Expression was normalized for-ActinmRNA levels, and relatively expressed to Commd1loxP/loxPmice.C.) Immunoblot analysis of liver tissue of Commd1loxP/loxPandCommd1hepmice at six weeks of age. liver up to a 20-fold increase compared to controls. These copper levels did not result in significant induction of the copper-responsive genes metallothionein I and II, neither was there evidence of biochemical liver injury nor overt liver pathology. The biosynthesis of ceruloplasmin was clearly augmented with age inCommd1hepmice. Although COMMD1 expression is associated with changes in ATP7B protein stability, no clear correlation between Atp7b levels and copper accumulation inCommd1hepmice could be detected. Despite the absence of hepatocellular toxicity inCommd1hepmice, the changes in liver copper displayed several parallels with copper toxicosis in Bedlington terriers. Thus, these results provide the first genetic evidence for COMMD1 to play an essential role in hepatic copper homeostasis and present a valuable mouse model for further understanding of the molecular mechanisms underlying hepatic copper homeostasis. == Introduction == As a redox catalyst, the trace element copper is essential to the well-being of all living organisms (reviewed by[1],[2],[3],[4]), in excess however, copper can be highly toxic due to its participation in the formation of reactive oxygen species (ROS). It is therefore important to maintain a strict balance between the essentiality and the toxicity of copper, and this involves a range of mechanisms mediating copper uptake, transport, storage and excretion. The importance of a balanced copper homeostasis in preventing toxicity is clearly illustrated by various inherited hepatic copper storage disorders such as Wilson disease (WD; OMIM #277900), Indian childhood cirrhosis (ICC; OMIM #215600), endemic Tyrolean infantile cirrhosis (ETIC; OMIM #215600) and idiopathic copper toxicosis (ICT; OMIM #215600). In WD, mutations in theATP7Bgene lead to copper accumulation in different tissues, particularly in liver and brain. SDF-5 The genetic defects underlying ICC, ETIC and ICT remain elusive, but the clinical manifestation of these non-Wilsonian copper storage disorders depends in most cases on an excessive dietary intake of copper[5],[6],[7]. Another well-documented copper Levocetirizine Dihydrochloride overload disorder is copper toxicosis (CT) in Bedlington terriers. CT is an autosomal recessive disease linked to a homozygous genomic deletion, encompassing exon 2, of theCOMMD1gene[8]. Affected dogs are characterized by hepatic copper overload, due to an inefficient copper excretion via the bile, resulting in liver fibrosis and eventually cirrhosis[9],[10]. In contrast to WD, Bedlington terriers affected with CT do not display any signs of neurological defects and have normal serum concentrations of the copper-bound ferroxidase ceruloplasmin (Cp)[10]. AlthoughCOMMD1has been suggested Levocetirizine Dihydrochloride as a candidate gene for the non-Wilsonian copper storage disorders ICC, ETIC and ICT, no mutations inCOMMD1have been identified in these patients so far[11],[12]. The 21 Levocetirizine Dihydrochloride kDa ubiquitously expressed COMMD1 protein is considered as the prototype of the COMMD protein family, which is highly conserved between eukaryotes and in some protozoa[13],[14]. The ten COMMD family members (COMMD1 10) share a C-terminal COMM domain of 7085 amino acids that mediates protein-protein interactions and nuclear export of COMMD proteins[15],[16],[17]. Except for COMMD1, the functions of most of the COMMD proteins are largely unknown. Several studies on COMMD1 have provided supportive evidence of its role in copper homeostasis. First, COMMD1 interacts with the copper transporter ATP7B, and is suggested to regulate its proteolysis[18],[19],[20]. Second, down-regulation of COMMD1 expression results in increased intracellular copper concentrations both in HEK293T cells and the mouse hepatoma Hepa1-6 cells[20],[21]. Third, we recently demonstrated that the copper transporting activity of ATP7A, a copper transporter with high homology to ATP7B, is also mediated by COMMD1 expression[22]. Besides its role in copper homeostasis, COMMD1 is also implicated in several other pathways, such as sodium transport, antioxidant defense, and NF-B and hypoxia signaling[17],[23],[24],[25],[26],[27],[28],[29],[30]. Interestingly, in contrast to dogs deficient forCOMMD1, a genetic deletion ofCommd1in mice results in embryonic lethality[31]. Altogether, these data illustrate that COMMD1 is a protein with a pleiotropic function, although its role in hepatic copper metabolism is still not well defined. To gain more insight into the function of COMMD1 in hepatic copper homeostasis in particular, and to circumvent the embryonic lethality of theCommd1knockout mice, we generated a hepatocyte-specificCommd1knockout mouse. Here, we provide the first genetic evidence that Commd1 is essential for hepatic copper excretion as Commd1-deficient mice show increased intrahepatic. Levocetirizine Dihydrochloride
