Influence of maternal low protein diet during pregnancy on hepatic gene expression signature in juvenile female porcine offspring

Low Protein Programming Causes Increased Mitochondrial Fusion and Decreased Oxygen Consumption in the Hepatocytes of Female Rats

The liver is one of the major organs involved in the regulation of glucose and lipid homeostasis. The effectiveness of metabolic activity in hepatocytes is determined by the quality and quantity of its mitochondria. Mitochondrial function is complex, and they act via various dynamic networks, which rapidly adapt to changes in the cellular milieu. Our present study aims to investigate the effects of low protein programming on the structure and function of mitochondria in the hepatocytes of adult females. Pregnant rats were fed with a control or isocaloric low-protein diet from gestational day 4 until delivery. A normal laboratory chow was given to all dams after delivery and to pups after weaning. The rats were euthanized at 4 months of age and the livers were collected from female offspring for investigating the mitochondrial structure, mtDNA copy number, mRNA, and proteins expression of genes associated with mitochondrial function. Primary hepatocytes were isolated and used for the analysis of the mitochondrial bioenergetics profiles. The mitochondrial ultrastructure showed that the in utero low-protein diet exposure led to increased mitochondrial fusion. Accordingly, there was an increase in the mRNA and protein levels of the mitochondrial fusion gene Opa1 and mitochondrial biogenesis genes Pgc1a and Essra, but Fis1, a fission gene, was downregulated. Low protein programming also impaired the mitochondrial function of the hepatocytes with a decrease in basal respiration ATP-linked respiration and proton leak. In summary, the present study suggests that the hepatic mitochondrial dysfunction induced by an in utero low protein diet might be a potential mechanism linking glucose intolerance and insulin resistance in adult offspring.

Protein restriction during lactation causes transgenerational metabolic dysfunction in adult rat offspring

Introduction

Protein restriction during lactation can induce metabolic dysfunctions and has a huge impact on the offspring's phenotype later in its life. We tested whether the effects of a maternal low-protein diet (LP) in rats can be transmitted to the F2 generation and increase their vulnerability to dietary insults in adulthood.

Methods

Female Wistar rats (F0) were fed either a low-protein diet (LP; 4% protein) during the first 2 weeks of lactation or a normal-protein diet (NP; 23% protein). The female offspring (F1 generation) were maintained on a standard diet throughout the experiment. Once adulthood was reached, female F1 offspring from both groups (i.e., NP-F1 and LP-F1) were bred to proven males, outside the experiment, to produce the F2 generation. Male F2 offspring from both groups (NP-F2 and LP-F2 groups) received a standard diet until 60 days old, at which point they received either a normal fat (NF; 4.5% fat) or a high fat diet (HF; 35% fat) for 30 days.

Results

At 90 days old, LPNF-F2 offspring had increased lipogenesis and fasting insulinemia compared to NPNF-F2, without alteration in insulin sensitivity. HF diet caused increased gluconeogenesis and displayed glucose intolerance in LPHF-F2 offspring compared to LPNF-F2 offspring. Additionally, the HF diet led to damage to lipid metabolism (such as steatosis grade 3), higher body weight, fat pad stores, and hepatic lipid content.

Discussion

We concluded that an F0 maternal protein restricted diet during lactation can induce a transgenerational effect on glucose and liver metabolism in the F2 generation, making the offspring's liver more vulnerable to nutritional injury later in life.

Current Knowledge on the Pathophysiology of Lean/Normal-Weight Type 2 Diabetes

Since early times, being overweight and obesity have been associated with impaired glucose metabolism and type 2 diabetes (T2D). Similarly, a less frequent adult-onset diabetes in low body mass index (BMI) people has been known for many decades. This form is mainly found in developing countries, whereby the largest increase in diabetes incidence is expected in coming years. The number of non-obese patients with T2D is also on the rise among non-white ethnic minorities living in high-income Western countries due to growing migratory flows. A great deal of energy has been spent on understanding the mechanisms that bind obesity to T2D. Conversely, the pathophysiologic features and factors driving the risk of T2D development in non-obese people are still much debated. To reduce the global burden of diabetes, we need to understand why not all obese people develop T2D and not all those with T2D are obese. Moreover, through both an effective prevention and the implementation of an individualized clinical management in all people with diabetes, it is hoped that this will help to reduce this global burden. The purpose of this review is to take stock of current knowledge about the pathophysiology of diabetes not associated to obesity and to highlight which aspects are worthy of future studies.

