Decreased Expression of the Slc31a1 Gene and Cytoplasmic Relocalization of Membrane CTR1 Protein in Renal Epithelial Cells: A Potent Protective Mechanism against Copper Nephrotoxicity in a Mouse Model of Menkes Disease.

Kidneys play an especial role in copper redistribution in the organism. The epithelial cells of proximal tubules perform the functions of both copper uptake from the primary urine and release to the blood. These cells are equipped on their apical and basal membrane with copper transporters CTR1 and ATP7A. Mosaic mutant mice displaying a functional dysfunction of ATP7A are an established model of Menkes disease. These mice exhibit systemic copper deficiency despite renal copper overload, enhanced by copper therapy, which is indispensable for their life span extension. The aim of this study was to analyze the expression of Slc31a1 and Slc31a2 genes (encoding CTR1/CTR2 proteins) and the cellular localization of the CTR1 protein in suckling, young and adult mosaic mutants. Our results indicate that in the kidney of both intact and copper-injected 14-day-old mutants showing high renal copper content, CTR1 mRNA level is not up-regulated compared to wild-type mice given a copper injection. The expression of the Slc31a1 gene in 45-day-old mice is even reduced compared with intact wild-type animals. In suckling and young copper-injected mutants, the CTR1 protein is relocalized from the apical membrane to the cytoplasm of epithelial cells of proximal tubules, the process which prevents copper transport from the primary urine and, thus, protects cells against copper toxicity.

Marginally reduced maternal hepatic and splenic ferroportin under severe nutritional iron deficiency in pregnancy maintains systemic iron supply.

The demand for iron is high in pregnancy to meet the increased requirements for erythropoiesis. Even pregnant females with initially iron-replete stores develop iron-deficiency anemia, due to inadequate iron absorption. In anemic females, the maternal iron supply is dedicated to maintaining iron metabolism in the fetus and placenta. Here, using a mouse model of iron deficiency in pregnancy, we show that iron recycled from senescent erythrocytes becomes a predominant source of this microelement that can be transferred to the placenta in females with depleted iron stores. Ferroportin is a key protein in the molecular machinery of cellular iron egress. We demonstrate that under iron deficiency in pregnancy, levels of ferroportin are greatly reduced in the duodenum, placenta and fetal liver, but not in maternal liver macrophages and in the spleen. Although low expression of both maternal and fetal hepcidin predicted ferroportin up-regulation in examined locations, its final expression level was very likely correlated with tissue iron status. Our results argue that iron released into the circulation of anemic females is taken up by the placenta, as evidenced by high expression of iron importers on syncytiotrophoblasts. Then, a substantial decrease in levels of ferroportin on the basolateral side of syncytiotrophoblasts, may be responsible for the reduced transfer of iron to the fetus. As attested by the lowest decrease in iron content among analyzed tissues, some part is retained in the placenta. These findings confirm the key role played by ferroportin in tuning iron turnover in iron-deficient pregnant mouse females and their fetuses.

Functional iron deficiency in toxic milk mutant mice (tx-J) despite high hepatic ferroportin: a critical role of decreased GPI-ceruloplasmin expression in liver macrophages.

Jackson toxic milk mutant mice (tx-J) carrying a missense mutation in the Atp7b gene are animal models of the Wilson disease. In both the Wilson patients and the tx-J mice, mutations in the ATP7B/Atp7b gene lead to disturbances in copper metabolism. The dysfunction of ATP7B/Atp7b leads to a reduction in the incorporation of copper into apoceruloplasmin; this decreases the ferroxidase activity of ceruloplasmin necessary for the efflux of iron from cells and reduces the release of copper from hepatocytes to the bile; this results in a massive hepatic copper accumulation. A decrease in the ferroxidase activity of ceruloplasmin in the tx-J mice emphasises the practicality of this animal model for the exploration of disturbances in iron balance triggered by dysregulation of copper metabolism. We found that 6-month-old tx-J mutants developed mild anaemia caused by functional iron deficiency. The tx-J mutants showed decreased plasma iron levels with concomitant iron accumulation in hepatocytes and liver macrophages. Hepatic iron retention was accompanied by decreased expression of the membrane form of ceruloplasmin in both liver cell types. Interestingly, in the liver of mutants, we found high levels of ferroportin (an iron exporter) on the surface of liver macrophages despite increased hepatic expression of hepcidin, a peptide inducing internalization and degradation of ferroportin. We conclude that even when the ferroportin expression is high, ceruloplasmin remains a limiting factor in the release of iron to the extracellular environment.