Date of Award
Master of Science (M.S.)
Jane I. Khudyakov
First Committee Member
Second Committee Member
Increasing anthropogenic disturbance in marine ecosystems such as fishing, oil-drilling, and noise pollution can have detrimental effects on the reproduction and survival of apex predators such as marine mammals. Stress activates the hypothalamic-pituitary-adrenal (HPA) axis, resulting in increased circulating glucocorticoid (GCs) hormones, which alter expression of target genes encoding metabolic enzymes and other mediators of stress. Prolonged HPA axis stimulation may increase catabolism of nutrient stores and suppress immune and reproductive functions, impacting the fitness of marine mammals. GCs measurements are used to identify wild animals experiencing stress. However, these measurements may not be sensitive enough to distinguish between an acutely and a chronically stressed individuals. In this study, we present a new approach of assessing stress states in marine mammals, by measuring expression levels of gene markers in blubber. We previously characterized transcriptional and metabolic profiles and identified genes and metabolites that were differentially expressed in response to single and repeated adrenocorticotropic hormone (ACTH) administration in juvenile northern elephant seals. We then measured expression of these target genes in blubber tissue collected from juvenile northern elephant seals in their natural baseline stress states (n=30), and correlated their gene expression values with cortisol, aldosterone, total triiodothyronine (tT3), reverse triiodothyronine (rT3), and triglyceride levels, and body condition index. We found that blubber genes that were upregulated in response to repeated ACTH administration in the previous study were positively correlated with cortisol and inversely correlated with tT3 in the baseline sample set. These markers included genes that encode a lipid particle protein (PLIN1), an adipogenesis promoting transcription factor (DKK1), an oxidative stress enzyme (GPX3), and a lipid metabolism enzyme (AZGP1). Blubber genes differentially expressed in response to acute ACTH administration in the previous study included an adipokine (ADIPOQ) and a ketogenesis enzyme (HMGCS2), which were upregulated, and an adipogenesis inhibitor, TGFBI, which was downregulated. ADIPOQ and HMGCS2 were positively correlated with cortisol and negatively correlated with tT3 levels, while TGFBI was positively correlated with tT3 and body condition index, and negatively correlated with rT3 in the baseline sample set. These results provide insights into the molecular mediators of the physiological stress response and provide markers that can be used as a part of a potential diagnostic panel for differentiating between acute and prolonged stress states in marine mammals.
Pujade, Laura. (2019). Development of a biomarker panel for identifying stressed marine mammals. University of the Pacific, Thesis. https://scholarlycommons.pacific.edu/uop_etds/3587
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