AMP Affects Intracellular Ca2+ Signaling, Migration, Cytokine Secretion and T Cell Priming Capacity of Dendritic Cells

The nucleotide adenosine-5′-monophosphate (AMP) can be released by various cell types and has been shown to elicit different cellular responses. In the extracellular space AMP is dephosphorylated to the nucleoside adenosine which can then bind to adenosine receptors. However, it has been shown that AMP can also activate A1 and A2a receptors directly. Here we show that AMP is a potent modulator of mouse and human dendritic cell (DC) function. AMP increased intracellular Ca2+ concentration in a time and dose dependent manner. Furthermore, AMP stimulated actin-polymerization in human DCs and induced migration of immature human and bone marrow derived mouse DCs, both via direct activation of A1 receptors. AMP strongly inhibited secretion of TNF-α and IL-12p70, while it enhanced production of IL-10 both via activation of A2a receptors. Consequently, DCs matured in the presence of AMP and co-cultivated with naive CD4+CD45RA+ T cells inhibited IFN-γ production whereas secretion of IL-5 and IL-13 was up-regulated. An enhancement of Th2-driven immune response could also be observed when OVA-pulsed murine DCs were pretreated with AMP prior to co-culture with OVA-transgenic naïve OTII T cells. An effect due to the enzymatic degradation of AMP to adenosine could be ruled out, as AMP still elicited migration and changes in cytokine secretion in bone-marrow derived DCs generated from CD73-deficient animals and in human DCs pretreated with the ecto-nucleotidase inhibitor 5′-(alpha,beta-methylene) diphosphate (APCP). Finally, the influence of contaminating adenosine could be excluded, as AMP admixed with adenosine desaminase (ADA) was still able to influence DC function. In summary our data show that AMP when present during maturation is a potent regulator of dendritic cell function and point out the role for AMP in the pathogenesis of inflammatory disorders.

核苷酸腺苷-5′-单磷酸 (AMP) 可由多种细胞类型释放，已被证实可引发不同的细胞应答。在细胞外间隙中，AMP会被去磷酸化转化为核苷腺苷，后者可结合腺苷受体。然而已有研究表明，AMP也可直接激活A1与A2a受体。本研究证实，AMP是小鼠与人类树突状细胞 (DC) 功能的强效调节因子。AMP可呈时间与剂量依赖性方式升高细胞内钙离子浓度。此外，AMP可通过直接激活A1受体，刺激人类树突状细胞的肌动蛋白聚合，并诱导未成熟人类树突状细胞及骨髓来源小鼠树突状细胞发生迁移。AMP可显著抑制肿瘤坏死因子-α (TNF-α) 与白细胞介素-12p70 (IL-12p70) 的分泌，同时通过激活A2a受体促进白细胞介素-10 (IL-10) 的产生。因此，在AMP存在下成熟并与初始CD4+CD45RA+ T细胞共培养的树突状细胞，可抑制干扰素-γ (IFN-γ) 的产生，同时上调白细胞介素-5 (IL-5) 与白细胞介素-13 (IL-13) 的分泌。当卵清蛋白 (OVA) 致敏的小鼠树突状细胞在与卵清蛋白 (OVA) 转基因初始OTII T细胞共培养前经AMP预处理时，同样可观察到Th2型免疫应答的增强。由于从CD73缺陷动物中获得的骨髓来源树突状细胞，以及经胞外核苷酸酶抑制剂5′-(α,β-亚甲基)二磷酸 (APCP) 预处理的人类树突状细胞中，AMP仍可引发迁移与细胞因子分泌的改变，因此可排除AMP经酶解为腺苷所产生的效应。此外，由于与腺苷脱氨酶 (ADA) 混合的AMP仍可影响树突状细胞功能，故可排除污染物腺苷的干扰。综上，本研究数据表明，在树突状细胞成熟过程中存在的AMP是其功能的强效调节因子，并揭示了AMP在炎症性疾病发病机制中的作用。