The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Carsten A Wagner - One of the best experts on this subject based on the ideXlab platform.
-
1 25 oh 2 vitamin d3 stimulates active phosphate transport but not paracellular phosphate absorption in mouse intestine
The Journal of Physiology, 2020Co-Authors: Nati Hernando, Thomas Knopfel, Eva Maria Pastorarroyo, J Marks, Udo Schnitzbauer, Matthias Burki, Carla Bettoni, Carsten A WagnerAbstract:Intestinal absorption of phosphate is stimulated by 1,25(OH)2 vitamin D3. At least two distinct mechanisms underlie phosphate absorption in the gut, an active transcellular transport requiring the Na+ /phosphate cotransporter NaPi-IIb/Slc34a2, and a poorly characterized paracellular passive pathway. 1,25(OH)2 vitamin D3 stimulates NaPi-IIb expression and function and loss of NaPi-IIb reduces intestinal phosphate absorption. However, it is remains unknown whether NaPi-IIb is the only target for hormonal regulation by 1,25(OH)2 vitamin D3 . Here we compared the effects of intraperitoneal administration of 1,25(OH)2 vitamin D3 (2 days, once per day) in wild type and intestinal-specific Slc34a2 deficient mice, and analyzed trans- vs paracellular routes of phosphate absorption. We found that treatment stimulated active transport of phosphate only in jejunum of wild type mice, though NaPi-IIb protein expression was upregulated in jejunum and ileum . In contrast, 1,25(OH)2 vitamin D3 administration had no effect in Slc34a2 deficient mice, suggesting that the hormone specifically regulates NaPi-IIb expression. In both groups, 1,25(OH)2 vitamin D3 elicited the expected increase of plasma FGF23 and reduction of PTH. Treatment resulted in hyperphosphaturia (and hypercalciuria) in both genotypes, though mice remained normophosphatemic. While increased intestinal absorption and higher FGF23 can trigger the hyperphosphaturic response in wild types, only the second one can explain the renal response in Slc34a2 deficient mice. Thus, 1,25(OH)2 vitamin D3 stimulates intestinal phosphate absorption by acting on the active transcellular pathway mostly mediated by NaPi-IIb while the paracellular pathway appears not to be affected. Intestinal absorption of phosphate proceeds via an active/transcellular route mostly mediated by NaPi-IIb/Slc34a2 and a poorly characterized passive/paracellular pathway. Intestinal phosphate absorption and expression of NaPi-IIb are stimulated by 1,25(OH)2 vitamin D3 but whether NaPi-IIb is the only target under hormonal control remains unknown. We report that administration of 1,25(OH)2 vitamin D3 to wild type mice results in the expected increase in active transport of phosphate in jejunum, without changing paracellular fluxes. Consequently, treatment failed to alter phosphate transport in intestinal-depleted Slc34a2 mice. In both genotypes, 1,25(OH)2 vitamin D3 induced similar hyperphosphaturic responses and changes in FGF23 and PTH. While urinary phosphate loss induced by administration of 1,25(OH)2 vitamin D3 did not alter plasma phosphate, further studies should investigate whether chronic administration would lead to phosphate imbalance in mice with reduced active intestinal absorption. This article is protected by copyright. All rights reserved.
-
Renal phosphate handling and inherited disorders of phosphate reabsorption: an update
Pediatric Nephrology, 2019Co-Authors: Carsten A Wagner, Isabel Rubio-aliaga, Nati HernandoAbstract:Renal phosphate handling critically determines plasma phosphate and whole body phosphate levels. Filtered phosphate is mostly reabsorbed by Na^+-dependent phosphate transporters located in the brush border membrane of the proximal tubule: NaPi-IIa (SLC34A1), NaPi-IIc (SLC34A3), and Pit-2 (SLC20A2). Here we review new evidence for the role and relevance of these transporters in inherited disorders of renal phosphate handling. The importance of NaPi-IIa and NaPi-IIc for renal phosphate reabsorption and mineral homeostasis has been highlighted by the identification of mutations in these transporters in a subset of patients with infantile idiopathic hypercalcemia and patients with hereditary hypophosphatemic rickets with hypercalciuria. Both diseases are characterized by disturbed calcium homeostasis secondary to elevated 1,25-(OH)_2 vitamin D_3 as a consequence of hypophosphatemia. In vitro analysis of mutated NaPi-IIa or NaPi-IIc transporters suggests defective trafficking underlying disease in most cases. Monoallelic pathogenic mutations in both SLC34A1 and SLC34A3 appear to be very frequent in the general population and have been associated with kidney stones. Consistent with these findings, results from genome-wide association studies indicate that variants in SLC34A1 are associated with a higher risk to develop kidney stones and chronic kidney disease, but underlying mechanisms have not been addressed to date.
-
Clinical aspects of the phosphate transporters NaPi-IIa and NaPi-IIb: mutations and disease associations
Pflügers Archiv: European Journal of Physiology, 2018Co-Authors: Eleanor D. Lederer, Carsten A WagnerAbstract:The Na-dependent phosphate transporter NaPi-IIa (SLC34A1) is mostly expressed in kidney, whereas NaPi-IIb (SLC34A2) has a wider tissue distribution with prominent expression in the lung and small intestine. NaPi-IIa is involved in renal reabsorption of inorganic phosphate (Pi) from urine, and patients with biallelic inactivating mutations in SLC34A1 develop hypophosphatemia, hypercalcemia, hypercalciuria and nephrocalcinosis, and nephrolithiasis in early childhood. Monoallelic mutations are frequent in the general population and may impact on the risk to develop kidney stones in adulthood. SNPs in close vicinity to the SLC34A1 locus associate with the risk to develop CKD. NaPi-IIb mediates high-affinity transport of Pi from the diet and appears to be mostly important during low Pi availability. Biallelic inactivating SLC34A2 mutations are found in patients with pulmonary alveolar microlithiasis, a lung disease characterized by the deposition of microcrystals. In contrast, no evidence for disturbed systemic Pi homeostasis has been reported in these patients to date. Nevertheless, NaPi-IIb-mediated intestinal Pi absorption may be a target for pharmaceutical interventions in patients with chronic kidney disease and Pi overload.
