1
|
Dittmer KE, Heathcott RW, Marshall JC, Azarpeykan S. Expression of Phosphatonin-Related Genes in Sheep, Dog and Horse Kidneys Using Quantitative Reverse Transcriptase PCR. Animals (Basel) 2020; 10:ani10101806. [PMID: 33027890 PMCID: PMC7601102 DOI: 10.3390/ani10101806] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Revised: 09/25/2020] [Accepted: 10/02/2020] [Indexed: 12/15/2022] Open
Abstract
Simple Summary Traditionally, it has been thought that control of body phosphorus was secondary to the tighter control of calcium. However, over the last 20 years, an extensive system for control of body phosphorus by proteins called phosphatonins has been shown to exist. Most research on phosphatonins has been done in rat or mouse models. This paper looks at whether important proteins and phosphorus channels in the phosphatonin pathways are present in the kidneys of dogs, horses and sheep. The results showed that all of the components of the phosphatonin system are present in these species, but that there are species differences in which protein or channel is most common, and in the relationships between the proteins and channels. This research is important because the phosphatonin system is involved in the progression of chronic kidney disease in humans and animals, and differences in the systems between animal species may affect treatment of chronic kidney disease. Abstract The aim of this preliminary study was to determine the relative expression of phosphatonin pathway-related genes in normal dog, sheep and horse kidneys and to explore the relationships between the different genes. Kidneys were collected post-mortem from 10 sheep, 10 horses and 8 dogs. RNA was extracted, followed by reverse transcriptase quantitative polymerase chain reaction for fibroblast growth factor receptor 1 IIIc (FGFR1IIIC), sodium-phosphate co-transporter (NPT) 1 (SLC17A1), NPT2a (SLC34A1), NPT2c (SLC34A3), parathyroid hormone 1 receptor (PTH1R), klotho (KL), vitamin D receptor (VDR), 1a-hydroxylase (CYP27B1) and 24-hydroxylase (CYP24A1). NPT2a was highly expressed in the dog kidneys, compared with those of the horses and sheep. NPT1 had greatest expression in horses and sheep, although the three different NPTs all had relatively similar expression in sheep. There was little variability in FGFR1IIIc expression, particularly in the dogs and horses. FGFR1IIIc expression was negatively correlated with NPT genes (except NPT2a in sheep), while NPT genes were all positively correlated with each other. Unexpectedly, klotho was positively correlated with NPT genes in all three species. These results provide the basis for further research into this important regulatory system. In particular, species differences in phosphatonin gene expression should be considered when considering the pathogenesis of chronic kidney disease.
Collapse
Affiliation(s)
- Keren E. Dittmer
- School of Veterinary Science, Massey University, Palmerston North 4410, New Zealand; (R.W.H.); (S.A.)
- Correspondence:
| | - Rosemary W. Heathcott
- School of Veterinary Science, Massey University, Palmerston North 4410, New Zealand; (R.W.H.); (S.A.)
| | - Jonathan C. Marshall
- School of Fundamental Sciences, Massey University, Palmerston North 4410, New Zealand;
| | - Sara Azarpeykan
- School of Veterinary Science, Massey University, Palmerston North 4410, New Zealand; (R.W.H.); (S.A.)
| |
Collapse
|
2
|
Song C, Yue Q, Moseley A, Al-Khalili O, Wynne BM, Ma H, Wang L, Eaton DC. Myristoylated alanine-rich C kinase substrate-like protein-1 regulates epithelial sodium channel activity in renal distal convoluted tubule cells. Am J Physiol Cell Physiol 2020; 319:C589-C604. [PMID: 32639874 DOI: 10.1152/ajpcell.00218.2020] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The epithelial sodium channel (ENaC) regulates blood pressure by fine-tuning distal nephron sodium reabsorption. Our previous work has shown that ENaC gating is regulated by anionic phospholipid phosphates, including phosphatidylinositol 4,5-bisphosphate (PIP2). The PIP2-dependent regulation of ENaC is mediated by the myristoylated alanine-rich protein kinase C substrate-like protein-1 (MLP-1). MLP-1 binds to and is a reversible source of PIP2 at the plasma membrane. We examined MLP-1 regulation of ENaC in distal convoluted tubule clonal cell line DCT-15 cells. Wild-type MLP-1 runs at an apparent molecular mass of 52 kDa despite having a predicted molecular mass of 21 kDa. Native MLP-1 consists of several distinct structural elements: an effector domain that is highly positively charged, sequesters PIP2, contains serines that are the target of PKC, and controls MLP-1 association with the membrane; a myristoylation domain that promotes association with the membrane; and a multiple homology 2 domain of previously unknown function. To further examine MLP-1 in DCT-15 cells, we constructed several MLP-1 mutants: WT, a full-length wild-type protein; S3A, three substitutions in the effector domain to prevent phosphorylation; S3D mimicked constitutive phosphorylation by replacing three serines with aspartates; and GA replaced the myristoylation site glycine with alanine, so GA could not be myristoylated. Each mutant was tagged with either NH2-terminal 3XFLAG or COOH-terminal mCherry or V5. Transfection with MLP mutants modified ENaC activity in DCT-15 cells: activity was highest in S3A and lowest in S3D, and the activity after transfection with either construct was significantly different from WT. In Western blots, when transfected with 3XFLAG-tagged MLP-1 mutants, the expression of the full length of MLP-1 at 52 kDa increased in mutant S3A-MLP-1-transfected DCT-15 cells and decreased in S3D-MLP-1-transfected DCT-15 cells. Several lower molecular mass bands were also detected that correspond to potential presumptive calpain cleavage products. Confocal imaging shows that the different mutants localize in different subcellular compartments consistent with their preferred location in the membrane or in the cytosol. Activation of protein kinase C increases phosphorylation of endogenous MLP-1 and reduces ENaC activity. Our results suggest a complicated role for proteolytic processing in MLP-1 regulation of ENaC.
