Metallochaperone for Cu,Zn-superoxide dismutase (CCS) protein but not mRNA is higher in organs from copper-deficient mice and rats

Protein Carbonyl, Lipid Peroxidation, Glutathione and Enzymatic Antioxidant Status in Male Wistar Brain Sub-regions After Dietary Copper Deficiency

Copper a quintessential transitional metal is required for development and function of normal brain and its deficiency has been associated with impairments in brain function. The present study investigates the effects of dietary copper deficiency on brain sub-regions of male Wistar rats for 2-, 4- and 6-week. Pre-pubertal rats were divided into four groups: negative control (NC), copper control (CC), pairfed (PF) and copper deficient (CD). In brain sub regions total protein concentration, glutathione concentration and Cu-Zn SOD activity were down regulated after 2-, 4- and 6 weeks compared to controls and PF groups. Significant increase in brain sub regions was observed in protein carbonyl and lipid peroxidation concentration as well as total SOD, Mn SOD and catalase activities after 2-, 4- and 6 weeks of dietary copper deficiency. Experimental evidences indicate that impaired copper homeostasis has the potential to generate reactive oxygen species enhancing the susceptibility to oxidative stress by inducing up- and down-regulation of non-enzymatic and enzymatic profile studied in brain sub regions causing loss of their normal function which can consequently lead to deterioration of cell structure and death if copper deficiency is prolonged.

A co-opted endogenous retroviral envelope promotes cell survival by controlling CTR1-mediated copper transport and homeostasis

Copper is a critical element for eukaryotic life involved in numerous cellular functions, including redox balance, but is toxic in excess. Therefore, tight regulation of copper acquisition and homeostasis is essential for cell physiology and survival. Here, we identify a different regulatory mechanism for cellular copper homeostasis that requires the presence of an endogenous retroviral envelope glycoprotein called Refrex1. We show that cells respond to elevated extracellular copper by increasing the expression of Refrex1, which regulates copper acquisition through interaction with the main copper transporter CTR1. Downmodulation of Refrex1 results in intracellular copper accumulation leading to reactive oxygen species (ROS) production and subsequent apoptosis, which is prevented by copper chelator treatment. Our results show that Refrex1 has been co-opted for its ability to regulate copper entry through CTR1 in order to limit copper excess, redox imbalance, and ensuing cell death, strongly suggesting that other endogenous retroviruses may have similar metabolic functions among vertebrates.

Molecular Mechanisms of Cellular Copper Homeostasis in Mammals

Copper (Cu) is a trace element necessary for the growth and development of all living organisms, and is the third most abundant trace metal in the body after iron and zinc. Copper is essential for maintaining the life processes in all living cells, because several copper-dependent enzymes play an important role in key physiological processes like cellular respiration, oxygen radical scavenging, the transport of iron and neurotransmitter synthesis. Maintaining copper homeostasis implies maintaining the constancy of copper levels in the cells and fluids throughout the body, in order to support the enzymes and other factors that underlie normal life processes. Therefore, living organisms have developed complex mechanisms for maintaining their physiological copper level, because an excess copper level can be toxic for the cells. In the cell, copper homeostasis is controlled by a network of copper-binding proteins and transporters. Furthermore, copper uptake is mediated by the membrane transporter CTR1 and CTR2 proteins. In the cytoplasm, it is bound to a unique group of metallochaperones (ATOX1, CCS COX17) and transported to different cell compartments, where it is linked to the recipient proteins. The Cu-transporting ATPases (ATP7A and ATP7B) are responsible for transferring copper into the Golgi apparatus, where the copper is added to the active sites of enzymes, and it is also directed onto the path of excess cellular copper removal to prevent the occurrence of toxicity.

Copper-catalyzed dicarbonyl stress in NAFLD mice: protective effects of Oleuropein treatment on liver damage

Background

Nonalcoholic fatty liver disease (NAFLD) or more appropriately, metabolic associated fatty liver disease (MAFLD), is the hepatic manifestation of metabolic syndrome. An imbalance of copper homeostasis has been described in the progression of NAFLD/MAFLD toward NASH/MASH. We were interested in understanding whether the chelating activity of Oleuropein (Ole) was able to improve the copper accumulation and the related pro-oxidant and glycative damage in the liver of mice fed HFD.

Methods

Twelve C57BL/6J mice fed normal diet (ND) or high-fat diet (HFD) for 16 weeks and then thirty two female and male mice fed ND or HFD for 8 weeks adding Ole for the following 8 weeks were studied.

Results

Altered expression of copper-trafficking genes and proteins (CTR1, CTR2, ATP7B, COX17, CCS, and ATOX1) induced imbalance of copper homeostasis combined with an increase in dicarbonyl stress in the liver of HFD fed mice. Interestingly enough, glyoxalase system was improved by Ole administration and the Ole related protective effects differ in the two sexes of mice.

Conclusions

Our study highlights the role of the dicarbonyl stress in the pathogenesis of NAFLD and suggests Ole as a natural copper chelator to prevent the liver damage induced by methyglyoxal pathway derangement.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12986-022-00641-z.

Crossroads between membrane trafficking machinery and copper homeostasis in the nerve system

Imbalanced copper homeostasis and perturbation of membrane trafficking are two common symptoms that have been associated with the pathogenesis of neurodegenerative and neurodevelopmental diseases. Accumulating evidence from biophysical, cellular and in vivo studies suggest that membrane trafficking orchestrates both copper homeostasis and neural functions-however, a systematic review of how copper homeostasis and membrane trafficking interplays in neurons remains lacking. Here, we summarize current knowledge of the general trafficking itineraries for copper transporters and highlight several critical membrane trafficking regulators in maintaining copper homeostasis. We discuss how membrane trafficking regulators may alter copper transporter distribution in different membrane compartments to regulate intracellular copper homeostasis. Using Parkinson's disease and MEDNIK as examples, we further elaborate how misregulated trafficking regulators may interplay parallelly or synergistically with copper dyshomeostasis in devastating pathogenesis in neurodegenerative diseases. Finally, we explore multiple unsolved questions and highlight the existing challenges to understand how copper homeostasis is modulated through membrane trafficking.

High fat suppresses SOD1 activity by reducing copper chaperone for SOD1 associated with neurodegeneration and memory decline

High fat consumption leads to reactive oxygen species (ROS) which is associated with age-progressive neurological disorders. Cu/Zn superoxide dismutase (SOD1) is a critical enzyme against ROS. However, the relationship between SOD1 and the high-fat-induced ROS and neurodegeneration is poorly known. Here we showed that, upon treatment with a saturated fatty acid palmitic acid (PA), the SOD1 activity was decreased in mouse neuronal HT-22 cell line accompanied by elevation of ROS, but not in mouse microglial BV-2 cell line. We further showed that PA decreased the levels of copper chaperone for SOD1 (CCS) in HT-22 cells, which promoted the nuclear import of SOD1 and decreased its activity. We demonstrated that the reduction of CCS is involved in the PA-induced decrease of SOD1 activity and elevation of ROS. In addition, compared with the adult mice fed with a standard diet, the high-fat-diet adult mice presented an increase of plasma free fatty acids, reduction of hippocampal SOD1 activity and CCS, mitochondrial degeneration and long-term memory decline. Taken together, our findings suggest that the high-fat-induced lower CCS level is essential for SOD1 suppression which may be associated with neurodegeneration and cognitive decline.

