Melanocortin 4 receptor stimulation prevents anti-depressant-associated weight gain in mice caused by long-term fluoxetine exposure

Contrasting with the predicted anorexigenic effect of increasing brain serotonin signaling, long-term use of selective serotonin reuptake inhibitors (SSRIs) antidepressants correlates with body weight gain. This adverse outcome increases the risk of transitioning to obesity and interferes with treatment compliance. Here we show that orally administered fluoxetine (Flx), a widely prescribed SSRI, increased body weight by enhancing food intake in healthy mice at two different time points and through two distinct mechanisms. Within hours, Flx decreased the activity of a subset of brainstem serotonergic neurons by triggering autoinhibitory signaling through the Htr1a receptor. Upon longer treatment Flx blunted Htr2c expression/signaling, decreased the phosphorylation of Creb and Stat3 and dampened the production of POMC/α-MSH in hypothalamic neurons, thereby increasing food intake. Accordingly, exogenous stimulation of the melanocortin 4 receptor (MC4R) by co-treating mice with Flx and lipocalin-2, an anorexigenic hormone signaling through this receptor, normalized feeding and body weight. Flx and other SSRIs also inhibit CREB/STAT3 phosphorylation in a human neuronal cell line suggesting that these non-canonical effects could also occur in long-term users of SSRIs. By defining the molecular basis of the long-term SSRIs-associated weight gain this study proposes a therapeutic strategy to counter it.

Analysis of regulation of the ilvGMEDA operon by using leader-attenuator-galK gene fusions

Five of the genes for the biosynthesis of isoleucine and valine form the ilvGMEDA operon of Escherichia coli K-12. Expression of the operon responds to changes in the availability of isoleucine, leucine, and valine (ILV). Addition of an excess of all three amino acids results in reduced expression of the operon, whereas limitation for one of the three amino acids causes an increase in expression. The operon is preceded by a leader-attenuator which clearly regulates the increased expression that occurs due to reduced aminoacylation of tRNA. To assess the factors that result in the reduced expression of this operon upon the addition of ILV, a series of plasmids were constructed in which the ilv regulatory region was fused to galK. In response to addition of the amino acids, expression of the galK gene fused to the leader-attenuator decreased five- to sevenfold, instead of the twofold observed for the chromosomal operon. A deletion analysis with these plasmids indicated that the ILV-specific decrease in expression required an intact leader-attenuator but not ilvGp2 or the DNA that precedes this promoter. This conclusion was supported by both S1 nuclease analysis of transcription initiation and determination of galK mRNA levels by RNA-RNA hybridization.

Binding of integration host factor (IHF) to the ilvGp1 promoter of the ilvGMEDA operon of Escherichia coli K12

Crude extracts of Escherichia coli K-12 were found to bind DNA restriction fragments containing ilvGp1. Our analysis using a series of restriction fragments and a BamHI linker mutation indicate that a factor binds to ilvGp1 or adjacent to it. Analysis with mutant strains of E. coli K-12 and purified IHF indicate that IHF binds to ilvGp1. Furthermore, both analysis in vivo and in vitro indicate that IHF precludes transcription from ilvGp1.

Effect of the deletion of upstream DNA sequences on expression from the ilvGp2 promoter of the ilvGMEDA operon of Escherichia coli K-12

Transcription in vitro of the regulatory region of the ilvGMEDA operon yields two attenuated RNAs initiated from the tandem promoters ilvGp1 and ilvGp2. Both S1 nuclease analysis and the fusion of ilvGp1 to galK indicate that transcription is not initiated in vivo from ilvGp1. However deletion of DNA sequences 150 to 100 bp upstream of ilvGp2 drastically reduces expression in vivo from ilvGp2. Both the distance separating ilvGp2 from the upstream DNA sequences and their relative orientation to each other on the DNA helix affect expression from ilvGp2. Deletion of DNA sequences approximately 400 bp upstream of ilvGp2 increases expression in vivo from this promoter. Analysis of products of transcription in vitro indicates that the effects observed in vivo are probably not due to DNA conformation or interactions of RNA polymerase.