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Hanai A, Kawabata A, Nakajima K, Masuda K, Urakawa I, Abe M, Yamazaki Y, Fukumoto S. Single-cell RNA sequencing identifies Fgf23-expressing osteocytes in response to 1,25-dihydroxyvitamin D 3 treatment. Front Physiol 2023; 14:1102751. [PMID: 36776964 PMCID: PMC9911654 DOI: 10.3389/fphys.2023.1102751] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2022] [Accepted: 01/16/2023] [Indexed: 01/28/2023] Open
Abstract
Fibroblast growth factor 23 (FGF23), a hormone, mainly produced by osteocytes, regulates phosphate and vitamin D metabolism. By contrast, 1,25-dihydroxyvitamin D3, the active form of vitamin D, has been shown to enhance FGF23 production. While it is likely that osteocytes are heterogenous in terms of gene expression profiles, specific subpopulations of Fgf23-expressing osteocytes have not been identified. Single-cell RNA sequencing (scRNA-seq) technology can characterize the transcriptome of an individual cell. Recently, scRNA-seq has been used for bone tissue analysis. However, owing to technical difficulties associated with isolation of osteocytes, studies using scRNA-seq analysis to characterize FGF23-producing osteocytes are lacking. In this study, we characterized osteocytes secreting FGF23 from murine femurs in response to calcitriol (1,25-dihydroxyvitamin D3) using scRNA-seq. We first detected Dmp1, Mepe, and Phex expression in murine osteocytes by in situ hybridization and used these as marker genes of osteocytes. After decalcification, enzyme digestion, and removal of CD45+ cells, femoral bone cells were subjected to scRNA-seq. We identified cell clusters containing osteocytes using marker gene expression. While Fgf23 expression was observed in some osteocytes isolated from femurs of calcitriol-injected mice, no Fgf23 expression was detected in untreated mice. In addition, the expression of several genes which are known to be changed after 1,25-dihydroxyvitamin D3 treatment such as Ccnd2, Fn1, Igfbp7, Pdgfa, and Timp1 was also affected by calcitriol treatment in Fgf23-expressing osteocytes, but not in those lacking Fgf23 expression, even after calcitriol administration. Furthermore, box-and-whisker plots indicated that Fgf23 expression was observed in osteocytes with higher expression levels of the Fam20c, Dmp1, and Phex genes, whose inactivating mutations have been shown to cause FGF23-related hypophosphatemic diseases. These results indicate that osteocytes are heterogeneous with respect to their responsiveness to 1,25-dihydroxyvitamin D3, and sensitivity to 1,25-dihydroxyvitamin D3 is one of the characteristics of osteocytes with Fgf23 expression. It is likely that there is a subpopulation of osteocytes expressing several genes, including Fgf23, involved in phosphate metabolism.
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Affiliation(s)
- Ayako Hanai
- R&D Division, Kyowa Kirin Co., Ltd., Tokyo, Japan,Department of Endocrinology, Metabolism and Hematology, Tokushima University Graduate School of Medical Sciences, Tokushima, Japan,*Correspondence: Ayako Hanai,
| | | | | | | | | | - Masahiro Abe
- Department of Endocrinology, Metabolism and Hematology, Tokushima University Graduate School of Medical Sciences, Tokushima, Japan
| | | | - Seiji Fukumoto
- Department of Molecular Endocrinology, Fujii Memorial Institute of Medical Sciences, Institute of Advanced Medical Sciences, Tokushima University, Tokushima, Japan
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2
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El Hakam C, Parenté A, Baraige F, Magnol L, Forestier L, Di Meo F, Blanquet V. PHEX L222P Mutation Increases Phex Expression in a New ENU Mouse Model for XLH Disease. Genes (Basel) 2022; 13:1356. [PMID: 36011266 PMCID: PMC9407253 DOI: 10.3390/genes13081356] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 07/26/2022] [Accepted: 07/26/2022] [Indexed: 02/02/2023] Open
Abstract
PhexL222P mouse is a new ENU mouse model for XLH disease due to Leu to Pro amino acid modification at position 222. PhexL222P mouse is characterized by growth retardation, hypophosphatemia, hypocalcemia, reduced body bone length, and increased epiphyseal growth plate thickness and femur diameter despite the increase in PHEXL222P expression. Actually, PhexL222P mice show an increase in Fgf23, Dmp1, and Mepe and Slc34a1 (Na-Pi IIa cotransporter) mRNA expression similar to those observed in Hyp mice. Femoral osteocalcin and sclerostin and Slc34a1 do not show any significant variation in PhexL222P mice. Molecular dynamics simulations support the experimental data. P222 might locally break the E217-Q224 β-sheet, which in turn might disrupt inter-β-sheet interactions. We can thus expect local protein misfolding, which might be responsible for the experimentally observed PHEXL222P loss of function. This model could be a valuable addition to the existing XLH model for further comprehension of the disease occurrence and testing of new therapies.
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Affiliation(s)
- Carole El Hakam
- INSERM U1094, INRAE USC1501, IRD U270, EpiMaCT-Epidemiology of Chronic Diseases in Tropical Zone, Univ. Limoges, 2 Rue Pr Descottes, F-87000 Limoges, France; (C.E.H.); (A.P.); (F.B.); (L.M.); (L.F.)
| | - Alexis Parenté
- INSERM U1094, INRAE USC1501, IRD U270, EpiMaCT-Epidemiology of Chronic Diseases in Tropical Zone, Univ. Limoges, 2 Rue Pr Descottes, F-87000 Limoges, France; (C.E.H.); (A.P.); (F.B.); (L.M.); (L.F.)
| | - Fabienne Baraige
- INSERM U1094, INRAE USC1501, IRD U270, EpiMaCT-Epidemiology of Chronic Diseases in Tropical Zone, Univ. Limoges, 2 Rue Pr Descottes, F-87000 Limoges, France; (C.E.H.); (A.P.); (F.B.); (L.M.); (L.F.)
| | - Laetitia Magnol
- INSERM U1094, INRAE USC1501, IRD U270, EpiMaCT-Epidemiology of Chronic Diseases in Tropical Zone, Univ. Limoges, 2 Rue Pr Descottes, F-87000 Limoges, France; (C.E.H.); (A.P.); (F.B.); (L.M.); (L.F.)
| | - Lionel Forestier
- INSERM U1094, INRAE USC1501, IRD U270, EpiMaCT-Epidemiology of Chronic Diseases in Tropical Zone, Univ. Limoges, 2 Rue Pr Descottes, F-87000 Limoges, France; (C.E.H.); (A.P.); (F.B.); (L.M.); (L.F.)
| | - Florent Di Meo
- INSERM U1248 Pharmacology & Transplantation, Univ. Limoges, 2 Rue Pr Descottes, F-87000 Limoges, France;
| | - Véronique Blanquet
- INSERM U1094, INRAE USC1501, IRD U270, EpiMaCT-Epidemiology of Chronic Diseases in Tropical Zone, Univ. Limoges, 2 Rue Pr Descottes, F-87000 Limoges, France; (C.E.H.); (A.P.); (F.B.); (L.M.); (L.F.)
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3
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Fuente R, García-Bengoa M, Fernández-Iglesias Á, Gil-Peña H, Santos F, López JM. Cellular and Molecular Alterations Underlying Abnormal Bone Growth in X-Linked Hypophosphatemia. Int J Mol Sci 2022; 23:ijms23020934. [PMID: 35055123 PMCID: PMC8778463 DOI: 10.3390/ijms23020934] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2021] [Revised: 01/12/2022] [Accepted: 01/13/2022] [Indexed: 12/21/2022] Open
Abstract
X-linked hypophosphatemia (XLH), the most common form of hereditary hypophosphatemic rickets, is caused by inactivating mutations of the phosphate-regulating endopeptidase gene (PHEX). XLH is mainly characterized by short stature, bone deformities and rickets, while in hypophosphatemia, normal or low vitamin D levels and low renal phosphate reabsorption are the principal biochemical aspects. The cause of growth impairment in patients with XLH is not completely understood yet, thus making the study of the growth plate (GP) alterations necessary. New treatment strategies targeting FGF23 have shown promising results in normalizing the growth velocity and improving the skeletal effects of XLH patients. However, further studies are necessary to evaluate how this treatment affects the GP as well as its long-term effects and the impact on adult height.
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Affiliation(s)
- Rocío Fuente
- Division of Pediatrics, Department of Medicine, Faculty of Medicine, University of Oviedo, 33006 Oviedo, Spain; (R.F.); (M.G.-B.); (Á.F.-I.); (H.G.-P.); (F.S.)
- Instituto de Investigación Sanitaria del Principado de Asturias (ISPA), 33011 Oviedo, Spain
- Institute of Physiology, Center for Integrative Human Physiology (ZIHP), University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
| | - María García-Bengoa
- Division of Pediatrics, Department of Medicine, Faculty of Medicine, University of Oviedo, 33006 Oviedo, Spain; (R.F.); (M.G.-B.); (Á.F.-I.); (H.G.-P.); (F.S.)
- Research Center for Emerging Infections and Zoonoses (RIZ), University of Veterinary Medicine Hannover, 30559 Hanover, Germany
| | - Ángela Fernández-Iglesias
- Division of Pediatrics, Department of Medicine, Faculty of Medicine, University of Oviedo, 33006 Oviedo, Spain; (R.F.); (M.G.-B.); (Á.F.-I.); (H.G.-P.); (F.S.)
- Instituto de Investigación Sanitaria del Principado de Asturias (ISPA), 33011 Oviedo, Spain
| | - Helena Gil-Peña
- Division of Pediatrics, Department of Medicine, Faculty of Medicine, University of Oviedo, 33006 Oviedo, Spain; (R.F.); (M.G.-B.); (Á.F.-I.); (H.G.-P.); (F.S.)
- Instituto de Investigación Sanitaria del Principado de Asturias (ISPA), 33011 Oviedo, Spain
- Department of Pediatrics, Hospital Universitario Central de Asturias (HUCA), 33011 Oviedo, Spain
| | - Fernando Santos
- Division of Pediatrics, Department of Medicine, Faculty of Medicine, University of Oviedo, 33006 Oviedo, Spain; (R.F.); (M.G.-B.); (Á.F.-I.); (H.G.-P.); (F.S.)
- Instituto de Investigación Sanitaria del Principado de Asturias (ISPA), 33011 Oviedo, Spain
- Department of Pediatrics, Hospital Universitario Central de Asturias (HUCA), 33011 Oviedo, Spain
| | - José Manuel López
- Department of Morphology and Cellular Biology, Faculty of Medicine, University of Oviedo, 33006 Oviedo, Spain
- Correspondence:
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The Aqueous Extract of Eucommia Leaves Promotes Proliferation, Differentiation, and Mineralization of Osteoblast-Like MC3T3-E1 Cells. EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE 2021; 2021:3641317. [PMID: 34249129 PMCID: PMC8238580 DOI: 10.1155/2021/3641317] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/14/2021] [Revised: 06/07/2021] [Accepted: 06/14/2021] [Indexed: 01/01/2023]
Abstract
Eucommia leaves are dry leaves of Eucommia ulmoides which have long been considered as a functional health food for the treatment of hypertension, hypercholesterolemia, fatty liver, and osteoporosis. With the recent development of Chinese medicine, Eucommia leaves are widely used for tonifying the kidneys and strengthening bone. However, the specific molecular mechanism of Eucommia leaves for strengthening bone remains largely unknown. Osteoblasts are the main functional cells of bone formation; thus, it is essential to study the effect of Eucommia leaves on osteoblasts to better understand their mechanism of action. In the present study, we prepared an aqueous extract of Eucommia leaves (ELAE) and determined its content by high-performance liquid chromatography (HPLC). The effects of ELAE on MC3T3-E1 cells were investigated by CCK-8 assay, alkaline phosphatase (ALP), and Alizarin red S staining assays, combined with RNA sequencing (RNA-seq) and qRT-PCR validation. We demonstrated that ELAE had a significant promoting effect on the proliferation of MC3T3-E1 cells and significantly enhanced extracellular matrix synthesis and mineralization, which were achieved by regulating various functional genes and related signaling pathways. ELAE significantly increased the expression level of genes promoting cell proliferation, such as Rpl10a, Adnp, Pex1, Inpp4a, Frat2, and Pcdhga1, and reduced the expression level of genes inhibiting cell proliferation, such as Npm1, Eif3e, Cbx3, Psmc6, Fgf7, Fxr1, Ddx3x, Mbnl1, and Cdc27. In addition, ELAE increased the expression level of gene markers in osteoblasts, such as Col5a2, Ubap2l, Dkk3, Foxm1, Col16a1, Col12a1, Usp7, Col4a6, Runx2, Sox4, and Bmp4. Taken together, our results suggest that ELAE could promote osteoblast proliferation, differentiation, and mineralization and prevent osteoblast apoptosis. These findings not only increase our understanding of ELAE on the regulation of bone development but also provide a possible strategy to further study the prevention and treatment of osteogenic related diseases by ELAE.
