Palmitate-induced activation of the hexosamine pathway in human myotubes: increased expression of glutamine:fructose-6-phosphate aminotransferase.
The nutrient sensing capacity of the hexosamine biosynthetic pathway (HBP) has been implicated in the development of insulin resistance of skeletal muscle. To study the molecular mechanism of the free fatty acid (FFA)-induced activation of the HBP myotubes obtained from muscle biopsies of metabolically characterized, subjects were stimulated with different fatty acids for 20 h. Incubation with the saturated fatty acids palmitate and stearate (0.5 mmol/l) resulted in a three- to fourfold increase in mRNA expression of glutamine:fructose-6-phosphate aminotransferase (GFAT), the key and rate-limiting enzyme of the hexosamine pathway. Unsaturated fatty acids or 30 mmol/l glucose had little or no effect. Palmitate increased the amount of GFAT protein nearly two-fold, and subsequently, the concentration of UDP-N-acetylglucosamine, the end product of the HBP, was 1.3-fold enhanced in the palmitate-stimulated myotubes. The nonmetabolized fatty acid bromopalmitate had no effect. The DNA binding activity of the transcription factor Sp1, a target downstream of the HBP, was increased by palmitate and completely lost after enzymatic removal of O-GlcNAc. No correlation was found between the palmitate-induced increase in GFAT protein and the insulin resistance in the respective subjects. The findings reveal a new mechanism for how FFAs induce the activation of the HBP.
Weigert
Cora
C
Department of Internal Medicine, Division of Endocrinology, Metabolism and Pathobiochemistry, University of Tübingen, Otfried-Müller-Strasse 10, D-72076 Tübingen, Germany.
Klopfer
Karsten
K
Kausch
Christiana
C
Brodbeck
Katrin
K
Stumvoll
Michael
M
Häring
Hans U
HU
Schleicher
Erwin D
ED
D002478:Cells, Cultured; D004247:DNA / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects*; D005947:Glucose / Q000494:pharmacology; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing) / Q000235:genetics*; D006595:Hexosamines / Q000096:biosynthesis*; D006801:Humans; D007333:Insulin Resistance; D018485:Muscle Fibers, Skeletal / Q000201:enzymology*; D018482:Muscle, Skeletal / Q000648:ultrastructure; D019308:Palmitic Acid / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis; D016329:Sp1 Transcription Factor / Q000378:metabolism; D013229:Stearic Acids / Q000494:pharmacology; D014537:Uridine Diphosphate N-Acetylglucosamine / Q000032:analysis
D005231:Fatty Acids, Unsaturated; D006595:Hexosamines; D012333:RNA, Messenger; D016329:Sp1 Transcription Factor; D013229:Stearic Acids; D019308:Palmitic Acid; C031183:stearic acid; D014537:Uridine Diphosphate N-Acetylglucosamine; D004247:DNA; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing); D005947:Glucose