1
|
Nakanishi T, Yamazaki M, Tachikawa K, Ueta A, Kawai M, Ozono K, Michigami T. Complex intrinsic abnormalities in osteoblast lineage cells of X-linked hypophosphatemia: Analysis of human iPS cell models generated by CRISPR/Cas9-mediated gene ablation. Bone 2024; 181:117044. [PMID: 38331306 DOI: 10.1016/j.bone.2024.117044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/16/2023] [Revised: 01/04/2024] [Accepted: 02/05/2024] [Indexed: 02/10/2024]
Abstract
X-linked hypophosphatemia (XLH) is caused by inactivating variants of the phosphate regulating endopeptidase homolog X-linked (PHEX) gene. Although the overproduction of fibroblast growth factor 23 (FGF23) is responsible for hypophosphatemia and impaired vitamin D metabolism, the pathogenesis of XLH remains unclear. We herein generated PHEX-knockout (KO) human induced pluripotent stem (iPS) cells by applying CRISPR/Cas9-mediated gene ablation to an iPS clone derived from a healthy male, and analyzed PHEX-KO iPS cells with deletions extending from exons 1 to 3 and frameshifts by inducing them to differentiate into the osteoblast lineage. We confirmed the increased production of FGF23 in osteoblast lineage cells differentiated from PHEX-KO iPS cells. In vitro mineralization was enhanced in osteoblast lineage cells from PHEX-KO iPS cells than in those from isogenic control iPS cells, which reminded us of high bone mineral density and enthesopathy in patients with XLH. The extracellular level of pyrophosphate (PPi), an inhibitor of mineralization, was elevated, and this increase appeared to be partly due to the reduced activity of tissue non-specific alkaline phosphatase (TNSALP). Osteoblast lineage cells derived from PHEX-KO iPS cells also showed the increased expression of multiple molecules such as dentine matrix protein 1, osteopontin, RUNX2, FGF receptor 1 and early growth response 1. This gene dysregulation was similar to that in the osteoblasts/osteocytes of Phex-deficient Hyp mice, suggesting that common pathogenic mechanisms are shared between human XLH and Hyp mice. Moreover, we found that the phosphorylation of CREB was markedly enhanced in osteoblast lineage cells derived from PHEX-KO iPS cells, which appeared to be associated with the up-regulation of the parathyroid hormone related protein gene. PHEX deficiency also affected the response of the ALPL gene encoding TNSALP to extracellular Pi. Collectively, these results indicate that complex intrinsic abnormalities in osteoblasts/osteocytes underlie the pathogenesis of human XLH.
Collapse
Affiliation(s)
- Tatsuro Nakanishi
- Department of Bone and Mineral Research, Research Institute, Osaka Women's and Children's Hospital, Osaka Prefectural Hospital Organization, Izumi, Osaka 594-1101, Japan; Department of Pediatrics, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871, Japan
| | - Miwa Yamazaki
- Department of Bone and Mineral Research, Research Institute, Osaka Women's and Children's Hospital, Osaka Prefectural Hospital Organization, Izumi, Osaka 594-1101, Japan
| | - Kanako Tachikawa
- Department of Bone and Mineral Research, Research Institute, Osaka Women's and Children's Hospital, Osaka Prefectural Hospital Organization, Izumi, Osaka 594-1101, Japan
| | - Ayu Ueta
- Department of Bone and Mineral Research, Research Institute, Osaka Women's and Children's Hospital, Osaka Prefectural Hospital Organization, Izumi, Osaka 594-1101, Japan; 1st Department of Oral and Maxillofacial Surgery, Osaka University Graduate School of Dentistry, Suita, Osaka 565-0871, Japan
| | - Masanobu Kawai
- Department of Bone and Mineral Research, Research Institute, Osaka Women's and Children's Hospital, Osaka Prefectural Hospital Organization, Izumi, Osaka 594-1101, Japan
| | | | - Toshimi Michigami
- Department of Bone and Mineral Research, Research Institute, Osaka Women's and Children's Hospital, Osaka Prefectural Hospital Organization, Izumi, Osaka 594-1101, Japan.
| |
Collapse
|
2
|
Wong SK, Fikri NIA, Munesveran K, Hisham NSN, Lau SHJ, Chin KY, Fahami NAM, Saad QHM, Kamisah Y, Abdullah A, Masbah N, Ima-Nirwana S. Effects of tocotrienol on osteocyte-mediated phosphate metabolism in high-carbohydrate high-fat diet-induced osteoporotic rats. J Funct Foods 2022. [DOI: 10.1016/j.jff.2022.105213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022] Open
|
3
|
Abstract
Inorganic phosphate (Pi) in the mammalian body is balanced by its influx and efflux through the intestines, kidneys, bones, and soft tissues, at which several sodium/Pi co-transporters mediate its active transport. Pi homeostasis is achieved through the complex counter-regulatory feedback balance between fibroblast growth factor 23 (FGF23), 1,25-dihydroxyvitamin D (1,25(OH)2D), and parathyroid hormone. FGF23, which is mainly produced by osteocytes in bone, plays a central role in Pi homeostasis and exerts its effects by binding to the FGF receptor (FGFR) and αKlotho in distant target organs. In the kidneys, the main target, FGF23 promotes the excretion of Pi and suppresses the production of 1,25(OH)2D. Deficient and excess FGF23 result in hyperphosphatemia and hypophosphatemia, respectively. FGF23-related hypophosphatemic rickets/osteomalacia include tumor-induced osteomalacia and various genetic diseases, such as X-linked hypophosphatemic rickets. Coverage by the national health insurance system in Japan for the measurement of FGF23 and the approval of burosumab, an FGF23-neutralizing antibody, have had a significant impact on the diagnosis and treatment of FGF23-related hypophosphatemic rickets/osteomalacia. Some of the molecules responsible for genetic hypophosphatemic rickets/osteomalacia are highly expressed in osteocytes and function as local regulators of FGF23 production. A number of systemic factors also regulate FGF23 levels. Although the mechanisms responsible for Pi sensing in mammals have not yet been elucidated in detail, recent studies have suggested the involvement of FGFR1. The further clarification of the mechanisms by which osteocytes detect Pi levels and regulate FGF23 production will lead to the development of better strategies to treat hyperphosphatemic and hypophosphatemic conditions.
Collapse
Affiliation(s)
- Toshimi Michigami
- Department of Bone and Mineral Research, Research Institute, Osaka Women's and Children's Hospital, Osaka 594-1101, Japan
| |
Collapse
|
4
|
PHEXL222P Mutation Increases Phex Expression in a New ENU Mouse Model for XLH Disease. Genes (Basel) 2022; 13:genes13081356. [PMID: 36011266 PMCID: PMC9407253 DOI: 10.3390/genes13081356] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [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.
Collapse
|
5
|
Javaid MK, Ward L, Pinedo-Villanueva R, Rylands AJ, Williams A, Insogna K, Imel EA. Musculoskeletal Features in Adults With X-linked Hypophosphatemia: An Analysis of Clinical Trial and Survey Data. J Clin Endocrinol Metab 2022; 107:e1249-e1262. [PMID: 34636401 PMCID: PMC8852215 DOI: 10.1210/clinem/dgab739] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/11/2021] [Indexed: 12/21/2022]
Abstract
CONTEXT Patients with X-linked hypophosphatemia (XLH) experience multiple musculoskeletal manifestations throughout adulthood. OBJECTIVE To describe the burden of musculoskeletal features and associated surgeries across the lifespan of adults with XLH. METHODS Three groups of adults were analyzed: subjects of a clinical trial, participants in an online survey, and a subgroup of the online survey participants considered comparable to the clinical trial subjects (according to Brief Pain Inventory worst pain scores of ≥ 4). In each group, the adults were categorized by age: 18-29, 30-39, 40-49, 50-59, and ≥ 60 years. Rates of 5 prespecified musculoskeletal features and associated surgeries were investigated across these age bands for the 3 groups. RESULTS Data from 336 adults were analyzed. In all 3 groups, 43% to 47% had a history of fracture, with the proportions increasing with age. The overall prevalence of osteoarthritis was > 50% in all 3 groups, with a rate of 23% to 37% in the 18- to 29-year-old group, and increasing with age. Similar patterns were observed for osteophytes and enthesopathy. Hip and knee arthroplasty was reported even in adults in their 30s. Spinal stenosis was present at a low prevalence, increasing with age. The proportion of adults with ≥ 2 musculoskeletal features was 59.1%, 55.0%, and 61.3% in the clinical trial group, survey group, and survey pain subgroup, respectively. CONCLUSION This analysis confirmed high rates of multiple musculoskeletal features beginning as early as age 20 years among adults with XLH and gradually accumulating with age.
Collapse
Affiliation(s)
- Muhammad Kassim Javaid
- Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK
- Correspondence: Dr. Muhammad Kassim Javaid, Associate Professor in Metabolic Bone Disease, Botnar Research Centre, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, UK.
| | - Leanne Ward
- Department of Pediatrics, University of Ottawa, Ottawa, ON, Canada
| | - Rafael Pinedo-Villanueva
- Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK
| | - Angela J Rylands
- Health Economics and Outcomes Research, Kyowa Kirin International, Marlow, UK
| | - Angela Williams
- Health Economics and Outcomes Research, Kyowa Kirin International, Marlow, UK
| | - Karl Insogna
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
| | - Erik A Imel
- Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
| |
Collapse
|
6
|
Abstract
Osteocytes are dendritic cells in the mineralized bone matrix that descend from osteoblasts. They play critical roles in controlling bone mass through the production of sclerostin, an inhibitor of bone formation, and receptor activator of nuclear factor κ B ligand, an inducer of osteoblastic bone resorption. Osteocytes also govern phosphate homeostasis through the production of fibroblast growth factor 23 (FGF23), which lowers serum phosphate levels by increasing renal phosphate excretion and reducing the synthesis of 1,25-dihydroxyvitamin D (1,25(OH)2D), an active metabolite of vitamin D. The production of FGF23 in osteocytes is regulated by various local and systemic factors. Phosphate-regulating gene homologous to endopeptidase on X chromosome (PHEX), dentin matrix protein 1 (DMP1), and family with sequence similarity 20, member C function as local negative regulators of FGF23 production in osteocytes, and their inactivation causes the overproduction of FGF23 and hypophosphatemia. Sclerostin has been suggested to regulate the production of FGF23, which may link the two functions of osteocytes, namely, the control of bone mass and regulation of phosphate homeostasis. Systemic regulators of FGF23 production include 1,25(OH)2D, phosphate, parathyroid hormone, insulin, iron, and inflammation. Therefore, the regulation of FGF23 in osteocytes is complex and multifactorial. Recent mouse studies have suggested that decreases in serum phosphate levels from youth to adulthood are caused by growth-related increases in FGF23 production by osteocytes, which are associated with the down-regulation of Phex and Dmp1.
