[STRESS REGULATING OSTEOGENIC DIFFERENTIATION OF HUMAN INTERVERTEBRAL DISC CARTILAGE ENDPLATE-DERIVED STEM CELLS]

To investigate the effect of cyclic stretch stress on the osteogenic differentiation of human cartilage endplate-derived stem cells (CESCs).

CESCs were isolated from the endplate cartilage tissues by the method of agarose suspension culture system. The endplate cartilage tissue was harvested for immunohistochemical staining. Flexercell-4000 Tension Plus system was used to apply cyclic stretch on CESCs at a frequency of 1 Hz and at a stretch rate of 10% for 1, 6, 12, or 24 hours (experimental group). No stretch stress was performed on CESCs in the same culture condition (control group). After mechanical loading, the protein expression of bone morphogenetic protein 2 (BMP-2) was measured by Western blot, and gene expressions of runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), and SOX9 were detected by real-time fluorescent quantitative PCR.

Immunohistochemical staining showed BMP-2 protein expression in chondrocytes. The continuous cyclic stretch stress of 10% can increase the expression of BMP-2 protein in CESCs. Significant differences were observed in the expressions of BMP-2 protein (P < 0.05) between 2 groups at the other time points except at 1 hour (P > 0.05), in a time-dependent manner. The real-time fluorescent quantitative PCR indicated that the gene expressions of Runx2 and ALP showed an increasing tendency with time in the experimental group when compared with the control group, but there was down-regulated expression of SOX9. Significant difference was found in mRNA expressions of Runx2 and ALP at 12 and 24 hours and in mRNA expressions of SOX9 at 6, 12, and 24 hours between 2 groups (P < 0.05), in a time-dependent manner.

Cyclic stretch stress may induce osteogenic differentiation of CESCs by regulating the expressions of some genes related osteogenesis in CESCs.