-
intestinal depletion of napi iib slc34a2 in mice renal and hormonal adaptation
Journal of Bone and Mineral Research, 2015Co-Authors: Nati Hernando, Komuraiah Myakala, Fabia Simona, Linto Thomas, Carsten A Wagner, Thomas Knopfel, Heini Murer, Jürg BiberAbstract:The Na(+) -dependent phosphate-cotransporter NaPi-IIb (SLC34A2) is widely expressed, with intestine, lung, and testis among the organs with highest levels of mRNA abundance. In mice, the intestinal expression of NaPi-IIb is restricted to the ileum, where the cotransporter localizes specifically at the brush border membrane (BBM) and mediates the active transport of inorganic phosphate (Pi). Constitutive full ablation of NaPi-IIb is embryonically lethal whereas the global but inducible removal of the transporter in young mice leads to intestinal loss of Pi and lung calcifications. Here we report the generation of a constitutive but intestinal-specific NaPi-IIb/Slc34a2-deficient mouse model. Constitutive intestinal ablation of NaPi-IIb results in viable pups with normal growth. Homozygous mice are characterized by fecal wasting of Pi and complete absence of Na/Pi cotransport activity in BBM vesicles (BBMVs) isolated from ileum. In contrast, the urinary excretion of Pi is reduced in these animals. The plasma levels of Pi are similar in wild-type and NaPi-IIb-deficient mice. In females, the reduced phosphaturia associates with higher expression of NaPi-IIa and higher Na/Pi cotransport activity in renal BBMVs, as well as with reduced plasma levels of intact FGF-23. A similar trend is found in males. Thus, NaPi-IIb is the only luminal Na(+) -dependent Pi transporter in the murine ileum and its absence is fully compensated for in adult females by a mechanism involving the bone-kidney axis. The contribution of this mechanism to the adaptive response is less apparent in adult males. © 2015 American Society for Bone and Mineral Research.
-
renal specific and inducible depletion of napi iic slc34a3 the cotransporter mutated in hhrh does not affect phosphate or calcium homeostasis in mice
American Journal of Physiology-renal Physiology, 2014Co-Authors: Komuraiah Myakala, Sarah E. Motta, Carsten A Wagner, Jürg Biber, Heini Murer, Robert Koesters, Nati HernandoAbstract:The proximal renal epithelia express three different Na-dependent inorganic phosphate (Pi) cotransporters: NaPi-IIa/SLC34A1, NaPi-IIc/SLC34A3, and PiT2/SLC20A2. Constitutive mouse knockout models of NaPi-IIa and NaPi-IIc suggested that NaPi-IIa mediates the bulk of renal reabsorption of Pi whereas the contribution of NaPi-IIc to this process is minor and probably restricted to young mice. However, many reports indicate that mutations of NaPi-IIc in humans lead to hereditary hypophosphatemic rickets with hypercalciuria (HHRH). Here, we report the generation of a kidney-specific and inducible NaPi-IIc-deficient mouse model based on the loxP-Cre system. We found that the specific removal of the cotransporter from the kidneys of young mice does not impair the capacity of the renal epithelia to transport Pi. Moreover, the levels of Pi in plasma and urine as well as the circulating levels of parathyroid hormone, FGF-23, and vitamin D3 remained unchanged. These findings are in agreement with the data obtained with the constitutive knockout model and suggest that, under steady-state conditions of normal dietary Pi, NaPi-IIc is not an essential Na-Pi cotransporter in murine kidneys. However, and unlike the constitutive mutants, the kidney-specific depletion of NaPi-IIc does not result in alteration of the homeostasis of calcium. This suggests that the calcium-related phenotype observed in constitutive knockout mice may not be related to inactivation of the cotransporter in kidney.
Jürg Biber - One of the best experts on this subject based on the ideXlab platform.
-
intestinal depletion of napi iib slc34a2 in mice renal and hormonal adaptation
Journal of Bone and Mineral Research, 2015Co-Authors: Nati Hernando, Komuraiah Myakala, Fabia Simona, Linto Thomas, Carsten A Wagner, Thomas Knopfel, Heini Murer, Jürg BiberAbstract:The Na(+) -dependent phosphate-cotransporter NaPi-IIb (SLC34A2) is widely expressed, with intestine, lung, and testis among the organs with highest levels of mRNA abundance. In mice, the intestinal expression of NaPi-IIb is restricted to the ileum, where the cotransporter localizes specifically at the brush border membrane (BBM) and mediates the active transport of inorganic phosphate (Pi). Constitutive full ablation of NaPi-IIb is embryonically lethal whereas the global but inducible removal of the transporter in young mice leads to intestinal loss of Pi and lung calcifications. Here we report the generation of a constitutive but intestinal-specific NaPi-IIb/Slc34a2-deficient mouse model. Constitutive intestinal ablation of NaPi-IIb results in viable pups with normal growth. Homozygous mice are characterized by fecal wasting of Pi and complete absence of Na/Pi cotransport activity in BBM vesicles (BBMVs) isolated from ileum. In contrast, the urinary excretion of Pi is reduced in these animals. The plasma levels of Pi are similar in wild-type and NaPi-IIb-deficient mice. In females, the reduced phosphaturia associates with higher expression of NaPi-IIa and higher Na/Pi cotransport activity in renal BBMVs, as well as with reduced plasma levels of intact FGF-23. A similar trend is found in males. Thus, NaPi-IIb is the only luminal Na(+) -dependent Pi transporter in the murine ileum and its absence is fully compensated for in adult females by a mechanism involving the bone-kidney axis. The contribution of this mechanism to the adaptive response is less apparent in adult males. © 2015 American Society for Bone and Mineral Research.
