Poor maternal nutrition and accelerated postnatal growth induces an accelerated aging phenotype and oxidative stress in skeletal muscle of male rats

The effect of low birth weight as an intrauterine exposure on the early onset of sarcopenia through possible molecular pathways

Sarcopenia, a musculoskeletal disease characterized by the progressive loss of skeletal muscle mass, strength, and physical performance, presents significant challenges to global public health due to its adverse effects on mobility, morbidity, mortality, and healthcare costs. This comprehensive review explores the intricate connections between sarcopenia and low birth weight (LBW), emphasizing the developmental origins of health and disease (DOHaD) hypothesis, inflammatory processes (inflammaging), mitochondrial dysfunction, circadian rhythm disruptions, epigenetic mechanisms, and genetic variations revealed through genome-wide studies (GWAS). A systematic search strategy was developed using PubMed to identify relevant English-language publications on sarcopenia, LBW, DOHaD, inflammaging, mitochondrial dysfunction, circadian disruption, epigenetic mechanisms, and GWAS. The publications consist of 46.2% reviews, 21.2% cohort studies, 4.8% systematic reviews, 1.9% cross-sectional studies, 13.4% animal studies, 4.8% genome-wide studies, 5.8% epigenome-wide studies, and 1.9% book chapters. The review identified key factors contributing to sarcopenia development, including the DOHaD hypothesis, LBW impact on muscle mass, inflammaging, mitochondrial dysfunction, the influence of clock genes, the role of epigenetic mechanisms, and genetic variations revealed through GWAS. The DOHaD theory suggests that LBW induces epigenetic alterations during foetal development, impacting long-term health outcomes, including the early onset of sarcopenia. LBW correlates with reduced muscle mass, grip strength, and lean body mass in adulthood, increasing the risk of sarcopenia. Chronic inflammation (inflammaging) and mitochondrial dysfunction contribute to sarcopenia, with LBW linked to increased oxidative stress and dysfunction. Disrupted circadian rhythms, regulated by genes such as BMAL1 and CLOCK, are associated with both LBW and sarcopenia, impacting lipid metabolism, muscle mass, and the ageing process. Early-life exposures, including LBW, induce epigenetic modifications like DNA methylation (DNAm) and histone changes, playing a pivotal role in sarcopenia development. Genome-wide studies have identified candidate genes and variants associated with lean body mass, muscle weakness, and sarcopenia, providing insights into genetic factors contributing to the disorder. LBW emerges as a potential early predictor of sarcopenia development, reflecting the impact of intrauterine exposures on long-term health outcomes. Understanding the complex interplay between LBW with inflammaging, mitochondrial dysfunction, circadian disruption, and epigenetic factors is essential for elucidating the pathogenesis of sarcopenia and developing targeted interventions. Future research on GWAS and the underlying mechanisms of LBW-associated sarcopenia is warranted to inform preventive strategies and improve public health outcomes.

Lifelong dietary protein restriction accelerates skeletal muscle loss and reduces muscle fibre size by impairing proteostasis and mitochondrial homeostasis

The early life environment significantly affects the development of age-related skeletal muscle disorders. However, the long-term effects of lactational protein restriction on skeletal muscle are still poorly defined. Our study revealed that male mice nursed by dams fed a low-protein diet during lactation exhibited skeletal muscle growth restriction. This was associated with a dysregulation in the expression levels of genes related to the ribosome, mitochondria and skeletal muscle development. We reported that lifelong protein restriction accelerated loss of type-IIa muscle fibres and reduced muscle fibre size by impairing mitochondrial homeostasis and proteostasis at 18 months of age. However, feeding a normal-protein diet following lactational protein restriction prevented accelerated fibre loss and fibre size reduction in later life. These findings provide novel insight into the mechanisms by which lactational protein restriction hinders skeletal muscle growth and includes evidence that lifelong dietary protein restriction accelerated skeletal muscle loss in later life.

Mitochondrial function declines with age within individuals but is not linked to the pattern of growth or mortality risk in zebra finch

Mitochondrial dysfunction is considered a highly conserved hallmark of ageing. However, most of the studies in both model and non-model organisms are cross-sectional in design; therefore, little is known, at the individual level, on how mitochondrial function changes with age, its link to early developmental conditions or its relationship with survival. Here we manipulated the postnatal growth in zebra finches (Taeniopygia guttata) via dietary modification that induced accelerated growth without changing adult body size. In the same individuals, we examined blood cells mitochondrial functioning (mainly erythrocytes) when they were young (ca. 36 weeks) and again in mid-aged (ca. 91 weeks) adulthood. Mitochondrial function was strongly influenced by age but not by postnatal growth conditions. Across all groups, within individual ROUTINE respiration, OXPHOS and OXPHOS coupling efficiency significantly declined with age, while LEAK respiration increased. However, we found no link between mitochondrial function and the probability of survival into relatively old age (ca. 4 years). Our results suggest that the association between accelerated growth and reduced longevity, evident in this as in other species, is not attributable to age-related changes in any of the measured mitochondrial function traits.

Maternal Fructose Intake, Programmed Mitochondrial Function and Predisposition to Adult Disease

Fructose consumption is now recognised as a major risk factor in the development of metabolic diseases, such as hyperlipidaemia, diabetes, non-alcoholic fatty liver disease and obesity. In addition to environmental, social, and genetic factors, an unfavourable intrauterine environment is now also recognised as an important factor in the progression of, or susceptibility to, metabolic disease during adulthood. Developmental trajectory in the short term, in response to nutrient restriction or excessive nutrient availability, may promote adaptation that serves to maintain organ functionality necessary for immediate survival and foetal development. Consequently, this may lead to decreased function of organ systems when presented with an unfavourable neonatal, adolescent and/or adult nutritional environment. These early events may exacerbate susceptibility to later-life disease since sub-optimal maternal nutrition increases the risk of non-communicable diseases (NCDs) in future generations. Earlier dietary interventions, implemented in pregnant mothers or those considering pregnancy, may have added benefit. Although, the mechanisms by which maternal diets high in fructose and the vertical transmission of maternal metabolic phenotype may lead to the predisposition to adult disease are poorly understood. In this review, we will discuss the potential contribution of excessive fructose intake during pregnancy and how this may lead to developmental reprogramming of mitochondrial function and predisposition to metabolic disease in offspring.

