Genetic deletion of aryl hydrocarbon receptor activates cardiac NLRP3-inflammasome and suppresses apoptosis in mice with acute myocardial infarction

Abstract

Abstract Background and purpose There is great interest in understanding the role of immune cells in the inflammatory mechanisms associated with acute myocardial infarction (AMI). Resident cardiac immune cells are activated by damage-associated molecular patterns interacting with specific pattern recognition receptors (PRRs), triggering inflammatory responses. Activated immune cells and fibroblasts then promote prohypertrophic and profibrotic signalling, which induces cardiac hypertrophy, fibrosis and remodelling after AMI. Nucleotide-binding domain leucine-rich repeat-containing proteins (NLRs) are PRRs that have emerged as key therapeutic targets in cardiovascular disease. NLRP3 assembles the inflammasome, which serves as molecular signalling platform to activate caspase-1 and regulate maturation of the potent proinflammatory cytokine IL-1β. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor of the basic Helix-Loop-Helix-PER-ARNT-SIM superfamily that mediates responses against environmental pollutants. Beyond its role in metabolising exogenous toxins as part of an adaptive chemical response, there is growing evidence that AhR is activated by endogenous ligands under physiological conditions. AhR has been proposed as a negative regulator of NLRP3-inflammasome activation. Here we studied the effects of defective AhR signalling on apoptosis, NLRP3-inflammasome activation and survival in a mouse model of AMI. Methods and results AMI was induced in 8–10-weeks-old AhR+/+ and AhR−/− mice by ligation of the left anterior descending coronary artery. Immunofluorescence analysis revealed that the number of TUNEL-positive nuclei and the expression of the apoptotic effector cleaved caspase-3 was higher in hearts from infarcted AhR+/+ mice than from sham-operated AhR+/+ mice 24 h after surgery. A similar analysis in AhR−/− mice revealed the absence of apoptotic markers after AMI. Gene analysis showed that cardiac levels of Nlrp3, apoptosis-associated speck-like protein (Asc) and Il1b were all significantly higher in AhR−/− mice than in AhR+/+ mice 24 h after AMI. Finally, survival analysis showed that 25% of AhR+/+ mice died 72 h after AMI surgery whereas the mortality in AhR−/− mice was 100%. Conclusion Our results show that loss of AhR inhibits cardiac apoptosis and increases NLRP3-mediated inflammation 24 h after AMI, highlighting a possible role for this nuclear receptor in cardiac remodelling post-AMI. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund