Metabolic and molecular bases of Menkes disease and occipital horn syndrome

ATP7A-related copper transport disorders: A systematic review and definition of the clinical subtypes

In patients with ATP7A-related disorders, counseling is challenging due to clinical overlap between the entities, the absence of predictive biomarkers and a clear genotype-phenotype correlation. We performed a systematic literature review by querying the MEDLINE and Embase databases identifying 143 relevant papers. We recorded data on the phenotype and genotype in 162 individuals with a molecularly confirmed ATP7A-related disorder in order to identify differentiating clinical criteria, evaluate genotype-phenotype correlations and propose management guidelines. Early seizures are specific for classical Menkes disease (CMD), that is characterized by early-onset neurodegenerative disease with high mortality rates. Ataxia is an independent indicator for atypical Menkes disease, that shows better survival rates than CMD. Bony exostoses, radial head dislocations, herniations and dental abnormalities are specific for occipital horn syndrome (OHS) that may further present with developmental delay and connective tissue manifestations. Intracranial tortuosity and bladder diverticula, both with high risk of complications, are common among all subtypes. Low ceruloplasmin is a more sensitive and discriminating biomarker for ATP7A-related disorders than serum copper. Truncating mutations are frequently associated with CMD, in contrast with splice site and intronic mutations which are more prevalent in OHS.

The Role of Cardiovascular Surgery in the Management of a Patient Diagnosed With Congenital Cutis Laxa Syndrome Complicated by Multivalvular Heart Disease

Cutis laxa syndrome is an uncommon connective tissue disorder affecting the major ultrastructure of the skin by progressive loss of elasticity. The results of this syndrome lead to the appearance of premature aging, which might also affect the internal organs. The disorder can be either congenital or acquired. The congenital form consists of autosomal dominant, autosomal recessive, and X-linked recessive patterns. The autosomal recessive pattern is the most common and severe one. Different systemic complications have been described in congenital cutis laxa syndrome, but the most serious and lethal one is cardiopulmonary abnormalities. In this report, we discuss the presentation of congenital cutis laxa syndrome with successful cardiovascular surgical management of multiple valvular heart diseases.

Investigation of Genetic Modifiers of Copper Toxicosis in Labrador Retrievers

Copper toxicosis is a complex genetic disorder in Labrador retrievers characterized by hepatic copper accumulation eventually leading to liver cirrhosis. The variation of hepatic copper levels in Labrador retrievers has been partly explained by mutations in ATP7A c.980C>T and ATP7B c.4358G>A. To further elucidate the genetic background of this disease, we used targeted Next Generation Sequencing (NGS) in a cohort of 95 Labrador retrievers to analyze 72 potential modifier genes for variations associated with hepatic copper levels. Variants associated with copper levels were subsequently evaluated in a replication cohort of 144 Labrador retrievers. A total of 44 variants in 25 different genes were identified, of which four showed significant association with copper levels. Of the four variants found associated with hepatic copper levels in the NGS cohort, one was validated in the replication cohort. The non-reference allele of the variant NC_006602.3.g.52434480C>T in RETN resulting in amino-acid change p.Leu7Phe was associated with decreased hepatic copper levels. In humans, resistin is associated with severity of non-alcoholic fatty liver disease, fibrosis, cirrhosis and mitochondrial dysfunction in hepatocytes. Further studies are needed to investigate the biological function of RETN p.Leu7Phe in the development of copper toxicosis in Labrador retrievers.

Insights from the in silico structural, functional and phylogenetic characterization of canine lysyl oxidase protein

Background

Lysyl oxidase is an extracellular regulatory enzyme with an imperative role in interlinking of collagen and elastin by oxidizing lysine residues. Lysyl oxidase has been implicated in incidence of mammary tumors in bitches. Therefore, it becomes significant to study the structural and functional features of this enzyme for a better understanding of its molecular mechanisms.

Results

The detailed computational investigation of the canine lysyl oxidase protein was analyzed in silico with respect to its physicochemical properties, secondary and tertiary structure predictions and functional analysis using standard bioinformatic tools. Lysyl oxidase is a flexible protein with an average molecular weight of around 46 kDa, unstable, hydrophilic, and extracellular (secretory) in nature. Twelve cysteine residues and a disulfide bridge were also found. Secondary structure analysis shows that most of the protein has predominant coiled configuration. A putative copper-binding region signature was predicted. The phylogenetic relationship of canine lysyl oxidase with a vast range of mammalian species indicates that the protein was very well conserved throughout the course of evolution. Top 10 interacting proteins were identified using STRING v10.0 analysis, elastin being the closest interacting protein. Functional analysis by InterproScan predicted protein’s biological role in oxidation-reduction process.

Conclusion

Understanding the structural and functional properties of the protein will facilitate a better understanding of its mechanism of enzyme action. Further, the predicted 3D model will serve as a cornerstone for further understanding towards the tumorigenesis potential of the protein.

Early-onset Wilson disease caused by ATP7B exon skipping associated with intronic variant

Wilson disease is a medically actionable rare autosomal recessive disorder of defective copper excretion caused by mutations in ATP7B, one of two highly evolutionarily conserved copper-transporting ATPases. Hundreds of disease-causing variants in ATP7B have been reported to public databases; more than half of these are missense changes, and a significant proportion are presumed unequivocal loss-of-function variants (nonsense, frameshift, and canonical splice site). Current molecular genetic testing includes sequencing all coding exons (±10 bp) as well as deletion/duplication testing, with reported sensitivity of >98%. We report a proband from a consanguineous family with a biochemical phenotype consistent with early-onset Wilson disease who tested negative on conventional molecular genetic testing. Using a combination of whole-genome sequencing and transcriptome sequencing, we found that the proband's disease is due to skipping of exons 6–7 of the ATP7B gene associated with a novel intronic variant (NM_000053.4:c.1947-19T > A) that alters a putative splicing enhancer element. This variant was also homozygous in the proband's younger sister, whose subsequent clinical evaluations revealed biochemical evidence of Wilson disease. Our work adds to emerging evidence that ATP7B exon skipping from deep intronic variants outside typical splice junctions is an important mechanism of Wilson disease; the variants responsible may elude standard genetic testing.

