Pathogenesis of vascular calcification in chronic kidney disease. Background. Hyperphosphatemia and hypercalcemia are independent risk factors for higher incidence of cardiovascular events in patients with chronic kidney disease. In addition to increased calcium-phosphate product, hyperphosphatemia accelerates the progression of secondary hyperparathyroidism with the concomitant bone loss, possibly linked to vascular calcium-phosphate precipitation. Results. The control of serum phosphate levels reduces vascular calcification not only by decreasing the degree of secondary hyperparathyroidism and calcium-phosphate product, but also by reducing the expression of proteins responsible for active bone mineral deposition in cells of the vasculature. The calcium and aluminum-free phosphate-binders provide a new and effective therapeutic tool in preventing vascular calcifications in chronic kidney disease in animal models and in hemodialysis patients. Conclusion. Additional investigations are necessary to examine the benefits of different phosphate-binders in reducing mortality from cardiovascular disease.

Monothiol glutaredoxins play a crucial role in iron-sulfur (Fe/S) protein biogenesis. Essentially all of them can coordinate a [2Fe-2S] cluster and have been proposed to mediate the transfer of clusters from scaffold proteins to target apo proteins, possibly by acting as cluster transfer proteins. The molecular basis of cluster transfer from monothiol glutaredoxins to target proteins is a fundamental, but still unresolved, aspect to be defined in Fe/S protein biogenesis. In mitochondria monothiol glutaredoxin 5 (GRX5) is involved in the maturation of all cellular Fe/S proteins and participates in cellular iron regulation. Here we show that the structural plasticity of the dimeric state of the [2Fe-2S] bound form of human GRX5 (holo hGRX5) is the crucial factor that allows an efficient cluster transfer to the partner proteins human ISCA1 and ISCA2 by a specific protein-protein recognition mechanism. Holo hGRX5 works as a metallochaperone preventing the [2Fe-2S] cluster to be released in solution in the presence of physiological concentrations of glutathione and forming a transient, cluster-mediated protein-protein intermediate with two physiological protein partners receiving the [2Fe-2S] cluster. The cluster transfer mechanism defined here may extend to other mitochondrial [2Fe-2S] target proteins.Fe/S protein maturation | [2Fe-2S] cluster transfer mechanism | monothiol Grxs | NMR G lutaredoxins (Grxs) and glutathione (GSH) are universally distributed among all organisms, and they have been shown to play a fundamental role in iron-sulfur (Fe/S) protein biogenesis (1-5). Specifically, the [2Fe-2S]-bound forms of monothiol Grxs and a [2Fe-2S]-glutathione complex are the species suggested to be responsible for trafficking [2Fe-2S] clusters within the cell (6-9). The current working model is that in the cell monothiol Grxs receive a [2Fe-2S] cluster from the scaffold protein ISCU (where de novo synthesis of the [2Fe-2S] cluster occurs) and transfer it to specific targeting proteins, which then facilitate Fe/S cluster insertion into the final acceptor apo protein (7, 10, 11). Another possible cluster transfer mechanism, which has been proposed (8), hypothesizes the cellular presence of a [2Fe-2S](GS) 4 complex, which could transiently store [2Fe-2S] clusters, facilitate cluster exchange with the cellular Fe/S cluster biosynthesis machineries, and regulate the biosynthesis of Fe/S clusters. However, a drawback of the latter model is that all of the Fe/S cellular trafficking processes will result to be protein-independent and therefore highly unspecific, thus potentially inflicting severe cellular damage.The mitochondrial, monothiol glutaredoxin 5 protein (GRX5) belongs to the core part of the mitochondrial Fe/S cluster (ISC) assembly system (10, 12, 13), is required in the maturation of all cellular [2Fe-2S] and [4Fe-4S] proteins (11), and participates in cellular iron regulation (14). Human GRX5 in vitro binds a [2Fe-2S] cluster (15) and yeast GRX5, which in vivo and in vitro binds a [2Fe-2S] cluster (11), has been...

