The Experts below are selected from a list of 1365 Experts worldwide ranked by ideXlab platform
Dirk G. Kurth - One of the best experts on this subject based on the ideXlab platform.
-
Green-to-Red Electrochromic Fe(II) Metallo-Supramolecular Polyelectrolytes Self-Assembled from Fluorescent 2,6-Bis(2-pyridyl)pyrimidine Bithiophene
2017Co-Authors: Sandesh Pai, Michael Moos, Maximilian H. Schreck, Christoph Lambert, Dirk G. KurthAbstract:The structure and properties of metallo-supramolecular polyelectrolytes (MEPEs) self-assembled from rigid 2,6-bis(2-pyridyl)pyrimidine and the metal ions FeII and CoII are presented. While FeL1-MEPE (L1 = 1,4-bis[2,6-bis(2-pyridyl)pyrimidin-4-yl]benzene) is deep blue, FeL2- and CoL2-MEPE (L2 = 5,5′-bis[2,6-bis(2-pyridyl)pyrimidin-4-yl]-2,2′-bithiophene) are intense green and red in color, respectively. These novel MEPEs display a high extinction coefficient and solvatochromism. Ligand L2 shows a high absolute fluorescence quantum yield (Φf = 82%). Viscosity and static light-scattering measurements reveal that the molar masses of these MEPEs are in the range of 1 × 108 g/mol under the current experimental conditions. In water, FeL1-MEPE forms a viscous gel at 20 °C (c = 8 mM). Thin films of high optical quality are fabricated by dip coating on transparent conducting indium tin oxide (ITO) glass substrate. Optical, electrochemical, and electrochromic properties of the obtained MEPEs are presented. Green to red and blue to colorless electrochromism is observed for FeL2-MEPE and FeL1-MEPE, respectively. The results show that the electrochromic properties are affected by the ligand topology. The Fe-MEPEs show a reversible redox behavior of the FeII/FeIII couple at 0.86 and 0.82 V versus Fc+/Fc and display an excellent redox cycle stability under switching conditions. FeL2-MEPE in its oxidized state exhibits a broad absorption band covering the near-IR region (ca. 1500 nm) due to the ligand-to-metal charge transfer transition originating due to charge delocalization in the bithiophene spacer
-
Growth and Differentiation of Myoblastic Precursor Cells on Thin Films of Metallo-Supramolecular Coordination Polyelectrolyte (MEPE)
Advanced Materials Interfaces, 2016Co-Authors: Janina Belka, Dirk G. Kurth, Tobias Weigel, Ann-kathrin Berninger, Joachim NickelAbstract:The interaction of cells with substrate surfaces is a key issue in tissue engineering. In a proof-of-concept study, the use of metallo-supramolecular polyelectrolytes (MEPE) as substrates for the adherent growth of eucaryotic cells is investigated. The chosen MEPE comprises iron(II), thus resulting in an overall positive charge of the surface, which is beneficial for cell adherence. Additionally, the metal ions can dissociate from the assembly thereby triggering cellular processes such as cell differentiation. As cell-based test system the well characterized cell line C2C12 is used. The investigated MEPE functions as noncytotoxic, biocompatible substrate. Additionally, the substrate positively affects the myogenic differentiation of the investigated cells. This proof-of-principle study suggests that MEPEs may be interesting as component for tissue engineering approaches.
-
Intercalation of Nickel(II) and Iron(II) Metallosupramolecular Polyelectrolytes in Montmorillonite: Nanocomposites and their Electrorheological Properties
ChemNanoMat, 2015Co-Authors: Matthias F. Geist, Claire Peyratout, Dirk G. KurthAbstract:Nanocomposites obtained from the montmorillonite clay (Na0.36(Al1.64Mg0.36)Si4O10(OH)2⋅n H2O) and metallosupramolecular polyelectrolytes (MEPE) with iron(II) and nickel(II) are prepared by an aqueous intercalation reaction. Intercalation of MEPE in the interlayer structure of montmorillonite (MMT) is confirmed by different analytical techniques including powder X-ray diffraction, FTIR spectroscopy, and thermal analysis. We note a difference in the intercalation behavior between NiII and FeII. The intercalation of Fe-MEPE is hindered by traces of Fe2O3 in MMT. Removal of the impurities with sodium dithionite and citrate buffer makes Fe-MEPE-MMT available. Electrorheological measurements reveal for both nanocomposites a distinctive ER effect. The effect depends on the intercalated coordination polymer. Dielectric spectroscopy shows a different polarization for Fe-MEPE-MMT and Ni-MEPE-MMT.
