P2X7 Deficiency Blocks Lesional Inflammasome Activity and Ameliorates Atherosclerosis in Mice

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Abstract

Background:

Extracellular adenosine triphosphate (ATP) binds as a danger signal to purinergic receptor P2X7 and promotes inflammasome assembly and interleukin-1β expression. We hypothesized a functional role of the signal axis ATP–P2X7 in inflammasome activation and the chronic inflammation driving atherosclerosis.

Methods:

P2X7-competent and P2X7-deficient macrophages were isolated and stimulated with lipopolysaccharide, ATP, or both. To assess whether P2X7 may have a role in atherosclerosis, P2X7 expression was analyzed in aortic arches from low density lipoprotein receptor-/- mice consuming a high-cholesterol or chow diet. P2X7+/+ and P2X7−/− low density lipoprotein receptor−/− mice were fed a high-cholesterol diet to investigate the functional role of P2X7 knockout in atherosclerosis. Human plaques were derived from carotid endarterectomy and stained against P2X7.

Results:

Lipopolysaccharide or ATP stimulation alone did not activate caspase 1 in isolated macrophages. However, priming with lipopolysaccharide, followed by stimulation with ATP, led to an activation of caspase 1 and interleukin-1β in P2X7-competent macrophages. In contrast, P2X7-deficient macrophages showed no activation of caspase 1 after sequential stimulation while still expressing a basal amount of interleukin-1β. P2X7 receptor was higher expressed in murine atherosclerotic lesions, particularly by lesional macrophages. After 16 weeks of a high-cholesterol diet, P2X7-deficient mice showed smaller atherosclerotic lesions than P2X7-competent mice (0.162 cm2±0.023 [n=9], P2X7−/− low density lipoprotein receptor−/− : 0.084 cm2±0.01 [n=11], P=0.004) with a reduced amount of lesional macrophages. In accord with our in vitro findings, lesional caspase 1 activity was abolished in P2X7−/− mice. In addition, intravital microscopy revealed reduced leukocyte rolling and adhesion in P2X7-deficient mice. Last, we observe increased P2X7 expression in human atherosclerotic lesions, suggesting that our findings in mice are relevant for human disease.

Conclusions:

P2X7 deficiency resolved plaque inflammation by inhibition of lesional inflammasome activation and reduced experimental atherosclerosis. Therefore, P2X7 represents an interesting potential new target to combat atherosclerosis.

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