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Christakos S, Veldurthy V, Patel N, Wei R. Intestinal Regulation of Calcium: Vitamin D and Bone Physiology. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1033:3-12. [PMID: 29101648 DOI: 10.1007/978-3-319-66653-2_1] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The principal function of vitamin D in the maintenance of calcium homeostasis is to increase intestinal calcium absorption. This conclusion was made from studies in vitamin D receptor (VDR) null mice which showed that rickets and osteomalacia were prevented when VDR null mice were fed a rescue diet that included high calcium, indicating that the skeletal abnormalities of the VDR null mice are primarily the result of impaired intestinal calcium absorption. Although vitamin D is critical for controlling intestinal calcium absorption, the mechanisms involved have remained incomplete. This chapter reviews studies, including studies in genetically modified mice, that have provided new insight and have challenged the traditional model of VDR-mediated calcium absorption.
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Affiliation(s)
- Sylvia Christakos
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers the State University of New Jersey, New Jersey Medical School, 185 South Orange Ave, Newark, NJ, 07103, USA.
| | - Vaishali Veldurthy
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers the State University of New Jersey, New Jersey Medical School, 185 South Orange Ave, Newark, NJ, 07103, USA
| | - Nishant Patel
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers the State University of New Jersey, New Jersey Medical School, 185 South Orange Ave, Newark, NJ, 07103, USA
| | - Ran Wei
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers the State University of New Jersey, New Jersey Medical School, 185 South Orange Ave, Newark, NJ, 07103, USA
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van Goor MKC, Hoenderop JGJ, van der Wijst J. TRP channels in calcium homeostasis: from hormonal control to structure-function relationship of TRPV5 and TRPV6. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2016; 1864:883-893. [PMID: 27913205 DOI: 10.1016/j.bbamcr.2016.11.027] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2016] [Accepted: 11/23/2016] [Indexed: 12/16/2022]
Abstract
Maintaining plasma calcium levels within a narrow range is of vital importance for many physiological functions. Therefore, calcium transport processes in the intestine, bone and kidney are tightly regulated to fine-tune the rate of absorption, storage and excretion. The TRPV5 and TRPV6 calcium channels are viewed as the gatekeepers of epithelial calcium transport. Several calciotropic hormones control the channels at the level of transcription, membrane expression, and function. Recent technological advances have provided the first near-atomic resolution structural models of several TRPV channels, allowing insight into their architecture. While this field is still in its infancy, it has increased our understanding of molecular channel regulation and holds great promise for future structure-function studies of these ion channels. This review will summarize the mechanisms that control the systemic calcium balance, as well as extrapolate structural views to the molecular functioning of TRPV5/6 channels in epithelial calcium transport.
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Affiliation(s)
- Mark K C van Goor
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud university medical center, Nijmegen, The Netherlands
| | - Joost G J Hoenderop
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud university medical center, Nijmegen, The Netherlands.
| | - Jenny van der Wijst
- Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud university medical center, Nijmegen, The Netherlands.
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Vitamin D, calcium homeostasis and aging. Bone Res 2016; 4:16041. [PMID: 27790378 PMCID: PMC5068478 DOI: 10.1038/boneres.2016.41] [Citation(s) in RCA: 195] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Revised: 08/31/2016] [Accepted: 09/04/2016] [Indexed: 12/15/2022] Open
Abstract
Osteoporosis is characterized by low bone mass and microarchitecture deterioration of bone tissue, leading to enhanced bone fragility and consequent increase in fracture risk. Evidence is accumulating for an important role of calcium deficiency as the process of aging is associated with disturbed calcium balance. Vitamin D is the principal factor that maintains calcium homeostasis. Increasing evidence indicates that the reason for disturbed calcium balance with age is inadequate vitamin D levels in the elderly. In this article, an overview of our current understanding of vitamin D, its metabolism, and mechanisms involved in vitamin D-mediated maintenance of calcium homeostasis is presented. In addition, mechanisms involved in age-related dysregulation of 1,25(OH)2D3 action, recommended daily doses of vitamin D and calcium, and the use of vitamin D analogs for the treatment of osteoporosis (which remains controversial) are reviewed. Elucidation of the molecular pathways of vitamin D action and modifications that occur with aging will be an active area of future research that has the potential to reveal new therapeutic strategies to maintain calcium balance.
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Abstract
Hypercalcemia occurs in up to 4% of the population in association with malignancy, primary hyperparathyroidism, ingestion of excessive calcium and/or vitamin D, ectopic production of 1,25-dihydroxyvitamin D [1,25(OH)2D], and impaired degradation of 1,25(OH)2D. The ingestion of excessive amounts of vitamin D3 (or vitamin D2) results in hypercalcemia and hypercalciuria due to the formation of supraphysiological amounts of 25-hydroxyvitamin D [25(OH)D] that bind to the vitamin D receptor, albeit with lower affinity than the active form of the vitamin, 1,25(OH)2D, and the formation of 5,6-trans 25(OH)D, which binds to the vitamin D receptor more tightly than 25(OH)D. In patients with granulomatous disease such as sarcoidosis or tuberculosis and tumors such as lymphomas, hypercalcemia occurs as a result of the activity of ectopic 25(OH)D-1-hydroxylase (CYP27B1) expressed in macrophages or tumor cells and the formation of excessive amounts of 1,25(OH)2D. Recent work has identified a novel cause of non-PTH-mediated hypercalcemia that occurs when the degradation of 1,25(OH)2D is impaired as a result of mutations of the 1,25(OH)2D-24-hydroxylase cytochrome P450 (CYP24A1). Patients with biallelic and, in some instances, monoallelic mutations of the CYP24A1 gene have elevated serum calcium concentrations associated with elevated serum 1,25(OH)2D, suppressed PTH concentrations, hypercalciuria, nephrocalcinosis, nephrolithiasis, and on occasion, reduced bone density. Of interest, first-time calcium renal stone formers have elevated 1,25(OH)2D and evidence of impaired 24-hydroxylase-mediated 1,25(OH)2D degradation. We will describe the biochemical processes associated with the synthesis and degradation of various vitamin D metabolites, the clinical features of the vitamin D-mediated hypercalcemia, their biochemical diagnosis, and treatment.
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Affiliation(s)
- Peter J Tebben
- Divisions of Endocrinology (P.J.T., R.K.) and Nephrology and Hypertension (R.K.), and Departments of Pediatric and Adolescent Medicine (P.J.T.), Internal Medicine (P.J.T., R.K.), Laboratory Medicine and Pathology (R.J.S.), and Biochemistry in Molecular Biology (R.K.), Mayo Clinic College of Medicine, Rochester, Minnesota 55905
| | - Ravinder J Singh
- Divisions of Endocrinology (P.J.T., R.K.) and Nephrology and Hypertension (R.K.), and Departments of Pediatric and Adolescent Medicine (P.J.T.), Internal Medicine (P.J.T., R.K.), Laboratory Medicine and Pathology (R.J.S.), and Biochemistry in Molecular Biology (R.K.), Mayo Clinic College of Medicine, Rochester, Minnesota 55905
| | - Rajiv Kumar
- Divisions of Endocrinology (P.J.T., R.K.) and Nephrology and Hypertension (R.K.), and Departments of Pediatric and Adolescent Medicine (P.J.T.), Internal Medicine (P.J.T., R.K.), Laboratory Medicine and Pathology (R.J.S.), and Biochemistry in Molecular Biology (R.K.), Mayo Clinic College of Medicine, Rochester, Minnesota 55905
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Abstract
Calcium is an important ion in cell signaling, hormone regulation, and bone health. Its regulation is complex and intimately connected to that of phosphate homeostasis. Both ions are maintained at appropriate levels to maintain the extracellular to intracellular gradients, allow for mineralization of bone, and to prevent extra skeletal and urinary calcification. The homeostasis involves the target organs intestine, parathyroid glands, kidney, and bone. Multiple hormones converge to regulate the extracellular calcium level: parathyroid hormone, vitamin D (principally 25(OH)D or 1,25(OH)2D), fibroblast growth factor 23, and α-klotho. Fine regulation of calcium homeostasis occurs in the thick ascending limb and collecting tubule segments via actions of the calcium sensing receptor and several channels/transporters. The kidney participates in homeostatic loops with bone, intestine, and parathyroid glands. Initially in the course of progressive kidney disease, the homeostatic response maintains serum levels of calcium and phosphorus in the desired range, and maintains neutral balance. However, once the kidneys are no longer able to appropriately respond to hormones and excrete calcium and phosphate, positive balance ensues leading to adverse cardiac and skeletal abnormalities. © 2016 American Physiological Society. Compr Physiol 6:1781-1800, 2016.
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Affiliation(s)
- Sharon M Moe
- Division of Nephrology, Indiana University School of Medicine, Roudebush Veterans Administration Medical Center, Indianapolis, Indiana.,Section of Nephrology, Roudebush Veterans Administration Medical Center, Indianapolis, Indiana
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Allais L, De Smet R, Verschuere S, Talavera K, Cuvelier CA, Maes T. Transient Receptor Potential Channels in Intestinal Inflammation: What Is the Impact of Cigarette Smoking? Pathobiology 2016; 84:1-15. [DOI: 10.1159/000446568] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2015] [Accepted: 05/02/2016] [Indexed: 11/19/2022] Open
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Granjon D, Bonny O, Edwards A. A model of calcium homeostasis in the rat. Am J Physiol Renal Physiol 2016; 311:F1047-F1062. [PMID: 27358053 DOI: 10.1152/ajprenal.00230.2016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Accepted: 06/27/2016] [Indexed: 12/14/2022] Open
Abstract
We developed a model of calcium homeostasis in the rat to better understand the impact of dysfunctions such as primary hyperparathyroidism and vitamin D deficiency on calcium balance. The model accounts for the regulation of calcium intestinal uptake, bone resorption, and renal reabsorption by parathyroid hormone (PTH), vitamin D3, and Ca2+ itself. It is the first such model to incorporate recent findings regarding the role of the calcium-sensing receptor (CaSR) in the kidney, the presence of a rapidly exchangeable pool in bone, and the delayed response of vitamin D3 synthesis. Accounting for two (fast and slow) calcium storage compartments in bone allows the model to properly predict the effects of bisphophonates on the plasma levels of Ca2+ ([Ca2+]p), PTH, and vitamin D3 Our model also suggests that Ca2+ exchange rates between plasma and the fast pool vary with both sex and age, allowing [Ca2+]p to remain constant in spite of sex- and age-based hormonal and other differences. Our results suggest that the inconstant hypercalciuria that is observed in primary hyperparathyroidism can be attributed in part to counterbalancing effects of PTH and CaSR in the kidney. Our model also correctly predicts that calcimimetic agents such as cinacalcet bring down [Ca2+]p to within its normal range in primary hyperparathyroidism. In addition, the model provides a simulation of CYP24A1 inactivation that leads to a situation reminiscent of infantile hypercalcemia. In summary, our model of calcium handling can be used to decipher the complex regulation of calcium homeostasis.
