JAK2/STAT5 signaling in the lipopolysaccharide (LPS)-induced inhibition of osteoblast differentiation

Bacterium infection commonly develops in bone fracture or in the followed open conduction and internal fixation, and Lipopolysaccharide (LPS) from bacteria has been recognized to be an important pathogenic factor in bone fracture healing. Therefore, the effects of LPS on bone metabolism are therefore relevant to clinical challenge of bone healing. In the present study, we investigated the role of JAK2/STAT5 signaling in the lipopolysaccharide (LPS)-induced inhibition of osteoblast differentiation. We investigated the influence of LPS treatment on the expression of JAK2/STAT5 signaling, with real-time quantitative PCR and western blotting. Then we determined the regulation of LPS on the osteoblast differentiation via measuring the Alkaline phosphatase (ALP) activity, matrix mineralization, and the expression of ALP, Procollagen type I N-terminal propeptide (PINP), Runt-related transcription factor 2 (RUNX2) AND Bone morphogenetic protein 2 (BMP-2) in the LPS-treated MC3T3-E1 cells. In addition, we evaluated the JAK2/STAT5 signaling-dependence of the influence by LPS on the osteoblast differencitaion with RNAi technology. It was demonstrated that LPS promoted JAK2/STAT5 signaling in both mRNA and protein levels in mouse osteoblast MC3T3-E1 cells, whereas inhibited the osteoblast differentiation via reducing the matrix mineralization, decreasing the ALP activity and suppressing the expression of such markers as ALP, PINP, RUNX2 and BMP2 in mRNA levels in MC3T3-E1 cells. On the other side, RNAi-mediated JAK2/STAT5 signaling knockdown abrogates the inhibition by LPS to osteoblast differentiation. In summary, this study has shown that LPS inhibits osteoblast differentiation by suppressing the expression of ALP, PINP and RUNX2, all of which are essential for the osteoblast differentiation, in a JAK2/STAT5 signaling-dependent manner. This study may provide insights into the signal pathway of LPS-induced bone loss or delayed bone fracture healing.