Nutrition in early life and the programming of adult disease: a review

Foetal development and infancy are life stages that are characterised by rapid growth, development and maturation of organs and systems. Variation in the quality or quantity of nutrients consumed by mothers during pregnancy, or infants during the first year of life, can exert permanent and powerful effects upon developing tissues. These effects are termed 'programming' and represent an important risk factor for noncommunicable diseases of adulthood, including the metabolic syndrome and coronary heart disease. This narrative review provides an overview of the evidence-base showing that indicators of nutritional deficit in pregnancy are associated with a greater risk of type-2 diabetes and cardiovascular mortality. There is also a limited evidence-base that suggests some relationship between breastfeeding and the timing and type of foods used in weaning, and disease in later life. Many of the associations reported between indicators of early growth and adult disease appear to interact with specific genotypes. This supports the idea that programming is one of several cumulative influences upon health and disease acting across the lifespan. Experimental studies have provided important clues to the mechanisms that link nutritional challenges in early life to disease in adulthood. It is suggested that nutritional programming is a product of the altered expression of genes that regulate the cell cycle, resulting in effective remodelling of tissue structure and functionality. The observation that traits programmed by nutritional exposures in foetal life can be transmitted to further generations adds weight the argument that heritable epigenetic modifications play a critical role in nutritional programming.

Epigenetics of insulin resistance: an emerging field in translational medicine

In this article, we review the current knowledge of and recent insights into the role of epigenetic factors in the development of insulin resistance (IR), with emphasis on peroxisome proliferator-activated receptor gamma coactivator 1α (PPARGC1A or PGC1α) methylation on fetal programming and liver modulation of glucose-related phenotypes. We discuss the pathogenesis of IR beyond the integrity of β-cell function and illustrate the novel concept of mitochondrial epigenetics to explain the pathobiology of metabolic-syndrome-related phenotypes. Moreover, we discuss whether epigenetic marks in genes of the circadian rhythm system are able to modulate insulin/glucose-related metabolic functions and place hypoxia inducible factor 1 α (HIF1α) as a part of the master CLOCK gene/protein interaction network that might modulate IR. Finally, we highlight relevant information about epigenetic marks and IR so that clinicians practicing in the community may envision future areas of medical intervention and predict putative biomarkers for early disease detection.

In utero oxidative stress epigenetically programs antioxidant defense capacity and adulthood diseases

SIGNIFICANCE

Maternal health and diet during gestation are critical for predicting fetal outcomes, both immediately at birth and in adulthood. While epigenetic modifications have previously been tightly linked to carcinogenesis, recent advances in the field have suggested that numerous adulthood diseases, including those characteristic of metabolic syndrome, could be programmed in utero in response to maternal exposures, and these "programmable" diseases are associated with epigenetic modifications of vital genes.

RECENT ADVANCES

While little is currently known about the epigenetic regulation of the antioxidant (AOX) defense system, several studies in animals show that AOX defense capacity may be programmed in utero, making it likely that the critical genes involved in this pathway are epigenetically regulated, either by DNA methylation or by the modification of histone tails.

CRITICAL ISSUES

This article presents the most current knowledge of the in utero regulation of the AOX defense capacity, and will specifically focus on the potential epigenetic regulation of this system in response to various in utero exposures or stimuli. The ability to appropriately respond to oxidative stress is critical for the health and survival of any organism, and the potential programming of this capacity may provide a link between the in utero environment and the tendency of certain individuals to be more susceptible toward disease stimuli in their postnatal environments.

FUTURE DIRECTIONS

We sincerely hope that future studies which result in a deeper understanding of the in utero programming of the epigenome will lead to novel and effective therapies for the treatment of epigenetically linked diseases.

mTOR phosphorylates IMP2 to promote IGF2 mRNA translation by internal ribosomal entry

Variants in the IMP2 (insulin-like growth factor 2 [IGF2] mRNA-binding protein 2) gene are implicated in susceptibility to type 2 diabetes. We describe the ability of mammalian target of rapamycin (mTOR) to regulate the cap-independent translation of IGF2 mRNA through phosphorylation of IMP2, an oncofetal RNA-binding protein. IMP2 is doubly phosphorylated in a rapamycin-inhibitable, amino acid-dependent manner in cells and by mTOR in vitro. Double phosphorylation promotes IMP2 binding to the IGF2 leader 3 mRNA 5' untranslated region, and the translational initiation of this mRNA through eIF-4E- and 5' cap-independent internal ribosomal entry. Unexpectedly, the interaction of IMP2 with mTOR complex 1 occurs through mTOR itself rather than through raptor. Whereas depletion of mTOR strongly inhibits IMP2 phosphorylation in cells, comparable depletion of raptor has no effect; moreover, the ability of mTOR to phosphorylate IMP2 in vitro is unaffected by the elimination of raptor. Dual phosphorylation of IMP2 at the mTOR sites is evident in the mouse embryo, likely coupling nutrient sufficiency to IGF2 expression and fetal growth. Doubly phosphorylated IMP2 is also widely expressed in adult tissues, including islets of Langerhans.

Gestational high fat diet programs hepatic phosphoenolpyruvate carboxykinase gene expression and histone modification in neonatal offspring rats

In insulin resistance and type II diabetes, there is an elevation of hepatic gluconeogenesis, which contributes to hyperglycaemia. Studies in experimental animals have provided evidence that consumption of high fat (HF) diets by female rats programs the progeny for glucose intolerance in adulthood, but the mechanisms behind the in utero programming remain poorly understood. The present study analysed the effect of a maternal HF diet on fetal gluconeogenic gene expression and potential regulation mechanism related to histone modifications. Dams were fed either a Control (C, 16% kcal fat) or a high-fat (HF, 45% kcal fat) diet throughout gestation. Livers of the offspring were collected on gestational day 21 and analysed to determine the consequences of a maternal HF diet on molecular markers of fetal liver gluconeogenesis. We demonstrated that offspring of HF-fed dams were significantly heavier and had significantly higher blood glucose levels at the time of delivery than offspring of dams fed the C diet. While maternal gluconeogenesis and plasma glucose were not affected by the HF diet, offspring of HF-fed dams had significantly higher mRNA contents of gluconeogenic genes in addition to the elevated plasma glucose. In addition to increased transcription rate, a gestational HF diet resulted in modifications of the Pck1 histone code in livers of offspring. Our results demonstrate that in utero exposure to HF diet has the potential to program the gluconeogenic capacity of offspring through epigenetic modifications, which could potentially lead to excessive glucose production and altered insulin sensitivity in adulthood.

The emerging genetic architecture of type 2 diabetes

Type 2 diabetes is a genetically heterogeneous disease, with several relatively rare monogenic forms and a number of more common forms resulting from a complex interaction of genetic and environmental factors. Previous studies using a candidate gene approach, family linkage studies, and gene expression profiling uncovered a number of type 2 genes, but the genetic basis of common type 2 diabetes remained unknown. Recently, a new window has opened on defining potential type 2 diabetes genes through genome-wide SNP association studies of very large populations of individuals with diabetes. This review explores the pathway leading to discovery of these genetic effects, the impact of these genetic loci on diabetes risk, the potential mechanisms of action of the genes to alter glucose homeostasis, and the limitations of these studies in defining the role of genetics in this important disease.