Urinary Copper Elevation in a Mouse Model of Wilson’s Disease Is a Regulated Process to Specifically Decrease the Hepatic Copper Load

Authors

Lawrence W. Gray, Johns Hopkins University
Fangyu Peng, University of Texas Southwestern Medical Center
Shannon A. Molloy, University of Illinois at Chicago
Venkata S. Pendyala, Johns Hopkins University
Abigael Muchenditsi, Johns Hopkins University
Otto Muzik, Wayne State University
Jaekwon Lee, University of Nebraska - LincolnFollow
Jack H. Kaplan, University of Illinois at Chicago
Svetlana Lutsenko, Johns Hopkins UniversityFollow

Document Type

Article

Date of this Version

6-2012

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

Comments

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

Abstract

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.