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Vitamin D activities and metabolic bone disease. Clin Chim Acta 2013; 425:148-52. [DOI: 10.1016/j.cca.2013.07.024] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2013] [Accepted: 07/23/2013] [Indexed: 12/16/2022]
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Chanakul A, Zhang MYH, Louw A, Armbrecht HJ, Miller WL, Portale AA, Perwad F. FGF-23 regulates CYP27B1 transcription in the kidney and in extra-renal tissues. PLoS One 2013; 8:e72816. [PMID: 24019880 PMCID: PMC3760837 DOI: 10.1371/journal.pone.0072816] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Accepted: 07/21/2013] [Indexed: 12/18/2022] Open
Abstract
The mitochondrial enzyme 25-hydroxyvitamin D 1α-hydroxylase, which is encoded by the CYP27B1 gene, converts 25OHD to the biological active form of vitamin D, 1,25-dihydroxyvitamin D (1,25(OH)2D). Renal 1α-hydroxylase activity is the principal determinant of the circulating 1,25(OH)2D concentration and enzyme activity is tightly regulated by several factors. Fibroblast growth factor-23 (FGF-23) decreases serum 1,25(OH)2D concentrations by suppressing CYP27B1 mRNA abundance in mice. In extra-renal tissues, 1α-hydroxylase is responsible for local 1,25(OH)2D synthesis, which has important paracrine actions, but whether FGF-23 regulates CYP27B1 gene expression in extra-renal tissues is unknown. We sought to determine whether FGF-23 regulates CYP27B1 transcription in the kidney and whether extra-renal tissues are target sites for FGF-23-induced suppression of CYP27B1. In HEK293 cells transfected with the human CYP27B1 promoter, FGF-23 suppressed promoter activity by 70%, and the suppressive effect was blocked by CI-1040, a specific inhibitor of extracellular signal regulated kinase 1/2. To examine CYP27B1 transcriptional activity in vivo, we crossed fgf-23 null mice with mice bearing the CYP27B1 promoter-driven luciferase transgene (1α-Luc). In the kidney of FGF-23 null/1α-Luc mice, CYP27B1 promoter activity was increased by 3-fold compared to that in wild-type/1α-Luc mice. Intraperitoneal injection of FGF-23 suppressed renal CYP27B1 promoter activity and protein expression by 26% and 60% respectively, and the suppressive effect was blocked by PD0325901, an ERK1/2 inhibitor. These findings provide evidence that FGF-23 suppresses CYP27B1 transcription in the kidney. Furthermore, we demonstrate that in FGF-23 null/1α-Luc mice, CYP27B1 promoter activity and mRNA abundance are increased in several extra-renal sites. In the heart of FGF-23 null/1α-Luc mice, CYP27B1 promoter activity and mRNA were 2- and 5-fold higher, respectively, than in control mice. We also observed a 3- to 10-fold increase in CYP27B1 mRNA abundance in the lung, spleen, aorta and testis of FGF-23 null/1α-Luc mice. Thus, we have identified novel extra-renal target sites for FGF-23-mediated regulation of CYP27B1.
