Research Spotlight: Studying "Obese" Whales to Understand Human Obesity
Expression of leptin pathways in whales
Leptin is a 16kDa peptide hormone secreted by adipose (fat) cells and encoded by the obese (ob) gene in vertebrates. Involved in many physiological pathways, leptin is most commonly associated with regulation of body mass and food intake, where the presence of the protein acts to decrease appetite and increase metabolic rate. Migrating and hibernating animals are able to temporarily overcome responses to leptin in order to build adipose stores, but questions exist about how some organisms chronically maintain large fat reserves in the presence of leptin signaling. Cetaceans and other arctic mammals express large adipose stores, sometimes called blubber, which are maintained throughout their lifetime. To explore how cetaceans and these maintain their fat reserves, investigations of the molecular evolution of the leptin receptor locus and the location and extent of expression of leptin message and protein in arctic mammalian tissues are being performed.
Arctic mammals have a diverse evolutionary history with polar bears being the most recently adapted (<500,000 years) to extreme polar environments, the Pinnipeds (seals and walruses) likely originated 5 to 15 million years ago and the cetaceans diversifying at least 25 million years ago. Although specific adaptations in each of these lineages to arctic environments isn’t well know, the likely significant differences in the timing of their adaptive radiations presents an opportunity to examine how these diverse lineages have adapted their fat regulating pathways to this unique environment. Do they all express large quantities of leptin or have different lineages changed their mode of expression of the leptin hormone? If they all produce large amounts of leptin how then do these mammals maintain and regulate their large fat reserves? Is there a difference in the location and expression of leptin receptor proteins between these different lineages of mammals? These are all questions that must first be addressed by accurately measuring when, where and how much leptin and its receptor proteins are expressed in these mammals.
Broader impacts to society:
Understanding how leptin functions in chronically “obese” mammal species, such as cetaceansallows for potential inferences to be drawn about the diversity or lack of diversity of leptins role in the regulation of fat reserves in mammals and in humans in particular. Migrating or hibernating species accumulate large fat reserves temporarily for fuel, but whales maintain their blubber layer chronically with changes in sex and season, possibly for insulation. Continual maintenance of blubber may inform how we view chronic obesity in humans. In addition to its scientific merit, this study will produce an assay that would allow veterinarians working with captive whales or monitoring wild populations of bears and seals to monitor fat stores, reproductive potential and overall health of these animals. The study will also provide clues about how arctic mammals whales may cope with the impacts of global warming, such as long-term environmental changes and alterations in the supply and distribution of prey species.