Chronic developmental hypoxia alters mitochondrial oxidative capacity and reactive oxygen species production in the fetal rat heart in a sex-dependent manner

Insufficient oxygen supply (hypoxia) during fetal development leads to cardiac remodeling and a predisposition to cardiovascular disease in later life. Previous work has shown hypoxia causes oxidative stress in the fetal heart and alters the activity and expression of mitochondrial proteins in a sex-dependent manner. However, the functional effects of these modifications on mitochondrial respiration remain unknown. Furthermore, while maternal antioxidant treatments are emerging as a promising new strategy to protect the hypoxic fetus, whether these treatments convey similar protection to cardiac mitochondria in the male or female fetus has not been investigated. Therefore, using an established rat model, we measured the sex-dependent effects of gestational hypoxia and maternal melatonin treatment on fetal cardiac mitochondrial respiration, reactive oxygen species (ROS) production, and lipid peroxidation. Pregnant Wistar rats were subjected to normoxia or hypoxia (13% oxygen) during gestational days (GDs) 6-20 (term ~22 days) with or without melatonin treatment (5 µg/ml in maternal drinking water). On GD 20, mitochondrial aerobic respiration and H2 O2 production were measured in fetal heart tissue, together with lipid peroxidation and citrate synthase (CS) activity. Gestational hypoxia reduced maternal body weight gain (p < .01) and increased placental weight (p < .05) but had no effect on fetal weight or litter size. Cardiac mitochondria from male but not female fetuses of hypoxic pregnancy had reduced respiratory capacity at Complex II (CII) (p < .05), and an increase in H2 O2 production/O2 consumption (p < .05) without any changes in lipid peroxidation. CS activity was also unchanged in both sexes. Despite maternal melatonin treatment increasing maternal and fetal plasma melatonin concentration (p < .001), melatonin treatment had no effect on any of the mitochondrial parameters investigated. To conclude, we show that gestational hypoxia leads to ROS generation from the mitochondrial electron transport chain and affects fetal cardiac mitochondrial respiration in a sex-dependent manner. We also show that maternal melatonin treatment had no effect on these relationships, which has implications for the development of future therapies for hypoxic pregnancies.

Transcriptomic signals of mitochondrial dysfunction and OXPHOS dynamics in fast-growth chicken

Introduction

Birds are equipped with unique evolutionary adaptations to counter oxidative stress. Studies suggest that lifespan is inversely correlated with oxidative damage in birds. Mitochondrial function and performance are critical for cellular homeostasis, but the age-related patterns of mitochondrial gene expression and oxidative phosphorylation (OXPHOS) in birds are not fully understood. The domestic chicken is an excellent model to understand aging in birds; modern chickens are selected for rapid growth and high fecundity and oxidative stress is a recurring feature in chicken. Comparing fast- and slow-growing chicken phenotypes provides us an opportunity to disentangle the nexus of oxidative homeostasis, growth rate, and age in birds.

Methods and Results

We compared pectoralis muscle gene expression patterns between a fast and a slow-growing chicken breed at 11 and 42 days old. Using RNAseq analyses, we found that mitochondrial dysfunction and reduced oxidative phosphorylation are major features of fast-growth breast muscle, compared to the slow-growing heritage breed. We found transcriptomic evidence of reduced OXPHOS performance in young fast-growth broilers, which declined further by 42 days.

Discussion

OXPHOS performance declines are a common feature of aging. Sirtuin signaling and NRF2 dependent oxidative stress responses support the progression of oxidative damage in fast-growth chicken. Our gene expression datasets showed that fast growth in early life places immense stress on oxidative performance, and rapid growth overwhelms the OXPHOS system. In summary, our study suggests constraints on oxidative capacity to sustain fast growth at high metabolic rates, such as those exhibited by modern broilers.

Maternal Fructose Intake Causes Developmental Reprogramming of Hepatic Mitochondrial Catalytic Activity and Lipid Metabolism in Weanling and Young Adult Offspring

Excess dietary fructose is a major public health concern, yet little is known about its influence on offspring development and later-life disease when consumed in excess during pregnancy. To determine whether increased maternal fructose intake could have long-term consequences on offspring health, we investigated the effects of 10% w/v fructose water intake during preconception and pregnancy in guinea pigs. Female Dunkin Hartley guinea pigs were fed a control diet (CD) or fructose diet (FD; providing 16% of total daily caloric intake) ad libitum 60 days prior to mating and throughout gestation. Dietary interventions ceased at day of delivery. Offspring were culled at day 21 (D21) (weaning) and at 4 months (4 M) (young adult). Fetal exposure to excess maternal fructose intake significantly increased male and female triglycerides at D21 and 4 M and circulating palmitoleic acid and total omega-7 through day 0 (D0) to 4 M. Proteomic and functional analysis of significantly differentially expressed proteins revealed that FD offspring (D21 and 4 M) had significantly increased mitochondrial metabolic activities of β-oxidation, electron transport chain (ETC) and oxidative phosphorylation and reactive oxygen species production compared to the CD offspring. Western blotting analysis of both FD offspring validated the increased protein abundances of mitochondrial ETC complex II and IV, SREBP-1c and FAS, whereas VDAC1 expression was higher at D21 but lower at 4 M. We provide evidence demonstrating offspring programmed hepatic mitochondrial metabolism and de novo lipogenesis following excess maternal fructose exposure. These underlying asymptomatic programmed pathways may lead to a predisposition to metabolic dysfunction later in life.