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Affiliation(s)
- Ankanee Chanakul
- Department of Pediatrics, University of California San Francisco, San Francisco, California, United States of America
| | - Martin Y. H. Zhang
- Department of Pediatrics, University of California San Francisco, San Francisco, California, United States of America
| | - Andrew Louw
- Department of Pediatrics, University of California San Francisco, San Francisco, California, United States of America
| | - Harvey J. Armbrecht
- Geriatric Research, Education, and Clinical Center, St. Louis Veterans Affairs Medical Center, St. Louis, Missouri, United States of America
| | - Walter L. Miller
- Department of Pediatrics, University of California San Francisco, San Francisco, California, United States of America
| | - Anthony A. Portale
- Department of Pediatrics, University of California San Francisco, San Francisco, California, United States of America
| | - Farzana Perwad
- Department of Pediatrics, University of California San Francisco, San Francisco, California, United States of America
- * E-mail:
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Anderson PH, Lam NN, Turner AG, Davey RA, Kogawa M, Atkins GJ, Morris HA. The pleiotropic effects of vitamin D in bone. J Steroid Biochem Mol Biol 2013; 136:190-4. [PMID: 22981997 DOI: 10.1016/j.jsbmb.2012.08.008] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/06/2012] [Revised: 08/09/2012] [Accepted: 08/14/2012] [Indexed: 01/01/2023]
Abstract
A current controversial question related to vitamin D supplementation is what level of serum 25-hydroxyvitamin D3 (25(OH)D3) is required to reduce the incidence of osteoporotic fractures. The reasoning behind vitamin D supplementation has been mostly derived from the role of vitamin D to promote intestinal calcium absorption and reduce bone resorption. While minimum 25(OH)D3 levels of 20nmol/L are required for sufficient intestinal calcium absorption to prevent osteomalacia, the mechanistic details of how higher 25(OH)D3 levels, well beyond that required for optimal calcium absorption, are able to prevent fractures and increase bone mineral density is unclear. Substantial evidence has arisen over the past decade that conversion of 25(OH)D3 to 1,25(OH)2D3via the 1-alpha hydroxylase (CYP27B1) enzyme in osteoblasts, osteocytes, chondrocytes and osteoclasts regulates processes such as cell proliferation, maturation and mineralization as well as bone resorption, which are all dependent on the presence the of the vitamin D receptor (VDR). We and others have also shown that increased vitamin D activity in mature osteoblasts by increasing levels of VDR or CYP27B1 leads to improved bone mineral volume using two separate transgenic mouse models. While questions remain regarding activities of vitamin D in bone to influence the anabolic and catabolic processes, the biological importance of vitamin D activity within the bone is unquestioned. However, a clearer understanding of the varied mechanisms by which vitamin D directly and indirectly influences mineral bone status are required to support evidence-based recommendations for vitamin D supplementation to reduce the risk of fractures. This article is part of a Special Issue entitled 'Vitamin D workshop'.
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Affiliation(s)
- Paul H Anderson
- School of Pharmacy and Medical Sciences, University of South Australia, Adelaide 5000, Australia.
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Affiliation(s)
- Howard A MORRIS
- Professor of Medical Sciences; School of Pharmacy and Medical Sciences; University of South Australia; Adelaide; South Australia; Australia
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Anderson PH, Atkins GJ, Turner AG, Kogawa M, Findlay DM, Morris HA. Vitamin D metabolism within bone cells: effects on bone structure and strength. Mol Cell Endocrinol 2011; 347:42-7. [PMID: 21664230 DOI: 10.1016/j.mce.2011.05.024] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/15/2011] [Revised: 05/04/2011] [Accepted: 05/09/2011] [Indexed: 11/16/2022]
Abstract
The endocrine activity of 1,25-dihydroxyvitamin D (1,25(OH)(2)D(3)) contributes to maintaining plasma calcium and phosphate homeostasis through actions on the intestine, kidney and bone. A significant body of evidence has been published over the last 10 years indicating that all major bone cells have the capacity to metabolise 25-hydroxyvitamin D (25(OH)D(3)) to 1,25(OH)(2)D(3), which in turn exerts autocrine/paracrine actions to regulate bone cell proliferation and maturation as well as bone mineralisation and resorption. In vivo and in vitro studies indicate that these autocrine/paracrine activities of 1,25(OH)(2)D(3) in bone tissue contribute to maintaining bone mineral homeostasis and enhancing skeletal health.
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Affiliation(s)
- Paul H Anderson
- Endocrine Bone Research Laboratory, Chemical Pathology, SA Pathology, Adelaide, SA 5000, Australia
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Anderson PH, Iida S, Tyson JHT, Turner AG, Morris HA. Bone CYP27B1 gene expression is increased with high dietary calcium and in mineralising osteoblasts. J Steroid Biochem Mol Biol 2010; 121:71-5. [PMID: 20236619 DOI: 10.1016/j.jsbmb.2010.03.021] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/02/2009] [Revised: 03/03/2010] [Accepted: 03/05/2010] [Indexed: 10/19/2022]
Abstract
Although the regulation of renal 25-hydroxyvitamin D 1alpha-hydroxylase (CYP27B1) is reasonably well understood, the same cannot be said about the regulation of bone CYP27B1 expression. We have compared the regulation of kidney and bone CYP27B1 expression with modulation of dietary vitamin D and calcium levels. Vitamin D-deplete and vitamin D-replete female Sprague-Dawley rats were fed either 1% Ca (HC) or 0.1% Ca (LC) diets from 6 months of age. At 9 months of age, animals were killed for mRNA analyses from kidney and bone by real-time RT-PCR. Additionally, primary bone cells were cultured from pCYP27B1-Luc reporter mice in pro-osteogenic media over 15 days and analysed for mRNA for CYP27B1 and other osteogenic markers. In vivo expression of bone CYP27B1 mRNA was independent of changes to kidney CYP27B1 levels with both serum 1,25D and PTH as negative determinants of bone CYP27B1 mRNA levels. Bone cells in pro-mineralising conditions significantly increased CYP27B1 promoter activity over 15 days (P<0.001) which preceded marked increases in alkaline phosphatase, osteocalcin and vitamin D receptor mRNA expression and mineral deposition. These findings confirm that the regulation of bone CYP27B1 is unique from that in the kidney, and may play an important role in bone formation.
