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Yang Y, Wang Y, Shen Y, Liu M, Dai S, Wang X, Liu H. Identification of a Novel Missense Mutation of the PHEX Gene in a Large Chinese Family with X-Linked Hypophosphataemia. Front Genet 2022; 13:792183. [PMID: 35251124 PMCID: PMC8891598 DOI: 10.3389/fgene.2022.792183] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2021] [Accepted: 01/18/2022] [Indexed: 11/13/2022] Open
Abstract
X-linked hypophosphataemia (XLH) is an X-linked dominant rare disease that refers to the most common hereditary hypophosphatemia (HH) caused by mutations in the phosphate-regulating endopeptidase homolog X-linked gene (PHEX; OMIM: * 300550). However, mutations that have already been reported cannot account for all cases of XLH. Extensive genetic analysis can thus be helpful for arriving at the diagnosis of XLH. Herein, we identified a novel heterozygous mutation of PHEX (NM_000444.5: c.1768G > A) in a large Chinese family with XLH by whole-exome sequencing (WES). In addition, the negative effect of this mutation in PHEX was confirmed by both bioinformatics analysis and in vitro experimentation. The three-dimensional protein-model analysis predicted that this mutation might impair normal zinc binding. Immunofluorescence staining, qPCR, and western blotting analysis confirmed that the mutation we detected attenuated PHEX protein expression. The heterozygous mutation of PHEX (NM_000444.5: c.1768G > A) identified in this study by genetic and functional experiments constitutes a novel genetic cause of XLH, but further study will be required to expand its use in clinical and molecular diagnoses of XLH.
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Affiliation(s)
- Yanting Yang
- Department of Obstetrics and Gynecology, West China Second University Hospital, Sichuan University, Chengdu, China
- Medical Genetics Department/Prenatal Diagnostic Center, West China Second University Hospital, Sichuan University, Chengdu, China
- Key Laboratory of Birth Defects and Related Diseases of Women and Children, Ministry of Education, Sichuan University, Chengdu, China
| | - Yuanda Wang
- State Key Laboratory of Biotherapy and Cancer Center, Sichuan University, Chengdu, China
| | - Ying Shen
- Department of Obstetrics/Gynecology, Joint Laboratory of Reproductive Medicine (SCU-CUHK), Key Laboratory of Obstetric, Gynecologic and Pediatric Diseases and Birth Defects of Ministry of Education, West China Second University Hospital, Sichuan University, Chengdu, China
| | - Mohan Liu
- State Key Laboratory of Biotherapy and Cancer Center, Sichuan University, Chengdu, China
| | - Siyu Dai
- Department of Obstetrics and Gynecology, West China Second University Hospital, Sichuan University, Chengdu, China
- Medical Genetics Department/Prenatal Diagnostic Center, West China Second University Hospital, Sichuan University, Chengdu, China
- Key Laboratory of Birth Defects and Related Diseases of Women and Children, Ministry of Education, Sichuan University, Chengdu, China
| | - Xiaodong Wang
- Department of Obstetrics and Gynecology, West China Second University Hospital, Sichuan University, Chengdu, China
- Key Laboratory of Birth Defects and Related Diseases of Women and Children, Ministry of Education, Sichuan University, Chengdu, China
- *Correspondence: Xiaodong Wang, ; Hongqian Liu,
| | - Hongqian Liu
- Department of Obstetrics and Gynecology, West China Second University Hospital, Sichuan University, Chengdu, China
- Medical Genetics Department/Prenatal Diagnostic Center, West China Second University Hospital, Sichuan University, Chengdu, China
- Key Laboratory of Birth Defects and Related Diseases of Women and Children, Ministry of Education, Sichuan University, Chengdu, China
- *Correspondence: Xiaodong Wang, ; Hongqian Liu,
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McKnight Q, Jenkins S, Li X, Nelson T, Marlier A, Cantley LG, Finberg KE, Fretz JA. IL-1β Drives Production of FGF-23 at the Onset of Chronic Kidney Disease in Mice. J Bone Miner Res 2020; 35:1352-1362. [PMID: 32154933 PMCID: PMC7363582 DOI: 10.1002/jbmr.4003] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Revised: 02/14/2020] [Accepted: 03/04/2020] [Indexed: 12/27/2022]
Abstract
FGF-23 has arisen as an early biomarker of renal dysfunction, but at the onset of chronic kidney disease (CKD), data suggest that FGF-23 may be produced independently of the parathyroid hormone (PTH), 1,25(OH)2 -vitamin D3 signaling axis. Iron status is inversely correlated to the level of circulating FGF-23, and improvement in iron bioavailability within patients correlates with a decrease in FGF-23. Alternately, recent evidence also supports a regulatory role of inflammatory cytokines in the modulation of FGF-23 expression. To determine the identity of the signal from the kidney-inducing upregulation of osteocytic FGF-23 at the onset of CKD, we utilized a mouse model of congenital CKD that fails to properly mature the glomerular capillary tuft. We profiled the sequential presentation of indicators of renal dysfunction, phosphate imbalance, and iron bioavailability and transport to identify the events that initiate osteocytic production of FGF-23 during the onset of CKD. We report here that elevations in circulating intact-FGF-23 coincide with the earliest indicators of renal dysfunction (P14), and precede changes in serum phosphate or iron homeostasis. Serum PTH was also not changed within the first month. Instead, production of the inflammatory protein IL-1β from the kidney and systemic elevation of it in the circulation matched the induction of FGF-23. IL-1β's ability to induce FGF-23 was confirmed on bone chips in culture and within mice in vivo. Furthermore, neutralizing antibody to IL-1β blocked FGF-23 expression in both our congenital model of CKD and a second nephrotoxic serum-mediated model. We conclude that early CKD resembles a situation of primary FGF-23 excess mediated by inflammation. These findings do not preclude that altered mineral availability or anemia can later modulate FGF-23 levels but find that in early CKD they are not the driving stimulus for the initial upregulation of FGF-23. © 2020 American Society for Bone and Mineral Research.
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Affiliation(s)
- Quiana McKnight
- Department of Internal Medicine (Nephrology), Yale University School of Medicine, New Haven, CT, USA
| | - Sarah Jenkins
- Department of Internal Medicine (Nephrology), Yale University School of Medicine, New Haven, CT, USA
| | - Xiuqi Li
- Department of Pathology, Yale University School of Medicine, New Haven, CT, USA
| | - Tracy Nelson
- Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT, USA
| | - Arnaud Marlier
- Department of Internal Medicine (Nephrology), Yale University School of Medicine, New Haven, CT, USA
| | - Lloyd G Cantley
- Department of Internal Medicine (Nephrology), Yale University School of Medicine, New Haven, CT, USA
| | - Karin E Finberg
- Department of Pathology, Yale University School of Medicine, New Haven, CT, USA
| | - Jackie A Fretz
- Department of Pathology, Yale University School of Medicine, New Haven, CT, USA.,Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT, USA
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Li B, Wang X, Hao X, Liu Y, Wang Y, Shan C, Ao X, Liu Y, Bao H, Li P. A novel c.2179T>C mutation blocked the intracellular transport of PHEX protein and caused X-linked hypophosphatemic rickets in a Chinese family. Mol Genet Genomic Med 2020; 8:e1262. [PMID: 32511895 PMCID: PMC7434742 DOI: 10.1002/mgg3.1262] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2020] [Accepted: 03/23/2020] [Indexed: 12/13/2022] Open
Abstract
Background X‐linked hypophosphatemic rickets (XLH) is a heterogeneous genetic phosphate wasting disorder that occupies the majority of inheritable hypophosphatemic rickets (HR). XLH is caused by loss‐of‐function mutations in the phosphate‐regulating endopeptidase gene (PHEX) located on the X chromosome. Method In this study, we performed whole‐exome sequencing (WES) on the proband to identify the causative gene. The mutations were analyzed by predictive online software, such as PolyPhen‐2. Plasmids containing the wild‐type (WT) and mutant cDNA of the candidate gene were transfected into HEK293, then, the expression, cellular localization, and glycosylation state of the candidate proteins were detected by western blot, immunostaining, and endoglycosidase H digestion. The expression and concentration of related factor were measured by RT‐PCR and ELISA. Results We identified a novel missense mutation c.2179T>C in the PHEX that results in the substitution of p.Phe727Leu (F727L). This mutation was predicted to be disease‐causing by all four predictive online software. In vitro studies demonstrated that the F727L substitution hindered the intracellular trafficking of the mutant PHEX, with ~59% of mutant PHEX protein retained in the endoplasmic reticulum (ER) and only ~16% of the mutant protein localized on the cell surface. Endoglycosidase H digestion assay showed that the mutant F727L PHEX protein was not fully glycosylated. The concentration of intact FGF23 in hFOB1.19 cell culture medium collected from the mutant PHEX group was the highest (62.9 pg/ml) compared to the WT group (32.1 pg/ml) and control group (23.5 pg/ml). Conclusion Our results confirmed that the mutant PHEX protein was lowly glycosylated and retarded within the ER, the intact FGF23 level in cell culture media caused by the mutant PHEX protein was significantly elevated compared to that of the WT group, which may explain why the single base mutation in the PHEX led to XLH syndrome in this family.