Collapse
|
7
|
Yamazaki M, Michigami T. Osteocytes and the pathogenesis of hypophosphatemic rickets. Front Endocrinol (Lausanne) 2022; 13:1005189. [PMID: 36246908 PMCID: PMC9556901 DOI: 10.3389/fendo.2022.1005189] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Accepted: 09/15/2022] [Indexed: 11/13/2022] Open
Abstract
Since phosphorus is a component of hydroxyapatite, its prolonged deprivation affects bone mineralization. Fibroblast growth factor 23 (FGF23) is essential for maintaining phosphate homeostasis and is mainly produced by osteocytes. FGF23 increases the excretion of inorganic phosphate (Pi) and decreases the production of 1,25-dihydroxyvitamin D in the kidneys. Osteocytes are cells of osteoblastic lineage that have undergone terminal differentiation and become embedded in mineralized bone matrix. Osteocytes express FGF23 and other multiple genes responsible for hereditary hypophosphatemic rickets, which include phosphate-regulating gene homologous to endopeptidase on X chromosome (PHEX), dentin matrix protein 1 (DMP1), and family with sequence similarity 20, member C (FAM20C). Since inactivating mutations in PHEX, DMP1, and FAM20C boost the production of FGF23, these molecules might be considered as local negative regulators of FGF23. Mouse studies have suggested that enhanced FGF receptor (FGFR) signaling is involved in the overproduction of FGF23 in PHEX-deficient X-linked hypophosphatemic rickets (XLH) and DMP1-deficient autosomal recessive hypophosphatemic rickets type 1. Since FGFR is involved in the transduction of signals evoked by extracellular Pi, Pi sensing in osteocytes may be abnormal in these diseases. Serum levels of sclerostin, an inhibitor Wnt/β-catenin signaling secreted by osteocytes, are increased in XLH patients, and mouse studies have suggested the potential of inhibiting sclerostin as a new therapeutic option for the disease. The elucidation of complex abnormalities in the osteocytes of FGF23-related hypophosphatemic diseases will provide a more detailed understanding of their pathogenesis and more effective treatments.
Collapse
|
8
|
Moreira CA, Costa TMRL, Marques JVO, Sylvestre L, Almeida ACR, Maluf EMCP, Borba VZC. Prevalence and clinical characteristics of X-linked hypophosphatemia in Paraná, southern Brazil. ARCHIVES OF ENDOCRINOLOGY AND METABOLISM 2021; 64:796-802. [PMID: 33049132 PMCID: PMC10528612 DOI: 10.20945/2359-3997000000296] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2020] [Accepted: 07/20/2020] [Indexed: 11/23/2022]
Abstract
OBJECTIVE The aim of this cross-sectional study was to estimate the prevalence of XLH in Paraná, a state in southern Brazil, and report the clinical features and complications of the disease. METHODS We invited all endocrinologists (n = 205), nephrologists (n = 221), orthopedic surgeons (n = 1020), and pediatricians (n = 1000) in Paraná to fill out an electronic survey with information on patients with X-linked hypophosphatemia (XLH), and searched the records of the state's health department for all calcitriol prescriptions in 2018. RESULTS In all, 244 (10%) specialists responded to the email, of whom 18 (7.4%) reported to be taking care of patients with XLH and answered the online survey. A total of 57 patients with XLH were identified (prevalence 5 per million inhabitants). The median age at diagnosis was 22 years, and 42.2% were children and adolescents. Fifteen patients had genetic testing showing a PHEX mutation. Overall, 91.2% had bone deformities, 30.8% had a history of fragility fractures, and 22.4% had renal complications. CONCLUSION This study demonstrated a prevalence of XLH of 5 cases per million inhabitants in the state of Paraná, a rate lower than the one reported in other countries. Manifestations of renal calcification and bone fragility were frequent among the patients. This is the first epidemiological study evaluating the prevalence and clinical presentation of XLH in Latin America.
Collapse
Affiliation(s)
- Carolina Aguiar Moreira
- Divisão de Endocrinologia (SEMPR), Hospital de Clínicas, Universidade Federal do Paraná, Curitiba, PR, Brasil,
- Lab PRO, Seção de Histomorfometria Óssea, Fundação Pró-Renal, Curitiba, PR, Brasil
| | - Tatiana M R Lemos Costa
- Divisão de Endocrinologia (SEMPR), Hospital de Clínicas, Universidade Federal do Paraná, Curitiba, PR, Brasil
| | | | - Lucimary Sylvestre
- Serviço de Nefrologia Pediátrica, Hospital Pequeno Príncipe, Curitiba, PR, Brasil
- Escola de Medicina, Pontifícia Universidade Católica do Paraná, Curitiba, PR, Brasil
| | - Ana Cristina R Almeida
- Escola de Medicina, Pontifícia Universidade Católica do Paraná, Curitiba, PR, Brasil
- Secretaria de Saúde do Paraná, Curitiba, PR, Brasil
| | - Eliane M C P Maluf
- Universidade Positivo, Curitiba, PR, Brasil
- Programa de Pós-Graduação, Universidade Federal do Paraná, Curitiba, PR, Brasil
| | - Victória Z C Borba
- Divisão de Endocrinologia (SEMPR), Hospital de Clínicas, Universidade Federal do Paraná, Curitiba, PR, Brasil
| |
Collapse
|
9
|
A 5-year-old girl with bony deformities and disproportionate short stature: Answers. Pediatr Nephrol 2021; 36:3117-3121. [PMID: 33730275 DOI: 10.1007/s00467-021-05038-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Revised: 02/19/2021] [Accepted: 02/26/2021] [Indexed: 10/21/2022]
|
10
|
Downs RP, Xiao Z, Ikedionwu MO, Cleveland JW, Lin Chin A, Cafferty AE, Darryl Quarles L, Carrick JD. Design and development of FGF-23 antagonists: Definition of the pharmacophore and initial structure-activity relationships probed by synthetic analogues. Bioorg Med Chem 2021; 29:115877. [PMID: 33232874 PMCID: PMC8007132 DOI: 10.1016/j.bmc.2020.115877] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Revised: 11/05/2020] [Accepted: 11/10/2020] [Indexed: 10/22/2022]
Abstract
Hereditary hypophosphatemic disorders, TIO, and CKD conditions are believed to be influenced by an excess of Fibroblast Growth Factor-23 (FGF-23) which activates a binary renal FGFRs / α-Klotho complex to regulate homeostatic metabolism of phosphate and vitamin D. Adaptive FGF-23 responses from CKD patients with excess FGF-23 frequently lead to increased mortality from cardiovascular disease. A reversibly binding small molecule therapeutic has yet to emerge from research and development in this area. Current outcomes described in this work highlight efforts related to lead identification and modification using organic synthesis of strategic analogues to probe structure-activity relationships and preliminarily define the pharmacophore of a computationally derived hit obtained from virtual high-throughput screening. Synthetic strategies for the initial hit and analogue preparation, as well as preliminary cellular in vitro assay results highlighting sub micromolar inhibition of the FGF-23 signaling sequence at a concentration well below cytotoxicity are reported herein.
Collapse
Affiliation(s)
- Ryan P Downs
- Department of Chemistry, Tennessee Technological University, Cookeville, TN 38505-0001, USA
| | - Zhousheng Xiao
- Department of Medicine, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38165, USA
| | - Munachi O Ikedionwu
- Department of Chemistry, Tennessee Technological University, Cookeville, TN 38505-0001, USA
| | - Jacob W Cleveland
- Department of Chemistry, Tennessee Technological University, Cookeville, TN 38505-0001, USA
| | - Ai Lin Chin
- Department of Chemistry, Tennessee Technological University, Cookeville, TN 38505-0001, USA
| | - Abigail E Cafferty
- Department of Chemistry, Tennessee Technological University, Cookeville, TN 38505-0001, USA
| | - L Darryl Quarles
- Department of Medicine, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38165, USA
| | - Jesse D Carrick
- Department of Chemistry, Tennessee Technological University, Cookeville, TN 38505-0001, USA.
| |
Collapse
|
11
|
Durup D, Diaz-delCastillo M, Morgenlykke J, Jensen LT, Frandsen E, Abelson KSP, Pedersen L, Lykkesfeldt J, Ding M, Jørgensen NR, Syberg S, Petersen S, Heegaard AM. Hypophosphatemic Hypovitaminosis D Induces Osteomalacia in the Adult Female Rat. Endocrinology 2020; 161:5863599. [PMID: 32591825 DOI: 10.1210/endocr/bqaa100] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/17/2020] [Accepted: 06/19/2020] [Indexed: 01/21/2023]
Abstract
Osteomalacia is a bone-demineralizing disease of adulthood, often caused by hypovitaminosis D. Current animal models of the disease mimic osteomalacia as a consequence of gastric bypass or toxic exposure to metals, but a relevant model of diet-induced osteomalacia is lacking. For that purpose, 7-month-old female Sprague Dawley rats were randomly assigned into 2 weight-stratified groups and maintained for 4 months on synthetic diets containing negligible or normal levels of vitamin D. The dietary regimen resulted in vitamin D deficiency as measured by 25-hydroxyvitamin D serum levels; however, hypovitaminosis D per se did not affect biomarkers of calcium metabolism and bone turnover, nor did it result in increased osteoid. Thus, vitamin D depletion through the diet was found to be insufficient to induce an osteomalacia-like phenotype in the adult rat. After 4 months, the phosphate content of the vitamin D-depleted diet had decreased to 0.16% (calcium:phosphorus ratio of 5.85), resulting in an osteomalacic-like condition (trabecular osteoid surface/bone surface constituted 33%; CI, 26-40). The diet change also affected both metabolic and bone turnover biomarkers, including significantly suppressing serum fibroblast growth factor 23. Furthermore, decreased dietary phosphate in a vitamin D-depleted diet led to microarchitectural changes of trabecular and cortical bone, lower bone mass density, lower bone mass content and decreased bone strength, all indicating reduced bone quality. Taken together, our results show that osteomalacia can be induced in the adult female rat by depleting vitamin D and lowering phosphate content in the diet.