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Affiliation(s)
- Paul H Anderson
- Chemical Pathology, SA Pathology, Frome Rd, Adelaide, SA 5000, Australia.
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The skeleton as an intracrine organ for vitamin D metabolism. Mol Aspects Med 2008; 29:397-406. [PMID: 18602685 DOI: 10.1016/j.mam.2008.05.003] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2008] [Accepted: 05/15/2008] [Indexed: 11/23/2022]
Abstract
The endocrine hormone, 1alpha,25-dihydroxyvitamin D(3) (1,25D) is an important regulator of calcium and phosphorus homeostasis. In this context, 1,25D is generally recognized as necessary for the maintenance of a healthy skeleton through its actions on the small intestine. In this review, we highlight the direct effects of 1,25D on the constituent cells of the bone, actions that are independent of effects on the intestine and kidney. We also consider the evidence that 25D levels, not 1,25D levels, correlate best with parameters of bone health, and that the bone itself is a site of metabolic conversion of 25D into 1,25D, by virtue of its expression of the 25-hydroxyvitamin D 1alpha-hydroxylase, CYP27B1. We review the evidence that at least osteoblasts and chondrocytes, and possibly also bone resorbing osteoclasts, are capable of such metabolic conversion, and therefore that these cells likely participate in autocrine and paracrine loops of vitamin D metabolism. We conclude that the skeleton is an intracrine organ for vitamin D metabolism, challenging the long-held notion that 1,25D is solely an endocrine hormone.
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Bajwa A, Forster MN, Maiti A, Woolbright BL, Beckman MJ. Specific regulation of CYP27B1 and VDR in proximal versus distal renal cells. Arch Biochem Biophys 2008; 477:33-42. [PMID: 18593564 DOI: 10.1016/j.abb.2008.06.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2008] [Revised: 06/11/2008] [Accepted: 06/12/2008] [Indexed: 11/20/2022]
Abstract
In this study, we utilized murine renal proximal (MPCT-G) and distal (DKC-8) tubular epithelial cell lines to compare the gene expressions and promoter activities of 1,25(OH)(2)D(3) receptor (VDR) and 25-hydroxyvitamin D-1alpha-hydroxylase (CYP27B1) in response to 50 nM of parathyroid hormone (PTH) and changes in extracellular calcium (Ca(2+)) concentration. In MPCT-G cells, VDR gene expression was suppressed by PTH, whereas CYP27B1 gene expression was elevated in response to PTH. In DKC-8 cells, treatment of PTH significantly increased the relative gene expression of VDR by 6.5-fold while CYP27B1 gene expression was unchanged. High Ca(2+) exposure stimulated VDR gene expression and repressed CYP27B1 gene expression in both dose and time-dependent fashion in MPCT-G but not DKC-8 cells. The analysis of promoter activities and VDR protein levels corresponded with the gene expression data. We conclude that PTH-mediated decrease in VDR and increase in renal CYP27B1 is proximal cell-specific.
