Neonatal exposure to leptin reduces glucose tolerance in adult mice

Early life nutrition and neuroendocrine programming

Alterations in the nutritional environment in early life can significantly increase the risk for obesity and a range of development of metabolic disorders in offspring in later life, effects that can be passed onto future generations. This process, termed development programming, provides the framework of the developmental origins of health and disease (DOHaD) paradigm. Early life nutritional compromise including undernutrition, overnutrition or specific macro/micronutrient deficiencies, results in a range of adverse health outcomes in offspring that can be further exacerbated by a poor postnatal nutritional environment. Although the mechanisms underlying programming remain poorly defined, a common feature across the phenotypes displayed in preclinical models is that of altered wiring of neuroendocrine circuits that regulate satiety and energy balance. As such, altered maternal nutritional exposures during critical early periods of developmental plasticity can result in aberrant hardwiring of these circuits with lasting adverse consequences for the offspring. There is also increasing evidence around the role of an altered epigenome and the gut-brain axis in mediating some of the central programming effects observed. Further, although such programming was once considered to result in a permanent change in developmental trajectory, there is evidence, at least from preclinical models, that programming can be reversed via targeted nutritional manipulations during early development. Further work is required at a mechanistic level to allow for identification for early markers of later disease risk, delineation of sex-specific effects and pathways to implementation of strategies aimed at breaking the transgenerational transmission of disease.

Temporal Leptin to Determine Cardiovascular and Metabolic Fate throughout the Life

Leptin links peripheral adiposity and the central nervous system (CNS) to regulate cardiometabolic physiology. Within the CNS, leptin receptor-expressing cells are a counterpart to circulating leptin, and leptin receptor-mediated neural networks modulate the output of neuroendocrine and sympathetic nervous activity to balance cardiometabolic homeostasis. Therefore, disrupted CNS leptin signaling is directly implicated in the development of metabolic diseases, such as hypertension, obesity, and type 2 diabetes. Independently, maternal leptin also plays a central role in the development and growth of the infant during gestation. Accumulating evidence points to the dynamic maternal leptin environment as a predictor of cardiometabolic fate in their offspring as it is directly associated with infant metabolic parameters at birth. In postnatal life, the degree of serum leptin is representative of the level of body adiposity/weight, a driving factor for cardiometabolic alterations, and therefore, the levels of blood leptin through the CNS mechanism, in a large part, are a strong determinant for future cardiometabolic fate. The current review focuses on highlighting and discussing recent updates for temporal dissection of leptin-associated programing of future cardiometabolic fate throughout the entire life.

Utility of Small Animal Models of Developmental Programming

Any effective strategy to tackle the global obesity and rising noncommunicable disease epidemic requires an in-depth understanding of the mechanisms that underlie these conditions that manifest as a consequence of complex gene-environment interactions. In this context, it is now well established that alterations in the early life environment, including suboptimal nutrition, can result in an increased risk for a range of metabolic, cardiovascular, and behavioral disorders in later life, a process preferentially termed developmental programming. To date, most of the mechanistic knowledge around the processes underpinning development programming has been derived from preclinical research performed mostly, but not exclusively, in laboratory mouse and rat strains. This review will cover the utility of small animal models in developmental programming, the limitations of such models, and potential future directions that are required to fully maximize information derived from preclinical models in order to effectively translate to clinical use.

Mendelian randomization supports causality between maternal hyperglycemia and epigenetic regulation of leptin gene in newborns

Leptin is an adipokine that acts in the central nervous system and regulates energy balance. Animal models and human observational studies have suggested that leptin surge in the perinatal period has a critical role in programming long-term risk of obesity. In utero exposure to maternal hyperglycemia has been associated with increased risk of obesity later in life. Epigenetic mechanisms are suspected to be involved in fetal programming of long term metabolic diseases. We investigated whether DNA methylation levels near LEP locus mediate the relation between maternal glycemia and neonatal leptin levels using the 2-step epigenetic Mendelian randomization approach. We used data and samples from up to 485 mother-child dyads from Gen3G, a large prospective population-based cohort. First, we built a genetic risk score to capture maternal glycemia based on 10 known glycemic genetic variants (GRS10) and showed it was an adequate instrumental variable (β = 0.046 mmol/L of maternal fasting glucose per additional risk allele; SE = 0.007; P = 7.8 × 10(-11); N = 467). A higher GRS10 was associated with lower methylation levels at cg12083122 located near LEP (β = -0.072 unit per additional risk allele; SE = 0.04; P = 0.05; N = 166). Direction and effect size of association between the instrumental variable GRS10 and methylation at cg12083122 were consistent with the negative association we observed using measured maternal glycemia. Lower DNA methylation levels at cg12083122 were associated with higher cord blood leptin levels (β = -0.17 log of cord blood leptin per unit; SE = 0.07; P = 0.01; N = 170). Our study supports that maternal glycemia is part of causal pathways influencing offspring leptin epigenetic regulation.

Potential of the application of epigenetics in animal production

Our many current environmental challenges, including worldwide abnormal weather, global warming, and pollution, necessitate a new and innovative strategy for animal production for the next generation. This strategy should incorporate not only higher-efficiency production, but also advanced biological concepts and multi-functional agricultural techniques, into environmentally friendly systems. Recent research has discovered a unique phenomenon referred to as ‘foetal and neonatal programming’, which is based on ‘the developmental origins of health and disease (DOHaD)’ concept. These studies have shown that alterations in foetal and early postnatal nutrition and endocrine status may result in developmental adaptations that permanently change the structure, physiology and metabolism of affected animals during adult life. Ruminants fill an important ecological niche that capitalises on the symbiotic relationship between fibre-fermenting ruminal microbes and the mammalian demand for usable nutrients. The timing of the perturbation in maternal nutrient availability plays an important role in determining the effect that the foetal and neonatal programming will have on the developing placenta or foetus and offspring performance. Developmental programming through nutritional manipulations may help the ruminant, as an effective grass–protein converter, fulfil its production potential.

