Prenatal transportation stress alters genome-wide DNA methylation in suckling Brahman bull calves

Authors: LITTLEJOHN, BRITTNI - Texas A&M Agrilife; PRICE, DEBORAH - Texas A&M Agrilife; NEUENDORFF, DON - Texas A&M Agrilife; Carroll, Jeffery - Jeff Carroll; VANN, RHONDA - Mississippi State University; RIGGS, PENNY - Texas A&M University; RILEY, DAVID - Texas A&M University; LONG, CHARLES - Texas A&M Agrilife; WELSH, THOMAS - Texas A&M Agrilife; RANDEL, RONALD - Texas A&M Agrilife

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2018
Publication Date: 8/28/2018
Citation: Littlejohn, B.P., Price, D.M., Neuendorff, D.A., Carroll, J.A., Vann, R.C., Riggs, P.K., Riley, D.G., Long, C.R., Welsh, T.H., Randel, R.D. 2018. Prenatal transportation stress alters genome-wide DNA methylation in suckling Brahman bull calves. Journal of Animal Science. 96(12):5075-5099. https://doi.org/10.1093/jas/sky350.
DOI: https://doi.org/10.1093/jas/sky350

Interpretive Summary: Elevated maternal cortisol may alter the fetal environment, thereby altering fetal development. Fetal programming is defined as the fetal response to a specific insult during a critical period that alters the trajectory of development. Alterations in the fetal environment program the fetal hypothalamic-pituitary-adrenal axis to prepare the neonate to survive in a stressful postnatal environment. Altered prenatal environment affects postnatal outcomes, in part, by epigenetic modifications, such as DNA methylation. DNA methylation is a covalent modification in which a methyl group is added to the carbon 5 position of a cytosine nucleotide. This chemical modification of DNA plays a crucial role in regulating unique functions between different cell types, despite each cell type having an identical genome. Therefore, a collaborative study was conducted with scientists from Texas A&M University, Mississippi State University, and the USDA-ARS Livestock Issues Research Unit to determine if exposing gestating calves to a prenatal transportation event would affect the postnatal genome-wide DNA methylation in Brahman calves. To test this hypotheses, an experiment was conducted that evaluated the effects of a repeated transportation event during five time periods of gestation. Specifically, ninety-six pregnant Brahman cows were assigned to either a transportation group or control group. The transported cows were transported for two hours at 60, 80, 100, 120, and 140 ± 5 days of gestation. The control cows were maintained in the same manner as stressed cows with the exception of being transported. Results from this study demonstrated that prenatal transportation stress in cattle altered genome-wide DNA methylation profiles, which were predicted to alter known pathways related to behavior, stress response, neural function, immune function, metabolism, reproduction, cell signaling, and other biological processes. To our knowledge, these data are the first reports of a genome-wide assessment of DNA methylation in the prenatally stressed calves. This information will be of specific interest to scientists working in the field of epigenetics, and increase the overall scientific knowledge base with regard to understanding of the impact of prenatal stress on economically and biologically relevant phenotypic traits in cattle.

Technical Abstract: The objective of this study was to assess the influence of prenatal stress (PNS) on innate immune response The objective of this experiment was to identify genome-wide differential methylation of DNA in young prenatally stressed (PNS) bull calves. Mature Brahman cows (n = 48) were transported for 2-h periods at 60 ± 5, 80 ± 5, 100 ± 5, 120 ± 5, and 140 ± 5 d of gestation or maintained as non-transported Controls (n = 48). Methylation of DNA from white blood cells from a subset of 28-d-old intact male offspring (n = 7 PNS; n = 7 Control) was assessed via reduced representation bisulfite sequencing. Compared with Control calves, PNS samples contained 16,128, 226, and 391 differentially methylated CG, CHG, and CHH sites, respectively (C = cytosine; G = guanine; H = either adenine, thymine, or cytosine). Of the CG sites, 7,407 were hypermethylated (at least 10% more methylated than Controls; P = 0.05) and 8,721 were hypomethylated (at least 10% less methylated than Controls; P = 0.05). Increased DNA methylation in gene promoter regions typically results in decreased transcriptional activity of the region. Therefore, differentially methylated CG sites located within promoter regions (n = 1,205) were used to predict (using Ingenuity Pathway Analysis software) alterations to canonical pathways in PNS compared with Control bull calves. In PNS bull calves, 113 pathways were altered (P = 0.05) compared to Controls. Among these were pathways related to behavior, stress response, immune function, metabolism, reproduction, and cell signaling. Predicted alterations in behavior, stress response, and reproductive endocrinology are supported by previously observed phenotypic differences in the larger population of PNS and Control calves from which bulls in this study were derived (Littlejohn et al., 2016; Littlejohn et al., 2017). Genome-wide differential DNA methylation and predicted alterations to pathways in PNS compared with Control bull alves suggest epigenetic programming of biological systems in utero.