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Zhu Z, Bo-Ran Ho B, Chen A, Amrhein J, Apetrei A, Carpenter TO, Lazaretti-Castro M, Colazo JM, McCrystal Dahir K, Geßner M, Gurevich E, Heier CA, Simmons JH, Hunley TE, Hoppe B, Jacobsen C, Kouri A, Ma N, Majumdar S, Molin A, Nokoff N, Ott SM, Peña HG, Santos F, Tebben P, Topor LS, Deng Y, Bergwitz C. An update on clinical presentation and responses to therapy of patients with hereditary hypophosphatemic rickets with hypercalciuria (HHRH). Kidney Int 2024; 105:1058-1076. [PMID: 38364990 DOI: 10.1016/j.kint.2024.01.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 12/23/2023] [Accepted: 01/08/2024] [Indexed: 02/18/2024]
Abstract
Pathogenic variants in solute carrier family 34, member 3 (SLC34A3), the gene encoding the sodium-dependent phosphate cotransporter 2c (NPT2c), cause hereditary hypophosphatemic rickets with hypercalciuria (HHRH). Here, we report a pooled analysis of clinical and laboratory records of 304 individuals from 145 kindreds, including 20 previously unreported HHRH kindreds, in which two novel SLC34A3 pathogenic variants were identified. Compound heterozygous/homozygous carriers show above 90% penetrance for kidney and bone phenotypes. The biochemical phenotype for heterozygous carriers is intermediate with decreased serum phosphate, tubular reabsorption of phosphate (TRP (%)), fibroblast growth factor 23, and intact parathyroid hormone, but increased serum 1,25-dihydroxy vitamin D, and urine calcium excretion causing idiopathic hypercalciuria in 38%, with bone phenotypes still observed in 23% of patients. Oral phosphate supplementation is the current standard of care, which typically normalizes serum phosphate. However, although in more than half of individuals this therapy achieves correction of hypophosphatemia it fails to resolve the other outcomes. The American College of Medical Genetics and Genomics score correlated with functional analysis of frequent SLC34A3 pathogenic variants in vitro and baseline disease severity. The number of mutant alleles and baseline TRP (%) were identified as predictors for kidney and bone phenotypes, baseline TRP (%) furthermore predicted response to therapy. Certain SLC34A3/NPT2c pathogenic variants can be identified with partial responses to therapy, whereas with some overlap, others present only with kidney phenotypes and a third group present only with bone phenotypes. Thus, our report highlights important novel clinical aspects of HHRH and heterozygous carriers, raises awareness to this rare group of disorders and can be a foundation for future studies urgently needed to guide therapy of HHRH.
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Affiliation(s)
- Zewu Zhu
- Department of Internal Medicine, Section of Endocrinology, Yale University School of Medicine, New Haven, Connecticut, USA; Department of Urology, Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Bryan Bo-Ran Ho
- Department of Internal Medicine, Section of Endocrinology, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Alyssa Chen
- Department of Internal Medicine, Section of Endocrinology, Yale University School of Medicine, New Haven, Connecticut, USA; Department of Otolaryngology, Harvard Medical School, Boston, Massachusetts, USA
| | - James Amrhein
- Pediatric Endocrinology and Diabetes, School of Medicine Greenville Campus, University of South Carolina, Greenville, South Carolina, USA
| | - Andreea Apetrei
- Caen University Hospital, Department of Genetics, UR7450 Biotargen, Reference Center for Rare Diseases of Calcium and Phosphate Metabolism, OSCAR Network, Caen, France
| | - Thomas Oliver Carpenter
- Department of Internal Medicine, Section of Endocrinology, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Marise Lazaretti-Castro
- Division of Endocrinology, Escola Paulista de Medicina-Universidade Federal de Sao Paulo (EPM-UNIFESP), Sao Paulo, Brazil
| | - Juan Manuel Colazo
- Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA
| | - Kathryn McCrystal Dahir
- Division of Endocrinology, Program for Metabolic Bone Disorders, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Michaela Geßner
- Pediatric Nephrology, Children's and Adolescents' Hospital, Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne, Germany
| | - Evgenia Gurevich
- Schneider Children's Medical Center of Israel, Pediatric Nephrology Institute, Petach Tikva, Israel; Faculty of Health Sciences, Ben Gurion University of the Negev, Beer Sheva, Israel
| | | | - Jill Hickman Simmons
- Department of Pediatrics, Division of Endocrinology and Diabetes, Vanderbilt University School of Medicine, Vanderbilt University, Nashville, Tennessee, USA
| | - Tracy Earl Hunley
- Division of Pediatric Nephrology, Vanderbilt University Medical Center, Monroe Carell Jr Children's Hospital at Vanderbilt, Nashville, Tennessee, USA
| | - Bernd Hoppe
- Division of Pediatric Nephrology, Department of Pediatrics, University of Bonn, Bonn, Germany
| | - Christina Jacobsen
- Division of Endocrinology, Harvard Medical School, Boston, Massachusetts, USA
| | - Anne Kouri
- Pediatric Nephrology, University of Minnesota, Minneapolis, Minnesota, USA
| | - Nina Ma
- Section of Pediatric Endocrinology, Children's Hospital Colorado, Aurora, Colorado, USA; Department of Pediatrics, University of Colorado School of Medicine, Aurora, Colorado, USA
| | - Sachin Majumdar
- Department of Internal Medicine, Section of Endocrinology, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Arnaud Molin
- Caen University Hospital, Department of Genetics, UR7450 Biotargen, Reference Center for Rare Diseases of Calcium and Phosphate Metabolism, OSCAR Network, Caen, France
| | - Natalie Nokoff
- Department of Pediatrics, Section of Endocrinology, University of Colorado Anschutz Medical Campus, Aurora, Colorado, USA
| | - Susan M Ott
- Department of Medicine, University of Washington, Seattle, Washington, USA
| | - Helena Gil Peña
- Department of Pediatrics, Hospital Universitario Central de Asturias (HUCA), Oviedo, Spain
| | - Fernando Santos
- Department of Pediatrics, Hospital Universitario Central de Asturias (HUCA), Oviedo, Spain
| | - Peter Tebben
- Division of Endocrinology, Diabetes, Metabolism, and Nutrition, Mayo Clinic, Rochester, Minnesota, USA; Division of Pediatric Endocrinology, Mayo Clinic, Rochester, Minnesota, USA
| | - Lisa Swartz Topor
- Division of Pediatric Endocrinology, Hasbro Children's Hospital, Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA
| | - Yanhong Deng
- Yale School of Public Health, New Haven, Connecticut, USA
| | - Clemens Bergwitz
- Department of Internal Medicine, Section of Endocrinology, Yale University School of Medicine, New Haven, Connecticut, USA.
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Dodamani MH, Memon SS, Karlekar M, Lila AR, Khan M, Sarathi V, Arya S, Jamale T, Thakare S, Patil VA, Shah NS, Bergwitz C, Bandgar TR. Hereditary Hypophosphatemic Rickets with Hypercalciuria Presenting with Enthesopathy, Renal Cysts, and High Serum c-Terminal FGF23: Single-Center Experience and Systematic Review. Calcif Tissue Int 2024; 114:137-146. [PMID: 37981601 DOI: 10.1007/s00223-023-01156-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2023] [Accepted: 10/10/2023] [Indexed: 11/21/2023]
Abstract
Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is a rare disorder of phosphate homeostasis. We describe a single-center experience of genetically proven HHRH families and perform systematic review phenotype-genotype correlation in reported biallelic probands and their monoallelic relatives. Detailed clinical, biochemical, radiological, and genetic data were retrieved from our center and a systematic review of Pub-Med and Embase databases for patients and relatives who were genetically proven. Total of nine subjects (probands:5) carrying biallelic SLC34A3 mutations (novel:2) from our center had a spectrum from rickets/osteomalacia to normal BMD, with hypophosphatemia and hypercalciuria in all. We describe the first case of genetically proven HHRH with enthesopathy. Elevated FGF23 in another patient with hypophosphatemia, iron deficiency anemia, and noncirrhotic periportal fibrosis led to initial misdiagnosis as tumoral osteomalacia. On systematic review of 58 probands (with biallelic SLC34A3 mutations; 35 males), early-onset HHRH and renal calcification were present in ~ 70% and late-onset HHRH in 10%. c.575C > T p.(Ser192Leu) variant occurred in 53% of probands without skeletal involvement. Among 110 relatives harboring monoallelic SLC34A3 mutation at median age 38 years, renal calcification, hypophosphatemia, high 1,25(OH)2D, and hypercalciuria were observed in ~30%, 22.3%, 40%, and 38.8%, respectively. Renal calcifications correlated with age but were similar across truncating and non-truncating variants. Although most relatives were asymptomatic for bone involvement, 6/12(50%) had low bone mineral density. We describe the first monocentric HHRH case series from India with varied phenotypes. In a systematic review, frequent renal calcifications and low BMD in relatives with monoallelic variants (HHRH trait) merit identification.
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Affiliation(s)
- Manjunath Havalappa Dodamani
- Department of Endocrinology, Seth G.S Medical College & KEM Hospital, OPD, Parel, Mumbai, Maharashtra, 400012, India
| | - Saba Samad Memon
- Department of Endocrinology, Seth G.S Medical College & KEM Hospital, OPD, Parel, Mumbai, Maharashtra, 400012, India.
| | - Manjiri Karlekar
- Department of Endocrinology, Seth G.S Medical College & KEM Hospital, OPD, Parel, Mumbai, Maharashtra, 400012, India
| | - Anurag Ranjan Lila
- Department of Endocrinology, Seth G.S Medical College & KEM Hospital, OPD, Parel, Mumbai, Maharashtra, 400012, India
| | - Mustafa Khan
- Department of Endocrinology, Brown University, 375 Wampanoag Trail, Providence, RI, 02913, USA
- Section Endocrinology and Metabolism, Yale University School of Medicine, Anlyan Center, Office S117, Lab S110, 1 Gilbert Street, New Haven, CT, 06519, USA
| | - Vijaya Sarathi
- Department of Endocrinology, Vydehi Institute of Medical Sciences and Research Centre, Bengaluru, Karnataka, India
| | - Sneha Arya
- Department of Endocrinology, Seth G.S Medical College & KEM Hospital, OPD, Parel, Mumbai, Maharashtra, 400012, India
| | - Tukaram Jamale
- Department of Nephrology, Seth G.S Medical College & KEM Hospital, Mumbai, Maharashtra, India
| | - Sayali Thakare
- Department of Nephrology, Seth G.S Medical College & KEM Hospital, Mumbai, Maharashtra, India
| | - Virendra A Patil
- Department of Endocrinology, Seth G.S Medical College & KEM Hospital, OPD, Parel, Mumbai, Maharashtra, 400012, India
| | - Nalini S Shah
- Department of Endocrinology, Seth G.S Medical College & KEM Hospital, OPD, Parel, Mumbai, Maharashtra, 400012, India
| | - Clemens Bergwitz
- Section Endocrinology and Metabolism, Yale University School of Medicine, Anlyan Center, Office S117, Lab S110, 1 Gilbert Street, New Haven, CT, 06519, USA
| | - Tushar R Bandgar
- Department of Endocrinology, Seth G.S Medical College & KEM Hospital, OPD, Parel, Mumbai, Maharashtra, 400012, India
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Sangadala S, Shore EM, Xu M, Bergwitz C, Lozano-Calderon SA, Lin AE, Boden SD, Kaplan FS. Multifocal heterotopic ossification in a man with germline variants of LIM Mineralization Protein-1 (LMP-1). Am J Med Genet A 2023. [PMID: 37218523 DOI: 10.1002/ajmg.a.63304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2022] [Revised: 04/26/2023] [Accepted: 05/10/2023] [Indexed: 05/24/2023]
Abstract
A 54-year-old man with a history of unimelic, post-traumatic multifocal heterotopic ossification (HO) and normal genetic analysis of ACVR1 and GNAS had variants of unknown significance (VUS) in PDLIM-7 (PDZ and LIM Domain Protein 7), the gene encoding LMP-1 (LIM Mineralization Protein-1), an intracellular protein involved in the bone morphogenetic protein (BMP) pathway signaling and ossification. In order to determine if the LMP-1 variants were plausibly responsible for the phenotype observed, a series of in vitro experiments were conducted. C2C12 cells were co-transfected with a BMP-responsive reporter as well as the LMP-1 wildtype (wt) construct or the LMP-1T161I or the LMP-1D181G constructs (herein designated as LMP-161 or LMP-181) corresponding to the coding variants detected in the patient. A significantly increased BMP-reporter activity was observed in LMP-161 or LMP-181 transfected cells compared to the wt cells. The LMP-181 variant exhibited BMP-reporter activity with a four-fold increase over the LMP-1 wt protein. Similarly, mouse pre-osteoblastic MC3T3 cells transfected with the patient's LMP-1 variants expressed higher levels of osteoblast markers both at mRNA and protein levels and preferentially mineralized when stimulated with recombinant BMP-2 compared to control cells. Presently, there are no pathogenic variants of LMP-1 known to induce HO in humans. Our findings suggest that the germline variants in LMP-1 detected in our patient are plausibly related to his multifocal HO (LMP1-related multifocal HO). Further observations will be required to firmly establish this gene-disease relationship.
