Zalavary S, Bengtsson T
Department of Health and Environment, Faculty of Health Sciences, Linköping University, Sweden.
Eur J Cell Biol. 1998 Feb;75(2):128-39. doi: 10.1016/S0171-9335(98)80055-1.
The mechanisms by which adenosine regulates the inflammatory reaction are poorly characterized. In this study, we investigated the effects of adenosine on neutrophil actin polymerization elicited by the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP) or IgG-opsonized yeast particles. We used bodipy-phallacidin staining in combination with flow cytometry and found that adenosine markedly reduced actin polymerization triggered by IgG-yeast, whereas the effect on the fMLP-response was less pronounced. Similar or even more pronounced effects were obtained with the adenosine A2 receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA), suggesting an A2 receptor-mediated mechanism. The following observations indicate that the A2 receptor-induced effects involve the cAMP-protein kinase A (PKA) signaling pathway: (1) a combination of NECA and the cAMP-specific phosphodiesterase (PDE) inhibitor Ro 20-1724 raised the cAMP content in both unstimulated and stimulated neutrophils and also further inhibited the actin dynamics; (2) the PKA inhibitor H89 reversed the inhibitory effects of NECA on the actin dynamics; (3) Ro 20-1724, isoproterenol and dibutyryl cAMP (DBcAMP) reduced actin polymerization in almost the same way as NECA did. NECA together with Ro 20-1724 impaired the fMLP-induced shape changes and cortical accumulation of actin filaments. In contrast, H89 potentiated the fMLP-induced formation of a submembranous ring of actin filaments. Neutrophils phagocytosing yeast particles in the presence of NECA and Ro 20-1724 were predominantly round in shape, and their ability to extend actin-rich pseudopods around the prey was reduced. These effects were partly antagonized by H89. In correlation with the effects on actin polymerization, NECA more effectively diminished IgG-induced upregulation of the beta2 integrin CD11b/CD18 than such upregulation induced by fMLP. The inhibitory effects of A2-receptor activation on actin dynamics and beta2 integrin expression in neutrophils exposed to IgG-yeast were also associated with a cAMP-dependent reduction of the phagocytic capacity. In conclusion, we show that adenosine inhibits actin dynamics and shape changes in neutrophils via a cAMP-dependent pathway. This finding further characterizes the mechanisms by which adenosine functions as an important modulator of the inflammatory response.
腺苷调节炎症反应的机制目前尚不清楚。在本研究中，我们研究了腺苷对趋化肽N-甲酰甲硫氨酰-亮氨酰-苯丙氨酸（fMLP）或IgG调理的酵母颗粒引发的中性粒细胞肌动蛋白聚合的影响。我们将硼二吡咯-鬼笔环肽染色与流式细胞术相结合，发现腺苷显著降低了IgG-酵母引发的肌动蛋白聚合，而对fMLP反应的影响则不那么明显。腺苷A2受体激动剂5'-N-乙基羧酰胺腺苷（NECA）也产生了相似甚至更明显的效果，提示存在A2受体介导的机制。以下观察结果表明，A2受体诱导的效应涉及cAMP-蛋白激酶A（PKA）信号通路：（1）NECA与cAMP特异性磷酸二酯酶（PDE）抑制剂Ro 20-1724联合使用，可提高未刺激和刺激的中性粒细胞中的cAMP含量，并进一步抑制肌动蛋白动力学；（2）PKA抑制剂H89可逆转NECA对肌动蛋白动力学的抑制作用；（3）Ro 20-1724、异丙肾上腺素和二丁酰cAMP（DBcAMP）对肌动蛋白聚合的抑制作用与NECA几乎相同。NECA与Ro 20-1724共同作用会损害fMLP诱导的肌动蛋白丝形状变化和皮质聚集。相反，H89增强了fMLP诱导的肌动蛋白丝膜下环的形成。在NECA和Ro 20-1724存在的情况下吞噬酵母颗粒的中性粒细胞主要呈圆形，它们在猎物周围伸出富含肌动蛋白的伪足的能力降低。这些效应部分被H89拮抗。与对肌动蛋白聚合的影响相关，NECA比fMLP诱导的上调更有效地减少了IgG诱导的β2整合素CD11b/CD18的上调。A2受体激活对暴露于IgG-酵母的中性粒细胞中肌动蛋白动力学和β2整合素表达的抑制作用也与吞噬能力的cAMP依赖性降低有关。总之，我们表明腺苷通过cAMP依赖性途径抑制中性粒细胞中的肌动蛋白动力学和形状变化。这一发现进一步阐明了腺苷作为炎症反应重要调节因子发挥作用的机制。
