| 1. |
- Björklund, Peyman, et al.
(författare)
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Type I membrane Klotho expression is decreased and inversely correlated to serum calcium in primary hyperparathyroidism
- 2008
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Ingår i: Journal of Clinical Endocrinology and Metabolism. - : The Endocrine Society. - 0021-972X .- 1945-7197. ; 93:10, s. 4152-4157
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Tidskriftsartikel (refereegranskat)abstract
- Context: The type I membrane protein Klotho was recently shownto mediate PTH secretion in parathyroid cells in response tolow extracellular calcium. In contrast, Klotho inhibits PTHsecretion indirectly through the action of fibroblast growthfactor-23. Abnormal Klotho expression in parathyroid disordersremains to be elucidated.Objective: The aim of the study was to determine: 1) Klothoexpression in parathyroid adenomas from patients with primaryhyperparathyroidism (pHPT) compared to normal tissue; and 2)its relation to the serum calcium and PTH levels.Design: Surgically removed parathyroid glands (n = 40) and fournormal parathyroid tissue specimens were analyzed for KlothomRNA and protein levels by quantitative real-time PCR and immunohistochemistry.In vitro effects of calcium on Klotho mRNA expression were studiedin bovine parathyroid cells.Results: Klotho mRNA levels were significantly decreased (n= 23) or undetectable (n = 17) in parathyroid adenomas comparedto normal tissues (P < 0.001). Reduced Klotho protein expressionwas confirmed by immunohistochemistry. Klotho mRNA levels wereinversely correlated to serum calcium (r = –0.97; P <0.0001), and calcium dose-dependently decreased Klotho mRNAexpression in normal parathyroid cells in vitro (P < 0.01).Serum calcium was the only significant marker of Klotho expressionin multivariate analysis with calcium, phosphate, PTH, and adenomaweight as independent variables.Conclusions: Parathyroid Klotho expression is decreased or undetectablein pHPT. We provide evidence that 1) serum calcium is stronglyassociated with parathyroid Klotho expression in pHPT; and 2)abnormal PTH secretion in hypercalcemic pHPT subjects is mediatedby Klotho-independent mechanisms.
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| 2. |
- Krajisnik, Tijana, 1981-
(författare)
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Fibroblast growth factor-23 and Klotho in bone/mineral and parathyroid disorders
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fibroblast growth factor-23 (FGF23) is a novel, bone-produced hormone that regulates renal phosphate (Pi) reabsorption and calcitriol metabolism. Disorders of mineral and bone metabolism, such as autosomal dominant hypophosphatemic rickets (ADHR) and hyperostosis-hyperphosphatemia syndrome (HHS), witness the importance of well-balanced serum levels of FGF23. Patients with chronic kidney disease (CKD) are highly morbid due to Pi retention/hyperphosphatemia and calcitriol deficiency, which lead to elevated serum levels of parathyroid hormone (PTH) and secondary hyperparathyroidism (sHPT). As a response to hyperphosphatemia, CKD patients have also remarkably high serum FGF23 levels, which are associated with cardiovascular risk factors and increased mortality in CKD. The overall aim of this dissertation was to discern a possible role of FGF23 in parathyroid biology. Our in vitro experiments on isolated bovine parathyroid cells demonstrate that FGF23 directly and dose-dependently suppresses the PTH production and secretion, while increasing the expression of the 25-hydroxyvitamin D3-activating enzyme 1α-hydroxylase. We investigated possible expressional changes in the FGF23 receptor co-factor Klotho in hyperparathyroid disorders and found that Klotho expression is decreased or absent and inversely correlated to serum calcium (Ca) in adenomas of primary HPT (pHPT). In the hyperplastic parathyroid glands of sHPT, Klotho expression declines in parallel with the kidney function and correlates with the glomerular filtration rate. Moreover, Klotho expression is suppressed by Ca and FGF23, increased by calcitriol, but unaffected by Pi and PTH in vitro. Finally, we identified a novel missense mutation in the gene encoding GALNT3, which is normally involved in the post-translational glycosylation of FGF23, as the cause of aberrant FGF23 processing in a patient with HHS. In summary, we provide evidence for a novel bone/parathyroid axis in which FGF23 functions as a direct, negative regulator of the PTH production. High extracellular Ca is a major determinant of the Klotho expression in pHPT, whereas the Klotho levels in sHPT may be attributed to a combination of the high FGF23 and Ca, and low calcitriol levels associated with CKD. Hence, the decreased Klotho expression in sHPT could explain the concomitantly high FGF23 and PTH levels, as well as the failure of FGF23 to prevent or mitigate the development of sHPT in CKD.