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Affiliation(s)
- David Granjon
- Sorbonne Universités, UPMC Univ Paris 06, Université Paris Descartes, Sorbonne Paris Cité, INSERM UMRS 1138, CNRS ERL 8228, Centre de Recherche des Cordeliers, Paris, France; and.,Department of Pharmacology and Toxicology, University of Lausanne, and Service of Nephrology, Lausanne University Hospital, Lausanne, Switzerland
| | - Olivier Bonny
- Department of Pharmacology and Toxicology, University of Lausanne, and Service of Nephrology, Lausanne University Hospital, Lausanne, Switzerland
| | - Aurélie Edwards
- Sorbonne Universités, UPMC Univ Paris 06, Université Paris Descartes, Sorbonne Paris Cité, INSERM UMRS 1138, CNRS ERL 8228, Centre de Recherche des Cordeliers, Paris, France; and
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Elfers K, Marr I, Wilkens MR, Breves G, Langeheine M, Brehm R, Muscher-Banse AS. Expression of Tight Junction Proteins and Cadherin 17 in the Small Intestine of Young Goats Offered a Reduced N and/or Ca Diet. PLoS One 2016; 11:e0154311. [PMID: 27120348 PMCID: PMC4847856 DOI: 10.1371/journal.pone.0154311] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2015] [Accepted: 04/12/2016] [Indexed: 12/14/2022] Open
Abstract
Diets fed to ruminants should contain nitrogen (N) as low as possible to reduce feed costs and environmental pollution. Though possessing effective N-recycling mechanisms to maintain the N supply for rumen microbial protein synthesis and hence protein supply for the host, an N reduction caused substantial changes in calcium (Ca) and phosphate homeostasis in young goats including decreased intestinal transepithelial Ca absorption as reported for monogastric species. In contrast to the transcellular component of transepithelial Ca transport, the paracellular route has not been investigated in young goats. Therefore, the aim of the present study was to characterise the effects of dietary N and/or Ca reduction on paracellular transport mechanisms in young goats. Electrophysiological properties of intestinal epithelia were investigated by Ussing chamber experiments. The expression of tight junction (TJ) and adherens junction (AJ) proteins in intestinal epithelia were examined on mRNA level by qPCR and on protein level by western blot analysis. Dietary N reduction led to a segment specific increase in tissue conductances in the proximal jejunum which might be linked to concomitantly decreased expression of cadherin 17 mRNA. Expression of occludin (OCLN) and zonula occludens protein 1 was increased in mid jejunal epithelia of N reduced fed goats on mRNA and partly on protein level. Reduced dietary Ca supply resulted in a segment specific increase in claudin 2 and claudin 12 expression and decreased the expression of OCLN which might have been mediated at least in part by calcitriol. These data show that dietary N as well as Ca reduction affected expression of TJ and AJ proteins in a segment specific manner in young goats and may thus be involved in modulation of paracellular Ca permeability.
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Affiliation(s)
- Kristin Elfers
- Department of Physiology, University of Veterinary Medicine Hannover, Bischofsholer Damm 15/102, 30173, Hannover, Germany
| | - Isabell Marr
- Department of Physiology, University of Veterinary Medicine Hannover, Bischofsholer Damm 15/102, 30173, Hannover, Germany
| | - Mirja R. Wilkens
- Department of Physiology, University of Veterinary Medicine Hannover, Bischofsholer Damm 15/102, 30173, Hannover, Germany
| | - Gerhard Breves
- Department of Physiology, University of Veterinary Medicine Hannover, Bischofsholer Damm 15/102, 30173, Hannover, Germany
| | - Marion Langeheine
- Institute of Anatomy, University of Veterinary Medicine Hannover, Bischofsholer Damm 15/122, 30173, Hannover, Germany
| | - Ralph Brehm
- Institute of Anatomy, University of Veterinary Medicine Hannover, Bischofsholer Damm 15/122, 30173, Hannover, Germany
| | - Alexandra S. Muscher-Banse
- Department of Physiology, University of Veterinary Medicine Hannover, Bischofsholer Damm 15/102, 30173, Hannover, Germany
- * E-mail:
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59
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Mady LJ, Ajibade DV, Hsaio C, Teichert A, Fong C, Wang Y, Christakos S, Bikle DD. The Transient Role for Calcium and Vitamin D during the Developmental Hair Follicle Cycle. J Invest Dermatol 2016; 136:1337-1345. [PMID: 26994969 DOI: 10.1016/j.jid.2016.02.813] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Revised: 02/02/2016] [Accepted: 02/15/2016] [Indexed: 12/14/2022]
Abstract
The role for 1,25-dihydroxyvitamin D3 and/or calcium in hair follicle cycling is not clear despite their impact on keratinocyte differentiation. We found that calbindin-D9k null (knockout) pups generated from calbindin-D9k knockout females fed a vitamin D-deficient, low-calcium (0.47%) diet develop transient alopecia. The pups appear phenotypically normal until 13 days of age, after which the hair progressively sheds in a caudocephalic direction, resulting in truncal alopecia totalis by 20-23 days, with spontaneous recovery by 28 days. Histological studies showed markedly dystrophic hair follicles, loss of hair shafts with increased apoptosis, and hyperplastic epidermis during this time. Ha1 expression is lost during catagen in all mice but recovers more slowly in the knockout pups on the vitamin D-deficient, low-calcium diet. Keratin 1 expression is reduced throughout days 19-28. The expressions of involucrin, loricrin, and cathepsin L is initially increased by day 19 but subsequently falls below those of controls by day 23, as does that of desmoglein 3. Feeding the mothers a high-vitamin D/high-calcium (2%)/lactose (20%) diet lessens the phenotype, and knockout pups fostered to mothers fed a normal diet do not develop alopecia. Our results show that in calbindin-D9k knockout pups, a maternal vitamin D-deficient/low-calcium diet leads to transient noncicatricial alopecia.
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Affiliation(s)
- Leila J Mady
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers University-New Jersey Medical School, Newark, New Jersey, USA
| | - Dare V Ajibade
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers University-New Jersey Medical School, Newark, New Jersey, USA
| | - Connie Hsaio
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers University-New Jersey Medical School, Newark, New Jersey, USA
| | - Arnaud Teichert
- Department of Medicine and Dermatology, Endocrine Unit, Veterans Affairs Medical Center, University of California, San Francisco, California, USA
| | - Chak Fong
- Department of Medicine and Dermatology, Endocrine Unit, Veterans Affairs Medical Center, University of California, San Francisco, California, USA
| | - Yongmei Wang
- Department of Medicine and Dermatology, Endocrine Unit, Veterans Affairs Medical Center, University of California, San Francisco, California, USA
| | - Sylvia Christakos
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers University-New Jersey Medical School, Newark, New Jersey, USA
| | - Daniel D Bikle
- Department of Medicine and Dermatology, Endocrine Unit, Veterans Affairs Medical Center, University of California, San Francisco, California, USA.
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Chen L, Tuo B, Dong H. Regulation of Intestinal Glucose Absorption by Ion Channels and Transporters. Nutrients 2016; 8:nu8010043. [PMID: 26784222 PMCID: PMC4728656 DOI: 10.3390/nu8010043] [Citation(s) in RCA: 99] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Revised: 12/18/2015] [Accepted: 01/06/2016] [Indexed: 12/14/2022] Open
Abstract
The absorption of glucose is electrogenic in the small intestinal epithelium. The major route for the transport of dietary glucose from intestinal lumen into enterocytes is the Na+/glucose cotransporter (SGLT1), although glucose transporter type 2 (GLUT2) may also play a role. The membrane potential of small intestinal epithelial cells (IEC) is important to regulate the activity of SGLT1. The maintenance of membrane potential mainly depends on the activities of cation channels and transporters. While the importance of SGLT1 in glucose absorption has been systemically studied in detail, little is currently known about the regulation of SGLT1 activity by cation channels and transporters. A growing line of evidence suggests that cytosolic calcium ([Ca2+]cyt) can regulate the absorption of glucose by adjusting GLUT2 and SGLT1. Moreover, the absorption of glucose and homeostasis of Ca2+ in IEC are regulated by cation channels and transporters, such as Ca2+ channels, K+ channels, Na+/Ca2+ exchangers, and Na+/H+ exchangers. In this review, we consider the involvement of these cation channels and transporters in the regulation of glucose uptake in the small intestine. Modulation of them may be a potential strategy for the management of obesity and diabetes.
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Affiliation(s)
- Lihong Chen
- Department of Gastroenterology, Affiliated Hospital, Zunyi Medical College, and Digestive Disease Institute of Guizhou Province, Zunyi 563003, China.
| | - Biguang Tuo
- Department of Gastroenterology, Affiliated Hospital, Zunyi Medical College, and Digestive Disease Institute of Guizhou Province, Zunyi 563003, China.
| | - Hui Dong
- Department of Gastroenterology, Affiliated Hospital, Zunyi Medical College, and Digestive Disease Institute of Guizhou Province, Zunyi 563003, China.
- Department of Gastroenterology, Xinqiao Hospital, Third Military Medical University, Chongqing 400037, China.
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Christakos S, Dhawan P, Verstuyf A, Verlinden L, Carmeliet G. Vitamin D: Metabolism, Molecular Mechanism of Action, and Pleiotropic Effects. Physiol Rev 2016; 96:365-408. [PMID: 26681795 PMCID: PMC4839493 DOI: 10.1152/physrev.00014.2015] [Citation(s) in RCA: 1071] [Impact Index Per Article: 133.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
1,25-Dihydroxvitamin D3 [1,25(OH)2D3] is the hormonally active form of vitamin D. The genomic mechanism of 1,25(OH)2D3 action involves the direct binding of the 1,25(OH)2D3 activated vitamin D receptor/retinoic X receptor (VDR/RXR) heterodimeric complex to specific DNA sequences. Numerous VDR co-regulatory proteins have been identified, and genome-wide studies have shown that the actions of 1,25(OH)2D3 involve regulation of gene activity at a range of locations many kilobases from the transcription start site. The structure of the liganded VDR/RXR complex was recently characterized using cryoelectron microscopy, X-ray scattering, and hydrogen deuterium exchange. These recent technological advances will result in a more complete understanding of VDR coactivator interactions, thus facilitating cell and gene specific clinical applications. Although the identification of mechanisms mediating VDR-regulated transcription has been one focus of recent research in the field, other topics of fundamental importance include the identification and functional significance of proteins involved in the metabolism of vitamin D. CYP2R1 has been identified as the most important 25-hydroxylase, and a critical role for CYP24A1 in humans was noted in studies showing that inactivating mutations in CYP24A1 are a probable cause of idiopathic infantile hypercalcemia. In addition, studies using knockout and transgenic mice have provided new insight on the physiological role of vitamin D in classical target tissues as well as evidence of extraskeletal effects of 1,25(OH)2D3 including inhibition of cancer progression, effects on the cardiovascular system, and immunomodulatory effects in certain autoimmune diseases. Some of the mechanistic findings in mouse models have also been observed in humans. The identification of similar pathways in humans could lead to the development of new therapies to prevent and treat disease.