Defining the Clinical, Molecular and Ultrastructural Characteristics in Occipital Horn Syndrome: Two New Cases and Review of the Literature

Occipital horn syndrome (OHS) is a rare connective tissue disorder caused by pathogenic variants in ATP7A, encoding a copper transporter. The main clinical features, including cutis laxa, bony exostoses, and bladder diverticula are attributed to a decreased activity of lysyl oxidase (LOX), a cupro-enzyme involved in collagen crosslinking. The absence of large case series and natural history studies precludes efficient diagnosis and management of OHS patients. This study describes the clinical and molecular characteristics of two new patients and 32 patients previously reported in the literature. We report on the need for long-term specialized care and follow-up, in which MR angiography, echocardiography and spirometry should be incorporated into standard follow-up guidelines for OHS patients, next to neurodevelopmental, orthopedic and urological follow-up. Furthermore, we report on ultrastructural abnormalities including increased collagen diameter, mild elastic fiber abnormalities and multiple autophagolysosomes reflecting the role of lysyl oxidase and defective ATP7A trafficking as pathomechanisms of OHS.

Classification and differential diagnosis of Wilson's disease

Wilson's disease is characterized by hepatic and extrapyramidal movement disorders (EPS) with variable manifestation primarily between age 5 and 45. This variability often makes an early diagnosis difficult. A classification defines different clinical variants of Wilson's disease, which enables classifying the current clinical findings and making an early tentative diagnosis. Until the unequivocal proof or an autosomal recessive disorder of the hepatic copper transporter ATP7B has been ruled out, differential diagnoses have to be examined. Laboratory-chemical parameters of copper metabolism can both be deviations from the norm not related to the disease as well as other copper metabolism disorders besides Wilson's disease. In addition to known diseases such as Menkes disease, occipital horn syndrome (OHS), Indian childhood cirrhosis (ICC) and ceruloplasmin deficiency, recently discovered disorders are taken into account. These include MEDNIK syndrome, Huppke-Brendel syndrome and CCS chaperone deficiency. Another main focus is on differential diagnoses of childhood icterus correlated with age and anaemia as well as disorders of the extrapyramidal motor system. The Kayser-Fleischer ring (KFR) is qualified as classical ophthalmologic manifestation. The recently described manganese storage disease presents another rare metabolic disorder with symptoms similar to Wilson's disease. As this overview shows, Wilson's disease fits into a broad spectrum of internal and neurological disease patterns with icterus, anaemia and EPS.

A Perspective - can copper complexes be developed as a novel class of therapeutics?

Although copper-ligand complexes appear to be promising as a new class of therapeutics, other than the family of copper(ii) coordination compounds referred to as casiopeínas these compounds have yet to reach the clinic for human use. The pharmaceutical challenges associated with developing copper-based therapeutics will be presented in this article along with a discussion of the potential for high-throughput chemistry, computer-aided drug design, and nanotechnology to address the development of this important class of drug candidates.

Disorders of metal metabolism

Trace elements are chemical elements needed in minute amounts for normal physiology. Some of the physiologically relevant trace elements include iodine, copper, iron, manganese, zinc, selenium, cobalt and molybdenum. Of these, some are metals, and in particular, transition metals. The different electron shells of an atom carry different energy levels, with those closest to the nucleus being lowest in energy. The number of electrons in the outermost shell determines the reactivity of such an atom. The electron shells are divided in sub-shells, and in particular the third shell has s, p and d sub-shells. Transition metals are strictly defined as elements whose atom has an incomplete d sub-shell. This incomplete d sub-shell makes them prone to chemical reactions, particularly redox reactions. Transition metals of biologic importance include copper, iron, manganese, cobalt and molybdenum. Zinc is not a transition metal, since it has a complete d sub-shell. Selenium, on the other hand, is strictly speaking a nonmetal, although given its chemical properties between those of metals and nonmetals, it is sometimes considered a metalloid. In this review, we summarize the current knowledge on the inborn errors of metal and metalloid metabolism.

Impact of copper oxide nanomaterials on differentiated and undifferentiated Caco-2 intestinal epithelial cells; assessment of cytotoxicity, barrier integrity, cytokine production and nanomaterial penetration

BACKGROUND

Copper oxide nanomaterials (CuO NMs) are exploited in a diverse array of products including antimicrobials, inks, cosmetics, textiles and food contact materials. There is therefore a need to assess the toxicity of CuO NMs to the gastrointestinal (GI) tract since exposure could occur via direct oral ingestion, mucocillary clearance (following inhalation) or hand to mouth contact.

METHODS

Undifferentiated Caco-2 intestinal cells were exposed to CuO NMs (10 nm) at concentrations ranging from 0.37 to 78.13 μg/cm2 Cu (equivalent to 1.95 to 250 μg/ml) and cell viability assessed 24 h post exposure using the alamar blue assay. The benchmark dose (BMD 20), determined using PROAST software, was identified as 4.44 μg/cm2 for CuO NMs, and 4.25 μg/cm2 for copper sulphate (CuSO4), which informed the selection of concentrations for further studies. The differentiation status of cells and the impact of CuO NMs and CuSO4 on the integrity of the differentiated Caco-2 cell monolayer were assessed by measurement of trans-epithelial electrical resistance (TEER), staining for Zonula occludens-1 (ZO-1) and imaging of cell morphology using scanning electron microscopy (SEM). The impact of CuO NMs and CuSO4 on the viability of differentiated cells was performed via assessment of cell number (DAPI staining), and visualisation of cell morphology (light microscopy). Interleukin-8 (IL-8) production by undifferentiated and differentiated Caco-2 cells following exposure to CuO NMs and CuSO4 was determined using an ELISA. The copper concentration in the cell lysate, apical and basolateral compartments were measured with Inductive Coupled Plasma Optical Emission Spectrometry (ICP-OES) and used to calculate the apparent permeability coefficient (Papp); a measure of barrier permeability to CuO NMs. For all experiments, CuSO4 was used as an ionic control.