Metabolic Disease Programming: From Mitochondria to Epigenetics, Glucocorticoid Signalling and Beyond

Embryonic and foetal development are critical periods of development in which several environmental cues determine health and disease in adulthood. Maternal conditions and an unfavourable intrauterine environment impact foetal development and may programme the offspring for increased predisposition to metabolic diseases and other chronic pathologic conditions throughout adult life. Previously, non-communicable chronic diseases were only associated with genetics and lifestyle. Now the origins of non-communicable chronic diseases are associated with early-life adaptations that produce long-term dysfunction. Early-life environment sets the long-term health and disease risk and can span through multiple generations. Recent research in developmental programming aims at identifying the molecular mechanisms responsible for developmental programming outcomes that impact cellular physiology and trigger adulthood disease. The identification of new therapeutic targets can improve offspring's health management and prevent or overcome adverse consequences of foetal programming. This review summarizes recent biomedical discoveries in the Developmental Origins of Health and Disease (DOHaD) hypothesis and highlight possible developmental programming mechanisms, including prenatal structural defects, metabolic (mitochondrial dysfunction, oxidative stress, protein modification), epigenetic and glucocorticoid signalling-related mechanisms suggesting molecular clues for the causes and consequences of programming of increased susceptibility of offspring to metabolic disease after birth. Identifying mechanisms involved in DOHaD can contribute to early interventions in pregnancy or early childhood, to re-set the metabolic homeostasis and break the chain of subsequent events that could lead to the development of disease.

Litter expansion alters metabolic homeostasis in a sex specific manner

Nutritional manipulations early in life have been shown to influence growth rate and elicit long lasting effects which in turn has been found to impact lifespan. Therefore, we studied the long-term effects of pre-weaning dietary restriction implemented by litter expansion (4, 6, 8, 10, and 12 pups per dam: LS4, LS6, LS8, LS10, LS12) on male and female C57BL/6J mice. After weaning, these mice were fed ad libitum a commercial lab chow for the 15-month duration of the study. The male mice from large litter size (LS12) were significantly leaner and had reduced total fat mass compared to the normal size litters (LS 6) starting from weaning through to 15 months of age. Male LS10 & 12 mice also showed significant reduction in their fat depot masses at 15 months of age: gonadal, subcutaneous, and brown fat whereas the females did not mimic these findings. At 9 months of age, only male LS12 mice showed improved glucose tolerance and male LS12 mice also showed improved insulin tolerance starting at 5 months of age. In addition, we found that the male LS8, 10 & 12 mice at 15 months of age showed significantly reduced IGF-1 levels in the serum and various other organs (liver, gastrocnemius and brain cortex). Interestingly, the female LS8, 10, 12 mice showed a different pattern with reduced IGF-1 levels in serum, liver and gastrocnemius but not in the brain cortex. Similarly, the litter expanded mice showed sex specific response to levels of FGF21 and adiponectin with only the male mice showing increased FGF21 and adiponectin levels at 15 months of age. In summary, our data show that, litter expansion results in long-lasting metabolic changes that are age and sex dependent with the male mice showing an early and robust response compared to female mice.

Serine Supplementation Alleviates Doxorubicin-Induced Oxidative Damage in Skeletal Muscle of Mice

Muscle weakness affects physical activity and quality of life of patients. Serine, a nutritionally non-essential amino acid has been reported to enhance protein synthesis and implicate in biosynthesis of multiple bioactive molecules. It remains unknown whether it can protect mice against oxidative stress-induced muscles weakness. This study was conducted to test the hypothesis that serine administration alleviates doxorubicin-induced oxidative damage in skeletal muscle of mice. Mice pre-treated with or without serine were intraperitoneally injected with either doxorubicin or equal volume of saline. Reactive oxygen species (ROS) accumulation, activity of antioxidant enzymes, oxidation product of protein, DNA, and lipid, activity of mitochondrial complex, and protein level of nuclear-factor-erythroid-2-related factor 2 (NRF2)/constitutive-androstane-receptor (CAR) signaling in skeletal muscle of mice were determined. Compared with the control, doxorubicin exposure led to oxidative damage as shown by increased ROS accumulation, decreased activity of antioxidant enzymes, and enhanced oxidative product of protein, DNA, and lipid in the skeletal muscle of mice. These effects of doxorubicin were associated with increased activity of complex I and reduced glutathione. Interestingly, doxorubicin-induced oxidative damage was alleviated by serine administration. Further study showed that the beneficial effect of serine was associated with enhanced NRF2/CAR signaling. Our result showed that serine attenuated doxorubicin-induced muscle weakness in mice. Serine supplementation might be a nutritional strategy to improve the function of skeletal muscle in patients exposed to doxorubicin.

Growth acceleration results in faster telomere shortening later in life

There is a wealth of evidence for a lifespan penalty when environmental conditions influence an individual's growth trajectory, such that growth rate is accelerated to attain a target size within a limited time period. Given this empirically demonstrated relationship between accelerated growth and lifespan, and the links between lifespan and telomere dynamics, increased telomere loss could underpin this growth-lifespan trade. We experimentally modified the growth trajectory of nestling zebra finches (Taeniopygia guttata), inducing a group of nestlings to accelerate their growth between 7 and 15 days of age, the main phase of body growth. We then sequentially measured their telomere length in red blood cells at various time points from 7 days to full adulthood (120 days). Accelerated growth between 7 and 15 days was not associated with a detectable increase in telomere shortening during this period compared with controls. However, only in the treatment group induced to show growth acceleration was the rate of growth during the experimental period positively related to the amount of telomere shortening between 15 and 120 days. Our findings provide evidence of a long-term influence of growth rate on later-life telomere shortening, but only when individuals have accelerated growth in response to environmental circumstances.

