Location: Children's Nutrition Research Center2011 Annual Report
1a. Objectives (from AD-416)
1) determine role of circadian clock in regulation of food intake and interaction between diet composition and circadian rhythms of food intake on body weight control during post-weaning and adult life; determine specific role of central and peripheral clocks, as well as circadian output pathways in maintaining homeostasis of food intake; (2-3 removed; SYs left); 4) investigate impact of prematurity on GI and metabolic response to perinatal nutrition; 5) compare impact of continuous vs. intermittent bolus delivery of nutrients provided enterally or parenterally on protein synthesis and accretion in neonatal models and identify intracellular signaling mechanism involved; 8) investigate changes of SIRT3 gene expression in the liver, and study effects of SIRT3 expression on hepatic metabolism, oxidative stress, and fat deposition; 9) determine role of protein kinase C interacting cousin of thioredoxin in insulin-mediated growth, macronutrient metabolism, and insulin resistance in the liver; 10) define action of glucagon-like peptide-2 (GLP-2) receptor on food intake and inter-organ macronutrient flux; 11) study ghrelin peptide expression profile under different diet regimes; 12) conduct mechanistic analyses of differences in metabolic profile between WT and null mice; 13) confirm predicted lipotropic effects of lecithin, choline and betaine in high-fat-fed mouse models of the metabolic syndrome; 14) test impact of liver specific LRH-1 knockout on the lipotropic effects of lecithin, choline and betaine in high-fat-fed mouse models of the metabolic syndrome; 15)identify genes that show epigenetic dysregulation in obesity; 16) determine if methylation and expression of specific genes in hypothalamus and/or adipose tissue differ between lean and obese animals and determine if maternal obesity and/or nutrition before and during pregnancy persistently alters epigenetic regulation in offspring; 17) determine if maternal obesity and/or nutrition before and during pregnancy persistently alters epigenetic regulation in offspring hypothalamus or adipose tissue; 18) identify placental epigenetic mechanisms that affect fetal nutrition, growth and development; 19) determine how programming of glucose intolerance, obesity, and the epigenetic dysregulation of skeletal muscle-growth in mice is affected by maternal diet during development; 20) determine if epigenetic programming and reprogramming contribute to lineage-specific patterns of gene expression; 21) develop targested knock-in mouse model to determine if nutrients can modulate hypermethylation, epigenetic silencing and increase susceptibility to disease; 22) evaluate leukocyte patterns, gene expression profiles, and inflammatory mediators in adipose tissue under influence of diatary manipulation that leads to obesity.
1b. Approach (from AD-416)
The research will be accomplished using a variety of animal models and scientific tools to simulate the human newborn and/or child. Animal models will be used to understand the central and peripheral circadian clock mechanisms that influence eating behavior, metabolism, and energy balance. Newborm animal models will be used to examine the effect of chronic parenteral nutrition during the neonatal period on glucose tolerance, insulin sensitivity, and body composition during late infancy and adolescence. Researchers will investigate the effects of intermittent bolus feeding versus continuous feeding, delivered either enterally or parenterally, on protein synthesis in neonatal animal models. This will allow our team to determine the long-term impact of these feeding modalities on growth and body composition. Various models will be placed on obesigenic diets at 5-6 weeks of age and evaluated at 7 days, 5 weeks, and 6 months to define a blood leukocyte expression profile at these time points. Children's Nutrition Research Center scientists will also characterize the functions of intracellular systems in the liver and their influences on the onset of fatty liver disease and glucose homeostasis. Additional investigation will occur on the intracellular signaling pathways of GLP-2 and their metabolic effects on food intake, energy expenditure, and glucose homeostasis. Various mouse models, and a human model of epigenetic dysregulation compromising placental development, will be used to test if maternal obesity and fetal nutrition during development affects the establishment of gene-specific DNA methylation patterns in the developing fetus, which would cause permanent changes in gene expression, metabolism, food intake regulation, and body weight. Additionally we will investigate the mechanisms regulating DNA methylation during development, and characterize their involvement in nutritional programming during critical ontogenic periods. We will characterize the role of ghrelin and its receptor in nutritional regulation of energy and glucose homeostasis.
