Distinct subcellular localisation of intramyocellular lipids and reduced PKCε/PKCθ activity preserve muscle insulin sensitivity in exercise-trained mice

Aims/hypothesis Athletes exhibit increased muscle insulin sensitivity, despite increased intramuscular triacylglycerol content. This phenomenon has been coined the 'athlete's paradox' and is poorly understood. Recent findings suggest that the subcellular distribution of sn-1,2-diacylglycerols (DAGs) in the plasma membrane leading to activation of novel protein kinase Cs (PKCs) is a crucial pathway to inducing insulin resistance. Here, we hypothesised that regular aerobic exercise would preserve muscle insulin sensitivity by preventing increases in plasma membrane sn-1,2-DAGs and activation of PKC epsilon and PKC theta despite promoting increases in muscle triacylglycerol content.Methods C57BL/6J mice were allocated to three groups (regular chow feeding [RC]; high-fat diet feeding [HFD]; RC feeding and running wheel exercise [RC-EXE]). We used a novel LC-MS/MS/cellular fractionation method to assess DAG stereoisomers in five subcellular compartments (plasma membrane [PM], endoplasmic reticulum, mitochondria, lipid droplets and cytosol) in the skeletal muscle.Results We found that the HFD group had a greater content of sn-DAGs and ceramides in multiple subcellular compartments compared with the RC mice, which was associated with an increase in PKC epsilon and PKC theta translocation. However, the RC-EXE mice showed, of particular note, a reduction in PM sn-1,2-DAG and ceramide content when compared with HFD mice. Consistent with the PM sn-1,2-DAG-novel PKC hypothesis, we observed an increase in phosphorylation of threonine(1150) on the insulin receptor kinase (IRKT1150), and reductions in insulin-stimulated IRKY1162 phosphorylation and IRS-1-associated phosphoinositide 3-kinase activity in HFD compared with RC and RC-EXE mice, which are sites of PKC epsilon and PKC theta action, respectively.Conclusions/interpretation These results demonstrate that lower PKC theta/PKC epsilon activity and sn-1,2-DAG content, especially in the PM compartment, can explain the preserved muscle insulin sensitivity in RC-EXE mice.

Automated summary

This study found that regular aerobic exercise can prevent the increase of muscle fat content, as well as reduce the content of sn-1,2-diacylglycerols (DAGs) in the cell membrane and the activation of protein kinase C (PKC), thus maintaining muscle insulin sensitivity.