2011 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.
Past research has shown that maternal undernutrition during pregnancy can induce epigenetic changes that can program adipocyte metabolism and fat mass to give rise to later obesity in offspring, especially when challenged postnatally with a caloric excess diet (that is a dietary mismatch between prenatal and postnatal development). Epigenetic processes are induced by cues from the early developmental environment and play a role in determining the phenotype of the offspring as part of a life-course strategy to match it to its developmental environment. If not appropriately matched, the risk of later disease, including obesity, is increased. To study the effect of maternal diet on health consequences of offspring, female rats were fed diets containing either low or adequate protein for three weeks prior to breeding. This diet continued throughout pregnancy and lactation. At weaning, offspring from these two maternal diet treatment groups were given diets that were adequate in protein but containing either a normal or high amount of fat. Twelve weeks post-weaning, body composition was determined. Offspring born to low-protein fed dams compared to offspring born to adequate-protein fed dams were considerably different. Regardless of amount of fat in the post-weaning diet, the offspring of the low-protein fed moms had a greater increase in adipose tissue mass compared to those offspring from moms fed adequate protein. Furthermore, offspring from the low-protein fed moms fed a high-fat post weaning diet had the greatest amount of adipose tissue calculated as fold increase. This suggests that the effect in offspring of postnatal diets is affected by their prenatal diet. Paralleling the adipose tissue mass increase in offspring from the low-protein fed moms fed a high-fat post weaning diet, we found that the expression of the imprinted gene Igf2 (a major fetal growth factor) in adipose tissue is markedly up-regulated. Ongoing work is designed to determine whether increased DNA methylation (an epigenetic effect) in the imprinting control region of the Igf2 gene is responsible for its altered expression. We also found that proinflammatory cytokine levels are increased with increased fat tissue mass and body weight. These findings help explain how maternal programming can affect health outcomes in offspring fed a mismatched diet.
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