RESULTS

CuO NMs and CuSO4 caused a concentration dependent decrease in cell viability in undifferentiated cells. CuO NMs and CuSO4 translocated across the differentiated Caco-2 cell monolayer. CuO NM mediated IL-8 production was over 2-fold higher in undifferentiated cells. A reduction in cell viability in differentiated cells was not responsible for the lower level of cytokine production observed. Both CuO NMs and CuSO4 decreased TEER values to a similar extent, and caused tight junction dysfunction (ZO-1 staining), suggesting that barrier integrity was disrupted.

CONCLUSIONS

CuO NMs and CuSO4 stimulated IL-8 production by Caco-2 cells, decreased barrier integrity and thereby increased the Papp and translocation of Cu. There was no significant enhancement in potency of the CuO NMs compared to CuSO4. Differentiated Caco-2 cells were identified as a powerful model to assess the impacts of ingested NMs on the GI tract.

Menkes disease: what a multidisciplinary approach can do

Disorders of copper homeostasis are currently recognized across the life span. Their recognition and links to human disease have spanned several decades, beginning with the recognition of a degenerative disorder in the offspring of sheep grazing in copper-deficient pastures, through to the description of infants suffering from a progressive neurodegenerative disorder characterized by epileptic seizures, developmental regression, failure to thrive, and an unusual hair quality (giving the condition its distinctive label of “kinky hair disease”). In this review, we trace the historical background and describe the biochemistry and physiology of copper metabolism and transport, inheritance patterns, molecular genetics, and genotype–phenotype correlations based on current understanding of the disorder. It is clear from the clinical presentations and variants that disorders of copper homeostasis include phenotypes ranging from mild occipital horn syndrome to intermediate and severe forms of classical Menkes disease. The symptoms involve multiple organ systems such as brain, lung, gastrointestinal tract, urinary tract, connective tissue, and skin. A multisystem disorder needs a multidisciplinary approach to care, as treatment interventions permit longer survival for some individuals. Animal models have been developed to help screen treatment options and provide a better understanding of these disorders in the laboratory. Finally, we propose a multidisciplinary approach to promote continued research (both basic and clinical) to improve survival, quality of life, and care for these conditions.

Characterizing the molecular phenotype of an Atp7a(T985I) conditional knock in mouse model for X-linked distal hereditary motor neuropathy (dHMNX)

ATP7A is a P-type ATPase essential for cellular copper (Cu) transport and homeostasis. Loss-of-function ATP7A mutations causing systemic Cu deficiency are associated with severe Menkes disease or its milder allelic variant, occipital horn syndrome. We previously identified two rare ATP7A missense mutations (P1386S and T994I) leading to a non-fatal form of motor neuron disorder, X-linked distal hereditary motor neuropathy (dHMNX), without overt signs of systemic Cu deficiency. Recent investigations using a tissue specific Atp7a knock out model have demonstrated that Cu plays an essential role in motor neuron maintenance and function, however the underlying pathogenic mechanisms of ATP7A mutations causing axonal degeneration remain unknown. We have generated an Atp7a conditional knock in mouse model of dHMNX expressing Atp7a(T985I), the orthologue of the human ATP7A(T994I) identified in dHMNX patients. Although a degenerative motor phenotype is not observed, the knock in Atp7a(T985I/Y) mice show altered Cu levels within the peripheral and central nervous systems, an increased diameter of the muscle fibres and altered myogenin and myostatin gene expression. Atp7a(T985I/Y) mice have reduced Atp7a protein levels and recapitulate the defective trafficking and altered post-translational regulatory mechanisms observed in the human ATP7A(T994I) patient fibroblasts. Our model provides a unique opportunity to characterise the molecular phenotype of dHMNX and the time course of cellular events leading to the process of axonal degeneration in this disease.

Experimental approaches to studying the nature and impact of splicing variation in zebrafish

From a fixed number of genes carried in all cells, organisms create considerable diversity in cellular phenotype through differential regulation of gene expression. One prevalent source of transcriptome diversity is alternative pre-mRNA splicing, which is manifested in many different forms. Zebrafish models of splicing dysfunction due to mutated spliceosome components provide opportunity to link biochemical analyses of spliceosome structure and function with whole organism phenotypic outcomes. Drawing from experience with two zebrafish mutants: cephalophŏnus (a prpf8 mutant, isolated for defects in granulopoiesis) and caliban (a rnpc3 mutant, isolated for defects in digestive organ development), we describe the use of glycerol gradient sedimentation and native gel electrophoresis to resolve components of aberrant splicing complexes. We also describe how RNAseq can be employed to examine relatively rare alternative splicing events including intron retention. Such experimental approaches in zebrafish can promote understanding of how splicing variation and dysfunction contribute to phenotypic diversity and disease pathogenesis.

