Department of Anesthetics, Chang Gung Memorial Hospital at Linkuo, and College of Medicine, Chang Gung University, Kwei-San, Tao-Yuan, Taiwan.
Mol Neurobiol. 2015;51(3):1103-15. doi: 10.1007/s12035-014-8777-7. Epub 2014 Jun 12.
Bradykinin (BK) is a proinflammatory mediator and elevated in several brain injury and inflammatory diseases. The deleterious effects of BK on brain astrocytes may aggravate brain inflammation mediated through the upregulation of cytosolic phospholipase A2 (cPLA2)/cyclooxygenase-2 (COX-2)-derived prostaglandin E2 (PGE2) production. However, the signaling mechanisms underlying BK-induced cPLA2 expression in brain astrocytes remain unclear. Herein, we investigated the effects of activation of cPLA2/COX-2 system on BK-induced cPLA2 upregulation in rat brain astrocytes (RBA-1). The data obtained with Western blotting, RT-PCR, and immunofluorescent staining analyses showed that BK-induced de novo cPLA2 expression was mediated through activation of cPLA2/COX-2 system. Upregulation of native cPLA2/COX-2 system by BK through activation of PKCδ, c-Src, MAPKs (ERK1/2 and JNK1/2) cascades led to PGE2 biosynthesis and release. Subsequently, the released PGE2 induced cPLA2 expression via the same signaling pathways (PKCδ, c-Src, ERK1/2, and JNK1/2) and then activated the cyclic AMP response element-binding protein (CREB) via B2 BK receptor-mediated cPLA2/COX-2 system-derived PGE2/EP-dependent manner. Finally, upregulation of cPLA2 by BK may promote more PGE2 production. These results demonstrated that in RBA-1, activation of CREB by PGE2/EP-mediated PKCδ/c-Src/MAPK cascades is essential for BK-induced de novo cPLA2 protein. More importantly, upregulation of cPLA2 by BK through native cPLA2/COX-2 system may be a positive feedback mechanism that enhances prolonged brain inflammatory responses. Understanding the mechanisms of cPLA2/COX-2 system upregulated by BK on brain astrocytes may provide rational therapeutic interventions for brain injury and inflammatory diseases.
缓激肽（BK）是一种促炎介质，在几种脑损伤和炎症性疾病中升高。BK 对脑星形胶质细胞的有害作用可能通过上调细胞质磷脂酶 A2（cPLA2）/环氧化酶-2（COX-2）衍生的前列腺素 E2（PGE2）的产生而加重脑炎症。然而，BK 诱导脑星形胶质细胞中 cPLA2 表达的信号机制尚不清楚。在此，我们研究了 cPLA2/COX-2 系统的激活对 BK 诱导大鼠脑星形胶质细胞（RBA-1）中 cPLA2 上调的影响。Western blot、RT-PCR 和免疫荧光染色分析的数据表明，BK 诱导的 cPLA2 表达是通过 cPLA2/COX-2 系统的激活介导的。BK 通过激活蛋白激酶 Cδ（PKCδ）、原癌基因 c-Src、丝裂原激活的蛋白激酶（MAPKs）（ERK1/2 和 JNK1/2）级联反应上调内源性 cPLA2/COX-2 系统，导致 PGE2 的生物合成和释放。随后，释放的 PGE2 通过相同的信号通路（PKCδ、c-Src、ERK1/2 和 JNK1/2）诱导 cPLA2 表达，然后通过 B2 BK 受体介导的 cPLA2/COX-2 系统衍生的 PGE2/EP 依赖性方式激活环磷酸腺苷反应元件结合蛋白（CREB）。最后，BK 上调的 cPLA2 可能促进更多的 PGE2 产生。这些结果表明，在 RBA-1 中，PGE2/EP 介导的 PKCδ/c-Src/MAPK 级联反应通过 CREB 的激活对于 BK 诱导的 cPLA2 蛋白的从头合成是必需的。更重要的是，BK 通过内源性 cPLA2/COX-2 系统上调 cPLA2 可能是增强长期脑炎症反应的正反馈机制。了解 BK 对脑星形胶质细胞中 cPLA2/COX-2 系统的上调机制可能为脑损伤和炎症性疾病提供合理的治疗干预。