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Affiliation(s)
- Sreedhara Sangadala
- The Department of Orthopaedic Surgery, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Eileen M Shore
- The Departments of Orthopaedic Surgery and Genetics, and The Center for Research in FOP & Related Disorders, The Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Meiqi Xu
- The Department of Orthopaedic Surgery and The Center for Research in FOP & Related Disorders, The Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Clemens Bergwitz
- Section of Endocrinology and Metabolism, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Santiago A Lozano-Calderon
- The Department of Orthopaedics, Massachusetts General Hospital and Harvard University School of Medicine, Boston, Massachusetts, USA
| | - Angela E Lin
- Department of Pediatrics, Medical Genetics Unit, Mass General for Children and Harvard University School of Medicine, Boston, Massachusetts, USA
| | - Scott D Boden
- The Department of Orthopaedic Surgery, Emory University School of Medicine, Atlanta, Georgia, USA
| | - Frederick S Kaplan
- The Departments of Orthopaedic Surgery and Medicine, and The Center for Research in FOP & Related Disorders, The Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA
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Chande S, Dijk F, Fetene J, Yannicelli S, Carpenter TO, van Helvoort A, Bergwitz C. Phosphorus bioaccessibility measured in four amino acid-based formulas using in-vitro batch digestion translates well into phosphorus bioavailability in mice. Nutrition 2021; 89:111291. [PMID: 34111672 DOI: 10.1016/j.nut.2021.111291] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2020] [Revised: 04/07/2021] [Accepted: 04/18/2021] [Indexed: 10/21/2022]
Abstract
OBJECTIVE The aim of this study was to quantify the bioaccessibility of phosphorus from amino acid-based formulas (AAFs) under different digestive conditions. METHODS We developed in-vitro batch digestion models with stomach digestion at different pH mimicking the normal digestive condition and conditions representing use of acid-suppressive medication. To validate bioaccessibility findings, we devised a low phosphorus murine model to test phosphorus bioavailability under compromised digestive conditions using proton pump inhibitors (PPIs) to neutralize stomach pH. RESULTS In vitro phosphorus bioaccessibility of AAFs Neocate® Infant and Neocate Junior ranged between 57% and 65% under normal digestive conditions for infants (stomach pH 3.5) and between 38% and 46% under conditions that simulated bypass of stomach acidification, which is comparable to control diet and two EleCare® AAFs. In vivo bioavailability analysis showed that both Neocate formulas were able to normalize plasma phosphorus levels when administered to low phosphorus mice along with PPIs (control diet + PPI 8 ± 0.4; Neocate Infant 10.1 ± 0.9; Neocate Junior 9.2 ± 0.6; EleCare Infant 8.6 ± 0.4; EleCare Junior 8.7 ± 0.5; n = 8-10; P < 0.0001 versus baseline 3.4 ± 0.2 mg/dL). In comparison, plasma phosphorus levels remained lower on the low phosphorus diet (5.7 ± 0.2 mg/dL). Furthermore, urinary phosphorus/creatinine and intact fibroblast growth factor 23 were significantly lowered by low phosphorus diet. In contrast, intact parathyroid hormone and 1,25-dihydroxy vitamin D decreased and increased, respectively, and these parameters likewise normalized in mice administered AAFs. CONCLUSION The present findings indicated that phosphorus bioaccessibility in the in-vitro batch digestion model translates well into phosphorus bioavailability in mice even under compromised digestive conditions that bypass gastric acidification.
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Affiliation(s)
- Sampada Chande
- Yale University School of Medicine, Section of Endocrinology and Metabolism, New Haven, Connecticut, USA
| | | | - Jonathan Fetene
- Yale University School of Medicine, Section of Endocrinology and Metabolism, New Haven, Connecticut, USA
| | | | - Thomas O Carpenter
- Yale University School of Medicine, Department of Pediatrics, New Haven, Connecticut, USA
| | - Ardy van Helvoort
- Danone Nutricia Research, Utrecht, The Netherlands; School of Nutrition and Translational Research in Metabolism, Maastricht University, Maastricht, The Netherlands
| | - Clemens Bergwitz
- Yale University School of Medicine, Section of Endocrinology and Metabolism, New Haven, Connecticut, USA.
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Abstract
Fibroblast growth factor 23 (FGF23) is a phosphotropic hormone that belongs to a subfamily of endocrine FGFs with evolutionarily conserved functions in worms and fruit flies. FAM20C phosphorylates FGF23 post-translationally, targeting it to proteolysis through subtilisin-like proprotein convertase FURIN, resulting in secretion of FGF23 fragments. O-glycosylation of FGF23 through GALNT3 appears to prevent proteolysis, resulting in secretion of biologically active intact FGF23. In the circulation, FGF23 may undergo further processing by plasminogen activators. Crystal structures show that the ectodomain of the cognate FGF23 receptor FGFR1c binds with the ectodomain of the co-receptor alpha-KLOTHO. The KLOTHO-FGFR1c double heterodimer creates a high-affinity binding site for the FGF23 C-terminus. The topology of FGF23 deviates from that of paracrine FGFs, resulting in poor affinity for heparan sulphate, which may explain why FGF23 diffuses freely in the bone matrix to enter the bloodstream following its secretion by cells of osteoblastic lineage. Intact FGF23 signalling by this canonical pathway activates FRS2/RAS/RAF/MEK/ERK1/2. It reduces serum phosphate by inhibiting 1,25-dihydroxyvitamin D synthesis, suppressing intestinal phosphate absorption, and by downregulating the transporters NPT2a and NPT2c, suppressing phosphate reabsorption in the proximal tubules. The physiological role of FGF23 fragments, which may be inhibitory, remains unclear. Pharmacological and genetic activation of canonical FGF23 signalling causes hypophosphatemic disorders, while its inhibition results in hyperphosphatemic disorders. Non-canonical FGF23 signalling through binding and activation of FGFR3/FGFR4/calcineurin/NFAT in an alpha-KLOTHO-independent fashion mainly occurs at extremely elevated circulating FGF23 levels and may contribute to mortality due to cardiovascular disease and left ventricular hypertrophy in chronic kidney disease.
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Affiliation(s)
- Bryan B Ho
- Department of Internal Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Clemens Bergwitz
- Department of Internal Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, Connecticut, USA
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Bergwitz C, Eussen SRBM, Janssens PLHR, Visser M, Carpenter TO, van Helvoort A. Different elemental infant formulas show equivalent phosphorus and calcium bioavailability in healthy volunteers. Nutr Res 2020; 85:71-83. [PMID: 33450668 DOI: 10.1016/j.nutres.2020.11.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2020] [Revised: 11/09/2020] [Accepted: 11/12/2020] [Indexed: 12/18/2022]
Abstract
Retrospective chart reviews have reported hypophosphatemia associated with elemental formula use in infants and children with systemic disease involving multiple diagnoses. The present study aims to evaluate the bioavailability of phosphorus from 2 commercial elemental formulas and to test our hypothesis of bioequivalence of the 2 products in healthy volunteers receiving gastric acid-suppressive medication. A single-center, double-blind, randomized, cross-over study was conducted in healthy volunteers with esomeprazole-induced hypochlorhydria. After a standardized low phosphorus meal followed by overnight fasting, subjects consumed 1 gram of phosphorus in a single oral dose of 1217 kcal of Product A (Neocate) or Product B (Elecare). The alternate product was given following a 1-week washout period. Blood and urine were collected at baseline and different time-points for up to 6 hours after product consumption. Area-under-the-curve (AUC) and peak values (Cpeak) for serum phosphate and calcium and urinary creatinine-corrected phosphate and calcium were assessed for bioequivalence of Products A and B. Results show that the geometric mean ratio (GMR) and 90% CI for serum phosphate were 1.041 (0.998-1.086) and 1.020 (0.963-1.080) for AUC0-360 and Cpeak, respectively, meeting the predetermined criteria for bioequivalence. Urinary creatinine-corrected phosphate followed a similar pattern after intake of Product A and B, but did not reach bioequivalence criteria (GMR: AUC70-370 = 1.105 (0.918-1.330); Cpeak = 1.182 (1.040-1.343)). Serum calcium concentrations (GMR: AUC0-360 = 1.002 (0.996-1.009); Cpeak = 0.991 (0.983-0.999)) and urinary creatinine-corrected calcium excretion (GMR: AUC70-370 = 1.117 (1.023-1.219); Cpeak = 1.157 (1.073-1.247)) demonstrated bioequivalence of the products. In conclusion, both elemental infant formulas showed equivalent serum phosphorus and calcium bioavailability in healthy volunteers even if combined with treatment with acid-suppressive medication.
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Affiliation(s)
- Clemens Bergwitz
- Yale University School of Medicine, Section of Endocrinology and Metabolism, New Haven, CT, USA
| | | | | | | | - Thomas O Carpenter
- Yale University School of Medicine, Department of Pediatrics, New Haven, CT, USA
| | - Ardy van Helvoort
- Danone Nutricia Research, Utrecht, The Netherlands; Maastricht University, NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht, The Netherlands
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Hartley IR, Miller CB, Papadakis GZ, Bergwitz C, Del Rivero J, Blau JE, Florenzano P, Berglund JA, Tassone J, Roszko KL, Moran S, Gafni RI, Isaacs R, Collins MT. Targeted FGFR Blockade for the Treatment of Tumor-Induced Osteomalacia. N Engl J Med 2020; 383:1387-1389. [PMID: 32905668 PMCID: PMC7561341 DOI: 10.1056/nejmc2020399] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Iris R Hartley
- National Institute of Dental and Craniofacial Research, Bethesda, MD
| | | | | | | | | | - Jenny E Blau
- National Institute of Diabetes and Digestive and Kidney Disease, Bethesda, MD
| | | | - Jason A Berglund
- University of Texas Health Science Center at Houston, Houston, TX
| | | | - Kelly L Roszko
- National Institute of Dental and Craniofacial Research, Bethesda, MD
| | | | - Rachel I Gafni
- National Institute of Dental and Craniofacial Research, Bethesda, MD
| | - Randi Isaacs
- Novartis Institutes of Biomedical Research, East Hanover, NJ
| | - Michael T Collins
- National Institute of Dental and Craniofacial Research, Bethesda, MD
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Chande S, Zeiss C, Vézier J, Chavkin NW, Hernando N, Giachelli CM, Wagner CA, Beck L, Beck-Cormier S, Bergwitz C. Ablation of Slc20a1/PitT1 and Slc20a2/PiT2 in mice in the osteogenic lineage causes dentin dysplasia and formation of ectopic enamel islands. Bone Rep 2020. [DOI: 10.1016/j.bonr.2020.100648] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Abstract
Inorganic phosphate (Pi) plays a critical function in many tissues of the body: for example, as part of the hydroxyapatite in the skeleton and as a substrate for ATP synthesis. Pi is the main source of dietary phosphorus. Reduced bioavailability of Pi or excessive losses in the urine causes rickets and osteomalacia. While critical for health in normal amounts, dietary phosphorus is plentiful in the Western diet and is often added to foods as a preservative. This abundance of phosphorus may reduce longevity due to metabolic changes and tissue calcifications. In this review, we examine how dietary phosphorus is absorbed in the gut, current knowledge about Pi sensing, and endocrine regulation of Pi levels. Moreover, we also examine the roles of Pi in different tissues, the consequences of low and high dietary phosphorus in these tissues, and the implications for healthy aging.
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Affiliation(s)
- Juan Serna
- Yale College, Yale University, New Haven, CT 06511, USA;
| | - Clemens Bergwitz
- Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale School of Medicine, New Haven, CT 06519, USA
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Dreimane D, Chen A, Bergwitz C. Description of a novel SLC34A3.c.671delT mutation causing hereditary hypophosphatemic rickets with hypercalciuria in two adolescent boys and response to recombinant human growth hormone. Ther Adv Musculoskelet Dis 2020; 12:1759720X20912862. [PMID: 32963591 PMCID: PMC7488884 DOI: 10.1177/1759720x20912862] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Accepted: 02/05/2020] [Indexed: 11/17/2022] Open
Abstract
Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is an autosomal recessive disorder characterized by hypophosphatemia, rickets, hyperphosphaturia, elevated 1,25(OH)2D, and hypercalciuria. Mutations in SLC34A3, the gene encoding the sodium-dependent cotransporter NPT2c, have previously been described as a cause of HHRH. Here, we describe two male siblings with rickets and hypercalciuric nephrolithiasis born to unrelated parents, and their response to oral phosphate supplementation and growth hormone therapy. Whole exome sequencing of the oldest brother, and polymerase chain reaction and Sanger sequence analysis of the identified SLC34A3 mutations, was performed for confirmation and to evaluate his siblings and parents. Serum and urine biochemical parameters of mineral homeostasis before and after therapy were evaluated. Whole exome sequencing analysis identified a previously reported heterozygous deletion SLC34A3.g.2259-2359del101bp on the maternal allele, and a novel heterozygous single nucleotide deletion SLC34A3.c.671delT on the paternal allele of the two affected brothers. The parents and the unaffected brother are heterozygous carriers. Recombinant human growth hormone (rHGH) plus oral phosphate in one affected brother improved the renal phosphate leak and resulted in accelerated linear growth superior to that seen with oral phosphate supplementation alone in the other affected brother. Our case study is the first to demonstrate that rHGH can be considered in addition to oral supplementation with phosphorus to improve linear growth in patients with this disorder, and suggests that renal phosphate reabsorption in response to rHGH is NPT2c-independent.