Collapse
Affiliation(s)
- Chang Song
- Department of Neurology, The Second Affiliated Hospital of Harbin Medical University, Harbin, China.,Division of Nephrology, Department of Medicine, Emory University, Atlanta, Georgia.,Department of Physiology, Emory University, Atlanta, Georgia
| | - Qiang Yue
- Division of Nephrology, Department of Medicine, Emory University, Atlanta, Georgia
| | - Auriel Moseley
- Division of Nephrology, Department of Medicine, Emory University, Atlanta, Georgia
| | - Otor Al-Khalili
- Division of Nephrology, Department of Medicine, Emory University, Atlanta, Georgia
| | - Brandi M Wynne
- Division of Nephrology & Hypertension, Department of Internal Medicine, University of Utah, Salt Lake City, Utah
| | - Heping Ma
- Department of Physiology, Emory University, Atlanta, Georgia
| | - Lihua Wang
- Department of Neurology, The Second Affiliated Hospital of Harbin Medical University, Harbin, China
| | - Douglas C Eaton
- Division of Nephrology, Department of Medicine, Emory University, Atlanta, Georgia
| |
Collapse
|
3
|
Abstract
Phosphate is an essential nutrient for life and is a critical component of bone formation, a major signaling molecule, and structural component of cell walls. Phosphate is also a component of high-energy compounds (i.e., AMP, ADP, and ATP) and essential for nucleic acid helical structure (i.e., RNA and DNA). Phosphate plays a central role in the process of mineralization, normal serum levels being associated with appropriate bone mineralization, while high and low serum levels are associated with soft tissue calcification. The serum concentration of phosphate and the total body content of phosphate are highly regulated, a process that is accomplished by the coordinated effort of two families of sodium-dependent transporter proteins. The three isoforms of the SLC34 family (SLC34A1-A3) show very restricted tissue expression and regulate intestinal absorption and renal excretion of phosphate. SLC34A2 also regulates the phosphate concentration in multiple lumen fluids including milk, saliva, pancreatic fluid, and surfactant. Both isoforms of the SLC20 family exhibit ubiquitous expression (with some variation as to which one or both are expressed), are regulated by ambient phosphate, and likely serve the phosphate needs of the individual cell. These proteins exhibit similarities to phosphate transporters in nonmammalian organisms. The proteins are nonredundant as mutations in each yield unique clinical presentations. Further research is essential to understand the function, regulation, and coordination of the various phosphate transporters, both the ones described in this review and the phosphate transporters involved in intracellular transport.
Collapse
Affiliation(s)
- Nati Hernando
- University of Zurich-Irchel, Institute of Physiology, Zurich, Switzerland; Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky; and Robley Rex VA Medical Center, Louisville, Kentucky
| | - Kenneth Gagnon
- University of Zurich-Irchel, Institute of Physiology, Zurich, Switzerland; Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky; and Robley Rex VA Medical Center, Louisville, Kentucky
| | - Eleanor Lederer
- University of Zurich-Irchel, Institute of Physiology, Zurich, Switzerland; Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky; and Robley Rex VA Medical Center, Louisville, Kentucky
| |
Collapse
|
4
|
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: 64] [Impact Index Per Article: 10.7] [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
|
5
|
Farrow EG, Imel EA, White KE. Miscellaneous non-inflammatory musculoskeletal conditions. Hyperphosphatemic familial tumoral calcinosis (FGF23, GALNT3 and αKlotho). Best Pract Res Clin Rheumatol 2011; 25:735-47. [PMID: 22142751 PMCID: PMC3233725 DOI: 10.1016/j.berh.2011.10.020] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2011] [Accepted: 10/13/2011] [Indexed: 11/18/2022]
Abstract
Familial tumoral calcinosis (TC) is a rare disorder distinguished by the development of ectopic and vascular calcified masses that occur in settings of hyperphosphatemia (hFTC) and normophosphatemia (nFTC). Serum phosphorus concentrations are relatively tightly controlled by interconnected endocrine activity at the level of the intestine, kidney, and skeleton. Discovering the molecular causes for heritable forms of hFTC has shed new light on the regulation of serum phosphate balance. This review will focus upon the genetic basis and clinical approaches for hFTC, due to genes that are related to the phosphaturic hormone fibroblast growth factor-23 (FGF23). These include FGF23 itself, an FGF23-glycosylating enzyme (GALNT3), and the FGF23 co-receptor α-Klotho (αKL). Our understanding of the molecular basis of hFTC will, in the short term, aid in understanding normal phosphate balance, and in the future, provide potential insight into the design of novel therapeutic strategies for both rare and common disorders of phosphate metabolism.
