Type 2 diabetes mellitus--genes or intrauterine environment? An embryo transfer paradigm in rats

Metabolic analysis of adipose tissues in a rodent model of pre-pregnancy maternal obesity combined with offsprings on high-carbohydrate diet

Maternal obesity is associated with adverse effects on the health of offsprings. Consumption of a high-carbohydrate (HC) diet has been found to promote abnormal fatty acid metabolism in adipose tissue. Therefore, we hypothesised that maternal obesity combined with an offspring HC diet would alter the fatty acid metabolism of adipose tissue and subsequently contribute to offspring obesity. Lepr^db/+ mice were used to model pre-pregnancy maternal obesity and the C57BL/6 wildtype were used as a control group. Offspring were fed either HC diet or a normal-carbohydrate (NC) diet after weaning. Brown adipose tissue (BAT) and white adipose tissue (WAT) were collected from offspring at 20 weeks of age and their fatty acid metabolome was characterized using gas chromatography-mass spectrometry. We found that HC diet increased the body weight of offspring (males increased by 14.70% and females increased by 1.05%) compared to control mothers. However, maternal obesity alone caused a 7.9% body weight increase in female offspring. Maternal obesity combined with an offspring HC diet resulted in dynamic alterations of the fatty acid profiles of adipose tissue in male offspring. Under the impact of a HC diet, the fatty acid metabolome was solely elevated in female WAT, whereas, the fatty acid metabolites in BAT showed a similar trend in the male and female offsprings. 6,9-octadecadienoic acid and 12,15-cis-octadecatrienoic acid were significantly affected in female WAT, in response to offspring consumption of a HC diet. Our study demonstrated that maternal obesity and offspring HC diet have different metabolic effects on adipose tissue in male and female offsprings.

Fetal sex modifies the effect of maternal macronutrient intake on the incidence of small-for-gestational-age births: a prospective observational cohort study

Background

Maternal macronutrient intake is likely to play a pivotal role in fetoplacental growth. Male fetuses grow faster and their growth is more responsive to maternal size.

Objective

We assessed the role of fetal sex in modifying the effect of maternal macronutrient intake on the risk of small-for-gestational-age (SGA) birth.

Design

This was a prospective, observational cohort study of 2035 births from an urban South Asian Indian population. Maternal intakes of total energy and macronutrients were recorded by validated food-frequency questionnaires. The interaction of trimester 1 macronutrient intake with fetal sex was tested on the outcome of SGA births.

Results

The prevalence of SGA was 28%. Trimester 1 macronutrient composition was high in carbohydrate and low in fat (means ± SDs-carbohydrate: 64.6% ± 5.1%; protein: 11.5% ± 1.1%; and fat: 23.9% ± 4.4% of energy). Higher carbohydrate and lower fat consumption were each associated with an increased risk of SGA [adjusted OR (AOR) per 5% of energy (95% CI): carbohydrate: 1.15 (1.01, 1.32); fat: 0.83 (0.71, 0.97)] specifically among male births (males: n = 1047; females: n = 988). Dietary intake of >70% of energy from carbohydrate was also associated with increased risk (AOR: 1.67; 95% CI: 1.00, 2.78), whereas >25% of energy from fat intake was associated with decreased risk (AOR: 0.61; 95% CI: 0.41, 0.90) of SGA in male births.

Conclusions

Higher carbohydrate and lower fat intakes early in pregnancy were associated with increased risk of male SGA births. Therefore, we speculate that fetal sex acts as a modifier of the role of maternal periconceptional nutrition in optimal fetoplacental growth.

Gene Expression and DNA Methylation of PPARGC1A in Muscle and Adipose Tissue From Adult Offspring of Women With Diabetes in Pregnancy

Prenatal exposure to maternal hyperglycemia is associated with an increased risk of later adverse metabolic health. Changes in the regulation of peroxisome proliferator-activated receptor-γ coactivator-1α (PPARGC1A) in skeletal muscle and subcutaneous adipose tissue (SAT) is suggested to play a role in the developmental programming of dysmetabolism based on studies of human subjects exposed to an abnormal intrauterine environment (e.g., individuals with a low birth weight). We studied 206 adult offspring of women with gestational diabetes mellitus (O-GDM) or type 1 diabetes (O-T1D) and of women from the background population (O-BP) using a clinical examination, oral glucose tolerance test, and gene expression and DNA methylation of PPARGC1A in skeletal muscle and SAT. Plasma glucose was significantly higher for both O-GDM and O-T1D compared with O-BP (P < 0.05). PPARGC1A gene expression in muscle was lower in O-GDM compared with O-BP (P = 0.0003), whereas no differences were found between O-T1D and O-BP in either tissue. PPARGC1A DNA methylation percentages in muscle and SAT were similar among all groups. Decreased PPARGC1A gene expression in muscle has previously been associated with abnormal insulin function and may thus contribute to the increased risk of metabolic disease in O-GDM. The unaltered PPARGC1A gene expression in muscle of O-T1D suggests that factors other than intrauterine hyperglycemia may contribute to the decreased PPARGC1A expression in O-GDM.

Maternal diabetes, gestational diabetes and the role of epigenetics in their long term effects on offspring

There is a global epidemic of obesity and diabetes, and current efforts to curb the diabetes epidemic have had limited success. Epidemiological studies have highlighted increased risk of obesity, diabetes and cardiovascular complications in offspring exposed to maternal diabetes, and gestational diabetes increases the risk of diabetes in subsequent generations, thereby setting up a vicious cycle of "diabetes begetting diabetes". This relationship between maternal hyperglycaemia and long-term health in the offspring is likely to become even more important with an increasing proportion of young woman being affected by diabetes, and the number of pregnancies complicated by hyperglycaemia continuing to rise. Animal models of gestational diabetes or maternal hyperglycaemia have highlighted long-term changes in the offspring with some instances of sex bias, including increased adiposity, insulin resistance, β-cell dysfunction, hypertension, as well as other structural and functional changes. Furthermore, several of these changes appear to be transmissible to later generations through the maternal line. Epigenetic changes play an important role in regulating gene expression, especially during early development. Recent studies have identified a number of epigenetic modifications in the offspring associated with maternal hyperglycaemia. In this review, we provide an overview of the epidemiological evidence linking maternal hyperglycaemia with adverse long-term outcome in the offspring, as well as of some of the studies that explore the underlying epigenetic mechanisms. A better understanding of the pathways involved may provide novel approaches for combating this global epidemic.