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Affiliation(s)
- Baowei Li
- Institute for Translational Medicine, Qingdao University, Qingdao, China
| | - Xiong Wang
- Department of Reproductive Medicine, Affiliated Yantai Yuhuangding Hospital of Qingdao University, Yantai, China
| | - Xiaodan Hao
- Institute for Translational Medicine, Qingdao University, Qingdao, China
| | - Yanran Liu
- School of Basic Medicine, Qingdao University, Qingdao, China
| | - Yin Wang
- Institute for Translational Medicine, Qingdao University, Qingdao, China
| | - Chan Shan
- Institute for Translational Medicine, Qingdao University, Qingdao, China
| | - Xiang Ao
- Institute for Translational Medicine, Qingdao University, Qingdao, China
| | - Ying Liu
- Institute for Translational Medicine, Qingdao University, Qingdao, China
| | - HongChu Bao
- Department of Reproductive Medicine, Affiliated Yantai Yuhuangding Hospital of Qingdao University, Yantai, China
| | - Peifeng Li
- Institute for Translational Medicine, Qingdao University, Qingdao, China
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Wang T, Yu X, He C. Pro-inflammatory Cytokines: Cellular and Molecular Drug Targets for Glucocorticoid-induced-osteoporosis via Osteocyte. Curr Drug Targets 2020; 20:1-15. [PMID: 29618305 DOI: 10.2174/1389450119666180405094046] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Revised: 03/11/2018] [Accepted: 03/21/2018] [Indexed: 02/08/2023]
Abstract
Glucocorticoids are widely used to treat varieties of allergic and autoimmune diseases, however, long-term application results in glucocorticoid-induced osteoporosis (GIOP). Inflammatory cytokines: tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) play important regulatory roles in bone metabolism, but their roles in GIOP remain largely unknown. Osteocytes can modulate the formation and function of both osteoblasts and osteoclasts, directly via gap junctions, or indirectly by transferring molecule signaling. Apoptotic osteocytes release RANKL, HMGB1 and pro-inflammatory cytokines to stimulate osteoclastogenesis. Moreover, osteocytes can secrete FGF23 to regulate bone metabolism. Exposure to high levels of GCs can drive osteocyte apoptosis and influence gap junctions, leading to bone loss. GCs treatment is regarded to produce more FGF23 to inhibit bone mineralization. GCs also disrupt the vascular to decrease osteocyte feasibility and mineral appositional rate, resulting in a decline in bone strength. Apoptotic bodies from osteocytes induced by GCs treatment can enhance production of TNF-α and IL-6. On the other hand, TNF-α and IL-6 show synergistic effects by altering osteocytes signaling towards osteoclasts and osteoblasts. In addition, TNF-α can induce osteocyte apoptosis and attribute to a worsened bone quality in GCs. IL-6 and osteocytes may interact with each other. Therefore, we hypothesize that GCs regulate osteocyteogenesis through TNF-α and IL-6, which are highly expressed around osteocyte undergoing apoptosis. In the present review, we summarized the roles of osteocytes in regulating osteoblasts and osteoclasts. Furthermore, the mechanism of GCs altered relationship between osteocytes and osteoblasts/osteoclasts. In addition, we discussed the roles of TNF-α and IL-6 in GIOP by modulating osteocytes. Lastly, we discussed the possibility of using pro-inflammatory signaling pathway as therapeutic targets to develop drugs for GIOP.
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Affiliation(s)
- Tiantian Wang
- Department of Rehabilitation Medicine, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China.,Key Laboratory of Rehabilitation Medicine, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China.,Laboratory of Endocrinology and Metabolism, Department of Endocrinology, National Key Laboratory of Biotherapy/Collaborative Innovation Center of Biotherapy and Cancer Center, West China Hospital, Sichuan University, 610041, China
| | - Xijie Yu
- Laboratory of Endocrinology and Metabolism, Department of Endocrinology, National Key Laboratory of Biotherapy/Collaborative Innovation Center of Biotherapy and Cancer Center, West China Hospital, Sichuan University, 610041, China
| | - Chengqi He
- Department of Rehabilitation Medicine, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China.,Key Laboratory of Rehabilitation Medicine, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China
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Yang M, Doshi KB, Roarke MC, Nguyen BD. Molecular Imaging in Diagnosis of Tumor-induced Osteomalacia. Curr Probl Diagn Radiol 2019; 48:379-386. [DOI: 10.1067/j.cpradiol.2018.06.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2018] [Revised: 05/31/2018] [Accepted: 06/20/2018] [Indexed: 11/22/2022]
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Weber TJ, Quarles LD. Molecular Control of Phosphorus Homeostasis and Precision Treatment of Hypophosphatemic Disorders. ACTA ACUST UNITED AC 2019; 5:75-85. [PMID: 31871877 DOI: 10.1007/s40610-019-0118-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Purpose of Review Serum phosphorus is maintained in a narrow range by balancing dietary phosphate absorption, influx and efflux of phosphorus from bone and intracellular stores, and renal reabsorption of filtered phosphate. Acute hypophosphatemia, typically caused by transient increases in cellular uptake, can lead to severe complications such as cardiopulmonary dysfunction and rhabdomyolysis that can warrant parenteral phosphate repletion. Chronic hypophosphatemia, however, generally represents true phosphate deficiency and may result in long-term metabolic and skeletal complications, particularly in children due to the critical importance of phosphorus to skeletal mineralization and longitudinal growth. Recent Findings In addition to the well characterized roles of vitamin D and parathyroid hormone (PTH), a new bone-kidney axis has been discovered that regulates phosphate homeostasis through the bone-derived hormone Fibroblast Growth Factor 23 (FGF23) and its phosphaturic actions that are mediated by activation of fibroblast growth factor receptors (FGFRs) complexed with α-Klotho in renal tubules. Chronic hypophosphatemia can now be classified as FGF23 dependent or independent. Summary In cases of FGF23 dependent hypophosphatemia, traditional non-specific treatments with elemental phosphorus and 1,25(OH)2 vitamin D (calcitriol) can now be replaced with a targeted approach by using an FGF-23 blocking antibody (Burosumab).
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Affiliation(s)
- Thomas J Weber
- Department of Medicine, Division of Endocrinology, Metabolism and Nutrition, 303 Baker House, DUMC 3470, Duke University Medical Center, Durham, NC 27710
| | - L Darryl Quarles
- Department of Medicine, Division of Nephrology 956 Court Ave, Suite B266, University of Tennessee Health Sciences Center, Memphis, TN 38163
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Courbebaisse M, Lanske B. Biology of Fibroblast Growth Factor 23: From Physiology to Pathology. Cold Spring Harb Perspect Med 2018; 8:a031260. [PMID: 28778965 PMCID: PMC5932574 DOI: 10.1101/cshperspect.a031260] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Fibroblast growth factor (FGF)23 is a phosphaturic hormone produced by osteocytes and osteoblasts that binds to FGF receptors in the presence of the transmembrane protein αKlotho. FGF23 mainly targets the renal proximal tubule to inhibit calcitriol production and the expression of the sodium/phosphate cotransporters NaPi2a and NaPi2c, thus inhibiting renal phosphate reabsorption. FGF23 also acts on the parathyroid glands to inhibit parathyroid hormone synthesis and secretion. FGF23 regulation involves many systemic and local factors, among them calcitriol, phosphate, and parathyroid hormone. Increased FGF23 is primarily observed in rare acquired or genetic disorders, but chronic kidney disease is associated with a reactional increase in FGF23 to combat hyperphosphatemia. However, high FGF23 levels induce left ventricular hypertrophy (LVH) and are associated with an increased risk of mortality. In this review, we describe FGF23 physiology and the pathological consequences of high or low FGF23 levels.
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Affiliation(s)
- Marie Courbebaisse
- Division of Bone and Mineral Research OMII, Harvard School of Dental Medicine, Boston, Massachusetts 02115
- Paris Descartes University, Paris 75006, France
| | - Beate Lanske
- Division of Bone and Mineral Research OMII, Harvard School of Dental Medicine, Boston, Massachusetts 02115
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114
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Connor J, Olear EA, Insogna KL, Katz L, Baker S, Kaur R, Simpson CA, Sterpka J, Dubrow R, Zhang JH, Carpenter TO. Conventional Therapy in Adults With X-Linked Hypophosphatemia: Effects on Enthesopathy and Dental Disease. J Clin Endocrinol Metab 2015; 100:3625-32. [PMID: 26176801 PMCID: PMC4596038 DOI: 10.1210/jc.2015-2199] [Citation(s) in RCA: 90] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
CONTEXT Treatment of X-linked hypophosphatemia (XLH) with active vitamin D metabolites and phosphate can partially correct skeletal deformities. It is unclear whether therapy influences the occurrence of two major long-term morbidities in XLH: enthesopathy and dental disease. OBJECTIVE The objective of the study was to investigate the relationship between treatment and enthesopathy and dental disease in adult XLH patients. DESIGN The study was designed as observational and cross-sectional. SETTING The study was conducted at an academic medical center's hospital research unit. PARTICIPANTS Fifty-two XLH patients aged 18 years or older at the time of the study participated in the study. INTERVENTIONS There were no interventions. MAIN OUTCOME MEASURES The number of enthesopathy sites identified by radiographic skeletal survey and dental disease severity (more than five or five or fewer dental abscesses), identified historically, were measured. METHODS Associations between proportion of adult life and total life with treatment and number of enthesopathy sites were assessed using multiple linear regression, whereas associations between these exposure variables and dental disease severity were assessed using multiple logistic regression. All models were adjusted for confounding factors. RESULTS Neither proportion of adult nor total life with treatment was a significant predictor of extent of enthesopathy. In contrast, both of these treatment variables were significant predictors of dental disease severity (multivariate-adjusted global P = .0080 and P = .0010, respectively). Participants treated 0% of adulthood were more likely to have severe dental disease than those treated 100% of adulthood (adjusted odds ratio 25 [95% confidence interval 1.2-520]). As the proportion of adult life with treatment increased, the odds of having severe dental disease decreased (multivariate-adjusted P for trend = .015). CONCLUSIONS Treatment in adulthood may not promote or prevent enthesopathy; however, it may be associated with a lower risk of experiencing severe dental disease.