Mottled Mice and Non-Mammalian Models of Menkes Disease

Menkes disease is a multi-systemic copper metabolism disorder caused by mutations in the X-linked ATP7A gene and characterized by progressive neurodegeneration and severe connective tissue defects. The ATP7A protein is a copper (Cu)-transporting ATPase expressed in all tissues and plays a critical role in the maintenance of copper homeostasis in cells of the whole body. ATP7A participates in copper absorption in the small intestine and in copper transport to the central nervous system (CNS) across the blood-brain-barrier (BBB) and blood–cerebrospinal fluid barrier (BCSFB). Cu is essential for synaptogenesis and axonal development. In cells, ATP7A participates in the incorporation of copper into Cu-dependent enzymes during the course of its maturation in the secretory pathway. There is a high degree of homology (>80%) between the human ATP7A and murine Atp7a genes. Mice with mutations in the Atp7a gene, called mottled mutants, are well-established and excellent models of Menkes disease. Mottled mutants closely recapitulate the Menkes phenotype and are invaluable for studying Cu-metabolism. They provide useful models for exploring and testing new forms of therapy in Menkes disease. Recently, non-mammalian models of Menkes disease, Drosophila melanogaster and Danio rerio mutants were used in experiments which would be technically difficult to carry out in mammals.

Impaired osteogenesis in Menkes disease-derived induced pluripotent stem cells

Introduction

Bone abnormalities, one of the primary manifestations of Menkes disease (MD), include a weakened bone matrix and low mineral density. However, the molecular and cellular mechanisms underlying these bone defects are poorly understood.

Methods

We present in vitro modeling for impaired osteogenesis in MD using human induced pluripotent stem cells (iPSCs) with a mutated ATP7A gene. MD-iPSC lines were generated from two patients harboring different mutations.

Results

The MD-iPSCs showed a remarkable retardation in CD105 expression with morphological anomalies during development to mesenchymal stem cells (MSCs) compared with wild-type (WT)-iPSCs. Interestingly, although prolonged culture enhanced CD105 expression, mature MD-MSCs presented with low alkaline phosphatase activity, reduced calcium deposition in the extracellular matrix, and downregulated osteoblast-specific genes during osteoblast differentiation in vitro. Knockdown of ATP7A also impaired osteogenesis in WT-MSCs. Lysyl oxidase activity was also decreased in MD-MSCs during osteoblast differentiation.

Conclusions

Our findings indicate that ATP7A dysfunction contributes to retardation in MSC development and impairs osteogenesis in MD.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0147-5) contains supplementary material, which is available to authorized users.

Targeting copper in cancer therapy: 'Copper That Cancer'

Copper is an essential micronutrient involved in fundamental life processes that are conserved throughout all forms of life. The ability of copper to catalyze oxidation-reduction (redox) reactions, which can inadvertently lead to the production of reactive oxygen species (ROS), necessitates the tight homeostatic regulation of copper within the body. Many cancer types exhibit increased intratumoral copper and/or altered systemic copper distribution. The realization that copper serves as a limiting factor for multiple aspects of tumor progression, including growth, angiogenesis and metastasis, has prompted the development of copper-specific chelators as therapies to inhibit these processes. Another therapeutic approach utilizes specific ionophores that deliver copper to cells to increase intracellular copper levels. The therapeutic window between normal and cancerous cells when intracellular copper is forcibly increased, is the premise for the development of copper-ionophores endowed with anticancer properties. Also under investigation is the use of copper to replace platinum in coordination complexes currently used as mainstream chemotherapies. In comparison to platinum-based drugs, these promising copper coordination complexes may be more potent anticancer agents, with reduced toxicity toward normal cells and they may potentially circumvent the chemoresistance associated with recurrent platinum treatment. In addition, cancerous cells can adapt their copper homeostatic mechanisms to acquire resistance to conventional platinum-based drugs and certain copper coordination complexes can re-sensitize cancer cells to these drugs. This review will outline the biological importance of copper and copper homeostasis in mammalian cells, followed by a discussion of our current understanding of copper dysregulation in cancer, and the recent therapeutic advances using copper coordination complexes as anticancer agents.

Increased apoptosis and hypomyelination in cerebral white matter of macular mutant mouse brain

Hypomyelination in developing brain is often accompanied by congenital metabolic disorders. Menkes kinky hair disease is an X-linked neurodegenerative disease of impaired copper transport, resulting from a mutation of the Menkes disease gene, a transmembrane copper-transporting p-type ATPase gene (ATP7A). In a macular mutant mouse model, the murine ortholog of Menkes gene (mottled gene) is mutated, and widespread neurodegeneration and subsequent death are observed. Although some biochemical analysis of myelin protein in macular mouse has been reported, detailed histological study of myelination in this mouse model is currently lacking. Since myelin abnormality is one of the neuropathologic findings of human Menkes disease, in this study early myelination in macular mouse brain was evaluated by immunohistochemistry. Two-week-old macular mice and normal littermates were perfused with 4% paraformaldehyde. Immunohistochemical staining of paraffin embedded and vibratome sections was performed using antibodies against either CNPase, cleaved caspase-3 or O4 (marker of immature oligodendrocytes). This staining showed that cerebral myelination in macular mouse was generally hypoplastic and that hypomyelination was remarkable in internal capsule, corpus callosum, and cingulate cortex. In addition, an increased number of cleaved caspase-3 positive cells were observed in corpus callosum and internal capsule. Copper deficiency induced by low copper diet has been reported to induce oligodendrocyte dysfunction and leads to hypomyelination in this mouse model. Taken together, hypomyelination observed in this study in a mouse model of Menkes disease is assumed to be induced by increased apoptosis of immature oligodendrocytes in developing cerebrum, through deficient intracellular copper metabolism.

Copper mediated neurological disorder: visions into amyotrophic lateral sclerosis, Alzheimer and Menkes disease

Copper (Cu) is a vital redox dynamic metal that is possibly poisonous in superfluous. Metals can traditionally or intricately cause propagation in reactive oxygen species (ROS) accretion in cells and this may effect in programmed cell death. Accumulation of Cu causes necrosis that looks to be facilitated by DNA damage, followed by activation of P53. Cu dyshomeostasis has also been concerned in neurodegenerative disorders such as Alzheimer, Amyotrophic lateral sclerosis (ALS) or Menkes disease and is directly related to neurodegenerative syndrome that usually produces senile dementia. These mortal syndromes are closely related with an immense damage of neurons and synaptic failure in the brain. This review focuses on copper mediated neurological disorders with insights into amyotrophic lateral sclerosis, Alzheimer and Menkes disease.