Collapse
Affiliation(s)
- Darshana Durup
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Marta Diaz-delCastillo
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jesper Morgenlykke
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | | | - Erik Frandsen
- Department of Nuclear Medicine, Herlev University, Herlev, Denmark
| | - Klas S P Abelson
- Department of Experimental Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | | | - Jens Lykkesfeldt
- Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Ming Ding
- Department of Orthopaedic Surgery and Traumatology, Odense University Hospital, Institute of Clinical Research, University of Southern Denmark, Odense, Denmark
| | | | - Susanne Syberg
- Osteoporosis Unit and Research Centre of Ageing and Osteoporosis, Department of Medicine, Glostrup University Hospital, Glostrup, Denmark
| | - Solveig Petersen
- Osteoporosis Unit and Research Centre of Ageing and Osteoporosis, Department of Medicine, Glostrup University Hospital, Glostrup, Denmark
| | - Anne-Marie Heegaard
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| |
Collapse
|
12
|
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.
Collapse
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
| |
Collapse
|
13
|
Abstract
Inorganic phosphate (Pi) is essential for signal transduction and cell metabolism, and is also an essential structural component of the extracellular matrix of the skeleton. Pi is sensed in bacteria and yeast at the plasma membrane, which activates intracellular signal transduction to control the expression of Pi transporters and other genes that control intracellular Pi levels. In multicellular organisms, Pi homeostasis must be maintained in the organism and at the cellular level, requiring an endocrine and metabolic Pi-sensing mechanism, about which little is currently known. This Review will discuss the metabolic effects of Pi, which are mediated by Pi transporters, inositol pyrophosphates and SYG1-Pho81-XPR1 (SPX)-domain proteins to maintain cellular phosphate homeostasis in the musculoskeletal system. In addition, we will discuss how Pi is sensed by the human body to regulate the production of fibroblast growth factor 23 (FGF23), parathyroid hormone and calcitriol to maintain serum levels of Pi in a narrow range. New findings on the crosstalk between iron and Pi homeostasis in the regulation of FGF23 expression will also be outlined. Mutations in components of these metabolic and endocrine phosphate sensors result in genetic disorders of phosphate homeostasis, cardiomyopathy and familial basal ganglial calcifications, highlighting the importance of this newly emerging area of research.
Collapse
Affiliation(s)
- Sampada Chande
- Section of Endocrinology and Metabolism, Yale University School of Medicine, New Haven, CT, USA
| | - Clemens Bergwitz
- Section of Endocrinology and Metabolism, Yale University School of Medicine, New Haven, CT, USA.
| |
Collapse
|
14
|
Bhan A, Qiu S, Rao SD. Bone histomorphometry in the evaluation of osteomalacia. Bone Rep 2018; 8:125-134. [PMID: 29955631 PMCID: PMC6020114 DOI: 10.1016/j.bonr.2018.03.005] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/15/2017] [Revised: 03/06/2018] [Accepted: 03/15/2018] [Indexed: 10/27/2022] Open
Abstract
With the widespread use of measurement of bone mineral density to detect, diagnose, and monitor therapy in the management of osteoporosis, bone histomorphometry has largely been relegated to research settings and academic pursuits. However, bone density measurement cannot distinguish between osteoporosis and other metabolic bone disorders such as different types of osteomalacia, osteitis fibrosa, renal osteodystrophy, hypophosphatasia, and Paget's disease of bone. Furthermore, bone density test cannot tell us anything about microarchitecture of bone, tissue level dynamics, bone cellular activity, bone mineralization and bone remodeling, understanding of which is essential to make a specific diagnosis of a suspected metabolic bone disease, to evaluate beneficial (or adverse) effects of various therapies, treatment (medical or surgical) decisions in hyperparathyroid states. As a research tool, bone histomorphometry contributed immensely to our understanding of bone biology, revolutionized the study of the mechanism of actions of various therapies, and provided crucial understanding of the adverse effects of drugs.
Collapse
Affiliation(s)
- Arti Bhan
- Division of Endocrinology, Diabetes, and Bone & Mineral Disorders, Henry Ford Health System, Detroit, MI, 48201, United States
| | - Shijing Qiu
- Bone & Mineral Research Laboratory, Henry Ford Health System, Detroit, MI, 48201, United States
| | - Sudhaker D Rao
- Bone & Mineral Research Laboratory, Henry Ford Health System, Detroit, MI, 48201, United States
| |
Collapse
|
15
|
Role of pyrophosphate in vascular calcification in chronic kidney disease. Nefrologia 2017; 38:250-257. [PMID: 29137892 DOI: 10.1016/j.nefro.2017.07.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2016] [Revised: 07/06/2017] [Accepted: 07/20/2017] [Indexed: 01/29/2023] Open
Abstract
Vascular calcification is a pathology characterized by the deposition of calcium-phosphate in cardiovascular structures, mainly in the form of hydroxyapatite crystals, resulting in ectopic calcification. It is correlated with increased risk of cardiovascular disease and myocardial infarction in diabetic patients and in those with chronic kidney disease (CKD). Vascular smooth muscle cells are sensitive to changes in inorganic phosphate (Pi) levels. They are able to adapt and modify some of their functions and promote changes which trigger calcification. Pi is regulated by parathyroid hormone and 1,25-dihydroxyvitamin D. Changes in the transport of Pi are the primary factor responsible for the regulation of Pi homeostasis and the calcification process. Synthesis of calcification inhibitors is the main mechanism by which cells are able to prevent vascular calcification. Extracellular pyrophosphate (PPi) is a potent endogenous inhibitor of calcium-phosphate deposition both in vivo and in vitro. Patients with CKD show lower levels of PPi and increased activity of the enzyme alkaline phosphatase. Numerous enzymes implicated in the metabolism of PPi have been associated with vascular calcifications. PPi is synthesized from extracellular ATP by nucleotide pyrophosphatase/phosphodiesterase from extracellular ATP hydrolysis. PPi is hydrolyzed into Pi by tissue-nonspecific alkaline phosphatase. ATP can be hydrolyzed to Pi via the ectonucleoside triphosphate diphosphohydrolase family. All these enzymes must be in balance, thereby preventing calcifications. However, diseases like CKD or diabetes induce alterations in their levels. Administration of PPi could open up new treatment options for these patients.
Collapse
|
16
|
Silva SRB, Illarramendi X, Tempone AJ, Silva PHL, Nery JAC, Monteiro AMV, Pessolani MCV, Boasquevisque E, Sarno EN, Pereira GMB, Esquenazi D. Downregulation of PHEX in multibacillary leprosy patients: observational cross-sectional study. J Transl Med 2015; 13:296. [PMID: 26362198 PMCID: PMC4566286 DOI: 10.1186/s12967-015-0651-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2015] [Accepted: 08/25/2015] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND Peripheral nerve injury and bone lesions, well known leprosy complications, lead to deformities and incapacities. The phosphate-regulating gene with homologies to endopeptidase on the X chromosome (PHEX) encodes a homonymous protein (PHEX) implicated in bone metabolism. PHEX/PHEX alterations may result in bone and cartilage lesions. PHEX expression is downregulated by intracellular Mycobacterium leprae (M. leprae) in cultures of human Schwann cells and osteoblasts. M. leprae in vivo effect on PHEX/PHEX is not known. METHODS Cross-sectional observational study of 36 leprosy patients (22 lepromatous and 14 borderline-tuberculoid) and 20 healthy volunteers (HV). The following tests were performed: PHEX flow cytometric analysis on blood mononuclear cells, cytokine production in culture supernatant, 25-hydroxyvitamin D (OHvitD) serum levels and (99m)Tc-MDP three-phase bone scintigraphy, radiography of upper and lower extremities and blood and urine biochemistry. RESULTS Significantly lower PHEX expression levels were observed in lepromatous patients than in the other groups (χ(2) = 16.554, p < 0.001 for lymphocytes and χ(2) = 13.933, p = 0.001 for monocytes). Low levels of 25-(OHvitD) were observed in HV (median = 23.0 ng/mL) and BT patients (median = 27.5 ng/mL) and normal serum levels were found in LL patients (median = 38.6 ng/mL). Inflammatory cytokines, such as TNF, a PHEX transcription repressor, were lower after stimulation with M. leprae in peripheral blood mononuclear cells from lepromatous in comparison to BT patients and HV (χ(2) = 10.820, p < 0.001). CONCLUSION Downregulation of PHEX may constitute an important early component of bone loss and joint damage in leprosy. The present results suggest a direct effect produced by M. leprae on the osteoarticular system that may use this mechanism.