-
State-of-the-art electrochromic materials based on metallo-supramolecular polymers
Solar Energy Materials and Solar Cells, 2014Co-Authors: Marco Schott, Henning Lorrmann, Wojciech Szczerba, Matthias Beck, Dirk G. KurthAbstract:Metal ion induced self-assembly of iron(II)-acetate with the rigid ditopic ligand 1,4-bis(2,2′:6′,2′′-terpyridin-4′-yl)benzene results in a metallo-supramolecular coordination polyelectrolyte (Fe-MEPE). Fe-MEPE shows a strong absorption band in the visible region around 590 nm, attributed to a metal-to-ligand-charge-transfer (MLCT) transition, which is responsible for the deep blue colour. Large area thin films of high optical quality can be readily fabricated by a dip coating process on transparent conducting electrodes. The Fe-MEPE films have a temperature stability up to 80 °C, measured by optical spectroscopy and XAFS (x-ray absorption fine structure). The cathodically coloured Fe-MEPE shows outstanding electrochromic properties and can be reversibly switched from Fe(II) (blue) to Fe(III) (colourless) by applying a potential of 4.1 V vs. Li/Li+. A very high optical contrast ΔT of 71% at a wavelength of 590 nm and a colouration efficiency of around 525 cm2 C−1 can be realized. The devices show a long-term stability about 10,000 cycles. Thus, Fe-MEPE is a very promising electrochromic material for future applications of smart windows
-
Fluorescent Fe(II) metallo-supramolecular polymers: metal-ion-directed self-assembly of new bisterpyridines containing triethylene glycol chains
Polymer Journal, 2010Co-Authors: Ravindra R. Pal, Masayoshi Higuchi, Yuichi Negishi, Tatsuya Tsukuda, Dirk G. KurthAbstract:We synthesized new ditopic bisterpyridine (BTPY) ligands (L2 and L4) containing triethylene glycol (TEG) chains at the ortho-position of the peripheral pyridine ring and succeeded in obtaining fluorescent Fe(II) metallo-supramolecular polyelectrolytes (FeL2-MEPE and FeL4-MEPE) through complexation of Fe(II) ions with L2 and L4, respectively. The Fe(II) ion is known to quench fluorescence, but FeL2-MEPE shows a retention of quantum yield that is nearly threefold higher than that of the unsubstituted analog (FeL3-MEPE). We investigated the substituent effects of TEG chains on metallo-supramolecular polymers and their fluorescent and electrochemical properties in detail.
Peter S N Rowe - One of the best experts on this subject based on the ideXlab platform.
-
MEPE is a novel regulator of growth plate cartilage mineralization
Bone, 2012Co-Authors: Katherine Staines, Peter S N Rowe, Neil Mackenzie, Claire E. Clarkin, Lesya Zelenchuk, Vicky E. Macrae, Colin FarquharsonAbstract:Matrix extracellular phosphoglycoprotein (MEPE) belongs to the SIBLING protein family which play key roles in biomineralization. Although the growth plates of MEPE-overexpressing mice display severe morphological disruption, the expression and function of MEPE in growth plate matrix mineralization remains largely undefined. Here we show MEPE and its cleavage product, the acidic serine aspartate-rich MEPE-associated motif (ASARM) peptide, to be localised to the hypertrophic zone of the growth plate. We also demonstrate that the phosphorylated (p)ASARM peptide inhibits ATDC5 chondrocyte matrix mineralization. Stable MEPE-overexpressing ATDC5 cells also had significantly reduced matrix mineralization in comparison to the control cells. Interestingly, we show that the addition of the non-phosphorylated (np)ASARM peptide promoted mineralization in the ATDC5 cells. The peptides and the overexpression of MEPE did not affect the differentiation of the ATDC5 cells. For a more physiologically relevant model, we utilized the metatarsal organ culture model. We show the pASARM peptide to inhibit mineralization at two stages of development, as shown by histological and μCT analysis. Like in the ATDC5 cells, the peptides did not affect the differentiation of the metatarsals indicating that the effects seen on mineralization are direct, as is additionally confirmed by no change in alkaline phosphatase activity or mRNA expression. In the metatarsal organ cultures, the pASARM peptide also reduced endothelial cell markers and vascular endothelial growth factor mRNA expression. Taken together these results show MEPE to be an important regulator of growth plate chondrocyte matrix mineralization through its cleavage to an ASARM peptide.
