Transcription Factor Runx2 in the Low Bone Mineral Density of Girls with Adolescent Idiopathic Scoliosis

Objective: The molecular mechanism of low bone mass in girls with adolescent idiopathic scoliosis (AIS) has not been ascertained. Runx2 is a critical transcription factor regulating osteoblast differentiation and maturation. The present study aimed to explore the possible relationship between Runx2 expression in osteoblasts and bone mineral density (BMD) in subjects with AIS. Methods: Twenty-two girls with AIS scheduled to corrective surgery with iliac crest as donor site of autograft for spinal fusion were recruited. The BMD of lumbar spine and femoral neck were assessed by dual-energy X-ray absorptiometry, then patients were divided into two groups with either normal or reduced BMD. Cancellous bone was harvested from their iliac crests for primary culture of osteoblasts. mRNA and protein expression of Runx2 were assayed by reverse transcription-polymerase chain reaction and western blotting, respectively. Results were compared between the two groups and correlated with BMD. Results: AIS patients with normal BMD showed comparable maturity and body mass index but significant lower Cobb angle of main curve than those of patients with reduced BMD. The mean BMD of lumbar spine and femoral neck were 0.993 g/m(2) and 0.911 g/m(2) in patients with normal BMD, and were 0.757 g/m(2) and 0.733 g/m(2) in those with reduced BMD, respectively. The differences were significant between two groups (P < 0.05). The relative mean mRNA and protein expression of Runx2 were 0.49 +/- 0.12 and 0.062 +/- 0.020 in AIS with normal BMD, 0.35 +/- 0.12 and 0.042 +/- 0.006 in AIS with reduced BMD, respectively. Significantly lower Runx2 mRNA and protein expression were found in patients with AIS patients with reduced BMD than in those with normal BMD (P < 0.05). After controlling for age, weight and body mass index, positive correlations were found between Runx2 expression of both mRNA and protein and BMD of lumbar spine and femoral neck. Conclusion: The abnormal expression of Runx2 in patients with AIS and reduced BMD indicates abnormal regulation of differentiation of their osteoblasts. Runx2 may play an important role in the pathogenesis of reduced BMD in patients with AIS.