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| 3. |
- Krajisnik, Tijana, et al.
(författare)
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Fibroblast growth factor-23 regulates parathyroid hormone and 1alpha-hydroxylase expression in cultured bovine parathyroid cells
- 2007
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Ingår i: Journal of Endocrinology. - 0022-0795 .- 1479-6805. ; 195:1, s. 125-131
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Tidskriftsartikel (refereegranskat)abstract
- Fibroblast growth factor-23 (FGF23) is a circulating factor that decreases serum levels of inorganic phosphate (Pi) as well as 1,25-dihydroxyvitamin D(3). Recent studies also suggest a correlation between serum levels of FGF23 and parathyroid hormone (PTH) in patients with chronic kidney disease. It is, however, unknown whether FGF23 directly modulates PTH expression, or whether the correlation is secondary to abnormalities in Pi and vitamin D metabolism. The objective of the current study was therefore to elucidate possible direct effects of FGF23 on bovine parathyroid cells in vitro. Treatment of parathyroid cells with a stabilized form of recombinant FGF23 (FGF23(R176Q)) induced a rise in early response gene-1 mRNA transcripts, a marker of FGF23 signaling. FGF23(R176Q) potently and dose-dependently decreased the PTH mRNA level within 12 h. In agreement, FGF23(R176Q) also decreased PTH secretion into conditioned media. In contrast, FGF23(R176Q) dose-dependently increased 1alpha-hydroxylase expression within 3 h. FGF23 (R176Q) did not affect cell viability nor induce apoptosis, whereas a small but significant increase in cell proliferation was found. We conclude that FGF23 is a negative regulator of PTH mRNA expression and secretion in vitro. Our data suggest that FGF23 may be a physiologically relevant regulator of PTH. This defines a novel function of FGF23 in addition to the previously established roles in controlling vitamin D and Pi metabolism.
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| 4. |
- Krajisnik, Tijana, et al.
(författare)
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Parathyroid Klotho and FGF-receptor 1 expression decline with renal function in hyperparathyroid patients with chronic kidney disease and kidney transplant recipients
- 2010
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Ingår i: Kidney International. - : Elsevier BV. - 0085-2538 .- 1523-1755. ; 78:10, s. 1024-1032
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Tidskriftsartikel (refereegranskat)abstract
- Current studies suggest that short-term exposure of parathyroid glands to fibroblast growth factor 23 (FGF23) reduces parathyroid hormone secretion. However, patients with chronic kidney disease (CKD) develop secondary hyperparathyroidism despite high levels of serum FGF23, indicating a parathyroid FGF23 'resistance'. Here we analyzed the expression of the FGF23 receptors Klotho and FGF receptor 1 (FGFR1) in 88 hyperplastic parathyroid glands from 31 patients with CKD (including 21 renal allograft recipients), and their regulation in isolated bovine and human hyperplastic parathyroid cells. Glandular expression was variable, yet the Klotho and FGFR1 mRNA levels declined in parallel with the decreasing glomerular filtration rate, significantly decreasing over CKD stages. We found no association between the expression of Klotho, FGFR1, and the proliferation marker Ki67. In vitro treatment of bovine cells with FGF23 or calcium reduced the Klotho level, whereas active vitamin D-3 compounds increased its expression. Phosphate and parathyroid hormone had no effect. Treatment had less impact on Klotho in cultured human cells than in the bovine healthy cell model, whereas FGFR1 expression was induced in the hyperplastic cells. Thus parathyroid Klotho and FGFR1 decrease with declining renal function, possibly because of alterations in mineral metabolism related to the failing kidney. This could explain the observed parathyroid resistance to FGF23 in late CKD.
