Mottled Mouse Mutants Research Articles

ATP7A Gene Addition to the Choroid Plexus Results in Long-term Rescue of the Lethal Copper Transport Defect in a Menkes Disease Mouse Model

Menkes disease is a lethal infantile neurodegenerative disorder of copper metabolism caused by mutations in a P-type ATPase, ATP7A. Currently available treatment (daily subcutaneous copper injections) is not entirely effective in the majority of affected individuals. The mottled-brindled (mo-br) mouse recapitulates the Menkes phenotype, including abnormal copper transport to the brain owing to mutation in the murine homolog, Atp7a, and dies by 14 days of age. We documented that mo-br mice on C57BL/6 background were not rescued by peripheral copper administration, and used this model to evaluate brain-directed therapies. Neonatal mo-br mice received lateral ventricle injections of either adeno-associated virus serotype 5 (AAV5) harboring a reduced-size human ATP7A (rsATP7A) complementary DNA (cDNA), copper chloride, or both. AAV5-rsATP7A showed selective transduction of choroid plexus epithelia and AAV5-rsATP7A plus copper combination treatment rescued mo-br mice; 86% survived to weaning (21 days), median survival increased to 43 days, 37% lived beyond 100 days, and 22% survived to the study end point (300 days). This synergistic treatment effect correlated with increased brain copper levels, enhanced activity of dopamine-β-hydroxylase, a copper-dependent enzyme, and correction of brain pathology. Our findings provide the first definitive evidence that gene therapy may have clinical utility in the treatment of Menkes disease.

Perinatal Copper Deficiency Alters Rat Cerebellar Purkinje Cell Size and Distribution

Copper is required for activity of several key enzymes and for optimal mammalian development, especially within the central nervous system. Copper-deficient (CuD) animals are visibly ataxic, and previous studies in rats have demonstrated impaired motor function through behavioral experiments consistent with altered cerebellar development. Perinatal copper deficiency was produced in Holtzman rat dams by restricting dietary copper during the last two thirds of gestation and lactation. Male offspring were evaluated at postnatal day 25. Compared to cerebella from copper-adequate pups, the CuD pups had larger Purkinje cell (PC) size and irregularities in the Purkinje cell monolayer. These results suggest that the ataxic behavioral phenotype of CuD rats may result from disrupted inhibitory pathways in the cerebellum. A similar PC phenotype is seen in Menkes disease and in mottled mouse mutants with genetic copper deficiency, suggesting that copper deficiency and not just specific loss of ATP7A function is responsible.

Expression and Accumulation of Lysyl Oxidase, Elastin, and Type I Procollagen in Human Menkes and Mottled Mouse Fibroblasts

Menkes syndrome in humans is an X-linked disorder characterized in part by abnormal copper transport, cellular copper sequestration, and defective crosslinking of collagen and elastin. A decrease in the functional activity of lysyl oxidase, a cuproenzyme, is thought in part to be responsible for the decreased crosslinking of collagen and elastin. It has also been suggested that low levels of lysyl oxidase activity may occur secondarily to disturbances in intracellular copper translocation and consequently impaired incorporation of copper into lysyl oxidase. Herein, we examine the expression and accumulation of selected extracellular matrix proteins in fibroblasts from a Menkes patient, as well as fibroblasts from the tortoiseshell (Mo To/y) mouse. The Mo To mutation is an allele of the mottled (Mo) locus, which is considered to be a murine analog of the human Menkes locus. In both Menkes and tortoiseshell fibroblasts, levels of lysyl oxidase mRNA transcripts were less than 15% of levels for corresponding controls. The level of elastin mRNA transcripts was also markedly lower in both cell lines in comparison to controls. In contrast, the levels of procollagen Type I mRNA were similar or enhanced in Menkes and Mo To/y fibroblasts compared to their respective controls. Consequently, we conclude that the connective tissue defects associated with Menkes syndrome and those occurring in mottled mouse mutants involve more than abnormal copper utilization in the formation of lysyl oxidase holoenzyme. Based on the present studies in cell culture, the production of essential enzymes and matrix proteins, such as lysyl oxidase and elastin, appear to be altered at the level of transcription or mRNA turnover.

Mutations in humans and animals which affect copper metabolism.

Various inherited disorders of copper metabolism in man and animals are reviewed. Emphasis is placed on the use of cultured cells from mutants to determine the primary molecular defects and to acquire basic knowledge of normal copper metabolism. This allows better diagnostic tests and possible treatment of the disorders. Menkes' disease in humans and mottled mouse mutants are discussed in detail, as they illustrate these approaches.

Copper metabolism in mottled mouse mutants. The effect of copper therapy on lysyl oxidase activity in brindled (Mobr) mice.

