Expression of Notch and Wnt/β-catenin signaling pathway in acute phase severe brain injury rats and the effect of exogenous thyroxine on those pathways

With the rapid development of economy, transportation and industry, the incidence of severe traumatic brain injury (sTBI) is rising rapidly, which is one of the main traumatic diseases threatening human life. It is very difficult for sTBI patients to regenerate and repair the central nervous and recover the brain function. Moreover, no effective neuroprotective drug has been found in the treatment of sTBI patients. Seeking drugs to promote nerve repair has become a hot and difficult problem. It is widely accepted that thyroxine is one of the essential hormones in the human body, which not only promotes the growth and development of the nervous system, but also plays an important role in maintaining adult brain function. There are many reports of modern research on thyroxine, mainly focusing on the changes of thyroid hormone levels and their effects on the prognosis after injury. Besides, most of them are observed in clinical cases. Currently, there are few dynamic experimental studies about observing whether thyroxine can promote the repair of central nervous system at different stages after sTBI. In our previous experiment, we found that Wnt/β-catenin signaling pathway, whose functions are opposite to Notch signaling pathway, can be further activated by exogenous thyroxine in rats with sTBI. As a result, we are interested in the expression of Notch and Wnt/β-catenin signaling pathway in acute phase sTBI rats and the effect of thyroxine on those pathways.

To investigate expression of Notch and Wnt/β-catenin signaling pathway in acute phase severe brain injury rats and the effect of thyroxine on those pathways by observing dynamically Notch and Wnt/β-catenin signaling pathway, NSS, GFAP, S100B, Bcl-2, Bax, etc.

108 rats were randomly divided into Group A (normal control group), Group B (normal-thyroxine group), Group C (TBI group), Group D (TBI+ low-dose thyroxine group), Group E (TBI + moderate-dose thyroxine) and Group F (TBI + high-dose thyroxine) with 18 rats in each group. The animal model was established according to Feeney's free-fall method, and administered with thyroxine or physiological saline at 6 h after sTBI. Six rats in each group were randomly killed on the 1st, 3rd and 7th days after intragastric administration. The changes of brain pathology and NSS were observed. The level of Wnt3a, β-catenin, Notch1 and Hes1 mRNA was detected by RT-PCR method, and the level of GFAP and S100B protein in serum was detected by ELISA. The expression of Bcl-2 and Bax was detected by immunohistochemistry.

(1) There was no significant change in brain pathology and NSS in groups A and B, but the changes of brain pathology and NSS in group D, E and F were significantly less than those in group C, especially in groups E and F. (2) RT-PCR showed that there was no change in the expression of Wnt3a mRNA, β-catenin mRNA, Notch1 and Hes1 mRNA in groups A and B. Compared with group C, the expression of Wnt3a mRNA and β-catenin mRNA in group D increased significantly on the 7th day after sTBI, especially in groups E and F; expression of Notch1 and Hes1 mRNA in groups D, E and F increased gradually with time, especially in group F. (3) ELISA showed that Compared with group C, GFAP and S100B in group D did not change significantly at 3 time points, GFAP in groups E and F decreased gradually with time and reached the lowest value on the 7th day, and S100B in groups E and F decreased gradually with time, especially in group F. (4) Compared with group C, the expression of BCL-2 in brain tissue of groups D, E and F increased gradually with time, and peaked on the 7th day, and the increase of E and F was more obvious. The expression of Bax in brain tissue of group D, E and F decreased gradually with time.

Exogenous thyroxine has no effect on Notch and Wnt/β-catenin signaling pathway in normal rats. After TBI, exogenous thyroxine can activate Notch and Wnt/β-catenin, and have a synergistic effect on the repair of central nervous system, which may be related to the up-regulation of Notch and Wnt/β-catenin signaling pathway mRNA expression and the increase of BDNF and NGF, and resist apoptosis in the brain of sTBI rats.