Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC98
Endurance exercise decreases the lipid droplet association with perilipin 2 in human skeletal muscle
S. Shepherd1, M. Cocks1, K. D. Tipton2, A. M. Ranasinghe3, T. A. Barker3, A. J. Wagenmakers1, C. S. Shaw1
1. Sport & Exercise Sciences, University of Birmingham, Birmingham, United Kingdom. 2. University of Stirling, Stirling, United Kingdom. 3. School of Clinical and Experimental Medicine, Cardiovascular and Respiratory Sciences, University of Birmingham, Birmingham, United Kingdom.
Intramuscular triglyceride-containing lipid droplets (LDs) are an important source of fuel during exercise in human skeletal muscle and a site for lipid storage during periods of elevated lipid availability. LDs exhibit a distinct array of proteins associated with their phospholipid monolayer. Perilipin 2 (traditionally termed ADRP/adipophilin) colocalizes with approximately 60% of LDs in skeletal muscle, while the other LDs do not contain perilipin 2. However, the function of perilipin 2 with regards to the metabolic regulation of skeletal muscle is currently unknown. Therefore, we measured LD and perilipin 2 content in skeletal muscle and examined potential changes in colocalisation in response to moderate intensity endurance exercise. Muscle biopsies were obtained (1% lidocaine local anaesthesia) from 7 lean, healthy males (22 ± 2 years, BMI 24.2 ± 0.9 kg.m2, VO2 peak 43.8 ± 1.4 ml.min-1.kg-1) before and after 1 h of moderate intensity cycling at ~65% VO2 peak. Five µm cryosections were stained using antibodies targeting perilipin 2 and myosin heavy chain type I and with the lipid dye oil red O. Slides were subsequently viewed using widefield and confocal fluorescence microscopy and image-processing software was used to analyse perilipin 2 and LD content, and perilipin 2-LD colocalisation. Negative controls performed on randomly selected images discounted chance colocalisation. Exercise induced a 50 ± 7% decrease in skeletal muscle LD content in type I fibres (pre 3.8 ± 0.4% area stained, post 1.9 ± 0.4%; P < 0.05) with no changes in type II fibres. The change in LD content was attributable to both a 50 ± 9% decrease in LD density and an 11 ± 4% decrease in LD size. In contrast, perilipin 2 content was unchanged in either fibre type in response to exercise. Prior to exercise, 67 ± 3% of perilipin 2 colocalised with LDs; however, the relative colocalisation was reduced to 51 ± 3% following exercise (P < 0.05). Further analysis revealed that the number of LDs containing perilipin-2 was reduced 31 ± 10% after exercise (pre 0.041 ± 0.003 LDs.µm-2, post 0.027 ± 0.002 LDs.µm-2; P < 0.05), whereas the number of LDs devoid of perilipin 2 detection was unchanged (pre 0.028 ± 0.003 LDs.µm-2, post 0.025 ± 0.004 LDs.µm-2; P = 0.53). In conclusion, this study shows that despite a decrease in skeletal muscle LD content immediately following a single bout of endurance exercise, perilipin 2 content in human skeletal muscle remains unchanged. Furthermore, the colocalisation of perilipin 2 and LDs is reduced post-exercise, apparently due to the preferential lipolysis of perilipin 2 containing LDs. These results are the first to show that perilipin 2 may play a regulatory function in skeletal muscle LD metabolism during exercise.
Where applicable, experiments conform with Society ethical requirements