Preferential utilization of perilipin 2-associated intramuscular triglycerides during 1 h of moderate-intensity endurance-type exercise

Abstract

The lipid droplet (LD)-associated protein perilipin 2 (PLIN2) appears to colocalize with LDs in human skeletal muscle fibres, although the function of PLIN2 in the regulation of intramuscular triglyceride (IMTG) metabolism is currently unknown. Here we investigated the hypothesis that the presence of PLIN2 in skeletal muscle LDs is related to IMTG utilisation during exercise. We therefore measured exercise-induced changes in IMTG and PLIN2 distribution and changes in their colocalization. Muscle biopsies from the vastus lateralis were obtained from seven lean, untrained men (22±2 years old, body mass index 24.2±0.9 kgm-2 and peak oxygen uptake 3.35±0.13 l min-1) before and after 1 h of moderate-intensity cycling at ∼65% peak oxygen uptake. Cryosections were stained for perilipin 2, IMTG and myosin heavy chain type I and viewed using wide-field and confocal fluorescence microscopy. Exercise induced a 50±7% decrease in IMTG content in type I fibres only (P less than 0.05), but no change in PLIN2 content. Colocalization analysis showed that the fraction of PLIN2 associated with IMTG was 0.67±0.03 before exercise, which was reduced to 0.51±0.01 postexercise (P less than 0.05). Further analysis revealed that the number of PLIN2-associated LDs was reduced by 31±10% after exercise (P less than 0.05), whereas the number of PLIN2-null LDs was unchanged. No such changes were seen in type II fibres. In conclusion, this study shows that PLIN2 content in skeletal muscle is unchanged in response to a single bout of endurance exercise. Furthermore, the PLIN2 and IMTG association is reduced postexercise, apparently due to preferential utilization of PLIN2- associated LDs. These results confirm the hypothesis that the PLIN2 association with IMTG is related to the utilization of IMTG as a fuel during exercise.