Nitric oxide increases GLUT4 expression and regulates AMPK signaling in skeletal muscle

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Abstract
Nitric oxide (NO) and 5′-AMP-activated protein kinase (AMPK) are involved in glucose transport and mitochondrial biogenesis in skeletal muscle. Here, we examined whether NO regulates the expression of the major glucose transporter in muscle (GLUT4) and whether it influences AMPK-induced upregulation of GLUT4. At low levels, the NO donor S -nitroso- N -penicillamine (SNAP, 1 and 10 μM) significantly increased GLUT4 mRNA (∼3-fold; P < 0.05) in L6 myotubes, and cotreatment with the AMPK inhibitor compound C ablated this effect. The cGMP analog 8-bromo-cGMP (8-Br-cGMP, 2 mM) increased GLUT4 mRNA by ∼50% ( P < 0.05). GLUT4 protein expression was elevated 40% by 2 days treatment with 8-Br-cGMP, whereas 6 days treatment with 10 μM SNAP increased GLUT4 expression by 65%. Cotreatment of cultures with the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one prevented the SNAP-induced increase in GLUT4 protein. SNAP (10 μM) also induced significant phosphorylation of α-AMPK and acetyl-CoA carboxylase and translocation of phosphorylated α-AMPK to the nucleus. Furthermore, L6 myotubes exposed to 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) for 16 h presented an approximately ninefold increase in GLUT4 mRNA, whereas cotreatment with the non-isoform-specific NOS inhibitor N G-nitro-l-arginine methyl ester, prevented ∼70% of this effect. In vivo, GLUT4 mRNA was increased 1.8-fold in the rat plantaris muscle 12 h after AICAR injection, and this induction was reduced by ∼50% in animals cotreated with the neuronal and inducible nitric oxide synthases selective inhibitor 1-(2-trifluoromethyl-phenyl)-imidazole. We conclude that, in skeletal muscle, NO increases GLUT4 expression via a cGMP- and AMPK-dependent mechanism. The data are consistent with a role for NO in the regulation of AMPK, possibly via control of cellular activity of AMPK kinases and/or AMPK phosphatases.