RESUMO
The NR4A orphan nuclear receptors function as early response genes to numerous stimuli. Our laboratory has previously demonstrated that overexpression of NR4A3 (NOR-1, MINOR) in 3T3-L1 adipocytes enhances insulin-stimulated glucose uptake. To assess the in vivo effect of NR4A3 on adipocytes, we generated transgenic mice with NR4A3 overexpression driven by the adipocyte fatty acid-binding protein (AP2) promoter (AP2-NR4A3 mice). We hypothesized that AP2-NR4A3 mice would display enhanced glucose tolerance and insulin sensitivity. However, AP2-NR4A3 mice exhibit metabolic impairment, including increased fasting glucose and insulin, impaired glucose tolerance, insulin resistance, decreased serum free fatty acids, and increased low-density lipoprotein-cholesterol. AP2-NR4A3 mice also display a significant reduction in serum epinephrine due to increased expression of catecholamine-catabolizing enzymes in adipose tissue, including monoamine oxidase-A. Furthermore, enhanced expression of monoamine oxidase-A is due to direct transcriptional activation by NR4A3. Finally, AP2-NR4A3 mice display cardiac and behavioral alterations consistent with chronically low circulating epinephrine levels. In conclusion, overexpression of NR4A3 in adipocytes produces a complex phenotype characterized by impaired glucose metabolism and low serum catecholamines due to enhanced degradation by adipose tissue.