Understanding the Long-Lasting Effects of Fetal Nutrient Restriction versus Exposure to an Obesogenic Diet on Islet-Cell Mass and Function

Early life represents a window of phenotypic plasticity. Thus, exposure of the developing fetus to a compromised nutritional environment can have long term consequences for their health. Indeed, undernutrition or maternal intake of an obesogenic diet during pregnancy leads to a heightened risk of type 2 diabetes (T2D) and obesity in her offspring in adult life. Given that abnormalities in beta-cell function are crucial in delineating the risk of T2D, studies have investigated the impact of these exposures on islet morphology and beta-cell function in the offspring in a bid to understand why they are more at risk of T2D. Interestingly, despite the contrasting maternal metabolic phenotype and, therefore, intrauterine environment associated with undernutrition versus high-fat feeding, there are a number of similarities in the genes/biological pathways that are disrupted in offspring islets leading to changes in function. Looking to the future, it will be important to define the exact mechanisms involved in mediating changes in the gene expression landscape in islet cells to determine whether the road to T2D development is the same or different in those exposed to different ends of the nutritional spectrum.

Repeated exposure to challenging environmental conditions influences telomere dynamics across adult life as predicted by changes in mortality risk

The effects of stress exposure are likely to vary depending on life-stage and stressor. While it has been postulated that mild stress exposure may have beneficial effects, the duration of such effects and the underlying mechanisms are unclear. While the long-term effects of early-life stress are relatively well studied, we know much less about the effects of exposure in adulthood since the early- and adult-life environments are often similar. We previously reported that repeated experimental exposure to a relatively mild stressor in female zebra finches, first experienced in young adulthood, initially had no effect on mortality risk, reduced mortality in middle age, but the apparently beneficial effects disappeared in old age. We show here that this is underpinned by differences between the control and stress-exposed group in the pattern of telomere change, with stress-exposed birds showing reduced telomere loss in middle adulthood. We thereby provide novel experimental evidence that telomere dynamics play a key role linking stress resilience and aging.

The Role of Cellular Stress in Intrauterine Growth Restriction and Postnatal Dysmetabolism

Disruption of the in utero environment can have dire consequences on fetal growth and development. Intrauterine growth restriction (IUGR) is a pathological condition by which the fetus deviates from its expected growth trajectory, resulting in low birth weight and impaired organ function. The developmental origins of health and disease (DOHaD) postulates that IUGR has lifelong consequences on offspring well-being, as human studies have established an inverse relationship between birth weight and long-term metabolic health. While these trends are apparent in epidemiological data, animal studies have been essential in defining the molecular mechanisms that contribute to this relationship. One such mechanism is cellular stress, a prominent underlying cause of the metabolic syndrome. As such, this review considers the role of oxidative stress, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and inflammation in the pathogenesis of metabolic disease in IUGR offspring. In addition, we summarize how uncontrolled cellular stress can lead to programmed cell death within the metabolic organs of IUGR offspring.

Small-RNA Sequencing Reveals Altered Skeletal Muscle microRNAs and snoRNAs Signatures in Weanling Male Offspring from Mouse Dams Fed a Low Protein Diet during Lactation

Maternal diet during gestation and lactation affects the development of skeletal muscles in offspring and determines muscle health in later life. In this paper, we describe the association between maternal low protein diet-induced changes in offspring skeletal muscle and the differential expression (DE) of small non-coding RNAs (sncRNAs). We used a mouse model of maternal protein restriction, where dams were fed either a normal (N, 20%) or a low protein (L, 8%) diet during gestation and newborns were cross-fostered to N or L lactating dams, resulting in the generation of NN, NL and LN offspring groups. Total body and tibialis anterior (TA) weights were decreased in weanling NL male offspring but were not different in the LN group, as compared to NN. However, histological evaluation of TA muscle revealed reduced muscle fibre size in both groups at weaning. Small RNA-sequencing demonstrated DE of multiple miRs, snoRNAs and snRNAs. Bioinformatic analyses of miRs-15a, -34a, -122 and -199a, in combination with known myomiRs, confirmed their implication in key muscle-specific biological processes. This is the first comprehensive report for the DE of sncRNAs in nutrition-associated programming of skeletal muscle development, highlighting the need for further research to unravel the detailed molecular mechanisms.

An incremental feeding pattern for Guangdong Small-ear Spotted gilts during gestation: effects on stillbirth rate and muscle weight of progeny

While an appropriate feed intake is crucial for the reproductive performance of sows, there is a lack of recommendations currently for feed allowance of Guangdong Small-ear Spotted gilts during gestation. The effects of 2 different feeding patterns during gestation on the reproductive performance of Guangdong Small-ear Spotted gilts were investigated by assigning 80 gilts to 2 feeding pattern groups with a randomized complete block design in accordance with initial body weight and back fat thickness, followed by treatment with an incremental feeding pattern (IFP) and a concaved feeding pattern, respectively, with no difference in total feed intake. The IFP group showed a significant decrease in the stillbirth rate (P < 0.05) and an upward trend in piglet mean birth weight (P = 0.06). Furthermore, the IFP group exhibited an increase in the weights of stomach, supraspinatus tendon, triceps, and psoas minor in neonatal piglets (P < 0.05). Overall, the results of the present investigation showed that IFP could significantly reduce the stillbirth rate of Guangdong Small-ear Spotted gilts and increase the muscle weight of progeny.

