Protective effect of mitochondrial ferritin on cytosolic iron dysregulation induced by doxorubicin in HeLa cells.

Doxorubicin (DOX) is an anticancer drug with cardiotoxic side effects mostly caused by iron homeostasis dysregulation. Mitochondria are involved in iron trafficking and mitochondrial ferritin (FtMt) was shown to provide protection against cellular iron imbalance. Therefore, we hypothesized that FtMt overexpression could limit DOX effects on iron homeostasis. Heart's homogenates of DOX-treated C57BL/6 mice were analyzed for cytosolic and mitochondrial iron-related proteins' expression and activity, revealing high cytosolic ferritin and ferritin-bound iron, low transferrin-receptor 1 and a strong hepcidin upregulation. Mitochondrial iron-related proteins (aconitase, succinate-dehydrogenase, frataxin) seemed, however, unaffected, although a partial inactivation of superoxide dismutase 2 was detected. Importantly, the ectopic expression of FtMt in human HeLa cells partially reverted DOX-induced iron imbalance. Our results, while confirming DOX effects on iron homeostasis, demonstrate that DOX affects more cytosolic than mitochondrial iron metabolism both in murine hearts and human HeLa cells and that FtMt overexpression is able to prevent most of these effects in HeLa cells.

Pantothenate kinase-2 (Pank2) silencing causes cell growth reduction, cell-specific ferroportin upregulation and iron deregulation.

Pantothenate kinase 2 (Pank2) is a mitochondrial enzyme that catalyses the first regulatory step of Coenzyme A synthesis and that is responsible for a genetic movement disorder named Pank-associated neurodegeneration (PKAN). This is characterized by abnormal iron accumulation in the brain, particularly in the globus pallidus. We downregulated Pank2 in some cell lines by using specific siRNAs to study its effect on iron homeostasis. In HeLa cells this caused a reduction of cell proliferation and of aconitase activity, signs of cytosolic iron deficiency without mitochondrial iron deposition, and a 12-fold induction of ferroportin mRNA. Pank2 silencing caused a strong induction of ferroportin mRNA also in hepatoma HepG2, a modest one in neuroblastoma SH-SY5Y and none in glioma U373 cells. A reduction of cell growth was observed in all these cell types. The strong Pank2-mediated alteration of ferroportin expression in some cell types might alter iron transfer to the brain and be connected with brain iron accumulation.

The effects of frataxin silencing in HeLa cells are rescued by the expression of human mitochondrial ferritin.

Frataxin is a ubiquitous mitochondrial iron-binding protein involved in the biosynthesis of Fe/S clusters and heme. Its deficiency causes Friedreich's ataxia, a severe neurodegenerative disease. Mitochondrial ferritin is another major iron-binding protein, abundant in the testis and in sideroblasts from patients with sideroblastic anemia. We previously showed that its expression rescued the defects caused by frataxin deficiency in the yeast. To verify if this occurs also in mammals, we silenced frataxin in HeLa cells. This caused a reduction of growth, inhibition of the activity of aconitase and superoxide dismutase-2 and reduction of cytosolic ferritins without alteration of mitochondrial iron content. None of these effects were evident when silencing was done in cells expressing mitochondrial ferritin. These data indicate that frataxin has some roles in controlling the balance between different mitochondrial iron pools that are partially in common with those of mitochondrial ferritin.

Engineering the vasculature of decellularized rat kidney scaffolds using human induced pluripotent stem cell-derived endothelial cells.

