Cytokines modulate glucose transport in skeletal muscle by inducing the expression of inducible nitric oxide synthase.
The principal goal of the present study was to test the hypothesis that cytokines modulate glucose transport in skeletal muscle by increasing nitric oxide production. Cultured L6 skeletal muscle cells were incubated in the presence of tumour necrosis factor-alpha, interferon-gamma or lipopolysaccharide (LPS) alone or in combination for 24 h. Neither cytokines nor LPS alone induced NO production, as measured by nitrite concentrations in the medium. However, when used in combination, the two cytokines significantly stimulated NO production, and this effect was synergistically enhanced by the presence of LPS. Reverse transcriptase-PCR (RT-PCR) analysis revealed that NO release was associated with the induction of inducible (macrophage-type) NO synthase (iNOS). The increase in iNOS expression was confirmed at the protein level by Western-blot analysis and NADPH/diaphorase histochemical staining. Cytokines and LPS markedly increased basal glucose transport in L6 myocytes. Insulin also stimulated basal glucose transport, but significantly less in cells chronically exposed to cytokines/LPS. The sensitivity of L6 muscle cells to insulin-stimulated glucose transport was also significantly decreased by cytokines/LPS treatment. The NOS inhibitor NG-nitro-l-arginine methyl ester (l-NAME) inhibited nitrite production in cytokine/LPS-treated cells, and this prevented the increase in basal glucose transport and restored muscle cell responsiveness to insulin. Cytokines/LPS exposure significantly increased GLUT1 transporter protein levels but decreased GLUT4 expression in L6 cells. l-NAME treatment prevented the increase in GLUT1 protein content but failed to restore GLUT4 transporter levels. These results demonstrate that cytokines and LPS affect glucose transport and insulin action by inducing iNOS expression and NO production in skeletal muscle cells. The data further indicate that cytokines and LPS increase the expression of the GLUT1 transporter protein by an NO-dependent mechanism.
Bédard
S
S
Department of Physiology and Lipid Research Unit, Laval University Hospital Research Center, Ste-Foy, Québec, Canada G1V 4G2.
Marcotte
B
B
Marette
A
A
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002460:Cell Line; D004790:Enzyme Induction; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D051272:Glucose Transporter Type 1; D007328:Insulin / Q000494:pharmacology; D007371:Interferon-gamma / Q000494:pharmacology*; D019344:Lactic Acid / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000096:biosynthesis*; D009573:Nitrites / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D051272:Glucose Transporter Type 1; D007328:Insulin; D008070:Lipopolysaccharides; D009004:Monosaccharide Transport Proteins; D009573:Nitrites; D012333:RNA, Messenger; D011994:Recombinant Proteins; C495679:Slc2a1 protein, rat; D014409:Tumor Necrosis Factor-alpha; D019344:Lactic Acid; D007371:Interferon-gamma; D019001:Nitric Oxide Synthase; D005947:Glucose; D019331:NG-Nitroarginine Methyl Ester