S100A9 Links Inflammation and Repair in Myocardial Infarction.

RATIONALE: The alarmin S100A9 has been identified as a potential therapeutic target in myocardial infarction. Short-term S100A9 blockade during the inflammatory phase post-myocardial infarction inhibits systemic and cardiac inflammation and improves cardiac function long term. OBJECTIVE: To evaluate the impact of S100A9 blockade on postischemic cardiac repair. METHODS AND RESULTS: We assessed cardiac function, hematopoietic response, and myeloid phagocyte dynamics in WT (wild type) C57BL/6 mice with permanent coronary artery ligation, treated with the specific S100A9 blocker ABR-238901 for 7 or 21 days. In contrast to the beneficial effects of short-term therapy, extended S100A9 blockade led to progressive deterioration of cardiac function and left ventricle dilation. The treatment reduced the proliferation of Lin-Sca-1+c-Kit+ hematopoietic stem and progenitor cells in the bone marrow and the production of proreparatory CD150+CD48-CCR2+ hematopoietic stem cells. Monocyte trafficking from the spleen to the myocardium and subsequent phenotype switching to reparatory Ly6CloMerTKhi macrophages was also impaired, leading to inefficient efferocytosis, accumulation of apoptotic cardiomyocytes, and a larger myocardial scar. The transcription factor Nur77 (Nr4a1 [nuclear receptor subfamily 4 group A member 1]) mediates the transition from inflammatory Ly6Chi monocytes to reparatory Ly6Clo macrophages. S100A9 upregulated the levels and activity of Nur77 in monocytes and macrophages in vitro and in Ly6Chi/int monocytes in vivo, and S100A9 blockade antagonized these effects. Finally, the presence of reparatory macrophages in the myocardium was also impaired in S100A9-/- mice with permanent myocardial ischemia, leading to depressed cardiac function long term. CONCLUSIONS: We show that S100A9 plays an important role in both the inflammatory and the reparatory immune responses to myocardial infarction. Long-term S100A9 blockade negatively impacts cardiac recovery and counterbalances the beneficial effects of short-term therapy. These results define a therapeutic window targeting the inflammatory phase for optimal effects of S100A9 blockade as potential immunomodulatory treatment in acute myocardial infarction.

Inhibition of pro-inflammatory myeloid cell responses by short-term S100A9 blockade improves cardiac function after myocardial infarction.

AIMS: Neutrophils have both detrimental and beneficial effects in myocardial infarction (MI), but little is known about the underlying pathways. S100A8/A9 is a pro-inflammatory alarmin abundantly expressed in neutrophils that is rapidly released in the myocardium and circulation after myocardial ischaemia. We investigated the role of S100A8/A9 in the innate immune response to MI. METHODS AND RESULTS: In 524 patients with acute coronary syndrome (ACS), we found that high plasma S100A8/A9 at the time of the acute event was associated with lower left ventricular ejection fraction (EF) at 1-year and increased hospitalization for heart failure (HF) during follow-up. In wild-type C57BL/6 mice with MI induced by permanent coronary artery ligation, treatment with the S100A9 blocker ABR-238901 during the inflammatory phase of the immune response inhibited haematopoietic stem cell proliferation and myeloid cell egression from the bone marrow. The treatment reduced the numbers of neutrophils and monocytes/macrophages in the myocardium, promoted an anti-inflammatory environment, and significantly improved cardiac function compared with MI controls. To mimic the clinical scenario, we further confirmed the effects of the treatment in a mouse model of ischaemia/reperfusion. Compared with untreated mice, 3-day ABR-238901 treatment significantly improved left ventricular EF (48% vs. 35%, P = 0.002) and cardiac output (15.7 vs. 11.1 mL/min, P = 0.002) by Day 21 post-MI. CONCLUSION: Short-term S100A9 blockade inhibits inflammation and improves cardiac function in murine models of MI. As an excessive S100A8/A9 release is linked to incident HF, S100A9 blockade might represent a feasible strategy to improve prognosis in ACS patients.