EMSCs-derived exosomes rescue p75NTR^-/- -mediated osteogenesis deficiency via PI3K/Akt/ERK1/2 signaling pathways

The repair of the critical-sized bone defects remains a major challenge for orthopedic surgeons, particularly when osteogenesis is impaired by p75 neurotrophin receptor (p75NTR) deficiency. However, the underlying molecular mechanisms are not fully understood. This study aimed to clarify the role of p75NTR in bone regeneration and to develop a cell-free approach to rescue p75NTR^-/- deficiency-mediated osteogenic deficiency through a controlled releasing of wild-type ectomesenchymal stem cells exosomes (WT-Exo) which were incorporated into silk fibroin/polycaprolactone_2:5/polyvinyl alcohol (SF/PCL_2:5/PVA) coaxial nanofibrous membranes. p75NTR^-/- mice exhibited a reduced bone mass and delayed ossification, while WT-Exo-loaded membranes partially restored osteogenic deficiency in p75NTR^-/- cells and enhanced expression of osteogenic markers such as alkaline phosphatase (ALP), collagen type I (Col-I), osteopontin (OPN) and runt-related transcription factor 2 (Runx2) aaccompanied by activating of phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway. Following implantation of the WT-Exo-loaded membranes into the critical-sized cranial defects in p75NTR^-/- mice, new bone formation in the defect site was significantly improved by a sustained release of WT-Exo. Overall, the findings in this study highlighted the critical role of p75NTR in osteogenic differentiation of ectomesenchymal stem cells (EMSCs) and demonstrated that WT-Exo, delivered via the coaxial electrospun membranes, represented an effective cell-free intervention method to reverse bone formation deficiency caused by p75NTR deficiency, providing a promising strategy for gene deficiency-related bone diseases.