Myeloid differentiation protein 2 silencing decreases LPS-induced cytokine production and TLR4/MyD88 pathway activity in alveolar macrophages

Abstract

Lipopolysaccharides (LPSs) activate the innate immune response during Gram-negative bacterial infections through the Toll-like receptor 4 (TLR4)/myeloid differentiation protein 2 (MD-2) complex. MD-2 binds LPS with high affinity and is critical for TLR4-dependent signal transduction. However, the exact role of MD-2 on LPS signal transduction and cytokine production in alveolar macrophages (AMs) remains unclear. This study showed that the transcription levels of MD-2, TLR4 and MyD88 in the NR8383 cell line were up-regulated after LPS stimulation and that the increased transcript levels were attenuated after RNA interference of MD-2. Similarly, LPS induced increases in TNF-α, IL-1β and IL-6 protein levels in NR8383 cell supernatants was significantly inhibited by MD-2 silencing. These results suggest that in association with the TLR4/MyD88 signaling pathway LPS-induced cytokine production can be partially reduced by MD-2 silencing in the rat pulmonary alveolar macrophage cell line NR8383. MD-2 silencing was proved to be a useful tool for testing the role of MD-2 in the LPS signaling pathway and may be a potential therapeutic tool against LPS-induced lung inflammation.