IL-7R blockade reduces post-myocardial infarction-induced atherosclerotic plaque inflammation in ApoE-/- mice

Abstract

Modulating inflammation by targeting IL-1β reduces recurrent athero-thrombotic cardiovascular events without lipid lowering. This presents an opportunity to explore other pathways associated with the IL-1β signaling cascade to modulate the inflammatory response post-myocardial infarction (MI). IL-7 is a mediator of the inflammatory pathway involved in monocyte trafficking into atherosclerotic plaques and levels of IL-7 have been shown to be elevated in patients with acute MI. Recurrent athero-thrombotic events are believed to be mediated in part by index MI-induced exacerbation of inflammation in atherosclerotic plaques. The objective of the study was to assess the feasibility of IL-7R blockade to modulate atherosclerotic plaque inflammation following acute MI in ApoE^-/- mice. Mice were fed Western diet for 12 weeks and then subjected to coronary occlusion to induce an acute MI. IL-7 expression was determined using qRT-PCR and immuno-staining, and IL-7R was assessed using flow cytometry. Plaque inflammation was evaluated using immunohistochemistry. IL-7R blockade was accomplished with monoclonal antibody to IL-7R. IL-7 mRNA expression was significantly increased in the cardiac tissue of mice subjected to MI but not in controls. IL-7 staining was observed in the coronary artery. Plaque macrophage and lipid content were significantly increased after MI. IL-7R antibody treatment but not control IgG significantly reduced macrophage and lipid content in atherosclerotic plaques. The results show that IL-7R antibody treatment reduces monocyte/macrophage and lipid content in the atherosclerotic plaque following MI suggesting a potential new target to mitigate increased plaque inflammation post-MI.

Keywords: IL-7R; Myocardial infarction; Plaque inflammation.

Fig. 1

IL-7 mRNA expression. IL-7 mRNA was assessed in myocardial tissue 1 week (A) and 6 weeks (B) after MI surgery. Bone marrow (C), lymph node (D), and spleen (E) were also assessed for IL-7 mRNA expression 1 week after MI. Bar over columns indicate statistical significance. N = 4–5 each group. (A) p = 0.02; (B) Control vs MI p = 0.015, Sham vs MI p = 0.04.

Fig. 2

IL-7 stain in coronary artery. Representative photos of IL-7 immuno-staining (reddish-brown) in the coronary arteries of control (A, N = 3), Sham (B, N = 3), and MI (C, N = 4) mice. Negative staining control (D) omitted the primary antibody. IL-7 stain area was measured and plotted (E). Scale bar = 0.01 mm. Bar over columns indicate statistical significance. Control vs MI p = 0.003; Sham vs MI p < 0.007.

Fig. 3

Monoclonal antibody blocking of IL-7R post-MI. Aortic sinus plaque lipid (A), macrophage (D), or T cells stained area (G) in mice subjected to MI and injected with IgG control (B and E) or IL-7R mAb (C and F). Scale bar = 0.1 mm (A) *p = 0.004; (B) *p = 0.014 t-test; N = 4 each. Splenocytes were analyzed using fluorescent staining and flow cytometry for percentage of macrophage (H) or T cells (I). Gating for CD11b + F4/80 + macrophages as shown in Supplemental Fig. 2A. Gating for T cells as shown in Supplemental Fig. 3A.

Fig. 4

Increased monocyte recruitment in vivo by IL-7. Matrigel plugs containing 15μg/ml IL-7 or PBS injected into flanks of mice fed high fat diet were collected after 3 days and subjected to digestion for cell recovery. The recovered cells were analyzed for fluorescent staining and flow cytometry. Gating for monocytes as depicted in Supplemental Fig. 2A. Gating for T cells as depicted in Supplemental Fig. 3A. Results are expressed as mean percentage of total cell infiltrates of each Matrigel plug. *p = 0.04 t-test; N = 6 each.