Update on vitamin D and evaluation of vitamin D status.

Knowledge about vitamin D has greatly improved during the last few years. Vitamin D cannot any more be considered as exclusively necessary to prevent ricket/osteomalacia. Its role in the prevention of some osteoporotic fractures in the elderly (in association with calcium nutrition) is now well demonstrated and many epidemiologic and laboratory data argue for a role in the prevention of several diseases or anomalies (cancer, auto-immune diseases, cardiovascular events, sarcopenia...). A few intervention studies confirming some of these effects also exist. Vitamin D status can easily be assessed by measuring serum 25 hydroxy vitamin D (25OHD) level. However, many experts have claimed that the population-based reference values for 25OHD are too low and that the cut-off value below which vitamin D insufficiency can be present is somewhere between 20 and 40ng/mL with a clear tendency to target values above 30ng/mL (75nmol/L). The main consequences are that vitamin D insufficiency is highly frequent whereas the currently recommended supplementation doses are not sufficient

A New Human NHERF1 Mutation Decreases Renal Phosphate Transporter NPT2a Expression by a PTH-Independent Mechanism

Background: The sodium-hydrogen exchanger regulatory factor 1 (NHERF1) binds to the main renal phosphate transporter NPT2a and to the parathyroid hormone (PTH) receptor. We have recently identified mutations in NHERF1 that decrease renal phosphate reabsorption by increasing PTH-induced cAMP production in the renal proximal tubule. Methods: We compared relevant parameters of phosphate homeostasis in a patient with a previously undescribed mutation in NHERF1 and in control subjects. We expressed the mutant NHERF1 protein in Xenopus Oocytes and in cultured cells to study its effects on phosphate transport and PTH-induced cAMP production. Results: We identified in a patient with inappropriate renal phosphate reabsorption a previously unidentified mutation (E68A) located in the PDZ1 domain of NHERF1.We report the consequences of this mutation on NHERF1 function. E68A mutation did not modify cAMP production in the patient. PTH-induced cAMP synthesis and PKC activity were not altered by E68A mutation in renal cells in culture. In contrast to wild-type NHERF1, expression of the E68A mutant in Xenopus oocytes and in human cells failed to increase phosphate transport. Pull down experiments showed that E68A mutant did not interact with NPT2a, which robustly interacted with wild type NHERF1 and previously identified mutants. Biotinylation studies revealed that E68A mutant was unable to increase cell surface expression of NPT2a. Conclusions: Our results indicate that the PDZ1 domain is critical for NHERF1- NPT2a interaction in humans and for th

The Phosphate Transporter PiT1 (Slc20a1) Revealed As a New Essential Gene for Mouse Liver Development

BACKGROUND: PiT1 (or SLC20a1) encodes a widely expressed plasma membrane protein functioning as a high-affinity Na(+)-phosphate (Pi) cotransporter. As such, PiT1 is often considered as a ubiquitous supplier of Pi for cellular needs regardless of the lack of experimental data. Although the importance of PiT1 in mineralizing processes have been demonstrated in vitro in osteoblasts, chondrocytes and vascular smooth muscle cells, in vivo evidence is missing. METHODOLOGY/PRINCIPAL FINDINGS: To determine the in vivo function of PiT1, we generated an allelic series of PiT1 mutations in mice by combination of wild-type, hypomorphic and null PiT1 alleles expressing from 100% to 0% of PiT1. In this report we show that complete deletion of PiT1 results in embryonic lethality at E12.5. PiT1-deficient embryos display severely hypoplastic fetal livers and subsequent reduced hematopoiesis resulting in embryonic death from anemia. We show that the anemia is not due to placental, yolk sac or vascular defects and that hematopoietic progenitors have no cell-autonomous defects in proliferation and differentiation. In contrast, mutant fetal livers display decreased proliferation and massive apoptosis. Animals carrying two copies of hypomorphic PiT1 alleles (resulting in 15% PiT1 expression comparing to wild-type animals) survive at birth but are growth-retarded and anemic. The combination of both hypomorphic and null alleles in heterozygous compounds results in late embryonic lethality (E14.5-E16.5) with phenotypic features intermediate between null and hypomorphic mice. In the three mouse lines generated we could not evidence defects in early skeleton formation. CONCLUSION/SIGNIFICANCE: This work is the first to illustrate a specific in vivo role for PiT1 by uncovering it as being a critical gene for normal developmental liver growth

