HF is a chronic heart syndrome; most patients live for an average of 5 years after diagnosis, and more than 25 million people are currently at risk of death worldwide. HF begins with pathological heart remodeling, in which the left ventricle and other cardiac chambers develop progressive structural and functional abnormalities in response to pathological stress (MD 2013). IHD and DCM are two important etiologies of HF (Tomasoni et al. 2019). The main manifestation of HF caused by DCM is ventricular enlargement, while IHD leads to decreased myocardial cell viability and increased ROS production due to continuous myocardial ischemia. ROS can directly act on cell membranes and induce myocardial cell apoptosis, resulting in decreased cardiac output. The gradual increase of cardiac load leads to ventricular remodeling, the final stage of which is ventricular dilation leading to HF. The pathways and molecules that differ between IHD and DCM and the mechanisms by which they cause HF have been explored (Sweet et al. 2018). However, there is a paucity of studies exploring the common pathways and molecules between the two HF etiologies.
This investigation employed bioinformatics methods using the GSE42955 and GS57338 datasets to screen DEGs shared by IHD and DCM. We then established an interaction network, and the analysis showed that the VCAM1 and ICAM1 genes showed the highest connectivity. Previous studies have shown that patients with HF have significantly higher levels of ICAM1 and VCAM1 compared to controls, and elevated VCAM1 was expression associated with HF severity (Tousoulis et al. 2001). We therefore set out to explore whether there is differential expression of VCAM1 and ICAM1 in failing heart tissue. Analysis of myocardial levels of VCAM1 and ICAM1 in the HF and control groups of the GSE57338 dataset showed that only VCAM1 was significantly differentially expressed. Correlation analysis between DEGs in the HF group and VCAM1 expression was conducted to identify genes with significant correlations. We propose that the expression of these genes was controlled by VCAM1. Finally, we established a risk prediction model with the genes correlated with VCAM1 expression. The subsequent analysis showed that the risk of HF increased with higher VCAM1 levels.
VCAM1 is an adhesion molecule; activation of this endothelial surface ligand enhances binding with white blood cells, thereby increasing leukocyte adhesion and epithelial cell migration (Wrigley et al. 2013). Experimental studies have shown that immune response mechanisms are correlated to pathologic heart remodeling, causing left ventricular dysfunction and eventually leading to HF. Based on this, we explored the relationship between VCAM1 and myocardial immune infiltration and examined how VCAM1 affects infiltrating immune cells and the subsequent effect on HF risk (Zhang et al. 2017). The xCell algorithm was used to predict the infiltration degree of various immune cells in cardiac tissue, and correlation analysis was conducted to assess the relationship between VCAM1 expression and the infiltration degrees of various immune cells. The results showed that VCAM1 level was positively correlated with the numbers of CD8 T cells, CD8 Tcm cells, CD4 naive T cells, conventional DCs, CMPs, and other immune cells. Notably, these cells showed higher degrees of immune infiltration degree in HF tissue compared to normal tissue. Previous studies have shown that infiltrated monocytes in the myocardium can differentiate into macrophages and promote tissue damage repair (Rhee and Lavine 2020). As highly specific antigen-presenting cells involved in adaptive and innate immunity, DCs also play an important role in the occurrence of HF. Animal experiments revealed that exogenous DCs can induce autoimmune inflammation mediated by CD4 + T cells to promote ventricular dilation and HF (Eriksson et al.). Increased T lymphocyte infiltration, which is involved in adaptive immunity, was also associated with HF risk (Strassheim et al. 2019). One of the most important features of chronic HF is the presence of numerous mature T cell infiltrates in the myocardial tissue (Moro-García et al. 2018; Ngwenyama et al. 2019). Animal studies have shown that T-cell-deficient mice are less likely to develop HF after aortic ligation (Gröschel et al. 2018), and remodeling of T cell subsets promotes HF development as indicated by elevated brain natriuretic peptide levels (Laroumanie et al. 2014). In vitro experiments revealed that Th1 cells—an important subset of T cells—can release interferon-g to promote the