-
sclerostin is a locally acting regulator of late osteoblast preosteocyte differentiation and regulates mineralization through a MEPE asarm dependent mechanism
Journal of Bone and Mineral Research, 2011Co-Authors: Gerald J. Atkins, Peter S N Rowe, Lesya Zelenchuk, Hui P Lim, Katie J. Welldon, Renee T. Ormsby, Asiri R. Wijenayaka, Andreas Evdokiou, David M. FindlayAbstract:The identity of the cell type responsive to sclerostin, a negative regulator of bone mass, is unknown. Since sclerostin is expressed in vivo by mineral-embedded osteocytes, we tested the hypothesis that sclerostin would regulate the behavior of cells actively involved in mineralization in adult bone, the preosteocyte. Differentiating cultures of human primary osteoblasts exposed to recombinant human sclerostin (rhSCL) for 35 days displayed dose- and time-dependent inhibition of in vitro mineralization, with late cultures being most responsive in terms of mineralization and gene expression. Treatment of advanced (day 35) cultures with rhSCL markedly increased the expression of the preosteocyte marker E11 and decreased the expression of mature markers DMP1 and SOST. Concomitantly, matrix extracellular phosphoglycoprotein (MEPE) expression was increased by rhSCL at both the mRNA and protein levels, whereas PHEX was decreased, implying regulation through the MEPE-ASARM axis. We confirmed that mineralization by human osteoblasts is exquisitely sensitive to the triphosphorylated ASARM-PO4 peptide. Immunostaining revealed that rhSCL increased the endogenous levels of MEPE-ASARM. Importantly, antibody-mediated neutralization of endogenous MEPE-ASARM antagonized the effect of rhSCL on mineralization, as did the PHEX synthetic peptide SPR4. Finally, we found elevated Sost mRNA expression in the long bones of HYP mice, suggesting that sclerostin may drive the increased MEPE-ASARM levels and mineralization defect in this genotype. Our results suggest that sclerostin acts through regulation of the PHEX/MEPE axis at the preosteocyte stage and serves as a master regulator of physiologic bone mineralization, consistent with its localization in vivo and its established role in the inhibition of bone formation.
-
Sclerostin is a locally acting regulator of late-osteoblast/preosteocyte differentiation and regulates mineralization through a MEPE-ASARM-dependent mechanism.
Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research, 2011Co-Authors: Gerald J. Atkins, Peter S N Rowe, Lesya Zelenchuk, Hui P Lim, Katie J. Welldon, Renee T. Ormsby, Asiri R. Wijenayaka, Andreas Evdokiou, David M. FindlayAbstract:The identity of the cell type responsive to sclerostin, a negative regulator of bone mass, is unknown. Since sclerostin is expressed in vivo by mineral-embedded osteocytes, we tested the hypothesis that sclerostin would regulate the behavior of cells actively involved in mineralization in adult bone, the preosteocyte. Differentiating cultures of human primary osteoblasts exposed to recombinant human sclerostin (rhSCL) for 35 days displayed dose- and time-dependent inhibition of in vitro mineralization, with late cultures being most responsive in terms of mineralization and gene expression. Treatment of advanced (day 35) cultures with rhSCL markedly increased the expression of the preosteocyte marker E11 and decreased the expression of mature markers DMP1 and SOST. Concomitantly, matrix extracellular phosphoglycoprotein (MEPE) expression was increased by rhSCL at both the mRNA and protein levels, whereas PHEX was decreased, implying regulation through the MEPE-ASARM axis. We confirmed that mineralization by human osteoblasts is exquisitely sensitive to the triphosphorylated ASARM-PO4 peptide. Immunostaining revealed that rhSCL increased the endogenous levels of MEPE-ASARM. Importantly, antibody-mediated neutralization of endogenous MEPE-ASARM antagonized the effect of rhSCL on mineralization, as did the PHEX synthetic peptide SPR4. Finally, we found elevated Sost mRNA expression in the long bones of HYP mice, suggesting that sclerostin may drive the increased MEPE-ASARM levels and mineralization defect in this genotype. Our results suggest that sclerostin acts through regulation of the PHEX/MEPE axis at the preosteocyte stage and serves as a master regulator of physiologic bone mineralization, consistent with its localization in vivo and its established role in the inhibition of bone formation.