Collapse
Affiliation(s)
- Emily G. Farrow
- Departments of Medical and Molecular Genetics, IN, 46202 USA
| | - Erik A. Imel
- Medicine Indiana University School of Medicine Indianapolis, IN, 46202 USA
| | | |
Collapse
|
6
|
Abstract
Inherited diseases of renal phosphate handling lead to urinary phosphate wasting and depletion of total body phosphorus stores. Clinical sequelae of inherited disorders that are associated with increased urinary phosphate excretion are deleterious and can lead to abnormal skeletal growth and deformities. This Review describes hereditary disorders of renal phosphate wasting taking into account developments in our understanding of renal phosphate handling from the last decade. The cloning of genes involved in these disorders and further studies on their pathophysiological mechanisms have given important insights in to how phosphatonins, such as FGF-23, regulate renal phosphate reabsorption in health and disease. X-linked dominant hypophosphatemic rickets results from mutation of a metalloprotease (PHEX) that has an unidentified role in FGF-23 degradation. Mutation of an RXXR proteolytic cleavage site in FGF-23 prevents degradation and increases circulating levels of FGF-23 in autosomal dominant hypophosphatemic rickets. FGF-23 acts to remove sodium phosphate co-transporters from the luminal membrane of proximal tubular cells with resultant renal phosphate wasting. Loss of function mutations in genes encoding the transporters NaPi-IIc and NaPi-IIa also result in renal phosphate wasting and rickets.
Collapse
|
7
|
Suzuki A, Ammann P, Nishiwaki-Yasuda K, Sekiguchi S, Asano S, Nagao S, Kaneko R, Hirabayashi M, Oiso Y, Itoh M, Caverzasio J. Effects of transgenic Pit-1 overexpression on calcium phosphate and bone metabolism. J Bone Miner Metab 2010; 28:139-48. [PMID: 19795094 DOI: 10.1007/s00774-009-0121-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/18/2008] [Accepted: 08/09/2009] [Indexed: 01/30/2023]
Abstract
The type III inorganic phosphate (Pi) transporter Pit-1 was previously found to be preferentially expressed in developing long bones. Several studies also described a regulation of its expression in cultured bone cells by osteotropic factors, suggesting a role of this transporter in bone metabolism. In the present study, we investigated the effects of the transgenic overexpression of Pit-1 in Wistar male rats on calcium phosphate and bone metabolism. A threefold increase and doubling of Pi transport activity were recorded in primary cultured osteoblastic cells derived from calvaria of two transgenic (Tg) lines compared with wild-type littermates (WT), respectively. Skeletal development was not affected by the transgene, and bone mass, analyzed by DXA, was slightly decreased in Tg compared with WT. Enhanced Pi uptake in calvaria-derived osteoblasts from Pit-1 Tg was associated with a significantly decreased expression of alkaline phosphatase activity and a normal deposition and calcification of the collagenous matrix. In 4-month-old adult Tg rats, serum Pi and renal Pi transport were increased compared with WT. The decrease of serum Ca concentration was associated with increased serum parathyroid hormone levels. Variations in serum Pi in Pit-1 Tg rats were negatively correlated with serum fibroblast growth factor-23, whereas 1,25-dihydroxyvitamin D(3) was not affected by Pit-1 overexpression. In conclusion, transgenic Pit-1 overexpression in rats affected bone and calcium phosphate metabolism. It also decreased alkaline phosphatase activity in osteoblasts without influencing bone matrix mineralization as well as skeletal development.
Collapse
Affiliation(s)
- Atsushi Suzuki
- Division of Endocrinology and Metabolism, Department of Internal Medicine, Fujita Health University, 1-98 Dengakugakubo, Kutsukake-cho, Toyoake, Aichi, 470-1192, Japan.
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
8
|
Abstract
Phosphate is critical for the maintenance of skeletal integrity, is a necessary component of important biomolecules, and is central to signal transduction and cell metabolism. It is becoming clear that endocrine communication between the skeleton, kidney, and the intestine is involved in maintaining appropriate serum phosphate concentrations, and that the kidney is the primary site for minute-to-minute regulation of phosphate levels. The identification of genetic alterations in Mendelian disorders of hypophosphatemia and hyperphosphatemia has led to the isolation of novel genes and the identification of new roles for existing proteins--such as fibroblast growth factor 23 and its processing systems, the co-receptor alpha-klotho, and phosphate transporters--in the control of renal phosphate handling. Recent findings also indicate that fibroblast growth factor 23 has feedback mechanisms involving parathyroid hormone and vitamin D that control phosphate homeostasis. This Review will highlight genetic, in vitro and in vivo findings, and will discuss how these clinical and experimental discoveries have uncovered novel aspects of renal phosphate handling and opened new research and therapeutic avenues.
Collapse
|
9
|
Cheng X, Klaassen CD. Tissue distribution, ontogeny, and hormonal regulation of xenobiotic transporters in mouse kidneys. Drug Metab Dispos 2009; 37:2178-85. [PMID: 19679677 DOI: 10.1124/dmd.109.027177] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Kidneys play important roles in the elimination of numerous endogenous and exogenous chemicals. In recent years, at least 37 xenobiotic transporters have been identified in mammalian kidneys. Although much progress has been made, information on 14 of these transporters (ATP-binding cassette [Abc] a1, apical sodium bile acid transporter [Asbt], breast cancer resistance protein, concentrative nucleoside transporter 1, equilibrative nucleoside transporter [Ent] 2, Ent3, sodium-phosphate cotransporter [Npt] 1, Npt2a, Npt2b, Npt2c, organic anion transporter [Oat] 5, organic anion-transporting polypeptide [Oatp] 4c1, peptide transporter 2, and uric acid transporter [Urat] 1) in kidneys is quite limited. Therefore, the purpose of the present study was to examine the tissue distribution, ontogeny, and hormonal regulation of these 14 transporters in kidneys of mice. Other than in kidneys, Npt2b is also highly expressed in liver and lung, Npt2c in liver and colon, Asbt in ileum, and Abca1 in liver, lung, testis, ovary, and placenta of mice. Most of these (13 of 14) transporters are lowly expressed in mouse kidneys until 15 days of age, which in part contributes to the immaturity of excretory function in fetal and newborn kidneys. One exception is Ent2, which is highly expressed before birth and gradually decreases after birth until reaching adult levels at 15 days of age. Gender-divergent expression of male-predominant (Urat1 and Oatp4c1) and female-predominant (Oat5) transporters in mouse kidneys is primarily due to stimulatory effects of androgens and estrogens, respectively. In conclusion, the mRNA expression of xenobiotic transporters in kidneys is determined by tissue, age, and sex hormones.
Collapse
Affiliation(s)
- Xingguo Cheng
- Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160, USA
| | | |
Collapse
|
10
|
Breusegem SY, Takahashi H, Giral-Arnal H, Wang X, Jiang T, Verlander JW, Wilson P, Miyazaki-Anzai S, Sutherland E, Caldas Y, Blaine JT, Segawa H, Miyamoto KI, Barry NP, Levi M. Differential regulation of the renal sodium-phosphate cotransporters NaPi-IIa, NaPi-IIc, and PiT-2 in dietary potassium deficiency. Am J Physiol Renal Physiol 2009; 297:F350-61. [PMID: 19493963 PMCID: PMC2724260 DOI: 10.1152/ajprenal.90765.2008] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Dietary potassium (K) deficiency is accompanied by phosphaturia and decreased renal brush border membrane (BBM) vesicle sodium (Na)-dependent phosphate (Pi) transport activity. Our laboratory previously showed that K deficiency in rats leads to increased abundance in the proximal tubule BBM of the apical Na-Pi cotransporter NaPi-IIa, but that the activity, diffusion, and clustering of NaPi-IIa could be modulated by the altered lipid composition of the K-deficient BBM (Zajicek HK, Wang H, Puttaparthi K, Halaihel N, Markovich D, Shayman J, Beliveau R, Wilson P, Rogers T, Levi M. Kidney Int 60: 694–704, 2001; Inoue M, Digman MA, Cheng M, Breusegem SY, Halaihel N, Sorribas V, Mantulin WW, Gratton E, Barry NP, Levi M. J Biol Chem 279: 49160–49171, 2004). Here we investigated the role of the renal Na-Pi cotransporters NaPi-IIc and PiT-2 in K deficiency. Using Western blotting, immunofluorescence, and quantitative real-time PCR, we found that, in rats and in mice, K deficiency is associated with a dramatic decrease in the NaPi-IIc protein abundance in proximal tubular BBM and in NaPi-IIc mRNA. In addition, we documented the presence of a third Na-coupled Pi transporter in the renal BBM, PiT-2, whose abundance is also decreased by dietary K deficiency in rats and in mice. Finally, electron microscopy showed subcellular redistribution of NaPi-IIc in K deficiency: in control rats, NaPi-IIc immunolabel was primarily in BBM microvilli, whereas, in K-deficient rats, NaPi-IIc BBM label was reduced, and immunolabel was prevalent in cytoplasmic vesicles. In summary, our results demonstrate that decreases in BBM abundance of the phosphate transporter NaPi-IIc and also PiT-2 might contribute to the phosphaturia of dietary K deficiency, and that the three renal BBM phosphate transporters characterized so far can be differentially regulated by dietary perturbations.
Collapse
Affiliation(s)
- Sophia Y Breusegem
- Department of Medicine, Division of Renal Diseases and Hypertension, University of Colorado Denver, Aurora, Colorado, USA.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
11
|
Villa-Bellosta R, Ravera S, Sorribas V, Stange G, Levi M, Murer H, Biber J, Forster IC. The Na+-Pi cotransporter PiT-2 (SLC20A2) is expressed in the apical membrane of rat renal proximal tubules and regulated by dietary Pi. Am J Physiol Renal Physiol 2009; 296:F691-9. [PMID: 19073637 PMCID: PMC2670642 DOI: 10.1152/ajprenal.90623.2008] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2008] [Accepted: 12/08/2008] [Indexed: 12/26/2022] Open
Abstract
The principal mediators of renal phosphate (P(i)) reabsorption are the SLC34 family proteins NaPi-IIa and NaPi-IIc, localized to the proximal tubule (PT) apical membrane. Their abundance is regulated by circulatory factors and dietary P(i). Although their physiological importance has been confirmed in knockout animal studies, significant P(i) reabsorptive capacity remains, which suggests the involvement of other secondary-active P(i) transporters along the nephron. Here we show that a member of the SLC20 gene family (PiT-2) is localized to the brush-border membrane (BBM) of the PT epithelia and that its abundance, confirmed by Western blot and immunohistochemistry of rat kidney slices, is regulated by dietary P(i). In rats treated chronically on a high-P(i) (1.2%) diet, there was a marked decrease in the apparent abundance of PiT-2 protein in kidney slices compared with those from rats kept on a chronic low-P(i) (0.1%) diet. In Western blots of BBM from rats that were switched from a chronic low- to high-P(i) diet, NaPi-IIa showed rapid downregulation after 2 h; PiT-2 was also significantly downregulated at 24 h and NaPi-IIc after 48 h. For the converse dietary regime, NaPi-IIa showed adaptation within 8 h, whereas PiT-2 and NaPi-IIc showed a slower adaptive trend. Our findings suggest that PiT-2, until now considered as a ubiquitously expressed P(i) housekeeping transporter, is a novel mediator of P(i) reabsorption in the PT under conditions of acute P(i) deprivation, but with a different adaptive time course from NaPi-IIa and NaPi-IIc.
