Figure 2. Effect of mechanical strain on PTHrP expression in chondrocytes. (A) The expression of PTHrP mRNA varies during chondrocyte differentiation in cultured growth plate chondrocytes. The time-dependent expressions of PTHrP mRNA were determined at four-day intervals between days 4 and 24 of culture by real-time RT-PCR. Values were normalized with the expression level of GAPDH and denoted as the fold-increase of PTHrP mRNA expression relative to those of day 4 (proliferating) chondrocytes. (B) Cyclic mechanical strain induces PTHrP mRNA that is dependent upon the status of cellular differentiation. Proliferating, matrix-forming, and hypertrophic chondrocytes were subjected to cyclic mechanical strains of 7% or 12% elongation for 12 hrs, and the expression of PTHrP mRNA was examined by real-time RT-PCR. Values were normalized with the expression level of GAPDH and denoted as the fold-increase of PTHrP mRNA expression relative to control samples (0% elongation). Mean ± SD, n = 3, **p < 0.01, *p < 0.05.