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Affiliation(s)
- Jessica Connor
- Departments of Epidemiology and Public Health (J.C., R.D.), Medicine (K.L.I., C.A.S., J.S.), Pediatrics (E.A.O., T.O.C.), and Diagnostic Imaging (L.K.), Yale University School of Medicine, Yale-New Haven Hospital Dentistry Program (S.B., R.K.), New Haven, Connecticut 06520; and the Veterans Administration Cooperative Studies Program Coordinating Center, Veterans Affairs Connecticut Healthcare System (J.H.Z.), West Haven, Connecticut 06516
| | - Elizabeth A Olear
- Departments of Epidemiology and Public Health (J.C., R.D.), Medicine (K.L.I., C.A.S., J.S.), Pediatrics (E.A.O., T.O.C.), and Diagnostic Imaging (L.K.), Yale University School of Medicine, Yale-New Haven Hospital Dentistry Program (S.B., R.K.), New Haven, Connecticut 06520; and the Veterans Administration Cooperative Studies Program Coordinating Center, Veterans Affairs Connecticut Healthcare System (J.H.Z.), West Haven, Connecticut 06516
| | - Karl L Insogna
- Departments of Epidemiology and Public Health (J.C., R.D.), Medicine (K.L.I., C.A.S., J.S.), Pediatrics (E.A.O., T.O.C.), and Diagnostic Imaging (L.K.), Yale University School of Medicine, Yale-New Haven Hospital Dentistry Program (S.B., R.K.), New Haven, Connecticut 06520; and the Veterans Administration Cooperative Studies Program Coordinating Center, Veterans Affairs Connecticut Healthcare System (J.H.Z.), West Haven, Connecticut 06516
| | - Lee Katz
- Departments of Epidemiology and Public Health (J.C., R.D.), Medicine (K.L.I., C.A.S., J.S.), Pediatrics (E.A.O., T.O.C.), and Diagnostic Imaging (L.K.), Yale University School of Medicine, Yale-New Haven Hospital Dentistry Program (S.B., R.K.), New Haven, Connecticut 06520; and the Veterans Administration Cooperative Studies Program Coordinating Center, Veterans Affairs Connecticut Healthcare System (J.H.Z.), West Haven, Connecticut 06516
| | - Suher Baker
- Departments of Epidemiology and Public Health (J.C., R.D.), Medicine (K.L.I., C.A.S., J.S.), Pediatrics (E.A.O., T.O.C.), and Diagnostic Imaging (L.K.), Yale University School of Medicine, Yale-New Haven Hospital Dentistry Program (S.B., R.K.), New Haven, Connecticut 06520; and the Veterans Administration Cooperative Studies Program Coordinating Center, Veterans Affairs Connecticut Healthcare System (J.H.Z.), West Haven, Connecticut 06516
| | - Raghbir Kaur
- Departments of Epidemiology and Public Health (J.C., R.D.), Medicine (K.L.I., C.A.S., J.S.), Pediatrics (E.A.O., T.O.C.), and Diagnostic Imaging (L.K.), Yale University School of Medicine, Yale-New Haven Hospital Dentistry Program (S.B., R.K.), New Haven, Connecticut 06520; and the Veterans Administration Cooperative Studies Program Coordinating Center, Veterans Affairs Connecticut Healthcare System (J.H.Z.), West Haven, Connecticut 06516
| | - Christine A Simpson
- Departments of Epidemiology and Public Health (J.C., R.D.), Medicine (K.L.I., C.A.S., J.S.), Pediatrics (E.A.O., T.O.C.), and Diagnostic Imaging (L.K.), Yale University School of Medicine, Yale-New Haven Hospital Dentistry Program (S.B., R.K.), New Haven, Connecticut 06520; and the Veterans Administration Cooperative Studies Program Coordinating Center, Veterans Affairs Connecticut Healthcare System (J.H.Z.), West Haven, Connecticut 06516
| | - John Sterpka
- Departments of Epidemiology and Public Health (J.C., R.D.), Medicine (K.L.I., C.A.S., J.S.), Pediatrics (E.A.O., T.O.C.), and Diagnostic Imaging (L.K.), Yale University School of Medicine, Yale-New Haven Hospital Dentistry Program (S.B., R.K.), New Haven, Connecticut 06520; and the Veterans Administration Cooperative Studies Program Coordinating Center, Veterans Affairs Connecticut Healthcare System (J.H.Z.), West Haven, Connecticut 06516
| | - Robert Dubrow
- Departments of Epidemiology and Public Health (J.C., R.D.), Medicine (K.L.I., C.A.S., J.S.), Pediatrics (E.A.O., T.O.C.), and Diagnostic Imaging (L.K.), Yale University School of Medicine, Yale-New Haven Hospital Dentistry Program (S.B., R.K.), New Haven, Connecticut 06520; and the Veterans Administration Cooperative Studies Program Coordinating Center, Veterans Affairs Connecticut Healthcare System (J.H.Z.), West Haven, Connecticut 06516
| | - Jane H Zhang
- Departments of Epidemiology and Public Health (J.C., R.D.), Medicine (K.L.I., C.A.S., J.S.), Pediatrics (E.A.O., T.O.C.), and Diagnostic Imaging (L.K.), Yale University School of Medicine, Yale-New Haven Hospital Dentistry Program (S.B., R.K.), New Haven, Connecticut 06520; and the Veterans Administration Cooperative Studies Program Coordinating Center, Veterans Affairs Connecticut Healthcare System (J.H.Z.), West Haven, Connecticut 06516
| | - Thomas O Carpenter
- Departments of Epidemiology and Public Health (J.C., R.D.), Medicine (K.L.I., C.A.S., J.S.), Pediatrics (E.A.O., T.O.C.), and Diagnostic Imaging (L.K.), Yale University School of Medicine, Yale-New Haven Hospital Dentistry Program (S.B., R.K.), New Haven, Connecticut 06520; and the Veterans Administration Cooperative Studies Program Coordinating Center, Veterans Affairs Connecticut Healthcare System (J.H.Z.), West Haven, Connecticut 06516
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Gupta A, Dwivedi A, Patel P, Gupta S. Hypophosphatemic osteomalacia in von Recklinghausen neurofibromatosis: Case report and literature review. Indian J Radiol Imaging 2015; 25:63-6. [PMID: 25709169 PMCID: PMC4329691 DOI: 10.4103/0971-3026.150155] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
Osteomalacia in neurofibromatosis is a rare entity and distinct from more common dysplastic skeletal affections of this disease. As a rule, it is characterized by later onset in adulthood. There is renal phosphate loss with hypophosphatemia and multiple pseudofractures in the typical cases. The hypophosphatemic conditions that interfere in bone mineralization comprise many hereditary or acquired diseases, all of them sharing the same pathophysiological mechanism-reduction in phosphate reabsorption by the renal tubuli. This process leads to chronic hyperphosphaturia and hypophosphatemia, associated with inappropriately normal or low levels of calcitriol, causing rickets in children and osteomalacia in adults.
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Affiliation(s)
- Aman Gupta
- Department of Radiodiagnosis, Sri Aurobindo Medical College and Post Graduate Institute, Indore, Madhya Pradesh, India
| | - Abhishek Dwivedi
- Department of Radiodiagnosis, Sri Aurobindo Medical College and Post Graduate Institute, Indore, Madhya Pradesh, India
| | - Priyanka Patel
- Department of Radiodiagnosis, Sri Aurobindo Medical College and Post Graduate Institute, Indore, Madhya Pradesh, India
| | - Somya Gupta
- Department of Radiodiagnosis, Sri Aurobindo Medical College and Post Graduate Institute, Indore, Madhya Pradesh, India
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10
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Yue H, Yu JB, He JW, Zhang Z, Fu WZ, Zhang H, Wang C, Hu WW, Gu JM, Hu YQ, Li M, Liu YJ, Zhang ZL. Identification of two novel mutations in the PHEX gene in Chinese patients with hypophosphatemic rickets/osteomalacia. PLoS One 2014; 9:e97830. [PMID: 24836714 PMCID: PMC4024000 DOI: 10.1371/journal.pone.0097830] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Accepted: 04/25/2014] [Indexed: 11/25/2022] Open
Abstract
Objective X-linked dominant hypophosphatemia (XLH) is the most prevalent form of inherited rickets/osteomalacia in humans. The aim of this study was to identify PHEX gene mutations and describe the clinical features observed in 6 unrelated Chinese families and 3 sporadic patients with hypophosphatemic rickets/osteomalacia. Methods For this study, 45 individuals from 9 unrelated families of Chinese Han ethnicity (including 16 patients and 29 normal phenotype subjects), and 250 healthy donors were recruited. All 22 exons and exon-intron boundaries of the PHEX gene were amplified by polymerase chain reaction (PCR) and directly sequenced. Results The PHEX mutations were detected in 6 familial and 3 sporadic hypophosphatemic rickets/osteomalacia. Altogether, 2 novel mutations were detected: 1 missense mutation c.1183G>C in exon 11, resulting in p.Gly395Arg and 1 missense mutation c.1751A>C in exon 17, resulting in p.His584Pro. No mutations were found in the 250 healthy controls. Conclusions Our study increases knowledge of the PHEX gene mutation types and clinical phenotypes found in Chinese patients with XLH, which is important for understanding the genetic basis of XLH. The molecular diagnosis of a PHEX genetic mutation is of great importance for confirming the clinical diagnosis of XLH, conducting genetic counseling, and facilitating prenatal intervention, especially in the case of sporadic patients.
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Affiliation(s)
- Hua Yue
- Department of Osteoporosis, Metabolic Bone Disease and Genetic Research Unit, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, P. R. China
| | - Jin-bo Yu
- Department of pediatrics, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, P. R. China
| | - Jin-wei He
- Department of Osteoporosis, Metabolic Bone Disease and Genetic Research Unit, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, P. R. China
| | - Zeng Zhang
- Department of Osteoporosis, Metabolic Bone Disease and Genetic Research Unit, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, P. R. China
- Department of Orthopedic Surgery, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, P.R. China
| | - Wen-zhen Fu
- Department of Osteoporosis, Metabolic Bone Disease and Genetic Research Unit, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, P. R. China
| | - Hao Zhang
- Department of Osteoporosis, Metabolic Bone Disease and Genetic Research Unit, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, P. R. China
| | - Chun Wang
- Department of Osteoporosis, Metabolic Bone Disease and Genetic Research Unit, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, P. R. China
| | - Wei-wei Hu
- Department of Osteoporosis, Metabolic Bone Disease and Genetic Research Unit, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, P. R. China
| | - Jie-mei Gu
- Department of Osteoporosis, Metabolic Bone Disease and Genetic Research Unit, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, P. R. China
| | - Yun-qiu Hu
- Department of Osteoporosis, Metabolic Bone Disease and Genetic Research Unit, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, P. R. China
| | - Miao Li
- Department of Osteoporosis, Metabolic Bone Disease and Genetic Research Unit, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, P. R. China
| | - Yu-juan Liu
- Department of Osteoporosis, Metabolic Bone Disease and Genetic Research Unit, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, P. R. China
| | - Zhen-Lin Zhang
- Department of Osteoporosis, Metabolic Bone Disease and Genetic Research Unit, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, Shanghai, P. R. China
- * E-mail:
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11
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Seitz S, Rendenbach C, Barvencik F, Streichert T, Jeschke A, Schulze J, Amling M, Schinke T. Retinol deprivation partially rescues the skeletal mineralization defects of Phex-deficient Hyp mice. Bone 2013; 53:231-8. [PMID: 23266491 DOI: 10.1016/j.bone.2012.12.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/09/2012] [Revised: 12/10/2012] [Accepted: 12/12/2012] [Indexed: 12/24/2022]
Abstract
X-linked hypophosphatemic rickets (XLH) is a genetic disorder caused by mutational inactivation of the PHEX gene, encoding a transmembrane endopeptidase expressed in osteoblasts. Since several experiments involving Phex-deficient Hyp mice have demonstrated that an increased expression of Fgf23 in osteoblasts is causative for the renal phosphate loss characteristic of XLH, we performed genome-wide expression analysis to compare differentiated osteoblasts from wildtype and Hyp mice. Here we did not only observe the expected increase of Fgf23 expression in the latter ones, but also a differential expression of genes that are either induced by or involved in retinoic acid signaling, which led us to analyze whether dietary retinol deprivation would influence the phenotype of Hyp mice. Unexpectedly, feeding a retinol-free diet resulted in a partial rescue of the growth plate and bone mineralization defects in 6 weeks old Hyp mice. When we fed the same diet for 24 weeks the amount of non-mineralized bone matrix (osteoid) was reduced by more than 70%, although phosphate homeostasis was unaffected. In contrast, a dietary normalization of serum phosphate levels in Hyp mice reduced the osteoid amount by less than 30%, thereby demonstrating a previously unknown impact of retinol on the cell-autonomous mineralization defect of Phex-deficient osteoblasts.
