Currently, the number of AS patients worldwide is increasing annually, with a trend toward younger age groups, and the complications it causes place a significant burden on patients[21]. The pathogenesis of atherosclerosis is complex and involves multiple cell types, including endothelial cells (ECs), vascular smooth muscle cells (SMCs), adventitial fibroblasts, macrophages, and other immune cells. Key factors in the development of atherosclerosis include endothelial dysfunction, leukocyte adhesion, foam cell formation, and SMC phenotypic transformation[22–23]. Notably, the pathological progression of AS is closely linked to cellular senescence and ferroptosis. Cellular senescence is a cell state triggered by endogenous or exogenous stimuli, characterized by stable cell cycle arrest and a complex senescence-associated secretory phenotype (SASP). Once senescent cells accumulate in tissues, they can accelerate the progression of age-related diseases such as atherosclerosis, osteoarthritis, and cancer[24]. senescent endothelial cells reduce NO production and impair the endothelial barrier function due to disruptions in intercellular adhesion and tight junctions in AS, [25]. The extent of endothelial coverage in AS lesions is a key protective factor for plaque stability, and the erosion of endothelial cells can lead to atherosclerotic thrombosis on the lesion surface. Additionally, increased endothelial inflammation is considered a harmful process in the chronic inflammatory environment of arteries. Senescent endothelial cells can exacerbate the inflammatory response by increasing the expression of adhesion molecules such as VCAM-1 and ICAM-1, which enhances the recruitment of leukocytes[26–27]. Ferroptosis is a distinct form of iron-dependent, lipid peroxidation-driven programmed cell death. In recent years, it has increasingly been recognized as an important process mediating the onset and progression of various cardiovascular diseases, including atherosclerosis, myocardial ischemia-reperfusion injury, and septic cardiomyopathy[28]. Furthermore, AS patients often exhibit changes in peripheral blood immune components during disease onset, reflecting the disease's severity. Therefore, exploring immune-related biomarkers and potential therapeutic targets is a research focus in this field[14].
This study identified 23 ferroptosis- and senescence-related DEGs. Based on these genes, unsupervised clustering analysis was performed using a consensus clustering algorithm to identify AS-related subtypes, resulting in 421 subtype DEGs. Immune infiltration analysis of these 421 DEGs revealed differences in eight immune cell types between the two subtypes: activated dendritic cells, Macrophages M0, resting NK cells, plasma cells, naive CD4 T cells, follicular helper T cells, gamma delta T cells, and regulatory T cells (Tregs). Previous studies have shown that both the innate and adaptive immune systems play key roles in driving AS-related chronic inflammation, with significant heterogeneity among leukocyte subtypes in the arterial wall, which regulate inflammation in atherosclerosis formation[29]. This study also identified two diagnostic biomarkers through machine learning methods based on the 421 ferroptosis- and senescence-related subtype DEGs, providing insights into AS-related immune genes. Currently, many immune infiltration algorithms have revealed differences in immune cell infiltration between disease groups and controls in AS onset. Jing Wang[30] using bioinformatics methods, studied the role of immune cells in the formation of unstable plaques and explored diagnostic biomarkers. Their findings indicated that M1 macrophages are an important factor in unstable plaque formation, and CD68, PAM, and IGFBP6 can serve as diagnostic markers for identifying unstable plaques. In future research, predictive biomarkers should not only involve the composition of immune infiltration and the characteristics of the inflammatory response but also reveal the heterogeneity of immune composition, spatial distribution, and function. GO analysis of the differentially expressed genes indicated that AS lesions involve biological processes such as myeloid leukocyte activation, phagocytosis, leukocyte-mediated immunity, leukocyte migration, positive regulation of cytokine production, positive regulation of tumor necrosis factor superfamily cytokine production, pattern recognition receptor activity, and immune receptor activity. KEGG enrichment analysis showed that pathways such as the Toll-like receptor signaling pathway, chemokine signaling pathway, leukocyte transendothelial migration, lipid and atherosclerosis, PPAR signaling pathway, apoptosis, and NF-κB signaling pathway are associated with AS onset. This suggests that the mechanisms of AS are closely related to biological processes such as fatty acid metabolism, inflammatory response, and immune regulation. For