Department of Neurology, Chongqing General Hospital, University of Chinese Academy of Sciences, Chongqing, China; Chongqing Key Laboratory of Neurodegenerative Diseases, Chongqing, 400013, China
Department of Histology and Embryology, Chongqing Medical University, Chongqing, 400016, China
Curr Alzheimer Res. 2020;17(8):735-752. doi: 10.2174/1567205017666201111120919.
Neuroinflammation plays an important role in the pathophysiological process of various neurodegenerative diseases. It is well known that curcumin has obvious anti-inflammatory effects in various neuroinflammation models. However, its effect on the modulation of microglial polarization is largely unknown.
This study aimed to investigate whether curcumin changed microglia to an anti-inflammatory M2-phenotype by activating the AMP-activated protein kinase (AMPK) signaling pathway.
LPS treatment was used to establish BV2 cells and primary microglia neuroinflammation models. The neuroinflammation mouse model was established by an intracerebroventricular (ICV) injection of lipopolysaccharide (LPS) in the lateral septal complex region of the brain. TNF-α was measured by ELISA, and cell viability was measured by Cell Counting Kit-8 (CCK-8). The expression of proinflammatory and anti-inflammatory cytokines was examined by Q-PCR and Western blot analysis. Phenotypic polarization of BV2 microglia was detected by immunofluorescence.
Curcumin enhanced AMPK activation in BV2 microglial cells in the presence and absence of LPS. Upon LPS stimulation, the addition of curcumin promoted M2 polarization of BV2 cells, as evidenced by suppressed M1 and the elevated M2 signature protein and gene expression. The effects of curcumin were inhibited by an AMPK inhibitor or AMPK knockdown. Calmodulin-dependent protein kinase kinase β (CaMKKβ) and liver kinase B1 (LKB1) are upstream kinases that activate AMPK. Curcumin can activate AMPK in Hela cells, which do not express LKB1. However, both the CaMKKβ inhibitor and siRNA blocked curcumin activation of AMPK in LPS-stimulated BV2 cells. Moreover, the CaMKKβ inhibitor and siRNA weaken the effect of curcumin suppression on M1 and enhancement of M2 protein and gene expression in LPS-stimulated BV2 cells. Finally, curcumin enhanced AMPK activation in the brain area where microglia were over-activated upon LPS stimulation in an in vivo neuroinflammation model. Moreover, curcumin also suppressed M1 and promoted M2 signature protein and gene expression in this in vivo model.
Curcumin enhances microglia M2 polarization via the CaMKKβ-dependent AMPK signaling pathway. Additionally, curcumin treatment was found to be neuroprotective and thus might be considered as a novel therapeutic agent to treat the neurodegenerative disease such as Alzheimer's disease, Parkinson's disease, etc.
神经炎症在各种神经退行性疾病的病理生理过程中起着重要作用。众所周知，姜黄素在各种神经炎症模型中具有明显的抗炎作用。然而，其对小胶质细胞极化的调节作用在很大程度上尚不清楚。
本研究旨在探讨姜黄素是否通过激活 AMP 激活的蛋白激酶（AMPK）信号通路使小胶质细胞向抗炎 M2 表型转化。
采用 LPS 处理建立 BV2 细胞和原代小胶质细胞神经炎症模型。通过在脑侧隔复合区脑室内注射脂多糖（LPS）建立神经炎症小鼠模型。通过 ELISA 检测 TNF-α，通过细胞计数试剂盒-8（CCK-8）检测细胞活力。通过 Q-PCR 和 Western blot 分析检测促炎和抗炎细胞因子的表达。通过免疫荧光检测 BV2 小胶质细胞的表型极化。
姜黄素在 LPS 存在或不存在的情况下增强了 BV2 小胶质细胞中的 AMPK 激活。在 LPS 刺激下，姜黄素促进了 BV2 细胞的 M2 极化，表现为 M1 抑制和 M2 特征蛋白和基因表达升高。AMPK 抑制剂或 AMPK 敲低抑制了姜黄素的作用。钙调蛋白依赖性蛋白激酶激酶β（CaMKKβ）和肝激酶 B1（LKB1）是激活 AMPK 的上游激酶。姜黄素可以在不表达 LKB1 的 Hela 细胞中激活 AMPK。然而，CaMKKβ 抑制剂和 siRNA 均阻断了 LPS 刺激的 BV2 细胞中姜黄素对 AMPK 的激活。此外，CaMKKβ 抑制剂和 siRNA 削弱了姜黄素抑制 LPS 刺激的 BV2 细胞中 M1 并增强 M2 蛋白和基因表达的作用。最后，在 LPS 刺激导致小胶质细胞过度激活的体内神经炎症模型中，姜黄素增强了大脑区域中 AMPK 的激活。此外，姜黄素还抑制了 M1，并促进了该体内模型中 M2 特征蛋白和基因表达。
姜黄素通过 CaMKKβ 依赖性 AMPK 信号通路增强小胶质细胞 M2 极化。此外，姜黄素的治疗被发现具有神经保护作用，因此可能被认为是治疗阿尔茨海默病、帕金森病等神经退行性疾病的一种新的治疗剂。
