Location:2012 Annual Report
1a. Objectives (from AD-416):
1. Establish benchmark transcriptome profiles induced by uterine stress during gestation that are predictive of altered physiological mechanisms in key organs critical to the piglet immune and metabolic stress responses. 2. Identify critical gene(s), gene products, and their mechanism of action in the stress response of piglets associated with morbidity, growth rate, and body composition. 2.A. Identify key secretory proteins that are regulated by stress in the preweaning pig. 2.B. Identify key secretory proteins produced by adipose tissue that are regulated by stress in the preweaning pig. 3. Develop comprehensive in vitro models to analyze the mechanistic role of select, important developmental or metabolic factors in mediating the organism’s response to stresses via functional genomic approaches. 3.A. Determine the physiological mechanisms of key stress-regulatory proteins that regulate nutrient partitioning in the liver and adipose tissue. 3.B. Characterize the role of trophectoderm-derived estrogen as a modulator of “programmed” set points that determines the development potential of the peri-implantation embryo. 4. Define the repertoire of biomarkers that may be predictive of neonatal growth potential by using models of induced metabolic stress.
1b. Approach (from AD-416):
High preweaning mortality or impaired stress-related growth of live-born piglets continue to be major problems that negatively impact commercial swine production. Piglets exhibiting decreased vitality are at greater risk of morbidity or death and a decreased growth rate extending the farrow-to-market time, which results in increased producer costs. Considering embryo development as a continuum, it is plausible that abnormal piglet development and loss through adulthood is a consequence of aberrant embryonic/uterine development. This research will identify physiological mechanisms modulating piglet stress responses to pinpoint targets for interventions to improve “at risk” piglet survival. The research addresses three elemental issues 1) elucidation of the relationship between developmental perturbations and etiology of abnormal postnatal stress responses, 2) paucity of predictive screening tools for “at risk” neonates, and 3) lack of interventions to ameliorate postnatal development of “at risk” piglets. The impact of the uterine milieu on alterations of key physiological mechanisms that modulate stress response in metabolic or immune organs will be evaluated by comparative transcriptomic analysis between induced intrauterine growth retardation (IUGR), i.e. runting, and control concepti. To identify postnatal stress responses that are disrupted and persist ex utero as a consequence of in utero growth retardation or parturition complications and detect compensatory mechanisms, the gene expression of key metabolic and immune tissues from growth retarded piglets, (induced IUGR or spontaneous IUGR) and piglets exhibiting decreased vitality will be assessed by in-depth proteomic or transcriptomic analyses throughout the preweaning period. Functional analyses utilizing in vitro model systems and technologies, such as RNAi, will evaluate the mechanistic role of specific stress-related factors/pathways that are identified in metabolically important tissues. The relevance of putative stress-related factors/pathways will be assessed in vivo, employing distinct models of induced metabolic stress. The knowledge acquired will enable 1) the discovery of new biomarkers indicative of metabolic or immune stress response, 2) the identification physiological mechanisms/factors that can be targeted to develop new improved interventions that decrease mortality and days to market of “at risk” piglets and 3) the establishment of public “systems biology” database for specific gestational and environmental stresses.
3. Progress Report:
Progress was made on all objectives to be addressed in FY12. For Objective 1, a study was completed to examine the expression of 18 genes in specialized structures of placental tissue (areolae) that are involved in the uptake of nutrients and other factors from the mother’s uterus; areolae gene expression was compared to that of whole placenta and differences were identified. Experiments performed for Objective 2 demonstrated that metabolic stress specifically increases interleukin 6 (IL6) expression by fat cells and not by other cells in fat tissue from neonatal pigs. Neonatal fat samples were shown to release IL6, indicating that IL6 is secreted by fat tissue. Lastly, serum IL6 concentrations were lower in slow growing, runt pigs than in their larger littermates, which parallels the smaller amounts of fat present in these slow growing pigs. For Objective 3, a unique form of transcription factor kappa B was observed in neonatal pig liver cells treated with tumor necrosis factor (TNF), a cytokine associated with cellular stress response. The transcription factor was purified, concentrated and identified. This factor was specifically activated by TNF, helping to define the intracellular pathways involved in metabolic signaling that are activated during stress in neonates. Also, TNF was shown to induce a very specific cascade of cytokine expression within neonatal pig fat. However, none of the expressed cytokines altered neonatal pig fat metabolism. Thus, these TNF stimulated cytokines must affect peripheral tissues other than fat. To address Objective 4, the proposed animal models were replaced due to development of a model with direct relevance to the swine industry; i.e., slow growing piglets cost the industry $100 million per year because they are not identified until after weaning. Precise monitoring of piglet growth identified that the change in growth rate occurs between 3 and 7 days of age. Therefore, intervention should occur prior to 7 days of age to limit the decline in preweaning growth performance. Quantification of the relative value of acid glycoprotein (AGP) as a prediction tool for pig performance was begun with the measurement of serum alpha 1 AGP in these monitored litters. Blood samples were collected at day 1 of age from several litters and piglet growth was monitored until weaning. Piglets born at a normal body weight, but which then experienced a drop in growth rate, were identified. Retroactive analysis of day 1 serum AGP concentrations predicted identification of the slow growing pigs with 75% accuracy. Since blood samples were collected prior to the decline in growth rate, AGP may function as a prediction tool for growth performance in pigs. This is the final report for this project. Key findings of this project were: 1) development and characterization of models for impaired prenatal and neonatal growth rate in swine; 2) identification of molecular markers for placenta, liver, skeletal muscle and fat that correlate with prenatal or postnatal piglet growth; 3) identification of AGP as a potential serum biomarker for predicting piglet growth rate.
1. Characterization of alpha 1- acid glycoprotein (AGP) as a biomarker for impaired growth in suckling pigs. Investigators at ARS, Beltsville, MD have previously indicated that there is an overall relationship between circulating levels of AGP and growth rate in the suckling pig. In this study, piglets born with average and similar birth weight, but with divergent growth rates were identified at weaning. The levels of AGP in blood collected at birth were significantly higher in the slower growing piglets. Current studies are being conducted to determine the reliability of predicting the slower growing piglets from each litter by using blood levels of AGP. Reliable and early prediction of poor growth will allow producers to identify these pigs shortly after birth and will give them an opportunity to apply interventional measures to decrease growth variability and maximize meat production and profitability.
2. Placental gene expression highlights changes factors that can influence placental function with the onset of intrauterine growth retardation (IUGR). In piglets, IUGR is coincident with diminished growth of the IUGR fetus and placenta early in gestation and, their subsequent high mortality contributes significantly to the ~ $1.6 billion neonatal loss in the swine industry. Development of the placental is key for the provision of nutrients and the production of hormones during gestation but information on alterations in porcine placental structure or function with the onset of IUGR is limited. Scientists at ARS examined the RNA expression of genes important for placental development, and/or altered with IUGR in other species at four significant fetal maturation time points. Overall, findings suggested that the major factor influencing the expression of genes in the placenta was age, not IUGR, suggesting the IUGR animal may just be less mature. However, genes whose expression was impacted by IUGR are known to regulate the function of specific placental cells, blood vessel maturation, cell growth and estrogen synthesis. These are all important mechanisms that when disrupted could influence fetal growth negatively, and thus provide targets to examine further for their role in the IUGR phenotype.
Mitchell, A.D., Ramsay, T.G., Scholz, A.M. 2012. Measurement of changes in body composition of piglets from birth to 4 kg using quantitative magnetic resonance (QMR). Archives of Animal Breeding. 55:64-71.