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Affiliation(s)
- Sebastian Seitz
- Department of Osteology and Biomechanics, University Medical Center Hamburg Eppendorf, Hamburg 20246, Germany
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12
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Abstract
The discovery of fibroblast growth factor 23 (FGF-23) has expanded our understanding of phosphate and vitamin D homeostasis and provided new insights into the pathogenesis of hereditary hypophosphatemic and hyperphosphatemic disorders, as well as acquired disorders of phosphate metabolism, such as chronic kidney disease. FGF-23 is secreted by osteoblasts and osteocytes in bone and principally targets the kidney to regulate the reabsorption of phosphate, the production and catabolism of 1,25-dihydroxyvitamin D and the expression of α-Klotho, an anti-ageing hormone. Secreted FGF-23 plays a central role in complex endocrine networks involving local bone-derived factors that regulate mineralization of extracellular matrix and systemic hormones involved in mineral metabolism. Inactivating mutations of PHEX, DMP1 and ENPP1, which cause hereditary hypophosphatemic disorders and primary defects in bone mineralization, stimulate FGF23 gene transcription in osteoblasts and osteocytes, at least in part, through canonical and intracrine FGF receptor pathways. These FGF-23 regulatory pathways may enable systemic phosphate and vitamin D homeostasis to be coordinated with bone mineralization. FGF-23 also functions as a counter-regulatory hormone for 1,25-dihydroxyvitamin D in a bone-kidney endocrine loop. FGF-23, through regulation of additional genes in the kidney and extrarenal tissues, probably has broader physiological functions beyond regulation of mineral metabolism that account for the association between FGF-23 and increased mortality and morbidity in chronic kidney disease.
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Affiliation(s)
- L Darryl Quarles
- Division of Nephrology, Department of Medicine, University of Tennessee Health Science Center, 19 South Manassas Street, Memphis, TN 38163, USA.
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13
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de Menezes Filho H, de Castro LCG, Damiani D. Hypophosphatemic rickets and osteomalacia. ACTA ACUST UNITED AC 2007; 50:802-13. [PMID: 17117305 DOI: 10.1590/s0004-27302006000400025] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2006] [Accepted: 05/08/2006] [Indexed: 01/31/2023]
Abstract
The hypophosphatemic conditions that interfere in bone mineralization comprise many hereditary or acquired diseases, all of them sharing the same pathophysiologic mechanism: reduction in the phosphate reabsorption by the renal tubuli. This process leads to chronic hyperphosphaturia and hypophosphatemia, associated with inappropriately normal or low levels of calcitriol, causing osteomalacia or rickets in children and osteomalacia in adults. X-linked hypophosphatemic rickets, autosomal-dominant hypophosphatemic rickets, and tumor-induced osteomalacia are the main syndromes involved in the hypophosphatemic rickets. Although these conditions exhibit different etiologies, there is a common link among them: increased activity of a phosphaturic factor, being the fibroblast growth factor 23 (FGF-23) the most studied one and to which is attributed a central role in the pathophysiology of the hyperphosphaturic disturbances. Activating mutations of FGF-23 and inactivating mutations in the PHEX gene (a gene on the X chromosome that codes for a Zn-metaloendopeptidase proteolytic enzyme which regulates the phosphate) involved in the regulation of FGF-23 have been identified and have been implicated in the pathogenesis of these disturbances. Genetic studies tend to show that the phosphorus homeostasis depends on a complex osteo-renal metabolic axis, whose mechanisms of interaction have been poorly understood so far. This paper reviews the current knowledge status concerning the pathophysiology of phosphate metabolism regulation and the pathophysiologic basis of hypophosphatemic rickets. It also analyzes the clinical picture and the therapeutic aspects of these conditions as well.
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Affiliation(s)
- Hamilton de Menezes Filho
- Instituto da Criança, Hospital das Clínicas, Medical School, São Paulo University, São Paulo, SP, Brazil
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Yamashita H, Yamazaki Y, Hasegawa H, Yamashita T, Fukumoto S, Shigematsu T, Kazama JJ, Fukagawa M, Noguchi S. Fibroblast growth factor-23 (FGF23) in patients with transient hypoparathyroidism: its important role in serum phosphate regulation. Endocr J 2007; 54:465-70. [PMID: 17464094 DOI: 10.1507/endocrj.k06-156] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Hypoparathyroidism is a complication of thyroidectomy that causes hyperphosphatemia primarily due to enhanced reabsorption of phosphate in the kidney resulting from decreased parathyroid hormone (PTH) secretion. Fibroblast growth factor-23 (FGF23) is a hormone-like factor that is thought to play an important role in phosphate homeostasis. However, the changes and role of FGF23 in transient hypoparathyroidism after thyroidectomy are not clear. We examined changes in serum levels of calcium, phosphate, intact PTH, 1,25-dihydroxyvitamin D, and FGF23 in 12 patients (10 women, 2 men; mean age, 51 yr) who developed transient hypoparathyroidism after thyroidectomy. Serum phosphate reached its peak level (5.9 +/- 0.5 mg/dl) approximately 4 days after development of hypoparathyroidism, and this was followed by a peak in the serum FGF23 level (71 +/- 28 ng/l). Serum levels of calcium, phosphate, and FGF23 normalized after recovery of parathyroid function. There was a significant positive correlation between serum phosphate and FGF23 levels (P<0.05). Serum FGF23 was elevated in patients with hypoparathyroidism and hyperphosphatemia and normalized along with normalized phosphate levels after recovery of parathyroid function. The peak level of phosphate always preceded that of FGF23 by several days, suggesting that elevated phosphate is a primary stimulus for release of FGF23. This homeostatic regulation of phosphate differs considerably from that of serum calcium whose change is rapidly corrected within minutes.
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15
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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.
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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
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Perwad F, Azam N, Zhang MYH, Yamashita T, Tenenhouse HS, Portale AA. Dietary and serum phosphorus regulate fibroblast growth factor 23 expression and 1,25-dihydroxyvitamin D metabolism in mice. Endocrinology 2005; 146:5358-64. [PMID: 16123154 DOI: 10.1210/en.2005-0777] [Citation(s) in RCA: 307] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Fibroblast growth factor-23 (FGF-23) is a novel circulating peptide that regulates phosphorus (Pi) and vitamin D metabolism, but the mechanisms by which circulating FGF-23 itself is regulated are unknown. To determine whether the serum FGF-23 concentration is regulated by dietary intake of Pi, we fed wild-type (WT), Npt2a gene-ablated (Npt2a(-/-)), and Hyp mice diets containing varying Pi contents (0.02-1.65%). In WT mice, increases in dietary Pi intake from 0.02-1.65% induced a 7-fold increase in serum FGF-23 and a 3-fold increase in serum Pi concentrations. Across the range of dietary Pi, serum FGF-23 concentrations varied directly with serum Pi concentrations (r(2) = 0.72; P < 0.001). In Npt2a(-/-) mice, serum FGF-23 concentrations were significantly lower than in WT mice, and these differences could be accounted for by the lower serum Pi levels in Npt2a(-/-) mice. The serum concentrations of FGF-23 in Hyp mice were 5- to 25-fold higher than values in WT mice, and the values varied with dietary Pi intake. Fgf-23 mRNA abundance in calvaria was significantly higher in Hyp mice than in WT mice on the 1% Pi diet; in both groups of mice, fgf-23 mRNA abundance in calvarial bone was suppressed by 85% on the low (0.02%) Pi diet. In WT mice fed the low (0.02%) Pi diet, renal mitochondrial 1alpha-hydroxylase activity and renal 1alpha-hydroxylase (P450c1alpha) mRNA abundance were significantly higher than in mice fed the higher Pi diets and varied inversely with serum FGF-23 concentrations (r(2) = 0.86 and r(2) = 0.64; P < 0.001, respectively). The present data demonstrate that dietary Pi regulates the serum FGF-23 concentration in mice, and such regulation is independent of phex function. The data suggest that genotype-dependent and dietary Pi-induced changes in the serum FGF-23 concentration reflect changes in fgf-23 gene expression in bone.
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Affiliation(s)
- Farzana Perwad
- Department of Pediatrics, University of California, San Francisco, 94143-0748, USA
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Abstract
OBJECTIVE To describe a patient with oncogenic osteomalacia whose symptoms were rapidly resolved after surgical removal of an organized hematoma of the hip. METHODS A case report is presented, including clinical and laboratory findings. The relevant literature is reviewed, and the current understanding of oncogenic osteomalacia is summarized. RESULTS In September 1996, a 44-year-old black woman presented with a 2-year history of bone pain, progressive muscle weakness, depression, osteomalacia, and hypophosphatemia. Her condition did not improve with use of calcitriol and phosphate replacement. During the previous year, her serum phosphorus levels were low, ranging from 1.0 to 2.2 mg/dL, and the levels of serum 1,25-dihydroxyvitamin D [1,25-(OH)2D] were very low, ranging from <5 to 19.4 pg/mL (normal, 15 to 60). The serum 25-hydroxyvitamin D levels were low, ranging from 8 to 14 ng/mL (normal, 9 to 52). The higher values were noted after she had received large doses of phosphate, 1,25-(OH)2D, and vitamin D. During the previous year, her serum alkaline phosphatase levels were high, ranging from 253 to 314 U/L; serum calcium and parathyroid hormone levels were normal. The abnormalities on physical examination were obesity and a 10- by 10-cm firm, poorly demarcated mass superior to the left greater trochanter. A computed tomographic scan of this region showed a water-density fluid collection in the left buttock measuring 7.8 by 7.8 cm, consistent with a chronic hematoma. The mass was resected, and histopathologic examination revealed features of an organized hematoma with areas of myxoid changes and cartilaginous metaplasia. Postoperatively, the patient's strength improved, and the levels of serum phosphorus and 1,25-(OH)2D became supranormal. CONCLUSION The symptoms and laboratory abnormalities of this patient with oncogenic osteomalacia promptly resolved after resection of an organized hematoma of the left hip.
