Influence of the weaning diet on the changes of glucose metabolism and of insulin sensitivity

Changes in transcriptomic landscape with macronutrients intake switch are independent from O-GlcNAcylation levels in heart throughout postnatal development in rats

Background

Dietary intake and metabolism variations are associated with molecular changes and more particularly in the transcriptome. O-GlcNAcylation is a post-translational modification added and removed respectively by OGT and OGA. The UDP-GlcNAc, the substrate of OGT, is produced by UAP1 and UAP1L1. O-GlcNAcylation is qualified as a metabolic sensor and is involved in the modulation of gene expression. We wanted to unveil if O-GlcNAcylation is linking metabolic transition to transcriptomic changes and to highlight modifications of O-GlcNAcylation during the postnatal cardiac development.

Methods

Hearts were harvested from rats at birth (D0), before (D12) and after suckling to weaning transition with normal (D28) or delayed weaning diet from D12 to D28 (D28F). O-GlcNAcylation levels and proteins expression were evaluated by Western blot. Cardiac transcriptomes were evaluated via 3'SRP analysis.

Results

Cardiac O-GlcNAcylation levels and nucleocytoplasmic OGT (ncOGT) were decreased at D28 while full length OGA (OGA) was increased. O-GlcNAcylation levels did not changed with delayed weaning diet while ncOGT and OGA were respectively increased and decreased. Uapl1 was the only O-GlcNAcylation-related gene identified as differentially expressed throughout postnatal development.

Conclusion

Macronutrients switch promotes changes in the transcriptome landscape that are independent from O-GlcNAcylation levels. UAP1 and UAP1L1 are not the main regulator element of O-GlcNAcylation throughout postnatal development.

Protein O-GlcNAcylation levels are regulated independently of dietary intake in a tissue and time-specific manner during rat postnatal development

Aim

Metabolic sources switch from carbohydrates in utero, to fatty acids after birth and then a mix once adults. O‐GlcNAcylation (O‐GlcNAc) is a post‐translational modification considered as a nutrient sensor. The purpose of this work was to assess changes in protein O‐GlcNAc levels, regulatory enzymes and metabolites during the first periods of life and decipher the impact of O‐GlcNAcylation on cardiac proteins.

Methods

Heart, brain and liver were harvested from rats before and after birth (D‐1 and D0), in suckling animals (D12), after weaning with a standard (D28) or a low‐carbohydrate diet (D28F), and adults (D84). O‐GlcNAc levels and regulatory enzymes were evaluated by western blots. Mass spectrometry (MS) approaches were performed to quantify levels of metabolites regulating O‐GlcNAc and identify putative cardiac O‐GlcNAcylated proteins.

Results

Protein O‐GlcNAc levels decrease drastically and progressively from D‐1 to D84 (13‐fold, P < .05) in the heart, whereas the changes were opposite in liver and brain. O‐GlcNAc levels were unaffected by weaning diet in any tissues. Changes in expression of enzymes and levels of metabolites regulating O‐GlcNAc were tissue‐dependent. MS analyses identified changes in putative cardiac O‐GlcNAcylated proteins, namely those involved in the stress response and energy metabolism, such as ACAT1, which is only O‐GlcNAcylated at D0.

Conclusion

Our results demonstrate that protein O‐GlcNAc levels are not linked to dietary intake and regulated in a time and tissue‐specific manner during postnatal development. We have identified by untargeted MS putative proteins with a particular O‐GlcNAc signature across the development process suggesting specific role of these proteins.

[Hepatic polyploidy: Dr Jekyll or Mr Hyde]

Polyploidy (alias whole genome amplification) refers to organisms containing more than two basic sets of chromosomes. Polyploidy was first observed in plants more than a century ago, and it is known that such processes occur in many eukaryotes under a variety of circumstances. In mammals, the development of polyploid cells can contribute to tissue differentiation and therefore possibly a gain of function. Alternately, it can be associated with development of disease such as cancer. Polyploidy can occur because of cell fusion or abnormal cell division. Polyploidy is a common characteristic of the mammalian liver. Polyploidization occurs notably during liver development, but also in adults because of cellular stress. Recent progresses have unraveled the mechanisms and functional consequences of hepatocytes polyploidization during normal and pathological liver growth.

