1
|
Calvo MS, Uribarri J. Perspective: Plant-based Whole-Grain Foods for Chronic Kidney Disease: The Phytate-Phosphorus Conundrum. Adv Nutr 2021; 12:2056-2067. [PMID: 34192744 PMCID: PMC8634414 DOI: 10.1093/advances/nmab066] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Revised: 04/21/2021] [Accepted: 05/04/2021] [Indexed: 12/15/2022] Open
Abstract
Restriction of dietary phosphorus intake is an important component of good clinical practice in kidney failure patients, particularly after dialysis initiation. Greater consumption of predominantly plant-based diets, including phytate-rich foods, is increasingly recommended for health maintenance/disease prevention in this population, with the implicit assumption that phytate-phosphorus in whole-grain cereals, legumes, pulses, and nuts is poorly absorbed. Review of human interventions with diets high in phytate-phosphorus indeed suggests an absorption of at least 50%, still less than animal protein-bound phosphorus, but higher than the generally believed 10-30%. Factors largely ignored up to now, but of potential influence on phytate-phosphorus bioavailability, include effect of food processing in releasing phosphorus, action of colonic bacteria that are able to release inorganic phosphorus, and capacity of the colon to absorb phosphorus. These issues may become increasingly important as new plant-based alternatives to meats, all containing phytate, are being rapidly introduced in the market.
Collapse
Affiliation(s)
- Mona S Calvo
- Division of Nephrology, Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Jaime Uribarri
- Division of Nephrology, Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| |
Collapse
|
2
|
Gloaguen C, Raimundo AF, Elie C, Schmitt A, Floriani M, Favard S, Monneret D, Imbert-Bismut F, Weiss N, Deli MA, Tack K, Lestaevel P, Benadjaoud MA, Legendre A. Passage of uranium through human cerebral microvascular endothelial cells: influence of time exposure in mono- and co-culture in vitro models. Int J Radiat Biol 2020; 96:1597-1607. [PMID: 32990492 DOI: 10.1080/09553002.2020.1828655] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
PURPOSE Depleted uranium (DU) has several civilian and military applications. The effects of this emerging environmental pollutant on human health raise some concerns. Previous experimental studies have shown that uranium (U) exposure can disturb the central nervous system. A small quantity of U reaches the brain via the blood, but the effects on the blood-brain barrier (BBB) remain unclear. MATERIALS AND METHODS In the present work, two cell culture models were exposed to DU for different times to study its cytotoxicity, paracellular permeability and extracellular concentration of U. The well-known immortalized human cerebral microvascular endothelial cells, hCMEC/D3, were cultured on the filter in the first model. In the second model, human primary cells of pericytes were cultured under the filter to understand the influence of cell environment after U exposure. RESULTS The results show that U is not cytotoxic to hCMEC/D3 cells or pericytes until 500 µM (1.6 Bq.L-1). In addition, acute or chronic low-dose exposure of U did not disturb permeability and was conserved in both cell culture models. However, U is able to reach the brain compartment. During the first hours of exposure, the passage of U to the abluminal compartment was significantly reduced in the presence of pericytes. Electronic microscopy studies evidenced the formation of needlelike structures, like urchin-shaped precipitates, from 1 h of exposure. Analytical microscopy confirmed the U composition of these precipitates. Interestingly, precipitated U was detected only in endothelial cells and not in pericytes. U was localized in multilamellar or multivesicular bodies along the endo-lysosomal pathway, suggesting the involvement of these traffic vesicles in U sequestration and/or elimination. CONCLUSIONS We show for the first time the in vitro passage of U across a human cerebral microvascular endothelial cells, and the intracellular localization of U precipitates without any cytotoxicity or modification of paracellular permeability. The difference between the results obtained with monolayers and co-culture models with pericytes illustrates the need to use complex in vitro models in order to mimic the neurovascular unit. Further in vivo studies should be performed to better understand the passage of U across the blood-brain barrier potentially involved in behavioral consequences.
