TDNs

Accumulating evidence supports an important role of phospholipase D3 (PLD3) in the pathogenesis of Alzheimer's disease (AD), while the actual expression level and distribution of PLD3 remains controversial in AD. Developing specific nanoprobes could be a promising strategy to understand PLD3 better, but there are limited approaches available in this field for a simple, reliable, and biocompatible biosensor. In this work, we report a PLD3-induced fluorescence resonance energy transfer (FRET) nanoprobe utilizing tetrahedral DNA nanostructures (TDNs) for visualizing the fluctuation of PLD3 at organ and subcellular levels in AD. Hydrolysis of PLD3 to a specific nucleotide strand on TDN will turn the FRET probe to an OFF state, which results in changes in fluorescent intensity. Immunofluorescent staining of brain sections proved the reliability of TDN nanoprobe to visualize PLD3 and the upregulation of PLD3 was observed in AD mice. Subsequent application of the nanoprobe uncovered PLD3 in the heart tissue of AD mice for the first time. Further investigations on the cellular level revealed a good colocalization of TDN nanoprobes with lysosomes in normal neurons, while their fluorescent signal overlaps better with mitochondria than lysosomes in AD neurons. Our finding provides not only insights into PLD3 but also an inspiring application of TDNs in the mechanism research of AD at multiple levels.

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.