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MESH Headings
- 25-Hydroxyvitamin D3 1-alpha-Hydroxylase/genetics
- 25-Hydroxyvitamin D3 1-alpha-Hydroxylase/metabolism
- Animals
- Blotting, Western
- Cell Line
- Immunohistochemistry
- Kidney Tubules, Distal/cytology
- Kidney Tubules, Distal/enzymology
- Kidney Tubules, Distal/metabolism
- Kidney Tubules, Proximal/cytology
- Kidney Tubules, Proximal/enzymology
- Kidney Tubules, Proximal/metabolism
- Mice
- Promoter Regions, Genetic
- Receptor, Parathyroid Hormone, Type 1/metabolism
- Receptors, Calcitriol/metabolism
- Receptors, Calcium-Sensing/metabolism
- Steroid Hydroxylases/metabolism
- Vitamin D3 24-Hydroxylase
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Affiliation(s)
- Amandeep Bajwa
- Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA 23298-0614, USA
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Anderson PH, Hendrix I, Sawyer RK, Zarrinkalam R, Manavis J, Sarvestani GT, May BK, Morris HA. Co-expression of CYP27B1 enzyme with the 1.5kb CYP27B1 promoter-luciferase transgene in the mouse. Mol Cell Endocrinol 2008; 285:1-9. [PMID: 18313834 DOI: 10.1016/j.mce.2007.12.018] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/18/2007] [Revised: 11/16/2007] [Accepted: 12/20/2007] [Indexed: 01/22/2023]
Abstract
The renal enzyme 25-hydroxyvitamin D 1alpha-hydroxylase (CYP27B1), responsible for the synthesis of circulating. 1,25-dihydroxyvitamin D (1,25D), is also expressed in a number of non-renal tissues. The regulation of CYP27B1 expression by the short flanking promoter outside the kidney is, however, largely unknown. We have used a transgenic mice expressing the 1.5kb promoter of the human CYP27B1 gene fused to the firefly luciferase gene in order to investigate tissue-specific CYP27B1 expression. These transgenic animals demonstrated co-localised luciferase and endogenous CYP27B1 expression in kidney proximal convoluted tubular cells. Strong co-expression of luciferase and CYP27B1 also occurred in neurons and Purkinje cells of the cerebellum and in Leydig and Sertoli cells of the testes. Other tissues to exhibit CYP27B1-promoter directed luciferase activity included lung, prostate, trabecular bone and jejunum as well as the choroid epithelium. The tissue specific changes in luciferase activity were age-related. These findings demonstrate that the proximal 1.5kb 5' flanking region of the CYP27B1 gene directs the expression of CYP27B1 in a number of known and novel tissues in a specific manner.
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Affiliation(s)
- Paul H Anderson
- Endocrine Research Laboratory, Hanson Institute, Frome Road, Adelaide 5000, SA, Australia.
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Maiti A, Hait NC, Beckman MJ. Extracellular Calcium-sensing Receptor Activation Induces Vitamin D Receptor Levels in Proximal Kidney HK-2G Cells by a Mechanism That Requires Phosphorylation of p38α MAPK. J Biol Chem 2008; 283:175-183. [DOI: 10.1074/jbc.m707269200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
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Wu S, Ren S, Nguyen L, Adams JS, Hewison M. Splice variants of the CYP27b1 gene and the regulation of 1,25-dihydroxyvitamin D3 production. Endocrinology 2007; 148:3410-8. [PMID: 17395703 DOI: 10.1210/en.2006-1388] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The cytochrome P450 25-hydroxyvitamin D3-1alpha-hydroxylase (CYP27b1) plays a pivotal role in vitamin D physiology by catalyzing synthesis of active 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. In common with other P450s, CYP27b1 is known to exhibit alternative splicing. Here we have cloned and sequenced several novel intron 2-containing, noncoding splice variant mRNAs for CYP27b1 in 1,25(OH)2D3-producing HKC-8 human proximal tubule and THP-1 monocytic cells. Regulation of 1,25(OH)2D3 synthesis in these cell lines by calciotropic and noncalciotropic factors was associated with altered expression of the CYP27b1 splice variants. To assess the functional significance of this, HKC-8 cells were transfected with short hairpin RNA (shRNA) to inhibit mRNAs containing sequences from intron 2. This resulted in a significant increase in the expression of CYP27b1 protein and synthesis of 1,25(OH)2D3 by HKC-8 cells compared with control cells for two different intron 2-containing shRNAs (both P<0.001). shRNA to intron 2 had no significant effect on the levels of wild-type CYP27b1 mRNA, suggesting a posttranscriptional mechanism of action. By contrast, shRNA to wild-type CYP27b1 suppressed transcription and activity of the enzyme by 70 and 31%, respectively (both P<0.01). These data indicate that noncoding splice variants of CYP27b1 are functionally active and may play a significant role in the regulation of 1,25(OH)2D3 synthesis during normal physiology.
