Trb3-Directed Target Therapy for Treating Osteoporotic Bone Defects

Objectives: Age-related osteoporosis, a leading public health concern, is characterized by metabolic imbalance and abnormal bone remodeling due to reduced bone mass and increased marrow fat. Regenerating bone injuries, especially in osteoporotic conditions, remains challenging. Dysregulated differentiation of mesenchymal stem cells (MSCs) within marrow causes an increase in adipocytes at the expense of osteoblasts, exacerbating osteoporosis. Modulating MSC lineage commitment emerges as a promising therapeutic strategy for combating osteoporotic bone loss. Trb3 was identified as a critical molecular switch governing MSC lineage fate. This study aims to investigate the therapeutic potential of targeting Trb3 for bone defect repair in osteoporosis.
Methods: Previous investigations have shown that exosome mimetics (EMs) enriched with endogenous therapeutic molecules can significantly enhance bone regeneration. Here, we developed modified EMs expressing endogenous Trb3 (EM-Trb3) through small molecule-treating hMSCs followed by an extrusion approach. The characterization of EM-Trb3 was conducted. The in-vitro osteogenic/adipogenic effects of EM-Trb3 were assessed using various molecular techniques. For in-vivo bone repair, EM-Trb3 was loaded onto an apatite-coated PLGA scaffold to create an EM-Trb3/scaffold complex. The characteristics of the complex were examined.
Results: Our results showed a significant increase of endogenous Trb3 expression in EM-Trb3. EM-Trb3 significantly enhanced MSC osteogenesis, indicated by increased expression levels of osteogenic genes, elevated ALP activity, and mineral deposition. Conversely, EM-Trb3 inhibited MSC adipogenesis, demonstrated by reduced adipogenic marker expression. Furthermore, the EM-Trb3/scaffold complex exhibited excellent cellular viability and effective osteogenesis, along with suppressed adipogenesis. Mechanistically, EM-Trb3 mediated the pro-osteogenic and anti-adipogenic effects by regulating Wnt/beta-catenin signaling.
Conclusions: EM-Trb3 effectively modulates the balance between osteogenesis and adipogenesis. These findings provide a substantial foundation for investigating bone defect repair in an ovariectomized mouse model. Successfully completing these studies holds promise for translating this approach into large bone defect reconstruction in osteoporotic patients.