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Young K, Beggs MR, Grimbly C, Alexander RT. Regulation of 1 and 24 hydroxylation of vitamin D metabolites in the proximal tubule. Exp Biol Med (Maywood) 2022; 247:1103-1111. [PMID: 35482362 PMCID: PMC9335508 DOI: 10.1177/15353702221091982] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Calcium and phosphate are critical for numerous physiological processes. Consequently, the plasma concentration of these ions are tightly regulated. Calcitriol, the active form of vitamin D, is a positive modulator of mineralization as well as calcium and phosphate metabolism. The molecular and physiological effects of calcitriol are well documented. Calcitriol increases blood calcium and phosphate levels by increasing absorption from the intestine, and resorption of bone. Calcitriol synthesis is a multistep process. A precursor is first made via skin exposure to UV, it is then 25-hydroxylated in the liver to form 25-hydroxyitamin D. The next hydroxylation step occurs in the renal proximal tubule via the 1-αhydroxylase enzyme (encoded by CYP27B1) thereby generating 1,25-dihydroxyvitamin D, that is, calcitriol. At the same site, the 25-hydroxyvitamin D 24-hydroxlase enzyme encoded by CYP24A1 can hydroxylate 25-hydroxyvitamin D or calcitriol to deactivate the hormone. Plasma calcitriol levels are primarily determined by the regulated expression of CYP27B1 and CYP24A1. This occurs in response to parathyroid hormone (increases CYP27B1), calcitriol itself (decreases CYP27B1 and increases CYP24A1), calcitonin (increases or decreases CYP24A1 and increases CYP27B1), FGF23 (decreases CYP27B1 and increases CYP24A1) and potentially plasma calcium and phosphate levels themselves (mixed effects). Herein, we review the regulation of CYP27B1 and CYP24A1 transcription in response to the action of classic phophocalciotropic hormones and explore the possibility of direct regulation by plasma calcium.
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Affiliation(s)
- Kennedi Young
- Department of Physiology, University of Alberta, Edmonton, AB T6G 2H7, Canada,Women and Children’s Health Institute, Edmonton, AB T6G 1C9, Canada
| | - Megan R Beggs
- Department of Physiology, University of Alberta, Edmonton, AB T6G 2H7, Canada,Women and Children’s Health Institute, Edmonton, AB T6G 1C9, Canada
| | - Chelsey Grimbly
- Department of Paediatrics, University of Alberta, Edmonton, AB T6G 1C9, Canada
| | - R Todd Alexander
- Department of Physiology, University of Alberta, Edmonton, AB T6G 2H7, Canada,Women and Children’s Health Institute, Edmonton, AB T6G 1C9, Canada,Department of Paediatrics, University of Alberta, Edmonton, AB T6G 1C9, Canada,R Todd Alexander.
