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      Impact of the Uremic Milieu on the Osteogenic Potential of Mesenchymal Stem Cells

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          Abstract

          Human mesenchymal stem cells (hMSCs), the precursors of osteoblasts during osteogenesis, play a role in the balance of bone formation and resorption, but their functioning in uremia has not been well defined. To study the effects of the uremic milieu on osteogenic properties, we applied an in vitro assay culturing hMSCs in osteogenic medium supplemented with serum from healthy donors and from uremic patients on hemodialysis. Compared to control, serum from uremic patients induces, in hMSC cultures, a modification of several key regulators of bone remodeling, in particular a reduction of the ratio Receptor Activator of Nuclear factor Kappa B Receptor (RANKL) over osteoprotegerin, indicating an adaptive response of the system to favor osteogenesis over osteoclastosis. However, the levels of osteopontin, osteocalcin, and collagen type I, are increased in cell medium, while BMP-2, and alizarin red staining were decreased, pointing to a reduction of bone formation favoring resorption. Selected uremic toxins, such as p-cresylsulfate, p-cresylglucuronide, parathyroid hormone, indoxyl sulfate, asymmetric dimethylarginine, homocysteine, were able to mimic some of the effects of whole serum from uremic patients. Serum from cinacalcet-treated patients antagonizes these effects. Hydrogen sulfide (H2S) donors as well as hemodialysis treatment are able to induce beneficial effects. In conclusion, bone modifications in uremia are influenced by the capability of the uremic milieu to alter hMSC osteogenic differentiation. Cinacalcet, H2S donors and a hemodialysis session can ameliorate the hampered calcium deposition.

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          Most cited references43

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          Cinacalcet for secondary hyperparathyroidism in patients receiving hemodialysis.

          Treatment of secondary hyperparathyroidism with vitamin D and calcium in patients receiving dialysis is often complicated by hypercalcemia and hyperphosphatemia, which may contribute to cardiovascular disease and adverse clinical outcomes. Calcimimetics target the calcium-sensing receptor and lower parathyroid hormone levels without increasing calcium and phosphorus levels. We report the results of two identical randomized, double-blind, placebo-controlled trials evaluating the safety and effectiveness of the calcimimetic agent cinacalcet hydrochloride. Patients who were receiving hemodialysis and who had inadequately controlled secondary hyperparathyroidism despite standard treatment were randomly assigned to receive cinacalcet (371 patients) or placebo (370 patients) for 26 weeks. Once-daily doses were increased from 30 mg to 180 mg to achieve intact parathyroid hormone levels of 250 pg per milliliter or less. The primary end point was the percentage of patients with values in this range during a 14-week efficacy-assessment phase. Forty-three percent of the cinacalcet group reached the primary end point, as compared with 5 percent of the placebo group (P<0.001). Overall, mean parathyroid hormone values decreased 43 percent in those receiving cinacalcet but increased 9 percent in the placebo group (P<0.001). The serum calcium-phosphorus product declined by 15 percent in the cinacalcet group and remained unchanged in the placebo group (P<0.001). Cinacalcet effectively reduced parathyroid hormone levels independently of disease severity or changes in vitamin D sterol dose. Cinacalcet lowers parathyroid hormone levels and improves calcium-phosphorus homeostasis in patients receiving hemodialysis who have uncontrolled secondary hyperparathyroidism. Copyright 2004 Massachusetts Medical Society
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            Osteopontin: a versatile regulator of inflammation and biomineralization.

            Osteopontin is a secreted glycoprotein with a multidomain structure and functions characteristic of a matricellular protein. Osteopontin interacts with cell surface receptors via arginine-glycine-aspartate (RGD)- and non-RGD containing adhesive domains, in addition to binding to components of the structural extracellular matrix. While normally expressed in bone and kidney, osteopontin levels are elevated during wound healing and inflammation in most tissues studied to date. Since 1986, over one thousand studies have been published on osteopontin, including recent experiments in osteopontin-deficient mice. These studies reveal osteopontin as a cell adhesive, signaling, migratory, and survival stimulus for various mesenchymal, epithelial, and inflammatory cells, in addition to being a potent regulator of osseous and ectopic calcification. Based on these reports, a general picture of osteopontin as an important regulator of inflammation and biomineralization is emerging. A common denominator in osteopontin function in these situations is its ability to regulate the function of macrophage and macrophage-derived cells (i.e. osteoclasts). While we have learned much about osteopontin and the processes it appears to regulate over the past decade, many questions regarding this important multifunctional protein remain unanswered and provide important directions for future studies.
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              Hydrogen sulfide maintains mesenchymal stem cell function and bone homeostasis via regulation of Ca(2+) channel sulfhydration.

              Gaseous signaling molecules such as hydrogen sulfide (H2S) are produced endogenously and mediate effects through diverse mechanisms. H2S is one such gasotransmitters that regulates multiple signaling pathways in mammalian cells, and abnormal H2S metabolism has been linked to defects in bone homeostasis. Here, we demonstrate that bone marrow mesenchymal stem cells (BMMSCs) produce H2S in order to regulate their self-renewal and osteogenic differentiation, and H2S deficiency results in defects in BMMSC differentiation. H2S deficiency causes aberrant intracellular Ca(2+) influx because of reduced sulfhydration of cysteine residues on multiple Ca(2+) TRP channels. This decreased Ca(2+) flux downregulates PKC/Erk-mediated Wnt/β-catenin signaling which controls osteogenic differentiation of BMMSCs. Consistently, H2S-deficient mice display an osteoporotic phenotype that can be rescued by small molecules that release H2S. These results demonstrate that H2S regulates BMMSCs and that restoring H2S levels via nontoxic donors may provide treatments for diseases such as osteoporosis that can arise from H2S deficiencies. Copyright © 2014 Elsevier Inc. All rights reserved.
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                Author and article information

                Contributors
                Role: Academic Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                2015
                30 January 2015
                : 10
                : 1
                : e0116468
                Affiliations
                [1 ]First Division of Nephrology, Department of Cardio-thoracic and Respiratory Sciences, Second University of Naples, School of Medicine, Napoli, Italy
                [2 ]Department of Biochemistry, Biophysics and General Pathology, Second University of Naples, School of Medicine, Napoli, Italy
                [3 ]Nephrology Section Department of Internal Medicine, Ghent University Hospital, Ghent, Belgium
                [4 ]Division of Medical Oncology and Hematology, Department of Clinical and Experimental Medicine, Second University of Naples, School of Medicine, Napoli, Italy
                [5 ]Institute of Molecular Cardiovascular Research (IMCAR), RWTH Aachen University, Aachen, Germany
                University of Catania, ITALY
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: DL AFP DI. Performed the experiments: DL AO AP SG ADN CV VJ JJ. Analyzed the data: DL RV AFP GC JJ DI. Contributed reagents/materials/analysis tools: DL AFP AO RV AP SG ADN CV GC VJ JJ DI. Wrote the paper: DL RV AFP DI.

                Article
                PONE-D-14-45545
                10.1371/journal.pone.0116468
                4312090
                25635832
                9ad592ca-f8ca-463a-bdaf-501c2adfa765
                Copyright @ 2015

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

                History
                : 14 October 2014
                : 9 December 2014
                Page count
                Figures: 7, Tables: 1, Pages: 17
                Funding
                This work was supported by the Italian Society of Nephrology (SIN), http://www.sin-italy.org, GRANT “Ricercando 2011” to AFP. Project name: “Exploring the osteogenic properties of mesenchymal stem cells for bone structural –functional repair in hemodialysis patients: role of uremic toxins.” The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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