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5
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Hoac B, Østergaard M, Wittig NK, Boukpessi T, Buss DJ, Chaussain C, Birkedal H, Murshed M, McKee MD. Genetic Ablation of Osteopontin in Osteomalacic Hyp Mice Partially Rescues the Deficient Mineralization Without Correcting Hypophosphatemia. J Bone Miner Res 2020; 35:2032-2048. [PMID: 32501585 DOI: 10.1002/jbmr.4101] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Revised: 05/24/2020] [Accepted: 06/01/2020] [Indexed: 11/09/2022]
Abstract
PHEX is predominantly expressed by bone and tooth-forming cells, and its inactivating mutations in X-linked hypophosphatemia (XLH) lead to renal phosphate wasting and severe hypomineralization of bones and teeth. Also present in XLH are hallmark hypomineralized periosteocytic lesions (POLs, halos) that persist despite stable correction of serum phosphate (Pi ) that improves bulk bone mineralization. In XLH, mineralization-inhibiting osteopontin (OPN, a substrate for PHEX) accumulates in the extracellular matrix of bone. To investigate how OPN functions in Hyp mice (a model for XLH), double-null (Hyp;Opn-/- ) mice were generated. Undecalcified histomorphometry performed on lumbar vertebrae revealed that Hyp;Opn-/- mice had significantly reduced osteoid area/bone area (OV/BV) and osteoid thickness of trabecular bone as compared to Hyp mice, despite being as hypophosphatemic as Hyp littermate controls. However, tibias examined by synchrotron radiation micro-CT showed that mineral lacunar volumes remained abnormally enlarged in these double-null mice. When Hyp;Opn-/- mice were fed a high-Pi diet, serum Pi concentration increased, and OV/BV and osteoid thickness normalized, yet mineral lacunar area remained abnormally enlarged. Enpp1 and Ankh gene expression were increased in double-null mice fed a high-Pi diet, potentially indicating a role for elevated inhibitory pyrophosphate (PPi ) in the absence of OPN. To further investigate the persistence of POLs in Hyp mice despite stable correction of serum Pi , immunohistochemistry for OPN on Hyp mice fed a high-Pi diet showed elevated OPN in the osteocyte pericellular lacunar matrix as compared to Hyp mice fed a control diet. This suggests that POLs persisting in Hyp mice despite correction of serum Pi may be attributable to the well-known upregulation of mineralization-inhibiting OPN by Pi , and its accumulation in the osteocyte pericellular matrix. This study shows that OPN contributes to osteomalacia in Hyp mice, and that genetic ablation of OPN in Hyp mice improves the mineralization phenotype independent of systemic Pi -regulating factors. © 2020 American Society for Bone and Mineral Research.
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Affiliation(s)
- Betty Hoac
- Faculty of Dentistry, McGill University, Montreal, QC, Canada
| | - Maja Østergaard
- Department of Chemistry and the Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Aarhus, Denmark
| | - Nina K Wittig
- Department of Chemistry and the Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Aarhus, Denmark
| | - Tchilalo Boukpessi
- Faculty of Dentistry, McGill University, Montreal, QC, Canada.,EA 2496, Laboratory Orofacial Pathologies, Imaging and Biotherapies, School of Dentistry Université de Paris, Paris, France.,Assistance Publique-Hôpitaux de Paris (AP-HP) Department of Odontology, Charles Foix and Bretonneau Hospitals and Reference Center for Rare Diseases of Calcium and Phosphorus Metabolism, Paris, France
| | - Daniel J Buss
- Department of Anatomy and Cell Biology, Faculty of Medicine, McGill University, Montreal, QC, Canada
| | - Catherine Chaussain
- EA 2496, Laboratory Orofacial Pathologies, Imaging and Biotherapies, School of Dentistry Université de Paris, Paris, France.,Assistance Publique-Hôpitaux de Paris (AP-HP) Department of Odontology, Charles Foix and Bretonneau Hospitals and Reference Center for Rare Diseases of Calcium and Phosphorus Metabolism, Paris, France
| | - Henrik Birkedal
- Department of Chemistry and the Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Aarhus, Denmark
| | - Monzur Murshed
- Faculty of Dentistry, McGill University, Montreal, QC, Canada.,Department of Medicine, Faculty of Medicine, McGill University, Montreal, QC, Canada.,Shriners Hospital for Children, Montreal, QC, Canada
| | - Marc D McKee
- Faculty of Dentistry, McGill University, Montreal, QC, Canada.,Department of Anatomy and Cell Biology, Faculty of Medicine, McGill University, Montreal, QC, Canada
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6
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Reznikov N, Hoac B, Buss DJ, Addison WN, Barros NMT, McKee MD. Biological stenciling of mineralization in the skeleton: Local enzymatic removal of inhibitors in the extracellular matrix. Bone 2020; 138:115447. [PMID: 32454257 DOI: 10.1016/j.bone.2020.115447] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Revised: 05/14/2020] [Accepted: 05/20/2020] [Indexed: 12/12/2022]
Abstract
Biomineralization is remarkably diverse and provides myriad functions across many organismal systems. Biomineralization processes typically produce hardened, hierarchically organized structures usually having nanostructured mineral assemblies that are formed through inorganic-organic (usually protein) interactions. Calcium‑carbonate biomineral predominates in structures of small invertebrate organisms abundant in marine environments, particularly in shells (remarkably it is also found in the inner ear otoconia of vertebrates), whereas calcium-phosphate biomineral predominates in the skeletons and dentitions of both marine and terrestrial vertebrates, including humans. Reconciliation of the interplay between organic moieties and inorganic crystals in bones and teeth is a cornerstone of biomineralization research. Key molecular determinants of skeletal and dental mineralization have been identified in health and disease, and in pathologic ectopic calcification, ranging from small molecules such as pyrophosphate, to small membrane-bounded matrix vesicles shed from cells, and to noncollagenous extracellular matrix proteins such as osteopontin and their derived bioactive peptides. Beyond partly knowing the regulatory role of the direct actions of inhibitors on vertebrate mineralization, more recently the importance of their enzymatic removal from the extracellular matrix has become increasingly understood. Great progress has been made in deciphering the relationship between mineralization inhibitors and the enzymes that degrade them, and how adverse changes in this physiologic pathway (such as gene mutations causing disease) result in mineralization defects. Two examples of this are rare skeletal diseases having osteomalacia/odontomalacia (soft bones and teeth) - namely hypophosphatasia (HPP) and X-linked hypophosphatemia (XLH) - where inactivating mutations occur in the gene for the enzymes tissue-nonspecific alkaline phosphatase (TNAP, TNSALP, ALPL) and phosphate-regulating endopeptidase homolog X-linked (PHEX), respectively. Here, we review and provide a concept for how existing and new information now comes together to describe the dual nature of regulation of mineralization - through systemic mineral ion homeostasis involving circulating factors, coupled with molecular determinants operating at the local level in the extracellular matrix. For the local mineralization events in the extracellular matrix, we present a focused concept in skeletal mineralization biology called the Stenciling Principle - a principle (building upon seminal work by Neuman and Fleisch) describing how the action of enzymes to remove tissue-resident inhibitors defines with precision the location and progression of mineralization.
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Affiliation(s)
- N Reznikov
- Object Research Systems Inc., 760 St. Paul West, Montreal, Quebec H3C 1M4, Canada.
| | - B Hoac
- Faculty of Dentistry, McGill University, 3640 University St., Montreal, Quebec H3A 0C7, Canada
| | - D J Buss
- Department of Anatomy and Cell Biology, McGill University, 3640 University St., Montreal, Quebec H3A 0C7, Canada
| | - W N Addison
- Department of Molecular Signaling and Biochemistry, Kyushu Dental University, 2-6-1 Manazuru, Kokurakita-ku, Kitakyushu, Fukuoka, Japan
| | - N M T Barros
- Departamento de Biofísica, São Paulo, Departamento de Ciências Biológicas, Universidade Federal de São Paulo, Diadema, Brazil
| | - M D McKee
- Faculty of Dentistry, McGill University, 3640 University St., Montreal, Quebec H3A 0C7, Canada; Department of Anatomy and Cell Biology, McGill University, 3640 University St., Montreal, Quebec H3A 0C7, Canada.
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7
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Li B, Wang X, Hao X, Liu Y, Wang Y, Shan C, Ao X, Liu Y, Bao H, Li P. A novel c.2179T>C mutation blocked the intracellular transport of PHEX protein and caused X-linked hypophosphatemic rickets in a Chinese family. Mol Genet Genomic Med 2020; 8:e1262. [PMID: 32511895 PMCID: PMC7434742 DOI: 10.1002/mgg3.1262] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2020] [Accepted: 03/23/2020] [Indexed: 12/13/2022] Open
Abstract
Background X‐linked hypophosphatemic rickets (XLH) is a heterogeneous genetic phosphate wasting disorder that occupies the majority of inheritable hypophosphatemic rickets (HR). XLH is caused by loss‐of‐function mutations in the phosphate‐regulating endopeptidase gene (PHEX) located on the X chromosome. Method In this study, we performed whole‐exome sequencing (WES) on the proband to identify the causative gene. The mutations were analyzed by predictive online software, such as PolyPhen‐2. Plasmids containing the wild‐type (WT) and mutant cDNA of the candidate gene were transfected into HEK293, then, the expression, cellular localization, and glycosylation state of the candidate proteins were detected by western blot, immunostaining, and endoglycosidase H digestion. The expression and concentration of related factor were measured by RT‐PCR and ELISA. Results We identified a novel missense mutation c.2179T>C in the PHEX that results in the substitution of p.Phe727Leu (F727L). This mutation was predicted to be disease‐causing by all four predictive online software. In vitro studies demonstrated that the F727L substitution hindered the intracellular trafficking of the mutant PHEX, with ~59% of mutant PHEX protein retained in the endoplasmic reticulum (ER) and only ~16% of the mutant protein localized on the cell surface. Endoglycosidase H digestion assay showed that the mutant F727L PHEX protein was not fully glycosylated. The concentration of intact FGF23 in hFOB1.19 cell culture medium collected from the mutant PHEX group was the highest (62.9 pg/ml) compared to the WT group (32.1 pg/ml) and control group (23.5 pg/ml). Conclusion Our results confirmed that the mutant PHEX protein was lowly glycosylated and retarded within the ER, the intact FGF23 level in cell culture media caused by the mutant PHEX protein was significantly elevated compared to that of the WT group, which may explain why the single base mutation in the PHEX led to XLH syndrome in this family.
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Affiliation(s)
- Baowei Li
- Institute for Translational Medicine, Qingdao University, Qingdao, China
| | - Xiong Wang
- Department of Reproductive Medicine, Affiliated Yantai Yuhuangding Hospital of Qingdao University, Yantai, China
| | - Xiaodan Hao
- Institute for Translational Medicine, Qingdao University, Qingdao, China
| | - Yanran Liu
- School of Basic Medicine, Qingdao University, Qingdao, China
| | - Yin Wang
- Institute for Translational Medicine, Qingdao University, Qingdao, China
| | - Chan Shan
- Institute for Translational Medicine, Qingdao University, Qingdao, China
| | - Xiang Ao
- Institute for Translational Medicine, Qingdao University, Qingdao, China
| | - Ying Liu
- Institute for Translational Medicine, Qingdao University, Qingdao, China
| | - HongChu Bao
- Department of Reproductive Medicine, Affiliated Yantai Yuhuangding Hospital of Qingdao University, Yantai, China
| | - Peifeng Li
- Institute for Translational Medicine, Qingdao University, Qingdao, China
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8
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Abstract
Hypophosphatemic rickets, mostly of the X-linked dominant form caused by pathogenic variants of the PHEX gene, poses therapeutic challenges with consequences for growth and bone development and portends a high risk of fractions and poor bone healing, dental problems and nephrolithiasis/nephrocalcinosis. Conventional treatment consists of PO4 supplements and calcitriol requiring monitoring for treatment-emergent adverse effects. FGF23 measurement, where available, has implications for the differential diagnosis of hypophosphatemia syndromes and, potentially, treatment monitoring. Newer therapeutic modalities include calcium sensing receptor modulation (cinacalcet) and biological molecules targeting FGF23 or its receptors. Their long-term effects must be compared with those of conventional treatments.
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Affiliation(s)
- Martin Bitzan
- Department of Pediatrics, The Montreal Children's Hospital, McGill University Health Centre, 1001 Boulevard Décarie, Room B RC.6164, Montreal, Quebec H4A 3J1, Canada.
| | - Paul R Goodyer
- The Research Institute of the McGill University Health Centre, 1001 Boulevard Décarie, Room EM1.2232, Montreal, Quebec H4A3J1, Canada
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9
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Minamizaki T, Konishi Y, Sakurai K, Yoshioka H, Aubin JE, Kozai K, Yoshiko Y. Soluble Klotho causes hypomineralization in Klotho-deficient mice. J Endocrinol 2018; 237:285-300. [PMID: 29632215 DOI: 10.1530/joe-17-0683] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/03/2018] [Accepted: 04/09/2018] [Indexed: 12/12/2022]
Abstract
The type I transmembrane protein αKlotho (Klotho) serves as a coreceptor for the phosphaturic hormone fibroblast growth factor 23 (FGF23) in kidney, while a truncated form of Klotho (soluble Klotho, sKL) is thought to exhibit multiple activities, including acting as a hormone, but whose mode(s) of action in different organ systems remains to be fully elucidated. FGF23 is expressed primarily in osteoblasts/osteocytes and aberrantly high levels in the circulation acting via signaling through an FGF receptor (FGFR)-Klotho coreceptor complex cause renal phosphate wasting and osteomalacia. We assessed the effects of exogenously added sKL on osteoblasts and bone using Klotho-deficient (kl/kl) mice and cell and organ cultures. sKL induced FGF23 signaling in bone and exacerbated the hypomineralization without exacerbating the hyperphosphatemia, hypercalcemia and hypervitaminosis D in kl/kl mice. The same effects were seen in rodent bone models in vitro, in which we also detected formation of a sKL complex with FGF23-FGFR and decreased Phex (gene responsible for X-linked hypophosphatemic rickets (XLH)/osteomalacia) expression. Further, sKL-FGF23-dependent hypomineralization in vitro was rescued by soluble PHEX. These data suggest that exogenously added sKL directly participates in FGF23 signaling in bone and that PHEX is a downstream effector of the sKL-FGF23-FGFR axis in bone.