Role of the P-Type ATPases, ATP7A and ATP7B in brain copper homeostasis

Over the past two decades there have been significant advances in our understanding of copper homeostasis and the pathological consequences of copper dysregulation. Cumulative evidence is revealing a complex regulatory network of proteins and pathways that maintain copper homeostasis. The recognition of copper dysregulation as a key pathological feature in prominent neurodegenerative disorders such as Alzheimer's, Parkinson's, and prion diseases has led to increased research focus on the mechanisms controlling copper homeostasis in the brain. The copper-transporting P-type ATPases (copper-ATPases), ATP7A and ATP7B, are critical components of the copper regulatory network. Our understanding of the biochemistry and cell biology of these complex proteins has grown significantly since their discovery in 1993. They are large polytopic transmembrane proteins with six copper-binding motifs within the cytoplasmic N-terminal domain, eight transmembrane domains, and highly conserved catalytic domains. These proteins catalyze ATP-dependent copper transport across cell membranes for the metallation of many essential cuproenzymes, as well as for the removal of excess cellular copper to prevent copper toxicity. A key functional aspect of these copper transporters is their copper-responsive trafficking between the trans-Golgi network and the cell periphery. ATP7A- and ATP7B-deficiency, due to genetic mutation, underlie the inherited copper transport disorders, Menkes and Wilson diseases, respectively. Their importance in maintaining brain copper homeostasis is underscored by the severe neuropathological deficits in these disorders. Herein we will review and update our current knowledge of these copper transporters in the brain and the central nervous system, their distribution and regulation, their role in normal brain copper homeostasis, and how their absence or dysfunction contributes to disturbances in copper homeostasis and neurodegeneration.

Inborn errors of copper metabolism

Two copper-transporting ATPases are essential for mammalian copper homeostasis: ATP7A, which mediates copper uptake in the gastrointestinal tract and copper delivery to the brain, and ATP7B, which mediates copper excretion by the liver into bile. Mutations in ATP7A may cause three distinct X-linked conditions in infants, children, or adolescents: Menkes disease, occipital horn syndrome (OHS), and a newly identified allelic variant restricted to motor neurons called X-linked distal hereditary motor neuropathy. These three disorders show variable neurological findings and ages of onset. Menkes disease presents in the first several months of life with failure to thrive, developmental delay, and seizures. OHS features more subtle developmental delays, dysautonomia, and connective tissue abnormalities beginning in early childhood. ATP7A-related distal motor neuropathy presents even later, often not until adolescence or early adulthood, and involves a neurological phenotype that resembles Charcot-Marie-Tooth disease, type 2. These disorders may be treatable through copper replacement or ATP7A gene therapy. In contrast, mutations in ATP7B cause a single known phenotype, Wilson disease, an autosomal recessive trait that results from copper overload rather than deficiency. Dysarthria, dystonia, tremor, gait abnormalities, and psychiatric problems may be presenting symptoms, at ages from 10 to 40 years. Excellent treatment options exist for Wilson disease, based on copper chelation. In the past 2 years (2012-2013), three new autosomal recessive copper metabolism conditions have been recognized: 1) Huppke-Brendel syndrome caused by mutations in an acetyl CoA transporter needed for acetylation of one or more copper proteins, 2) CCS deficiency caused by mutations in the copper chaperone to SODI, and 3) MEDNIK syndrome, which revealed that mutations in the σ1A subunit of adaptor protein complex 1 (AP-1) have detrimental effects on trafficking of ATP7A and ATP7B.

Impairment of interrelated iron- and copper homeostatic mechanisms in brain contributes to the pathogenesis of neurodegenerative disorders

Iron and copper are important co-factors for a number of enzymes in the brain, including enzymes involved in neurotransmitter synthesis and myelin formation. Both shortage and an excess of iron or copper will affect the brain. The transport of iron and copper into the brain from the circulation is strictly regulated, and concordantly protective barriers, i.e., the blood-brain barrier (BBB) and the blood-cerebrospinal fluid (CSF) barrier (BCB) have evolved to separate the brain environment from the circulation. The uptake mechanisms of the two metals interact. Both iron deficiency and overload lead to altered copper homeostasis in the brain. Similarly, changes in dietary copper affect the brain iron homeostasis. Moreover, the uptake routes of iron and copper overlap each other which affect the interplay between the concentrations of the two metals in the brain. The divalent metal transporter-1 (DMT1) is involved in the uptake of both iron and copper. Furthermore, copper is an essential co-factor in numerous proteins that are vital for iron homeostasis and affects the binding of iron-response proteins to iron-response elements in the mRNA of the transferrin receptor, DMT1, and ferroportin, all highly involved in iron transport. Iron and copper are mainly taken up at the BBB, but the BCB also plays a vital role in the homeostasis of the two metals, in terms of sequestering, uptake, and efflux of iron and copper from the brain. Inside the brain, iron and copper are taken up by neurons and glia cells that express various transporters.

Occipital horn syndrome in a woman: skeletal radiological findings

Ehlers-Danlos type IX syndrome, also called occipital horn syndrome (OHS), is a milder and rare form of Menkes disease where the patient reaches adulthood. As an X-linked disease, it typically occurs in male subjects, while female subjects are usually healthy carriers. OHS is mainly characterized by connective tissue disorders and slightly subnormal intelligence or signs of autonomic dysfunction are the only apparent neurological abnormalities, in connection with molecular defects in copper metabolism. Our purpose is to report on radiological skeletal findings that may be incidental or investigated when OHS is suspected and to underline the possible involvement and expression in the female. Moreover, the impact of skeletal findings is also highlighted in the prevention of serious complications of the disease.

