S100A8∕A9 is a valuable biomarker and treatment target to detect and modulate neutrophil involvement in myocardial infarction

Abstract

Myocardial infarction (MI) leads to irreversible ischemic damage of the heart muscle and is the leading cause of heart failure. The ischemic cardiac injury triggers a potent local and systemic immune response. In the acute phase post-MI, neutrophils infiltrate the myocardium in large numbers and induce further cardiomyocyte death, expanding the infarcted area. The alarmin S100A8∕A9 is a proinflammatory mediator primarily produced by myeloid cells, with an emerging role in MI. We previously demonstrated that short-term inhibition of S100A8∕A9 during the inflammatory phase of the immune response to MI improves long-term cardiac function. In the present study, we investigated the effects of S100A8∕A9 blockade on myocardial inflammation and post-ischemic myocardial injury in a mouse model of coronary artery ligation. Immunohistochemical (IHC) staining revealed that the presence of S100A9 is strongly correlated with neutrophil infiltration in the myocardium on days 1 and 3 post-MI. A 3-day treatment with the S100A8∕A9 blocker ABR-238901 starting immediately after MI decreased the number of neutrophils and S100A9 presence in the myocardium and had a positive impact on cardiac damage, reducing infarction size. These findings promote S100A9 as an IHC biomarker of neutrophil infiltration and a promising immunomodulatory target to regulate neutrophil recruitment, reduce ischemic injury and promote long-term beneficial cardiac recovery after MI.

Figure 1

Neutrophil infiltration and S100A9 presence in the myocardium on day 1 post-MI: (A) Representative images of HE staining of left ventricular sections from the sham and MI groups treated with PBS (MI) or ABR-238901 (MI+ABR), respectively, collected on day 1 after myocardial ischemia (400×); (B) Ly6G-positive staining identifying neutrophil infiltration (400×); (C) S100A9-positive immunohistochemical staining in the same areas as in (A) and (B) (400×). HE: Hematoxylin–Eosin; Ly6G: Lymphocyte antigen 6 family member G6D; MI: Myocardial infarction; PBS: Phosphate-buffered saline

Figure 2

Neutrophil infiltration and S100A9 presence in the myocardium on day 3 post-MI: (A) Representative images of HE staining of left ventricular sections from the sham and the two MI groups receiving PBS (MI) or ABR-238901 (MI+ABR) treatment, collected on day 3 post-MI (400×); (B) Ly6G-positive neutrophil staining (400×); (C) S100A9 staining in the same areas as in (A) and (B) (400×

Figure 3

The S100A9 presence in the infarcted myocardium reflects neutrophil infiltration and the effect of the treatment. Correlations between neutrophil infiltration, expressed as Ly6G-positive staining, and S100A9 staining in myocardium collected on day 1 (A) and day 3 (B) post-MI. The stained area is reported as an average percentage of left ventricular area on five consecutive sections collected at 300 μm intervals

Figure 4

Inhibition of S100A8/A9 signaling reduces the extent of MI on day 3 post-MI: (A) Representative HE staining of cardiac sections from the PBS- and ABR-238901-treated mice, three days after induced MI; (B) Masson’s trichrome staining of fibrous scar formation in the infarcted area; (C) Quantification of MI size, expressed as percentage of left ventricular (LV) volume