Collapse
Affiliation(s)
- Sandra R Boiça Silva
- Disciplina de Patologia Geral e Laboratório de Imunopatologia, Departamento de Patologia e Laboratórios, Faculdade de Ciências Médicas, Universidade do Estado do Rio de Janeiro (UERJ), Av Professor Manuel de Abreu 444, Vila Isabel, Rio de Janeiro, RJ, 20550-170, Brazil.
| | - Ximena Illarramendi
- Laboratório de Hanseníase, Instituto Oswaldo Cruz (IOC) - Oswaldo Cruz Foundation (FIOCRUZ), Av. Brasil 4365, Manguinhos, Rio de Janeiro, RJ, 21040-360, Brazil.
| | - Antonio J Tempone
- Laboratório de Biologia Molecular de Parasitas e Vetores, Instituto Oswaldo Cruz (IOC) - Oswaldo Cruz Foundation (FIOCRUZ), Av. Brasil 4365, Manguinhos, Rio de Janeiro, RJ, 21040-360, Brazil.
| | - Pedro H L Silva
- Laboratório de Hanseníase, Instituto Oswaldo Cruz (IOC) - Oswaldo Cruz Foundation (FIOCRUZ), Av. Brasil 4365, Manguinhos, Rio de Janeiro, RJ, 21040-360, Brazil.
| | - José A C Nery
- Laboratório de Hanseníase, Instituto Oswaldo Cruz (IOC) - Oswaldo Cruz Foundation (FIOCRUZ), Av. Brasil 4365, Manguinhos, Rio de Janeiro, RJ, 21040-360, Brazil.
| | - Alexandra M V Monteiro
- Serviço de Medicina Nuclear, Departamento de Radiologia, Faculdade de Ciências Médicas, Universidade do Estado do Rio de Janeiro (UERJ), Av. Prof. Manuel de Abreu 444, Vila Isabel, Rio de Janeiro, RJ, 20550-170, Brazil.
| | - Maria Cristina V Pessolani
- Laboratório de Microbiologia Celular, Instituto Oswaldo Cruz (IOC) - Oswaldo Cruz Foundation (FIOCRUZ), Av. Brasil 4365, Manguinhos, Rio de Janeiro, RJ, 21040-360, Brazil.
| | - Edson Boasquevisque
- Serviço de Medicina Nuclear, Departamento de Radiologia, Faculdade de Ciências Médicas, Universidade do Estado do Rio de Janeiro (UERJ), Av. Prof. Manuel de Abreu 444, Vila Isabel, Rio de Janeiro, RJ, 20550-170, Brazil.
| | - Euzenir N Sarno
- Laboratório de Hanseníase, Instituto Oswaldo Cruz (IOC) - Oswaldo Cruz Foundation (FIOCRUZ), Av. Brasil 4365, Manguinhos, Rio de Janeiro, RJ, 21040-360, Brazil.
| | - Geraldo M B Pereira
- Laboratório de Microbiologia Celular, Instituto Oswaldo Cruz (IOC) - Oswaldo Cruz Foundation (FIOCRUZ), Av. Brasil 4365, Manguinhos, Rio de Janeiro, RJ, 21040-360, Brazil. .,Disciplina de Patologia Geral e Laboratório de Imunopatologia, Departamento de Patologia e Laboratórios, Faculdade de Ciências Médicas, Universidade do Estado do Rio de Janeiro (UERJ), Av Professor Manuel de Abreu 444, Vila Isabel, Rio de Janeiro, RJ, 20550-170, Brazil.
| | - Danuza Esquenazi
- Laboratório de Hanseníase, Instituto Oswaldo Cruz (IOC) - Oswaldo Cruz Foundation (FIOCRUZ), Av. Brasil 4365, Manguinhos, Rio de Janeiro, RJ, 21040-360, Brazil. .,Disciplina de Patologia Geral e Laboratório de Imunopatologia, Departamento de Patologia e Laboratórios, Faculdade de Ciências Médicas, Universidade do Estado do Rio de Janeiro (UERJ), Av Professor Manuel de Abreu 444, Vila Isabel, Rio de Janeiro, RJ, 20550-170, Brazil.
| |
Collapse
|
17
|
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.
Collapse
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:
| |
Collapse
|
18
|
Zou J, Xiong X, Lai B, Sun M, Tu X, Gao X. Glucose metabolic abnormality is associated with defective mineral homeostasis in skeletal disorder mouse model. SCIENCE CHINA-LIFE SCIENCES 2015; 58:359-67. [DOI: 10.1007/s11427-015-4827-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2014] [Accepted: 12/31/2014] [Indexed: 12/17/2022]
|
19
|
Owen C, Chen F, Flenniken AM, Osborne LR, Ichikawa S, Adamson SL, Rossant J, Aubin JE. A novel Phex mutation in a new mouse model of hypophosphatemic rickets. J Cell Biochem 2012; 113:2432-41. [PMID: 22573557 DOI: 10.1002/jcb.24115] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
X-linked hypophosphatemic rickets (XLH) is a dominantly inherited disease characterized by renal phosphate wasting, aberrant vitamin D metabolism, and defective bone mineralization. It is known that XLH in humans and in certain mouse models is caused by inactivating mutations in PHEX/Phex (phosphate-regulating gene with homologies to endopeptidases on the X chromosome). By a genome-wide N-ethyl-N-nitrosourea (ENU)-induced mutagenesis screen in mice, we identified a dominant mouse mutation that exhibits the classic clinical manifestations of XLH, including growth retardation, skeletal abnormalities (rickets/osteomalacia), hypophosphatemia, and increased serum alkaline phosphatase (ALP) levels. Mapping and sequencing revealed that these mice carry a point mutation in exon 14 of the Phex gene that introduces a stop codon at amino acid 496 of the coding sequence (Phex(Jrt) also published as Phex(K496X) [Ichikawa et al., 2012]). Fgf23 mRNA expression as well as that of osteocalcin, bone sialoprotein, and matrix extracellular phosphoglycoprotein was upregulated in male mutant long bone, but that of sclerostin was unaffected. Although Phex mRNA is expressed in bone from mutant hemizygous male mice (Phex(Jrt)/Y mice), no Phex protein was detected in immunoblots of femoral bone protein. Stromal cultures from mutant bone marrow were indistinguishable from those of wild-type mice with respect to differentiation and mineralization. The ability of Phex(Jrt)/Y osteoblasts to mineralize and the altered expression levels of matrix proteins compared with the well-studied Hyp mice makes it a unique model with which to further explore the clinical manifestations of XLH and its link to FGF23 as well as to evaluate potential new therapeutic strategies.
Collapse
Affiliation(s)
- Celeste Owen
- Centre For Modeling Human Disease, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada
| | | | | | | | | | | | | | | |
Collapse
|
20
|
Graham RP, Hodge JC, Folpe AL, Oliveira AM, Meyer KJ, Jenkins RB, Sim FH, Sukov WR. A cytogenetic analysis of 2 cases of phosphaturic mesenchymal tumor of mixed connective tissue type. Hum Pathol 2012; 43:1334-8. [DOI: 10.1016/j.humpath.2011.11.020] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/11/2011] [Accepted: 11/29/2011] [Indexed: 11/30/2022]
|
21
|
Shimada T, Fukumoto S. FGF23 as a Novel Therapeutic Target. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 728:158-70. [DOI: 10.1007/978-1-4614-0887-1_10] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
|
22
|
Andreopoulou P, Dumitrescu CE, Kelly MH, Brillante BA, Cutler Peck CM, Wodajo FM, Chang R, Collins MT. Selective venous catheterization for the localization of phosphaturic mesenchymal tumors. J Bone Miner Res 2011; 26:1295-302. [PMID: 21611969 PMCID: PMC3179290 DOI: 10.1002/jbmr.316] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Tumor-induced osteomalacia (TIO) is characterized by renal phosphate wasting, hypophosphatemia, and aberrant vitamin D(3) metabolism and is caused by fibroblast growth factor 23 (FGF-23)-producing mesenchymal tumors, which are often difficult to locate. We investigated the utility of selective venous sampling in tumor localization. The primary endpoint was identification of the FGF-23 concentration ratio between the venous drainage of the tumor bed and the general circulation that was diagnostic of the location of an FGF-23-secreting tumor. Fourteen subjects underwent 15 sampling procedures after functional and anatomic imaging studies. Subjects fit into three imaging categories: no suspicious site, multiple sites, and single site (positive controls). FGF-23 levels were measured by ELISA. Suspicious tumors were resected for diagnosis, confirmation, and cure. In subjects with a positive venous sampling study and subsequent cure, a minimum ratio of 1.6 was diagnostic. In 7 of 14 subjects there was suggestive imaging, a diagnostic ratio, and an associated TIO tumor (true positive). Four of these required complicated resection procedures. In 4 of 14 subjects with no suspicious site on imaging studies, an FGF-23 diagnostic ratio was not detected (true negative). Biopsy or resection of a single lesion in 2 of 14 subjects with a diagnostic ratio failed to identify a TIO tumor (false positive). A diagnostic FGF-23 ratio was absent in 1 of 14 subjects whose tumor was a single highly suspicious lesion on imaging studies (false negative). These data yield a sensitivity of 0.87 [95% confidence interval (CI) 0.47-0.99] and a specificity of 0.71 (95% CI 0.29-0.96). Selective venous sampling for FGF-23 was particularly useful in subjects with multiple suspicious sites or an anatomically challenging planned resection but not in the absence of a suspicious lesion on imaging studies.
Collapse
Affiliation(s)
- Panagiota Andreopoulou
- Skeletal Clinical Studies Unit, Craniofacial and Skeletal Diseases Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892-4320, USA
| | | | | | | | | | | | | | | |
Collapse
|
23
|
Chu EY, Fong H, Blethen FA, Tompkins KA, Foster BL, Yeh KD, Nagatomo KJ, Matsa-Dunn D, Sitara D, Lanske B, Rutherford RB, Somerman MJ. Ablation of systemic phosphate-regulating gene fibroblast growth factor 23 (Fgf23) compromises the dentoalveolar complex. Anat Rec (Hoboken) 2010; 293:1214-26. [PMID: 20583265 DOI: 10.1002/ar.21152] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Fibroblast growth factor-23 (FGF23) is a hormone that modulates circulating phosphate (P(i)) levels by controlling P(i) reabsorption from the kidneys. When FGF23 levels are deficient, as in tumoral calcinosis patients, hyperphosphatemia ensues. We show here in a murine model that Fgf23 ablation disrupted morphology and protein expression within the dentoalveolar complex. Ectopic matrix formation in pulp chambers, odontoblast layer disruption, narrowing of periodontal ligament space, and alteration of cementum structure were observed in histological and electron microscopy sections. Because serum P(i) levels are dramatically elevated in Fgf23(-/-), we assayed for apoptosis and expression of members from the small integrin-binding ligand, N-linked glycoprotein (SIBLING) family, both of which are sensitive to elevated P(i) in vitro. Unlike X-linked hypophosphatemic (Hyp) and wild-type (WT) specimens, numerous apoptotic osteocytes and osteoblasts were detected in Fgf23(-/-) specimens. Further, in comparison to Hyp and WT samples, decreased bone sialoprotein and elevated dentin matrix protein-1 protein levels were observed in cementum of Fgf23(-/-) mice. Additional dentin-associated proteins, such as dentin sialoprotein and dentin phosphoprotein, exhibited altered localization in both Fgf23(-/-) and Hyp samples. Based on these results, we propose that FGF23 and (P(i)) homeostasis play a significant role in maintenance of the dentoalveolar complex.
