Objective  Low-density lipoprotein cholesterol (LDL-C) is causally associated with atherosclerotic cardiovascular disease (ASCVD). Proprotein convertase subtilisin/kexin type 9 (PCSK9) increases the degradation of low-density lipoprotein receptor (LDL-R), thereby promoting lipid accumulation. This study investigated the mechanism of microRNA(miRNA)-125a-5p in regulating PCSK9 transcriptional expression and lipid accumulation through histone deacetylase sirtuin 6 (SIRT6)-mediated histone acetylation.

Methods  RAW264.7 macrophages exposed to oxidized low-density lipoprotein (ox-LDL) were used to establish a macrophage lipid accumulation model. The cells were divided into eight groups: control group (Group A), ox-LDL group (Group B), SIRT6 agonist group (Group C), si-SIRT6 group (Group D), miR-125a-5p mimic group (Group E), miR-125a-5p mimic negative control group (Group F), miR-125a-5p inhibitor group (Group G), and miR-125a-5p inhibitor negative control group (Group H). Oil red O staining was used to verify lipid accumulation in macrophages. Real-time fluorescent quantitative polymerase chain reaction (PCR) was employed to detect the gene expression levels of miR-125a-5p, SIRT6 and PCSK9. Western blotting was used to detect the protein expression levels of SIRT6, histone 3 lysine 9 acetylation (H3K9ac), histone 3 (H3), and PCSK9. An LDL-C kit was used to measure cellular LDL-C content.

Results  Compared with Group A, Group B exhibited increased relative gene expression of miR-125a-5p, decreased relative SIRT6 gene and its protein expression, increased H3K9ac/H3 ratio, increased relative gene and protein expression of PCSK9, and elevated LDL-C levels, with statistically significant differences (P < 0.01). In Group B, a positive correlation was observed between H3K9ac and PCSK9 protein expression (r=0.935 0, P < 0.01), as well as between PCSK9 and LDL-C (r=0.981 3, P < 0.01). Compared with Group B, Group C showed no significant change in miR-125a-5p expression (P>0.05), but increased relative SIRT6 gene and its protein expression, decreased H3K9ac/H3 ratio, decreased relative gene and protein expression of PCSK9, and reduced LDL-C levels (P < 0.01). In contrast, Group D, compared with Group B, had no significant change in miR-125a-5p gene expression (P>0.05), but decreased relative gene and protein expression of SIRT6, increased H3K9ac/H3 ratio, increased relative PCSK9 gene and its protein expression, and elevated LDL-C levels (P < 0.05 or P < 0.01). Group E, compared with Group B, showed increased relative gene expression of miR-125a-5p, decreased relative SIRT6 gene and its protein expression, increased H3K9ac/H3, increased relative PCSK9 gene and its protein expression, and elevated LDL-C levels (P < 0.01). Group G, compared with Group B, had decreased relative gene expression of miR-125a-5p, increased relative gene and protein expression of SIRT6, decreased H3K9ac/H3 ratio, decreased relative PCSK9 gene and protein expression, and reduced LDL-C levels (P < 0.01). No significant changes were observed in miR-125a-5p, SIRT6, H3K9ac/H3 ratio, PCSK9, or LDL-C levels in Groups F and H compared with Group B (P>0.05).

Conclusion  Epigenetics is an important regulatory mechanism in the development of atherosclerosis (AS). Elevated LDL-C is a significant risk factor for AS, and increased PCSK9 expression exacerbates lipid accumulation. Imbalance in histone acetylation is a novel mechanism involved in PCSK9-mediated lipid accumulation, potentially serving as an early detection marker for lipid metabolism disorders. SIRT6 acts as a protective factor by reversibly regulating PCSK9 transcriptional expression, reducing lipid accumulation, and delaying AS progression. MiR-125a-5p, as an upstream regulatory gene of SIRT6, targets and inhibits SIRT6 transcription, thereby modulating histone acetylation, and may serve as a new target for early screening and prevention of dyslipidemia.