Recent Endeavors on Molecular Imaging for Mapping Metals in Biology

Abstract

Transition metals such as zinc, copper and iron play vital roles in maintaining physiological functions and homeostasis of living systems. Molecular imaging, including two-photon imaging (TPI), bioluminescence imaging (BLI) and photoacoustic imaging (PAI), could act as non-invasive toolkits for capturing dynamic events in living cells, tissues and whole animals. Herein, we review the recent progress in the development of molecular probes for essential transition metals and their biological applications. We emphasize the contributions of metallostasis to health and disease, and discuss the future research directions about how to harness the great potential of metal sensors.

Graphic Abstract

Copper interferes with selenoprotein synthesis and activity

Selenium and copper are essential trace elements for humans, needed for the biosynthesis of enzymes contributing to redox homeostasis and redox-dependent signaling pathways. Selenium is incorporated as selenocysteine into the active site of redox-relevant selenoproteins including glutathione peroxidases (GPX) and thioredoxin reductases (TXNRD). Copper-dependent enzymes mediate electron transfer and other redox reactions. As selenoprotein expression can be modulated e.g. by H2O2, we tested the hypothesis that copper status affects selenoprotein expression. To this end, hepatocarcinoma HepG2 cells and mice were exposed to a variable copper and selenium supply in a physiologically relevant concentration range, and transcript and protein expression as well as GPX and TXNRD activities were compared. Copper suppressed selenoprotein mRNA levels of GPX1 and SELENOW, downregulated GPX and TXNRD activities and decreased UGA recoding efficiency in reporter cells. The interfering effects were successfully suppressed by applying the copper chelators bathocuproinedisulfonic acid or tetrathiomolybdate. In mice, a decreased copper supply moderately decreased the copper status and negatively affected hepatic TXNRD activity. We conclude that there is a hitherto unknown interrelationship between copper and selenium status, and that copper negatively affects selenoprotein expression and activity most probably via limiting UGA recoding. This interference may be of physiological relevance during aging, where a particular shift in the selenium to copper ratio has been reported. An increased concentration of copper in face of a downregulated selenoprotein expression may synergize and negatively affect the cellular redox homeostasis contributing to disease processes.

Copper therapy reduces intravascular hemolysis and derepresses ferroportin in mice with mosaic mutation (Atp7amo-ms): An implication for copper-mediated regulation of the Slc40a1 gene expression

Mosaic mutant mice displaying functional dysfunction of Atp7a copper transporter (the Menkes ATPase) are an established animal model of Menkes disease and constitute a convenient tool for investigating connections between copper and iron metabolisms. This model allows to explore changes in iron metabolism in suckling mutant mice suffering from systemic copper deficiency as well as in young and adult ones undergone copper therapy, which reduces lethal effect of the Atp7a gene mutation. Our recent study demonstrated that 14-day-old mosaic mutant males display blood cell abnormalities associated with intravascular hemolysis, and show disturbances in the functioning of the hepcidin-ferroportin regulatory axis, which controls systemic iron homeostasis. We thus aimed to check whether copper supplementation recovers mutants from hemolytic insult and rebalance systemic iron regulation. Copper supplementation of 14-day-old mosaic mutants resulted in the reestablishment of hematological status, attenuation of hepicidin and concomitant induction of the iron exporter ferroportin/Slc40a1 expression in the liver, down-regulated in untreated mutants. Interestingly, treatment of wild-type males with copper, induced hepcidin-independent up-regulation of ferroportin protein level in hepatic macrophages in both young and adult (6-month-old) animals. Stimulatory effect of copper on ferroportin mRNA and protein levels was confirmed in bone marrow-derived macrophages isolated from both wild-type and mosaic mutant males. Our study indicates that copper is an important player in the regulation of the Slc40a1 gene expression.

In vivo bioluminescence imaging reveals copper deficiency in a murine model of nonalcoholic fatty liver disease

Copper is a required metal nutrient for life, but global or local alterations in its homeostasis are linked to diseases spanning genetic and metabolic disorders to cancer and neurodegeneration. Technologies that enable longitudinal in vivo monitoring of dynamic copper pools can help meet the need to study the complex interplay between copper status, health, and disease in the same living organism over time. Here, we present the synthesis, characterization, and in vivo imaging applications of Copper-Caged Luciferin-1 (CCL-1), a bioluminescent reporter for tissue-specific copper visualization in living animals. CCL-1 uses a selective copper(I)-dependent oxidative cleavage reaction to release d-luciferin for subsequent bioluminescent reaction with firefly luciferase. The probe can detect physiological changes in labile Cu+ levels in live cells and mice under situations of copper deficiency or overload. Application of CCL-1 to mice with liver-specific luciferase expression in a diet-induced model of nonalcoholic fatty liver disease reveals onset of hepatic copper deficiency and altered expression levels of central copper trafficking proteins that accompany symptoms of glucose intolerance and weight gain. The data connect copper dysregulation to metabolic liver disease and provide a starting point for expanding the toolbox of reactivity-based chemical reporters for cell- and tissue-specific in vivo imaging.

Cu, Zn-Superoxide Dismutase is Lower and Copper Chaperone CCS is Higher in Erythrocytes of Copper-Deficient Rats and Mice

Discovery of a sensitive blood biochemical marker of copper status would be valuable for assessing marginal copper intakes. Rodent models were used to investigate whether erythrocyte concentrations of copper, zinc–superoxide dismutase (SOD), and the copper metallochaperone for SOD (CCS) were sensitive to dietary copper changes. Several models of copper deficiency were studied in postweanling male Holtzman rats, male Swiss Webster mice offspring, and both rat and mouse dams. Treatment resulted in variable but significantly altered copper status as evaluated by the presence of anemia, and lower liver copper and higher liver iron concentrations in copper-deficient compared with copper-adequate animals. Associated with this copper deficiency were consistent reductions in immunoreactive SOD and robust enhancements in CCS. In most cases, the ratio of CCS:SOD was several-fold higher in red blood cell extracts from copper-deficient compared with copper-adequate rodents. Determination of red cell CCS:SOD may be useful for assessing copper status of humans.