Complementary feeding: a commentary by the ESPGHAN Committee on Nutrition

This position paper on complementary feeding summarizes evidence for health effects of complementary foods. It focuses on healthy infants in Europe. After reviewing current knowledge and practices, we have formulated these conclusions: Exclusive or full breast-feeding for about 6 months is a desirable goal. Complementary feeding (ie, solid foods and liquids other than breast milk or infant formula and follow-on formula) should not be introduced before 17 weeks and not later than 26 weeks. There is no convincing scientific evidence that avoidance or delayed introduction of potentially allergenic foods, such as fish and eggs, reduces allergies, either in infants considered at increased risk for the development of allergy or in those not considered to be at increased risk. During the complementary feeding period, >90% of the iron requirements of a breast-fed infant must be met by complementary foods, which should provide sufficient bioavailable iron. Cow's milk is a poor source of iron and should not be used as the main drink before 12 months, although small volumes may be added to complementary foods. It is prudent to avoid both early (<4 months) and late (>or=7 months) introduction of gluten, and to introduce gluten gradually while the infant is still breast-fed, inasmuch as this may reduce the risk of celiac disease, type 1 diabetes mellitus, and wheat allergy. Infants and young children receiving a vegetarian diet should receive a sufficient amount ( approximately 500 mL) of breast milk or formula and dairy products. Infants and young children should not be fed a vegan diet.

Distinct and overlapping functions of insulin and IGF-I receptors

Targeted gene mutations have established distinct, yet overlapping, developmental roles for receptors of the insulin/IGF family. IGF-I receptor mediates IGF-I and IGF-II action on prenatal growth and IGF-I action on postnatal growth. Insulin receptor mediates prenatal growth in response to IGF-II and postnatal metabolism in response to insulin. In rodents, unlike humans, insulin does not participate in embryonic growth until late gestation. The ability of the insulin receptor to act as a bona fide IGF-II-dependent growth promoter is underscored by its rescue of double knockout Igf1r/Igf2r mice. Thus, IGF-II is a true bifunctional ligand that is able to stimulate both insulin and IGF-I receptor signaling, although with different potencies. In contrast, the IGF-II/cation-independent mannose-6-phosphate receptor regulates IGF-II clearance. The growth retardation of mice lacking IGF-I and/or insulin receptors is due to reduced cell number, resulting from decreased proliferation. Evidence from genetically engineered mice does not support the view that insulin and IGF receptors promote cellular differentiation in vivo or that they are required for early embryonic development. The phenotypes of insulin receptor gene mutations in humans and in mice indicate important differences between the developmental roles of insulin and its receptor in the two species.

Are dietary recommendations for dietary fat reduction achievable?

Despite several sets of dietary guidelines aimed at reducing fat intakes in the UK populations the actual fat intake in the UK has remained remarkably constant over the last decade. It is therefore of utmost importance to understand why the advice of the 1980s was not taken on board by the nation, to enable the achievement of current nutritional targets for dietary fat set for 2005. The nature of the diets of those individuals in the UK who have low fat intakes in line with the dietary goals are considered here, with the aim to increase our understanding of how the goals can be achieved in the free-living population. This paper postulates that a low fat diet will be easier to achieve, more palatable and hence more acceptable to the consumer if the dietary fat is replaced with a mixture of energy from sugar and starch. Further research is required to gain a greater understanding of what type of dietary composition will enable the free-living population to achieve a reduction in their dietary fat intake. This in turn will allow the dissemination of appropriate nutritional advice in the future and inform product development initiatives in the food industry.