Gestational Protein Restriction Impairs Glucose Disposal in the Gastrocnemius Muscles of Female Rats

Dietary protein restriction during pregnancy and/or early weaning reduces the number of goblet cells in the small and large intestines of female mice pups

Background

It remains unclear whether goblet cell numbers in offspring are altered by maternal nutritional status and/or early weaning. Herein, using a murine model, we clarified whether a low-protein (LP) diet during pregnancy and/or early weaning changes villus structures, goblet cell numbers, mucin intensity, and mucin mRNA expression in the mucosal layer throughout the intestines in mice offspring.

Methods

We examined villus-crypt structures and goblet cell numbers using hematoxylin-eosin staining. By performing alcian blue-PAS staining and RT-qPCR, we investigated mucin intensity in the mucosal layer and mRNA expressions of Muc2 and Muc4, respectively, in 17 (early weaning)-, 21 (normal weaning)- and 28-day old mice born from LP diet-fed mothers or those born from control diet-fed mothers during pregnancy.

Results

Dietary protein restriction reduced goblet cell numbers in throughout the intestine, particularly in the duodenum and jejunum, and mucin intensity in the mucosal layer at the border of the jejunum and colon. The LP diet increased villus height and decreased villus thickness throughout the small intestine and crypt depth and width in the cecum and colon.

Conclusions

Dietary protein restriction during pregnancy and/or early weaning decreased the number of goblet cells, mucin intensity in the mucosal layer, and the Muc2 and Muc4 mRNA expressions in the small and large intestines, and affected the villus and crypt structures in the small and large intestines in female offspring mice during and after weaning.

General significance

Dietary abnormalities in fetal and weaning periods affects intestinal function.

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.

Gestational low dietary protein induces intrauterine inflammation and alters the programming of adiposity & insulin sensitivity in the adult offspring

Malnutrition associated with low dietary protein can induce gestational inflammation and sets a long-lasting metabolic impact on the offspring even after replenishment. The work investigated whether a low-protein diet (LPD) during pregnancy and lactation induces intrauterine inflammation and predisposes offspring to adiposity and insulin resistance in their adult life. Female Golden Syrian hamsters were fed LPD (10.0% energy from protein) or a control diet (CD, 20.0 % energy from protein) from preconception until lactation. All pups were switched to CD after lactation and continued until the end. Maternal LPD increased intrauterine inflammation by enhancing neutrophil infiltration, amniotic hsCRP, oxidative stress, and mRNA expression of NFκβ, IL8, COX2, and TGFβ in the chorioamniotic membrane (P<.05). The prepregnancy body weight, placental, and fetal weights, serum AST and ALT were decreased, while blood platelets, lymphocytes, insulin, and HDL were significantly increased in LPD-fed dams (P<.05). A postnatal switch to an adequate protein could not prevent hyperlipidemia in the 6-months LPD/CD offspring. The lipid profile and liver functions were restored over 10 months of protein feeding but failed to normalize fasting glucose and body fat accumulation compared to CD/CD. LPD/CD showed elevated GLUT4 expression & activated pIRS1 in the skeletal muscle and increased expression of IL6, IL1β, and p65-NFκB proteins in the liver (P<.05). In conclusion, present data suggest that maternal protein restriction may induce intrauterine inflammation and affect liver inflammation in the adult offspring by an influx of fats from adipose that may alter lipid metabolism and reduce insulin sensitivity in skeletal muscle.

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.