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2
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Huang A, Binmahfouz L, Hancock DP, Anderson PH, Ward DT, Conigrave AD. Calcium-Sensing Receptors Control CYP27B1-Luciferase Expression: Transcriptional and Posttranscriptional Mechanisms. J Endocr Soc 2021; 5:bvab057. [PMID: 34337274 PMCID: PMC8317635 DOI: 10.1210/jendso/bvab057] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Indexed: 12/19/2022] Open
Abstract
25-hydroxyvitamin D 1α-hydroxylase (encoded by CYP27B1), which catalyzes the synthesis of 1,25-dihydroxyvitamin D3, is subject to negative or positive modulation by extracellular Ca2+ (Ca2+o) depending on the tissue. However, the Ca2+ sensors and underlying mechanisms are unidentified. We tested whether calcium-sensing receptors (CaSRs) mediate Ca2+o-dependent control of 1α-hydroxylase using HEK-293 cells stably expressing the CaSR (HEK-CaSR cells). In HEK-CaSR cells, but not control HEK-293 cells, cotransfected with reporter genes for CYP27B1-Photinus pyralis (firefly) luciferase and control Renilla luciferase, an increase in Ca2+o from 0.5mM to 3.0mM induced a 2- to 3-fold increase in firefly luciferase activity as well as mRNA and protein levels. Surprisingly, firefly luciferase was specifically suppressed at Ca2+o ≥ 5.0mM, demonstrating biphasic Ca2+o control. Both phases were mediated by CaSRs as revealed by positive and negative modulators. However, Ca2+o induced simple monotonic increases in firefly luciferase and endogenous CYP27B1 mRNA levels, indicating that the inhibitory effect of high Ca2+o was posttranscriptional. Studies with inhibitors and the CaSR C-terminal mutant T888A identified roles for protein kinase C (PKC), phosphorylation of T888, and extracellular regulated protein kinase (ERK)1/2 in high Ca2+o-dependent suppression of firefly luciferase. Blockade of both PKC and ERK1/2 abolished Ca2+o-stimulated firefly luciferase, demonstrating that either PKC or ERK1/2 is sufficient to stimulate the CYP27B1 promoter. A key CCAAT box (−74 bp to −68 bp), which is regulated downstream of PKC and ERK1/2, was required for both basal transcription and Ca2+o-mediated transcriptional upregulation. The CaSR mediates Ca2+o-dependent transcriptional upregulation of 1α-hydroxylase and an additional CaSR-mediated mechanism is identified by which Ca2+o can promote luciferase and possibly 1α-hydroxylase breakdown.
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Affiliation(s)
- Alice Huang
- School of Life and Environmental Sciences, Charles Perkins Centre (D17), University of Sydney, NSW 2006Australia
| | - Lenah Binmahfouz
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, UK.,Department of Pharmacology and Toxicology, Faculty of Pharmacy, King Abdulaziz University, Jeddah 21589, Saudi Arabia
| | - Dale P Hancock
- School of Life and Environmental Sciences, Charles Perkins Centre (D17), University of Sydney, NSW 2006Australia
| | - Paul H Anderson
- Clinical and Health Sciences, Health and Biomedical Innovation, University of South Australia, Adelaide, SA, 5001, Australia
| | - Donald T Ward
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, UK
| | - Arthur D Conigrave
- School of Life and Environmental Sciences, Charles Perkins Centre (D17), University of Sydney, NSW 2006Australia
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3
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Tan RSG, Lee CHL, Dimke H, Todd Alexander R. The role of calcium-sensing receptor signaling in regulating transepithelial calcium transport. Exp Biol Med (Maywood) 2021; 246:2407-2419. [PMID: 33926258 DOI: 10.1177/15353702211010415] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The calcium-sensing receptor (CaSR) plays a critical role in sensing extracellular calcium (Ca2+) and signaling to maintain Ca2+ homeostasis. In the parathyroid, the CaSR regulates secretion of parathyroid hormone, which functions to increase extracellular Ca2+ levels. The CaSR is also located in other organs imperative to Ca2+ homeostasis including the kidney and intestine, where it modulates Ca2+ reabsorption and absorption, respectively. In this review, we describe CaSR expression and its function in transepithelial Ca2+ transport in the kidney and intestine. Activation of the CaSR leads to G protein dependent and independent signaling cascades. The known CaSR signal transduction pathways involved in modulating paracellular and transcellular epithelial Ca2+ transport are discussed. Mutations in the CaSR cause a range of diseases that manifest in altered serum Ca2+ levels. Gain-of-function mutations in the CaSR result in autosomal dominant hypocalcemia type 1, while loss-of-function mutations cause familial hypocalciuric hypercalcemia. Additionally, the putative serine protease, FAM111A, is discussed as a potential regulator of the CaSR because mutations in FAM111A cause Kenny Caffey syndrome type 2, gracile bone dysplasia, and osteocraniostenosis, diseases that are characterized by hypocalcemia, hypoparathyroidism, and bony abnormalities, i.e. share phenotypic features of autosomal dominant hypocalcemia. Recent work has helped to elucidate the effect of CaSR signaling cascades on downstream proteins involved in Ca2+ transport across renal and intestinal epithelia; however, much remains to be discovered.
