Role of the AP-1 transcription factors FosB and 2 FosB in the regulation of osteoblast differentiation and bone formation in response to mechanostimulation
Final Report Abstract
Overexpression of the AP-1 transcription factor ∆FosB and its isoform ∆2∆FosB leads to a striking osteosclerotic phenotype in vivo and to an increased expression of osteoblast markers as well as to an increased mineralization ex vivo and in vitro. Mechanical stretch induced FosB gene expression in human mesenchymal precursor cells in a time- and amplitude-dependent manner. Physical forces enhanced the progression of the progenitor cell population towards an osteogenic fate, demonstrated by the increased levels of Runx2, the master regulator of osteoblast differentiation, and collagen 1 expression. In order to find a mechanism by which ∆FosB and ∆2∆FosB cause a high bone mass phenotype, we screened an osteoblast library in a yeast twohybrid assay and identified a novel zinc finger protein termed Zfp521 as a ∆2∆FosB interacting partner. Zfp521 is a 180 kDa protein consisting of 30 Krüppel-like zinc fingers and is expressed in the periphery of mesenchymal condensations as early as day E12.5. At later stages, Zfp521 is present in the perichondrium, the periosteum, in osteoblast- and chondroblast precursors, in prehypertrophic chondrocytes, in osteoblasts, and in osteocytes. Zfp521 localizes to the nucleus, suggesting a role in transcriptional regulation, and its expression is inhibited by BMP-2-induced osteoblast differentiation. Overexpression of Zfp521 dose-dependently and cell-autonomously inhibits osteoblast differentiation in vitro and ex vivo and reduces the expression of alkaline phosphatase and several other osteoblast marker genes, whereas RNAi-mediated knockdown favors osteoblast differentiation. Runx2 dose-dependently rescued the Zfp521-induced restriction of the osteoblast phenotype, suggesting that Zfp521 acts as a Runx2 antagonist. Zfp521 associates with the N-terminus and the DNA-binding domain of Runx2 and strongly represses Runx2 transcriptional activity via zinc finger domains 6 and 26. Although Zfp521 inhibits early stages of osteoblast differentiation, overexpression of Zfp521 in transgenic mice under the control of both the osteoblast-specific osteocalcin promoter and the more widely expressed enolase 2 promoter resulted in an osteosclerotic phenotype. However, Runx2 plays a dual role by favoring early osteoblast differentiation and inhibiting mature osteoblasts at later stages. We propose that Zfp521 antagonizes Runx2 activity, thereby repressing early osteoblast differentiation and promoting fully mature osteoblasts at terminal differentiation stages. The balance between Zfp521 and Runx2 may therefore determine the rate of osteoblast differentiation and bone formation. These findings provide novel insights in the regulation of osteoblast differentiation and bone formation and may lead to the identification of drug targets for the treatment of patients with a reduced bone mass.
Publications
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Mechanoinduction of FosB in human bone marrow stromal cells. American Society for Bone and Mineral Research, 27th Annual Meeting, Nashville, Tennessee, USA, 23-27 September 2005
Hesse E, Jagodzinski M, Wehmeier M, Horne WC, Baron R
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Mechanoinduction of FosB in human bone marrow stromal cells. American Society for Bone and Mineral Research, 27th Annual Meeting, Nashville, Tennessee, USA, 23-27 September 2005. (JBMR; Vol. 20, Suppl. 1, pp S356, September 2005)
Hesse E, Jagodzinski M, Wehmeier M, Horne WC, Baron R
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Role of the AP-1 transcription factor FosB and its splice variants in the regulation of osteoblast differentiation in response to mechanostimulation. Annual MD/PhD Meeting, Stephansstift, Hannover, Germany, 10-12 March 2005
Hesse E, Baron R, Horne WC, Krug N
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Role of the AP-1 transcription factor FosB and its splice variants in the regulation of osteoblast differentiation in response to mechanostimulation. Annual MD/PhD Meeting, Stephansstift, Hannover, Germany, 10-12 March 2005
Hesse E, Baron R, Horne WC, Krug N