Prenatal Low-Protein Diet Affects Mitochondrial Structure and Function in the Skeletal Muscle of Adult Female Offspring

Gestational low-protein (LP) diet leads to glucose intolerance and insulin resistance in adult offspring. We had earlier demonstrated that LP programming affects glucose disposal in females. Mitochondrial health is crucial for normal glucose metabolism in skeletal muscle. In this study, we sought to analyze mitochondrial structure, function, and associated genes in skeletal muscles to explore the molecular mechanism of insulin resistance LP-programmed female offspring. On day four of pregnancy, rats were assigned to a control diet containing 20% protein or an isocaloric 6% protein-containing diet. Standard laboratory diet was given to the dams after delivery until the end of weaning and to pups after weaning. Gestational LP diet led to changes in mitochondrial ultrastructure in the gastrocnemius muscles, including a nine-fold increase in the presence of giant mitochondria along with unevenly formed cristae. Further, functional analysis showed that LP programming caused impaired mitochondrial functions. Although the mitochondrial copy number did not show significant changes, key genes involved in mitochondrial structure and function such as Fis1, Opa1, Mfn2, Nrf1, Nrf2, Pgc1b, Cox4b, Esrra, and Vdac were dysregulated. Our study shows that prenatal LP programming induced disruption in mitochondrial ultrastructure and function in the skeletal muscle of female offspring.

In utero low-protein-diet-programmed type 2 diabetes in adult offspring is mediated by sex hormones in rats†

Sex steroids regulate insulin sensitivity and glucose metabolism. We had characterized a lean type 2 diabetes (T2D) rat model using gestational low-protein (LP) diet programming. Our objective was to identify if endocrine dysfunction leading to decreased sex hormone levels will precede the development of T2D and if steroid replacement will prevent the onset of the disease. Pregnant rats were fed control or isocaloric LP diet from gestational day 4 until delivery. Normal diet was given to all mothers after delivery and to pups after weaning. LP offspring developed glucose intolerance and insulin resistance at 4 months. We measured sex steroid hormone profiles and expression of key genes involved in steroidogenesis in testis and ovary. Furthermore, one-month old rats were implanted with 90-day slow release T and E2 pellets for males and females, respectively. Glucose tolerance test (GTT) and euglycemic hyperinsulinemic clamp was performed at 4 months. LP-programmed T2D males had low T levels and females had low E2 levels due to dysregulated gene expression during steroidogenesis in gonads. GTT and euglycemic hyperinsulinemic clamp showed that LP males and females were glucose intolerant and insulin resistant; however, steroid supplementation prevented the onset of glucose intolerance and insulin resistance. Rats that developed T2D by LP programming have compromised gonadal steroidogenesis leading to low T and E2 in males and females, respectively. Sex steroid supplementation prevented the onset of glucose intolerance and insulin resistance indicating low sex steroid levels could cause compromised glucose metabolism ultimately leading to T2D.

Maternal physical activity prevents the overexpression of hypoxia-inducible factor 1-α and cardiorespiratory dysfunction in protein malnourished rats

Maternal physical activity attenuates cardiorespiratory dysfunctions and transcriptional alterations presented by the carotid body (CB) of rats. Rats performed physical activity and were classified as inactive/active. During gestation and lactation, mothers received either normoprotein (NP-17% protein) or low-protein diet (LP-8% protein). In offspring, biochemical serum levels, respiratory parameters, cardiovascular parameters and the mRNA expression of hypoxia-inducible factor 1-alpha (HIF-1α), tyrosine hydroxylase (TH) and purinergic receptors were evaluate. LP-inactive pups presented lower RF from 1^st to 14^th days old, and higher RF at 30 days than did NP-inactive and NP-active pups. LP-inactive pups presented with reduced serum protein, albumin, cholesterol and triglycerides levels and an increased fasting glucose level compared to those of NP-inactive and NP-active groups. LP and LP-inactive animals showed an increase in the cardiac variability at the Low-Frequency bands, suggesting a major influence of sympathetic nervous activity. In mRNA analyses, LP-inactive animals showed increased HIF-1α expression and similar expression of TH and purinergic receptors in the CB compared to those of NP groups. All these changes observed in LP-inactive pups were reversed in the pups of active mothers (LP-active). Maternal physical activity is able to attenuate the metabolic, cardiorespiratory and HIF-1α transcription changes induced by protein malnutrition.

