NLRP3 inflammasome activation during myocardial ischemia reperfusion is cardioprotective.

BACKGROUND: The innate immune receptor NLRP3 recognizes tissue damage and initiates inflammatory processes through formation multiprotein complexes with the adaptor protein ASC and caspase-1, i.e. NLRP3 inflammasomes, which through cleavage of pro-IL-1ß mediates release of bioactive IL-1ß. We hypothesized that NLRP3 mediates tissue damage during acute myocardial infarction (MI) and sought to investigate the mechanisms herein in an experimental MI model in mice. METHODS AND RESULTS: The left coronary artery (LCA) of WT, NLRP3(-/-) and ASC(-/-) mice of both genders was ligated for 30 min followed by 3 or 24 h reperfusion. For pre-conditioning studies, the TLR2 agonist Pam3CSK4 or PBS was injected intraperitoneally 60 min prior to LCA ligation. For mechanistic investigations, blood plasmas and left ventricle tissues were collected, and a hypothesis-driven selection of protein or mRNA targets was investigated. Surprisingly, hearts from NLRP3-deficient mice featured larger infarct size than WT mice (p = 0.0048). In general, there were only modest changes with no significant pattern in myocardial infiltration of neutrophils and macrophages and systemic and myocardial cytokine expression between the three genotypes. Preconditioning with the TLR2 agonist Pam3CSK4 induced Akt phosphorylation and reduced infarct size in WT but not NLRP3 -or ASC -deficient hearts. CONCLUSION: Absence of NLRP3 results in increased myocardial infarct size after in vivo ischemia reperfusion, seemingly due to dysfunction of the cardioprotective RISK pathway. Our data imply that NLRP3 contributes to cardio-protection during I/R and do not support a role for NLRP3 or ASC inhibition in the management of acute MI including revascularization therapy.

The cardiokine secreted Frizzled-related protein 3, a modulator of Wnt signalling, in clinical and experimental heart failure.

OBJECTIVES: Experimental studies have shown involvement of Wnt signalling in heart failure (HF). We hypothesized that secreted frizzled-related protein 3 (sFRP3), a modulator of Wnt signalling, is related to the progression of HF. DESIGN: Circulating sFRP3 was measured in 153 HF patients and compared with 25 healthy controls. The association of sFRP3 with mortality was evaluated in 1202 patients (GISSI-HF trial). sFRP3 mRNA expression was assessed in failing human and murine left ventricles (LV), and cellular localization was determined after fractioning of myocardial tissue. In vitro studies were carried out in cardiac fibroblasts subjected to cyclic mechanical stretch. RESULTS: (i) Heart failure patients had significantly raised serum sFRP3 levels compared with controls, (ii) during a median follow-up of 47 months, 315 patients died in the GISSI-HF substudy. In univariable Cox regression, tertiles of baseline sFRP3 concentration were significantly associated with all-cause and cardiovascular mortality. After adjustment for demographic and clinical variables, but not for CRP and NT-proBNP, the associations with mortality remained significant for the third tertile (all-cause, HR 1.45, P = 0.011; cardiovascular, HR 1.66, P = 0.003), (iii) sFRP3 mRNA expression was increased in failing human LV, with a decline following LV assist device therapy. LV from post-MI mice showed an increased sFRP3 mRNA level, particularly in cardiac fibroblasts, and (iv) mechanical stretch enhanced sFRP3 expression and release in myocardial fibroblasts. CONCLUSION: There is an association between increased sFRP3 expression and adverse outcome in HF, suggesting that the failing myocardium itself contributes to an increase in circulating sFRP3.