Probing macrophage cell nucleotide sensing and calcium signaling through computation

Loyola University Chicago, Maywood IL

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Abstract

While inflammation is a natural immune system response that begins the healing process, chronic inflam- mation is tied to many human diseases including cancer, cardiac dysfunction, and sepsis. A key element of inflammatory responses are macrophages, a white blood cell that eliminates pathogens or dying tissues. An endogenous 'danger signal', adenosine triphosphate (ATP), stimulates Ca-dependent inflammatory pathways in macrophages. While previous research has made great strides in understanding inflammation, my lab seeks to uncover roles of ATP in driving macrophage inflammatory responses through multi-scale computational models we develop. With new models of inflammatory responses in macrophages, our lab can predict protein and cell behavior in integrated, physiological systems to better understand the immune system. The current paradigm for ATP-triggered inflammation in macrophages is that upregulation of nucleotide- sensing P2X channels sensitizes inflammatory responses, including cytokine and reactive oxygen species (ROS) release. However, this paradigm does not account for several observations. One, while P2X expression is increased in inflammatory macrophages, these receptors also support phagocytosis and migration in resting macrophages. How these processes are selectively controlled by P2X subtypes like P2X4 and P2X7 is unresolved. Two, inflammatory macrophages harbor post-translational modifications (PTMs) of many proteins that sense Ca, yet little is known about how PTMs impact immune pathways they control. Three, release and degradation of ATP by pannexins and ectonucleotidases control ATP that activates P2X, yet few studies have evaluated their coupling. Our lab is uniquely positioned to extend this paradigm by probing mechanisms underlying these observations and the largely unstudied coupling of P2X-, ATP-, and Ca-driven inflammation. Our lab and assembled collab- orators will investigate the overall hypothesis via computational modeling and experimental approaches: P2X channels in macrophages help nucleate chronic inflammation via ATP-induced ATP release (autocrinic) mechanisms that selectively prime Ca-dependent, pro-inflammatory signaling pathways. This hypothesis stems from questions that emerged from our investigations during the initial ESI MIRA award: 1. Does increased P2X4 and P2X7 expression and the resulting Ca signals they induce in macrophages prolong pro-inflammatory release of cytokines and ROS? 2. Do PTMs like ROS oxidation in the Ca-sensor calmodulin (CaM) attenuate its activation of pro-inflammatory signaling pathways? 3. Do (autocrinic) ATP-induced, ATP release in macrophages prolong pro-inflammatory increases in intracellular Ca? Our long-term goal to understand macrophage physiology through computation will be accelerated by the proposed investigations. Key expected outcomes from this grant period include new mechanisms and simulation tools for autocrinic, ATP-driven inflammatory responses mediated by P2X receptors. Since all Eukaryotic cells use Ca, insights from modeling macrophages will have broad impacts beyond immune function.