糖尿病患者伴发抑郁症的概率远高于常人，且共患抑郁后更不利于血糖控制，给临床治疗带来了挑战。我们前期通过基因芯片分析和验证工作，发现糖尿病时海马组织中组织激肽释放酶相关肽酶8(KLK8)表达增多；KLK8基因敲除可减轻、而转基因过表达KLK8可加重糖尿病抑郁样行为；运动锻炼可能通过促进同型半胱氨酸（Hcy）代谢酶CBS表达、减少Hcy蓄积，从而提高KLK8基因启动子甲基化水平、抑制KLK8表达，改善糖尿病抑郁样行为。结合免疫共沉淀、质谱分析和验证工作，我们发现具有抗抑郁作用的神经元膜蛋白NCAM1可能是KLK8的酶切底物。在此基础上，本项目将利用KLK8转基因和KLK8基因敲除两种模式动物，首先证实CBS/Hcy代谢通路调节KLK8表达在运动干预改善糖尿病抑郁样行为中的作用，进而将围绕KLK8/NCAM1信号途径探讨其分子机制，由此为运动干预作为糖尿病并发抑郁症的非药物防治手段提供理论依据。

Compared to the general population, diabetic patients have significant higher chances to develop depression. Moreover, depression is found to worsen glycemic control in diabetes, with higher risk to develop complications and adverse outcomes, which brings bigger challenges to clinical treatment. By using bioinformatics analysis of microarray studies of hippocampal samples obtained from STZ-induced diabetic animals, it was found that the tissue kallikrein-related peptidase (KLK) 8 was significantly elevated in the hippocampus of diabetic animals. Our preliminary study showed for the first time that transgenic-mediated KLK8 overexpression aggravated, wheareas KLK8 deficiency significantly alleviated the diabetes-associated depression-like behavior. Cystathionine beta-synthase (CBS) is the first, and rate-limiting enzyme in the transsulfuration metabolic pathway of homocysteine (Hcy), thus playing an important role in the maintenance of a normal Hcy level. Our preliminary study showed that treadmill exercise training for 4 weeks signicifantly increased hippocampal CBS expression, whereas decreased hippocampal Hcy accumulation, KLK8 expression and diabetes-associated depression-like behavior. In central nervous systems, it has been found that high Hcy level results in DNA hypomethylation, which subsequently leads to abnormal regulation of gene transcription, and plays critical roles in the pathogenesis of various diseases. Since a CpG island has been found in the promoter of KLK8 gene promoter, we hypothesized that inhibition of Hcy-induced DNA hypomethylation of KLK8 gene promoter might contribute to the protective effects of treadmill exercise on diabetes-associated depression-like behavior. In addition, using co-immunoprecipitation and mass spectrometry, we obtained a number of potential target proteins which might be associated with KLK8. We then determined that neuronal cell adhesion molecule 1 (NCAM1), a neuronal membrane protein which has been reported to exert anti-depressant effects, might associate with KLK8 in the hippocampus. On the basis of these results, the present proposal will firstly verify that CBS/Hcy metabolic pathway-induced regulation of hippocampal KLK8 expression does contribute to the protective effects of exercise training on diabetes-associated depression-like behavior, by using both KLK8 transgenic and KLK8 knockout rodent models. Since KLK8 associates with the neuronal membrane protein NCAM1 in the hippocampus, we will then clarify whether upregulation of KLK8 leads to cleavage of NCAM1, thus resulting in inactivation of the intracellular signal transduction pathways mediated by NCAM1. Finally, the role of KLK8/NCAM1 signaling pathway in the protective effects of exercise training on diabetes-associated depression-like behavior will be elucidated. This study not only clarifies the mechanisms underlying how exercise training improves the diabetes- associated depression-like behavior, but also shares alternative non-drug interventions for prevention of depression in diabetes patients.