The plastidial Arabidopsis thaliana NFU1 protein binds and delivers [4Fe-4S] clusters to specific client proteins.

Proteins incorporating iron-sulfur (Fe-S) co-factors are required for a plethora of metabolic processes. Their maturation depends on three Fe-S cluster assembly machineries in plants, located in the cytosol, mitochondria, and chloroplasts. After de novo formation on scaffold proteins, transfer proteins load Fe-S clusters onto client proteins. Among the plastidial representatives of these transfer proteins, NFU2 and NFU3 are required for the maturation of the [4Fe-4S] clusters present in photosystem I subunits, acting upstream of the high-chlorophyll fluorescence 101 (HCF101) protein. NFU2 is also required for the maturation of the [2Fe-2S]-containing dihydroxyacid dehydratase, important for branched-chain amino acid synthesis. Here, we report that recombinant Arabidopsis thaliana NFU1 assembles one [4Fe-4S] cluster per homodimer. Performing co-immunoprecipitation experiments and assessing physical interactions of NFU1 with many [4Fe-4S]-containing plastidial proteins in binary yeast two-hybrid assays, we also gained insights into the specificity of NFU1 for the maturation of chloroplastic Fe-S proteins. Using bimolecular fluorescence complementation and in vitro Fe-S cluster transfer experiments, we confirmed interactions with two proteins involved in isoprenoid and thiamine biosynthesis, 1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate synthase and 4-amino-5-hydroxymethyl-2-methylpyrimidine phosphate synthase, respectively. An additional interaction detected with the scaffold protein SUFD enabled us to build a model in which NFU1 receives its Fe-S cluster from the SUFBC2D scaffold complex and serves in the maturation of specific [4Fe-4S] client proteins. The identification of the NFU1 partner proteins reported here more clearly defines the role of NFU1 in Fe-S client protein maturation in Arabidopsis chloroplasts among other SUF components.

Identification of client iron-sulfur proteins of the chloroplastic NFU2 transfer protein in Arabidopsis thaliana.

Iron-sulfur (Fe-S) proteins have critical functions in plastids, notably participating in photosynthetic electron transfer, sulfur and nitrogen assimilation, chlorophyll metabolism, and vitamin or amino acid biosynthesis. Their maturation relies on the so-called SUF (sulfur mobilization) assembly machinery. Fe-S clusters are synthesized de novo on a scaffold protein complex and then delivered to client proteins via several transfer proteins. However, the maturation pathways of most client proteins and their specificities for transfer proteins are mostly unknown. In order to decipher the proteins interacting with the Fe-S cluster transfer protein NFU2, one of the three plastidial representatives found in Arabidopsis thaliana, we performed a quantitative proteomic analysis of shoots, roots, and seedlings of nfu2 plants, combined with NFU2 co-immunoprecipitation and binary yeast two-hybrid experiments. We identified 14 new targets, among which nine were validated in planta using a binary bimolecular fluorescence complementation assay. These analyses also revealed a possible role for NFU2 in the plant response to desiccation. Altogether, this study better delineates the maturation pathways of many chloroplast Fe-S proteins, considerably extending the number of NFU2 clients. It also helps to clarify the respective roles of the three NFU paralogs NFU1, NFU2, and NFU3.

Roles and maturation of iron-sulfur proteins in plastids.

One reason why iron is an essential element for most organisms is its presence in prosthetic groups such as hemes or iron-sulfur (Fe-S) clusters, which are notably required for electron transfer reactions. As an organelle with an intense metabolism in plants, chloroplast relies on many Fe-S proteins. This includes those present in the electron transfer chain which will be, in fact, essential for most other metabolic processes occurring in chloroplasts, e.g., carbon fixation, nitrogen and sulfur assimilation, pigment, amino acid, and vitamin biosynthetic pathways to cite only a few examples. The maturation of these Fe-S proteins requires a complex and specific machinery named SUF (sulfur mobilisation). The assembly process can be split in two major steps, (1) the de novo assembly on scaffold proteins which requires ATP, iron and sulfur atoms, electrons, and thus the concerted action of several proteins forming early acting assembly complexes, and (2) the transfer of the preformed Fe-S cluster to client proteins using a set of late-acting maturation factors. Similar machineries, having in common these basic principles, are present in the cytosol and in mitochondria. This review focuses on the currently known molecular details concerning the assembly and roles of Fe-S proteins in plastids.

