Urinary Copper Elevation in a Mouse Model of Wilsonâ•ŽsDisease Is a Regulated Process to Specifically Decreasethe Hepatic Copper Load

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. Citation: Gray LW, Peng F, Molloy SA, Pendyala VS, Muchenditsi A, et al. (2012) Urinary Copper Elevation in a Mouse Model of Wilson’s Disease Is a Regulated Process to Specifically Decrease the Hepatic Copper Load. PLoS ONE 7(6): e38327. doi:10.1371/journal.pone.0038327 Editor: Paul Cobine, Auburn University, United States of America Received February 21, 2012; Accepted May 3, 2012; Published June 22, 2012 Copyright: 2012 Gray et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by the National Institutes of Health grants 5F31DK084730 to LWG, 5R01DK079209 to JL, and 5P01GM067166 to SL and JHK. The mass-spectrometry work was done at the Metal Ion Core (Oregon Health and Science University), supported by NIH instrumentation grant S10-RR025512. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: [email protected]