Unraveling the Athlete’s Paradox—Higher Insulin Sensitivity and Lower PKC? Activation Despite Higher Bioactive Lipids in Endurance-Trained Athletes

Abstract

High intramyocellular lipid (IMCL) content associates negatively with insulin sensitivity (IS) in insulin resistant, but not in endurance-trained humans. It has been hypothesized that different cellular distribution of bioactive lipids such as diacylglycerols (DAG) and ceramides (CER) could interfere with insulin action and underlie this “athlete’s paradox.” We examined endurance-trained athletes (ATH; n=9) and sedentary individuals (SED; n=12) with comparable total IMCL, as measured by 1H-magnetic resonance spectroscopy, who underwent spiroergometry and hyperinsulinemic-euglycemic clamps to assess maximal oxidative capacity and IS, respectively. In skeletal muscle biopsies, translocation of protein kinase C (PKC) θ and ε were determined by Western blotting and concentrations of DAG and CER were measured using targeted LC-tandem mass spectrometry upon separating fractions of cellular membranes, lipid droplets and cytosol by ultracentrifugation. Maximal oxidative capacity and IS were 46% and 47% higher in ATH than in SED (both p<0.01), respectively. The membrane:cytosol ratio of PKCθ, which reflects PKCθ activity, was 62% lower in ATH consistent with their increased IS (p<0.01), while there was no group difference for PKCε. Total and membrane DAG (40% and 48%, both p<0.01) as well as membrane CER (15%, p<0.05) were higher in ATH while the respective concentrations in lipid droplets and cytosol did not differ. In SED, IS correlated inversely with all stereoselective subspecies of lipid-droplet DAG. On the other hand, cytosolic sn-1,2 (C16:0-C18:2) and sn-1,3 (C18:1-C18:0) DAG correlated positively with IS in ATH. In conclusion, higher IS in endurance-trained ATH can be explained by lower muscle PKCθ activation, which may be due to differences in the stereoselectivity and/or subcompartmentation of cellular DAG between ATH and insulin resistant SED. Disclosure D. Pesta: None. E. Anadol-Schmitz: None. S. Gancheva: None. D.F. Markgraf: None. O.P. Zaharia: None. H. Katsuyama: None. Y. Kupriyanova: None. J. Hwang: None. D. Zhang: None. G.I. Shulman: Advisory Panel; Self; AstraZeneca, Janssen Research & Development, Merck & Co., Inc., Novo Nordisk Inc.. Research Support; Self; Gilead Sciences, Inc. M. Roden: Speaker's Bureau; Self; Boehringer Ingelheim GmbH. Research Support; Self; Boehringer Ingelheim GmbH. Consultant; Self; Poxel SA. Research Support; Self; Danone Nutricia Early Life Nutrition, GlaxoSmithKline plc., Nutricia Advanced Medical Nutrition, Sanofi.

Pathophysiology of Physical Inactivity-Dependent Insulin Resistance: A Theoretical Mechanistic Review Emphasizing Clinical Evidence

“…Similarly, abdominal obesity and dysregulated lipid profile were reported as underlying culprits of insulin resistance in physically inactive individuals [ 56 ]. It must be noted that active people with endurance training may have higher intramuscular lipid, which has no adverse effects on insulin sensitivity (known as athletes' paradox) [ 57 ]. This exception may be due to lower DAG or ceramide levels in trained individuals [ 57 ].…”

“…It must be noted that active people with endurance training may have higher intramuscular lipid, which has no adverse effects on insulin sensitivity (known as athletes' paradox) [ 57 ]. This exception may be due to lower DAG or ceramide levels in trained individuals [ 57 ]. In total, obesity and dysregulated lipid profiles are potential links between physical inactivity and insulin resistance.…”