Molecular pathology of Wilson’s disease: A brief
Authors: Vassiliki Lalioti, Ignacio Sandoval, Doris Cassio, Jean-Charles Duclos-Vallée
Journal: Journal of Hepatology (2010)

Wilson disease (WD) is a rare autosomal recessive disorder of Cu metabolism linked to dysfunction of the Cu translocase ATP7B expressed in hepatocytes [[1]Bull P.C. Thomas G.R. Rommens J.M. Forbes J.R. Cox D.W. The Wilson disease gene is a putative copper transporting P-type ATPase similar to the Menkes gene.Nat Genet. 1993; 5: 327-337Crossref PubMed Scopus (1688) Google Scholar]. ATP7B is critical in the distribution and elimination of excess Cu from the organism. Malfunctioning of the translocase interferes with the distribution of Cu among organs and tissues and results in the imbalance between Cu absorption and excretion, thus causing Cu toxicosis.The levels of Cu regulate the distribution and traffic of ATP7B in the hepatocyte. While at normal Cu concentrations, ATP7B remains in the TGN (trans-Golgi network) to supply Cu to the newly synthesized cuproproteins; at Cu concentrations exceeding the physiological limits it is transferred to the membranes of the bile canaliculi to dissipate the toxic levels of Cu [[2]Hernandez S. Tsuchiya Y. García-Ruiz J.P. Lalioti V. Nielsen S. Cassio D. et al.ATP7B copper-regulated traffic and association with the tight junctions: copper excretion into the bile.Gastroenterology. 2008; 134: 1215-1223Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar].Proper cellular distribution and functioning of ATP7B requires the coordinated interaction between its separate modules. Whereas the six Cu+-binding domains in its long N-cytoplasmic domain play a major role in the acceptance of Cu+ and in controlling the phosphorylation, traffic, and activity of the translocase, the clustering of its eight transmembrane helixes forms the Cu+ pore, and the connecting loops in the cytoplasmic side are involved in the cyclic phosphorylation that controls the activity of the translocase (Fig. 1A and B) [[3]Lutsenko S.E. LeShane S. Shinde U. Biochemical basis of regulation of human copper-transporting ATPases.Arch Biochem Biophys. 2007; 463: 134-148Crossref PubMed Scopus (110) Google Scholar]. In addition, there is evidence that the C-cytoplasmic domain may also play an important role in the traffic and cellular distribution of the translocase [3Lutsenko S.E. LeShane S. Shinde U. Biochemical basis of regulation of human copper-transporting ATPases.Arch Biochem Biophys. 2007; 463: 134-148Crossref PubMed Scopus (110) Google Scholar, 4Petris M.J. Camakaris J. Greenough M. LaFontaine S. Mercer J.F. A C-terminal di-leucine is required for localization of the Menkes protein in the trans-Golgi network.Hum Mol Genet. 1998; 7: 2063-2071Crossref PubMed Scopus (134) Google Scholar].Over 300 mutations in the ATP7B gene have been associated with WD, the majority missense mutations (60%). Mutations affecting to different extents the binding of Cu, the cyclic phosphorylation, traffic, and posttranslational modifications of ATP7B as well as its physiological interaction with other proteins, may potentially interfere with the dual role of ATP7B in excreting excess Cu into the bile and in the biosynthesis of the ceruloplasmin essential for proper iron (Fe) metabolism.The most prevailing mutations in Wilson patients are H1069Q/G in Europe and North America, and R778L in southeast Asia [[5]Ferenci P. Regional distribution of mutations of the ATP7B gene in patients with Wilson disease: impact on genetic testing.Hum Genet. 2006; 120: 151-159Crossref PubMed Scopus (197) Google Scholar]. Though H1069 residue plays a critical role in the ATP-binding to the N-domain of ATP7B, the demonstration that the H1069Q mutant is retained and quickly degraded in the ER suggests that this is the primary cause of the WD. The same traffic defect has been found in studies of the R778L mutant [[6]Forbes J.R. Cox D.W. Copper-dependent trafficking of Wilson disease mutant ATP7B proteins.Hum Mol Genet. 2000; 9: 1927-1935Crossref PubMed Scopus (137) Google Scholar]. Besides, the association of WD with more than 40 different mutations in the N-site of ATP7B and the fact that only four of these mutations affect residues implicated in ATP-binding, point to the importance of cooperation between a large number of residues in the construction of a functional N-domain. The disruption of ATP7B-trafficking and the hampering of its phosphorylation provokes its dysfunction in the hepatocyte and explains the inhibition of Cu elimination into the bile. Interestingly, the liver from patients with G943S and M769V mutations, that inhibit the apical trafficking of ATP7B without interfering with its retention in the TGN, produces normal ceruloplasmin levels and as a result may not develop severe CNS intoxication.Clinical symptoms in WD include cirrhosis and chronic hepatitis that end in liver failure, neurological defects that course with parkinsonian symptoms and seizures, and psychiatric features [[7]Ala A. Walker A.P. Ashkan K. Dooley J.S. Schilsky M.L. Wilson's disease.Lancet. 