Effects of different maternal feeding strategies from day 1 to day 85 of gestation on glucose tolerance and muscle development in both low and normal birth weight piglets

BACKGROUND

Maternal nutrition during gestation plays a vital role in fetal development. The effects of different maternal feeding strategies from day 1 to day 85 of gestation on glucose tolerance and muscle development in low and normal birth weight offspring were investigated by using 80 gilts randomly allotted to T1 and T2 groups and treated respectively with a gradual-increase (T1) and a convex transition (T2) feeding strategy, with no difference in total feed intake.

RESULTS

T2 group was seen to have a higher percentage of piglets with birth weight less than 500 g, while T1 group was shown to have a higher percentage of piglets with birth weight over 700 g. Meanwhile, for both low and normal birth weight piglets, T1 group was higher than T2 group in terms of muscle free amino acid concentration, mRNA expression levels of muscle growth-related factors, relative muscle fiber number and cross-sectional area. We must emphasize that the T2 group was shown to improve glucose tolerance, slow-twitch muscle fiber protein levels, and muscle mitochondrial function only in low birth weight piglets.

CONCLUSION

The convex transition feeding strategy can decrease the percentage of piglets with birth weight over 700 g, while improving glucose tolerance, slow-twitch muscle fiber protein levels, and muscle mitochondrial function in low birth weight piglets. Our findings provide new evidence for the potential importance of nutritional strategies during gestation, especially for improving the glucose tolerance and muscle development of low birth weight neonatal. © 2020 Society of Chemical Industry.

Developmental programming of mitochondrial biology: a conceptual framework and review

Research on mechanisms underlying the phenomenon of developmental programming of health and disease has focused primarily on processes that are specific to cell types, organs and phenotypes of interest. However, the observation that exposure to suboptimal or adverse developmental conditions concomitantly influences a broad range of phenotypes suggests that these exposures may additionally exert effects through cellular mechanisms that are common, or shared, across these different cell and tissue types. It is in this context that we focus on cellular bioenergetics and propose that mitochondria, bioenergetic and signalling organelles, may represent a key cellular target underlying developmental programming. In this review, we discuss empirical findings in animals and humans that suggest that key structural and functional features of mitochondrial biology exhibit developmental plasticity, and are influenced by the same physiological pathways that are implicated in susceptibility for complex, common age-related disorders, and that these targets of mitochondrial developmental programming exhibit long-term temporal stability. We conclude by articulating current knowledge gaps and propose future research directions to bridge these gaps.

Intergenerational effects on offspring telomere length: interactions among maternal age, stress exposure and offspring sex

Offspring produced by older parents often have reduced longevity, termed the Lansing effect. Because adults usually have similar-aged mates, it is difficult to separate effects of maternal and paternal age, and environmental circumstances are also likely to influence offspring outcomes. The mechanisms underlying the Lansing effect are poorly understood. Variation in telomere length and loss, particularly in early life, is linked to longevity in many vertebrates, and therefore changes in offspring telomere dynamics could be very important in this context. We examined the effect of maternal age and environment on offspring telomere length in zebra finches. We kept mothers under either control (ad libitum food) or more challenging (unpredictable food) circumstances and experimentally minimized paternal age and mate choice effects. Irrespective of the maternal environment, there was a substantial negative effect of maternal age on offspring telomere length, evident in longitudinal and cross-sectional comparisons (average of 39% shorter). Furthermore, in young mothers, sons reared by challenged mothers had significantly shorter telomere lengths than sons reared by control mothers. This effect disappeared when the mothers were old, and was absent in daughters. These findings highlight the importance of telomere dynamics as inter-generational mediators of the evolutionary processes determining optimal age-specific reproductive effort and sex allocation.

Maternal pro-inflammatory state during pregnancy and newborn leukocyte telomere length: A prospective investigation

INTRODUCTION

Telomere biology plays a fundamental role in maintaining the integrity of the genome and cell, and shortened telomeres have been linked to several age-related diseases. The initial (newborn) telomere length (TL) represents a critically important feature of the telomere biology system. Exposure to a variety of adverse prenatal conditions such as maternal stress, suboptimal diet, obesity, and obstetric complications, is associated with shorter offspring TL at birth and in adult life. Many, if not all, of these exposures are believed to have an inflammatory component. In this context, stress-related immunological processes during pregnancy may constitute a potential additional biological pathway because they can affect telomere length and telomerase activity via transcriptions factors such as cyclic adenosine monophosphate-dependent transcription factor (ATF7) and nuclear factor-kappa B (NF-κB). Thus, in the present study we examined the hypothesis that maternal pro-inflammatory state across pregnancy, operationalized as the balance between tumor necrosis factor (TNF)-α, a major pro-inflammatory cytokine, and interleukin-10 (IL-10), the major anti-inflammatory cytokine, is associated with newborn leukocyte telomere length (LTL) at birth.

METHODS AND MATERIALS

Participants were healthy women (N = 112) recruited in early pregnancy. Concentrations of TNF- α and IL-10 were quantified in early, mid and late pregnancy from maternal blood samples. Telomere length was assessed in newborn blood samples soon after birth.

RESULTS

After adjusting for maternal age, maternal pre-pregnancy BMI, birth weight percentile, and infant sex, a higher mean TNF-α/IL-10 ratio across pregnancy was significantly associated with shorter newborn TL (β = -.205, p = .030). Newborn TL was, on average, 10% shorter in offspring of women in the upper compared to lower quartile of the TNF-α/IL-10 ratio during pregnancy.

DISCUSSION

These findings provide new evidence in humans for a potential "programming" mechanism linking maternal systemic pro-inflammatory processes during pregnancy with the initial (newborn) setting of her offspring's telomere system.

Developmental Programming of Body Composition: Update on Evidence and Mechanisms

PURPOSE OF REVIEW

A growing body of epidemiological and experimental data indicate that nutritional or environmental stressors during early development can induce long-term adaptations that increase risk of obesity, diabetes, cardiovascular disease, and other chronic conditions-a phenomenon termed "developmental programming." A common phenotype in humans and animal models is altered body composition, with reduced muscle and bone mass, and increased fat mass. In this review, we summarize the recent literature linking prenatal factors to future body composition and explore contributing mechanisms.