Collapse
Affiliation(s)
- E Y Chu
- Department of Periodontics, School of Dentistry, University of Washington, Seattle, Washington, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
24
|
Laroche M, Boyer JF, Jahafar H, Allard J, Tack I. Normal FGF23 levels in adult idiopathic phosphate diabetes. Calcif Tissue Int 2009; 84:112-7. [PMID: 19148564 DOI: 10.1007/s00223-008-9204-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/23/2008] [Accepted: 11/07/2008] [Indexed: 12/16/2022]
Abstract
Fibroblast growth factor 23 (FGF23), a recently discovered phosphaturic substance playing a key role in genetic and oncogenic phosphate diabetes, is involved in the physiological regulation of phosphate metabolism. Moderate idiopathic phosphate diabetes (IPD) leading to male osteoporosis and diffuse pain resembling fibromyalgia has been described. The aim of our study was to define the role of FGF23 in the mechanism of IPD. The study concerned 29 patients with IPD, mean age 53 +/- 11 years, of whom 72% were men. Fifteen subjects without bone disease and with normal serum phosphate and calcium levels were used as controls. Phosphate diabetes was confirmed by phosphate reabsorption level <85% and phosphate reabsorption threshold (TmPO4/GFR) <0.83. Known causes of phosphate diabetes were excluded. Fasting level of FGF23, serum phosphate, 1-25(OH)2D3, and parathyroid hormone were measured in patients and compared with FGF23 and serum phosphate in healthy controls. Spinal and hip bone mineral density (BMD) were measured by osteodensitometry. Sixteen of 29 patients had diffuse pain, 10 had osteoporosis according to the World Health Organization criteria, and 11 had osteopenia. Serum phosphate was significantly lower in patients than in controls, but FGF23 levels did not differ. Compared to patients with normal bone status, patients with osteopenia and osteoporosis had significantly decreased FGF23 levels, whereas serum phosphate was identical in the two groups. In all patients, serum phosphate and FGF23 were positively correlated and FGF23 and 1-25(OH)2D3 were negatively correlated. FGF23 seems not be a cause of IPD, and the FGF23/phosphate/1-25(OH)2D3 axis appeared to be functional.
Collapse
Affiliation(s)
- M Laroche
- Service de Rhumatologie, CHU Rangueil, Toulouse, France.
| | | | | | | | | |
Collapse
|
25
|
Abstract
Under physiological conditions, homeostasis of inorganic phosphate (Pi) is tightly controlled by a network of increasingly more complex interactions and direct or indirect feedback loops among classical players, such as vitamin D (1,25(OH)2D3), parathyroid hormone (PTH), intestinal and renal phosphate transporters, and the recently described phosphatonins and minhibins. A series of checks and balances offsets the effects of 1,25(OH)2D3 and PTH to enable fine-tuning of intestinal and renal Pi absorptive capacity and bone resorption and mineralization. The latter include PHEX, FGF-23, MEPE, DMP1, and secreted FRP4. Despite this large number of regulatory components with complex interactions, the system has limited redundancy and is prone to dysregulation under pathophysiological conditions. This article reviews and synthesizes recent advances to present a new model of Pi homeostasis.
Collapse
|
26
|
Abstract
The serum phosphorus level is maintained through a complex interplay between intestinal absorption, exchange intracellular and bone storage pools, and renal tubular reabsorption. The kidney plays a major role in regulation of phosphorus homeostasis by renal tubular reabsorption. Type IIa and type IIc Na+/Pi transporters are important renal Na+-dependent inorganic phosphate (Pi) transporters, which are expressed in the brush border membrane of proximal tubular cells. Both are regulated by dietary Pi intake, vitamin D, fibroblast growth factor 23 (FGF23) and parathyroid hormone. The expression of type IIa Na+/Pi transporter result from hypophosphatemia quickly. However, type IIc appears to act more slowly. Physiological and pathophysiological alteration in renal Pi reabsorption are related to altered brush border membrane expression/content of the type II Na+/Pi cotransporter. Many studies of genetic and acquired renal phosphate wasting disorders have led to the identification of novel genes. Two novel Pi regulating genes, PHEX and FGF23, play a role in the pathophysiology of genetic and acquired renal phosphate wasting disorders and studies are underway to define their mechanism on renal Pi regulation. In recent studies, sodium-hydrogen exchanger regulatory factor 1 (NHERF1) is reported as another new regulator for Pi reabsorption mechanism.
Collapse
Affiliation(s)
- Nak-Won Choi
- Depatment of internal Medicine, Konyang University College of Medicine, Daejeon, Korea
| |
Collapse
|
27
|
Vanacker A, Segaert M, Verbanck J, Van Dorpe J, Poppe B, Maes B. Slow progression of chronic renal failure in a woman of short stature and leg deformities: what is the link? NDT Plus 2008; 1:257-61. [PMID: 25983897 PMCID: PMC4421228 DOI: 10.1093/ndtplus/sfn062] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2008] [Accepted: 05/10/2008] [Indexed: 11/12/2022] Open
Affiliation(s)
- An Vanacker
- Department of Nephrology, Heilig Hartziekenhuis Roeselare-Menen, B-8800 Roeselare
| | - Marc Segaert
- Department of Nephrology, Heilig Hartziekenhuis Roeselare-Menen, B-8800 Roeselare
| | - Johan Verbanck
- Department of Nephrology, Heilig Hartziekenhuis Roeselare-Menen, B-8800 Roeselare
| | - Jo Van Dorpe
- Department of Pathology, Heilig Hartziekenhuis Roeselare-Menen, B-8800 Roeselare
| | - Bruce Poppe
- Center for Medical Genetics , Ghent University Hospital , B-9000 Ghent , Belgium
| | - Bart Maes
- Department of Nephrology, Heilig Hartziekenhuis Roeselare-Menen, B-8800 Roeselare
| |
Collapse
|
28
|
Shaikh A, Berndt T, Kumar R. Regulation of phosphate homeostasis by the phosphatonins and other novel mediators. Pediatr Nephrol 2008; 23:1203-10. [PMID: 18288501 PMCID: PMC2441591 DOI: 10.1007/s00467-008-0751-z] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/11/2007] [Revised: 11/29/2007] [Accepted: 12/03/2007] [Indexed: 01/23/2023]
Abstract
A variety of factors regulate the efficiency of phosphate absorption in the intestine and phosphate reabsorption in kidney. Apart from the well-known regulators of phosphate homeostasis, namely parathyroid hormone (PTH) and the vitamin D-endocrine system, a number of peptides collectively known as the "phosphatonins" have been recently identified as a result of the study of various diseases associated with hypophosphatemia. These factors, fibroblast growth factor 23 (FGF-23), secreted frizzled-related protein 4 (sFRP-4), fibroblast growth factor 7 (FGF-7) and matrix extracellular phosphoglycoprotein (MEPE), have been shown to play a role in the pathogenesis of various hypophosphatemic and hyperphosphatemic disorders, such as oncogenic osteomalacia, X-linked hypophosphatemic rickets, autosomal dominant hypophosphatemic rickets, autosomal recessive hypophosphatemia and tumoral calcinosis. Whether these factors are true hormones, in the sense that they are regulated by the intake of dietary phosphorus and the needs of the organism for higher or lower amounts of phosphorus, remains to be firmly established in humans. Additionally, new information demonstrates that the intestine "senses" luminal concentrations of phosphate and regulates the excretion of phosphate in the kidney by elaborating novel factors that alter renal phosphate reabsorption.
Collapse
Affiliation(s)
- Aisha Shaikh
- Division of Nephrology and Hypertension, Department of Internal Medicine, Mayo Clinic Rochester, 200 First St SW, Rochester, MN 55905 USA
| | - Theresa Berndt
- Division of Nephrology and Hypertension, Department of Internal Medicine, Mayo Clinic Rochester, 200 First St SW, Rochester, MN 55905 USA ,Department of Physiology and Biomedical Engineering, Mayo Clinic Rochester, Rochester, MN USA
| | - Rajiv Kumar
- Division of Nephrology and Hypertension, Department of Internal Medicine, Mayo Clinic Rochester, 200 First St SW, Rochester, MN 55905 USA ,Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN USA
| |
Collapse
|
29
|
Otukesh H, Hoseini R, Chalian H, Chalian M, Safarzadeh AE, Shakiba M, Poorian A. Hyperostosis with hyperphosphatemia and tumoral calcinosis: a case report. Pediatr Nephrol 2007; 22:1235-7. [PMID: 17437133 DOI: 10.1007/s00467-007-0476-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/24/2006] [Revised: 02/09/2007] [Accepted: 02/20/2007] [Indexed: 10/23/2022]
Abstract
The combination of hyperostosis and hyperphosphatemia is very rare. In this case report, we present a boy with a combination of diffuse hyperostosis and hyperphosphatemia. We evaluated most possible known causes of hyperphosphatemia and hyperostosis. He had normal renal function and serum parathormone level. Concerning some few similar cases, most of them from Middle Eastern countries, we present this combination (diffuse hyperostosis and hyperphosphatemia) as a new syndrome to be discussed in pediatric textbooks.
Collapse
|
30
|
Sommer S, Berndt T, Craig T, Kumar R. The phosphatonins and the regulation of phosphate transport and vitamin D metabolism. J Steroid Biochem Mol Biol 2007; 103:497-503. [PMID: 17224271 DOI: 10.1016/j.jsbmb.2006.11.010] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Phosphate homeostasis is preserved during variations in phosphate intake by short-term intrinsic renal and intestinal adaptations in transport processes, and by more long-term hormonal mechanisms, which regulate the efficiency of phosphate transport in the kidney and intestine. Recently, several phosphaturic peptides such as fibroblast growth factor 23 (FGF-23), secreted frizzled-related protein-4 (sFRP-4), extracellular phosphoglycoprotein (MEPE) and fibroblast growth factor 7 (FGF-7) have been shown to play a pathogenic role in several hypophosphatemic disorders such as tumor-induced osteomalacia (TIO), autosomal dominant hypophosphatemic rickets (ADHR), X-linked hypophosphatemic rickets (XLH), the McCune-Albright syndrome (MAS) and fibrous dysplasia (FD). These proteins induce phosphaturia and hypophosphatemia in vivo, and inhibit sodium-dependent renal phosphate transport in cultured renal epithelial cells. Interestingly, despite the induction of hypophosphatemia by FGF-23 and sFRP-4 in vivo, serum 1, 25-dihydroxyvitamin D (1alpha,25(OH)(2)D) concentrations are decreased or remain inappropriately normal, suggesting an inhibitory effect of these proteins on 25-hydroxyvitamin D 1alpha-hydroxylase activity. In FGF-23 knockout mice, 25-hydroxyvitamin D 1alpha-hydroxylase expression is increased and elevated serum 1alpha,25(OH)(2)D levels cause significant hypercalcemia and hyperphosphatemia. MEPE, however, increases circulating 1alpha,25(OH)(2)D. Circulating or local concentrations of these peptides/proteins may regulate 25-hydroxyvitamin D 1alpha-hydroxylase activity in renal tissues under physiologic circumstances.