-
Abnormal Presence of the Matrix Extracellular Phosphoglycoprotein-Derived Acidic Serine- and Aspartate-Rich Motif Peptide in Human Hypophosphatemic Dentin
The American journal of pathology, 2010Co-Authors: Tchilalo Boukpessi, Peter S N Rowe, Celine Gaucher, Matthew Garabedian, Benjamin Salmon, Thibaut Léger, Julie Le Faouder, Cyril Willig, Olivier Meilhac, Catherine ChaussainAbstract:Severe dental troubles are associated with X-linked hypophosphatemic rickets and are mainly related to impaired dentin mineralization. In dentin matrix, matrix extracellular phosphoglycoprotein (MEPE) may be protected from proteolysis by a specific interaction with PHEX (phosphate regulating gene with homologies to endopeptidases on the X chromosome). The objective of our work was to determine whether PHEX impairment induces MEPE cleavage in dentin and the subsequent release of the C-terminal acidic serine- and aspartate-rich motif (ASARM) peptide, which is known to inhibit mineralization. By Western blot analysis, we explored dentin extracts from seven hypophosphatemic patients with mutations of the PHEX gene. A proteomic approach combining immunoprecipitation, surface-enhanced laser desorption/ionization-time of flight-mass spectrometry and matrix-assisted laser desorption ionization-time of flight analysis of the samples completed this exploration. This study shows a 4.1-kDa peptide containing the MEPE-derived ASARM peptide in hypophosphatemic samples. The presence of ASARM was less marked in patients treated with 1-hydroxylated vitamin D and phosphate during growth. Moreover, recombinant ASARM implanted in a rat pulp injury model disturbed the formation of the reparative dentin bridge. These results suggest that abnormal MEPE cleavage occurs when PHEX activity is deficient in humans, the ASARM peptide may be involved in the mineralization defects and the PHEX-MEPE interaction may be indirect, as ensuring a better phosphate and vitamin D environment to the mineralizing dentin prevents MEPE cleavage.
-
MEPE of45 as a new target for sensitizing human tumour cells to dna damage inducers
British Journal of Cancer, 2010Co-Authors: P Zhang, Peter S N Rowe, H Wang, Y WangAbstract:Matrix extracellular phosphoglycoprotein/osteoblast factor 45 (MEPE/OF45) was originally cloned from a human oncogenetic hypophosphataemia tumour (Rowe et al, 2000) and then identified in rat bone-marrow-derived osteoblasts (Petersen et al, 2000). The murine homologue of MEPE/OF45 was reported the following year (Argiro et al, 2001). Since the identification of MEPE/OF45, its function related to bone metabolism has been widely investigated. We previously identified that MEPE/OF45, as a cofactor of CHK1, protects cells from DNA damage-induced killing in rat embryo fibroblast cells (Liu et al, 2009). However, because human MEPE/OF45 (hMEPE/OF45) has only ∼50% homology with rat MEPE/OF45 (rMEPE/OF45), it remained unclear whether hMEPE/OF45 has similar function to rMEPE/OF45. CHK1 is one of the essential checkpoint proteins involved in cellular response to multiple DNA damage inducers (Liu et al, 2000; Zhao et al, 2002). It is believed that upregulated CHK1 protects cells from DNA damage-induced cell killing, including that induced by ionising radiation (IR) and camptothecin (CPT) (Hu et al, 2001, 2005a; Zhao et al, 2002; Wang et al, 2002b; Brown and Baltimore, 2003), by promoting homologous recombination repair (HRR) (Sorensen et al, 2005; Hu et al, 2005b). Despite the importance of CHK1 in DNA damage response, the regulation of CHK1 in mammalian cells is not well understood, partly because of its essential nature (Liu et al, 2000; Lam et al, 2004). In this study, on the basis of our previous report about the new role of rMEPE/OF45 in protecting cells from DNA damage-induced killing (Liu et al, 2009), we investigate whether hMEPE/OF45 is generally expressed in different types of tumour cells, whether the expression levels were relevant to the resistance of tumour cells to DNA damage inducers and whether, similar to rMEPE/OF45, hMEPE/OF45 (as a cofactor of CHK1) could be a new target for sensitizing human tumour cells to DNA damage inducers.
Eui Kyun Park - One of the best experts on this subject based on the ideXlab platform.