3. Progress Report
Proj. 1 We investigated the molecular mechanism of circadian control of leptin expression in the fat tissue and bile acid synthesis, metabolism, and signaling in the liver and found that the circadian clock is involved in regulating leptin expression and bile acid synthesis at the transcriptional level, and disruption of circadian rhythm disrupts the balance of leptin interaction with brain centers controlling energy balance. Proj. 2 We showed in models that parenteral vs. enteral nutrition results in poor metabolic condition marked by increased fat, glucose intolerance, and inflammatory stress. We showed that intermittent bolus feeding stimulates protein synthesis by activating the signaling proteins that regulate protein synthesis, but the time course varies among tissues. Proj. 3 We conducted gene expression analysis on blood, liver, and fat tissues from mice fed a high or a low fat diet. We studied mice with a CD11c deficiency to see if CD11c was important to the inflammation that occurs in the fat tissues of the obese mice. Proj. 4 We examined the effects of nutritional or hormone changes on SIRT3 expression in cultured hepatocytes, the primary cells of the liver. We generated transgenic mice targeting the specific gene Grx3, that will be used as a genetic tool to delete the Grx3 gene in specific tissues. We conducted studies to determine the physiological role of GLP-2, a gut hormone, in the central nervous system in the control of blood glucose; we deleted GLP-2R in hypothalamic neurons and demonstrated that GLP-2R deletion in these neurons increases glucose production in the liver by decreasing insulin responsiveness, suggesting that brain GLP-2R activation is important for maintaining blood glucose levels. We have generated a new 5-HT2CR floxed mouse model. In parallel, we used mouse models with estrogen receptor-alpha (a receptor that is activated by the sex hormone estrogen) deleted in the central nervous system. Proj. 5 We studied if early postnatal over nutrition by suckling in small litters induces permanent increases in weight and fatness, relative to mice suckled in normal size control litters. We used a genome-wide method (MSAM) to screen for persistent changes in hypothalamic DNA methylation in these models, but no major differences were detected. We profiled DNA methylation across the genome to compare androgenetic hydatidiform, ovarian teratomas, and normal placentas. We studied the function of NLRP7 to confirm in various cell lines that this protein interacts with CTCF and YY1, two proteins important in the regulation of imprinting, as well as with NPM1, a protein that we found to bind to NRLP7. We performed gene expression profiling using RNA from liver and muscle of mice born to mothers fed a low-protein diet. We found many expression changes in liver at age 1 yr. We completed MSAM to compare methylation in human embryonic stem cells before and after induced differentiation and identified 3% of genomic regions that are targets for programmed methylation. We are developing a model to understand the signals that determine locus-specific DNA methylation in vivo.
1. The brain may be a target for energy balance and reproduction concerns. Estrogens act upon estrogen receptor-alpha (ERa) to regulate body weight and reproduction, but ERa expressing cells that are critical for these effects have not been identified. Researchers at the Children's Nutrition Research Center, Houston, TX, demonstrated that ERa in the brain is required to mediate estrogenic effects on the regulation of body weight and reproduction. These findings may provide rational targets for the development of new therapeutic interventions that may be used to treat and prevent obesity and infertility in women.
2. A nuclear-receptor-dependent phosphatidylcholine pathway with antidiabetic effects. Nuclear hormone receptors are important regulators of metabolism, and their activity is controlled by binding of hormones or other specific ligands. Loss of appropriate metabolic control occurs in obesity and diabetes. Researchers at the Children's Nutrition Research Center, in Houston, TX, have discovered a new ligand for the nuclear receptor LRH-1 (also known as NR5A2), that is an unusual but natural lipid species called dilauroyl phosphatidylcholine (DLPC). DLPC treatment of mice lowers liver fat and improves control of sugar metabolism in mouse diabetes models. These findings identify LRH-1 as a new metabolic regulator and suggest that DLPC may be useful in treating metabolic disorders. The antidiabetic effects of DLPC are currently being examined in a small clinical trial in obese humans.
3. GLP-2 receptor deficiency impairs glucose balance. Hyperglycemia is a common problem with diabetes, and is primarily attributed to glucose production. The brain can sense hormones and nutrients to control energy and glucose homeostasis but, the physiological significance of a particular brain GLP-2 receptor (GLP-2R) has not been defined. Researchers at the Children's Nutrition Research Center in Houston, TX, demonstrated that GLP-2R deficiency in brain neurons impairs glucose homeostasis by decreasing insulin sensitivity, which suggests that the brain GLP-2R plays an important role in the control of glucose homeostasis. GLP-2R signaling in the brain may be a potential target for future interventions for the treatment of diabetes and obesity.
