Human Obesity Associated with an Intronic SNP in the Brain-Derived Neurotrophic Factor Locus.

Brain-derived neurotrophic factor (BDNF) plays a key role in energy balance. In population studies, SNPs of the BDNF locus have been linked to obesity, but the mechanism by which these variants cause weight gain is unknown. Here, we examined human hypothalamic BDNF expression in association with 44 BDNF SNPs. We observed that the minor C allele of rs12291063 is associated with lower human ventromedial hypothalamic BDNF expression (p < 0.001) and greater adiposity in both adult and pediatric cohorts (p values < 0.05). We further demonstrated that the major T allele for rs12291063 possesses a binding capacity for the transcriptional regulator, heterogeneous nuclear ribonucleoprotein D0B, knockdown of which disrupts transactivation by the T allele. Binding and transactivation functions are both disrupted by substituting C for T. These findings provide a rationale for BDNF augmentation as a targeted treatment for obesity in individuals who have the rs12291063 CC genotype.

Chronic fluoxetine upregulates activity, protein and mRNA levels of cytosolic phospholipase A2 in rat frontal cortex.

Chronic lithium and carbamazepine, which are effective against mania in bipolar disorder, decrease the activity of cytosolic phospholipase A(2) (cPLA(2)) and the turnover rate of arachidonic acid in phospholipids in rat brain. Assuming that stages of bipolar disorder are related to brain arachidonic acid metabolism, we hypothesized that drugs effective in depression would increase cPLA(2) activity. To test this hypothesis, adult male CDF-344 rats were administered fluoxetine (10 mg/kg intraperitoneally (i.p.) or saline (control) (i.p.) chronically for 21 days. Frontal cortex cPLA(2) protein, phosphorylated cPLA(2), activity and mRNA levels were increased after chronic fluoxetine. Transcription factors (activator protein-1, activator protein-2, glucocorticoid response element, polyoma enhancer element-3 and nuclear factor-kappa B) that are known to regulate cPLA(2) gene expression were not significantly changed by chronic fluoxetine, but nuclear AU-rich element/poly(U)-binding/degradation factor-1 RNA-stabilizing protein was increased significantly. The results suggest that chronic fluoxetine increases brain cPLA(2) gene expression post-transcriptionally by increasing cPLA(2) mRNA stabilization. Chronic fluoxetine's effect on cPLA(2) expression was opposite to the effect reported with chronic lithium or carbamazepine administration, and may be part of fluoxetine's mode of action.

A hairpin-like structure within an AU-rich mRNA-destabilizing element regulates trans-factor binding selectivity and mRNA decay kinetics.

In mammals, rapid mRNA turnover directed by AU-rich elements (AREs) is mediated by selective association of cellular ARE-binding proteins. These trans-acting factors display overlapping RNA substrate specificities and may act to either stabilize or destabilize targeted transcripts; however, the mechanistic features of AREs that promote preferential binding of one trans-factor over another are not well understood. Here, we describe a hairpin-like structure adopted by the ARE from tumor necrosis factor alpha (TNFalpha) mRNA that modulates its affinity for selected ARE-binding proteins. In particular, association of the mRNA-destabilizing factor p37(AUF1) was strongly inhibited by adoption of the higher order ARE structure, whereas binding of the inducible heat shock protein Hsp70 was less severely compromised. By contrast, association of the mRNA-stabilizing protein HuR was only minimally affected by changes in ARE folding. Consistent with the inverse relationship between p37(AUF1) binding affinity and the stability of ARE folding, mutations that stabilized the ARE hairpin also inhibited its ability to direct rapid mRNA turnover in transfected cells. Finally, phylogenetic analyses and structural modeling indicate that TNFalpha mRNA sequences flanking the ARE are highly conserved and may stabilize the hairpin fold in vivo. Taken together, these data suggest that local higher order structures involving AREs may function as potent regulators of mRNA turnover in mammalian cells by modulating trans-factor binding selectivity.