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Mechanisch induzierte Expression von FosB in humanen Knochenmarkstromazellen. Deutscher Kongress für Orthopädie und Unfallchirurgie 2006, Berlin, Germany, 2-6 October 2006
Hesse E, Jagodzinski M, Drescher M, Haasper C, Wehmeier M, Krettek C
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Mechanisch induzierte Expression von FosB in humanen Knochenmarkstromazellen. Deutscher Kongress für Orthopädie und Unfallchirurgie 2006, Berlin, Germany, 2-6 October 2006
Hesse E, Jagodzinski M, Drescher M, Haasper C, Wehmeier M, Krettek C
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Characterization and functional analysis of Zfp521, a novel AP-1 interacting zincfinger protein that modulates Runx2 activity and promotes bone formation in vivo. Annual MD/PhD Meeting, Stephansstift, Hannover, Germany, 15-16 March 2007
Hesse E
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Characterization and functional analysis of Zfp521, a novel AP-1 interacting zincfinger protein that modulates Runx2 activity and promotes bone formation in vivo. Annual MD/PhD Meeting, Stephansstift, Hannover, Germany, 15-16 March 2007
Hesse E
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Characterization and structure-function analysis of Zfp521, a novel key player in the regulation of osteoblast differentiation and bone formation. PhD thesis defense, Trauma Surgery, Hannover Medical School and Orthopaedics & Cell Biology, Yale University School of Medicine, Hannover, Germany, 9 November 2007
Eric Hesse
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Characterization and structure-function analysis of Zfp521, a novel key player in the regulation of osteoblast differentiation and bone formation. Thesis for the degree of Doctor of Philosophy (PhD). Eric Hesse, 2007, Hannover Medical School, International MD/PhD program “Molecular Medicine”, in Hannover Biomedical Research School (HBRS), Department of Trauma Surgery and Yale University School of Medicine Departments of Orthopaedics & Cell Biology
Eric Hesse
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Zfp521 antagonisiert Runx2 und inhibiert die Osteoblastendifferenzierung in vitro. Deutscher Kongress für Orthopädie und Unfallchirurgie, Berlin, Germany, 24-27 October 2007
Hesse E, Wu M, Morvan F, Neff L, Horne WC, Baron R
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Zfp521 antagonisiert Runx2 und inhibiert die Osteoblastendifferenzierung in vitro. Deutscher Kongress für Orthopädie und Unfallchirurgie, Berlin, Germany, 24-27 October 2007
Hesse E, Wu M, Morvan F, Neff L, Horne WC, Baron R
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Zfp521 antagonizes Runx2 activity and inhibits osteoblast differentiation in vitro. International Bone and Mineral Society (IBMS), 17th Scientific Meeting, Montréal, Canada, 24-29 June 2007
Hesse E, Wu M, Rowe GC, Neff L, Horne WC, Baron R
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Zfp521 antagonizes Runx2 activity and inhibits osteoblast differentiation in vitro. International Bone and Mineral Society (IBMS), 17th Scientific Meeting, Montréal, Canada, 24-29 June 2007. (Bone; Vol. 40, No. 6, Suppl. 2, #006, S110, June 2007)
Hesse E, Wu M, Rowe GC, Neff L, Horne WC, Baron R
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Zfp521, a ∆2∆FosB-interacting protein, is a novel inhibitor of Runx2 activity with opposite effects on osteoblasts and bone formation in vitro and in vivo. American Society for Bone and Mineral Research, 29th Annual Meeting, Honolulu, Hawaii, USA, 16-19 September 2007
Hesse E, Wu M, Rowe GC, Neff L, Horne WC, Baron R
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Zfp521, a ∆2∆FosB-interacting protein, is a novel inhibitor of Runx2 activity with opposite effects on osteoblasts and bone formation in vitro and in vivo. American Society for Bone and Mineral Research, 29th Annual Meeting, Honolulu, Hawaii, USA, 16-19 September 2007. (JBMR; Vol. 22, Suppl. 1, 1250, S70, September 2007)
Hesse E, Wu M, Rowe GC, Neff L, Horne WC, Baron R
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Cyclic strain induces FosB and initiates osteogenic differentiation of mesenchymal cells. Exp Toxicol Pathol. 2008 Jan 24 [Epub ahead of print]
Haasper C, Jagodzinski M, Drescher M, Meller R, Wehmeier M, Krettek C, Hesse E