Does exposure to hyperglycaemia in utero increase the risk of obesity and diabetes in the offspring? A critical reappraisal

BACKGROUND

The idea that exposure to hyperglycaemia in utero is an important factor in the development of obesity and diabetes in the offspring has become entrenched as popular belief.

AIM

To appraise the literature supporting this hypothesis in the light of recent studies that have clarified the main drivers of obesity in children and adolescents.

METHODS

A review of published evidence from animal studies, human observational studies, systematic reviews and experimental trials that address the impact of diabetes (Types 1 and 2, genetic or gestational) on the future risk of obesity and/or glucose intolerance in the offspring.

RESULTS

Some animal studies support a relationship between exposure to hyperglycaemia in utero and future development of obesity and diabetes, but the results are inconsistent. Most of the human studies claiming to show a relationship have not taken into account important known confounders, such as maternal and paternal BMI. Evidence supporting a dose-response relationship between maternal hyperglycaemia exposure and obesity and diabetes in the offspring is weak, and there is no convincing evidence that treating gestational diabetes reduces the later risk of offspring obesity or glucose intolerance.

CONCLUSIONS

Exposure to hyperglycaemia in utero has minimal direct effect on the later risk of obesity and Type 2 diabetes. The increased risk of obesity in the offspring of women with Type 2 or gestational diabetes can be explained by confounding factors, such as parental obesity.

Epigenetics and life-long consequences of an adverse nutritional and diabetic intrauterine environment

The phenomenon that adverse environmental exposures in early life are associated with increased susceptibilities for many adult, particularly metabolic diseases, is now referred to as ‘developmental origins of health and disease (DOHAD)’ or ‘Barker’ hypothesis. Fetal overnutrition and undernutrition have similar long-lasting effects on the setting of the neuroendocrine control systems, energy homeostasis, and metabolism, leading to life-long increased morbidity. There are sensitive time windows during early development, where environmental cues can program persistent epigenetic modifications which are generally assumed to mediate these gene–environment interactions. Most of our current knowledge on fetal programing comes from animal models and epidemiological studies in humans, in particular the Dutch famine birth cohort. In industrialized countries, there is more concern about adverse long-term consequences of fetal overnutrition, i.e. by exposure to gestational diabetes mellitus and/or maternal obesity which affect 10–20% of pregnancies. Epigenetic changes due to maternal diabetes/obesity may predispose the offspring to develop metabolic disease later in life and, thus, transmit the adverse environmental exposure to the next generation. This vicious cycle could contribute significantly to the worldwide metabolic disease epidemics. In this review article, we focus on the epigenetics of an adverse intrauterine environment, in particular gestational diabetes, and its implications for the prevention of complex disease.

Maternal diabetes, programming of beta-cell disorders and intergenerational risk of type 2 diabetes

A substantial body of evidence suggests that an abnormal intra-uterine milieu elicited by maternal metabolic disturbances as diverse as malnutrition, placental insufficiency, diabetes and obesity may be able to programme susceptibility of the foetus to later develop chronic degenerative diseases such as obesity, hypertension, cardiovascular diseases and type 2 diabetes (T2D). As insulin-producing cells have been placed centre stage in the development of T2D, this review examines developmental programming of the beta-cell mass (BCM) in various rodent models of maternal protein restriction, calorie restriction, overnutrition and diabetes. The main message is that whatever the initial maternal insult (F0 generation) and whether alone or in combination, it gives rise to the same programmed BCM outcome in the daughter generation (F1). The altered BCM phenotype in F1 females prohibits normal BCM adaptation during pregnancy and, thus, diabetes (gestational diabetes) ensues. This gestational diabetes is then passed from one generation (F1) to the next (F2, F3 and so on). This review highlights a number of studies that have identified epigenetic mechanisms that may contribute to altered BCM development and beta-cell failure, as observed in diabetes. In addition to their role in instilling the programmed defect, these non-genomic mechanisms may also be involved in its intergenerational transmission.

Intergenerational effects of prenatal ethanol on glucose tolerance and insulin response

Consequences of prenatal exposure to ethanol (E) include morphological, physiological, and cognitive deficits and are collectively classified as fetal alcohol spectrum disorders. Adult prenatal E exposed offspring show insulin resistance, and given that in utero hyperglycemic environment can cause metabolic disorders in subsequent generations; we investigated the effects of grandmaternal E on functional glucose and insulin responses of the second generation. Sprague-Dawley (S) rat dams, mated with S males, received E-containing liquid diet and two different control diets between gestational days 8 and 20. Additionally, because prenatal E-induced behavioral deficits can be reversed by simultaneous thyroxine (T4) treatment, another group of dams received 0.3 mg/l T4 in their E diet. Their first-generation (F1) offspring were mated with control Brown Norway (B) males or females to produce SB and BS F2 progeny. Dams consuming E during pregnancy were hyperglycemic, and their F1 offspring showed insulin resistance in the glucose tolerance test (GTT). However, F2 responses to GTT varied based on the sex of prenatal E-exposed parent. BS F2 females, and both male and female SB F2 progeny, displayed hypoglycemic and hyperinsulinemic GTT response patterns. Although administering T4 to E dams normalized thyroid function of the F1 generation, it did not reverse their prenatal E-induced metabolic dysfunction. In contrast, administration of T4 to the alcohol-consuming grandmother reversed or alleviated the aberrant GTT responses of the F2 progeny. Prenatal E-induced dysregulation of glucose metabolism can affect the next generation, possibly via ethanol effects on the germline of the F1 fetus.