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| 5. |
- Krajisnik, Tijana, 1981-, et al.
(författare)
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Parathyroid Klotho Expression Declines with Renal Function in Hyperparathyroid CKD Patients
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Current data suggest that type I membrane-bound α-Klotho plays a dual role in the regulation of PTH secretion. While stimulating PTH release during hypocalcemia, Klotho inhibits PTH production by mediating the suppressive effect of fibroblast growth factor-23 (FGF23). In chronic kidney disease (CKD), secondary hyperparathyroidism (sHPT) often develops in the presence of high serum FGF23, indicating parathyroid resistance to FGF23 action. This could in part be due to reduced Klotho expression, as reported in kidneys of CKD patients. Herein, we analyzed parathyroid Klotho expression level in 31 patients with sHPT as well as regulation of Klotho in isolated bovine parathyroid cells using real-time PCR analysis and IHC staining. Klotho expression was variable in secondary hyperplastic glands, yet the mRNA levels correlated positively with glomerular filtration rate and significantly decreased over CKD stages. In vitro treatment with either FGF23 or calcium dose-dependently reduced the Klotho level, whereas vitamin D treatment increased its expression. This stimulatory effect was blunted in the presence of either high FGF23 or calcium. No effect on Klotho level was observed after treatment with phosphate or PTH. In summary, parathyroid Klotho expression was variable in sHPT but decreased with declining renal function. This may be due to a complex co-regulation by calcium, FGF23 and vitamin D, and explain the lack of suppressive effects of FGF23 on PTH secretion in late CKD.
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| 6. |
- Marsell, Richard, et al.
(författare)
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Fibroblast growth factor-23 is associated with parathyroid hormone and renal function in a population-based cohort of elderly men.
- 2008
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Ingår i: European journal of endocrinology / European Federation of Endocrine Societies. - 1479-683X .- 0804-4643. ; 158:1, s. 125-9
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Fibroblast growth factor-23 (FGF23) is a circulating factor involved in phosphate (Pi) and vitamin D metabolism. Serum FGF23 is increased at later stages of chronic kidney disease due to chronic hyperphosphatemia and decreased renal clearance. Recent studies also indicate that FGF23 may directly regulate the expression of parathyroid hormone (PTH) in vitro. Therefore, the objective of the current study was to determine the relationship between FGF23, PTH, and other biochemistries in vivo in subjects with no history of renal disease. DESIGN: Serum biochemistries were measured in a subsample of the population-based Swedish part of the MrOS study. In total, 1000 Caucasian men aged 70-80 years were randomly selected from the population. METHODS: Intact FGF23, Pi, calcium, albumin, estimated glomerular filtration rate (eGFR, calculated from cystatin C), PTH, and 25(OH)D3 were measured. Association studies were performed using linear univariate and multivariate regression analyses. RESULTS: The median FGF23 level was 36.6 pg/ml, ranging from 0.63 to 957 pg/ml. There was a significant correlation between log FGF23 and eGFR (r=-0.21; P<0.00001) and log PTH (r=0.13; P<0.001). These variables remained as independent predictors of FGF23 in multivariate analysis. In addition, log PTH (beta=0.082; P<0.05) and eGFR (beta=-0.090; P<0.05) were associated with log FGF23 in subjects with eGFR>60 ml/min. Only eGFR (beta=-0.35; P<0.0001) remained as a predictor of log FGF23 in subjects with eGFR<60 ml/min. CONCLUSIONS: Serum FGF23 and PTH are associated in vivo, supporting recent findings that FGF23 directly regulates PTH expression in vitro. Additionally, eGFR is associated with FGF23 in subjects with normal or mildly impaired renal function, indicating that GFR may modulate FGF23 levels independent of serum Pi.
