Acute myocardial infarction (AMI) refers to hypoxia caused by coronary atherosclerosis stenosis and myocardial necrosis caused by acute and persistent ischemia 18. Dyslipidemia is a known risk factor for AMI 19, and lipid-lowering therapy is the treatment cornerstone. Several convincing studies have shown that the combined effect of lowering triglyceride, LDL cholesterol, and total cholesterol levels yield higher cardiovascular risk than lowering LDL cholesterol levels alone 20–22. The accumulated molecular genetic data indicate that many genes are related to AMI occurrence, including lipid-related genes 23. However, the lipid-related genes involved in AMI have not been completely identified. Thus, it is necessary to comprehend the role of lipid-related genes in AMI diagnosis and treatment.
Herein, we retrieved data of AMI patients (GSE66360) and subjected it to differential genes analysis, and identified lipid-related DEGs associated with AMI. Lipid-related DEGs were then subjected to GO and KEGG enrichment analyses. LASSO regression is a machine learning method that recognizes variables by looking for a λ value for a minimal classification error 24. SVM-RFE is another machine learning method that finds optimal variables through subtracting SVM-generated feature vectors 25. We used these two algorithms to screen characteristic variables and created an optimal classification model. Four lipid-related genes (ASCL1, CH25H, GPCPD1, and PLA2G12A) were identified based on these two models, which significantly impact AMI diagnosis. Moreover, the findings of CH25H were controversial compared with previous studies and should be interpreted with caution. Nevertheless, the p values of these four lipid-related genes were < 0.05, verified by RT-qPCR and consistent with our bioinformatic analysis results.
ACSL1 is a key rate-limiting enzyme in lipid metabolism 26, catalyzing the energy production of fatty acids or the production of phospholipids, cholesterol esters, and triglycerides 27. Previous studies have shown that heart-specific overexpression of ACSL1 in mice increases triglyceride accumulation in cardiomyocytes 28. Yuanlong Li et al. demonstrated that inhibiting ACSL1 expression in the heart can reduce lipid metabolism and promote the regeneration of cardiomyocytes 29. A cohort study has shown that the expression level of ACSL1 in peripheral blood leukocytes of AMI patients was higher than that of healthy controls, and this high expression was a risk factor for AMI 30. These results supported the findings of our bioinformatic analysis and suggested that ACSL1 might be a promising AMI biomarker. Moreover, PLA2G12A is a secreted phospholipase A2, but its physiological function is largely unclear. In humans, there is a suggestive association between a PLA2G12A polymorphism and response to anti-vascular endothelial growth factor therapy in patients with exudative age-related macular degeneration 31. Nicolaou, A et al. showed that PLA2G12A is highly expressed in aortic endothelial cells in vivo and may inhibit atherosclerosis by reducing the adhesion properties of vascular endothelial cells, which confirmed PLA2G12A as a candidate gene for atherosclerosis protection 32. This was consistent with our findings that PLA2G12A was downregulated in AMI samples and was a protective gene, possibly by reducing vascular adhesion to decrease AMI incidence.
CH25H regulates cholesterol and lipid metabolism by converting cholesterol to 25-HC, and plays an important role in regulating cellular inflammatory states and cholesterol biosynthesis in endothelial cells and monocytes 33. Elizabeth S et al. showed that 25-HC production promotes the formation of macrophage foam cells and increases susceptibility to atherosclerosis, thereby increasing AMI risk 34. However, the pro-inflammatory role of CH25H in atherosclerosis remains controversial. Other studies have shown that CH25H is involved in macrophages' functional endothelium and anti-inflammatory phenotype and that CH25H ablation increases susceptibility to atherosclerosis 35. Our current study suggested that CH25H was upregulated in AMI samples, consistent with the Elizabeth S et al. results. This contradiction might be partly due to different experimental conditions requiring further study. Additionally, GPCPD1 is a key enzyme in choline and phospholipid metabolism. It can cleave glycerophocholine to form glycerol-3-phosphate and choline 36. GPCPD1 has been reported to promote cell migration, metastasis, adhesion, and diffusion in breast, endometrial, and ovarian cancers. However, its biological role in cardiovascular disease remains unclear. Hence, more studies are needed to further verify our current findings.
The functional analyses were also performed to evaluate the potential biological functions of lipid-related DEGs. The GO enrichment analysis showed that these genes were closely related to fatty acid metabolism. Furthermore, the KEGG enrichment analysis revealed that the lipid-related genes were primarily associated with the PPAP signaling pathway. PPAR is activated by fatty acids and their derivatives, thereby creating a lipid signaling network between the cell surface and the nucleus 37. As lipid sensors and master regulators, PPAR controls the expression of genes that function in lipid metabolism 38. The PPAR signaling pathway, a crossing regulator of lipid signaling and inflammation, 37 was enriched, indicating that it plays a crucial role in lipid metabolism response to AMI. A previous study has found that the downregulation of PPARγ contributes to the activation and aggregation, eventually forming micro-thromboses, finally leading to myocardial dysfunction 39. These results indicated that these lipid-related genes might affect AMI occurrence through the PPAR signaling pathway. Further research is required to confirm the biological functions of lipid-related DEGs.
However, our current study also has some limitations. First, we used the dataset from circulating endothelial cells to perform the bioinformatics analysis, and used the peripheral blood mononuclear cells from myocardial infarction and normal people for verification. Although there was some sample heterogeneity, our research, like other studies using GSE66360 dataset 40–42, obtained a satisfactory result, which fully supported our conclusion. However, more studies are needed to further confirm our findings. Second, the included clinical samples were relatively small. Therefore, our conclusions must be verified by a larger AMI cohort. Third, lipid-related DEGs were only confirmed in clinical samples, and their potential functions were not demonstrated in AMI cells or animal models. Hence, more in vivo and in vitro studies are needed to clarify the underlying mechanisms of these key genes in AMI.