Involvement of bone morphogenic protein‐2 (BMP‐2) in the pathological ossification process of the spinal ligament

Abstract
Objective. To investigate the function of bone morphogenic protein‐2 (BMP‐2) in the ossification of the spinal ligament (OSL). Methods. Total RNA was prepared from the cultured spinal ligament cells from patients with OSL and analysed by reverse transcription–polymerase chain reaction using specific primers for BMP‐2. BMP‐2 mRNA expression in ligament tissues was examined by in situ hybridization. Spinal ligament cells from patients without OSL were treated with BMP‐2 and examined for alkaline phosphatase activity. Results. Expression of the BMP‐2 gene was detected in cultured spinal ligament cells. In ligament tissues, BMP‐2 mRNA was present in the chondrocyte‐like cells in the fibrocartilage zone. Exogenous BMP‐2 increased alkaline phosphatase activity in spinal ligament cells from patients without OSL. Conclusion. The BMP‐2 gene is expressed in the spinal ligaments of OSL patients, and exogenous BMP‐2 stimulates osteogenic differentiation of spinal ligament cells. The expression of BMP‐2 in the spinal ligaments could be a clue in elucidating how heterotrophic osteogenesis develops in ligament tissue.