ATP7A-related copper transport diseases-emerging concepts and future trends

This Review summarizes recent advances in understanding copper-transporting ATPase 1 (ATP7A), and examines the neurological phenotypes associated with dysfunction of this protein. Involvement of ATP7A in axonal outgrowth, synapse integrity and neuronal activation underscores the fundamental importance of copper metabolism to neurological function. Defects in ATP7A cause Menkes disease, an infantile-onset, lethal condition. Neonatal diagnosis and early treatment with copper injections enhance survival in patients with this disease, and can normalize clinical outcomes if mutant ATP7A molecules retain small amounts of residual activity. Gene replacement rescues a mouse model of Menkes disease, suggesting a potential therapeutic approach for patients with complete loss-of-function ATP7A mutations. Remarkably, a newly discovered ATP7A disorder-isolated distal motor neuropathy-has none of the characteristic clinical or biochemical abnormalities of Menkes disease or its milder allelic variant occipital horn syndrome (OHS), instead resembling Charcot-Marie-Tooth disease type 2. These findings indicate that ATP7A has a crucial but previously unappreciated role in motor neuron maintenance, and that the mechanism underlying ATP7A-related distal motor neuropathy is distinct from Menkes disease and OHS pathophysiology. Collectively, these insights refine our knowledge of the neurology of ATP7A-related copper transport diseases and pave the way for further progress in understanding ATP7A function.

Advances in the understanding of mammalian copper transporters

Copper (Cu) is an essential micronutrient. Its ability to exist in 2 oxidation states (Cu(1+) and Cu(2+)) allows it to function as an enzymatic cofactor in hydrolytic, electron transfer, and oxygen utilization reactions. Cu transporters CTR1, ATP7A, and ATP7B play key roles in ensuring that adequate Cu is available for Cu-requiring processes and the prevention of excess Cu accumulation within cells. Two diseases of Cu metabolism, Menkes disease and Wilson disease, which are caused by mutations in ATP7A and ATP7B, respectively, exemplify the critical importance of regulating Cu balance in humans. Herein, we review recent studies of the biochemical and cell biological characteristics of CTR1, ATP7A, and ATP7B, as well as emerging roles for Cu in new areas of physiology.

Genetics of early onset cognitive impairment

Intellectual disability (ID) is the leading socio-economic problem of health care, but compared to autism and schizophrenia, it has received very little public attention. Important risk factors for ID are malnutrition, cultural deprivation, poor health care, and parental consanguinity. In the Western world, fetal alcohol exposure is the most common preventable cause. Most severe forms of ID have genetic causes. Cytogenetically detectable and submicroscopic chromosomal rearrangements account for approximately 25% of all cases. X-linked gene defects are responsible in 10-12% of males with ID; to date, 91 of these defects have been identified. In contrast, autosomal gene defects have been largely disregarded, but due to coordinated efforts and the advent of next-generation DNA sequencing, this is about to change. As shown for Fra(X) syndrome, this renewed focus on autosomal gene defects will pave the way for molecular diagnosis and prevention, shed more light on the pathogenesis of ID, and reveal new opportunities for therapy.

Decreased erythrocyte CCS content is a biomarker of copper overload in rats

Copper (Cu) is an essential trace metal that is toxic in excess. It is therefore important to be able to accurately assess Cu deficiency or overload. Cu chaperone for Cu/Zn superoxide dismutase (CCS) protein expression is elevated in tissues of Cu-deficient animals. Increased CCS content in erythrocytes is particularly sensitive to decreased Cu status. Given the lack of a non-invasive, sensitive and specific biomarker for the assessment of Cu excess, we investigated whether CCS expression in erythrocytes reflects Cu overload. Rats were fed diets containing normal or high levels of Cu for 13 weeks. Diets contained 6.3 +/- 0.6 (Cu-N), 985 +/- 14 (Cu-1000) or 1944 +/- 19 (Cu-2000) mg Cu/kg diet. Rats showed a variable response to the high Cu diets. Some rats showed severe Cu toxicity, while other rats showed no visible signs of toxicity and grew normally. Also, some rats had high levels of Cu in liver, whereas others had liver Cu concentrations within the normal range. Erythrocyte CCS protein expression was 30% lower in Cu-2000 rats compared to Cu-N rats (P < 0.05). Notably, only rats that accumulated high levels of Cu in liver had lower erythrocyte CCS (47% reduction, P < 0.05) compared to rats fed normal levels of Cu. Together, these data indicate that decreased erythrocyte CCS content is associated with Cu overload in rats and should be evaluated further as a potential biomarker for assessing Cu excess in humans.

Interaction between periostin and BMP-1 promotes proteolytic activation of lysyl oxidase

Intra- and intermolecular covalent cross-linking between collagen fibrils, catalyzed by lysyl oxidase (LOX), determines the mechanical properties of connective tissues; however, mechanisms that regulate the collagen cross-linking according to tissue specificity are not well understood. Here we show that periostin, a secretory protein in the dense connective tissues, promotes the activation of LOX. Previous studies showed that periostin null mice exhibit reduced collagen cross-linking in their femurs, periosteum, infarcted myocardium, and tendons. Presently, we showed that active LOX protein, formed by cleavage of its propeptide by bone morphogenetic protein-1 (BMP-1), was decreased in calvarial osteoblast cells derived from periostin null mice. Overexpression of periostin promoted the proteolytic cleavage of the propeptide, which increased the amount of active LOX protein. The results of co-immunoprecipitation and solid phase binding assays revealed that periostin interacted with BMP-1. Furthermore, this interaction probably resulted in enhanced deposition of BMP-1 on the extracellular matrix, suggesting that this enhanced deposition would lead to cleavage of the propeptide of LOX. Thus, we demonstrated that periostin supported BMP-1-mediated proteolytic activation of LOX on the extracellular matrix, which promoted collagen cross-linking.