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Affiliation(s)
- Daina Dreimane
- Department of Pediatrics, Division of Endocrinology and Diabetes, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX, USA
| | - Alyssa Chen
- Department of Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, CT, USA
| | - Clemens Bergwitz
- Department of Medicine, Section Endocrinology, Yale University School of Medicine, 1 Gilbert Street, New Haven, CT 06519, USA
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Chande S, Caballero D, Ho BB, Fetene J, Serna J, Pesta D, Nasiri A, Jurczak M, Chavkin NW, Hernando N, Giachelli CM, Wagner CA, Zeiss C, Shulman GI, Bergwitz C. Slc20a1/Pit1 and Slc20a2/Pit2 are essential for normal skeletal myofiber function and survival. Sci Rep 2020; 10:3069. [PMID: 32080237 PMCID: PMC7033257 DOI: 10.1038/s41598-020-59430-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2019] [Accepted: 01/29/2020] [Indexed: 01/25/2023] Open
Abstract
Low blood phosphate (Pi) reduces muscle function in hypophosphatemic disorders. Which Pi transporters are required and whether hormonal changes due to hypophosphatemia contribute to muscle function is unknown. To address these questions we generated a series of conditional knockout mice lacking one or both house-keeping Pi transporters Pit1 and Pit2 in skeletal muscle (sm), using the postnatally expressed human skeletal actin-cre. Simultaneous conditional deletion of both transporters caused skeletal muscle atrophy, resulting in death by postnatal day P13. smPit1-/-, smPit2-/- and three allele mutants are fertile and have normal body weights, suggesting a high degree of redundance for the two transporters in skeletal muscle. However, these mice show a gene-dose dependent reduction in running activity also seen in another hypophosphatemic model (Hyp mice). In contrast to Hyp mice, grip strength is preserved. Further evaluation of the mechanism shows reduced ERK1/2 activation and stimulation of AMP kinase in skeletal muscle from smPit1-/-; smPit2-/- mice consistent with energy-stress. Similarly, C2C12 myoblasts show a reduced oxygen consumption rate mediated by Pi transport-dependent and ERK1/2-dependent metabolic Pi sensing pathways. In conclusion, we here show that Pit1 and Pit2 are essential for normal myofiber function and survival, insights which may improve management of hypophosphatemic myopathy.
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Affiliation(s)
- Sampada Chande
- Department of Internal Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, CT, USA
| | - Daniel Caballero
- Department of Internal Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, CT, USA
| | - Bryan B Ho
- Department of Internal Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, CT, USA
| | - Jonathan Fetene
- Department of Internal Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, CT, USA
| | - Juan Serna
- Department of Internal Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, CT, USA
| | - Dominik Pesta
- Department of Cellular&Molecular Physiology, Yale University School of Medicine, New Haven, CT, USA
- German Diabetes Center, Düsseldorf, Germany, University of Washington, Box 355061, Foege Hall Seattle, WA, 98195, USA
| | - Ali Nasiri
- Department of Cellular&Molecular Physiology, Yale University School of Medicine, New Haven, CT, USA
| | - Michael Jurczak
- Department of Internal Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, CT, USA
- Department of Medicine, Division of Endocrinology, University of Pittsburgh, University of Washington, Box 355061, Foege Hall Seattle, WA, 98195, USA
| | - Nicholas W Chavkin
- Department of Bioengineering, University of Washington, Box 355061, Foege Hall Seattle, WA, 98195, USA
| | - Nati Hernando
- Institute of Physiology, University of Zürich, Switzerland and National Center of Competence in Research NCCR Kidney.CH, Zürich, Switzerland
| | - Cecilia M Giachelli
- Department of Bioengineering, University of Washington, Box 355061, Foege Hall Seattle, WA, 98195, USA
| | - Carsten A Wagner
- Institute of Physiology, University of Zürich, Switzerland and National Center of Competence in Research NCCR Kidney.CH, Zürich, Switzerland
| | - Caroline Zeiss
- Comparative Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Gerald I Shulman
- Department of Internal Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, CT, USA
- Department of Cellular&Molecular Physiology, Yale University School of Medicine, New Haven, CT, USA
| | - Clemens Bergwitz
- Department of Internal Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, CT, USA.
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12
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Chande S, Ho B, Fetene J, Bergwitz C. Transgenic mouse model for conditional expression of influenza hemagglutinin-tagged human SLC20A1/PIT1. PLoS One 2019; 14:e0223052. [PMID: 31613887 PMCID: PMC6793878 DOI: 10.1371/journal.pone.0223052] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2019] [Accepted: 09/12/2019] [Indexed: 11/19/2022] Open
Abstract
To further investigate the role of the phosphate (Pi) transporter PIT1 in Pi homeostasis and tissue mineralization, we developed a transgenic mouse expressing the C-terminal influenza hemagglutinin (HA) epitope-tagged human PIT1 transporter under control of the cytomegalovirus/chicken beta actin/rabbit beta-globin gene (CAG) promotor and a loxP-stop-loxP (LSL) cassette permitting conditional activation of transgene expression (LSL-HA-hPITtg/+). For an initial characterization of this conditional mouse model, germline excision of the LSL cassette was performed to induce expression of the transgene in all mouse tissues (HA-hPIT1tg/+). Recombination was confirmed using genomic DNA obtained from blood samples of these mice. Furthermore, expression of HA-hPIT1 was found to be at least 10-fold above endogenous mouse Pit1 in total RNA isolated from multiple tissues and from cultured primary calvaria osteoblasts (PCOB) estimated by semi-quantitative RT-PCR. Robust expression of the HA-hPIT1 protein was also observed upon immunoblot analysis in most tissues and permits HA-mediated immunoprecipitation of the transporter. Characterization of the phenotype of HA-hPIT1tg/+ mice at 80 days of age when fed a standard chow (0.7% Pi and 1% calcium) showed elevated plasma Pi, but normal plasma iPTH, iFGF23, serum calcium, BUN, 1,25-dihydroxy vitamin D levels and urine Pi, calcium and protein excretion when compared to WT littermates. Likewise, no change in bone mineral density was observed upon uCT analysis of the distal femur obtained from these mice. In conclusion, heterozygous overexpression of HA-hPIT1 is compatible with life and causes hyperphosphatemia while bone and mineral metabolism of these mice are otherwise normal.
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Affiliation(s)
- Sampada Chande
- Section of Endocrinology and Metabolism, Yale University School of Medicine, New Haven, CT, United States of America
| | - Bryan Ho
- Section of Endocrinology and Metabolism, Yale University School of Medicine, New Haven, CT, United States of America
| | - Jonathan Fetene
- Section of Endocrinology and Metabolism, Yale University School of Medicine, New Haven, CT, United States of America
| | - Clemens Bergwitz
- Section of Endocrinology and Metabolism, Yale University School of Medicine, New Haven, CT, United States of America
- * E-mail:
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13
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Rose E, Lee D, Xiao E, Zhao W, Wee M, Cohen J, Bergwitz C. Endocrine regulation of MFS2 by branchless controls phosphate excretion and stone formation in Drosophila renal tubules. Sci Rep 2019; 9:8798. [PMID: 31217461 PMCID: PMC6584732 DOI: 10.1038/s41598-019-45269-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Accepted: 04/16/2019] [Indexed: 12/15/2022] Open
Abstract
How inorganic phosphate (Pi) homeostasis is regulated in Drosophila is currently unknown. We here identify MFS2 as a key Pi transporter in fly renal (Malpighian) tubules. Consistent with its role in Pi excretion, we found that dietary Pi induces MFS2 expression. This results in the formation of Malpighian calcium-Pi stones, while RNAi-mediated knockdown of MFS2 increases blood (hemolymph) Pi and decreases formation of Malpighian tubule stones in flies cultured on high Pi medium. Conversely, microinjection of adults with the phosphaturic human hormone fibroblast growth factor 23 (FGF23) induces tubule expression of MFS2 and decreases blood Pi. This action of FGF23 is blocked by genetic ablation of MFS2. Furthermore, genetic overexpression of the fly FGF branchless (bnl) in the tubules induces expression of MFS2 and increases Malpighian tubule stones suggesting that bnl is the endogenous phosphaturic hormone in adult flies. Finally, genetic ablation of MFS2 increased fly life span, suggesting that Malpighian tubule stones are a key element whereby high Pi diet reduces fly longevity previously reported by us. In conclusion, MFS2 mediates excretion of Pi in Drosophila, which is as in higher species under the hormonal control of FGF-signaling.
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Affiliation(s)
- Emily Rose
- Section Endocrinology, Yale School of Medicine, New Haven, CT, USA
| | - Daniela Lee
- Section Endocrinology, Yale School of Medicine, New Haven, CT, USA
| | - Emily Xiao
- Section Endocrinology, Yale School of Medicine, New Haven, CT, USA
| | - Wenzhen Zhao
- Section Endocrinology, Yale School of Medicine, New Haven, CT, USA
| | - Mark Wee
- Endocrine Unit, Massachusetts General Hospital, Boston, MA, USA
| | - Jonathan Cohen
- Endocrine Unit, Massachusetts General Hospital, Boston, MA, USA
| | - Clemens Bergwitz
- Section Endocrinology, Yale School of Medicine, New Haven, CT, USA.
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14
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Chen A, Ro H, Mundra VRR, Joseph K, Brenner D, Carpenter TO, Rizk DV, Bergwitz C. Description of 5 Novel SLC34A3/NPT2c Mutations Causing Hereditary Hypophosphatemic Rickets With Hypercalciuria. Kidney Int Rep 2019; 4:1179-1186. [PMID: 31440709 PMCID: PMC6698313 DOI: 10.1016/j.ekir.2019.05.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Accepted: 05/06/2019] [Indexed: 12/29/2022] Open
Affiliation(s)
- Alyssa Chen
- Section Endocrinology, Department of Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.,AI Therapeutics, Guilford, Connecticut, USA
| | - Hannah Ro
- Section Endocrinology, Department of Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Venkat Ram Rakesh Mundra
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Kelly Joseph
- Pediatric Endocrinology, Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Dennis Brenner
- Division of Pediatric Endocrinology, Saint Barnabas Medical Center, New Jersey Medical School, Livingston, New Jersey, USA
| | - Thomas O Carpenter
- Pediatric Endocrinology, Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Dana V Rizk
- Division of Nephrology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Clemens Bergwitz
- Section Endocrinology, Department of Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
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15
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Abstract
Inorganic phosphate (Pi) is essential for signal transduction and cell metabolism, and is also an essential structural component of the extracellular matrix of the skeleton. Pi is sensed in bacteria and yeast at the plasma membrane, which activates intracellular signal transduction to control the expression of Pi transporters and other genes that control intracellular Pi levels. In multicellular organisms, Pi homeostasis must be maintained in the organism and at the cellular level, requiring an endocrine and metabolic Pi-sensing mechanism, about which little is currently known. This Review will discuss the metabolic effects of Pi, which are mediated by Pi transporters, inositol pyrophosphates and SYG1-Pho81-XPR1 (SPX)-domain proteins to maintain cellular phosphate homeostasis in the musculoskeletal system. In addition, we will discuss how Pi is sensed by the human body to regulate the production of fibroblast growth factor 23 (FGF23), parathyroid hormone and calcitriol to maintain serum levels of Pi in a narrow range. New findings on the crosstalk between iron and Pi homeostasis in the regulation of FGF23 expression will also be outlined. Mutations in components of these metabolic and endocrine phosphate sensors result in genetic disorders of phosphate homeostasis, cardiomyopathy and familial basal ganglial calcifications, highlighting the importance of this newly emerging area of research.
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Affiliation(s)
- Sampada Chande
- Section of Endocrinology and Metabolism, Yale University School of Medicine, New Haven, CT, USA
| | - Clemens Bergwitz
- Section of Endocrinology and Metabolism, Yale University School of Medicine, New Haven, CT, USA.
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16
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Bergwitz C, Miyamoto KI. Hereditary hypophosphatemic rickets with hypercalciuria: pathophysiology, clinical presentation, diagnosis and therapy. Pflugers Arch 2018; 471:149-163. [PMID: 30109410 DOI: 10.1007/s00424-018-2184-2] [Citation(s) in RCA: 58] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Revised: 07/06/2018] [Accepted: 07/10/2018] [Indexed: 12/24/2022]
Abstract
Hereditary hypophosphatemic rickets with hypercalciuria (HHRH; OMIM: 241530) is a rare autosomal recessive disorder with an estimated prevalence of 1:250,000 that was originally described by Tieder et al. Individuals with HHRH carry compound-heterozygous or homozygous (comp/hom) loss-of-function mutations in the sodium-phosphate co-transporter NPT2c. These mutations result in the development of urinary phosphate (Pi) wasting and hypophosphatemic rickets, bowing, and short stature, as well as appropriately elevated 1,25(OH)2D levels, which sets this fibroblast growth factor 23 (FGF23)-independent disorder apart from the more common X-linked hypophosphatemia. The elevated 1,25(OH)2D levels in turn result in hypercalciuria due to enhanced intestinal calcium absorption and reduced parathyroid hormone (PTH)-dependent calcium-reabsorption in the distal renal tubules, leading to the development of kidney stones and/or nephrocalcinosis in approximately half of the individuals with HHRH. Even heterozygous NPT2c mutations are frequently associated with isolated hypercalciuria (IH), which increases the risk of kidney stones or nephrocalcinosis threefold in affected individuals compared with the general population. Bone disease is generally absent in individuals with IH, in contrast to those with HHRH. Treatment of HHRH and IH consists of monotherapy with oral Pi supplements, while active vitamin D analogs are contraindicated, mainly because the endogenous 1,25(OH)2D levels are already elevated but also to prevent further worsening of the hypercalciuria. Long-term studies to determine whether oral Pi supplementation alone is sufficient to prevent renal calcifications and bone loss, however, are lacking. It is also unknown how therapy should be monitored, whether secondary hyperparathyroidism can develop, and whether Pi requirements decrease with age, as observed in some FGF23-dependent hypophosphatemic disorders, or whether this can lead to osteoporosis.