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Affiliation(s)
- Sylvia Christakos
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers, The State University of New Jersey, New Jersey Medical School, Newark, New Jersey; and Laboratory of Clinical and Experimental Endocrinology, KU Leuven, Leuven, Belgium
| | - Puneet Dhawan
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers, The State University of New Jersey, New Jersey Medical School, Newark, New Jersey; and Laboratory of Clinical and Experimental Endocrinology, KU Leuven, Leuven, Belgium
| | - Annemieke Verstuyf
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers, The State University of New Jersey, New Jersey Medical School, Newark, New Jersey; and Laboratory of Clinical and Experimental Endocrinology, KU Leuven, Leuven, Belgium
| | - Lieve Verlinden
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers, The State University of New Jersey, New Jersey Medical School, Newark, New Jersey; and Laboratory of Clinical and Experimental Endocrinology, KU Leuven, Leuven, Belgium
| | - Geert Carmeliet
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers, The State University of New Jersey, New Jersey Medical School, Newark, New Jersey; and Laboratory of Clinical and Experimental Endocrinology, KU Leuven, Leuven, Belgium
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Schröder B, Wilkens MR, Ricken GE, Leonhard-Marek S, Fraser DR, Breves G. Calcium transport in bovine rumen epithelium as affected by luminal Ca concentrations and Ca sources. Physiol Rep 2015; 3:3/11/e12615. [PMID: 26564067 PMCID: PMC4673643 DOI: 10.14814/phy2.12615] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The quantitative role of different segments of the gastrointestinal tract for Ca absorption, the respective mechanisms, and their regulation are not fully identified for ruminants, that is, cattle. In different in vitro experiments the forestomach wall has been demonstrated to be a major site for active Ca absorption in sheep and goats. In order to further clarify the role of the bovine rumen for Ca transport with special attention to luminal Ca concentrations, its ionic form, and pH, electrophysiological and unidirectional flux rate measurements were performed with isolated bovine rumen epithelial tissues. For Ca flux studies (Jms, Jsm) in vitro Ussing chamber technique was applied. Standard RT-PCR method was used to characterize TRPV6 and PMCA1 as potential contributors to transepithelial active Ca transport. At Ca concentrations of 1.2 mmol L(-1) on both sides of the tissues, Jms were higher than Jsm resulting under some conditions in significant Ca net flux rates (Jnet), indicating the presence of active Ca transport. In the absence of an electrical gradient, Jnet could significantly be stimulated in the presence of luminal short-chain fatty acids (SCFAs). Increasing the luminal Ca concentrations up to 11.2 mmol L(-1) resulted in significant increases in Jms without influencing Jsm. Providing Ca in its form as respective chloride, formate, or propionate salts there was no significant effect on Jms. No transcripts specific for Ca channel TRPV6 could be demonstrated. Our results indicate different mechanisms for Ca absorption in bovine rumen as compared with those usually described for the small intestines.
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Affiliation(s)
- Bernd Schröder
- Department of Physiology, University of Veterinary Medicine, Foundation, Hannover, Germany
| | - Mirja R Wilkens
- Department of Physiology, University of Veterinary Medicine, Foundation, Hannover, Germany
| | - Gundula E Ricken
- Department of Physiology, University of Veterinary Medicine, Foundation, Hannover, Germany
| | - Sabine Leonhard-Marek
- Department of Physiology, University of Veterinary Medicine, Foundation, Hannover, Germany
| | - David R Fraser
- Faculty of Veterinary Science, University of Sydney, Sydney, Australia
| | - Gerhard Breves
- Department of Physiology, University of Veterinary Medicine, Foundation, Hannover, Germany
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Dietary and pharmacological compounds altering intestinal calcium absorption in humans and animals. Nutr Res Rev 2015; 28:83-99. [PMID: 26466525 DOI: 10.1017/s0954422415000050] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The intestine is the only gate for the entry of Ca to the body in humans and mammals. The entrance of Ca occurs via paracellular and intracellular pathways. All steps of the latter pathway are regulated by calcitriol and by other hormones. Dietary and pharmacological compounds also modulate the intestinal Ca absorption process. Among them, dietary Ca and P are known to alter the lipid and protein composition of the brush-border and basolateral membranes and, consequently, Ca transport. Ca intakes are below the requirements recommended by health professionals in most countries, triggering important health problems. Chronic low Ca intake has been related to illness conditions such as osteoporosis, hypertension, renal lithiasis and incidences of human cancer. Carbohydrates, mainly lactose, and prebiotics have been described as positive modulators of intestinal Ca absorption. Apparently, high meat proteins increase intestinal Ca absorption while the effect of dietary lipids remains unclear. Pharmacological compounds such as menadione, dl-butionine-S,R-sulfoximine and ursodeoxycholic acid also modify intestinal Ca absorption as a consequence of altering the redox state of the epithelial cells. The paracellular pathway of intestinal Ca absorption is poorly known and is under present study in some laboratories. Another field that needs to be explored more intensively is the influence of the gene × diet interaction on intestinal Ca absorption. Health professionals should be aware of this knowledge in order to develop nutritional or medical strategies to stimulate the efficiency of intestinal Ca absorption and to prevent diseases.
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Ryan ZC, Craig TA, Filoteo AG, Westendorf JJ, Cartwright EJ, Neyses L, Strehler EE, Kumar R. Deletion of the intestinal plasma membrane calcium pump, isoform 1, Atp2b1, in mice is associated with decreased bone mineral density and impaired responsiveness to 1, 25-dihydroxyvitamin D3. Biochem Biophys Res Commun 2015; 467:152-6. [PMID: 26392310 DOI: 10.1016/j.bbrc.2015.09.087] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Accepted: 09/16/2015] [Indexed: 01/01/2023]
Abstract
The physiological importance of the intestinal plasma membrane calcium pump, isoform 1, (Pmca1, Atp2b1), in calcium absorption and homeostasis has not been previously demonstrated in vivo. Since global germ-line deletion of the Pmca1 in mice is associated with embryonic lethality, we selectively deleted the Pmca1 in intestinal absorptive cells. Mice with loxP sites flanking exon 2 of the Pmca1 gene (Pmca1(fl/fl)) were crossed with mice expressing Cre recombinase in the intestine under control of the villin promoter to give mice in which the Pmca1 had been deleted in the intestine (Pmca1(EKO) mice). Pmca1(EKO) mice were born at a reduced frequency and were small at the time of birth when compared to wild-type (Wt) littermates. At two months of age, Pmca1(EKO) mice fed a 0.81% calcium, 0.34% phosphorus, normal vitamin D diet had reduced whole body bone mineral density (P < 0.037), and reduced femoral bone mineral density (P < 0.015). There was a trend towards lower serum calcium and higher serum parathyroid hormone (PTH) and 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) concentrations in Pmca1(EKO) mice compared to Wt mice but the changes were not statistically significant. The urinary phosphorus/creatinine ratio was increased in Pmca1(EKO) mice (P < 0.004). Following the administration of 200 ng of 1α,25(OH)2D3 intraperitoneally to Wt mice, active intestinal calcium transport increased ∼2-fold, whereas Pmca1(EKO) mice administered an equal amount of 1α,25(OH)2D3 failed to show an increase in active calcium transport. Deletion of the Pmca1 in the intestine is associated with reduced growth and bone mineralization, and a failure to up-regulate calcium absorption in response to 1α,25(OH)2D3.
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Affiliation(s)
- Zachary C Ryan
- Nephrology Research, Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA
| | - Theodore A Craig
- Nephrology Research, Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA
| | - Adelaida G Filoteo
- Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA
| | - Jennifer J Westendorf
- Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA; Department of Orthopedic Surgery, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA
| | | | - Ludwig Neyses
- Institute of Cardiovascular Sciences, University of Manchester, Manchester, M13 9PT, UK; University of Luxembourg, L-4365, Esch-sur-Alzette, Luxembourg
| | - Emanuel E Strehler
- Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA.
| | - Rajiv Kumar
- Nephrology Research, Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA; Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA.
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Reyes-Fernandez PC, Fleet JC. Luminal glucose does not enhance active intestinal calcium absorption in mice: evidence against a role for Ca(v)1.3 as a mediator of calcium uptake during absorption. Nutr Res 2015; 35:1009-15. [PMID: 26403486 DOI: 10.1016/j.nutres.2015.08.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Revised: 08/25/2015] [Accepted: 08/27/2015] [Indexed: 12/12/2022]
Abstract
Intestinal Ca absorption occurs through a 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-regulated transcellular pathway, especially when habitual dietary Ca intake is low. Recently the L-type voltage-gated Ca channel, Cav1.3, was proposed to mediate active, transcellular Ca absorption in response to membrane depolarization caused by elevated luminal glucose levels after a meal. We tested the hypothesis that high luminal glucose could reveal a role for Cav1.3 in active intestinal Ca absorption in mice. Nine-week-old male C57BL/6 J mice were fed AIN93G diets containing either low (0.125%) or high (1%) Ca for 1 week, and Ca absorption was examined by an oral gavage method using a 45Ca-transport buffer containing 25 mmol/L of glucose or fructose. Transient receptor potential vanilloid 6 (TRPV6), calbindin D9k (CaBPD9k), and Cav1.3 messenger RNA (mRNA) levels were measured in the duodenum, jejunum, and ileum. TRPV6 and CaBPD9k expressions were highest in the duodenum, where active, 1,25(OH)2D3-regulated Ca absorption occurs, whereas Cav1.3 mRNA levels were similar across the intestinal segments. As expected, the low-Ca diet increased renal cytochrome p450-27B1 (CYP27B1) mRNA (P = .003), serum 1,25(OH)2D3 (P < .001), and Ca absorption efficiency by 2-fold with the fructose buffer. However, the glucose buffer used to favor Cav1.3 activation did not increase Ca absorption efficiency (P = .6) regardless of the dietary Ca intake level. Collectively, our results show that glucose did not enhance Ca absorption and they do not support a critical role for Cav1.3 in either basal or vitamin D-regulated intestinal Ca absorption in vivo.
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Affiliation(s)
| | - James C Fleet
- Department of Nutrition Science, Purdue University, West Lafayette, IN 47907-2059, USA.
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66
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Carmeliet G, Dermauw V, Bouillon R. Vitamin D signaling in calcium and bone homeostasis: a delicate balance. Best Pract Res Clin Endocrinol Metab 2015; 29:621-31. [PMID: 26303088 DOI: 10.1016/j.beem.2015.06.001] [Citation(s) in RCA: 89] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Loss-of-function mutations in genes involved in the vitamin D/vitamin D receptor system have clearly evidenced its critical role for mineral and skeletal homeostasis. Adequate levels of 1,25-dihydroxyvitamin D [1,25(OH)2D], the active form of vitamin D are therefore required and depend on sufficient sunlight exposure or dietary intake. Intestinal calcium absorption is a primary target of 1,25(OH)2D action and this pathway indirectly promotes calcium incorporation in bone. Severe vitamin D deficiency may thus decrease bone quality and leads to osteomalacia, whereas less severe deficiency increases the risk of osteoporosis and bone fractures. On the other hand, high vitamin D levels together with low dietary calcium intake will increase bone resorption and decrease bone mineralization in order to maintain normal serum calcium levels. Appropriate dietary calcium intake and sufficient serum vitamin D levels are thus important for skeletal health. Dosing of calcium and vitamin D supplements is still debated and requires further investigation.
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Affiliation(s)
- Geert Carmeliet
- Laboratory of Clinical and Experimental Endocrinology, Department of Clinical and Experimental Medicine, KU Leuven, 3000 Leuven, Belgium
| | - Veronique Dermauw
- Laboratory of Clinical and Experimental Endocrinology, Department of Clinical and Experimental Medicine, KU Leuven, 3000 Leuven, Belgium
| | - Roger Bouillon
- Laboratory of Clinical and Experimental Endocrinology, Department of Clinical and Experimental Medicine, KU Leuven, 3000 Leuven, Belgium.
