Abstract
The differentiation of bone marrow mesenchymal stem cells (MSCs) into osteoblasts is a crucial step in bone formation. However, the mechanisms involved in the early stages of osteogenic differentiation are not well understood. In this study, we identified FHL2, a member of the LIM-only subclass of the LIM protein superfamily, that is up-regulated during early osteoblast differentiation induced by dexamethasone in murine and human MSCs. Gain-of-function studies showed that FHL2 promotes the expression of the osteoblast transcription factor Runx2, alkaline phosphatase, type I collagen, as well as in vitro extracellular matrix mineralization in murine and human mesenchymal cells. Knocking down FHL2 using sh-RNA reduces basal and dexamethasone-induced osteoblast marker gene expression in MSCs. We demonstrate that FHL2 interacts with beta-catenin, a key player involved in bone formation induced by Wnt signaling. FHL2-beta-catenin interaction potentiates beta-catenin nuclear translocation and TCF/LEF transcription, resulting in increased Runx2 and alkaline phosphatase expression, which was inhibited by the Wnt inhibitor DKK1. Reduction of Runx2 transcriptional activity using a mutant Runx2 results in inhibition of FHL2-induced alkaline phosphatase expression in MSCs. These findings reveal that FHL2 acts as an endogenous activator of mesenchymal cell differentiation into osteoblasts and mediates osteogenic differentiation induced by dexamethasone in MSCs through activation of Wnt/beta-catenin signaling- dependent Runx2 expression.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Active Transport, Cell Nucleus / drug effects
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Active Transport, Cell Nucleus / physiology
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Alkaline Phosphatase
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Animals
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Anti-Inflammatory Agents / pharmacology*
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Calcification, Physiologic / drug effects
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Calcification, Physiologic / physiology
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Cell Differentiation / drug effects*
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Cell Differentiation / physiology
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Cell Line
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Cell Nucleus / genetics
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Cell Nucleus / metabolism*
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Cells, Cultured
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Collagen Type I / genetics
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Collagen Type I / metabolism
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Core Binding Factor Alpha 1 Subunit / biosynthesis*
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Core Binding Factor Alpha 1 Subunit / genetics
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Dexamethasone / pharmacology*
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Enzyme Activators / metabolism
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Extracellular Matrix / genetics
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Extracellular Matrix / metabolism
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Homeodomain Proteins / genetics
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Homeodomain Proteins / metabolism*
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Humans
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Intercellular Signaling Peptides and Proteins / genetics
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Intercellular Signaling Peptides and Proteins / metabolism
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LIM-Homeodomain Proteins
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Mesenchymal Stem Cells / cytology
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Mesenchymal Stem Cells / metabolism*
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Mice
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Muscle Proteins / genetics
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Muscle Proteins / metabolism*
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Mutation
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Osteogenesis / drug effects
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Osteogenesis / physiology
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Signal Transduction / drug effects*
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Signal Transduction / physiology
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TCF Transcription Factors / genetics
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TCF Transcription Factors / metabolism
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Transcription Factors / genetics
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Transcription Factors / metabolism*
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Up-Regulation / drug effects
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Up-Regulation / physiology*
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Wnt Proteins / genetics
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Wnt Proteins / metabolism*
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beta Catenin / genetics
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beta Catenin / metabolism*
Substances
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Anti-Inflammatory Agents
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CTNNB1 protein, human
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CTNNB1 protein, mouse
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Collagen Type I
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Core Binding Factor Alpha 1 Subunit
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DKK1 protein, human
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Dkk1 protein, mouse
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Enzyme Activators
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FHL2 protein, human
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Fhl2 protein, mouse
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Homeodomain Proteins
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Intercellular Signaling Peptides and Proteins
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LIM-Homeodomain Proteins
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Muscle Proteins
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RUNX2 protein, human
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Runx2 protein, mouse
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TCF Transcription Factors
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Transcription Factors
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Wnt Proteins
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beta Catenin
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Dexamethasone
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Alkaline Phosphatase