-
surface immobilization of MEPE peptide onto ha β tcp ceramic particles enhances bone regeneration and remodeling
Journal of Biomedical Materials Research Part B, 2012Co-Authors: Bodhraj Acharya, So Young Chun, Shin Yoon Kim, Cheil Moon, Hong In Shin, Eui Kyun ParkAbstract:Calcium phosphate ceramics have been widely used as scaffolds for bone regeneration. Here, to improve the osteogenic potential of hydroxyapatite/β-tricalcium phosphate (HA/β-TCP) and to apply the bioactive peptide in situ, matrix extracellular phosphoglycoprotein (MEPE) peptide, which has been shown to stimulate osteoblast differentiation, was covalently and directionally immobilized on HA/β-TCP particles. The free-hydroxyl groups on the surface of the HA/β-TCP particles were sequentially conjugated with APTES, PEG-(SS)2, and the synthetic MEPE peptide. Using FTIR and XPS, immobilization of the MEPE peptide on the HA/β-TCP was confirmed. Implantation of the MEPE peptide-immobilized HA/β-TCP into calvarial defect and subsequent analyses using a micro CT and histology showed significant bone regeneration and increased bone area (9.89-fold) as compared to that of unmodified HA/β-TCP. Moreover, tartrate-resistant acid phosphatase-positive osteoclasts were observed in regenerated bone by the MEPE peptide-immobilized HA/β-TCP, indicating that the bones newly formed by the MEPE peptide-immobilized HA/β-TCP are actively remodeled by osteoclasts. Therefore, our data demonstrate that MEPE peptide immobilization onto the HA/β-TCP surface stimulates bone regeneration associated with physiological bone remodeling. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2012.
-
Surface immobilization of MEPE peptide onto HA/β‐TCP ceramic particles enhances bone regeneration and remodeling
Journal of biomedical materials research. Part B Applied biomaterials, 2012Co-Authors: Bodhraj Acharya, So Young Chun, Shin Yoon Kim, Cheil Moon, Hong In Shin, Eui Kyun ParkAbstract:Calcium phosphate ceramics have been widely used as scaffolds for bone regeneration. Here, to improve the osteogenic potential of hydroxyapatite/β-tricalcium phosphate (HA/β-TCP) and to apply the bioactive peptide in situ, matrix extracellular phosphoglycoprotein (MEPE) peptide, which has been shown to stimulate osteoblast differentiation, was covalently and directionally immobilized on HA/β-TCP particles. The free-hydroxyl groups on the surface of the HA/β-TCP particles were sequentially conjugated with APTES, PEG-(SS)(2), and the synthetic MEPE peptide. Using FTIR and XPS, immobilization of the MEPE peptide on the HA/β-TCP was confirmed. Implantation of the MEPE peptide-immobilized HA/β-TCP into calvarial defect and subsequent analyses using a micro CT and histology showed significant bone regeneration and increased bone area (9.89-fold) as compared to that of unmodified HA/β-TCP. Moreover, tartrate-resistant acid phosphatase-positive osteoclasts were observed in regenerated bone by the MEPE peptide-immobilized HA/β-TCP, indicating that the bones newly formed by the MEPE peptide-immobilized HA/β-TCP are actively remodeled by osteoclasts. Therefore, our data demonstrate that MEPE peptide immobilization onto the HA/β-TCP surface stimulates bone regeneration associated with physiological bone remodeling.
Shiguang Liu - One of the best experts on this subject based on the ideXlab platform.
-
phosphorylated acidic serine aspartate rich MEPE associated motif peptide from matrix extracellular phosphoglycoprotein inhibits phosphate regulating gene with homologies to endopeptidases on the x chromosome enzyme activity
Journal of Endocrinology, 2007Co-Authors: Shiguang Liu, Peter S N Rowe, Jianping Zhou, Luke Vierthaler, Darryl L QuarlesAbstract:Inactivating PHEX (phosphate regulating gene with homologies to endopeptidases on the X chromosome) mutations cause X-linked hypophosphatemia in humans and mice (Hyp) through overproduction of fibroblast growth factor 23 (FGF23) a phosphaturic factor, by osteocytes. Matrix extracellular phosphoglycoprotein (MEPE) is also elevated in Hyp and other hypophosphatemic disorders. In addition, the administration of an ASARM (acidic serine-aspartate rich MEPE-associated motif) peptide derived from MEPE causes phosphaturia and inhibits bone mineralization in mice, suggesting that MEPE also plays a role in phosphate homeostasis. Since recent studies found that MEPE binds specifically to PHEX in vitro, we tested the effect of recombinant-MEPE and its ASARM peptide on PHEX enzyme activity in vitro and FGF23 expression in bone marrow stromal cell cultures ex vivo. We found that both recombinant MEPE and synthetic phosphorylated ASARM peptide (ASARM-PO(4)) inhibit PHEX enzyme activities in an in vitro fluorescent-quenched PHEX enzyme activity assay. The ASARM-PO(4) peptide inhibits PHEX enzyme activity in a dose-dependent manner with a K(i) of 128 nM and V(max-i) of 100%. Recombinant MEPE also inhibits PHEX activity (K(i) = 2 nM and V(max-i) = 26%). Long-term bone marrow stromal cell cultures supplemented with 10 microM ASARM-PO(4) peptide resulted in significant elevation of FGF23 transcripts and inhibition of mineralization. These findings suggest that MEPE inhibits mineralization and PHEX activity and leads to increased FGF23 production. The resulting coordination of mineralization and release of a phosphaturic factor by MEPE may serve a physiological role in regulating systemic phosphate homeostasis to meet the needs for bone mineralization.
