Location: Healthy Body Weight Research2013 Annual Report
1a. Objectives (from AD-416):
It is not clear whether or how maternal nutrient status during pregnancy epigenetically affects mitochondrial energy metabolism in offspring to increase their susceptibility for developing obesity. Thus, the overall objective is to determine, using animal models, whether low protein intake, high energy intake, or low iron intake during pregnancy influence the development of obesity in offspring through the nutritional programming of mitochondrial function during early development. Specific objectives are: (1) determine whether maternal energy and key nutrient intakes produce epigenetic changes in energy metabolism that contribute to obesity in the offspring, and (2) determine the functional effects of energy, key nutrient intakes and physical activity on obesity-related changes in the expression of genes and protein components of energy metabolism pathways. Within the context of these objectives, the goals of the research are: (1) determine whether protein restriction during pregnancy produces epigenetic changes that, by compromising physiological function, increase the susceptibility of offspring to obesity when fed energy-dense diets; (2) determine whether consumption of diets having excess energy during pregnancy produces long-term mitochondrial dysfunction in offspring that increases their susceptibility to obesity; (3) determine whether low maternal intakes of iron during pregnancy produce mitochondrial dysfunction related to increased susceptibility to obesity in the offspring; and (4) determine whether low maternal intakes of iron during pregnancy impairs mitochondrial adaptation to physical activity in offspring that decreases the effectiveness of physical activity in reducing body weight.
1b. Approach (from AD-416):
Three dietary models will be used with laboratory animals. (1) Female rats will be fed diets containing low or normal levels of protein throughout pregnancy. Immediately after birth, the rats fed low protein diets will be changed to normal protein diets. Half of the offspring born to dams fed low protein diet during pregnancy will be weaned to high fat diets and half will be weaned to normal fat diets. Offspring of dams fed normal protein diet during pregnancy will be treated identically. The offspring will remain on the postweaning diets for the remainder of the experiment. (2) Female rats will be fed high or normal fat diets 14 days prior to conception and throughout pregnancy and lactation. Half of the offspring born to dams fed high fat during pregnancy will be weaned to high fat diets and half will be weaned to normal fat diets. Offspring of dams fed normal fat during pregnancy will be treated identically. (3) Female rats will be fed low or normal iron diets 21 days prior to conception and throughout pregnancy and lactation. Half of the offspring born to dams fed low iron during pregnancy will be weaned to high fat diets and half will be weaned to normal fat diets. Offspring of dams fed normal iron during pregnancy will be treated identically. In a variation of the low/normal maternal iron model, the offspring will be maintained on either normal or high fat diets for 8 weeks. At the end of 8 weeks, all the offspring will be given normal fat diet and half will be subjected to exercise for 6 weeks. Offspring will be tested for epigenetic changes, changes in glycolytic and oxidative metabolism, muscle and liver mitochondrial function, and mitochondrial oxidative damage over a period of 6 to 36 weeks after being weaned to their postnatal diets. Epigenetic changes will be assessed by determining DNA methylation and the up- and/or down-regulation of differentially methylated genes will be confirmed by real-time PCR. Measurements of mitochondrial function will include respiration, respiratory complex activity and composition, and reactive oxygen production. Oxidative and glycolytic metabolism will be assessed by measuring the activity of key enzymes in the glycolytic and oxidative pathways. Mitochondria are a major source of reactive oxygen species. Assessment of the outcomes of mitochondrial dysfunction will extend to measurement of oxidative and nitrosative damage to mitochondrial proteins and DNA. For metabolic assessment, blood will be analyzed for glucose, triglyceride, insulin, leptin, and adiponectin concentrations. In addition to body weights, adiposity, lean tissue mass, and total body water components of body composition will be assessed by quantitative magnetic resonance.
