• TLR-stimulated macrophages synthesize, release, and hydrolyze ATP via CD39 to regulate their own activation state.• The loss of macrophage CD39 prevents regulatory macrophage development and leads to lethal inflammatory responses and septic shock in mice.Sepsis is a highly fatal disease caused by an initial hyperinflammatory response followed by a state of profound immunosuppression. Although it is well appreciated that the initial production of proinflammatory cytokines by macrophages accompanies the onset of sepsis, it remains unclear what causes the transition to an immunosuppressive state. In this study, we reveal that macrophages themselves are key regulators of this transition and that the surface enzyme CD39 plays a critical role in self-limiting the activation process. We demonstrate that Toll-like receptor (TLR)-stimulated macrophages modulate their activation state by increasing the synthesis and secretion of adenosine triphosphate (ATP). This endogenous ATP is paradoxically immunosuppressive due to its rapid catabolism into adenosine by CD39. Macrophages lacking CD39 are unable to transition to a regulatory state and consequently continue to produce inflammatory cytokines. The importance of this transition is demonstrated in a mouse model of sepsis, where small numbers of CD39-deficient macrophages were sufficient to induce lethal endotoxic shock. Thus, these data implicate CD39 as a key "molecular switch" that allows macrophages to self-limit their activation state. We propose that therapeutics targeting the release and hydrolysis of ATP by macrophages may represent new ways to treat inflammatory diseases. (Blood. 2013;122(11):1935-1945 IntroductionFailure to control inflammatory macrophage activation responses can lead to pathological diseases, best exemplified by sepsis. Despite our growing understanding of its pathogenesis, sepsis continues to affect more than 200 000 people annually in the United States, with a mortality rate as high as 50%.1,2 The severe pathology associated with sepsis occurs in response to the hyperproduction of macrophagederived inflammatory cytokines, which can lead to vascular and tissue destruction, multiple organ failure, shock, and death.3 Intriguingly, macrophages isolated from late-stage septic individuals exhibit the phenotype of immunosuppressive, regulatory macrophages, expressing high levels of the anti-inflammatory cytokine interleukin-10 (IL-10) and low levels of tumor necrosis factor a (TNF-a) and IL-12. [4][5][6] These observations suggest the transition from inflammatory to immunosuppressive macrophages may be critical to control initial inflammatory responses and prevent lethal septic shock. 4,7,8 However, the molecular mechanism by which this transition is achieved remains poorly understood.In the present work, we examine the role that endogenous CD39 and adenosine triphosphate (ATP) play in regulating the macrophage inflammatory response. Recently, extracellular ATP (eATP) has been characterized as a "danger signal" that can promote inflammation through ...

Lithium carbonate, a drug for the treatment of bipolar disorder, provides mood stability to mitigate recurrent episodes of mania and/or depression. Despite its long-term and widespread use, the mechanism by which lithium acts to elicit these psychological changes has remained unknown. Using nuclear magnetic resonance (NMR) methods, in this study we characterized the association of lithium with adenosine triphosphate (ATP) and identified a bimetallic (Mg·Li) ATP complex. Lithium's affinity to form this complex was found to be relatively high (Kd ∼1.6 mM) compared with other monovalent cations and relevant, considering lithium dosing and physiological concentrations of Mg(2+) and ATP. The ATP·Mg·Li complex reveals, for the first time, to the best of our knowledge, that lithium can associate with magnesium-bound phosphate sites and then act to modulate purine receptor activity in neuronal cells, suggesting a molecular mode for in vivo lithium action.

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