Collapse
Affiliation(s)
- Stacy Sommer
- Nephrology and Hypertension Research, Department of Medicine, Biochemistry and Molecular Biology, Mayo Clinic, MS 1-120, 200 First Street SW, Rochester, MN 55905, USA
| | | | | | | |
Collapse
|
31
|
Abstract
Inorganic phosphate (P(i)) is required for energy metabolism, nucleic acid synthesis, bone mineralization, and cell signaling. The activity of cell-surface sodium-phosphate (Na(+)-P(i)) cotransporters mediates the uptake of P(i) from the extracellular environment. Na(+)-P(i) cotransporters and organ-specific P(i) absorptive processes are regulated by peptide and sterol hormones, such as parathyroid hormone (PTH) and 1alpha,25-dihydroxyvitamin D (1alpha,25(OH)(2)D(3)), which interact in a coordinated fashion to regulate P(i) homeostasis. Recently, several phosphaturic peptides such as fibroblast growth factor-23 (FGF-23), secreted frizzled related protein-4 (sFRP-4), matrix extracellular phosphoglycoprotein, and fibroblast growth factor-7 have been demonstrated to play a pathogenic role in several hypophosphatemic disorders. By inhibiting Na(+)-P(i) transporters in renal epithelial cells, these proteins increase renal P(i) excretion, resulting in hypophosphatemia. FGF-23 and sFRP-4 inhibit 25-hydroxyvitamin D 1alpha-hydroxylase activity, reducing 1alpha,25(OH)(2)D(3) synthesis and thus intestinal P(i) absorption. This review examines the role of these factors in P(i) homeostasis in health and disease.
Collapse
Affiliation(s)
- Theresa Berndt
- Nephrology and Hypertension Research, Department of Medicine, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA
| | | |
Collapse
|
32
|
Burnett SAM, Gunawardene SC, Bringhurst FR, Jüppner H, Lee H, Finkelstein JS. Regulation of C-terminal and intact FGF-23 by dietary phosphate in men and women. J Bone Miner Res 2006; 21:1187-96. [PMID: 16869716 DOI: 10.1359/jbmr.060507] [Citation(s) in RCA: 331] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
UNLABELLED FGF-23 is a novel regulator of phosphate metabolism. We studied the regulation of FGF-23 by dietary phosphate in 66 men and women using two assays. Dietary phosphate restriction decreased FGF-23 and loading increased FGF-23 significantly. An assay that measured intact FGF-23 showed the effects of dietary phosphate much more clearly than an assay that also measures presumed biologically inactive fragments. Dietary phosphate is a key regulator of circulating FGF-23; choice of assay is critical when studying FGF-23 physiology. INTRODUCTION Fibroblast growth factor 23 (FGF-23) is a novel phosphaturic factor discovered through genetic studies of patients with renal phosphate wasting disorders. Ablation of the FGF-23 gene in mice reduces renal phosphate excretion and increases serum phosphate, suggesting that FGF-23 is critical for normal phosphate homeostasis. We examined the role of dietary phosphate in the regulation of FGF-23 in humans. MATERIALS AND METHODS Sixty-six healthy males and females were randomized to either phosphate-depleted or -loaded diets for 5 days, after a 4-day run-in diet. FGF-23 was measured using an "intact" assay that only detects intact FGF-23 peptide and with a "C-terminal" assay that measures both intact FGF-23 peptide and presumed biologically inactive carboxyl terminal fragments. The main outcome was the within group change in FGF-23 with either phosphate depletion or loading. RESULTS Using the intact FGF-23 assay, mean FGF-23 area under the curve (AUC) decreased by 9 +/- 16% with phosphate depletion (p = 0.0041) and increased by 35 +/- 29% with loading (p < 0.0001). Using the C-terminal FGF-23 assay, mean FGF-23 AUC decreased by 8 +/- 12% with phosphate depletion (p = 0.0003) and increased by 13 +/- 20% with loading (p = 0.0016). Increases in FGF-23 with phosphate loading were greater with the intact assay than with the C-terminal assay (p = 0.0003). Using the intact assay only, FGF-23 was significantly associated with serum phosphate (r = 0.39, p < 0.01), 24-h urinary phosphate (r = 0.47, p < 0.01), fractional excretion of phosphate (r = 0.29, p < 0.01), and 1,25-dihydroxyvitamin D (r = -0.30, p < 0.01). The association between the assays was weak (r = 0.26, p < 0.01). CONCLUSIONS Dietary phosphate is a key regulator of circulating FGF-23 levels in humans. Additionally, choice of assay is critical when performing physiologic investigations of FGF-23.
Collapse
|
33
|
Uno JK, Kolek OI, Hines ER, Xu H, Timmermann BN, Kiela PR, Ghishan FK. The role of tumor necrosis factor alpha in down-regulation of osteoblast Phex gene expression in experimental murine colitis. Gastroenterology 2006; 131:497-509. [PMID: 16890604 DOI: 10.1053/j.gastro.2006.05.020] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/13/2005] [Accepted: 05/04/2006] [Indexed: 02/02/2023]
Abstract
BACKGROUND & AIMS Reduced bone mass is a common complication of inflammatory bowel disease (IBD), although the mechanisms that contribute to osteopenia are not completely understood. Tumor necrosis factor alpha (TNF-alpha) is up-regulated in patients with IBD and has detrimental effects on osteoblasts. Phex gene is expressed predominantly in osteoblasts, and its disruption results in defective bone mineralization. The aim of this study was to evaluate whether TNF-alpha regulates Phex gene expression thus contributing to the abnormal bone metabolism observed in IBD. METHODS Phex gene expression was evaluated in calvaria of 6-7-week-old mice administered with trinitrobenzene sulfonic acid (TNBS) with or without neutralizing anti-TNF-alpha antibody, dietary curcumin, or systemically with recombinant TNF-alpha. TNF-alpha-treated UMR-106 osteoblasts were also examined. Phex promoter activity was assayed in transiently transfected TNF-alpha-treated UMR-106 cells. RESULTS Compared with control animals, Phex messenger RNA (mRNA) expression decreased by 40%-50% in both TNBS colitis and TNF-alpha-injected mice. Dietary curcumin and anti-TNF-alpha antibody counteracted the detrimental effect of TNBS on Phex gene expression. TNF-alpha-treated UMR-106 cells showed a concentration-dependent and transcriptionally mediated decrease in Phex mRNA and gene promoter activity, with the -133 to -74 bp region of the Phex promoter likely involved in the mechanism of TNF-alpha action. Coinciding with decreased Phex protein level, TNF-alpha drastically reduced mineralization in UMR-106 osteoblasts. CONCLUSIONS Acute colitis and TNF-alpha decrease Phex mRNA and protein expression via a transcriptional mechanism. TNF-alpha-mediated reduction in Phex protein is at least in part responsible for inhibition of osteoblast mineralization, and the described mechanism may contribute to the abnormal bone metabolism associated with IBD.
Collapse
Affiliation(s)
- Jennifer K Uno
- Department of Pediatrics, Steele Children's Research Center, University of Arizona Health Sciences Center, Tucson, Arizona 85724, USA
| | | | | | | | | | | | | |
Collapse
|
34
|
Correction of the mineralization defect in hyp mice treated with protease inhibitors CA074 and pepstatin. Bone 2006; 39:773-86. [PMID: 16762607 DOI: 10.1016/j.bone.2006.04.012] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2005] [Revised: 03/23/2006] [Accepted: 04/04/2006] [Indexed: 12/15/2022]
Abstract
Increased expression of several osteoblastic proteases and MEPE (a bone matrix protein) occurs in X-linked hypophosphatemic rickets (hyp). This is associated with an increased release of a protease-resistant MEPE peptide (ASARM peptide), a potent inhibitor of mineralization. Cathepsin B cleaves MEPE releasing ASARM peptide and hyp osteoblast/osteocyte cells hypersecrete cathepsin D, an activator of cathepsin B. Our aims were to determine whether cathepsin inhibitors correct the mineralization defect in vivo and whether hyp-bone ASARM peptide levels are reduced after protease treatment. Normal littermates and hyp mice (n = 6) were injected intraperitoneally once a day for 4 weeks with pepstatin, CAO74 or vehicle. Animals were then sacrificed and bones plus serum removed for comprehensive analysis. All hyp mice groups (treated and untreated) remained hypophosphatemic with serum 1,25 vitamin D3 inappropriately normal. Serum PTH was significantly elevated in all hyp mice groups relative to normal mice (P = 0.0017). Untreated hyp mice had six-fold elevated levels of serum alkaline-phosphatase and two-fold elevated levels of ASARM peptides relative to normal mice (P < 0.001). In contrast, serum alkaline phosphatase and serum ASARM peptides were significantly reduced (normalized) in hyp mice treated with CA074 or pepstatin. Serum FGF23 levels remained high in all hyp animal groups (P < 0.0001). Hyp mice treated with protease inhibitors showed dramatic reductions in unmineralized osteoid (femurs) compared to control hyp mice (Goldner staining). Also, hyp animals treated with protease inhibitors showed marked and significant improvements in growth plate width (42%), osteoid thickness (40%) and cortical area (40%) (P < 0.002). The mineralization apposition rate, bone formation rate and mineralization surface were normalized by protease-treatment. High-resolution pQCT mineral histomorphometry measurements and uCT also confirmed a marked mineralization improvement. Finally, the growth plate and cortical bone of hyp femurs contained a massive accumulation of osteoblast-derived ASARM peptide(s) that was reduced in hyp animals treated with CA074 or pepstatin. This study confirms in vivo administration of cathepsin inhibitors improves bone mineralization in hyp mice. This may be due to a protease inhibitor mediated decrease in proteolytic degradation of the extracellular matrix and a reduced release of ASARM peptides (potent mineralization inhibitors).