Epigenetics of gestational diabetes mellitus and offspring health: the time for action is in early stages of life

The epidemic increase of type 2 diabetes and obesity in developed countries cannot be explained by overnutrition, physical inactivity and/or genetic factors alone. Epidemiologic evidence suggests that an adverse intrauterine environment, in particular a shortage or excess of nutrients is associated with increased risks for many complex diseases later in life. An impressive example for the 'fetal origins of adult disease' is gestational diabetes mellitus which usually presents in 1% to >10% of third trimester pregnancies. Intrauterine hyperglycemia is not only associated with increased perinatal morbidity and mortality, but also with increased lifelong risks of the exposed offspring for obesity, metabolic, cardiovascular and malignant diseases. Accumulating evidence suggests that fetal overnutrition (and similarly undernutrition) lead to persistent epigenetic changes in developmentally important genes, influencing neuroendocrine functions, energy homeostasis and metabolism. The concept of fetal programming has important implications for reproductive medicine. Because during early development the epigenome is much more vulnerable to environmental cues than later in life, avoiding adverse environmental factors in the periconceptional and intrauterine period may be much more important for the prevention of adult disease than any (i.e. dietetic) measures in infants and adults. A successful pregnancy should not primarily be defined by the outcome at birth but also by the health status in later life.

Embryo-transfer of the F2 postnatal calorie restricted female rat offspring into a control intra-uterine environment normalizes the metabolic phenotype

OBJECTIVE

Postnatal calorie and growth restriction (PNGR) in the first generation (F1) rat female offspring causes a lean and glucose tolerant phenotype associated with hypoinsulinemia and reduced glucose-stimulated insulin secretion (GSIS). Despite the absence of gestational hyperglycemia in the F1 PNGR female, naturally born second generation (F2) PNGR female adult offspring reportedly exhibit obesity, hyperglycemia with insulin resistance. The objective of this study was to determine the role of the intrauterine environment on the heritability of the trans-generational phenotypic expression in the F2 PNGR female adult offspring.

MATERIALS/METHODS

We performed embryo transfer (ET) of the F2 embryos from the procreating F1 pregnant PNGR or control (CON) females to gestate in control recipient rat mothers. Employing stable isotopes glucose metabolic kinetics was determined.

RESULTS

Birth weight, postnatal growth pattern and white adipose tissue in female F2 ET-PNGR were similar to ET-CON. Similarly, no differences in basal glucose and insulin concentrations, GSIS, glucose futile cycling and glucose clearance were seen. When compared to F2 ET-CON, F2 ET-PNGR showed no overall difference in glucose or hepatic glucose production (HGP) AUCs with minimal hyperglycemia (p<0.04) as a result of unsuppressed endogenous HGP (p<0.02) observed only during the first phase of IVGTT.

CONCLUSIONS

We conclude that the lean, glucose tolerant and hypoinsulinemic phenotype with reduced GSIS in the F1 generation is nearly normalized when the embryo-transferred F2 offspring gestates in a normal metabolic environment. This observation supports a role for the intra-uterine environment in modifying the heritability of the trans-generational PNGR phenotype.

A euglycaemic/non-diabetic perinatal environment does not alleviate early beta cell maldevelopment and type 2 diabetes risk in the GK/Par rat model

AIMS/HYPOTHESIS

We used the GK/Par rat, a spontaneous model of type 2 diabetes with early defective beta cell neogenesis, to determine whether the development of GK/Par offspring in a non-diabetic intrauterine/postnatal environment would prevent the alteration of fetal beta cell mass (BCM) and ultimately decrease the risk of diabetes later in adult life.

METHODS

We used an embryo-transfer approach, with fertilised GK/Par ovocytes (oGK) being transferred into pregnant Wistar (W) or GK/Par females (pW and pGK). Offspring were phenotyped at fetal age E18.5 and at 10 weeks of age, for BCM, expression of genes of pancreatic progenitor cell regulators (Igf2, Igf1r, Sox9, Pdx1 and Ngn3), glucose tolerance and insulin secretion.

RESULTS

(1) Alterations in neogenesis markers/regulators and BCM were as severe in the oGK/pW E18.5 fetuses as in the oGK/pGK group. (2) Adult offspring from oGK transfers into GK (oGK/pGK/sGK) had the expected diabetic phenotype compared with unmanipulated GK rats. (3) Adult offspring from oGK reared in pW mothers and milked by GK foster mothers had reduced BCM, basal hyperglycaemia, glucose intolerance and low insulin, to an extent similar to that of oGK/pGK/sGK offspring. (4) In adult offspring from oGK transferred into pW mothers and milked by their W mothers (oGK/pW/sW), the phenotype was similar to that in oGK/pGK/sGK or oGK/pW/sGK offspring.

CONCLUSIONS/INTERPRETATION

These data support the conclusion that early BCM alteration and subsequent diabetes risk in the GK/Par model are not removed despite normalisation of the prenatal and postnatal environments, either isolated or combined.

The GK rat: a prototype for the study of non-overweight type 2 diabetes

Type 2 diabetes mellitus (T2D) arises when the endocrine pancreas fails to secrete sufficient insulin to cope with the metabolic demand because of β-cell secretory dysfunction and/or decreased β-cell mass. Defining the nature of the pancreatic islet defects present in T2D has been difficult, in part because human islets are inaccessible for direct study. This review is aimed to illustrate to what extent the Goto Kakizaki rat, one of the best characterized animal models of spontaneous T2D, has proved to be a valuable tool offering sufficient commonalities to study this aspect. A comprehensive compendium of the multiple functional GK abnormalities so far identified is proposed in this perspective, together with their time-course and interactions. A special focus is given toward the pathogenesis of defective β-cell number and function in the GK model. It is proposed that the development of T2D in the GK model results from the complex interaction of multiple events: (1) several susceptibility loci containing genes responsible for some diabetic traits; (2) gestational metabolic impairment inducing an epigenetic programming of the offspring pancreas and the major insulin target tissues; and (3) environmentally induced loss of β-cell differentiation due to chronic exposure to hyperglycemia/hyperlipidemia, inflammation, and oxidative stress.

Maternal diabetes and perinatal programming

Alterations of the intrauterine and neonatal environment may predispose for disorders and diseases throughout later life (perinatal programming). Especially, hormones and nutrients are dose-dependent organizers of the developing organism. Studies in offspring of diabetic mothers (ODM) have paradigmatically contributed to the perception of this developmental principle and our understanding of causal mechanisms. Fetal and neonatal hyperinsulinism in consequence of materno-fetal hyperglycaemia is the pathognomic feature in ODM. Epidemiological, clinical, as well as experimental data indicate that both insulin and glucose, when occurring in elevated concentrations during perinatal life, may epigenetically program a predisposition for obesity and diabetes later on. Similar may occur due to pre- and neonatal overfeeding. From a clinical point of view, avoidance of materno-fetal overnutrition, universal diabetes screening in all pregnant women and adequate therapy of all forms of diabetes during pregnancy, as well as avoidance of neonatal overfeeding are therefore recommended. These measures might serve as causal approaches of a genuine prevention to the benefit of long-term offspring health.

Early-life origins of type 2 diabetes: fetal programming of the beta-cell mass

A substantial body of evidence suggests that an abnormal intrauterine milieu elicited by maternal metabolic disturbances as diverse as undernutrition, placental insufficiency, diabetes or obesity, may program susceptibility in the fetus to later develop chronic degenerative diseases, such as obesity, hypertension, cardiovascular diseases and diabetes. This paper examines the developmental programming of glucose intolerance/diabetes by disturbed intrauterine metabolic condition experimentally obtained in various rodent models of maternal protein restriction, caloric restriction, overnutrition or diabetes, with a focus on the alteration of the developing beta-cell mass. In most of the cases, whatever the type of initial maternal metabolic stress, the beta-cell adaptive growth which normally occurs during gestation, does not take place in the pregnant offspring and this results in the development of gestational diabetes. Therefore gestational diabetes turns to be the ultimate insult targeting the offspring beta-cell mass and propagates diabetes risk to the next generation again. The aetiology and the transmission of spontaneous diabetes as encountered in the GK/Par rat model of type 2 diabetes, are discussed in such a perspective. This review also discusses the non-genomic mechanisms involved in the installation of the programmed effect as well as in its intergenerational transmission.

Dietary-resistant starch improves maternal glycemic control in Goto-Kakizaki rat

SCOPE

Dietary prebiotics show potential in anti-diabetes. Dietary resistant starch (RS) has a favorable impact on gut hormone profiles, including glucagon-like peptide-1 (GLP-1) consistently released, a potent anti-diabetic incretin. Also RS reduced body fat and improved glucose tolerance in rats and mice. In the current project, we hypothesize that dietary-resistant starch can improve insulin sensitivity and pancreatic β cell mass in a type 2 diabetic rat model. Altered gut fermentation and microbiota are the initial mechanisms, and enhancement in serum GLP-1 is the secondary mechanism.

METHODS AND RESULTS

In this study, GK rats were fed an RS diet with 30% RS and an energy control diet. After 10 wk, these rats were mated and went through pregnancy and lactation. At the end of the study, pancreatic β cell mass, insulin sensitivity, pancreatic insulin content, total GLP-1 levels, cecal short-chain fatty acid concentrations and butyrate producing bacteria in cecal contents were greatly improved by RS feeding. The offspring of RS-fed dams showed improved fasting glucose levels and normal growth curves.

CONCLUSION

Dietary RS is potentially of great therapeutic importance in the treatment of diabetes and improvement in outcomes of pregnancy complicated by diabetes.

Synergistic effects of genetic beta cell dysfunction and maternal glucose intolerance on offspring metabolic phenotype in mice

AIMS/HYPOTHESIS

Diabetes in pregnancy is linked to development of obesity in the offspring, but the mechanisms are not fully understood. Gestational diabetes mellitus (GDM) occurs when beta cells are unable to compensate for the normal insulin resistance of late pregnancy. In this study, we used a murine model of beta cell dysfunction to examine the effects of maternal GDM on phenotype in male offspring with and without an inherited predisposition for beta cell dysfunction.

METHODS

Beta cell-specific aryl-hydrocarbon receptor nuclear translocator-null (βArnt) mice develop GDM from beta cell dysfunction. βArnt and control female mice were used to induce GDM and non-diabetic pregnancies, respectively.

RESULTS

Offspring from GDM pregnancies became spontaneously obese on a normal-chow diet. They were heavier than offspring from non-diabetic pregnancies, with increased body fat. Respiratory exchange ratio (RER) was higher, indicating decreased capacity to switch to lipid oxidation. Metabolic rate in GDM offspring was decreased prior to onset of obesity. The phenotype was more pronounced in βArnt GDM offspring than in GDM offspring of control genotype, demonstrating an interaction between genotype and pregnancy exposure. βArnt GDM offspring had increased hypothalamic neuropeptide Y (Npy) and decreased pro-opiomelanocortin (Pomc) expression. Weight, body fat, insulin sensitivity and RER in all mice, and hypothalamic Npy in βArnt mice were significantly correlated with AUC of maternal late pregnancy glucose tolerance tests (p < 0.01), but not with litter size, maternal weight, triacylglycerol or pre-pregnancy glycaemia.

CONCLUSIONS/INTERPRETATION

In βArnt mice, exposure to GDM and inheritance of genetic beta cell dysfunction had additive effects on male offspring obesity; severity of the offspring phenotype correlated with maternal glycaemia.