RECENT FINDINGS

Many prenatal exposures, including intrauterine growth restriction, extremes of birth weight, maternal obesity, and maternal diabetes, are associated with increased fat mass, reduced muscle mass, and decreased bone density, with effects reported throughout infancy and childhood, and persisting into middle age. Mechanisms and mediators include maternal diet, breastmilk composition, metabolites, appetite regulation, genetic and epigenetic influences, stem cell commitment and function, and mitochondrial metabolism. Differences in body composition are a common phenotype following disruptions to the prenatal environment, and may contribute to developmental programming of obesity and diabetes risk.

Oxidative Stress, Intrauterine Growth Restriction, and Developmental Programming of Type 2 Diabetes

Intrauterine growth restriction (IUGR) leads to reduced birth weight and the development of metabolic diseases such as Type 2 diabetes in adulthood. Mitochondria dysfunction and oxidative stress are commonly found in key tissues (pancreatic islets, liver, and skeletal muscle) of IUGR individuals. In this review, we explore the role of oxidative stress in IUGR-associated diabetes etiology.

Microinjection and Oviduct Transfer Procedures for Rat Model Generation with CRISPR-Cas9 Technology

Since the first knockout rat model was generated with zinc-finger nucleases (ZFNs) by Geurt's group in 2009, the demand for making targeted rat models has increased tremendously. The advent of the clustered regularly interspaced short palindromic repeats-CRISPR associated protein 9 (CRISPR-Cas9) system provides researchers with a more efficient method for producing modified animals, which has since then been developed and applied in rat. Since we established a rat model production system at our facility in 2014, we have consistently generated rat models. Due to differences in physiology and embryology between mouse and rat, species-specific protocols for superovulation conditions, microinjection, and embryo transfer (among others) are required. There are over 100 rat strains, and Sprague Dawley is one of the commonly used outbred strains in biomedical research. In this chapter, we describe in detail a range of topics including donor and recipient preparation, microinjection setup, CRISPR reagent preparation, and oviduct transfer procedures for making rat models in the Sprague Dawley background.

Poor Early Growth and Age-Associated Disease

The prevalence of age-associated disease is increasing at a striking rate globally and there is evidence to suggest that the ageing process may actually begin before birth. It has been well-established that the status of both the maternal and early postnatal environments into which an individual is exposed can have huge implications for the risk of developing age-associated disease, including cardiovascular disease (CVD), type-2 diabetes (T2D) and obesity in later life. Therefore, the dissection of underlying molecular mechanisms to explain this phenomenon, known as 'developmental programming' is a highly investigated area of research. This book chapter will examine the epidemiological evidence and the animal models of suboptimal maternal and early postnatal environments 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.

Early life environment influences the trajectory of post-partum weight loss in adult female rats

RESEARCH QUESTION

The physiological processes of pregnancy and lactation require profound changes in maternal metabolism and energy balance. The timescale of metabolic reversion after pregnancy, in particular post-partum weight loss, is highly variable between individuals. Currently, mechanisms influencing post-partum metabolic recovery are not well understood. The hypothesis tested here is that, in common with other metabolic and obesity-related outcomes, capacity for post-partum weight loss is influenced by developmental programming.

DESIGN

Adult female Wistar rats exposed to a maternal low-protein diet in utero then weaned onto a control diet post-natally (recuperated group) were compared with controls. Adult females from both groups underwent pregnancy at 3 months of age. Weight changes and metabolic parameters during pregnancy and lactation were compared between control and recuperated groups, and also with non-pregnant littermates.

RESULTS

Pregnancy weight gain was not different between the control and recuperated groups, but post-partum recuperated animals remained significantly heavier than both post-partum control animals (P<0.05) and their non-pregnant recuperated littermates (P<0.05) at the end of lactation. Post-partum recuperated animals had more intra-abdominal fat mass (P<0.05) and higher serum triglyceride concentrations (P<0.01) than controls. Post-partum recuperated animals also had increased expression of IL6, NRF2 and ALOX12 (key regulators of inflammation and lipoxygenase activity) in the intra-abdominal adipose tissue compared with control groups.

CONCLUSIONS

Mothers who themselves have been exposed to adverse early life environments are likely to have slower metabolic recovery from pregnancy than controls. Failure to return to pre-pregnancy weight after delivery predisposes to persisting sequential inter-pregnancy weight gain, which can represent a significant metabolic burden across a life course involving several pregnancies.

Age-related changes in skeletal muscle: changes to life-style as a therapy

As we age, there is an age-related loss in skeletal muscle mass and strength, known as sarcopenia. Sarcopenia results in a decrease in mobility and independence, as well as an increase in the risk of other morbidities and mortality. Sarcopenia is therefore a major socio-economical problem. The mechanisms behind sarcopenia are unclear and it is likely that it is a multifactorial condition with changes in numerous important mechanisms all contributing to the structural and functional deterioration. Here, we review the major proposed changes which occur in skeletal muscle during ageing and highlight evidence for changes in physical activity and nutrition as therapeutic approaches to combat age-related skeletal muscle wasting.