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Affiliation(s)
- Tomoko Minamizaki
- Department of Calcified Tissue Biology, School of Dentistry, Hiroshima University Graduate School of Biomedical & Health Sciences, Hiroshima, Japan
| | - Yukiko Konishi
- Department of Calcified Tissue Biology, School of Dentistry, Hiroshima University Graduate School of Biomedical & Health Sciences, Hiroshima, Japan
- Department of Pediatric Dentistry, School of Dentistry, Hiroshima University Graduate School of Biomedical & Health Sciences, Hiroshima, Japan
| | - Kaoru Sakurai
- Department of Calcified Tissue Biology, School of Dentistry, Hiroshima University Graduate School of Biomedical & Health Sciences, Hiroshima, Japan
- Department of Pediatric Dentistry, School of Dentistry, Hiroshima University Graduate School of Biomedical & Health Sciences, Hiroshima, Japan
| | - Hirotaka Yoshioka
- Department of Calcified Tissue Biology, School of Dentistry, Hiroshima University Graduate School of Biomedical & Health Sciences, Hiroshima, Japan
| | - Jane E Aubin
- Department of Molecular Genetics, University of Toronto, 1 King's College Circle, Toronto, Canada
| | - Katsuyuki Kozai
- Department of Pediatric Dentistry, School of Dentistry, Hiroshima University Graduate School of Biomedical & Health Sciences, Hiroshima, Japan
| | - Yuji Yoshiko
- Department of Calcified Tissue Biology, School of Dentistry, Hiroshima University Graduate School of Biomedical & Health Sciences, Hiroshima, Japan
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Liao H, Zhu HM, Liu HQ, Li LP, Liu SL, Wang H. Two novel variants of the PHEX gene in patients with X‑linked dominant hypophosphatemic rickets and prenatal diagnosis for fetuses in these families. Int J Mol Med 2018; 41:2012-2020. [PMID: 29393334 PMCID: PMC5810233 DOI: 10.3892/ijmm.2018.3402] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2017] [Accepted: 01/05/2018] [Indexed: 11/06/2022] Open
Abstract
X-linked hypophosphatemic rickets (XLHR; OMIM 307800) is an X-linked dominant disorder caused by mutations in the phosphate-regulating neutral endopeptidase homolog X-linked (PHEX) gene, which is located at Xp22.11. In the present study, two novel variants of the PHEX gene were identified in two unrelated families with XLHR by directly sequencing all 22 exon regions and intron/exon boundaries of the PHEX gene. One missense variant, NM_000444.5: c.1721T>A, was identified in exon 17 of the PHEX gene in Family 1, which led to an amino acid change in the p.Ile574Lys protein. The other splicing variant identified was NM_000444.5: c.591A>G, in exon 5 in Family 2, resulting in a deletion of 77 bp in the 3′ site of exon 5 during splicing, which was verified by direct cDNA sequencing of the PHEX gene. According to the results of reverse transcription-quantitative polymerase chain reaction analysis, the affected male with the splicing variant c.591A>G showed normal gene expression of PHEX, whereas the affected female exhibited low gene expression, compared with normal females. Based on these findings, prenatal diagnoses were made for the fetuses with a family history of XLHR using the backup amniotic fluid samples. One fetus without the missense variant was confirmed to be a healthy girl in a follow-up visit 1 month following birth.
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Affiliation(s)
- Hong Liao
- Department of Obstetrics and Gynecology, West China Second University Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China
| | - Hong-Mei Zhu
- Department of Obstetrics and Gynecology, West China Second University Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China
| | - Hong-Qian Liu
- Department of Obstetrics and Gynecology, West China Second University Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China
| | - Ling-Ping Li
- Department of Obstetrics and Gynecology, West China Second University Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China
| | - Shan-Ling Liu
- Department of Obstetrics and Gynecology, West China Second University Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China
| | - He Wang
- Department of Obstetrics and Gynecology, West China Second University Hospital, Sichuan University, Chengdu, Sichuan 610041, P.R. China
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Qin C, Baba O, Butler WT. Post-translational Modifications of SIBLING Proteins and Their Roles in Osteogenesis and Dentinogenesis. ACTA ACUST UNITED AC 2016; 15:126-36. [PMID: 15187031 DOI: 10.1177/154411130401500302] [Citation(s) in RCA: 323] [Impact Index Per Article: 40.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The extracellular matrix (ECM) of bone and dentin contains several non-collagenous proteins. One category of non-collagenous protein is termed the SIBLING (Small Integrin-Binding LIgand, N-linked Glycoprotein) family, that includes osteopontin (OPN), bone sialoprotein (BSP), dentin matrix protein 1 (DMP1), dentin sialophosphoprotein (DSPP), and matrix extracellular phosphoglycoprotein (MEPE). These polyanionic SIBLING proteins are believed to play key biological roles in the mineralization of bone and dentin. Although the specific mechanisms involved in controlling bone and dentin formation are still unknown, it is clear that some functions of the SIBLING family members are dependent on the nature and extent of post-translational modifications (PTMs), such as phosphorylation, glycosylation, and proteolytic processing, since these PTMs would have significant effects on their structure. OPN and BSP are present in the ECM of bone and dentin as full-length forms, whereas amino acid sequencing indicates that DMP1 and DSPP exist as proteolytically processed fragments that result from scission of X-Asp bonds. We hypothesized that the processing of DMP1 and DSPP is catalyzed by the PHEX enzyme, since this protein, an endopeptidase that is predominantly expressed in bone and tooth, has a strong preference for cleavage at the NH2-terminus of aspartyl residue. We envision that the proteolytic processing of DMP1 and DSPP may be an activation process that plays a significant, crucial role in osteogenesis and dentinogenesis, and that a failure in this processing would cause defective mineralization in bone and dentin, as observed in X-linked hypophosphatemic rickets.
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Affiliation(s)
- C Qin
- The Department of Endodontics and Periodontics, University of Texas-Houston Health Science Center, Dental Branch, Houston, TX 77030, USA.
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12
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Novel de novo nonsense mutation of the PHEX gene (p.Lys50Ter) in a Chinese patient with hypophosphatemic rickets. Gene 2015; 565:150-4. [DOI: 10.1016/j.gene.2015.03.066] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2015] [Revised: 03/18/2015] [Accepted: 03/29/2015] [Indexed: 01/20/2023]
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Ma SL, Vega-Warner V, Gillies C, Sampson MG, Kher V, Sethi SK, Otto EA. Whole Exome Sequencing Reveals Novel PHEX Splice Site Mutations in Patients with Hypophosphatemic Rickets. PLoS One 2015; 10:e0130729. [PMID: 26107949 PMCID: PMC4479593 DOI: 10.1371/journal.pone.0130729] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Accepted: 05/24/2015] [Indexed: 01/25/2023] Open
Abstract
Objective Hypophosphatemic rickets (HR) is a heterogeneous genetic phosphate wasting disorder. The disease is most commonly caused by mutations in the PHEX gene located on the X-chromosome or by mutations in CLCN5, DMP1, ENPP1, FGF23, and SLC34A3. The aims of this study were to perform molecular diagnostics for four patients with HR of Indian origin (two independent families) and to describe their clinical features. Methods We performed whole exome sequencing (WES) for the affected mother of two boys who also displayed the typical features of HR, including bone malformations and phosphate wasting. B-lymphoblast cell lines were established by EBV transformation and subsequent RT-PCR to investigate an uncommon splice site variant found by WES. An in silico analysis was done to obtain accurate nucleotide frequency occurrences of consensus splice positions other than the canonical sites of all human exons. Additionally, we applied direct Sanger sequencing for all exons and exon/intron boundaries of the PHEX gene for an affected girl from an independent second Indian family. Results WES revealed a novel PHEX splice acceptor mutation in intron 9 (c.1080-3C>A) in a family with 3 affected individuals with HR. The effect on splicing of this mutation was further investigated by RT-PCR using RNA obtained from a patient’s EBV-transformed lymphoblast cell line. RT-PCR revealed an aberrant splice transcript skipping exons 10-14 which was not observed in control samples, confirming the diagnosis of X-linked dominant hypophosphatemia (XLH). The in silico analysis of all human splice sites adjacent to all 327,293 exons across 81,814 transcripts among 20,345 human genes revealed that cytosine is, with 64.3%, the most frequent nucleobase at the minus 3 splice acceptor position, followed by thymidine with 28.7%, adenine with 6.3%, and guanine with 0.8%. We generated frequency tables and pictograms for the extended donor and acceptor splice consensus regions by analyzing all human exons. Direct Sanger sequencing of all PHEX exons in a sporadic case with HR from the Indian subcontinent revealed an additional novel PHEX mutation (c.1211_1215delACAAAinsTTTACAT, p.Asp404Valfs*5, de novo) located in exon 11. Conclusions Mutation analyses revealed two novel mutations and helped to confirm the clinical diagnoses of XLH in two families from India. WES helped to analyze all genes implicated in the underlying disease complex. Mutations at splice positions other than the canonical key sites need further functional investigation to support the assertion of pathogenicity.
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Affiliation(s)
- Sara L. Ma
- College of Literature, Science, and the Arts, University of Michigan, Ann Arbor, MI, United States of America
| | - Virginia Vega-Warner
- Division of Nephrology, Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI, United States of America
| | - Christopher Gillies
- Division of Nephrology, Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI, United States of America
| | - Matthew G. Sampson
- Division of Nephrology, Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI, United States of America
| | - Vijay Kher
- Kidney and Urology Institute, Medanta, The Medicity Hospital, Gurgaon, India
| | - Sidharth K. Sethi
- Kidney and Urology Institute, Medanta, The Medicity Hospital, Gurgaon, India
| | - Edgar A. Otto
- Division of Nephrology, Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI, United States of America
- * E-mail:
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Abstract
Traditionally, control of phosphorus in the body has been considered secondary to the tighter control of calcium by parathyroid hormone and vitamin D. However, over the past decade, substantial advances have been made in understanding the control of phosphorus by the so-called phosphatonin system, the lynchpin of which is fibroblast growth factor 23 (FGF23). FGF23 binds to the klotho/FGFR1c receptor complex in renal tubular epithelial cells, leading to upregulation of Na/Pi cotransporters and subsequent excretion of phosphorus from the body. In addition, FGF23 inhibits parathyroid hormone and the renal 1α-hydroxylase enzyme, while it stimulates 24-hydroxylase, leading to decreased 1,25-dihydroxyvitamin D3. FGF23 is intimately involved in the pathogenesis of a number of diseases, particularly the hereditary hypophosphatemic rickets group and chronic kidney disease, and is a target for the development of new treatments in human medicine. Little work has been done on FGF23 or the other phosphatonins in veterinary medicine, but increases in FGF23 are seen with chronic kidney disease in cats, and increased FGF23 expression has been found in soft tissue sarcomas in dogs.
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Affiliation(s)
- M. R. Hardcastle
- Gribbles Veterinary Pathology Ltd, Mt Wellington, Auckland, New Zealand
| | - K. E. Dittmer
- Animal and Biomedical Sciences, Institute of Veterinary, Massey University, Palmerston North, New Zealand
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Yorgan T, Rendenbach C, Jeschke A, Amling M, Cheah KSE, Schinke T. Increased Col10a1 expression is not causative for the phenotype of Phex-deficient Hyp mice. Biochem Biophys Res Commun 2013; 442:209-13. [PMID: 24269824 DOI: 10.1016/j.bbrc.2013.11.033] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Accepted: 11/07/2013] [Indexed: 12/25/2022]
Abstract
X-linked hypophosphatemic rickets (XLHR) is a severe disorder of phosphate homeostasis and skeletal mineralization caused by mutations of PHEX, encoding a bone-specific endopeptidase. Phex-deficient Hyp mice have been extensively studied to understand the molecular bases of XLHR, and here it was found that Fgf23, encoding a major phosphaturic hormone, was transcriptionally activated in bone-forming osteoblasts. We and others could additionally show that Col10a1 expression is increased in Hyp osteoblasts and bones, thereby raising the possibility that ectopic production of type X collagen could contribute to the impaired mineralization of the Hyp bone matrix. Here we show that an additional deficiency of the Col10a1 gene does not overtly affect the skeletal phenotype of Hyp mice. More specifically, Col10a1-deficient Hyp mice displayed severe disturbances of skeletal growth, bone mass acquisition and bone matrix mineralization, and they were essentially indistinguishable from Hyp littermates. This was confirmed by non-decalcified histology and bone-specific histomorphometry quantifying all relevant parameters of growth plate maturation, trabecular bone architecture and osteoid accumulation. Taken together, our results show that increased Col10a1 expression in Phex-deficient osteoblasts is not a major cause of the XLHR phenotype, which was an important issue to address based on the previous findings.