Collapse
Affiliation(s)
- Ricardo Villa-Bellosta
- Institute of Physiology, Univ. of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
| | | | | | | | | | | | | | | |
Collapse
|
12
|
Biber J, Hernando N, Forster I, Murer H. Regulation of phosphate transport in proximal tubules. Pflugers Arch 2008; 458:39-52. [PMID: 18758808 DOI: 10.1007/s00424-008-0580-8] [Citation(s) in RCA: 145] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2008] [Accepted: 08/13/2008] [Indexed: 12/13/2022]
Abstract
Homeostasis of inorganic phosphate (P(i)) is primarily an affair of the kidneys. Reabsorption of the bulk of filtered P(i) occurs along the renal proximal tubule and is initiated by apically localized Na(+)-dependent P(i) cotransporters. Tubular P(i) reabsorption and therefore renal excretion of P(i) is controlled by a number of hormones, including phosphatonins, and metabolic factors. In most cases, regulation of P(i) reabsorption is achieved by changing the apical abundance of Na(+)/Pi cotransporters. The regulatory mechanisms involve various signaling pathways and a number of proteins that interact with Na(+)/P(i) cotransporters.
Collapse
Affiliation(s)
- J Biber
- Institute of Physiology and Zurich Center for Integrative Human Physiology, University of Zurich, Switzerland.
| | | | | | | |
Collapse
|
13
|
Renal phosphaturia during metabolic acidosis revisited: molecular mechanisms for decreased renal phosphate reabsorption. Pflugers Arch 2008; 457:539-49. [PMID: 18535837 DOI: 10.1007/s00424-008-0530-5] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2008] [Accepted: 05/08/2008] [Indexed: 10/22/2022]
Abstract
During metabolic acidosis (MA), urinary phosphate excretion increases and contributes to acid removal. Two Na(+)-dependent phosphate transporters, NaPi-IIa (Slc34a1) and NaPi-IIc (Slc34a3), are located in the brush border membrane (BBM) of the proximal tubule and mediate renal phosphate reabsorption. Transcriptome analysis of kidneys from acid-loaded mice revealed a large decrease in NaPi-IIc messenger RNA (mRNA) and a smaller reduction in NaPi-IIa mRNA abundance. To investigate the contribution of transporter regulation to phosphaturia during MA, we examined renal phosphate transporters in normal and Slc34a1-gene ablated (NaPi-IIa KO) mice acid-loaded for 2 and 7 days. In normal mice, urinary phosphate excretion was transiently increased after 2 days of acid loading, whereas no change was found in Slc34a1-/- mice. BBM Na/Pi cotransport activity was progressively and significantly decreased in acid-loaded KO mice, whereas in WT animals, a small increase after 2 days of treatment was seen. Acidosis increased BBM NaPi-IIa abundance in WT mice and NaPi-IIc abundance in WT and KO animals. mRNA abundance of NaPi-IIa and NaPi-IIc decreased during MA. Immunohistochemistry did not indicate any change in the localization of NaPi-IIa and NaPi-IIc along the nephron. Interestingly, mRNA abundance of both Slc20 phosphate transporters, Pit1 and Pit2, was elevated after 7 days of MA in normal and KO mice. These data demonstrate that phosphaturia during acidosis is not caused by reduced protein expression of the major Na/Pi cotransporters NaPi-IIa and NaPi-IIc and suggest a direct inhibitory effect of low pH mainly on NaPi-IIa. Our data also suggest that Pit1 and Pit2 transporters may play a compensatory role.
Collapse
|
14
|
Ma M, Jiang YJ. Jagged2a-notch signaling mediates cell fate choice in the zebrafish pronephric duct. PLoS Genet 2007; 3:e18. [PMID: 17257056 PMCID: PMC1781496 DOI: 10.1371/journal.pgen.0030018] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2006] [Accepted: 11/13/2006] [Indexed: 11/24/2022] Open
Abstract
Pronephros, a developmental model for adult mammalian kidneys (metanephros) and a functional kidney in early teleosts, consists of glomerulus, tubule, and duct. These structural and functional elements are responsible for different kidney functions, e.g., blood filtration, waste extraction, salt recovery, and water balance. During pronephros organogenesis, cell differentiation is a key step in generating different cell types in specific locations to accomplish designated functions. However, it is poorly understood what molecules regulate the differentiation of different cell types in different parts of the kidney. Two types of epithelial cells, multi-cilia cells and principal cells, are found in the epithelia of the zebrafish distal pronephric duct. While the former is characterized by at least 15 apically localized cilia and expresses centrin2 and rfx2, the latter is characterized by a single primary cilium and sodium pumps. Multi-cilia cells and principal cells differentiate from 17.5 hours post-fertilization onwards in a mosaic pattern. Jagged2a-Notch1a/Notch3-Her9 is responsible for specification and patterning of these two cell types through a lateral inhibition mechanism. Furthermore, multi-cilia cell hyperplasia was observed in mind bomb mutants and Mind bomb was shown to interact with Jagged2a and facilitate its internalization. Taken together, our findings add a new paradigm of Notch signaling in kidney development, namely, that Jagged2a-Notch signaling modulates cell fate choice in a nephric segment, the distal pronephric duct. The kidney is a complex organ that regulates blood homeostasis through the maintenance of fluid and ion balance and disposal of metabolic waste. We used zebrafish pronephros, a primordial vertebrate kidney, to address how a kidney tissue acquires its cell types and pattern. Two types of epithelial cells were found in the pronephric duct: multi-cilia cells and principal cells, which could be distinguished based on morphology and expression of different marker genes. In the pronephric duct, the multi-cilia cells and principal cells form a “salt and pepper,” or mosaic, pattern. Using existing zebrafish mutants and a knockdown technique, we demonstrated that the mosaic pattern and differentiation of these two cell types are controlled through a Notch-dependent lateral inhibition mechanism. Notch signaling has been shown to be essential for other aspects of kidney development, such as formation of the glomerulus and the tubule. Here, to our knowledge for the first time, we show that the same signaling pathway is required for the differentiation of two different epithelial cells in a kidney segment known as the distal pronephric duct. The same mechanism is very likely to be employed by other similar developmental processes in the same context to generate distinct cell types in a tissue.
Collapse
Affiliation(s)
- Ming Ma
- Laboratory of Developmental Signalling and Patterning, Institute of Molecular and Cell Biology, Singapore, Singapore
| | - Yun-Jin Jiang
- Laboratory of Developmental Signalling and Patterning, Institute of Molecular and Cell Biology, Singapore, Singapore
- * To whom correspondence should be addressed. E-mail:
| |
Collapse
|
15
|
Srivastava T, Alon US. Pathophysiology of hypercalciuria in children. Pediatr Nephrol 2007; 22:1659-73. [PMID: 17464515 PMCID: PMC6904412 DOI: 10.1007/s00467-007-0482-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/02/2007] [Revised: 03/11/2007] [Accepted: 03/12/2007] [Indexed: 12/17/2022]
Abstract
Urinary excretion of calcium is the result of a complex interplay between three organs-namely, the gastrointestinal tract, bone, and kidney-which is finely orchestrated by multiple hormones. Hypercalciuria is believed to be a polygenic trait and is influenced significantly by diet. This paper briefly reviews calcium handling by the renal tubule in normal and in hereditary disorders as it relates to the pathophysiology of hypercalciuria. The effects of dietary sodium, potassium, protein, calcium, and phosphate on calcium excretion, and the association of hypercalciuria with bone homeostasis is discussed, leading to recommendations on means to address excessive urinary calcium excretion.
Collapse
Affiliation(s)
- Tarak Srivastava
- Section of Nephrology, Bone and Mineral Disorder Clinic, The Children’s Mercy Hospital and Clinics, University of Missouri, 2401 Gillham Road, Kansas City, MO 64108 USA
| | - Uri S. Alon
- Section of Nephrology, Bone and Mineral Disorder Clinic, The Children’s Mercy Hospital and Clinics, University of Missouri, 2401 Gillham Road, Kansas City, MO 64108 USA
| |
Collapse
|
16
|
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: 297] [Impact Index Per Article: 16.5] [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
|
17
|
Anderle P, Sengstag T, Mutch DM, Rumbo M, Praz V, Mansourian R, Delorenzi M, Williamson G, Roberts MA. Changes in the transcriptional profile of transporters in the intestine along the anterior-posterior and crypt-villus axes. BMC Genomics 2005; 6:69. [PMID: 15882471 PMCID: PMC1145182 DOI: 10.1186/1471-2164-6-69] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2005] [Accepted: 05/10/2005] [Indexed: 01/03/2023] Open
Abstract
Background The purpose of this work was to characterize the expression of drug and nutrient carriers along the anterior-posterior and crypt-villus axes of the intestinal epithelium and to study the validity of utilizing whole gut tissue rather than purified epithelial cells to examine regional variations in gene expression. Results We have characterized the mRNA expression profiles of 76 % of all currently known transporters along the anterior-posterior axis of the gut. This is the first study to describe the expression profiles of the majority of all known transporters in the intestine. The expression profiles of transporters, as defined according to the Gene Ontology consortium, were measured in whole tissue of the murine duodenum, jejunum, ileum and colon using high-density microarrays. For nine transporters (Abca1, Abcc1, Abcc3, Abcg8, Slc10a2, Slc28a2, Slc2a1, Slc34a2 and Slc5a8), the mRNA profiles were further measured by RT-PCR in laser micro-dissected crypt and villus epithelial cells corresponding to the aforementioned intestinal regions. With respect to differentially regulated transporters, the colon had a distinct expression profile from small intestinal segments. The majority (59 % for p cutoff ≤ 0.05) of transporter mRNA levels were constant across the intestinal sections studied. For the transporter subclass "carrier activity", which contains the majority of known carriers for biologically active compounds, a significant change (p ≤ 0.05) along the anterior-posterior axis was observed. Conclusion All nine transporters examined in laser-dissected material demonstrated good replication of the region-specific profiles revealed by microarray. Furthermore, we suggest that the distribution characteristics of Slc5a8 along the intestinal tract render it a suitable candidate carrier for monocarboxylate drugs in the posterior portion of the intestine. Our findings also predict that there is a significant difference in the absorption of carrier-mediated compounds in the different intestinal segments. The most pronounced differences can be expected between the adjoining segments ileum and colon, but the differences between the other adjoining segments are not negligible. Finally, for the examined genes, profiles measured in whole intestinal tissue extracts are representative of epithelial cell-only gene expression.
