The Orphan Nuclear Receptor, NOR-1, a Target of β-Adrenergic Signaling, Regulates Gene Expression that Controls Oxidative Metabolism in Skeletal Muscle

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Abstract

β1-3-Adrenoreceptor (AR)-deficient mice are unable to regulate energy expenditure and develop diet-induced obesity on a high-fat diet. We determined previously that β2-AR agonist treatment activated expression of the mRNA encoding the orphan nuclear receptor, NOR-1, in muscle cells and plantaris muscle. Here we show that β2-AR agonist treatment significantly and transiently activated the expression of NOR-1 (and the other members of the NR4A subgroup) in slow-twitch oxidative soleus muscle and fast-twitch glycolytic tibialis anterior muscle. The activation induced by β-adrenergic signaling is consistent with the involvement of protein kinase A, MAPK, and phosphorylation of cAMP response element-binding protein. Stable cell lines transfected with a silent interfering RNA targeting NOR-1 displayed decreased palmitate oxidation and lactate accumulation. In concordance with these observations, ATP production in the NOR-1 silent interfering RNA (but not control)-transfected cells was resistant to (azide-mediated) inhibition of oxidative metabolism and expressed significantly higher levels of hypoxia inducible factor-1α. In addition, we observed the repression of genes that promote fatty acid oxidation (peroxisomal proliferator-activated receptor-γ coactivator-1α/β and lipin-1α) and trichloroacetic acid cycle-mediated carbohydrate (pyruvate) oxidation [pyruvate dehydrogenase phosphatase 1 regulatory and catalytic subunits (pyruvate dehydrogenase phosphatases-1r and -c)]. Furthermore, we observed that β2-AR agonist administration in mouse skeletal muscle induced the expression of genes that activate fatty acid oxidation and modulate pyruvate use, including PGC-1α, lipin-1α, FOXO1, and PDK4. Finally, we demonstrate that NOR-1 is recruited to the lipin-1α and PDK-4 promoters, and this is consistent with NOR-1-mediated regulation of these genes. In conclusion, NOR-1 is necessary for oxidative metabolism in skeletal muscle.

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