星形胶质细胞ErbB4异常激活促NO生成的机制及其介导糖尿病海马神经元退行性变的作用研究

The reactive astrocytes from diabetes had important effects on neuronal functions through releasing of detrimental factors. In pre-experiment, we observed that the expression and distribution of ErbB4 in astrocytes had significantly changed in hippocampus of diabetic mice. And, either ErbB4 inhibitor or nitric oxide synthase inhibitor could prevent the degeneration of hippocampal neurons induced by high glucose mediated astrocyte-conditioned medium (ACM). We also found that the overexpression of ErbB4 increased the expression of iNOS at the post-transcriptional level. Previous report has indicated that the transcriptional regulator MEX-3 could inhibit the translation of iNOS. Here, we speculate that hyperactivity ErbB4 induced by high glucose in astrocytes interacts with MEX-3C and thereby turn on the transcription of iNOS gene. Subsequently, robust expression of iNOS increases the level of NO, ultimately leading to neuronal degeneration. In our project, we firstly confirm that astrocyte-derived ErbB4 mediates hippocampal neuronal degeneration via increasing the level of NO. Next, we investigated whether ErbB4-mediated iNOS expression at the post-transcriptional level is associated with MEX-3C pathway by performing the electrophoretic mobility shift assay and co-immunoprecipitation analyses. Moreover, we tried to reveal the critical regions of ErbB4 that binds to MEX-3C. Together, this project will provide new insights into the mechanisms of diabetic neurodegeneration.

异常活化的糖尿病星形胶质细胞通过促进关键因子分泌而影响神经元功能。预实验发现：ErbB4在糖尿病小鼠海马区星形胶质细胞的表达及分布发生明显变化；ErbB4抑制剂及NOS抑制剂均能逆转高糖星形胶质细胞条件培养液诱导的海马神经元退行性变；过表达ErbB4在转录后水平促进iNOS表达。基于转录后调控子MEX-3能抑制iNOS翻译，我们推测：星形胶质细胞ErbB4被高糖激活后，通过与MEX-3C相互作用而干扰MEX-3C与iNOSmRNA的结合，促进iNOS翻译、增加NO生成，进而加速神经元退行性变。本项目拟先确认星形胶质细胞上异常激活的ErbB4通过iNOS/NO途径加速神经元退行性变，再结合EMSA及Co-IP技术探讨ErbB4调控iNOS表达的机制是否涉及MEX-3C。本项目有助于阐明糖尿病神经退行性变的发病机制。

糖尿病（diabetes mellitus，DM）慢性并发症可累及中枢神经系统，导致认知障碍。糖尿病时，异常活化的星形胶质细胞可能通过促进关键因子的分泌而影响周围海马神经元的功能。ErbB4表达异常参与多种神经精神疾病的发生与发展。本项目拟研究星形胶质细胞ErbB4异常激活促NO生成的机制及其介导糖尿病海马神经元退行性变的作用。结果显示：①糖尿病小鼠脑组织海马辐射层及分子陷窝层ErbB4阳性的星形胶质细胞数目明显增加；对照组ErbB4主要在星形胶质细胞的胞浆表达，而糖尿病组ErbB4主要在星形胶质细胞的胞核表达；②高浓度葡萄糖明显增加体外培养的星形胶质细胞ErbB4表达水平；③糖尿病星形胶质细胞ErbB4异常激活加速海马神经元退行性变的机制涉及iNOS/NO途径；④星形胶质细胞ErbB4异常激活在转录后水平调控iNOS表达的机制可能与MEX-3C蛋白发生相互作用有关；⑤本项目还拓展研究并证实海马神经元ErbB4异常表达参与糖尿病海马神经元退行性变的发生，其机制与激活mTOR通路调节tau蛋白过度磷酸化有关。