Effect and mechanism of hyperbaric oxygen combined with aquaporin-4 gene silencing on cognitive dysfunction in rats with traumatic brain injury / 中华行为医学与脑科学杂志

ABSTRACT

Objective:To investigate the effect of hyperbaric oxygen combined with RNA interference (RNAi) technology targeting aquaporin-4 (AQP-4) on improving cognitive function in rats with traumatic brain injury (TBI), and to explore its mechanism.Methods:Totally 112 adult male SD rats were randomly divided into four groups control group, hyperbaric oxygen(HBO) group, AQP-4 RNAi group and combined treatment group, with 28 rats in each group.The TBI model of rat was established by hydraulic percussion and siRNA targeting aquaporin 4 was constructed. Rats were given corresponding intervention according to their groups.Then the modified neurological severity scores(mNSS)was evaluated on the 7th day and 21th day after operation. Morris water maze test was carried out from the 21st day to 25th day after operation and the percentage of target quadrant and daily escape latency were recorded.The changes of the brain permeability of blood-brain barrier and moisture in brain tissues were measured by Evans blue fluorometry and a wet-dry-weighing technique respectively. The protein expression levels of AQP-4, Caspase-3, Bcl-2, MMP-2 and MMP-9 were detected by Western blot method. The mRNA expression of AQP-4 in TBI brain tissue was measured by RT-PCR method, and the apoptosis rate of TBI brain cells was detected by TUNEL and AnnexinV methods on the 7th day after operation. SPSS 23.0 and Graphpad Prism 7.0 softwares were used for data analysis.One-way ANOVA was used for inter group comparison.Repeated measurement ANOVA was used for Morris results, and the LSD- t test was used for pairwise comparisons. Results:The results of mNSS showed that there were significant differences among the groups on the 7th day and 21st day after operation ( F=4.89, 7.59, both P<0.05). The scores of each treatment group were lower than that of the control group, and the effect of the combined treatment group was the best (7th day t=3.98, -7.75, both P<0.05; 21st day t=47.82, 7.94, both P<0.05). The results of Morris water maze test showed that the time and group interaction of rats in the target quadrant residence time and escape latency were not statistically significant( F=1.83, 8.42, both P>0.05). The escape latency and the percentage of stay in the target quadrant in the combined treatment group were better than those in other groups on the 24th and 25th day after operation (all P<0.05). Evans blue staining showed that the contents of Evans blue in AQP-4 RNAi group, hyperbaric oxygen group and combined treatment group were lower than that in the control group(all P<0.05), and that in the combined treatment group was the lowest( t=6.19, P<0.05). The results of dry-wet specific gravity method showed that the water content of brain tissue in the combined treatment group((68.15±1.52)%) was the lowest, and that in the AQP-4 RNAi group((76.71±1.06)%) was lower than that in the HBO group ((80.23±1.43)%)( t=4.38, P<0.05). The results of Western blot showed that the protein levels of AQP-4, Caspase-3, MMP-2 and MMP-9 in the combined treatment group were significantly lower than those in other groups(all P<0.05), while the expression of Bcl-2 was increased in the combined treatment group( P<0.05). RT-PCR results (gray value ratio) showed that AQP-4 mRNA levels in AQP-4 RNAi group(0.61±0.21), HBO group (0.83±0.12), combined treatment group(0.22±0.05) and CON group (1.31 ± 0.25) were significantly different( F=175.05, P<0.05), while the AQP-4 mRNA levels decreased in AQP-4 RNAi group which was better than that in hyperbaric oxygen group ( t=5.25, P<0.05). The decrease was the most obvious in the combined treatment group ( t=58.94, P<0.05). The results of TUNEL and AnnexinV showed that the treatment groups were more effective than the control group in inhibiting neuronal apoptosis, especially in the combined treatment group ( P<0.01). Conclusion:The combination of targeted AQP-4 RNAi and hyperbaric oxgen can effectively promote the recovery of neurological and cognitive function, and the mechanism may be related to protecting the integrity of blood-brain barrier, alleviating brain edema and inhibiting apoptosis of nerve cells after TBI.