Animal models in diabetes and pregnancy

The worldwide increase in the incidence of diabetes, the increase in type 2 diabetes in women at reproductive ages, and the cross-generation of the intrauterine programming of type 2 diabetes are the bases for the growing interest in the use of experimental diabetic models in order to gain insight into the mechanisms of induction of developmental alterations in maternal diabetes. In this scenario, experimental models that present the most common features of diabetes in pregnancy are highly required. Several important aspects of human diabetic pregnancies such as the increased rates of spontaneous abortions, malformations, fetoplacental impairments, and offspring diseases in later life can be approached by using the appropriate animal models. The purpose of this review is to give a practical and critical guide into the most frequently used experimental models in diabetes and pregnancy, discuss their advantages and limitations, and describe the aspects of diabetes and pregnancy for which these models are thought to be adequate. This review provides a comprehensive view and an extensive analysis of the different models and phenotypes addressed in diabetic animals throughout pregnancy. The review includes an analysis of the surgical, chemical-induced, and genetic experimental models of diabetes and an evaluation of their use to analyze early pregnancy defects, induction of congenital malformations, placental and fetal alterations, and the intrauterine programming of metabolic diseases in the offspring's later life.

Developmental programming and diabetes - The human experience and insight from animal models

Children born to mothers, rather than to fathers, with type 1 diabetes (type 1 DM) or type 2 diabetes (type 2 DM) may have a greater susceptibility to diabetes and obesity in later life, inferring a role for in utero or early post-natal influences on the developing child. This review summarises the studies contributing to this hypothesis, noting some of the controversies including the potential for residual confounding and the influence of maternal BMI. Animal models demonstrate that maternal hyperglycaemia leads to persistent disorders of offspring pancreatic β cell secretory capacity, abnormal insulin signaling in insulin-sensitive tissues and abnormal development of the hypothalamus, associated with aberrant control of energy regulation and obesity in adult life. Prospective studies, particularly follow-up of children born to diabetic mothers participating in RCTs of improved glycemic control are needed to accurately assess the transgenerational influences of maternal diabetes and to evaluate mechanisms inferred from animal data.

Hepatocyte nuclear factor (HNF)-4alpha-driven epigenetic silencing of the human PED gene

AIMS/HYPOTHESIS

Overexpression of PED (also known as PEA15) determines insulin resistance and impaired insulin secretion and may contribute to progression toward type 2 diabetes. Recently, we found that the transcription factor hepatocyte nuclear factor (HNF)-4alpha binds to PED promoter and represses its transcription. However, the molecular details responsible for regulation of PED gene remain unclear.

METHODS

Here we used gain and loss of function approaches to investigate the hypothesis that HNF-4alpha controls chromatin remodelling at the PED promoter in human cell lines.

RESULTS

HNF-4alpha production and binding induce chromatin remodelling at the -250 to 50 region of PED, indicating that remodelling is limited to two nucleosomes located at the proximal promoter. Chromatin immunoprecipitation assays also revealed concomitant HNF-4alpha-induced deacetylation of histone H3 at Lys9 and Lys14, and increased dimethylation of histone H3 at Lys9. The latter was followed by reduction of histone H3 Lys4 dimethylation. HNF-4alpha was also shown to target the histone deacetylase complex associated with silencing mediator of retinoic acid and thyroid hormone receptor, both at the PED promoter, and at GRB14 and USP21 regulatory regions, leading to a reduction of mRNA levels. Moreover, HNF-4alpha silencing and PED overexpression were accompanied by a significant reduction of hepatic glycogen content.

CONCLUSIONS/INTERPRETATION

These results show that HNF-4alpha serves as a scaffold protein for histone deacetylase activities, thereby inhibiting liver expression of genes including PED. Dysregulation of these mechanisms may lead to upregulation of the PED gene in type 2 diabetes.

Islet structure and function in the GK rat

Type 2 diabetes mellitus (T2D) arises when the endocrine pancreas fails to secrete sufficient insulin to cope with the metabolic demand because of beta-cell secretory dysfunction and/or decreased beta-cell mass. Defining the nature of the pancreatic islet defects present in T2D has been difficult, in part because human islets are inaccessible for direct study. This review is aimed to illustrate to what extent the Goto-Kakizaki rat, one of the best characterized animal models of spontaneous T2D, has proved to be a valuable tool offering sufficient commonalities to study this aspect. A comprehensive compendium of the multiple functional GK islet abnormalities so far identified is proposed in this perspective. The pathogenesis of defective beta-cell number and function in the GK model is also discussed. It is proposed that the development of T2D in the GK model results from the complex interaction of multiple events: (i) several susceptibility loci containing genes responsible for some diabetic traits (distinct loci encoding impairment of beta-cell metabolism and insulin exocytosis, but no quantitative trait locus for decreased beta-cell mass); (ii) gestational metabolic impairment inducing an epigenetic programming of the offspring pancreas (decreased beta-cell neogenesis and proliferation) transmitted over generations; and (iii) loss of beta-cell differentiation related to chronic exposure to hyperglycaemia/hyperlipidaemia, islet inflammation, islet oxidative stress, islet fibrosis and perturbed islet vasculature.

Maternal obesity and fetal programming: effects of a high-carbohydrate nutritional modification in the immediate postnatal life of female rats

Our earlier studies have shown that the artificial rearing of newborn rat pups [first generation high carbohydrate (1-HC)] on an HC milk formula resulted in chronic hyperinsulinemia and adult-onset obesity (HC phenotype). Offspring [second-generation HC (2-HC)] of 1-HC female rats spontaneously acquired the HC phenotype in the postweaning period. In this study, we have characterized the development of the abnormal intrauterine environment in the 1-HC female rats and the effects on fetal development under such pregnancy conditions for the offspring. 1-HC female rats demonstrated hyperphagia on laboratory chow and increased body weight gain beginning from the immediate postweaning period along with hyperinsulinemia and hyperleptinemia. During pregnancy, 1-HC female rats showed several metabolic alterations including increased body weight gain and increased plasma levels of insulin, leptin, proinflammatory markers, and lipid peroxidation products. Although there were no significant changes in the body weights or litter size of term 2-HC fetuses, the plasma levels of insulin and leptin were significantly higher compared with those of control term fetuses. Quantitation of mRNA levels by real-time RT-PCR indicated significant increases in the mRNA levels of orexigenic neuropeptides in the hypothalamus of 2-HC term fetuses. Collectively, these results indicate that the HC diet in infancy results in an adverse pregnancy condition in female rats with deleterious consequences for the offspring.

High prevalence of type 2 diabetes and pre-diabetes in adult offspring of women with gestational diabetes mellitus or type 1 diabetes: the role of intrauterine hyperglycemia

OBJECTIVE

The role of intrauterine hyperglycemia and future risk of type 2 diabetes in human offspring is debated. We studied glucose tolerance in adult offspring of women with either gestational diabetes mellitus (GDM) or type 1 diabetes, taking the impact of both intrauterine hyperglycemia and genetic predisposition to type 2 diabetes into account.

RESEARCH DESIGN AND METHODS

The glucose tolerance status following a 2-h 75-g oral glucose tolerance test (OGTT) was evaluated in 597 subjects, primarily Caucasians, aged 18-27 years. They were subdivided into four groups according to maternal glucose metabolism during pregnancy and genetic predisposition to type 2 diabetes: 1) offspring of women with diet-treated GDM (O-GDM), 2) offspring of genetically predisposed women with a normal OGTT (O-NoGDM), 3) offspring of women with type 1 diabetes (O-type 1), and 4) offspring of women from the background population (O-BP).

RESULTS

The prevalence of type 2 diabetes and pre-diabetes (impaired glucose tolerance or impaired fasting glucose) in the four groups was 21, 12, 11, and 4%, respectively. In multiple logistic regression analysis, the adjusted odds ratios (ORs) for type 2 diabetes/pre-diabetes were 7.76 (95% CI 2.58-23.39) in O-GDM and 4.02 (1.31-12.33) in O-type 1 compared with O-BP. In O-type 1, the risk of type 2 diabetes/pre-diabetes was significantly associated with elevated maternal blood glucose in late pregnancy: OR 1.41 (1.04-1.91) per mmol/l.

CONCLUSIONS

A hyperglycemic intrauterine environment appears to be involved in the pathogenesis of type 2 diabetes/pre-diabetes in adult offspring of primarily Caucasian women with either diet-treated GDM or type 1 diabetes during pregnancy.

Follow-up of GK rats during prediabetes highlights increased insulin action and fat deposition despite low insulin secretion

The adult Goto-Kakizaki (GK) rat is characterized by impaired glucose-induced insulin secretion in vivo and in vitro, decreased beta-cell mass, decreased insulin sensitivity in the liver, and moderate insulin resistance in muscles and adipose tissue. GK rats do not exhibit basal hyperglycemia during the first 3 wk after birth and therefore could be considered prediabetic during this period. Our aim was to identify the initial pathophysiological changes occurring during the prediabetes period in this model of type 2 diabetes (T2DM). To address this, we investigated beta-cell function, insulin sensitivity, and body composition in normoglycemic prediabetic GK rats. Our results revealed that the in vivo secretory response of GK beta-cells to glucose is markedly reduced and the whole body insulin sensitivity is increased in the prediabetic GK rats in vivo. Moreover, the body composition of suckling GK rats is altered compared with age-matched Wistar rats, with an increase of the number of adipocytes before weaning despite a decreased body weight and lean mass in the GK rats. None of these changes appeared to be due to the postnatal nutritional environment of GK pups as demonstrated by cross-fostering GK pups with nondiabetic Wistar dams. In conclusion, in the GK model of T2DM, beta-cell dysfunction associated with increased insulin sensitivity and the alteration of body composition are proximal events that might contribute to the establishment of overt diabetes in adult GK rats.

Defective functional β-cell mass and Type 2 diabetes in the Goto-Kakizaki rat model

Increasing evidence indicates that decreased functional β-cell mass is the hallmark of Type 2 diabetes mellitus. Therefore, the debate focuses on the possible mechanisms responsible for abnormal islet microenvironment, decreased β-cell number, impaired β-cell function and their multifactorial etiologies. The information available on the Goto-Kakizaki/Par rat line, one of the best characterized animal models of spontaneous Type 2 diabetes mellitus, are reviewed in such a perspective. We propose that the defective β-cell mass and function in the Goto-Kakizaki/Par model reflect the complex interactions of multiple pathogenic players, including several independent loci containing genes responsible for some diabetic traits (but not decreased β-cell mass), gestational metabolic impairment inducing an epigenetic programming of the pancreas (decreased β-cell neogenesis), which is transmitted to the next generation, and loss of β-cell differentiation due to chronic exposure to hyperglycemia, inflammatory mediators, oxidative stress and perturbed islet microarchitecture.

Report on the IASO Stock Conference 2006: early and lifelong environmental epigenomic programming of metabolic syndrome, obesity and type II diabetes

Now that analysis of the organization of the human genome sequence is reaching completion, studies of the finely tuned chromatin epigenetic networks, DNA methylation and histone modifications, are required to determine how the same DNA sequence generates different cells, lineages and organs, i.e. the phenotype. Maternal nutrition, behaviour and metabolic disturbances as well as other environmental factors have been shown to have major effects on these epigenetic processes, potentially affecting the predisposition of offspring to obesity and related adult disorders. The March 2006 Stock Conference considered the latest evidence from studies in the field of obesity and other related areas that elucidate mechanisms by which the environment can modify gene expression and the resulting individual phenotype. Presentations included evaluation of the molecular basis of epigenetic memory and the nature of relevant sequence targets, windows of susceptibility, and maternal dietary and behavioural factors that determine epigenetic changes. Imprinted genes, age and tissue-related exposures, transgenerational and potential interventions were also discussed. In summary, it is clear that epigenetic alterations can no longer be ignored in evaluations of the causes of obesity and its associated disorders. There is a need for systematic large-scale epigenetic studies of obesity, employing appropriate strategies and techniques and appropriately chosen environmental factors in critical spatio-temporal windows.

