P2X7 Deficiency Blocks Lesional Inflammasome Activity and Ameliorates Atherosclerosis in Mice
Background—Extracellular ATP binds as a danger signal to purinergic receptor P2X7, promotes inflammasome assembly, and IL-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 -deficient macrophages were isolated and stimulated with LPS, ATP, or both. To assess whether P2X7 may have a role in atherosclerosis, P2X7 expression was analyzed in aortic arches from LDLR-/- mice consuming high cholesterol diet (HCD) or chow diet. P2X7+/+ and P2X7-/- LDLR-/- mice were fed a HCD to investigate the functional role of P2X7 knockout in atherosclerosis. Human plaques were derived from carotid endarterectomy and stained against P2X7.
Results—LPS or ATP stimulation alone did not activate caspase 1 in isolated macrophages. However, priming with LPS followed by stimulation with ATP lead to an activation of caspase 1 and IL-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 IL-1β. P2X7 receptor was higher expressed in murine atherosclerotic lesions, particularly by lesional macrophages. After 16 weeks of high cholesterol diet P2X7-deficient mice showed smaller atherosclerotic lesions than P2X7-competent mice (0.162cm2 ± 0.023 (n=9), P2X7-/- LDLR-/-: 0.084cm2 ± 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. Additionally, intravital microscopy revealed reduced leukocyte rolling and adhesion in P2X7-deficient mice. Finally, 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.
- Received January 15, 2017.
- Revision received March 7, 2017.
- Accepted March 24, 2017.