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Affiliation(s)
- Timur Yorgan
- Department of Osteology and Biomechanics, University Medical Center Hamburg Eppendorf, Hamburg, Germany
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16
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McKee MD, Hoac B, Addison WN, Barros NM, Millán JL, Chaussain C. Extracellular matrix mineralization in periodontal tissues: Noncollagenous matrix proteins, enzymes, and relationship to hypophosphatasia and X-linked hypophosphatemia. Periodontol 2000 2013; 63:102-22. [PMID: 23931057 PMCID: PMC3766584 DOI: 10.1111/prd.12029] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/15/2012] [Indexed: 12/26/2022]
Abstract
As broadly demonstrated for the formation of a functional skeleton, proper mineralization of periodontal alveolar bone and teeth - where calcium phosphate crystals are deposited and grow within an extracellular matrix - is essential for dental function. Mineralization defects in tooth dentin and cementum of the periodontium invariably lead to a weak (soft or brittle) dentition in which teeth become loose and prone to infection and are lost prematurely. Mineralization of the extremities of periodontal ligament fibers (Sharpey's fibers) where they insert into tooth cementum and alveolar bone is also essential for the function of the tooth-suspensory apparatus in occlusion and mastication. Molecular determinants of mineralization in these tissues include mineral ion concentrations (phosphate and calcium), pyrophosphate, small integrin-binding ligand N-linked glycoproteins and matrix vesicles. Amongst the enzymes important in regulating these mineralization determinants, two are discussed at length here, with clinical examples given, namely tissue-nonspecific alkaline phosphatase and phosphate-regulating gene with homologies to endopeptidases on the X chromosome. Inactivating mutations in these enzymes in humans and in mouse models lead to the soft bones and teeth characteristic of hypophosphatasia and X-linked hypophosphatemia, respectively, where the levels of local and systemic circulating mineralization determinants are perturbed. In X-linked hypophosphatemia, in addition to renal phosphate wasting causing low circulating phosphate levels, phosphorylated mineralization-regulating small integrin-binding ligand N-linked glycoproteins, such as matrix extracellular phosphoglycoprotein and osteopontin, and the phosphorylated peptides proteolytically released from them, such as the acidic serine- and aspartate-rich-motif peptide, may accumulate locally to impair mineralization in this disease.
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Affiliation(s)
- Marc D. McKee
- Faculty of Dentistry, McGill University, Montreal, QC, Canada
- Department of Anatomy and Cell Biology, Faculty of Dentistry, McGill University, Montreal, QC, Canada
| | - Betty Hoac
- Faculty of Dentistry, McGill University, Montreal, QC, Canada
| | - William N. Addison
- Department of Oral Medicine, Infection and Immunity, Harvard University School of Dental Medicine, Boston, MA, USA
| | - Nilana M.T. Barros
- Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, SP, Brasil, and Departamento de Ciências Exatas e da Terra, Universidade Federal de São Paulo, Diadema, SP, Brasil
| | - José Luis Millán
- Sanford Children's Health Research Center, Sanford-Burnham Medical Research Institute, La Jolla, CA, USA
| | - Catherine Chaussain
- EA 2496, UFR Odontologie, University Paris Descartes PRES Sorbonne Paris Cité; AP-HP: Odontology Department Bretonneau, Paris and Centre de Référence des Maladies Rares du Métabolisme du Phosphore et du Calcium, Kremlin Bicêtre, France
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17
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Seitz S, Rendenbach C, Barvencik F, Streichert T, Jeschke A, Schulze J, Amling M, Schinke T. Retinol deprivation partially rescues the skeletal mineralization defects of Phex-deficient Hyp mice. Bone 2013; 53:231-8. [PMID: 23266491 DOI: 10.1016/j.bone.2012.12.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/09/2012] [Revised: 12/10/2012] [Accepted: 12/12/2012] [Indexed: 12/24/2022]
Abstract
X-linked hypophosphatemic rickets (XLH) is a genetic disorder caused by mutational inactivation of the PHEX gene, encoding a transmembrane endopeptidase expressed in osteoblasts. Since several experiments involving Phex-deficient Hyp mice have demonstrated that an increased expression of Fgf23 in osteoblasts is causative for the renal phosphate loss characteristic of XLH, we performed genome-wide expression analysis to compare differentiated osteoblasts from wildtype and Hyp mice. Here we did not only observe the expected increase of Fgf23 expression in the latter ones, but also a differential expression of genes that are either induced by or involved in retinoic acid signaling, which led us to analyze whether dietary retinol deprivation would influence the phenotype of Hyp mice. Unexpectedly, feeding a retinol-free diet resulted in a partial rescue of the growth plate and bone mineralization defects in 6 weeks old Hyp mice. When we fed the same diet for 24 weeks the amount of non-mineralized bone matrix (osteoid) was reduced by more than 70%, although phosphate homeostasis was unaffected. In contrast, a dietary normalization of serum phosphate levels in Hyp mice reduced the osteoid amount by less than 30%, thereby demonstrating a previously unknown impact of retinol on the cell-autonomous mineralization defect of Phex-deficient osteoblasts.
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Affiliation(s)
- Sebastian Seitz
- Department of Osteology and Biomechanics, University Medical Center Hamburg Eppendorf, Hamburg 20246, Germany
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18
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Barros NMT, Hoac B, Neves RL, Addison WN, Assis DM, Murshed M, Carmona AK, McKee MD. Proteolytic processing of osteopontin by PHEX and accumulation of osteopontin fragments in Hyp mouse bone, the murine model of X-linked hypophosphatemia. J Bone Miner Res 2013; 28:688-99. [PMID: 22991293 DOI: 10.1002/jbmr.1766] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Revised: 08/21/2012] [Accepted: 09/07/2012] [Indexed: 12/11/2022]
Abstract
X-linked hypophosphatemia (XLH/HYP)-with renal phosphate wasting, hypophosphatemia, osteomalacia, and tooth abscesses-is caused by mutations in the zinc-metallopeptidase PHEX gene (phosphate-regulating gene with homologies to endopeptidase on the X chromosome). PHEX is highly expressed by mineralized tissue cells. Inactivating mutations in PHEX lead to distal renal effects (implying accumulation of a secreted, circulating phosphaturic factor) and accumulation in bone and teeth of mineralization-inhibiting, acidic serine- and aspartate-rich motif (ASARM)-containing peptides, which are proteolytically derived from the mineral-binding matrix proteins of the SIBLING family (small, integrin-binding ligand N-linked glycoproteins). Although the latter observation suggests a local, direct matrix effect for PHEX, its physiologically relevant substrate protein(s) have not been identified. Here, we investigated two SIBLING proteins containing the ASARM motif-osteopontin (OPN) and bone sialoprotein (BSP)-as potential substrates for PHEX. Using cleavage assays, gel electrophoresis, and mass spectrometry, we report that OPN is a full-length protein substrate for PHEX. Degradation of OPN was essentially complete, including hydrolysis of the ASARM motif, resulting in only very small residual fragments. Western blotting of Hyp (the murine homolog of human XLH) mouse bone extracts having no PHEX activity clearly showed accumulation of an ∼35 kDa OPN fragment that was not present in wild-type mouse bone. Immunohistochemistry and immunogold labeling (electron microscopy) for OPN in Hyp bone likewise showed an accumulation of OPN and/or its fragments compared with normal wild-type bone. Incubation of Hyp mouse bone extracts with PHEX resulted in the complete degradation of these fragments. In conclusion, these results identify full-length OPN and its fragments as novel, physiologically relevant substrates for PHEX, suggesting that accumulation of mineralization-inhibiting OPN fragments may contribute to the mineralization defect seen in the osteomalacic bone characteristic of XLH/HYP.
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Affiliation(s)
- Nilana M T Barros
- Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, Brazil.
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Kang QL, Xu J, Zhang Z, He JW, Lu LS, Fu WZ, Zhang ZL. Three novel PHEX gene mutations in four Chinese families with X-linked dominant hypophosphatemic rickets. Biochem Biophys Res Commun 2012; 423:793-8. [PMID: 22713460 DOI: 10.1016/j.bbrc.2012.06.042] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2012] [Accepted: 06/09/2012] [Indexed: 01/19/2023]
Abstract
BACKGROUND X-linked hypophosphatemia (XLH), the most common form of inherited rickets, is a dominant disorder that is characterized by renal phosphate wasting with hypophosphatemia, abnormal bone mineralization, short stature, and rachitic manifestations. The related gene with inactivating mutations associated with XLH has been identified as PHEX, which is a phosphate-regulating gene with homologies to endopeptidases on the X chromosome. In this study, a variety of PHEX mutations were identified in four Chinese families with XLH. METHODS We investigated four unrelated Chinese families who exhibited typical features of XLH by using PCR to analyze mutations that were then sequenced. The laboratory and radiological investigations were conducted simultaneously. RESULTS Three novel mutations were found in these four families: one frameshift mutation, c.2033dupT in exon 20, resulting in p.T679H; one nonsense mutation, c.1294A>T in exon 11, resulting in p.K432X; and one missense mutation, c.2192T>C in exon 22, resulting in p.F731S. CONCLUSIONS We found that the PHEX gene mutations were responsible for XLH in these Chinese families. Our findings are useful for understanding the genetic basis of Chinese patients with XLH.
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Affiliation(s)
- Qing-lin Kang
- Department of Orthopedic Surgery, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai 200233, PR China
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20
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Pellicelli M, Taheri M, St-Louis M, Bériault V, Desgroseillers L, Boileau G, Moreau A. PTHrP(1-34)-mediated repression of the PHEX gene in osteoblastic cells involves the transcriptional repressor E4BP4. J Cell Physiol 2012; 227:2378-87. [DOI: 10.1002/jcp.22973] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Martin A, Quarles LD. Evidence for FGF23 involvement in a bone-kidney axis regulating bone mineralization and systemic phosphate and vitamin D homeostasis. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 728:65-83. [PMID: 22396162 PMCID: PMC6350529 DOI: 10.1007/978-1-4614-0887-1_4] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Bone is involved in the maintenance of phosphate and vitamin D homeostasis via its production and secretion of FGF23 and serves as a reservoir for the storage and release of calcium and phosphate into the circulation. Alterations in mineralization of extracellular matrix and the remodeling activities of the skeleton are coupled to the kidney conservation of phosphate and production of 1,25(OH)2D via the regulation of FGF23 production by osteocytes through yet-to-be defined locally derived factors. In addition, FGF23 production is regulated by 1,25(OH)2D in a feedback loop where FGF23 stimulate Cyp24 mediated degradation of 1,25(OH)2D that serves to protect the organism from the toxic effects of vitamin D excess. In this chapter, we will review the regulation and function of FGF23.
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Affiliation(s)
- Aline Martin
- University of Tennessee Health Science Center, Department of Medicine, Memphis, Tennessee, USA
| | - L. Darryl Quarles
- University of Tennessee Health Science Center, Department of Medicine, Memphis, Tennessee, USA
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22
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Martin A, Liu S, David V, Li H, Karydis A, Feng JQ, Quarles LD. Bone proteins PHEX and DMP1 regulate fibroblastic growth factor Fgf23 expression in osteocytes through a common pathway involving FGF receptor (FGFR) signaling. FASEB J 2011; 25:2551-62. [PMID: 21507898 PMCID: PMC3136343 DOI: 10.1096/fj.10-177816] [Citation(s) in RCA: 198] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2010] [Accepted: 04/07/2011] [Indexed: 12/19/2022]
Abstract
Fibroblastic growth factor 23 (FGF23) is a circulating phosphaturic hormone. Inactivating mutations of the endopeptidase PHEX or the SIBLING protein DMP1 result in equivalent intrinsic bone mineralization defects and increased Fgf23 expression in osteocytes. The mechanisms whereby PHEX and DMP1 regulate Fgf23 expression are unknown. We examined the possibility that PHEX and DMP1 regulate Fgf23 through a common pathway by analyzing the phenotype of compound Phex and Dmp1 mutant mice (Hyp/Dmp1(-/-)). Compared to single-mutant littermates, compound-mutant Hyp/Dmp1(-/-) mice displayed nonadditive elevations of serum FGF23 (1912 ± 183, 1715 ± 178, and 1799 ± 181 pg/ml), hypophosphatemia (P(i): 6.0 ± 0.3, 5.8 ± 0.2, and 5.4 ± 0.1 mg/dl), and severity of rickets/osteomalacia (bone mineral density: -36, -36, and -30%). Microarray analysis of long bones identified gene expression profiles implicating common activation of the FGFR pathway in all the mutant groups. Furthermore, inhibiting FGFR signaling using SU5402 in Hyp- and Dmp1(-/-)-derived bone marrow stromal cells prevented the increase in Fgf23 mRNA expression (129- and 124-fold increase in Hyp and Dmp1(-/-) vs. 1.3-fold in Hyp+SU5402 and 2.5-fold in Dmp1(-/-)+SU5402, P<0.05). For all analyses, samples collected from nonmutant wild-type littermates served as controls. These findings indicate that PHEX and DMP1 control a common pathway regulating bone mineralization and FGF23 production, the latter involving activation of the FGFR signaling in osteocytes.
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Affiliation(s)
- Aline Martin
- University of Tennessee Health Science Center, Memphis, Tennessee, USA
| | | | - Valentin David
- University of Tennessee Health Science Center, Memphis, Tennessee, USA
| | - Hua Li
- University of Tennessee Health Science Center, Memphis, Tennessee, USA
| | | | - Jian Q. Feng
- Department of Biomedical Sciences, Baylor College of Dentistry, Dallas, Texas, USA
| | - L. Darryl Quarles
- University of Tennessee Health Science Center, Memphis, Tennessee, USA
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Gorski JP. Biomineralization of bone: a fresh view of the roles of non-collagenous proteins. Front Biosci (Landmark Ed) 2011; 16:2598-621. [PMID: 21622198 DOI: 10.2741/3875] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The impact of genetics has dramatically affected our understanding of the functions of non-collagenous proteins. Specifically, mutations and knockouts have defined their cellular spectrum of actions. However, the biochemical mechanisms mediated by non-collagenous proteins in biomineralization remain elusive. It is likely that this understanding will require more focused functional testing at the protein, cell, and tissue level. Although initially viewed as rather redundant and static acidic calcium binding proteins, it is now clear that non-collagenous proteins in mineralizing tissues represent diverse entities capable of forming multiple protein-protein interactions which act in positive and negative ways to regulate the process of bone mineralization. Several new examples from the author's laboratory are provided which illustrate this theme including an apparent activating effect of hydroxyapatite crystals on metalloproteinases. This review emphasizes the view that secreted non-collagenous proteins in mineralizing bone actively participate in the mineralization process and ultimately control where and how much mineral crystal is deposited, as well as determining the quality and biomechanical properties of the mineralized matrix produced.