Transgenerational inheritance of the insulin-resistant phenotype in embryo-transferred intrauterine growth-restricted adult female rat offspring

To determine mechanisms underlying the transgenerational presence of metabolic perturbations in the intrauterine growth-restricted second-generation adult females (F2 IUGR) despite normalizing the in utero metabolic environment, we examined in vivo glucose kinetics and in vitro skeletal muscle postinsulin receptor signaling after embryo transfer of first generation (F1 IUGR) to control maternal environment. Female F2 rats, procreated by F1 pre- and postnatally nutrient- and growth-restricted (IUGR) mothers but embryo transferred to gestate in control mothers, were compared with similarly gestating age- and sex-matched control (CON) F2 progeny. Although there were no differences in birth weight or postnatal growth patterns, the F2 IUGR had increased hepatic weight, fasting hyperglycemia, hyperinsulinemia, and unsuppressed hepatic glucose production, with no change in glucose futile cycling or clearance, compared with F2 CON. These hormonal and metabolic aberrations were associated with increased skeletal muscle total GLUT4 and pAkt concentrations but decreased plasma membrane-associated GLUT4, total pPKCzeta, and PKCzeta enzyme activity, with no change in total SHP2 and PTP1B concentrations in IUGR F2 compared with F2 CON. We conclude that transgenerational presence of aberrant glucose/insulin metabolism and skeletal muscle insulin signaling of the adult F2 IUGR female offspring is independent of the immediate intrauterine environment, supporting nutritionally induced heritable mechanisms contributing to the epidemic of type 2 diabetes mellitus.

Adipose tissue in offspring of Lepr(db/+) mice: early-life environment vs. genotype

Gravidas with obesity and diabetes ("diabesity") may transmit this syndrome to their children through genetic and nongenetic mechanisms. Here, we used the Lepr(db/+) diabese mouse to examine the magnitude of these transmission modes, focusing on adipose tissue (AT). We compared the following six groups: wild-type (+/+) offspring from +/+ or db/+ dams (different early life environment) and db/+ offspring from db/+ dams, fed a standard or high-fat diet. Weight gain (0-8 wk) was higher in +/+ offspring from db/+ vs. +/+ mothers, and even higher in db/+ vs. +/+ offspring from db/+ mothers. In addition, we observed a stepwise increase in AT and adipocyte size in +/+ from +/+ mice, +/+ from db/+ mice, and db/+ mice at 8 wk. Differences in weight and adiposity between +/+ offspring from db/+ vs. +/+ dams were more pronounced in males than in females. Leptin and apelin mRNA levels in white and brown AT were higher in +/+ offspring from db/+ vs. +/+ dams; however, leptin, apelin, and tumor necrosis factor-alpha expression were boosted more robustly in db/+ offspring. The high-fat diet amplified AT differences between db/+ vs. +/+ offspring from db/+ dams, but not between +/+ offspring from db/+ vs. +/+ dams. Moreover, db/+ but not +/+ offspring from db/+ mothers were insulin-resistant and hyperinsulinemic after a glucose challenge. In conclusion, the genetic transmission of the diabesity phenotype clearly prevailed, but the early-life diabesity environment had discernible effects on postnatal weight gain as well as on adipocyte size and adipokine expression at a postpubertal age.

Is defective pancreatic beta-cell mass environmentally programmed in Goto-Kakizaki rat model of type 2 diabetes?: insights from crossbreeding studies during suckling period

OBJECTIVE

The Goto-Kakizaki (GK) rat is a spontaneous model of type 2 diabetes with a well established pathological pancreatic beta-cell development. Hyperglycemia experienced during early postnatal life contributes to the programming of endocrine pancreas. We have analyzed the consequences of hyperglycemic versus euglycemic suckling period for the pancreatic beta-cell mass and the in vivo glucose tolerance and insulin secretion in 4-week-old unweaned control Wistar (W), diabetic GK, and in offspring issued from crosses between normoglycemic W and diabetic GK rats.

METHODS

Mother/father crosses yielded offspring designated as follows: W/W, GK/GK, W/GK, and GK/W. In vivo glucose tolerance and insulin secretion tests were performed on males 4 weeks after birth, that is, just before weaning. Beta-cell mass was determined by immunohistochemistry and morphometry.

RESULTS

Four-week-old W/GK and GK/W rats are normoglycemic, normoinsulinemic, and display a similarly small beta-cell mass. Both W/GK and GK/W rats exhibit in vivo glucose intolerance and defective insulin secretion in response to glucose.

CONCLUSIONS

Our data obtained from crossbreeding studies during suckling period suggest that the defective pancreatic beta-cell mass is not environmentally programmed in the GK model of type 2 diabetes. Rather, they support the hypothesis that the beta-cell mass defect in the GK is linked to genetic determinism.

Consequences of fetal exposure to maternal diabetes in offspring

CONTEXT

Type 2 diabetes is the result of both genetic and environmental factors. Fetal exposure to maternal diabetes is associated with a higher risk of abnormal glucose homeostasis in offspring beyond that attributable to genetic factors, and therefore, may participate in the excess of maternal transmission of type 2 diabetes.

EVIDENCE ACQUISITION

A MEDLINE search covered the period from 1960-2005.

EVIDENCE SYNTHESIS

Human studies performed in children and adolescents suggest that offspring who had been exposed to maternal diabetes during fetal life exhibit higher prevalence of impaired glucose tolerance and markers of insulin resistance. Recent studies that directly measured insulin sensitivity and insulin secretion have shown an insulin secretory defect even in the absence of impaired glucose tolerance in adult offspring. In animal models, exposure to a hyperglycemic intrauterine environment also led to the impairment of glucose tolerance in the adult offspring. These metabolic abnormalities were transmitted to the next generations, suggesting that in utero exposure to maternal diabetes has an epigenetic impact. At the cellular level, some findings suggest an impaired pancreatic beta-cell mass and function. Several mechanisms such as defects in pancreatic angiogenesis and innervation, or modification of parental imprinting, may be implicated, acting either independently or in combination.