Accumulation of copper in the kidney of pigs fed high dietary zinc is due to metallothionein expression with minor effects on genes involved in copper metabolism

A study was conducted to determine the effect of high dietary zinc (Zn) oxide on trace element accumulation in various organs with special emphasis on the kidney. A total of 40 weaned piglets were allocated into two groups with 16 and 24 piglets each receiving a diet containing normal (NZn; 100mg Zn/kg) or high (HZn; 2,100mg Zn/kg) Zn concentration, respectively. After two weeks, eight piglets from each treatment were killed and organ samples were taken. Eight piglets from the remaining 16 pigs fed HZn diets were changed to NZn diets (CZn). All remaining piglets were killed after another two weeks for organ sampling. Trace element concentration was determined in the jejunum, liver, kidney, pancreas, bone (metacarpal IV), spleen, lung, thymus, tonsils and lymph nodes of jejunum, ileum and colon. Kidney mRNA expression of Zn transporter ZnT1 and ZIP4, genes involved in Cu metabolism (Ctr1, Atox1, SOD1, ATP7A, CCS, CP) and divalent metal ion transport (DMT1) and binding (MT-1a, MT-2b, MT-3) were determined. The Zn concentration in jejunum, liver, pancreas tissue and metacarpal IV was higher (P<0.05) in HZn group compared with NZn and CZn groups. Trace element concentration in organs of CZn pigs was similar to those fed NZn diets. Zn concentration in muscle, lung and lymphatic organs as thymus, tonsils, spleen and lymph nodes of jejunum, ileum and colon did not differ between the groups. Zn and Cu were positively correlated (R=0.67; P<0.05) in the kidney. No significant differences for Cu chaperones, Cu transporters and Cu-dependent factors were determined despite decreased expression of Atox1 after two weeks and increased Ctr1 expression over time in the HZn group. Expression of MT-1a, MT-2b and MT-3 were significantly higher in HZn fed pigs with most pronounced effects for MT-1a > MT-2b > MT-3. Gene expression of MTs in pigs fed CZn diets did not differ from pigs fed NZn diets. The data suggest that high dietary Zn feeding in pigs leads to Cu co-accumulation in the kidney of pigs with minor effect on genes relevant for Cu metabolism. In addition, the organ Zn and Cu accumulation is reversible after two weeks of withdrawal of high dietary Zn.

Featured Article: Effect of copper on nuclear translocation of copper chaperone for superoxide dismutase-1

Copper chaperone for superoxide dismutase-1 (CCS-1), facilitating copper insertion into superoxide dismutase 1 (SOD-1), is present in the nucleus. However, it is unknown how CCS-1 is translocated to the nucleus. The present study was undertaken to determine the effect of copper on nuclear translocation of CCS-1. Human umbilical vein endothelial cells (HUVECs) were subjected to hypoxia, causing an increase in both copper and CCS-1 in the nucleus. Treatment with tetraethylenepentamine (TEPA) not only decreased the total cellular concentration and the nuclear translocation of copper, but also completely suppressed the entry of CCS-1 to the nucleus. On the other hand, siRNA targeting CCS-1 neither inhibited the increase in total concentrations nor blocked the nuclear translocation of copper. This study thus demonstrates that under hypoxia condition, both copper and CCS-1 are transported to the nucleus. The nuclear translocation of CCS-1 is copper dependent, but the nuclear translocation of copper could take place alternatively in a CCS-1-independent pathway.

Transcriptional regulation of copper metabolism genes in the liver of fetal and neonatal control and iron-deficient rats

Copper and iron metabolism have been known to interact for many years. We have previously shown, during pregnancy, that copper levels in the maternal liver rise as a consequence of iron deficiency, but that levels in the fetal liver decrease. In this paper, we measure expression of genes involved in copper metabolism in fetal and postnatal liver, to test whether alterations can explain this observation. Additionally, we study the extent to which gene expression changes in the latter stages of pregnancy and in the perinatal period. Ctr1 expression levels dropped to term, rising again thereafter. There was no difference in gene expression between control and iron deficient animals. Atox1 expression remained approximately stable until term, and then there was a rise to a maximum at about Day 8. Atp7a expression levels remained constant, except for a brief drop at term. Atp7b levels, in contrast, decreased from a maximum early in gestation to low levels in the term and post-natal livers. Ceruloplasmin expression appeared to be diametrically opposite to Atp7b. The other two metallochaperones showed the same pattern of expression as Atox1, with a decrease to term, a rise at Day 1, or a rise after birth followed by a brief decrease at about Day 3. None of the genes were significantly affected by iron deficiency, suggesting that changes in expression cannot explain the altered copper levels in the fetal and neonatal liver.

Investigating the role of transferrin in the distribution of iron, manganese, copper, and zinc

The essential role of transferrin in mammalian iron metabolism is firmly established. Integral to our understanding of transferrin, studies in hypotransferrinemic mice, a model of inherited transferrin deficiency, have demonstrated that transferrin is essential for iron delivery for erythropoiesis and in the regulation of expression of hepcidin, a hormone that inhibits macrophage and enterocyte iron efflux. Here we investigate a potential role for transferrin in the distribution of three other physiologic metals, manganese, copper, and zinc. We first assessed metal content in transferrin-rich fractions of wild-type mouse sera and demonstrate that although both iron and manganese cofractionated predominantly with transferrin, the absolute levels of manganese are several orders of magnitude lower than those of iron. We next measured metal content in multiple tissues in wild-type and hypotransferrinemic mice of various ages. Tissue metal imbalances were severe for iron and minimal to moderate for some metals in some tissues in hypotransferrinemic mice. Metal levels measured in a transferrin-replete yet hepcidin-deficient and iron-loaded mouse strain suggested that the observed imbalances in tissue copper, zinc, and manganese levels were not all specific to hypotransferrinemic mice or caused directly by transferrin deficiency. Overall, our results suggest that transferrin does not have a primary role in the distribution of manganese, copper, or zinc to tissues and that the abnormalities observed in tissue manganese levels are not attributable to a direct role for transferrin in manganese metabolism but rather are attributable to an indirect effect of transferrin deficiency on hepcidin expression and/or iron metabolism.

Impact of copper deficiency in humans

Humans consume about 1 mg of copper daily, an amount thought adequate for most needs. Genetic, environmental, or physiological alterations can impose a higher copper set point, increasing risk for copper-limited pathophysiology. Humans express about a dozen proteins that require copper for function (cuproenzymes). Limitation in the activity of cuproenzymes can explain the pleiotropic effect of copper deficiency. However, for most of the salient features of human copper deficiency, the precise molecular mechanisms are unknown. This is true for the two most common clinical features, hypochromic anemia and adult onset peripheral neuropathy/ataxia, a condition described frequently in the last decade due to multiple etiologies. The challenge for future scientists will be to identify the mechanisms underlying the pathophysiology of copper deficiency so appropriate screening and treatment can occur. The need for a strong copper biomarker to aid in this screening is critical.

