👤 Jane I Khudyakov

Animals in nature potentially experience multiple stressors, and those of anthropogenic origin are likely to be repeated or chronic. However, stress hormone levels are highly context-dependent and are not consistent predictors of chronic stress in wildlife. Profiling the downstream consequences of repeated stress responses, such as changes in metabolism or gene expression, may be more informative for predicting their individual-level health consequences and population-level impacts, which are key objectives for wildlife conservation. We previously found that in free-ranging juvenile elephant seals, the blubber transcriptome and proteome, but not cortisol levels, could distinguish between responses to single versus repeated stress axis stimulation. However, the blubber proteome response to stress was limited and mainly involved extra-cellular matrix proteins. In this study, we examined the plasma proteome response of four of the same animals to the repeated stress experiment, since multiple organs secrete proteins into the circulation, providing a readout of their activity and integration. We isolated plasma proteins, identified and quantified them using liquid chromatography and tandem mass spectrometry (LC-MS/MS) and compared their abundance between sampling times. We identified >200 proteins in plasma, of which 42 were altered in abundance, revealing complex protein dynamics in response to repeated stress challenges. These changes were delayed but sustained, suggesting that the plasma proteome may reflect longer term integration of multi-organ responses to recent, rather than immediate, challenges. Differentially abundant proteins included components of the osmoregulatory system, acute phase and complement proteins, organokines, apolipoproteins and hormone transport proteins, which coordinate physiological processes with significant implications for marine mammal health and may explain several aspects of marine mammal stress physiology, such as insulin resistance and high aldosterone levels. We identified several potentially novel biomarkers, such as AGT, HPX, TTR and APOA4, that may be useful for detecting recent and repeated stress exposure in marine mammals. Show less

Unlike many animals that reduce activity during fasting, northern elephant seals (NES) undergo prolonged fasting during energy-intensive life-history stages such as reproduction and molting, fueling fasting energy needs by mobilizing fat stores accrued during foraging. NES display several unique metabolic features such as high fasting metabolic rates, elevated blood lipid and high-density lipoprotein (HDL) cholesterol levels, efficient protein sparing and resistance to oxidative stress during fasting. However, the cellular mechanisms that regulate these adaptations are still not fully understood. To examine how metabolic coordination is achieved during prolonged fasting, we profiled changes in blubber, skeletal muscle and plasma proteomes of adult female NES over a 5 week fast associated with molting. We found that while blubber and muscle proteomes were remarkably stable over fasting, over 50 proteins changed in abundance in plasma, including those associated with lipid storage, mobilization, oxidation and transport. Apolipoproteins dominated the blubber, plasma and muscle proteome responses to fasting. APOA4, APOE and APOC3, which are associated with lipogenesis and triglyceride accumulation, decreased, while APOA1, APOA2 and APOM, which are associated with lipid mobilization and HDL function, increased over fasting. Our findings suggest that changes in apolipoprotein composition may underlie the maintenance of high HDL levels and, together with adipokines and hepatokines that facilitate lipid catabolism, may mediate the metabolic transitions between feeding and fasting in NES. Many of these proteins have not been previously studied in this species and provide intriguing hypotheses about metabolic regulation during prolonged fasting in mammals. Show less