Induction of leptin receptor expression in the liver by leptin and food deprivation.

Leptin resistance is a common feature of obesity and the metabolic syndrome. However, the regulated expression of the leptin receptor (Ob-R) has not been studied in detail. Expression profiling of liver mRNA in leptin-treated wild-type mice revealed a marked increase in leptin receptor mRNA levels, which had not previously been described. This was confirmed by isoform-specific real-time PCR, which showed a >25-fold increase in the mRNAs encoding the short forms (Ob-Ra, Ob-Rc) and a >10-fold increase in the mRNA encoding the long (Ob-Rb) form of the leptin receptor in liver. In parallel, we also observed induction of plasma-soluble leptin receptor (SLR) protein by leptin administration, pair feeding, and short term food restriction. However, induction of SLR by leptin is abolished in mice with selective deletion of Ob-R from liver using Cre-LoxP technology. These data suggest that the liver is a major source of Ob-R mRNA expression under conditions of negative energy balance. Membrane-bound Ob-R is then shed into the circulation as SLR. Our study thus reveals an unexpected role of the liver in modulating total circulating leptin levels and possibly its biological activity.