Location: Children's Nutrition Research Center2013 Annual Report
1a. Objectives (from AD-416):
It has now been convincingly demonstrated by human epidemiological investigations that the origins of many of the major chronic diseases that are manifest in adult life have their origins during development. Additionally, molecular, cellular and animal studies have now shown conclusively that interference with, or alteration of, developmental pathways during critical windows of development can provide the pathophysiological basis for the events that take place later in adult life. Our research attempts to answer the following: 1) differentiate the effects of fetal versus postnatal maternal dietary protein restriction on satellite cell accretion and skeletal muscle mass; 2) determine if impaired catch-up growth upon nutritional rehabilitation is due to aberrant epigenetic mechanisms intrinsic to the satellite cell and/or an absence of the extracellular cues necessary to sufficiently accelerate satellite cell division; 3) develop novel techniques to study amino acid metabolism in conscious mouse models, with special emphasis on hepatic and enteral metabolism; 4)determine the role of urea cycle intermediates in maintaining nitric oxide and ureagenesis during different physiological and pathophysiological conditions; 5) determine gene expression in human lactating mammary epithelium; 6) characterize inbred mouse strains for lactation performance, gene expression, and weight gain among offspring in lean and obese animals, making use of a cross-fostering design where appropriate; 7) study the effect of nutrients on mammary gland development and function in mouse models; define the critical window for effects on mammary gland development and function; 8) elucidate the role of vitamin A in vascular development and hematopoiesis using mouse embryos, in vitro assays, and complementary techniques; and 9) identify target genes downstream of retinoic acid signaling that are required for blood and blood vessel development.
1b. Approach (from AD-416):
These research studies will use various techniques to accomplish the research to be undertaken. Establishing the critical window of development during which an inadequate nutrient supply permanently compromises the growth of the skeletal muscle and to understand the responsible mechanisms is of great importance. Research studies will focus on the satellite cell in animal models in order to understand how the nutrition of the fetus and infant has lifelong consequences for the health of the individual. Studies will take place on the role of amino acids in the urea cycle (crucial for nitric oxide synthesis), which is in demand for physiological (growth, pregnancy) and pathophysiological (trauma, sepsis) conditions. Lactation research will be conducted in mouse models to obtain an improved understanding of the genomic factors regulating mammary gland function that is central to providing therapeutic interventions that can aid women to establish and maintain a productive lactation. Since the abnormal formation of blood and blood vessels in adults is central to the progression of prevalent pathologies, including atherosclerosis, tumor angiogenesis, and anemia, researchers will develop an understanding of the cellular and molecular regulation of blood and blood vessel formation. Scientists will study retinoids in their role in the formation and maturation of blood vessels, as well as hematopoiesis, during embryonic development. Additionally, CNRC researchers will investigate, on a cellular and molecular level, the role of retinoid signaling in the regulation of these processes.
3. Progress Report:
Significant research progress was accomplished during the year. To review the progress, please refer to project 6250-51000-054-10S (Project 1), 6250-51000-054-20S (Project 2), and 6250-51000-054-30S (Project 3).
1. Hormone and gene regulation of human lactation. Little is known about the gene regulation of milk production in humans. A number of women struggle to successfully breastfeed their infants; of specific note are those who are obese, teenage mothers, and mothers with premature infants. Using messenger RNA (molecular signal that causes the expression of genes) found in human milk, scientists at the Children's Nutrition Research Center in Houston, Texas, have been able to determine some of the factors that affect milk production and have traced the changes in gene expression over the first 42 days of lactation in normal women, and are now applying that knowledge to obese women. The primary trigger of the initiation of lactation in humans is unknown, but one of the factors is the withdrawal of progesterone (a hormone made in the placenta during pregnancy) with the removal of the placenta as a result of the birth process. As a result of these studies, therapeutic approaches may be available in the future to increase the success rates of breastfeeding.
2. Identifying genes regulated by the Hedgehog (Hh) pathway during brown fat development. Because of its unique ability to burn calories to generate heat, brown fat could potentially be utilized to counteract weight gain. Brown fat is generated during development by an array of genes whose identities are largely unknown. In Houston, Texas, Children's Nutrition Research Center scientists have performed studies regarding the link between Hh signaling and brown fat formation and have identified a group of genes whose expression is regulated by the Hh pathway during brown fat development. Understanding the roles of these novel genes in the regulation of brown fat development will significantly advance our knowledge of adipose tissue biology and may provide new therapeutic targets for counteracting obesity.
3. Lactation defects in obese mice are linked to increased inflammation. Maternal obesity is known to negatively affect lactation. By comparing mammary tissue among lean and obese mice during early lactation scientists at the Children's Nutrition Research Center in Houston, Texas, have found that defects in lactation in response to maternal obesity are associated with elevated mammary tissue macrophages, increased mammary cell apoptosis, and increased phosphorylation of the transcriptional regulator STAT3. We have concluded that the mineralocorticoid receptor is abnormally activated in mammary tissue of obese females during early lactation. This data is significant because if provides the identity of pathways that could be targeted as a means to remedy the negative affects of maternal obesity on lactation.
4. Mapping of genes linked to mammary ductal development. The extent of genetic variation in mammary ductal development is unknown. Analysis of mammary ductal development among strains of mouse models has revealed greater variation in mammary ductal patterning than previously known. Using this data in conjunction with single nucleotide polymorphism (SNP) data, researchers at the Children's Nutrition Research Center in Houston, Texas, have identified several regions in the mouse genome that have many of the same SNPs associated with specific traits. The genes underlying these regions have been linked to breast cancer in humans or anomalies in mammary gland development. These results support the conclusion that variations in mammary ductal development can be attributable to specific regions within the genome, which could play a role in breast cancer and could possibly influence mammary gland function during lactation.
Yazndani, P., Lin, Y., Raman, V., Haymond, M.W. 2012. A single sample GnRHa stimulation test in the diagnosis of precocious puberty. International Journal of Pediatric Endocrinology. 23:1-6.