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Affiliation(s)
- Jeffrey Paul Gorski
- Center of Excellence in the Study of Musculoskeletal and Dental Tissues and Dept. of Oral Biology, Sch. Of Dentistry, Univ. of Missouri-Kansas City, Kansas City, MO 64108, USA.
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Ruppe MD, Brosnan PG, Au KS, Tran PX, Dominguez BW, Northrup H. Mutational analysis of PHEX, FGF23 and DMP1 in a cohort of patients with hypophosphatemic rickets. Clin Endocrinol (Oxf) 2011; 74:312-8. [PMID: 21050253 PMCID: PMC3035757 DOI: 10.1111/j.1365-2265.2010.03919.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
BACKGROUND X-linked hypophosphatemic rickets, autosomal dominant hypophosphatemic rickets and autosomal recessive hypophosphatemic rickets make up a group of renal phosphate wasting disorders with common clinical and biochemical characteristics. These three types of rickets are related to mutations in PHEX, FGF23 and dentin matrix protein 1 (DMP1), respectively. OBJECTIVE The objective of the study was to evaluate the frequency of mutations that occur in these three genes associated with hypophosphatemic rickets. PATIENTS AND METHODS In this study, we sequenced these genes in 76 members of 46 kindreds from a large hypophosphatemic rickets cohort. RESULTS Forty-two individuals from 27 kindreds were found to have mutations in PHEX; 16 of which were novel. One subject had an FGF23 mutation. No individuals were found to have mutations in DMP1 consistent with the presence of recessive hypophosphatemic rickets. CONCLUSIONS Our data highlight the wide spectrum of genetic variation that can be seen in PHEX, FGF23 and DMP1 when screening a large cohort with hypophosphatemic rickets.
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Affiliation(s)
- Mary D Ruppe
- Department of Medicine, University of Texas Health Science Center at Houston, TX 77030, USA.
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25
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Abstract
Inherited diseases of renal phosphate handling lead to urinary phosphate wasting and depletion of total body phosphorus stores. Clinical sequelae of inherited disorders that are associated with increased urinary phosphate excretion are deleterious and can lead to abnormal skeletal growth and deformities. This Review describes hereditary disorders of renal phosphate wasting taking into account developments in our understanding of renal phosphate handling from the last decade. The cloning of genes involved in these disorders and further studies on their pathophysiological mechanisms have given important insights in to how phosphatonins, such as FGF-23, regulate renal phosphate reabsorption in health and disease. X-linked dominant hypophosphatemic rickets results from mutation of a metalloprotease (PHEX) that has an unidentified role in FGF-23 degradation. Mutation of an RXXR proteolytic cleavage site in FGF-23 prevents degradation and increases circulating levels of FGF-23 in autosomal dominant hypophosphatemic rickets. FGF-23 acts to remove sodium phosphate co-transporters from the luminal membrane of proximal tubular cells with resultant renal phosphate wasting. Loss of function mutations in genes encoding the transporters NaPi-IIc and NaPi-IIa also result in renal phosphate wasting and rickets.
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Zhang B, Sun Y, Chen L, Guan C, Guo L, Qin C. Expression and distribution of SIBLING proteins in the predentin/dentin and mandible of hyp mice. Oral Dis 2010; 16:453-64. [PMID: 20233318 DOI: 10.1111/j.1601-0825.2010.01656.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVES Human X-linked hypophosphatemia (XLH) and its murine homologue, Hyp are caused by inactivating mutations in PHEX gene. The protein encoded by PHEX gene is an endopeptidase whose physiological substrate(s) has not been identified. Dentin matrix protein 1 (DMP1) and dentin sialophosphoprotein (DSPP), two members of the Small Integrin-Binding LIgand, N-linked Glycoprotein (SIBLING) family are proteolytically processed. It has been speculated that PHEX endopeptidase may be responsible for the proteolytic cleavage of DMP1 and DSPP. To test this hypothesis and to analyse the distribution of SIBLING proteins in the predentin/dentin complex and mandible of Hyp mice, we compared the expression of four SIBLING proteins, DMP1, DSPP, bone sialoprotein (BSP) and osteopontin (OPN) between Hyp and wild-type mice. METHODS These SIBLING proteins were analysed by protein chemistry and immunohistochemistry. RESULTS (1) Dentin matrix protein 1 and DSPP fragments are present in the extracts of Hyp predentin/dentin and bone; (2) the level of DMP1 proteoglycan form, BSP and OPN is elevated in the Hyp bone. CONCLUSIONS The PHEX protein is not the enzyme responsible for the proteolytic processing of DMP1 and DSPP. The altered distribution of SIBLING proteins may be involved in the pathogenesis of bone and dentin defects in Hyp and XLH.
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Affiliation(s)
- B Zhang
- Department of Oral and Maxillofacial Surgery, 2nd Affiliated Hospital of Harbin Medical University, Harbin, Heilongjiang, China.
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Boskey A, Frank A, Fujimoto Y, Spevak L, Verdelis K, Ellis B, Troiano N, Philbrick W, Carpenter T. The PHEX transgene corrects mineralization defects in 9-month-old hypophosphatemic mice. Calcif Tissue Int 2009; 84:126-37. [PMID: 19082853 PMCID: PMC2657219 DOI: 10.1007/s00223-008-9201-y] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/22/2008] [Accepted: 11/21/2008] [Indexed: 01/30/2023]
Abstract
Hypophosphatemia is an X-linked dominant disorder resulting from a mutation in the PHEX gene. While osteoblast-specific expression of the PHEX transgene has been reported to decrease the phosphate wasting associated with the disease in male hypophosphatemic (HYP) mice, there are reports that the mineralization defect is only partially corrected in young animals. To test the hypothesis that osteoblast-specific expression of the PHEX gene for a longer time would correct the mineralization defect, this study examined the bones of 9-month-old male and female HYP mice and their wild-type controls with or without expression of the transgene under a collagen type I promoter. Serum phosphate levels, alkaline phosphatase activity, and FGF23 levels were also measured. Mineral analyses based on wide-angle X-ray diffraction, Fourier transform-infrared (FT-IR) spectroscopy, and FT-IR imaging confirmed the decreased mineral content and increased mineral crystal size in male HYP humerii compared to wild-type males and females with or without the transgene and in female HYP mice with or without the transgene. There was a significant increase in mineral content and a decrease in crystallinity in the HYP males' bones with the transgene, compared to those without. Of interest, expression of the transgene in wild-type animals significantly increased the mineral content in both males and females without having a detectable effect on crystallinity or carbonate content. In contrast to the bones, based on micro-computed tomography and FT-IR imaging, at 9 months there were no significant differences between the HYP and the WT teeth, precluding analysis of the effect of the transgene.
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Affiliation(s)
- Adele Boskey
- Musculoskeletal Integrity Program, Hospital for Special Surgery, Weill Medical College, Cornell University, 535 East 70th Street, New York, NY 10021, USA.
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28
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Abstract
Given the dramatic increase in skeletal size during growth, the need to preserve skeletal mass during adulthood, and the large capacity of bone to store calcium and phosphate, juxtaposed with the essential role of phosphate in energy metabolism and the adverse effects of hyperphosphatemia, it is not surprising that a complex systems biology has evolved that permits cross-talk between bone and other organs to adjust phosphate balance and bone mineralization in response to changing physiological requirements. This review examines the newly discovered signaling pathways involved in the endocrine functions of bone, such as those mediated by the phosphaturic and 1,25(OH)2D-regulating hormone FGF23, and the broader systemic effects associated with abnormalities of calcium and phosphate homeostasis.
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Affiliation(s)
- L Darryl Quarles
- The Kidney Institute, University of Kansas Medical Center, Kansas City, Kansas 66160, USA.
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29
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Affiliation(s)
- Adele L Boskey
- Musculoskeletal Integrity Program, Hospital for Special Surgery, 535 East 70th Street, New York, New York 10021, USA.
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30
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Elabd C, Chiellini C, Massoudi A, Cochet O, Zaragosi LE, Trojani C, Michiels JF, Weiss P, Carle G, Rochet N, Dechesne CA, Ailhaud G, Dani C, Amri EZ. Human adipose tissue-derived multipotent stem cells differentiate in vitro and in vivo into osteocyte-like cells. Biochem Biophys Res Commun 2007; 361:342-8. [PMID: 17651696 DOI: 10.1016/j.bbrc.2007.06.180] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2007] [Accepted: 06/29/2007] [Indexed: 11/29/2022]
Abstract
Cell-based therapies are used to treat bone defects. We recently described that human multipotent adipose-derived stem (hMADS) cells, which exhibit a normal karyotype, self renewal, and the maintenance of their differentiation properties, are able to differentiate into different lineages. Herein, we show that hMADS cells can differentiate into osteocyte-like cells. In the presence of a low amount of serum and EGF, hMADS cells express specific molecular markers, among which alkaline phosphatase, CBFA-1, osteocalcin, DMP1, PHEX, and podoplanin and develop functional gap-junctions. When loaded on a hardening injectable bone substitute (HIBS) biomaterial and injected subcutaneously into nude mice, hMADS cells develop mineralized woven bone 4 weeks after implantation. Thus hMADS cells represent a valuable tool for pharmacological and biological studies of osteoblast differentiation in vitro and bone development in vivo.
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Affiliation(s)
- Christian Elabd
- ISBDC, Université de Nice Sophia-Antipolis, CNRS, 28 Avenue de Valrose, 06100 Nice, France
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Xiong X, Qi X, Ge X, Gu P, Zhao J, Zhao Q, Gao X. A novel Phex mutation with defective glycosylation causes hypophosphatemia and rickets in mice. J Biomed Sci 2007; 15:47-59. [PMID: 17710565 DOI: 10.1007/s11373-007-9199-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2007] [Accepted: 07/21/2007] [Indexed: 11/30/2022] Open
Abstract
N-ethyl-N-nitrosourea (ENU) mutagenesis is a phenotype-driven approach with potential to assign function to every locus in the mouse genome. In this article, we describe a new mutation, Pug, as a mouse model for X-linked hypophosphatemic rickets (XLH) in human. Mice carrying the Pug mutation exhibit abnormal phenotypes including growth retardation, hypophosphatemia and decreased bone mineral density (BMD). The new mutation was mapped to X-chromosome between 65.4 cM and 66.6 cM, where Phex gene resides. Sequence analysis revealed a unique T-to-C transition mutation resulting in Phe-to-Ser substitution at amino acid 80 of PHEX protein. In vitro studies of Pug mutation demonstrated that PHEX(pug) was incompletely glycosylated and sequestrated in the endoplasmic reticulum region of cell, whereas wild-type PHEX could be fully glycosylated and transported to the plasma membrane to exert its function as an endopeptidase. Taken together, the Pug mutant directly confirms the role of Phex in phosphate homeostasis and normal skeletal development and may serves as a new disease model of human hypophosphatemic rickets.
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Affiliation(s)
- Xiwen Xiong
- Model Animal Research Center, Nanjing University, 12 Xuefu Road, Pukou District, Nanjing, 210061, PR China
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32
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Abstract
BACKGROUND The study of a distinct group of renal phosphate wasting disorders with bone disease which comprise X-linked hypophosphatemic rickets (XLH), autosomal dominant hypophosphatemic rickets (ADHR) and tumour-induced osteomalacia (TIO) gave rise to the identification of different hormone-like peptides, also known as phosphatonins. These factors are responsible for the major disease features that characterize XLH, ADHR and TIO. Recent reports on one of these phosphatonins, fibroblast growth factor-23 (FGF-23), point to a general role of this factor in mineral ion metabolism. OBJECTIVES The main focus regards recent evidence implicating FGF-23 in normal and disordered mineral homeostasis with special emphasis on chronic kidney disease. The interactions of FGF-23 with phosphate, parathyroid hormone and vitamin D are discussed in detail. SUMMARY The FGF-23 has been shown to increase urinary phosphate excretion, inhibit bone mineralization and suppress 1,25-dihydroxy vitamin D(3)[1,25(OH)(2)D(3)], the main characteristics that XLH, ADHR and TIO have in common. Apart from its role in these phosphate wasting disorders serum FGF-23 is elevated in hypoparathyroidism and humoral hypercalcaemia of malignancy and responds to altered dietary phosphate and calcium supply in healthy subjects. The FGF-23 is also variably elevated in chronic kidney disease and associated secondary hyperparathyroidism where it correlates positively with serum phosphate and parathyroid hormone and negatively with 1,25(OH)(2)D(3). Such relationships, along with data from experimental studies, raise the question of whether FGF-23 contributes to the pathophysiology of chronic kidney disease.
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Affiliation(s)
- B Bielesz
- Institute of Physiology, Zurich, Switzerland.