Maternal low protein diet and fetal programming of lean type 2 diabetes

Maternal nutrition is found to be the key factor that determines fetal health in utero and metabolic health during adulthood. Metabolic diseases have been primarily attributed to impaired maternal nutrition during pregnancy, and impaired nutrition has been an immense issue across the globe. In recent years, type 2 diabetes (T2D) has reached epidemic proportion and is a severe public health problem in many countries. Although plenty of research has already been conducted to tackle T2D which is associated with obesity, little is known regarding the etiology and pathophysiology of lean T2D, a variant of T2D. Recent studies have focused on the effects of epigenetic variation on the contribution of in utero origins of lean T2D, although other mechanisms might also contribute to the pathology. Observational studies in humans and experiments in animals strongly suggest an association between maternal low protein diet and lean T2D phenotype. In addition, clear sex-specific disease prevalence was observed in different studies. Consequently, more research is essential for the understanding of the etiology and pathophysiology of lean T2D, which might help to develop better disease prevention and treatment strategies. This review examines the role of protein insufficiency in the maternal diet as the central driver of the developmental programming of lean T2D.

The Effect of Dietary Protein Imbalance during Pregnancy on the Growth, Metabolism and Circulatory Metabolome of Neonatal and Weaned Juvenile Porcine Offspring

Protein imbalance during pregnancy affects women in underdeveloped and developing countries and is associated with compromised offspring growth and an increased risk of metabolic diseases in later life. We studied in a porcine model the glucose and urea metabolism, and circulatory hormone and metabolite profile of offspring exposed during gestation, to maternal isoenergetic low-high (LP-HC), high-low (HP-LC) or adequate (AP) protein-carbohydrate ratio diets. At birth, LP-HC were lighter and the plasma acetylcarnitine to free carnitine ratios at 1 day of life was lower compared to AP offspring. Plasma urea concentrations were lower in 1 day old LP-HC offspring than HP-LC. In the juvenile period, increased insulin concentrations were observed in LP-HC and HP-LC offspring compared to AP, as was body weight from HP-LC compared to LP-HC. Plasma triglyceride concentrations were lower in 80 than 1 day old HP-LC offspring, and glucagon concentrations lower in 80 than 1 day old AP and HP-LC offspring. Plasma urea and the ratio of glucagon to insulin were lower in all 80 than 1 day old offspring. Aminoacyl-tRNA, arginine and phenylalanine, tyrosine and tryptophan metabolism, histidine and beta-alanine metabolism differed between 1 and 80 day old AP and HP-LC offspring. Maternal protein imbalance throughout pregnancy did not result in significant consequences in offspring metabolism compared to AP, indicating enormous plasticity by the placenta and developing offspring.

Maternal Protein Restriction Altered Insulin Resistance and Inflammation-Associated Gene Expression in Adipose Tissue of Young Adult Mouse Offspring in Response to a High-Fat Diet

Maternal protein restriction is associated with increased risk of insulin resistance and inflammation in adulthood offspring. Here, we investigated whether maternal protein restriction could alter the risk of metabolic syndrome in postweaning high-fat (HF)-diet-challenged offspring, with focus on epididymal adipose tissue gene expression profile. Female ICR mice were fed a control (C) or a low-protein (LP) diet for two weeks before mating and throughout gestation and lactation, and their male offspring were fed an HF diet for 22 weeks (C/HF and LP/HF groups). A subset of offspring of control dams was fed a low-fat control diet (C/C group). In response to postweaning HF diet, serum insulin level and the homeostasis model assessment of insulin resistance (HOMA-IR) were increased in control offspring. Maternal LP diet decreased HOMA-IR and adipose tissue inflammation, and increased serum adiponectin level in the HF-diet-challenged offspring. Accordingly, functional analysis revealed that differentially expressed genes (DEGs) enriched in cytokine production were downregulated in the LP/HF group compared to the C/HF group. We also observed the several annotated gene ontology terms associated with innate immunity and phagocytosis in down-regulated DEGs between LP/HF and C/C groups. In conclusion, maternal protein restriction alleviated insulin resistance and inflammation in young offspring mice fed a HF diet but may impair development of immune system in offspring.

