Nasu-Tada Kaoru, Koizumi Schuichi, Inoue Kazuhide
Division of Pharmacology, National Institute of Health Sciences, Setagaya, Tokyo, Japan.
Glia. 2005 Nov 1;52(2):98-107. doi: 10.1002/glia.20224.
Microglia are immune cells in the brain; their activation, migration, and proliferation have pivotal roles in brain injuries and diseases. Microglia are known to attach firmly to fibronectin, the upregulation of which is associated with several pathological conditions in the CNS, through beta1 integrin and become activated. Extracellular nucleotides can serve as potent signaling molecules. Recently, ATP and ADP were revealed to possess chemoattractive properties to microglia via Gi-coupled P2Y receptors. In the present study, we report that the ADP-induced chemotaxis of microglia is mediated by P2Y12/13 receptors and is beta1 integrin-dependent in the presence of fibronectin. Signals from P2Y12/13 receptors also cause beta1 integrin translocation to the membrane ruffle regions, but this redistribution was lost when the intracellular cyclic AMP (cAMP) was increased by forskolin or dibutyryl cAMP. This inhibitory effect of cAMP-elevating agents did not appear when microglia were co-incubated with a protein kinase A (PKA) inhibitor, KT-5720, suggesting that PKA is a negative regulator of the beta1 integrin translocation. We also show that the engagement of beta1 integrin enhanced microglial proliferation. Signals from P2Y12/13 receptors attenuated the proliferation, whereas ADP itself had no effect on microglial growth. Furthermore, beta1 integrin-induced proliferation is positively regulated by the cAMP-dependent PKA. Together, these results indicate the involvement of beta1 integrin in microglial proliferation and chemotaxis, both of which have clinical importance. The data also suggest that PKA is inversely involved in these two cellular functions.
小胶质细胞是大脑中的免疫细胞；它们的激活、迁移和增殖在脑损伤和疾病中起着关键作用。已知小胶质细胞通过β1整合素与纤连蛋白紧密结合，纤连蛋白的上调与中枢神经系统的几种病理状况相关，并会激活小胶质细胞。细胞外核苷酸可作为有效的信号分子。最近，研究发现三磷酸腺苷（ATP）和二磷酸腺苷（ADP）通过Gi偶联的P2Y受体对小胶质细胞具有化学吸引特性。在本研究中，我们报告ADP诱导的小胶质细胞趋化作用由P2Y12/13受体介导，并且在纤连蛋白存在的情况下依赖于β1整合素。来自P2Y12/13受体的信号也会导致β1整合素转运至膜褶皱区域，但当用福司可林或二丁酰环磷腺苷（dbcAMP）提高细胞内环磷腺苷（cAMP）水平时，这种重新分布就会消失。当小胶质细胞与蛋白激酶A（PKA）抑制剂KT-5720共同孵育时，cAMP升高剂的这种抑制作用并未出现，这表明PKA是β1整合素转运的负调节因子。我们还表明，β1整合素的结合增强了小胶质细胞的增殖。来自P2Y12/13受体的信号减弱了增殖，而ADP本身对小胶质细胞生长没有影响。此外，β1整合素诱导的增殖受到cAMP依赖性PKA的正向调节。总之，这些结果表明β1整合素参与了小胶质细胞的增殖和趋化作用，这两者都具有临床重要性。数据还表明PKA在这两种细胞功能中起相反作用。
