Indiana University-Purdue University Indianapolis (IUPUI) / Fibroblast growth factor-23 (FGF23) is a hormone produced in bone that acts upon the kidney to control blood phosphate and 1,25-(OH)2 vitamin D concentrations. Chronic kidney disease-mineral bone disorder (CKD-MBD) is a major public health problem, affecting 1 in 8 individuals. These patients can have markedly elevated FGF23 at end stage disease which is associated with metabolic bone anomalies, left ventricular hypertrophy, as well as increased mortality (>6-fold). The FGF23 co-receptor αKlotho (αKL) is a membrane-bound protein (mKL) that forms heteromeric complexes with FGF receptors (FGFRs) to initiate intracellular signaling. It also circulates as a cleavage product of mKL (‘cleaved’, or cKL). Previously, a patient with increased plasma cKL from a balanced translocation between chromosomes 9 and 13 in the KLOTHO gene presented with metabolic bone disease and a complex endocrine profile, despite hypophosphatemia. The lack of a reliable cell model in which to study potential FGF23-cKL interactions is a major hurdle for the field of phosphate metabolism. The goal of the present studies was to test and characterize bone cell lines that may respond to FGF23 and/or cKL, permitting study of novel aspects of phosphate handling and control of FGF23 expression. It was confirmed that stable delivery of cKL via AAV2/8 to wild type (WT) and KL-KO mice resulted in highly elevated bone FGF23 mRNA. MC3T3 (mouse) and ROS (rat) osteoblastic cell lines were tested for p-ERK1/2 responses to control FGFs, as well as FGF23 and cKL, alone or in combination. Importantly, both cell lines demonstrated responsiveness to FGF23+cKL only, and not the individual factors. To test responsiveness at the cell level, EGR1 mRNA was tested as an index of FGFR activity and showed modest increases with the same treatments, supporting that other factors may be required for full transcriptional effects. The present studies show that MC3T3 have FGF-dependent signaling capabilities, and that the combination of FGF23+cKL is required for efficient MAPK signaling. These results demonstrated that cKL provision is permissive for efficient FGF23 signaling in bone, and revealed important implications for the regulation of FGF23 and cKL in Mendelian, and common, genetic disorders of phosphate handling and biomineralization.

This thesis focuse on bariatric-metabolic surgery and its impact on serum concentrations of various metabolic parameters. The thesis is divided into two parts - theoretical and practical. Basic facts about bariatric-metabolic surgery such as its history, indications, contraindications, surgical methods and their results, nutrition after surgery and the frequency of micronutrient's deficits are described in the theoretical part. Furthermore, information about calcium-phosphate metabolism and metabolites such as calcium, phosphorus, magnesium, vitamin D, vitamin K, parathyroid hormone and osteomarkers is also included. The influence of nutrition and nutritional status on the quality of bone tissue is also mentioned. Last section of the theoretical part is focused on the important vitamins and minerals. The practical part discusses measurements of selected metabolites in serum before and half a year after the surgery. Results of questionnaires which were given to respondents are also included. Questionnaires were focused on lifestyle, nutrition, physical activities and whether the patients take some supplements of micronutrients and protein concentrates. The goal of this work is to evaluate the effect of the surgery on serum concentrations of metabolic parameters and their effect on the health and...

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Introduction: This thesis deals with the calcium-phosphate metabolism and its role in the development of chronic diabetic complications. It examines calcium sensitive receptor, which can be crucial in affecting calcium metabolism. Calcium-sensitive receptor may play a role in intracellular signaling and metabolic pathways that lead to cell proliferation and extracellular matrix early diabetic nephropathy. We investigated two polymorphisms of the gene for calcium-sensitive receptor (intron 4 and codon 990). Material and Methods: The study included 313 diabetic patients, 41 patients with type 1 diabetes, 106 patients with type 2 diabetes, 110 diabetic patients with type 2 diabetes who had diabetic nephropathy and 56 patients with renal failure non-diabetic (NDRD). It was also examined 72 non-diabetic patients with chronic renal failure (CKD) and 96 healthy blood donors (ZK). Classification of diagnoses is listed in the theory. DNA was isolated by QIAamp DNA Blood Mini Kit and salting method. The specific fragments of gene for the CaSR were amplified by PCR. For detection, restriction fragment length polymorphism and TaqMan probes were used. The expression levels of mRNA were determined by real-time PCR. Results: For the codon 990 polymorphism, we found statistical significance of the genotype frequencies (AA,...

Biochemical assays and radioabsorptiometry evaluated the relationship of mineral and bone metabolism to the systemic response to neurotrauma or orthopaedic trauma of adult males. Forty-one adult males (29.4±9.3 years) participated of which 37 had a primary diagnosis of traumatic spinal cord injury (SCI) and four were vertebral fracture controls. Biochemical abnormalities found included hyperphosphataemia, in association with low or low normal serum levels of 1,25-dihydroxyvitmain D (1,25(OH)₂D) and of parathyroid hormone (PTH), whilst patients remained normocalcaemic. These disturbances of phosphate and vitamin D metabolism and the markedly accelerated resorption of bone were strongly associated with the interval since injury and the severity of injury, but none of these relationships was correlated with the level of the injury, the sensory status of a patient or the presence of spine fracture. The disturbances of phosphate and vitamin D metabolism and the markedly accelerated resorption of bone found in this study are a mirror image of the data of patients with the heritable disorders autosomal dominant hyperphosphataemic rickets (ADHR), which results from an inactivating mutation of the gene encoding fibroblast growth factor 23 (FGF23) and autosomal recessive hypophosphataemic rickets (ARHR), which is caused by a mutation of the gene encoding dentin matrix protein-1 (DMP-1). It is potentially important that the hormone/proteolytic enzyme/extra-cellular matrix protein cascade associated with these disorders is counter-regulated by 1,25(OH)₂D, acting either directly or indirectly. The present results suggest that the serum levels of 1,25(OH)₂D of the neurotrauma patients chosen for study may have been inappropriately high with respect to the “physiological and metabolic set” of serum levels of phosphate and ionised calcium in the period corresponding to the uncoupling of the resorption and formation of bone, at least in males, prompting further investigation. The findings are consistent with a new “physiological set,” possibly involving an abnormality in the synthesis or processing of the endocrine fibroblast growth factors or other circulating phosphatonins, which may act as an additional level of regulation of the renal–bone axis, rather than renal failure. Strongly supporting this was the dynamic pattern of the biochemistry and radiological data of these neurotrauma patients and also, preliminary evidence of disturbances in circulating levels of other systemic modulators of mineral and bone metabolism. The relationships that were observed potentially may be explained by the diversity of the physiological activities of the endocrine fibroblast growth factors and the modes of actions of secreted FGF23 in bone. The findings provide an understanding of why bone loss occurs and may form the target for safe and cost effective interventions. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1345019 / Thesis (Ph.D.) - University of Adelaide, School of Medicine, Discipline of Orthopaedics and Trauma, 2008

Biochemical assays and radioabsorptiometry evaluated the relationship of mineral and bone metabolism to the systemic response to neurotrauma or orthopaedic trauma of adult males. Forty-one adult males (29.4±9.3 years) participated of which 37 had a primary diagnosis of traumatic spinal cord injury (SCI) and four were vertebral fracture controls. Biochemical abnormalities found included hyperphosphataemia, in association with low or low normal serum levels of 1,25-dihydroxyvitmain D (1,25(OH)₂D) and of parathyroid hormone (PTH), whilst patients remained normocalcaemic. These disturbances of phosphate and vitamin D metabolism and the markedly accelerated resorption of bone were strongly associated with the interval since injury and the severity of injury, but none of these relationships was correlated with the level of the injury, the sensory status of a patient or the presence of spine fracture. The disturbances of phosphate and vitamin D metabolism and the markedly accelerated resorption of bone found in this study are a mirror image of the data of patients with the heritable disorders autosomal dominant hyperphosphataemic rickets (ADHR), which results from an inactivating mutation of the gene encoding fibroblast growth factor 23 (FGF23) and autosomal recessive hypophosphataemic rickets (ARHR), which is caused by a mutation of the gene encoding dentin matrix protein-1 (DMP-1). It is potentially important that the hormone/proteolytic enzyme/extra-cellular matrix protein cascade associated with these disorders is counter-regulated by 1,25(OH)₂D, acting either directly or indirectly. The present results suggest that the serum levels of 1,25(OH)₂D of the neurotrauma patients chosen for study may have been inappropriately high with respect to the “physiological and metabolic set” of serum levels of phosphate and ionised calcium in the period corresponding