Ultrastructural evaluation of B-cell recruitment in virgin and pregnant offspring of diabetic mothers

Vitamin B6 deficiency disrupts serotonin signaling in pancreatic islets and induces gestational diabetes in mice

In pancreatic islets, catabolism of tryptophan into serotonin and serotonin receptor 2B (HTR2B) activation is crucial for β-cell proliferation and maternal glucose regulation during pregnancy. Factors that reduce serotonin synthesis and perturb HTR2B signaling are associated with decreased β-cell number, impaired insulin secretion, and gestational glucose intolerance in mice. Albeit the tryptophan-serotonin pathway is dependent on vitamin B6 bioavailability, how vitamin B6 deficiency impacts β-cell proliferation during pregnancy has not been investigated. In this study, we created a vitamin B6 deficient mouse model and investigated how gestational deficiency influences maternal glucose tolerance. Our studies show that gestational vitamin B6 deficiency decreases serotonin levels in maternal pancreatic islets and reduces β-cell proliferation in an HTR2B-dependent manner. These changes were associated with glucose intolerance and insulin resistance, however insulin secretion remained intact. Our findings suggest that vitamin B6 deficiency-induced gestational glucose intolerance involves additional mechanisms that are complex and insulin independent.

Fields et al. investigate the impact of vitamin B6 deficiency on islet β-cell proliferation during pregnancy, using vitamin B6-deficient mice. They find that gestational vitamin B6 deficiency decreases serotonin levels in pancreatic islets and reduces β-cell proliferation, showing that vitamin B6 deficiency regulates maternal glucose tolerance in a serotonin-dependent manner.

Regulation of fetal lung development in response to maternal overnutrition

With the worldwide obesity epidemic, the proportion of women entering pregnancy overweight or obese has increased significantly in recent years. Babies born to obese women are at an increased risk of respiratory complications at birth and in childhood. In addition to maternal diabetes, there are a number of metabolic changes that the fetus of an overnourished mother experiences in utero that may modulate lung development and represent the mechanisms underlying the increased risk of respiratory complications. Herein we highlight a series of factors associated with the intrauterine environment of an overnourished mother that may impact on fetal lung development and lead to an increased risk of complications at birth or in postnatal life.

Advancements and challenges in generating accurate animal models of gestational diabetes mellitus

The maintenance of glucose homeostasis during pregnancy is critical to the health and well-being of both the mother and the developing fetus. Strikingly, approximately 7% of human pregnancies are characterized by insufficient insulin production or signaling, resulting in gestational diabetes mellitus (GDM). In addition to the acute health concerns of hyperglycemia, women diagnosed with GDM during pregnancy have an increased incidence of complications during pregnancy as well as an increased risk of developing type 2 diabetes (T2D) later in life. Furthermore, children born to mothers diagnosed with GDM have increased incidence of perinatal complications, including hypoglycemia, respiratory distress syndrome, and macrosomia, as well as an increased risk of being obese or developing T2D as adults. No single environmental or genetic factor is solely responsible for the disease; instead, a variety of risk factors, including weight, ethnicity, genetics, and family history, contribute to the likelihood of developing GDM, making the generation of animal models that fully recapitulate the disease difficult. Here, we discuss and critique the various animal models that have been generated to better understand the etiology of diabetes during pregnancy and its physiological impacts on both the mother and the fetus. Strategies utilized are diverse in nature and include the use of surgical manipulation, pharmacological treatment, nutritional manipulation, and genetic approaches in a variety of animal models. Continued development of animal models of GDM is essential for understanding the consequences of this disease as well as providing insights into potential treatments and preventative measures.

Maternal rat diabetes mellitus deleteriously affects insulin sensitivity and Beta-cell function in the offspring

This study was designed to assess the effect of maternal diabetes in rats on serum glucose and insulin concentrations, insulin resistance, histological architecture of pancreas and glycogen content in liver of offspring. The pregnant rat females were allocated into two main groups: normal control group and streptozotocin-induced diabetic group. After birth, the surviving offspring were subjected to biochemical and histological examination immediately after delivery and at the end of the 1st and 2nd postnatal weeks. In comparison with the offspring of normal control dams, the fasting serum glucose level of offspring of diabetic mothers was significantly increased at the end of the 1st and 2nd postnatal weeks. Serum insulin level of offspring of diabetic dams was significantly higher at birth and decreased significantly during the following 2 postnatal weeks, while in normal rat offspring, it was significantly increased with progress of time. HOMA Insulin Resistance (HOMA-IR) was significantly increased in the offspring of diabetic dams at birth and after 1 week than in normal rat offspring, while HOMA insulin sensitivity (HOMA-IS) was significantly decreased. HOMA beta-cell function was significantly decreased at all-time intervals in offspring of diabetic dams. At birth, islets of Langerhans as well as beta cells in offspring of diabetic dams were hypertrophied. The cells constituting islets seemed to have a high division rate. However, beta-cells were degenerated during the following 2 post-natal weeks and smaller insulin secreting cells predominated. Vacuolation and necrosis of the islets of Langerhans were also observed throughout the experimental period. The carbohydrate content in liver of offspring of diabetic dams was at all-time intervals lower than that in control. The granule distribution was more random. Overall, the preexisting maternal diabetes leads to glucose intolerance, insulin resistance, and impaired insulin sensitivity and β -cell function in the offspring at different postnatal periods.

