Mechanistic Study on MSC-EXO Loaded with Salubrinal for the Treatment of Osteomyelitis-Induced Bone Defects

Osteomyelitis-related bone defects arise from bacterial infection-induced tissue damage and inadequate repair, resulting in pain, swelling, and functional loss. Here, we evaluated locally delivered salubrinal-loaded mesenchymal stem cell-derived exosomes (Sal-MSC-exo) in a rat model of infectious osteomyelitis. After characterizing MSCs, their exosomes, and drug-loading efficiency, we established a Staphylococcus aureus-induced osteomyelitis model and assigned rats to five groups: control, infected, salubrinal (Sal), exosome (Exo), and Sal-MSC-exo. Outcomes included histology and micro-CT, osteoblast proliferation (EdU), ER ultrastructure (electron microscopy), immunohistochemistry, Western blotting, and cell migration assays (transwell and scratch). These analyses assessed osteoblast proliferation and apoptosis, ER-stress signaling, extracellular matrix proteins, autophagy-related markers, and inflammatory activation. Sal-MSC-exo partially restored trabecular architecture, suppressed osteoblast apoptosis, and enhanced osteoblast migration compared with infected controls and single-agent groups. Mechanistically, Sal-MSC-exo attenuated ER stress, evidenced by upregulation of p-eIF2α and ATF4 with concomitant reduction of CHOP. In parallel, Sal-MSC-exo modulated autophagy-associated with increased p-eIF2α, eIF2α, LC3-I/II, and ALP and reduced p62-consistent with relief of maladaptive ER-stress-autophagy cross talk. Collectively, these findings indicate that Sal-MSC-exo mitigates osteomyelitis-associated bone loss and supports bone repair, highlighting its translational potential as a localized therapy for infection-induced bone defects.