To observe the changes of expression of microRNA-3976 (miR-3976) in serum and serum exosomes of patients with different Wagner grades of foot ulcers and explore the potential mechanism involved.

Peripheral blood serum samples of 28 patients with diabetic foot of different Wagner grades from Sun Yat-sen Memorial Hospital were used for RNA extraction or exosomal RNA extraction, and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used to verify the difference of miR-3976 expression among patients in different groups. The t-test was performed to compare serum and serum exosomal miR-3976 expression levels among different groups of patients. Fibroblasts and HaCaT cells were cultured in medium with mannitol or high or normal level of glucose, and the level of miR-3976 expression in these cells was further detected and analyzed by one-way ANOVA. Bioinformatic analysis was used to explore the function of miR-3976.

The expression of miR-3976 increased significantly in serum samples of patients with Wagner grades 3 and 4 disease compared with those with Wagner grades 0-2 (1.588±1.118 vs 1.068±0.108, t=3.256, P=0.0031). Serum exosomal miR-3976 increased more significantly than serum miR-3976 in patients with Wagner grades 3 and 4 (2.885±0.742 vs 1.156±0.220, t=2.435, P=0.0255). The level of miR-3976 expression increased significantly in fibroblasts treated with high sugar than in those treated with normal sugar (q=6.497, P<0.05) or mannitol (q=3.992, P<0.05), while there was no difference in HaCaT cells among different groups (F=0.249, P=0.789). Kytoencyclopedia of genes and genomes (KEGG) pathway enrichment analysis of target genes of miR-3976 indicated that the target genes are enriched most in the pathway of tight junction.

The upregulated expression of miRNA-3976 in patients with Wagner grades 3 and 4 diabetic foot may occur mainly in exosomes, which might mainly come from fibroblasts in the local wound. Exosomal miR-3976 may be transferred to cells involved in skin recovery and affect the expression of junctional molecules, thus inhibiting wound healing.