-
renal specific and inducible depletion of napi iic slc34a3 the cotransporter mutated in hhrh does not affect phosphate or calcium homeostasis in mice
American Journal of Physiology-renal Physiology, 2014Co-Authors: Komuraiah Myakala, Sarah E. Motta, Carsten A Wagner, Jürg Biber, Heini Murer, Robert Koesters, Nati HernandoAbstract:The proximal renal epithelia express three different Na-dependent inorganic phosphate (Pi) cotransporters: NaPi-IIa/SLC34A1, NaPi-IIc/SLC34A3, and PiT2/SLC20A2. Constitutive mouse knockout models of NaPi-IIa and NaPi-IIc suggested that NaPi-IIa mediates the bulk of renal reabsorption of Pi whereas the contribution of NaPi-IIc to this process is minor and probably restricted to young mice. However, many reports indicate that mutations of NaPi-IIc in humans lead to hereditary hypophosphatemic rickets with hypercalciuria (HHRH). Here, we report the generation of a kidney-specific and inducible NaPi-IIc-deficient mouse model based on the loxP-Cre system. We found that the specific removal of the cotransporter from the kidneys of young mice does not impair the capacity of the renal epithelia to transport Pi. Moreover, the levels of Pi in plasma and urine as well as the circulating levels of parathyroid hormone, FGF-23, and vitamin D3 remained unchanged. These findings are in agreement with the data obtained with the constitutive knockout model and suggest that, under steady-state conditions of normal dietary Pi, NaPi-IIc is not an essential Na-Pi cotransporter in murine kidneys. However, and unlike the constitutive mutants, the kidney-specific depletion of NaPi-IIc does not result in alteration of the homeostasis of calcium. This suggests that the calcium-related phenotype observed in constitutive knockout mice may not be related to inactivation of the cotransporter in kidney.
-
The SLC34 family of sodium-dependent phosphate transporters
Pflügers Archiv: European Journal of Physiology, 2013Co-Authors: Carsten A Wagner, Nati Hernando, Ian C. Forster, Jürg BiberAbstract:The SLC34 family of sodium-driven phosphate cotransporters comprises three members: NaPi-IIa (SLC34A1), NaPi-IIb (SLC34A2), and NaPi-IIc (SLC34A3). These transporters mediate the translocation of divalent inorganic phosphate (HPO4 2−) together with two (NaPi-IIc) or three sodium ions (NaPi-IIa and NaPi-IIb), respectively. Consequently, phosphate transport by NaPi-IIa and NaPi-IIb is electrogenic. NaPi-IIa and NaPi-IIc are predominantly expressed in the brush border membrane of the proximal tubule, whereas NaPi-IIb is found in many more organs including the small intestine, lung, liver, and testis. The abundance and activity of these transporters are mostly regulated by changes in their expression at the cell surface and are determined by interactions with proteins involved in scaffolding, trafficking, or intracellular signaling. All three transporters are highly regulated by factors including dietary phosphate status, hormones like parathyroid hormone, 1,25-OH2 vitamin D3 or FGF23, electrolyte, and acid–base status. The physiological relevance of the three members of the SLC34 family is underlined by rare Mendelian disorders causing phosphaturia, hypophosphatemia, or ectopic organ calcifications.
-
The phosphate transporter NaPi-IIa determines the rapid renal adaptation to dietary phosphate intake in mouse irrespective of persistently high FGF23 levels
Pflügers Archiv - European Journal of Physiology, 2013Co-Authors: Soline Bourgeois, Jürg Biber, Heini Murer, Gerti Stange, Paola Capuano, Reto Mühlemann, Carsten A WagnerAbstract:Renal reabsorption of inorganic phosphate (Pi) is mediated by the phosphate transporters NaPi-IIa, NaPi-IIc, and Pit-2 in the proximal tubule brush border membrane (BBM). Dietary Pi intake regulates these transporters; however, the contribution of the specific isoforms to the rapid and slow phase is not fully clarified. Moreover, the regulation of PTH and FGF23, two major phosphaturic hormones, during the adaptive phase has not been correlated. C57/BL6 and NaPi-IIa^−/− mice received 5 days either 1.2 % (HPD) or 0.1 % (LPD) Pi-containing diets. Thereafter, some mice were acutely switched to LPD or HPD. Plasma Pi concentrations were similar under chronic diets, but lower when mice were acutely switched to LPD. Urinary Pi excretion was similar in C57/BL6 and NaPi-IIa^−/− mice under HPD. During chronic LPD, NaPi-IIa^−/− mice lost phosphate in urine compensated by higher intestinal Pi absorption. During the acute HPD-to-LPD switch, NaPi-IIa^−/− mice exhibited a delayed decrease in urinary Pi excretion. PTH was acutely regulated by low dietary Pi intake. FGF23 did not respond to low Pi intake within 8 h whereas the phospho-adaptator protein FRS2 α necessary for FGF-receptor cell signaling was downregulated. BBM Pi transport activity and NaPi-IIa but not NaPi-IIc and Pit-2 abundance acutely adapted to diets in C57/BL6 mice. In NaPi-IIa^−/−, Pi transport activity was low and did not adapt. Thus, NaPi-IIa mediates the fast adaptation to Pi intake and is upregulated during the adaptation to low Pi despite persistently high FGF23 levels. The sensitivity to FGF23 may be regulated by adapting FRS2α abundance and phosphorylation.
