The relationship of excess copper accumulation by fibroblasts from the brindled mouse model of Menkes disease to the primary defect

Diagnostic copper imaging of Menkes disease by synchrotron radiation-generated X-ray fluorescence analysis

Copper (Cu) is an indispensable metal for normal development and function of humans, especially in central nervous system (CNS). However, its redox activity requires accurate Cu transport system. ATP7A, a main Cu(2+) transporting-ATPase, is necessary to efflux Cu across the plasma membrane and synthesize cuproenzymes. Menkes disease (MD) is caused by mutations in ATP7A gene. Clinically, MD is Cu deficiency syndrome and is treated with Cu-histidine injections soon after definite diagnosis. But outcome of the most remains poor. To estimate the standard therapy, Cu distribution in the treated classic MD patients is analyzed by synchrotron-generated X-ray fluorescence technique (SR-XRF), which identifies and quantifies an individual atom up to at subcellular level of resolution with wide detection area. SR-XRF analysis newly reveals that Cu exists in spinal cord parenchyma and flows out via venous and lymph systems. By systemic analysis, excess Cu is detected in the proximal tubular cells of the kidney, the mucosal epithelial cells of the intestine, and the lymph and venous systems. The current study suggests that the standard therapy supply almost enough Cu for patient tissues. But given Cu passes through the tissues to venous and lymph systems, or accumulate in the cells responsible for Cu absorption.

Metallothionein is crucial for safe intracellular copper storage and cell survival at normal and supra-physiological exposure levels

MTs (metallothioneins) increase the resistance of cells to exposure to high Cu (copper) levels. Characterization of the MT-Cu complex suggests that MT has an important role in the cellular storage and/or delivery of Cu ions to cuproenzymes. In this work we investigate how these properties contribute to Cu homoeostasis by evaluating the uptake, accumulation and efflux of Cu in wild-type and MT I/II null rat fibroblast cell lines. We also assessed changes in the expression of Cu metabolism-related genes in response to Cu exposure. At sub-physiological Cu levels (0.4 microM), the metal content was not dependent on MT; however, when extracellular Cu was increased to physiological levels (10 microM), MTs were required for the cell's ability to accumulate the metal. The subcellular localization of the accumulated metal in the cytoplasm was MT-dependent. Following supra-physiological Cu exposure (>50 microM), MT null cells had a decreased capacity for Cu storage and an elevated sensitivity to a minor increment in intracellular metal levels, suggesting that intracellular Cu toxicity is due not to the metal content but to the interactions of the metal with cellular components. Moreover, MT null cells failed to show increased levels of mRNAs encoding MT I, SOD1 (superoxide dismutase 1) and Ccs1 (Cu chaperone for SOD) in response to Cu exposure. These results support a role for MT in the storage of Cu in a safe compartment and in sequestering an intracellular excess of Cu in response to supra-physiological Cu exposure. Gene expression analysis suggests the necessity of having MT as part of the signalling pathway that induces gene expression in response to Cu.

A 31P-magnetic resonance spectroscopy and biochemical study of the mo(vbr) mouse: potential model for the mitochondrial encephalomyopathies

31P-magnetic resonance spectroscopy (31P-MRS) provides new biochemical information on mitochondrial disorders affecting brain and muscle. To elucidate the mechanisms of mitochondrial abnormalities, however, animal models are needed. We assessed the mo(vbr) (mottled viable brindled) mouse for its value in studying (1) energetics of a mitochondrial disorder and (2) 31P-MRS changes associated with mitochondrial abnormalities in vivo. The maximal activity of succinate-cytochrome c reductase was significantly reduced in mo(vbr) muscle compared to controls, whereas cytochrome oxidase activity was only reduced in mo(vbr) brain. 31P-MRS of mo(vbr) brain showed an increased pH, but no changes in any metabolite ratios. The phosphocreatine (PCr) recovery rate after exercise was reduced in muscles from mo(vbr) mice, indicating impairment of oxidative metabolism. We conclude that mo(vbr) brain and muscle tissue have biochemical abnormalities consistent with mitochondrial impairment. The PCr recovery rate, measured by 31P-MRS, was sensitive to the muscle abnormality. This strain is best described as having chronic mitochondrial dysfunction.

