Objective: To observe the effects of diammonium glycyrrhizinate (DG) on nerve regeneration repair in rats with severe traumatic brain injury (STBI) from the perspective of Wnt/β-catenin signaling pathway.
Methods: Seventy-two Sprague-Dawle (SD) male rats were randomly divided into normal group, STBI model group, ganglioside (GA) treatment group and DG treatment group. The STBI animal model was reproduced referring to modified Feeney free fall impact model. No injury was made in normal group. Six hours after modeling, monosialotetrahexosylganglioside sodium injection and DG injection were injected via tail vein of rats in GA treatment group and DG treatment group respectively, once a day for 7 days. Normal group and STBI model group were given the same amount of normal saline. Six rats in each group were sacrificed on the 1st, 3rd and 7th day after the challenge for neurological severity score (NSS), and then the blood of abdominal aorta was drawn and brain tissue was harvested. The contents of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in serum were detected by enzyme linked immunosorbent assay (ELISA). The pathological changes of sub-granular zone (SGZ) were observed under light microscope after hematoxylin eosin (HE) staining. Real-time quantitative reverse transcription-polymerase chain reaction (RT-qPCR) was used to detect the mRNA expressions of Wnt3a, β-catenin, glycogen synthetase kinase-3β (GSK-3β) and Axin.
Results: (1) There was no neurological deficit in the normal group and NSS was 0. NSS score of rats increased significantly on the first day after modeling, and then decreased gradually over time. NSS of the rats treated with GA and DG were significantly lower than that of the STBI model rats (score: 7.33±2.07, 6.17±2.23 vs. 9.33±1.63, both P < 0.01). Though NSS gradually decreased over time, the differences were still statistically significant on the 7th day (score: 2.67±0.82, 1.00±0.00 vs. 6.17±2.23, both P < 0.01), and NSS of DG treatment group was significantly lower than that of GA treatment group. (2) In SGZ of rats, cells were arranged in a compact and orderly way in the normal group, but neurons and tissues were damaged and destroyed at different time points in the STBI model group. After either GA or DG treatment, the damage of nerve tissue was improved gradually over time, and the effect of DG was more obvious. (3) In the normal group, the mRNA expressions of Wnt3a and β-catenin were almost not expressed, the mRNA expressions of GSK-3β and Axin were higher, and the contents of BDNF and NGF in serum were less. On the 1st day after STBI, the mRNA expressions of Wnt3a and β-catenin in hippocampus, the contents of BDNF and NGF in serum were significantly increased, and the mRNA expressions of GSK-3β and Axin were significantly decreased. The mRNA expressions of Wnt3a and β-catenin in the hippocampus and the contents of BDNF and NGF in serum were significantly higher than those in the model group 1 day after GA or DG was added, the mRNA expressions of GSK-3β and Axin were significantly decreased, and the effect of DG was more significant than that of GA [Wnt3a mRNA (2-ΔΔCt): 3.51±0.14 vs. 2.93±0.05, β-catenin mRNA (2-ΔΔCt): 1.90±0.08 vs. 1.75±0.04, BDNF (ng/L): 4.06±0.55 vs. 3.16±0.64, NGF (ng/L): 9.53±1.08 vs. 7.26±0.43, GSK-3β mRNA (2-ΔΔCt): 0.75±0.01 vs. 0.79±0.01, Axin mRNA (2-ΔΔCt): 0.74±0.02 vs. 0.76±0.02, all P < 0.05]. It was gradually increasing or decreasing over time and the difference was still statistically significant up to the 7th day.
Conclusions: DG can promote the recovery of nerve function in rats with STBI, and its mechanism may be related to the regeneration of nerve cells proliferation and differentiation by Wnt/β-catenin signaling pathway and the reconstruction of nerve tissue in SGZ of hippocampus.