to the uncoupling of the resorption and formation of bone, at least in males, prompting further investigation. The findings are consistent with a new “physiological set,” possibly involving an abnormality in the synthesis or processing of the endocrine fibroblast growth factors or other circulating phosphatonins, which may act as an additional level of regulation of the renal–bone axis, rather than renal failure. Strongly supporting this was the dynamic pattern of the biochemistry and radiological data of these neurotrauma patients and also, preliminary evidence of disturbances in circulating levels of other systemic modulators of mineral and bone metabolism. The relationships that were observed potentially may be explained by the diversity of the physiological activities of the endocrine fibroblast growth factors and the modes of actions of secreted FGF23 in bone. The findings provide an understanding of why bone loss occurs and may form the target for safe and cost effective interventions. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1345019 / Thesis (Ph.D.) - University of Adelaide, School of Medicine, Discipline of Orthopaedics and Trauma, 2008

Biochemical assays and radioabsorptiometry evaluated the relationship of mineral and bone metabolism to the systemic response to neurotrauma or orthopaedic trauma of adult males. Forty-one adult males (29.4±9.3 years) participated of which 37 had a primary diagnosis of traumatic spinal cord injury (SCI) and four were vertebral fracture controls. Biochemical abnormalities found included hyperphosphataemia, in association with low or low normal serum levels of 1,25-dihydroxyvitmain D (1,25(OH)₂D) and of parathyroid hormone (PTH), whilst patients remained normocalcaemic. These disturbances of phosphate and vitamin D metabolism and the markedly accelerated resorption of bone were strongly associated with the interval since injury and the severity of injury, but none of these relationships was correlated with the level of the injury, the sensory status of a patient or the presence of spine fracture. The disturbances of phosphate and vitamin D metabolism and the markedly accelerated resorption of bone found in this study are a mirror image of the data of patients with the heritable disorders autosomal dominant hyperphosphataemic rickets (ADHR), which results from an inactivating mutation of the gene encoding fibroblast growth factor 23 (FGF23) and autosomal recessive hypophosphataemic rickets (ARHR), which is caused by a mutation of the gene encoding dentin matrix protein-1 (DMP-1). It is potentially important that the hormone/proteolytic enzyme/extra-cellular matrix protein cascade associated with these disorders is counter-regulated by 1,25(OH)₂D, acting either directly or indirectly. The present results suggest that the serum levels of 1,25(OH)₂D of the neurotrauma patients chosen for study may have been inappropriately high with respect to the “physiological and metabolic set” of serum levels of phosphate and ionised calcium in the period corresponding to the uncoupling of the resorption and formation of bone, at least in males, prompting further investigation. The findings are consistent with a new “physiological set,” possibly involving an abnormality in the synthesis or processing of the endocrine fibroblast growth factors or other circulating phosphatonins, which may act as an additional level of regulation of the renal–bone axis, rather than renal failure. Strongly supporting this was the dynamic pattern of the biochemistry and radiological data of these neurotrauma patients and also, preliminary evidence of disturbances in circulating levels of other systemic modulators of mineral and bone metabolism. The relationships that were observed potentially may be explained by the diversity of the physiological activities of the endocrine fibroblast growth factors and the modes of actions of secreted FGF23 in bone. The findings provide an understanding of why bone loss occurs and may form the target for safe and cost effective interventions. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1345019 / Thesis (Ph.D.) - University of Adelaide, School of Medicine, Discipline of Orthopaedics and Trauma, 2008