-
Phosphorylated acidic serine–aspartate-rich MEPE-associated motif peptide from matrix extracellular phosphoglycoprotein inhibits phosphate regulating gene with homologies to endopeptidases on the X-chromosome enzyme activity
The Journal of endocrinology, 2007Co-Authors: Shiguang Liu, Peter S N Rowe, Jianping Zhou, Luke Vierthaler, L. Darryl QuarlesAbstract:Inactivating PHEX (phosphate regulating gene with homologies to endopeptidases on the X chromosome) mutations cause X-linked hypophosphatemia in humans and mice (Hyp) through overproduction of fibroblast growth factor 23 (FGF23) a phosphaturic factor, by osteocytes. Matrix extracellular phosphoglycoprotein (MEPE) is also elevated in Hyp and other hypophosphatemic disorders. In addition, the administration of an ASARM (acidic serine-aspartate rich MEPE-associated motif) peptide derived from MEPE causes phosphaturia and inhibits bone mineralization in mice, suggesting that MEPE also plays a role in phosphate homeostasis. Since recent studies found that MEPE binds specifically to PHEX in vitro, we tested the effect of recombinant-MEPE and its ASARM peptide on PHEX enzyme activity in vitro and FGF23 expression in bone marrow stromal cell cultures ex vivo. We found that both recombinant MEPE and synthetic phosphorylated ASARM peptide (ASARM-PO(4)) inhibit PHEX enzyme activities in an in vitro fluorescent-quenched PHEX enzyme activity assay. The ASARM-PO(4) peptide inhibits PHEX enzyme activity in a dose-dependent manner with a K(i) of 128 nM and V(max-i) of 100%. Recombinant MEPE also inhibits PHEX activity (K(i) = 2 nM and V(max-i) = 26%). Long-term bone marrow stromal cell cultures supplemented with 10 microM ASARM-PO(4) peptide resulted in significant elevation of FGF23 transcripts and inhibition of mineralization. These findings suggest that MEPE inhibits mineralization and PHEX activity and leads to increased FGF23 production. The resulting coordination of mineralization and release of a phosphaturic factor by MEPE may serve a physiological role in regulating systemic phosphate homeostasis to meet the needs for bone mineralization.
-
Role of Matrix Extracellular Phosphoglycoprotein in the Pathogenesis of X-Linked Hypophosphatemia
Journal of the American Society of Nephrology : JASN, 2005Co-Authors: Shiguang Liu, Zhousheng Xiao, Thomas A. Brown, Jianping Zhou, Hani A. Awad, Farshid Guilak, L. Darryl QuarlesAbstract:X-linked hypophosphatemia (XLH), a disorder characterized by hypophosphatemia, impaired skeletal mineralization, and aberrant regulation of 1, 25(OH) 2 D 3 , is caused by inactivating mutations of Phex, which results in the accumulation of putative phosphaturic factors, called phosphatonins. Matrix extracellular phosphoglycoprotein (MEPE) is a proposed candidate for phosphatonin. The authors found that Hyp mice had increased expression of the MEPE and another phosphaturic factor, Fgf23. To establish MEPE’s role in the pathogenesis of the XLH, MEPE -deficient mice were back-crossed onto the Hyp mouse homologue of XLH and phenotypes of wild-type, MEPE −/− , Hyp , and MEPE −/− / Hyp mice were examined. Transfer of MEPE deficiency onto the Phex -deficient Hyp mouse background failed to correct hypophosphatemia and aberrant serum 1,25(OH) 2 D 3 levels. Increased Fgf23 levels in Hyp mice were not affected by superimposed MEPE deficiency. In addition, MEPE -deficient Hyp mice retained bone mineralization defects in vivo , characterized by decreased bone mineral density, reduced mineralized trabecular bone volume, lower flexural strength, and histologic evidence of osteomalacia; however, cultures of Hyp -derived bone marrow stromal cells in the absence of MEPE showed improved mineralization and normalization of osteoblast gene expression profiles observed in cells derived from MEPE -null mice. These results demonstrate that MEPE elevation in Hyp mice does not contribute to the hypophosphatemia associated with inactivating Phex mutations and is therefore not phosphatonin.
