Fatty acid-induced defects in insulin signalling, in myotubes derived from children, are related to ceramide production from palmitate rather than the accumulation of intramyocellular lipid.
The elevation of free fatty acids (FFAs), observed in childhood obesity results in intramyocellular lipid (IMCL) accumulation with consequent insulin resistance. Using in vitro differentiated myotubes from normal weight pre-pubertal children (n = 8), we examined the effects of saturated (palmitate) and unsaturated (oleate) FFAs on insulin-stimulated AKT phosphorylation (pAKT) and IMCL accumulation. Palmitate decreased pAKT (Mean [SEM] % change pAKT with palmitate 750 microM vs. control; pThr308 site -50.5% [28.7] and pSer473 site -38.7% [11.7]; P < 0.001) with no effect on IMCL formation. Equimolar bromopalmitate did not effect pAKT and blocking ceramide production abolished the palmitate-induced reduction in signalling, suggesting that ceramide synthesis is critical for palmitate's actions. Oleate did not effect pAKT (1,000 microM oleate; pSer473 site -3.4% [11.4]; P = NS) but increased IMCL accumulation (+32.3% [7.1%]; P < 0.001). Co-administration of oleate diminished the reduction in pAKT seen with palmitate (+36.4% [23.6] vs. -13.3% [13.6]; P = 0.28), with similar IMCL levels to oleate alone. Co-administration also caused a significant reduction in 14C-ceramide synthesis from 14C-palmitate (101.6 [21.6] vs. 371.5 [122.4] DPM/mg protein; P < 0.001). In summary, palmitate appears to cause insulin resistance in children's myotubes via its metabolism to ceramide, and this process appears unrelated to IMCL formation and is ameliorated by oleate.
Sabin
Matthew A
MA
Institute of Child Life and Health and Clinical Science at North Bristol, The University of Bristol and Royal Hospital for Children, Bristol, United Kingdom.
Stewart
Claire E H
CE
Crowne
Elizabeth C
EC
Turner
Stephen J
SJ
Hunt
Linda P
LP
Welsh
Gavin I
GI
Grohmann
Malcolm J
MJ
Holly
Jeff M P
JM
Shield
Julian P H
JP
D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D002518:Ceramides / Q000096:biosynthesis*; D002648:Child; D002675:Child, Preschool; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007223:Infant; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D050356:Lipid Metabolism / Q000187:drug effects; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism*; D019301:Oleic Acid / Q000494:pharmacology; D010078:Oxazines; D010168:Palmitates / Q000378:metabolism* / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism; D010768:Phosphoserine / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors
D002518:Ceramides; D007328:Insulin; D010078:Oxazines; D010168:Palmitates; D010750:Phosphoproteins; D010768:Phosphoserine; D019301:Oleic Acid; D051057:Proto-Oncogene Proteins c-akt; C044808:nile red