Changes in copper concentrations affect the protein levels but not the mRNA levels of copper chaperones in human umbilical vein endothelial cells

Copper chaperones are critical regulators of intracellular copper metabolism and distribution. The present study was undertaken to investigate the effects of changes in copper concentrations on the abundance of copper chaperones. Human umbilical vein endothelial cells (HUVECs) were treated with siRNA targeting copper transporter 1 (CTR1) or tetraethylenepentamine (TEPA) to decrease, or with copper sulfide to increase, intracellular copper concentrations, assayed using an atomic absorption spectrophotometer. Western blot analyses showed that CTR1 silencing or TEPA treatment increased the protein levels of copper chaperone ATOX1 and copper chaperone for superoxide dismutase 1 (CCS-1), but decreased copper chaperone for cytochrome c oxidase (COX17). In contrast, copper supplementation decreased the protein levels of ATOX1 and CCS-1 and increased COX17. Real-time RT-PCR analyses found no difference in the mRNA levels of the copper chaperones examined under the conditions defined above. This study thus demonstrated that changes in copper concentrations alter the protein levels, but not the mRNA levels, of copper chaperones, suggesting a role of copper in the post-translational modification of these proteins.

Copper toxicity induced hepatocerebral and neurodegenerative diseases: an urgent need for prognostic biomarkers

Copper (Cu) has been the subject of intensive research over several decades as numerous evidence robustly support the involvement of excess Cu induced neurotoxicity in hepatocerebral (Wilson's disease) and neurodegenerative disorders (especially Alzheimer's disease and Parkinson's disease); notwithstanding, the ideal Cu neurotoxicity biomarker/s for early prognosis remains elusive. Non-ceruloplasmin bound Cu is a biological marker of Wilson's disease and recent studies have shown that its levels are also increased in Alzheimer's disease. Copper chaperone for superoxide dismutase seems to be the other most promising biomarker of Cu toxicity (subject to its validation). Serum/plasma Cu, urine Cu and ceruloplasmin concentrations, most widely used laboratory indicators to diagnose Wilson's disease, are not specific for Cu excess milieu as these are also influenced by age, sex, inflammation and hormonal status. High inter-individual variability, nonexistence of standardized assays and non-specificity limit the use of other cuproenzymes as biomarkers of Cu neurotoxicity. The majority of Cu neurotoxicity biomarker research has focused in plasma/serum where other factors including inflammation, oxidative stress, dietary and environmental factors influence the Cu condition being studied. Proteomics study of cerebrospinal fluid, due to its high specificity and sensitivity represents an alternative approach to study early peripheral Cu neurotoxicity biomarker/s in experimental animals. In addition, network biology, transcriptomics in conjunction with novel in vivo Cu imaging techniques allow us to explore other potential candidates and propose new targets to be studied for chronic Cu neurotoxicity biomarker/s, and for possible therapeutic interventions.

Friedreich's ataxia causes redistribution of iron, copper, and zinc in the dentate nucleus

Friedreich's ataxia (FRDA) causes selective atrophy of the large neurons of the dentate nucleus (DN). High iron (Fe) concentration and failure to clear the metal from the affected brain tissue are potential risk factors in the progression of the lesion. The DN also contains relatively high amounts of copper (Cu) and zinc (Zn), but the importance of these metals in FRDA has not been established. This report describes nondestructive quantitative X-ray fluorescence (XRF) and "mapping" of Fe, Cu, and Zn in polyethylene glycol–dimethylsulfoxide (PEG/DMSO)-embedded DN of 10 FRDA patients and 13 controls. Fe fluorescence arose predominantly from the hilar white matter, whereas Cu and Zn were present at peak levels in DN gray matter. Despite collapse of the DN in FRDA, the location of the peak Fe signal did not change. In contrast, the Cu and Zn regions broadened and overlapped extensively with the Fe-rich region. Maximal metal concentrations did not differ from normal (in micrograms per milliliter of solid PEG/DMSO as means ± S.D.): Fe normal, 364 ± 117, FRDA, 344 ± 159; Cu normal, 33 ± 13, FRDA, 33 ± 18; and Zn normal, 32 ± 16, FRDA, 33 ± 19. Tissues were recovered from PEG/DMSO and transferred into paraffin for matching with immunohistochemistry of neuron-specific enolase (NSE), glutamic acid decarboxylase (GAD), and ferritin. NSE and GAD reaction products confirmed neuronal atrophy and grumose degeneration that coincided with abnormally diffuse Cu and Zn zones. Ferritin immunohistochemistry matched Fe XRF maps, revealing the most abundant reaction product in oligodendroglia of the DN hilus. In FRDA, these cells were smaller and more numerous than normal. In the atrophic DN gray matter of FRDA, anti-ferritin labeled mostly hypertrophic microglia. Immunohistochemistry and immunofluorescence of the Cu-responsive proteins Cu,Zn-superoxide dismutase and Cu⁺⁺-transporting ATPase α-peptide did not detect specific responses to Cu redistribution in FRDA. In contrast, metallothionein (MT)-positive processes were more abundant than normal and contributed to the gliosis of the DN. The isoforms of MT, MT-1/2, and brain-specific MT-3 displayed only limited co-localization with glial fibrillary acidic protein. The results suggest that MT can provide effective protection against endogenous Cu and Zn toxicity in FRDA, similar to the neuroprotective sequestration of Fe in holoferritin.

Zinc supplementation does not alter sensitive biomarkers of copper status in healthy boys

The tolerable upper intake levels (UL) for zinc for children were based on limited data and there is concern that the UL may be set too low. The first effect of excessive zinc intake is a reduction in copper status. The primary objective of this study was to examine the effect of zinc supplementation on copper status in children. Healthy, 6- to 8-y-old boys from Ontario, Canada were assigned to take a placebo (n = 10) or 5 mg (n = 10), 10 mg (n = 9), or 15 mg (n = 8) of zinc supplement daily for 4 mo in a double-blinded, placebo-controlled, randomized trial. Biochemical measures were evaluated at baseline and after 2 and 4 mo of supplementation. Food records were completed near the baseline and 4-mo visits. Age and anthropometric measurements did not differ (P > 0.05) between treatment groups at baseline. Mean zinc intakes from food alone (10.9-14.8 mg zinc/d) approached or exceeded the UL of 12 mg/d. Compared with the placebo group, the zinc groups had a greater change in the urine zinc:creatinine ratio at 4 mo (P = 0.02). Traditional (plasma copper and ceruloplasmin activity) and more sensitive biomarkers of copper status, including erythrocyte SOD1 activity and the erythrocyte CCS:SOD1 protein ratio, were unchanged in zinc-supplemented boys, demonstrating that copper status was not depressed. Serum lipid measures and hemoglobin concentrations were also unaffected and gastrointestinal symptoms were not reported. These data provide evidence in support of the need for reexamining the current UL for zinc for children.

Copper: effects of deficiency and overload

Copper is an essential trace metal that is required for the catalysis of several important cellular enzymes. However, since an excess of copper can also harm cells due to its potential to catalyze the generation of toxic reactive oxygen species, transport of copper and the cellular copper content are tightly regulated. This chapter summarizes the current knowledge on the importance of copper for cellular processes and on the mechanisms involved in cellular copper uptake, storage and export. In addition, we will give an overview on disturbances of copper homeostasis that are characterized by copper overload or copper deficiency or have been connected with neurodegenerative disorders.