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| 7. |
- Marsell, Richard, et al.
(författare)
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Gene expression analysis of kidneys from transgenic mice expressing fibroblast growth factor-23.
- 2008
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Ingår i: Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association. - : Oxford University Press (OUP). - 1460-2385 .- 0931-0509. ; 23:3, s. 827-33
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Fibroblast growth factor-23 (FGF23), a circulating protein produced in bone, causes decreased renal inorganic phosphate (Pi) reabsorption by reducing the expression of the sodium phosphate cotransporter type 2a (Npt2a). We have previously generated transgenic mice expressing human wild-type (WT) FGF23 under the control of the alpha1 (I) collagen promoter. METHODS: In this study, we performed a large-scale gene expression study of kidneys from FGF23 transgenic mice and WT littermates. Microarray expression data of key transcripts were verified by real-time RT-PCR analysis. RESULTS: Several genes that play a role in Pi regulation revealed decreased expression levels in the transgenic mice, such as Npt2a and Pdzk1, a scaffolding protein known to interact with Npt2a. Importantly, Klotho, a suggested FGF23 receptor cofactor, was the most significantly decreased transcript and alpha2-Na(+)/K(+)-ATPase (Atp1a2), a gene isoform of alpha1-Na(+)/K(+)-ATPase (Atp1a1) which has recently been shown to interact with Klotho and regulate calcium metabolism, was the most increased transcript. In contrast, other genes proposed to regulate Pi levels, such as secreted frizzled-related protein-4 (sFrp4) and Na(+)/H(+) exchanger regulatory factor-1 (Nherf1) revealed no changes. CONCLUSIONS: FGF23 transgenic mice display differentially expressed transcript levels of several genes essential in renal Pi regulation. These findings may lead to further understanding of how FGF23 mediates its actions on renal Pi regulation.
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| 8. |
- Olauson, Hannes, et al.
(författare)
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A novel missense mutation in GALNT3 causing hyperostosis-hyperphosphataemia syndrome
- 2008
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Ingår i: European Journal of Endocrinology. - Bristol : BioScientifica Ltd. - 0804-4643 .- 1479-683X. ; 158:6, s. 929-934
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Hyperostosis–hyperphosphataemia syndrome (HHS) is a rare hereditary disorder characterized by hyperphosphataemia, inappropriately normal or elevated 1,25-dihydroxyvitamin D3 and localized painful cortical hyperostosis. HHS was shown to be caused by inactivating mutations in GALNT3, encoding UDP-N-acetyl-a-D-galactosamine: polypeptide N-acetylgalactosaminyltransferase 3 (GalNAc-transferase; GALNT3). Herein,we sought to identify the genetic cause of hyperphosphataemia and tibial hyperostosis in a 19-year-old girl of Colombian origin. Methods: Genomic DNA was extracted and sequencing analysis of the GALNT3 and fibroblast growth factor 23 (FGF23) genes performed. Serum levels of intact and C-terminal FGF23 were measured using two different ELISA methods. Results: Mutational analysis identified a novel homozygous missense mutation in exon 6 of GALNT3 (1584 GOA), leading to an amino acid shift from Arg to His at residue 438 (R438H). The mutation was not found in over 200 control alleles or in any single nucleotide polymorphism databases. The R438 residue is highly conserved throughout species and in all known GalNAc-transferase family members. Modelling predicted the substitution deleterious for protein structure. Importantly, the phosphaturic factor FGF23 was differentially processed, as reflected by low intact (15 pg/ml) but high C-terminal (839 RU/ml) serum FGF23 levels. Conclusions: We report on the first missense mutation in GALNT3 giving rise to HHS, since previous GALNT3 mutations in HHS caused aberrant splicing or premature truncation of the protein. The R438H substitution likely abrogates GALNT3 activity, in turn causing enhanced FGF23 degradation and subsequent hyperostosis/hyperphosphataemia.
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