Menkes disease: recent advances and new insights into copper metabolism

A 37-year-old Menkes disease patient-Residual ATP7A activity and early copper administration as key factors in beneficial treatment

Menkes disease (MD) is a lethal disorder characterized by severe neurological symptoms and connective tissue abnormalities; and results from malfunctioning of cuproenzymes, which cannot receive copper due to a defective intracellular copper transporting protein, ATP7A. Early parenteral copper-histidine supplementation may modify disease progression substantially but beneficial effects of long-term treatment have been recorded in only a few patients. Here we report on the eldest surviving MD patient (37 years) receiving early-onset and long-term copper treatment. He has few neurological symptoms without connective tissue disturbances; and a missense ATP7A variant, p.(Pro852Leu), which results in impaired protein trafficking while the copper transport function is spared. These findings suggest that some cuproenzymes maintain their function when sufficient copper is provided to the cells; and underline the importance of early initiated copper treatment, efficiency of which is likely to be dependent on the mutant ATP7A function.

A pilot study into a possible relationship between diet and stuttering

PURPOSE

There are theoretical and empirical reasons to consider a potential role for copper metabolism in the brain in how it could influence stuttering. However, a link between stuttering and dietary intake has never been researched in a systematic way. This pilot study therefore aimed to explore a possible association between ingested amounts of copper and thiamine (vitamin B1) with stuttering frequency using a double blind cross-over longitudinal paradigm.

METHODS

19 adults who stutter between 20 and 51 years old filled out an online survey for 9 consecutive weeks. The survey consisted of self-assessed fluency and mood state scales, as well as food journals. After 4 weeks, the participants consumed either copper or thiamine supplements for 2 weeks, followed by a 1-week washout period, and another period of two weeks taking the other supplement. Formal speech assessments were done pre/post baseline and at the end of each supplement intake. Participants were not informed about the nature of the supplements during the experiment and the investigators were blinded to the order of the supplements.

RESULTS

The results demonstrated that copper and thiamine had no measurable effect on the amount of stuttering (self and formal assessments) but there was a moderate, significant correlation between mood state and fluency.

CONCLUSION

The findings do not support notions of dietary influences of ingested copper or thiamine on stuttering but do provide modest support for a relationship between variations in stuttering and self-perceived anxiety.

Detection of genetically altered copper levels in Drosophila tissues by synchrotron x-ray fluorescence microscopy

Tissue-specific manipulation of known copper transport genes in Drosophila tissues results in phenotypes that are presumably due to an alteration in copper levels in the targeted cells. However direct confirmation of this has to date been technically challenging. Measures of cellular copper content such as expression levels of copper-responsive genes or cuproenzyme activity levels, while useful, are indirect. First-generation copper-sensitive fluorophores show promise but currently lack the sensitivity required to detect subtle changes in copper levels. Moreover such techniques do not provide information regarding other relevant biometals such as zinc or iron. Traditional techniques for measuring elemental composition such as inductively coupled plasma mass spectroscopy are not sensitive enough for use with the small tissue amounts available in Drosophila research. Here we present synchrotron x-ray fluorescence microscopy analysis of two different Drosophila tissues, the larval wing imaginal disc, and sectioned adult fly heads and show that this technique can be used to detect changes in tissue copper levels caused by targeted manipulation of known copper homeostasis genes.

The multi-layered regulation of copper translocating P-type ATPases

The copper-translocating Menkes (ATP7A, MNK protein) and Wilson (ATP7B, WND protein) P-type ATPases are pivotal for copper (Cu) homeostasis, functioning in the biosynthetic incorporation of Cu into copper-dependent enzymes of the secretory pathway, Cu detoxification via Cu efflux, and specialized roles such as systemic Cu absorption (MNK) and Cu excretion (WND). Essential to these functions is their Cu and hormone-responsive distribution between the trans-Golgi network (TGN) and exocytic vesicles located at or proximal to the apical (WND) or basolateral (MNK) cell surface. Intriguingly, MNK and WND Cu-ATPases expressed in the same tissues perform distinct yet complementary roles. While intramolecular differences may specify their distinct roles, cellular signaling components are predicted to be critical for both differences and synergy between these enzymes. This review focuses on these mechanisms, including the cell signaling pathways that influence trafficking and bi-functionality of Cu-ATPases. Phosphorylation events are hypothesized to play a central role in Cu homeostasis, promoting multi-layered regulation and cross-talk between cuproenzymes and Cu-independent mechanisms.