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Affiliation(s)
- S Wu
- Burns and Allen Research Institute, Division of Endocrinology, Diabetes and Metabolism, Cedars-Sinai Medical Center, Los Angeles, School of Medicine, California 90048, USA
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12
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Atkins GJ, Anderson PH, Findlay DM, Welldon KJ, Vincent C, Zannettino ACW, O'Loughlin PD, Morris HA. Metabolism of vitamin D3 in human osteoblasts: evidence for autocrine and paracrine activities of 1 alpha,25-dihydroxyvitamin D3. Bone 2007; 40:1517-28. [PMID: 17395559 DOI: 10.1016/j.bone.2007.02.024] [Citation(s) in RCA: 182] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/04/2006] [Revised: 01/31/2007] [Accepted: 02/21/2007] [Indexed: 11/19/2022]
Abstract
Circulating 1 alpha,25-dihydroxyvitamin D(3) (1,25D) derives from renal conversion of 25-hydroxyvitamin D(3) (25D), by the 25D 1 alpha-hydroxylase (CYP27B1). Blood 25D levels, but not 1,25D levels, are the best indicator of vitamin D status and predict fracture risk in the elderly. We examined the extent to which osteoblasts can metabolize 25D. Well-characterized human primary osteoblasts and osteosarcoma (OS) cell lines were examined for the expression and regulation of genes associated with vitamin D metabolism, using real-time PCR. Primary osteoblasts and OS cell lines were found to express CYP27B1 mRNA and secreted detectable 1,25D in response to 25D. Of the OS cell lines tested, HOS expressed the most CYP27B1 mRNA and secreted the highest levels of 1,25D. All osteoblastic cells examined up-regulated expression of the catabolic regulator of 1,25D, the 25-hydroxyvitamin D-24-hydroxylase (CYP24), when incubated with either 1,25D or 25D. Exposure to physiological levels of 25D resulted in up-regulated transcription of the 1,25D responsive genes, osteocalcin (OCN), osteopontin (OPN) and RANKL. Specific knockdown of CYP27B1 in HOS cells using siRNA resulted in up to 80% reduction in both 1,25D secretion and the transcription of OCN and CYP24, strongly implying that the 25D effect in osteoblasts is preceded by conversion to 1,25D. Incubation with 25D, like 1,25D, inhibited primary osteoblast proliferation and promoted in vitro mineralization. Finally, we detected expression by osteoblasts of receptors for vitamin D binding protein (DBP), cubilin and megalin, suggesting that osteoblasts are able to internalize DBP-25D complexes in vivo. Together, our results suggest that autocrine, and perhaps paracrine, pathways of vitamin D(3) metabolism may regulate key osteoblast functions independently of circulating, kidney derived 1,25D. Our results are therefore consistent with the reported benefits of maintaining a healthy vitamin D status in the elderly to reduce the risk of fractures.
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Affiliation(s)
- Gerald J Atkins
- Department of Orthopaedics and Trauma, University of Adelaide, Adelaide, South Australia 5000, Australia.
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Turunen MM, Dunlop TW, Carlberg C, Väisänen S. Selective use of multiple vitamin D response elements underlies the 1 alpha,25-dihydroxyvitamin D3-mediated negative regulation of the human CYP27B1 gene. Nucleic Acids Res 2007; 35:2734-47. [PMID: 17426122 PMCID: PMC1885674 DOI: 10.1093/nar/gkm179] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2006] [Revised: 03/12/2007] [Accepted: 03/12/2007] [Indexed: 11/13/2022] Open
Abstract
The human 25-hydroxyvitamin D3 (25(OH)D3) 1alpha-hydroxylase, which is encoded by the CYP27B1 gene, catalyzes the metabolic activation of the 25(OH)D3 into 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3), the most biologically potent vitamin D3 metabolite. The most important regulator of CYP27B1 gene activity is 1alpha,25(OH)2D3 itself, which down-regulates the gene. The down-regulation of the CYP27B1 gene has been proposed to involve a negative vitamin D response element (nVDRE) that is located approximately 500 bp upstream from transcription start site (TSS). In this study, we reveal the existence of two new VDR-binding regions in the distal promoter, 2.6 and 3.2 kb upstream from the TSS, that bind vitamin D receptor-retinoid X receptor complexes. Since the down regulation of the CYP27B1 gene is tissue- and cell-type selective, a comparative study was done for the new 1alpha,25(OH)2D3-responsive regions in HEK-293 human embryonic kidney and MCF-7 human breast cancer cells that reflect tissues that, respectively, are permissive and non-permissive to the phenomenon of 1alpha,25(OH)2D3-mediated down-regulation of this gene. We found significant differences in the composition of protein complexes associated with these CYP27B1 promoter regions in the different cell lines, some of which reflect the capability of transcriptional repression of the CYP27B1 gene in these different cells. In addition, chromatin architecture differed with respect to chromatin looping in the two cell lines, as the new distal regions were differentially connected with the proximal promoter. This data explains, in part, why the human CYP27B1 gene is repressed in HEK-293 but not in MCF-7 cells.