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67
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Diaz de Barboza G, Guizzardi S, Tolosa de Talamoni N. Molecular aspects of intestinal calcium absorption. World J Gastroenterol 2015; 21:7142-7154. [PMID: 26109800 PMCID: PMC4476875 DOI: 10.3748/wjg.v21.i23.7142] [Citation(s) in RCA: 126] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2015] [Revised: 03/21/2015] [Accepted: 04/17/2015] [Indexed: 02/06/2023] Open
Abstract
Intestinal Ca2+ absorption is a crucial physiological process for maintaining bone mineralization and Ca2+ homeostasis. It occurs through the transcellular and paracellular pathways. The first route comprises 3 steps: the entrance of Ca2+ across the brush border membranes (BBM) of enterocytes through epithelial Ca2+ channels TRPV6, TRPV5, and Cav1.3; Ca2+ movement from the BBM to the basolateral membranes by binding proteins with high Ca2+ affinity (such as CB9k); and Ca2+ extrusion into the blood. Plasma membrane Ca2+ ATPase (PMCA1b) and sodium calcium exchanger (NCX1) are mainly involved in the exit of Ca2+ from enterocytes. A novel molecule, the 4.1R protein, seems to be a partner of PMCA1b, since both molecules co-localize and interact. The paracellular pathway consists of Ca2+ transport through transmembrane proteins of tight junction structures, such as claudins 2, 12, and 15. There is evidence of crosstalk between the transcellular and paracellular pathways in intestinal Ca2+ transport. When intestinal oxidative stress is triggered, there is a decrease in the expression of several molecules of both pathways that inhibit intestinal Ca2+ absorption. Normalization of redox status in the intestine with drugs such as quercetin, ursodeoxycholic acid, or melatonin return intestinal Ca2+ transport to control values. Calcitriol [1,25(OH)2D3] is the major controlling hormone of intestinal Ca2+ transport. It increases the gene and protein expression of most of the molecules involved in both pathways. PTH, thyroid hormones, estrogens, prolactin, growth hormone, and glucocorticoids apparently also regulate Ca2+ transport by direct action, indirect mechanism mediated by the increase of renal 1,25(OH)2D3 production, or both. Different physiological conditions, such as growth, pregnancy, lactation, and aging, adjust intestinal Ca2+ absorption according to Ca2+ demands. Better knowledge of the molecular details of intestinal Ca2+ absorption could lead to the development of nutritional and medical strategies for optimizing the efficiency of intestinal Ca2+ absorption and preventing osteoporosis and other pathologies related to Ca2+ metabolism.
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Lee SM, Riley EM, Meyer MB, Benkusky NA, Plum LA, DeLuca HF, Pike JW. 1,25-Dihydroxyvitamin D3 Controls a Cohort of Vitamin D Receptor Target Genes in the Proximal Intestine That Is Enriched for Calcium-regulating Components. J Biol Chem 2015; 290:18199-18215. [PMID: 26041780 DOI: 10.1074/jbc.m115.665794] [Citation(s) in RCA: 72] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Indexed: 12/15/2022] Open
Abstract
1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) plays an integral role in calcium homeostasis in higher organisms through its actions in the intestine, kidney, and skeleton. Interestingly, although several intestinal genes are known to play a contributory role in calcium homeostasis, the entire caste of key components remains to be identified. To examine this issue, Cyp27b1 null mice on either a normal or a high calcium/phosphate-containing rescue diet were treated with vehicle or 1,25(OH)2D3 and evaluated 6 h later. RNA samples from the duodena were then subjected to RNA sequence analysis, and the data were analyzed bioinformatically. 1,25(OH)2D3 altered expression of large collections of genes in animals under either dietary condition. 45 genes were found common to both 1,25(OH)2D3-treated groups and were composed of genes previously linked to intestinal calcium uptake, including S100g, Trpv6, Atp2b1, and Cldn2 as well as others. An additional distinct network of 56 genes was regulated exclusively by diet. We then conducted a ChIP sequence analysis of binding sites for the vitamin D receptor (VDR) across the proximal intestine in vitamin D-sufficient normal mice treated with vehicle or 1,25(OH)2D3. The residual VDR cistrome was composed of 4617 sites, which was increased almost 4-fold following hormone treatment. Interestingly, the majority of the genes regulated by 1,25(OH)2D3 in each diet group as well as those found in common in both groups contained frequent VDR sites that likely regulated their expression. This study revealed a global network of genes in the intestine that both represent direct targets of vitamin D action in mice and are involved in calcium absorption.
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Affiliation(s)
- Seong Min Lee
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Erin M Riley
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Mark B Meyer
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Nancy A Benkusky
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Lori A Plum
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Hector F DeLuca
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - J Wesley Pike
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706.
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Abstract
For humans and rodents, duodenum is a very important site of calcium absorption since it is exposed to ionized calcium released from dietary complexes by gastric acid. Calcium traverses the duodenal epithelium via both transcellular and paracellular pathways in a vitamin D-dependent manner. After binding to the nuclear vitamin D receptor, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] upregulates the expression of several calcium transporter genes, e.g., TRPV5/6, calbindin-D9k, plasma membrane Ca(2+)-ATPase1b, and NCX1, thereby enhancing the transcellular calcium transport. This action has been reported to be under the regulation of parathyroid-kidney-intestinal and bone-kidney-intestinal axes, in which the plasma calcium and fibroblast growth factor-23 act as negative feedback regulators, respectively. 1,25(OH)2D3 also modulates the expression of tight junction-related genes and convective water flow, presumably to increase the paracellular calcium permeability and solvent drag-induced calcium transport. However, vitamin D-independent calcium absorption does exist and plays an important role in calcium homeostasis under certain conditions, particularly in neonatal period, pregnancy, and lactation as well as in naturally vitamin D-impoverished subterranean mammals.
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70
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Liu W, Liu MR, Zhang H. Expression of TRPV5 and TRPV6 in development of colonic adenocarcinoma. Shijie Huaren Xiaohua Zazhi 2014; 22:5422-5431. [DOI: 10.11569/wcjd.v22.i35.5422] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
AIM: To investigate the expression of transient receptor potential cation channel, subfamily V, member 5 (TRPV5) and TRPV6 in the development of colon adenocarcinoma and to discuss the role of TRPV5 and TRPV6 in the carcinogenesis of this malignancy.
METHODS: TRPV5, TRPV6 and Ki-67 expression was examined by immunohistochemical staining, RT-PCR, and Western blot in 20 colonic hyperplastic polyp, 20 colonic adenoma (40 for immunohistochemical staining), 20 colonic adenocarcinoma, and 20 normal colonic mucosal tissues obtained by endoscopic biopsy, surgical resection or endoscopic polypectomy. The relationship between the expression of TRPV6 and TRPV5 and the carcinogenesis of colon adenocarcinoma was then assessed.
RESULTS: TRPV5 and TRPV6 expression was detectable in the normal colon, colonic polyp and colonic cancer tissues, mainly localized in the cytoplasm. The expression of Ki-67 increased with the increase in TRPV5 and TRPV6 expression (P < 0.05). TRPV5 and TRPV6 proteins and mRNAs were weakly or not expressed in normal intestinal mucosa and non-adenoma polyps (P > 0.05), but were highly expressed in colon adenoma and colon adenocarcinoma (P < 0.05). TRPV5 and TRPV6 expression had a significant correlation with histological type (P < 0.05). In the colonic mucosa, TRPV5 expression was lower than TRPV6 expression (P < 0.05).
CONCLUSION: TRPV5 and TRPV6 show high expression in colon adenoma and adenocarcinoma, and Ki-67 expression is correlated with TRPV5 and TRPV6 expression. TRPV5 and TRPV6 might be related with the extent of tissue proliferation and the risk of malignant transformation of polyps. TRPV5 and TRPV6 may play an important role in the carcinogenesis and development of colonic adenocarcinoma.
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71
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Kovacs CS. Bone development and mineral homeostasis in the fetus and neonate: roles of the calciotropic and phosphotropic hormones. Physiol Rev 2014; 94:1143-218. [PMID: 25287862 DOI: 10.1152/physrev.00014.2014] [Citation(s) in RCA: 129] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Mineral and bone metabolism are regulated differently in utero compared with the adult. The fetal kidneys, intestines, and skeleton are not dominant sources of mineral supply for the fetus. Instead, the placenta meets the fetal need for mineral by actively transporting calcium, phosphorus, and magnesium from the maternal circulation. These minerals are maintained in the fetal circulation at higher concentrations than in the mother and normal adult, and such high levels appear necessary for the developing skeleton to accrete a normal amount of mineral by term. Parathyroid hormone (PTH) and calcitriol circulate at low concentrations in the fetal circulation. Fetal bone development and the regulation of serum minerals are critically dependent on PTH and PTH-related protein, but not vitamin D/calcitriol, fibroblast growth factor-23, calcitonin, or the sex steroids. After birth, the serum calcium falls and phosphorus rises before gradually reaching adult values over the subsequent 24-48 h. The intestines are the main source of mineral for the neonate, while the kidneys reabsorb mineral, and bone turnover contributes mineral to the circulation. This switch in the regulation of mineral homeostasis is triggered by loss of the placenta and a postnatal fall in serum calcium, and is followed in sequence by a rise in PTH and then an increase in calcitriol. Intestinal calcium absorption is initially a passive process facilitated by lactose, but later becomes active and calcitriol-dependent. However, calcitriol's role can be bypassed by increasing the calcium content of the diet, or by parenteral administration of calcium.
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Affiliation(s)
- Christopher S Kovacs
- Faculty of Medicine-Endocrinology, Memorial University of Newfoundland, St. John's, Newfoundland, Canada
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72
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Stoerger C, Flockerzi V. The transient receptor potential cation channel subfamily V member 6 (TRPV6): genetics, biochemical properties, and functions of exceptional calcium channel proteins. Biochem Cell Biol 2014; 92:441-8. [PMID: 25372600 DOI: 10.1139/bcb-2014-0063] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The transient receptor potential cation channel subfamily V member 6 (TRPV6) gene and cDNA were identified 15 years ago and exceptional observations on TrpV6 proteins and their function as a Ca(2+)-selective cation channel have been made since then. In this review we will summarize recent studies regarding the genetics, biochemical properties, and physiological functions of murine and human TrpV6 channel proteins. We will focus on TRPV6 gene polymorphisms, the start of TRPV6 translation at a non-AUG codon and the functions of TRPV6 in intestinal Ca(2+) uptake, sperm maturation, and male fertility.
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Affiliation(s)
- Christof Stoerger
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, 66421 Homburg, Germany
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73
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Krupa-Kozak U. Pathologic bone alterations in celiac disease: etiology, epidemiology, and treatment. Nutrition 2014; 30:16-24. [PMID: 24290593 DOI: 10.1016/j.nut.2013.05.027] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2013] [Revised: 05/29/2013] [Accepted: 05/31/2013] [Indexed: 12/13/2022]
Abstract
Low bone mineral density (BMD), osteopenia, and osteoporosis are frequent complications of celiac disease (CD). The etiology of pathologic bone alterations in CD is multifactorial; however, two main mechanisms are involved: intestinal malabsorption and chronic inflammation. A strict gluten-free diet (GFD) is thought to be the only effective treatment for CD; but treating bone complications related to CD remains complex. The objective of this review is to elucidate the bones problems related to CD and to increase awareness of osteoporosis development, considered as a sign of atypical CD presentation. Currently, a question of whether GFD alone is an effective treatment to correct the bone alterations in patients with CD is under debate. This review presents factors contributing to pathologic bone derangement, recent research on the epidemiology of low BMD, osteoporosis, and fractures, and the treatment of bone problems in patients with CD. The roles of calcium and transport mechanisms are additionally presented.
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Affiliation(s)
- Urszula Krupa-Kozak
- Institute of Animal Reproduction and Food Research of the Polish Academy of Sciences, Department of Chemistry and Biodynamics of Food, Olsztyn, Poland.