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Affiliation(s)
- Rebecca Siu Ga Tan
- Department of Physiology, University of Alberta, Edmonton T6G 1C9, Canada.,Membrane Protein Disease Research Group, University of Alberta, Edmonton T6G 1C9, Canada
| | | | - Henrik Dimke
- Department of Cardiovascular and Renal Research, Institute of Molecular Medicine, University of Southern Denmark, Odense 5000, Denmark.,Department of Nephrology, Odense University Hospital, Odense 5000, Denmark
| | - R Todd Alexander
- Department of Physiology, University of Alberta, Edmonton T6G 1C9, Canada.,Membrane Protein Disease Research Group, University of Alberta, Edmonton T6G 1C9, Canada.,Department of Pediatrics, University of Alberta, Edmonton T6G 1C9, Canada
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4
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Bouillon R, Bikle D. Vitamin D Metabolism Revised: Fall of Dogmas. J Bone Miner Res 2019; 34:1985-1992. [PMID: 31589774 PMCID: PMC9000993 DOI: 10.1002/jbmr.3884] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Revised: 09/06/2019] [Accepted: 09/24/2019] [Indexed: 12/19/2022]
Affiliation(s)
- Roger Bouillon
- Laboratory of Clinical and Experimental Endocrinology, Department of Chronic Diseases Metabolism and Ageing, KU Leuven, Leuven, Belgium
| | - Dan Bikle
- Medicine and Dermatology, University of California San Francisco and VA Medical Center, San Francisco, CA, USA
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5
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Clinkenbeard EL, Noonan ML, Thomas JC, Ni P, Hum JM, Aref M, Swallow EA, Moe SM, Allen MR, White KE. Increased FGF23 protects against detrimental cardio-renal consequences during elevated blood phosphate in CKD. JCI Insight 2019; 4:123817. [PMID: 30830862 DOI: 10.1172/jci.insight.123817] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Accepted: 01/14/2019] [Indexed: 12/23/2022] Open
Abstract
The phosphaturic hormone FGF23 is elevated in chronic kidney disease (CKD). The risk of premature death is substantially higher in the CKD patient population, with cardiovascular disease (CVD) as the leading mortality cause at all stages of CKD. Elevated FGF23 in CKD has been associated with increased odds for all-cause mortality; however, whether FGF23 is associated with positive adaptation in CKD is unknown. To test the role of FGF23 in CKD phenotypes, a late osteoblast/osteocyte conditional flox-Fgf23 mouse (Fgf23fl/fl/Dmp1-Cre+/-) was placed on an adenine-containing diet to induce CKD. Serum analysis showed casein-fed Cre+ mice had significantly higher serum phosphate and blood urea nitrogen (BUN) versus casein diet and Cre- genotype controls. Adenine significantly induced serum intact FGF23 in the Cre- mice over casein-fed mice, whereas Cre+ mice on adenine had 90% reduction in serum intact FGF23 and C-terminal FGF23 as well as bone Fgf23 mRNA. Parathyroid hormone was significantly elevated in mice fed adenine diet regardless of genotype, which significantly enhanced midshaft cortical porosity. Echocardiographs of the adenine-fed Cre+ hearts revealed profound aortic calcification and cardiac hypertrophy versus diet and genotype controls. Thus, these studies demonstrate that increased bone FGF23, although associated with poor outcomes in CKD, is necessary to protect against the cardio-renal consequences of elevated tissue phosphate.