Moderate high or low maternal protein diets change gene expression but not the phenotype of skeletal muscle from porcine fetuses

The aim of our study was to characterize the immediate phenotypic and adaptive regulatory responses of fetuses to different in utero conditions reflecting inadequate maternal protein supply during gestation. The gilts fed high- (250% above control) or low- (50% under control) protein diets isoenergetically adjusted at the expense of carbohydrates from the day of insemination until the fetuses were collected at day 64 or 94 of gestation. We analyzed body composition, histomorphology, biochemistry, and messenger RNA (mRNA) expression of fetal skeletal muscle. Both diets had only marginal effects on body composition and muscular cellularity of fetuses including an unchanged total number of myofibers. However, mRNA expression of myogenic regulatory factors (MYOG, MRF4, P ≤ 0.1), IGF system (IGF1, IGF1R, P ≤ 0.05) and myostatin antagonist FST (P = 0.6, in males only) was reduced in the fetal muscle exposed to a maternal low-protein diet. As a result of excess protein, MYOD, MYOG, IGF1R, and IGFBP5 mRNA expression (P ≤ 0.05) was upregulated in fetal muscle. Differences in muscular mRNA expression indicate in utero regulatory adaptive responses to maternal diet. Modulation of gene expression immediately contributes to the maintenance of an appropriate fetal phenotype that would be similar to that observed in the control fetuses. Moreover, we suggest that the modified gene expression in fetal skeletal muscle can be viewed as the origin of developmental muscular plasticity involved in the concept of fetal programming.

TRIENNIAL LACTATION SYMPOSIUM: Nutrigenomics in livestock: Systems biology meets nutrition

The advent of high-throughput technologies to study an animal's genome, proteome, and metabolome (i.e., "omics" tools) constituted a setback to the use of reductionism in livestock research. More recent development of "next-generation sequencing" tools was instrumental in allowing in-depth studies of the microbiome in the rumen and other sections of the gastrointestinal tract. Omics, along with bioinformatics, constitutes the foundation of modern systems biology, a field of study widely used in model organisms (e.g., rodents, yeast, humans) to enhance understanding of the complex biological interactions occurring within cells and tissues at the gene, protein, and metabolite level. Application of systems biology concepts is ideal for the study of interactions between nutrition and physiological state with tissue and cell metabolism and function during key life stages of livestock species, including the transition from pregnancy to lactation, in utero development, or postnatal growth. Modern bioinformatic tools capable of discerning functional outcomes and biologically meaningful networks complement the ever-increasing ability to generate large molecular, microbial, and metabolite data sets. Simultaneous visualization of the complex intertissue adaptations to physiological state and nutrition can now be discerned. Studies to understand the linkages between the microbiome and the absorptive epithelium using the integrative approach are emerging. We present examples of new knowledge generated through the application of functional analyses of transcriptomic, proteomic, and metabolomic data sets encompassing nutritional management of dairy cows, pigs, and poultry. Published work to date underscores that the integrative approach across and within tissues may prove useful for fine-tuning nutritional management of livestock. An important goal during this process is to uncover key molecular players involved in the organismal adaptations to nutrition.

Maternal high-protein diet during pregnancy, but not during suckling, induced altered expression of an increasing number of hepatic genes in adult mouse offspring

PURPOSE

Indirect effects of a high-protein maternal diet are not well understood. In this study, we analyzed short-term and sustainable effects of a prenatal versus early postnatal maternal high-protein diet on growth and hepatic gene expression in mouse offspring.

METHODS

Dams were exposed to an isoenergetic high-protein (HP, 40 % w/w) diet during pregnancy or lactation. Growth and hepatic expression profiles of male offspring were evaluated directly after weaning and 150 days after birth. Offspring from two dietary groups, high-protein diet during pregnancy and control diet during lactation (HPC), and control diet during pregnancy and high-protein diet during lactation (CHP), were compared with offspring (CC) from control-fed dams.

RESULTS

Maternal CHP treatment was associated with sustained offspring growth retardation, but decreased numbers of affected hepatic genes in adults compared to weanlings. In contrast, offspring of the HPC group did not show persistent effects on growth parameters, but the number of affected hepatic genes was even increased at adult age. In both dietary groups, however, only a small subset of genes was affected in weanlings as well as in adults.

CONCLUSIONS

We conclude that (1) prenatal and early postnatal maternal HP diet caused persistent, but (2) different effects and partially complementary trends on growth characteristics and on the hepatic transcriptome and associated pathways and that (3) only a small number of genes and associated upstream regulators might be involved in passing early diet-induced imprints to adulthood.