Journal
PHYSIOLOGICAL REPORTS
Volume 2, Issue 11, Pages -Publisher
WILEY
DOI: 10.14814/phy2.12187
Keywords
Electron microscopy; exercise; insulin sensitivity; lipid droplets; lipophagy; muscle
Categories
Funding
- Helse SorOst
- Johan Throne Holst Foundation for Nutrition Research
- Freia Medical Research Fund
- Anders Jahre Foundation and NutriTech
- European Commission Funded FP7 Research Project [289511]
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Muscle lipid stores and insulin sensitivity have a recognized association although the mechanism remains unclear. We investigated how a 12-week supervised combined endurance and strength exercise intervention influenced muscle lipid stores in sedentary overweight dysglycemic subjects and normal weight control subjects (n = 18). Muscle lipid stores were measured by magnetic resonance spectroscopy (MRS), electron microscopy (EM) point counting, and direct EM lipid droplet measurements of subsarcolemmal (SS) and intramyofibrillar (IMF) regions, and indirectly, by deep sequencing and realtime PCR of mRNA of lipid droplet-associated proteins. Insulin sensitivity and VO(2)max increased significantly in both groups after 12 weeks of training. Muscle lipid stores were reduced according to MRS at baseline before and after the intervention, whereas EM point counting showed no change in LD stores post exercise, indicating a reduction in muscle adipocytes. Large-scale EM quantification of LD parameters of the subsarcolemmal LD population demonstrated reductions in LD density and LD diameters. Lipid droplet volume in the subsarcolemmal LD population was reduced by similar to 80%, in both groups, while IMF LD volume was unchanged. Interestingly, the lipid droplet diameter (n = 10 958) distribution was skewed, with a lack of small diameter lipid droplets (smaller than similar to 200 nm), both in the SS and IMF regions. Our results show that the SS LD lipid store was sensitive to training, whereas the dominant IMF LD lipid store was not. Thus, net muscle lipid stores can be an insufficient measure for the effects of training.
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