Prenatal metformin exposure in mice programs the metabolic phenotype of the offspring during a high fat diet at adulthood

AIMS

The antidiabetic drug metformin is currently used prior and during pregnancy for polycystic ovary syndrome, as well as during gestational diabetes mellitus. We investigated the effects of prenatal metformin exposure on the metabolic phenotype of the offspring during adulthood in mice.

METHODS

Metformin (300 mg/kg) or vehicle was administered orally to dams on regular diet from the embryonic day E0.5 to E17.5. Gene expression profiles in liver and brain were analysed from 4-day old offspring by microarray. Body weight development and several metabolic parameters of offspring were monitored both during regular diet (RD-phase) and high fat diet (HFD-phase). At the end of the study, two doses of metformin or vehicle were given acutely to mice at the age of 20 weeks, and Insig-1 and GLUT4 mRNA expressions in liver and fat tissue were analysed using qRT-PCR.

RESULTS

Metformin exposed fetuses were lighter at E18.5. There was no effect of metformin on the maternal body weight development or food intake. Metformin exposed offspring gained more body weight and mesenteric fat during the HFD-phase. The male offspring also had impaired glucose tolerance and elevated fasting glucose during the HFD-phase. Moreover, the expression of GLUT4 mRNA was down-regulated in epididymal fat in male offspring prenatally exposed to metformin. Based on the microarray and subsequent qRT-PCR analyses, the expression of Insig-1 was changed in the liver of neonatal mice exposed to metformin prenatally. Furthermore, metformin up-regulated the expression of Insig-1 later in development. Gene set enrichment analysis based on preliminary microarray data identified several differentially enriched pathways both in control and metformin exposed mice.

CONCLUSIONS

The present study shows that prenatal metformin exposure causes long-term programming effects on the metabolic phenotype during high fat diet in mice. This should be taken into consideration when using metformin as a therapeutic agent during pregnancy.

Early determinants of type-2 diabetes

The global prevalence of type-2 diabetes (T2D) has more than doubled in the last 30 years and is predicted to continue to rise at an alarming rate. The associated health and financial burdens are considerable. The aetiology of common forms of T2D is multifactorial and involves a complex interplay between genetic, epigenetic and environmental factors. The influential role of the environment, in particular our diet and sedentary lifestyles, in diabetes risk is well established. Of major concern is the increasing prevalence of early onset T2D or pre-diabetic characteristics in children. In recent years, the role of the early life environment in programming diabetes risk has been the focus of numerous human and animal studies. Historical studies highlighted an association between low birthweight, a proxy for suboptimal in utero growth, and diabetes risk in adulthood. Over more recent years it has become apparent that a variety of expositions, including maternal obesity and/or maternal diabetes, can have a significant effect on offspring health outcomes. Further complicating matters, paternal and transgenerational transmission of T2D can occur thus mediating a perpetuating cycle of disease risk between generations. It is imperative for the underlying mechanisms to be elucidated so that interventions can be introduced. In doing so, it may be possible to prevent, delay or reverse a pre-programmed risk for T2D induced by pre- and/or postnatal environmental factors to improve health outcomes and curb premature metabolic decline. This review presents evidence for how the early life environment may programme T2D risk and suggests some mechanisms by which this may occur.

Leptin as mediator of the effects of developmental programming

Considerable epidemiological, experimental and clinical data have amassed showing that the risk of developing disease in later life is dependent upon early life conditions. In particular, altered maternal nutrition, including undernutrition and overnutrition, can lead to metabolic disorders in offspring characterised by obesity and leptin resistance. The adipokine leptin has received significant interest as a potential programming factor; alterations in the profile of leptin in early life are associated with altered susceptibility to obesity and metabolic disorders in adulthood. Maintenance of a critical leptin level during early development facilitates the normal maturation of tissues and signalling pathways involved in metabolic homeostasis. A period of relative hypo- or hyperleptinemia during this window of development will induce some of the metabolic adaptations which underlie developmental programming. However, it remains unclear whether leptin alone is a critical factor for the programming of obesity. At least in animal experimental studies, developmental programming is potentially reversible by manipulating the concentration of circulating leptin during a critical window of developmental plasticity and offers an exciting new approach for therapeutic intervention.

Strategies for reversing the effects of metabolic disorders induced as a consequence of developmental programming

Obesity and the metabolic syndrome have reached epidemic proportions worldwide with far-reaching health care and economic implications. The rapid increase in the prevalence of these disorders suggests that environmental and behavioral influences, rather than genetic causes, are fueling the epidemic. The developmental origins of health and disease hypothesis has highlighted the link between the periconceptual, fetal, and early infant phases of life and the subsequent development of metabolic disorders in later life. In particular, the impact of poor maternal nutrition on susceptibility to later life metabolic disease in offspring is now well documented. Several studies have now shown, at least in experimental animal models, that some components of the metabolic syndrome, induced as a consequence of developmental programming, are potentially reversible by nutritional or targeted therapeutic interventions during windows of developmental plasticity. This review will focus on critical windows of development and possible therapeutic avenues that may reduce metabolic and obesogenic risk following an adverse early life environment.