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Affiliation(s)
- Clemens Bergwitz
- Section Endocrinology and Metabolism, Yale University School of Medicine, Anlyan Center, Office S117, Lab S110, 1 Gilbert Street, New Haven, CT 06519, USA.
| | - Ken-Ichi Miyamoto
- Department of Molecular Nutrition, Tokushima University Graduate School of Biomedical Sciences, Tokushima, Japan
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17
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Caballero D, Li Y, Fetene J, Ponsetto J, Chen A, Zhu C, Braddock DT, Bergwitz C. Intraperitoneal pyrophosphate treatment reduces renal calcifications in Npt2a null mice. PLoS One 2017; 12:e0180098. [PMID: 28704395 PMCID: PMC5509111 DOI: 10.1371/journal.pone.0180098] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2017] [Accepted: 06/09/2017] [Indexed: 12/12/2022] Open
Abstract
Mutations in the proximal tubular sodium-dependent phosphate co-transporters NPT2a and NPT2c have been reported in patients with renal stone disease and nephrocalcinosis, however the relative contribution of genotype, dietary calcium and phosphate, and modifiers of mineralization such as pyrophosphate (PPi) to the formation of renal mineral deposits is unclear. In the present study, we used Npt2a-/- mice to model the renal calcifications observed in these disorders. We observed elevated urinary excretion of PPi in Npt2a-/- mice when compared to WT mice. Presence of two hypomorphic Extracellular nucleotide pyrophosphatase phosphodiesterase 1 (Enpp1asj/asj) alleles decreased urine PPi and worsened renal calcifications in Npt2a-/- mice. These studies suggest that PPi is a thus far unrecognized factor protecting Npt2a-/- mice from the development of renal mineral deposits. Consistent with this conclusion, we next showed that renal calcifications in these mice can be reduced by intraperitoneal administration of sodium pyrophosphate. If confirmed in humans, urine PPi could therefore be of interest for developing new strategies to prevent the nephrocalcinosis and nephrolithiasis seen in phosphaturic disorders.
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Affiliation(s)
- Daniel Caballero
- Department of Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, CT, United States of America
| | - Yuwen Li
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, United States of America
- Department of Pediatrics, The First Affiliated Hospital, Nanjing Medical University, Nanjing, Jiangsu Province, China
| | - Jonathan Fetene
- Department of Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, CT, United States of America
| | - Julian Ponsetto
- Department of Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, CT, United States of America
| | - Alyssa Chen
- Department of Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, CT, United States of America
| | - Chuanlong Zhu
- Gastroenterology Unit, Massachusetts General Hospital and Harvard Medical School, Boston, United States of America
- Department of Infectious Diseases, The First Affiliated Hospital, Nanjing Medical University, Nanjing, Jiangsu Province, China
| | - Demetrios T. Braddock
- Department of Pathology, Yale University School of Medicine, New Haven, CT, United States of America
| | - Clemens Bergwitz
- Department of Medicine, Section Endocrinology, Yale University School of Medicine, New Haven, CT, United States of America
- * E-mail:
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18
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Li Y, Caballero D, Ponsetto J, Chen A, Zhu C, Guo J, Demay M, Jüppner H, Bergwitz C. Response of Npt2a knockout mice to dietary calcium and phosphorus. PLoS One 2017; 12:e0176232. [PMID: 28448530 PMCID: PMC5407772 DOI: 10.1371/journal.pone.0176232] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Accepted: 04/08/2017] [Indexed: 01/08/2023] Open
Abstract
Mutations in the renal sodium-dependent phosphate co-transporters NPT2a and NPT2c have been reported in patients with renal stone disease and nephrocalcinosis, but the relative contribution of genotype, dietary calcium and phosphate to the formation of renal mineral deposits is unclear. We previously reported that renal calcium phosphate deposits persist and/or reappear in older Npt2a-/- mice supplemented with phosphate despite resolution of hypercalciuria while no deposits are seen in wild-type (WT) mice on the same diet. Addition of calcium to their diets further increased calcium phosphate deposits in Npt2a-/-, but not WT mice. The response of PTH to dietary phosphate of Npt2a-/- was blunted when compared to WT mice and the response of the urinary calcium x phosphorus product to the addition of calcium and phosphate to the diet of Npt2a-/- was increased. These finding suggests that Npt2a-/- mice respond differently to dietary phosphate when compared to WT mice. Further evaluation in the Npt2a-/- cohort on different diets suggests that urinary calcium excretion, plasma phosphate and FGF23 levels appear to be positively correlated to renal mineral deposit formation while urine phosphate levels and the urine anion gap, an indirect measure of ammonia excretion, appear to be inversely correlated. Our observations in Npt2a-/- mice, if confirmed in humans, may be relevant for the optimization of existing and the development of novel therapies to prevent nephrolithiasis and nephrocalcinosis in human carriers of NPT2a and NPT2c mutations.
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Affiliation(s)
- Yuwen Li
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, United States of America
- Department of Pediatrics, The First Affiliated Hospital, Nanjing Medical University, Nanjing, Jiangsu Province, China
| | - Daniel Caballero
- Section Endocrinology, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Julian Ponsetto
- Section Endocrinology, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Alyssa Chen
- Section Endocrinology, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Chuanlong Zhu
- Gastroenterology Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, United States of America
- Department of Infectious Diseases, The First Affiliated Hospital, Nanjing Medical University, Nanjing, Jiangsu Province, China
| | - Jun Guo
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, United States of America
| | - Marie Demay
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, United States of America
| | - Harald Jüppner
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, United States of America
- Pediatric Nephrology Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, United States of America
| | - Clemens Bergwitz
- Section Endocrinology, Yale University School of Medicine, New Haven, Connecticut, United States of America
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19
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Caballero D, Li Y, Ponsetto J, Zhu C, Bergwitz C. Impaired urinary osteopontin excretion in Npt2a-/- mice. Am J Physiol Renal Physiol 2016; 312:F77-F83. [PMID: 27784695 PMCID: PMC5283892 DOI: 10.1152/ajprenal.00367.2016] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Revised: 10/17/2016] [Accepted: 10/23/2016] [Indexed: 01/04/2023] Open
Abstract
Mutations in the renal sodium-dependent phosphate cotransporters NPT2a and NPT2c have been reported in patients with renal stone disease and nephrocalcinosis. Oral phosphate supplementation is currently thought to reduce risk by reversing the hypercalciuria, but the exact mechanism remains unclear and the relative contribution of modifiers of mineralization such as osteopontin (Opn) to the formation of renal mineral deposits in renal phosphate wasting disorders has not been studied. We observed a marked decrease of renal gene expression and urinary excretion of Opn in Npt2a-/- mice, a mouse model of these disorders, at baseline. Following supplementation with phosphate Opn gene expression was restored to wild-type levels in Npt2a-/- mice; however, urine excretion of the protein remained low. To further investigate the role of Opn, we used a double-knockout strategy, which provides evidence that loss of Opn worsens the nephrocalcinosis and nephrolithiasis observed in these mice on a high-phosphate diet. These studies suggest that impaired Opn gene expression and urinary excretion in Npt2a-/- mice may be an additional risk factor for nephrolithiasis, and normalizing urine Opn levels may improve the therapy of phosphaturic disorders.
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Affiliation(s)
- Daniel Caballero
- Section of Endocrinology and Metabolism, Yale University School of Medicine, New Haven, Connecticut
| | - Yuwen Li
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts.,Department of Pediatrics, The First Affiliated Hospital, Nanjing Medical University, Nanjing, China
| | - Julian Ponsetto
- Section of Endocrinology and Metabolism, Yale University School of Medicine, New Haven, Connecticut
| | - Chuanlong Zhu
- Department of Infectious Diseases, The First Affiliated Hospital, Nanjing Medical University, Nanjing, China; and
| | - Clemens Bergwitz
- Section of Endocrinology and Metabolism, Yale University School of Medicine, New Haven, Connecticut;
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20
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Pesta DH, Tsirigotis DN, Befroy DE, Caballero D, Jurczak MJ, Rahimi Y, Cline GW, Dufour S, Birkenfeld AL, Rothman DL, Carpenter TO, Insogna K, Petersen KF, Bergwitz C, Shulman GI. Hypophosphatemia promotes lower rates of muscle ATP synthesis. FASEB J 2016; 30:3378-3387. [PMID: 27338702 PMCID: PMC5024687 DOI: 10.1096/fj.201600473r] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Accepted: 06/14/2016] [Indexed: 12/13/2022]
Abstract
Hypophosphatemia can lead to muscle weakness and respiratory and heart failure, but the mechanism is unknown. To address this question, we noninvasively assessed rates of muscle ATP synthesis in hypophosphatemic mice by using in vivo saturation transfer [31P]-magnetic resonance spectroscopy. By using this approach, we found that basal and insulin-stimulated rates of muscle ATP synthetic flux (VATP) and plasma inorganic phosphate (Pi) were reduced by 50% in mice with diet-induced hypophosphatemia as well as in sodium-dependent Pi transporter solute carrier family 34, member 1 (NaPi2a)-knockout (NaPi2a-/-) mice compared with their wild-type littermate controls. Rates of VATP normalized in both hypophosphatemic groups after restoring plasma Pi concentrations. Furthermore, VATP was directly related to cellular and mitochondrial Pi uptake in L6 and RC13 rodent myocytes and isolated muscle mitochondria. Similar findings were observed in a patient with chronic hypophosphatemia as a result of a mutation in SLC34A3 who had a 50% reduction in both serum Pi content and muscle VATP After oral Pi repletion and normalization of serum Pi levels, muscle VATP completely normalized in the patient. Taken together, these data support the hypothesis that decreased muscle ATP synthesis, in part, may be caused by low blood Pi concentrations, which may explain some aspects of muscle weakness observed in patients with hypophosphatemia.-Pesta, D. H., Tsirigotis, D. N., Befroy, D. E., Caballero, D., Jurczak, M. J., Rahimi, Y., Cline, G. W., Dufour, S., Birkenfeld, A. L., Rothman, D. L., Carpenter, T. O., Insogna, K., Petersen, K. F., Bergwitz, C., Shulman, G. I. Hypophosphatemia promotes lower rates of muscle ATP synthesis.
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Affiliation(s)
- Dominik H Pesta
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Dimitrios N Tsirigotis
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Douglas E Befroy
- Department of Radiology and Biomedical Engineering, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Daniel Caballero
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Michael J Jurczak
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Yasmeen Rahimi
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Gary W Cline
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Sylvie Dufour
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Andreas L Birkenfeld
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Douglas L Rothman
- Department of Radiology and Biomedical Engineering, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Thomas O Carpenter
- Department of Pediatrics, Yale University School of Medicine, New Haven, Connecticut, USA; and
| | - Karl Insogna
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Kitt Falk Petersen
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA; Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Copenhagen, Denmark
| | - Clemens Bergwitz
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Gerald I Shulman
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA; Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, USA; Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA; Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Copenhagen, Denmark
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21
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Miller CB, Bergwitz C, Blau J, Boyce A, Gafni RI, Guthrie L, Papadakis GZ, Miranda F, Slosberg ED, Graus-Porter D, Hopmann C, Glass E, Isaacs R, Collins MT. Response of tumor-induced osteomalacia (TIO) to the FGFR inhibitor BGJ398. J Clin Oncol 2016. [DOI: 10.1200/jco.2016.34.15_suppl.e22500] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Affiliation(s)
| | | | - Jenny Blau
- Office of the Scientific Director, NICHD,NIH, Bethesda, MD
| | - Alison Boyce
- Skeletal Clinical Studies Unit, Craniofacial and Skeletal Diseases Branch, NIDCR, NIH, Bethesda, MD
| | - Rachel I Gafni
- Skeletal Clinical Studies Unit, Craniofacial and Skeletal Diseases Branch, NIDCR, NIH, Bethesda, MD
| | - Lori Guthrie
- Skeletal Clinical Studies Unit, Craniofacial and Skeletal Diseases Branch, NIDCR, NIH, Bethesda, MD
| | | | | | | | | | | | | | - Randi Isaacs
- Translational Clinical Oncology, NIBR, Novartis Pharmaceuticals Corporation, East Hanover, NJ
| | - Michael T. Collins
- Skeletal Clinical Studies Unit, Craniofacial and Skeletal Diseases Branch, NIDCR, NIH, Bethesda, MD
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Dasgupta D, Wee MJ, Reyes M, Li Y, Simm PJ, Sharma A, Schlingmann KP, Janner M, Biggin A, Lazier J, Gessner M, Chrysis D, Tuchman S, Baluarte HJ, Levine MA, Tiosano D, Insogna K, Hanley DA, Carpenter TO, Ichikawa S, Hoppe B, Konrad M, Sävendahl L, Munns CF, Lee H, Jüppner H, Bergwitz C. Mutations in SLC34A3/NPT2c are associated with kidney stones and nephrocalcinosis. J Am Soc Nephrol 2014; 25:2366-75. [PMID: 24700880 DOI: 10.1681/asn.2013101085] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Compound heterozygous and homozygous (comp/hom) mutations in solute carrier family 34, member 3 (SLC34A3), the gene encoding the sodium (Na(+))-dependent phosphate cotransporter 2c (NPT2c), cause hereditary hypophosphatemic rickets with hypercalciuria (HHRH), a disorder characterized by renal phosphate wasting resulting in hypophosphatemia, correspondingly elevated 1,25(OH)2 vitamin D levels, hypercalciuria, and rickets/osteomalacia. Similar, albeit less severe, biochemical changes are observed in heterozygous (het) carriers and indistinguishable from those changes encountered in idiopathic hypercalciuria (IH). Here, we report a review of clinical and laboratory records of 133 individuals from 27 kindreds, including 5 previously unreported HHRH kindreds and two cases with IH, in which known and novel SLC34A3 mutations (c.1357delTTC [p.F453del]; c.G1369A [p.G457S]; c.367delC) were identified. Individuals with mutations affecting both SLC34A3 alleles had a significantly increased risk of kidney stone formation or medullary nephrocalcinosis, namely 46% compared with 6% observed in healthy family members carrying only the wild-type SLC34A3 allele (P=0.005) or 5.64% in the general population (P<0.001). Renal calcifications were also more frequent in het carriers (16%; P=0.003 compared with the general population) and were more likely to occur in comp/hom and het individuals with decreased serum phosphate (odds ratio [OR], 0.75, 95% confidence interval [95% CI], 0.59 to 0.96; P=0.02), decreased tubular reabsorption of phosphate (OR, 0.41; 95% CI, 0.23 to 0.72; P=0.002), and increased serum 1,25(OH)2 vitamin D (OR, 1.22; 95% CI, 1.05 to 1.41; P=0.008). Additional studies are needed to determine whether these biochemical parameters are independent of genotype and can guide therapy to prevent nephrocalcinosis, nephrolithiasis, and potentially, CKD.
