Lipopolysaccharide (LPS) Induces the Apoptosis and Inhibits Osteoblast Differentiation Through JNK Pathway in MC3T3-E1 C
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Lipopolysaccharide (LPS) Induces the Apoptosis and Inhibits Osteoblast Differentiation Through JNK Pathway in MC3T3-E1 Cells Chun Guo,1,3 Lei Yuan,1 Jian-guo Wang,1 Fei Wang,1 Xu-Kai Yang,2 Fu-hua Zhang,1 Jin-ling Song,1 Xu-yuan Ma,1 Qi Cheng,1 and Guo-hua Song1
Abstract—Bone degradation is a serious complication of chronic inflammatory diseases such as septic arthritis, osteomyelitis, and infected orthopedic implant failure. Up to date, effective therapeutic treatments for bacteria-caused bone destruction are limited. In our previous study, we found that LPS promoted osteoclast differentiation and activity through activation of mitogen-activated protein kinases (MAPKs) pathway such as c-Jun N-terminal kinases (JNK) and extracellular signal regulated kinase (ERK1/2). The current study was to evaluate the mechanism of LPS on the apoptosis and osteoblast differentiation in MC3T3-E1 cells. MC3T3-E1 osteoblasts were non-treated, treated with LPS. After treatment, the cell viability, the activity of alkaline phosphatase (ALP) and caspase-3 were measured. The expressions of osteoblast-specific genes and Bax, Bcl-2, and caspase-3 were determined by real-time quantitative polymerase chain reaction (qPCR). Protein levels of Bax, Bcl-2, caspase-3, and phosphorylation of MAPKs were measured using Western blotting assays. The MAPK signaling pathway was blocked by pretreatment with JNK inhibitor SP600125. LPS treatment induced a significant decrease in cell metabolism, viability, and ALP activity in MC3T3-E1 cells. LPS also significantly decreased mRNA expressions of osteoblast-related genes in MC3T3-E1 cells. On the other hand, LPS significantly upregulated mRNA expressions and protein levels of Bax and caspase-3 as well as activation of caspase3, whereas decreased Bcl-2 expression in MC3T3-E1 cells. Furthermore, LPS significantly promoted MAPK pathway including the phosphorylation of JNK and the phosphorylation of ERK1/2; moreover, pretreatment with JNK inhibitor not only attenuated both of phosphorylation-JNK and ERK1/2 enhanced by LPS in MC3T3-E1 cells, but also reversed the downregulated expressions of osteoblast-specific genes including ALP and BSP induced by LPS. In conclusion, LPS could induce osteoblast apoptosis and inhibit osteoblast differentiation via activation of JNK pathway. KEY WORDS: lipopolysaccharide; osteoblasts; apoptosis; differentiation; c-Jun N-terminal kinases (JNK).
INTRODUCTION Bone is a dynamic tissue that constantly undergoes remodeling in which a coupled process of bone formation by osteoblasts and resorption by osteoclasts continues Chun Guo, Lei Yuan, and Jian-guo Wang contributed equally to this study. 1
Luohe Medical College, 148 Daxue Road, Luohe 462002( Henan, People’s Republic of China 2 Department of Urology, Lanzhou General Hospital of Lanzhou Command, Lanzhou, Gansu, People’s Republic of China 3 To whom correspondence should be addressed at Luohe Medical College, 148 Daxue Road, Luohe 462002( Henan, People’s Republic of China. E-mail: [email protected]
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