Brain-derived neurotrophic factors increase the proliferation and differentiation of endogenous neural stem cells in mouse models of cerebral infarction ○

Abstract

Background It has been confirmed that brain-derived neurotrophic factor (BDNF) can promote the proliferation of neural stem cells (NSCs) and protect neuron-like cells in vitro. However, its effect on endogenous NSCs in vivo is still unclear. Objective To evaluate whether BDNF can induce the endogenous NSCs to proliferate and differentiate into the neurons in the mice model of cerebral infarction. Design A synchronal controlled observation. Settings Department of Neurology, Microbiology Division of the Department of Laboratory, Tianjin First Central Hospital; Howard Florey Institute, Medical College, the University of Melbourne. Materials Twenty-four pure breed C57BL/6J mice at the age of 10 weeks old (12 males and 12 females) were divided into saline control group and BDNF-treated group, 6 males and 6 females in each group. Methods The experiments were performed at the University of Melbourne from July 2004 to February 2005. ▪ The left middle cerebral artery (MCA) was ligated in both groups to establish models of cerebral infarction and the Matsushita measuring method was used to monitor the blood flow of the lesioned region supplied by MCA. 75% reduction of blood flow should be reached in the lesioned region. ▪ At 24 hours after infarction, mice in the BDNF-treated group were administrated with BDNF, which was slowly delivered using an ALZET osmium pump design. BDNF was dissolved in saline at the dosage of 500 mg/kg and injected into the pump, which could release the solution consistently in the following 28 days. The mice in the saline control group accepted the same volume of saline at 24 hours after infarction. ▪ The Rotarod function test began at 1 week preoperatively, the time stayed on Rotarod was recorded. The mice were tested once a day till the end of the experiment. At 4 weeks post cerebral infarction, double labeling of Nestin and GFAP, BIII tubulin and CNPase immunostaining was performed to observe the differentiation directions of the re-expressed endogenous NSCs, and the percentages of the cells differentiated into astrocytes, neurons and oligodendrocytes were calculated. Main outcome measures ▪ The differentiation directions of the re-expressed endogenous NSCs, and the percentage of the cells differentiated into astrocytes, neurons and oligodendrocytes. ▪ Comparison of motor function between the two groups. Results All the 24 pure C57BL/6J mice were involved in the analysis of results. ▪ Positively expressed endogenous NSCs appeared in the mice of both groups, and they mainly distributed around the focus of lesion, as well as the contralateral side. The expressed cells in the BDNF-treated group were obviously more than those in the saline control group. ▪Activations of endogenous NSCs: At 4 weeks after infarction, re-expressions of endogenous NSCs appeared in both groups. The number of the re-expressed cells in the BDNF-treated group was about 4.2 times higher than that in the saline control group. The percentage of the cells differentiated into neurons in the BDNF-treated group was significantly higher than that in the saline control group (36%, 15%), the percentage of the cells differentiated into astrocytes was lower than that in the saline control group (54%, 77%), whereas the percentage of the cells differentiated into oligodendrocytes was similar to that in the saline control group (10%, 8%). ▪ Results of motor functional test: Compared with before cerebral infarction, the mice in both groups manifested as obvious decrease in motor function at 1 week after infarction, whereas the recovery of motor function in the BDNF-treated group was significantly superior to that in the saline control group at 2, 3 and 4 weeks ( P < 0.01). Conclusion BDNF can promote the proliferation of endogenous NSCs in the brain of mice with cerebral infarction, it can decrease the differentiation rate of astrocytes, and increase the differentiation rate of neurons. BDNF has small influence on the differentiation of endogenous NSCs into oligodendrocytes, which was not benefit for the recovery of neural axon. Endogenous NSCs may improve the motor function of mice through the above pathways.