Weanling Offspring of Dams Maintained on Serine-Deficient Diet Are Vulnerable to Oxidative Stress

Serine plays an important role in the antioxidant defense system. However, the effects of maternal serine deficiency on the antioxidant ability of weanling offspring have not been reported. In the present study, we investigated the oxidative status of offspring of dams that are maintained on serine-deficient diet and subjected to diquat challenge. Individual pregnant animals were randomly divided into two dietary groups, namely, the control diet group and the serine- and glycine-deficient diet group. Samples were collected from weanling offspring at the age of 3 weeks after diquat challenge. Our results showed that maternal serine deficiency did not affect the levels of antioxidant enzymes and reactive oxygen species, as well as the expression of cellular and mitochondrial stress markers (Hspd1 and Hspa1a), which indicated that maternal serine deficiency did not affect basal oxidative status in weanling offspring. However, the weanling offspring were found to be vulnerable to oxidative challenges. Furthermore, our results suggested that the dysfunctional antioxidant system in response to oxidative stress in offspring of dams fed with serine-deficient diet was primarily caused by reduced availability of nicotinamide adenine dinucleotide phosphate. Furthermore, impairment of the antioxidant defense system caused by maternal serine deficiency was mediated by the Akt/AMPK/Sirt1 pathway. Our results indicated that maternal serine availability is important for maintaining antioxidant defense against oxidative challenge in weanling offspring.

Maternal obesity has sex-dependent effects on insulin, glucose and lipid metabolism and the liver transcriptome in young adult rat offspring

KEY POINTS

Maternal high-fat diet consumption predisposes to metabolic dysfunction in male and female offspring at young adulthood. Maternal obesity programs non-alcoholic fatty liver disease (NAFLD) in a sex-dependent manner. We demonstrate sex-dependent liver transcriptome profiles in rat offspring of obese mothers. In this study, we focused on pathways related to insulin, glucose and lipid signalling. These results improve understanding of the mechanisms by which a maternal high-fat diet affects the offspring.

ABSTRACT

Maternal obesity (MO) predisposes offspring (F1) to obesity, insulin resistance (IR) and non-alcoholic fatty liver disease (NAFLD). MO's effects on the F1 liver transcriptome are poorly understood. We used RNA-seq to determine the liver transcriptome of male and female F1 of MO and control-fed mothers. We hypothesized that MO-F1 are predisposed to sex-dependent adult liver dysfunction. Female Wistar rat mothers ate a control (C) or obesogenic (MO) diet from the time they were weaned through breeding at postnatal day (PND) 120, delivery and lactation. After weaning, all male and female F1 ate a control diet. At PND 110, F1 serum, liver and fat were collected to analyse metabolites, histology and liver differentially expressed genes. Male and female MO-F1 showed increased adiposity index, triglycerides, insulin and homeostatic model assessment vs. C-F1 with similar body weight and glucose serum concentrations. MO-F1 males presented greater physiological and histological NAFLD characteristics than MO-F1 females. RNA-seq revealed 1365 genes significantly changed in male MO-F1 liver and only 70 genes in female MO-F1 compared with controls. GO and KEGG analysis identified differentially expressed genes related to metabolic processes. Male MO-F1 liver showed the following altered pathways: insulin signalling (22 genes), phospholipase D signalling (14 genes), NAFLD (13 genes) and glycolysis/gluconeogenesis (7 genes). In contrast, few genes were altered in these pathways in MO-F1 females. In summary, MO programs sex-dependent F1 changes in insulin, glucose and lipid signalling pathways, leading to liver dysfunction and insulin resistance.

[AMPK regulates mitochondrial oxidative stress in C2C12 myotubes induced by electrical stimulations of different intensities]

OBJECTIVE

To study effect of electrical stimulations of different intensities on mitochondrial oxidative stress in C2C12 myotubes and explore the molecular mechanisms.

METHODS

After 7 days of differentiation, C2C12 myotubes were subjected to electrical stimulations (15 V, 3Hz, 30 ms) for 60, 120, or 180 min, and the morphological changes of muscular tubes were observed under inverted microscope. The levels of MDA and SOD activity of the cells were detected, and flow cytometry was used to detect mitochondrial reactive oxygen species (ROS) and membrane potential. Western blotting was used to detect the expression of PGC1, AMPK-Ser485, AMPK-Thr172, and AMPK in the cells.

RESULTS

No significant changes occurred in the morphology of C2C12 myotubes in response to electrical stimulations. Electrical stimulation for 60 min resulted in significantly increased levels of MDA, AMPK-Ser485 and AMPK-Thr172 in the cells (P<0.05); simulations of the cells for 120 and 180 min caused significantly increased MDA, ROS, mitochondrial ROS, AMPK-Ser485 and PGC1 along with marked reduction of mitochondrial membrane potential (P<0.05).

CONCLUSION

Electrical stimulation significantly activates oxidative stress, and a longer stimulation time causes stronger mitochondrial oxidation. AMPK-Thr172 regulates oxidative stress induced by stimulations for a moderate time length, while AMPK-Ser485 and PGC1 function to modulate oxidative stress following prolonged stimulations.

Dynamic changes in morphology, gene expression and microbiome in the jejunum of compensatory-growth rats induced by protein restriction

We previously reported that protein‐restricted rats experienced compensatory growth when they were switched to a normal protein diet (NPD). This study aimed to investigate the changes in gene expression and microbiome in the jejunum of compensatory‐growth rats. Weaned Sprague‐Dawley rats were assigned to an N group, an LN group and an L group. The rats in the L and N groups were fed a low protein diet (LPD) and the NPD respectively. The rats in the LN group were fed with the LPD for 2 weeks, followed by the NPD. The experiment lasted 70 days, and the rats were sacrificed for sampling on days 14, 28 and 70 to determine the jejunal morphology, microbiome and gene expression related to digestive, absorptive and barrier function. The results showed that, although rats in the LN group had temporarily impaired morphology and gene expression in the jejunum on day 14 in response to the LPD, they had improved jejunal morphology and gene expression related to jejunal function on day 28 compared to rats in the N group. This improvement might promote compensatory growth of rats. However, lower expression of genes related to nutrient absorption and undifferentiated villous height (VH) were observed in the jejunum of rats in the LN group on day 70. In contrast, rats in the L group had lower VH on day 28 and day 70, while the expression of absorptive genes increased on day 28 compared to rats in the N group. Additionally, dramatic microbial changes in the jejunum of compensatory‐growth rats were observed, principally for Lactobacillus, Streptococcus, Corynebacterium and Staphylococcus. Moreover, the abundance of Lactobacillus, Streptococcus, Corynebacterium and Staphylococcus significantly correlated with gene expression in the jejunum as revealed by the correlation analysis.