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74
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Liu W, Liu MR, Zhang H. Novel calcium ion channels TRPV5 and TRPV6 and gastrointestinal tumors. Shijie Huaren Xiaohua Zazhi 2014; 22:1966-1971. [DOI: 10.11569/wcjd.v22.i14.1966] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Transient receptor potential cation channel, subfamily V, member 5 (TRPV5) and TRPV6 are the subfamily members of the transient receptor potential (TRP), representing new highly selective Ca2+ membrane transport channels, which are mainly responsible for active transport of Ca2+ across the cell membrane and participate in regulation of many physiological activities in the body. This paper discusses the structures and electrophysiological properties of TRPV5 and TRPV6, their related factors and their relationship with gastrointestinal tumors, highlighting the role of TRPV5 and TRPV6 in the formation of gastrointestinal tumors.
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75
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Douard V, Patel C, Lee J, Tharabenjasin P, Williams E, Fritton JC, Sabbagh Y, Ferraris RP. Chronic high fructose intake reduces serum 1,25 (OH)2D3 levels in calcium-sufficient rodents. PLoS One 2014; 9:e93611. [PMID: 24718641 PMCID: PMC3981704 DOI: 10.1371/journal.pone.0093611] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2013] [Accepted: 03/05/2014] [Indexed: 12/14/2022] Open
Abstract
Excessive fructose consumption inhibits adaptive increases in intestinal Ca2+ transport in lactating and weanling rats with increased Ca2+ requirements by preventing the increase in serum levels of 1,25(OH)2D3. Here we tested the hypothesis that chronic fructose intake decreases 1,25(OH)2D3 levels independent of increases in Ca2+ requirements. Adult mice fed for five wk a high glucose-low Ca2+ diet displayed expected compensatory increases in intestinal and renal Ca2+ transporter expression and activity, in renal CYP27B1 (coding for 1α-hydroxylase) expression as well as in serum 1,25(OH)2D3 levels, compared with mice fed isocaloric glucose- or fructose-normal Ca2+ diets. Replacing glucose with fructose prevented these increases in Ca2+ transporter, CYP27B1, and 1,25(OH)2D3 levels induced by a low Ca2+ diet. In adult mice fed for three mo a normal Ca2+ diet, renal expression of CYP27B1 and of CYP24A1 (24-hydroxylase) decreased and increased, respectively, when the carbohydrate source was fructose instead of glucose or starch. Intestinal and renal Ca2+ transporter activity and expression did not vary with dietary carbohydrate. To determine the time course of fructose effects, a high fructose or glucose diet with normal Ca2+ levels was fed to adult rats for three mo. Serum levels of 1,25(OH)2D3 decreased and of FGF23 increased significantly over time. Renal expression of CYP27B1 and serum levels of 1,25(OH)2D3 still decreased in fructose- compared to those in glucose-fed rats after three mo. Serum parathyroid hormone, Ca2+ and phosphate levels were normal and independent of dietary sugar as well as time of feeding. Thus, chronically high fructose intakes can decrease serum levels of 1,25(OH)2D3 in adult rodents experiencing no Ca2+ stress and fed sufficient levels of dietary Ca2+. This finding is highly significant because fructose constitutes a substantial portion of the average diet of Americans already deficient in vitamin D.
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Affiliation(s)
- Veronique Douard
- Department of Pharmacology and Physiology, New Jersey Medical School, Rutgers Biomedical and Health Sciences (RBHS), Newark, New Jersey, United States of America
- * E-mail:
| | - Chirag Patel
- Department of Pharmacology and Physiology, New Jersey Medical School, Rutgers Biomedical and Health Sciences (RBHS), Newark, New Jersey, United States of America
| | - Jacklyn Lee
- Department of Pharmacology and Physiology, New Jersey Medical School, Rutgers Biomedical and Health Sciences (RBHS), Newark, New Jersey, United States of America
| | - Phuntila Tharabenjasin
- Department of Pharmacology and Physiology, New Jersey Medical School, Rutgers Biomedical and Health Sciences (RBHS), Newark, New Jersey, United States of America
| | - Edek Williams
- Department of Biomedical Engineering, Rutgers University, Piscataway, New Jersey, United States of America
| | - J. Christopher Fritton
- Department of Biomedical Engineering, Rutgers University, Piscataway, New Jersey, United States of America
- Department of Orthopaedics, New Jersey Medical School, RBHS, Newark, New Jersey, United States of America
| | - Yves Sabbagh
- Tissue Protection and Repair, Sanofi-Genzyme R&D Center, Genzyme, a Sanofi Company, Framingham, Massachusetts, United States of America
| | - Ronaldo P. Ferraris
- Department of Pharmacology and Physiology, New Jersey Medical School, Rutgers Biomedical and Health Sciences (RBHS), Newark, New Jersey, United States of America
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76
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Replogle RA, Li Q, Wang L, Zhang M, Fleet JC. Gene-by-diet interactions influence calcium absorption and bone density in mice. J Bone Miner Res 2014; 29:657-65. [PMID: 23955923 PMCID: PMC10591522 DOI: 10.1002/jbmr.2065] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Revised: 07/10/2013] [Accepted: 07/29/2013] [Indexed: 12/14/2022]
Abstract
Dietary calcium (Ca) intake is needed to attain peak bone mineral density (BMD). Habitual low Ca intake increases intestinal Ca absorption efficiency to protect bone mass, but the mechanism controlling, and the impact of genetics on, this adaptive response is not clear. We fed 11 genetically diverse inbred mouse lines a normal (0.5%) or low (0.25%) Ca diet from 4 to 12 weeks of age (n = 8 per diet per line) and studied the independent and interacting effects of diet and genetics on Ca and bone metabolism. Significant genetic variation was observed in all bone, renal, and intestinal phenotypes measured including Ca absorption. Also, adaptation of Ca absorption and bone parameters to low dietary Ca was significantly different among the lines. Ca absorption was positively correlated to femur BMD (r = 0.17, p = 0.02), and distal femur bone volume/tissue volume (BV/TV) (r = 0.34, p < 0.0001). Although Ca absorption was correlated to 1,25 dihydroxyvitamin D (1,25(OH)2 D) (r = 0.35, p < 0.0001), the adaptation of Ca absorption to low Ca intake did not correlate to diet-induced adaptation of 1,25(OH)2 D across the 11 lines. Several intestinal proteins have been proposed to mediate Ca absorption: claudins 2 and 12, voltage gated Ca channel v1.3 (Cav1.3), plasma membrane Ca ATPase 1b (PMCA1b), transient receptor potential vanilloid member 6 (TRPV6), and calbindin D9k (CaBPD9k). Only the mRNA levels for TRPV6, CaBPD9k, and PMCA1b were related to Ca absorption (r = 0.42, 0.43, and 0.21, respectively). However, a significant amount of the variation in Ca absorption is not explained by the current model and suggests that novel mechanisms remain to be determined. These observations lay the groundwork for discovery-focused initiatives to identify novel genetic factors controlling gene-by-diet interactions affecting Ca/bone metabolism.
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Affiliation(s)
- Rebecca A Replogle
- Department of Nutrition Science, Purdue University, West Lafayette, IN, USA
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77
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Christakos S, Lieben L, Masuyama R, Carmeliet G. Vitamin D endocrine system and the intestine. BONEKEY REPORTS 2014; 3:496. [PMID: 24605213 DOI: 10.1038/bonekey.2013.230] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2013] [Accepted: 10/25/2013] [Indexed: 12/12/2022]
Abstract
Calcium and phosphate regulate numerous biological processes and they are essential for bone mass and bone quality. The calcium and phosphate balance largely depends on intestinal absorption, and the dietary content of these ions determines the type of transport. High dietary intake of calcium and phosphate enables absorption by passive transport, but often the dietary content of these ions is in the low-normal range, especially for calcium. In this condition, the contribution of active intestinal calcium transport will increase to maintain normal serum levels. This adaptation is mainly regulated by the active form of vitamin D, 1,25 dihydroxyvitamin D, and requires normal concentrations of the precursor 25-hydroxyvitamin D. When intestinal calcium absorption is insufficient, hormonal adaptations will release calcium from bones to secure normocalcemia, not only by increasing bone loss but also by decreasing bone mineralization. These data underline the fact that adequate calcium intake is critical to secure skeletal integrity. Despite the insights that sufficient dietary calcium intake and normal 25-hydroxyvitamin D levels are critical for calcium and bone homeostasis, surprisingly little is known on the proteins that mediate intestinal calcium transport. Also, the interaction between the intestine and the kidney to control serum phosphate levels is still incompletely understood.
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Affiliation(s)
- Sylvia Christakos
- Department of Biochemistry and Molecular biology, New Jersey Medical School , Newark, NJ, USA
| | - Liesbet Lieben
- Systems biology of bone, Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus , Hinxton, Cambridgeshire, UK
| | - Ritsuko Masuyama
- Department of Molecular Bone Biology, Nagasaki University , Nagasaki, Japan
| | - Geert Carmeliet
- Clinical and Experimental Endocrinology, KU Leuven , Leuven, Belgium
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78
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Tharabenjasin P, Douard V, Patel C, Krishnamra N, Johnson RJ, Zuo J, Ferraris RP. Acute interactions between intestinal sugar and calcium transport in vitro. Am J Physiol Gastrointest Liver Physiol 2014; 306:G1-12. [PMID: 24177030 DOI: 10.1152/ajpgi.00263.2013] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Fructose consumption by Americans has increased markedly, whereas Ca(2+) intake has decreased below recommended levels. Because fructose metabolism decreases enterocyte ATP concentrations, we tested the hypothesis that luminal fructose acutely reduces active, diet-inducible Ca(2+) transport in the small intestine. We confirmed that the decrease in ATP concentrations was indeed greater in fructose- compared with glucose-incubated mucosal homogenates from wild-type and was prevented in fructose-incubated homogenates from ketohexokinase (KHK)(-/-) mice. We then induced active Ca(2+) transport by chronically feeding wild-type, fructose transporter glucose transporter 5 (GLUT5)(-/-), as well as KHK(-/-) mice a low Ca(2+) diet and measured transepithelial Ca(2+) transport in everted duodenal sacs incubated in solutions containing glucose, fructose, or their nonmetabolizable analogs. The diet-induced increase in active Ca(2+) transport was proportional to dramatic increases in expression of the Ca(2+)-selective channel transient receptor potential vanilloid family calcium channel 6 as well as of the Ca(2+)-binding protein 9k (CaBP9k) but not that of the voltage-dependent L-type channel Ca(v)1.3. Crypt-villus distribution of CaBP9k seems heterogeneous, but low Ca(2+) diets induce expression in more cells. In contrast, KHK distribution is homogeneous, suggesting that fructose metabolism can occur in all enterocytes. Diet-induced Ca(2+) transport was not enhanced by addition of the enterocyte fuel glutamine and was always greater in sacs of wild-type, GLUT5(-/-), and KHK(-/-) mice incubated with fructose or nonmetabolizable sugars than those incubated with glucose. Thus duodenal Ca(2+) transport is not affected by fructose and enterocyte ATP concentrations but instead may decrease with glucose metabolism, as Ca(2+) transport remains high with 3-O-methylglucose that is also transported by sodium-glucose cotransporter 1 but cannot be metabolized.
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Affiliation(s)
- Phuntila Tharabenjasin
- Dept. of Pharmacology & Physiology, Rutgers Biomedical and Health Sciences, New Jersey Medical School (NJMS 185 South Orange Ave., Newark, NJ 07103.
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79
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Abstract
TRPV6 (former synonyms ECAC2, CaT1, CaT-like) displays several specific features which makes it unique among the members of the mammalian Trp gene family (1) TRPV6 (and its closest relative, TRPV5) are the only highly Ca(2+)-selective channels of the entire TRP superfamily (Peng et al. 1999; Wissenbach et al. 2001; Voets et al. 2004). (2) Translation of Trpv6 initiates at a non-AUG codon, at ACG, located upstream of the annotated AUG, which is not used for initiation (Fecher-Trost et al. 2013). The ACG codon is nevertheless decoded by methionine. Not only a very rare event in eukaryotic biology, the full-length TRPV6 protein existing in vivo comprises an amino terminus extended by 40 amino acid residues compared to the annotated truncated TRPV6 protein which has been used in most studies on TRPV6 channel activity so far. (In the following numbering occurs according to this full-length protein, with the numbers of the so far annotated truncated protein in brackets). (3) Only in humans a coupled polymorphism of Trpv6 exists causing three amino acid exchanges and resulting in an ancestral Trpv6 haplotype and a so-called derived Trpv6 haplotype (Wissenbach et al. 2001). The ancestral allele encodes the amino acid residues C197(157), M418(378) and M721(681) and the derived alleles R197(157), V418(378) and T721(681). The ancestral haplotype is found in all species, the derived Trpv6 haplotype has only been identified in humans, and its frequency increases with the distance to the African continent. Apparently the Trpv6 gene has been a strong target for selection in humans, and its derived variant is one of the few examples showing consistently differences to the orthologues genes of other primates (Akey et al. 2004, 2006; Stajich and Hahn 2005; Hughes et al. 2008). (4) The Trpv6 gene expression is significantly upregulated in several human malignancies including the most common cancers, prostate and breast cancer (Wissenbach et al. 2001; Zhuang et al. 2002; Fixemer et al. 2003; Bolanz et al. 2008). (5) Male mice lacking functional TRPV6 channels are hypo-/infertile making TRPV6 one of the very few channels essential for male fertility (Weissgerber et al. 2011, 2012).
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Affiliation(s)
- Claudia Fecher-Trost
- Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, 66421, Homburg, Germany
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80
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Biological significance of calbindin-D9k within duodenal epithelium. Int J Mol Sci 2013; 14:23330-40. [PMID: 24287909 PMCID: PMC3876048 DOI: 10.3390/ijms141223330] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2013] [Revised: 11/22/2013] [Accepted: 11/22/2013] [Indexed: 12/23/2022] Open
Abstract
Calbindin-D9k (CaBP-9k) binds calcium with high affinity and regulates the distribution of free calcium in the cytoplasm. The expression of CaBP-9k is detected primarily in intestine that is vitamin D target tissue, and accumulates in the enterocytes of the duodenal villi. These enterocytes are the clearest example of vitamin D responsive cells, and the presence of CaBP-9k within them accentuates calcium absorption mediated by active transcellular calcium transport. It has been well established that the expression of CaBP-9k is mediated with vitamin D response element on its promoter and it regulates the amount of intracellular calcium in order to prevent cell death from reaching the toxicity of free calcium. There is now little doubt that glucocorticoid also decreases CaBP-9k expression in duodenal epithelial cells. In addition, it was reported that the level of CaBP-9k gene in enterocytes is increased in pregnancy when the plasma estradiol concentration is generally associated with a concomitant increase. Although calcium homeostasis was not disturbed in mice lacking the CaBP-9k gene, we found that CaBP-9k has a buffering role of free calcium in the cytosolic environment beyond that of calcium transfer. To expand our knowledge of the biological functions of CaBP-9k, our research has focused on defining the biological significance of intracellular CaBP-9k. Our findings suggest that the CaBP-9k gene is involved in compensatory induction of other calcium transporter genes in duodenal epithelial cells. This article summarizes the findings from recent studies on the expression and the functions of CaBP-9k in the small intestine.
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81
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Kirby BJ, Ma Y, Martin HM, Buckle Favaro KL, Karaplis AC, Kovacs CS. Upregulation of calcitriol during pregnancy and skeletal recovery after lactation do not require parathyroid hormone. J Bone Miner Res 2013; 28:1987-2000. [PMID: 23505097 DOI: 10.1002/jbmr.1925] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/08/2012] [Revised: 02/16/2013] [Accepted: 03/04/2013] [Indexed: 12/14/2022]
Abstract
Pregnancy invokes a doubling of intestinal calcium absorption whereas lactation programs skeletal resorption to provide calcium to milk. Postweaning bone formation restores the skeleton's bone mineral content (BMC), but the factors that regulate this are not established. We used Pth-null mice to test whether parathyroid hormone (PTH) is required for postweaning skeletal recovery. On a normal 1% calcium diet, wild-type (WT) and Pth-null mice each gained BMC during pregnancy, declined 15% to 18% below baseline during lactation, and restored the skeleton above baseline BMC within 14 days postweaning. A 2% calcium diet reduced the lactational decline in BMC without altering the gains achieved during pregnancy and postweaning. The hypocalcemia and hyperphosphatemia of Pth-null mice normalized during lactation and serum calcium remained normal during postweaning. Osteocalcin and propeptide of type 1 collagen (P1NP) each rose significantly after lactation to similar values in WT and Pth-null. Serum calcitriol increased fivefold during pregnancy in both genotypes whereas vitamin D binding protein levels were unchanged. Absence of PTH blocked a normal rise in fibroblast growth factor-23 (FGF23) during pregnancy despite high calcitriol. A 30-fold higher expression of Cyp27b1 in maternal kidneys versus placenta suggests that the pregnancy-related increase in calcitriol comes from the kidneys. Conversely, substantial placental expression of Cyp24a1 may contribute significantly to the metabolism of calcitriol. In conclusion, PTH is not required to upregulate renal expression of Cyp27b1 during pregnancy or to stimulate recovery from loss of BMC caused by lactation. A calcium-rich diet in rodents suppresses skeletal losses during lactation, unlike clinical trials that showed no effect of supplemental calcium on lactational decline in BMC.
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Affiliation(s)
- Beth J Kirby
- Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland, Canada
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82
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Rievaj J, Pan W, Cordat E, Alexander RT. The Na⁺/H⁺ exchanger isoform 3 is required for active paracellular and transcellular Ca²⁺ transport across murine cecum. Am J Physiol Gastrointest Liver Physiol 2013; 305:G303-13. [PMID: 23764894 PMCID: PMC4959879 DOI: 10.1152/ajpgi.00490.2012] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Intestinal calcium (Ca²⁺) absorption occurs via paracellular and transcellular pathways. Although the transcellular route has been extensively studied, mechanisms mediating paracellular absorption are largely unexplored. Unlike passive diffusion, secondarily active paracellular Ca²⁺ uptake occurs against an electrochemical gradient with water flux providing the driving force. Water movement is dictated by concentration differences that are largely determined by Na⁺ fluxes. Consequently, we hypothesized that Na⁺ absorption mediates Ca²⁺ flux. NHE3 is central to intestinal Na⁺ absorption. NHE3 knockout mice (NHE3-/-) display impaired intestinal Na⁺, water, and Ca²⁺ absorption. However, the mechanism mediating this latter abnormality is not clear. To investigate this, we used Ussing chambers to measure net Ca²⁺ absorption across different segments of wild-type mouse intestine. The cecum was the only segment with net Ca²⁺ absorption. Quantitative RT-PCR measurements revealed cecal expression of all genes implicated in intestinal Ca²⁺ absorption, including NHE3. We therefore employed this segment for further studies. Inhibition of NHE3 with 100 μM 5-(N-ethyl-N-isopropyl) amiloride decreased luminal-to-serosal and increased serosal-to-luminal Ca²⁺ flux. NHE3-/- mice had a >60% decrease in luminal-to-serosal Ca²⁺ flux. Ussing chambers experiments under altered voltage clamps (-25, 0, +25 mV) showed decreased transcellular and secondarily active paracellular Ca²⁺ absorption in NHE3-/- mice relative to wild-type animals. Consistent with this, cecal Trpv6 expression was diminished in NHE3-/- mice. Together these results implicate NHE3 in intestinal Ca(2+) absorption and support the theory that this is, at least partially, due to the role of NHE3 in Na⁺ and water absorption.
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Affiliation(s)
- Juraj Rievaj
- Dept. of Pediatrics, 4-585 Edmonton Clinic Health Academy, 11405 87th Ave., Univ. of Alberta, Edmonton, Alberta, T6G 2R7, Canada.
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83
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Clinckspoor I, Verlinden L, Mathieu C, Bouillon R, Verstuyf A, Decallonne B. Vitamin D in thyroid tumorigenesis and development. ACTA ACUST UNITED AC 2013; 48:65-98. [PMID: 23890557 DOI: 10.1016/j.proghi.2013.07.001] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Besides its classical role in bone and calcium homeostasis, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), the active form of vitamin D, has many non-classical effects; antiproliferative, anti-apoptotic and prodifferentiating effects of 1,25(OH)2D3 have been described in several tumour types in preclinical models. This review focuses on the insights gained in the elucidation of the role of 1,25(OH)2D3 in the normal thyroid and in the pathogenesis, progression and treatment of thyroid cancer, the most common endocrine malignancy. An increasing amount of observations points towards a role for impaired 1,25(OH)2D3-VDR signalling in the occurrence and progression of thyroid cancer, and a potential for structural analogues in the multimodal treatment of dedifferentiated iodine-resistant thyroid cancer. A role for vitamin D in thyroid-related autoimmunity is less convincing and needs further study. Altered 1,25(OH)2D3-VDR signalling does not influence normal thyroid development nor thyrocyte function, but does affect C-cell function, at least in rodents. If these findings also apply to humans deserves further study.
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Affiliation(s)
- Isabelle Clinckspoor
- Laboratory of Clinical and Experimental Endocrinology, KU Leuven, Bus 902, Herestraat 49, 3000 Leuven, Belgium
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84
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Christakos S, Seth T, Hirsch J, Porta A, Moulas A, Dhawan P. Vitamin D Biology Revealed Through the Study of Knockout and Transgenic Mouse Models. Annu Rev Nutr 2013; 33:71-85. [DOI: 10.1146/annurev-nutr-071812-161249] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Sylvia Christakos
- Department of Biochemistry and Molecular Biology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey 07103;
| | - Tanya Seth
- Department of Biochemistry and Molecular Biology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey 07103;
| | - Jennifer Hirsch
- Department of Biochemistry and Molecular Biology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey 07103;
| | - Angela Porta
- Department of Biochemistry and Molecular Biology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey 07103;
| | - Anargyros Moulas
- Department of Biochemistry and Molecular Biology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey 07103;
| | - Puneet Dhawan
- Department of Biochemistry and Molecular Biology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey 07103;
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85
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Lieben L, Carmeliet G. The delicate balance between vitamin D, calcium and bone homeostasis: lessons learned from intestinal- and osteocyte-specific VDR null mice. J Steroid Biochem Mol Biol 2013; 136:102-6. [PMID: 23022574 DOI: 10.1016/j.jsbmb.2012.09.019] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/06/2012] [Revised: 09/14/2012] [Accepted: 09/17/2012] [Indexed: 12/14/2022]
Abstract
The serum calcium levels and the calcium content of the skeleton are highly interdependent. Indeed, bone requires calcium to preserve its strength, but it is at the same time also the predominant calcium storage from which calcium can be mobilized to supply the serum pool. The active form of vitamin D [1,25(OH)2D] plays a crucial role in regulating the transfer of calcium between blood and bone, evidenced by experimental data obtained from systemic, intestinal-specific and osteocyte-specific vitamin D receptor (Vdr) null mice. In fact, 1,25(OH)2D is required to maintain normocalcemia and bone health by enhancing intestinal calcium absorption when dietary calcium intake is normal/low. When, however, insufficient calcium is absorbed via the intestine, 1,25(OH)2D levels will increase and will act on mature osteoblasts and osteocytes to minimize calcium levels in bone tissue in favor of the blood calcium pool. Mechanistically, the high 1,25(OH)2D levels enhance bone remodeling which leads to osteopenia, and suppress bone matrix mineralization by increasing the levels of mineralization inhibitors, which causes hyperosteoidosis and hypomineralization. Thus, depending on the intestinal calcium acquisition, 1,25(OH)2D will target the intestine and/or the skeleton to maintain calcium levels in serum within a normal range.
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Affiliation(s)
- Liesbet Lieben
- Clinical and Experimental Endocrinology, KU Leuven, Leuven, Belgium
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86
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Douard V, Sabbagh Y, Lee J, Patel C, Kemp FW, Bogden JD, Lin S, Ferraris RP. Excessive fructose intake causes 1,25-(OH)(2)D(3)-dependent inhibition of intestinal and renal calcium transport in growing rats. Am J Physiol Endocrinol Metab 2013; 304:E1303-13. [PMID: 23571713 PMCID: PMC3680696 DOI: 10.1152/ajpendo.00582.2012] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
We recently discovered that chronic high fructose intake by lactating rats prevented adaptive increases in rates of active intestinal Ca(2+) transport and in levels of 1,25-(OH)2D3, the active form of vitamin D. Since sufficient Ca(2+) absorption is essential for skeletal growth, our discovery may explain findings that excessive consumption of sweeteners compromises bone integrity in children. We tested the hypothesis that 1,25-(OH)2D3 mediates the inhibitory effect of excessive fructose intake on active Ca(2+) transport. First, compared with those fed glucose or starch, growing rats fed fructose for 4 wk had a marked reduction in intestinal Ca(2+) transport rate as well as in expression of intestinal and renal Ca(2+) transporters that was tightly associated with decreases in circulating levels of 1,25-(OH)2D3, bone length, and total bone ash weight but not with serum parathyroid hormone (PTH). Dietary fructose increased the expression of 24-hydroxylase (CYP24A1) and decreased that of 1α-hydroxylase (CYP27B1), suggesting that fructose might enhance the renal catabolism and impair the synthesis, respectively, of 1,25-(OH)2D3. Serum FGF23, which is secreted by osteocytes and inhibits CYP27B1 expression, was upregulated, suggesting a potential role of bone in mediating the fructose effects on 1,25-(OH)2D3 synthesis. Second, 1,25-(OH)2D3 treatment rescued the fructose effect and normalized intestinal and renal Ca(2+) transporter expression. The mechanism underlying the deleterious effect of excessive fructose intake on intestinal and renal Ca(2+) transporters is a reduction in serum levels of 1,25-(OH)2D3. This finding is significant because of the large amounts of fructose now consumed by Americans increasingly vulnerable to Ca(2+) and vitamin D deficiency.
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Affiliation(s)
- Veronique Douard
- Department of Pharmacology and Physiology, University of Medicine and Dentistry of New Jersey - New Jersey Medical School, Newark, New Jersey
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87
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Abstract
Age-related changes affect vitamin D metabolism and increase the requirement for vitamin D in the elderly. Also there is an age related decrease in calcium absorption and a higher calcium intake is needed. Increasing calcium from dietary sources may be better than supplements, and requires increasing the intake of dairy products or other and calcium-fortified foods. Evidence suggests that vitamin D and calcium nutrition can be improved in the elderly by increasing the vitamin D intake to 800 IU daily together with a total calcium intake of 1000 mg daily. This combination is a simple, inexpensive strategy that can reduce fractures in institutionalized individuals by 30%.
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88
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Kopic S, Geibel JP. Gastric acid, calcium absorption, and their impact on bone health. Physiol Rev 2013; 93:189-268. [PMID: 23303909 DOI: 10.1152/physrev.00015.2012] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.
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Affiliation(s)
- Sascha Kopic
- Department of Surgery and Cellular and Molecular Physiology, Yale School of Medicine, New Haven, Connecticut, USA
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89
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Haussler MR, Whitfield GK, Kaneko I, Haussler CA, Hsieh D, Hsieh JC, Jurutka PW. Molecular mechanisms of vitamin D action. Calcif Tissue Int 2013; 92:77-98. [PMID: 22782502 DOI: 10.1007/s00223-012-9619-0] [Citation(s) in RCA: 478] [Impact Index Per Article: 43.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Accepted: 05/15/2012] [Indexed: 12/14/2022]
Abstract
The hormonal metabolite of vitamin D, 1α,25-dihydroxyvitamin D(3) (1,25D), initiates biological responses via binding to the vitamin D receptor (VDR). When occupied by 1,25D, VDR interacts with the retinoid X receptor (RXR) to form a heterodimer that binds to vitamin D responsive elements in the region of genes directly controlled by 1,25D. By recruiting complexes of either coactivators or corepressors, ligand-activated VDR-RXR modulates the transcription of genes encoding proteins that promulgate the traditional functions of vitamin D, including signaling intestinal calcium and phosphate absorption to effect skeletal and calcium homeostasis. Thus, vitamin D action in a particular cell depends upon the metabolic production or delivery of sufficient concentrations of the 1,25D ligand, expression of adequate VDR and RXR coreceptor proteins, and cell-specific programming of transcriptional responses to regulate select genes that encode proteins that function in mediating the effects of vitamin D. For example, 1,25D induces RANKL, SPP1 (osteopontin), and BGP (osteocalcin) to govern bone mineral remodeling; TRPV6, CaBP(9k), and claudin 2 to promote intestinal calcium absorption; and TRPV5, klotho, and Npt2c to regulate renal calcium and phosphate reabsorption. VDR appears to function unliganded by 1,25D in keratinocytes to drive mammalian hair cycling via regulation of genes such as CASP14, S100A8, SOSTDC1, and others affecting Wnt signaling. Finally, alternative, low-affinity, non-vitamin D VDR ligands, e.g., lithocholic acid, docosahexaenoic acid, and curcumin, have been reported. Combined alternative VDR ligand(s) and 1,25D/VDR control of gene expression may delay chronic disorders of aging such as osteoporosis, type 2 diabetes, cardiovascular disease, and cancer.
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Affiliation(s)
- Mark R Haussler
- Department of Basic Medical Sciences, University of Arizona College of Medicine-Phoenix, 425 North 5th Street, Phoenix, AZ 85004-2157, USA.
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90
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Demay MB. Physiological insights from the vitamin D receptor knockout mouse. Calcif Tissue Int 2013; 92:99-105. [PMID: 22903507 PMCID: PMC3511627 DOI: 10.1007/s00223-012-9633-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/07/2011] [Accepted: 07/16/2012] [Indexed: 12/14/2022]
Abstract
Identification of vitamin D as a potent antirachitic factor almost a century ago prompted investigations aimed at addressing its mechanism of action and key target tissues. Studies in vitamin D deficiency models and in kindreds with impaired hormone activation and function were critical in identifying key steps in the vitamin D signaling pathway. Studies in humans with vitamin D receptor (VDR) mutations provided a tremendous amount of information regarding the role of this receptor in calcium and skeletal homeostasis. The availability of mouse models of VDR ablation provided an important tool for detailed molecular analyses of the pathophysiologic basis for the skeletal, parathyroid and cutaneous phenotypes observed in mice and humans with impaired VDR function. These investigations revealed that a critical action of the liganded receptor is the promotion of intestinal calcium absorption. Bypassing this defect by dietary or transgenic rescue prevents the severe skeletal phenotype of the VDR ablated mice, as well as the development of hyperparathyroidism. In contrast, intestine specific ablation of the receptor results in marked skeletal pathology. Like their human counterparts, VDR knockout mice develop alopecia. Studies in these mice demonstrated that the actions of the VDR required for cyclical regeneration of the hair follicle and prevention of alopecia were shown independent of 1,25-dihydroxyvitamin D demonstrating that the unliganded receptor has an important role in the cutaneous homeostasis.
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Affiliation(s)
- Marie B Demay
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Thier 11, 50 Blossom St., Boston, MA, USA.
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91
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Frick KK, Asplin JR, Favus MJ, Culbertson C, Krieger NS, Bushinsky DA. Increased biological response to 1,25(OH)(2)D(3) in genetic hypercalciuric stone-forming rats. Am J Physiol Renal Physiol 2013; 304:F718-26. [PMID: 23344574 DOI: 10.1152/ajprenal.00645.2012] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Genetic hypercalciuric stone-forming (GHS) rats, bred to maximize urine (U) calcium (Ca) excretion, have increased intestinal Ca absorption and bone Ca resorption and reduced renal Ca reabsorption, leading to increased UCa compared with the Sprague-Dawley (SD) rats. GHS rats have increased vitamin D receptors (VDR) at each of these sites, with normal levels of 1,25(OH)(2)D(3) (1,25D), indicating that their VDR is undersaturated with 1,25D. We tested the hypothesis that 1,25D would induce a greater increase in UCa in GHS rats by feeding both strains ample Ca and injecting 1,25D (25 ng · 100 g body wt(-1) · day(-1)) or vehicle for 16 days. With 1,25D, UCa in SD increased from 1.7 ± 0.3 mg/day to 24.4 ± 1.2 (Δ = 22.4 ± 1.5) and increased more in GHS from 10.5 ± 0.7 to 41.9 ± 0.7 (Δ = 29.8 ± 1.8; P = 0.003). To determine the mechanism of the greater increase in UCa in GHS rats, we measured kidney RNA expression of components of renal Ca transport. Expression of transient receptor potential vanilloid (TRPV)5 and calbindin D(28K) were increased similarly in SD + 1,25D and GHS + 1,25D. The Na(+)/Ca(2+) exchanger (NCX1) was increased in GHS + 1,25D. Klotho was decreased in SD + 1,25D and GHS + 1,25D. TRPV6 was increased in SD + 1,25D and increased further in GHS + 1,25D. Claudin 14, 16, and 19, Na/K/2Cl transporter (NKCC2), and secretory K channel (ROMK) did not differ between SD + 1,25D and GHS + 1,25D. Increased UCa with 1,25D in GHS exceeded that of SD, indicating that the increased VDR in GHS induces a greater biological response. This increase in UCa, which must come from the intestine and/or bone, must exceed any effect of 1,25D on TRPV6 or NCX1-mediated renal Ca reabsorption.
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Affiliation(s)
- Kevin K Frick
- Division of Nephrology, Department of Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA.
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92
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Colombini A, Perego S, Ardoino I, Marasco E, Lombardi G, Fiorilli A, Biganzoli E, Tettamanti G, Ferraretto A. Evaluation of a possible direct effect by casein phosphopeptides on paracellular and vitamin D controlled transcellular calcium transport mechanisms in intestinal human HT-29 and Caco2 cell lines. Food Funct 2013; 4:1195-203. [DOI: 10.1039/c3fo60099h] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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93
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Tiosano D, Gepstein V. Vitamin D action: lessons learned from hereditary 1,25-dihydroxyvitamin-D-resistant rickets patients. Curr Opin Endocrinol Diabetes Obes 2012; 19:452-9. [PMID: 23128575 DOI: 10.1097/med.0b013e32835a3415] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
PURPOSE OF REVIEW Hereditary 1,25-dihydroxyvitamin-D [1,25(OH)(2)D(3)]-resistant rickets (HVDRR) is a rare genetic disease caused by generalized resistance to 1,25(OH)(2)D(3). Less than 100 cases are reported in the literature. These patients provide an experiment by nature enabling us to understand the role of vitamin D, especially in light of the ongoing debate concerning normal vitamin D levels and the supplement dosage that should be recommended. This article summarizes the role of vitamin D in calcium absorption, rennin-angiotensin system (RAS), and cardiac state in HVDRR patients. RECENT FINDINGS The precise spectrum of vitamin D activities can now be better evaluated by critical analysis of mouse models with targeted deletion of the gene encoding the vitamin D receptor (VDR). Of special interest is the unraveling of the role of VDR in calcium absorption and cardiac status in VDR-knockout mice. The facts that VDR-knockout mice up-regulate intestinal calcium absorption and skeletal mineralization independently of the VDR during pregnancy and lactation point to the existence of VDR-independent mechanisms that are involved in calcium absorption. The observation that mice with genetic disruption of the 1α-hydroxylase gene or of the VDR gene have an overstimulated RAS and consequently develop high blood pressure and cardiac hypertrophy raised concern about potential risks to the cardiovascular system in HVDRR patients. SUMMARY The current review summarizes the new understanding of the effects of vitamin D on calcium absorption, the RAS, and heart hypertrophy derived from studying HVDRR patients from infancy to their mid-30s.
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Affiliation(s)
- Dov Tiosano
- Pediatric Endocrinology, Meyer Children's Hospital, Rambam Healthcare Campus, Haifa, Israel.
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94
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van der Eerden BC, Fratzl-Zelman N, Nijenhuis T, Roschger P, Zügel U, Steinmeyer A, Hoenderop JG, Bindels RJ, Klaushofer K, van Leeuwen JP. The vitamin D analog ZK191784 normalizes decreased bone matrix mineralization in mice lacking the calcium channel TRPV5. J Cell Physiol 2012; 228:402-7. [DOI: 10.1002/jcp.24144] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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95
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Cui M, Li Q, Johnson R, Fleet JC. Villin promoter-mediated transgenic expression of transient receptor potential cation channel, subfamily V, member 6 (TRPV6) increases intestinal calcium absorption in wild-type and vitamin D receptor knockout mice. J Bone Miner Res 2012; 27:2097-107. [PMID: 22589201 PMCID: PMC3430830 DOI: 10.1002/jbmr.1662] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Transient receptor potential cation channel, subfamily V, member 6 (TRPV6) is an apical membrane calcium (Ca) channel in the small intestine proposed to be essential for vitamin D-regulated intestinal Ca absorption. Recent studies have challenged the proposed role for TRPV6 in Ca absorption. We directly tested intestinal TRPV6 function in Ca and bone metabolism in wild-type (WT) and vitamin D receptor knockout (VDRKO) mice. TRPV6 transgenic mice (TG) were made with intestinal epithelium-specific expression of a 3X Flag-tagged human TRPV6 protein. TG and VDRKO mice were crossed to make TG-VDRKO mice. Ca and bone metabolism was examined in WT, TG, VDRKO, and TG-VDRKO mice. TG mice developed hypercalcemia and soft tissue calcification on a chow diet. In TG mice fed a 0.25% Ca diet, Ca absorption was more than three-fold higher and femur bone mineral density (BMD) was 26% higher than WT. Renal 1α hydroxylase (CYP27B1) mRNA and intestinal expression of the natural mouse TRPV6 gene were reduced to <10% of WT but small intestine calbindin-D(9k) expression was elevated >15 times in TG mice. TG-VDRKO mice had high Ca absorption that prevented the low serum Ca, high renal CYP27B1 mRNA, low BMD, and abnormal bone microarchitecture seen in VDRKO mice. In addition, small intestinal calbindin D(9K) mRNA and protein levels were elevated in TG-VDRKO. Transgenic TRPV6 expression in intestine is sufficient to increase Ca absorption and bone density, even in VDRKO mice. VDR-independent upregulation of intestinal calbindin D(9k) in TG-VDRKO suggests this protein may buffer intracellular Ca during Ca absorption. © 2012 American Society for Bone and Mineral Research.
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Affiliation(s)
- Min Cui
- Department of Nutrition Science, Purdue University, West Lafayette, IN 47907-2059, USA
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96
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Woudenberg-Vrenken TE, Lameris AL, Weißgerber P, Olausson J, Flockerzi V, Bindels RJM, Freichel M, Hoenderop JGJ. Functional TRPV6 channels are crucial for transepithelial Ca2+ absorption. Am J Physiol Gastrointest Liver Physiol 2012; 303:G879-85. [PMID: 22878123 DOI: 10.1152/ajpgi.00089.2012] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
TRPV6 is considered the primary protein responsible for transcellular Ca2+ absorption. In vitro studies demonstrate that a negatively charged amino acid (D) within the putative pore region of mouse TRPV6 (position 541) is critical for Ca2+ permeation of the channel. To elucidate the role of TRPV6 in transepithelial Ca2+ transport in vivo, we functionally analyzed a TRPV6D541A/D541A knockin mouse model. After weaning, mice were fed a regular (1% wt/wt) or Ca2+-deficient (0.02% wt/wt) diet and housed in metabolic cages. Blood was sampled for Ca2+ measurements, and the expression of Ca2+ transport proteins was analyzed in kidney and duodenum. Intestinal 45Ca2+ uptake was measured in vivo by an absorption assay. Challenging the mice with the Ca2+-deficient diet resulted in hypocalcemia in wild-type and TRPV6D541A/D541A mice. On a low-Ca2+ diet both mouse strains displayed increased expression of intestinal TRPV6, calbindin-D(9K), and renal TRPV5. TRPV6D541A/D541A mice showed significantly impaired intestinal Ca2+ uptake compared with wild-type mice, and duodenal TRPV5 expression was increased in TRPV6D541A/D541A mice. On a normal diet, serum Ca2+ concentrations normalized in both mouse strains. Under these conditions, intestinal Ca2+ uptake was similar, and the expression levels of renal and intestinal Ca2+ transport proteins were not affected. We demonstrate that TRPV6D541A/D541A mice exhibit impaired transcellular Ca2+ absorption. Duodenal TRPV5 expression was increased in TRPV6D541A/D541A mice, albeit insufficient to correct for the diminished Ca2+ absorption. Under normal conditions, when passive Ca2+ transport is predominant, no differences between wild-type and TRPV6D541A/D541A mice were observed. Our results demonstrate a specific role for TRPV6 in transepithelial Ca2+ absorption.
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Affiliation(s)
- Titia E Woudenberg-Vrenken
- Department of Physiology, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands
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97
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Hubbard MJ, McHugh NJ, Mangum JE. Exclusion of all three calbindins from a calcium-ferry role in rat enamel cells. Eur J Oral Sci 2012; 119 Suppl 1:112-9. [PMID: 22243236 DOI: 10.1111/j.1600-0722.2011.00890.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
It is widely accepted that healthy enamel formation depends on a steady supply of calcium, yet only fragmentary understanding exists about the mechanisms underlying transepithelial calcium transport. Several lines of evidence indicate that calcium principally follows a transcellular route, which classically is thought to be facilitated by cytosolic calcium-binding proteins termed calbindins. In enamel cells, however, this 'calcium-ferry' dogma appears to fail as we previously found that the major calbindin in murine enamel cells (calbindin-28 kDa) was down-regulated during the peak period of calcium transport and enamel was formed normally in mice lacking calbindin-28 kDa. It remains to be clarified whether the two other known calbindins could function as calcium ferries instead. This study used biochemical and proteomic approaches to obtain definitive identification and quantification of the 30-kDa calbindin (calretinin) and calbindin-9 kDa (S100-G) in enamel epithelium from rat. By establishing that both of these calbindins contribute insufficient calcium capacities in molars and incisors, our results render the calcium-ferry dogma untenable. Of significance to enamel defects and dental bioengineering, these findings support other evidence for an alternative organelle-based mode of calcium transport (calcium transcytosis) and also implicate S100-G/calbindin-9 kDa, but not calretinin, in a calcium-signaling role during enamel maturation.
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Affiliation(s)
- Michael J Hubbard
- Department of Biochemistry, University of Otago, Dunedin, New Zealand.
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98
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Abstract
Vitamin D deficiency is increasing worldwide. Ultraviolet rays are supposed to provide humans over 80% of our vitamin D requirement; the rest is received through diet and supplements. In addition to enhancing calcium absorption from the intestine and mineralization of the osteoid tissue, vitamin D has many other physiological effects, including neuromodulation, improving muscle strength and coordination, insulin release, immunity and prevention of infections, and curtailing cancer. Whether the increased incidence of vitamin D deficiency is related to increased incidences of nonskeletal disorders remains to be determined. Serum levels of 25-hydroxyvitamin [25(OH)D] above 30 ng/mL indicate vitamin D sufficiency. An additional 1,000 IU of vitamin D/day is sufficient for most lighter-skinned individuals, whereas an extra 2,000 IU/day is needed by the elderly and dark-skinned individuals to maintain normal 25(OH)D levels. Additional research is needed to clarify the relationship between vitamin D and the nonskeletal systems, nonclassic functions, and targets of vitamin D.
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Affiliation(s)
- Sunil J Wimalawansa
- Division of Endocrinology, Metabolism & Nutrition, Department of Medicine, and UMDNJ, Robert Wood Johnson Medical School, Physiology and Integrative Biology, Graduate School of Biomedical Sciences, New Brunswick, New Jersey 08903-0019, USA.
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99
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Pike JW, Meyer MB. The vitamin D receptor: new paradigms for the regulation of gene expression by 1,25-dihydroxyvitamin D3. Rheum Dis Clin North Am 2012; 38:13-27. [PMID: 22525840 DOI: 10.1016/j.rdc.2012.03.004] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
This article represents a summary of what is known of the VDR protein and its molecular mechanism of action at target genes. New methodologies now used, such as ChIP-chip and ChIP-seq, as well as novel reporter studies using large BAC clones stably transfected into culture cells or introduced as transgenes in mice, are providing new insights into how 1,25(OH)2D3-activated VDR modulates the expression of genes at single gene loci and at the level of gene networks. Many of these insights are unexpected and suggest that gene regulation is even more complex than previously appreciated. These studies also highlight new technologies and their central role in establishing fundamental biologic principles.
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Affiliation(s)
- J Wesley Pike
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.
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100
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Kovacs CS. The role of vitamin D in pregnancy and lactation: insights from animal models and clinical studies. Annu Rev Nutr 2012; 32:97-123. [PMID: 22483092 DOI: 10.1146/annurev-nutr-071811-150742] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Maternal adaptations during pregnancy and lactation appear to provide calcium to fetus and neonate without relying on vitamin D or calcitriol. Consequently, the blood calcium, calciotropic hormones, and skeleton appear normal at birth in the offspring of mothers who are severely vitamin D deficient or who lack calcitriol or its receptor. It remains unclear whether skeletal or extraskeletal problems will develop postnatally from exposure to vitamin D deficiency in utero. During the neonatal period, calcitriol-stimulated intestinal calcium absorption becomes the dominant mechanism of calcium delivery. The vitamin D-deficient neonate is at risk to develop hypocalcemia, rickets, and possibly extraskeletal disorders (e.g., type 1 diabetes). Breastfed babies are at higher risk of vitamin D deficiency because normally little vitamin D or 25-hydroxyvitamin D passes into breast milk. Dosing recommendations during pregnancy and lactation should ensure that the baby is born vitamin D sufficient and maintained that way during infancy and beyond.
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Affiliation(s)
- Christopher S Kovacs
- Health Sciences Centre, Memorial University of Newfoundland, St. John's, NL, Canada.
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