Study on biomarkers of homocysteine-induced transformation of vascular smooth muscle cells into foam cells

Homocysteine (Hcy) is an independent risk factor for atherosclerosis (AS). Hcy induces the transformation of vascular smooth muscle cells (VSMCs) into foam cells, which play a crucial role in this process. However, the detailed mechanism is still unclear. To identify the key regulatory proteins during this process and clarify the possible mechanism of Hcy-induced foam cell formation in VSMCs, thereby providing theoretical support for the intervention of AS. VSMCs were allocated into two groups: a control cohort and a group exposed to Hcy to simulate an AS-like state. Quantitative proteomic profiling was performed using the label-free quantitative DIA (LFQ-DIA) approach to detect differentially expressed proteins between these groups. To explore functional implications, enrichment analyses involving Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were conducted. Protein-protein interaction networks were constructed using the STRING database to identify central interactors. Target proteins were subsequently validated through parallel reaction monitoring (PRM). Furthermore, histological analyses (hematoxylin and eosin (HE) staining, Oil Red O staining), biochemical assays of lipid content (total cholesterol (TC) and triglycerides (TG)), and Western blot analysis were utilized to confirm the role and mechanism of identified proteins in the context of Hcy-driven foam cell conversion. The results showed that proteomic analysis identified 4804 proteins in total, of which 4799 passed missing-value filtering and were retained for downstream quantitative analysis. A total of 54 proteins were identified as differentially expressed using thresholds of adjusted p-value < 0.05 and fold change > 1.5. Among them, 13 proteins were upregulated, while 41 were downregulated in response to Hcy treatment. For PRM validation, 20 candidate proteins were selected according to proteomic evidence, biological relevance, and technical feasibility. Among them, 16 proteins (COX7C, STX5, UBQLN2, DDX50, TBCB, GSR, PCNP, CDV3, PEBP1, PPIA, S100A6, EIF4E2, UBQLN1, ARMC1, NUDCD2, and H1-2) showed the same direction of fold-change values as in the LFQ-DIA dataset, thereby underscoring the reliability of the proteomic analysis. Data are available via ProteomeXchange with identifier PXD064315. Histological staining demonstrated enhanced lipid accumulation, and the protein expression of the contraction phenotype marker a-SMA decreased, while the protein expression of the synthesis phenotype marker OPN increased. This indicates that Hcy induces VSMCs to transform from a contraction phenotype to a synthesis phenotype, resulting in the formation of foam cells. The protein levels of COX7C and sterol regulatory element-binding proteins (SREBP1C and SREBP2) were elevated upon Hcy exposure. Overexpression of COX7C further augmented the expression of SREBP1C and SREBP2, exacerbated lipid accumulation, and promoted foam cell transformation in Hcy-treated VSMCs. On the other hand, knockdown of COX7C had the opposite effect. Overall, the results of the present study suggest that COX7C plays a crucial regulatory role in Hcy-induced transformation of VSMCs into foam cells. Its pathogenic role is likely mediated through the upregulation of SREBP1C and SREBP2, thereby promoting lipid accumulation. These findings provide new insights into AS pathogenesis and identify COX7C maybe a potential therapeutic target.