Abstract
Intracellular ATP is the universal energy carrier that fuels many cellular processes. However, immune cells can also release a portion of their ATP into the extracellular space. There, ATP activates purinergic receptors that mediate autocrine and paracrine signaling events needed for the initiation, modulation, and termination of cell functions. Mitochondria contribute to these processes by producing ATP that is released. Here, we summarize the synergistic interplay between mitochondria and purinergic signaling that regulates T cell functions. Specifically, we discuss how mitochondria interact with P2X1, P2X4, and P2Y11 receptors to regulate T cell metabolism, cell migration, and antigen recognition. These mitochondrial and purinergic signaling mechanisms are indispensable for host immune defense. However, they also represent an Achilles heel that can render the host susceptible to infections and inflammatory disorders. Hypoxia and mitochondrial dysfunction deflate the purinergic signaling mechanisms that regulate T cells, while inflammation and tissue damage generate excessive systemic ATP levels that distort autocrine purinergic signaling and impair T cell function. An improved understanding of the metabolic and purinergic signaling mechanisms that regulate T cells may lead to novel strategies for the diagnosis and treatment of infectious and inflammatory diseases.
Highlights
ATP is the main energy carrier of living cells
Mitochondrial defects and T cell suppression are cardinal features of sepsis that correlate with morbidity and clinical outcome [44, 46,47,48,49]. These findings suggest that P2X1 receptormediated Ca2+ influx, mitochondrial ATP production, basal ATP release, and autocrine feedback through P2X1 receptors represent a purinergic-metabolic signaling loop that maintains cell metabolism of quiescent T cells and allows these cells to mount the responses needed for effective host immune defense following chemokine or antigen stimulation (Figure 1A)
The suppressive effect of A2a receptor stimulation on various T cell functions has been studied in great detail in mice [107]
Summary
ATP is the main energy carrier of living cells. it came as a surprise to many when Geoffrey Burnstock first reported that neurons release a portion of their cellular ATP and that the released ATP acts as a signaling molecule for cell-to-cell communication [1]. ATP release and its breakdown products defines immune cell functions by autocrine stimulation of three different families of purinergic receptors, namely P1, P2X, and P2Y receptors. CD39 (ENTPD1) that converts extracellular ATP and ADP into AMP, and CD73 that degrades AMP to adenosine are important modulators of purinergic signaling in immune cells [26, 27].
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