title: Irx3 and Bmp2 regulate mouse mesenchymal cell chondrogenic differentiation in both a Sox9-dependent and -independent manner.
abstract: Sox9, a master regulator of cartilage development, controls the cell fate decision to differentiate from mesenchymal to chondrogenic cells. In addition, Sox9 regulates the proliferation and differentiation of chondrocytes, as well as the production of cartilage-specific proteoglycans. The existence of Sox9-independent mechanisms in cartilage development remains to be determined. Here, we attempted to identify genes involved in such putative mechanisms via microarray analysis using a mouse chondrogenic cell line, N1511. We first focused on transcription factors that exhibited upregulated expression following Bmp2 treatment, which was not altered by subsequent treatment with Sox9 siRNA. Among these, we selected positive regulators for chondrogenesis and identified Iroquois-related homeobox 3 (Irx3) as one of the candidate genes. Irx3 expression gradually increased with chondrocyte terminal differentiation in a reciprocal manner to Sox9 expression, and promoted the chondrogenic differentiation of mesenchymal cells upon Bmp2 treatment. Furthermore, Irx3 partially rescued impaired chondrogenesis by upregulating the expression of epiphycan and lumican under reduced Sox9 expression. Finally, Irx3 was shown to act in concert with Bmp2 signaling to activate the p38 MAPK pathway, which in turn stimulated Sox9 expression, as well as the expression of epiphycan and lumican in a Sox9-independent manner. These results indicate that Irx3 represents a novel chondrogenic factor of mesenchymal cells, acts synergistically with Bmp2-mediated signaling, and regulates chondrogenesis independent of the transcriptional machinery associated with Sox9-mediated regulation.
authors.affiliation: School of Health and Sports Science, Mukogawa Women's University, Nishinomiya, Japan.
authors.forename: Yoshihiro
authors.identifier: http://orcid.org/0000-0002-3673-9224
authors.initials: Y
authors.lastname: Tamamura
authors.affiliation: Faculty of Human Care, Department of Nursing Science, Tohto College of Health Sciences, Saitama, Japan.
authors.forename: Kenichi
authors.initials: K
authors.lastname: Katsube
authors.affiliation: School of Health and Sports Science, Mukogawa Women's University, Nishinomiya, Japan.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Mera
authors.affiliation: School of Health and Sports Science, Mukogawa Women's University, Nishinomiya, Japan.|Department of Orthopedic Surgery, Osaka City University Graduate School of Medicine, Osaka, Japan.
authors.forename: Maki
authors.initials: M
authors.lastname: Itokazu
authors.affiliation: School of Health and Sports Science, Mukogawa Women's University, Nishinomiya, Japan.
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Wakitani
mesh_terms: D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D059630:Mesenchymal Stem Cells / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: C525718:BMP2 protein, human; D055396:Bone Morphogenetic Protein 2; D018398:Homeodomain Proteins; C501599:Irx3 protein, mouse; D014157:Transcription Factors
keywords: Bmp2; Irx3; Sox9; chondrogenic differentiation; mesenchymal cell