Urinary copper elevation in a mouse model of Wilson's disease is a regulated process to specifically decrease the hepatic copper load.
PLoS One 2012;
7:e38327. [PMID:
22802922 PMCID:
PMC3390108 DOI:
10.1371/journal.pone.0038327]
[Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Accepted: 05/03/2012] [Indexed: 12/19/2022] Open
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.
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