Blubber transcriptome response to acute stress axis activation involves transient changes in adipogenesis and lipolysis in a fasting-adapted marine mammal

Abstract

Stress can compromise an animal’s ability to conserve metabolic stores and participate in energy-demanding activities that are critical for fitness. Understanding how wild animals, especially those already experiencing physiological extremes (e.g. fasting), regulate stress responses is critical for evaluating the impacts of anthropogenic disturbance on physiology and fitness, key challenges for conservation. However, studies of stress in wildlife are often limited to baseline endocrine measurements and few have investigated stress effects in fasting-adapted species. We examined downstream molecular consequences of hypothalamic-pituitary-adrenal (HPA) axis activation by exogenous adrenocorticotropic hormone (ACTH) in blubber of northern elephant seals due to the ease of blubber sampling and its key role in metabolic regulation in marine mammals. We report the first phocid blubber transcriptome produced by RNAseq, containing over 140,000 annotated transcripts, including metabolic and adipocytokine genes of interest. The acute response of blubber to stress axis activation, measured 2 hours after ACTH administration, involved highly specific, transient (lasting <24 hours) induction of gene networks that promote lipolysis and adipogenesis in mammalian adipocytes. Differentially expressed genes included key adipogenesis factors which can be used as blubber-specific markers of acute stress in marine mammals of concern for which sampling of other tissues is not possible.

Response to capture stress involves multiple corticosteroids and is associated with serum thyroid hormone concentrations in Guadalupe fur seals (Arctocephalus philippii townsendi)

“…Some of these effects enhance and mediate the stress response while others limit the stress response and enhance the recovery from it ( e.g ., Khudyakov et al . ). These acute responses can include interactions with other endocrine hormone axes (Ensminger et al .…”

Function and evolution of specialized endogenous lipids in toothed whales

“…Although the prospects of obtaining exceptionally fresh tissue (e.g. Khudyakov et al, 2017) to determine messenger RNA levels are slim, it might be possible to use proteomics to determine which enzymes are being synthesized in different tissues, in different regions of the same tissue, and at different life-history stages. It would also be interesting to compare the genes of toothed whales with those of baleen whales, to identify which aspects of metabolism are altered for echolocation.…”

New Technologies for Monitoring Marine Mammal Health

“…An example comes from a study of the cellular responses to hypothalamic-pituitary-adrenal axis stimulation by measuring corticosteroid hormones, metabolites, and muscle gene expression before, during, and following administration of exogenous adrenocorticotropic hormone (ACTH); results suggests a compensatory, tissue-sparing mechanism used to maintain cortisol and aldosterone sensitivity while avoiding deleterious long-term consequences of stress (Khudyakov et al, 2015b). Reference sequences specific to elephant seals were also obtained from the blubber tissue and used to profile the transcriptomic response to hypothalamic-pituitary-adrenal stress axis activation and to identify tissue-specific molecular markers of stress in the pinniped fasting-adapted species (Khudyakov et al, 2017).…”