Variable response of selected cuproproteins in rat choroid plexus and cerebellum following perinatal copper deficiency

Recent immunohistochemical characterization of the copper transport protein, Ctr1, reported enriched levels in mouse choroid plexus, and enhancement by copper deficiency. To extend and confirm this, experiments were conducted with Holtzman rats. Following perinatal copper deficiency there was an 80% reduction in brain copper of 24-27 day old copper-deficient (Cu-) rat pups compared to copper-adequate (Cu+) controls. Choroid plexus immunoblot analysis with rabbit anti-hCtr1 demonstrated a 50% higher Ctr1 protein expression in Cu-samples. However, levels of copper chaperone for superoxide dismutase (CCS) were unchanged, suggesting that Ctr1 buffers the choroid plexus against copper deficiency, since CCS normally is much higher in Cu-tissues. There were 13% lower levels of cytochrome c oxidase subunit IV (COX IV) detected in Cuchoroid plexus. In contrast, in cerebellum of Cu-rats CCS was 2-fold higher and COXIV 1.7-fold lower than Cu+ rats consistent with severe copper deficiency. Brain mitochondria from Cu-rats had severe reductions in COXIV content and CCO activity and modest but significant elevations in CCS and reductions in Cu, Zn-superoxide dismutase. COXIV may be a more sensitive marker for copper deficiency than CCS and may prove useful to assess copper status.

Expression Profiling of Solute Carrier Gene Families at the Blood-CSF Barrier

The choroid plexus (CP) is a highly vascularized tissue in the brain ventricles and acts as the blood-cerebrospinal fluid (CSF) barrier (BCSFB). A main function of the CP is to secrete CSF, which is accomplished by active transport of small ions and water from the blood side to the CSF side. The CP also supplies the brain with certain nutrients, hormones, and metal ions, while removing metabolites and xenobiotics from the CSF. Numerous membrane transporters are expressed in the CP in order to facilitate the solute exchange between the blood and the CSF. The solute carrier (SLC) superfamily represents a major class of transporters in the CP that constitutes the molecular mechanisms for CP function. Recently, we systematically and quantitatively examined Slc gene expression in 20 anatomically comprehensive brain areas in the adult mouse brain using high-quality in situ hybridization data generated by the Allen Brain Atlas. Here we focus our analysis on Slc gene expression at the BCSFB using previously obtained data. Of the 252 Slc genes present in the mouse brain, 202 Slc genes were found at detectable levels in the CP. Unsupervised hierarchical cluster analysis showed that the CP Slc gene expression pattern is substantially different from the other 19 analyzed brain regions. The majority of the Slc genes in the CP are expressed at low to moderate levels, whereas 28 Slc genes are present in the CP at the highest levels. These highly expressed Slc genes encode transporters involved in CSF secretion, energy production, and transport of nutrients, hormones, neurotransmitters, sulfate, and metal ions. In this review, the functional characteristics and potential importance of these Slc transporters in the CP are discussed, with particular emphasis on their localization and physiological functions at the BCSFB.

Conditional knockout of the Menkes disease copper transporter demonstrates its critical role in embryogenesis

The transition metal, copper (Cu), is an enzymatic cofactor required for a wide range of biochemical processes. Its essentiality is demonstrated by Menkes disease, an X-linked copper deficiency disorder characterized by defects in nervous-, cardiovascular- and skeletal systems, and is caused by mutations in the ATP7A copper transporter. Certain ATP7A mutations also cause X-linked Spinal Muscular Atrophy type 3 (SMAX3), which is characterized by neuromuscular defects absent an underlying systemic copper deficiency. While an understanding of these ATP7A-related disorders would clearly benefit from an animal model that permits tissue-specific deletion of the ATP7A gene, no such model currently exists. In this study, we generated a floxed mouse model allowing the conditional deletion of the Atp7a gene using Cre recombinase. Global deletion of Atp7a resulted in morphological and vascular defects in hemizygous male embryos and death in utero. Heterozygous deletion in females resulted in a 50% reduction in live births and a high postnatal lethality. These studies demonstrate the essential role of the Atp7a gene in mouse embryonic development and establish a powerful model for understanding the tissue-specific roles of ATP7A in copper metabolism and disease.

Molecular and biochemical characterization of a unique mutation in CCS, the human copper chaperone to superoxide dismutase

Copper (Cu) is a trace metal that readily gains and donates electrons, a property that renders it desirable as an enzyme cofactor but dangerous as a source of free radicals. To regulate cellular Cu metabolism, an elaborate system of chaperones and transporters has evolved, although no human Cu chaperone mutations have been described to date. We describe a child from a consanguineous family who inherited homozygous mutations in the SLC33A1, encoding an acetyl CoA transporter, and in CCS, encoding the Cu chaperone for superoxide dismutase. The CCS mutation, p.Arg163Trp, predicts substitution of a highly conserved arginine residue at position 163, with tryptophan in domain II of CCS, which interacts directly with superoxide dismutase 1 (SOD1). Biochemical analyses of the patient's fibroblasts, mammalian cell transfections, immunoprecipitation assays, and Lys7Δ (CCS homolog) yeast complementation support the pathogenicity of the mutation. Expression of CCS was reduced and binding of CCS to SOD1 impaired. As a result, this mutation causes reduced SOD1 activity and may impair other mechanisms important for normal Cu homeostasis. CCS-Arg163Trp represents the primary example of a human mutation in a gene coding for a Cu chaperone.

Charting the travels of copper in eukaryotes from yeast to mammals

Throughout evolution, all organisms have harnessed the redox properties of copper (Cu) and iron (Fe) as a cofactor or structural determinant of proteins that perform critical functions in biology. At its most sobering stance to Earth's biome, Cu biochemistry allows photosynthetic organisms to harness solar energy and convert it into the organic energy that sustains the existence of all nonphotosynthetic life forms. The conversion of organic energy, in the form of nutrients that include carbohydrates, amino acids and fatty acids, is subsequently released during cellular respiration, itself a Cu-dependent process, and stored as ATP that is used to drive a myriad of critical biological processes such as enzyme-catalyzed biosynthetic processes, transport of cargo around cells and across membranes, and protein degradation. The life-supporting properties of Cu incur a significant challenge to cells that must not only exquisitely balance intracellular Cu concentrations, but also chaperone this redox-active metal from its point of cellular entry to its ultimate destination so as to avert the potential for inappropriate biochemical interactions or generation of damaging reactive oxidative species (ROS). In this review we chart the travels of Cu from the extracellular milieu of fungal and mammalian cells, its path within the cytosol as inferred by the proteins and ligands that escort and deliver Cu to intracellular organelles and protein targets, and its journey throughout the body of mammals. This article is part of a Special Issue entitled: Cell Biology of Metals.