-
Inhibition of MEPE cleavage by Phex.
Biochemical and biophysical research communications, 2002Co-Authors: Rong Guo, Peter S N Rowe, Leigh G Simpson, Zhousheng Xiao, Shiguang Liu, L. Darryl QuarlesAbstract:X-linked hypophosphatemia (XLH) and the Hyp-mouse disease homolog are caused by inactivating mutations of Phex which results in the local accumulation of an unknown autocrine/paracrine factor in bone that inhibits mineralization of extracellular matrix. In these studies, we evaluated whether the matrix phosphoglycoprotein MEPE, which is increased in calvaria from Hyp mice, is a substrate for Phex. Using recombinant full-length Phex (rPhexWT) produced in Sf9 cells, we failed to observe Phex-dependent hydrolysis of recombinant human MEPE (rMEPE). Rather, we found that rPhex-WT inhibited cleavage of rMEPE by endogenous cathepsin-like enzyme activity present in Sf9 membrane. Sf9 membranes as well as purified cathepsin B cleaved MEPE into two major fragments of approximately 50 and approximately 42kDa. rPhexWT protein in Sf9 membrane fractions, co-incubation of rPhexWT and cathepsin B, and pre-treatment of Sf9 membranes with leupeptin prevented the hydrolysis of MEPE in vitro. The C-terminal domain of Phex was required for inhibition of MEPE cleavage, since the C-terminal deletion mutant rPhex (1-433) [rPhex3(')M] failed to inhibit Sf9-dependent metabolism of MEPE. Phex-dependent inhibition of MEPE degradation, however, did not require Phex enzymatic activity, since EDTA, an inhibitor of rPhex, failed to block rPhexWT inhibition of MEPE cleavage by Sf9 membranes. Since we were unable to identify interactions of Phex with MEPE or actions of Phex to metabolize cathepsin B, Phex may be acting to interfere with the actions of other enzymes that degrade extracellular matrix proteins. Although the molecular mechanism and biological relevance of non-enzymatic actions of Phex need to be established, these findings indicate that MEPE may be involved in the pathogenesis defective mineralization due to Phex deficiency in XLH and the Hyp-mouse.
L. Darryl Quarles - One of the best experts on this subject based on the ideXlab platform.
-
Phosphorylated acidic serine–aspartate-rich MEPE-associated motif peptide from matrix extracellular phosphoglycoprotein inhibits phosphate regulating gene with homologies to endopeptidases on the X-chromosome enzyme activity
The Journal of endocrinology, 2007Co-Authors: Shiguang Liu, Peter S N Rowe, Jianping Zhou, Luke Vierthaler, L. Darryl QuarlesAbstract:Inactivating PHEX (phosphate regulating gene with homologies to endopeptidases on the X chromosome) mutations cause X-linked hypophosphatemia in humans and mice (Hyp) through overproduction of fibroblast growth factor 23 (FGF23) a phosphaturic factor, by osteocytes. Matrix extracellular phosphoglycoprotein (MEPE) is also elevated in Hyp and other hypophosphatemic disorders. In addition, the administration of an ASARM (acidic serine-aspartate rich MEPE-associated motif) peptide derived from MEPE causes phosphaturia and inhibits bone mineralization in mice, suggesting that MEPE also plays a role in phosphate homeostasis. Since recent studies found that MEPE binds specifically to PHEX in vitro, we tested the effect of recombinant-MEPE and its ASARM peptide on PHEX enzyme activity in vitro and FGF23 expression in bone marrow stromal cell cultures ex vivo. We found that both recombinant MEPE and synthetic phosphorylated ASARM peptide (ASARM-PO(4)) inhibit PHEX enzyme activities in an in vitro fluorescent-quenched PHEX enzyme activity assay. The ASARM-PO(4) peptide inhibits PHEX enzyme activity in a dose-dependent manner with a K(i) of 128 nM and V(max-i) of 100%. Recombinant MEPE also inhibits PHEX activity (K(i) = 2 nM and V(max-i) = 26%). Long-term bone marrow stromal cell cultures supplemented with 10 microM ASARM-PO(4) peptide resulted in significant elevation of FGF23 transcripts and inhibition of mineralization. These findings suggest that MEPE inhibits mineralization and PHEX activity and leads to increased FGF23 production. The resulting coordination of mineralization and release of a phosphaturic factor by MEPE may serve a physiological role in regulating systemic phosphate homeostasis to meet the needs for bone mineralization.
