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Atherosclerosis (AS) is a chronic inflammatory disease of the vascular wall with multiple causes. AS is the primary pathological basis of cardiovascular disease and stroke. Moreover, carotid plaque rupture and thrombus formation are the main causes of ischemic stroke. Therefore, understanding the formation of carotid plaques may help improve the prediction and prevention of cardiovascular and cerebrovascular events. Endothelial cell dysfunction results in re-endothelialization and angiogenesis in atherosclerotic plaques, thus promoting plaque destabilization. The aim of the present study was to evaluate the effect of circular RNA (circRNA) molecules in serum exosomes (serum-Exos) from patients with stable plaque atherosclerosis (SA) and unstable/vulnerable plaque atherosclerosis (UA). Specifically, the effect of circRNA on human umbilical vein endothelial cell (HUVEC) behavior and the mechanisms underlying plaque destabilization in AS were evaluated. Serum-Exos were isolated, then identified using transmission electron microscopy, nanoparticle tracking analysis and western blotting. The serum-Exo-circRNA expression profile of patients with SA or UA was investigated using a circRNA array. The relationship between circRNA-006896 in serum-Exos and biochemical parameters of patients with SA and UA were analyzed using Spearman's correlation. In addition, HUVECs were incubated with serum-Exos for in vitro functional assays. The present study demonstrated that circRNAs expression profiles in SA and UA serum-Exos were significantly different, indicating a potential role for circRNAs in carotid plaque destabilization. The expression of circRNA-0006896 was positively correlated with triglyceride, low-density lipoprotein cholesterol (LDL-C) and C-reactive protein levels, and negatively correlated with albumin levels in patients with UA. However, circRNA-0006896 expression was positively correlated with LDL-C in patients with SA. Using bioinformatic analysis, a competing endogenous RNA (ceRNA) network was selected to study the regulatory roles of circRNA-0006896 in serum-Exos. Additionally, in HUVECs treated with serum-Exos derived from patients with UA, the expression of circRNA-0006896 in HUVECs was upregulated. This was accompanied by decreased expression of microRNA-1264 and SOCS3, increased levels of DNMT1 and phosphorylated STAT3. HUVEC proliferation and migration were significantly increased in the UA group, compared with the mock and SA groups. This finding indicates that the circRNA-0006896-miR-1264-DNMT1 axis plays an important role in carotid plaque destabilization by regulating the behavior of endothelial cells. Moreover, it suggests that circRNA-0006896 may represent a therapeutic target for controlling JNK/STAT3 signaling in HUVECs. Thus, this study may provide insight on potential interventions against vulnerable plaque formation in patients with AS.