example, PPARs are a class of ligand-activated transcription factors that regulate genes related to lipid metabolism. PPARα, one of its subtypes, is highly expressed in the heart and vascular walls and regulates target genes closely related to lipid metabolism and inflammation. Activation of the PPARα pathway can reduce autophagy-dependent ferroptosis caused by mitochondrial DNA damage and alleviate hyperlipidemia-induced vascular calcification[31]. Studies have also shown that senescent immune cells in AS undergo cell cycle arrest, morphological changes, and phenotypic alterations in their abundance and secretory profiles, including cytokines, chemokines, matrix metalloproteinases, and Toll-like receptor expression. Currently, the clearance of senescent cells is considered a key target for preventing or treating AS[32]. GSEA analysis showed that these gene sets are associated with the upregulation of the cellular senescence pathway and the NOD-like receptor signaling pathway, and the downregulation of cholesterol metabolism and ferroptosis pathways. Since the production of free radicals, increased fatty acid supply, and enhanced lipid peroxidation are key inducers of ferroptosis, they may influence ferroptosis by regulating lipid metabolism and fatty acid metabolism, thereby mediating the onset of AS[10, 33]. Senescence is associated with elevated levels of inflammatory cytokines in the aorta, and impaired vascular mitochondrial function accelerates the formation of AS. Of course, this requires further study[34]. Research has found that macrophages, vascular endothelial cells, and vascular smooth muscle cells are in a senescent state at atherosclerotic lesion sites. Additionally, bacterial infections and the accumulation of lipopolysaccharides have been observed in AS patients, along with a SASP. Therefore, some studies suggest that LPS derived from Gram-negative bacteria may exacerbate AS lesions by inducing and enhancing the senescence of specific vascular cells and SASP-associated inflammatory characteristics in AS lesions[35].
In recent years, machine learning has been widely applied in the clinical field and is considered an important tool in healthcare[36]. This study identified IL1B and CCL4 as ferroptosis- and senescence-related biomarkers for AS, and validation showed that these biomarkers have good diagnostic value for AS. Previous studies have confirmed that IL-1β is associated with acute and chronic inflammation and plays an immunoregulatory role in the development of AS. Anti-inflammatory treatment with canakinumab, targeting the IL-1β innate immune pathway, has been shown to significantly reduce the recurrence rate of cardiovascular events compared to placebo[37]. In APOE−/− mice, upregulation of IL-1β expression increased the area of atherosclerotic lesions in the ascending aorta and aortic root[38]. However, it is important to note that most previous studies on IL-1β have focused on its regulation of immune or inflammatory cells. Recent research has found that IL-1β can regulate iron-sulfur cluster homeostasis by inducing acetylation of the mitochondrial inner membrane protein NNT in tumor cells, thereby inhibiting ferroptosis and mediating resistance to immunotherapy[39]. This finding provides insights into potential AS treatments. Additionally, studies have shown that inhibiting the secretion of IL-1β can improve doxorubicin-induced senescence in cardiac fibroblasts and improve poor prognosis in heart disease[40].IL-1β, as a key biomarker of vascular calcification, may also be involved in the senescence of VSMCs. Linzi Han and colleagues found that IL-1β induces VSMC senescence and promotes VSMC calcification by activating the NF-κB/p53/p21 signaling pathway, which may be associated with AS plaque formation[41]. CCL4, also known as macrophage inflammatory protein MIP-1β, belongs to the CC chemokine family and can be secreted by monocytes, B cells, T cells, NK cells, dendritic cells, neutrophils, fibroblasts, endothelial cells, and epithelial cells[42]. Elevated levels of CCL4 have been reported in the peripheral blood of AS patients. Inhibiting CCL4 levels can reduce the activity of metalloproteinases-2 and − 9 in macrophages, suppress the production of TNF-α and IL-6, and decrease the activation of endothelial cells and macrophages, suggesting that CCL4 has potential as a new therapeutic target for AS[43]. Some studies hypothesize that CCL4 may also play a crucial role in aging-related vascular dysfunction. CCL4 promotes inflammation and cellular senescence by stimulating ROS production, leading to impaired cell function, and may be a potential therapeutic target for vascular protection during aging[44]. Currently, there is limited research on the relationship between CCL4 and ferroptosis. Future studies could explore the relationship between ferroptosis and immune cells during AS onset to develop new therapeutic strategies for AS.
