Identification of the type II Na+-Pi cotransporter (Npt2) in the osteoclast and the skeletal phenotype of Npt2−/− mice

Gupta, Arun; Tenenhouse, Harriet S.; Hoag, H; Wang, D; Khadeer, Mohammed; Namba, Noriyuki; Xu, Feng; Hruska, Keith A.

doi:10.1016/s8756-3282(01)00601-9

Cited by 63 publications

(73 citation statements)

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“…These biochemical features are typical of patients with hereditary hypophosphatemic rickets with hypercalciuria (HHRH), a Mendelian disorder of renal P i reabsorption (6,30). However, in contrast to patients with HHRH, Npt2a Ϫ/Ϫ mice do not exhibit rickets and osteomalacia (2,7,28), and linkage analyses indicated that the Npt2a gene is not a candidate for HHRH patients (9,33).…”

Section: Additional Biochemical Findings In Npt2amentioning

confidence: 99%

Parathyroid hormone-dependent endocytosis of renal type IIc Na-P_icotransporter

Segawa¹,

Yamanaka²,

Onitsuka³

et al. 2007

American Journal of Physiology-Renal Physiology

128

105

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Hereditary hypophosphatemic rickets with hypercalciuria results from mutations of the renal type IIc Na-Pi cotransporter gene, suggesting that the type IIc transporter plays a prominent role in renal phosphate handling. The goal of the present study was to investigate the regulation of the type IIc Na-Pi cotransporter by parathyroid hormone (PTH). Type IIc Na-Pi cotransporter levels were markedly increased in thyroparathyroidectomized (TPTX) rats. Four hours after administration of PTH, type IIc transporter protein levels were markedly decreased in the apical membrane fraction but recovered to baseline levels at 24 h. Immunohistochemical analyses demonstrated the presence of the type IIc transporter in the apical membrane and subapical compartments in the proximal tubular cells in TPTX animals. After administration of PTH, the intensity of immunoreactive signals in apical and subapical type IIc transporter decreased in the renal proximal tubular cells in TPTX rats. Colchicine completely blocked the internalization of the type IIc transporter. In addition, leupeptin prevented the PTH-mediated degradation of the type IIa transporter in lysosomes but had no effect on PTH-mediated degradation of the lysosomal type IIc transporter. In PTH-treated TPTX rats, the internalization of the type IIc transporter occurred after administration of PTH(1-34) (PKA and PKC activator) or PTH(3-34) (PKC activator). Thus the present study demonstrated that PTH is a major hormonal regulator of the type IIc Na-Pi cotransporter in renal proximal tubules. phosphate transporter; proximal tubule; regulation INORGANIC PHOSPHATE (P i ) reabsorption in the renal proximal tubule is required for body P i homeostasis, and Na ϩ -dependent P i (Na-P i ) transporters in the brush-border membrane (BBM) of proximal tubular cells mediate the rate-limiting step in the overall P i -reabsorptive process (17, 19 -21). The type IIa and type IIc Na-P i cotransporters are expressed in the apical membrane of proximal tubular cells and mediate Na-P i cotransport, and the extent of P i reabsorption in the proximal tubules is determined largely by the abundance of the type IIa Na-P i cotransporter (17, 19 -21, 28). Indeed, Na-P i cotransporter type IIa-deficient mice (Npt2a Ϫ/Ϫ mice) exhibit increased urinary P i excretion, hypophosphatemia, and an appropriate adaptive increase in the circulating concentration of 1,25(OH) 2 D 3 (2, 28). Additional biochemical findings in Npt2aϪ/Ϫ mice include hypercalcemia, hypercalciuria, decreased serum parathyroid hormone (PTH) levels, and elevated serum alkaline phosphatase activity (2, 28). These biochemical features are typical of patients with hereditary hypophosphatemic rickets with hypercalciuria (HHRH), a Mendelian disorder of renal P i reabsorption (6, 30). However, in contrast to patients with HHRH, Npt2a Ϫ/Ϫ mice do not exhibit rickets and osteomalacia (2, 7, 28), and linkage analyses indicated that the Npt2a gene is not a candidate for HHRH patients (9, 33).More recently, two groups demonstrated that HHRH results f...

