IL-1 induces apoptosis and inhibits the osteoblast differentiation of MC3T3-E1 cells through the JNK and p38 MAPK pathways

Abstract

Interleukin (IL)-1 is a proinflammatory cytokine that plays important roles in inflammation and host responses to infection. The present study aimed to evaluate the effects of IL-1 on the apoptosis and differentiation of osteoblasts, and to elucidate the mechanism responsible for these effects in the osteoblastlike cell line MC3T3-E1. The MC3T3-E1 cells were non-treated or treated with IL-1. Following treatment, cell viability, alkaline phosphatase (ALP) activity and caspase-3 activity were evaluated. The expression of osteoblast-specific genes as well as Bax, Bcl-2 and caspase-3 were determined by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The protein levels of Bax, Bcl-2, caspase-3 and the phosphorylation of mitogen-activated protein kinases (MAPKs, also known as MAP kinases) were evaluated using western blot analysis. The MAPK signaling pathway was blocked by pre-treatment with MAPK inhibitors SB203580, PD98059 and SP600125. IL-1 treatment induced a significant decrease in cell viability and ALP activity in the MC3T3-E1 cells. IL-1 also significantly decreased the mRNA expression and protein levels of osteoblast-related genes in the MC3T3-E1 cells. On the other hand, IL-1 significantly upregulated the mRNA expression and protein levels of Bax and caspase-3 as well as caspase-3 activity, whereas Bcl-2 expression was decreased in the MC3T3-E1 cells. Furthermore, IL-1 activated the apoptotic signaling pathway by increasing the phosphorylation of c-Jun N-terminal kinase (JNK) and p38-MAPK, whereas it inhibited the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2). Moreover, pre-treatment with MAPK inhibitors attenuated the phosphorylation of JNK, p38 and Bax expression enhanced by IL-1. However, MAPK inhibitors markedly increased the protein expression of osteoblast-related genes and Bcl-xL in the MC3T3-E1 cells downregulated by IL-1. Taken together, these findings suggest that IL-1 induces the apoptosis of osteoblasts and inhibits osteoblast differentiation by activating the JNK and the p38 MAPK pathways.