-
Acute parathyroid hormone differentially regulates renal brush border membrane phosphate cotransporters
Pflügers Archiv - European Journal of Physiology, 2010Co-Authors: Nicolas Picard, Jürg Biber, Heini Murer, Brigitte Kaissling, Gerti Stange, Paola Capuano, Marija Mihailova, Carsten A WagnerAbstract:Renal phosphate reabsorption across the brush border membrane (BBM) in the proximal tubule is mediated by at least three transporters, NaPi-IIa (SLC34A1), NaPi-IIc (SLC34A3), and Pit-2 (SLC20A2). Parathyroid hormone (PTH) is a potent phosphaturic factor exerting an acute and chronic reduction in proximal tubule phosphate reabsorption. PTH acutely induces NaPi-IIa internalization from the BBM and lysosomal degradation, but its effects on NaPi-IIc and Pit-2 are unknown. In rats adapted to low phosphate diet, acute (30 and 60 min) application of PTH decreased BBM phosphate transport rates both in the absence and the presence of phosphonoformic acid, an inhibitor of SLC34 but not SLC20 transporters. Immunohistochemistry showed NaPi-IIa expression in the S1 to the S3 segment of superficial and juxtamedullary nephrons; NaPi-IIc was only detectable in S1 segments and Pit-2 in S1 and weakly in S2 segments of superficial and juxtamedullary nephrons. PTH reduced NaPi-IIa staining in the BBM with increased intracellular and lysosomal appearance. NaPi-IIa internalization was most prominent in S1 segments of superficial nephrons. We did not detect changes in NaPi-IIc and Pit-2 staining over this time period. Blockade of lysosomal protein degradation with leupeptin revealed NaPi-IIa accumulation in lysosomes, but no lysosomal staining for NaPi-IIc or Pit-2 could be detected. Immunoblotting of BBM confirmed the reduction in NaPi-IIa abundance and the absence of any effect on NaPi-IIc expression. Pit-2 protein abundance was also significantly reduced by PTH. Thus, function and expression of BBM phosphate cotransporters are differentially regulated allowing for fine-tuning of renal phosphate reabsorption.
Heini Murer - One of the best experts on this subject based on the ideXlab platform.
-
intestinal depletion of napi iib slc34a2 in mice renal and hormonal adaptation
Journal of Bone and Mineral Research, 2015Co-Authors: Nati Hernando, Komuraiah Myakala, Fabia Simona, Linto Thomas, Carsten A Wagner, Thomas Knopfel, Heini Murer, Jürg BiberAbstract:The Na(+) -dependent phosphate-cotransporter NaPi-IIb (SLC34A2) is widely expressed, with intestine, lung, and testis among the organs with highest levels of mRNA abundance. In mice, the intestinal expression of NaPi-IIb is restricted to the ileum, where the cotransporter localizes specifically at the brush border membrane (BBM) and mediates the active transport of inorganic phosphate (Pi). Constitutive full ablation of NaPi-IIb is embryonically lethal whereas the global but inducible removal of the transporter in young mice leads to intestinal loss of Pi and lung calcifications. Here we report the generation of a constitutive but intestinal-specific NaPi-IIb/Slc34a2-deficient mouse model. Constitutive intestinal ablation of NaPi-IIb results in viable pups with normal growth. Homozygous mice are characterized by fecal wasting of Pi and complete absence of Na/Pi cotransport activity in BBM vesicles (BBMVs) isolated from ileum. In contrast, the urinary excretion of Pi is reduced in these animals. The plasma levels of Pi are similar in wild-type and NaPi-IIb-deficient mice. In females, the reduced phosphaturia associates with higher expression of NaPi-IIa and higher Na/Pi cotransport activity in renal BBMVs, as well as with reduced plasma levels of intact FGF-23. A similar trend is found in males. Thus, NaPi-IIb is the only luminal Na(+) -dependent Pi transporter in the murine ileum and its absence is fully compensated for in adult females by a mechanism involving the bone-kidney axis. The contribution of this mechanism to the adaptive response is less apparent in adult males. © 2015 American Society for Bone and Mineral Research.
-
renal specific and inducible depletion of napi iic slc34a3 the cotransporter mutated in hhrh does not affect phosphate or calcium homeostasis in mice
American Journal of Physiology-renal Physiology, 2014Co-Authors: Komuraiah Myakala, Sarah E. Motta, Carsten A Wagner, Jürg Biber, Heini Murer, Robert Koesters, Nati HernandoAbstract:The proximal renal epithelia express three different Na-dependent inorganic phosphate (Pi) cotransporters: NaPi-IIa/SLC34A1, NaPi-IIc/SLC34A3, and PiT2/SLC20A2. Constitutive mouse knockout models of NaPi-IIa and NaPi-IIc suggested that NaPi-IIa mediates the bulk of renal reabsorption of Pi whereas the contribution of NaPi-IIc to this process is minor and probably restricted to young mice. However, many reports indicate that mutations of NaPi-IIc in humans lead to hereditary hypophosphatemic rickets with hypercalciuria (HHRH). Here, we report the generation of a kidney-specific and inducible NaPi-IIc-deficient mouse model based on the loxP-Cre system. We found that the specific removal of the cotransporter from the kidneys of young mice does not impair the capacity of the renal epithelia to transport Pi. Moreover, the levels of Pi in plasma and urine as well as the circulating levels of parathyroid hormone, FGF-23, and vitamin D3 remained unchanged. These findings are in agreement with the data obtained with the constitutive knockout model and suggest that, under steady-state conditions of normal dietary Pi, NaPi-IIc is not an essential Na-Pi cotransporter in murine kidneys. However, and unlike the constitutive mutants, the kidney-specific depletion of NaPi-IIc does not result in alteration of the homeostasis of calcium. This suggests that the calcium-related phenotype observed in constitutive knockout mice may not be related to inactivation of the cotransporter in kidney.