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Affiliation(s)
| | | | | | - Pu Ni
- Department of Medical and Molecular Genetics
| | - Julia M Hum
- Department of Medical and Molecular Genetics
| | | | | | - Sharon M Moe
- Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA
| | | | - Kenneth E White
- Department of Medical and Molecular Genetics.,Department of Anatomy and Cell Biology, and
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6
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Hernando N, Wagner CA. Mechanisms and Regulation of Intestinal Phosphate Absorption. Compr Physiol 2018; 8:1065-1090. [PMID: 29978897 DOI: 10.1002/cphy.c170024] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
States of hypo- and hyperphosphatemia have deleterious consequences including rickets/osteomalacia and renal/cardiovascular disease, respectively. Therefore, the maintenance of appropriate plasma levels of phosphate is an essential requirement for health. This control is executed by the collaborative action of intestine and kidney whose capacities to (re)absorb phosphate are regulated by a number of hormonal and metabolic factors, among them parathyroid hormone, fibroblast growth factor 23, 1,25(OH)2 vitamin D3 , and dietary phosphate. The molecular mechanisms responsible for the transepithelial transport of phosphate across enterocytes are only partially understood. Indeed, whereas renal reabsorption entirely relies on well-characterized active transport mechanisms of phosphate across the renal proximal epithelia, intestinal absorption proceeds via active and passive mechanisms, with the molecular identity of the passive component still unknown. The active absorption of phosphate depends mostly on the activity and expression of the sodium-dependent phosphate cotransporter NaPi-IIb (SLC34A2), which is highly regulated by many of the factors, mentioned earlier. Physiologically, the contribution of NaPi-IIb to the maintenance of phosphate balance appears to be mostly relevant during periods of low phosphate availability. Therefore, its role in individuals living in industrialized societies with high phosphate intake is probably less relevant. Importantly, small increases in plasma phosphate, even within normal range, associate with higher risk of cardiovascular disease. Therefore, therapeutic approaches to treat hyperphosphatemia, including dietary phosphate restriction and phosphate binders, aim at reducing intestinal absorption. Here we review the current state of research in the field. © 2017 American Physiological Society. Compr Physiol 8:1065-1090, 2018.
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Affiliation(s)
- Nati Hernando
- National Center for Competence in Research NCCR Kidney.CH, Institute of Physiology, University Zurich-Irchel, Zurich, Switzerland
| | - Carsten A Wagner
- National Center for Competence in Research NCCR Kidney.CH, Institute of Physiology, University Zurich-Irchel, Zurich, Switzerland
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7
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Bikle DD, Patzek S, Wang Y. Physiologic and pathophysiologic roles of extra renal CYP27b1: Case report and review. Bone Rep 2018; 8:255-267. [PMID: 29963603 PMCID: PMC6021194 DOI: 10.1016/j.bonr.2018.02.004] [Citation(s) in RCA: 61] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Revised: 02/06/2018] [Accepted: 02/23/2018] [Indexed: 01/13/2023] Open
Abstract
Although the kidney was initially thought to be the sole organ responsible for the production of 1,25(OH)2D via the enzyme CYP27b1, it is now appreciated that the expression of CYP27b1 in tissues other than the kidney is wide spread. However, the kidney is the major source for circulating 1,25(OH)2D. Only in certain granulomatous diseases such as sarcoidosis does the extra renal tissue produce sufficient 1,25(OH)2D to contribute to the circulating levels, generally associated with hypercalcemia, as illustrated by the case report preceding the review. Therefore the expression of CYP27b1 outside the kidney under normal circumstances begs the question why, and in particular whether the extra renal production of 1,25(OH)2D has physiologic importance. In this chapter this question will be discussed. First we discuss the sites for extra renal 1,25(OH)2D production. This is followed by a discussion of the regulation of CYP27b1 expression and activity in extra renal tissues, pointing out that such regulation is tissue specific and different from that of CYP27b1 in the kidney. Finally the physiologic significance of extra renal 1,25(OH)2D3 production is examined, with special focus on the role of CYP27b1 in regulation of cellular proliferation and differentiation, hormone secretion, and immune function. At this point the data do not clearly demonstrate an essential role for CYP27b1 expression in any tissue outside the kidney, but several examples pointing in this direction are provided. With the availability of the mouse enabling tissue specific deletion of CYP27b1, the role of extra renal CYP27b1 expression in normal and pathologic states can now be addressed definitively.