Collapse
Affiliation(s)
- C Gloaguen
- Institut de Radioprotection et Sûreté Nucléaire (IRSN), PSE-SANTE/SESANE/LRTOX, PSE-SANTE/SERAMED, Fontenay aux Roses, France
| | - A F Raimundo
- Institut de Radioprotection et Sûreté Nucléaire (IRSN), PSE-SANTE/SESANE/LRTOX, PSE-SANTE/SERAMED, Fontenay aux Roses, France
| | - C Elie
- Institut de Radioprotection et Sûreté Nucléaire (IRSN), PSE-SANTE/SESANE/LRTOX, PSE-SANTE/SERAMED, Fontenay aux Roses, France
| | - A Schmitt
- Electronic Microscopy Facility, INSERM UMR 1016, Cochin Institute, Paris, France
| | - M Floriani
- Institut de Radioprotection et Sûreté Nucléaire (IRSN), PSE-ENV/SRTE/LECO Saint Paul Lez Durance, France
| | - S Favard
- Department of Metabolic Biochemistry, La Pitié- Salpétrière- Charles Foix University Hospital (APHP), Paris, France
| | - D Monneret
- Department of Metabolic Biochemistry, La Pitié- Salpétrière- Charles Foix University Hospital (APHP), Paris, France
| | - F Imbert-Bismut
- Department of Metabolic Biochemistry, La Pitié- Salpétrière- Charles Foix University Hospital (APHP), Paris, France
| | - N Weiss
- Sorbonne Université, Brain Liver Pitié-Salpêtrière (BLIPS) Study Group, INSERM, Centre de Recherche Saint-Antoine, Assistance Publique - Hôpitaux de Paris, Groupement Hospitalier Pitié-Salpêtrière Charles Foix, Département de Neurologie, Unité de réanimation neurologique, Paris, France.,Unité de réanimation neurologique, Pôle des Maladies du Système Nerveux, Groupe Hospitalier Pitié-Salpêtrière Charles Foix, Assistance Publique - Hôpitaux de Paris, et Institut de Neurosciences Translationnelles IHU-A-ICM, Paris, France
| | - M A Deli
- Institute of Biophysics, Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary
| | - K Tack
- Institut de Radioprotection et Sûreté Nucléaire (IRSN), PSE-SANTE/SESANE/LRTOX, PSE-SANTE/SERAMED, Fontenay aux Roses, France
| | - P Lestaevel
- Institut de Radioprotection et Sûreté Nucléaire (IRSN), PSE-SANTE/SESANE/LRTOX, PSE-SANTE/SERAMED, Fontenay aux Roses, France
| | - M A Benadjaoud
- Institut de Radioprotection et Sûreté Nucléaire (IRSN), PSE-SANTE/SESANE/LRTOX, PSE-SANTE/SERAMED, Fontenay aux Roses, France
| | - A Legendre
- Institut de Radioprotection et Sûreté Nucléaire (IRSN), PSE-SANTE/SESANE/LRTOX, PSE-SANTE/SERAMED, Fontenay aux Roses, France
| |
Collapse
|
3
|
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] [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.
Collapse
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
| |
Collapse
|
4
|
Taub M. Gene Level Regulation of Na,K-ATPase in the Renal Proximal Tubule Is Controlled by Two Independent but Interacting Regulatory Mechanisms Involving Salt Inducible Kinase 1 and CREB-Regulated Transcriptional Coactivators. Int J Mol Sci 2018; 19:E2086. [PMID: 30021947 PMCID: PMC6073390 DOI: 10.3390/ijms19072086] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2018] [Revised: 07/13/2018] [Accepted: 07/16/2018] [Indexed: 12/26/2022] Open
Abstract
For many years, studies concerning the regulation of Na,K-ATPase were restricted to acute regulatory mechanisms, which affected the phosphorylation of Na,K-ATPase, and thus its retention on the plasma membrane. However, in recent years, this focus has changed. Na,K-ATPase has been established as a signal transducer, which becomes part of a signaling complex as a consequence of ouabain binding. Na,K-ATPase within this signaling complex is localized in caveolae, where Na,K-ATPase has also been observed to regulate Inositol 1,4,5-Trisphosphate Receptor (IP3R)-mediated calcium release. This latter association has been implicated as playing a role in signaling by G Protein Coupled Receptors (GPCRs). Here, the consequences of signaling by renal effectors that act via such GPCRs are reviewed, including their regulatory effects on Na,K-ATPase gene expression in the renal proximal tubule (RPT). Two major types of gene regulation entail signaling by Salt Inducible Kinase 1 (SIK1). On one hand, SIK1 acts so as to block signaling via cAMP Response Element (CRE) Binding Protein (CREB) Regulated Transcriptional Coactivators (CRTCs) and on the other hand, SIK1 acts so as to stimulate signaling via the Myocyte Enhancer Factor 2 (MEF2)/nuclear factor of activated T cell (NFAT) regulated genes. Ultimate consequences of these pathways include regulatory effects which alter the rate of transcription of the Na,K-ATPase β1 subunit gene atp1b1 by CREB, as well as by MEF2/NFAT.
Collapse
Affiliation(s)
- Mary Taub
- Biochemistry Dept., Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, 955 Main Street, Suite 4902, Buffalo, NY 14203, USA.
| |
Collapse
|
5
|
Murray RD, Holthouser K, Clark BJ, Salyer SA, Barati MT, Khundmiri SJ, Lederer ED. Parathyroid hormone (PTH) decreases sodium-phosphate cotransporter type IIa (NpT2a) mRNA stability. Am J Physiol Renal Physiol 2013; 304:F1076-85. [DOI: 10.1152/ajprenal.00632.2012] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The acute inhibitory effects of parathyroid hormone (PTH) on proximal tubule Na+-K+-ATPase (Na-K) and sodium-dependent phosphate (NaPi) transport have been extensively studied, while little is known about the chronic effects of PTH. Patients with primary hyperparathyroidism, a condition characterized by chronic elevations in PTH, exhibit persistent hypophosphatemia but not significant evidence of salt wasting. We postulate that chronic PTH stimulation results in differential desensitization of PTH responses. To address this hypothesis, we compared the effects of chronic PTH stimulation on Na-Pi cotransporter (Npt2a) expression and Na-K activity and expression in Sprague Dawley rats, transgenic mice featuring parathyroid-specific cyclin D1 overexpression (PTH-D1), and proximal tubule cell culture models. We demonstrated a progressive decrease in brush-border membrane (BBM) expression of Npt2a from rats treated with PTH for 6 h or 4 days, while Na-K expression and activity in the basolateral membranes (BLM) exhibited an initial decrease followed by recovery to control levels by 4 days. Npt2a protein expression in PTH-D1 mice was decreased relative to control animals, whereas levels of Na-K, NHERF-1, and PTH receptor remained unchanged. In PTH-D1 mice, NpT2a mRNA expression was reduced by 50% relative to control mice. In opossum kidney proximal tubule cells, PTH decreased Npt2a mRNA levels. Both actinomycin D and cycloheximide treatment prevented the PTH-mediated decrease in Npt2a mRNA, suggesting that the PTH response requires transcription and translation. These findings suggest that responses to chronic PTH exposure are selectively regulated at a posttranscriptional level. The persistence of the phosphaturic response to PTH occurs through posttranscriptional mechanisms.
Collapse
Affiliation(s)
- Rebecca D. Murray
- Department of Physiology and Biophysics, University of Louisville, Louisville, Kentucky
| | - Kristine Holthouser
- Department of Physiology and Biophysics, University of Louisville, Louisville, Kentucky
- Department of Medicine/Kidney Disease Program, University of Louisville, Louisville, Kentucky; and
| | - Barbara J. Clark
- Department of Biochemistry, University of Louisville, Louisville, Kentucky
| | - Sarah A. Salyer
- Department of Physiology and Biophysics, University of Louisville, Louisville, Kentucky
| | - Michelle T. Barati
- Department of Medicine/Kidney Disease Program, University of Louisville, Louisville, Kentucky; and
| | - Syed J. Khundmiri
- Robley Rex Veterans Affairs Medical Center, Louisville, Kentucky
- Department of Physiology and Biophysics, University of Louisville, Louisville, Kentucky
- Department of Medicine/Kidney Disease Program, University of Louisville, Louisville, Kentucky; and
| | - Eleanor D. Lederer
- Robley Rex Veterans Affairs Medical Center, Louisville, Kentucky
- Department of Physiology and Biophysics, University of Louisville, Louisville, Kentucky
- Department of Medicine/Kidney Disease Program, University of Louisville, Louisville, Kentucky; and
| |
Collapse
|
6
|
Ito M, Sakurai A, Hayashi K, Ohi A, Kangawa N, Nishiyama T, Sugino S, Uehata Y, Kamahara A, Sakata M, Tatsumi S, Kuwahata M, Taketani Y, Segawa H, Miyamoto KI. An apical expression signal of the renal type IIc Na+-dependent phosphate cotransporter in renal epithelial cells. Am J Physiol Renal Physiol 2010; 299:F243-54. [PMID: 20410212 DOI: 10.1152/ajprenal.00189.2009] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The type IIc Na(+)-dependent phosphate cotransporter (NaPi-IIc) is specifically targeted to, and expressed on, the apical membrane of renal proximal tubular cells and mediates phosphate transport. In the present study, we investigated the signals that determine apical expression of NaPi-IIc with a focus on the role of the N- and the C-terminal tails of mouse NaPi-IIc in renal epithelial cells [opossum kidney (OK) and Madin-Darby canine kidney cells]. Wild-type NaPi-IIc, the cotransporter NaPi-IIa, as well as several IIa-IIc chimeras and deletion mutants, were fused to enhanced green fluorescent protein (EGFP), and their cellular localization was analyzed in polarized renal epithelial cells by confocal microscopy and by cell-surface biotinylation. Fluorescent EGFP-fused NaPi-IIc transporter proteins are correctly expressed in the apical membrane of OK cells. The apical expression of N-terminal deletion mutants (deletion of N-terminal 25, 50, or 69 amino acids) was not affected by truncation. In contrast, C-terminal deletion mutants (deletion of C-terminal 45, 50, or 62 amino acids) did not have correct apical expression. A more detailed mutational analysis indicated that a domain (amino acids WLHSL) in the cytoplasmic C terminus is required for apical expression of NaPi-IIc in renal epithelial cells. We conclude that targeting of NaPi-IIc to the apical cell surface is regulated by a unique amino acid motif in the cytoplasmic C-terminal domain.
Collapse
Affiliation(s)
- Mikiko Ito
- Department of Molecular Nutrition, Institute of Health Biosciences, University of Tokushima Graduate School, Tokushima, Japan
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
7
|
Thyroid hormones regulate phosphate homoeostasis through transcriptional control of the renal type IIa sodium-dependent phosphate co-transporter (Npt2a) gene. Biochem J 2010; 427:161-9. [PMID: 20088828 DOI: 10.1042/bj20090671] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The type IIa renal sodium-dependent phosphate (Na/Pi) co-transporter Npt2a is implicated in the control of serum phosphate levels. It has been demonstrated previously that renal Npt2a protein and its mRNA expression are both up-regulated by the thyroid hormone T3 (3,3',5-tri-iodothyronine) in rats. However, it has never been established whether the induction was mediated by a direct effect of thyroid hormones on the Npt2a promoter. To address the role of Npt2a in T3-dependent regulation of phosphate homoeostasis and to identify the molecular mechanisms by which thyroid hormones modulate Npt2a gene expression, mice were rendered pharmacologically hypo- and hyper-thyroid. Hypothyroid mice showed low levels of serum phosphate and a marked decrease in renal Npt2a protein abundance. Importantly, we also showed that Npt2a-deficient mice had impaired serum phosphate responsiveness to T3 compared with wild-type mice. Promoter analysis with a luciferase assay revealed that the transcriptional activity of a reporter gene containing the Npt2a promoter and intron 1 was dependent upon TRs (thyroid hormone receptors) and specifically increased by T3 in renal cells. Deletion analysis and EMSAs (electrophoretic mobility-shift assays) determined that there were unique TREs (thyroid-hormone-responsive elements) within intron 1 of the Npt2a gene. These results suggest that Npt2a plays a critical role as a T3-target gene, to control phosphate homoeostasis, and that T3 transcriptionally activates the Npt2a gene via TRs in a renal cell-specific manner.
Collapse
|
8
|
de Menezes Filho H, de Castro LCG, Damiani D. Hypophosphatemic rickets and osteomalacia. ACTA ACUST UNITED AC 2007; 50:802-13. [PMID: 17117305 DOI: 10.1590/s0004-27302006000400025] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2006] [Accepted: 05/08/2006] [Indexed: 01/31/2023]
Abstract
The hypophosphatemic conditions that interfere in bone mineralization comprise many hereditary or acquired diseases, all of them sharing the same pathophysiologic mechanism: reduction in the phosphate reabsorption by the renal tubuli. This process leads to chronic hyperphosphaturia and hypophosphatemia, associated with inappropriately normal or low levels of calcitriol, causing osteomalacia or rickets in children and osteomalacia in adults. X-linked hypophosphatemic rickets, autosomal-dominant hypophosphatemic rickets, and tumor-induced osteomalacia are the main syndromes involved in the hypophosphatemic rickets. Although these conditions exhibit different etiologies, there is a common link among them: increased activity of a phosphaturic factor, being the fibroblast growth factor 23 (FGF-23) the most studied one and to which is attributed a central role in the pathophysiology of the hyperphosphaturic disturbances. Activating mutations of FGF-23 and inactivating mutations in the PHEX gene (a gene on the X chromosome that codes for a Zn-metaloendopeptidase proteolytic enzyme which regulates the phosphate) involved in the regulation of FGF-23 have been identified and have been implicated in the pathogenesis of these disturbances. Genetic studies tend to show that the phosphorus homeostasis depends on a complex osteo-renal metabolic axis, whose mechanisms of interaction have been poorly understood so far. This paper reviews the current knowledge status concerning the pathophysiology of phosphate metabolism regulation and the pathophysiologic basis of hypophosphatemic rickets. It also analyzes the clinical picture and the therapeutic aspects of these conditions as well.
Collapse
Affiliation(s)
- Hamilton de Menezes Filho
- Instituto da Criança, Hospital das Clínicas, Medical School, São Paulo University, São Paulo, SP, Brazil
| | | | | |
Collapse
|
9
|
Rosenberg T, Shachaf C, Tzukerman M, Skorecki K. A murine transgenic model for transcriptional regulation of the Na/Pi-IIa major renal phosphate cotransporter. Am J Physiol Renal Physiol 2007; 292:F1617-25. [PMID: 17287201 DOI: 10.1152/ajprenal.00412.2006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Levels of the type IIa Na/P(i) (Na/Pi-IIa) cotransporter, which serves as the principal mediator of phosphate reabsorption in the kidney, can be modulated through posttranscriptional or posttranslational mechanisms by dietary, hormonal, and pharmacological influences. Previous studies have not demonstrated clear-cut evidence for modulation of Na/Pi-IIa cotransporter levels through transcriptional mechanisms. We have previously demonstrated that a 4.7-kb rat genomic fragment upstream of the rodent Npt2 gene encoding the Na/Pi-IIa cotransporter, is sufficient to mediate its transcriptional activity in vitro (Shachaf C, Skorecki KL, Tzukerman M. Am J Physiol Renal Physiol 278: F406-F416, 2000). Accordingly, we have established an in vivo experimental model in which this Npt2 genomic fragment fused upstream of a Lac Z reporter gene was expressed as a transgene in mice. The nine independent transgenic founder lines generated exhibited Lac Z reporter gene expression specifically in the renal cortex. This renal cortical-specific expression driven by the Npt2 promoter was confirmed at the mRNA and protein levels using RT-PCR, histochemistry, and Lac Z enzymatic activity. Furthermore, the expression of the transgene correlated with expression of the endogenous Npt2 gene during embryonic and early postnatal development. Thus we have generated a transgenic mouse model which will enable in vivo investigation of the contribution of transcriptional mechanisms to the overall regulation of Na/Pi-IIa expression under physiological and pathophysiological conditions.
Collapse
Affiliation(s)
- Tzur Rosenberg
- Rambam Medical Center, Technion-Israel Institute of Technology, Haifa, Israel
| | | | | | | |
Collapse
|
10
|
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] [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.
Collapse
Affiliation(s)
- Clemens Bergwitz
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
11
|
Xu H, Collins JF, Bai L, Kiela PR, Ghishan FK. Regulation of the human sodium-phosphate cotransporter NaP(i)-IIb gene promoter by epidermal growth factor. Am J Physiol Cell Physiol 2001; 280:C628-36. [PMID: 11171583 DOI: 10.1152/ajpcell.2001.280.3.c628] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The intestinal sodium-phosphate cotransporter (NaP(i)-IIb) plays a major role in intestinal P(i) absorption. Epidermal growth factor (EGF) is involved in the regulation of P(i) homeostasis. However, the role of EGF in intestinal NaP(i)-IIb regulation is not clear. The current studies showed that EGF decreased NaP(i)-IIb mRNA abundance by 40-50% in both rat intestine and Caco-2 cells. To understand the mechanism of this regulation, we cloned the human NaP(i)-IIb gene and promoter region and studied the effect of EGF on NaP(i)-IIb gene transcription. The human NaP(i)-IIb gene has 12 exons and 11 introns. Two transcription initiation sites were identified by primer extension. Additionally, 2.8 kb of the 5'-flanking region of the gene was characterized as a functional promoter in human intestinal (Caco-2) and human lung (A549) cells. Additional studies showed that EGF inhibited promoter activity by 40-50% in Caco-2 cells and that actinomycin D treatment abolished this inhibition. EGF had no effect on promoter activity in lung (A549) cells. We conclude that the human NaP(i)-IIb gene promoter is functional in Caco-2 and A549 cells and that the gene is responsive to EGF by a transcriptionally mediated mechanism in intestinal cells.
Collapse
Affiliation(s)
- H Xu
- Departments of Pediatrics and Physiology, Steele Memorial Children's Research Center, University of Arizona Health Sciences Center, Tucson, Arizona 85724, USA
| | | | | | | | | |
Collapse
|
12
|
Abstract
Membrane transport systems for P(i) transport are key elements in maintaining homeostasis of P(i) in organisms as diverse as bacteria and human. Two Na-P(i) cotransporter families with well-described functional properties in vertebrates, namely NaPi-II and NaPi-III, show conserved structural features with prokaryotic origin. A clear vertical relationship can be established among the mammalian protein family NaPi-III, a homologous system in C. elegans, the yeast system Pho89, and the bacterial P(i) transporter Pit. An alternative lineage connects the mammalian NaPi-II-related transporters with homologous proteins from Caenorhabditis elegans and Vibrio cholerae. The present review focuses on the molecular evolution of the NaPi-II protein family. Preliminary results indicate that the NaPi-II homologue cloned from V. cholerae is indeed a functional P(i) transporter when expressed in Xenopus oocytes. The closely related NaPi-II isoforms NaPi-IIa and NaPi-IIb are responsible for regulated epithelial Na-dependent P(i) transport in all vertebrates. Most species express two different NaPi-II proteins with the exception of the flounder and Xenopus laevis, which rely on only a single isoform. Using an RT-PCR-based approach with degenerate primers, we were able to identify NaPi-II-related mRNAs in a variety of vertebrates from different families. We hypothesize that the original NaPi-IIb-related gene was duplicated early in vertebrate development. The appearance of NaPi-IIa correlates with the development of the mammalian nephron.
Collapse
Affiliation(s)
- A Werner
- Department of Physiological Sciences, University of Newcastle, Newcastle upon Tyne NE2 4HH, United Kingdom.
| | | |
Collapse
|
13
|
Hernando N, Forster IC, Biber J, Murer H. Molecular characteristics of phosphate transporters and their regulation. EXPERIMENTAL NEPHROLOGY 2000; 8:366-75. [PMID: 11014934 DOI: 10.1159/000020691] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
A key process in overall P(i)-homeostasis is renal proximal tubular reabsorption of inorganic phosphate (P(i)), which involves secondary active sodium/phosphate (Na(+)/P(i)) cotransport reabsorption at the brush border membrane. Among the two different molecularly identified Na(+)/P(i) cotransporters, the type-IIa Na(+)/P(i) cotransporter (NaPi-IIa) accounts for up to 70% of brush border membrane transport. Regulation of renal P(i) reabsorption centers around brush border membrane insertion and retrieval of transporter protein under the influence of hormonal and nonhormonal factors. Immunohistochemical and fluorescence techniques have provided new insights into the tissue distribution and the regulation processes. The intrinsic electrogenicity of NaPi-IIa, has allowed detailed studies of the transport kinetics of NaPi-IIa and, combined with mutagenesis methods, structure-function information at the protein level is emerging.
Collapse
Affiliation(s)
- N Hernando
- Institute of Physiology, University of Zurich, Switzerland.
| | | | | | | |
Collapse
|
14
|
Murer H, Hernando N, Forster I, Biber J. Proximal tubular phosphate reabsorption: molecular mechanisms. Physiol Rev 2000; 80:1373-409. [PMID: 11015617 DOI: 10.1152/physrev.2000.80.4.1373] [Citation(s) in RCA: 390] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Renal proximal tubular reabsorption of P(i) is a key element in overall P(i) homeostasis, and it involves a secondary active P(i) transport mechanism. Among the molecularly identified sodium-phosphate (Na/P(i)) cotransport systems a brush-border membrane type IIa Na-P(i) cotransporter is the key player in proximal tubular P(i) reabsorption. Physiological and pathophysiological alterations in renal P(i) reabsorption are related to altered brush-border membrane expression/content of the type IIa Na-P(i) cotransporter. Complex membrane retrieval/insertion mechanisms are involved in modulating transporter content in the brush-border membrane. In a tissue culture model (OK cells) expressing intrinsically the type IIa Na-P(i) cotransporter, the cellular cascades involved in "physiological/pathophysiological" control of P(i) reabsorption have been explored. As this cell model offers a "proximal tubular" environment, it is useful for characterization (in heterologous expression studies) of the cellular/molecular requirements for transport regulation. Finally, the oocyte expression system has permitted a thorough characterization of the transport characteristics and of structure/function relationships. Thus the cloning of the type IIa Na-P(i )cotransporter (in 1993) provided the tools to study renal brush-border membrane Na-P(i) cotransport function/regulation at the cellular/molecular level as well as at the organ level and led to an understanding of cellular mechanisms involved in control of proximal tubular P(i) handling and, thus, of overall P(i) homeostasis.
Collapse
Affiliation(s)
- H Murer
- Institute of Physiology, University of Zürich, Zürich, Switzerland.
| | | | | | | |
Collapse
|
15
|
Shachaf C, Skorecki KL, Tzukerman M. Role of AP2 consensus sites in regulation of rat Npt2 (sodium-phosphate cotransporter) promoter. Am J Physiol Renal Physiol 2000; 278:F406-16. [PMID: 10710545 DOI: 10.1152/ajprenal.2000.278.3.f406] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Expression of the Npt2 gene, encoding the type II sodium-dependent phosphate cotransporter, is restricted to renal proximal tubule epithelium. We have isolated a 4,740-bp fragment of the 5'-flanking sequence of the rat Npt2 gene, identified the transcription initiation site, and demonstrated that this 5'-flanking sequence drives luciferase-reporter gene expression, following transfection in the proximal tubule cell-derived opossum kidney (OK) cell line but not in unrelated cell lines. Analysis of the promoter sequence revealed the presence of 10 consensus binding motifs for the AP2 transcription factor. Transient transfection assays revealed an important effect of the number of tandemly repeated AP2 sites in enhancing promoter activity. The promoter sequence also revealed a pair of inverted repeats enclosing 1,324 bp of intervening sequence and containing 8 of the total 10 AP2 consensus sites in the promoter sequence. Deletion or reversal of orientation of the distal inverted repeat resulted in marked enhancement of promoter activity. Electrophoretic mobility shift analysis revealed a distinct pattern of transcription factor binding to oligonucleotides containing AP2 sites, using nuclear extracts from OK cells, compared with unrelated cell lines. Taken together, these results suggest an important role for AP2 consensus binding sites in regulating Npt2 gene expression and suggest a mechanism of regulation mediated by the interaction of inverted repeats enclosing these sites.
Collapse
Affiliation(s)
- C Shachaf
- Bruce Rappaport Faculty of Medicine and Research Institute, Technion, Israel Institute of Technology, Department of Molecular Medicine, Rambam Medical Center, Haifa 31096, Israel
| | | | | |
Collapse
|