DLX5 regulates the osteogenic differentiation of spinal ligaments cells derived from ossification of the posterior longitudinal ligament patients via NOTCH signaling

BACKGROUND: Ossification of the posterior longitudinal ligaments (OPLL) is common disorder characterized by heterotopic ossification of the spinal ligaments. Mechanical stimulation (MS) plays an important role in OPLL. DLX5 is an essential transcription factor required for osteoblast differentiation. However, the role of DLX5 during in OPLL is unclear. This study aims to investigate whether DLX5 is associated with OPLL progression under MS. METHODS: Stretch stimulation was applied to spinal ligaments cells derived from OPLL (OPLL cells) and non‐OPLL (non‐OPLL cells) patients. Expression of DLX5 and osteogenesis‐related genes were determined by quantitative real‐time polymerase chain reaction and Western blot. The osteogenic differentiation ability of the cells was measured using alkaline phosphatase (ALP) staining and alizarin red staining. The protein expression of DLX5 in the tissues and the nuclear translocation of NOTCH intracellular domain (NICD) was examined by immunofluorescence. RESULTS: Compared with non‐OPLL cells, OPLL cells expressed higher levels of DLX5 in vitro and vivo (p < 0.01). Upregulated expression of DLX5 and osteogenesis‐related genes (OSX, RUNX2, and OCN) were observed in OPLL cells induced with stretch stimulation and osteogenic medium, whereas there was no change in the non‐OPLL cells (p < 0.01). Cytoplasmic NICD protein translocated from the cytoplasm to the nucleus inducing DLX5 under stretch stimulation, which was reduced by the NOTCH signaling inhibitors (DAPT) (p < 0.01). CONCLUSIONS: These data suggest that DLX5 play a critical role in MS‐induced progression of OPLL through NOTCH signaling, which provides a new insight into the pathogenesis of OPLL.