Luo Huaiqing, Xiang Yang, Qu Xiangping, Liu Huijun, Liu Chi, Li Guangyi, Han Li, Qin Xiaoqun
Department of Physiology, School of Basic Medical Science, Central South University, Changsha, China.
Department of Anatomy, Histology and Embryology, Changsha Medical University, Changsha, China.
Front Pharmacol. 2019 Apr 16;10:395. doi: 10.3389/fphar.2019.00395. eCollection 2019.
Alzheimer's disease (AD), a progressive neurodegenerative disease characterized by impairments of cognitive function as a result of synaptic deficits and neuronal loss, is associated with inflammation. Apelin-13, a predominant neuropeptide with inhibiting effect on inflammation, has beneficial effects on cognition memory and neuronal damage. However, whether apelin-13 can protect neurons to ameliorate cognitive deficits in AD by inhibiting the inflammatory response remains largely unknown. To test this hypothesis, rats were intracerebroventricularly (ICV) injected with streptozotocin (3 mg/kg) alone or in combination with apelin-13 (2 μg). And tyrosine receptor kinase B (TrkB) blocker K252a (200 nM) was administrated 10 min before apelin injection. Furthermore, cognitive performance was assessed by new object recognition (NOR) and Y-maze tests. Protein expression of apelin, APJ, microglial marker (IBA1), astroglia marker (GFAP), interleukin 1 beta (IL-1β), tumor necrosis factor-α (TNF-α), synaptophysin (SYP), brain-derived neurotrophic factor (BDNF), TrkB, phospho-TrkB (p-TrkB) in the hippocampus were examined by western blotting or immunohistochemistry. And the gene expression of IBA1, GFAP, IL-1β, TNF-α, and SYP were detected by real-time quantitative polymerase chain reaction (PCR). Inflammatory disorder in the hippocampus was tested by hematoxylin and eosin (H&E) staining. The enzyme-linked immunosorbent assay (ELISA) was used to study the expression level of acetylcholine. And the activity of acetylcholinesterase was detected by Acetylcholinesterase Assay Kit. We observed that apelin/APJ signaling was downregulated in the hippocampus of rats administrated with STZ. Apelin-13 was found to significantly ameliorate STZ-induced AD-like phenotypes including congnitive deficit, cholinergic disfunction and the damage of neuron and synaptic plasticity. Moreover, apelin-13 inhibited microglia and astrocyte activation, reduced IL-1β and TNF-α expression and hippocampal BDNF/TrkB expression deficit in AD rats. Finally, apelin-13-mediated effects were blocked by TrkB receptor antagonist K252a. These results suggest that apelin-13 upregulates BDNF/TrkB pathway against cognitive deficit in a STZ-induced rat model of sporadic AD by attenuating inflammation.
阿尔茨海默病（AD）是一种进行性神经退行性疾病，其特征是由于突触缺陷和神经元丢失导致认知功能受损，与炎症相关。Apelin-13是一种对炎症有抑制作用的主要神经肽，对认知记忆和神经元损伤具有有益作用。然而，Apelin-13是否能通过抑制炎症反应来保护神经元以改善AD中的认知缺陷，在很大程度上仍不清楚。为了验证这一假设，将大鼠脑室内（ICV）单独注射链脲佐菌素（3mg/kg）或与Apelin-13（2μg）联合注射。在注射Apelin前10分钟给予酪氨酸受体激酶B（TrkB）阻断剂K252a（200nM）。此外，通过新物体识别（NOR）和Y迷宫试验评估认知能力。通过蛋白质免疫印迹法或免疫组织化学法检测海马中Apelin、APJ、小胶质细胞标志物（IBA1）、星形胶质细胞标志物（GFAP）、白细胞介素1β（IL-1β）、肿瘤坏死因子-α（TNF-α）、突触素（SYP）、脑源性神经营养因子（BDNF）、TrkB、磷酸化TrkB（p-TrkB）的蛋白表达。通过实时定量聚合酶链反应（PCR）检测IBA1、GFAP、IL-1β、TNF-α和SYP的基因表达。通过苏木精和伊红（H&E）染色检测海马中的炎症紊乱。采用酶联免疫吸附测定（ELISA）研究乙酰胆碱的表达水平。并使用乙酰胆碱酯酶检测试剂盒检测乙酰胆碱酯酶的活性。我们观察到，在给予STZ的大鼠海马中，Apelin/APJ信号通路被下调。发现Apelin-13能显著改善STZ诱导的AD样表型，包括认知缺陷、胆碱能功能障碍以及神经元和突触可塑性损伤。此外，Apelin-13抑制小胶质细胞和星形胶质细胞活化，降低AD大鼠海马中IL-1β和TNF-α表达以及BDNF/TrkB表达缺陷。最后，Apelin-13介导的效应被TrkB受体拮抗剂K252a阻断。这些结果表明，在STZ诱导的散发性AD大鼠模型中，Apelin-13通过减轻炎症上调BDNF/TrkB通路以对抗认知缺陷。