-
The phosphate transporter NaPi-IIa determines the rapid renal adaptation to dietary phosphate intake in mouse irrespective of persistently high FGF23 levels
Pflügers Archiv - European Journal of Physiology, 2013Co-Authors: Soline Bourgeois, Jürg Biber, Heini Murer, Gerti Stange, Paola Capuano, Reto Mühlemann, Carsten A WagnerAbstract:Renal reabsorption of inorganic phosphate (Pi) is mediated by the phosphate transporters NaPi-IIa, NaPi-IIc, and Pit-2 in the proximal tubule brush border membrane (BBM). Dietary Pi intake regulates these transporters; however, the contribution of the specific isoforms to the rapid and slow phase is not fully clarified. Moreover, the regulation of PTH and FGF23, two major phosphaturic hormones, during the adaptive phase has not been correlated. C57/BL6 and NaPi-IIa^−/− mice received 5 days either 1.2 % (HPD) or 0.1 % (LPD) Pi-containing diets. Thereafter, some mice were acutely switched to LPD or HPD. Plasma Pi concentrations were similar under chronic diets, but lower when mice were acutely switched to LPD. Urinary Pi excretion was similar in C57/BL6 and NaPi-IIa^−/− mice under HPD. During chronic LPD, NaPi-IIa^−/− mice lost phosphate in urine compensated by higher intestinal Pi absorption. During the acute HPD-to-LPD switch, NaPi-IIa^−/− mice exhibited a delayed decrease in urinary Pi excretion. PTH was acutely regulated by low dietary Pi intake. FGF23 did not respond to low Pi intake within 8 h whereas the phospho-adaptator protein FRS2 α necessary for FGF-receptor cell signaling was downregulated. BBM Pi transport activity and NaPi-IIa but not NaPi-IIc and Pit-2 abundance acutely adapted to diets in C57/BL6 mice. In NaPi-IIa^−/−, Pi transport activity was low and did not adapt. Thus, NaPi-IIa mediates the fast adaptation to Pi intake and is upregulated during the adaptation to low Pi despite persistently high FGF23 levels. The sensitivity to FGF23 may be regulated by adapting FRS2α abundance and phosphorylation.
-
Acute parathyroid hormone differentially regulates renal brush border membrane phosphate cotransporters
Pflügers Archiv - European Journal of Physiology, 2010Co-Authors: Nicolas Picard, Jürg Biber, Heini Murer, Brigitte Kaissling, Gerti Stange, Paola Capuano, Marija Mihailova, Carsten A WagnerAbstract:Renal phosphate reabsorption across the brush border membrane (BBM) in the proximal tubule is mediated by at least three transporters, NaPi-IIa (SLC34A1), NaPi-IIc (SLC34A3), and Pit-2 (SLC20A2). Parathyroid hormone (PTH) is a potent phosphaturic factor exerting an acute and chronic reduction in proximal tubule phosphate reabsorption. PTH acutely induces NaPi-IIa internalization from the BBM and lysosomal degradation, but its effects on NaPi-IIc and Pit-2 are unknown. In rats adapted to low phosphate diet, acute (30 and 60 min) application of PTH decreased BBM phosphate transport rates both in the absence and the presence of phosphonoformic acid, an inhibitor of SLC34 but not SLC20 transporters. Immunohistochemistry showed NaPi-IIa expression in the S1 to the S3 segment of superficial and juxtamedullary nephrons; NaPi-IIc was only detectable in S1 segments and Pit-2 in S1 and weakly in S2 segments of superficial and juxtamedullary nephrons. PTH reduced NaPi-IIa staining in the BBM with increased intracellular and lysosomal appearance. NaPi-IIa internalization was most prominent in S1 segments of superficial nephrons. We did not detect changes in NaPi-IIc and Pit-2 staining over this time period. Blockade of lysosomal protein degradation with leupeptin revealed NaPi-IIa accumulation in lysosomes, but no lysosomal staining for NaPi-IIc or Pit-2 could be detected. Immunoblotting of BBM confirmed the reduction in NaPi-IIa abundance and the absence of any effect on NaPi-IIc expression. Pit-2 protein abundance was also significantly reduced by PTH. Thus, function and expression of BBM phosphate cotransporters are differentially regulated allowing for fine-tuning of renal phosphate reabsorption.
-
the na pi cotransporter pit 2 slc20a2 is expressed in the apical membrane of rat renal proximal tubules and regulated by dietary pi
American Journal of Physiology-renal Physiology, 2009Co-Authors: Ricardo Villabellosta, Jürg Biber, Moshe Levi, Heini Murer, Gerti Stange, Victor Sorribas, Silvia Ravera, Ian C. ForsterAbstract:The principal mediators of renal phosphate (Pi) reabsorption are the SLC34 family proteins NaPi-IIa and NaPi-IIc, localized to the proximal tubule (PT) apical membrane. Their abundance is regulated...
Nati Hernando - One of the best experts on this subject based on the ideXlab platform.