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Affiliation(s)
- Daniel D Bikle
- Department of Medicine, Endocrine Research Unit, Veterans Affairs Medical Center, University of California San Francisco, United States
| | - Sophie Patzek
- Department of Medicine, Endocrine Research Unit, Veterans Affairs Medical Center, University of California San Francisco, United States
| | - Yongmei Wang
- Department of Medicine, Endocrine Research Unit, Veterans Affairs Medical Center, University of California San Francisco, United States
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8
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Abstract
PTH and Vitamin D are two major regulators of mineral metabolism. They play critical roles in the maintenance of calcium and phosphate homeostasis as well as the development and maintenance of bone health. PTH and Vitamin D form a tightly controlled feedback cycle, PTH being a major stimulator of vitamin D synthesis in the kidney while vitamin D exerts negative feedback on PTH secretion. The major function of PTH and major physiologic regulator is circulating ionized calcium. The effects of PTH on gut, kidney, and bone serve to maintain serum calcium within a tight range. PTH has a reciprocal effect on phosphate metabolism. In contrast, vitamin D has a stimulatory effect on both calcium and phosphate homeostasis, playing a key role in providing adequate mineral for normal bone formation. Both hormones act in concert with the more recently discovered FGF23 and klotho, hormones involved predominantly in phosphate metabolism, which also participate in this closely knit feedback circuit. Of great interest are recent studies demonstrating effects of both PTH and vitamin D on the cardiovascular system. Hyperparathyroidism and vitamin D deficiency have been implicated in a variety of cardiovascular disorders including hypertension, atherosclerosis, vascular calcification, and kidney failure. Both hormones have direct effects on the endothelium, heart, and other vascular structures. How these effects of PTH and vitamin D interface with the regulation of bone formation are the subject of intense investigation.
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Affiliation(s)
- Syed Jalal Khundmiri
- Department of Medicine, University of Louisville, Louisville, Kentucky, USA
- Department of Physiology and Biophysics, University of Louisville, Louisville, Kentucky, USA
| | - Rebecca D. Murray
- Department of Medicine, University of Louisville, Louisville, Kentucky, USA
- Department of Physiology and Biophysics, University of Louisville, Louisville, Kentucky, USA
| | - Eleanor Lederer
- Department of Medicine, University of Louisville, Louisville, Kentucky, USA
- Department of Physiology and Biophysics, University of Louisville, Louisville, Kentucky, USA
- Robley Rex VA Medical Center, University of Louisville, Louisville, Kentucky, USA
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9
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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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Chronic kidney disease and diabetes mellitus predict resistance to vitamin D replacement therapy. Am J Med Sci 2013; 345:314-320. [PMID: 23221508 DOI: 10.1097/maj.0b013e31826af2d3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
BACKGROUND 25-Hydroxyvitamin D [25(OH)D] is a marker of nutritional status; however, chronic kidney disease (CKD) results in alterations in vitamin D metabolism, including the loss of vitamin D-binding proteins and alterations in CYP27B1 and CYP24 enzymes that metabolize 25(OH)D. This study was designed to determine the predictors of responsiveness to correction of vitamin D deficiency with oral vitamin D2 (ergocalciferol) in adults. METHODS A retrospective study of 183 veterans with 25(OH)D level <30 ng/mL, who were treated with 50,000 IU per week of vitamin D2, was performed. Logistic regression models were developed to determine the factors predicting the response to treatment, defined as either the change in serum 25(OH)D level/1000 IU of vitamin D2 or the number of vitamin D2 doses (50,000 IU per dose) administered. RESULTS The mean age of the patients was 63 ± 12 years. About 87% were men and 51% diabetic, and 29% had an estimated glomerular filtration rate of <60 mL/min/1.73 m. The average number of vitamin D2 doses was 10.91 ± 5.95; the average increase in 25(OH)D level was 18 ± 10.80 ng/mL. 25(OH)D levels remained <30 ng/mL in 61 patients after treatment. A low estimated glomerular filtration rate and the presence of diabetes mellitus were significant independent predictors for inadequate response to vitamin D2 treatment in logistic regression models. Patients with CKD required greater amounts of vitamin D2 to achieve similar increases in 25(OH)D levels, versus non-CKD patients. CONCLUSIONS The presence of CKD and diabetes mellitus is associated with resistance to correction of 25(OH)D deficiency with vitamin D2 therapy. The underlying mechanism needs to be evaluated in prospective studies.
