Location: Children's Nutrition Research Center
2014 Annual Report
Objectives
The goal of this research is to identify strategies to optimize the nutrition and health of infants and their development. CNRC researchers will: 1) investigate the impact of perinatal nutrition in the model system of premature piglets on the prevention of parenteral nutrition-associated liver disease (PNALD) and necrotizing enterocolitis (NEC); 2) define the role of liver receptor homolog-1 (LRH-1) as a factor in hepatic lipotropic responses, including the influence of methionine/choline deficient diets (MCD); 3) characterize the effect of the loss of hepatic LRH-1 in the lipotropic response to methyl pool supplementation in the standard mouse model of diet induced obesity; 4) determine the influence of leucine supplementation in stimulating protein synthesis, enhancing lean growth, and reducing protein degradation in healthy neonatal piglets and during catabolic conditions such as sepsis; 5) determine whether the deficit in lean deposition incurred with continuous as compared to intermittent bolus feeding during the neonatal period can be prevented by leucine supplementation or recuperated by initiation of intermittent bolus feeding; 6) determine whether citrulline plasma concentration is an early indicator for gut immaturity and gut dysfunction in a piglet model of prematurity; 7) determine if arginine and citrulline supplementation are able to reduce the incidence of necrotizing enterocolitis; 8) identify the cellular signaling networks that modify leptin-signal transducer and activator of transcription 3 (STAT3) signaling and potentially contribute to leptin resistance; 9) determine, using genetically engineered mouse models, the role of a cellular leptin signaling modifier in high fat diet-induced leptin resistance and subsequent alterations in energy and glucose homeostasis, and adiposity; 10) study the mechanism of circadian dysfunction-induced leptin resistance and the role of leptin resistance in obesity development; 11) determine the contributions of alpha Beta and yoT cells to inflammation in skeletal muscle; 12) determine the mechanisms leading to early anti-inflammatory macrophage polarization in mesenteric adipose tissue and the peritoneal cavity of C57BL/6J mice; 13) define how tissue healing is dysregulated in Western-style diet-induced obesity; 14) determine if Matrix Metalloproteinase 12 influences the development of insulin resistance and tissue inflammation in the context of high fat, Western-type diet-induced obesity; 15) determine if Matrix Metalloproteinase 12 influences white adipose tissue extracellular matrix remodeling under conditions of Western-type diet feeding.
Approach
The research will be accomplished using a variety of models and scientific tools to simulate the human newborn and/or child. Researchers will perform tissue transcriptomic profiling to identify novel genes, gene networks and metabolic pathways that are differentially affected by two lipid emulsions. We will also quantify expression of targeted genes involved in hepatic bile acid metabolism. In mouse models, physiologic studies will be performed that will include analysis of serum and hepatic levels of trigylcerides, free fatty acids, total cholesterol and total phosphatidylcholine. Using porcine models, we will perform protein synthesis experiments in leucine-infused endotoxemic pigs. Additionally we will use porcine models to determine if arginine and citrulline supplementation reduces the incidence of necrotizing enterocolitis. CNRC researchers will also employ an ex vivo model to determine if STAT3 signaling acts as a signaling hub for distinct signaling pathways mediating cellular leptin resistance. Complicated studies will be performed to study the mechanism of reciprocal interactions between the central circadian clock and hypothalamic arcuate nucleus in maintaining homeostasis of leptin signaling. Researchers will also study the role of circadian dysfunction of sympathetic nervous system (SNS) signaling in the development of leptin resistance and diet-induced obesity. And finally scientists will use a murine model (that develops chronic inflammation similar to that observed in obese humans) of diet-induced obesity and will use short- and long-term feeding techniques for the localization and phenotypic characterization of lymphocytes in skeletal muscle, and techniques for depletion of lymphocyte subsets.
Progress Report
Project 1. We have initiated studies in Objective 1B and expect to have the animal experiments done by the end of 2014. We have submitted samples for microbiome and metabolome analysis and expect to have these results in the spring of 2015. We have begun laboratory analysis of tissue gene expression profiling and histopathology in all three treatment groups. Our preliminary results are consistent with the hypothesis that lactose- vs. corn syrup solid (CSS)-based formula protects against necrotizing enterocolitis (NEC) in preterm piglets. The NEC incidences in the lactose, lactose-CSS, and CSS groups were 12%, 40% and 35%. We are expecting to have sufficient results for submission of an abstract to present at national scientific meetings in spring 2015. Our goal for studies in Objective 2 is to use wild type mice and liver specific LRH-1 knockouts to further define the role of LRH-1 in both beneficial and deleterious effects of the liver to nutritional stresses and signals. We have initiated the treatments and anticipate successful completion of these studies later in the current year. Studies in Objective 4A are determining whether supplementation of the diet with the amino acid leucine can stimulate the synthesis of protein in skeletal muscle, leading to an increase in lean body mass in neonates. Our previous studies, using the neonatal pig as an animal model, have shown that leucine acts as a nutrient signal to stimulate protein synthesis in muscle of the neonate. This increase in protein synthesis occurs when leucine is supplemented either enterally in the formula provided orally or when leucine is supplemented parenterally by intravenous infusion. However, all previous leucine supplementation studies were performed in the short-term, i.e., 24 hours or less. We are currently conducting long-term studies to examine the effectiveness of leucine supplementation to enhance protein synthesis chronically and whether this will lead to an increase in lean gain. Studies to meet Objectives 6 and 7 are scheduled to start in September 2014.
Project 2. We have recently initiated studies to investigate the molecular mechanisms of cellular leptin resistance and the role of the circadian clock in the prevention of obesity. The current experiments are focused on generating mouse models and establishing essential techniques for the experiments proposed.
Project 3. During inflammation, white blood cells migrate into inflamed tissues. There are many different types of white blood cells and they each produce and release many different substances, some of which promote inflammation while others inhibit. We are studying one substance called Matrix Metalloproteinase 12 (MMP12) that is released by one type of white blood cell found in fat tissues during the development of obesity. Our recent studies show that when mice that are deficient in MMP12 are fed a high fat, high calorie diet they become obese at the same rate as normal mice, but they show less inflammation. MMP12 is an enzyme, and studying how this enzyme promotes inflammation in animals on a high fat diet is an important direction for this research.
Accomplishments
