MSC-Derived Apoptotic Vesicles Restore Bone Marrow Niche Homeostasis in Postmenopausal Osteoporosis by miRNA-Mediated Suppression of MAPK and NF-κB Signaling Nodes.

Background

Postmenopausal osteoporosis is associated with cellular senescence and the accumulation of the senescence-associated secretory phenotype (SASP). While mesenchymal stem cell (MSC)-derived exosomes show tissue repair potential, the efficacy and mechanisms of MSC-derived apoptotic vesicles (apoVs) remain unclear. This study compared MSC-apoVs and exosomes in postmenopausal osteoporosis and investigated the underlying epigenetic mechanisms.

Methods

Therapeutic efficacy was evaluated in an ovariectomized (OVX) mouse model and senescent human bone marrow mesenchymal stem cells (hBMMSCs). Small RNA sequencing identified differential microRNA (miRNA) cargos between vesicle types. SASP-related cytokine expression (IL-6, TNF-α, MCP-1) and pathway activation were assessed by RT-qPCR, ELISA, and Western blot.

Results

MSC-apoV treatment attenuated bone loss in OVX mice and reduced SASP expression in senescent hBMMSCs to a greater extent than exosomes. Small RNA sequencing revealed that apoVs were enriched with a specific miRNA cluster, including hsa-let-7b-5p, hsa-miR-92a-3p, and hsa-miR-98-5p. Bioinformatic analyses identified BRAF and CRKL as downstream targets of this miRNA cluster, supported by reduced protein levels after apoV treatment. Subsequent molecular assays showed that apoV treatment inhibited the phosphorylation of both the MAPK (p38 and JNK) and NF-κB (p65) signaling pathways, which correlated with reduced local inflammation in the bone marrow microenvironment and preserved osteogenic differentiation capacity.

Conclusions

MSC-apoVs attenuate postmenopausal osteoporosis more effectively than exosomes. This enhanced efficacy is associated with the delivery of an enriched miRNA cluster that inhibits MAPK and NF-κB signaling, together with suppression of BRAF and CRKL protein expression. ApoVs may represent a cell-free therapeutic strategy for age-related bone loss.