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11
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Cheng Z, Liang N, Chen TH, Li A, Maria CS, You M, Ho H, Song F, Bikle D, Tu C, Shoback D, Chang W. Sex and age modify biochemical and skeletal manifestations of chronic hyperparathyroidism by altering target organ responses to Ca2+ and parathyroid hormone in mice. J Bone Miner Res 2013; 28:1087-100. [PMID: 23239173 PMCID: PMC3617088 DOI: 10.1002/jbmr.1846] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/24/2012] [Revised: 11/15/2012] [Accepted: 11/26/2012] [Indexed: 12/20/2022]
Abstract
We studied mice with or without heterozygous deletion of the Casr in the parathyroid gland (PTG) [(PTG) CaSR(+/-)] to delineate effects of age and sex on manifestations of hyperparathyroidism (HPT). In control mice, aging induced a left-shift in the Ca(2+) /parathyroid hormone (PTH) set point accompanied by increased PTG CaSR expression along with lowered serum Ca(2+) and mildly increased PTH levels, suggesting adaptive responses of PTGs to aging-induced changes in mineral homeostasis. The aging effects on Ca(2+) /PTH set point and CaSR expression were significantly blunted in (PTG) CaSR(+/-) mice, who showed instead progressively elevated PTH levels with age, especially in 12-month-old females. These 12-month-old knockout mice demonstrated resistance to their high PTH levels in that serum 1,25-dihydroxyvitamin D (1,25-D) levels and RNA expression of renal Cyp27b1 and expression of genes involved in Ca(2+) transport in kidney and intestine were unresponsive to the rising PTH levels. Such changes may promote negative Ca(2+) balance, which further exacerbate the HPT. Skeletal responses to HPT were age-, sex-, and site-dependent. In control mice of either sex, trabecular bone in the distal femur decreased whereas cortical bone in the tibiofibular junction increased with age. In male (PTG) CaSR(+/-) mice, anabolic actions of the elevated PTH levels seemed to protect against trabecular bone loss at ≥ 3 months of age at the expense of cortical bone loss. In contrast, HPT produced catabolic effects on trabecular bone and anabolic effects on cortical bone in 3-month-old females; but these effects reversed by 12 months, preserving trabecular bone in aging mice. We demonstrate that the CaSR plays a central role in the adaptive responses of parathyroid function to age-induced changes in mineral metabolism and in target organ responses to calciotropic hormones. Restraining the ability of the PTG to upregulate CaSRs by heterozygous gene deletion contributes to biochemical and skeletal manifestations of HPT, especially in aging females.
