Animal models of Wilson disease

Abstract

Wilson disease (WD) is an autosomal recessive disorder of copper metabolism manifesting with hepatic, neurological and psychiatric symptoms. The limitations of the currently available therapy for WD (particularly in the management of neuropsychiatric disease), together with our limited understanding of key aspects of this illness (e.g. neurological vs. hepatic presentation) justify the ongoing need to study WD in suitable animal models. Four animal models of WD have been established: the Long-Evans Cinnamon rat, the toxic-milk mouse, the Atp7b knockout mouse and the Labrador retriever. The existing models of WD all show good similarity to human hepatic WD and have been helpful in developing an improved understanding of the human disease. As mammals, the mouse, rat and canine models also benefit from high homology to the human genome. However, important differences exist between these mammalian models and human disease, particularly the absence of a convincing neurological phenotype. This review will first provide an overview of our current knowledge of the orthologous genes encoding ATP7B and the closely related ATP7A protein in C. elegans, Drosophila and zebrafish (Danio rerio) and then summarise key characteristics of rodent and larger mammalian models of ATP7B-deficiency.

Keywords: Animal models; Wilson disease.

Fig. 1

A dendrogram demonstrating the evolutionary relationships of the P_1B- type ATPases from human, zebrafish, rat, mouse, macaque, sheep, Xenopus (frog), Drosophila (fruit fly), C. elegans (roundworm) and S. cerevisiae (yeast). Orthologues were identified on Blast and the protein sequences for each were identified on Ensembl and the dendrogram generated using Clustal Omega.

Fig. 2

Whole mount atp7b in situ hybridisation of zebrafish embryos. (a) Dorsal and left lateral views zebrafish embryos at 5 days post fertilization, stained with the antisense atp7b probe demonstrating expression of atp7b in the head, and liver at this age. (b) Dorsal and lateral view of embryo stained with sense atp7b control/sense probe, demonstrating absence of staining.

Fig. 3

Atp7b deficiency results in marked reduction of the liver marker expression fabp10a and a severe neurological disease phenotype in zebrafish embryos at 4 days post fertilization (dpf). (a, b, c) Whole mount in-situ hybridisation using a probe for liver marker fabp10a was performed on control morpholino-injected, atp7b morpholino-injected and atp7b and p53 morpholino co-injected embryos. p53 morpholino co-injection was used to demonstrate that the phenotype was unlikely to be due to p53-mediated off-target effects of the morpholino. A decrease in expression of fabp10a, presumably reflecting a decrease in size or absence of the liver in was seen in atp7b morphants. (a) control morpholino-injected. (b) atp7b morphants. (c) atp7b morphants co-injected with p53 morpholino. (d, e, f) A transgenic HuC reporter line was used to study the effect of Atp7b deficiency on brain size. (d) control morpholino-injected. (e) atp7b morpholino-injected. (f) atp7b and p53 morpholino co-injected. Atp7b deficiency was associated with a decreased in the size of the brain. (g, h, i) WTos4 embryos which express DsRed on the hsp70 promoter show increased fluorescence in the zebrafish hind brain (green and blue arrows) in response to Atp7b deficiency. (g) control morpholino-injected. (h) atp7b morpholino-injected. (i) atp7b and p53 morpholino co-injected.