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. 2015 Aug 1;36(29):1923-34.
doi: 10.1093/eurheartj/ehv195. Epub 2015 May 16.

Acute Myocardial Infarction Activates Distinct Inflammation and Proliferation Pathways in Circulating Monocytes, Prior to Recruitment, and Identified Through Conserved Transcriptional Responses in Mice and Humans

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Free PMC article

Acute Myocardial Infarction Activates Distinct Inflammation and Proliferation Pathways in Circulating Monocytes, Prior to Recruitment, and Identified Through Conserved Transcriptional Responses in Mice and Humans

Neil Ruparelia et al. Eur Heart J. .
Free PMC article

Abstract

Aims: Monocytes play critical roles in tissue injury and repair following acute myocardial infarction (AMI). Specifically targeting inflammatory monocytes in experimental models leads to reduced infarct size and improved healing. However, data from humans are sparse, and it remains unclear whether monocytes play an equally important role in humans. The aim of this study was to investigate whether the monocyte response following AMI is conserved between humans and mice and interrogate patterns of gene expression to identify regulated functions.

Methods and results: Thirty patients (AMI) and 24 control patients (stable coronary atherosclerosis) were enrolled. Female C57BL/6J mice (n = 6/group) underwent AMI by surgical coronary ligation. Myocardial injury was quantified by magnetic resonance imaging (human) and echocardiography (mice). Peripheral monocytes were isolated at presentation and at 48 h. RNA from separated monocytes was hybridized to Illumina beadchips. Acute myocardial infarction resulted in a significant peripheral monocytosis in both species that positively correlated with the extent of myocardial injury. Analysis of the monocyte transcriptome following AMI demonstrated significant conservation and identified inflammation and mitosis as central processes to this response. These findings were validated in both species.

Conclusions: Our findings show that the monocyte transcriptome is conserved between mice and humans following AMI. Patterns of gene expression associated with inflammation and proliferation appear to be switched on prior to their infiltration of injured myocardium suggesting that the specific targeting of inflammatory and proliferative processes in these immune cells in humans are possible therapeutic strategies. Importantly, they could be effective in the hours after AMI.

Keywords: Acute myocardial infarction; Genomics; Inflammation; Mitosis; Monocytes.

