Lipid remodeling and an altered membrane-associated proteome may drive the differential effects of EPA and DHA treatment on skeletal muscle glucose uptake and protein accretion.

Stewart Jeromson,Andy Shaw,Gordon Bell,Iain Gallagher,Ivor Mackenzie,Andrew Philp,D Lee Hamilton,Phillip D Whitfield,Stuart D R Galloway,James Dick,Francesco V Rao,Stephen P Ashcroft,Mary K Doherty

doi:10.1152/ajpendo.00438.2015

Abstract

In striated muscle, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have differential effects on the metabolism of glucose and differential effects on the metabolism of protein. We have shown that, despite similar incorporation, treatment of C2C12 myotubes (CM) with EPA but not DHA improves glucose uptake and protein accretion. We hypothesized that these differential effects of EPA and DHA may be due to divergent shifts in lipidomic profiles leading to altered proteomic profiles. We therefore carried out an assessment of the impact of treating CM with EPA and DHA on lipidomic and proteomic profiles. Fatty acid methyl esters (FAME) analysis revealed that both EPA and DHA led to similar but substantials changes in fatty acid profiles with the exception of arachidonic acid, which was decreased only by DHA, and docosapentanoic acid (DPA), which was increased only by EPA treatment. Global lipidomic analysis showed that EPA and DHA induced large alterations in the cellular lipid profiles and in particular, the phospholipid classes. Subsequent targeted analysis confirmed that the most differentially regulated species were phosphatidylcholines and phosphatidylethanolamines containing long-chain fatty acids with five (EPA treatment) or six (DHA treatment) double bonds. As these are typically membrane-associated lipid species we hypothesized that these treatments differentially altered the membrane-associated proteome. Stable isotope labeling by amino acids in cell culture (SILAC)-based proteomics of the membrane fraction revealed significant divergence in the effects of EPA and DHA on the membrane-associated proteome. We conclude that the EPA-specific increase in polyunsaturated long-chain fatty acids in the phospholipid fraction is associated with an altered membrane-associated proteome and these may be critical events in the metabolic remodeling induced by EPA treatment.

Highlights

FATTY ACIDS play an important role in skeletal muscle metabolism, as substrates for oxidative phosphorylation or vital structural components of membranes and as regulators of enzyme activities and signaling molecules [8]
The addition of n-3 fatty acids to a lipid infusion of n-6 fatty acids attenuated the decline in insulin-stimulated glucose disposal caused by n-6 infusion alone, suggesting that the n-3 fatty acids have a protective effect on glucose metabolism in the presence of an n-6 overload [46]
This study is the first to carry out a comprehensive analysis of the lipidomic profiles of a skeletal muscle cell line in response to two differentially bioactive n-3 fatty acids

Summary

Introduction

FATTY ACIDS play an important role in skeletal muscle metabolism, as substrates for oxidative phosphorylation or vital structural components of membranes and as regulators of enzyme activities and signaling molecules [8]. Several n-3 supplementation studies in humans have observed beneficial effects ranging from an increased sensitivity to anabolic stimuli [43, 44] and muscle function [40, 45]. In other striated muscle models such as cardiomyocytes, EPA but not DHA increases glucose and fatty acid uptake despite similar effects on cell signaling [18]. In plasma, both EPA and DHA reduced triacylglycerol (TAG), but only DHA modulates high-density lipoprotein (HDL) and low-density lipoprotein (LDL) particle size [53]. These data suggest that in certain contexts, EPA and DHA can have differential biological effects

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Conclusion