-
1 25 oh 2 vitamin d3 stimulates active phosphate transport but not paracellular phosphate absorption in mouse intestine
The Journal of Physiology, 2020Co-Authors: Nati Hernando, Thomas Knopfel, Eva Maria Pastorarroyo, J Marks, Udo Schnitzbauer, Matthias Burki, Carla Bettoni, Carsten A WagnerAbstract:Intestinal absorption of phosphate is stimulated by 1,25(OH)2 vitamin D3. At least two distinct mechanisms underlie phosphate absorption in the gut, an active transcellular transport requiring the Na+ /phosphate cotransporter NaPi-IIb/Slc34a2, and a poorly characterized paracellular passive pathway. 1,25(OH)2 vitamin D3 stimulates NaPi-IIb expression and function and loss of NaPi-IIb reduces intestinal phosphate absorption. However, it is remains unknown whether NaPi-IIb is the only target for hormonal regulation by 1,25(OH)2 vitamin D3 . Here we compared the effects of intraperitoneal administration of 1,25(OH)2 vitamin D3 (2 days, once per day) in wild type and intestinal-specific Slc34a2 deficient mice, and analyzed trans- vs paracellular routes of phosphate absorption. We found that treatment stimulated active transport of phosphate only in jejunum of wild type mice, though NaPi-IIb protein expression was upregulated in jejunum and ileum . In contrast, 1,25(OH)2 vitamin D3 administration had no effect in Slc34a2 deficient mice, suggesting that the hormone specifically regulates NaPi-IIb expression. In both groups, 1,25(OH)2 vitamin D3 elicited the expected increase of plasma FGF23 and reduction of PTH. Treatment resulted in hyperphosphaturia (and hypercalciuria) in both genotypes, though mice remained normophosphatemic. While increased intestinal absorption and higher FGF23 can trigger the hyperphosphaturic response in wild types, only the second one can explain the renal response in Slc34a2 deficient mice. Thus, 1,25(OH)2 vitamin D3 stimulates intestinal phosphate absorption by acting on the active transcellular pathway mostly mediated by NaPi-IIb while the paracellular pathway appears not to be affected. Intestinal absorption of phosphate proceeds via an active/transcellular route mostly mediated by NaPi-IIb/Slc34a2 and a poorly characterized passive/paracellular pathway. Intestinal phosphate absorption and expression of NaPi-IIb are stimulated by 1,25(OH)2 vitamin D3 but whether NaPi-IIb is the only target under hormonal control remains unknown. We report that administration of 1,25(OH)2 vitamin D3 to wild type mice results in the expected increase in active transport of phosphate in jejunum, without changing paracellular fluxes. Consequently, treatment failed to alter phosphate transport in intestinal-depleted Slc34a2 mice. In both genotypes, 1,25(OH)2 vitamin D3 induced similar hyperphosphaturic responses and changes in FGF23 and PTH. While urinary phosphate loss induced by administration of 1,25(OH)2 vitamin D3 did not alter plasma phosphate, further studies should investigate whether chronic administration would lead to phosphate imbalance in mice with reduced active intestinal absorption. This article is protected by copyright. All rights reserved.
-
Renal phosphate handling and inherited disorders of phosphate reabsorption: an update
Pediatric Nephrology, 2019Co-Authors: Carsten A Wagner, Isabel Rubio-aliaga, Nati HernandoAbstract:Renal phosphate handling critically determines plasma phosphate and whole body phosphate levels. Filtered phosphate is mostly reabsorbed by Na^+-dependent phosphate transporters located in the brush border membrane of the proximal tubule: NaPi-IIa (SLC34A1), NaPi-IIc (SLC34A3), and Pit-2 (SLC20A2). Here we review new evidence for the role and relevance of these transporters in inherited disorders of renal phosphate handling. The importance of NaPi-IIa and NaPi-IIc for renal phosphate reabsorption and mineral homeostasis has been highlighted by the identification of mutations in these transporters in a subset of patients with infantile idiopathic hypercalcemia and patients with hereditary hypophosphatemic rickets with hypercalciuria. Both diseases are characterized by disturbed calcium homeostasis secondary to elevated 1,25-(OH)_2 vitamin D_3 as a consequence of hypophosphatemia. In vitro analysis of mutated NaPi-IIa or NaPi-IIc transporters suggests defective trafficking underlying disease in most cases. Monoallelic pathogenic mutations in both SLC34A1 and SLC34A3 appear to be very frequent in the general population and have been associated with kidney stones. Consistent with these findings, results from genome-wide association studies indicate that variants in SLC34A1 are associated with a higher risk to develop kidney stones and chronic kidney disease, but underlying mechanisms have not been addressed to date.
-
intestinal depletion of napi iib slc34a2 in mice renal and hormonal adaptation
Journal of Bone and Mineral Research, 2015Co-Authors: Nati Hernando, Komuraiah Myakala, Fabia Simona, Linto Thomas, Carsten A Wagner, Thomas Knopfel, Heini Murer, Jürg BiberAbstract:The Na(+) -dependent phosphate-cotransporter NaPi-IIb (SLC34A2) is widely expressed, with intestine, lung, and testis among the organs with highest levels of mRNA abundance. In mice, the intestinal expression of NaPi-IIb is restricted to the ileum, where the cotransporter localizes specifically at the brush border membrane (BBM) and mediates the active transport of inorganic phosphate (Pi). Constitutive full ablation of NaPi-IIb is embryonically lethal whereas the global but inducible removal of the transporter in young mice leads to intestinal loss of Pi and lung calcifications. Here we report the generation of a constitutive but intestinal-specific NaPi-IIb/Slc34a2-deficient mouse model. Constitutive intestinal ablation of NaPi-IIb results in viable pups with normal growth. Homozygous mice are characterized by fecal wasting of Pi and complete absence of Na/Pi cotransport activity in BBM vesicles (BBMVs) isolated from ileum. In contrast, the urinary excretion of Pi is reduced in these animals. The plasma levels of Pi are similar in wild-type and NaPi-IIb-deficient mice. In females, the reduced phosphaturia associates with higher expression of NaPi-IIa and higher Na/Pi cotransport activity in renal BBMVs, as well as with reduced plasma levels of intact FGF-23. A similar trend is found in males. Thus, NaPi-IIb is the only luminal Na(+) -dependent Pi transporter in the murine ileum and its absence is fully compensated for in adult females by a mechanism involving the bone-kidney axis. The contribution of this mechanism to the adaptive response is less apparent in adult males. © 2015 American Society for Bone and Mineral Research.
