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Reversal of mineral ion homeostasis and soft-tissue calcification of klotho knockout mice by deletion of vitamin D 1alpha-hydroxylase.

ABSTRACT: Changes in the expression of klotho, a beta-glucuronidase, contribute to the development of features that resemble those of premature aging, as well as chronic renal failure. Klotho knockout mice have increased expression of the sodium/phosphate cotransporter (NaPi2a) and 1alpha-hydroxylase in their kidneys, along with increased serum levels of phosphate and 1,25-dihydroxyvitamin D. These changes are associated with widespread soft-tissue calcifications, generalized tissue atrophy, and a shorter lifespan in the knockout mice. To determine the role of the increased vitamin D activities in klotho knockout animals, we generated klotho and 1alpha-hydroxylase double-knockout mice. These double mutants regained body weight and developed hypophosphatemia with a complete elimination of the soft-tissue and vascular calcifications that were routinely found in klotho knockout mice. The markedly increased serum fibroblast growth factor 23 and the abnormally low serum parathyroid hormone levels, typical of klotho knockout mice, were significantly reversed in the double-knockout animals. These in vivo studies suggest that vitamin D has a pathologic role in regulating abnormal mineral ion metabolism and soft-tissue anomalies of klotho-deficient mice.

SUBMITTER: Ohnishi M

PROVIDER: S-EPMC3143194 | biostudies-literature | 2009 Jun

REPOSITORIES: biostudies-literature

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Reversal of mineral ion homeostasis and soft-tissue calcification of klotho knockout mice by deletion of vitamin D 1alpha-hydroxylase.

Ohnishi Mutsuko M Nakatani Teruyo T Lanske Beate B Razzaque M Shawkat MS

Kidney international 20090218 11

Changes in the expression of klotho, a beta-glucuronidase, contribute to the development of features that resemble those of premature aging, as well as chronic renal failure. Klotho knockout mice have increased expression of the sodium/phosphate cotransporter (NaPi2a) and 1alpha-hydroxylase in their kidneys, along with increased serum levels of phosphate and 1,25-dihydroxyvitamin D. These changes are associated with widespread soft-tissue calcifications, generalized tissue atrophy, and a shorter ...[more]

PMID: 19225558

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Project description:The cytochrome P450 mitochondrial enzyme 25-hydroxyvitamin D3 1alpha-hydroxylase (1alpha-hydroxylase) of renal tubule cells hydroxylates the major circulating form of vitamin D (25(OH)D3) to the active systemic hormone 1,25(OH)2D3. Local production of 1,25(OH)2D3 appears to occur also at other sites where 1alpha-hydroxylase is expressed for autocrine/paracrine regulation. To reduce risks of hypercalcemia during treatment with vitamin D, we have previously suggested use of non-1alpha-hydroxylated vitamin D analogues to target tissues where 1alpha-hydroxylase is expressed, including the parathyroid glands in secondary hyperparathyroidism. The present study was undertaken to examine expression of 1alpha-hydroxylase in breast cancer and to investigate whether a non-1alpha-hydroxylated vitamin D analogue displayed biological function. In addition, expression of the 25-hydroxyvitamin D3 24-hydroxylase (24-hydroxylase) and the vitamin D receptor (VDR) was investigated.The expression of 1alpha-hydroxylase, 24-hydroxylase and VDR was investigated in breast cancer specimens (n = 19) and normal breast tissues (n = 10) by immunohistochemistry and/or RT-PCR. Consecutive cryosections of 6 mum essentially free of immune cells were used in the analyses. The effect of vitamin D analogues on transcriptional activation was analyzed in transiently transfected MCF-7 breast cancer cells.1alpha-hydroxylase protein was demonstrated in 79% and 100% of breast cancer specimens and normal breast, respectively. The overall relative mRNA levels of 1alpha-hydroxylase and 24-hydroxylase in normal breast compared to breast tumors were: 1alpha-hydroxylase, 1 +/- 0.07 versus 0.7 +/- 0.05, respectively (p < 0.001); 24-hydroxylase, 1 +/- 0.08 verus 2.1 +/- 0.2, respectively (p < 0.001). The VDR was expressed in 95% of the tumors as expected, with mRNA levels of 1 +/- 0.09 and 1.4 +/- 0.12 (p < 0.05) in breast cancer and normal breast, respectively. The ketoconazole-sensitive transcription activation potential of the non-1alpha-hydroxylated vitamin D analogue prodrug of EB1089 (EB1285) was demonstrated in MCF-7 cells, which express 1alpha-hydroxylase. The activity of EB1285 was about 20% of 1,25(OH)2D3.These results demonstrate nearly normal expression levels of 1alpha-hydroxylase, 24-hydroxylase and VDR in the majority of investigated breast cancer specimens. A non-1alpha-hydroxylated vitamin D analogue displayed activity in breast cancer cells. Such analogues may present future therapeutic options for proliferative disorders where 1alpha-hydroxylase is expressed.

Dataset Information

Reversal of mineral ion homeostasis and soft-tissue calcification of klotho knockout mice by deletion of vitamin D 1alpha-hydroxylase.

Publications

Reversal of mineral ion homeostasis and soft-tissue calcification of klotho knockout mice by deletion of vitamin D 1alpha-hydroxylase.

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