Establishment of new kinin-network via microglia in the central nervous system

缓激肽（BK）已被报道为急性损伤脑损伤的介质。我们发现BK受体存在于小胶质细胞上，这是大脑的病理感受器（Noda et al., 2003）。在这里，我们报道BK通过小胶质细胞具有两种功能；意想不到的神经保护作用和化学吸引作用。1) BK通过微细胞的神经保护作用。BK可减弱lps诱导的TNF-α和IL-1β的释放，从而起到抗炎介质的作用。这种效应可以通过提高细胞内cAMP来模拟。增加细胞内cAMP的机制是通过激活前列腺素受体。事实上，我们发现BK增加了前列腺素E_2的释放，增强了微粒体前列腺素E合成酶和前列腺素受体EP2和EP4的表达，这表明了一个自分泌扩增环。BK对lps诱导的TNF-α释放的抑制作用被EP2/EP4激动剂模拟，而它被cAMP拮抗剂（前列腺素受体拮抗剂或诱导型环氧化酶（COX-2）抑制剂）所消除。后一种效应可以通过我们的观察来解释，即mPGES的表达被COX-2阻滞剂抑制。由于LPS和BK均增加了B_1和B_2受体的表达，这一信号级联进一步放大。利用生理技术，我们不仅在培养中，而且在急性脑切片的小胶质细胞中鉴定了功能性BK受体。为了研究BK抗炎作用的影响，我们将LPS应用于神经元-小胶质细胞共培养：BK可以减轻神经元死亡，另一方面，在纯神经元培养中，BK不影响TNF-□诱导的神经元死亡。我们的数据表明，BK通过调节小胶质细胞功能在中枢神经系统中具有抗炎和神经保护作用。2) bk诱导的小胶质细胞迁移。在中枢神经系统中，病理状态下，小胶质细胞向受损组织的迁移在再生中起作用。在本研究中，我们发现缓激肽（BK）诱导培养的小胶质细胞的迁移，被charybdotoxin（一种大电导Ca^<2+>依赖性K^+通道的阻滞剂）阻断，但不被百日毒（PTX）阻断。这些结果表明，bk诱导的小胶质细胞迁移需要激活大电导Ca^<2+> -激活的K^+通道，而ptx敏感的G蛋白则不需要激活。我们的发现可能有助于理解激肽在大脑中的功能以及小胶质细胞在脑损伤反应中的作用。少

Bradykinin (BK) has been reported as a mediator of brain damage in acute insults. We had found that receptors for BK were identified on microglia, the pathologic sensors of the brain (Noda et al., 2003). Here we report that BK has two functions via microglia ; unexpected neuroprotective effects and chemoattracting effect.1)Neuroprotective effects of BK via microelia. BK attenuated LPS-induced release of TNF-α and IL-1β, thus acting as an anti-inflammatory mediator. This effect was mimicked by raising intracellular cAMP. A mechanism to increase intracellular cAMP is via activation of prostanoid receptors. Indeed we found that BK increased the release of prostaglandin E_2, enhanced the expression of microsomal prostaglandin E synthase and the prostanoid receptors EP2 and EP4 indicating an autocrine amplification loop. This is supported by the observation that the inhibitory effect of BK on LPS-induced TNF-α release was mimicked by EP2/EP4 agonists, while it was abolished by a cAMP antago … More nist, a prostanoid receptor antagonist or an inhibitor of inducible type of cyclooxygenase (COX-2). The latter effect is explained by our observation that expression of mPGES was inhibited by a blocker of COX-2. This signaling cascade was further amplified since both LPS and BK increased expression of B_1 and B_2 receptors. Using physiological techniques we identified functional BK receptors not only in culture, but also in microglia from acute brain slices. To study the impact of the anti-inflammatory effect of BK, we applied LPS to neuron-microglia co-cultures : neuronal death was attenuated by BK. On the other hand, TNF-□-induced neuronal death was not affected by BK in pure neuronal cultures. Our data imply that BK has anti-inflammatory and neuroprotective effects in the CNS by modulating microglial function.2)BK-induced micrglial migration. In the central nervous system, migration of microglia towards damaged tissue plays a role in regeneration under pathological condition. In the present study, we found that bradykinin (BK) induced migration of cultured microglia, which was blocked by charybdotoxin, a blocker of large conductance Ca^<2+>-dependent K^+ channels, but not by pertussis toxin (PTX). These results indicate that activation of large conductance Ca^<2+> -activated K^+ channel is required for BK-induced microglial migration, while activation of PTX-sensitive G protein is not. Our findings may help to understand the function of kinins in the brain and the role of microglia in response to brain injury. Less