Carboxy-terminal fragment of fibroblast growth factor 23 induces heart hypertrophy in sickle cell disease

International audienc

Functional Interaction between CFTR and the Sodium-Phosphate Co-Transport Type 2a in Xenopus laevis Oocytes

A growing number of proteins, including ion transporters, have been shown to interact with Cystic Fibrosis Transmembrane conductance Regulator (CFTR). CFTR is an epithelial chloride channel that is involved in Cystic Fibrosis (CF) when mutated; thus a better knowledge of its functional interactome may help to understand the pathophysiology of this complex disease. In the present study, we investigated if CFTR and the sodium-phosphate co-transporter type 2a (NPT2a) functionally interact after heterologous expression of both proteins in Xenopus laevis oocytes.NPT2a was expressed alone or in combination with CFTR in X. laevis oocytes. Using the two-electrode voltage-clamp technique, the inorganic phosphate-induced current (IPi) was measured and taken as an index of NPT2a activity. The maximal IPi for NPT2a substrates was reduced when CFTR was co-expressed with NPT2a, suggesting a decrease in its expression at the oolemna. This was consistent with Western blot analysis showing reduced NPT2a plasma membrane expression in oocytes co-expressing both proteins, whereas NPT2a protein level in total cell lysate was the same in NPT2a- and NPT2a+CFTR-oocytes. In NPT2a+CFTR- but not in NPT2a-oocytes, IPi and NPT2a surface expression were increased upon PKA stimulation, whereas stimulation of Exchange Protein directly Activated by cAMP (EPAC) had no effect. When NPT2a-oocytes were injected with NEG2, a short amino-acid sequence from the CFTR regulatory domain that regulates PKA-dependent CFTR trafficking to the plasma membrane, IPi values and NPT2a membrane expression were diminished, and could be enhanced by PKA stimulation, thereby mimicking the effects of CFTR co-expression.We conclude that when both CFTR and NPT2a are expressed in X. laevis oocytes, CFTR confers to NPT2a a cAMPi-dependent trafficking to the membrane. This functional interaction raises the hypothesis that CFTR may play a role in phosphate homeostasis

Race-free estimated glomerular filtration rate equation in kidney transplant recipients:development and validation study

OBJECTIVE: To compare the performance of a newly developed race-free kidney recipient specific glomerular filtration rate (GFR) equation with the three current main equations for measuring GFR in kidney transplant recipients.DESIGN: Development and validation study SETTING: 17 cohorts in Europe, the United States, and Australia (14 transplant centres, three clinical trials).PARTICIPANTS: 15 489 adults (3622 in development cohort (Necker, Saint Louis, and Toulouse hospitals, France), 11 867 in multiple external validation cohorts) who received kidney transplants between 1 January 2000 and 1 January 2021.MAIN OUTCOME MEASURE: The main outcome measure was GFR, measured according to local practice. Performance of the GFR equations was assessed using P 30 (proportion of estimated GFR (eGFR) within 30% of measured GFR (mGFR)) and correct classification (agreement between eGFR and mGFR according to GFR stages). The race-free equation, based on creatinine level, age, and sex, was developed using additive and multiplicative linear regressions, and its performance was compared with the three current main GFR equations: Modification of Diet in Renal Disease (MDRD) equation, Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) 2009 equation, and race-free CKD-EPI 2021 equation. RESULTS: The study included 15 489 participants, with 50 464 mGFR and eGFR values. The mean GFR was 53.18 mL/min/1.73m 2 (SD 17.23) in the development cohort and 55.90 mL/min/1.73m 2 (19.69) in the external validation cohorts. Among the current GFR equations, the race-free CKD-EPI 2021 equation showed the lowest performance compared with the MDRD and CKD-EPI 2009 equations. When race was included in the kidney recipient specific GFR equation, performance did not increase. The race-free kidney recipient specific GFR equation showed significantly improved performance compared with the race-free CKD-EPI 2021 equation and performed well in the external validation cohorts (P 30 ranging from 73.0% to 91.3%). The race-free kidney recipient specific GFR equation performed well in several subpopulations of kidney transplant recipients stratified by race (P 30 73.0-91.3%), sex (72.7-91.4%), age (70.3-92.0%), body mass index (64.5-100%), donor type (58.5-92.9%), donor age (68.3-94.3%), treatment (78.5-85.2%), creatinine level (72.8-91.3%), GFR measurement method (73.0-91.3%), and timing of GFR measurement post-transplant (72.9-95.5%). An online application was developed that estimates GFR based on recipient's creatinine level, age, and sex (https://transplant-prediction-system.shinyapps.io/eGFR_equation_KTX/). CONCLUSION: A new race-free kidney recipient specific GFR equation was developed and validated using multiple, large, international cohorts of kidney transplant recipients. The equation showed high accuracy and outperformed the race-free CKD-EPI 2021 equation that was developed in individuals with native kidneys.TRIAL REGISTRATION: ClinicalTrials.gov NCT05229939.</p