transformation of myocardial fibroblasts into a-smooth muscle actin fibroblasts, which can promote myocardial fibrosis, an important ventricular remodeling process (Travers et al. 2016). Therefore, T cells and their subsets play important roles in HF occurrence and pathogenesis (Nevers et al. 2017). Myeloid immune cells are the most abundant immune cells in myocardium. Immune cells in healthy subjects do not produce harmful chronic inflammation under physiologic conditions, but in pathological conditions such as acute or chronic ischemia, the degree of myeloid immune cell infiltration in the myocardium increases, and they release a variety of inflammatory mediators that stimulate chronic fibrosis and remodeling to exacerbate HF (Matthias 2018). The results of this study revealed an increased degree of infiltration of myeloid progenitors and cells in HF tissues. This was positively correlated with the expression of VCAM1 that can stimulate their differentiation macrophages and monocytes. Moreover, an uncontrolled inflammatory response in the pathological state triggers a large number of monocytes to differentiate into macrophages and cause tissue damage, and extensive monocyte infiltration in cardiac tissue has been associated with increased risk of HF (Shahid et al. 2018). Because most immune cells are recruited from the blood, as an adhesion factor expressed on the vascular endothelium, VCAM1 can recruit myeloid progenitor cells to infiltrate the myocardium and differentiate into various subsets of myeloid immune cells to promote HF (Sager et al. 2016). In our study, VCAM1 expression was positively correlated with the infiltration of these immune cells, which led us to hypothesize that the increased risk of HF caused by elevated VCAM1 expression was associated with VCAM1 regulation of immune cell infiltration.
We also conducted a GSEA of immune-infiltration-related KEGG pathways comparing HF and normal tissues and high- and low-VCAM1 expression groups. The results showed that immune-related pathways were enriched in both HF and myocardial tissues with increased VCAM1 expression, and the enrichments included graft-versus-host- and Th17 differentiation-related signaling pathways. The proportion of Th17 cells in the blood circulation and the amounts of cytokines they secrete are reportedly increased in patients with HF (Myers et al. 2016). In addition, Th17 cell differentiation often requires transforming growth factor-b and interleukin (IL)-6, which are involved in myocardial fibrosis development. In addition, IL-23 secreted by Th17 cells can promote the secretion of granulocyte-macrophage colony-stimulating factor by Th17 cells, infiltration of other immune cells, and a chronic inflammatory response (El-Behi et al. 2011). An increase in Th17 cells is often accompanied by a decrease in Treg cells (Lu et al. 2020), which is consistent with the results observed in this study. Therefore, we propose that VCAM1 promotes HF by regulating Th17 cell infiltration. We also observed that autoimmune-related graft-versus-host and xenograft rejection pathways were significantly enriched in the myocardial tissues of patients with HF and subjects with increased VCAM1 expression, and the autoimmune response is one of the important mechanisms for HF occurrence and development (Marty et al. 2006). B-cell pathways were also enriched in HF tissues and myocardial tissue with increased VCAM1 expression, and B-cell activation has been associated with the production of autoimmune antibodies (Hofmann et al. 2018). Cytotoxic pathways of NK cells that play a role in graft immune rejection and cause cell damage through direct contact with graft cells (Gill and Lin 2019) were also enriched in our results. Based on our observation of more infiltrated NK cells in the myocardial tissue of patients with HF, VCAM1 may regulate the cytotoxicity of NK cells and promote myocardial injury by participating in related signaling pathways. On the other hand, GSEA revealed that functions associated with T and B cell activation were obviously enriched in HF patients and subjects with high VCAM1 expression, providing additional evidence that VCAM1 is related to the regulation of immune cell infiltration in HF.
We also established a risk model of HF that showed good performance in the training and validation cohorts. This could benefit clinical application in predicting the risk of HF and serve as single biomarker in risk prediction. With regard to HF therapies, there have been limited studies on those targeting VCAM1, and our results may provide evidence for future treatments.