P < 0.001) and decreased ( P < 0.05) in 12-mo recuperated thymi. Age-associated decreases in thymic-epithelial cell ( P < 0.01) and thymocyte markers ( P < 0.01) were observed in both groups and was decreased ( P < 0.05) in recuperated thymi. These data demonstrate effects of developmental programming upon thymic involution. The recuperated group had longer thymic telomeres than controls ( P < 0.001) at 22 d and at 3 mo, which was associated with increased expression of telomere-length maintenance molecules [telomerase RNA component ( Terc; P < 0.01), P23 ( P = 0.02), and Ku70 and Ku80 ( P < 0.01)]. By 12 mo, recuperated offspring had shorter thymic telomeres than controls had ( P < 0.001) and reduced DNA damage-response markers [( DNA-PKcs, Mre11 ( P < 0.01), Xrcc4 ( P = 0.02), and γ-H2ax ( P < 0.001], suggesting failure of earlier compensatory responses. Our results suggest that low birth weight with rapid postnatal growth results in premature thymic maturation, resulting in accelerated thymic aging. This could lead to increased age-associated vulnerability to infection.-Tarry-Adkins, J. L., Aiken, C. E., Ashmore, T. J., Fernandez-Twinn, D. S., Chen, J.-H., Ozanne, S. E. A suboptimal maternal diet combined with accelerated postnatal growth results in an altered aging profile in the thymus of male rats.

Enriched environment regulates thymocyte development and alleviates experimental autoimmune encephalomyelitis in mice

Environmental and social factors have profound impacts on immune homeostasis. Our work on environmental enrichment (EE) has revealed a novel anti-obesity and anticancer phenotype associated with enhanced activity of CD8+ cytotoxic T lymphocytes in secondary lymphoid tissues. Here we investigated how an EE modulated thymus and thymocyte development. EE decreased thymus mass and cellularity, decreased the double positive thymocyte population, increased the proportion of CD8+ T cells, reduced the CD4:CD8 ratio, and downregulated CD69 expression in T cells. In a model of multiple sclerosis: experimental autoimmune encephalomyelitis (EAE), EE alleviated symptoms, inhibited spinal cord inflammation through regulation of type 1 T-helper cells mediated by glucocorticoid receptor signaling, and prevented EAE-induced thymic disturbance. Our mechanistic studies demonstrated that hypothalamic BDNF activated a hypothalamic-pituitary-adrenal axis mediating the EE's thymic effects. Our results indicate that a lifestyle intervention links the nervous, endocrine, and adaptive immune system, allowing the body to adapt to internal and external environments.

Nutritional Programming Effects on the Immune System

The relationship between patterns of early growth and age-associated diseases such as type 2 diabetes and cardiovascular disease is well established. There is also strong evidence from both human and animal studies that early environmental factors such as maternal nutrition may influence lifespan. Interestingly, more recent studies have demonstrated that nutritional programming in early life effects immunity, such that altered lifespan can also lead to programmed changes in immune function. Here we describe the use of immunohistology and flow cytometry techniques to study two key immune lymphoid organs: one that is involved in developing immune cells (thymus) and another which is the site of immune activation (spleen).

Nutritional Programming Effects on Development of Metabolic Disorders in Later Life

Developmental programming resulting from maternal malnutrition can lead to an increased risk of metabolic disorders such as obesity, insulin resistance, type 2 diabetes and cardiovascular disorders in the offspring in later life. Furthermore, many conditions linked with developmental programming are also known to be associated with the aging process. This review summarizes the available evidence about the molecular mechanisms underlying these effects, with the potential to identify novel areas of therapeutic intervention. This could also lead to the discovery of new treatment options for improved patient outcomes.

Nutrition in early life and age-associated diseases

The prevalence of age-associated disease is increasing at a striking rate globally. It is known that a strong association exists between a suboptimal maternal and/or early-life environment and increased propensity of developing age-associated disease, including cardiovascular disease (CVD), type-2 diabetes (T2D) and obesity. The dissection of underlying molecular mechanisms to explain this phenomenon, which is known as 'developmental programming' is still emerging; however three common mechanisms have emerged in many models of developmental programming. These mechanisms are (a) changes in tissue structure, (b) epigenetic regulation and (c) accelerated cellular ageing. This review will examine the epidemiological evidence and the animal models of suboptimal maternal environments, focusing upon these molecular mechanisms and will discuss the progress being made in the development of safe and effective intervention strategies which ultimately could target those 'programmed' individuals who are known to be at-risk of age-associated disease.