4. A possible role for cohesins in the developmental origins of health and disease. Developmental exposure to adverse environments, such as poor maternal nutrition, has long-term effects on gene expression that influence overall adult health and susceptibility to disease. In Houston, TX, Children's Nutrition Research Center researchers have demonstrated that livers of adult mice that had been born to mothers fed a low protein diet show significant changes in expression of genes encoding a class of proteins called cohesins. Cohesins play a role in how DNA is organized in the nucleus and how certain controlling regions of DNA interact with the genes they control. This exciting new finding suggests a previously undiscovered mechanism by which early nutritional exposures can induce persistent changes in gene expression. These findings help scientists unravel the biological impact that poor nutrition early in life can have in adulthood.
5. Deletion of the ghrelin receptor "turns up the heat" to increase energy expenditure. Energy balance is determined by energy intake and energy expenditures. Non-shivering thermogenesis in brown fat plays a pivotal role in energy balance in rodents, and its significance has recently been recognized in adult humans. Thermogenic function is severely impaired in obese individuals. Children's Nutrition Research Center researchers found that ghrelin receptor ablation elevates thermogenesis in brown fat, and produces higher core body temperatures. This is the first evidence that grhelin signaling has a role in thermogenesis, suggesting that suppression of the ghrelin receptor may represent an attractive novel option for combating obesity and insulin resistance by "turning up the heat".
6. Circadian homeostasis is an independent factor for obesity prevention. Obesity and its related diseases are among the most profound public health problems today. Simplistic explanations such as over-consumption of food, poor diet choice, or lack of physical activities are likely inadequate to completely account for the prevalence of obesity in our world. Recent studies have revealed that circadian homeostasis of energy balance may be an important factor for body weight control, but an experimental demonstration of such hypothesis is lacking. Scientists at the Children's Nutrition Research Center in Houston, TX, have found that physical activities, feeding, and energy expenditure in mammals follow a circadian rhythm and that disruption of this rhythm alone could increase the risk of metabolic syndromes and cancers. Further study of the mechanisms of circadian homeostasis on body weight control will have the potential for a very high impact on the prevention and treatment of obesity and obesity-related diseases. This research is important, especially in the US, where nearly 20% of the workforce is on rotating shift schedules, and it is these individuals that are nearly 2X greater risk of developing metabolic syndromes and cancers.
7. Feeding premature infants intravenously affects the infants' health and ability to regulate blood sugar levels. More than half a million infants are born prematurely in the United States every year, and for very-low-birth-weight infants that are unable to handle normal feeding by mouth, intravenous feeding, also known as total parenteral nutrition (TPN), becomes vital for life. However, no study with human infants has yet delineated a possible role of TPN in insulin resistance. Scientists at the Children's Nutrition Research Center in Houston, TX, conducted studies that revealed piglets given continuous TPN for their first two weeks of life were less able to control their blood glucose levels (by 40% less) than their orally fed counterparts, who were fed individual meals of milk-based formula four times a day. These findings are important for the pediatric community as it documents poor blood glucose control in newborns fed intravenously and suggests possible lifetime consequences.
8. An antioxidant protein feels "heat". Global environmental temperature changes (global warming) threaten agriculture practice and food production, as well as human health. How cells feel "heat" and further adapt their metabolism and behaviors to the environmental changes is poorly understood. Scientists at the Children's Nutrition Research Center in Houston, TX, showed that a type of antioxidant protein, called AtGRXS17, helps protect plants from high temperature. These findings provide unique insights into the biological function of these proteins.
9. Characterization of three mouse SIRT3 enzyme isoforms. SIRT3 is an important protein modification enzyme (deacetylase) that regulates the function of many metabolic enzymes. It was recently found that three variants can be expressed from the mouse SIRT3 gene. Scientists at the Children's Nutrition Research Center in Houston, TX, characterized the tissue distribution of these three SIRT3 variants and examined the cellular localization and maturation of the three protein isoforms of mouse SIRT3. Since the human SIRT3 gene also has these same transcript variants, our finding sheds light on the possible functional difference of human SIRT3 isoforms. This is important since our finding helps scientists to understand if any SIRT3 isoform plays a role in the regulation of aging or age-related diseases.
Davis, T.A., Suryawan, A., Orellana, R.A., Fiorotto, M.L., Burrin, D.G. 2010. Amino acids and insulin are regulators of muscle protein synthesis in neonatal pigs. Animal. 4(11):1790-1796.