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Affiliation(s)
- Edward Colt
- Columbia University College of Physicians and Surgeons, Department of Medicine, St. Luke's-Roosevelt Hospital Center, New York, New York 10025, USA
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18
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Yamashita H, Yamazaki Y, Hasegawa H, Yamashita T, Fukumoto S, Shigematsu T, Kazama JJ, Fukagawa M, Noguchi S. Fibroblast growth factor-23 in patients with Graves' disease before and after antithyroid therapy: its important role in serum phosphate regulation. J Clin Endocrinol Metab 2005; 90:4211-5. [PMID: 15827108 DOI: 10.1210/jc.2004-2498] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
Abstract
OBJECTIVE Hyperthyroidism is a well-described cause of hyperphosphatemia. We aimed to clarify the physiological role of fibroblast growth factor (FGF)-23 in serum phosphate homeostasis in patients with Graves' disease during the course of treatment for hyperthyroidism. CONTEXT The study group comprised 56 patients (45 for a cross-sectional study and 11 for a longitudinal study) with Graves' disease. For the cross-sectional study, patients were assigned, on the basis of their serum phosphate level, to a hypophosphatemia group (n = 14), a normophosphatemia group (n = 16), or a hyperphosphatemia group (n = 15). Serum FGF-23, calcium, phosphate, PTH, and 1,25-dihydroxyvitamin D [1,25(OH)(2)D] levels were compared between the three groups. For the longitudinal study, we assessed changes in these biochemical indices before and after antithyroid treatment. RESULTS In the cross-sectional study, the serum FGF-23 level was significantly higher (P < 0.05) in the hyperphosphatemia group than in the other groups (61 +/- 36 ng/liter vs. 31 +/- 22 ng/liter and 30 +/- 9 ng/liter). In the longitudinal study, serum levels of FGF-23 decreased significantly (P < 0.05) from a high of 54 +/- 12 ng/liter before treatment to 29 +/- 14 ng/liter after treatment. In contrast, the serum 1,25(OH)(2)D level increased significantly (P < 0.005) from 55 +/- 22 pmol/liter before treatment to 185 +/- 76 pmol/liter 3 months after treatment. Serum FGF-23 levels were positively correlated with serum phosphate levels (P < 0.0001) and negatively correlated with serum 1,25(OH)(2)D levels (P < 0.0001). CONCLUSIONS The significant positive correlation between serum levels of phosphate and FGF-23 indicates that FGF-23 may play an important role in serum phosphate homeostasis by its up-regulation in the hyperphosphatemic condition.
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Affiliation(s)
- Hiroyuki Yamashita
- Noguchi Thyroid Clinic and Hospital Foundation, 6-33 Noguchi-Nakamachi, Beppu Oita 874-0932, Japan.
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19
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Paula LM, Melo NS, Silva Guerra EN, Mestrinho DH, Acevedo AC. Case report of a rare syndrome associating amelogenesis imperfecta and nephrocalcinosis in a consanguineous family. Arch Oral Biol 2005; 50:237-42. [PMID: 15721155 DOI: 10.1016/j.archoralbio.2004.11.023] [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: 09/12/2004] [Accepted: 11/19/2004] [Indexed: 10/25/2022]
Abstract
A rare syndrome associating amelogenesis imperfecta (AI) with nephrocalcinosis has been reported. The purpose of this study is to characterise the phenotype of a consanguineous family presenting amelogenesis imperfecta, delayed permanent teeth eruption and nephrocalcinosis. Six family members were examined. Ground sections of the case index deciduous teeth and biopsies of enlarged dental follicles were analysed. The patients's parents were first cousins. The case index had yellow discoloration and altered teeth shapes, retention of deciduous teeth, and delayed eruption. Panoramic radiographs revealed multiple enlarged pericoronal follicles in unerupted teeth and generalised intrapulpal calcifications. Renal ultrasound showed the presence of nephrocalcinosis. No other family members presented enamel defects or nephrocalcinosis. Histologically, the enamel appeared hypoplastic, and dental follicles indicated pericoronal hamartoma. The consanguineous marriage suggests an autosomal recessive mode of inheritance. Further studies are necessary to clarify the genetic defect behind this syndrome that associates AI, nephrocalcinosis and impaired tooth eruption.
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Affiliation(s)
- L M Paula
- Dental Anomalies Clinic, University Hospital of Brasilia, Department of Dentistry, Faculty of Health Science, University of Brasilia, SMDB Conjunto 29, Lote 3, Lago Sul, Brasilia 71680-290, DF, Brazil.
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20
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Akkus O. Elastic Deformation of Mineralized Collagen Fibrils: An Equivalent Inclusion Based Composite Model. J Biomech Eng 2005; 127:383-90. [PMID: 16060345 DOI: 10.1115/1.1894204] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Mineralized collagen fibrils are the basic building blocks of bone tissue at the supramolecular level. Several disease states, manipulation of the expression of specific proteins involved in biomineralization, and treatment with different agents alter the extent of mineralization as well as the morphology of mineral crystals which in turn affect the mechanical function of bone tissue. An experimental assessment of mineralized fibers’ mechanical properties is challenged by their small size, leaving analytical and computational models as a viable alternative for investigation of the fibril-level mechanical properties. In the current study the variation of the elastic stiffness tensor of mineralized collagen fibrils with changing mineral volume fraction and mineral aspect ratios was predicted via a micromechanical model. The partitioning of applied stresses between mineral and collagen phases is also predicted for normal and shear loading of fibrils. Model predictions resulted in transversely isotropic collagen fibrils in which the modulus along the longer axis of the fibril was the greatest. All the elastic moduli increased with increasing mineral volume fraction whereas Poisson’s ratios decreased with the exception of ν12(=ν21). The partitioning of applied stresses were such that the stresses acting on mineral crystals were about 1.5, 15, and 3 times greater than collagen stresses when fibrils were loaded transversely, longitudinally, and in shear, respectively. In the overall the predictions were such that: (a) greatest modulus along longer axis; (b) the greatest mineral/collagen stress ratio along the longer axis of collagen fibers (i.e., greatest relief of stresses acting on collagen); and (c) minimal lateral contraction when fibers are loaded along the longer axis. Overall, the pattern of mineralization as put forth in this model predicts a superior mechanical function along the longer axis of collagen fibers, the direction which is more likely to experience greater stresses.
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Affiliation(s)
- Ozan Akkus
- Department of Bioengineering, The University of Toledo, 2801 W Bancroft St., Mail Stop 303, Toledo, OH 43606-3390, USA.
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21
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Rowe PSN, Garrett IR, Schwarz PM, Carnes DL, Lafer EM, Mundy GR, Gutierrez GE. Surface plasmon resonance (SPR) confirms that MEPE binds to PHEX via the MEPE-ASARM motif: a model for impaired mineralization in X-linked rickets (HYP). Bone 2005; 36:33-46. [PMID: 15664000 PMCID: PMC3361744 DOI: 10.1016/j.bone.2004.09.015] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2004] [Revised: 09/21/2004] [Accepted: 09/24/2004] [Indexed: 02/08/2023]
Abstract
Matrix Extracellular Phospho-glycoprotEin (MEPE) and proteases are elevated and PHEX is defective in HYP. PHEX prevents proteolysis of MEPE and release of a protease-resistant MEPE-ASARM peptide, an inhibitor of mineralization (minhibin). Thus, in HYP, mutated PHEX may contribute to increased ASARM peptide release. Moreover, binding of MEPE by PHEX may regulate this process in normal subjects. The nature of the PHEX-MEPE nonproteolytic interaction(s) (direct or indirect) is/are unknown. Our aims were to determine (1) whether PHEX binds specifically to MEPE, (2) whether the binding involves the ASARM motif region, and (3) whether free ASARM peptide affects mineralization in vivo in mice. Protein interactions between MEPE and recombinant soluble PHEX (secPHEX) were measured using surface plasmon resonance (SPR). Briefly, secPHEX, MEPE, and control protein (IgG) were immobilized on a Biacore CM5 sensor chip, and SPR experiments were performed on a Biacore 3000 high-performance research system. Pure secPHEX was then injected at different concentrations, and interactions with immobilized proteins were measured. To determine MEPE sequences interacting with secPHEX, the inhibitory effects of MEPE-ASARM peptides (phosphorylated and nonphosphorylated), control peptides, and MEPE midregion RGD peptides on secPHEX binding to chip-immobilized MEPE were measured. ASARM peptide and etidronate-mediated mineralization inhibition in vivo and in vitro were determined by quenched calcein fluorescence in hind limbs and calvariae in mice and by histological Sanderson stain. A specific, dose-dependent and Zn-dependent protein interaction between secPHEX and immobilized MEPE occurs (EC50 of 553 nM). Synthetic MEPE PO4-ASARM peptide inhibits the PHEX-MEPE interaction (K(D(app)) = 15 uM and B(max/inhib) = 68%). In contrast, control and MEPE-RGD peptides had no effect. Subcutaneous administration of ASARM peptide resulted in marked quenching of fluorescence in calvariae and hind limbs relative to vehicle controls indicating impaired mineralization. Similar results were obtained with etidronate. Sanderson-stained calvariae also indicated a marked increase in unmineralized osteoid with ASARM peptide and etidronate groups. We conclude that PHEX and MEPE form a nonproteolytic protein interaction via the MEPE carboxy-terminal ASARM motif, and the ASARM peptide inhibits mineralization in vivo. The binding of MEPE and ASARM peptide by PHEX may explain why loss of functional osteoblast-expressed PHEX results in defective mineralization in HYP.