Lysyl oxidase activity in extracts of skin from 1-day-old Mobr/Y mice was found to be between 50 and 60% of that in corresponding extracts from littermate +/Y mice of the same age. It was increased to 84-150% of that in the latter by prior treatment of the Mobr/Y mice at 7 days of age with a single subcutaneous injection of 50 micrograms of copper, retained as Cu+ in an alkyl polyether/sebacic acid solution. This suggests that in this form the copper is able to by-pass the block in copper metabolism and is deliverable to copper-requiring processes.

Copper metabolism in mottled mouse mutants: copper therapy of brindled (Mobr) mice.

Copper therapy was applied to brindled mouse mutants, which suffer from lethal hypocupraemia, by using cuprous and cupric solutions. The method of treatment was a single subcutaneous injection of 50 microgram of copper at 7 days of age. Early effects of the dose were: prevention of the tremors and spasms seen in untreated mutants, raising to normal and near-normal of caeruloplasmin oxidase and lysyl oxidase activities and pigmentation of skin and fur. Growth of mutants was retarded up to 23 days of age, but thereafter they rapidly gained weight to be nearly normal by 60 days of age. At 3 days after injection, copper concentrations in previously deficient mutant organs apart from liver were at least as much as those of treated normals, which had remained unchanged. Copper in mutant livers had increased only slightly in comparison with the normal control. A state of copper deficiency recurred in mutant tissues by 25 days after injection. A solution of Cu+, retained as such by an alkyl polyether, and sebacic acid resulted in greater growth rates after 23 days than did three other copper treatments. Cu+ may have resulted in an improved growth response owing to it being more readily metabolized than C12+. Delayed release of copper from the site of injection may have played an important role.

Copper metabolism in mottled mouse mutants: distribution of 64Cu in brindled (Mobr) mice.

1. Duodenal injection of 64Cu in treated adult mutant mice (Mobr/y) revealed severe malabsorption of copper. In suckling mutants, malabsorption was less severe, owing to delayed absorption between 2 and 5 h after injection. Pinocytosis at the distal small intestine seems the likely explanation for this difference, and this is supported by results of ileal injection of radioisotope in the suckling mice. 2. The distribution of 64 Cu in various organs was measured in suckling normal, mutant and heterozygote mice and in adult normal and mutant mice during 48 h after intracardiac injection. Excessive accumulation of radioisotope was observed in most extrahepatic organs of mutant and heterozygote mice and was most pronounced in kidney. This could not be explained by initial copper deficiency. The livers of suckling mutant and heterozygote mice lost radioisotope rapidly after normal initial uptake. This pattern was not seen in adult mutants.

Copper metabolism in mottled mouse mutants: copper concentrations in tissues during development.

The copper content of various organs of ;brindled' female heterozygotes and male mice affected by this X-linked mutation are documented at the last day of intrauterine development, at 1 day after birth and at 11 days of age. The findings indicate defective placental transfer of copper in utero, and an even more marked defect in intestinal absorption of copper after birth. In addition there is an abnormal distribution of copper among the tissues of the body once it is absorbed. The mutation produces abnormal accumulation of copper in kidney, in gut mucosa and in testis, whereas liver, brain, plasma and most other organs show diminished copper concentrations. The intestinal malabsorption of copper is accompanied by accumulation of abnormal amounts of the metal in the intestinal-mucosa cells. Copper concentrations in both mucosa and luminal contents rise progressively from duodenum to ileum. Defective upper-intestinal absorption, consequent progressive increase in luminal copper concentration and pinocytosis in the ileum would seem to explain the findings. Radioisotopic studies eliminated the possibility of excessive excretion of copper in bile or across the intestinal mucosa. Detailed comparison with findings in humans with Menkes' syndrome is difficult because of the different stages of development at which the studies have been performed, but the results seem in general to conform very satisfactorily. Those differences seen are probably explicable by known species differences. All the findings are in accord with a hypothesis that the basic defect involves accumulation and retention of copper in the cells of affected tissues such as kidney, gut mucosa and placenta.

Catecholamine biosynthesis and the activity of a number of copper-dependent enzymes in the copper deficient mottled mouse mutants

1. The activity of the copper enzymes cytochrome c oxidase and superoxide dismutase is reduced in brain tissue from the copper deficient brindled ( Mo br ) mutant in the mouse. In contrast, the activity of copper-enzymes in liver tissue is unaffected. 2. An elevated activity of adrenal dopamine-β-hydroxylase in blotchy ( Mo blo ) hemizygotes is also reported, together with a reduction in adrenal tissue from brindled hemizygotes in the activities of phenylethanolamine N-methyltransferase and monoamine oxidase, and in the total concentration of catecholamines. 3. The significance of these results to the regulation of cathecholamine biosynthesis is discussed.