Placenta-derived small extracellular vesicles transfer miR-520d-5p to mediate pancreatic β-cell injury in gestational diabetes mellitus by targeting SIRT1

BACKGROUND: Small extracellular vesicles (sEV) mediate intercellular communication in gestational diabetes mellitus (GDM). However, the mechanisms by which GDM-derived placental sEV induce pancreatic islet cell injury remain unclear. Here, we investigated the functions and underlying mechanisms of placenta-derived sEV (Pd-sEV)-associated miRNAs in GDM. METHODS: Pregnant women with normal glucose tolerance (NGT) or GDM were recruited, and clinical characteristics and inflammatory indices were assessed. Pd-sEVs were isolated and characterized. The effects of GDM-derived Pd-sEVs on insulin secretion and apoptosis in β-cells were evaluated. Following miRNA sequencing and diagnostic assessment, bioinformatic analysis identified downstream targets. Finally, miRNA mimics, specific inhibitors, and Sirtuin 1 (SIRT1) overexpression, and enzymatic activity assays were used to validate the regulatory mechanisms. RESULTS: GDM patients exhibited a sustained inflammatory state and significantly elevated levels of Pd-sEVs. These GDM-derived Pd-sEVs were efficiently internalized by β-cells, impairing glucose-stimulated insulin secretion (GSIS) and inducing apoptosis. Sequencing revealed selective alterations in the miRNA profile in GDM-sEV, with 4 significantly upregulated and 11 downregulated miRNAs. Among these, miR-520d-5p showed the most robust alteration in vivo and demonstrated the highest diagnostic sensitivity and specificity. Notably, circulating miR-520d-5p levels positively correlated with 75-g oral glucose tolerance test (OGTT) glucose levels. Bioinformatics analysis identified 707 high-confidence target genes, with SIRT1 identified as a core gene. Additionally, miR-520d-5p mimics or GDM-derived Pd-sEVs significantly reduced SIRT1 levels and impaired its enzymatic deacetylation activity. Mechanistically, miR-520d-5p directly targeted the SIRT1 3'-UTR, while miR-520d-5p inhibition or SIRT1 overexpression significantly attenuated the Pd-sEV-induced functional defects. CONCLUSIONS: This study supports that miR-520d-5p shuttled by Pd-sEVs mediates pancreatic β-cell injury in GDM via targeting SIRT1. These findings suggest that Pd-sEV-associated miR-520d-5p serves as a promising diagnostic biomarker, and targeting the miR-520d-5p/SIRT1 axis offers a potential therapeutic strategy for preserving β-cell function in GDM.