Promotion of osteogenesis in BMSC under hypoxia by ATF4 via the PERK-eIF2α signaling pathway

Mandibular distraction osteogenesis (MDO) is an endogenous tissue engineering technology in which bone marrow mesenchymal stem cells (BMSC) play a key role in MDO-related osteogenesis. Activating transcription factor 4 (ATF4) is involved in osteogenesis through activation of PERK (Protein kinase R-like endoplasmic reticulum kinase) in endoplasmic reticulum stress (ERS) condition under hypoxia. However, the specific role of ATF4 in MDO with BMSC remains unknown. The aim of this study was to explore the effects of ATF4 in MDO with BMSC under hypoxia. Briefly, canine BMSCs were cultured in a hypoxic chamber, and effects of hypoxia were evaluated using cell migration assay and Alizarin Red S staining. Expression levels of protein kinase R-like endoplasmic reticulum kinase, eukaryotic translation initiation factor 2 alpha, ATF4, osteocalcin, and bone sialoprotein were evaluated using quantitative polymerase chain reaction and western blotting. BMSCs were transduced with the ATF4-small interfering RNA lentivirus. The effects were evaluated using all the aforementioned experiments. The results showed that hypoxia promoted migration, osteoblast differentiation, and ATF4 expression in BMSC. ATF4 knockdown in BMSC significantly inhibited migration and osteoblast differentiation abilities, while hypoxia reversed these effects to some extent. In addition, the molecular mechanism partly depended on the ERS signaling pathway, with ATF4 as the key factor. In summary, we presented a novel mechanism of ATF4-mediated regulation of BMSC under hypoxia.