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Affiliation(s)
| | | | | | | | - Peter J Simm
- Institute of Endocrinology and Diabetes, Children's Hospital at Westmead, Westmead, New South Wales, Australia; Discipline of Pediatrics and Child Health, University of Sydney, Sydney, Australia
| | - Amita Sharma
- Pediatric Nephrology Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts
| | | | - Marco Janner
- Division of Pediatric Endocrinology, Diabetology and Metabolism, University Children's Hospital, Bern, Germany
| | - Andrew Biggin
- Institute of Endocrinology and Diabetes, Children's Hospital at Westmead, Westmead, New South Wales, Australia
| | - Joanna Lazier
- Department of Medical Genetics, University of Calgary, Calgary, Alberta, Canada
| | - Michaela Gessner
- Division of Pediatric Nephrology, Department of Pediatrics, University Hospital, Köln, Germany
| | - Dionisios Chrysis
- Division of Endocrinology, Department of Pediatrics, University of Patras Medical School, Patras, Greece
| | - Shamir Tuchman
- Division of Pediatric Nephrology, Children's National Medical Center, The George Washington University School of Medicine, Washington, District of Columbia
| | - H Jorge Baluarte
- University of Pennsylvania, School of Medicine, Division of Pediatric Nephrology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania
| | - Michael A Levine
- Division of Endocrinology and Diabetes, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania
| | - Dov Tiosano
- Division of Pediatric Endocrinology, Meyer Children's Hospital, Rambam Health Care Campus, Haifa, Israel
| | - Karl Insogna
- Division of Endocrinology, Department of Medicine and
| | - David A Hanley
- Departments of Medicine, Community Health Sciences, and Oncology, University of Calgary Faculty of Medicine, Calgary, Alberta, Canada
| | - Thomas O Carpenter
- Department of Pediatrics (Endocrinology), Yale University School of Medicine, New Haven, Connecticut
| | - Shoji Ichikawa
- Division of Endocrinology, Indiana University School of Medicine, Indianapolis, Indiana
| | - Bernd Hoppe
- Division of Pediatric Nephrology, Department of Pediatrics, University Hospital, Köln, Germany
| | - Martin Konrad
- Department of General Pediatrics, University Children's Hospital, Münster, Germany
| | - Lars Sävendahl
- Pediatric Endocrinology Unit, Department of Women's and Children´s Health, Karolinska Institutet, Stockholm, Sweden; and
| | - Craig F Munns
- Institute of Endocrinology and Diabetes, Children's Hospital at Westmead, Westmead, New South Wales, Australia; Discipline of Pediatrics and Child Health, University of Sydney, Sydney, Australia
| | - Hang Lee
- Biostatistics Center, Massachusetts General Hospital, Boston, Massachusetts
| | - Harald Jüppner
- Endocrine Unit, and Pediatric Nephrology Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts
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Abstract
Phosphate is required for many important cellular processes and having too little phosphate (hypophosphatemia) or too much (hyperphosphatemia) can cause disease and reduce lifespan in humans. Drosophila melanogaster has been a powerful tool to discover evolutionarily well-conserved nutrient-sensing pathways that are important for the lifespan extension. We have established Drosophila as a model system for studying the effects of dietary phosphate during development and adult life. When absorption of phosphate is blocked by sevelamer or cellular uptake is inhibited by phosphonoformic acid (PFA), larval development is delayed in a phosphate-dependent fashion. Conversely, restriction of phosphate absorption with sevelamer or reduced cellular uptake after treatment with PFA is able to extend the adult lifespan of otherwise normal flies. Gaining an understanding of the specific pathways and mediators that regulate cellular and organismic phosphate levels might ultimately lead to the development of improved dietary and therapeutic approaches to the treatment of human disorders of hypo- and hyperphosphatemia.
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24
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Bergwitz C, Wee MJ, Sinha S, Huang J, DeRobertis C, Mensah LB, Cohen J, Friedman A, Kulkarni M, Hu Y, Vinayagam A, Schnall-Levin M, Berger B, Perkins LA, Mohr SE, Perrimon N. Genetic determinants of phosphate response in Drosophila. PLoS One 2013; 8:e56753. [PMID: 23520455 PMCID: PMC3592877 DOI: 10.1371/journal.pone.0056753] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Accepted: 01/14/2013] [Indexed: 11/30/2022] Open
Abstract
Phosphate is required for many important cellular processes and having too little phosphate or too much can cause disease and reduce life span in humans. However, the mechanisms underlying homeostatic control of extracellular phosphate levels and cellular effects of phosphate are poorly understood. Here, we establish Drosophila melanogaster as a model system for the study of phosphate effects. We found that Drosophila larval development depends on the availability of phosphate in the medium. Conversely, life span is reduced when adult flies are cultured on high phosphate medium or when hemolymph phosphate is increased in flies with impaired Malpighian tubules. In addition, RNAi-mediated inhibition of MAPK-signaling by knockdown of Ras85D, phl/D-Raf or Dsor1/MEK affects larval development, adult life span and hemolymph phosphate, suggesting that some in vivo effects involve activation of this signaling pathway by phosphate. To identify novel genetic determinants of phosphate responses, we used Drosophila hemocyte-like cultured cells (S2R+) to perform a genome-wide RNAi screen using MAPK activation as the readout. We identified a number of candidate genes potentially important for the cellular response to phosphate. Evaluation of 51 genes in live flies revealed some that affect larval development, adult life span and hemolymph phosphate levels.
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Affiliation(s)
- Clemens Bergwitz
- Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts, United States of America.
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Mannstadt M, Magen D, Segawa H, Stanley T, Sharma A, Sasaki S, Bergwitz C, Mounien L, Boepple P, Thorens B, Zelikovic I, Jüppner H. Fanconi-Bickel syndrome and autosomal recessive proximal tubulopathy with hypercalciuria (ARPTH) are allelic variants caused by GLUT2 mutations. J Clin Endocrinol Metab 2012; 97:E1978-86. [PMID: 22865906 PMCID: PMC3462928 DOI: 10.1210/jc.2012-1279] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
CONTEXT Many inherited disorders of calcium and phosphate homeostasis are unexplained at the molecular level. OBJECTIVE The objective of the study was to identify the molecular basis of phosphate and calcium abnormalities in two unrelated, consanguineous families. PATIENTS The affected members in family 1 presented with rickets due to profound urinary phosphate-wasting and hypophosphatemic rickets. In the previously reported family 2, patients presented with proximal renal tubulopathy and hypercalciuria yet normal or only mildly increased urinary phosphate excretion. METHODS Genome-wide linkage scans and direct nucleotide sequence analyses of candidate genes were performed. Transport of glucose and phosphate by glucose transporter 2 (GLUT2) was assessed using Xenopus oocytes. Renal sodium-phosphate cotransporter 2a and 2c (Npt2a and Npt2c) expressions were evaluated in transgenically rescued Glut2-null mice (tgGlut2-/-). RESULTS In both families, genetic mapping and sequence analysis of candidate genes led to the identification of two novel homozygous mutations (IVS4-2A>G and R124S, respectively) in GLUT2, the gene mutated in Fanconi-Bickel syndrome, a rare disease usually characterized by renal tubulopathy, impaired glucose homeostasis, and hepatomegaly. Xenopus oocytes expressing the [R124S]GLUT2 mutant showed a significant reduction in glucose transport, but neither wild-type nor mutant GLUT2 facilitated phosphate import or export; tgGlut2-/- mice demonstrated a profound reduction of Npt2c expression in the proximal renal tubules. CONCLUSIONS Homozygous mutations in the facilitative glucose transporter GLUT2, which cause Fanconi-Bickel syndrome, can lead to very different clinical and biochemical findings that are not limited to mild proximal renal tubulopathy but can include significant hypercalciuria and highly variable degrees of urinary phosphate-wasting and hypophosphatemia, possibly because of the impaired proximal tubular expression of Npt2c.
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Affiliation(s)
- Michael Mannstadt
- Massachusetts General Hospital, Endocrine Unit, Harvard Medical School, Thier 1051, 55 Fruit Street, Boston Massachusetts 02114, USA.
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26
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Yu Y, Sanderson S, Reyes M, Sharma A, Dunbar N, Srivastava T, Jüppner H, Bergwitz C. Novel NaPi-IIc mutations causing HHRH and idiopathic hypercalciuria in several unrelated families: long-term follow-up in one kindred. Bone 2012; 50:1100-6. [PMID: 22387237 PMCID: PMC3322249 DOI: 10.1016/j.bone.2012.02.015] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/28/2011] [Revised: 02/09/2012] [Accepted: 02/15/2012] [Indexed: 02/06/2023]
Abstract
Homozygous and compound heterozygous mutations in SLC34A3, the gene encoding the sodium-dependent co-transporter NaPi-IIc, cause hereditary hypophosphatemic rickets with hypercalciuria (HHRH), a disorder characterized by renal phosphate-wasting resulting in hypophosphatemia, elevated 1,25(OH)(2) vitamin D levels, hypercalciuria, rickets/osteomalacia, and frequently kidney stones or nephrocalcinosis. Similar albeit less severe biochemical changes are also observed in heterozygous carriers, which are furthermore indistinguishable from those encountered in idiopathic hypercalciuria (IH). We now searched for SLC34A3 mutations (exons and introns) in two previously not reported HHRH kindreds, which resulted in the identification of three novel mutations. The affected members of kindred A were compound heterozygous for two different mutations, c.1046_47del and the intronic mutation c.560+23_561-42del, while the index case in kindred B was homozygous for the nonsense SLC34A3 mutation c.1764C>G (p.Y588X). The patient in kindred C was diagnosed with IH because of bilateral medullary nephrocalcinosis, suppressed PTH levels, and hypercalciuria; she was found to have a novel heterozygous c.1571_1880del mutation. The HHRH patients in kindred A were treated for up to 7years with oral phosphate, which led to reversal of hypophosphatemia, hypercalciuria, and prevention or healing of the mild bone abnormalities. PTH levels were normal throughout the observation period, while 1,25(OH)(2) vitamin D levels remained elevated and may thus be helpful for assessing treatment efficacy and patient compliance in HHRH.
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Affiliation(s)
- Y. Yu
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | - S.R. Sanderson
- Pediatric Endocrinology, Horizon Health Network, Saint John, New Brunswick E2L 4L2, Canada
| | - M. Reyes
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | - A. Sharma
- Pediatric Nephrology Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | - N. Dunbar
- Pediatric Endocrinology, Baystate Medical Center, Springfield, MA 01199, USA
| | - T. Srivastava
- Bone and Mineral Disorder Clinic, Section of Pediatric Nephrology, The Children’s Mercy Hospital and Clinics, University of Missouri at Kansas City, Kansas City, MO 64108, USA
| | - H. Jüppner
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
- Pediatric Nephrology Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | - C. Bergwitz
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
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27
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Abstract
Fibroblast growth factor 23 (FGF23) is part of a previously unrecognized hormonal bone-parathyroid-kidney axis, which is modulated by 1,25(OH)(2)-vitamin D (1,25(OH)(2)D), dietary and circulating phosphate and possibly PTH. FGF23 was discovered as the humoral factor in tumors that causes hypophosphatemia and osteomalacia and through the identification of a mutant form of FGF23 that leads to autosomal dominant hypophosphatemic rickets (ADHR), a rare genetic disorder. FGF23 appears to be mainly secreted by osteocytes where its expression is up-regulated by 1,25(OH)(2)D and probably by increased serum phosphate levels. Its synthesis and secretion is reduced through yet unknown mechanisms that involve the phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX), dentin matrix protein 1 (DMP1) and ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1). Consequently, loss-of-function mutations in these genes underlie hypophosphatemic disorders that are either X-linked or autosomal recessive. Impaired O-glycosylation of FGF23 due to the lack of UDP-N-acetyl-alpha-D-galactosamine:polypeptide N-acetylgalactosaminyl-transferase 3 (GALNT3) or due to certain homozygous FGF23 mutations results in reduced secretion of intact FGF23 and leads to familial hyperphosphatemic tumoral calcinosis. FGF23 acts through FGF-receptors and the coreceptor Klotho to reduce 1,25(OH)(2)D synthesis in the kidney and probably the synthesis of parathyroid hormone (PTH) by the parathyroid glands. It furthermore synergizes with PTH to increase renal phosphate excretion by reducing expression of the sodium-phosphate cotransporters NaPi-IIa and NaPi-IIc in the proximal tubules. Loss-of-function mutations in these two transporters lead to autosomal recessive Fanconi syndrome or to hereditary hypophosphatemic rickets with hypercalciuria, respectively.