Figures

Figure 1
Figure 1
Acute myocardial infarction results in an increase in total peripheral circulating monocytes of an inflammatory phenotype in both mice and humans. (A) Fluorescence-activate cell sorting (FACS) gating strategy to identify monocytes in peripheral blood (mice, n = 6/group). (B) Acute myocardial infarction results in a significant 4-fold increase in total monocytes (P < 0.001), which were predominately of an inflammatory Ly6Chi phenotype (C). (D) Human monocyte (and monocyte subset) gating strategy (n = 24 control group, n = 30 acute myocardial infarction group). (E) Acute myocardial infarction results in a significant 2-fold increase in total monocytes (P < 0.001) at 48 h following injury but not at the hyperacute (at presentation) timepoint (F). (G) Monocytes at both the hyperacute and 48 h time points exhibited an inflammatory CD14++CD16 phenotype. Data are represented by mean ± standard deviation.
Figure 2
Figure 2
The extent of the monocyte response correlates with the extent of myocardial injury. (A) Transthoracic echocardiography of mouse hearts following acute myocardial infarction (n = 6/group). (B) Cardiac magnetic resonance imaging to quantify area of injury (T2-weighted sequence) and infarction (LGE sequence) in humans (n = 30 acute timepoint, n = 23 follow up). (C) In mice, the total peripheral monocyte count was highly correlated with size of infarct (r2 = 0.72, P < 0.001). (D) In humans, the magnitude of the monocyte response for each patient following acute myocardial infarction correlated with the extent of irreversible myocardial injury determined by LGE at 6 months (r2 = 0.42, P = 0.001) and weakly (non-linear relationship) with the area of risk, as measured by oedema (r2 = 0.29, P = 0.021, E).
Figure 3
Figure 3
Acute myocardial infarction results in differential expression of genes in circulating monocytes in both humans and mice. (A) Analysis of the transciptome in mouse monocytes revealed differential expression of 196 genes (fold change >2; P < 0.01) of which 168 genes were significantly up-regulated and 28 genes were significantly down-regulated (n = 6/group). (B) In humans, 122 genes were differentially expressed (fold change > 2; P < 0.01) of which 72 genes were significantly up-regulated and 50 genes were significantly down-regulated (n = 24, control group, n = 30, AMI group).
Figure 4
Figure 4
Monocytes from myocardial infarction in mouse and human are transcriptionally similar. (A) Mouse monocyte gene signature in acute myocardial infarction strongly enriches in the ranked gene list of human blood monocytes 48 h following infarct compared with the stable state (left) and vice versa (right). (B) Overlap of genes in same top enriching gene sets with the ranked gene list of the infarct vs. baseline state of monocytes in human (left) and mouse (right). (C) Number of gene sets in ImmuneSigDB v1.0 strongly enriching (FDR < 0.01) in infarct human and/or mouse monocytes. (D) Representation of genes in the leading edges of the 163 shared enriched gene sets. Genes were ranked from most to least represented in human dataset and shown is the number of times that gene appears in the leading edge of the enriched gene sets. Similarity of genes enriching in leading edges of enriched gene sets in both organisms was assessed by Spearman correlation.
Figure 5
Figure 5
Leading-edge analysis identifies inflammation and cell cycling as novel biological states underlying the monocyte response to acute myocardial infarction. Leading-edge analysis of most significantly enriching gene sets (FDR < 0.01) in mouse monocytes following myocardial infarction reveals metagenes involved in inflammatory and cell cycle processes. Representative genes in these metagenes are listed in Supplementary material online, Table.
Figure 6
Figure 6
Inflammatory and mitosis pathways are up-regulated in circulating monocytes en route to inflamed myocardium. (A) Flow cytometry of peripheral circulating monocytes 48 h following acute myocardial infarction in humans identified a significant increase in the expression of TLR2 (P < 0.001) but not TLR4 (P = 0.14, B) (n = 12/group). (C) Ki67 expression was significantly up-regulated in monocytes at 48 h following injury but not hyperacutely (at presentation) in comparison with controls (P < 0.001) (n = 12/group). (D and E) Immunohistochemistry of mouse hearts (blue: DAPI, red: CD11b, green Ki67) following acute myocardial infarction confirmed a significant increase in the number of leukocytes expressing Ki67 (white arrows) (P < 0.001) indicating up-regulation of mitosis pathways in infarcted myocardium (n = 3/group). Data are represented by mean ± standard deviation.

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References

    1. Matzinger P. The danger model: a renewed sense of self. Science 2002;296:301–305. - PubMed
    1. Nahrendorf M, Pittet MJ, Swirski FK. Monocytes: protagonists of infarct inflammation and repair after myocardial infarction. Circulation 2010;121:2437–2445. - PMC - PubMed
    1. Hilgendorf I, Gerhardt LM, Tan TC, Winter C, Holderried TA, Chousterman BG, Iwamoto Y, Liao R, Zirlik A, Scherer-Crosbie M, Hedrick CC, Libby P, Nahrendorf M, Weissleder R, Swirski FK. Ly-6Chigh Monocytes Depend on Nr4a1 to Balance Both Inflammatory and Reparative Phases in the Infarcted Myocardium. Circ Res 2014;114:1611–1622. - PMC - PubMed
    1. Majmudar MD, Keliher EJ, Heidt T, Leuschner F, Truelove J, Sena BF, Gorbatov R, Iwamoto Y, Dutta P, Wojtkiewicz G, Courties G, Sebas M, Borodovsky A, Fitzgerald K, Nolte MW, Dickneite G, Chen JW, Anderson DG, Swirski FK, Weissleder R, Nahrendorf M. Monocyte-directed RNAi targeting CCR2 improves infarct healing in atherosclerosis-prone mice. Circulation 2013;127:2038–2046. - PMC - PubMed
    1. Leuschner F, Dutta P, Gorbatov R, Novobrantseva TI, Donahoe JS, Courties G, Lee KM, Kim JI, Markmann JF, Marinelli B, Panizzi P, Lee WW, Iwamoto Y, Milstein S, Epstein-Barash H, Cantley W, Wong J, Cortez-Retamozo V, Newton A, Love K, Libby P, Pittet MJ, Swirski FK, Koteliansky V, Langer R, Weissleder R, Anderson DG, Nahrendorf M. Therapeutic siRNA silencing in inflammatory monocytes in mice. Nat Biotechnol 2011;29:1005–1010. - PMC - PubMed

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