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Evaluation of White Blood Cell DNA Methylation as a Tool to Predict DNA Methylation of the Adrenal Axis in Prenatally Stressed, Mature Brahman Cows
This dissertation project evaluated whether methylation of DNA of peripheral white blood cells (WBC) is predictive of methylation of DNA in components of the hypothalamic-pituitary-adrenal (HPA) axis of mature Brahman cows; and if so, to what extent. This question was assessed by use of DNA extracted from the WBC, paraventricular nucleus of the hypothalamus, anterior pituitary gland, adrenal cortex, and adrenal medulla of 5-year-old Brahman cows derived from dams that served as a control group or from dams that experienced prenatal transportation stress (PNS). The present study sought to determine if stress endured prenatally would result in long term DNA methylation changes to HPA-axis tissues, and if those changes would be reflected in WBC. A group of 5-year-old Brahman cows having been subjected to prenatal transportation stress (n = 6) were used against a control group of 5-year-old Brahman cows (n = 8) that were not exposed to the same stressor prenatally. Global methylation analyses of HPA-axis tissues to WBC, as well as tissue-to-tissue analyses were conducted using EdgeR software. Results showed tissue specific methylation patterns among the HPA-axis tissues that were not well reflected by WBC. The adrenal cortex and adrenal medulla showed consistency with one another, while the anterior pituitary appeared to be the least affected tissue, with the smallest differences in both control and PNS groups across all comparisons to WBC and other tissues. Otherwise, patterns of methylation were inconsistent when tissues were compared against each other. It is likely the consequences of prenatal stress in mature Brahman cows does not manifest in a global nature. In order to determine consistency between methylation patterns of a tissue and WBC, a change from control to PNS must be apparent and measurable, and to where the patterns of both tissue and WBC correspond in a way that reflects that difference. No such pattern consistency was observed between tissue and WBC, however, a global shift between control PNS was also not observed. Polar methylation relationships were explored between the control and prenatally stressed groups where LogFC values reflected inverted ratios of differential methylation between HPA-axis tissues and WBC. Genes with differentially methylated CpG sites in the promoter region were targeted and a total of 668 sites were identified as having an inverted ratio of HPA-axis tissue methylation relative to WBC in the control group compared to the prenatally stressed group. Genes such as FLI1, TINF2, MRE11, and BCL2L11 were identified as having multiple differentially methylated sites in their promoter region. While these results do not support the use of WBC for global methylation prediction of DNA in specific neuroendocrine components of the adrenal system in mature Brahman cows, they do propose an alternative perspective for further assessment on how to best characterize the use of WBC as a diagnostic biomarker. The electronic version of this dissertation is accessible from https://hdl.handle.net/1969.1/198805
Doctor of Philosophy Texas A&M University 2022 https://hdl.handle.net/1969.1/198805