Norepinephrine Is Required for Leptin Effects on Gene Expression in Brown and White Adipose Tissue

Exogenous leptin enhances energy utilization in ob/ob mice by binding its hypothalamic receptor and selectively increasing peripheral fat oxidation. Leptin also increases uncoupling protein 1 (UCP1) expression in brown adipose tissue (BAT), but the neurotransmitter that mediates this effect has not been established. The present experiments sought to determine whether leptin regulates UCP1 expression in BAT and its own expression in white adipose tissue (WAT) through the long or short forms of leptin receptor and modulation of norepinephrine release. Mice lacking dopamineβ -hydroxylase (Dbh−/−), the enzyme responsible for synthesizing norepinephrine and epinephrine from dopamine, were treated with leptin (20 μg/g body weight/day) for 3 days before they were euthanized. UCP1 messenger RNA (mRNA) and protein expression were 5-fold higher in BAT from control (Dbh+/−) compared with Dbh−/− mice. Leptin produced a 4-fold increase in UCP1 mRNA levels in Dbh+/− mice but had no effect on UCP1 expression in Dbh−/−. Theβ3-adrenergic agonist, CL-316,243 increased UCP1 expression and established that BAT from both groups of mice was capable of responding to β-adrenergic stimulation. Similarly, exogenous leptin reduced leptin mRNA in WAT from Dbh+/− but not Dbh−/− mice. In separate experiments, leptin produced comparable reductions in food intake in both Dbh+/− and Dbh−/− mice, illustrating that norepinephrine is not required for leptin’s effect on food intake. Lastly, db/db mice lacking the long form of the leptin receptor failed to increase UCP1 mRNA in response to exogenous leptin but increased UCP1 mRNA in response to CL-316,243. These studies establish that norepinephrine is required for leptin to regulate its own expression in WAT and UCP1 expression in BAT and indicate that these effects are likely mediated through the centrally expressed long form of the leptin receptor.