2007; 369: 397-408Abstract Full Text Full Text PDF PubMed Scopus (831) Google Scholar]. The Kayser–Fleischer ring, a deposition of Cu visible as a golden ring in the periphery of the cornea, low serum levels of ceruloplasmin, and high levels of Cu in the urine are helpful in the diagnosis of the disease. The age of presentation of the WD syndrome, the predominance of hepatic versus neurological symptoms and their severity are strikingly variable. Excessive Cu-derived oxidants produced by free Cu2+ - catalyzed Fenton reactions and reduced superoxide dismutase and glutathione activities, appear to contribute decisively to the development and progression of liver abnormalities in WD [[8]Nagasaka H. Inoue I. Inui A. Komatsu H. Sogo T. Murayama K. et al.Relationship between oxidative stress and antioxidant systems in the liver of patients with Wilson's disease: hepatic manifestation in Wilson disease as a consequence of augmented oxidative stress.Pediatr Res. 2006; 60: 472-477Crossref PubMed Scopus (61) Google Scholar]. Furthermore, the toxic accumulation of Cu and the development of hepatic abnormalities without neurological symptoms in a group of WD patients is mimicked in the Cu toxicosis developed by the Long-Evans cinnamon rat (5′ deletion) and the 'toxic milk' mouse. Genotype variations in the mutations may partly explain the variability behind the clinical symptoms but is also likely that this also results from the activity of modifier genes and gene-environment interactions. Moreover, increased binding of Wilson's disease ATP7B with COMMD1, a negative regulator of protein stability involved in the quality control of ATP7B and absent in Bedlington terriers suffering from copper toxicosis, results in a decrease of their stability that may result in the amplification of the mutation effects and partially explains the clinical heterogeneity observed in WD [[9]de Bie P. van de Sluis B. Burstein E. van de Berghe P.V. Muller P. Berger R. et al.Distinct Wilson's disease mutations in ATP7B are associated with enhanced binding to COMMD1 and reduced stability of ATP7B.Gastroenterology. 2007; 133: 1316-1326Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar].The capacity of Zn to induce metallothionein (MT) and the formation of tight MT–Cu complexes in the intestinal mucosa explains the effectiveness of the oral administration of Zn acetate in reducing dietary Cu absorption and the levels of intestinal haefestin, responses that ameliorate the clinical manifestations associated with Cu and iron accumulation in WD patients [[10]Sinha S. Taly A.B. Withdrawal of penicillamine from zinc sulphate–penicillamine maintenance therapy in Wilson's disease: promising, safe and cheap.J Neurol Sci. 2007; 264: 129-132Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar].Conflict of InterestThe authors who have taken part in this study declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript. Wilson disease (WD) is a rare autosomal recessive disorder of Cu metabolism linked to dysfunction of the Cu translocase ATP7B expressed in hepatocytes [[1]Bull P.C. Thomas G.R. Rommens J.M. Forbes J.R. Cox D.W. The Wilson disease gene is a putative copper transporting P-type ATPase similar to the Menkes gene.Nat Genet. 1993; 5: 327-337Crossref PubMed Scopus (1688) Google Scholar]. ATP7B is critical in the distribution and elimination of excess Cu from the organism. Malfunctioning of the translocase interferes with the distribution of Cu among organs and tissues and results in the imbalance between Cu absorption and excretion, thus causing Cu toxicosis. The levels of Cu regulate the distribution and traffic of ATP7B in the hepatocyte. While at normal Cu concentrations, ATP7B remains in the TGN (trans-Golgi network) to supply Cu to the newly synthesized cuproproteins; at Cu concentrations exceeding the physiological limits it is transferred to the membranes of the bile canaliculi to dissipate the toxic levels of Cu [[2]Hernandez S. Tsuchiya Y. García-Ruiz J.P. Lalioti V. Nielsen S. Cassio D. et al.ATP7B copper-regulated traffic and association with the tight junctions: copper excretion into the bile.Gastroenterology. 2008; 134: 1215-1223Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar]. Proper cellular distribution and functioning of ATP7B requires the coordinated interaction between its separate modules. Whereas the six Cu+-binding domains in its long N-cytoplasmic domain play a major role in the acceptance of Cu+ and in controlling the phosphorylation, traffic, and activity of the translocase, the clustering of its eight transmembrane helixes forms the Cu+ pore, and the connecting loops in the cytoplasmic side are involved in the cyclic phosphorylation that controls the activity of the translocase (Fig. 1A and B) [[3]Lutsenko S.E. LeShane S. Shinde U. Biochemical basis of regulation of human copper-transporting ATPases.Arch Biochem Biophys. 2007; 463: 134-148Crossref PubMed Scopus (110) Google Scholar]. In addition, there is evidence that the C-cytoplasmic domain may also play an important role in the traffic and cellular distribution of the translocase [3Lutsenko S.E. LeShane S. Shinde U. Biochemical basis of regulation of human copper-transporting ATPases.Arch Biochem Biophys. 2007; 463: 134-148Crossref PubMed Scopus (110) Google Scholar, 4Petris M.J. Camakaris J. Greenough M. LaFontaine S. Mercer J.F. A C-terminal di-leucine is required for localization of the Menkes protein in the trans-Golgi network.Hum Mol Genet. 1998; 7: 2063-2071Crossref PubMed Scopus (134) Google Scholar]. Over 300 mutations in the ATP7B gene have been associated with WD, the majority missense mutations (60%). Mutations affecting to different extents the binding of Cu, the cyclic phosphorylation, traffic, and posttranslational modifications of ATP7B as well as its physiological interaction with other proteins, may potentially interfere with the dual role of ATP7B in excreting excess Cu into the bile and in the biosynthesis of the ceruloplasmin essential for proper iron (Fe) metabolism. The most prevailing mutations in Wilson patients are H1069Q/G in Europe and North America, and R778L in southeast Asia [[5]Ferenci P. Regional distribution of mutations of the ATP7B gene in patients with Wilson disease: impact on genetic testing.Hum Genet. 2006; 120: 151-159Crossref PubMed Scopus (197) Google Scholar]. Though H1069 residue plays a critical role in the ATP-binding to the N-domain of ATP7B, the demonstration that the H1069Q mutant is retained and quickly degraded in the ER suggests that this is the primary cause of the WD. The same traffic defect has been found in studies of the R778L mutant [[6]Forbes J.R. Cox D.W. Copper-dependent trafficking of Wilson disease mutant ATP7B proteins.Hum Mol Genet. 2000; 9: 1927-1935Crossref PubMed Scopus (137) Google Scholar]. Besides, the association of WD with more than 40 different mutations in the N-site of ATP7B and the fact that only four of these mutations affect residues implicated in ATP-binding, point to the importance of cooperation between a large number of residues in the construction of a functional N-domain. The disruption of ATP7B-trafficking and the hampering of its phosphorylation provokes its dysfunction in the hepatocyte and explains the inhibition of Cu elimination into the bile. Interestingly, the liver from patients with G943S and M769V mutations, that inhibit the apical trafficking of ATP7B without interfering with its retention in the TGN, produces normal ceruloplasmin levels and as a result may not develop severe CNS intoxication. Clinical symptoms in WD include cirrhosis and chronic hepatitis that end in liver failure, neurological defects that course with parkinsonian symptoms and seizures, and psychiatric features [[7]Ala A. Walker A.P. Ashkan K. Dooley J.S. Schilsky M.L. Wilson's disease.Lancet. 2007; 369: 397-408Abstract Full Text Full Text PDF PubMed Scopus (831) Google Scholar]. The Kayser–Fleischer ring, a deposition of Cu visible as a golden ring in the periphery of the cornea, low serum levels of ceruloplasmin, and high levels of Cu in the urine are helpful in the diagnosis of the disease. The age of presentation of the WD syndrome, the predominance of hepatic versus neurological symptoms and their severity are strikingly variable. Excessive Cu-derived oxidants produced by free Cu2+ - catalyzed Fenton reactions and reduced superoxide dismutase and glutathione activities, appear to contribute decisively to the development and progression of liver abnormalities in WD [[8]Nagasaka H. Inoue I. Inui A. Komatsu H. Sogo T. Murayama K. et al.Relationship between oxidative stress and antioxidant systems in the liver of patients with Wilson's disease: hepatic manifestation in Wilson disease as a consequence of augmented oxidative stress.Pediatr Res. 2006; 60: 472-477Crossref PubMed Scopus (61) Google Scholar]. Furthermore, the toxic accumulation of Cu and the development of hepatic abnormalities without neurological symptoms in a group of WD patients is mimicked in the Cu toxicosis developed by the Long-Evans cinnamon rat (5′ deletion) and the 'toxic milk' mouse. Genotype variations in the mutations may partly explain the variability behind the clinical symptoms but is also likely that this also results from the activity of modifier genes and gene-environment interactions. Moreover, increased binding of Wilson's disease ATP7B with COMMD1, a negative regulator of protein stability involved in the quality control of ATP7B and absent in Bedlington terriers suffering from copper toxicosis, results in a decrease of their stability that may result in the amplification of the mutation effects and partially explains the clinical heterogeneity observed in WD [[9]de Bie P. van de Sluis B. Burstein E. van de Berghe P.V. Muller P. Berger R. et al.Distinct Wilson's disease mutations in ATP7B are associated with enhanced binding to COMMD1 and reduced stability of ATP7B.Gastroenterology. 2007; 133: 1316-1326Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar]. The capacity of Zn to induce metallothionein (MT) and the formation of tight MT–Cu complexes in the intestinal mucosa explains the effectiveness of the oral administration of Zn acetate in reducing dietary Cu absorption and the levels of intestinal haefestin, responses that ameliorate the clinical manifestations associated with Cu and iron accumulation in WD patients [[10]Sinha S. Taly A.B. Withdrawal of penicillamine from zinc sulphate–penicillamine maintenance therapy in Wilson's disease: promising, safe and cheap.J Neurol Sci. 2007; 264: 129-132Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar]. Conflict of InterestThe authors who have taken part in this study declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript. The authors who have taken part in this study declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript.