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      A novel role for the mineralocorticoid receptor in glucocorticoid driven vascular calcification

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          Abstract

          Vascular calcification, which is common in the elderly and in patients with atherosclerosis, diabetes and chronic renal disease, increases the risk of cardiovascular morbidity and mortality. It is a complex, active and highly regulated cellular process that resembles physiological bone formation. It has previously been established that pharmacological doses of glucocorticoids facilitate arterial calcification. However, the consequences for vascular calcification of endogenous glucocorticoid elevation have yet to be established. Glucocorticoids (cortisol, corticosterone) are released from the adrenal gland, but can also be generated within cells from 11-keto metabolites of glucocorticoids (cortisone, 11-dehydrocorticosterone [11-DHC]) by the enzyme, 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). In the current study we hypothesized that endogenous glucocorticoids facilitate vascular smooth muscle cell (VSMC) calcification and investigated the receptor-mediated mechanism underpinning this process.

          In vitro studies revealed increased phosphate-induced calcification in mouse VSMCs following treatment for 7 days with corticosterone (100 nM; 7.98 fold; P < 0.01), 11-DHC (100 nM; 7.14 fold; P < 0.05) and dexamethasone (10 nM; 7.16 fold; P < 0.05), a synthetic glucocorticoid used as a positive control. Inhibition of 11β-HSD isoenzymes by 10 μM carbenoxolone reduced the calcification induced by 11-DHC (0.37 fold compared to treatment with 11-DHC alone; P < 0.05). The glucocorticoid receptor (GR) antagonist mifepristone (10 μM) had no effect on VSMC calcification in response to corticosterone or 11-DHC. In contrast, the mineralocorticoid receptor (MR) antagonist eplerenone (10 μM) significantly decreased corticosterone- (0.81 fold compared to treatment with corticosterone alone; P < 0.01) and 11-DHC-driven (0.64 fold compared to treatment with 11-DHC alone; P < 0.01) VSMC calcification, suggesting this glucocorticoid effect is MR-driven and not GR-driven. Neither corticosterone nor 11-DHC altered the mRNA levels of the osteogenic markers PiT-1, Osx and Bmp2. However, DAPI staining of pyknotic nuclei and flow cytometry analysis of surface Annexin V expression showed that corticosterone induced apoptosis in VSMCs.

          This study suggests that in mouse VSMCs, corticosterone acts through the MR to induce pro-calcification effects, and identifies 11β-HSD-inhibition as a novel potential treatment for vascular calcification.

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          Most cited references 49

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          Apoptosis regulates human vascular calcification in vitro: evidence for initiation of vascular calcification by apoptotic bodies.

          The mechanisms involved in the initiation of vascular calcification are not known, but matrix vesicles, the nucleation sites for calcium crystal formation in bone, are likely candidates, because similar structures have been found in calcified arteries. The regulation of matrix vesicle production is poorly understood but is thought to be associated with apoptotic cell death. In the present study, we investigated the role of apoptosis in vascular calcification. We report that apoptosis occurs in a human vascular calcification model in which postconfluent vascular smooth muscle cell (VSMC) cultures form nodules spontaneously and calcify after approximately 28 days. Apoptosis occurred before the onset of calcification in VSMC nodules and was detected by several methods, including nuclear morphology, the TUNEL technique, and external display of phosphatidyl serine. Inhibition of apoptosis with the caspase inhibitor ZVAD.fmk reduced calcification in nodules by approximately 40%, as measured by the cresolphthalein method and alizarin red staining. In addition, when apoptosis was stimulated in nodular cultures with anti-Fas IgM, there was a 10-fold increase in calcification. Furthermore, incubation of VSMC-derived apoptotic bodies with (45)Ca demonstrated that, like matrix vesicles, they can concentrate calcium. These observations provide evidence that apoptosis precedes VSMC calcification and that apoptotic bodies derived from VSMCs may act as nucleating structures for calcium crystal formation.
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            Unique coexpression in osteoblasts of broadly expressed genes accounts for the spatial restriction of ECM mineralization to bone.

            Extracellular matrix (ECM) mineralization is a physiological process in bone and a pathological one in soft tissues. The mechanisms determining the spatial restriction of ECM mineralization to bone physiologically are poorly understood. Here we show that a normal extracellular phosphate concentration is required for bone mineralization, while lowering this concentration prevents mineralization of any ECM. However, simply raising extracellular phosphate concentration is not sufficient to induce pathological mineralization, this is because of the presence in all ECMs of pyrophosphate, an inhibitor of mineralization. ECM mineralization occurs only in bone because of the exclusive coexpression in osteoblasts of Type I collagen and Tnap, an enzyme that cleaves pyrophosphate. This dual requirement explains why Tnap ectopic expression in cells producing fibrillar collagen is sufficient to induce pathological mineralization. This study reveals that coexpression in osteoblasts of otherwise broadly expressed genes is necessary and sufficient to induce bone mineralization and provides evidence that pathological mineralization can be prevented by modulating extracellular phosphate concentration.
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              Differentiation of human bone marrow osteogenic stromal cells in vitro: induction of the osteoblast phenotype by dexamethasone.

              Human bone marrow stromal cells were examined for their osteogenic potential in an in vitro cell culture system. Dexamethasone (Dex) treatment induced morphological transformation of these cells from an elongated to a more cuboidal shape, increased their alkaline phosphatase activity and cAMP responses to PTH and prostaglandin E2, and was essential for mineralization of the extracellular matrix. Dex-induced differentiation of human bone marrow stromal cells was apparent after 2-3 days of treatment and reached a maximum at 7-14 days, as judged by alkaline phosphatase activity, although induction of osteocalcin by 1,25-dihydroxyvitamin D3 was attenuated by Dex. Withdrawal of Dex resulted in an enhancement of the 1,25-dihydroxyvitamin D3-induced secretion of osteocalcin, whereas alkaline phosphatase activity and the cAMP response to PTH remained at prewithdrawal levels. The steady state mRNA level of osteonectin was not affected by Dex. Our results, which demonstrate that Dex conditions the differentiation of human bone marrow osteogenic stromal cells into osteoblast-like cells, support the hypothesis of a permissive effect of glucocorticoids in ensuring an adequate supply of mature osteoblast populations. Furthermore, the established human bone marrow stromal cell culture provides a good model of an in vitro system to study the regulation of differentiation of human bone osteoprogenitor cells.
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                Author and article information

                Contributors
                Journal
                Vascul Pharmacol
                Vascul. Pharmacol
                Vascular Pharmacology
                Elsevier Science
                1537-1891
                1879-3649
                1 November 2016
                November 2016
                : 86
                : 87-93
                Affiliations
                [a ]The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Midlothian EH25 9RG, UK
                [b ]University/BHF Centre for Cardiovascular Sciences, University of Edinburgh, The Queen's Medical Research Institute, 47 Little France Crescent, Edinburgh EH16 4TJ, UK
                Author notes
                [* ]Corresponding author at: The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Roslin, Midlothian EH25 9RG, UK.The Roslin Institute and Royal (Dick) School of Veterinary StudiesUniversity of EdinburghEaster BushRoslinMidlothianEH25 9RGUK vicky.macrae@ 123456roslin.ed.ac.uk
                Article
                S1537-1891(15)30124-5
                10.1016/j.vph.2016.04.005
                5111541
                27153999
                © 2016 The Authors

                This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

                Categories
                Article

                Pharmacology & Pharmaceutical medicine

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