Rapid alteration in rat red blood cell copper chaperone for superoxide dismutase after marginal copper deficiency and repletion

There is increased incidence of human copper deficiency (CuD). A sensitive and reliable blood biomarker may reveal additional cases of marginal deficiency. Two experiments were designed to test the hypothesis that the copper chaperone for superoxide dismutase (CCS) would be a robust marker after marginal CuD. Experiment 1 used weanling male Sprague-Dawley rats that were offered a CuD diet for 4 weeks, and samples were evaluated after 1, 2, and 4 weeks and compared with copper-adequate (CuA) controls. Furthermore, iron-deficient rats were included for comparison after 2 weeks of depletion. Red blood cell and plasma cuproenzymes were evaluated through Western blot analysis. Superoxide dismutase (Sod1) and ceruloplasmin protein were found to be altered by both iron and CuD, whereas CCS and CCS/Sod1 ratio were found to only be altered only in CuD rats and, importantly, after only 1 week of treatment. Two weeks on CuA diet restored cuproenzyme levels to control values after 4 weeks of CuD depletion. In experiment 2, marginal CuD (CuM) rats were compared with CuA and CuD rats after 2 weeks of treatment. Superoxide dismutase, ceruloplasmin, and CCS/Sod1 abundances were lower in CuM and CuD groups compared with CuA rats, but there was no statistical difference between CuM and CuD rats. However, CCS was statistically different between all groups, and abundance highly correlated with liver copper concentration. Results suggest that red blood cell CCS may be an excellent biomarker for diagnosis of rapid and marginal CuD.

Erythrocyte copper chaperone for superoxide dismutase is increased following marginal copper deficiency in adult and postweanling mice

A sensitive and reliable biomarker has yet to be identified for marginal copper deficiency in humans. The need for such a biomarker is critical, because increased cases of human copper deficiency evolve following bariatric surgery and other secondary factors besides diet. Four experiments were devised to induce marginal copper deficiency through copper-deficient (CuD) diets (5 wk for mice and 4 wk for rats). In Expt. 1 and 2, male postweanling mice were raised in either solid-bottom plastic cages (Expt. 1) or stainless steel hanging cages (Expt. 2) and compared. Postweanling rats (Expt. 3) and adult mice (Expt. 4) were also studied using stainless steel cages. Copper-adequate controls were fed a semipurified diet containing 9 mg Cu/kg. CuD rats exhibited the most severe changes in biomarkers due to copper limitation, including major reductions in plasma ceruloplasmin (Cp) and erythrocyte superoxide dismutase (Sod1) and augmentation in copper chaperone for Sod1 (CCS). The CuD mice in Expt. 2 were more deficient than the CuD mice in Expt. 1, likely due to coprophagia differences. In fact, the CuD mice in Expt. 1 had unaltered Sod1 or Cp levels. Importantly though, these marginally deficient mice and CuD adult mice that had no changes in Cp activity or liver copper level had robust augmentation of CCS. Erythrocyte CCS was the only consistent biomarker to change in copper deficiency for all dietary groups, suggesting that CCS may be an excellent biomarker for human confirmation of marginal copper deficiency.

Administration of high doses of copper to capuchin monkeys does not cause liver damage but induces transcriptional activation of hepatic proliferative responses

Liver cells respond to copper loading upregulating protective mechanisms. However, to date, except for liver content, there are no good indicators that identify individuals with excess liver copper. We hypothesized that administering high doses of copper to young (5.5 mg Cu · kg⁻¹ . d⁻¹) and adult (7.5 mg Cu · kg⁻¹ . d⁻¹) capuchin monkeys would induce detectable liver damage. Study groups included adult monkeys (2 females, 2 males) 3-3.5 y old at enrollment treated with copper for 36 mo (ACu); age-matched controls (1 female, 3 males) that did not receive additional copper (AC); young monkeys (2 female, 2 males) treated from birth with copper for 36 mo (YCu); and young age-matched controls (2 female, 2 males) that did not receive additional copper (YC). We periodically assessed clinical, blood biochemical, and liver histological indicators and at 36 mo the hepatic mRNA abundance of MT2a, APP, DMT1, CTR1, HGF, TGFβ, and NFκΒ only in adult monkeys. After 36 mo, the liver copper concentration was 4-5 times greater in treated monkeys relative to controls. All monkeys remained healthy with normal routine serum biochemical indices and there was no evidence of liver tissue damage. Relative mRNA abundance of HGF, TGFβ and NFκB was significantly greater in ACu than in AC monkeys. In conclusion, capuchin monkeys exposed to copper at doses up to 50 times the current upper level enhanced expression of genes related to inflammation and injury without clinical, blood biochemical, or histological evidence of liver damage.

Presenilins promote the cellular uptake of copper and zinc and maintain copper chaperone of SOD1-dependent copper/zinc superoxide dismutase activity

Dyshomeostasis of extracellular zinc and copper has been implicated in β-amyloid aggregation, the major pathology associated with Alzheimer disease. Presenilin mediates the proteolytic cleavage of the β-amyloid precursor protein to release β-amyloid, and mutations in presenilin can cause familial Alzheimer disease. We tested whether presenilin expression affects copper and zinc transport. Studying murine embryonic fibroblasts (MEFs) from presenilin knock-out mice or RNA interference of presenilin expression in HEK293T cells, we observed a marked decrease in saturable uptake of radiolabeled copper and zinc. Measurement of basal metal levels in 6-month-old presenilin 1 heterozygous knock-out (PS1(+/-)) mice revealed significant deficiencies of copper and zinc in several tissues, including brain. Copper/zinc superoxide dismutase (SOD1) activity was significantly decreased in both presenilin knock-out MEFs and brain tissue of presenilin 1 heterozygous knock-out mice. In the MEFs and PS1(+/-) brains, copper chaperone of SOD1 (CCS) levels were decreased. Zinc-dependent alkaline phosphatase activity was not decreased in the PS null MEFs. These data indicate that presenilins are important for cellular copper and zinc turnover, influencing SOD1 activity, and having the potential to indirectly impact β-amyloid aggregation through metal ion clearance.

Peptidylgycine α-amidating monooxygenase and copper: a gene-nutrient interaction critical to nervous system function

Peptidylgycine alpha-amidating monooxygenase (PAM), a highly conserved copper-dependent enzyme, is essential for the synthesis of all amidated neuropeptides. Biophysical studies revealed that the binding of copper to PAM affects its structure, and cell biological studies demonstrated that the endocytic trafficking of PAM was sensitive to copper. We review data indicating that genetic reduction of PAM expression and mild copper deficiency in mice cause similar alterations in several physiological functions known to be regulated by neuropeptides: thermal regulation, seizure sensitivity, and anxiety-like behavior.