New developments in the regulation of intestinal copper absorption

The transition metal copper is an essential trace element involved in many enzymatic processes that require redox-chemistry. The redox-activity of copper is potentially harmful. Severe imbalance of copper homeostasis can occur with some hereditary disorders of copper metabolism. Copper is acquired from the diet by intestinal absorption and is subsequently distributed throughout the body. The regulation of intestinal copper absorption to maintain whole-body copper homeostasis is currently poorly understood. This review evaluates novel findings regarding the molecular mechanism of intestinal copper uptake. The role of recently identified transporters in enterocyte copper uptake and excretion into the portal circulation is described, and the regulation of dietary copper uptake during physiological and pathophysiological conditions is discussed.

The use of categorical regression in modeling copper exposure-response relationships

Characterization of the exposure-response relationship for copper (Cu) is an essential step in identifying a range of exposures that can prevent against toxicity from either excess or deficiency. Categorical regression is a exposure-response modeling technique that can be used to model data from multiple studies with diverse endpoints simultaneously by organizing the toxicity data into ordered categories of severity. This study describes how categorical regression can be used to model the exposure-response relationship for Cu and presents a preliminary analysis of the comprehensive database on Cu-induced toxicity due to either excess or deficiency. Categorical regression provides a useful tool for summarizing and describing the available data on Cu excess and deficiency, as well as in identifying data gaps in Cu exposure-response. This methodology also allows for a diverse database with considerable variability in animal species, strain, age, and study design to be analyzed in its entirety. The present application of the Cu toxicity database suggests that there is a lack of information on the potential adverse health effects from chronic exposure to Cu; there are also a limited number of studies using marginally excess and deficient levels of Cu. The database presently includes insufficient data to create a complex model that accounts for a large proportion of the heterogeneity in toxicity seen among the available studies on Cu-induced toxicity. The current Cu database is presently being updated in order to permit more comprehensive categorical regression analyses with finer stratification options. The resulting exposure-response model could be used to provide information in the determination of an acceptable range of oral intake for Cu.

Mental retardation and inborn errors of metabolism

In countries where clinical phenylketonuria is detected by newborn screening inborn errors of metabolism are rare causes of isolated mental retardation. There is no international agreement about what type of metabolic tests must be applied in patients with unspecific mental retardation. However, and although infrequent, there are a number of inborn errors of metabolism that can present in this way. Because of the high recurrence risk and the possibility of specific therapies, guidelines need to be developed and adapted to different populations. The application of a universal protocol may result in a low diagnostic performance in individual ethnic populations. Consideration of associated signs (extraneurological manifestations, psychiatric signs, autistic traits, cerebellar dysfunction, epilepsy or dysmorphic traits) greatly improves the diagnostic fulfilment.

Copper transport into the secretory pathway is regulated by oxygen in macrophages

Copper is an essential nutrient for a variety of biochemical processes; however, the redox properties of copper also make it potentially toxic in the free form. Consequently, the uptake and intracellular distribution of this metal is strictly regulated. This raises the issue of whether specific pathophysiological conditions can promote adaptive changes in intracellular copper distribution. In this study, we demonstrate that oxygen limitation promotes a series of striking alterations in copper homeostasis in RAW264.7 macrophage cells. Hypoxia was found to stimulate copper uptake and to increase the expression of the copper importer, CTR1. This resulted in increased copper delivery to the ATP7A copper transporter and copper-dependent trafficking of ATP7A to cytoplasmic vesicles. Significantly, the ATP7A protein was required to deliver copper into the secretory pathway to ceruloplasmin, a secreted copperdependent enzyme, the expression and activity of which were stimulated by hypoxia. However, the activities of the alternative targets of intracellular copper delivery, superoxide dismutase and cytochrome c oxidase, were markedly reduced in response to hypoxia. Collectively, these findings demonstrate that copper delivery into the biosynthetic secretory pathway is regulated by oxygen availability in macrophages by a selective increase in copper transport involving ATP7A.

[From gene to disease: copper-transporting P ATPases alteration]

Copper is a trace metal, essential for many biological processes. Copper is also toxic if in excessive amounts; its homeostatic balance requires a delicate regulation. Several severe hereditary human disorders of copper regulatory mechanisms have been identified; they are related to mutations in gene ATP7A and ATP7B coding for copper-transporting proteins. Those mutations result in copper deficiency for ATP7A (Menkes disease) and copper overload for ATP7B (Wilson disease). Usually, clinical and biochemical phenotypes of these diseases are disparate. This article focuses on the molecular pathogenesis of Wilson and Menkes disease, and discusses how causing mutations are correlated with molecular defects and disease phenotypes.

The soluble metal-binding domain of the copper transporter ATP7B binds and detoxifies cisplatin

Wilson disease ATPase (ATP7B) has been implicated in the resistance of cancer cells to cisplatin. Using a simple in vivo assay in bacterial culture, in the present study we demonstrate that ATP7B can confer resistance to cisplatin by sequestering the drug in its N-terminal metal-binding domain without active drug extrusion from the cell. Expression of a protein fragment containing four N-terminal MBRs (metal-binding repeats) of ATP7B (MBR1-4) protects cells from the toxic effects of cisplatin. One MBR1-4 molecule binds up to three cisplatin molecules at the copper-binding sites in the MBRs. The findings of the present study suggest that suppressing enzymatic activity of ATP7B may not be an effective way of combating cisplatin resistance. Rather, the efforts should be directed at preventing cisplatin binding to the protein.