Collapse
|
35
|
Abstract
Complete and limited proteolysis represents key events that regulate many biological processes. At least 5% of the human genome codes for components of proteolytic processes if proteases, inhibitors, and cofactors are taken into account. Accordingly, disruption of proteolysis is involved in numerous pathological conditions. In particular, molecular genetic studies have identified a growing number of monogenic disorders caused by mutations in protease coding genes, highlighting the importance of this class of enzymes in development, organogenesis, immunity, and brain function. This review provides insights into the current knowledge about the molecular genetic causes of these disorders. It should be noted that most are due to loss of function mutations, indicating absolute requirement of proteolytic activities for normal cellular functions. Recent progress in understanding the function of the implicated proteins and the disease pathogenesis is detailed. In addition to providing important clues to the diagnosis, treatment, and pathophysiology of disease, functional characterisation of mutations in proteolytic systems emphasises the pleiotropic functions of proteases in the body homeostasis.
Collapse
Affiliation(s)
- I Richard
- Généthon CNRS UMR8115, 1, rue de l'internationale, 91000 Evry, France.
| |
Collapse
|
36
|
Pande S, Ritter CS, Rothstein M, Wiesen K, Vassiliadis J, Kumar R, Schiavi SC, Slatapolsky E, Brown AJ. FGF-23 and sFRP-4 in chronic kidney disease and post-renal transplantation. Nephron Clin Pract 2006; 104:p23-32. [PMID: 16691036 PMCID: PMC4446726 DOI: 10.1159/000093277] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2005] [Accepted: 02/02/2006] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND The phosphatonins fibroblast growth factor-23 (FGF-23) and FRP-4 are inhibitors of tubular phosphate reabsorption that may play a role in the hyperphosphatemia associated with chronic kidney disease (CKD) or in the hypophosphatemia associated with renal transplants. METHODS Plasma FGF-23, FRP-4, phosphorus and parathyroid hormone were measured in patients at all stages of CKD. Phosphate regulation of FGF-23 and secreted frizzled related protein-4 (sFRP-4) was examined in end-stage renal disease patients in the presence and absence of therapeutic phosphate binder usage. In renal transplant patients, plasma FGF-23, sFRP-4 and phosphorus concentrations were determined before and 4-5 days after transplantation. RESULTS Plasma FGF-23 correlated with creatinine clearance (r2 = -0.584, p < 0.0001) and plasma phosphorus (r2 = 0.347, p < 0.001) in CKD patients and with plasma phosphorus (r2 = 0.448, p < 0.001) in end-stage renal disease patients. Phosphate binder withdrawal increased FGF-23 levels. In kidney transplant patients, dramatic decreases in FGF-23 (-88.8 +/- 5.4%) and phosphorus (-64 +/- 10.2%) were observed by 4-5 days post-transplantation. In patients with post-transplant hypophosphatemia, FGF-23 levels correlated inversely with plasma phosphorus (r2 = 0.661, p < 0.05). sFRP-4 levels did not change with creatinine clearance or hyperphosphatemia in CKD or end-stage renal disease patients, and no relation was noted between post-transplant sFRP-4 levels and hypophosphatemia. CONCLUSIONS In CKD, FGF-23 levels rose with decreasing creatinine clearance rates and increasing plasma phosphorus levels, and rapidly decreased post-transplantation suggesting FGF-23 is cleared by the kidney. Residual FGF-23 may contribute to the hypophosphatemia in post-transplant patients.
Collapse
Affiliation(s)
- Sangeeta Pande
- Renal Division, Washington University School of Medicine, St Louis, MO
| | - Cynthia S. Ritter
- Renal Division, Washington University School of Medicine, St Louis, MO
| | - Marcos Rothstein
- Renal Division, Washington University School of Medicine, St Louis, MO
| | - Karen Wiesen
- Renal Division, Washington University School of Medicine, St Louis, MO
| | | | - Rajiv Kumar
- Mayo Clinic and Foundation, Rochester, Minnesota
| | | | | | - Alex J. Brown
- Renal Division, Washington University School of Medicine, St Louis, MO
| |
Collapse
|
37
|
Affiliation(s)
- R Kumar
- Division of Nephrology and Hypertension, Department of Medicine, Mayo Clinic, Rochester, MN 55905, USA
| |
Collapse
|
38
|
Ebert R, Schütze N, Adamski J, Jakob F. Vitamin D signaling is modulated on multiple levels in health and disease. Mol Cell Endocrinol 2006; 248:149-59. [PMID: 16406653 DOI: 10.1016/j.mce.2005.11.039] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Vitamin D signaling is dependent on the availability and turnover of the active Vitamin D receptor (VDR) ligand 1,25-dihydroxycholecalciferol and on the efficiency of VDR transactivation. Activating and inactivating secosteroid metabolizing p450 enzymes, e.g. 25-hydroxylases, 1alpha-hydroxylase and 24-hydroxylase, are responsible for ligand availability on the basis of substrate production in the skin and of nutritional intake of precursors. Net availability of active hormone depends on the delivery of substrate and the balance of activating and inactivating enzymes. 1Alpha-hydroxylase is the critical activating enzyme. It is expressed in the kidney for systemic supply and in target tissues for local secosteroid activation. It is upregulated in the kidney by low calcium intake and parathyroid hormone, downregulated by phosphatonins and proinflammatory signal transduction. Transactivation of VDR depends on the correct molecule structure, effective nuclear translocation and the presence of the unliganded heterodimer partner retinoid X-receptor (RXR) and other nuclear cofactors. Rapid Vitamin D-dependent membrane associated effects and consecutive second messenger activation exert an own pattern of gene regulation. A membrane receptor for these effects is hypothesized but not yet identified. Rickets is the long known clinical syndrome of impaired Vitamin D signaling due to Vitamin D3 deficiency. It can be caused by inherited defects of the cascade, nutritional deficits, lack of sunlight exposure, malabsorption and underlying diseases like chronic inflammation. It has been shown during the last decades that many modifiers of Vitamin D signaling are targets of disease in terms of inherited and acquired syndromes and that Vitamin D signaling is modulated at multiple levels and is more complex than mere mechanistic ligand/receptor/DNA interaction.
Collapse
Affiliation(s)
- Regina Ebert
- Musculosceletal Research Center, Orthopedic Department, University of Wuerzburg, Brettreichstrasse 11, D-97074 Wuerzburg, Germany
| | | | | | | |
Collapse
|
39
|
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.
Collapse
Affiliation(s)
- Nathalie Alos
- Genetics Unit, Shriners Hospital, Departments of Surgery and Human Genetics, McGill University, Montreal, Quebec, Canada.
| | | |
Collapse
|
40
|
Laroche M, Boyer JF. Phosphate diabetes, tubular phosphate reabsorption and phosphatonins. Joint Bone Spine 2005; 72:376-81. [PMID: 16214071 DOI: 10.1016/j.jbspin.2004.07.013] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2004] [Accepted: 07/23/2004] [Indexed: 01/20/2023]
Abstract
Phosphate diabetes is defined as inadequate tubular reabsorption. Hypophosphatemia is responsible for most of the clinical manifestations, which vary with the age of the patient and the severity of the phosphate wasting. Vitamin D-resistant rickets in children or osteomalacia in adults, osteoporosis, bone pain including spinal pain, and pain in the joints and periarticular areas are the main manifestations. Several factors are known to affect tubular phosphate reabsorption via the sodium/phosphate cotransporters located on the tubular cell membranes. Factors that decrease phosphate reabsorption include a high intake of dietary phosphate, acidosis, parathyroid hormone (PTH), PTH-related peptide (PTHrp), glucocorticoid therapy, calcitonin, and vitamin D. On the other hand, a low-phosphate diet, alkalosis, growth hormone, insulin, IGF-1, and thyroid hormones increase tubular phosphate reabsorption. Physiological concepts about tubular phosphate reabsorption have been radically changed by the recent identification of phosphaturic factors called phosphatonins. The most extensively studied phosphatonin to date is fibroblast growth factor 23 (FGF23), which was first identified in patients with tumor-induced osteomalacia and shown to be secreted by the neoplastic cells. The FGF23 has also been implicated in autosomal dominant hypophosphatemic rickets, in which a gene mutation results in production of abnormal FGF23 that resists hydrolysis. In healthy individuals, FGF23 contributes to regulate phosphate reabsorption via Na/Pi cotransporters. Other phosphatonins may exist, such as matrix extracellular phosphoglycoprotein (MEPE) and secreted frizzled-related protein 4 (SFRP4), whose role remains to be defined. The part played by these proteins in idiopathic renal phosphate wasting in adults needs to be investigated.
Collapse
Affiliation(s)
- Michel Laroche
- Rheumatology Department, Rangueil Teaching Hospital, Toulouse, France.
| | | |
Collapse
|
41
|
Cho HY, Lee BH, Kang JH, Ha IS, Cheong HI, Choi Y. A clinical and molecular genetic study of hypophosphatemic rickets in children. Pediatr Res 2005; 58:329-33. [PMID: 16055933 DOI: 10.1203/01.pdr.0000169983.40758.7b] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
X-linked hypophosphatemic rickets (XLH), autosomal dominant hypophosphatemic rickets, hereditary hypophosphatemic rickets with hypercalciuria, and tumor-induced osteomalacia share clinical and biochemical features, and are collectively referred to as hypophosphatemic rickets (HR). Recently, the molecular bases of HR were elucidated. A review of medical records and mutational analyses of the PHEX and FGF23 genes were performed on 17 unrelated Korean children with HR. The male-to-female ratio was 3:14, and 5 patients were familial. Initial laboratory tests revealed typical features of HR. Seven different PHEX mutations were detected in 8 patients: 2 missense mutations, 2 nonsense mutations, and 3 short deletions. No functional FGF23 mutation was detected in any patient. Patients with the PHEX mutation tended to have more severe skeletal disease than those without. Of the patients with this mutation, no genotype-phenotype correlation and no gene dosage effect were noted. Treatment with vitamin D and phosphate resulted in only a partial growth improvement in most cases, and was frequently complicated by hypercalciuria, hypercalcemia, nephrocalcinosis, or hyperparathyroidism. Renal glycosuria was detected in six cases and was associated with more severe skeletal disease. We conclude that current HR treatment is not fully safe or effective, and that close monitoring of treatment effectiveness and for complications should be performed during long-term treatment. No genotype-phenotype correlation in XLH was detected in this study, but a large-scaled study on this topic is warranted. The large proportion of patients with a normal genetic study suggests the possibility of other causative gene(s).
