Objective: To investigate the effect of lipopolysaccharide (LPS) on gene expression of Toll-Like receptor 4 (TLR4) and myeloid differentiation protein-2 (MD-2) in rat alveolar macrophage NR8383 cell and its secretion of inflammation cytokines with or without small interference RNA target MD-2 (MD2-siRNA) treatment.
Methods: NR8383 cell was cultured with F-12K medium and stimulated with LPS (0.01 approximately 10 mg/L) for 2 h or stimulated with 1 microg/ml LPS for 2-24 h. MD2-siRNA oligo was transfected into NR8383 cell by Lipofectamine 2000. The expression of TLR4 mRNA and MD-2 mRNA in cell were detected by semi-quantitative revels transcription polymerase (RT-PCR). The contents of TNF-alpha, IL-6 and IL-1beta in the cell cultured supernatant were tested by ELISA. One way ANOVA was used for difference comparison during groups and Pearson correlation was used for correlation analysis.
Results: (1) The mRNA expression of TLR4 and MD-2 in control NR8383 cell were 0.52+/-0.05 and 0.44+/-0.09, respectively. There was no obviously change after 0.01 mg/L LPS stimulation. The increase occurred in a dose dependent manner from 0.1 mg/L to 10 mg/L. The highest TLR4 and MD-2 mRNA expression were 0.72+/-0.06 and 0.65+/-0.10 (F=17.255 and 6.045, P<0.01). The changes of TNF-alpha, IL-6 and IL-1beta contents in cell cultured supernatant were similar with that of TLR4 and MD-2 gene expression. TNF-alpha, IL-6 and IL-1beta content were (25.8+/-3.4) ng/L, (62.4+/-4.7) ng/L and (31.6+/-1.7) ng/L in control group, while the corresponding contents were (58.9+/-5.3) ng/L, (96.5+/-3.9) ng/L and (55.4+/-5.4) ng/L after 10 mg/L LPS simulation (F=29.55, 54. 47 and 31.45, P<0. 01). (2) When stimulated with 1 microg/ml LPS, the mRNA expressions of TLR4 and MD-2 in NR8383 cell were increased from hour 2. The highest mRNA expressions of TLR4 and MD-2 occurred at hour 6, and then decreased slowly from hour 8. The mRNA expressions at hour 24 were still higher than those in cells without LPS stimulation (F=5.279 and 4.106, P<0.01). The changes of TNF-alpha, IL-6 and IL-1beta content in cell cultured supernatant were also similar with that of gene expression (F=10.64, 11.23 and 17.58, P<0. 01). The secretion peaks of TNF-alpha and IL-1beta occurred from hour 6 to hour 8, and the secretion peak of IL-6 occurred from hour 8 to hour12. (3) The mRNA expression of MD-2 was related with that of TLR4 positively (r=0.513, P<0.01). (4) The interfere efficiency of MD-2 siRNA was 67%. There was no obvious increase of TNF-alpha, Il-1beta and IL-6 in MD-2 siRNA treated group after LPS stimulation.
Conclusion: Higher dose LPS can up-regulate the gene expression of TLR4 and MD-2 in rat alveolar macrophage NR8383 cell with a long time and promote the secretion of TNF-alpha, IL-6 and IL-1beta. MD-2 siRNA can inhibit NR8383 cell secrete TNF-alpha, IL-6 and IL-1beta induced by LPS.