Maternal iron supplementation attenuates the impact of perinatal copper deficiency but does not eliminate hypotriiodothyroninemia nor impaired sensorimotor development

Copper, iron and iodine/thyroid hormone (TH) deficiencies disrupt brain development. Neonatal Cu deficiency causes Fe deficiency and may impact thyroidal status. One purpose of these studies was to determine the impact of improved iron status following Cu deficiency by supplementing the diet with iron. Cu deficiency was produced in pregnant Holtzman [Experiment 1 (Exp. 1)] or Sprague-Dawley [Experiment 2 (Exp. 2)] rats using two different diets. In Exp. 2, dietary Fe content was increased from 35 to 75 mg/kg according to NRC guidelines for reproduction. Cu-deficient (CuD) Postnatal Day 24 (P24) rats from both experiments demonstrated lower hemoglobin, serum Fe and serum triiodothyronine (T3) concentrations. However, brain Fe was lower only in CuD P24 rats in Exp. 1. Hemoglobin and serum Fe were higher in Cu adequate (CuA) P24 rats from Exp. 2 compared to Exp. 1. Cu- and TH-deficient rats from Exp. 2 exhibited a similar sensorimotor functional deficit following 3 months of repletion. Results suggest that Cu deficiency may impact TH status independent of its impact on iron biology. Further research is needed to clarify the individual roles for Cu, Fe and TH in brain development.

Risks and benefits of copper in light of new insights of copper homeostasis

Copper is an essential micronutrient involved in a variety of biological processes indispensable to sustain life. At the same time, it can be toxic when present in excess, the most noticeable chronic effect being liver damage. Potent, efficient regulatory mechanisms control copper absorption in the digestive tract and copper biliary excretion; absorption ranges between 12 and 60% in humans, depending on Cu intake, presence of other factors in the diet that may promote or inhibit its absorption and on the copper status of the individual. Current evidence suggests that copper deficiency may be more prevalent than previously thought, while copper toxicity is uncommon under customary daily life conditions. Menkes syndrome and Wilson disease are genetic conditions associated with severe copper deficiency and severe copper toxicity, respectively. Effects of milder degrees of copper deficiency and excess copper exposure are not well described, mainly due to lack of sensitive and specific indicators; serum copper concentration and ceruloplasmin are the most frequently used indicators, but they only detect rather intense changes of copper status. Of the many proteins assessed as potential markers of copper status the chaperone of Zn-Cu superoxide dismutase (CCS1) has yielded promising results; data on its performance under different conditions are needed to confirm its use as an indicator of early copper deficiency. Defining copper requirements and upper safe limits of consumption (UL) is a complex process since there are adverse health consequences from both copper deficiency and copper excess (U shape curve). The regulatory framework for risk assessment of essential trace elements introduced by the International Programme on Chemical Safety (IPCS) has proposed a homeostatic model to determine the Adequate Range of Oral Intake (AROI) of essential trace elements; the nadir of the resulting U shape curve serves to define the AROI. At this range of intake physiological mechanisms allow for normal homeostasis and basically, there are no detectable adverse effects. At present, Recommended Dietary Intakes (DRIs) and Adequate Intakes (AIs) are used to recommend copper intakes at different ages and life situations. Evidence obtained in humans and non-human primates presented here suggest that current copper UL should be re evaluated. Developing the scientific basis for a copper UL and evaluating the relevance of copper deficiency globally are future key challenges for copper researchers.

Copper transporter 2 content is lower in liver and heart of copper-deficient rats

Copper (Cu) transporter 2 (Ctr2) is a transmembrane protein that transports Cu across cell membranes and increases cytosolic Cu levels. Experiments using cell lines have suggested that Ctr2 expression is regulated by Cu status. The importance of changes in Ctr2 expression is underscored by recent studies demonstrating that lower Ctr2 content in cells increases the cellular uptake of platinum-containing cancer drugs and toxicity to the drugs. In this study, we examined whether Ctr2 expression is altered by a nutritional Cu deficiency in vivo. Ctr2 mRNA and protein in liver and heart from rats fed a normal (Cu-N), moderately deficient (Cu-M) or deficient (Cu-D) Cu diet was measured. Rats fed the Cu-deficient diets showed a dose-dependent decrease in liver Ctr2 protein compared to Cu-N rats. Ctr2 protein was 42% and 85% lower in Cu-M and Cu-D rats, respectively. Liver Ctr2 mRNA was 50% lower in Cu-D rats and unaffected in Cu-M rats. In heart, Ctr2 protein was only lower in Cu-D rats (46% lower). These data show that Cu deficiency decreases Ctr2 content in vivo.

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.

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.

Peripheral nerve and brain differ in their capacity to resolve N,N-diethyldithiocarbamate-mediated elevations in copper and oxidative injury

Previous studies have demonstrated that N,N-diethyldithiocarbamate (DEDC) elevates copper and promotes oxidative stress within the nervous system. However, whether these effects resolve following cessation of exposure or have the potential to persist and result in cumulative injury has not been determined. In this study, an established model for DEDC myelin injury in the rat was used to determine whether copper levels, oxidative stress, and neuromuscular deficits resolve following the cessation of DEDC exposure. Rats were exposed to DEDC for 8 weeks and then either euthanized or maintained for 2, 6 or 12 weeks after cessation of exposure. At each time point copper levels were measured by inductively coupled mass spectrometry to assess the ability of sciatic nerve, brain, spinal cord and liver to eliminate excess copper post-exposure. The protein expression levels of glutathione transferase alpha, heme oxygenase 1 and superoxide dismutase 1 in peripheral nerve and brain were also determined by western blot to assess levels of oxidative stress as a function of post-exposure duration. As an initial assessment of the bioavailability of the excess copper in brain the protein expression levels of copper chaperone for superoxide dismutase 1, and prion protein were determined by western blot as a function of exposure and post-exposure duration. Neuromuscular function in peripheral nerve was evaluated using grip strengths, nerve conduction velocities, and morphologic changes at the light microscope level. The data demonstrated that in peripheral nerve, copper levels and oxidative stress return to control levels within several weeks after cessation of exposure. Neuromuscular function also showed a trend towards pre-exposure values, although the resolution of myelin lesions was more delayed. In contrast, total copper and antioxidant enzyme levels remained significantly elevated in brain for longer post-exposure periods. The persistence of effects observed in brain suggests that the central nervous system is more susceptible to long-term cumulative adverse effects from dithiocarbamates. Additionally, significant changes in expression levels of chaperone for superoxide dismutase 1, and prion protein were observed consistent with at least a portion of the excess copper being bioactive.

Anemic copper-deficient rats, but not mice, display low hepcidin expression and high ferroportin levels

The transmembrane protein ferroportin (Fpn) is essential for iron efflux from the liver, spleen, and duodenum. Fpn is regulated predominantly by the circulating iron regulatory hormone hepcidin, which binds to cell surface Fpn, initiating its degradation. Accordingly, when hepcidin concentrations decrease, Fpn levels increase. A previous study found that Fpn levels were not elevated in copper-deficient (CuD) mice that had anemia, a condition normally associated with dramatic reductions in hepcidin. Lack of change in Fpn levels may be because CuD mice do not display reduced concentrations of plasma iron (holotransferrin), a modulator of hepcidin expression. Here, we examined Fpn protein levels and hepcidin expression in CuD rats, which exhibit reduced plasma iron concentrations along with anemia. We also examined hepcidin expression in anemic CuD mice with normal plasma iron levels. We found that CuD rats had higher liver and spleen Fpn levels and markedly lower hepatic hepcidin mRNA expression than did copper-adequate (CuA) rats. In contrast, hepcidin levels did not differ between CuD and CuA mice. To examine potential mediators of the reduced hepcidin expression in CuD rats, we measured levels of hepatic transferrin receptor 2 (TfR2), a putative iron sensor that links holotransferrin to hepcidin production, and transcript abundance of bone morphogenic protein 6 (BMP6), a key endogenous positive regulator of hepcidin production. Diminished hepcidin expression in CuD rats was associated with lower levels of TfR2, but not BMP6. Our data suggest that holotransferrin and TfR2, rather than anemia or BMP6, are signals for hepcidin synthesis during copper deficiency.