The generation of [4Fe-4S] clusters in mitochondria critically depends, in both yeast and human cells, on two A-type ISC proteins (in mammals named ISCA1 and ISCA2), which perform a nonredundant functional role forming in vivo a heterocomplex. The molecular function of ISCA1 and ISCA2 proteins, i.e., how these proteins help in generating [4Fe-4S] clusters, is still unknown. In this work we have structurally characterized the Fe/S cluster binding properties of human ISCA2 and investigated in vitro whether and how a [4Fe-4S] cluster is assembled when human ISCA1 and ISCA2 interact with the physiological [2Fe-2S](2+) cluster-donor human GRX5. We found that (i) ISCA2 binds either [2Fe-2S] or [4Fe-4S] cluster in a dimeric state, and (ii) two molecules of [2Fe-2S](2+) GRX5 donate their cluster to a heterodimeric ISCA1/ISCA2 complex. This complex acts as an "assembler" of [4Fe-4S] clusters; i.e., the two GRX5-donated [2Fe-2S](2+) clusters generate a [4Fe-4S](2+) cluster. The formation of the same [4Fe-4S](2+) cluster-bound heterodimeric species is also observed by having first one [2Fe-2S](2+) cluster transferred from GRX5 to each individual ISCA1 and ISCA2 proteins to form [2Fe-2S](2+) ISCA2 and [2Fe-2S](2+) ISCA1, and then mixing them together. These findings imply that such heterodimeric complex is the functional unit in mitochondria receiving [2Fe-2S] clusters from hGRX5 and assembling [4Fe-4S] clusters before their transfer to the final target apo proteins.

Ϫ EJB 98 0390/3 β2-microglobulin fibrils have been extracted from the femoral head of a patient who has been under chronic haemodialysis for 11 years. The primary structure of the N-terminal portion of the protein and mass determination by electrospray mass spectrometry demonstrate that β2-microglobulin, extracted as fibrils by the water extraction procedure, was not glycated and that Asn17 was not deamidated. Limited proteolysis was observed in more than 20% of β2-microglobulin molecules and the main cleavage sites were at the C-terminus of Lys6 and Tyr10. β2-microglobulin from fibrils has been purified by gel filtration in 6 M Gdn/HCl and submitted to a refolding procedure. The refolding conditions have been determined through the study of the unfolding pathway of the native protein. β2-microglobulin is stable at neutral pH where it displays a lower tendency to self-aggregate than in acidic conditions. Pulse dilution and extensive dialysis in refolding buffer at pH 7.5 yields β2-microglobulin with a tertiary structure identical to that of the native form. The CD spectrum in the near-ultraviolet region and the spectrum of the intrinsic fluorescence of Trp overlap those of the native protein, but the CD spectrum in the far-ultraviolet region is affected by the contribution of oligomers created by β2-microglobulin fragments that reduce the positive light polarisation at 205 nm typical of native β2-microglobulin.Keywords : amyloidosis; fibril; β2-microglobulin; structure ; refolding.Chronic kidney failure and the haemodialytic procedure are associated with a high prevalence of a particular form of amyloidosis, mainly involving the muscle-skeletal system, in which the amyloid fibrils are composed of β2-microglobulin (β2-m) [1]. In this form, as in all of the amyloidoses, the fibrillar deposits represent the central component of the disease; this component exists in a dynamic equilibrium between soluble amyloidogenic protein precursors on the one hand and the amyloid catabolic pathway on the other. The progression of the disease requires that protein accumulation is favoured, but in certain cases amyloid deposits can be partially or completely reabsorbed when the supply of amyloidogenic precursor is reduced [2] as in AA and AL amyloidosis or in some cases of dialysis-related amyloidosis (DRA) after kidney transplantation. The question of β2-m reabsorption in DRA patients submitted to kidney transplantation is still open. The group of Pepys has shown by SAP scan, a reduction of the amyloid deposits [3], but other groups have bioptically demonstrated the persistence of amyloid fibrils in the deposits ten years after the renal transplantation [4]. The mechanism of amyloid reabsorption in this form, as in the other types of amyloidosis, is not known, but it can probably follow Correspondence to V. Bellotti, Dipartimento di Biochimica, Università degli Studi di Pavia, via Taramelli 3b, I-27100 Pavia, ItalyFax: ϩ39 382 423108. E-mail: stoppini@unipv.it Abbreviations. Gdn/HCl, guanidine hydrochloride ; EM, electron microsc...

