Hereditary hyperferritinaemia/ cataract syndrome

H ferritin silencing induces protein misfolding in K562 cells: A Raman analysis

The redox state of the cell is involved in the regulation of many physiological functions as well as in the pathogenesis of several diseases, and is strictly dependent on the amount of iron in its catalytically active state. Alterations of iron homeostasis determine increased steady-state concentrations of Reactive Oxygen Species (ROS) that cause lipid peroxidation, DNA damage and altered protein folding. Ferritin keeps the intracellular iron in a non-toxic and readily available form and consequently plays a central role in iron and redox homeostasis. The protein is composed by 24 subunits of the H- and L-type, coded by two different genes, with structural and functional differences. The aim of this study was to shed light on the role of the single H ferritin subunit (FHC) in keeping the native correct protein three-dimensional structure. To this, we performed Raman spectroscopy on protein extracts from K562 cells subjected to FHC silencing. The results show a significant increase in the percentage of disordered structures content at a level comparable to that induced by H2O2 treatment in control cells. ROS inhibitor and iron chelator were able to revert protein misfolding. This integrated approach, involving Raman spectroscopy and targeted-gene silencing, indicates that an imbalance of the heavy-to-light chain ratio in the ferritin composition is able to induce severe but still reversible modifications in protein folding and uncovers new potential pathogenetic mechanisms associated to intracellular iron perturbation.

Homeostatic mechanisms for iron storage revealed by genetic manipulations and live imaging of Drosophila ferritin

Ferritin is a symmetric, 24-subunit iron-storage complex assembled of H and L chains. It is found in bacteria, plants, and animals and in two classes of mutations in the human L-chain gene, resulting in hereditary hyperferritinemia cataract syndrome or in neuroferritinopathy. Here, we examined systemic and cellular ferritin regulation and trafficking in the model organism Drosophila melanogaster. We showed that ferritin H and L transcripts are coexpressed during embryogenesis and that both subunits are essential for embryonic development. Ferritin overexpression impaired the survival of iron-deprived flies. In vivo expression of GFP-tagged holoferritin confirmed that iron-loaded ferritin molecules traffic through the Golgi organelle and are secreted into hemolymph. A constant ratio of ferritin H and L subunits, secured via tight post-transcriptional regulation, is characteristic of the secreted ferritin in flies. Differential cellular expression, conserved post-transcriptional regulation via the iron regulatory element, and distinct subcellular localization of the ferritin subunits prior to the assembly of holoferritin are all important steps mediating iron homeostasis. Our study revealed both conserved features and insect-specific adaptations of ferritin nanocages and provides novel imaging possibilities for their in vivo characterization.

Understanding iron homeostasis through genetic analysis of hemochromatosis and related disorders

Genetic analysis of hemochromatosis has led to the discovery of a number of genes whose mutations disrupt iron homeostasis and lead to iron overload. The introduction of molecular tests into clinical practice has provided a tool for early diagnosis of these conditions. It has become clear that hemochromatosis includes a spectrum of disorders that range from simple biochemical abnormalities to chronic asymptomatic tissue damage in midlife to serious life-threatening diseases in young subjects. Molecular studies have identified the systemic loop that controls iron homeostasis and is centered on the hepcidin-ferroportin interaction. The complexity of this regulatory pathway accounts for the genetic heterogeneity of hemochromatosis and related disorders and raises the possibility that genes encoding components of the pathway may be modifiers of the main genotype. Molecular diagnosis has improved the classification of the genetic conditions leading to iron overload and identified novel entities, characterized by both iron loading and variable degrees of anemia. Despite the progress in the diagnosis, classification, and mechanisms of iron overload disorders, the treatment of affected patients continues to rely on regular phlebotomy. Understanding the molecular circuitry of iron control may lead to the identification of potential therapeutic targets for novel treatment strategies to be used in association with or as an alternative to phlebotomy.

Recent advances in hereditary hemochromatosis

Hereditary hemochromatosis, a very common genetic defect in the Caucasian population, is characterized by progressive tissue iron overload which leads to irreversible organ damage if it is not treated in a timely manner. Recent developments in the field of molecular medicine have radically improved the understanding of the physiopathology and diagnosis of this disease. However, transferrin saturation and serum ferritin are still the most reliable tests for identifying subjects with hereditary hemochromatosis. Therapeutic phlebotomy is the mainstay of the treatment of this disease and the life expectancy of these patients is similar to that of the normal population if phlebotomy is started before the onset of irreversible organ damage. In this review we discuss the genetics, pathophysiology, diagnosis, clinical features, and management of hereditary hemochromatosis.

Scanning mutations of the 5'UTR regulatory sequence of L-ferritin by denaturing high-performance liquid chromatography: identification of new mutations

Hereditary hyperferritinaemia cataract syndrome is an autosomal dominant disorder caused by heterogeneous mutations of the iron regulatory element (IRE) in the ferritin l-chain mRNA. The mutations are rare and fast DNA scanning would facilitate diagnosis. The aim of the study was to compare the analytical performances of two fast DNA scanning techniques: denaturing high-performance liquid chromatography (DHPLC) and double-gradient denaturing gradient gel electrophoresis (DG-DGGE). We analysed the sequence encoding the 5' untranslated flanking region of ferritin l-chain mRNA, which includes an IRE stem loop structure. The two systems unambiguously identified all the 12 accessible mutations in a single run, including the difficult C-G transversions. DHPLC and DG-DGGE identified seven abnormal patterns in DNA samples from 47 subjects with unexplained hyperferritinaemia; all had mutations in the IRE sequence, including two not reported before: C36G and A37G. The scanning of 250 DNA samples from subjects genotyped for HFE led to the identification of four new mutations, all outside the IRE structure: C10T, C16T, C90T and del-T156. We conclude that DHPLC, similar to DG-DGGE, detects all the mutations in the l-ferritin 5'UTR sequence in a single run, and that various mutations occur outside the IRE structure.