Protective Effects Of BDNF On Hippocampal Neurons Under High Glucose Condition

PartⅠ The expression of BDNF, CREB and Arc protein in the hippocampus of diabetic rats and the relationship with cognitive declineObjective To investigate the relationship between changes of cognitive function and the expression of synaptic plasticity associated proteins,including brain derived neurotrophic factor(BDNF), c AMP response element binding protein(CREB) and activity-regulated cytoskeleton protein(Arc). Methods 30 SPF 8-week-old male Sprague Dawley rats were randomly assigned to control group and diabetes group. After 4 weeks of high-fat feeding, rats in diabetes group were given streptozotocin(STZ, 30mg/kg) through intraperitoneal injection to build type 2 diabetes mellitus(T2DM) rat model. Body weight, fasting blood glucose(FBG), fasting serum insulin(FSI) were tested. At the end of the experiment, cognitive ability in two groups were evaluated by Morris water maze test. The concentration of beta-amyloid(Aβ) in hippocampus of diabetic rats were tested by enzyme-linked immuno sorbent assay, the expression of Aβ was observed by immunohistochemistry, the expression of BDNF, CREB, p CREB and Arc proteins were detected through western blotting. Result Compared with the control group, fasting blood glucose and fasting serum insulin of diabetic rats were higher(both P<0.001), and body weight was less(p<0.001). Time spent in the target quadrant of diabetes mellitus group was shorter than the control group(P<0.01). The frequency of rats crossing the original site was less in the diabetes mellitus group than the control group(P<0.01).The expression of BDNF, CREB, p CREB and Arc protein were lower in diabetes mellitus group(P <0.01). The expression level of Aβ was increased in diabetes mellitus group by immunohistochemistry. Conclusion T2 DM can induce DE. DE rat showed cognition impairment in the aspects of spatial learning and memory, the mechanism of which may be associated with the decreased expression of proteins associated with synaptic plasticity, including BDNF, CREB and Arc.PartⅡ Protective effects of BDNF on hippocampal neurons under high glucose condtion through PI3K-Akt-m TOR pathwayObjective This study aims to take hyperglycemia hippocampal neurons models as subjects to explore the protective effects of exogenous BDNF on hyperglycemia hippocampal neurons and the possible intracellular signal transmission mechanism of the protective function of hyperglycemia hippocampal neurons. Methods Put glucose with different concentrations(25、50、75 and 100mmol/L) on primary cultured hippocampal neurons of SD neonatal rats for different time periods(24、48、72 and 96h). Then CCK8 was used to detect the survival rate of neurons to identify the most suitable glucose concentrations and time in order to build the hyperglycemia model of primary hippocampal neurons. Put 50ng/m L BDNF on hyperglycemia hippocampal neurons for 96 h, after that, cellular apoptosis of neurons in control group, high glucose group and high glucose+BDNF group were tested by FCM. Western Blotting was used to detect the expression levels of tyrosine receptor kinase B(Trk B), Protein Kinase B(Akt), phosphor-Akt(p Akt), CREB, phosphorCREB(p CREB), Arc and synaptophysin protein of five groups(control group, high glucose group, high glucose +BDNF group, high glucose +BDNF +wortmannin group and high glucose +BDNF +rapamycin group). Reaults OD value of the 75mmol/L glucose group decreased significantly at 72 h compared with the control group(P < 0.01). The apoptosis rate of the control group, hyperglycemia group and hyperglycemia +BDNF group was 2.80%, 38.86% and 11.49% respectively. Compared with the control group, protein expressions of synaptophysin, CREB, and Arc all decreased significantly(all p < 0.05); Compared with the high glucose group, protein expressions of synaptophysin, Trk B, Akt, CREB and Arc levels were significantly increased in the high glucose +BDNF group(p < 0.05); Compared with the high glucose +BDNF group, the expression of Syn、Akt、p Akt、CREB 、 p CREB and Arc protein decreased significantly in high glucose +BDNF +wortmannin group(all p < 0.05), the expression of CREB, p CREB and Arc protein in hyperglycemia +BDNF +rapamycin group also decreased significantly(all p < 0.05). Conclusion High glucose can induce apoptosis of hippocampal neurons. Exogenous BDNF can conserve the apoptosis of hyperglycemia hippocampal neurons and increased the expression of synaptophysin, CREB and Arc in protein levels, and this effect can be blocked by PI3 K inhibitor wortmannin and m TOR inhibitor rapamycin. BDNF may play the role of protection of neurons through activating the PI3K-Akt-m TOR signaling pathway.