1Universitätsklinikum Würzburg Medizinische Klinik und Poliklinik I Würzburg, Deutschland; 2Charité - Universitätsmedizin Berlin CC6: Klinik für Radiologie Berlin, Deutschland; 3Universitätsklinikum Würzburg Deutsches Zentrum für Herzinsuffizienz Würzburg, Deutschland; 4Universität Würzburg Institut für Virologie und Immunbiologie Würzburg, Deutschland
Background: Myocardial infarction (MI) in pigs is a well-established translational large animal model. However, the immune response to myocardial injury and healing has not yet been extensively characterized in this species.
Methods and results: We used a closed-chest model to induce MI by 90-minute occlusion of the left anterior descending artery and performed bulk tissue RNA sequencing of samples from the infarct core, the border zone, and the remote myocardium on days 3, 7, and 14 post-MI. Compared to sham, the most differentially expressed genes were found within the infarct core at all time points analyzed. We performed gene set enrichment analysis for genes expressed in the infarct core to explore changes in transcriptomic patterns over time. Top hallmark gene sets on days 3 and 7 were related to proliferation, while the top gene set on day 14 was "epithelial to mesenchymal transition". Among the top-ranked genes on day 3 were cytokines, growth factors, plasminogen regulatory proteins, and metalloproteinases (including IL6, AREG, MMP14, TIMP1, PLAUR, SERPINE1), while on day 14 genes related to activated, i.e. POSTN-expressing fibroblasts and collagen synthesis were prominent. The hallmark gene set "inflammatory response" was among the most enriched gene sets at all time points. Genes related to innate immunity, such as CLEC5A, MSR1, CSF3R, NLRP3, TLR2, CCL2, and CD14, were among the top-ranked transcripts on day 3, whereas on day 7 and 14 more genes related to lymphocyte biology, like CCR7, CD70, IL7R, LCK, and IL18R appeared. Accordingly, the hallmark gene set "allograft rejection" was among the top upregulated gene sets in the infarct core on day 14. This gene set is enriched for transcripts related to adaptive immune responses, suggesting a prominent involvement of lymphocytes at this stage. Furthermore, we examined the temporal and spatial patterns of chemokine expression as a major regulatory mechanism of leukocyte recruitment. Notably, among other chemokines, CXCL8 (IL-8), which is not expressed in mice but in injured human myocardium, was significantly upregulated in the porcine infarct core on days 3, 7, and 14. We further validated the presence of CXCL8 protein in our myocardial samples by immunofluorescence microscopy and found that CXCL8 protein expression was mainly confined to the border zone where it co-localized with macrophages.
Conclusion: Our data provide a resource for translational studies in the pig. CXCL8 (IL-8) expression detected in the infarcted porcine myocardium specifically illustrates the value of this species for translational cardioimmunological studies.