Metabolic activity in a non-model system: Leptin and lipolysis in bowhead (Balaena mysticetus) and beluga (Delphinapterus leucas) whales.

摘要

The discovery of leptin provided a long-anticipated feedback mechanism in vertebrates linking metabolic requirements with adipose deposits. Encoded by the obese (ob) gene and demonstrating a highly conserved primary amino acid sequence across vertebrates, the role of leptin in a plethora of interconnected systems is well documented. Effects of hibernation, migration and temporal influences and sex-specific variations are also well-known in mammals.;Migrating or hibernating species frequently require large seasonal changes in overall adipose stores. Temporal leptin resistance in these species is a natural adaptation; allowing them to overcome normal physiological effects of leptin, which result in a reduction in appetite and an increase in metabolic rate. In these instances, adipose stores are increased in preparation for seasonal energetic demands and serve as excellent examples of the allostatic model of leptin function in action. Overall adipose stores increase without an expected correlated increase in leptin titer and mRNA expression; possibly through modulation of leptin receptor isoforms or modifications to other downstream signaling processes.;Bowhead and beluga whales possess life histories which mimic that of other seasonally migrating mammals. In the study population, bi-annual migrations each occur between summering grounds in the Beaufort Sea and Bering Sea wintering grounds. Additionally, bowhead whales represent a physiological extreme in terms of adipose deposition.;Here, variations in leptin transcript expression and that of two associated genes (leptin receptor and leptin-receptor gene-related product) were examined to understand and detect seasonal and ontogenetic variation and assess the effects on cetacean physiology. Correlations to leptin protein titer were also assessed. Additionally, variation in expression of two lipolysis-associated genes adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) were examined and detected seasonal and ontogenetic differences in utilization of adipose deposits in these marine mammals.