-
Role of Matrix Extracellular Phosphoglycoprotein in the Pathogenesis of X-Linked Hypophosphatemia
Journal of the American Society of Nephrology : JASN, 2005Co-Authors: Shiguang Liu, Zhousheng Xiao, Thomas A. Brown, Jianping Zhou, Hani A. Awad, Farshid Guilak, L. Darryl QuarlesAbstract:X-linked hypophosphatemia (XLH), a disorder characterized by hypophosphatemia, impaired skeletal mineralization, and aberrant regulation of 1, 25(OH) 2 D 3 , is caused by inactivating mutations of Phex, which results in the accumulation of putative phosphaturic factors, called phosphatonins. Matrix extracellular phosphoglycoprotein (MEPE) is a proposed candidate for phosphatonin. The authors found that Hyp mice had increased expression of the MEPE and another phosphaturic factor, Fgf23. To establish MEPE’s role in the pathogenesis of the XLH, MEPE -deficient mice were back-crossed onto the Hyp mouse homologue of XLH and phenotypes of wild-type, MEPE −/− , Hyp , and MEPE −/− / Hyp mice were examined. Transfer of MEPE deficiency onto the Phex -deficient Hyp mouse background failed to correct hypophosphatemia and aberrant serum 1,25(OH) 2 D 3 levels. Increased Fgf23 levels in Hyp mice were not affected by superimposed MEPE deficiency. In addition, MEPE -deficient Hyp mice retained bone mineralization defects in vivo , characterized by decreased bone mineral density, reduced mineralized trabecular bone volume, lower flexural strength, and histologic evidence of osteomalacia; however, cultures of Hyp -derived bone marrow stromal cells in the absence of MEPE showed improved mineralization and normalization of osteoblast gene expression profiles observed in cells derived from MEPE -null mice. These results demonstrate that MEPE elevation in Hyp mice does not contribute to the hypophosphatemia associated with inactivating Phex mutations and is therefore not phosphatonin.
-
Inhibition of MEPE cleavage by Phex.
Biochemical and biophysical research communications, 2002Co-Authors: Rong Guo, Peter S N Rowe, Leigh G Simpson, Zhousheng Xiao, Shiguang Liu, L. Darryl QuarlesAbstract:X-linked hypophosphatemia (XLH) and the Hyp-mouse disease homolog are caused by inactivating mutations of Phex which results in the local accumulation of an unknown autocrine/paracrine factor in bone that inhibits mineralization of extracellular matrix. In these studies, we evaluated whether the matrix phosphoglycoprotein MEPE, which is increased in calvaria from Hyp mice, is a substrate for Phex. Using recombinant full-length Phex (rPhexWT) produced in Sf9 cells, we failed to observe Phex-dependent hydrolysis of recombinant human MEPE (rMEPE). Rather, we found that rPhex-WT inhibited cleavage of rMEPE by endogenous cathepsin-like enzyme activity present in Sf9 membrane. Sf9 membranes as well as purified cathepsin B cleaved MEPE into two major fragments of approximately 50 and approximately 42kDa. rPhexWT protein in Sf9 membrane fractions, co-incubation of rPhexWT and cathepsin B, and pre-treatment of Sf9 membranes with leupeptin prevented the hydrolysis of MEPE in vitro. The C-terminal domain of Phex was required for inhibition of MEPE cleavage, since the C-terminal deletion mutant rPhex (1-433) [rPhex3(')M] failed to inhibit Sf9-dependent metabolism of MEPE. Phex-dependent inhibition of MEPE degradation, however, did not require Phex enzymatic activity, since EDTA, an inhibitor of rPhex, failed to block rPhexWT inhibition of MEPE cleavage by Sf9 membranes. Since we were unable to identify interactions of Phex with MEPE or actions of Phex to metabolize cathepsin B, Phex may be acting to interfere with the actions of other enzymes that degrade extracellular matrix proteins. Although the molecular mechanism and biological relevance of non-enzymatic actions of Phex need to be established, these findings indicate that MEPE may be involved in the pathogenesis defective mineralization due to Phex deficiency in XLH and the Hyp-mouse.