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Affiliation(s)
| | | | | | - Sami Väisänen
- Department of Biochemistry, University of Kuopio, FIN-70211 Kuopio, Finland
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Wang Y, Zhou J, Minto AW, Hack BK, Alexander JJ, Haas M, Li YC, Heilig CW, Quigg RJ. Altered vitamin D metabolism in type II diabetic mouse glomeruli may provide protection from diabetic nephropathy. Kidney Int 2006; 70:882-91. [PMID: 16820793 DOI: 10.1038/sj.ki.5001624] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The db/db mouse develops features of type II diabetes mellitus as the result of impaired signaling through its abnormal leptin receptor. In spite of accurate metabolic features of diabetes, renal disease manifestations in these mice are not as severe as in humans suggesting the presence of protective genes. There is a growing body of evidence in humans for the relevance of vitamin D in diabetes. Here we followed a large cohort of db/db mice and their non-diabetic db/+ littermates. Transcriptional profiling revealed significant upregulation of 23 genes involved in Ca2+ homeostasis and vitamin D metabolism in db/db glomeruli relative to db/+ glomeruli. Increased glomerular expression of vitamin D3 1alpha-hydroxylase, vitamin D binding protein, calbindins D9K and D28K, and calcyclin mRNA was confirmed by quantitative reverse transcription-polymerase chain reaction in 20-, 36-, and 52-week-old db/db glomeruli. Although vitamin D3 1alpha-hydroxylase protein was primarily expressed and upregulated in db/db renal tubules, it was also expressed in glomerular podocytes in vivo. Serum 1,25-dihydroxyvitamin D3 and urinary Ca2+ excretion were increased >3-fold in db/db mice compared to db/+ mice. Cultured glomerular podocytes had mRNA for vitamin D3 1alpha-hydroxylase, vitamin D receptor, and calbindin D28K, each of which was increased in high glucose conditions. High glucose also led to enhanced production of fibronectin and collagen IV protein, which was blocked by 1,25-dihydroxyvitamin D3. These results show that vitamin D metabolism is altered in db/db mice leading to metabolic and transcriptional effects. The podocyte is affected by paracrine and potentially autocrine effects of vitamin D, which may explain why db/db mice are resistant to progressive diabetic nephropathy.
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Affiliation(s)
- Y Wang
- Department of Medicine, The University of Chicago, Chicago, Illinois 60637, USA
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Abstract
Renal osteodystrophy (ROD) associated with chronic kidney disease (CKD) involves a complex interrelationship of the loss of divalent mineral homeostasis, hyperparathyroidism, and gene modulation. In affected children, ROD leads to impaired linear growth as well as to the development of other significant skeletal and extraskeletal manifestations. Despite the success of kidney transplantation, many ROD complications cannot be completely reversed; and thus, patients with CKD and ROD require long-term follow-up. Although the availability of vitamin D analogues has advanced ROD management, it has also created new issues for clinicians to address, motivating future investigations of calcimimetic therapies. An algorithmic approach to the management of ROD in children is presented; to be most effective, this approach requires close and frequent surveillance to prevent side effects related to potent therapies.
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Affiliation(s)
- Craig B Langman
- Feinberg School of Medicine, Northwestern University, and Children's Memorial Hospital, 2300 Children's Plaza, MS #37, Chicago, IL 60614, USA.
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