Maternal obesity: how big an impact does it have on offspring prenatally and during postnatal life?

Obesity is increasing at an epidemic rate in women of reproductive age. Not only does obesity during pregnancy lead to increased maternal health concerns, it is also linked to an increase in adiposity and components of the metabolic syndrome in the children and grandchildren of obese women. The potential transgenerational impact of maternal obesity on the health of future generations will undoubtedly result in increasing healthcare costs for society. This review will describe what is known about the specific impacts of maternal obesity on offspring in the human population as well as discuss how controlled animal experiments have shed light on the specific physiological mechanisms involved. Furthermore, preliminary experiments are presented describing potential dietary methods for preventing obesity-induced programming of offspring health concerns in postnatal life.

The influence of exposure to maternal diabetes in utero on the rate of decline in β-cell function among youth with diabetes

Abstract We explored the influence of exposure to maternal diabetes in utero on β cell decline measured by fasting C-peptide (FCP) among 1079 youth <20 years with diabetes, including 941 with type 1 and 138 with type 2 diabetes. Youths exposed to maternal diabetes had FCP levels that were 17% lower among youth with type 2 diabetes [95% confidence interval (CI): -34%, +6%] and 15% higher among youth with type 1 diabetes (95%CI: -14%, +55%) than their unexposed counterparts, although differences were not statistically significant (p=0.13 and p=0.35, respectively). Exposure to maternal diabetes was not associated with FCP decline in youth with type 2 (p=0.16) or type 1 diabetes (p=0.90); nor was the effect of in utero exposure on FCP modified by diabetes type. Findings suggest that exposure to maternal diabetes in utero may not be an important determinant of short-term β-cell function decline in youth with type 1 or type 2 diabetes.

Wild-type offspring of heterozygous prolactin receptor-null female mice have maladaptive β-cell responses during pregnancy

Abstract  β-Cell mass increases during pregnancy in adaptation to the insulin resistance of pregnancy. This increase is accompanied by an increase in β-cell proliferation, a process that requires intact prolactin receptor (Prlr) signalling. Previously, it was found that during pregnancy, heterozygous prolactin receptor-null (Prlr(+/-)) mice had lower number of β-cells, lower serum insulin and higher blood glucose levels than wild-type (Prlr(+/+)) mice. An unexpected observation was that the glucose homeostasis of the experimental mouse depends on the genotype of her mother, such that within the Prlr(+/+) group, the Prlr(+/+) offspring derived from Prlr(+/+) mothers (Prlr(+/+(+/+))) had higher β-cell mass and lower blood glucose than those derived from Prlr(+/-) mothers (Prlr(+/+(+/-))). Pathways that are known to regulate β-cell proliferation during pregnancy include insulin receptor substrate-2, Akt, menin, the serotonin synthetic enzyme tryptophan hydroxylase-1, Forkhead box M1 and Forkhead box D3. The aim of the present study was to determine whether dysregulation in these signalling molecules in the islets could explain the maternal effect on the phenotype of the offspring. It was found that the pregnancy-induced increases in insulin receptor substrate-2 and Akt expression in the islets were attenuated in the Prlr(+/+(+/-)) mice in comparison to the Prlr(+/+(+/+)) mice. The expression of Forkhead box D3, which plays a permissive role for β-cell proliferation during pregnancy, was also lower in the Prlr(+/+(+/-)) mice. In contrast, the pregnancy-induced increases in phospho-Jak2, tryptophan hydroxylase-1 and FoxM1, as well as the pregnancy-associated reduction in menin expression, were comparable between the two groups. There was also no difference in expression levels of genes that regulate insulin synthesis and secretion (i.e. glucose transporter 2, glucokinase and pancreatic and duodenal homeobox-1) between these two groups. Taken together, these results suggest that the in utero environment of the Prlr(+/-) mother confers long-term changes in the pancreatic islets of her offspring such that when the offspring themselves became pregnant, they cannot adapt to the increased insulin demands of their own pregnancy.

Expansion of beta-cell mass in response to pregnancy

Inadequate beta-cell mass can lead to insulin insufficiency and diabetes. During times of prolonged metabolic demand for insulin, the endocrine pancreas can respond by increasing beta-cell mass, both by increasing cell size and by changing the balance between beta-cell proliferation and apoptosis. In this paper, we review recent advances in our understanding of the mechanisms that control the adaptive expansion of beta-cell mass, focusing on the islet's response to pregnancy, a physiological state of insulin resistance. Functional characterization of factors controlling both beta-cell proliferation and survival might not only lead to the development of successful therapeutic strategies to enhance the response of the beta-cell to increased metabolic loads, but also improve islet transplantation regimens.

