Role and mechanism of signal pathway mediated by Toll-like receptor 9-myeloid differentiation factor 88 in alveolar macrophages in ventilator-induced lung injury in rats / 中华危重病急救医学

ABSTRACT

Objective To investigate the role of Toll-like receptor9 (TLR9)-myeloid differentiation factor 88 (MyD88) signal pathway in alveolar macrophages in ventilator-induced lung injury (VILI).Methods 30 adult male Sprague-Dawley (SD) rats were randomly assigned to three groups (with 10 rats in each group).Group A was the control group,with spontaneous respiration after tracheostomy.Rats in group B received mechanical ventilation for 4 hours with normal tidal volume (VT) 7 ml/kg after tracheostomy,and group C rats received mechanical ventilation with VT 40 ml/kg for 4 hours.After termination of ventilation,examination with transmission electron microscopy was performed to observe the ultrastructure changes in alveolar epithelial cell type Ⅱ (AEC Ⅱ) of the lung.Lung wet/dry ratios (W/D) and total protein concentration,the concentration of interleukins (IL-6 and IL-1 β) in bronchoalveolar lavage fluid (BALF) were determined.The protein and mRNA expressions of TLR9,MyD88 and nuclear factor-κB (NF-κB) in alveolar macrophages were assayed by Western Blot and real-time reverse transcription-polymerase chain reaction (RT-PCR).Results The ultrastructure of AEC Ⅱ in the group A and group B was almost normal,whereas the chromatin of the nuclei,the lamellar corpuscles in the cytoplasm,the cell membrane and the microvilli of the AEC Ⅱ in the group C showed injurious changes in various degrees.When the group C was compared with the group A and the group B,it was shown that the W/D ratios (5.54 ± 0.17 vs.4.58 ± 0.17,4.69 ± 0.16) and total protein concentration (g/L6.33 ± 0.61 vs.0.45 ± 0.05,0.47 ± 0.04),IL-6 (μg/L1.989 ± 0.103 vs.1.033 ± 0.061,1.010 ± 0.069) and IL-lβ (ng/L2.79 ±0.25 vs.1.05 ±0.15,1.23 ±0.22) in BALF,the protein expressions of TLR9,MyD88 and NF-κB [TLR9 (A value)0.770 ±0.042 vs.0.300 ±0.027,0.310 ±0.037; MyD88 (A value)0.950 ±0.091 vs.0.560 ±0.082,0.580±0.084; NF-κB(A value)1.020 ±0.076 vs.0.740 ±0.052,0.700 ±0.076] in alveolar macrophages were all increased significantly,and all of which showed significant difference (P＜0.05 or P＜0.01).The mRNA levels of TLR9,MyD88 and NF-κB in alveolar macrophages in the group B were (1.13 ± 0.32),(1.18 ± 0.33),and (1.11 ± 0.22) folds of those of the group A,respectively,but there were no significant differences (all P＞0.05).While the mRNA levels of TLR9,MyD88 and NF-κB of alveolar macrophages in the group C were (8.66 ± 0.69),(6.41 ± 0.53) and (5.29 ± 0.71) folds of those of the group A,respectively,and all of them showed significant difference (all P＜0.01).Conclusion TLR9-MyD88 signaling in alveolar macrophages plays a role in pathogenesis of VILI.