SP600125 reduces lipopolysaccharide-induced apoptosis and restores the early-stage differentiation of osteoblasts inhibited by LPS through the MAPK pathway in MC3T3-E1 cells

Abstract

Bone degradation is a serious complication of chronic inflammatory diseases such as septic arthritis, osteomyelitis, and infected orthopedic implant failure. Effective therapeutic treatments for bacteria-caused bone destruction are limited. In a previous study, we found that lipopolysaccharide (LPS) induced osteoblast apoptosis and inhibited early and late-stage differentiation of osteoblasts via activation of the C-Jun N-terminal kinase (JNK) pathway. This study aimed to investigate the effect of JNK inhibition by SP600125 on the apoptosis and differentiation of MC3T3-E1 osteoblasts suppressed by LPS. Following pretreatment with SP600125 for 2 h, MC3T3-E1 cells were treated LPS. Following this treatment, cell viability, activity of alkaline phosphatase (ALP) and caspase-3 were measured. mRNA and protein expression of osteoblast-specific genes, mitogen-activated protein kinases (MAPKs), Bax, Bcl-2 and caspase-3 were determined by quantitative polymerase chain reaction (qPCR) and western blot analysis. The results showed that SP600125 significantly restored LPS-inhibited cell metabolism and ALP activity and reduced the upregulated caspase-3 activity of MC3T3-E1 cells induced by LPS. SP600125 also significantly restored the LPS-suppressed mRNA and protein expression levels of early-stage osteoblast-associated genes in a dose-dependent manner. SP600125 significantly downregulated expression of Bax and caspase-3 but upregulated Bcl-2 expression in MC3T3-E1 cells stimulated by LPS. Furthermore, SP600125 selectively triggered the MAPK pathway by reducing the expression of JNK1, while enhancing the expression of extracellular signal-regulated kinase 1 (ERK1). Our results suggested that SP600125 reduced LPS-induced osteoblast apoptosis and restored early-stage differentiation of osteoblasts inhibited by LPS through MAPK signaling. These findings suggest that the therapeutic agent that inhibited JNK1 is of potential use for the restoration of osteoblast function in bacteria-induced bone diseases.