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28
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Affiliation(s)
- Clemens Bergwitz
- Division of Endocrinology, Massachusetts General Hospital, and Department of Medicine, Harvard Medical School, Boston, USA
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29
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Hu Y, Flockhart I, Vinayagam A, Bergwitz C, Berger B, Perrimon N, Mohr SE. An integrative approach to ortholog prediction for disease-focused and other functional studies. BMC Bioinformatics 2011; 12:357. [PMID: 21880147 PMCID: PMC3179972 DOI: 10.1186/1471-2105-12-357] [Citation(s) in RCA: 471] [Impact Index Per Article: 36.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2011] [Accepted: 08/31/2011] [Indexed: 12/12/2022] Open
Abstract
Background Mapping of orthologous genes among species serves an important role in functional genomics by allowing researchers to develop hypotheses about gene function in one species based on what is known about the functions of orthologs in other species. Several tools for predicting orthologous gene relationships are available. However, these tools can give different results and identification of predicted orthologs is not always straightforward. Results We report a simple but effective tool, the Drosophila RNAi Screening Center Integrative Ortholog Prediction Tool (DIOPT; http://www.flyrnai.org/diopt), for rapid identification of orthologs. DIOPT integrates existing approaches, facilitating rapid identification of orthologs among human, mouse, zebrafish, C. elegans, Drosophila, and S. cerevisiae. As compared to individual tools, DIOPT shows increased sensitivity with only a modest decrease in specificity. Moreover, the flexibility built into the DIOPT graphical user interface allows researchers with different goals to appropriately 'cast a wide net' or limit results to highest confidence predictions. DIOPT also displays protein and domain alignments, including percent amino acid identity, for predicted ortholog pairs. This helps users identify the most appropriate matches among multiple possible orthologs. To facilitate using model organisms for functional analysis of human disease-associated genes, we used DIOPT to predict high-confidence orthologs of disease genes in Online Mendelian Inheritance in Man (OMIM) and genes in genome-wide association study (GWAS) data sets. The results are accessible through the DIOPT diseases and traits query tool (DIOPT-DIST; http://www.flyrnai.org/diopt-dist). Conclusions DIOPT and DIOPT-DIST are useful resources for researchers working with model organisms, especially those who are interested in exploiting model organisms such as Drosophila to study the functions of human disease genes.
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Affiliation(s)
- Yanhui Hu
- Drosophila RNAi Screening Center, Department of Genetics, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA
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30
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Abstract
Human phosphate homeostasis is regulated at the level of intestinal absorption of phosphate from the diet, release of phosphate through bone resorption, and renal phosphate excretion, and involves the actions of parathyroid hormone, 1,25-dihydroxy-vitamin D, and fibroblast growth factor 23 to maintain circulating phosphate levels within a narrow normal range, which is essential for numerous cellular functions, for the growth of tissues and for bone mineralization. Prokaryotic and single cellular eukaryotic organisms such as bacteria and yeast "sense" ambient phosphate with a multi-protein complex located in their plasma membrane, which modulates the expression of genes important for phosphate uptake and metabolism (pho pathway). Database searches based on amino acid sequence conservation alone have been unable to identify metazoan orthologs of the bacterial and yeast phosphate sensors. Thus, little is known about how human and other metazoan cells sense inorganic phosphate to regulate the effects of phosphate on cell metabolism ("metabolic" sensing) or to regulate the levels of extracellular phosphate through feedback system(s) ("endocrine" sensing). Whether the "metabolic" and the "endocrine" sensor use the same or different signal transduction cascades is unknown. This article will review the bacterial and yeast phosphate sensors, and then discuss what is currently known about the metabolic and endocrine effects of phosphate in multicellular organisms and human beings.
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Affiliation(s)
- Clemens Bergwitz
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
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31
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Pallais JC, Kemp EH, Bergwitz C, Kantham L, Slovik DM, Weetman AP, Brown EM. Autoimmune hypocalciuric hypercalcemia unresponsive to glucocorticoid therapy in a patient with blocking autoantibodies against the calcium-sensing receptor. J Clin Endocrinol Metab 2011; 96:672-80. [PMID: 21159843 PMCID: PMC3047232 DOI: 10.1210/jc.2010-1739] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/28/2010] [Accepted: 11/04/2010] [Indexed: 12/24/2022]
Abstract
CONTEXT Autoantibodies directed against the calcium-sensing receptor (CaSR) have been reported in several individuals with various autoimmune disorders and PTH-mediated hypercalcemia. Previously, glucocorticoid treatment has been shown to decrease the CaSR autoantibody titers and normalize the hypercalcemia in a patient with autoimmune hypocalciuric hypercalcemia (AHH). OBJECTIVE The objective of the study was to evaluate a patient with AHH for the presence of blocking autoantibodies against the CaSR and to monitor her biochemical and serological responses to a trial of glucocorticoid therapy. RESULTS Glucocorticoid treatment had no effect on serum total or ionized calcium concentration or serum PTH levels, all of which remained at higher than normal levels. In contrast, on prednisone, urinary calcium excretion increased from overtly hypocalciuric levels to normal values. Anti-CaSR autoantibodies were detected at similar levels in the patient's serum before, during, and after glucocorticoid treatment. Functional testing of these antibodies showed that they inhibited the stimulatory effect of extracellular Ca(2+) on ERK1/2 but did not suppress the calcium-induced accumulation of inositol-1-phosphate. CONCLUSIONS We report a patient with AHH with frankly elevated PTH levels who was found to have autoantibodies against the CaSR. The hypercalcemia and CaSR autoantibody titers failed to respond to glucocorticoid therapy, unlike a previously reported patient with similar clinical and biochemical features. The anti-CaSR antibody-mediated inhibition of CaSR-stimulated ERK1/2 activity, but not of inositol-1-phosphate accumulation, suggests that ERK1/2 may mediate, at least in part, the regulation of PTH secretion and urinary calcium excretion by the CaSR.
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Affiliation(s)
- J Carl Pallais
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114, USA.
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32
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Phulwani P, Bergwitz C, Jaureguiberry G, Rasoulpour M, Estrada E. Hereditary hypophosphatemic rickets with hypercalciuria and nephrolithiasis-identification of a novel SLC34A3/NaPi-IIc mutation. Am J Med Genet A 2011; 155A:626-33. [PMID: 21344632 DOI: 10.1002/ajmg.a.33832] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2010] [Accepted: 11/02/2010] [Indexed: 11/09/2022]
Abstract
Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is characterized by rickets, hyperphosphaturia, hypophosphatemia, elevated 1,25-dihydroxyvitamin-D, increased gastrointestinal calcium absorption and hypercalciuria. Serum calcium, 25-hydroxyvitamin-D and PTH levels are normal. Here we describe a boy with HHRH, nephrolithiasis, and compound heterozygosity for one previously described mutation (g.4225_50del) and a novel splice mutation (g.1226G>A) in SLC34A3, the gene encoding the renal sodium-phosphate co-transporter NaPi-IIc. The patient's mother and grandmother are carriers of g.4225_50del, and both have a history of nephrolithiasis associated with hypercalciuria and elevated 1,25-dihydroxyvitamin-D. His three siblings (2-6 years old), who are also carriers of g.4225_50del, have hypercalciuria but so far their renal ultrasounds are normal. Thus, SLC34A3/NaPi-IIc mutations appear to be associated with variable phenotypic changes at presentation, which can include recurrent nephrolithiasis.
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Affiliation(s)
- Priya Phulwani
- Department of Pediatric Endocrinology and Diabetes, Connecticut Children's Medical Center, Hartford, USA.
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33
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Nagai S, Okazaki M, Segawa H, Bergwitz C, Dean T, Potts JT, Mahon MJ, Gardella TJ, Jüppner H. Acute down-regulation of sodium-dependent phosphate transporter NPT2a involves predominantly the cAMP/PKA pathway as revealed by signaling-selective parathyroid hormone analogs. J Biol Chem 2010; 286:1618-26. [PMID: 21047792 DOI: 10.1074/jbc.m110.198416] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor (PTHR1) in cells of the renal proximal tubule mediates the reduction in membrane expression of the sodium-dependent P(i) co-transporters, NPT2a and NPT2c, and thus suppresses the re-uptake of P(i) from the filtrate. In most cell types, the liganded PTHR1 activates Gα(S)/adenylyl cyclase/cAMP/PKA (cAMP/PKA) and Gα(q/11)/phospholipase C/phosphatidylinositol 1,4,5-trisphosphate (IP(3))/Ca(2+)/PKC (IP(3)/PKC) signaling pathways, but the relative roles of each pathway in mediating renal regulation P(i) transport remain uncertain. We therefore explored the signaling mechanisms involved in PTH-dependent regulation of NPT2a function using potent, long-acting PTH analogs, M-PTH(1-28) (where M = Ala(1,12), Aib(3), Gln(10), Har(11), Trp(14), and Arg(19)) and its position 1-modified variant, Trp(1)-M-PTH(1-28), designed to be phospholipase C-deficient. In cell-based assays, both M-PTH(1-28) and Trp(1)-M-PTH(1-28) exhibited potent and prolonged cAMP responses, whereas only M-PTH(1-28) was effective in inducing IP(3) and intracellular calcium responses. In opossum kidney cells, a clonal cell line in which the PTHR1 and NPT2a are endogenously expressed, M-PTH(1-28) and Trp(1)-M-PTH(1-28) each induced reductions in (32)P uptake, and these responses persisted for more than 24 h after ligand wash-out, whereas that of PTH(1-34) was terminated by 4 h. When injected into wild-type mice, both M-modified PTH analogs induced prolonged reductions in blood P(i) levels and commensurate reductions in NPT2a expression in the renal brush border membrane. Our findings suggest that the acute down-regulation of NPT2a expression by PTH ligands involves mainly the cAMP/PKA signaling pathway and are thus consistent with the elevated blood P(i) levels seen in pseudohypoparathyroid patients, in whom Gα(s)-mediated signaling in renal proximal tubule cells is defective.
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Affiliation(s)
- So Nagai
- Endocrine Unit, Departments of Medicine and Pediatrics, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
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34
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Abstract
In contrast to the regulation of calcium homeostasis, which has been extensively studied over the past several decades, relatively little is known about the regulation of phosphate homeostasis. Fibroblast growth factor 23 (FGF23) is part of a previously unrecognized hormonal bone-parathyroid-kidney axis, which is modulated by PTH, 1,25(OH)(2)-vitamin D (1,25(OH)(2)D), dietary and serum phosphorus levels. Synthesis and secretion of FGF23 by osteocytes are positively regulated by 1,25(OH)(2)D and serum phosphorus and negatively regulated, through yet unknown mechanisms, by the phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX) and by dentin matrix protein 1 (DMP1). In turn, FGF23 inhibits the synthesis of 1,25(OH)(2)D, and it may negatively regulate the secretion of parathyroid hormone (PTH) from the parathyroid glands. However, FGF23 synergizes with PTH to increase renal phosphate excretion by reducing expression of the renal sodium-phosphate cotransporters NaPi-IIa and NaPi-IIc in the proximal tubules. Most insights gained into the regulation of phosphate homeostasis by these factors are derived from human genetic disorders and genetically engineered mice, which are reviewed in this paper.
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Affiliation(s)
- Clemens Bergwitz
- Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA.
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Bergwitz C, Banerjee S, Abu-Zahra H, Kaji H, Miyauchi A, Sugimoto T, Jüppner H. Defective O-glycosylation due to a novel homozygous S129P mutation is associated with lack of fibroblast growth factor 23 secretion and tumoral calcinosis. J Clin Endocrinol Metab 2009; 94:4267-74. [PMID: 19837926 PMCID: PMC2775647 DOI: 10.1210/jc.2009-0961] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
BACKGROUND Homozygous mutations in fibroblast growth factor (FGF23) have recently been described as the genetic cause of one form of hyperphosphatemic tumoral calcinosis (HFTC). However, it remained unclear to date how these mutations lead to loss of biologically active FGF23 in the circulation. METHODS We here report a novel homozygous mutation, c.385T>C in FGF23 exon 2, which changes codon 129 from serine to proline (S129P) in a previously described individual affected by HFTC. The S129P mutation as well as two known FGF23 mutations, S71G and S129F, were introduced into an expression vector encoding wild-type (wt) human (h) FGF23 to yield [P129]hFGF23, [F129]hFGF23, and [G71]hFGF23; whole lysates, glycoprotein fractions, and conditioned media from HEK293 and COS-7 cells expressing these constructs were subjected to Western blot analysis using affinity-purified goat anti-hFGF23(51-69) and anti-hFGF23(206-222) antibodies. RESULTS We detected 25- and 32-kDa protein species in total lysates of HEK293 cells expressing wt-hFGF23. The 32-kDa band, representing O-glycosylated hFGF23, was not detectable in the glycoprotein fraction of lysates from HEK293 cells expressing [P129]hFGF23, and in comparison with wt-FGF23 only small amounts of [P129]hFGF23 were secreted into the medium. Similar results were obtained for cells expressing [G71]hFGF23 and [F129]hFGF23. CONCLUSION Our data for the first time directly show that FGF23 mutations associated with HFTC impair O-glycosylation in vitro resulting in poor secretion of the mutant hormone thereby explaining the characteristic hyperphosphatemic phenotype of homozygous carriers in vivo.
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Affiliation(s)
- Clemens Bergwitz
- Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
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Page K, Bergwitz C, Jaureguiberry G, Harinarayan CV, Insogna K. A patient with hypophosphatemia, a femoral fracture, and recurrent kidney stones: report of a novel mutation in SLC34A3. Endocr Pract 2009; 14:869-74. [PMID: 18996815 DOI: 10.4158/ep.14.7.869] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
OBJECTIVE To determine if there was a genetic contribution to our patient's unusual clinical presentation of nephrolithiasis and nonhealing stress fracture. METHODS We describe a 31-year-old man who had rickets as a child and developed a femur insufficiency fracture and recurrent nephrolithiasis as an adult after moving to the United States from India. The patient's clinical course and results from radiographic and biochemical analyses are described. Analysis of the SLC34A3 gene was performed using genomic DNA samples from the patient and his family members. RESULTS Before referral to the Yale Bone Center, the patient was treated with calcitriol, ergocalciferol, and phosphate. Changing therapy to phosphate alone led to clinical improvement. Genetic analysis revealed that the patient is a compound heterozygote for mutations in the SLC34A3 gene. On 1 allele, he has a previously described missense mutation in exon 7: c.575C>T (p.Ser192Leu). The other allele carries a novel nonsense mutation in exon 3: c.145C>T (p.Gln49X). One unaffected sibling is a carrier of the missense mutation and 1 sister with a history of flank pain is a carrier of the novel mutation. CONCLUSIONS Hereditary hypophosphatemic rickets with hypercalciuria is a rare metabolic disorder associated with mutations in SLC34A3, the gene that encodes the renal sodium phosphate cotransporter NaPi-IIc. Although hypercalciuria is a distinguishing feature of the disease, nephrolithiasis is rarely described. The patient's atypical clinical presentation illustrates that both environmental and genetic factors potentially affect phenotypic expression of SLC34A3 mutations.