-
renal specific and inducible depletion of napi iic slc34a3 the cotransporter mutated in hhrh does not affect phosphate or calcium homeostasis in mice
American Journal of Physiology-renal Physiology, 2014Co-Authors: Komuraiah Myakala, Sarah E. Motta, Carsten A Wagner, Jürg Biber, Heini Murer, Robert Koesters, Nati HernandoAbstract:The proximal renal epithelia express three different Na-dependent inorganic phosphate (Pi) cotransporters: NaPi-IIa/SLC34A1, NaPi-IIc/SLC34A3, and PiT2/SLC20A2. Constitutive mouse knockout models of NaPi-IIa and NaPi-IIc suggested that NaPi-IIa mediates the bulk of renal reabsorption of Pi whereas the contribution of NaPi-IIc to this process is minor and probably restricted to young mice. However, many reports indicate that mutations of NaPi-IIc in humans lead to hereditary hypophosphatemic rickets with hypercalciuria (HHRH). Here, we report the generation of a kidney-specific and inducible NaPi-IIc-deficient mouse model based on the loxP-Cre system. We found that the specific removal of the cotransporter from the kidneys of young mice does not impair the capacity of the renal epithelia to transport Pi. Moreover, the levels of Pi in plasma and urine as well as the circulating levels of parathyroid hormone, FGF-23, and vitamin D3 remained unchanged. These findings are in agreement with the data obtained with the constitutive knockout model and suggest that, under steady-state conditions of normal dietary Pi, NaPi-IIc is not an essential Na-Pi cotransporter in murine kidneys. However, and unlike the constitutive mutants, the kidney-specific depletion of NaPi-IIc does not result in alteration of the homeostasis of calcium. This suggests that the calcium-related phenotype observed in constitutive knockout mice may not be related to inactivation of the cotransporter in kidney.
-
The SLC34 family of sodium-dependent phosphate transporters
Pflügers Archiv: European Journal of Physiology, 2013Co-Authors: Carsten A Wagner, Nati Hernando, Ian C. Forster, Jürg BiberAbstract:The SLC34 family of sodium-driven phosphate cotransporters comprises three members: NaPi-IIa (SLC34A1), NaPi-IIb (SLC34A2), and NaPi-IIc (SLC34A3). These transporters mediate the translocation of divalent inorganic phosphate (HPO4 2−) together with two (NaPi-IIc) or three sodium ions (NaPi-IIa and NaPi-IIb), respectively. Consequently, phosphate transport by NaPi-IIa and NaPi-IIb is electrogenic. NaPi-IIa and NaPi-IIc are predominantly expressed in the brush border membrane of the proximal tubule, whereas NaPi-IIb is found in many more organs including the small intestine, lung, liver, and testis. The abundance and activity of these transporters are mostly regulated by changes in their expression at the cell surface and are determined by interactions with proteins involved in scaffolding, trafficking, or intracellular signaling. All three transporters are highly regulated by factors including dietary phosphate status, hormones like parathyroid hormone, 1,25-OH2 vitamin D3 or FGF23, electrolyte, and acid–base status. The physiological relevance of the three members of the SLC34 family is underlined by rare Mendelian disorders causing phosphaturia, hypophosphatemia, or ectopic organ calcifications.
Ian C. Forster - One of the best experts on this subject based on the ideXlab platform.
-
The SLC34 family of sodium-dependent phosphate transporters
Pflügers Archiv: European Journal of Physiology, 2013Co-Authors: Carsten A Wagner, Nati Hernando, Ian C. Forster, Jürg BiberAbstract:The SLC34 family of sodium-driven phosphate cotransporters comprises three members: NaPi-IIa (SLC34A1), NaPi-IIb (SLC34A2), and NaPi-IIc (SLC34A3). These transporters mediate the translocation of divalent inorganic phosphate (HPO4 2−) together with two (NaPi-IIc) or three sodium ions (NaPi-IIa and NaPi-IIb), respectively. Consequently, phosphate transport by NaPi-IIa and NaPi-IIb is electrogenic. NaPi-IIa and NaPi-IIc are predominantly expressed in the brush border membrane of the proximal tubule, whereas NaPi-IIb is found in many more organs including the small intestine, lung, liver, and testis. The abundance and activity of these transporters are mostly regulated by changes in their expression at the cell surface and are determined by interactions with proteins involved in scaffolding, trafficking, or intracellular signaling. All three transporters are highly regulated by factors including dietary phosphate status, hormones like parathyroid hormone, 1,25-OH2 vitamin D3 or FGF23, electrolyte, and acid–base status. The physiological relevance of the three members of the SLC34 family is underlined by rare Mendelian disorders causing phosphaturia, hypophosphatemia, or ectopic organ calcifications.
