Cell signaling relies extensively on dynamic pools of redox-inactive metal ions such as sodium, potassium, calcium, and zinc, but their redox-active transition metal counterparts such as copper and iron have been studied primarily as static enzyme cofactors. Here we report that copper is an endogenous regulator of lipolysis, the breakdown of fat, which is an essential process in maintaining the body's weight and energy stores. Utilizing a murine model of genetic copper misregulation, in combination with pharmacological alterations in copper status and imaging studies in a 3T3-L1 white adipocyte model, we demonstrate that copper regulates lipolysis at the level of the second messenger, cyclic AMP (cAMP), by altering the activity of the cAMP-degrading phosphodiesterase PDE3B. Biochemical studies of the copper-PDE3B interaction establish copper-dependent inhibition of enzyme activity and identify a key conserved cysteine residue within a PDE3-specific loop that is essential for the observed copper-dependent lipolytic phenotype.

Body copper homeostasis is regulated by the liver, which removes excess copper via bile. In Wilson's disease (WD), this function is disrupted due to inactivation of the copper transporter ATP7B resulting in hepatic copper overload. High urinary copper is a diagnostic feature of WD linked to liver malfunction; the mechanism behind urinary copper elevation is not fully understood. Using Positron Emission Tomography-Computed Tomography (PET-CT) imaging of live Atp7b−/− mice at different stages of disease, a longitudinal metal analysis, and characterization of copper-binding molecules, we show that urinary copper elevation is a specific regulatory process mediated by distinct molecules. PET-CT and atomic absorption spectroscopy directly demonstrate an age-dependent decrease in the capacity of Atp7b−/− livers to accumulate copper, concomitant with an increase in urinary copper. This reciprocal relationship is specific for copper, indicating that cell necrosis is not the primary cause for the initial phase of metal elevation in the urine. Instead, the urinary copper increase is associated with the down-regulation of the copper-transporter Ctr1 in the liver and appearance of a 2 kDa Small Copper Carrier, SCC, in the urine. SCC is also elevated in the urine of the liver-specific Ctr1 −/− knockouts, which have normal ATP7B function, suggesting that SCC is a normal metabolite carrying copper in the serum. In agreement with this hypothesis, partially purified SCC-Cu competes with free copper for uptake by Ctr1. Thus, hepatic down-regulation of Ctr1 allows switching to an SCC-mediated removal of copper via kidney when liver function is impaired. These results demonstrate that the body regulates copper export through more than one mechanism; better understanding of urinary copper excretion may contribute to an improved diagnosis and monitoring of WD.

Wilson disease (WD) is a hepatoneurologic disorder caused by mutations in the copper-transporter ATP7B. Copper accumulation in the liver is a hallmark of WD. Current therapy is based on copper chelation, which decreases the manifestations of liver disease, but often worsens neurologic symptoms. We demonstrate that in Atp7b−/− mice, an animal model of WD, liver function can be significantly improved without copper chelation. Analysis of transcriptional and metabolic changes in samples from WD patients and Atp7b−/− mice identified disregulation of nuclear receptors (NR), especially the LXR/RXR heterodimer, as an important event in WD pathogenesis. Treating Atp7b−/− mice with the LXR agonist T0901317 ameliorated disease manifestations despite significant copper overload. Genetic markers of liver fibrosis and inflammatory cytokines were significantly decreased, lipid profiles normalized and liver function and histology was improved. In conclusion, the results demonstrate the major role of an altered nuclear receptor function in the pathogenesis of WD; and suggest that modulation of nuclear receptor activity should be explored as a supplementary approach to improving liver function in WD.