Rapamycin-induced small extracellular vesicles under GelMA scaffolds facilitate diabetic wound repair through accelerating angiogenesis and alleviating macrophage-mediated inflammation via PI3K/Akt signaling pathway

Recently, small extracellular vesicles (sEVs) isolated from mesenchymal stem cells (MSCs) show superior therapeutic potential in diabetic wound repair. Pretreated MSCs with biological or chemical agents could boost the activities of MSC-derived sEVs. This study aims to investigate whether sEVs derived from the human umbilical cord MSCs (hUCMSCs) pretreated with rapamycin (RAPA) exhibit elevated efficacy in improving diabetic wound healing and to elucidate the underlying mechanisms involved. The sEVs extracted from RAPA pretreated hUCMSCs (RAPA-sEVs) were successfully characterized in terms of their morphology, structural features, and concentration. In vitro studies revealed that RAPA-sEVs suppressed the proliferative and migratory capabilities of macrophages and reduced the expression of pro-inflammatory mediators including TNF-α, IL-1β and iNOS. Meanwhile, they promoted the migration and tube formation of endothelial cells, and increased the level of VEGF. More importantly, full-thickness skin defect models were established in streptozotocin (STZ)-induced diabetic mice. Gelatin methacryloyl (GelMA) carrying sEVs applied to the surface of damaged skin. RAPA-sEVs exhibited exceptional efficacy in accelerating the wound repair via propelling angiogenesis, reducing the percentage of M1-type macrophages, and mitigating excessive inflammatory response under superior biosafety conditions. Mechanistically, the biological activities of RAPA-sEVs were dependent on the PI3K/Akt signaling pathway, and the pro-angiogenic and anti-inflammatory effects of RAPA-sEVs were alleviated after the pathway being inhibited by a PI3K inhibitor PI103. Overall, RAPA-sEVs-based therapy might serve as a promising strategy for diabetic wound healing through fueling angiogenesis and alleviating macrophage-mediated inflammation via activating PI3K/Akt signaling pathway.