The effects of aging and maternal protein restriction during lactation on thymic involution and peripheral immunosenescence in adult mice

Environmental factors such as nutrition during early life can influence long-term health, a concept termed developmental programming. Initial research was focused towards the effects on metabolic health but more recent studies have demonstrated effects on parameters such as lifespan and immunity. In this study we report that maternal protein restriction during lactation in mice, that is known to prolong lifespan, slows aging of the central and peripheral immune systems. Offspring of dams fed a postnatal low-protein (PLP) diet during lactation had a significant increase in thymic cellularity and T cell numbers across their lifespan compared to controls, and a less marked age-associated decrease in thymocyte cluster of differentiation (CD) 3 expression. PLP animals also demonstrated increased relative splenic cellularity, increased naïve: memory CD4⁺ and CD8⁺ T cell ratios, increased staining and density of germinal centres, and decreased gene expression of p16 in the spleen, a robust biomarker of aging. A slower rate of splenic aging in PLP animals would be expected to result in decreased susceptibility to infection and neoplasia. In conclusion nutritionally-induced slow postnatal growth leads to delayed aging of the adaptive immune system, which may contribute towards the extended lifespan observed in these animals.

Nutritional limitation in early postnatal life and its effect on aging and longevity in rodents

Nutrient limitation in the form of chronic dietary restriction (DR), or more specifically a life-long reduction of total daily nutritional intake, was first shown to extend longevity in rats more than eight decades ago and is one of the most robust anti-aging interventions known. More recently, it has become apparent that dietary restriction limited to only the first few weeks of life in rodents is also capable of significantly impacting aging and longevity. The imposition of nutrient limitation is often achieved via the manipulation of litter size or the modulation of maternal nutrient intake during the lactational period. Not surprisingly, nutrient limited pups are smaller at weaning, and remain so throughout their life, while exhibiting signs of slowed aging. In this review, we discuss potential mechanisms that account for the anti-aging effects of postnatal undernutrition with an emphasis on those pathways that parallel changes seen with chronic DR.

Early life nutritional programming of health and disease in The Gambia

Exposures during the early life (periconceptional, prenatal and early postnatal) period are increasingly recognized as playing an important role in the aetiology of chronic non-communicable diseases (NCD), including coronary heart disease, stroke, hypertension, Type 2 diabetes and osteoporosis. The 'Developmental Origins of Health and Disease' (DOHaD) hypothesis states that these disorders originate through unbalanced nutrition early in life and risk is highest when there is a 'mismatch' between the early- and later-life environments. Thus, the DOHaD hypothesis would predict highest risk in countries where an excess of infants are born with low birth weight and where there is a rapid transition to nutritional adequacy or excess in adulthood. Here, I will review data from work conducted in rural Gambia, West Africa. Using demographic data dating back to the 1940s, the follow-up of randomized controlled trials of nutritional supplementation in pregnancy and the 'experiment of nature' that seasonality in this region provides, we have investigated the DOHaD hypothesis in a population with high rates of maternal and infant under-nutrition, a high burden from infectious disease, and an emerging risk of NCDs.

Pre-birth world and the development of the immune system: mum's diet affects our adult health: new insight on how the diet during pregnancy permanently influences offspring health and immune fitness

Secondary lymphoid organs form in utero through an inherited and well-established developmental program. However, maternal non-heritable features can have a major impact on the gene expression of the embryo, hence influencing the future health of the offspring. Recently, maternal retinoids were shown to regulate the formation of immune structures, shedding light on the role of maternal nutrition in the genetic signature of emergent immune cells. Here we highlight evidence showing how the maternal diet influences the establishment of the immune system, and we also discuss how unbalanced maternal diets may set the response to infection and vaccination in the progeny.

Early-life nutritional programming of longevity

Available data from both experimental and epidemiological studies suggest that inadequate diet in early life can permanently change the structure and function of specific organs or homoeostatic pathways, thereby ‘programming’ the individual’s health status and longevity. Sufficient evidence has accumulated showing significant impact of epigenetic regulation mechanisms in nutritional programming phenomenon. The essential role of early-life diet in the development of aging-related chronic diseases is well established and described in many scientific publications. However, the programming effects on lifespan have not been extensively reviewed systematically. The aim of the review is to provide a summary of research findings and theoretical explanations that indicate that longevity can be influenced by early nutrition.

Thymus development and infant and child mortality in rural Bangladesh

BACKGROUND

Data from West Africa indicate that a small thymus at birth and at 6 months of age is a strong and independent risk factor for infection-related mortality up to 24 and 36 months of age, respectively. We investigated the association between thymus size (thymic index, TI) in infancy and subsequent infant and child survival in a contemporary South Asian population.

METHODS

The study focused on the follow-up of a randomized trial of prenatal nutritional interventions in rural Bangladesh (ISRCTN16581394), with TI measured longitudinally in infancy (at birth and weeks 8, 24 and 52 of age) and accurate recording of mortality up to 5 years of age.

RESULTS

A total of 3267 infants were born into the Maternal and Infant Nutrition Interventions, Matlab study; data on TI were available for 1168 infants at birth, increasing to 2094 infants by 52 weeks of age. TI in relation to body size was largest at birth, decreasing through infancy. For infants with at least one measure of TI available, there were a total of 99 deaths up to the age of 5 years. No association was observed between TI and subsequent mortality when TI was measured at birth. However, an association with mortality was observed with TI at 8 weeks of age [odds ratio (OR) for change in mortality risk associated with 1 standard deviation change in TI: all deaths: OR = 0.64, 95% confidence interval (CI) 0.41, 0.98; P = 0.038; and infection-related deaths only: OR = 0.32, 95% CI 0.14, 0.74; P = 0.008]. For TI when measured at 24 and 52 weeks of age, the numbers of infection-related deaths were too few (3 and 1, respectively) for any meaningful association to be observed.

