501-P: Lower Plasma Membrane Sn-1,2-Diacylglycerol Content and PKCepsilon/theta Activity Explain the Athlete’s Paradox
Authors: GASPAR RAFAEL C. , LYU KUN , HUBBARD BRANDON T. , LEITNER BROOKS , LUUKKONEN PANU , HIRABARA SANDRO , SAKUMA IKKI , NASIRI ALI , ZHANG DONGYAN , KAHN MARIO , CLINE GARY , PAULI JOSÉ R. , PERRY RACHEL J. , PETERSEN KITT , SHULMAN GERALD I. 
Published: June 2021

Increases in intramyocellular lipids (IMCL) are strongly associated with muscle insulin resistance. An important exception to this observation occurs in athletes, who manifest increased IMCL content despite increased muscle insulin sensitivity. This phenomenon has been coined the “Athlete’s Paradox” and is not well understood. Here, we examined the hypothesis that the Athlete’s Paradox can be explained by lower plasma membrane (PM) associated sn-1,2-diacylglycerol (DAG) content leading to lower PKCε and PKCθ translocation in skeletal muscle despite increased muscle triglyceride (TAG) content. To address this hypothesis we studied 3 groups of male C57BL/6J mice following 6 weeks of: 1) Regular chow feeding (RC), 2) High-fat diet feeding (HFD); 3) RC-feeding and running wheel exercise (EX). DAG stereoisomers were assessed in five subcellular compartments [PM, endoplasmic reticulum (ER), mitochondria (Mito), and lipid droplet (LD)] using a novel liquid chromatography-tandem mass spectrometry/cellular fractionation method. Consistent with the Athlete’s Paradox we found that EX mice manifested improved glucose tolerance and muscle insulin sensitivity compared to HFD mice, as assessed by glucose tolerance and hyperinsulinemic-euglycemic clamp studies, despite similar increases in muscle TAG content (RC=5.7 ± 3.2 µg/mg; HFD=17.8 ± 6.0 µg/mg; EX=13.7 ± 5.2 µg/mg) compared to RC mice (RC vs. HFD P&lt;0.01, RC vs. EX P&lt;0.01 and HFD vs. EX P=NS). However, in contrast to the EX and RC mice the HFD group had a 2-fold increase in PM sn-1,2-DAG content compared to the RC and EX mice (both P&lt;0.01), which was associated with a 2-3 fold increase in PKCε and PKCθ translocation (both P&lt;0.05 compared to HFD) and reduced insulin-stimulated InsrY1162/AKT473 phosphorylation and glucose transport (all P&lt;0.01 vs. HFD).
Conclusion: Lower PM sn-1,2-DAG content and PKCε/PKCθ activity provides an explanation for the preserved insulin sensitivity in EX mice and thus the Athlete’s Paradox.

Disclosure
R. C. Gaspar: None. M. Kahn: None. G. Cline: None. J. R. Pauli: None. R. J. Perry: None. K. Petersen: Advisory Panel; Spouse/Partner; AstraZeneca, iMetabolic Biopharma Corporation, Janssen Research & Development, LLC, Merck & Co., Inc., Consultant; Spouse/Partner; Aegerion Pharmaceuticals Inc., Novo Nordisk, Research Support; Self; Gilead Sciences, Inc., Merck & Co., Inc. G. I. Shulman: Consultant; Self; 89bio, Inc., BridgeBio, Ionis Pharmaceuticals, Maze Therapeutics, Novo Nordisk, Other Relationship; Self; AstraZeneca, Esperion Therapeutics, Inc, Generian Pharmaceuticals, Inc., Gilead Sciences, Inc., iMetabolic Biopharma Corporation, Janssen Research & Development, LLC, Merck & Co., Inc., The Liver Company. K. Lyu: None. B. T. Hubbard: None. B. Leitner: None. P. Luukkonen: Consultant; Self; Boehringer Ingelheim Pharmaceuticals, Inc., Research Support; Self; Novo Nordisk Foundation. S. Hirabara: None. I. Sakuma: None. A. Nasiri: Employee; Spouse/Partner; Medtronic. D. Zhang: None.

Funding
São Paulo Research Foundation (2019/11338-9, 2017/20542-3); National Institutes of Health (R01DK116774, P30DK045735)