Identification of a major hepatic copper binding protein as S-adenosylhomocysteine hydrolase

The properties of a mouse liver copper binding protein (CuBP) and human placental S-adenosylhomocysteine hydrolase (SAHH) were compared to test the hypothesis that CuBP is SAHH. CuBP and SAHH migrated identically on SDS-polyacrylamide gel electrophoresis gels, and their 48-kDa monomers both self-associate to tetramers. Human placental SAHH cross-reacted with polyclonal antibodies to mouse liver CuBP, and CuBP from mouse liver cross-reacted with two monoclonal antibodies to human placental SAHH. A third monoclonal antibody to human placenta SAHH reacted weakly with the mouse liver protein but well with CuBP from human lymphoblasts. NAD(+)-activated CuBP has high SAHH enzymatic activity. Moreover, human placental SAHH, like mouse liver CuBP, has a single high affinity copper binding site per 48-kDa subunit. Thus, the data confirm that CuBP is SAHH, and SAHH is proposed to be a bifunctional protein with roles in sulfur-amino acid metabolism and copper metabolism. The copper binding activity of SAHH is proposed to play a significant role in the intracellular distribution of copper, and SAHH enzymatic activity may influence copper metabolism through its role in cysteine biosynthesis from methionine.

Copper binding to mouse liver S-adenosylhomocysteine hydrolase and the effects of copper on its levels

The dissociation constant and stoichiometry of copper binding to mouse liver S-adenosylhomocysteine hydrolase (SAHH) was determined as part of characterizing the possible roles of SAHH in copper metabolism. Copper (64Cu(II)) binding was measured by an ultrafiltration method in the presence of EDTA as a competing ligand. The KD was 3.9 +/- 0.7 x 10(-16) M, and the stoichiometry was one g atom of copper per 48-kDa subunit. Western blots indicated that the liver contains approximately 12 times more SAHH than the kidney, which in turn contains approximately 5 times more SAHH than the brain. The high concentration and copper affinity of SAHH in the liver may contribute to the liver's ability to preferentially accumulate copper, and the low levels of SAHH in the brain may contribute to the sensitivity of the brain to copper deficiency. The effects of genetic defects of copper metabolism and copper deficiency on SAHH were also determined. Normal SAHH levels were detected in brindled mouse liver, kidney, and brain. However, SAHH from brindled mouse liver eluted abnormally from phenyl Superose columns implying an effect of the brindled mouse defect on SAHH protein structure. Hepatic cytosols from the toxic milk mouse contained approximately 42% the amount of SAHH detected in controls, and hepatic levels of SAHH were also decreased by approximately 45% in copper-deficient mice. The binding properties of SAHH and the effects of abnormal states of copper metabolism on its levels are consistent with significant roles for SAHH in normal and abnormal copper metabolism. SAHH may have roles in regulating tissue copper levels and the distribution of intracellular copper.

Menkes' disease: perspective and update on a fatal copper disorder

Although the causes of the abnormal copper utilization seen in Menkes' disease remain unknown, a candidate gene reported by three laboratories has narrowed the search for the defective or missing factor. These genetic studies also suggest that a copper ATPase may be important in normal copper metabolism.

Isolation of a candidate gene for Menkes disease and evidence that it encodes a copper-transporting ATPase

Menkes disease is an X-linked disorder of copper transport characterized by progressive neurological degeneration and death in early childhood. We have isolated a candidate gene (Mc1) for Menkes disease and find qualitative or quantitative abnormalities in the mRNA in sixteen of twenty-one Menkes patients. Four patients lacking Mc1RNA showed rearrangements of the Menkes gene. The gene codes for a 1,500 amino acid protein, predicted to be a P-type cation-transporting ATPase. The gene product is most similar to a bacterial copper-transporting ATPase and additionally contains six putative metal-binding motifs at the N-terminus. The gene is transcribed in all cell types tested except liver, consistent with the expression of the Menkes defect.

Uptake of 67Cu by isolated human trophoblast cells

The isolated human trophoblast was used as a system to analyze the effects of different physiological ligands on cellular uptake of copper. The results show that the uptake of copper by these cells follows a similar pattern for the ligands tested (histidine, albumin and ceruloplasmin) as that for copper chloride. The process follows a typical hyperbolic curve at 37 degrees C. The initial phase of uptake follows a linear pattern during 30 min at 37 degrees C and at least 60 min at 4 degrees C from which the uptake rate is calculated. However, a significant decrease in the uptake rate is observed for albumin. The effect of histidine on stimulating copper transport is observed in the presence of serum, a phenomenon which is considered to be due to the release of copper that is bound to albumin. These results support the role of ceruloplasmin as a copper transport protein which releases copper at the cell surface, and a subsequent transport of the released copper in a manner similar to that of copper chloride or copper-histidine complexes.