Isoquercitrin protects HUVECs against high glucose‑induced apoptosis through regulating p53 proteasomal degradation.

High glucose (HG)‑induced endothelial apoptosis serves an important role in the vascular dysfunction associated with diabetes mellitus (DM). It has been reported that isoquercitrin (IQC), a flavonoid glucoside, possesses an anti‑DM effect, but the mechanism requires further investigation. The present study investigated the effect of IQC against HG‑induced apoptosis in human umbilical vein endothelial cells (HUVECs) and explored its molecular mechanism. HUVECs were treated with 5 or 30 mM glucose for 48 h. Endothelial cell viability was monitored using the Cell Counting Kit‑8 assay. Mitochondrial membrane potential was detected by JC‑1 staining. Apoptosis was observed by TUNEL staining and flow cytometry. Western blotting was used for the analysis of apoptosis‑associated proteins Bax, Bcl‑2, cleaved (C)‑caspase3, total‑caspase3, p53 and phosphorylated p53. Reverse transcription‑quantitative PCR was used to analyze the mRNA expression levels of Bax, Bcl‑2 and p53. Immunofluorescence staining was utilized to detect the expression levels and distribution of p53 and ubiquitin specific peptidase 10 (USP10) in HUVECs. The results revealed that IQC significantly attenuated HG‑induced endothelial apoptosis, as shown by decreased apoptotic cells observed by TUNEL, JC‑1 staining and flow cytometry. Moreover, under HG stress, IQC treatment markedly inhibited the increased expression levels of the pro‑apoptotic proteins p53, Bax and C‑caspase3, and increased the expression levels of the anti‑apoptotic protein Bcl‑2 in HUVECs. However, the anti‑apoptotic effect of IQC against HG was partially blunted by increasing p53 protein levels in vitro. IQC influenced the mRNA expression levels of Bax and Bcl‑2 in response to HG, but it did not affect the transcription of p53. Notably, IQC inhibited the HG‑induced phosphorylation of p53 at Ser15 and the nuclear transport of USP10, destabilizing p53 and increasing the proteasomal degradation of the p53 protein. The current findings revealed that IQC exerted a protective effect against the HG‑induced apoptosis of endothelial cells by regulating the proteasomal degradation of the p53 protein, suggesting that IQC may be used as a novel therapeutic compound to ameliorate DM‑induced vascular complications.