Effect of hypothermia on TLR2/MyD88 signal pathway in lung tissue in rats with acute lung injury induced by lipopolysaccharide / 中华危重病急救医学

ABSTRACT

Objective To investigate the effect of hypothermia on the expression Toll-like receptor 2 (TLR2),myeloid differentiation factor 88(MyD88),nuclear factor-κBp65(NF-κBp65),plasminogen activator inhibitor-1(PAI-1)in the TLR2/MyD88 pathway in rats with acute lung injury(ALI)induced by lipopolysaccharide (LPS)inhalation. Methods Ninety male Sprague-Dawley(SD)rats were randomly divided into control group (n=18),hypothermia group(n=24),temperature controlled group(n=24),and temperature-uncontrolled group(n=24). The ALI model was reproduced by 0.5 mL/kg LPS intratracheal instillation,while only normal saline was instilled intratracheally for control group. Arterial blood was collected and physical cooling was started 1 hour after instillation. The body temperature was lowered to 32-34 ℃in hypothermia group and 36-37 ℃in temperature controlled group,and no intervention was used for temperature-uncontrolled group and control group. The arterial blood gas was determined in all the groups before and 1 hour after instillation of saline or LPS and 1,6, 12 hours after intervention. Rats were sacrificed respectively at 1,6 and 12 hours after temperature control therapy, the morphological changes in lung tissue were observed under light microscope. The protein expression of PAI-1 in bronchoalveolar lavage fluid(BALF)was determined by enzyme linked immunosorbent assay(ELISA). TLR2 mRNA and MyD88 mRNA transcriptional level were determined by reverse transcription-polymeras chain reaction (RT-PCR). NF-κBp65 protein level was determined by Western Blot. Results After instillation of LPS,the oxygenation index(PaO2/FiO2)of each group was decreased obviously,the damage of lung tissues was aggravating,the lung injury score was increased significantly,PAI-1 protein in BALF and the expressions of TLR2 mRNA,MyD88 mRNA, NF-κBp65 protein in lung tissues were increased obviously. Each index was improved by therapeutic Hypothermia, the effect of which was best in using a cooling period in the 1-6 hours,while might be benefit at 6-12 hours. Compared with temperature controlled group,PaO2/FiO2(mmHg,1 mmHg=0.133 kPa)at 1 hour and 6 hours of hypothermia group was improved(1 hour:402.49±38.61 vs. 324.36±28.93,6 hours:349.72±98.20 vs. 284.35±13.68, both P<0.01),the lung injury score at 1,6 and 12 hours were significantly decreased(1 hour:6.04±0.74 vs. 7.96±0.65,6 hours:9.09±0.80 vs. 13.13±1.02,12 hours:10.79±1.42 vs. 13.42±0.68,all P<0.01),the PAI-1 protein(ng/L)in BALF at 1,6 and 12 hours were significantly decreased(1 hour:121.36±4.62 vs. 197.74±9.42, 6 hours:230.53±10.76 vs. 294.06±16.60,12 hours:270.48±13.20 vs. 319.40±10.24,all P<0.01),TLR2 mRNA and MyD88 mRNA expressions(2-ΔΔCt)in the lung tissues at 1,6 and 12 hours were significantly decreased (TLR2 mRNA 1 hour:2.18±0.26 vs. 3.04±0.39,6 hours:4.09±0.29 vs. 4.90±0.35,12 hours:6.02±0.43 vs. 7.10±0.54;MyD88 mRNA 1 hour:2.25±0.41 vs. 3.04±0.30,6 hours:5.67±0.55 vs. 7.01±0.76,12 hours:7.14±0.60 vs. 8.87±0.54,all P<0.01),NF-κBp65 protein expression(A value)at 6 hours and 12 hours was significantly decreased(6 hours:0.31±0.08 vs. 0.53±0.12,12 hours:1.05±0.17 vs. 1.76±0.35,both P<0.01). There was no difference in each index between temperature controlled group and temperature-uncontrolled group. Conclusion Hypothermia can down-regulate the expression of TLR2 mRNA,MyD88 mRNA,NF-κBp65 protein and PAI-1 in the TLR2/MyD88 pathway to protect lung tissue of rats with ALI induced by LPS inhalation from injury.