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33
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Baum M, Syal A, Quigley R, Seikaly M. Role of prostaglandins in the pathogenesis of X-linked hypophosphatemia. Pediatr Nephrol 2006; 21:1067-74. [PMID: 16721588 DOI: 10.1007/s00467-006-0126-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/12/2006] [Revised: 02/04/2006] [Accepted: 02/08/2006] [Indexed: 01/18/2023]
Abstract
X-linked hypophosphatemia is an X-linked dominant disorder resulting from a mutation in the PHEX gene. PHEX stands for phosphate-regulating gene with endopeptidase activity, which is located on the X chromosome. Patients with X-linked hypophosphatemia have hypophosphatemia due to renal phosphate wasting and low or inappropriately normal levels of 1,25-dihydroxyvitamin D. The renal phosphate wasting is not intrinsic to the kidney but likely due to an increase in serum levels of fibroblast growth factor-23 (FGF-23), and perhaps other phosphate-wasting peptides previously known as phosphatonins. Patients with X-linked hypophosphatemia have short stature, rickets, bone pain and dental abscesses. Current therapy is oral phosphate and vitamin D which effectively treats the rickets and bone pain but does not adequately improve short stature. In this review, we describe recent observations using Hyp mice; mice with the same mutation as patients with X-linked hypophosphatemia. We have recently found that Hyp mice have abnormal renal prostaglandin production, which may be an important factor in the pathogenesis of this disorder. Administration of FGF-23 in vivo results in phosphaturia and an increase in prostaglandin excretion, and FGF-23 increases proximal tubule prostaglandin production in vitro. In Hyp mice, indomethacin improves the phosphate transport defect in vitro and in vivo. Whether indomethacin has the same effect in patients with X-linked hypophosphatemia is unknown.
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Affiliation(s)
- Michel Baum
- Department of Pediatrics, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75235-9063, USA.
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34
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Abstract
Inactivating mutations of the PHEX (phosphate-regulating gene with homologies to endopeptidases on the X chromosome) endopeptidase, the disease-causing gene in X-linked hypophosphatemia (XLH), results in increased circulating levels of fibroblastic growth factor-23 (FGF23), a bone-derived phosphaturic factor. To determine the causal role of FGF23 in XLH, we generated a combined Fgf23-deficient enhanced green fluorescent protein (eGFP) reporter and Phex-deficient Hyp mouse model (Fgf23(+/-)/Hyp). eGFP expression was expressed in osteocytes embedded in bone that exhibited marked upregulation of eGFP in response to Phex deficiency and in CD31-positive cells in bone marrow venules that expressed low eGFP levels independently of Phex. In bone marrow stromal cells (BMSCs) derived from Fgf23(-/-)/Hyp mice, eGFP expression was also selectively increased in osteocyte-like cells within mineralization nodules and detected in low levels in CD31-positive cells. Surprisingly, eGFP expression was not increased in cell surface osteoblasts, indicating that Phex deficiency is necessary but not sufficient for increased Fgf23 expression in the osteoblast lineage. Additional factors, associated with either osteocyte differentiation and/or extracellular matrix, are necessary for Phex deficiency to stimulate Fgf23 gene transcription in bone. Regardless, the deletion of Fgf23 from Hyp mice reversed the hypophosphatemia, abnormal 1,25(OH)(2)D(3) levels, rickets, and osteomalacia associated with Phex deficiency. These results suggest that Fgf23 acts downstream of Phex to cause both the renal and bone phenotypes in Hyp mice.
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Affiliation(s)
- Shiguang Liu
- The Kidney Institute, The University of Kansas Medical Center, Kansas City, KS 66160, USA.
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35
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Goji K, Ozaki K, Sadewa AH, Nishio H, Matsuo M. Somatic and germline mosaicism for a mutation of the PHEX gene can lead to genetic transmission of X-linked hypophosphatemic rickets that mimics an autosomal dominant trait. J Clin Endocrinol Metab 2006; 91:365-70. [PMID: 16303832 DOI: 10.1210/jc.2005-1776] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
Abstract
CONTEXT Familial hypophosphatemic rickets is usually transmitted as an X-linked dominant disorder (XLH), although autosomal dominant forms have also been observed. Genetic studies of these disorders have identified mutations in PHEX and FGF23 as the causes of X-linked dominant disorder and autosomal dominant forms, respectively. OBJECTIVE The objective of the study was to describe the molecular genetic findings in a family affected by hypophosphatemic rickets with presumed autosomal dominant inheritance. PATIENTS We studied a family in which the father and the elder of his two daughters, but not the second daughter, were affected by hypophosphatemic rickets. The pedigree interpretation of the family suggested that genetic transmission of the disorder occurred as an autosomal dominant trait. METHODS AND RESULTS Direct nucleotide sequencing of FGF23 and PHEX revealed that the elder daughter was heterozygous for an R567X mutation in PHEX, rather than FGF23, suggesting that the genetic transmission occurred as an X-linked dominant trait. Unexpectedly, the father was heterozygous for this mutation. Single-nucleotide primer extension and denaturing HPLC analysis of the father using DNA from single hair roots revealed that he was a somatic mosaic for the mutation. Haplotype analysis confirmed that the father transmitted the genotypes for 18 markers on the X chromosome equally to his two daughters. The fact that the father transmitted the mutation to only one of his two daughters indicated that he was a germline mosaic for the mutation. CONCLUSIONS Somatic and germline mosaicism for an X-linked dominant mutation in PHEX may mimic autosomal dominant inheritance.
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Affiliation(s)
- Katsumi Goji
- Department of Endocrinology and Metabolism, Kobe Children's Hospital, 1-1-1 Takakuradai, Suma-ku, Kobe 654-0081, Japan.
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36
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Alos N, Ecarot B. Downregulation of osteoblast Phex expression by PTH. Bone 2005; 37:589-98. [PMID: 16084134 DOI: 10.1016/j.bone.2005.05.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2005] [Revised: 04/25/2005] [Accepted: 05/04/2005] [Indexed: 01/28/2023]
Abstract
Human/murine X-linked hypophosphatemia is a dominant disorder associated with renal phosphate wasting and defective bone mineralization. This disorder results from mutations in the PHEX/Phex (Phosphate-regulating gene with homologies to endopeptidases on the X chromosome) gene, which is expressed in fully differentiated osteoblasts. The purpose of the present study was to assess whether PTH, a major regulator of bone development and turnover, modulates osteoblastic Phex expression. The effects of different concentrations of PTH (rat fragment 1-34) were determined on Phex mRNA and protein expression in vitro using MC3T3-E1 osteoblastic cells and mouse primary osteoblasts; and in vivo using 45-day-old mice infused for 3 days with PTH. Phex mRNA levels were quantitated on Northern blots by densitometric analysis relative to GAPDH mRNA levels. Phex protein levels were analyzed by immunoprecipitation of 35S-methionine-labeled osteoblast lysates or by immunoblotting of calvaria membrane extracts using a polyclonal rabbit antiserum raised against a mouse Phex carboxy-terminal peptide. Fully differentiated MC3T3-E1 cells were incubated for 4 to 48 h with increasing concentrations of PTH (10(-11) to 10(-7) M). PTH inhibited Phex mRNA expression in both mineralizing and nonmineralizing osteoblast cultures in a dose- and time-dependent manner with a maximal inhibition at 10(-7) M PTH after 24 h (15+/-7% of control levels, n=5, P<0.001). The PTH-mediated downregulation of Phex mRNA levels was associated with corresponding decreases in Phex protein synthesis and suppression at 10(-7) M PTH. Similar results were obtained with primary osteoblasts isolated from newborn mouse calvaria. Consistent with the in vitro findings, continuous PTH infusion to mice elicited decreases in Phex expression in calvaria. The effect of PTH was also assessed on matrix mineralization by mature MC3T3-E1 cells by measuring 45Ca accumulation in cell layers. PTH (10(-7) M) inhibited the initiation (57+/-2% of control levels, n=5, P<0.001) and the progression of matrix mineralization (75+/-1% of control levels, n=5, P<0.001). In summary, PTH inhibits osteoblastic Phex expression in vitro and in vivo. The downregulation of Phex expression by PTH in vitro is associated with inhibition of matrix mineralization, consistent with a role for Phex in bone mineralization.
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Affiliation(s)
- Nathalie Alos
- Genetics Unit, Shriners Hospital, Departments of Surgery and Human Genetics, McGill University, Montreal, Quebec, Canada.
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37
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Gu G, Nars M, Hentunen TA, Metsikkö K, Väänänen HK. Isolated primary osteocytes express functional gap junctions in vitro. Cell Tissue Res 2005; 323:263-71. [PMID: 16175387 DOI: 10.1007/s00441-005-0066-3] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2005] [Accepted: 07/25/2005] [Indexed: 11/26/2022]
Abstract
The osteocyte is the most abundant cell type in bone and is embedded in mineralized bone matrix. Osteocytes are still poorly characterized because of their location and the lack of primary osteocyte isolation methods. Data on the cell biology of osteocytes is especially limited. We have isolated primary osteocytes from rat cortical bone by applying repeated enzymatic digestion and decalcification. The isolated osteocytes expressed typical osteocytic morphology with cell-cell contacts via long protrusions after a 1-day culture. These cells were negative or faintly positive for alkaline phosphatase but expressed high levels of osteocalcin, PHEX (phosphate-regulating gene with homology to endopeptidases on the X chromosome), and DMP1 (dentin matrix protein 1). These cells also revealed patchy membrane staining for connexin43. For studying the function of gap junctions in isolated osteocytes, we microinjected rhodamine-labeled dextran (MW: 10,000) and Lucifer yellow (MW: 457) and found that Lucifer yellow was rapidly transmitted to several surrounding cells, whereas dextran remained in the injected cells. Heptanol and 18alpha-glycyrrhetinic acid inhibited the transfer of Lucifer yellow. This clearly showed the existence of functional gap junctions in cultured osteocytes. Enveloped viruses, such as vesicular stomatitis virus and influenza A virus, were used for studying cell polarity. We were unable to demonstrate plasma membrane polarization with enveloped viruses in isolated primary osteocytes in culture. Our results suggest that osteocytes do not possess apical and basolateral plasma membrane domains as do osteoblasts, which are their precursors.
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Affiliation(s)
- Guoliang Gu
- Department of Anatomy, Institute of Biomedicine, University of Turku, Turku 20520, Finland
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38
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Günther T, Poli C, Müller JM, Catala-Lehnen P, Schinke T, Yin N, Vomstein S, Amling M, Schüle R. Fhl2 deficiency results in osteopenia due to decreased activity of osteoblasts. EMBO J 2005; 24:3049-56. [PMID: 16079911 PMCID: PMC1201354 DOI: 10.1038/sj.emboj.7600773] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2005] [Accepted: 07/14/2005] [Indexed: 11/09/2022] Open
Abstract
Osteoporosis is one of the major health problems today, yet little is known about the loss of bone mass caused by reduced activity of the bone-forming osteoblasts. Here we show that mice deficient for the transcriptional cofactor four and a half LIM domains 2 (Fhl2) exhibit a dramatic decrease of bone mass in both genders. Osteopenia is caused by a reduced bone formation rate that is solely due to the diminished activity of Fhl2-deficient osteoblasts, while their number remains unchanged. The number and activity of the bone-resorbing cells, the osteoclasts, is not altered. Enforced expression of Fhl2 in differentiated osteoblasts boosts mineralization in cell culture and, importantly, enhances bone formation in transgenic animals. Fhl2 increases the transcriptional activity of runt-related transcription factor 2 (Runx2), a key regulator of osteoblast function, and both proteins interact in vitro and in vivo. In summary, we present Fhl2-deficient mice as a unique model for osteopenia due to decreased osteoblast activity. Our data offer a novel concept to fight osteoporosis by modulating the anabolic activity of osteoblasts via Fhl2.