3. Progress Report:
Objective 1.A. This study determines whether protein restriction during pregnancy produces epigenetic changes that result in obesity in offspring. The project team conducted studies to determine how prenatal low protein (LP) and postnatal high fat (HF) diets influence obesity, adipose tissue growth, insulin like growth factor 2 (IGF2) gene expression, and energy utilization resulting in obesity and increased risk for type 2 diabetes (T2D) in rats. We demonstrated that prenatal LP and postnatal HF intake increase the rate of adipose tissue growth in offspring through alterations in adipocyte numbers and sizes, expression of the epigenetically imprinted IGF2 gene, and by affecting adipose tissue energy utilization. Data also demonstrated that these alterations might increase risk for T2D development. This work is in press in Journal of Nutrition. To determine the mechanisms underlying prenatal low protein (LP) and postnatal high fat (HF) diet-induced obesity and adipose tissue inflammation, we showed that adipose tissue immune cell numbers were increased with HF and decreased with LP diets. In addition to findings from the adipose tissue, data from the liver samples of LP prenatal diet showed decreased expression of genes that are involved in energy production. Taken together, knowledge gained from our research provides the optimal maternal nutrition information for optimal fetal growth and postnatal development of offspring. We presented these data at the 2013 meeting of the American Nutrition Society; a manuscript is in press in the Journal of Nutrition. Objective 1.B. This study determines whether consumption of diets having excess energy (high fat or HF) during pregnancy produces long-term mitochondrial dysfunction in offspring that increases their susceptibility to obesity. We have initiated this study and it has a projected completion date of November 2013.
1. Demonstrated that maternal low protein diet followed by a postnatal high fat diet exacerbates obesity and insulin resistance in Sprague Dawley rats. ARS scientists in Grand Forks, ND determined the mechanisms of how maternal undernutrition during pregnancy results in obesity in offspring, especially when challenged postnatally with a high fat diet. When offspring were challenged with the high fat diet after weaning, those who were exposed to maternal low protein diet had greater adipose tissue growth rate, insulin-like growth factor 2 (IGF2) gene expression and IGF2 DNA methylation, and reduced energy utilization in the adipose tissue. Combined with higher serum concentrations of inflammatory cytokines and increased insulin resistance in the same offspring, these findings provided new insight into how low maternal protein intake and postnatal high fat diet contribute to obesity and insulin resistance.
2. Demonstrated that a maternal low protein diet followed by a postnatal high fat diet results in increased adipose tissue inflammation and insulin resistance by increased adipose tissue inflammatory immune cell (macrophage) numbers. ARS researchers in Grand Forks, ND determined the mechanisms underlying prenatal low protein and postnatal high fat diet-induced adipose tissue inflammation. One of the well established characteristics of obesity is accumulation inflammatory immune cells such as macrophages in adipose tissue. Once localized within the adipose tissue from circulating blood, adipose tissue resident macrophages promote adipose tissue inflammation and consequently increased risk for insulin resistance. The research showed that adipose tissue resident macrophage numbers are increased in the high fat fed group regardless of prenatal diet. The data also showed inflammatory subtype macrophage (M2 macrophages) numbers are decreased due to LP prenatal diet. These findings help determine how adipose tissue inflammation caused by inflammatory immune cells contribute to the development of insulin resistance.
3. Demonstrated that a maternal low protein combined with a postnatal high fat diet decreased offspring birth weight due to increased energy expenditure in the brown adipose tissue. Offspring of dams fed a low protein prenatal diet have higher resting metabolic rates which are accompanied by greater energy utilization and body temperature. To determine if a prenatal low protein diet increases metabolism, ARS scientists in Grand Forks, ND assessed the expression of genes involved in energy utilization in the brown adipose tissue from the neonates. A maternal low protein diet was associated with reduced birth weights and increased expression of energy utilization genes in the brown adipose tissue. These findings help to understand how prenatal protein restriction increases the risk for low birth weight through increased energy expenditure in the offspring.
4. Demonstrated that maternal low protein and postnatal high fat diets induce obesity by causing epigenetic changes in the offspring’s muscle tissues. Muscle tissues are considered metabolically active and utilize stored energy. To determine if maternal low protein intake causes changes in liver and muscle energy utilization and storage in offspring fed high fat postnatal diets, ARS scientists in Grand Forks, ND measured expression of genes that are involved in mitochondrial biogenesis and thermogenesis. The offspring fed low protein prenatal diet had decreased expression of genes located in the liver and muscles that are involved in mitochondrial biogenesis and thermogenesis. Preliminary data indicated that other genes that are regulated epigenetically such as Igf2/H19 locus are differentially methylated due to prenatal low protein and postnatal high fat diets. These findings help to understand how the prenatal maternal diet programs metabolically active tissues in the body to adapt and increase the risk for obesity development when offspring are challenged by high fat diet after weaning.
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