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Affiliation(s)
- Kathleen Page
- Section of Endocrinology, Department of Medicine, Yale School of Medicine, New Haven, CT 06520-8020, USA.
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Abstract
Phosphate is absorbed from the diet in the gut, stored as hydroxyapatite in the skeleton, and excreted with the urine. The balance between these compartments determines the circulating phosphate concentration. Fibroblast growth factor 23 (FGF23) has recently been discovered and is part of a previously unrecognised hormonal bone-kidney axis. Phosphate-regulating gene with homologies to endopeptidases on the X chromosome, and dentin matrix protein 1 regulate the expression of FGF23 in osteocytes, which then is O-glycosylated by UDP-N-acetyl-alpha-D-galactosamine: polypeptide N-acetylgalactosaminyl-transferase 3 and secreted into the circulation. FGF23 binds with high affinity to fibroblast growth factor receptor 1c in the presence of its co-receptor Klotho. It inhibits, either directly or indirectly, reabsorption of phosphate and the synthesis of 1,25-dihydroxy-vitamin-D by the renal proximal tubule and the secretion of parathyroid hormone by the parathyroid glands. Acquired or inborn errors affecting this newly discovered hormonal system can lead to abnormal phosphate homeostasis and/or tissue mineralisation. This chapter will provide an update on the current knowledge of the pathophysiology, the clinical presentation, diagnostic evaluation and therapy of the disorders of phosphate homeostasis and tissue mineralisation.
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Affiliation(s)
- Clemens Bergwitz
- Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA.
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Sitara D, Kim S, Razzaque MS, Bergwitz C, Taguchi T, Schüler C, Erben RG, Lanske B. Genetic evidence of serum phosphate-independent functions of FGF-23 on bone. PLoS Genet 2008; 4:e1000154. [PMID: 18688277 PMCID: PMC2483943 DOI: 10.1371/journal.pgen.1000154] [Citation(s) in RCA: 146] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2007] [Accepted: 07/08/2008] [Indexed: 12/21/2022] Open
Abstract
Maintenance of physiologic phosphate balance is of crucial biological importance, as it is fundamental to cellular function, energy metabolism, and skeletal mineralization. Fibroblast growth factor-23 (FGF-23) is a master regulator of phosphate homeostasis, but the molecular mechanism of such regulation is not yet completely understood. Targeted disruption of the Fgf-23 gene in mice (Fgf-23−/−) elicits hyperphosphatemia, and an increase in renal sodium/phosphate co-transporter 2a (NaPi2a) protein abundance. To elucidate the pathophysiological role of augmented renal proximal tubular expression of NaPi2a in Fgf-23−/− mice and to examine serum phosphate–independent functions of Fgf23 in bone, we generated a new mouse line deficient in both Fgf-23 and NaPi2a genes, and determined the effect of genomic ablation of NaPi2a from Fgf-23−/− mice on phosphate homeostasis and skeletal mineralization. Fgf-23−/−/NaPi2a−/− double mutant mice are viable and exhibit normal physical activities when compared to Fgf-23−/− animals. Biochemical analyses show that ablation of NaPi2a from Fgf-23−/− mice reversed hyperphosphatemia to hypophosphatemia by 6 weeks of age. Surprisingly, despite the complete reversal of serum phosphate levels in Fgf-23−/−/NaPi2a−/−, their skeletal phenotype still resembles the one of Fgf23−/− animals. The results of this study provide the first genetic evidence of an in vivo pathologic role of NaPi2a in regulating abnormal phosphate homeostasis in Fgf-23−/− mice by deletion of both NaPi2a and Fgf-23 genes in the same animal. The persistence of the skeletal anomalies in double mutants suggests that Fgf-23 affects bone mineralization independently of systemic phosphate homeostasis. Finally, our data support (1) that regulation of phosphate homeostasis is a systemic effect of Fgf-23, while (2) skeletal mineralization and chondrocyte differentiation appear to be effects of Fgf-23 that are independent of phosphate homeostasis. Regulation of phosphate homeostasis is a tightly controlled hormonal process involving the intestine, kidneys, and bone, and imbalance of this homeostasis may influence overall mineralization. Fibroblast growth factor-23 (FGF-23) is a circulating hormone produced in the bone that mainly targets the kidneys to control the activity of the sodium/phosphate co-transporters NaPi2a and NaPi2c. These transporters are responsible for actively reabsorbing phosphate ions into the body to maintain physiological serum phosphate levels. Changes in FGF-23 activity lead to human disorders associated with either phosphate wasting or retention. Genetically altered mice in which Fgf-23 activity is lost exhibit severe hyperphosphatemia accompanied by increased NaPi2a activity, and they develop abnormal bone mineralization. Here we describe a new mouse model in which we eliminated NaPi2a from Fgf-23 null mice and show reversal of hyperphosphatemia to hypophosphatemia, suggesting that NaPi2a is the major regulator of phosphate homeostasis. However, the skeletal mineralization defect observed in mice lacking Fgf-23 function remained unchanged in the absence of NaPi2a in these mice. Thus our data indicate that Fgf-23 has a role in controlling bone mineralization independent of systemic phosphate levels.
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Affiliation(s)
- Despina Sitara
- Department of Developmental Biology, Harvard School of Dental Medicine, Boston, Massachusetts, United States of America
| | - Somi Kim
- Department of Developmental Biology, Harvard School of Dental Medicine, Boston, Massachusetts, United States of America
| | - Mohammed S. Razzaque
- Department of Developmental Biology, Harvard School of Dental Medicine, Boston, Massachusetts, United States of America
| | - Clemens Bergwitz
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, United States of America
| | - Takashi Taguchi
- Department of Pathology, Nagasaki University School of Biomedical Sciences, Nagasaki, Japan
| | - Christiane Schüler
- Department of Natural Sciences, University of Veterinary Medicine, Vienna, Austria
| | - Reinhold G. Erben
- Department of Natural Sciences, University of Veterinary Medicine, Vienna, Austria
| | - Beate Lanske
- Department of Developmental Biology, Harvard School of Dental Medicine, Boston, Massachusetts, United States of America
- * E-mail:
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Kremke B, Bergwitz C, Ahrens W, Schütt S, Schumacher M, Wagner V, Holterhus PM, Jüppner H, Hiort O. Hypophosphatemic rickets with hypercalciuria due to mutation in SLC34A3/NaPi-IIc can be masked by vitamin D deficiency and can be associated with renal calcifications. Exp Clin Endocrinol Diabetes 2008; 117:49-56. [PMID: 18523928 DOI: 10.1055/s-2008-1076716] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is caused by mutations in SLC34A3, the gene encoding the renal sodium-phosphate co-transporter NaPi-IIc. Despite increased urinary calcium excretion, HHRH is typically not associated with kidney stones prior to treatment. However, here we describe two sisters, who displayed nephrolithiasis or nephrocalcinosis upon presentation. The index patient, II-4, presented with short stature, bone pain, and knee X-rays suggestive of mild rickets at age 8.5 years. Laboratory evaluation showed hypophosphatemia, elevated 1,25(OH) (2) vitamin D levels, and hypercalciuria, later also developing vitamin D deficiency. Her sister, II-6, had a low normal serum phosphorous level, biochemically vitamin D deficiency and no evidence for osteomalacia, but had undergone left nephro-ureterectomy at age 17 because of ureteral stricture secondary to renal calculi. Nucleotide sequence analysis of DNA from II-4 and II-6 revealed a homozygous missense mutation c.586G>A (p.G196R) in SLC34A3/NaPi-IIc. Ultrasonographic examinations prior to treatment showed grade I nephrocalcinosis for II-4, while II-6 had grade I-II nephrocalcinosis in her remaining kidney. Four siblings and the mother were heterozygous carriers of the mutation, but showed no biochemical abnormalities. With oral phosphate supplements, hypophosphatemia and hypercalciuria improved in both homozygous individuals. Renal calcifications that are presumably due to increased urinary calcium excretion can be the presenting finding in homozygous carriers of G196R in SLC34A3/NaPi-IIc, and some or all laboratory features of HHRH may be masked by vitamin D deficiency.
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Affiliation(s)
- B Kremke
- Department of Pediatrics and Adolescent Medicine, Division of Pediatric Endocrinology and Diabetology, University of Lübeck, Lübeck, Germany
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Jaureguiberry G, Carpenter TO, Forman S, Jüppner H, Bergwitz C. A novel missense mutation in SLC34A3 that causes hereditary hypophosphatemic rickets with hypercalciuria in humans identifies threonine 137 as an important determinant of sodium-phosphate cotransport in NaPi-IIc. Am J Physiol Renal Physiol 2008; 295:F371-9. [PMID: 18480181 DOI: 10.1152/ajprenal.00090.2008] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The present study describes two novel compound heterozygous mutations, c.410C>T(p.T137M) (T137M) on the maternal and g.4225_50del on the paternal allele of SLC34A3, in a previously reported male with hereditary hypophosphatemic rickets with hypercalciuria (HHRH) and recurrent kidney stones (Chen C, Carpenter T, Steg N, Baron R, Anast C. Pediatrics 84: 276-280, 1989). For functional analysis in vitro, we generated expression plasmids encoding enhanced green fluorescence protein (EGFP) concatenated to the NH2 terminus of wild-type or mutant human type IIc Na-Pi cotransporter (NaPi-IIc), i.e., EGFP-hNaPi-IIc, EGFP-[M137]hNaPi-IIc, or EGFP-[Stop446]hNaPi-IIc. The V446Stop mutant showed complete loss of expression and function when assayed for apical patch expression in opossum kidney (OK) cells and sodium-dependent 33P uptake into Xenopus laevis oocytes. Conversely, EGFP-[M137]hNaPi-IIc was inserted into apical patches of OK cells and into oocyte membranes. However, when quantified by confocal microscopy, surface fluorescence was reduced to 40% compared with wild-type. After correction for surface expression, the rate of 33P uptake by oocytes mediated by EGFP-[M137]hNaPi-IIc was decreased by an additional 60%. The resulting overall reduction of function of this NaPi-IIc mutant to 16%, taken together with complete loss of expression and function of g.4225_50del(V446Stop), thus appears to be sufficient to explain the phenotype in our patient. Furthermore, the stoichiometric ratio of 22Na and 33P uptake was increased to 7.1 +/- 3.65 for EGFP-[M137]hNaPi-IIc compared with wild-type. Two-electrode studies indicate that EGFP-[M137]hNaPi-IIc is nonelectrogenic but displayed a significant phosphate-independent inward-rectified sodium current, which appears to be insensitive to phosphonoformic acid. M137 thus may uncouple sodium-phosphate cotransport, suggesting that this amino acid residue has an important functional role in human NaPi-IIc.
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Bergwitz C, Jaureguiberry G, Carpenter TO, Forman S, Jüppner H. 25: Functional Analysis of Human Mutations in NAPI-IIC Reveals Important Residues for Surface Expression and Sodium-Phosphate Co-Transport. Am J Kidney Dis 2008. [DOI: 10.1053/j.ajkd.2008.02.030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Bergwitz C, Roslin NM, Tieder M, Loredo-Osti JC, Bastepe M, Abu-Zahra H, Frappier D, Burkett K, Carpenter TO, Anderson D, Garabedian M, Sermet I, Fujiwara TM, Morgan K, Tenenhouse HS, Juppner H. SLC34A3 mutations in patients with hereditary hypophosphatemic rickets with hypercalciuria predict a key role for the sodium-phosphate cotransporter NaPi-IIc in maintaining phosphate homeostasis. Am J Hum Genet 2006; 78:179-92. [PMID: 16358214 PMCID: PMC1380228 DOI: 10.1086/499409] [Citation(s) in RCA: 290] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2005] [Accepted: 11/07/2005] [Indexed: 12/22/2022] Open
Abstract
Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is a rare disorder of autosomal recessive inheritance that was first described in a large consanguineous Bedouin kindred. HHRH is characterized by the presence of hypophosphatemia secondary to renal phosphate wasting, radiographic and/or histological evidence of rickets, limb deformities, muscle weakness, and bone pain. HHRH is distinct from other forms of hypophosphatemic rickets in that affected individuals present with hypercalciuria due to increased serum 1,25-dihydroxyvitamin D levels and increased intestinal calcium absorption. We performed a genomewide linkage scan combined with homozygosity mapping, using genomic DNA from a large consanguineous Bedouin kindred that included 10 patients who received the diagnosis of HHRH. The disease mapped to a 1.6-Mbp region on chromosome 9q34, which contains SLC34A3, the gene encoding the renal sodium-phosphate cotransporter NaP(i)-IIc. Nucleotide sequence analysis revealed a homozygous single-nucleotide deletion (c.228delC) in this candidate gene in all individuals affected by HHRH. This mutation is predicted to truncate the NaP(i)-IIc protein in the first membrane-spanning domain and thus likely results in a complete loss of function of this protein in individuals homozygous for c.228delC. In addition, compound heterozygous missense and deletion mutations were found in three additional unrelated HHRH kindreds, which supports the conclusion that this disease is caused by SLC34A3 mutations affecting both alleles. Individuals of the investigated kindreds who were heterozygous for a SLC34A3 mutation frequently showed hypercalciuria, often in association with mild hypophosphatemia and/or elevations in 1,25-dihydroxyvitamin D levels. We conclude that NaP(i)-IIc has a key role in the regulation of phosphate homeostasis.