Correlation analysis between Hub genes and immune cells revealed that the IL1B gene is significantly associated with T cells.follicular.helper and T cells.gamma.delta, while the CCL4 gene is significantly associated with T cells.follicular.helper and T cells.regulatory (Tregs). T cells.follicular.helper (Tfh) have recently been defined as a new subset of CD4 + T cells, primarily expressing surface molecules such as CXC chemokine receptor 5 and inducible costimulatory molecule, and secreting the cytokine interleukin-21. The key transcription factor for Tfh cells is B-cell lymphoma 6. Tfh cells are found in the germinal centers of lymphoid tissues and peripheral blood, where they promote B-cell maturation and differentiation, germinal center formation, and antibody production, playing an important role in the pathogenesis of various autoimmune diseases[45]. T cells.gamma.delta (γδT cells) are lymphocytes with multiple functions in innate and adaptive immune responses, pathogen defense, antigen presentation, and inflammation regulation, participating in the early development of atherosclerosis[46]. Duc M Vu revealed the pathogenic role of γδT cells in early AS formation through animal experiments, with a mechanism that may involve IL-17 production and neutrophil induction. Therefore, γδT cells are promising targets for AS intervention, potentially reducing plaque accumulation and inhibiting inflammatory responses[47]. Studies have shown that T cells.regulatory (Tregs) account for 5–10% of the total CD4 + T lymphocytes in peripheral blood and have been proven to have a protective effect against atherosclerosis, making them a new target for cardiovascular disease and atherosclerosis[48]. Monika Sharma[49] also found that in several mouse models of AS regression, an increase in Tregs was a common feature of plaque regression. In summary, the Hub genes are closely associated with these immune cells, leading us to speculate that CCL4 and IL1B may influence the onset and progression of AS by regulating these cells. Correlation analysis between CCL4 and IL1B with CF-DEGs revealed that these genes are highly correlated with PTPN6 and ZEB1.
The emergence of single-cell biology has opened a new chapter in understanding the biological processes of disease development and in diagnostics, monitoring, and treatment. This technology can identify novel cell populations that play critical roles in the progression of AS and assist in exploring new therapeutic strategies[50]. The infiltration of immune cells is closely related to the progression of AS and its response to immunotherapy. Studies using single-cell sequencing technology have explored the immune heterogeneity of atherosclerosis and identified interferon-induced CD8 + T cells and macrophage subpopulations as cells that influence AS progression and poor prognosis, which is of significant value for developing new AS immunotherapies[51]. In this study, 6 different cell types were identified through single-cell analysis, including ECs, Fibroblasts, Macrophages, Monocytes, T cells, and VSMC, providing a deeper understanding of the cellular diversity within atherosclerotic plaques and surrounding tissues. It was also found that the Hub gene IL1B is highly expressed in Macrophages and Monocytes, while CCL4 is significantly expressed in Macrophages, Monocytes, and T cells. Additionally, this study visualized the communication between different types of cells, confirming a close relationship between immune cells and stromal cells in the onset and progression of AS. Using the "Monocle3" package, the pseudotime algorithm was applied to single-cell RNA-Seq data to order and arrange individual cells based on their states during differentiation and other biological processes, revealing the connection between gene expression changes and cell fate determination[52]. Through this method, it was observed that IL1B and CCL4 expression levels change during the dynamic transition of macrophages and monocytes. These results suggest that Hub genes may influence the onset and progression of AS by regulating immune cell function.
This study has several limitations. First, the available AS-related RNA-seq and scRNA-seq datasets are limited, with small sample sizes. In the future, larger AS datasets will need to be analyzed to validate the findings derived from GSE10097, GSE132651, and GSE159677. Second, it should be noted that the key effectors involved in ferroptosis and cellular senescence pathways are mostly regulated at the post-translational level. Therefore, the post-translational levels of these molecules are crucial for maintaining cellular function and should be considered. This study is limited by the lack of corresponding proteomics data, as we only screened ferroptosis- and cellular senescence-related genes based on RNA-seq datasets. Additionally, at the beginning of the study, important diagnostic genes were screened solely from candidate genes related to ferroptosis and senescence. Consequently, only genes with significant diagnostic value were retained to establish the predictive model, while genes closely related to ferroptosis and senescence but with lower diagnostic value were excluded.