Generating new kidneys using tissue engineering technologies is an innovative strategy for overcoming the shortage of donor organs for transplantation. Here we report how to efficiently engineer the kidney vasculature of decellularized rat kidney scaffolds by using human induced pluripotent stem cell (hiPSCs)-derived endothelial cells (hiPSC-ECs). In vitro, hiPSC-ECs responded to flow stress by acquiring an alignment orientation, and attached to and proliferated on the acellular kidney sections, maintaining their phenotype. The hiPSC-ECs were able to self-organize into chimeric kidney organoids to form vessel-like structures. Ex vivo infusion of hiPSC-ECs through the renal artery and vein of acellular kidneys resulted in the uniform distribution of the cells in all the vasculature compartments, from glomerular capillaries to peritubular capillaries and small vessels. Ultrastructural analysis of repopulated scaffolds through transmission and scanning electron microscopy demonstrated the presence of continuously distributed cells along the vessel wall, which was also confirmed by 3D reconstruction of z-stack images showing the continuity of endothelial cell coverage inside the vessels. Notably, the detection of fenestrae in the endothelium of glomerular capillaries but not in the vascular capillaries was clear evidence of site-specific endothelial cell specialisation.

Renal progenitors derived from human iPSCs engraft and restore function in a mouse model of acute kidney injury.

Acute kidney injury (AKI) is one of the most relevant health issues, leading to millions of deaths. The magnitude of the phenomenon remarks the urgent need for innovative and effective therapeutic approaches. Cell-based therapy with renal progenitor cells (RPCs) has been proposed as a possible strategy. Studies have shown the feasibility of directing embryonic stem cells or induced Pluripotent Stem Cells (iPSCs) towards nephrogenic intermediate mesoderm and metanephric mesenchyme (MM). However, the functional activity of iPSC-derived RPCs has not been tested in animal models of kidney disease. Here, through an efficient inductive protocol, we directed human iPSCs towards RPCs that robustly engrafted into damaged tubuli and restored renal function and structure in cisplatin-mice with AKI. These results demonstrate that iPSCs are a valuable source of engraftable cells with regenerative activity for kidney disease and create the basis for future applications in stem cell-based therapy.

RNA silencing of the mitochondrial ABCB7 transporter in HeLa cells causes an iron-deficient phenotype with mitochondrial iron overload.

X-linked sideroblastic anemia with ataxia (XLSA/A) is caused by defects of the transporter ABCB7 and is characterized by mitochondrial iron deposition and excess of protoporphyrin in erythroid cells. We describe ABCB7 silencing in HeLa cells by performing sequential transfections with siRNAs. The phenotype of the ABCB7-deficient cells was characterized by a strong reduction in proliferation rate that was not rescued by iron supplementation, by evident signs of iron deficiency, and by a large approximately 6-fold increase of iron accumulation in the mitochondria that was poorly available to mitochondrial ferritin. The cells showed an increase of protoporphyrin IX, a higher sensitivity to H(2)O(2) toxicity, and a reduced activity of mitochondrial superoxide dismutase 2 (SOD2), while the activity of mitochondrial enzymes, such as citrate synthase or succinate dehydrogenase, and ATP content were not decreased. In contrast, aconitase activity, particularly that of the cytosolic, IRP1 form, was reduced. The results support the hypothesis that ABCB7 is involved in the transfer of iron from mitochondria to cytosol, and in the maturation of cytosolic Fe/S enzymes. In addition, the results indicate that anemia in XLSA/A is caused by the accumulation of iron in a form that is not readily usable for heme synthesis.

Recombinant human hepcidin expressed in Escherichia coli isolates as an iron containing protein.

Hepcidin is a small peptide that acts as a regulator of systemic iron homeostasis. To study some of its functional properties, a synthetic cDNA for the minimal, 20-amino-acid, form of human hepcidin was cloned into different constructs for expression in Escherichia coli. The fusion ferritin-hepcidin produced molecules retaining most of ferritin structural and functional properties, including ferroxidase and iron incorporation activities. However, it showed spectroscopic properties compatible with the presence of iron-sulfur complexes on the hepcidin moiety, which was buried into protein cavity. Similar complexes were reconstituted by in vitro incubation of the iron-free protein with iron and sulfide salts. Two other unrelated fusion products were constructed, which, when expressed in E. coli, formed insoluble aggregates retaining a large proportion of total bacterial iron. Analysis of the solubilized preparations showed them to contain iron-sulfur complexes. We concluded that the cysteine-rich hepcidin acts as an iron-sequestering molecule during expression in E. coli. This may have implications for the biological functions of this key protein of iron metabolism.