Background and purpose: Shear stress-mediated mechanical stress induces cell adhesion in monocyte cell lines. In addition, THP-1 cells, stimulated by platelet-derived micro particles produced by high shear stress, induce cytokines expression including TNF-α and IL-1β. These alterations of monocytes can induce the progression of atherosclerosis on the blood vessel wall. The other way, some researchers reported that mechanical stress such as shear stress regulates cellular signaling and endothelial cell function, and diminishes atherogenesis. However, the regulatory mechanism of pro-inflammatory cytokine expression by mechanical stress is also insufficient. Therefore, we examined the expression pattern of TNF-α by mechanical stress in THP-1 monocyte cells and the necessity of TLR signaling in this study.
Results: Mechanical stress (mild-centrifugation) induced TNF-α expression in monocyte-cell line THP-1. The induction of TNF-α caused by mechanical stress was dependent on the centrifugation speed, and showed the highest level (10.3 folds increase, p<0.05) after 1 h of stimulation. TNF-α expression was recovered to normal state after 12 h of stimulation. Mechanical stress also induced TLR2 mRNA in proportion to TNF-α expression (7.3 folds increase, p<0.05). The signaling inhibition of TLR2 using dominant negative MyD88 showed that TNF-α expression had no more responded to mechanical stress (3.99 fold decrease, p<0.01). After transiently over-expression of TLR2 in HEK293 cells, mechanical stress induced TNF-α mRNA production was 3.86 fold higher than non over-expressed cells(p<0.01), and NF-kB activity was 32% increased (p<0.05).
Conclusions: These results suggested that the TLR2 signal pathway was used in mechanical stress-mediated TNF-α production, and the TNF-α expressed by mechanical stress regulated TLR2 expression. We conclude that TNF-α production induced by mechanical stress depends on MyD88-dependent TLR2 signaling resulted in NF-kB activation in monocyte cell lines.
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