title: Isoquercitrin and polyphosphate co-enhance mineralization of human osteoblast-like SaOS-2 cells via separate activation of two RUNX2 cofactors AFT6 and Ets1.
abstract: Isoquercitrin, a dietary phytoestrogen, is a potential stimulator of bone mineralization used for prophylaxis of osteoporotic disorders. Here we studied the combined effects of isoquercitrin, a cell membrane permeable 3-O-glucoside of quercetin, and polyphosphate [polyP], a naturally occurring inorganic polymer inducing bone formation, on mineralization of human osteoblast-like SaOS-2 cells. Both compounds isoquercitrin and polyP induce at non-toxic concentrations the mineralization process of SaOS-2 cells. Co-incubation experiments revealed that isoquercitrin (at 0.1 and 0.3μM), if given simultaneously with polyP (as Ca(2+) salt; at 3, 10, 30 and 100μM) amplifies the mineralization-enhancing effect of the inorganic polymer. The biomineralization process induced by isoquercitrin and polyP is based on two different modes of action. After incubation of the cells with isoquercitrin or polyP the expression of the Runt-related transcription factor 2 [RUNX2] is significantly upregulated. In addition, isoquercitrin causes a strong increase of the steady-state-levels of the two co-activators of RUNX2, the activating transcription factor 6 [ATF6] and the Ets oncogene homolog 1 [Ets1]. The activating effect of isoquercitrin occurs via a signal transduction pathway involving ATF6, and by that, is independent from the induction cascade initiated by polyP. This conclusion is supported by the finding that isoquercitrin upregulates the expression of the gene encoding for osteocalcin, while polyP strongly increases the expression of the Ets1 gene and of the alkaline phosphatase. We show that the two compounds, polyP and isoquercitrin, have a co-enhancing effect on bone mineral formation and in turn might be of potential therapeutic value for prevention/treatment of osteoporosis.
authors.affiliation: ERC Advanced Investigator Grant Research Group at Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz, Duesbergweg 6, D-55128 Mainz, Germany. Electronic address: wang013@uni-mainz.de.
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Wang
authors.affiliation: ERC Advanced Investigator Grant Research Group at Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz, Duesbergweg 6, D-55128 Mainz, Germany. Electronic address: hschroed@uni-mainz.de.
authors.forename: Heinz C
authors.initials: HC
authors.lastname: Schröder
authors.affiliation: Laboratory of Advanced Materials, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China. Electronic address: biomater@mail.tsinghua.edu.cn.
authors.forename: Qingling
authors.initials: Q
authors.lastname: Feng
authors.affiliation: NanotecMARIN GmbH, Duesbergweg 6, D-55128 Mainz, Germany. Electronic address: DiehlSei@mail.uni-mainz.de.
authors.forename: Bärbel
authors.initials: B
authors.lastname: Diehl-Seifert
authors.affiliation: ERC Advanced Investigator Grant Research Group at Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz, Duesbergweg 6, D-55128 Mainz, Germany. Electronic address: grebenyu@uni-mainz.de.
authors.forename: Vladislav A
authors.initials: VA
authors.lastname: Grebenjuk
authors.affiliation: ERC Advanced Investigator Grant Research Group at Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz, Duesbergweg 6, D-55128 Mainz, Germany. Electronic address: wmueller@uni-mainz.de.
authors.forename: Werner E G
authors.initials: WE
authors.lastname: Müller
mesh_terms: D051702:Activating Transcription Factor 6 / Q000235:genetics / Q000378:metabolism*; D002113:Calcification, Physiologic / Q000187:drug effects* / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D045744:Cell Line, Tumor; D004357:Drug Synergism; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D010006:Osteoblasts / Q000187:drug effects* / Q000502:physiology; D011122:Polyphosphates / Q000008:administration & dosage / Q000494:pharmacology*; D050784:Proto-Oncogene Protein c-ets-1 / Q000235:genetics / Q000378:metabolism*; D011794:Quercetin / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D051702:Activating Transcription Factor 6; C494041:ETS1 protein, human; D011122:Polyphosphates; D050784:Proto-Oncogene Protein c-ets-1; C016527:isoquercitrin; D011794:Quercetin; D002118:Calcium
keywords: Alkaline phosphatase; Bone metabolism; Isoquercitrin; Osteoblasts; Osteocalcin; Quercetin