-
Conferring electrogenicity to the electroneutral phosphate cotransporter NaPi-IIc (SLC34A3) reveals an internal cation release step
Pflügers Archiv - European Journal of Physiology, 2013Co-Authors: Monica Patti, Chiara Ghezzi, Ian C. ForsterAbstract:The SLC34 family of Na^+-dependent inorganic phosphate cotransporters comprises two electrogenic isoforms (NaPi-IIa, NaPi-IIb) and an electroneutral isoform (NaPi-IIc). Both fulfill essential physiological roles in mammalian phosphate homeostasis. By substitution of three conserved amino acids, found in all electrogenic isoforms, at corresponding sites in NaPi-IIc, electrogenicity was re-established and the Na^+/ P _ i stoichiometry increased from 2:1 to 3:1. However, this engineered electrogenic construct (AAD-IIc) had a reduced apparent P _ i affinity and different presteady-state kinetics from the wild-type NaPi-IIa/b. We investigated AAD-IIc using electrophysiology and voltage clamp fluorometry to elucidate the compromised behavior. The activation energy for cotransport was threefold higher than for NaPi-IIc and 1.5-fold higher than for NaPi-IIa and the temperature dependence of presteady-state charge displacements suggested that the large activation energy was associated with the empty carrier reorientation. AAD-IIc shows a weak interaction of external Na^+ ions with the electric field, and thus retains the electroneutral cooperative interaction of two Na^+ ions preceding external P _ i binding of NaPi-IIc. Most of the presteady-state charge movement was accounted for by the empty carrier (in the absence of external P _ i ), and the cytosolic release of one Na^+ ion (in the presence of P _ i ). Simulations using a kinetic model recapitulated the presteady-state and steady-state behavior and allowed identification of two critical partial reactions: the final release of Na^+ to the cytosol and external P _ i binding. Fluorometric recordings from AAD-IIc mutants with Cys substituted at functionally important sites established that AAD-IIc undergoes substrate- and voltage-dependent conformational changes that correlated qualitatively with its presteady-state kinetics.
-
the na pi cotransporter pit 2 slc20a2 is expressed in the apical membrane of rat renal proximal tubules and regulated by dietary pi
American Journal of Physiology-renal Physiology, 2009Co-Authors: Ricardo Villabellosta, Jürg Biber, Moshe Levi, Heini Murer, Gerti Stange, Victor Sorribas, Silvia Ravera, Ian C. ForsterAbstract:The principal mediators of renal phosphate (Pi) reabsorption are the SLC34 family proteins NaPi-IIa and NaPi-IIc, localized to the proximal tubule (PT) apical membrane. Their abundance is regulated...
-
Electrogenic Kinetics of a Mammalian Intestinal Type IIb Na^+/P_i Cotransporter
The Journal of Membrane Biology, 2006Co-Authors: Ian C. Forster, Leila V Virkki, Heini Murer, Elena Bossi, Jürg BiberAbstract:The kinetics of a type IIb Na^+-coupled inorganic phosphate (P_i) cotransporter (NaPi-IIb) cloned from mouse small intestine were studied using the two-electrode voltage clamp applied to Xenopus oocytes. In the steady state, mouse NaPi-IIb showed a curvilinear I-V relationship, with rate-limiting behavior only for depolarizing potentials. The P_i dose dependence was Michaelian, with an apparent affinity constant for P_i ( $ {K_{\rm m}}^{\rm P_i} $ ) of 10 ± 1 μ M at −60 m V . Unlike for rat NaPi-IIa, $ {K_{\rm m}}^{\rm P_i} $ increased with membrane hyperpolarization, as reported for human NaPi-IIa, flounder NaPi-IIb and zebrafish NaPi-IIb2. The apparent affinity constant for Na^+ ( $ {K_{\rm m}}^{\rm Na} $ ) was 23 ± 1 m M at −60 m V , and the Na^+ activation was cooperative with a Hill coefficient of approximately 2. Pre-steady-state currents were documented in the absence of P_i and showed a strong dependence on external Na^+. The hyperpolarizing shift of the charge distribution midpoint potential was 65 m V /log[Na]. Approximately half the moveable charge was attributable to the empty carrier. A comparison of the voltage dependence of steady-state P_i-induced current and pre-steady-state charge movement indicated that for −120 m V ≤ V ≤ 0 m V the voltage dependence of the empty carrier was the main determinant of the curvilinear steady-state cotransport characteristic. External protons partially inhibited NaPi-IIb steady-state activity, independent of the titration of mono- and divalent P_i, and immobilized pre-steady-state charge movements associated with the first Na^+ binding step.
-
renouncing electroneutrality is not free of charge switching on electrogenicity in a na coupled phosphate cotransporter
Proceedings of the National Academy of Sciences of the United States of America, 2005Co-Authors: Andrea Bacconi, Leila V Virkki, Jürg Biber, Heini Murer, Ian C. ForsterAbstract:Renal type IIa Na+-coupled inorganic phosphate (Pi) cotransporters (NaPi-IIa) mediate divalent Pi transport in an electrogenic manner, whereas the renal type IIc isoform (NaPi-IIc) is electroneutral, yet it shows high sequence identity with NaPi-IIa. Dual uptake (32Pi/22Na) assays confirmed that NaPi-IIc displayed Na+-coupled Pi cotransport with a 2:1 (Na+:Pi) stoichiometry compared with 3:1 established for NaPi-IIa. This finding suggested that the electrogenicity of NaPi-IIa arises from the interaction of an additional Na+ ion compared with NaPi-IIc. To identify the molecular elements responsible for the functional difference between isoforms, we used chimera and amino acid replacement approaches. Transport activity of chimeras constructed with NaPi-IIa and NaPi-IIc indicated that residues within the first six transmembrane domains were essential for the electrogenicity of NaPi-IIa. Sequence comparison between electrogenic and electroneutral isoforms revealed differences in the charge and polarity of residues clustered in three areas, one of which included part of the predicted third transmembrane domain. Here, substitution of three residues with their NaPi-IIa equivalents in NaPi-IIc (S189A, S191A, and G195D) resulted in a transporter that displayed a 1:1 charge/Pi coupling, a 3:1 Na+:Pi stoichiometry, and transient currents that resembled pre-steady-state relaxations. The mutant's weaker voltage dependency and 10-fold lower apparent Pi affinity compared with NaPi-IIa indicated that other residues important for the NaPi-IIa kinetic fingerprint exist. Our findings demonstrate that, through a minimal number of side chain substitutions, we can effect a switch from electroneutral to electrogenic cotransporter function, concomitant with the appearance of a cosubstrate interaction site.