Correction to: Roles and maturation of iron-sulfur proteins in plastids.

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Autosomal dominant polycystic kidney disease: risk factor for nonmelanoma skin cancer following kidney transplantation.

Nonmelanoma skin cancers (NMSC) are the most common malignant tumors following solid organ transplantation. Risk factors for NMSC mainly include immunosuppression, age, sun exposure and patient phototype. Recent findings have suggested that autosomal dominant polycystic kidney disease (ADPKD) may increase the risk of developing NMSC. We performed a monocenter retrospective study including all kidney recipients between 1985 and 2006 (n = 1019). We studied the incidence of NMSC, solid cancers and post-transplantation lymphoproliferative disease (PTLD), and analyzed the following parameters: age, gender, phototype, time on dialysis, graft rank, immunosuppressive regimen, history of cancer and kidney disease (ADPKD versus others). Median follow-up was 5.5 years (range: 0.02-20.6; 79 838 patient-years). The cumulated incidence of NMSC 10 years after transplantation was 12.7% (9.3% for solid cancers and 3.5% for PTLD). Autosomal dominant polycystic kidney disease and age were risk factors for NMSC (HR 2.63; P < 0.0001 and HR 2.21; P < 0.001, respectively) using univariate analysis. The association between ADPKD and NMSC remained significant after adjustments for age, gender and phototype using multivariate analysis (HR 1.71; P = 0.0145) and for immunosuppressive regimens (P < 0.0001). Autosomal dominant polycystic kidney disease was not a risk factor for the occurrence of solid cancers after transplantation (HR 0.96; P = 0.89). Our findings suggest that ADPKD is an independent risk factor for developing NMSC after kidney transplantation.

[Treatment of chronic kidney disease: therapeutic strategy]. / Traitement de l'insuffisance rénale chronique : stratégie thérapeutique.

The objectives are to slow the progression of chronic kidney disease (CKD), to take all the cardiovascular risk factors into account, to screen for and treat specific complications and to prepare, if necessary, for renal replacement treatment (transplantation or dialysis). The principal treatment targets are: blood pressure less than 130/80 mmHg and proteinuria less than 0.5 g/day (ratio of proteinuria/creatinuria <50mg/mmol). The first-line treatment to reach these goals is angiotensin conversion enzyme inhibitors (ACE inhibitors), combined with diet and other life style changes. The periodicity of clinical and laboratory assessments depends on the CKD stage, the speed of disease progression and the need to reassess the impact of therapeutic interventions. Comprehensive multidisciplinary management can slow or even stop the progression of CKD and reduce its cardiovascular complications, which are the leading cause of death in these patients.

Renal endpoints in renal and cardiovascular randomized clinical trials: time for a consensus?

Several recent major randomized clinical trials (RCTs) using renal outcomes resulted in conflicting results. We searched MEDLINE via PubMed with the search request '(dialysis OR end-stage renal disease) and creatinine' in six major general journals and two leading journals of nephrology; 123 articles were found; 17/123 were relevant RCTs. Some disagreement among surrogate endpoints in 11/15 articles (missing data in two RCTs) and between surrogate and hard renal endpoints in 10/13; the intervention effects were in the opposite direction in 4/15, mostly in patients with cardiovascular disease, but discrepancies and conflicting results were also found among renal trials. Among our selected RCTs, 14/17 used composite endpoints: vital and renal endpoints were mixed in 11/14 trials, the components of the composite endpoints were of similar importance in 0/14 trials and of similar frequency in 1/11 trials, the intervention was likely to have a similar effect on the components in 4/14 trials, and the relative risk reduction was similar for the different components in 2/10 trials. None of the trials fulfiled all conditions of validation. Based on this analysis, we believe that the current use of renal endpoints in RCTs must be reviewed and their conditions of validation defined.

