Bone marrow stromal cell‐derived exosomal circular RNA improves diabetic foot ulcer wound healing by activating the nuclear factor erythroid 2‐related factor 2 pathway and inhibiting ferroptosis

Abstract Background Diabetic foot ulcer (DFU) remains a serious chronic diabetic complication that can lead to disability. CircRNA‐itchy E3 ubiquitin protein ligase (circ‐ITCH) was observed to be down‐regulated in diabetic retinopathy and diabetic nephropathy, and overexpression of circ‐ITCH could inhibit the processes of these diseases. However, the detailed physiological and pathological functions of circ‐ITCH in wound healing of DFU remain undetermined. Methods Exosomes derived from bone marrow stromal cells (BMSCs) were isolated and identified. Cell viability and angiogenesis of human umbilical vein endothelial cells (HUVECs) were evaluated by cell counting kit‐8 (CCK‐8) and tube formation assays, respectively. The interplays of circ‐ITCH, TATA‐Box‐binding protein associated factor 15 (TAF15) and nuclear factor erythroid 2‐related factor 2 (Nrf2) mRNA were analysed by RNA immunoprecipitation (RIP), fluorescence in situ hybridization (FISH) combined immunofluorescent staining and RNA pull‐down assays. qRT‐PCR, western blot or immunohistochemistry (IHC) were used to measure the expression of circ‐ITCH, TAF15, Nrf2, vascular endothelial growth factor (VEGFR) and ferroptosis‐related makers. The mice DFU model was established to verify the in vitro results. Results Circ‐ITCH was down‐regulated in in vitro and in vivo models of DFU. Deferoxamine (DFO), an iron chelating agent, improved the viability and angiogenic ability of high glucose (HG)‐treated HUVECs. Overexpression of circ‐ITCH or co‐cultured with exosomal circ‐ITCH from BMSCs could alleviate HG‐induced ferroptosis and improve the angiogenesis ability of HUVECs. Circ‐ITCH in HUVECs recruited TAF15 protein to stabilize Nrf2 mRNA, thus activating the Nrf2 signalling pathway and suppressing ferroptosis. Exosomal circ‐ITCH from BMSCs also accelerated the wound healing process by inhibiting ferroptosis in the DFU mice in a time‐dependent manner. Conclusion Exosomal circ‐ITCH from BMSCs inhibited ferroptosis and improved the angiogenesis of HUVECs through activation of the Nrf2 signalling pathway by recruiting TAF15 protein, ultimately accelerating the wound healing process in DFU.