CONCLUSION

These results confirm that thymus size in early infancy predicts subsequent survival in a lower mortality setting than West Africa. The absence of an effect at birth and its appearance at 8 weeks of age suggests early postnatal influences such as breast milk trophic factors.

DNA methylation at differentially methylated regions of imprinted genes is resistant to developmental programming by maternal nutrition

The nutritional environment in which the mammalian fetus or infant develop is recognized as influencing the risk of chronic diseases, such as type 2 diabetes and hypertension, in a phenomenon that has become known as developmental programming. The late onset of such diseases in response to earlier transient experiences has led to the suggestion that developmental programming may have an epigenetic component, because epigenetic marks such as DNA methylation or histone tail modifications could provide a persistent memory of earlier nutritional states. One class of genes that has been considered a potential target or mediator of programming events is imprinted genes, because these genes critically depend upon epigenetic modifications for correct expression and because many imprinted genes have roles in controlling fetal growth as well as neonatal and adult metabolism. In this study, we have used an established model of developmental programming-isocaloric protein restriction to female mice during gestation or lactation-to examine whether there are effects on expression and DNA methylation of imprinted genes in the offspring. We find that although expression of some imprinted genes in liver of offspring is robustly and sustainably changed, methylation of the differentially methylated regions (DMRs) that control their monoallelic expression remains largely unaltered. We conclude that deregulation of imprinting through a general effect on DMR methylation is unlikely to be a common factor in developmental programming.

Catch-up and targeted growth following variable duration protein restriction: effects on bone and body mass

Protein malnutrition leads to growth retardation that can be reversed through catch-up growth, once normative nutrition is restored. Because growth is a dynamic process, catch-up capacity is likely influenced by the maturity of the animal and/or the duration of the insult, in addition to the type of insult experienced. We compared length of malnutrition, sexual dimorphism, body mass, and skeletal growth. Eighty Rattus norvegicus were divided into 10 treatment groups (five diets; male and female) and followed for more than 1 year. At weaning, animals were placed on either a control or low-protein isocaloric diet. Three experimental groups were switched to the control diet at 40, 60, or 90 days. Beginning with 21 days of age, animals were weighed daily and radiographed throughout the study. To determine the presence of catch-up growth, growth rates (GRs) were calculated (linear regression) for 20-day time spans before and after diet changes and compared among treatment groups. Targeted growth was measured as final size or as the coefficient of variation with age. These results show that 1) protein-restricted animals experience catch-up growth with dietary rehabilitation; 2) for females, catch-up GRs are proportional to GRs in control animals at the same age as the timing of dietary rehabilitation but not for males; and 3) targeted growth was observed in some, but not all, aspects of anatomy. The length of the tibia and humerus was indistinguishable from controls, regardless of length of malnutrition or gender, whereas the ulna and male body mass exceeded control sizes. Although most measures decreased in variation with ontogeny, the tibia failed to do so. These results support a complex biological regulation of catch-up and targeted growth. The implications for selection are that flexible and responsive developmental trajectories may have an advantage over those programed into a single size.

Maternal protein restriction affects gene expression profiles in the kidney at weaning with implications for the regulation of renal function and lifespan

Nutritionally induced alterations in early growth can influence health and disease in later adult life. We have demonstrated previously that low birthweight resulting from maternal protein restriction during pregnancy followed by accelerated growth in rodents was associated with shortened lifespan, whereas protein restriction and slow growth during lactation increased lifespan. Thus early life events can also have a long lasting impact on longevity. In the present study, we show that long-lived PLP (postnatal low protein) mice were protected from developing albuminuria, whereas short-lived recuperated mice demonstrated an age-dependent increase in albuminuria in old age. Microarray analysis of kidneys from 21-day-old mice revealed that gene expression profiles were differentially affected depending on whether protein restriction was imposed during pregnancy or lactation. The differentially expressed genes were involved in diverse biological functions such as cytoprotective functions, vitamin D synthesis, protein homoeostasis, regulation of antioxidant enzymes and cellular senescence. Significantly, up-regulation of Hmox1 (haem oxygenase 1) in kidneys from PLP mice suggests that tissues of long-lived mice are equipped with a better cytoprotective function. In contrast, up-regulation of Nuak2 (NUAK family, SNF1-like kinase 2) and down-regulation of Lonp2 (Lon peptidase 2), Foxo3a (forkhead box O3a), Sod1 (copper/zinc superoxide dismutase) and Sesn1 (sestrin 1) in the kidneys of recuperated offspring suggest that protein homoeostasis and resistance to oxidative stress are compromised, leading to accelerated cellular senescence in these shorter-lived mice.