Proceedings of The Physiological Society

Obesity (2014) Proc Physiol Soc 32, PC044

Poster Communications

Fat but fit: Regulation of adipokine production and adipose tissue function in an animal model of obesity and extreme weight change

K. A. Bennett1, J. Hughes1, R. Samuel1, R. Coppock1, A. J. Hall2

1. MBERC, Plymouth University, Plymouth, Devon, United Kingdom. 2. SMRU, University of St Andrews, St Andrews, Fife, United Kingdom.

Obesity is characterised by large fat depots, dysregulation of adipose tissue and increased visceral fat. Seals are informative models for the study of obesity because they a. are up to 45% body fat (1) with ‘diabetic' metabolic profiles (2); b. undergo substantial mass changes throughout their lifecycle - pups triple in mass as they deposit fat while suckling (3) - and c. store fat almost exclusively as subcutaneous blubber. However, regulation of their fat storage and utilisation is poorly understood. Here we tested the hypothesis that changes in gene expression of adipokines, which contribute to fat balance in humans, are regulated by physiological state or body mass in naturally feeding and fasting grey seals. Using ex vivo blubber explants, we also tested the hypothesis that adipokine and lipase gene expression are altered by high glucose, free fatty acids and glucocorticoids (GCs) in seals, as in humans and rodents. Handling procedures were performed under Home Office project licence 60/4009 and conformed to the UK Animals (Scientific Procedures) Act. Grey seal pups (n = 10) were captured early (day 5) and late (day 15) during suckling, and the same pups were captured again early (day 5) and late (day 15) during their postweaning fast. Blubber samples were taken using standard techniques and appropriate general (0.01ml/ 10kg zoletil100 TM i.v.) and local (2ml 2% w/v lignocaine (Lignol) s.c.) anaesthesia (4). Blubber leptin and adiponectin gene expression were measured in triplicate using qPCR. Mean CT value for each gene was normalized to S9, expressed as fold difference relative to the early suckling sample for each animal using the Pfaffl method (5) and analysed in R using linear mixed effects models (LME). Blubber leptin and adiponectin mRNA abundance did not change during feeding or fasting, and was not related to body mass (LME: p > 0.05). Blubber samples from adult grey seals (n=10), captured using tangle nets at Abertay Sands and anaesthetised with 0.05ml/ 10kg zoletil100 TM i.v. and Lignol, were washed in Krebs Ringer solution, minced and incubated overnight in media supplemented with high glucose (25mM); palmitate (100mM) or hydrocortisone (500nM). Exposure to palmitate or hydrocortisone had no effect on abundance of leptin, adiponectin, adipose triglyceride lipase (ATGL) and hormone sensitive lipase (HSL) mRNA expressed relative to CycA (REST 2009; p > 0.05). ATGL mRNA abundance tended to increase in high glucose media (REST2009; p = 0.076). Our data suggest key functional genes are not regulated in seal blubber as they are in human fat. Our findings and approach may be informative in elucidating mechanisms that control subcutaneous fat deposition in mammals. We hope to promote discussion of the utility of this animal model of extreme fat accumulation in the study of human obesity.

Where applicable, experiments conform with Society ethical requirements