Collapse
Affiliation(s)
- Pascale Anderle
- ISREC, Swiss Institute for Experimental Cancer Research, 1066 Epalinges s/Lausanne, Switzerland
| | - Thierry Sengstag
- Swiss Institute for Experimental Cancer Research (ISREC) and Swiss Institute of Bioinformatics (SIB), NCCR Molecular Oncology, CH-1066 Epalinges s/Lausanne, Switzerland
| | - David M Mutch
- Nestle Research Center, Vers-chez-les-Blanc, 1000 Lausanne 26, Switzerland
| | - Martin Rumbo
- ISREC, Swiss Institute for Experimental Cancer Research, 1066 Epalinges s/Lausanne, Switzerland
| | - Viviane Praz
- ISREC and Swiss Institute of Bioinformatics, 1066 Epalinges s/Lausanne, Switzerland
| | - Robert Mansourian
- Nestle Research Center, Vers-chez-les-Blanc, 1000 Lausanne 26, Switzerland
| | - Mauro Delorenzi
- Swiss Institute for Experimental Cancer Research (ISREC) and Swiss Institute of Bioinformatics (SIB), NCCR Molecular Oncology, CH-1066 Epalinges s/Lausanne, Switzerland
| | - Gary Williamson
- Nestle Research Center, Vers-chez-les-Blanc, 1000 Lausanne 26, Switzerland
| | | |
Collapse
|
18
|
Madjdpour C, Bacic D, Kaissling B, Murer H, Biber J. Segment-specific expression of sodium-phosphate cotransporters NaPi-IIa and -IIc and interacting proteins in mouse renal proximal tubules. Pflugers Arch 2004; 448:402-10. [PMID: 15007650 DOI: 10.1007/s00424-004-1253-x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2004] [Accepted: 02/10/2004] [Indexed: 10/26/2022]
Abstract
Sodium-dependent phosphate cotransport in renal proximal tubules (PTs) is heterogeneous with respect to proximal tubular segmentation (S1 vs. S3) and nephron generation (superficial vs. juxtamedullary). In the present study, S1 and S3 segments of superficial and juxtamedullary nephrons were laser-microdissected and mRNA and protein expression of the Na/Pi-cotransporters NaPi-IIa and NaPi-IIc and the PDZ proteins NHERF-1 and PDZK1 determined. Expression of NaPi-IIa mRNA decreased axially in juxtamedullary nephrons. There was no effect of dietary Pi content on NaPi-lla mRNA expression in any proximal tubular segment. The abundance of the NaPi-IIa cotransporter in the brush-border membrane showed inter- and intranephron heterogeneity and increased in response to a low-Pi diet (5 days), suggesting that up-regulation of NaPi-lla occurs via post-transcriptional mechanisms. In contrast, NaPi-IIc mRNA and protein was up-regulated by the low-Pi diet in all nephron generations analysed. NHERF-1 and PDZK1, at both mRNA and protein levels, were distributed evenly along the PTs and did not change after a low-Pi diet.
Collapse
Affiliation(s)
- C Madjdpour
- Institute of Anatomy, University of Zurich, 8057, Zurich, Switzerland
| | | | | | | | | |
Collapse
|
19
|
Abstract
The physiological tuning and pathophysiological alterations of renal proximal reabsorption of inorganic phosphate can be ascribed to the net amount of the Na/Pi-cotransporter NaPi-IIa localized in the brush border membrane. The net amount of NaPi-IIa appears to be the result of an endocytotic rate regulated by a complex network of different protein kinases. New approaches demonstrated that NaPi-IIa is part of heteromeric protein complexes, organized by PDZ (postsynaptic protein PSD95, Drosophila junction protein Disc-large, tight junction protein ZO-1) proteins. Such complexes are thought to play important roles in the apical positioning and regulated endocytosis of NaPi-IIa and therefore such interactions have to be considered when explaining proximal phosphate ion reabsorption.
Collapse
Affiliation(s)
- Heini Murer
- Institute of Physiology, University Zürich, 8057 Switzerland.
| | | | | | | |
Collapse
|
20
|
Khadeer MA, Tang Z, Tenenhouse HS, Eiden MV, Murer H, Hernando N, Weinman EJ, Chellaiah MA, Gupta A. Na+-dependent phosphate transporters in the murine osteoclast: cellular distribution and protein interactions. Am J Physiol Cell Physiol 2003; 284:C1633-44. [PMID: 12606316 DOI: 10.1152/ajpcell.00580.2002] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We previously demonstrated that inhibition of Na-dependent phosphate (P(i)) transport in osteoclasts led to reduced ATP levels and diminished bone resorption. These findings suggested that Na/P(i) cotransporters in the osteoclast plasma membrane provide P(i) for ATP synthesis and that the osteoclast may utilize part of the P(i) released from bone resorption for this purpose. The present study was undertaken to define the cellular localization of Na/P(i) cotransporters in the mouse osteoclast and to identify the proteins with which they interact. Using glutathione S-transferase (GST) fusion constructs, we demonstrate that the type IIa Na/P(i) cotransporter (Npt2a) in osteoclast lysates interacts with the Na/H exchanger regulatory factor, NHERF-1, a PDZ protein that is essential for the regulation of various membrane transporters. In addition, NHERF-1 in osteoclast lysates interacts with Npt2a in spite of deletion of a putative PDZ-binding domain within the carboxy terminus of Npt2a. In contrast, deletion of the carboxy-terminal TRL amino acid motif of Npt2a significantly reduced its interaction with NHERF-1 in kidney lysates. Studies in osteoclasts transfected with green fluorescent protein-Npt2a constructs indicated that Npt2a colocalizes with NHERF-1 and actin at or near the plasma membrane of the osteoclast and associates with ezrin, a linker protein associated with the actin cytoskeleton, likely via NHERF-1. Furthermore, we demonstrate by RT/PCR of osteoclast RNA and in situ hybridization that the type III Na/P(i) cotransporter, PiT-1, is also expressed in mouse osteoclasts. To examine the cellular distribution of PiT-1, we infected mouse osteoclasts with a retroviral vector encoding PiT-1 fused to an epitope tag. PiT-1 colocalizes with actin and is present on the basolateral membrane of the polarized osteoclast, similar to that previously reported for Npt2a. Taken together, our data suggest that association of Npt2a with NHERF-1, ezrin, and actin, and of PiT-1 with actin, may be responsible for membrane sorting and regulation of these Na/P(i) cotransporters in the osteoclast.