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Section: Additional Biochemical Findings In Npt2amentioning

confidence: 99%

Parathyroid hormone-dependent endocytosis of renal type IIc Na-P_icotransporter

Segawa¹,

Yamanaka²,

Onitsuka³

et al. 2007

American Journal of Physiology-Renal Physiology

128

105

View full text Add to dashboard Cite

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“…Conversely, the type II sodium phosphate cotransporter (Npt2a) knockout mice that exhibit hypophosphatemia, an appropriate elevation of 1,25(OH) 2 D, hypercalcemia, and hypoparathyroidism have not been reported to develop rickets (24,25). However, almost half of these mice die before weaning, and those that do survive maintain serum phosphate levels that are 65-80% of those of their wild-type littermates, whereas the mouse models in our studies had a 50% decrease in their serum phosphate levels.…”

Section: Discussionmentioning

confidence: 99%

Hypophosphatemia leads to rickets by impairing caspase-mediated apoptosis of hypertrophic chondrocytes

Sabbagh

Carpenter

Demay

2005

Proc. Natl. Acad. Sci. U.S.A.

231

171

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Rickets is seen in association with vitamin D deficiency and in several genetic disorders associated with abnormal mineral ion homeostasis. Studies in vitamin D receptor (VDR)-null mice have demonstrated that expansion of the late hypertrophic chondrocyte layer, characteristic of rickets, is secondary to impaired apoptosis of these cells. The observation that normalization of mineral ion homeostasis in the VDR-null mice prevents rachitic changes suggests that rickets is secondary to hypocalcemia, hypophosphatemia, or hyperparathyroidism, rather than impaired VDR action. To determine which of these abnormalities is responsible for impaired chondrocyte apoptosis and subsequent rachitic changes, two additional models were examined: diet-induced hypophosphatemia͞hypercalcemia and hypophosphatemia secondary to mutations in the Phex gene. The former model is associated with suppressed parathyroid hormone levels as a consequence of hypercalcemia. The latter model demonstrates normal calcium and parathyroid hormone levels, but 1,25-dihydroxyvitamin D levels that are inappropriately low for the degree of hypophosphatemia. Our studies demonstrate that normal phosphorus levels are required for growth plate maturation and implicate a critical role for phosphate-regulated apoptosis of hypertrophic chondrocytes via activation of the caspase-9-mediated mitochondrial pathway. (2). Rachitic growth plates also are associated with inherited mutations that impair the actions of the Phex gene (X-linked hypophosphatemic rickets) (3, 4) and the metabolism of FGF-23 (autosomal dominant hypophosphatemic rickets) (5). Both of these disorders are associated with reduced 25-hydroxyvitamin D 1-␣-hydroxylase activity, leading to a reduction in 1,25(OH) 2 D synthesis. It was, therefore, unclear whether the pathophysiologic abnormality leading to rachitic growth plates in the hereditary hypophosphatemias is similar to that underlying rickets due to VDR deficiency and whether these rachitic changes are a direct consequence of impaired 1,25(OH) 2 D action.Targeted ablation of the VDR in mice is a phenocopy of the human disease hereditary vitamin D resistant rickets (6). These mice are born metabolically normal, but as a consequence of impaired 1,25(OH) 2 D-dependent intestinal calcium absorption, they develop hypocalcemia and secondary hyperparathyroidism, the latter of which leads to an increase in urinary phosphate excretion resulting in hypophosphatemia. The VDR-null mice develop rickets and osteomalacia by the fourth week of life. Investigations addressing the cellular basis for these rachitic changes demonstrate that the growth-plate abnormality in the VDR-null mice is due to an expansion of the late hypertrophic chondrocyte layer, a consequence of impaired apoptosis of these cells. Chondrocyte proliferation and acquisition of markers of chondrocyte differentiation as proliferative chondrocytes mature are unaffected by VDR ablation, as is signaling for vascular invasion assessed by VEGF mRNA expression (7). Of note, prevention of abnormal ...