Narrow-bore HPLC-ICP-MS for speciation of copper in mutant mouse neonates bearing a defect in Cu metabolism

Minute amounts of tissue supernatants from mouse neonates bearing a mutation in the copper (Cu)-transporter gene, Atp7a, were injected into narrow-bore HPLC coupled with an inductively coupled plasma-mass spectrometer (ICP-MS) to examine Cu metabolism. In the 14-day-old mutant neonates, Cu accumulated in the intestine in the metallothionein (MT)-bound form, and mRNA expression of the two MT isoforms was increased. Meanwhile, Cu in the MT-bound form (Cu-MT) was depleted in the liver and mRNA expression decreased in comparison with wild-type mice. These results suggest that Cu is not secreted by intestinal microvillus cells into bloodstream due to the defect of Atp7a, and systemic depletion of Cu occurred. On the other hand, in the kidneys of mutant mice, Cu accumulated in the MT-bound form despite the fact that mRNA expression of the two MT isoforms was low. Part of Cu-MT in microvillus cells may be released into bloodstream at turnover and be preferably taken up by the kidneys. Consequently, the mRNA expression of MT isoforms was not always coincident with the amounts of MT proteins binding Cu, and narrow bore HPLC-ICP-MS used for MT protein determination is a complementary technique to real-time RT-PCR used for MT mRNA determination in Cu speciation.

Function and regulation of human copper-transporting ATPases

Copper-transporting ATPases (Cu-ATPases) ATP7A and ATP7B are evolutionarily conserved polytopic membrane proteins with essential roles in human physiology. The Cu-ATPases are expressed in most tissues, and their transport activity is crucial for central nervous system development, liver function, connective tissue formation, and many other physiological processes. The loss of ATP7A or ATP7B function is associated with severe metabolic disorders, Menkes disease, and Wilson disease. In cells, the Cu-ATPases maintain intracellular copper concentration by transporting copper from the cytosol across cellular membranes. They also contribute to protein biosynthesis by delivering copper into the lumen of the secretory pathway where metal ion is incorporated into copper-dependent enzymes. The biosynthetic and homeostatic functions of Cu-ATPases are performed in different cell compartments; targeting to these compartments and the functional activity of Cu-ATPase are both regulated by copper. In recent years, significant progress has been made in understanding the structure, function, and regulation of these essential transporters. These studies raised many new questions related to specific physiological roles of Cu-ATPases in various tissues and complex mechanisms that control the Cu-ATPase function. This review summarizes current data on the structural organization and functional properties of ATP7A and ATP7B as well as their localization and functions in various tissues, and discusses the current models of regulated trafficking of human Cu-ATPases.

NH2-terminal signals in ATP7B Cu-ATPase mediate its Cu-dependent anterograde traffic in polarized hepatic cells

Cu is an essential cofactor of cellular proteins but is toxic in its free state. The hepatic Cu-ATPase ATP7B has two functions in Cu homeostasis: it loads Cu+ onto newly synthesized apoceruloplasmin in the secretory pathway, thereby activating the plasma protein; and it participates in the excretion of excess Cu+ into the bile. To carry out these two functions, the membrane protein responds to changes in intracellular Cu levels by cycling between the Golgi and apical region. We used polarized hepatic WIF-B cells and high-resolution confocal microscopy to map the itinerary of endogenous and exogenous ATP7B under different Cu conditions. In Cu-depleted cells, ATP7B resided in a post-trans-Golgi network compartment that also contained syntaxin 6, whereas in Cu-loaded cells, the protein relocated to unique vesicles very near to the apical plasma membrane as well as the membrane itself. To determine the role of ATP7B's cytoplasmic NH2 terminus in regulating its intracellular movements, we generated seven mutations/deletions in this large [approximately 650 amino acid (AA)] domain and analyzed the Cu-dependent behavior of the mutant ATP7B proteins in WIF-B cells. Truncation of the ATP7B NH2 terminus up to the fifth copper-binding domain (CBD5) yielded an active ATPase that was insensitive to cellular Cu levels and constitutively trafficked to the opposite (basolateral) plasma membrane domain. Fusion of the NH2-terminal 63 AA of ATP7B to the truncated protein restored both its Cu responsiveness and correct intracellular targeting. These results indicate that important targeting information is contained in this relatively short sequence, which is absent from the related CuATPase, ATP7A.