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Affiliation(s)
- Peter S N Rowe
- Department of Periodontics, University of Texas Health Science Center at San Antonio, San Antonio, TX, 78229, USA.
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Bresler D, Bruder J, Mohnike K, Fraser WD, Rowe PSN. Serum MEPE-ASARM-peptides are elevated in X-linked rickets (HYP): implications for phosphaturia and rickets. J Endocrinol 2004; 183:R1-9. [PMID: 15590969 PMCID: PMC3357083 DOI: 10.1677/joe.1.05989] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
MEPE (Matrix Extracellular PhosphoglycoprotEin) expression is markedly elevated in X-linked-hypophosphatemic-rickets (HYP) and tumor-induced osteomalacia (TIO). In normal individuals, circulating serum-levels of MEPE are tightly correlated with serum-phosphorus, parathyroid hormone (PTH) and bone mineral density (BMD). Also, MEPE derived, C-terminal ASARM-peptides are candidate minhibins and/or phosphatonins. Our aims were to determine: 1. whether MEPE-ASARM-peptide(s) are abnormally elevated in HYP/hyp serum, and, 2. whether the ASARM-peptide(s) accumulate in hyp mice kidney renal-tubules. Using a specific competitive ELISA we measured a five fold increase (P=0.007) of serum ASARM-peptide(s) in human HYP patients (normal subjects 3.25 microM n=9; S.E.M.=0.51 and HYP-patients 15.74 microM, n=9; S.E.M.=3.32). A 6.23 fold increase (P=0.008) was measured in hyp male mice compared with their normal male siblings (normal-siblings, 3.73 muM, S.E.M.=0.57, n=3; and hyp-mice 23.4 microM, n=3, S.E.M.=4.01). Renal immuno-histological screening also revealed a dramatic increase of ASARM-peptides in regions anatomically consistent with the proximal convoluted tubules. This study demonstrates for the first time that markedly elevated serum levels of protease-resistant ASARM-peptide(s) occur in HYP/hyp and they accumulate in murine hyp kidneys. These peptides are thus likely responsible for the phosphaturia and defective mineralization in HYP/hyp and TIO.
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Affiliation(s)
- Doron Bresler
- United States Air Force (USAF) Lackland, San Antonio, Texas, USA
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23
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Rowe PSN. The wrickkened pathways of FGF23, MEPE and PHEX. CRITICAL REVIEWS IN ORAL BIOLOGY AND MEDICINE : AN OFFICIAL PUBLICATION OF THE AMERICAN ASSOCIATION OF ORAL BIOLOGISTS 2004; 15:264-81. [PMID: 15470265 PMCID: PMC3361894 DOI: 10.1177/154411130401500503] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The last 350 years since the publication of the first medical monograph on rickets (old English term wrickken) (Glisson et al., 1651) have seen spectacular advances in our understanding of mineral-homeostasis. Seminal and exciting discoveries have revealed the roles of PTH, vitamin D, and calcitonin in regulating calcium and phosphate, and maintaining healthy teeth and skeleton. However, it is clear that the PTH/Vitamin D axis does not account for the entire picture, and a new bone-renal metabolic milieu has emerged, implicating a novel set of matrix proteins, hormones, and Zn-metallopeptidases. The primary defects in X-linked hypophosphatemic rickets (HYP) and autosomal-dominant hypophosphatemic rickets (ADHR) are now identified as inactivating mutations in a Zn-metalloendopeptidase (PHEX) and activating mutations in fibroblast-growth-factor-23 (FGF23), respectively. In oncogenic hypophosphatemic osteomalacia (OHO), several tumor-expressed proteins (MEPE, FGF23, and FRP-4) have emerged as candidate mediators of the bone-renal pathophysiology. This has stimulated the proposal of a global model that takes into account the remarkable similarities between the inherited diseases (HYP and ADHR) and the tumor-acquired disease OHO. In HYP, loss of PHEX function is proposed to result in an increase in uncleaved full-length FGF23 and/or inappropriate processing of MEPE. In ADHR, a mutation in FGF23 results in resistance to proteolysis by PHEX or other proteases and an increase in half-life of full-length phosphaturic FGF23. In OHO, over-expression of FGF23 and/or MEPE is proposed to result in abnormal renal-phosphate handling and mineralization. Although this model is attractive, many questions remain unanswered, suggesting a more complex picture. The following review will present a global hypothesis that attempts to explain the experimental and clinical observations in HYP, ADHR, and OHO, plus diverse mouse models that include the MEPE null mutant, HYP-PHEX transgenic mouse, and MEPE-PHEX double-null-mutant.
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Affiliation(s)
- Peter S N Rowe
- Department of Periodontics, The University of Texas Health Science Center at San Antonio, Mail Code 7894, 7703 Floyd Curl Drive, Room 3.579U, San Antonio, TX 78229-3900, USA.
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Hayashibara T, Hiraga T, Yi B, Nomizu M, Kumagai Y, Nishimura R, Yoneda T. A synthetic peptide fragment of human MEPE stimulates new bone formation in vitro and in vivo. J Bone Miner Res 2004; 19:455-62. [PMID: 15040834 DOI: 10.1359/jbmr.0301263] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2003] [Revised: 09/02/2003] [Accepted: 10/03/2003] [Indexed: 01/16/2023]
Abstract
UNLABELLED Matrix extracellular phosphoglycoprotein (MEPE) was proposed as a candidate for the phosphaturic hormone phosphatonin. We found that a synthetic peptide fragment of MEPE containing the RGD and SGDG sequence stimulated new bone formation in vitro and in vivo. INTRODUCTION Matrix extracellular phosphoglycoprotein (MEPE) was recently identified as a candidate for the phosphaturic hormone phosphatonin, which has been implicated in disturbed phosphate metabolism, rickets, and osteomalacia associated with X-linked hypophosphatemic rickets (XLH) and oncogenic hypophosphatemic osteomalacia (OHO). MEPE expression was predominantly found in osteoblasts, and mice deficient in a homolog of MEPE showed increased bone density, suggesting that MEPE produced in osteoblasts negatively regulates bone formation. In this study, we examined the effects of a synthetic 23mer peptide fragment of MEPE (AC-100, region 242-264) containing the RGD (integrin-binding) and SGDG (glycosaminoglycan-attachment) motif on bone formation in vitro and in vivo. MATERIALS AND METHODS The osteogenic activity of AC-100 was examined in organ cultures of neonatal mouse calvariae and in vivo by injecting AC-100 onto the calvariae of mice. RESULTS Histomorphometric examination showed that AC-100 stimulated new bone formation with increased numbers of osteoblasts in neonatal mouse calvariae in organ culture. In contrast, synthetic MEPE fragment peptides without either the RGD or SGDG motif failed to increase new bone formation. Repeated daily subcutaneous injections of AC-100 onto the calvariae in mice increased bone thickness and stimulated new bone formation as determined by the calcein double-labeling technique. However, peptides in which the RGD or SGDG sequence was scrambled did not stimulate new bone formation in vivo. AC-100 increased cell proliferation and alkaline phosphatase activity and activated focal adhesion kinase (FAK) and extracellular signal-regulated protein kinase (ERK) in human primary osteoblasts. CONCLUSION Our results show that a synthetic peptide corresponding with the sequence of human MEPE fragment stimulates new bone formation with increased number of osteoblasts. The results also suggest that the RGD and SGDG motifs are critical to the osteogenic activity of AC-100, presumably through activating integrin signaling pathways in osteoblasts. The anabolic effects of AC-100 may be beneficial for bone diseases associated with decreased bone formation.
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Affiliation(s)
- Tetsuyuki Hayashibara
- Department of Biochemistry, Graduate School of Dentistry, Osaka University, Suita, Osaka, Japan
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Shimada T, Hasegawa H, Yamazaki Y, Muto T, Hino R, Takeuchi Y, Fujita T, Nakahara K, Fukumoto S, Yamashita T. FGF-23 is a potent regulator of vitamin D metabolism and phosphate homeostasis. J Bone Miner Res 2004; 19:429-35. [PMID: 15040831 DOI: 10.1359/jbmr.0301264] [Citation(s) in RCA: 1273] [Impact Index Per Article: 63.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/29/2003] [Revised: 08/05/2003] [Accepted: 10/10/2003] [Indexed: 01/05/2023]
Abstract
UNLABELLED We analyzed the effects of an FGF-23 injection in vivo. FGF-23 caused a reduction in serum 1,25-dihydroxyvitamin D by altering the expressions of key enzymes for the vitamin D metabolism followed by hypophosphatemia. This study indicates that FGF-23 is a potent regulator of the vitamin D and phosphate metabolism. INTRODUCTION The pathophysiological contribution of FGF-23 in hypophosphatemic diseases was supported by animal studies in which the long-term administration of recombinant fibroblast growth factor-23 reproduced hypophosphatemic rickets with a low serum 1,25-dihydroxyvitamin D [1,25(OH)2D] level. However, there is no clear understanding of how FGF-23 causes these changes. MATERIALS AND METHODS To elucidate the molecular mechanisms of the FGF-23 function, we investigated the short-term effects of a single administration of recombinant FGF-23 in normal and parathyroidectmized animals. RESULTS An injection of recombinant FGF-23 caused a reduction in serum phosphate and 1,25(OH)2D levels. A decrease in serum phosphate was first observed 9 h after the injection and was accompanied with a reduction in renal mRNA and protein levels for the type IIa sodium-phosphate cotransporter (NaPi-2a). There was no increase in the parathyroid hormone (PTH) level throughout the experiment, and hypophosphatemia was reproduced by FGF-23 in parathyroidectomized rats. Before this hypophosphatemic effect, the serum 1,25(OH)2D level had already descended at 3 h and reached the nadir 9 h after the administration. FGF-23 reduced renal mRNA for 25-hydroxyvitamin D-1alpha-hydroxylase and increased that for 25-hydroxyvitamin D-24-hydroxylase starting at 1 h. In addition, an injection of calcitriol into normal mice increased the serum FGF-23 level within 4 h. CONCLUSIONS FGF-23 regulates NaPi-2a independently of PTH and the serum 1,25(OH)2D level by controlling renal expressions of key enzymes of the vitamin D metabolism. In conclusion, FGF-23 is a potent regulator of phosphate and vitamin D homeostasis.
