| Summary: | Marine mammals such as elephant seals (Mirounga angustirostris) are unique in their ability to fast from food for months while undergoing energetically demanding processes such as molting and reproduction on land. To gain insights into energy provisioning during fasting, we examined protein expression in the energy rich inner blubber tissue layer collected from adult female elephant seals at the beginning and end of their monthlong molting fast. We developed tissue lysis and protein extraction methods for marine mammal blubber shotgun proteomics using phenolchloroform. Changes in protein abundance and composition in blubber during fasting were analyzed using isobaric labeling and orbitrap mass spectrometry. We were able to identify and annotate hundreds of proteins using a blubber transcriptome as reference. These included proteins involved in hormone signalling pathways, such as glucagon, estrogen, insulin, and aldosterone, carbohydrate and fatty acid metabolism, protein digestion, absorption, and processing, biosynthesis of amino acids, immune signaling, and many others. This work lends insights into metabolic homeostasis during fasting in adipose tissue, validates previous transcriptome analyses, and yields protein sequence information for further targeted assays.
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