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Affiliation(s)
- Clemens Bergwitz
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
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Kozloff KM, Carden A, Bergwitz C, Forlino A, Uveges TE, Morris MD, Marini JC, Goldstein SA. Brittle IV mouse model for osteogenesis imperfecta IV demonstrates postpubertal adaptations to improve whole bone strength. J Bone Miner Res 2004; 19:614-22. [PMID: 15005849 DOI: 10.1359/jbmr.040111] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/21/2003] [Revised: 10/28/2003] [Accepted: 11/14/2003] [Indexed: 01/24/2023]
Abstract
UNLABELLED The Brtl mouse model for type IV osteogenesis imperfecta improves its whole bone strength and stiffness between 2 and 6 months of age. This adaptation is accomplished without a corresponding improvement in geometric resistance to bending, suggesting an improvement in matrix material properties. INTRODUCTION The Brittle IV (Brtl) mouse was developed as a knock-in model for osteogenesis imperfecta (OI) type IV. A Gly349Cys substitution was introduced into one col1a1 allele, resulting in a phenotype representative of the disease. In this study, we investigate the effect of the Brtl mutation on whole bone architecture, strength, and composition across a range of age groups. MATERIALS AND METHODS One-, 2-, 6-, and 12-month-old Brtl and wildtype (WT) mice were analyzed. Femurs were assessed at the central diaphysis for cortical geometric parameters using microCT and were subsequently mechanically tested to failure by four-point bending. Matrix material properties were predicted using microCT data to normalize data from mechanical tests. Raman spectroscopy and DXA were used to assess matrix composition. RESULTS Our findings show a postpubertal adaptation in which Brtl femoral strength and stiffness increase through a mechanism independent of changes in whole bone geometry. These findings suggest an improvement in the material properties of the bone matrix itself, rather than improvements in whole bone geometry, as seen in previous mouse models of OI. Raman spectroscopic results suggest these findings may be caused by changes in mineral/matrix balance rather than improvements in mineral crystallinity. CONCLUSIONS Our findings parallel the currently unexplained clinical observation of decreased fractures in human OI patients after puberty. The Brtl mouse remains an important tool for investigating therapeutic interventions for OI.
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Affiliation(s)
- Kenneth M Kozloff
- Orthopaedic Research Laboratories, Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, Michigan 48109-0486, USA
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Bergwitz C, Brabant G, Trautwein C, Manns MP. A patient with autoimmune hepatitis type I, Addison's disease, atrophic thyroiditis, atrophic gastritis, exocrine pancreatic insufficiency, and heterozygous alpha1-antitrypsin deficiency. Am J Gastroenterol 2002; 97:1050-2. [PMID: 12003388 DOI: 10.1111/j.1572-0241.2002.05628.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
This report describes a 60-yr-old white male presenting with decompensated liver cirrhosis. He had a history of Addison's disease for 36 yr, primary hypothyroidism for 5 yr, and moderate alcohol consumption. His laboratory studies and a liver biopsy supported the diagnosis of autoimmune hepatitis. Furthermore, he was found to be heterozygous for the piZ allele of the alpha1-antitrypsin gene with normal serum alpha1-antitrypsin levels and absence of pulmonary affection. Mucosal biopsies revealed moderately severe atrophic gastritis; however, signs of pernicious anemia were missing. An association of autoimmune hepatitis with endocrine disorders and atrophic gastritis has been described. Long term hydrocortisone therapy for his adrenal insufficiency may have prevented a faster course of the liver disease, whereas the heterozygous alpha1-antitrypsin deficiency and moderate alcohol consumption constituted additional risk factors ultimately leading to the development of cirrhosis.
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Affiliation(s)
- C Bergwitz
- Abteilung Klinische Endokrinologie und Abteilung für Gastroenterologie der Medizinischen Hochschule, Hannover, Germany
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Schöfl C, Waring M, Bergwitz C, Arseniev L, von zur Muhlen A, Brabant G. Cyclic-adenosine 3',5'-monophosphate-stimulated c-fos gene transcription involves distinct calcium pathways in single beta-cells. Mol Cell Endocrinol 2002; 186:121-31. [PMID: 11850128 DOI: 10.1016/s0303-7207(01)00609-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
In beta-cells activation of the cyclic AMP (cAMP)-signaling cascade stimulates c-fos mRNA expression, which involves cAMP- and Ca(2+)-mediated mechanisms. To delineate potential crosstalk between both pathways at the transcriptional level we simultaneously measured c-fos promoter-driven enhanced green fluorescent protein (EGFP) expression and cytosolic free calcium ([Ca(2+)](i)) in single beta-cells (HIT-T15). Forskolin stimulated a rapid rise in cellular cAMP and in [Ca(2+)](i) through activation of voltage-sensitive Ca(2+)-influx and enhanced wild-type c-fos promoter-driven EGFP (pF711d2EGFP) expression about 4-fold after 6 h. The voltage-sensitive Ca(2+) channel (VSCC)-blocker nifedipine, which completely blocked the forskolin-induced rise in [Ca(2+)](i), partially inhibited the forskolin-induced increase in pF711d2EGFP expression, while it was completely abolished in Ca(2+)-free medium. VSCC-dependent Ca(2+)-influx per se when stimulated by K(+) (45 mM) increased pF711d2EGFP expression only minimally. No correlations could be delineated between the forskolin-induced amplitude of the Ca(2+) signal and the expression of pF711d2EGFP at the single cell level, which may indicate that small rises in [Ca(2+)](i) are sufficient to fully activate the Ca(2+)-dependent pathways required for cAMP-dependent c-fos promoter regulation. In experiments with various deletion constructs of the c-fos promoter, it could be shown that cAMP-mediated activation of the c-fos promoter involves both the cAMP-responsive element (CRE) and the serum-responsive element (SRE). While nifedipine completely abrogated the cAMP-dependent activation of c-fos transcription via the SRE, the CRE-mediated effect of cAMP on the c-fos promoter remained unaffected by nifedipine. Thus, cAMP and Ca(2+) are required for full c-fos promoter activation by the cAMP-signaling pathway in beta-cells. cAMP-dependent Ca(2+)-influx through VSCC is crucial for c-fos gene transcription via the SRE, whereas cAMP-mediated activation of the CRE demands Ca(2+)-influx, which is distinct from voltage-sensitive Ca(2+)-influx. This indicates a complex interplay between cAMP and Ca(2+) in controlling c-fos gene transcription and suggests that the mode of Ca(2+) entry may differentially act on signaling pathways leading to gene transcription in beta-cells.
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Affiliation(s)
- Christof Schöfl
- Abteilung Klinische Endokrinologie, Medizinische Hochschule Hannover, 30623, Hannover, Germany.
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Bergwitz C, Prochnau A, Mayr B, Kramer FJ, Rittierodt M, Berten HL, Hausamen JE, Brabant G. Identification of novel CBFA1/RUNX2 mutations causing cleidocranial dysplasia. J Inherit Metab Dis 2001; 24:648-56. [PMID: 11768584 DOI: 10.1023/a:1012758925617] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Core binding factor A1 (CBFA1/RUNX2) is a runt-like transcription factor essential for osteoblast differentiation. Haplotype insufficiency causes cleidocranial dysplasia (CCD), a syndrome featuring supernumerary tooth buds, delayed tooth eruption, patent fontanels, Wormian bones, short stature, dysplasia of the clavicles, growth retardation and hypoplasia of the distal phalanges. We identified novel CBFAI/RUNX2 mutations after PCR and direct sequencing of patient leukocyte DNA. In family 1 mother and son are affected by CCD. Both carry the missense mutation R190W (CGG > TGG). This nucleotide change introduced a BsmI restriction site, which was used to independently confirm the mutation. It was absent in healthy members of the family. Family 2, in which father and daughter are affected by CCD, shows a deletion of nucleotide C821. This deletion causes a frameshift mutation with premature stop after the insertion of 18 aberrant amino acids. Healthy family members did not have this mutation. The clavicular dysplasia was more pronounced with the R19OW mutation, while the bone density was markedly reduced in individuals with either mutation, suggesting a previously underemphasized increased risk for osteoporosis in CCD.
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Affiliation(s)
- C Bergwitz
- Abteilung für Klinische Endokrinologie, Hochschule Hannover, Germany.
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Abstract
The 23-year-old Caucasian male propositus presented with symptomatic hypercalcemia, hypophosphatemia and normocalciuria for 2 months. His 29-year-old brother had undergone an operation for recurrent parathyroid adenoma at age 26 and 28. No other member of the family was affected. His father and mother were second-degree relatives. Laboratory studies showed primary hyperparathyroidism (pHPT), while the remaining endocrine studies and genetic testing for multiple endocrine neoplasia 1 and 2A were normal. Technetium-cardiolite scintigraphy and ultrasound scans revealed a parathyroid mass at the left lower neck. Apart from bilateral hearing loss due to gentamicin treatment as a pre-term child, the patient was in of good health. Signs or symptoms of other endocrinopathies were absent. The patient was referred for parathyroidectomy with subsequent autotransplantation of the remaining glands into his sternocleidomastoid muscle. Histological examination revealed an adenoma with oncocytic differentiation, similar to that seen in his brother. The disease may follow a recessive mode of inheritance or may be due to a dominant germ-cell mutation in one of the parents. The presented case may ultimately help in elucidating the molecular genetic basis of this rare form of pHPT.
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Affiliation(s)
- C Bergwitz
- Dept. of Clinical Endocrinology, Medical School of Hannover, Germany.
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Bergwitz C, Wendlandt T, Kispert A, Brabant G. Wnts differentially regulate colony growth and differentiation of chondrogenic rat calvaria cells. Biochim Biophys Acta 2001; 1538:129-40. [PMID: 11336784 DOI: 10.1016/s0167-4889(00)00123-3] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The wingless- and int-related proteins (Wnts) have an important role during embryonic development and limb patterning. To investigate their function during chondrocyte differentiation, we used NIH3T3 cells producing seven members of the Wnt family and secreted frizzled-related protein (sFRP-2) for co-culture experiments with the rat chondrogenic cell line pColl(II)-EGFP-5. Pilot experiments showed a negative effect of Wnt-7a on the proliferation of three rodent chondrogenic cell lines, RCJ3.1(C5.18), CFK-2, and C1. To establish a reporter system for chondrogenic differentiation we then produced a stably transfected chondrogenic cell line based on RCJ3.1(C5.18) for further experiments, which expresses green fluorescence protein (EGFP) under the collagen type II promoter (pColl(II)-EGFP-5). This cell line permits convenient observation of green fluorescence as a marker for differentiation in life cultures. The colony size of this cell line in agarose suspension cultures was reduced to 20-40% of control, when exposed to Wnt-1, 3a, 4, 7a, and 7b for 14 days. Similarly, reporter gene expression and the synthesis of cartilage-specific proteoglycans were inhibited by this group of Wnts. In contrast, pColl(II)-EGFP-5 cells exposed to Wnt-5a and Wnt-11 reached 140% of control, and reporter gene expression and proteoglycan synthesis were stimulated. The effects of Wnt-7a and Wnt-5a were additive in pColl(II)-EGFP-5 cells and some but not all Wnt effects were antagonized by the inhibition of proteoglycan sulfation with chlorate, by sFRP-2, which may modulate Wnt receptor binding, or by inhibitors of protein kinase C. These results suggest two functional Wnt subclasses that differentially regulate proliferation and chondrogenic differentiation in vitro which may have implications for cartilage differentiation in vivo. Since some, but not all Wnt effects were sensitive to inhibitors of proteoglycan synthesis or protein kinase C, multiple modes of signal transduction may be involved.
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Affiliation(s)
- C Bergwitz
- Abteilung für Klinische Endokrinologie, Medizinische Hochschule Hannover, Germany.
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Bergwitz C, Wendlandt T, Pötter E, Glomb I, Gras K, von zur Mühlen A, Brabant G. A versatile chondrogenic rat calvaria cell line R-tTA-24 that permits tetracycline-regulated gene expression. Histochem Cell Biol 2000; 113:145-50. [PMID: 10766267 DOI: 10.1007/s004180050017] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
The clonal rat calvaria cell line RCJ3.1C5.18 (RCJ) undergoes chondrogenic differentiation after long-term culture post confluence. To allow flexible genetic manipulation, a tetracycline-regulated gene expression system was established in this cell line. Treatment with tetracycline in operational doses does not affect the differentiation of RCJ cells with respect to the markers tested. After stable transfection with pUHD15.1 containing the tetracycline transactivator (tTA) in the presence of pTK-hyg for hygromycin selection, 28 clones were isolated and characterized for alcian blue staining of cartilage-specific proteoglycans and for collagen type II expression. Clone R-tTA-24 was selected on the basis of phenotype and displayed tetracycline-dependent down-regulation of luciferase activity (tet-OFF system) by two orders of magnitude (57-149-fold) after stable transfection with the reporter gene pBI-EGFP/luc. The novel, chondrogenic cell line R-tTA-24 may be stably transfected with various genes of interest for tetracycline-regulated gene expression using neomycin selection and may be a valuable tool to study the process of chondrogenic differentiation in vitro.
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Affiliation(s)
- C Bergwitz
- Abt. für Klinische Endokrinologie, Medizinische Hochschule Hannover, Germany
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