In present study, we identified 5 immune-related hub genes of CXCL8, TLR2, MMP9, CXCL1 and FPR1 and immune-related pathways in patients with AMI. In addition, we also identified other 5 DEGs of TNFAIP6, ADM, TRIB1, AQP9 and IL1R2 relative to ventricular remodeling in AMI patients complicating HF, which are potential genetic biomarkers for predicting HF at post-MI follow-up.
Based on integrated bioinformatic analysis, we screened out five hub genes and found that they are key in immune response after AMI, which is essential in the dissolution, absorption and reparative process of necrotic myocardium. C-X-C motif chemokine ligand (CXCL) is important in chemotactic recruitment of neutrophils to necrotic myocardium post AMI. CXCL8, also known as IL-8, got the highest degree in above PPI analysis. Its level upregulated in the infarcted area (8) and is reported to be the major mediator of inflammatory response and may induce neutrophils infiltration after ischemic injury (9). Moreover, higher plasma IL-8 levels were associated with larger infarct size and adverse outcome in patients with AMI undergoing percutaneous coronary intervention (10). CXCL1 is also important in inflammation and act as a chemoattractant for neutrophils (11). As different researches reported, the plasma levels of CXCL1 chemokine in AMI patients were notably higher than in healthy participants (12, 13), suggesting an increased mobilization and recruitment of neutrophils in AMI patients. Matrix metalloproteinases (MMPs) participated in numerous disease process including cardiovascular disease, while MMP9 played an important role in regulation of inflammatory response and scar formation post AMI (14). In response to infarction, infiltrating neutrophils and macrophages produce cytokines and chemokines that stimulate production and release of MMP-9(15). In turn, MMP9 regulates the inflammatory response via activating related inflammatory molecules (16), influencing the fibrotic healing process of infarcted myocardium at different stage post-AMI. As a member of Toll-like receptors (TLRs) family, TLR2 is vital in activating innate immunity and the upregulated level of TLR2 in circulating inflammatory cells have been reported to be associated with increased infarct size post AMI (17). Besides, anti-TLR2 therapy exerted cardioprotective effects via reducing leukocyte influx, cytokine production and proapoptotic signaling (18). In our study, we discovered TLR2 to be a crucial DEG in AMI which is enriched in immune response, suggesting that TLR2 might be tightly associated with dissolution and absorption of necrotic myocardium. Formyl peptide receptors 1 (FPR1) is key in regulating inflammation level, cardiomyocyte apoptosis and ventricular remodeling (19). Furthermore, Qin et al. revealed that targeting FPR1 have cardioprotective effects, making it a potential novel target in AMI treatment (20).
Further analysis of the significant module revealed that BP and KEGG pathways mainly enriched in immune responses and pathways, especially IL-17 and chemokine signaling pathway. As is known, massive of cardiomyocytes are lost and a large number of inflammatory cytokines including IL-17 are released post AMI. In turn, IL-17 aggravate cardiomyocytes apoptosis (21) and promotes leukocytes (22) and neutrophils (23) accumulation. Besides, IL-17 could induce macrophages infiltration and activate Nod-like receptor protein 3 inflammasome contributing to aggravating inflammatory response during AMI (24). Moreover, the enhancement of IL-17 signaling contributes to ventricular remodeling in infarcted heart (25, 26), making it a key part in the development of AMI and a novel therapeutic target. On the other hand, chemokines are essential in regulating leukocytes infiltration and modulating infarct angiogenesis as well as fibrous tissue deposition post AMI, among which CXC chemokines and CC chemokines are two major subfamilies. Timely and effective suppression of chemokine signaling may contribute to regulating inflammatory response and preventing heart from adverse remodeling (27). Therefore, the five hub genes and the two signaling pathways were involved in immunomodulation and inflammatory response to different degree, and played central roles in the process of dissolution, removal and repair of necrotic myocardium after AMI.
By further overlapping analysis, we identified TNFAIP6, ADM, TRIB1, AQP9 and IL1R2 were related to HF. They have already been reported to be associated with HF and immune response, making them potential biomarkers for predicting HF at an early stage after AMI. Due to AMI, sudden loss of massive cardiomyocytes triggers an intense immune response, inducing the expression of proinflammatory cytokines and chemokines (28). But prolonged or exaggerated inflammation, or improper suppression of inflammation contribute to worsen tissue damage, adverse remodeling, chamber dilation and HF (29). A better understanding of specific immune-related molecules or signaling pathways associated with adverse remodeling and HF post AMI might help to diagnose HF at an early stage and provide novel therapeutic targets (30, 31). The increased level of adrenomedullin (ADM) have been confirmed to be correlated with adverse cardiovascular outcomes in patients with AMI and complicating HF in several different studies (32). Matthew et al. found that one nmol/l increase in midregional proadrenomedullin was associated with hazard ratio ranging from 1.77 to 2.79 for death in patients with HF, making it a prognostic biomarker for patients with AMI and HF (33). Aquaporins (AQP) is of great importance in participating in inflammatory process (34), among which AQP9 is one important member. After AMI, the level of AQP9 in peripheral blood were notably elevated and AQP9 gene silencing in rats could significantly attenuate myocardial inflammatory response and improve cardiac function, making it an important target in the treatment of AMI (35). Furthermore, overexpression of miR-212 inhibited AQP9 and alleviated ventricular remodeling post AMI (36). Dysregulated interleukin 1 (IL-1) signaling following MI can disturb infarct healing and cause collateral damage as well as contributing to maladaptive left ventricular remodeling, while IL-1 activity is tightly regulated at the receptor level (37). Interleukin 1 receptor type 2 (IL1R2) can act as a decoy receptor to avoid excessive inflammatory response. Levels of IL1R2 remained elevated in acute and chronic phase post AMI and it was associated with development of left ventricular remodeling (38), making it a possible biomarker for predicting HF after AMI. However, further studies are needed to confirm the association between TNF Alpha Induced Protein 6 (TNFAIP6) and Tribbles pseudokinase 1 (TRIB1) with HF. TNFAIP6 is expressed by many different cell types in response to proinflammatory cytokines and participate in the protection of tissues from the damaging consequences of acute inflammation (39). Plasma TNFAIP6 levels were significantly higher in a comparison between 135 patients with coronary artery disease (CAD) and 47 patients controls (40). TRIB1 is correlated with diverse human pathologies, and it is overexpressed in human atherosclerotic arteries and reported to control smooth muscle cell proliferation and chemotaxis in the arterial intima (41). Utilizing the results from > 71000 individuals, Anette et al. revealed that TRIB1 was associated with increased risk of ischemic heart disease and MI in general population (42). The ROC analysis further confirmed that TNFAIP6, ADM, TRIB1, AQP9 and IL1R2 are likely to be genetic biomarkers for predicting whether the patients would develop the symptom of HF post AMI during 6 months follow-up.
However, there are some limitations of the present study. Firstly, the DEGs were identified by bioinformatic analysis, and there is a lack of in vitro and in vivo validation. Secondly, the sample size of patients with HF and non-HF post MI is relatively small, thus needing a larger and multi-center research. Despite these limitations, this study still provides novel insights into the important roles of genes to play in the healing process of inflammation, remodeling and development of AMI and HF.