Collapse
Affiliation(s)
- Mohammed A Khadeer
- Department of Oral and Craniofacial Biological Sciences, University of Maryland, Baltimore, Maryland 21201, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
21
|
Soumounou Y, Gauthier C, Tenenhouse HS. Murine and human type I Na-phosphate cotransporter genes: structure and promoter activity. Am J Physiol Renal Physiol 2001; 281:F1082-91. [PMID: 11704559 DOI: 10.1152/ajprenal.0092.2001] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Na-phosphate (P(i)) cotransporters in the apical membrane of renal proximal tubular cells play a major role in the maintenance of P(i) homeostasis. Although two such cotransporters, Npt1 and Npt2, have been identified, little is known about the function and regulation of Npt1. We cloned and characterized the murine (Npt1) and human (NPT1) genes, isolated the 5'-flanking region of Npt1, and analyzed its promoter activity. Npt1 is approximately 29 kb with 12 exons, whereas NPT1 is approximately 49 kb with one additional exon. The Npt1 promoter has a TATA-like box but no CAAT box, and the transcription start site was identified by primer extension and 5'-rapid amplification of cDNA ends. Transfection of opossum kidney cells with Npt1 promoter-reporter gene constructs demonstrated significant activity in a 570-bp fragment that was completely inhibited by cotransfection with the transcription factor, hepatocyte nuclear factor (HNF)-3 beta. Deletion of 200 bp from the 3'-end of the 570-bp fragment abrogated its promoter activity. In addition, promoter activity of a 4.5-kb fragment, but not the 570-bp fragment, was stimulated fourfold by cotransfection with HNF-1 alpha. Other well-characterized cis-acting elements were identified in the Npt1 promoter. We suggest that Npt1 expression is transcriptionally regulated and provide a basis for the investigation of Npt1 function by targeted mutagenesis.
Collapse
Affiliation(s)
- Y Soumounou
- McGill University-Montreal Children's Hospital Research Institute, McGill University, Montreal, Quebec, Canada H3Z 2Z3
| | | | | |
Collapse
|
22
|
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
|
23
|
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
|
24
|
Affiliation(s)
- P S Rowe
- Royal Free and University College Medical School, Department of Biochemistry and Molecular Biology, Centre for Molecular Osteo-Renal Research, Rowland Hill Street, Hampstead, London NW3 2PF, UK.
| |
Collapse
|
25
|
Hoag HM, Martel J, Gauthier C, Tenenhouse HS. Effects of Npt2 gene ablation and low-phosphate diet on renal Na(+)/phosphate cotransport and cotransporter gene expression. J Clin Invest 1999; 104:679-86. [PMID: 10491403 PMCID: PMC408436 DOI: 10.1172/jci7103] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The renal Na(+)/phosphate (Pi) cotransporter Npt2 is expressed in the brush border membrane (BBM) of proximal tubular cells. We examined the effect of Npt2 gene knockout on age-dependent BBM Na(+)/Pi cotransport, expression of Na(+)/Pi cotransporter genes Npt1, Glvr-1, and Ram-1, and the adaptive response to chronic Pi deprivation. Na(+)/Pi cotransport declines with age in wild-type mice (Npt2(+/+)), but not in mice homozygous for the disrupted Npt2 allele (Npt2(-/-)). At all ages, Na(+)/Pi cotransport in Npt2(-/-) mice is approximately 15% of that in Npt2(+/+) littermates. Only Npt1 mRNA abundance increases with age in Npt2(+/+) mice, whereas Npt1, Glvr-1, and Ram-1 mRNAs show an age-dependent increase in Npt2(-/-) mice. Pi deprivation significantly increases Na(+)/Pi cotransport, Npt2 protein, and mRNA in Npt2(+/+) mice. In contrast, Pi-deprived Npt2(-/-) mice fail to show the adaptive increase in transport despite exhibiting a fall in serum Pi. We conclude that (a) Npt2 is a major determinant of BBM Na(+)/Pi cotransport; (b) the age-dependent increase in Npt1, Glvr-1, and Ram-1 mRNAs in Npt2(-/-) mice is insufficient to compensate for loss of Npt2; and (c) Npt2 is essential for the adaptive BBM Na(+)/Pi cotransport response to Pi deprivation.
Collapse
Affiliation(s)
- H M Hoag
- Department of Biology, Department of Pediatrics, McGill University-Montreal Children's Hospital Research Institute, Montreal, Quebec H3H 1P3, Canada
| | | | | | | |
Collapse
|