The developmentally regulated expression of Menkes protein ATP7A suggests a role in axon extension and synaptogenesis

Menkes disease (MD) is a neurodegenerative disorder caused by mutation of the copper transporter ATP7A. While several enzymes expressed in mature neurons require copper, MD neurodegenerative changes cannot be explained by known requirements for ATP7A in neuronal development. To investigate additional roles for ATP7A during development, we characterized its pattern of expression using the olfactory system as a neurodevelopmental model. ATP7A expression in neurons was developmentally regulated rather than constitutively. Initially expressed in the cell bodies of developing neurons, ATP7A protein later shifted to extending axons, peaking prior to synaptogenesis. Similarly, after injury-stimulated neurogenesis, ATP7A expression increased in neurons and axons preceding synaptogenesis. Interestingly, copper-transport-deficient ATP7A still exhibits axonal localization. These results support a role for ATP7A in axon extension, which may contribute to the severe neurodegeneration characteristic of MD.

Menkes disease: a rare cause of bilateral inguinal hernias

This case of Menkes disease presented with the uncommon association of bilateral inguinal hernias at the age of 4 months. Further investigation demonstrated classical skeletal and neurological changes of this rare neurodegenerative disorder.

Identification of three novel mutations in Japanese patients with Menkes disease and mutation screening by denaturing high performance liquid chromatography

BACKGROUND

Menkes disease is an X-linked recessive disorder resulting in a connective-tissue disturbance and profound neurodegeneration in early childhood. The gene for Menkes disease has been isolated and predicted to code for copper transporting ATPase. In this study, a mutation analysis in Japanese patients with Menkes disease was performed, as was a mutation screening by denaturing high performance liquid chromatography (DHPLC).

METHODS

A mutation analysis on five Japanese patients with Menkes disease was performed using a direct sequencing method and DHPLC.

RESULTS

Two nonsense mutations, two missense mutations and one splice donor site mutation were found. The DHPLC analysis showed differences in the peaks between the DNA fragments of wild type and heteroduplex (wild type and mutant).

CONCLUSIONS

Three novel mutations (Asp1044Gly, Pro1279Leu and IVS21+1 g to a) were detected. The Asp1044Gly mutation destroys the highly conserved phosphorylation domain in exon 16. The splice site abnormality leads to a skipping of exon 21 coding for part of the seventh transmembrane domain. These two mutations could cause a severe protein dysfunction. Another missense mutation, Pro1279Leu, in exon 20 was found in a patient with a mild type of Menkes disease. It is speculated that this mutation partially maintains the ATP7A function is. A DHPLC analysis could detect these mutations. It is concluded that the best way to make a molecular diagnosis for Menkes disease is to first screen DNA samples for all exons using DHPLC, and thereafter perform direct sequencing for exons which have an abnormal elution profile in order to rapidly detect such mutations.

The plausibility of micronutrient deficiencies being a significant contributing factor to the occurrence of pregnancy complications

Numerous studies support the concept that a major cause of pregnancy complications can be suboptimal embryonic and fetal nutrition. Although the negative effects of diets low in energy on pregnancy outcome are well documented, less clear are the effects of diets that are low in one or more essential micronutrients. However, several observational and intervention studies suggest that diets low in essential vitamins and minerals can pose a significant reproductive risk in diverse human populations. Although maternal nutritional deficiencies typically occur as a result of low dietary intakes of essential nutrients, nutritional deficiencies at the level of the conceptus can arise through multiple mechanisms. Evidence from experimental animals supports the concept that in addition to primary deficiencies, secondary embryonic and fetal nutritional deficiencies can be caused by diverse factors including genetics, maternal disease, toxicant insults and physiological stressors that can trigger a maternal acute phase response. These secondary responses may be significant contributors to the occurrence of birth defects. An implication of the above is that the frequency and severity of pregnancy complications may be reduced through an improvement in the micronutrient status of the mother.

Developmental consequences of trace mineral deficiencies in rodents: acute and long-term effects

Approximately 3% of infants born have at least one serious congenital malformation. In the U.S., an average of 10 infants per thousand die before 1 y of life; about half of these deaths can be attributed to birth defects, low birth weight or prematurity. Although the causes of developmental abnormalities are clearly multifactorial in nature, we suggest that a common factor contributing to the occurrence of developmental abnormalities is suboptimal mineral nutrition during embryonic and fetal development. Using zinc and copper as examples, evidence is presented that nutritional deficiencies can rapidly affect the developing conceptus and result in gross structural abnormalities. Deficits of zinc or copper can result in rapid changes in cellular redox balance, tissue oxidative stress, inappropriate patterns of cell death, alterations in the migration of neural crest cells and changes in the expression of key patterning genes. In addition to well-recognized malformations, mineral deficiencies during perinatal development can result in behavioral, immunological and biochemical abnormalities that persist into adulthood. Although these persistent defects can in part be attributed to subtle morphological abnormalities, in other cases they may be secondary to epigenetic or developmental changes in DNA methylation patterns. Epigenetic defects combined with subtle morphological abnormalities can influence an individual's risk for certain chronic diseases and thus influence his or her risk for morbidity and mortality later in life.

