Role of Toll-like receptor 4 in mechanical ventilation-induced neuronal apoptosis in brain tissues of mice

Abstract

Objective To investigate the role of Toll-like receptor 4 (TLR4) in mechanical ventilation-induced neuronal apoptosis in brain tissues of mice. Methods Forty-two healthy male TLR4 gene knockout (J003752)C57BL/10ScNJNju mice and 42 wild type C56BL/6 mice, aged 10-12 weeks, weighing 20-25 g, were used in the study.The mice of either type were randomly divided into 2 groups (n=21 each) using a random number table: sham operation group (group S) and mechanical ventilation group (group MV). In group S, the mice were exposed to isoflurane for 6 h in an anesthesia chamber.In group MV, the mice were mechanically ventilated for 6 h after tracheal intubation when anesthesia was maintained with isoflurane.Twelve mice were selected from each group at 1 and 3 days after ventilation, fear conditioning test was performed to assess the cognitive function, and the ratio of freezing time was recorded.Three mice in each group were sacrificed at 1 day after ventilation, the brains were removed for detection of neuronal apoptosis in the hippocampal CA1 region in the brain tissue by TUNEL, and the apoptosis index was calculated.Six mice in each group were sacrificed at 1 day after ventilation, the hippocampi were isolated for determination of the expression of Bax, Bcl-2, activated caspase-9 and activated caspase-3 by Western blot, and the Bax/Bcl-2 ratio was calculated. Results Compared with group S, the ratio of freezing time was significantly decreased at 1 and 3 days after ventilation, the apoptosis index and Bax/Bcl-2 ratio were significantly increased, and the expression of activated caspase-9 and activated caspase-3 was significantly up-regulated in group MV of TLR4 gene knockout and wild type mice (P<0.05 or 0.01). Compared with group MV of wild type mice, the ratio of freezing time was significantly increased at 1 and 3 days after ventilation, the apoptosis index and Bax/Bcl-2 ratio were significantly decreased, and the expression of activated caspase-9 and activated caspase-3 was significantly down-regulated in group MV of TLR4 gene knockout mice (P<0.05 or 0.01). Conclusion TLR4 is partially involved in mechanical ventilation-induced neuronal apoptosis in brain tissues of mice. Key words: Toll like receptor 4; Respiration, artificial; Apoptosis; Neurons; Brain