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Affiliation(s)
- Zhiqiang Cheng
- Endocrine Research Unit, Department of Veterans Affairs Medical Center, Department of Medicine, University of California, San Francisco, CA 94121, USA
| | - Nathan Liang
- Endocrine Research Unit, Department of Veterans Affairs Medical Center, Department of Medicine, University of California, San Francisco, CA 94121, USA
| | - Tsui-Hua Chen
- Endocrine Research Unit, Department of Veterans Affairs Medical Center, Department of Medicine, University of California, San Francisco, CA 94121, USA
| | - Alfred Li
- Endocrine Research Unit, Department of Veterans Affairs Medical Center, Department of Medicine, University of California, San Francisco, CA 94121, USA
| | - Christian Santa Maria
- Endocrine Research Unit, Department of Veterans Affairs Medical Center, Department of Medicine, University of California, San Francisco, CA 94121, USA
| | - Michael You
- Endocrine Research Unit, Department of Veterans Affairs Medical Center, Department of Medicine, University of California, San Francisco, CA 94121, USA
| | - Hanson Ho
- Endocrine Research Unit, Department of Veterans Affairs Medical Center, Department of Medicine, University of California, San Francisco, CA 94121, USA
| | - Fuqing Song
- Endocrine Research Unit, Department of Veterans Affairs Medical Center, Department of Medicine, University of California, San Francisco, CA 94121, USA
| | - Daniel Bikle
- Endocrine Research Unit, Department of Veterans Affairs Medical Center, Department of Medicine, University of California, San Francisco, CA 94121, USA
| | - Chialing Tu
- Endocrine Research Unit, Department of Veterans Affairs Medical Center, Department of Medicine, University of California, San Francisco, CA 94121, USA
| | - Dolores Shoback
- Endocrine Research Unit, Department of Veterans Affairs Medical Center, Department of Medicine, University of California, San Francisco, CA 94121, USA
| | - Wenhan Chang
- Endocrine Research Unit, Department of Veterans Affairs Medical Center, Department of Medicine, University of California, San Francisco, CA 94121, USA
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12
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Adams JS, Ramin J, Rafison B, Windon C, Windon A, Liu PT. Redefining Human Vitamin D Sufficiency: Back to the Basics. Bone Res 2013; 1:2-10. [PMID: 25285234 DOI: 10.4248/br201301002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Affiliation(s)
- John S Adams
- Orthopaedic Hospital Research Center, UCLA-Orthopaedic Hospital Department of Orthopaedic Surgery, David Geffen School of Medicine at UCLA ; Department of Molecular, Cell and Developmental Biology, Division of Life Sciences, College of Letters and Science, UCLA
| | - Jonathan Ramin
- Orthopaedic Hospital Research Center, UCLA-Orthopaedic Hospital Department of Orthopaedic Surgery, David Geffen School of Medicine at UCLA
| | - Brandon Rafison
- Orthopaedic Hospital Research Center, UCLA-Orthopaedic Hospital Department of Orthopaedic Surgery, David Geffen School of Medicine at UCLA
| | - Charles Windon
- Orthopaedic Hospital Research Center, UCLA-Orthopaedic Hospital Department of Orthopaedic Surgery, David Geffen School of Medicine at UCLA
| | - Annika Windon
- Orthopaedic Hospital Research Center, UCLA-Orthopaedic Hospital Department of Orthopaedic Surgery, David Geffen School of Medicine at UCLA
| | - Philip T Liu
- Orthopaedic Hospital Research Center, UCLA-Orthopaedic Hospital Department of Orthopaedic Surgery, David Geffen School of Medicine at UCLA
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Sterling KA, Eftekhari P, Girndt M, Kimmel PL, Raj DS. The immunoregulatory function of vitamin D: implications in chronic kidney disease. Nat Rev Nephrol 2012; 8:403-12. [PMID: 22614789 DOI: 10.1038/nrneph.2012.93] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Cardiovascular and infectious diseases remain the most common causes of death among patients with chronic kidney disease (CKD) and end-stage renal disease (ESRD). Basic science and epidemiological studies indicate that vitamin D has importance not only for cardiovascular health, but also for the immune response. Vitamin D signaling pathways regulate both innate and adaptive immunity, maintaining the associated inflammatory response within physiological limits. Levels of both the inactive as well as active form of vitamin D (25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, respectively) are decreased in patients with CKD and ESRD. It is reasonable to hypothesize, therefore, that the immune dysfunction associated with vitamin D deficiency in patients with CKD and ESRD in part explains the misdirected inflammatory response and increased susceptibility to infection seen in this population. Indeed, observational studies show that vitamin D deficiency in patients with ESRD is associated with increased mortality, and treatment with vitamin D is associated with a decreased risk of infection, as well as reduced all-cause mortality. However, whether different vitamin D preparations have differential effects on physiological function and clinical outcomes is still unclear. A proper understanding of the immune regulatory function of vitamin D is important for the development of future therapeutic strategies.
