DNA Tetrahedron Delivering miR‐21‐5p Promotes Senescent Bone Defects Repair through Synergistic Regulation of Osteogenesis and Angiogenesis

Abstract Compromised osteogenesis and angiogenesis is the character of stem cell senescence, which brought difficulties for bone defects repairing in senescent microenvironment. As the most abundant bone‐related miRNA, miRNA‐21‐5p plays a crucial role in inducing osteogenic and angiogenic differentiation. However, highly efficient miR‐21‐5p delivery still confronts challenges including poor cellular uptake and easy degradation. Herein, TDN‐miR‐21‐5p nanocomplex is constructed based on DNA tetrahedral (TDN) and has great potential in promoting osteogenesis and alleviating senescence of senescent bone marrow stem cells (O‐BMSCs), simultaneously enhancing angiogenic capacity of senescent endothelial progenitor cells (O‐EPCs). Of note, the activation of AKT and Erk signaling pathway may direct regulatory mechanism of TDN‐miR‐21‐5p mediated osteogenesis and senescence of O‐BMSCs. Also, TDN‐miR‐21‐5p can indirectly mediate osteogenesis and senescence of O‐BMSCs through pro‐angiogenic growth factors secreted from O‐EPCs. In addition, gelatin methacryloyl (GelMA) hydrogels are mixed with TDN and TDN‐miR‐21‐5p to fabricate delivery scaffolds. TDN‐miR‐21‐5p@GelMA scaffold exhibits greater bone repair with increased expression of osteogenic‐ and angiogenic‐related markers in senescent critical‐size cranial defects in vivo. Collectively, TDN‐miR‐21‐5p can alleviate senescence and induce osteogenesis and angiogenesis in senescent microenvironment, which provides a novel candidate strategy for senescent bone repair and widen clinical application of TDNs‐based gene therapy.