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Affiliation(s)
- Thomas Günther
- Universitäts-Frauenklinik und Zentrum für Klinische Forschung, Klinikum der Universität Freiburg, Freiburg, Germany
| | - Cecilia Poli
- Universitäts-Frauenklinik und Zentrum für Klinische Forschung, Klinikum der Universität Freiburg, Freiburg, Germany
| | - Judith M Müller
- Universitäts-Frauenklinik und Zentrum für Klinische Forschung, Klinikum der Universität Freiburg, Freiburg, Germany
| | - Philip Catala-Lehnen
- Department of Trauma, Hand and Reconstructive Surgery, Hamburg University School of Medicine, Hamburg, Germany
- Experimental Trauma Surgery and Skeletal Biology, Center for Biomechanics, Hamburg University School of Medicine, Hamburg, Germany
| | - Thorsten Schinke
- Department of Trauma, Hand and Reconstructive Surgery, Hamburg University School of Medicine, Hamburg, Germany
- Experimental Trauma Surgery and Skeletal Biology, Center for Biomechanics, Hamburg University School of Medicine, Hamburg, Germany
| | - Na Yin
- Universitäts-Frauenklinik und Zentrum für Klinische Forschung, Klinikum der Universität Freiburg, Freiburg, Germany
| | - Sandra Vomstein
- Universitäts-Frauenklinik und Zentrum für Klinische Forschung, Klinikum der Universität Freiburg, Freiburg, Germany
| | - Michael Amling
- Department of Trauma, Hand and Reconstructive Surgery, Hamburg University School of Medicine, Hamburg, Germany
- Experimental Trauma Surgery and Skeletal Biology, Center for Biomechanics, Hamburg University School of Medicine, Hamburg, Germany
| | - Roland Schüle
- Universitäts-Frauenklinik und Zentrum für Klinische Forschung, Klinikum der Universität Freiburg, Freiburg, Germany
- Zentrum für Klinische Forschung, Molekulare Gynäkologie, Universitäts-Frauenklinik, Breisacherstr. 66, 79106 Freiburg, Germany. Tel.: +49 761 270 6310; Fax: +49 761 270 6311; E-mail:
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Erben RG, Mayer D, Weber K, Jonsson K, Jüppner H, Lanske B. Overexpression of human PHEX under the human beta-actin promoter does not fully rescue the Hyp mouse phenotype. J Bone Miner Res 2005; 20:1149-60. [PMID: 15940367 DOI: 10.1359/jbmr.050212] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/28/2004] [Revised: 01/29/2005] [Accepted: 02/18/2005] [Indexed: 12/13/2022]
Abstract
UNLABELLED XLH in humans and the Hyp phenotype in mice are caused by inactivating Phex mutations. Overexpression of human PHEX under the human beta-actin promoter in Hyp mice rescued the bone phenotype almost completely, but did not affect phosphate homeostasis, suggesting that different, possibly independent, pathophysiological mechanisms contribute to hyperphosphaturia and bone abnormalities in XLH. INTRODUCTION Mutations in PHEX, a phosphate-regulating gene with homologies to endopeptidases on the X chromosome, are responsible for X-linked hypophosphatemia (XLH) in humans, and its mouse homologs, Hyp, Phex(Hyp-2J), Phex(Hyp-Duk), Gy, and Ska1. PHEX is thought to inactivate a phosphaturic factor, which may be fibroblast growth factor 23 (FGF)-23. Consistent with this hypothesis, FGF-23 levels were shown to be elevated in most patients with XLH and in Hyp mice. The aim of this study was, therefore, to examine whether transgenic overexpression of PHEX under the human beta-actin promoter would rescue the Hyp phenotype. MATERIALS AND METHODS We tested this hypothesis by generating two mouse lines expressing human PHEX under the control of a human beta-actin promoter (PHEX-tg). With the exception of brain, RT-PCR analyses showed transgene expression in all tissues examined. PHEX protein, however, was only detected in bone, muscle, lung, skin, and heart. To assess the role of the mutant PHEX, we crossed female heterozygous Hyp mice with male heterozygous PHEX-tg mice to obtain wildtype (WT), PHEX-tg, Hyp, and Hyp/PHEX-tg offspring, which were examined at 3 months of age. RESULTS PHEX-tg mice exhibited normal bone and mineral ion homeostasis. Hyp mice showed the known phenotype with reduced body weight, hypophosphatemia, hyperphosphaturia, and rickets. Hyp/PHEX-tg mice had almost normal body weight relative to WT controls, showed a dramatic improvement in femoral BMD, almost normal growth plate width, and, despite remaining disturbances in bone mineralization, almost normal bone architecture and pronounced improvements of osteoidosis and of halo formation compared with Hyp mice. However, Hyp and Hyp/PHEX-tg mice had comparable reductions in tubular reabsorption of phosphate and were hypophosphatemic relative to WT controls. CONCLUSION Our data suggest that different, possibly independent, pathophysiological mechanisms contribute to renal phosphate wasting and bone abnormalities in Hyp and XLH.
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Affiliation(s)
- Reinhold G Erben
- Institute of Physiology, Physiological Chemistry and Animal Nutrition, Ludwig Maximilians University, Munich, Germany
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Liu S, Brown TA, Zhou J, Xiao ZS, Awad H, Guilak F, Quarles LD. Role of matrix extracellular phosphoglycoprotein in the pathogenesis of X-linked hypophosphatemia. J Am Soc Nephrol 2005; 16:1645-53. [PMID: 15843468 PMCID: PMC1484502 DOI: 10.1681/asn.2004121060] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
X-linked hypophosphatemia (XLH), a disorder characterized by hypophosphatemia, impaired skeletal mineralization, and aberrant regulation of 1, 25(OH)(2)D(3), is caused by inactivating mutations of Phex, which results in the accumulation of putative phosphaturic factors, called phosphatonins. Matrix extracellular phosphoglycoprotein (Mepe) is a proposed candidate for phosphatonin. The authors found that Hyp mice had increased expression of the MEPE and another phosphaturic factor, Fgf23. To establish MEPE's role in the pathogenesis of the XLH, Mepe-deficient mice were back-crossed onto the Hyp mouse homologue of XLH and phenotypes of wild-type, Mepe(-/-), Hyp, and Mepe(-/-)/Hyp mice were examined. Transfer of Mepe deficiency onto the Phex-deficient Hyp mouse background failed to correct hypophosphatemia and aberrant serum 1,25(OH)(2)D(3) levels. Increased Fgf23 levels in Hyp mice were not affected by superimposed Mepe deficiency. In addition, Mepe-deficient Hyp mice retained bone mineralization defects in vivo, characterized by decreased bone mineral density, reduced mineralized trabecular bone volume, lower flexural strength, and histologic evidence of osteomalacia; however, cultures of Hyp-derived bone marrow stromal cells in the absence of Mepe showed improved mineralization and normalization of osteoblast gene expression profiles observed in cells derived from Mepe-null mice. These results demonstrate that MEPE elevation in Hyp mice does not contribute to the hypophosphatemia associated with inactivating Phex mutations and is therefore not phosphatonin.
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Affiliation(s)
- Shiguang Liu
- Department of Internal Medicine and the Kidney Institute, the University of Kansas Medical Center, Kansas City, Kansas
| | - Thomas A. Brown
- Groton Laboratories, Pfizer Global Research and Development, Groton, Connecticut
| | - Jianping Zhou
- Department of Internal Medicine and the Kidney Institute, the University of Kansas Medical Center, Kansas City, Kansas
| | - Zhou-Sheng Xiao
- Department of Internal Medicine and the Kidney Institute, the University of Kansas Medical Center, Kansas City, Kansas
| | - Hani Awad
- Department of Surgery, Duke University Medical Center, Durham, North Carolina
| | - Farshid Guilak
- Department of Surgery, Duke University Medical Center, Durham, North Carolina
| | - L. Darryl Quarles
- Department of Internal Medicine and the Kidney Institute, the University of Kansas Medical Center, Kansas City, Kansas
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41
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Drezner MK. X-Linked Hypophosphatemia: New Horizons. Clin Pediatr Endocrinol 2005. [DOI: 10.1297/cpe.14.s23_21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
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Mirams M, Robinson BG, Mason RS, Nelson AE. Bone as a source of FGF23: regulation by phosphate? Bone 2004; 35:1192-9. [PMID: 15542045 DOI: 10.1016/j.bone.2004.06.014] [Citation(s) in RCA: 167] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/14/2004] [Revised: 06/03/2004] [Accepted: 06/21/2004] [Indexed: 12/11/2022]
Abstract
The identification of FGF23 as a factor involved in several disorders of phosphate regulation and of PHEX as the gene mutated in X-linked Hypophosphatemic Rickets indicates that both these genes may be involved in phosphate homeostasis, although their physiological roles are unclear. In this study, FGF23 mRNA expression was analyzed by real-time RT-PCR and found to be higher in normal human bone than in kidney, liver, thyroid, or parathyroid tissue, while expression in oncogenic osteomalacia tumor tissue was several hundred-fold higher than in bone. Expression of FGF23 mRNA in human osteoblast-like bone cells, quantitated by real-time RT-PCR, increased with increasing extracellular phosphate and was 2-fold higher in cells treated with 2 mM extracellular phosphate compared to 0 mM phosphate treatment. PHEX mRNA expression increased 1.3-fold after treatment with 2 mM phosphate. FGF23 expression in the bone cells increased with increased mineralization over a 20-day treatment period under mineralizing conditions with beta-glycerophosphate, while PHEX expression decreased. The results indicate that FGF23 mRNA expression in bone cells is regulated by extracellular phosphate and by mineralization. These results support proposals that bone may be a source of circulating FGF23 and suggest that FGF23 expression by bone is regulated.
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Affiliation(s)
- Michiko Mirams
- Department of Physiology, Institute for Biomedical Research F13, University of Sydney, Sydney NSW 2006, Australia.
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Baum M, Moe OW, Zhang J, Dwarakanath V, Quigley R. Phosphatonin washout in Hyp mice proximal tubules: evidence for posttranscriptional regulation. Am J Physiol Renal Physiol 2004; 288:F363-70. [PMID: 15454393 PMCID: PMC4129231 DOI: 10.1152/ajprenal.00217.2004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
X-linked hypophosphatemia is the most common inherited form of rickets. It is characterized by renal phosphate wasting, leading to hypophosphatemia and an inappropriately normal or low serum level of 1,25(OH)2 vitamin D. Previous studies have pointed to a circulating factor or phosphatonin-inhibiting phosphate transport by decreasing mRNA of the proximal tubule NaP(i) cotransporter NaPi-2A. The present study examined the hypothesis that there was also posttranscriptional regulation of the NaPi-2A cotransporter in Hyp mice proximal tubules and whether the phosphate transport defect in Hyp mice persisted when they were studied in vitro. We found that the rate of phosphate transport in Hyp mice was <50% that in C57/B6 control mice. While phosphate transport remained stable during incubation with time in C57/B6 mice proximal tubules, it increased from 0.46 +/- 0.47 to 1.83 +/- 0.40 pmol x mm(-1) x min(-1) in Hyp proximal tubules (P < 0.01) consistent with phosphatonin washout in Hyp proximal tubules perfused in vitro. This time-dependent increase in phosphate transport was still observed in the presence of cycloheximide. There was also a reduction of proximal tubule apical NaPi-2A expression from Hyp mice compared with C57/B6 mice using single-tubule immunohistochemistry. Using immunohistochemistry, we demonstrate an increase in apical expression of the NaPi-2A transporter in proximal tubules perfused in vitro in Hyp mice even in the presence of bath cycloheximide. The increase in apical expression of the NaPi-2A transporter in proximal tubules perfused in vitro in Hyp mice was blocked by colchicine. These data are consistent with a rapidly reversible posttranscriptional defect in Hyp mice causing a reduction in phosphate transport.
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Affiliation(s)
- Michel Baum
- Department of Pediatrics, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75235-9063, USA.
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Rowe PSN. The wrickkened pathways of FGF23, MEPE and PHEX. CRITICAL REVIEWS IN ORAL BIOLOGY AND MEDICINE : AN OFFICIAL PUBLICATION OF THE AMERICAN ASSOCIATION OF ORAL BIOLOGISTS 2004; 15:264-81. [PMID: 15470265 PMCID: PMC3361894 DOI: 10.1177/154411130401500503] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The last 350 years since the publication of the first medical monograph on rickets (old English term wrickken) (Glisson et al., 1651) have seen spectacular advances in our understanding of mineral-homeostasis. Seminal and exciting discoveries have revealed the roles of PTH, vitamin D, and calcitonin in regulating calcium and phosphate, and maintaining healthy teeth and skeleton. However, it is clear that the PTH/Vitamin D axis does not account for the entire picture, and a new bone-renal metabolic milieu has emerged, implicating a novel set of matrix proteins, hormones, and Zn-metallopeptidases. The primary defects in X-linked hypophosphatemic rickets (HYP) and autosomal-dominant hypophosphatemic rickets (ADHR) are now identified as inactivating mutations in a Zn-metalloendopeptidase (PHEX) and activating mutations in fibroblast-growth-factor-23 (FGF23), respectively. In oncogenic hypophosphatemic osteomalacia (OHO), several tumor-expressed proteins (MEPE, FGF23, and FRP-4) have emerged as candidate mediators of the bone-renal pathophysiology. This has stimulated the proposal of a global model that takes into account the remarkable similarities between the inherited diseases (HYP and ADHR) and the tumor-acquired disease OHO. In HYP, loss of PHEX function is proposed to result in an increase in uncleaved full-length FGF23 and/or inappropriate processing of MEPE. In ADHR, a mutation in FGF23 results in resistance to proteolysis by PHEX or other proteases and an increase in half-life of full-length phosphaturic FGF23. In OHO, over-expression of FGF23 and/or MEPE is proposed to result in abnormal renal-phosphate handling and mineralization. Although this model is attractive, many questions remain unanswered, suggesting a more complex picture. The following review will present a global hypothesis that attempts to explain the experimental and clinical observations in HYP, ADHR, and OHO, plus diverse mouse models that include the MEPE null mutant, HYP-PHEX transgenic mouse, and MEPE-PHEX double-null-mutant.
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Affiliation(s)
- Peter S N Rowe
- Department of Periodontics, The University of Texas Health Science Center at San Antonio, Mail Code 7894, 7703 Floyd Curl Drive, Room 3.579U, San Antonio, TX 78229-3900, USA.
