LPS-stimulated inflammatory environment inhibits BMP-2-induced osteoblastic differentiation through crosstalk between TLR4/MyD88/NF-κB and BMP/Smad signaling.
Bone morphogenetic protein-2 (BMP-2) is a novel differentiation factor that is capable of inducing osteoblast differentiation and bone formation, making it an attractive option in treatment of bone defects, fractures, and spine fusions. Inflammation, which was a common situation during bone healing, is recognized to inhibit osteogenic differentiation and bone formation. However, the effect of inflammation on BMP-2-induced osteoblastic differentiation remains ambiguous. In this study, we showed that an inflammatory environment triggered by lipopolysaccharide (LPS) in vitro would suppress BMP-2-induced osteogenic differentiation of bone marrow mesenchymal stem cells, which represented by decreased alkaline phosphatase (ALPase) activity and down-regulated osteogenic genes. In addition, LPS activated nuclear factor-κB (NF-κB) via a TLR4/MyD88-dependent manner and inhibited BMP-2-induced phosphorylation and nuclear translocation of Smad1/5/8. The blocking of NF-κB signaling by pretreatment with specific inhibitors such as BAY-11-7082, TPCK and PDTC, or by transfection with plasmids encoding p65 siRNA or IκBα siRNA could significantly reverse the inhibitory effect of LPS on BMP-2-induced BMP/Smad signaling and osteogenic differentiation. By contrast, even without stimulation of LPS, overexpression of p65 gene showed obvious inhibitory effects on BMP-2-induced BMP/Smad signaling and ALPase activity. These data indicate that the LPS-mediated inflammatory environment inhibits BMP-2-induced osteogenic differentiation, and that the crosstalk between TLR4/MyD88/NF-κB and BMP/Smad signaling negatively modulates the osteoinductive capacity of BMP-2.
1 Department of Plastic and Reconstructive Surgery, Shanghai Ninth People's Hospital, Shanghai JiaoTong University School of Medicine , Shanghai, China .
Ru-Lin
RL
Huang
Yuwen
Y
Yuan
Gang-Ming
GM
Zou
Guangwang
G
Liu
Jun
J
Tu
Qingfeng
Q
Li
D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000378:metabolism* / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D049109:Cell Proliferation; D005786:Gene Expression Regulation; D006801:Humans; D008070:Lipopolysaccharides / Q000494:pharmacology; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000378:metabolism*; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D061251:Primary Cell Culture; D015398:Signal Transduction; D051785:Smad Proteins / Q000235:genetics / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*
C525718:BMP2 protein, human; D055396:Bone Morphogenetic Protein 2; D008070:Lipopolysaccharides; C507779:MYD88 protein, human; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D051785:Smad Proteins; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4