Menkes disease after copper histidine replacement therapy: case report

Menkes disease (MD) is an X-linked recessive disorder of copper metabolism, characterized in its untreated state by progressive disorders of multiple systems, especially the central nervous system (CNS) and connective tissue, and death by 3 years of age. Recently, therapy with copper-histidine has modified the severity of MD and permitted survival into adolescence. Clinical response has been greater for the neurological abnormalities than for the connective tissue abnormalities. In this report, we describe the postmortem pathology of one individual who had received copper-histidine therapy and died at age 10; we believe this to be the first such pathological report. The postmortem examination demonstrated significant pathology of mesenchymal tissues, including skeletal abnormalities, vascular degeneration, and bladder diverticula. The CNS, by contrast, showed minimal pathology. The phenotype was more consistent with occipital horn syndrome, a milder allelic disorder of copper metabolism, than with classic MD. The differential sensitivity of CNS and mesenchymal tissues to copper-histidine therapy may result from heterogeneity in the response of different copper-dependent enzymes.

Expression, purification and copper-binding studies of the first metal-binding domain of Menkes protein

The cDNA, coding for the first metal-binding domain (MBD1) of Menkes protein, was cloned into the T7-system based vector, pCA. The T7 lysozyme-encoding plasmid, pLysS, is shown to be crucial for expression, suggesting that the protein is toxic to the cells. Adding copper to the growth medium did not affect the plasmid stability. MBD1 is purified in two steps with a typical yield of 12 mg.L-1. Menkes protein, a P-type ATPase, contains a sequence GMXCXSC that is repeated six times, at the N-terminus. The paired cysteine residues are involved in metal binding. MBD1 has only two cysteine residues, which can exist as free thiol groups (reduced), as a disulphide bond (oxidized) or bound to a metal ion [e.g. Cu(I)-MBD1]. These three MBD1 forms have been investigated using CD. No major spectral change was seen between the different MBD1 forms, indicating that the folding is not changed upon metal binding. A copper-bound MBD1 was also studied by EPR, and the lack of an EPR signal suggests that the oxidation state of copper bound to MBD1 is Cu(I). Cu(I) binding studies were performed by equilibrium dialysis and revealed a stoichiometry of 1 : 1 and an apparent Kd = 46 microM. Oxidized MBD1, however, is not able to bind copper. Different copper complexes were investigated for their ability to reconstitute apo-MBD1. Given the same total copper concentration CuCl43- was superior to Cu(I)-thiourea (structural analogue of metallothionein) and Cu(I)-glutathione (used at fivefold higher copper concentration) although the latter two were able to partially reconstitute apo-MBD1. Cu(II) was not able to reconstitute apo-MBD1, presumably due to Cu(II)-induced oxidation of the thiol groups. Based on our results, glutathione and/or metallothionein are likely candidates for the in vivo incorporation of copper to Menkes protein.

Newly discovered redox cofactors: possible nutritional, medical, and pharmacological relevance to higher animals

Research spurred by the discovery of pyrroloquinoline quinone (PPQ) in 1979 led to the discovery of four additional oxidation-reduction (redox) cofactors, all of which result from transmogrification of amino acyl side chains in respective enzymes. These cofactors are (a) topa quinone in copper-containing amine oxidases, enzymes found in nearly all forms of life, including human; (b) lysyl topa quinone of the copper protein lysyl oxidase, an enzyme required for proper cross-linking of collagen and elastin; (c) tryptophan tryptophylquinone of alkylamine dehydrogenases from gram-negative soil bacteria; and (d) the copper-complexed cysteinyltyrosyl radical of fungal galactose oxidase. Originally, PQQ was thought to be a covalently bound cofactor in numerous enzymes from eukaryotes and prokaryotes. Today, PQQ is only found as a noncovalent cofactor in bacterial enzymes. The ubiquity of PQQ in the environment and its steady accessibility in the human diet has raised questions concerning its role as a vitamin, or an essential or helpful nutrient. The relevance to nutrition, medicine, and pharmacology of PQQ, topa quinone, lysyl topa quinone, tryptophan trytophylquinone, the galactose oxidase cofactor, and the enzymes harboring these cofactors are discussed in this review.