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Affiliation(s)
- Takashi Shimada
- Pharmaceutical Research Laboratories, KIRIN Brewery Co., Ltd., Takasaki, Gumma, Japan.
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Pronicka E, Popowska E, Rowińska E, Arasimowicz E, Syczewska M, Jurkiewicz D, Lebiedowski M. Anthropometric characteristics of X-linked hypophosphatemia. ACTA ACUST UNITED AC 2004; 126A:141-9. [PMID: 15057978 DOI: 10.1002/ajmg.a.20572] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
An anthropometric study was undertaken to assess head proportions of patients with X-linked hypophosphatemia (XLH). Fourteen morphometric parameters of the head were measured and 10 cephalic indices calculated in 82 affected persons (57 females and 25 males) from 55 unrelated families with XLH, and compared with the results obtained in the group of their healthy relatives (37 females and 33 males), as well as with general population control values. Normalized values (SD, z-score) were analyzed statistically. The group of healthy relatives, both males and females, differed significantly from Polish population control values in most of the normalized variables measured, making population control values useless as a control group for the analyzed XLH group. Intrafamilial values of cephalic parameters in healthy relatives of the XLH patients were finally applied for statistical analysis. Generally patients with XLH showed highly statistically significant increase in head length (males 0.95 +/- 1.07 vs. -0.37 +/- 1.02, females 0.57 +/- 1.59 vs. -0.06 +/- 1.15), significant decrease in occipital breadth (males -0.56 +/- 1.27 vs. 0.70 +/- 1.28, females -0.59 +/- 1.7 vs. 0.13 +/- 1.1) and several milder anomalies of craniofacial proportions. Mean cephalic index was significantly lower in XLH patients when compared with the healthy relatives (males -0.909 vs. 0.278 P < 0.0001, females -0.705 vs. 0.381 P = 0.007). The cephalic changes were found both in XLH children and XLH adults and were more pronounced in affected males than in females. There were no differences between offspring born by hypophosphatemic and normophosphatemic mothers.
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Affiliation(s)
- Ewa Pronicka
- Department of Metabolic Diseases, The Children's Memorial Health Institute, Al Dzieci Polskich 20, 04-736 Warsaw, Poland.
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Quarles LD. Evidence for a bone-kidney axis regulating phosphate homeostasis. J Clin Invest 2003; 112:642-6. [PMID: 12952909 PMCID: PMC182218 DOI: 10.1172/jci19687] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
A novel circulation phosphaturic hormone is postulated to regulate systemic phosphate homeostasis. Two new studies reveal that the phosphaturic factor FGF-23 is increased in hypophosphatemic subjects with McCune-Albright syndrome and that secreted frizzled-related protein-4 (sFRP-4), a factor produced by tumors derived from subjects with tumor-induced osteomalacia, also has phosphaturic activity. It remains to be established whether FGF-23 and sFRP-4 represent two distinct phosphatonins or are somehow integrated in a novel phosphate-regulating bone-kidney axis.
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Affiliation(s)
- L Darryl Quarles
- Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA.
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Campos M, Couture C, Hirata IY, Juliano MA, Loisel TP, Crine P, Juliano L, Boileau G, Carmona AK. Human recombinant endopeptidase PHEX has a strict S1' specificity for acidic residues and cleaves peptides derived from fibroblast growth factor-23 and matrix extracellular phosphoglycoprotein. Biochem J 2003; 373:271-9. [PMID: 12678920 PMCID: PMC1223479 DOI: 10.1042/bj20030287] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2003] [Revised: 04/03/2003] [Accepted: 04/04/2003] [Indexed: 01/31/2023]
Abstract
The PHEX gene (phosphate-regulating gene with homologies to endopeptidases on the X chromosome) encodes a protein (PHEX) with structural homologies to members of the M13 family of zinc metallo-endopeptidases. Mutations in the PHEX gene are responsible for X-linked hypophosphataemia in humans. However, the mechanism by which loss of PHEX function results in the disease phenotype, and the endogenous PHEX substrate(s) remain unknown. In order to study PHEX substrate specificity, combinatorial fluorescent-quenched peptide libraries containing o -aminobenzoic acid (Abz) and 2,4-dinitrophenyl (Dnp) as the donor-acceptor pair were synthesized and tested as PHEX substrates. PHEX showed a strict requirement for acidic amino acid residues (aspartate or glutamate) in S(1)' subsite, with a strong preference for aspartate. Subsites S(2)', S(1) and S(2) exhibited less defined specificity requirements, but the presence of leucine, proline or glycine in P(2)', or valine, isoleucine or histidine in P(1) precluded hydrolysis of the substrate by the enzyme. The peptide Abz-GFSDYK(Dnp)-OH, which contains the most favourable residues in the P(2) to P(2)' positions, was hydrolysed by PHEX at the N-terminus of aspartate with a k(cat)/ K(m) of 167 mM(-1) x s(-1). In addition, using quenched fluorescence peptides derived from fibroblast growth factor-23 and matrix extracellular phosphoglycoprotein sequences flanked by Abz and N -(2,4-dinitrophenyl)ethylenediamine, we showed that these physiologically relevant proteins are potential PHEX substrates. Finally, our results clearly indicate that PHEX does not have neprilysin-like substrate specificity.
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Affiliation(s)
- Marcelo Campos
- Department of Biophysics, Universidade Federal de São Paulo, Escola Paulista de Medicina, Rua Três de Maio 100, 04044-020, São Paulo, Brazil
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Abstract
There is evidence for a hormone/enzyme/extracellular matrix protein cascade involving fibroblastic growth factor 23 (FGF23), a phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX), and a matrix extracellular phosphoglycoprotein (MEPE) that regulates systemic phosphate homeostasis and mineralization. Genetic studies of autosomal dominant hypophosphatemic rickets (ADHR) and X-linked hypophosphatemia (XLH) identified the phosphaturic hormone FGF23 and the membrane metalloprotease PHEX, and investigations of tumor-induced osteomalacia (TIO) discovered the extracellular matrix protein MEPE. Similarities between ADHR, XLH, and TIO suggest a model to explain the common pathogenesis of renal phosphate wasting and defective mineralization in these disorders. In this model, increments in FGF23 and MEPE, respectively, cause renal phosphate wasting and intrinsic mineralization abnormalities. FGF23 elevations in ADHR are due to mutations of FGF23 that block its degradation, in XLH from indirect actions of inactivating mutations of PHEX to modify the expression and/or degradation of FGF23 and MEPE, and in TIO because of increased production of FGF23 and MEPE. Although this model is attractive, several aspects need to be validated. First, the enzymes responsible for metabolizing FGF23 and MEPE need to be established. Second, the physiologically relevant PHEX substrates and the mechanisms whereby PHEX controls FGF23 and MEPE metabolism need to be elucidated. Finally, additional studies are required to establish the molecular mechanisms of FGF23 and MEPE actions on kidney and bone, as well as to confirm the role of these and other potential "phosphatonins," such as frizzled related protein-4, in the pathogenesis of the renal and skeletal phenotypes in XLH and TIO. Unraveling the components of this hormone/enzyme/extracellular matrix pathway will not only lead to a better understanding of phosphate homeostasis and mineralization but may also improve the diagnosis and treatment of hypo- and hyperphosphatemic disorders.
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Affiliation(s)
- L Darryl Quarles
- Department of Medicine, Center for Bone and Mineral Disorders, Duke University Medical Center, Durham, North Carolina 27710, USA.
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Abstract
UNLABELLED We investigated if the circulating levels of the phosphaturic factor FGF23 are elevated in subjects with XLH. Although we failed to find a statistically significant increase, FGF23 levels were significantly correlated with the degree of hypophosphatemia in XLH. In contrast, FGF23 levels were markedly increased in subjects with ESRD and correlated inversely with the degree of hyperphosphatemia. INTRODUCTION Inactivating mutations of PHEX cause renal phosphate wasting in X-linked hypophosphatemic rickets (XLH) because of the accumulation of a phosphaturic hormone called phosphatonin. The recent discovery that FGF23 is the circulating phosphaturic factor in autosomal dominant hypophosphatemia raises the possibility that FGF23 is phosphatonin. METHODS Fasting serum FGF23 levels and serum biochemical parameters were measured using a human FGF23 (C-terminal) ELISA assay in 11 subjects with XLH and 42 age-matched controls, 5 subjects with hypophosphatemia of unknown cause, and 14 hyperphosphatemic subjects with end stage renal disease (ESRD). Associations between variables were examined using the Spearman's correlation coefficient and linear regression analysis. RESULTS AND CONCLUSIONS FGF23 (RU/ml) concentrations were not different (p = 0.11) between control and hypophosphatemic XLH subjects, but were significantly increased in hyperphosphatemic subjects with ESRD (p < 0.001). Western blot analysis found the presence of both full-length and C-terminal FGF23 fragments in serum from ESRD subjects. There was a strong inverse correlation between FGF23 and serum phosphorus (r = -0.60) and calcium and phosphorus (Ca x P) product (r = -0.65) in XLH, and a strong positive relationship between FGF23 and Pi (r = 0.50) and Ca x P product (r = 0.62) in ESRD. FGF23 levels were variably elevated in subjects with hypophosphatemia of unknown cause, one of which had tumor-induced osteomalacia (TIO). Removal of the tumor resulted in rapid reduction in serum FGF23 levels. These findings suggest that FGF23 has a possible role in mediating hypophosphatemia in XLH and TIO, but the overlapping levels of FGF23 in hypophosphatemic disorders and normal subjects indicate that serum phosphorus and FGF23 can also be independently regulated.
