Introduction: Generalized osteopenia has been well reported in adolescent idiopathic scoliosis (AIS). Runx2 is an important transcription factor in regulating osteoblast differentiation and maturation. It was also known that osteoblasts synthesized receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) are key factors in regulating osteoclasts activity. Abnormal expressions of Runx2, RANKL and OPG have been reported in bone mesenchymal stem cells from AIS. Significant higher serum RANKL/OPG ratio was also reported in AIS.
Objectives: To investigate the expression of Runx2, RANKL and OPG in osteoblasts from AIS and their association with the bone mineral density (BMD).
Materials and Methods: 28 AIS (12~18yrs) and 8 age-matched control were recruited in this pilot study. BMD of lumbar spine and proximal femur was measured using DEXA. Cancellous bone biopsies were harvested for osteoblasts primary culture. The mRNA and protein expression of Runx2, RANKL and OPG were detected by RT-PCR and Western blotting, respectively.
Results: AIS patients showed significantly lower BMD than control group. In 20 AIS patients with RANKL and OPG determined, the RANKL/OPG ratio was significantly higher when compare to control. By grouping with BMD result, the expression of Runx2 was similar in AIS with normal BMD (n=15) and control but significantly lower in AIS with low BMD (n=13).
Conclusion: AIS patients with reduced BMD have decreased expression of Runx2 but higher RANKL/OPG ratio in osteoblasts, indicating a lower activity in osteoblasts but higher activity of osteoclasts.
Significance: Both osteoblast and osteoclast were likely to be involved in the pathogenesis of osteopenia in AIS.