title: Short-term exposure to tumor necrosis factor-alpha enables human osteoblasts to direct adipose tissue-derived mesenchymal stem cells into osteogenic differentiation.
abstract: Tumor necrosis factor-alpha (TNF-α) is one major inflammatory factor peaking at 24 h after bone fracture in response to injury; its role in bone healing is controversial. The aims of this study were to investigate whether the duration of exposure to TNF-α is crucial for the initiation of bone regeneration and to determine its underlying mechanism(s). We demonstrated that 24 h of TNF-α treatment significantly abrogated osteocalcin gene expression by human primary osteoblasts (HOBs). However, when TNF-α was withdrawn after 24 h, bone sialoprotein and osteocalcin gene expression levels in HOBs at day 7 were significantly up-regulated compared with the HOBs without TNF-α treatment. In contrast, continuous TNF-α treatment down-regulated bone sialoprotein and osteocalcin gene expression. In addition, in an indirect co-culture system, HOBs pretreated with TNF-α for 24 h induced significantly greater osteogenic differentiation of adipose tissue-derived mesenchymal stem cells (ASCs) than the HOBs without TNF-α treatment. TNF-α treatment also promoted endogenous bone morphogenetic protein 2 (BMP-2) production in HOBs, while blocking the BMP-2 signaling pathway with Noggin inhibited osteogenic differentiation of ASCs in the co-culture system. Furthermore, activation of the p38 mitogen-activated protein kinase (MAPK) signaling pathway after TNF-α treatment occurred earlier than BMP-2 protein expression. BMP-2 production by HOBs and osteogenic differentiation of ASCs in the co-culture system with HOBs was significantly decreased when HOBs were pretreated with TNF-α in combination with the p38 MAPK-specific inhibitor (SB203580). Taken together, we provide evidence that exposure duration is a critical element in determining TNF-α's effects on bone regeneration. We also demonstrate that the p38 MAPK signaling pathway regulates the expression of BMP-2 in osteoblasts, which then acts through a paracrine loop, to direct the osteoblast lineage commitment of mesenchymal stem cells.
authors.affiliation: Biomaterials and Tissue Engineering Research Unit, School of AMME, The University of Sydney, Sydney, Australia.
authors.forename: ZuFu
authors.initials: Z
authors.lastname: Lu
authors.forename: Guocheng
authors.initials: G
authors.lastname: Wang
authors.forename: Colin R
authors.initials: CR
authors.lastname: Dunstan
authors.forename: Hala
authors.initials: H
authors.lastname: Zreiqat
mesh_terms: D000273:Adipose Tissue / Q000166:cytology*; D000293:Adolescent; D055396:Bone Morphogenetic Protein 2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D001861:Bone Regeneration; D002352:Carrier Proteins / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects*; D049109:Cell Proliferation; D002648:Child; D018920:Coculture Techniques; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D058574:Integrin-Binding Sialoprotein / Q000235:genetics / Q000378:metabolism; D020935:MAP Kinase Signaling System; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000187:drug effects; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D015675:Osteocalcin / Q000235:genetics / Q000378:metabolism; D010012:Osteogenesis; D011725:Pyridines / Q000494:pharmacology; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D055815:Young Adult; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D000099176:Noggin Protein
chemical_list: D055396:Bone Morphogenetic Protein 2; D002352:Carrier Proteins; D050659:Core Binding Factor Alpha 1 Subunit; D007093:Imidazoles; D058574:Integrin-Binding Sialoprotein; D015675:Osteocalcin; D011725:Pyridines; D014409:Tumor Necrosis Factor-alpha; D048051:p38 Mitogen-Activated Protein Kinases; D000099176:Noggin Protein; C525718:BMP2 protein, human; C493709:RUNX2 protein, human; C093642:SB 203580