Biochemical assays and radioabsorptiometry evaluated the relationship of mineral and bone metabolism to the systemic response to neurotrauma or orthopaedic trauma of adult males. Forty-one adult males (29.4±9.3 years) participated of which 37 had a primary diagnosis of traumatic spinal cord injury (SCI) and four were vertebral fracture controls. Biochemical abnormalities found included hyperphosphataemia, in association with low or low normal serum levels of 1,25-dihydroxyvitmain D (1,25(OH)₂D) and of parathyroid hormone (PTH), whilst patients remained normocalcaemic. These disturbances of phosphate and vitamin D metabolism and the markedly accelerated resorption of bone were strongly associated with the interval since injury and the severity of injury, but none of these relationships was correlated with the level of the injury, the sensory status of a patient or the presence of spine fracture. The disturbances of phosphate and vitamin D metabolism and the markedly accelerated resorption of bone found in this study are a mirror image of the data of patients with the heritable disorders autosomal dominant hyperphosphataemic rickets (ADHR), which results from an inactivating mutation of the gene encoding fibroblast growth factor 23 (FGF23) and autosomal recessive hypophosphataemic rickets (ARHR), which is caused by a mutation of the gene encoding dentin matrix protein-1 (DMP-1). It is potentially important that the hormone/proteolytic enzyme/extra-cellular matrix protein cascade associated with these disorders is counter-regulated by 1,25(OH)₂D, acting either directly or indirectly. The present results suggest that the serum levels of 1,25(OH)₂D of the neurotrauma patients chosen for study may have been inappropriately high with respect to the “physiological and metabolic set” of serum levels of phosphate and ionised calcium in the period corresponding to the uncoupling of the resorption and formation of bone, at least in males, prompting further investigation. The findings are consistent with a new “physiological set,” possibly involving an abnormality in the synthesis or processing of the endocrine fibroblast growth factors or other circulating phosphatonins, which may act as an additional level of regulation of the renal–bone axis, rather than renal failure. Strongly supporting this was the dynamic pattern of the biochemistry and radiological data of these neurotrauma patients and also, preliminary evidence of disturbances in circulating levels of other systemic modulators of mineral and bone metabolism. The relationships that were observed potentially may be explained by the diversity of the physiological activities of the endocrine fibroblast growth factors and the modes of actions of secreted FGF23 in bone. The findings provide an understanding of why bone loss occurs and may form the target for safe and cost effective interventions. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1345019 / Thesis (Ph.D.) - University of Adelaide, School of Medicine, Discipline of Orthopaedics and Trauma, 2008

Le phosphate inorganique (Pi) est un minéral essentiel de notre organisme, qui intervient dans la composition des acides nucléiques et des phospholipides, dans la minéralisation des os et des dents, dans la production d’énergie, et dans la régulation des voies de signalisation. L’homéostasie du Pi est étroitement régulée par différents transporteurs, et des anomalies du transport de Pi peuvent avoir des conséquences cliniques sévères. Chez l’homme, ils existent 3 transporteurs de Pi distincts de type SLC (solute carrier) avec une distribution tissulaire large et initialement identifiés en tant que récepteurs de rétrovirus : PiT1/SLC20A1, PiT2/SLC20A2, et XPR1/SLC53A1.Des mutations dans PiT2 sont associées à une maladie rare, la calcification cérébrale primaire familiale (PFBC), caractérisée par des dépôts de phosphate de calcium dans les noyaux gris centraux et par l’expression de troubles neuropsychiatriques. Alors que PiT1 ne semble pas être impliqué dans cette maladie, nous avons découvert que des mutations dans XPR1 étaient présentes chez des patients PFBC, renforçant le lien entre la maladie PFBC et les désordres de l’homéostasie du phosphate.Dans ce travail, nous avons cherché à comprendre comment PiT2 et XPR1, deux transporteurs de Pi mais de flux opposés peuvent conduire à une même maladie. Pour cela, nous avons étudié le lien entre PiT2 et XPR1 dans la régulation du Pi ainsi que les domaines de XPR1 impliqués dans le transport. Nous avons d’abord identifié de nouveaux variants PFBC dans PiT2 et XPR1 et confirmé l'effet délétère de ces mutations sur l’import et l’export. Nous avons pu distinguer des mutations qui abolissaient l’expression en surface de XPR1, et donc indirectement l’export de Pi, alors que d’autres avaient un impact fonctionnel direct sur les transporteurs pourtant présents à la membrane plasmique.L’inactivation de XPR1 dans des cellules haploïdes humaines induit une altération profonde de l’export de Pi sans effet notable sur l’import. De manière surprenante, l’inactivation de PiT2 entraine un effet modéré sur l’import, probablement dû à l'activité complémentaire de PiT1, avec une chute de l’export dépendant de XPR1. Cet effet identifie une boucle de régulation que nous avons montrée être essentielle au maintien des niveaux de phosphate et d’ATP. Ces résultats révèlent que le défaut d’export de phosphate par inactivation de PiT2 et XPR1 est susceptible d’être l’étape-clé qui conduit à une maladie commune, la PFBC.Nous nous sommes concentrés sur cette étape d‘export régulée en étudiant le domaine SPX de XPR1 dans lequel