Doubling of serum creatinine in clinical trials, cost-effectiveness studies, and individual patients: adequate use in renal transplantation.

BACKGROUND: The predictive value of doubling of serum creatinine (DSC) has never been assessed in renal transplantation. We evaluated it in terms of its use for clinical trials, cost-effectiveness studies, and individual patients. METHODS: Retrospective longitudinal study in 896 renal transplant recipients. RESULTS: Death-censored graft loss occurred in 133 patients, during follow-up (up to 21 years). DSC was a risk factor for graft loss; however, the relative risk was different in patients with glomerular filtration rate less than 40 vs. more than or equal to 40 mL/min (hazard ratio: 14.5 [95% confidence interval: 7.4-28.4] vs. 47.8 [28.4-80.6], P=0.0051). Parameters influencing creatinine value (weight, age, sex) did not modify DSC's predictive value. The use of the composite endpoint DSC or death-censored graft loss instead of death-censored graft loss alone in clinical trials would reduce sample size by 7.1% to 9.0%. The annual probability of DSC to graft loss transition decreased from 76% (follow-up <1 year) to 5% (follow-up ≥10 years). Median graft half-life after DSC was 10 months [95% confidence interval: 6-18] but varied with increasing time to DSC (<1 year: 1 month [0.5-6]; 3-4.9 years: 15 months 5/67) and reference creatinine (<130 µmol/L: 3 months 2/6); ≥130 µmol/L: 25 months 15/37). CONCLUSIONS: DSC may be adequately used to refine the risk of death-censored graft loss for individual patients. However, the use of DSC as an endpoint in clinical trials marginally affects sample size, and the probability of DSC to graft loss transition is not constant, which limits the use of DSC in cost-effectiveness analyses of renal transplantation.

Immunosuppressive medications, clinical and metabolic parameters in new-onset diabetes mellitus after kidney transplantation.

New-onset diabetes after transplantation (NODAT) is a growing concern in transplantation. All modifiable risk factors are not yet identified. We assessed the relationship between baseline clinical and biochemical parameters and NODAT. Eight-hundred and fifty-seven in-Caucasian renal transplant recipients were included. Charts were individually reviewed. The follow-up was 5.3 years (ranges: 0.25-20.8; 5613 patient-years). The incidence of NODAT was 15.0%, 18.4% and 22.0% at 10, 15 and 20 years following transplantation. Age, body mass index (BMI), glucose (all P < 0.0001) and triglycerides [hazard ratio (HR) per 1 mmol/l: 1.44 [1.17-1.77], P = 0.0006] were potent risk factors whereas steroid withdrawal (HR: 0.69 [0.47-1.01], P = 0.0601) reduced the risk. As compared to cyclosporine, sirolimus (HR: 3.26 [1.63-6.49], P = 0.0008) and tacrolimus (HR: 3.04 [2.02-4.59], P < 0.0001) were risk factors for NODAT. The risk of NODAT was comparable for sirolimus (HR: 2.35 [1.06-5.19], P = 0.0350) and tacrolimus (HR: 2.34 [1.46-3.75], P = 0.0004) after adjustments on age, BMI, glucose and steroid withdrawal; however, unlike sirolimus, tacrolimus remained significant after adjustment on triglycerides. The risk of NODAT appeared similar, but its pathophysiology seemed different in sirolimus- and tacrolimus-treated patients; this observation needs confirmation. However, main independent risk factors were age, BMI, initial glucose and triglycerides.