Somatic growth and telomere dynamics in vertebrates: relationships, mechanisms and consequences

Much telomere loss takes place during the period of most rapid growth when cell proliferation and potentially energy expenditure are high. Fast growth is linked to reduced longevity. Therefore, the effects of somatic cell proliferation on telomere loss and cell senescence might play a significant role in driving the growth-lifespan trade-off. While different species will have evolved a growth strategy that maximizes lifetime fitness, environmental conditions encountered during periods of growth will influence individual optima. In this review, we first discuss the routes by which altered cellular conditions could influence telomere loss in vertebrates, with a focus on oxidative stress in both in vitro and in vivo studies. We discuss the relationship between body growth and telomere length, and evaluate the empirical evidence that this relationship is generally negative. We further discuss the potentially conflicting hypotheses that arise when other factors are taken into account, and the further work that needs to be undertaken to disentangle confounding variables.This article is part of the theme issue 'Understanding diversity in telomere dynamics'.

Reactive oxygen species enhance mitochondrial function, insulin sensitivity and glucose uptake in skeletal muscle of senescence accelerated prone mice SAMP8

Whereas reactive oxygen species (ROS) can have opposite impacts on insulin signaling, they have mainly been associated with mitochondrial dysfunction in skeletal muscle. We analyzed the relationship between these three features in skeletal muscle of senescence accelerated mice (SAM) prone (P8), which are characterized by enhanced oxidative stress compared to SAM resistant (R1). Oxidative stress, ROS production, antioxidant system, mitochondrial content and functioning, as well as in vitro and in vivo insulin signaling were investigated in gastrocnemius and quadriceps muscles. In SAMP8 compared to SAMR1, muscle content in carbonylated proteins was two-fold (p < 0.01) and ROS production by xanthine oxidase 70% (p < 0.05) higher. Furthermore, insulin-induced Akt phosphorylation measured in vivo and ex vivo as well as muscle glucose uptake measured ex vivo were significantly higher (p < 0.05). Mitochondrial respiration evidenced uncoupling and higher respiration rates with substrates of complexes II and IV, in agreement with higher maximal activity of complexes II and IV (+ 18% and 62%, respectively, p < 0.05). By contrast, maximal activity of complex I was 22% lower (p < 0.05). All strain differences were corrected after 6 months of N-acetylcysteine (NAC) treatment, thus supporting the involvement of high ROS production in these differences. In conclusion in muscle of SAMP8 compared to SAMR1, high ROS production is associated to higher insulin sensitivity and glucose uptake but to lower mitochondrial complex I activity. These conflicting adaptations, with regards to the resulting imbalance between NADH production and use, were associated with intrinsic adjustments in the mitochondrial respiration chain (mitochondrial uncoupling, enhanced complexes II and IV activity). We propose that these bioenergetics adaptations may help at preserving muscle metabolic flexibility of SAMP8.

Naked mole-rats maintain healthy skeletal muscle and Complex IV mitochondrial enzyme function into old age

The naked mole-rat (NMR) Heterocephalus glaber is an exceptionally long-lived rodent, living up to 32 years in captivity. This extended lifespan is accompanied by a phenotype of negligible senescence, a phenomenon of very slow changes in the expected physiological characteristics with age. One of the many consequences of normal aging in mammals is the devastating and progressive loss of skeletal muscle, termed sarcopenia, caused in part by respiratory enzyme dysfunction within the mitochondria of skeletal muscle fibers. Here we report that NMRs avoid sarcopenia for decades. Muscle fiber integrity and mitochondrial ultrastructure are largely maintained in aged animals. While mitochondrial Complex IV expression and activity remains stable, Complex I expression is significantly decreased. We show that aged naked mole-rat skeletal muscle tissue contains some mitochondrial DNA rearrangements, although the common mitochondrial DNA deletions associated with aging in human and other rodent skeletal muscles are not present. Interestingly, NMR skeletal muscle fibers demonstrate a significant increase in mitochondrial DNA copy number. These results have intriguing implications for the role of mitochondria in aging, suggesting Complex IV, but not Complex I, function is maintained in the long-lived naked mole rat, where sarcopenia is avoided and healthy muscle function is maintained for decades.

A RATional choice for translational research?

Future prospects continue to be strong for research using the rat as a model organism. New technology has enabled the proliferation of many new transgenic and knockout rat strains, the genomes of more than 40 rat strains have been sequenced, publications using the rat as a model continue to be produced at a steady rate, and discoveries of disease-associated genes and mechanisms from rat experiments abound, frequently with conservation of function between rats and humans. However, advances in genome technology have led to increasing insights into human disease directly from human genetic studies, pulling more and more researchers into the human genetics arena and placing funding for model organisms and their databases under threat. This, therefore, is a pivotal time for rat-based biomedical research - a timely moment to review progress and prospects - providing the inspiration for a new Special Collection focused on the impact of the model on translational science, launched in this issue of Disease Models & Mechanisms. What disease areas are most appropriate for research using rats? Why should the rat be favoured over other model organisms, and should the present levels of funding be continued? Which approaches should we expect to yield biologically and medically useful insights in the coming years? These are key issues that are addressed in the original Research Articles and reviews published in this Special Collection, and in this introductory Editorial. These exemplar articles serve as a landmark for the present status quo after a decade of major advances using the rat model and could help to guide the direction of rat research in the coming decade.