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 ac-cumulation 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 con-tent.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 rati-o,increased relative gene and protein expression of PCSK9,and elevated LDL-C levels,with statis-tically 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 expres-sion,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 signifi-cant 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 ex-pression,and elevated LDL-C levels(P＜0.01).Group G,compared with Group B,had de-creased 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 ather-osclerosis(AS).Elevated LDL-C is a significant risk factor for AS,and increased PCSK9 expres-sion 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 me-tabolism 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 up-stream regulatory gene of SIRT6,targets and inhibits SIRT6 transcription,thereby modulating his-tone acetylation,and may serve as a new target for early screening and prevention of dyslipidemia.