la plupart des mutations PFBC ont été retrouvées. Nous avons identifié la tankyrase (TNK) comme interactant cellulaire, et localisé son site d’interaction à la bordure carboxyle de SPX. Nous avons observé que la délétion de SPX entrainait un défaut d’export de Pi, et que la perte d’interaction de TNK à XPR1 par mutagenèse ponctuelle avait le même effet, suggérant que TNK et SPX sont 2 composants essentiels à l’export de phosphate. Enfin, nous avons identifié de nouvelles mutations de XPR1 à l'extrémité C-terminale qui abolissaient l’export de Pi, et montré que la délétion de ce domaine entrainait un défaut d’expression de XPR1 à la membrane plasmique. Nos résultats indiquent donc que les domaines N- et C-terminaux jouent un rôle clé dans l’export, et donc dans l’homéostasie du phosphate, avec le domaine C-terminal jouant plutôt un rôle dans le trafic en surface de XPR1.L’ensemble de ce travail a permis de documenter de nouvelles mutations PFBC dans les gènes PiT2 et XPR1, de démontrer que ces transporteurs étaient impliqués dans l’homéostasie intracellulaire du phosphate, en dévoilant que l’export de phosphate est vraisemblablement l’étape clé de la PFBC, ouvrant ainsi de nouvelles pistes dans la compréhension de cette maladie. Nous avons également identifié des domaines de XPR1 et un partenaire cellulaire, essentiels à l’export de Pi et/ou au trafic membranaire. / Phosphate (Pi) is a key mineral that participates directly in the synthesis of nucleic acids and membranes, bone and tooth mineralization, energy production, and signal transduction. Pi homeostasis is tightly regulated by transporter-mediated fluxes that adjust Pi concentration in real time, and defect in Pi transport has been associated with several pathologies. In humans, three Pi transporters, which belong to the solute carrier (SLC) superfamily, are widely expressed: PiT1/SLC20A1, PiT2/SLC20A2, and XPR1/SLC53A1. Interestingly, all three were initially identified as receptors for mammalian gammaretroviruses.Mutations in PiT2/SLC20A2 are responsible for a rare neurodegenerative disorder, the primary familial brain calcification (PFBC), characterized by deposits of calcium Pi in the basal ganglia and other regions of the brain, and associated with diverse neuropsychiatric clinical manifestations. While PiT1/SLC20A1 has not been involved in PFBC, we recently identified mutations in XPR1/SLC53A1 as causative for PFBC, thus linking further the disease with cellular Pi homeostasis dysfunction.In this work, we aimed to understand how defects of opposite Pi transport functions lead to PFBC, investigated the relationship between PiT2 and XPR1 in cellular Pi regulation, and studied XPR1 domains in Pi transport. We first identified several PFBC mutations in PiT2/SLC20A2 and XPR1/SLC53A1, and confirmed their impact on Pi import or export, respectively. Some of the mutations altered transporter cell surface expression, resulting in Pi transport impairment, while others did neither alter cell surface expression, nor retroviral receptor functions, confirming that Pi transport function and viral envelope glycoprotein binding can be structurally distinguished.Using single gene knock-out human haploid cells, we showed that depletion of XPR1/SLC53A1 resulted in a dramatic Pi export alteration, with no detectable effect on Pi import, in agreement with Pi exporter function of XPR1. Interestingly, depletion of PiT2/SLC20A2 had little impact on Pi uptake, most likely due to compensatory function of PiT1/SLC20A1, with, however, a surprising impact on Pi export mediated by XPR1. This effect is reminiscent to a regulation loop that we found to maintain both Pi and ATP constant. This results unveil for the first time that Pi export alteration, and not Pi import, is likely to be the common pathophysiological impact of mutations in both PiT2 and XPR1. This would explain the synonymous pathological effects of two transporters that have opposite transport activity.We further explored this regulated phosphate export by characterizing the SPX N-terminal cytoplasmic domain of XPR1, which harbors most of the PFBC mutations. We identified a cellular tankyrase (TNK) as a binding partner and mapped the TNK-binding site to the carboxyl border of SPX; furthermore, we found that mutations that abolished TNK binding resulted in loss of Pi export. Full deletion of SPX domain maintained cell surface expression but altered export, suggesting that both TNK and SPX are essential components for Pi export. Finally, during this work, we identified mutations in the XPR1 C-terminal domain as responsible for PFBC that also impaired Pi export, and showed that deletion of this domain prevented XPR1 cell surface expression. Our results therefore indicate that N- and C-terminal domains of XPR1 play a key role in phosphate homeostasis, the latter domain appearing to exert a more prominent role in XPR1 membrane trafficking and/or folding.