Sex Dependent Dysregulation of Hepatic Glucose Production in Lean Type 2 Diabetic Rats

We have characterized a lean type 2 diabetic rat model by gestational low protein programming. We aimed to identify if the regulation of hepatic glucose production (HGP) via gluconeogenesis and glycogenolysis is affected and if there are any sex differences. Fasting (6-7 months old) type 2 diabetic rats received 2H2O followed by a primed constant rate infusion of [6,6-2H2] glucose. Blood samples were drawn during steady states after 4 h of fasting and following a euglycemic hyperinsulinemic clamp. HGP and the fraction of glucose derived from gluconeogenesis under fasting and euglycemic states were measured from steady state glucose enrichments after the infusion of [6,6-2H2]glucose and 2H2O tracers. Glycogenolysis was determined by calculating the difference between total HGP and gluconeogenesis rates. Hepatic gene expression of enzymes involved in HGP were quantified using qPCR. HGP rates was similar during fasting in both groups and sexes. However, under simulated fed condition, HGP rate was suppressed in controls but not in type 2 diabetic rats. They also showed inefficient HGP suppression in a simulated fed state. Differential analysis showed that suppression of both gluconeogenesis and glycogenolysis under simulated fed state was affected in these low protein programmed type 2 diabetic rats. These effects were greater in females when compared to males. Further, key genes involved in these processes like G6Pase, Pepck, pyruvate carboxylase, and glycogen phosphorylase in liver were dysregulated. Our data shows impaired suppression of HGP via gluconeogenesis and glycogenolysis in type 2 diabetic rats with greater effects on females.

Folate treatment partially reverses gestational low-protein diet-induced glucose intolerance and the magnitude of reversal is age and sex dependent

OBJECTIVES

Gestational low-protein (LP) programming causes glucose intolerance (GI) and insulin resistance (IR) in adult offspring. Folate supplementation has been shown to rescue the offspring from various programming effects. The aim of this study was to investigate whether folate supplementation during pregnancy reverses LP-induced GI and IR.

METHODS

Pregnant rats were fed control (20% protein), isocaloric low-protein (LP, 6%) or LP with 5 mg/kg folate (LPF) diets from gestational day 4 to delivery. The control diet was given during lactation and to pups after weaning. Glucose tolerance test was done at 1, 2, and 3 mo of age followed by euglycemic-hyperinsulinemic clamp at 4 mo. Rats were sacrificed at 4 mo and their gonadal, renal, inguinal, brown fat, and pancreas were weighed and expressed relative to their body weight.

RESULTS

LP- and LPF-fed dams showed similar weight loss during late pregnancy after decreased feed intake. Both LP and LPF pups were smaller at birth but their weights caught up like that of controls by 3 mo. In males, folate supplementation reduced LP-induced GI at 2 mo (glucose area under the curve [AUC]: 1940 mmol/L × 180 min in LP, 1629 mmol/L × 180 min in LPF, and 1653 mmol/L × 180 min in controls; P <0.05, LP versus control and P <0.01, LP versus LPF) but the effect diminished at 3 mo. In females, folate reduced GI at 1 mo (glucose AUC: 1406 mmol/L × 180 min in LP, 1264 mmol/L × 180 min in LPF, and 1281 mmol/L × 180 min in controls; P <0.05, LP versus control and LP versus LPF) but had no effect at 2 and 3 mo. Interestingly, the LPF group had higher pancreatic weights than other groups, suggesting that folate helps in pancreatic development enabling the LPF rats to produce/secrete more insulin to maintain euglycemia. Euglycemic-hyperinsulinemic clamp shows both LP and LPF are insulin resistant compared with controls by 4 mo with LPF more severe than LP in males. Interestingly, females were more insulin resistant than males.

CONCLUSIONS

Folate treatment partially reverses LP-induced GI and the magnitude of reversal is age and sex dependent. Furthermore, folate treatment does not reverse IR in either sex but makes it worse in males at 4 mo. The present study demonstrated that folate treatment is not sufficient to rescue the LP programming effects.