The cellular toxicity of copper is usually associated with its ability to generate reactive oxygen species. However, recent studies in bacterial organisms showed that copper toxicity is also strictly connected to iron-sulfur cluster proteins and to their assembly processes. Mitochondria of eukaryotic cells contain a labile copper(I) pool localized in the matrix where also the mitochondrial iron-sulfur (Fe/S) cluster assembly machinery resides to mature mitochondrial Fe/S cluster-containing proteins. Misregulation of copper homeostasis might therefore damage mitochondrial Fe/S protein maturation. To describe, from a molecular perspective, the effects of copper(I) toxicity on such a maturation process, we have here investigated the still unknown mechanism of [4Fe-4S] cluster formation conducted by the mitochondrial ISCA1/ISCA2 and GLRX5 proteins, and defined how copper(I) can impair this process. The molecular model here proposed indicates that the copper(I) and Fe/S protein maturation cellular pathways need to be strictly regulated to avoid copper(I) ion from blocking mitochondrial [4Fe-4S] protein maturation.

Objectives: Poor medication adherence is common in end-stage renal disease and may cause suboptimal outcomes and increased healthcare costs. We assessed the association between regimen complexity, perceived burden of oral therapy (BOT) and medication adherence in a large sample of hemodialysis (HD) patients. Methods: 1,238 HD patients in 54 Italian centers participated. Data were collected on patients’ socio-demographic characteristics, perceived BOT, quality of life, healthcare satisfaction, social support and medication adherence with a self-administered questionnaire. Data on medication regimen, comorbidities, hospitalizations, and transplant listing status were provided by the nursing staff. We estimated the adjusted association of regimen complexity, BOT and medication adherence with logistic regression. Results: There were 789 (64%) men and the median age was 67 years. Mean daily burden was 9.7 tablets and 48% of patients were adherent to medication prescriptions. The number of tablets prescribed in the medication regimen was associated to adherence likelihood after adjustment for possible confounders. Perceived BOT moderated the association between tablet count and self-reported adherence. Conclusion: Poor adherence was very common in our sample. Reducing tablet burden might help patients be adherent. However, our results suggest that modulating regimen complexity might be ineffective if patients’ negative attitudes toward medications are not addressed concurrently.

Tuberous sclerosis complex (TSC) is a tumor suppressor gene disorder characterized by mutations in the TSC1 or TSC2 genes. These mutations lead to the development of benign tumors involving smooth muscle cells, causing life-threatening lymphangioleiomyomatosis. We isolated and characterized two types of cells bearing a mutation in TSC2 exon 18 from a renal angiomyolipoma of a TSC patient: one population of alpha-actin-positive smooth muscle-like cells with loss of heterozygosity for the TSC2 gene (A(+) cells) and another of nonloss of heterozygosity keratin 8/18-positive epithelial-like cells (R(+) cells). Unlike control aortic vascular smooth muscle cells, A(+) cells required epidermal growth factor (EGF) to grow and substituting EGF with insulin-like growth factor (IGF)-1 failed to increase the cell number; however, omission of EGF did not cause cell loss. The A(+) cells constantly released IGF-1 into the culture medium and constitutively showed a high degree of S6K phosphorylation even when grown in serum-free medium. Exposure to antibodies against EGF and IGF-1 receptors caused a rapid loss of A(+) cells: 50% by 5 days and 100% by 12 days. Signal transduction mediated by EGF and IGF-I receptors is therefore involved in A(+) cell survival. These results may offer a novel therapeutic perspective for the treatment of TSC complications and lymphangioleiomyomatosis.

G-quadruplex (G4) and i-motif (iM) are four-stranded non-canonical nucleic acid structural arrangements. Recent evidences suggest that these DNA structures exist in living cells and could be involved in several cancer-related processes, thus representing an attractive target for anticancer drug discovery. Efforts toward the development of G4 targeting compounds have led to a number of effective bioactive ligands. Herein, employing several biophysical methodologies, we studied the ability of some well-known G4 ligands to interact with iM-forming DNA. The data showed that the investigated compounds are actually able to interact with both DNA in vitro, thus acting de facto as multi-target-directed agents. Interestingly, while all the compounds stabilize the G4, some of them significantly reduce the stability of the iM. The present study highlights the importance, when studying G4-targeting compounds, of evaluating also their behavior toward the i-motif counterpart.