CONCLUSION

Thus, fetal exposure to maternal diabetes may contribute to the worldwide diabetes epidemic. Public health interventions targeting high-risk populations should focus on long-term follow-up of subjects who have been exposed in utero to a diabetic environment and on a better glycemic control during pregnancy.

Intrauterine environment and later disease development: Infertility treatment and the risk of diabetes in offspring

The phenotype of an individual, including their susceptibility to disease, is governed by several factors including parental genes and intrauterine environment. Thus, the risk of developing Type 2 diabetes is modulated by the inheritance of specific genetic variants that are slowly being characterised by the techniques of linkage analysis and population association studies using either a candidate gene or genome-wide scan approach. At the same time, evidence has accrued that alterations in the nutritional status of the developing foetus also increase the risk of diabetes in later life. Restricting protein intake in pregnant dams or interfering with placental function increases the risk of diabetes in offspring and light weight babies are more likely to develop Type 2 diabetes as adults than heavier ones. The oocyte plays a key role, since it contains not only the maternal haplotype but other information such as mitochondrial DNA and factors that modulate the expression of genes in the developing foetus. Although the ovaries contain a huge number of primordial follicles, generally each month only one oocyte matures to ovulation. Little is known about the processes that control this phenomenon. Certainly, primordial follicles and oocytes are not all the same, differing especially in mitochondrial DNA content. As women age, the oocytes released are more likely to contain genetic errors, explaining the increased risk of Trisomy 21 with maternal age. It is generally assumed that primordial follicle development and the selection of a single ooctye for ovulation is a random process. This paper suggests that this may not be the case but that a carefully controlled system may allow the mother to release an oocyte that is best suited to the prevailing environment. This would represent an important mechanism for species adaptation. Many human infertility treatments involve pharmacological superovulation, egg harvesting and culture prior to in vitro fertilisation and reimplantation. These will bypass any system of controlled ovulation and therefore might alter the risk of diseases such as Type 2 diabetes mellitus in later life. Although the offspring of human infertility treatments are generally born healthy, it is important to note that the oldest "test-tube" baby is still less than 30-years old, so the risk of late-onset diseases is still unknown.

Early detection and prevention of diabetic nephropathy: a challenge calling for mandatory action for Mexico and the developing world

During the last decades, developing countries have experienced an epidemiologic transition characterized by a reduction of infectious diseases and an increase of chronic degenerative diseases. This situation is generating tormenting public health, financial, and social consequences. Of particular relevance is type 2 diabetes mellitus and its chronic complications, particularly cardiovascular disease and diabetic nephropathy, because mortality of the patient with diabetes is, in most instances, related to these complications. There is a clear need to implement diagnostic and treatment strategies to reduce risk factors for development of diabetes (primary prevention), to detect risk factors of chronic complications in early stages of diabetes (secondary prevention), and to prevent further progression of those that already have renal injury (tertiary prevention). Microalbuminuria is an early marker of renal injury in diabetes, and its early detection can help the timely use of renal preventive measures, which would avoid the extremely high costs of renal replacement treatment for end-stage renal disease as well as that of other cardiovascular complications. Preventive strategies are of very little or no impact, if the primary physician has limited knowledge about the natural history of diabetic nephropathy, the beneficial effect of early preventive maneuvers for delaying its progression, and the social and economic impact of end-stage renal disease. It is therefore imperative to assure in our health systems that general practitioners have the ability and commitment to detect early diabetes complications, in order to promote actions that support regression or retard highly morbid cardiovascular and renal conditions.

Programmed disorders of beta-cell development and function as one cause for type 2 diabetes? The GK rat paradigm

Now that the reduction in beta-mass has been clearly established in humans with type 2 diabetes mellitus (T2DM) 1-4, the debate focuses on the possible mechanisms responsible for decreased beta-cell number and impaired beta-cell function and their multifactorial etiology. Appropriate inbred rodent models are essential tools for identification of genes and environmental factors that increase the risk of abnormal beta-cell function and of T2DM. The information available in the Goto-Kakizaki (GK) rat, one of the best characterized animal models of spontaneous T2DM, are reviewed in such a perspective. We propose that the defective beta-cell mass and function in the GK model reflect the complex interactions of three pathogenic players: (1) several independent loci containing genes causing impaired insulin secretion; (2) gestational metabolic impairment inducing a programming of endocrine pancreas (decreased beta-cell neogenesis) which is transmitted to the next generation; and (3) secondary (acquired) loss of beta-cell differentiation due to chronic exposure to hyperglycemia (glucotoxicity). An important message is that the 'heritable' determinants of T2DM are not simply dependant on genetic factors, but probably involve transgenerational epigenetic responses.

Animal models of diabetes mellitus

Animal models have been used extensively in diabetes research. Early studies used pancreatectomised dogs to confirm the central role of the pancreas in glucose homeostasis, culminating in the discovery and purification of insulin. Today, animal experimentation is contentious and subject to legal and ethical restrictions that vary throughout the world. Most experiments are carried out on rodents, although some studies are still performed on larger animals. Several toxins, including streptozotocin and alloxan, induce hyperglycaemia in rats and mice. Selective inbreeding has produced several strains of animal that are considered reasonable models of Type 1 diabetes, Type 2 diabetes and related phenotypes such as obesity and insulin resistance. Apart from their use in studying the pathogenesis of the disease and its complications, all new treatments for diabetes, including islet cell transplantation and preventative strategies, are initially investigated in animals. In recent years, molecular biological techniques have produced a large number of new animal models for the study of diabetes, including knock-in, generalized knock-out and tissue-specific knockout mice.