Dans le rachitisme hypophosphatémique lié à l’X (XLH), MEPE (Matrix Extracellular PhosphoglycoprotEin), une protéine non collagénique impliquée dans la biominéralisation, subit un clivage pathologique de son extrémité C-terminale. Les peptides ainsi libérés sont porteurs d’un domaine ASARM (acidic serine- and aspartate- rich motif) très conservé dans l’évolution. ASARM inhibe la réabsorption tubulaire du phosphate et la minéralisation de la matrice extracellulaire osseuse. Précédemment, notre équipe a identifié des taux élevés de ce peptide ASARM dérivé de MEPE dans la dentine issue de patients XLH. Ce travail a pour objectif principal d’étudier l’effet d’ASARM sur la minéralisation dentinaire afin de mieux comprendre son implication dans les anomalies dentaires observées chez les malades. Des lattis de collagène ensemencés avec des cellules souches pulpaires SHEDs (Dental pulp stem cells derived from deciduous teeth) englobés dans une tranche de dent humaine ont été cultivés dans des conditions d’induction odontoblastique avec et sans 20 µM de chacune des formes phosphorylé (p-ASARM) ou non phosphorylé (np-ASARM) du peptide recombinant. La minéralisation a été appréciée par microscopie électronique à balayage et colorations de von Kossa. L’expression des marqueurs odontogéniques (DSPP, ostéocalcine, MEPE) a été évaluée par immunohistochimie, qPCR et Western-blot. Parallèlement, des billes d’agarose imprégnées p-ASARM et np-ASARM ont été implantées dans un modèle d’effraction pulpaire chez le rat, dans lequel un pont de dentine de réparation se forme spontanément. La minéralisation dans la chambre pulpaire a été évaluée par micro-CT et immunohistochimie. Dans le modèle in vitro 3D, p-ASARM a inhibé la différenciation des SHEDs, ce qui s’est traduit par 1) l’absence de formation de nodule de minéralisation, 2) la diminution des marqueurs odontogéniques, 3) la surexpression de MEPE, comparativement au contrôle ou au traitement du milieu par np-ASARM. In vivo, p-ASARM a perturbé le processus de réparation dentinaire et a entrainé une surexpression de MEPE. Ces résultats confirment notre hypothèse selon laquelle p-ASARM inhibe la différenciation odonblastique et la minéralisation de la dentine. De plus, l’effet inducteur de p-ASARM sur l’expression de MEPE suggère l’existence d’une boucle de rétrocontrôle positif impliquée dans l’étiopathogénie du XLH. Ainsi, les défauts de minéralisation de la dentine hypophosphatémique sont probablement une conséquence de la libération du peptide ASARM dans la matrice extracellulaire. / In X-linked familial hypophosphatemic rickets (XLH), MEPE (Matrix Extracellular PhosphoglycoprotEin) is cleaved, releasing phosphorylated ASARM (acidic serine- and aspartate- rich motif) peptides that inhibit mineralization of bone extracellular matrix (ECM), and renal tubular phosphate reabsorption. We recently identified high levels of MEPE-derived ASARM peptides in human XLH dentin. The present study was aimed to investigate their effects on dentin mineralization in order to better understand their role in the etiology of tooth abnormalities observed in XLH patients. Dental pulp stem cells derived from deciduous teeth (SHEDs) were seeded in a collagen scaffold, cultured in human tooth slices under mineralizing conditions as a control, and with 20 µM of either phosphorylated (p-ASARM) or non-phosphorylated (np-ASARM) MEPE-derived ASARM peptides. Mineralization was assessed by scanning electron microscopy and von Kossa staining. Odontogenic markers (DSPP, osteocalcin, MEPE) were assessed by immunohistochemistry, RT-PCR and Western blot. In parallel, agarose beads soaked with recombinant ASARM peptides were implanted in a rat pulp injury model where a reparative dentin bridge is spontaneously formed; the repair process was evaluated by micro-CT and IHC. In the tooth slice culture model, p-ASARM inhibited SHED differentiation, with 1) no formation of mineralization nodule, 2) decreased odontogenic marker expression, and 3) up-regulation of MEPE expression, in contrast with np-ASARM and control. In the rat pulp injury model, p-ASARM impaired the formation of the reparative dentin bridge and increased MEPE expression. The present data support our hypothesis that p-ASARM impairs odontogenic differentiation process and the resulting mineralization of dentin. Moreover, the identification of a stimulating effect of p-ASARM on MEPE expression suggests a positive feedback loop in the pathogenicity of XLH disease. Accordingly, the mineralized defects in XLH tooth dentin may be a direct consequence of the release of ASARM peptides in the ECM.