Although the early diagnosis and treatment of IA has been greatly improved, surgical treatment is still the only treatment for IA(17). Surgical risks and postoperative complications are still major problems in the treatment of IA. Therefore, exploring the formation and development mechanism of IA and finding potential drug therapy targets is expected to become a new therapeutic direction for IA(3). Inflammation and immune cell infiltration as important mechanisms for the growth and expansion of IA have been confirmed by many studies(4, 18–20). At present, although there are studies targeting inflammatory genes to treat IA, the results are not satisfactory(10). Therefore, this study will use bioinformatics combined with machine learning to find the core genes of inflammatory aneurysm formation, explore the potential mechanism of IA formation and discover IA inflammatory therapeutic targets, and provide a new direction for non-surgical treatment of IA.
We downloaded 2 datasets from the GEO database, and obtained a total of 74 differentially expressed inflammatory genes, including 58 up-regulated genes and 16 down-regulated genes, through differential analysis and intersection with inflammatory genes. We constructed a PPI network of these genes from the STRING database. Through the analysis of the PPI network, we found that there are complex regulatory relationships among these differentially expressed genes, and TLR4, as the core gene of the PPI network, has regulatory relationships with most of the genes in the network. At present, many studies have found that TLR4 plays an important role in the formation, expansion and rupture of IA. Kazuha Mitsui et al found that the TLR4 pathway promotes the development of intracranial aneurysm rupture by accelerating aneurysm wall inflammation, and TLR4 inhibition significantly reduced the rupture rate and proinflammatory cytokine levels of aneurysm rupture(21). Liang Liu et al. also found that TLR4 is associated with susceptibility to IA(22). Subsequently, we performed functional enrichment analysis on DEGs of inflammation. Results of BP and MF in GO enrichment analysis These genes were associated with inflammatory response, expression of inflammatory factors and regulation of inflammatory cells. The results of the MF analysis were mainly related to lipid metabolism. The study of Zhao et al. showed that inflammation-dependent hyperlipidemia is one of the mechanisms of aneurysm formation(23). The results of KEGG enrichment analysis were also related to inflammatory pathways and lipid metabolism pathways. Li et al. show that SRPK1 gene silencing increases vascular smooth muscle cell proliferation and vascular remodeling in IA through the PI3 K/Akt signaling pathway, which helps inhibit progression in arteries(24). By analyzing ruptured IA, Korostynski et al. found that Cytokine-cytokine receptor interaction is an important mechanism of IA rupture(25). The results of DO enrichment analysis indicated that the inflammatory DEGs obtained by our analysis were associated with vascular disease. Subsequently, we performed GSEA enrichment analysis, which showed that these genes were associated with inflammatory responses, immune regulation, and regulation of immune cells. The above analysis confirmed the accuracy of our results. It also demonstrated the important role of inflammatory response and immune cell infiltration in the formation, development and rupture of IA. Therefore, it is expected to be a safe and effective treatment for IA by regulating the expression of inflammatory genes and local immune cell infiltration. Identifying the core genes in the formation of IA through bioinformatics and machine learning, and clarifying the correlation between the expression of core genes and immune cells, is helpful for the non-surgical treatment of IA.
Based on two machine learning algorithms, 3 core genes were identified. Due to the important regulatory role of TLR4 in the PPI network, we also included it as a core gene in subsequent analyses. RTP4 encodes a protein associated with cell surface opioid receptor expression. No research on RTP4 in IA has been found so far. Of note is the important role of RTP4 in the immune response. For example, RTP4 can induce the body's immune response to malaria, reduce the virus titer in the brain of infected mice, and alleviate the neurological symptoms of the mice(26). Furthermore, RTP4 is required for antigen-dependent immunoediting of cancer cells using CRISPR screens(27). Therefore, we judged that RTP4 may play an important role in the formation of IA. However, further in vivo and in vitro experiments are still needed to prove it. CLEC7A, also known as dectin-1, is involved in various pathophysiological processes including infection, allergy, regulation of inflammation, cancer and other diseases(28). Studies have shown that Dectin-1 plays an important role in the immune regulation of the central system and can promote tolerance, anti-inflammatory and neuroprotective responses(29). Dectin-1 Regulating Macrophage Polarization and Neutrophil Infiltration in Myocardial Ischemia-Reperfusion Injury(30). Interestingly, the two types of immune cells mentioned above confirm important inflammatory cells in the formation and progression of intracranial aneurysms(31, 32).SOX11, a member of the SRY box (SOX) family, emerges as an important transcriptional regulator that controls cell fate and differentiation as a whole(33). It is also involved in regulating the inflammatory response in the body. The study by Feng et al found that the decrease of SOX11 expression can alleviate the inflammatory response in spinal cord injury(34).
Types of immune cell infiltration in IA and superficial temporal artery samples were assessed using CIBERSOTR. It was found that various immune cell subtypes were closely related to the important biological processes of IA. T cells regulatory (Tregs), Mast cells resting, decreased infiltration of Neutrophils and increased infiltration of Monocytes were found to be related to the formation and development of IA. In addition, through correlation analysis of CLEC7A, RTP4, SOX11, TLR4 and immune cells, it was found that CLEC7A, RTP4, SOX11 and TLR4 were all associated with T cells regulatory (Tregs) and Monocytes. Our findings were also confirmed in other studies. T cells regulatory (Tregs) can significantly reduce the incidence and severity of IA, but it is often present at low levels or insufficient activity in IA tissues T cells regulatory (Tregs) can significantly reduce the incidence and severity of IA, but it is often present at low levels or insufficient activity in IA tissues(35, 36). Sun et al. found that increasing the number of T cells regulatory (Tregs) is beneficial to improve the remodeling of IA cases(37). During homeostasis and inflammation, circulating monocytes can infiltrate the vasculature, where they develop into macrophages and regulate immune responses(20). Subsequently, the polarization of macrophages regulates the formation and progression of intracranial aneurysms by releasing cytokines and modulating the inflammatory response of other immune cells, as well as releasing different cytokines to regulate the process of extracellular matrix remodeling. Increased phagocytic infiltration is responsible for the formation and progression of IA(38). Zhang et al. found that monocytes promote a higher inflammatory state in IA by causing a loss of balance of CD4(+) T cell subsets(39).
However, the limitations of this study should also be acknowledged. First of all, our data are obtained from public datasets, and the reproducibility needs to be further verified. Secondly, the sample size of this study may still be insufficient, and the key genes and immune cell infiltration of IA cannot be well identified. In addition, some of the inflammatory hub genes we identified have not been studied in IA and need further experimental verification..