Prolactin receptor is required for normal glucose homeostasis and modulation of beta-cell mass during pregnancy

Increased islet mass is an adaptive mechanism that occurs to combat insulin resistance during pregnancy. Prolactin (PRL) can enhance beta-cell proliferation and insulin secretion in vitro, yet whether it is PRL or other pregnancy-related factors that mediate these adaptive changes during pregnancy is unknown. The objective of this study was to determine whether prolactin receptor (Prlr) is required for normal maternal glucose homeostasis during pregnancy. An ip glucose tolerance test was performed on timed-pregnant Prlr(+/+) and heterozygous null Prlr(+/-) mice on d 0, 15, and 18 of pregnancy. Compared with Prlr(+/+) mice, Prlr(+/-) mice had impaired glucose clearance, decreased glucose-stimulated insulin release, higher nonfasted blood glucose, and lower insulin levels during but not before pregnancy. There was no difference in their insulin tolerance. Prlr(+/+) mice show a significant incremental increase in islet density and beta-cell number and mass throughout pregnancy, which was attenuated in the Prlr(+/-) mice. Prlr(+/+) mice also had a more robust beta-cell proliferation rate during pregnancy, whereas there was no difference in apoptosis rate between the Prlr(+/+) and Prlr(+/-) mice before, during, or after pregnancy. Interestingly, genotype of the mothers had a significant impact on the offspring's phenotype, such that daughters derived from Prlr(+/-) mothers had a more severe phenotype than those derived from Prlr(+/+) mothers. In conclusion, this is the first in vivo demonstration that the action of pregnancy hormones, acting through Prlr, is required for normal maternal glucose tolerance during pregnancy by increasing beta-cell mass.

Animal evidence for the transgenerational development of diabetes mellitus

The mammalian fetus develops inside the uterus of its mother and is completely dependent on the nutrients supplied by its mother. Disturbances in the maternal metabolism that alter this nutrient supply from mother to fetus can induce structural and functional adaptations during fetal development, with lasting consequences for growth and metabolism of the offspring throughout life. This effect has been investigated, by several research groups, in different experimental models where the maternal metabolism during pregnancy was experimentally manipulated (maternal diabetes and maternal malnutrition) and the effect on the offspring was investigated. The altered maternal/fetal metabolism appears to be associated with a diabetogenic effect in the adult offspring, including gestational diabetes. This diabetic pregnancy in the offspring again induces a diabetogenic effect into the next generation, via adaptations during fetal development. These experimental data in laboratory animals are confirmed by epidemiological studies on infants of mothers suffering from diabetes or malnutrition during pregnancy. It can be concluded that fetal development in an abnormal intra-uterine milieu can induce alterations in the fetal metabolism, with lasting consequences for the glucose tolerance of the offspring in adult life. The most marked effect is the development of gestational diabetes, thereby transmitting the diabetogenic tendency to the next generation again. The concept of fetal origin of adult diabetes therefore is of major significance for public health in the immediate and the far future.

Developmental origins of the metabolic syndrome: prediction, plasticity, and programming

The "fetal" or "early" origins of adult disease hypothesis was originally put forward by David Barker and colleagues and stated that environmental factors, particularly nutrition, act in early life to program the risks for adverse health outcomes in adult life. This hypothesis has been supported by a worldwide series of epidemiological studies that have provided evidence for the association between the perturbation of the early nutritional environment and the major risk factors (hypertension, insulin resistance, and obesity) for cardiovascular disease, diabetes, and the metabolic syndrome in adult life. It is also clear from experimental studies that a range of molecular, cellular, metabolic, neuroendocrine, and physiological adaptations to changes in the early nutritional environment result in a permanent alteration of the developmental pattern of cellular proliferation and differentiation in key tissue and organ systems that result in pathological consequences in adult life. This review focuses on those experimental studies that have investigated the critical windows during which perturbations of the intrauterine environment have major effects, the nature of the epigenetic, structural, and functional adaptive responses which result in a permanent programming of cardiovascular and metabolic function, and the role of the interaction between the pre- and postnatal environment in determining final health outcomes.

Intra-uterine transmission of disease

Fetal development is dependent on maternal supply of fuels and building blocks. Disturbed maternal metabolism or inappropriate maternal nutrition confronts the fetus with an unfavourable intra-uterine milieu. Structural and functional adaptations occur during development and maturation of organs. Consequences of these fetal alterations persist postnatally and may result in metabolic alterations throughout life. Gestational diabetes can occur in these offspring and transmit the effect to the next generation. These alterations in fetal development can be associated with fetal macrosomia (maternal diabetes) or fetal growth-restriction (maternal/fetal malnutrition). The relation between birth weight and later metabolic disease therefore is U-shaped. Adult metabolic condition is thus to a considerable extent programmed in utero, fetal and neonatal weight being symptoms of disturbed fetal development. This concept of intra-uterine programming of disease is illustrated with a review of epidemiological human studies and experimental animal studies.