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Miao D, Bai X, Panda DK, Karaplis AC, Goltzman D, McKee MD. Cartilage abnormalities are associated with abnormal Phex expression and with altered matrix protein and MMP-9 localization in Hyp mice. Bone 2004; 34:638-47. [PMID: 15050894 DOI: 10.1016/j.bone.2003.12.015] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/26/2003] [Revised: 12/05/2003] [Accepted: 12/11/2003] [Indexed: 11/16/2022]
Abstract
X-linked hypophosphatemic rickets (HYP) in humans is caused by mutations in the PHEX gene. This gene mutation is also found in Hyp mice, the murine homologue of the human disease. At present, it is unknown why loss of Phex function leads to cartilage abnormalities in Hyp mice. In the present study, we compared in wild-type and Hyp mice Phex protein localization in cartilage of developing long bone as well as localization of skeletal matrix proteins and matrix metalloproteinase-9 (MMP-9). Also compared were chondrocyte apoptosis in the growth plate, mineralization and cartilage remnant retention in the metaphysis, and chondroclast/osteoclast characteristics in the primary spongiosa. Phex protein was detected in proliferating and hypertrophic chondrocytes in growth plate cartilage of wild-type mice, but not in Hyp mice. Hyp mice exhibited a widened and irregular hypertrophic zone in growth plate cartilage showing hypomineralization, increased cartilage remnants from the growth plate in both metaphyseal trabecular and cortical bone, and fewer and smaller chondroclasts/osteoclasts in the primary spongiosa. Increased link protein and C-propeptide of type II procollagen of Hyp mice reflected the increase in chondrocytes and matrix in the cartilaginous growth plate and in bone. In addition, growth plate osteocalcin and bone sialoprotein levels were decreased, while osteonectin was increased, in hypertrophic chondrocytes and cartilage matrix in Hyp mice. MMP-9 in hypertrophic chondrocytes was also reduced in Hyp mice and fewer apoptotic hypertrophic chondrocytes were detected. These findings suggest that Phex may control mineralization and removal of hypertrophic chondrocytes and cartilage matrix in growth plate by regulating the synthesis and deposition of certain bone matrix proteins and proteases such as MMP-9.
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Affiliation(s)
- Dengshun Miao
- Department of Medicine, McGill University, Montreal, QC, Canada
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Hayashibara T, Hiraga T, Yi B, Nomizu M, Kumagai Y, Nishimura R, Yoneda T. A synthetic peptide fragment of human MEPE stimulates new bone formation in vitro and in vivo. J Bone Miner Res 2004; 19:455-62. [PMID: 15040834 DOI: 10.1359/jbmr.0301263] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2003] [Revised: 09/02/2003] [Accepted: 10/03/2003] [Indexed: 01/16/2023]
Abstract
UNLABELLED Matrix extracellular phosphoglycoprotein (MEPE) was proposed as a candidate for the phosphaturic hormone phosphatonin. We found that a synthetic peptide fragment of MEPE containing the RGD and SGDG sequence stimulated new bone formation in vitro and in vivo. INTRODUCTION Matrix extracellular phosphoglycoprotein (MEPE) was recently identified as a candidate for the phosphaturic hormone phosphatonin, which has been implicated in disturbed phosphate metabolism, rickets, and osteomalacia associated with X-linked hypophosphatemic rickets (XLH) and oncogenic hypophosphatemic osteomalacia (OHO). MEPE expression was predominantly found in osteoblasts, and mice deficient in a homolog of MEPE showed increased bone density, suggesting that MEPE produced in osteoblasts negatively regulates bone formation. In this study, we examined the effects of a synthetic 23mer peptide fragment of MEPE (AC-100, region 242-264) containing the RGD (integrin-binding) and SGDG (glycosaminoglycan-attachment) motif on bone formation in vitro and in vivo. MATERIALS AND METHODS The osteogenic activity of AC-100 was examined in organ cultures of neonatal mouse calvariae and in vivo by injecting AC-100 onto the calvariae of mice. RESULTS Histomorphometric examination showed that AC-100 stimulated new bone formation with increased numbers of osteoblasts in neonatal mouse calvariae in organ culture. In contrast, synthetic MEPE fragment peptides without either the RGD or SGDG motif failed to increase new bone formation. Repeated daily subcutaneous injections of AC-100 onto the calvariae in mice increased bone thickness and stimulated new bone formation as determined by the calcein double-labeling technique. However, peptides in which the RGD or SGDG sequence was scrambled did not stimulate new bone formation in vivo. AC-100 increased cell proliferation and alkaline phosphatase activity and activated focal adhesion kinase (FAK) and extracellular signal-regulated protein kinase (ERK) in human primary osteoblasts. CONCLUSION Our results show that a synthetic peptide corresponding with the sequence of human MEPE fragment stimulates new bone formation with increased number of osteoblasts. The results also suggest that the RGD and SGDG motifs are critical to the osteogenic activity of AC-100, presumably through activating integrin signaling pathways in osteoblasts. The anabolic effects of AC-100 may be beneficial for bone diseases associated with decreased bone formation.
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Affiliation(s)
- Tetsuyuki Hayashibara
- Department of Biochemistry, Graduate School of Dentistry, Osaka University, Suita, Osaka, Japan
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Rowe PSN, Kumagai Y, Gutierrez G, Garrett IR, Blacher R, Rosen D, Cundy J, Navvab S, Chen D, Drezner MK, Quarles LD, Mundy GR. MEPE has the properties of an osteoblastic phosphatonin and minhibin. Bone 2004; 34:303-19. [PMID: 14962809 PMCID: PMC3357088 DOI: 10.1016/j.bone.2003.10.005] [Citation(s) in RCA: 216] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/11/2003] [Revised: 10/20/2003] [Accepted: 10/22/2003] [Indexed: 11/23/2022]
Abstract
Matrix extracellular phosphoglycoprotein (MEPE) is expressed exclusively in osteoblasts, osteocytes and odontoblasts with markedly elevated expression found in X-linked hypophosphatemic rickets (Hyp) osteoblasts and in oncogenic hypophosphatemic osteomalacia (OHO) tumors. Because these syndromes are associated with abnormalities in mineralization and renal phosphate excretion, we examined the effects of insect-expressed full-length human-MEPE (Hu-MEPE) on serum and urinary phosphate in vivo, (33)PO(4) uptake in renal proximal tubule cultures and mineralization of osteoblast cultures. Dose-dependent hypophosphatemia and hyperphosphaturia occurred in mice following intraperitoneal (IP) administration of Hu-MEPE (up to 400 microg kg(-1) 31 h(-1)), similar to mice given the phosphaturic hormone PTH (80 microg kg(-1) 31 h(-1)). Also the fractional excretion of phosphate (FEP) was stimulated by MEPE [65.0% (P < 0.001)] and PTH groups [53.3% (P < 0.001)] relative to the vehicle group [28.7% (SEM 3.97)]. In addition, Hu-MEPE significantly inhibited (33)PO(4) uptake in primary human proximal tubule renal cells (RPTEC) and a human renal cell line (Hu-CL8) in vitro (V(max) 53.4% inhibition; K(m) 27.4 ng/ml, and V(max) 9.1% inhibition; K(m) 23.8 ng/ml, respectively). Moreover, Hu-MEPE dose dependently (50-800 ng/ml) inhibited BMP2-mediated mineralization of a murine osteoblast cell line (2T3) in vitro. Inhibition of mineralization was localized to a small (2 kDa) cathepsin B released carboxy-terminal MEPE peptide (protease-resistant) containing the acidic serine-aspartate-rich motif (ASARM peptide). We conclude that MEPE promotes renal phosphate excretion and modulates mineralization.
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Affiliation(s)
- P S N Rowe
- Department of Periodontics, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA.
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Vargas MA, St-Louis M, Desgroseillers L, Charli JL, Boileau G. Parathyroid hormone-related protein(1-34) regulates Phex expression in osteoblasts through the protein kinase A pathway. Endocrinology 2003; 144:4876-85. [PMID: 12960044 DOI: 10.1210/en.2003-0253] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Phex (a phosphate-regulating gene with homologies to endopeptidases on the X chromosome) is expressed predominantly in bone in which it has been implicated in the mineralization process. Multiple factors and hormones, including PTHrP, regulate formation, development, and/or homeostasis of bone. The purpose of the present study was to determine whether PTHrP(1-34) regulates Phex expression and identify the signaling pathway used. Phex mRNA and protein levels were analyzed by RT-PCR and immunoblotting, respectively. In UMR-106 cells, PTHrP(1-34) caused a time- and concentration-dependent decrease in Phex expression. Forskolin, an adenylate cyclase activator, had the same effect. Dibutiryl cAMP also decreased Phex expression, and its effect was blocked by H89, a protein kinase A (PKA) inhibitor. In contrast, 12-O-tetradecanoyl phorbol-13-acetate, a protein kinase C (PKC) activator, increased Phex expression in a time- and dose-dependent manner. This effect was reversed by bisindolylmaleimide Iota, a PKC inhibitor. Bovine PTH(3-34), which activates PKC but not PKA, had no effect. On the contrary, human PTH(1-31), which activates PKA but not PKC, decreased Phex expression. H89 but not bisindolylmaleimide Iota blocked the effect of PTHrP(1-34). PTHrP(1-34) also decreased Phex expression in cultures of fetal rat calvaria cells at d 7 of culture but not at later stages. These data demonstrate that PTHrP(1-34), through PKA, down-regulates Phex expression in osteoblasts.
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Affiliation(s)
- Miguel Angel Vargas
- Département de Biochimie, Faculté de Médecine, Université de Montréal, Montréal, Québec, Canada H3C 3J7
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Liu S, Guo R, Simpson LG, Xiao ZS, Burnham CE, Quarles LD. Regulation of fibroblastic growth factor 23 expression but not degradation by PHEX. J Biol Chem 2003; 278:37419-26. [PMID: 12874285 DOI: 10.1074/jbc.m304544200] [Citation(s) in RCA: 360] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Inactivating mutations of Phex cause X-linked hypophosphatemia (XLH) by increasing levels of a circulating phosphaturic factor. FGF23 is a candidate for this phosphaturic factor. Elevated serum FGF23 levels correlate with the degree of hypophosphatemia in XLH, suggesting that loss of Phex function in this disorder results in either diminished degradation and/or increased biosynthesis of FGF23. To establish the mechanisms whereby Phex regulates FGF23, we assessed Phex-dependent hydrolysis of recombinant FGF23 in vitro and measured fgf23 message levels in the Hyp mouse homologue of XLH. In COS-7 cells, overexpression of FGF23 resulted in its degradation into N- and C-terminal fragments by an endogenous decanoyl-Arg-Val-Lys-Arg-chloromethyl ketone-sensitive furin-type convertase. Phex-dependent hydrolysis of full-length FGF23 or its N- and C-terminal fragments could not be demonstrated in the presence or absence of decanoyl-Arg-Val-Lys-Arg-chloromethyl ketone in COS-7 cells expressing Phex and FGF23. In a reticulolysate system, apparent cleavage of FGF23 occurred with wild-type Phex, the inactive Phex-3'M mutant, and vector controls, indicating nonspecific metabolism of FGF23 by contaminating enzymes. These findings suggest that FGF23 is not a direct Phex substrate. In contrast, by real-time reverse transcriptase PCR, the levels of fgf23 transcripts were highest in bone, the predominant site of Phex expression. In addition, Hyp mice displayed a bone-restricted increase in fgf23 transcripts in association with inactivating Phex mutations. Increased expression of fgf23 was also observed in Hyp-derived osteoblasts in culture. These findings suggest that Phex, possibly through the actions of unidentified Phex substrates or other downstream effectors, regulates fgf23 expression as part of a potential hormonal axis between bone and kidney that controls systemic phosphate homeostasis and mineralization.
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Affiliation(s)
- Shiguang Liu
- Department of Medicine, Center for Bone and Mineral Disorders, Duke University Medical Center, Durham, North Carolina 27710, USA
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Baum M, Loleh S, Saini N, Seikaly M, Dwarakanath V, Quigley R. Correction of proximal tubule phosphate transport defect in Hyp mice in vivo and in vitro with indomethacin. Proc Natl Acad Sci U S A 2003; 100:11098-103. [PMID: 12953100 PMCID: PMC196933 DOI: 10.1073/pnas.1834060100] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2003] [Accepted: 07/08/2003] [Indexed: 01/12/2023] Open
Abstract
X-linked hypophosphatemia is the most prevalent inherited form of rickets. In this disorder, rickets results from hyperphosphaturia and inappropriately normal levels of 1,25(OH)2-vitamin D. Current therapy with oral phosphate and vitamin D improves the rickets, but has significant morbidity and does not significantly affect the short stature and hypophosphatemia. In the present study, we demonstrate that Hyp mice, which have a mutation homologous to that in patients with X-linked hypophosphatemia, have a 2-fold greater urinary prostaglandin E2 (PGE2) excretion than C57/B6 mice. To determine whether PGs were involved in the pathogenesis of this disorder, Hyp and C57/B6 mice received i.p. injections with vehicle or indomethacin (1 mg/kg of body weight twice daily for 4 days) and were studied approximately 12 h after the last dose of indomethacin. In the Hyp mice, indomethacin treatment decreased the fractional excretion of phosphate from 13.0 +/- 3.2% to 2.2 +/- 1.1% (P < 0.05), and increased serum phosphate from 2.9 +/- 0.2 mg/dl to 4.1 +/- 0.2 mg/dl (P < 0.05). There was no effect of indomethacin in C57/B6 mice. Indomethacin did not affect serum creatinine or inulin clearance, demonstrating that the normalization of urinary phosphate excretion was not caused by changes in glomerular filtration rate. Indomethacin treatment increased renal brush border membrane vesicle NaPi-2 protein abundance in Hyp mice to levels comparable to that of C57/B6 mice, but had no effect in C57/B6 mice. In vitro isolated perfused proximal tubule studies demonstrate directly that 10-6 M bath indomethacin normalized the phosphate transport defect in Hyp mice but had no effect on C57/B6 mice. In conclusion, there is dysregulation of renal PG metabolism in Hyp mice, and indomethacin treatment normalizes the urinary excretion of phosphate by a direct tubular effect.
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Affiliation(s)
- Michel Baum
- Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, TX 75235-9063, USA.
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