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Affiliation(s)
- Kevin A Sterling
- Division of Renal Diseases and Hypertension, Department of Medicine, The George Washington University School of Medicine, 2150 Pennsylvania Avenue NW, Washington, DC 20037, USA
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Diaz D, Allamneni K, Tarrant JM, Lewin-Koh SC, Pai R, Dhawan P, Cain GR, Kozlowski C, Hiraragi H, La N, Hartley DP, Ding X, Dean BJ, Bheddah S, Dambach DM. Phosphorous dysregulation induced by MEK small molecule inhibitors in the rat involves blockade of FGF-23 signaling in the kidney. Toxicol Sci 2011; 125:187-95. [PMID: 21976371 DOI: 10.1093/toxsci/kfr263] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
MEK, a kinase downstream of Ras and Raf oncogenes, constitutes a high priority target in oncology research. MEK small molecule inhibitors cause soft tissue mineralization in rats secondary to serum inorganic phosphorus (iP) elevation, but the molecular mechanism for this toxicity remains undetermined. We performed investigative studies with structurally distinct MEK inhibitors GEN-A and PD325901 (PD-901) in Sprague-Dawley rats. Our data support a mechanism that involves FGF-23 signal blockade in the rat kidney, causing transcriptional upregulation of 25-hydroxyvitamin D(3) 1-alpha-hydroxylase (Cyp27b1), the rate-limiting enzyme in vitamin D activation, and downregulation of 1,25-dihydroxyvitamin D(3) 24-hydroxylase (Cyp24a1), the enzyme that initiates the degradation of the active form of vitamin D. These transcriptional changes increase serum vitamin D levels, which in turn drive the increase in serum iP, leading to soft tissue mineralization in the rat.
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Affiliation(s)
- Dolores Diaz
- Safety Assessment, Genentech Inc., South San Francisco, California 94080, USA.
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Abstract
Fundamental to understanding the way in which perturbations in the vitamin D endocrine system can affect human health is an appreciation of the steps involved in the production of the well-recognized active hormonal form, 1,25-dihydroxyvitamin D(3). Thus this paper focuses first on the nature and regulation of the two enzymes responsible for the production of 1,25-dihydroxyvitamin D(3), the 25-hydroxylase in the liver and the 1α-hydroxylase in the kidney. The most important regulators of the 1α-hydroxylase in the kidney are 1,25-dihydroxyvitamin D(3) itself, parathyroid hormone and FGF23. The extent and importance of extra-renal, 1,25-dihydroxyvitamin D(3) synthesis is then considered. Finally the features of the 24R-hydroxylase, which produces 24R,25-dihydroxyvitamin D(3) in the kidney and is induced by and inactivated, 1,25-dihydroxyvitamin D(3)in target cells are described.
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Affiliation(s)
- Helen L Henry
- Department of Biochemistry, University of California, Riverside, CA 92521, USA.
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Abstract
Evidence of the role of vitamin D in the regulation of T and B cells, macrophages, dendritic cells, and keratinocytes continues to accumulate and provides a link between vitamin D and many autoimmune diseases, including Crohn's disease, juvenile diabetes mellitus, multiple sclerosis, asthma, and rheumatoid arthritis. Considering the influence of vitamin D on the immune system, it may have potential as a treatment for immune-mediated diseases, even if additional research is required to better quantify dosage. But the biggest obstacle to its clinical use is its potent hypercalcemic effect. The calcium status of the host may influence the effect of vitamin D on immunity.
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Affiliation(s)
- Nicola Maruotti
- Rheumatology Clinic Mario Carrozzo, D'Avanzo Hospital, Viale degli Aviatori 1, I-71100 Foggia, Italy
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Torres VE. Type II Calcimimetics and Polycystic Kidney Disease: Unanswered Questions. J Am Soc Nephrol 2009; 20:1421-5. [DOI: 10.1681/asn.2009050501] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
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