Abstract 18918: Disruption of Myeloid Differentiation Factor-88 Signaling Prevents the Formation of the Nlrp3 Inflammasome in the Heart in Acute Myocardial Infarction in the Mouse
Introduction: The NLRP3 inflammasome is activated in the heart during acute myocardial infarction (AMI), leading to caspase-1 activation and cardiac dysfunction. This process appears to be a finely regulated mechanism requiring an adequate expression of the structural components of the inflammasome (priming) occurring through myeloid differentiation factor-88 (MyD88) signaling, and NLRP3 activation (triggering).
Hypothesis: Disruption of MyD88 signaling inhibits priming and prevents inflammasome formation and caspase-1 activation in the heart.
Methods: AMI was induced in 10 weeks old mice by surgical ligation of the left anterior descending coronary artery. Pre-treatment with MyD88-targeted small interfering RNA (siRNA; 0.5 mg/kg; i.p.) was used to knockdown MyD88 expression systemically. Scrambled non-targeting siRNA was used as control. We measured NLRP3 mRNA expression (qPCR), reflecting priming, and caspase-1 activity (enzymatic assay). To explore the contribution of the leukocytes infiltrating the heart during AMI, we repeated all experiments in mice carrying a floxed MyD88 and the Cre recombinase expressed under the control of the lysozyme 2 promoter, leading to selective deletion of MyD88 in myeloid cells, and matched wild-type controls.
Results: MyD88 silencing had no effects on cardiac dimension or function at baseline. MyD88 knockdown (>90%) with siRNA prevented priming, measured as NLRP3 mRNA expression 72 hours following AMI (Figure A), and attenuated the formation of an active inflammasome, measured as caspase-1 activity (Figure B). Caspase-1 activity in the heart was also significantly lower in myeloid-restricted MyD88 knockout mice compared with control mice (Figure C).
Conclusions: The formation of an active NLRP3 inflammasome in the heart during the acute phases of AMI requires intact MyD88 signaling in myeloid cells infiltrating the heart.
Author Disclosures: S. Toldo: None. E. Mezzaroma: None. B.W. Van Tassell: None. C. Mezzaroma: None. S. Carbone: None. A.G. Mauro: None. F.N. Salloum: None. A. Abbate: Research Grant; Modest; Grifols. Other Research Support; Modest; Swedish Orphan Biovitrum. Research Grant; Significant; Novartis.
This research has received full or partial funding support from the American Heart Association.
- © 2014 by American Heart Association, Inc.