Department of Chemistry, University of Kentucky, Lexington, KY, USA.
College of Medicine, University of Kentucky, Lexington, KY, USA.
J Physiol. 2019 Feb;597(3):799-818. doi: 10.1113/JP277377. Epub 2018 Dec 17.
A computational model of P2X channel activation in microglia was developed that includes downfield Ca -dependent signalling pathways. This model provides quantitative insights into how diverse signalling pathways in microglia converge to control microglial function.
Microglia function is orchestrated through highly coupled signalling pathways that depend on calcium (Ca ). In response to extracellular ATP, transient increases in intracellular Ca driven through the activation of purinergic receptors, P2X and P2Y, are sufficient to promote cytokine synthesis. Although the steps comprising the pathways bridging purinergic receptor activation with transcriptional responses have been probed in great detail, a quantitative model for how these steps collectively control cytokine production has not been established. Here we developed a minimal computational model that quantitatively links extracellular stimulation of two prominent ionotropic purinergic receptors, P2X4 and P2X7, with the graded production of a gene product, namely the tumour necrosis factor α (TNFα) cytokine. In addition to Ca handling mechanisms common to eukaryotic cells, our model includes microglia-specific processes including ATP-dependent P2X4 and P2X7 activation, activation of nuclear factor of activated T-cells (NFAT) transcription factors, and TNFα production. Parameters for this model were optimized to reproduce published data for these processes, where available. With this model, we determined the propensity for TNFα production in microglia, subject to a wide range of ATP exposure amplitudes, frequencies and durations that the cells could encounter in vivo. Furthermore, we have investigated the extent to which modulation of the signal transduction pathways influence TNFα production. Our results suggest that pulsatile stimulation of P2X4 via micromolar ATP may be sufficient to promote TNFα production, whereas high-amplitude ATP exposure is necessary for production via P2X7. Furthermore, under conditions that increase P2X4 expression, for instance, following activation by pathogen-associated molecular factors, P2X4-associated TNFα production is greatly enhanced. Given that Ca homeostasis in microglia is profoundly important to its function, this computational model provides a quantitative framework to explore hypotheses pertaining to microglial physiology.
开发了一种包含远场 Ca 依赖性信号通路的 P2X 通道激活的计算模型。该模型提供了定量的见解，了解微胶质中的不同信号通路如何汇聚以控制微胶质功能。
微胶质功能通过高度耦合的信号通路来协调，这些信号通路依赖于钙 (Ca 2+)。细胞外 ATP 激活后，通过嘌呤能受体（P2X 和 P2Y）的激活导致细胞内 Ca 2+短暂增加，足以促进细胞因子的合成。虽然已经详细探测了将嘌呤能受体激活与转录反应联系起来的途径中的步骤，但尚未建立这些步骤如何共同控制细胞因子产生的定量模型。在这里，我们开发了一个最小的计算模型，该模型将两个主要的离子型嘌呤能受体 P2X4 和 P2X7 的细胞外刺激与分级产生一种基因产物（即肿瘤坏死因子 α (TNFα)细胞因子）定量地联系起来。除了真核细胞共有的 Ca 处理机制外，我们的模型还包括微胶质特异性过程，包括 ATP 依赖性 P2X4 和 P2X7 激活、核因子激活 T 细胞 (NFAT) 转录因子的激活以及 TNFα 的产生。针对这些过程，优化了该模型的参数，尽可能地重现已发表的数据。通过该模型，我们确定了在微胶质中 TNFα 产生的倾向，这些倾向受细胞在体内可能遇到的广泛的 ATP 暴露幅度、频率和持续时间的影响。此外，我们研究了信号转导途径的调制在多大程度上影响 TNFα 的产生。我们的结果表明，通过微摩尔 ATP 对 P2X4 进行脉冲刺激可能足以促进 TNFα 的产生，而通过 P2X7 进行高幅度 ATP 暴露则是必需的。此外，在增加 P2X4 表达的情况下，例如在病原体相关分子因子激活后，P2X4 相关的 TNFα 产生大大增强。鉴于 Ca 2+ 稳态在微胶质功能中非常重要，该计算模型为探索与微胶质生理学相关的假说提供了定量框架。
