Enrichment of miR-17-5p enhances the protective effects of EPC-EXs on vascular and skeletal muscle injury in a diabetic hind limb ischemia model.

Background/aims: Diabetes mellitus (DM) is highly susceptible to diabetic hind limb ischemia (DHI). MicroRNA (MiR)-17-5p is downregulated in DM and plays a key role in vascular protection. Endothelial progenitor cell (EPC)-released exosomes (EPC-EXs) contribute to vascular protection and ischemic tissue repair by transferring their contained miRs to target cells. Here, we investigated whether miR-17-5p-enriched EPC-EXs (EPC-EXs) had conspicuous effects on protecting vascular and skeletal muscle in DHI in vitro and in vivo.

Methods: EPCs transfected with scrambled control or miR-17-5p mimics were used to generate EPC-EXs and EPC-EXs. Db/db mice were subjected to hind limb ischemia. After the surgery, EPC-EXs and EPC-EXs were injected into the gastrocnemius muscle of the hind limb once every 7 days for 3 weeks. Blood flow, microvessel density, capillary angiogenesis, gastrocnemius muscle weight, structure integrity, and apoptosis in the hind limb were assessed. Vascular endothelial cells (ECs) and myoblast cells (C2C12 cells) were subjected to hypoxia plus high glucose (HG) and cocultured with EPC-EXs and EPC-EXs. A bioinformatics assay was used to analyze the potential target gene of miR-17-5p, the levels of SPRED1, PI3K, phosphorylated Akt, cleaved caspase-9 and cleaved caspase-3 were measured, and a PI3K inhibitor (LY294002) was used for pathway analysis.

Results: In the DHI mouse model, miR-17-5p was markedly decreased in hind limb vessels and muscle tissues, and infusion of EPC-EXs was more effective than EPC-EXs in increasing miR-17-5p levels, blood flow, microvessel density, and capillary angiogenesis, as well as in promoting muscle weight, force production and structural integrity while reducing apoptosis in gastrocnemius muscle. In Hypoxia plus HG-injured ECs and C2C12 cells, we found that EPC-EXs could deliver their carried miR-17-5p into target ECs and C2C12 cells and subsequently downregulate the target protein SPRED1 while increasing the levels of PI3K and phosphorylated Akt. EPC-EXs were more effective than EPC-EXs in decreasing apoptosis and necrosis while increasing viability, migration, and tube formation in Hypoxia plus HG-injured ECs and in decreasing apoptosis while increasing viability and myotube formation in C2C12 cells. These effects of EPC-EXs could be abolished by a PI3K inhibitor (LY294002).

Conclusion: Our results suggest that miR-17-5p promotes the beneficial effects of EPC-EXs on DHI by protecting vascular ECs and muscle cell functions.