Aptamer-functionalized tetrahedral framework nucleic acid delivery of siBhlhe22 for repairing osteoporotic bone defects via dual modulation of PI3K-Akt signaling and purine metabolism

Osteoporosis is characterized by an imbalance between bone formation and resorption, and the dysregulated differentiation of bone marrow mesenchymal stem cells (BMSCs) plays a central role. Our previous study identified Bhlhe22 as a key negative regulator of osteogenic differentiation; here, we further validate its role in osteoporotic BMSCs (OP-BMSCs) and investigate its therapeutic potential. Knocking down Bhlhe22 enhanced osteogenesis by upregulating key osteogenic markers (RUNX2, ALP, OPN) and suppressing the PI3K-Akt signaling pathway. To enable targeted delivery of siBhlhe22, we designed an aptamer-functionalized tetrahedral framework nucleic acid-based nanocarrier (Apt19S-tFNA-siBhlhe22, ATS). The ATS system exhibited well-defined nanostructure, excellent biocompatibility, and high cellular uptake efficiency in OP-BMSCs. In vitro, ATS-mediated Bhlhe22 knockdown significantly promoted osteogenic differentiation and matrix mineralization. This effect depended on the inhibition of PI3K-Akt signaling, as demonstrated by rescue experiments using the agonist Recilisib. Non-targeted metabolomics revealed that osteoporosis was associated with disruption of nucleotide and purine metabolism, which was effectively reversed by ATS treatment. Functional studies confirmed that intact purine metabolism, which was essential for ATP production and redox balance, was required for the pro-osteogenic effect of ATS. In an osteoporotic rat bone defect model, ATS delivered via GelMA hydrogel promoted bone regeneration. This was accompanied by in vivo suppression of PI3K-Akt signaling and upregulation of OCN and OPN. Our findings establish a novel gene therapy strategy that targets Bhlhe22 to simultaneously modulate pro-osteogenic signaling and metabolic reprogramming, offering a promising anabolic approach for osteoporosis treatment.