(ANK) gene and extracellular nucleotide phosphatase/phosphodiesterase (ENPP)1 mRNA expression and TGF-β1 protein expression in rat endplate chondrocytes in vitro. Endplate chondrocytes were isolated and cultured in vitro. Following identification with toluidine blue and immunocytochemical staining, chondrocytes

We investigated the effects of mechanical strain on the progressive ankylosis (ANK) gene and extracellular nucleotide phosphatase/phosphodiesterase (ENPP)1 mRNA expression and TGF-β1 protein expression in rat endplate chondrocytes in vitro. Endplate chondrocytes were isolated and cultured in vitro. Following identification with toluidine blue and immunocytochemical staining, chondrocytes were subjected to 10% elongation with various frequencies (0.5, 1, 1.5 and 2 Hz) using a Flexercell Tension Plus system at various intervals (3, 6, 12, 24, 36 and 48 h). As a control, cells that had been cultured statically on the same type of plate but were not subjected to stretch were also observed. Real-time reverse transcription-polymerase chain reaction and the enzyme-linked immunosorbent assay were used to study the effects of mechanical strain on ANK and ENPP1 mRNA expression and TGF-β1 concentration in the supernatant, respectively. Following treatment, the shape of the chondrocytes displayed a significant change from the original polygon to a typical spindle cell morphology; and the arrangement of the cells exhibited a change from a haphazard arrangement to an alignment with a certain direction. In the 0.5 Hz, 24-h group, the ANK gene expression was significantly increased compared to the control group (P<0.05); whereas in the other groups, the ANK and ENPP1 expression levels were reduced. With the increased frequencies in the 24-h group, the ANK gene expression gradually reduced. Changes in the expression of ANK and ENPP1 followed similar trends. TGF-β1 in the supernatant increased gradually in each frequency group, with a clear increase in the 0.5 Hz group. We conclude that various frequencies of mechanical strain can affect the expression of ANK, ENPP1 and endogenous TGF-β1 in endplate chondrocytes. Our results indicate that 0.5 Hz, 24 h may be the optimal stimulation condition to prevent calcification occurrence and to maintain the function of endplate chondrocytes.