Regulation of the copper chaperone CCS by XIAP-mediated ubiquitination

In order to balance the cellular requirements for copper with its toxic properties, an elegant set of mechanisms has evolved to regulate and buffer intracellular copper. The X-linked inhibitor of apoptosis (XIAP) protein was recently identified as a copper-binding protein and regulator of copper homeostasis, although the mechanism by which XIAP binds copper in the cytosol is unclear. Here we describe the identification of the copper chaperone for superoxide dismutase (CCS) as a mediator of copper delivery to XIAP in cells. We also find that CCS is a target of the E3 ubiquitin ligase activity of XIAP, although interestingly, ubiquitination of CCS by XIAP was found to lead to enhancement of its chaperone activity toward its physiologic target, superoxide dismutase 1, rather than proteasomal degradation. Collectively, our results reveal novel links among apoptosis, copper metabolism, and redox regulation through the XIAP-CCS complex.

Differential impact of copper deficiency in rats on blood cuproproteins

Sensitive blood biochemical markers of dietary copper status are not yet known. Rat models were used to investigate the response of severe copper deficiency in dams and pups by comparing abundance of several cuproproteins in erythrocytes, white blood cells, and platelets. The hypothesis tested was that copper deficiency would result in changes in abundance of cuproproteins in blood cells. Copper-deficient (CuD) Holtzman dams and pups had signs consistent with severe copper deficiency compared with copper-adequate controls including lower liver copper and hemoglobin levels and near total loss of plasma ceruloplasmin diamine oxidase activity. Copper-deficient erythrocytes had lower copper, zinc superoxide dismutase (SOD1) but higher copper metallochaperone for SOD1 (CCS) compared with copper-adequate, resulting in higher CCS/SOD1 levels. This ratio was more sensitive in CuD erythrocytes than CuD white cells and especially in CuD platelets. However, both white blood cells and platelets from CuD dams and pups had nearly nondetectable levels of cytochrome c oxidase subunit IV. Because isolation of relatively pure populations of erythrocytes and platelets is feasible, and reagents for immunoblot methods are available, determination of CCS/SOD1 and cytochrome c oxidase subunit IV protein levels may be useful to assess copper status of humans.

Interactions of peptide amidation and copper: novel biomarkers and mechanisms of neural dysfunction

Mammalian genomes encode only a small number of cuproenzymes. The many genes involved in coordinating copper uptake, distribution, storage and efflux make gene/nutrient interactions especially important for these cuproenzymes. Copper deficiency and copper excess both disrupt neural function. Using mice heterozygous for peptidylglycine alpha-amidating monooxygenase (PAM), a cuproenzyme essential for the synthesis of many neuropeptides, we identified alterations in anxiety-like behavior, thermoregulation and seizure sensitivity. Dietary copper supplementation reversed a subset of these deficits. Wildtype mice maintained on a marginally copper-deficient diet exhibited some of the same deficits observed in PAM(+/-) mice and displayed alterations in PAM metabolism. Altered copper homeostasis in PAM(+/-) mice suggested a role for PAM in the cell type specific regulation of copper metabolism. Physiological functions sensitive to genetic limitations of PAM that are reversed by supplemental copper and mimicked by copper deficiency may serve as indicators of marginal copper deficiency.

Technical note: copper chaperone for copper, zinc superoxide dismutase: a potential biomarker for copper status in cattle

Copper chaperone for Cu, Zn superoxide dismutase (CCS) has been shown to be reflective of Cu status in mice and rats. The objective of this study was to evaluate liver and erythrocyte CCS as an indicator of Cu status in beef cattle (Exp. 1), and to test the acute-phase properties of CCS under conditions of inflammation (Exp. 2). In Exp. 1, samples of whole blood and liver were collected at slaughter (492 d of age) from 15 Cu-deficient and 6 Cu-adequate Angus calves. At the time of tissue collection, severe Cu deficiency had been achieved and differences (P < 0.0001) in plasma and liver Cu among Cu-adequate and Cu-deficient calves were extreme (1.26 vs. 0.19 mg/L and 208.4 vs. 6.3 mg/kg for plasma and liver Cu, respectively). Protein levels of CCS were greater in liver (40%; P = 0.02) and erythrocytes (65%; P < 0.0001) of Cu-deficient vs. Cu-adequate calves. In Exp. 2, inflammatory responses were elicited in beef heifers by administration of a Mannheimia hemolytica vaccine. Four days after vaccination, plasma concentrations of the Cu-dependent protein ceruloplasmin and the Cu-independent protein haptoglobin were increased (P < 0.001) by 71 and 83%, respectively. In contrast, detection of CCS protein in samples of liver and erythrocytes did not differ (P >or= 0.45) between baseline (d 0) and d 4 after vaccination. These data demonstrate that bovine erythrocyte and liver CCS protein levels increase in Cu-deficient cattle. Furthermore, levels of CCS protein do not change after a vaccine-induced inflammatory response, suggesting that unlike ceruloplasmin, CCS may be a reliable indicator of Cu status in cattle.

Augmented cerebellar lactate in copper deficient rat pups originates from both blood and cerebellum

Copper (Cu) is essential for proper brain development, particularly the cerebellum, and functions as a cofactor for enzymes including mitochondrial cytochrome c oxidase (CCO). Cu deficiency severely limits CCO activity. Augmented lactate in brain of Cu deficient (Cu-) humans and cerebella of Cu- rats is though to originate from impaired mitochondria. However, brain lactate may also originate from elevated blood lactate. The hypothesis that cerebellar lactate originates from elevated blood lactate in Cu- rat pups was tested. Analysis of Cu- and Cu adequate (Cu+) rat pups (experiment I) revealed blood lactate was elevated in Cu- rat pups and cerebellar lactate levels were closely correlated to blood lactate concentration. A second rat experiment (experiment II) assessed Cu- cerebellar lactate without the confounding factor of elevated blood lactate. Blood lactate levels of Cu- rat pups in experiment II were equal to those of controls; however, Cu- cerebellar lactate was still elevated, suggesting mitochondrial impairment by Cu deficiency. Treatment of rat pups with dichloroacetate (DCA), an activator of mitochondrial pyruvate dehydrogenase complex (PDC), lowered Cu- cerebellar lactate to control levels suggesting PDC inhibition is a site of mitochondrial impairment in Cu- cerebella. Results suggest Cu- cerebellar lactate originates from blood and cerebellum.