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“…For example, null-mutant Na-dependent phosphate co-transporter (NPT2−/−) mice are hypophosphatemic but do not have rickets or osteomalacia. Indeed these animals have an age-dependent overcompensation of the skeletal phenotype [5,13,33]. Also, these mice have a predisposition to develop massive renal stones [13].…”

Section: Discussionmentioning

confidence: 99%

Correction of the mineralization defect in hyp mice treated with protease inhibitors CA074 and pepstatin

Rowe

Matsumoto

et al. 2006

Bone

118

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Increased expression of several osteoblastic proteases and MEPE (a bone matrix protein) occurs in X-linked hypophosphatemic rickets (hyp). This is associated with an increased release of a protease-resistant MEPE peptide (ASARM peptide), a potent inhibitor of mineralization. Cathepsin B cleaves MEPE releasing ASARM peptide and hyp osteoblast/osteocyte cells hypersecrete cathepsin D, an activator of cathepsin B. Our aims were to determine whether cathepsin inhibitors correct the mineralization defect in vivo and whether hyp-bone ASARM peptide levels are reduced after protease treatment. Normal littermates and hyp mice (n = 6) were injected intraperitoneally once a day for 4 weeks with pepstatin, CAO74 or vehicle. Animals were then sacrificed and bones plus serum removed for comprehensive analysis. All hyp mice groups (treated and untreated) remained hypophosphatemic with serum 1,25 vitamin D3 inappropriately normal. Serum PTH was significantly elevated in all hyp mice groups relative to normal mice (P = 0.0017). Untreated hyp mice had six-fold elevated levels of serum alkaline-phosphatase and twofold elevated levels of ASARM peptides relative to normal mice (P < 0.001). In contrast, serum alkaline phosphatase and serum ASARM peptides were significantly reduced (normalized) in hyp mice treated with CA074 or pepstatin. Serum FGF23 levels remained high in all hyp animal groups (P < 0.0001). Hyp mice treated with protease inhibitors showed dramatic reductions in unmineralized osteoid (femurs) compared to control hyp mice (Goldner staining). Also, hyp animals treated with protease inhibitors showed marked and significant improvements in growth plate width (42%), osteoid thickness (40%) and cortical area (40%) (P < 0.002). The mineralization apposition rate, bone formation rate and mineralization surface were normalized by protease-treatment. High-resolution pQCT mineral histomorphometry measurements and uCT also confirmed a marked mineralization improvement. Finally, the growth plate and cortical bone of hyp femurs contained a massive accumulation of osteoblast-derived ASARM peptide(s) that was reduced in hyp animals treated with CA074 or pepstatin. This study confirms in vivo administration of cathepsin inhibitors improves bone mineralization in hyp mice. This may be due to a protease inhibitor mediated decrease in proteolytic degradation of the extracellular matrix and a reduced release of ASARM peptides (potent mineralization inhibitors).

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Identification of the type II Na+-Pi cotransporter (Npt2) in the osteoclast and the skeletal phenotype of Npt2−/− mice

Cited by 63 publications

References 50 publications

Parathyroid hormone-dependent endocytosis of renal type IIc Na-P_icotransporter

Parathyroid hormone-dependent endocytosis of renal type IIc Na-P_icotransporter

Hypophosphatemia leads to rickets by impairing caspase-mediated apoptosis of hypertrophic chondrocytes

Correction of the mineralization defect in hyp mice treated with protease inhibitors CA074 and pepstatin

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Identification of the type II Na+-Pi cotransporter (Npt2) in the osteoclast and the skeletal phenotype of Npt2−/− mice

Cited by 63 publications

References 50 publications

Parathyroid hormone-dependent endocytosis of renal type IIc Na-Picotransporter

Parathyroid hormone-dependent endocytosis of renal type IIc Na-Picotransporter

Hypophosphatemia leads to rickets by impairing caspase-mediated apoptosis of hypertrophic chondrocytes

Correction of the mineralization defect in hyp mice treated with protease inhibitors CA074 and pepstatin

Contact Info

Product

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Parathyroid hormone-dependent endocytosis of renal type IIc Na-P_icotransporter

Parathyroid hormone-dependent endocytosis of renal type IIc Na-P_icotransporter