Role of copper in human neurological disorders

Copper is a trace element present in all tissues and is required for cellular respiration, peptide amidation, neurotransmitter biosynthesis, pigment formation, and connective tissue strength. Copper is a cofactor for numerous enzymes and plays an important role in central nervous system development; low concentrations of copper may result in incomplete development, whereas excess copper maybe injurious. Copper may be involved in free radical production, via the Haber-Weiss reaction, that results in mitochondrial damage, DNA breakage, and neuronal injury. Evidence of abnormal copper transport and aberrant copper-protein interactions in numerous human neurological disorders supports the critical importance of this trace metal for proper neurodevelopment and neurological function. The biochemical phenotypes of human disorders that involve copper homeostasis suggest possible biomarkers of copper status that may be applicable to general populations.

Localization of the Wilson disease protein in murine intestine

Wilson disease is an inherited disorder of human copper metabolism, characterized by gradual accumulation of copper in tissues, predominantly liver and brain. The gene defect lies in the Wilson disease protein ATP7B, a copper transporting ATPase highly active in hepatocytes. In the liver, ATP7B is essential for excretion of excess copper into the bile and for copper loading of ceruloplasmin in the Golgi apparatus. The extrahepatic role of ATP7B is not yet completely understood. We analysed the intestinal expression of ATP7B in mice using RT-PCR, Western blot and indirect immunofluorescence. We found abundant expression of ATP7B in stomach and small intestine, but not in colon. Using confocal microscopy we demonstrate a Golgi localization of ATP7B in enterocytes. In response to elevated copper, the Wilson disease protein shows an intracellular trafficking pattern in the intestinal polarized cell line CaCo-2, moving away from the Golgi apparatus to dispersed vesicles. This suggests a role for intestinal ATP7B in sequestration of copper in intracellular vesicles for maintenance of copper homeostasis in the enterocyte. In conclusion, the expression of ATP7B in the small intestine might represent an additional regulatory mechanism to fine-tune intestinal copper absorption.

In vivo correction of a Menkes disease model using antisense oligonucleotides

Although the molecular basis of many inherited metabolic diseases has been defined, the availability of effective therapies in such disorders remains problematic. Menkes disease is a fatal neurodegenerative disorder due to loss-of-function mutations in the ATP7A gene encoding a copper-transporting P-type Atpase. To develop therapeutic approaches in affected patients, we have identified a zebrafish model of Menkes disease termed calamity that results from splicing defects in the zebrafish orthologue of the ATP7A gene. Embryonic-recessive lethal mutants have impaired copper homeostasis that results in absent melanin pigmentation, impaired notochord formation, and hindbrain neurodegeneration. In this current study, we have attempted to rescue these striking phenotypic alterations by using a series of antisense morpholino oligonucleotides directed against the splice-site junctions of two mutant calamity alleles. Our findings reveal a robust and complete correction of the copper-deficient defects of calamity in association with the generation of the WT Menkes protein in all rescued mutants. Interestingly, a quantitative analysis of atp7a-specific transcripts suggests that competitive translational regulation may account for the synthesis of WT protein in these embryos. This in vivo correction of Menkes disease through the rescue of aberrant splicing may provide therapeutic options in this fatal disease and illustrates the potential for zebrafish models of human genetic disease in the development of treatments based on the principles of interactions of synthetic oligonucleotide analogues with mRNA.

Trace element transport in the mammary gland

The mammary gland has a remarkable capacity to adapt to maternal deficiency or excess of iron, copper, and zinc and to homeostatically control milk concentrations of these essential nutrients. Similarly, it can regulate changes in concentrations of iron, copper, and zinc change during lactation. For iron, this regulation is achieved by transferrin receptor, DMT1, and ferroportin, whereas mammary gland copper metabolism is regulated by Ctr1, ATP7A, and ATP7B. Zinc homeostasis is complex, involving both zinc importers (Zip3) and zinc exporters (ZnT-1, ZnT-2, and ZnT-4). Both transcriptional and post-translational regulation can affect protein abundance and cellular localization of these transporters, finely orchestrating uptake, intracellular trafficking, and secretion of iron, copper, and zinc. The control of mammary gland uptake and milk secretion of iron, copper, and zinc protects both the mammary gland and the breast-fed infant against deficiency and excess of these nutrients.

Activation of ADP-ribosylation factor regulates biogenesis of the ATP7A-containing trans-Golgi network compartment and its Cu-induced trafficking

ATP7A (MNK) regulates copper homeostasis by translocating from a compartment localized within the trans-Golgi network to the plasma membrane (PM) in response to increased copper load. The mechanisms that regulate the biogenesis of the MNK compartment and the trafficking of MNK are unclear. Here we show that the architecture of the MNK compartment is linked to the structure of the Golgi ribbon. Depletion of p115 tethering factor, which causes fragmentation of the Golgi ribbon, also disrupts the MNK compartment. In p115-depleted cells, MNK localizes to punctate structures that pattern on Golgi ministacks dispersed throughout the cell. Despite altered localization MNK trafficking still occurs, and MNK relocates from and returns to the fragmented compartment in response to copper. We further show that the biogenesis of the MNK compartment requires activation of ADP-ribosylation factor (Arf)1 GTPase, shown previously to facilitate the biogenesis of the Golgi ribbon. Activation of cellular Arf1 is prevented by 1) expressing an inactive "empty" form of Arf (Arf1/N126I), 2) expressing an inactive form of GBF1 (GBF1/E794K), guanine nucleotide exchange factor for Arf1, or 3) treating cells with brefeldin A, an inhibitor of GBF1 that disrupts MNK into a diffuse pattern. Importantly, preventing Arf activation inhibits copper-responsive trafficking of MNK to the PM. Our findings support a model in which active Arf is essential for the generation of the MNK compartment and for copper-responsive trafficking of MNK from there to the PM. Our findings provide an exciting foundation for identifying Arf1 effectors that facilitate the biogenesis of the MNK compartment and MNK traffic.