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Affiliation(s)
- Thomas J Weber
- Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA
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Fujiwara I, Aravindan R, Horst RL, Drezner MK. Abnormal regulation of renal 25-hydroxyvitamin D-1alpha-hydroxylase activity in X-linked hypophosphatemia: a translational or post-translational defect. J Bone Miner Res 2003; 18:434-42. [PMID: 12619927 DOI: 10.1359/jbmr.2003.18.3.434] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The hyp mouse exhibits abnormal metabolic/hormonal regulation of renal 25(OH)D-1alpha-hydroxylase activity. Whether this results from aberrant transcriptional regulation of the 1alpha-hydroxylase gene, CYP27B1, remains unknown. To investigate this possibility, we compared phosphate and parathyroid hormone effects on renal proximal convoluted tubule and thyrocalcitonin effects on proximal straight tubule enzyme activity and mRNA expression in normal and hyp mice. We assayed 25(OH)D-1alpha-hydroxylase activity by measuring 1,25(OH)2D production and mRNA by ribonuclease protection. Phosphate-depleted mice exhibited a 3-fold increment of 25(OH)D-1alpha-hydroxylase activity compared with normals, whereas hyp mice displayed no enhanced enzyme function. Phosphate-depleted mice concurrently displayed a 2-fold increase in mRNA transcripts; in contrast, despite failure to alter enzyme activity, hyp mice exhibited a similar increment in mRNA transcripts. Parathyroid hormone stimulation of normal mice increased 25(OH)D-1alpha-hydroxylase activity 10-fold, while eliciting only a 2-fold increment in hyp mouse enzyme function. This disparity occurred despite increments of mRNA transcripts to comparable levels (22.2 +/- 3.5- vs. 19.9 +/- 1.8-fold). The dissociation between phosphate- and parathyroid hormone-mediated transcriptional activity and protein function was not universal. Thus, thyrocalcitonin stimulation of normal and hyp mice resulted in comparable enhancement of mRNA transcripts and enzyme activity. These observations indicate that abnormal regulation of vitamin D metabolism in hyp mice occurs in the proximal convoluted tubule and results, not from aberrant transcriptional regulation, but from a defect in translational or post-translational activity.
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Affiliation(s)
- Ikuma Fujiwara
- Department of Pediatrics, Tohoku University, Sendai, Japan
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Guo R, Rowe PSN, Liu S, Simpson LG, Xiao ZS, Quarles LD. Inhibition of MEPE cleavage by Phex. Biochem Biophys Res Commun 2002; 297:38-45. [PMID: 12220505 DOI: 10.1016/s0006-291x(02)02125-3] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
X-linked hypophosphatemia (XLH) and the Hyp-mouse disease homolog are caused by inactivating mutations of Phex which results in the local accumulation of an unknown autocrine/paracrine factor in bone that inhibits mineralization of extracellular matrix. In these studies, we evaluated whether the matrix phosphoglycoprotein MEPE, which is increased in calvaria from Hyp mice, is a substrate for Phex. Using recombinant full-length Phex (rPhexWT) produced in Sf9 cells, we failed to observe Phex-dependent hydrolysis of recombinant human MEPE (rMEPE). Rather, we found that rPhex-WT inhibited cleavage of rMEPE by endogenous cathepsin-like enzyme activity present in Sf9 membrane. Sf9 membranes as well as purified cathepsin B cleaved MEPE into two major fragments of approximately 50 and approximately 42kDa. rPhexWT protein in Sf9 membrane fractions, co-incubation of rPhexWT and cathepsin B, and pre-treatment of Sf9 membranes with leupeptin prevented the hydrolysis of MEPE in vitro. The C-terminal domain of Phex was required for inhibition of MEPE cleavage, since the C-terminal deletion mutant rPhex (1-433) [rPhex3(')M] failed to inhibit Sf9-dependent metabolism of MEPE. Phex-dependent inhibition of MEPE degradation, however, did not require Phex enzymatic activity, since EDTA, an inhibitor of rPhex, failed to block rPhexWT inhibition of MEPE cleavage by Sf9 membranes. Since we were unable to identify interactions of Phex with MEPE or actions of Phex to metabolize cathepsin B, Phex may be acting to interfere with the actions of other enzymes that degrade extracellular matrix proteins. Although the molecular mechanism and biological relevance of non-enzymatic actions of Phex need to be established, these findings indicate that MEPE may be involved in the pathogenesis defective mineralization due to Phex deficiency in XLH and the Hyp-mouse.
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Affiliation(s)
- Rong Guo
- Department of Medicine, The Center for Bone and Mineral Disorders, Duke University Medical Center, Box 3036, Durham, NC 27710, USA
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De Beur SMJ, Finnegan RB, Vassiliadis J, Cook B, Barberio D, Estes S, Manavalan P, Petroziello J, Madden SL, Cho JY, Kumar R, Levine MA, Schiavi SC. Tumors associated with oncogenic osteomalacia express genes important in bone and mineral metabolism. J Bone Miner Res 2002; 17:1102-10. [PMID: 12054166 DOI: 10.1359/jbmr.2002.17.6.1102] [Citation(s) in RCA: 175] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Oncogenic osteomalacia (OOM) is associated with primitive mesenchymal tumors that secrete phosphaturic factors resulting in low serum concentrations of phosphate and calcitriol, phosphaturia, and defective bone mineralization. To identify overexpressed genes in these tumors, we compared gene expression profiles of tumors resected from patients with OOM and histologically similar control tumors using serial analysis of gene expression (SAGE). Three hundred and sixty-four genes were expressed at least twofold greater in OOM tumors compared with control tumors. A subset of 67 highly expressed genes underwent validation with an extended set of OOM and control tumors using array analysis or reverse-transcription polymerase chain reaction (RT-PCR). Ten of these validated genes were consistently overexpressed in all OOM tumors relative to control tumors. Strikingly, genes with roles in bone matrix formation, mineral ion transport, and bone mineralization were highly expressed in the OOM tumors.
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Affiliation(s)
- Suzanne M Jan De Beur
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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Liu S, Guo R, Tu Q, Quarles LD. Overexpression of Phex in osteoblasts fails to rescue the Hyp mouse phenotype. J Biol Chem 2002; 277:3686-97. [PMID: 11713245 DOI: 10.1074/jbc.m107707200] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Inactivating mutations of Phex, a phosphate-regulating endopeptidase, cause hypophosphatemia and impaired mineralization in X-linked hypophosphatemia (XLH) and its mouse homologue, Hyp. Because Phex is predominantly expressed in bone and cultured osteoblasts from Hyp mice display an apparent intrinsic mineralization defect, it is thought that reduced expression of Phex in mature osteoblasts is the primary cause of XLH. To test this hypothesis, we studied both targeted expression of Phex to osteoblasts in vivo under the control of the mouse osteocalcin (OG2) promoter and retroviral mediated overexpression of Phex in Hyp-derived osteoblasts (TMOb-Hyp) in vitro. Targeted overexpression of Phex to osteoblasts of OG2 Phex transgenic Hyp mice normalized Phex endopeptidase activity in bone but failed to correct the hypophosphatemia, rickets, or osteomalacia. OG2 Phex transgenic Hyp mice did exhibit a small, but significant, increase in bone mineral density and dry ashed weight, suggesting a partial mineralization effect from restoration of Phex function in mature osteoblasts. Similarly, retroviral mediated overexpression of Phex in TMOb-Hyp osteoblasts restored Phex mRNA levels, protein expression, and endopeptidase activity but failed to correct their intrinsic mineralization defect. In addition, we failed to detect the Phex substrate FGF-23 in osteoblasts. Taken together, these in vivo and in vitro data indicate that expression of Phex in osteoblasts is not sufficient to rescue the Hyp phenotype and that other sites of Phex expression and/or additional factors are likely to be important in the pathogenesis of XLH.
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Affiliation(s)
- Shiguang Liu
- Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA
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Guo R, Liu S, Spurney RF, Quarles LD. Analysis of recombinant Phex: an endopeptidase in search of a substrate. Am J Physiol Endocrinol Metab 2001; 281:E837-47. [PMID: 11551862 DOI: 10.1152/ajpendo.2001.281.4.e837] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
X-linked hypophosphatemia (XLH) is caused by inactivating mutations of Phex, a phosphate-regulating endopeptidase. Further advances in our knowledge of the pathogenesis of XLH require identification of the biological function of Phex and its physiologically relevant substrates. We evaluated several potential substrates using mouse recombinant wild-type Phex proteins (rPhex-WT) and inactive mutant Phex proteins (rPhex-3'M) lacking the COOH-terminal catalytic domain as controls. By Western blot analysis, we demonstrated that Phex is a membrane-bound 100-kDa glycosylated monomer. Neither casein, a substrate for the related endopeptidase thermolysin, human stanniocalcin 1 (hSTC-1), an osteoblast-derived phosphate-regulating factor, nor FGF-23 peptide (amino acid 172-186), comprising the region mutated in autosomal dominant hypophosphatemia, was cleaved by rPhex-WT. In addition, membranes expressing rPhex-WT, rPhex-3'M, and the empty vector hydrolyzed parathyroid hormone-(1-34), indicating the lack of Phex-specific cleavage of parathyroid hormone. In contrast, rPhex-WT did display an EDTA-dependent cleavage of the neutral endopeptidase substrate [Leu]enkephalin. Further studies with wild-type and mutant rPhex proteins should permit the identification of physiologically relevant substrates involved in the pathogenesis of XLH.
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Affiliation(s)
- R Guo
- Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA
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Bowe AE, Finnegan R, Jan de Beur SM, Cho J, Levine MA, Kumar R, Schiavi SC. FGF-23 inhibits renal tubular phosphate transport and is a PHEX substrate. Biochem Biophys Res Commun 2001; 284:977-81. [PMID: 11409890 DOI: 10.1006/bbrc.2001.5084] [Citation(s) in RCA: 276] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Oncogenic osteomalacia (OOM), X-linked hypophosphatemia (XLH), and autosomal dominant hypophosphatemic rickets (ADHR) are phenotypically similar disorders characterized by hypophosphatemia, decreased renal phosphate reabsorption, normal or low serum calcitriol concentrations, normal serum concentrations of calcium and parathyroid hormone, and defective skeletal mineralization. XLH results from mutations in the PHEX gene, encoding a membrane-bound endopeptidase, whereas ADHR is associated with mutations of the gene encoding FGF-23. Recent evidence that FGF-23 is expressed in mesenchymal tumors associated with OOM suggests that FGF-23 is responsible for the phosphaturic activity previously termed "phosphatonin." Here we show that both wild-type FGF-23 and the ADHR mutant, FGF-23(R179Q), inhibit phosphate uptake in renal epithelial cells. We further show that the endopeptidase, PHEX, degrades native FGF-23 but not the mutant form. Our results suggest that FGF-23 is involved in the pathogenesis of these three hypophosphatemic disorders and directly link PHEX and FGF-23 within the same biochemical pathway.
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Affiliation(s)
- A E Bowe
- Applied Genomics, Genzyme, Framingham, Massachusetts 01701-9322, USA
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