Molecular mechanisms of the inhibitory effect of lipopolysaccharide (LPS) on osteoblast differentiation

• Published in: Biochemical and biophysical research communications 2010-11, Vol.402 (4), p.755-761
• Main Authors: Bandow, Kenjiro, Maeda, Aya, Kakimoto, Kyoko, Kusuyama, Joji, Shamoto, Mitsuo, Ohnishi, Tomokazu, Matsuguchi, Tetsuya
• Format: Article
• Language: English
• Subjects: Activating transcription factor 4; Activating Transcription Factor 4 - antagonists & inhibitors; Activating Transcription Factor 4 - genetics; adaptor proteins; Animals; Cbfa-1 protein; Cell Differentiation; Core Binding Factor Alpha 1 Subunit - antagonists & inhibitors; Core Binding Factor Alpha 1 Subunit - genetics; Cot/Tpl2; Cytokines; Extracellular signal-regulated kinase; Gene expression; Lipopolysaccharides; Lipopolysaccharides - metabolism; Lipopolysaccharides - pharmacology; LPS; MAP kinase; MAP Kinase Kinase Kinases - genetics; MAP Kinase Kinase Kinases - metabolism; Mice; Mice, Inbred C57BL; Mice, Knockout; Mineralization; Molecular modelling; Myd88; MyD88 protein; Myeloid Differentiation Factor 88 - genetics; Myeloid Differentiation Factor 88 - metabolism; Osteoblastogenesis; Osteoblasts; Osteoblasts - drug effects; Osteoblasts - physiology; Osteocytes; Osteocytes - cytology; Osteogenesis; Protein-serine/threonine kinase; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - metabolism; Sp7 Transcription Factor; TLR4; TLR4 protein; Toll-Like Receptor 4 - metabolism; Toll-like receptors; Transcription factors; Transcription Factors - antagonists & inhibitors; Transcription Factors - genetics
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2010.10.103

► LPS inhibits osteoblast differentiation through down-regulating Runx2, Osterix (Sp7), and ATF4 expression. ► Myd88 is absolutely essential for LPS-induced inhibition of osteoblast differentiation. ► Myd88 is essential for LPS-induced down-regulation of Runx2, Osterix (Sp7), and ATF4 expression. ► Cot/Tpl2 kinase is required for LPS-induced down-regulation of Runx2, Osterix (Sp7), and ATF4 expression in the early phase of osteoblast differentiation. ► Cot/Tpl2 is only partially responsible for LPS-induced down-regulation of Runx2, Osterix (Sp7), and ATF4 expression in the late osteoblast differentiation phase. Osteoblasts express Toll like receptor (TLR) 4 and produce osteoclast-activating cytokines in response to the stimulation by lipopolysaccharide (LPS). It has recently been reported that LPS exerts an inhibitory effect on osteoblast differentiation into osteocytes. However, the molecular mechanisms of this inhibitory effect remain ambiguous. The downstream signals of TLR4 are mediated by adaptor molecules including myeloid differentiation factor 88 (MyD88), leading to the activation of mitogen-activated protein kinases (MAPKs), such as extracellular signal-regulated kinases (ERKs), whose activation by LPS requires the upstream serine/threonine kinase, Cot/Tpl2. To determine the signal molecules responsible for the inhibitory effects of LPS on osteoblast differentiation, we examined the in vitro differentiation of the primary osteoblasts from myd88−/− and cot/tpl2−/− mice. The matrix mineralization by the wild-type and cot/tpl2−/− osteoblasts was significantly inhibited by LPS, whereas that of myd88−/− was not affected. During differentiation, LPS suppressed the mRNA expression of runt related transcription factor 2 (Runx2), osterix (Sp7), and activating transcription factor 4 (ATF4) in the wild-type, but not in the myd88−/− osteoblasts. The inhibitory effect of LPS on the mRNA expression of these transcription factors was absent in the early phase but partially impaired in the late phase of differentiation in the cot/tpl2−/− osteoblasts. Thus, the inhibitory effect of LPS on osteoblast differentiation is Myd88-dependent, whereas the degree of its requirement for Cot/Tpl2 varies depending on the differentiation phase.