Collapse
Affiliation(s)
- Hee Y Cho
- Department of Pediatrics, Seoul National University Children's Hospital, Seoul 110-744, Korea
| | | | | | | | | | | |
Collapse
|
42
|
Beraud G, Perimenis P, Velayoudom FL, Wemeau JL, Vantyghem MC. [Genetic hypophosphatemia: recent advances in physiopathogenic concept]. ANNALES D'ENDOCRINOLOGIE 2005; 66:109-16. [PMID: 15959411 DOI: 10.1016/s0003-4266(05)81707-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Renal proximal tubular reabsorption of phosphate and intestinal absorption both regulate phosphate homeostasis. Brush-border membrane Npt2a cotransporter is the key element in proximal tubular P (i) reabsorption. Inactivating mutations of Npt2a cause bone demineralisation and urolithiasis. An excess of a phosphaturic factor, called "Phosphatonin", could modulate phosphate reabsorption by inhibition on Npt2a. Inactivating mutation of PHEX, an endopeptidase-membrane coding gene, is responsible for X-linked Hypophosphatemia (XLH), because of an impaired degradation of phosphatonine by PHEX product. Autosomic Dominant Hypophosphatemic Rickets (ADHR) is explained by a mutation preventing FGF23 (one of the best identified phosphatonines) from cleavage. According recent data, FGF23, MEPE (Matrix Extracellular Phosphoglycoprotein) et FRP4 (frizzled related protein-4) are 3 putative "phosphatonines".
Collapse
Affiliation(s)
- G Beraud
- Service d'Endocrinologie et Métabolisme, 6, rue du Pr. Laguesse, Centre hospitalo-universitaire, 59037 Lille Cedex, France
| | | | | | | | | |
Collapse
|
43
|
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
|
44
|
Tanaka H. New Horizon of X-Linked Hypophosphatemia: Overview. Clin Pediatr Endocrinol 2005. [DOI: 10.1297/cpe.14.s23_17] [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
|
45
|
Shimada T. Possible Roles of Fibroblast Growth Factor 23 in Developing X-Linked Hypophosphatemia. Clin Pediatr Endocrinol 2005. [DOI: 10.1297/cpe.14.s23_33] [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
|
46
|
Hines ER, Kolek OI, Jones MD, Serey SH, Sirjani NB, Kiela PR, Jurutka PW, Haussler MR, Collins JF, Ghishan FK. 1,25-dihydroxyvitamin D3 down-regulation of PHEX gene expression is mediated by apparent repression of a 110 kDa transfactor that binds to a polyadenine element in the promoter. J Biol Chem 2004; 279:46406-14. [PMID: 15337762 DOI: 10.1074/jbc.m404278200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The PHEX gene encodes an endopeptidase expressed in osteoblasts that inactivates an uncharacterized peptide hormone, phosphatonin, which suppresses bone mineralization as well as renal phosphate reabsorption and vitamin D bioactivation. We demonstrate that 1alpha-25-dihydroxyvitamin D (1,25(OH)2D3), the, active renal vitamin D metabolite, decreases PHEX mRNA in the rat osteoblastic cell line, UMR-106, as well as in mouse calvaria. Promoter/reporter construct analysis of the murine PHEX gene in transfected UMR-106 cells localized the repressive effect of 1,25(OH)2D3 to the -133 to -74 bp region, and gel mobility shift experiments revealed that 1,25(OH)2D3 treatment of the cells diminished the binding of a nuclear protein(s) to a stretch of 17 adenines from bp -116 to -100 in the proximal PHEX promoter. Either overexpression of a dominant-negative vitamin D receptor (VDR) or deletion of this sequence of 17 A-T base pairs abolished the repressive effect of 1,25(OH)2D3 by attenuating basal promoter activity, indicating that this region mediates the 1,25(OH)2D3 response and is involved in basal transcription. South-western blot analysis and DNA affinity purification show that an unidentified 110 kDa nuclear protein binds to the poly(A) element. Because 1,25(OH)2D3-liganded VDR neither binds to the polyadenine region of the PHEX promoter nor directly influences the association of the 110 kDa transfactor, we conclude that 1,25(OH)2D3 indirectly decreases PHEX expression via VDR-mediated repression (or modification) of this novel transactivator. Thus, we have identified a cis-element required for PHEX gene transcription that participates in negative feedback control of PHEX expression and thereby modulates the actions of phosphatonin.
Collapse
MESH Headings
- Adenine/chemistry
- Animals
- Base Sequence
- Binding Sites
- Blotting, Northern
- Blotting, Southern
- Blotting, Western
- Bone and Bones/metabolism
- Calcitriol/pharmacology
- Cell Line
- Cell Nucleus/metabolism
- DNA/metabolism
- Down-Regulation
- Gene Deletion
- Genes, Dominant
- Hormones/chemistry
- Ligands
- Male
- Mice
- Mice, Inbred C57BL
- Models, Genetic
- Molecular Sequence Data
- Osteoblasts/metabolism
- PHEX Phosphate Regulating Neutral Endopeptidase
- Poly A
- Promoter Regions, Genetic
- Protein Structure, Tertiary
- Proteins/genetics
- Proteins/metabolism
- RNA, Messenger/metabolism
- Rats
- Reverse Transcriptase Polymerase Chain Reaction
- Sarcoma/metabolism
- Time Factors
- Transcription, Genetic
- Transcriptional Activation
- Transfection
Collapse
Affiliation(s)
- Eric R Hines
- Department of Pediatrics, College of Medicine, Steele Memorial Children's Research Center, University of Arizona, Tucson, Arizona 85724, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
47
|
Abstract
PURPOSE OF REVIEW The search for hormones which specifically regulate phosphate metabolism has fuelled recent tantalizing studies. These studies have been motivated by diseases involving renal phosphate wasting, including tumor-induced osteomalacia, X-linked hypophosphatemic rickets, and autosomal dominant hypophosphatemia. This review focuses on likely candidate 'phosphatonins' and their possible physiological significance. RECENT FINDINGS Candidate phosphatonins include fibroblast growth factor 23, matrix extracellular phosphoglycoprotein, stanniocalcin, and Frizzled-related protein 4. Fibroblast growth factor 23 has emerged as the prime candidate explaining pathophysiology of these diseases. FGF-23 is expressed in most tumors in tumor-induced osteomalacia. Serum fibroblast growth factor 23 is increased in most patients with X-linked hypophosphatemic rickets and tumor-induced osteomalacia. Injection of recombinant fibroblast growth factor 23 induces phosphaturia, hypophosphatemia, and suppression of 1,25-dihydroxyvitamin D in animals. Many unanswered questions remain, including the relationship between PHEX (phosphate-regulating gene with homologies to endopeptidases on the X chromosome) mutations and elevated fibroblast growth factor 23. It is also not clear whether these candidate phosphatonins play a role in phosphate or vitamin D metabolism in healthy humans, or that this role is endocrine. The most compelling evidence derives from the fibroblast growth factor 23-knockout mouse which shows hyperphosphatemia and increased serum 1,25-dihydroxyvitamin D. A physiologically relevant phosphatonin should explain renal adaptation to variable dietary phosphate intake. The tissue source and determinants of serum fibroblast growth factor 23 are unknown. SUMMARY Pathophysiological and animal studies serve as a logical foundation on which to base further questions of human physiology. The definition of what is or is not a phosphatonin may need to be refined. There is a need to return to 'old-fashioned' human physiology studies to place recent findings in perspective.
Collapse
Affiliation(s)
- Aubrey Blumsohn
- Academic Unit of Bone Metabolism, Division of Clinical Sciences (North), University of Sheffield, Sheffield, UK.
| |
Collapse
|
48
|
Seifi S, Pezeshki ML, Khatami MR, Mazdeh MM, Ahmadi F, Maziar S. Post-renal transplantation hypophosphatemia. Transplant Proc 2004; 35:2645-6. [PMID: 14612053 DOI: 10.1016/j.transproceed.2003.08.056] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- S Seifi
- Department of Nephrology, Imam Khomeni Hospital, Tehran University of Medical Sciences, Tehran, Iran.
| | | | | | | | | | | |
Collapse
|
49
|
|
50
|
Tartaix PH, Doulaverakis M, George A, Fisher LW, Butler WT, Qin C, Salih E, Tan M, Fujimoto Y, Spevak L, Boskey AL. In Vitro Effects of Dentin Matrix Protein-1 on Hydroxyapatite Formation Provide Insights into in Vivo Functions. J Biol Chem 2004; 279:18115-20. [PMID: 14769788 DOI: 10.1074/jbc.m314114200] [Citation(s) in RCA: 148] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Dentin matrix protein-1 (DMP1) is a mineralized tissue matrix protein synthesized by osteoblasts, hypertrophic chondrocytes, and ameloblasts as well as odontoblasts. DMP1 is believed to have multiple in vivo functions, acting both as a signaling molecule and a regulator of biomineralization. Using a cell-free system in vitro, we evaluated the action of DMP1 in the regulation of hydroxylapatite (HA) formation and crystal growth. The non-phosphorylated recombinant protein acted as an HA nucleator, increasing the amount of mineral formed in a gelatin gel HA growth system relative to protein-free controls. The recombinant protein phosphorylated in vitro had no detectable effect on HA formation and growth. In contrast, phosphorylated bovine DMP1 expressed in marrow stromal cells with an adenovirus vector containing 29.7 phosphates/mol was an effective inhibitor of HA formation and growth. The native full-length protein appeared to be absent or present in only small amounts in the extracellular matrix of bones and teeth. However, two highly phosphorylated fragments representing the N- and C-terminal portions of DMP1 have been identified, apparently arising from proteolytic cleavage of four X-Asp bonds. The highly phosphorylated C-terminal 57-kDa fragment (containing 42 phosphates/mol), like the non-phosphorylated DMP1, was an HA nucleator. These data suggest that, in its native form, DMP1 inhibits mineralization, but when cleaved or dephosphorylated, it initiates mineralization. These in vitro data are consistent with the findings in the DMP1 knockout mouse.
Collapse
Affiliation(s)
- Philippe H Tartaix
- Columbia University School of Dental and Oral Surgery, New York, New York 10032, USA
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|