Le facteur de croissance des fibroblastes 23 et son récepteur Klotho

Le rein tient une place centrale dans la détermination de la phosphatémie. Il adapte la réabsorption de phosphate dans le tubule proximal aux besoins de l’organisme et il contrôle l’absorption digestive de phosphate et de calcium par l’intermédiaire du calcitriol qu’il synthétise. La découverte du FGF23 (fibroblast growth factor 23) et son identification comme une hormone qui contrôle le métabolisme du phosphate et du calcitriol a permis de préciser les mécanismes par lesquels les fonctions de réabsorption du phosphate et de synthèse hormonale dans le tubule proximal rénal sont couplées. L’identification du FGF23 a mis en évidence un axe os-rein qui contrôle la minéralisation osseuse. L’étude de modèles animaux a considérablement amélioré notre compréhension de l’homéostasie du phosphate et a fait émerger le rôle de la protéine klotho qui est indispensable à l’action du FGF23. Cette revue détaille les fonctions du FGF23 et de klotho en physiologie et au cours de différentes maladies d’origine génétique ou acquise. Le phosphate est impliqué dans les processus de calcification vasculaire et tissulaire, et de prolifération cellulaire. Les anomalies touchant l’axe FGF23-Klotho altèrent l’espérance de vie et sont impliquées dans les processus de vieillissement

Effets non osseux de la vitamine D

Actuellement, la vitamine D doit être considérée comme une prohormone dont les effets dépassent la prévention du rachitisme/ostéomalacie. De nombreux tissus sont capables de convertir localement la 25-hydroxyvitamine D en calcitriol qui aura alors des actions auto/paracrines sur la prolifération et la différenciation cellulaires, l’apoptose, les sécrétions d’insuline et de rénine, la production d’interleukines et la bactéricidie. Des données épidémiologiques et expérimentales sont en faveur d’un rôle protecteur de la vitamine D contre les cancers, le diabète de type 2, les maladies cardiovasculaires, auto-immunes, infectieuses, rénales et le déficit musculaire. Quelques études d’intervention confirment certains de ces effets

Thorigny-sur-Marne (Seine-et-Marne), Les Sauvières : rapport de diagnostic

A Thorigny-sur-Marne, le lieu-dit Les Sauvières se trouve aux confins sud-est de la commune, en limite du lit majeur de la Marne. Les tranchées y ont fréquemment rencontré une succession de terrains naturels et peu perturbés, comprenant un paléosol au sommet du substrat de sable, et sous les colluvions supérieures (limon sableux et autres sables bruns). En bas de coteau (dans la tranchée n°1 au 75, rue de Dampmart par exemple), ce paléosol peut-être associé à un épandage d'artéfacts, voire à des vestiges archéologiques organisés comme la fosse F1. Ces vestiges peuvent être conservés à partir de 1 m (Tr.11) à 2 m (Tr.1) sous la surface et sur une épaisseur d'une trentaine de centimètres au minimum.Le matériel associe de la céramique roulée et des os de faune très fragmentés à des pièces lithiques. Ces dernières sont composées de silex tertiaires locaux et exogènes, et ne sont pas chauffées. Les productions laminaires et d'éclats (éclats retouchés et micro-denticulés) y sont obtenues par percussion directe au percuteur tendre. Les haches sont représentées par un éclat de hache polie (à méplat latéral) et une pièce bifaciale (réutilisation d'un support non viable de la chaîne opératoire ?). Cet ensemble lithique possède donc à la fois des similitudes et des divergences avec les séries lithiques des sites d'habitat de la fin du Néolithique en vallée de la Marne, pour la production d'éclats, d'outillage, de laminaire et bifaciale. Il pourrait correspondre à des rejets domestiques liés à un habitat, sans certitude. Le matériel céramique ne permet qu'une datation d'époque protohistorique de manière large