Fig. 1

Induction of gremlin-1 by excessive mechanical loading. a Time-course of Mmp13 mRNA levels in mouse primary chondrocytes after tensile stress loading (stress+), or without loading (stress −). Cells were cultured up to 72 h after uniaxial cyclic tensile strain (10%, 0.5 Hz, 30 min). ^#P < 0.005, ^##P < 0.001 versus stress—at each time-point (two-way ANOVA test). b Gremlin-1 mRNA levels in mouse primary chondrocytes after tensile stress loading. *P < 0.05 versus 0 h (one-way ANOVA test). c Gremlin-1 protein expression in mouse primary chondrocytes 24 h after tensile stress loading (stress+), or without loading (stress −). Nuclei were stained with DAPI (blue). Scale bars, 50 µm. d Gremlin-1 mRNA levels in mouse femoral head cartilage after hydrostatic pressure loading (5 or 20 MPa, 0.1 Hz, 30 min). ^#P < 0.005 versus stress− (Student’s unpaired two-tailed t-test). e Gremlin-1 immunofluorescence in mouse femoral head cartilage after 20 MPa hydrostatic pressure loading. Nuclei were stained with DAPI (blue). Scale bars, 100 µm. f Safranin O staining and gremlin-1 immunofluorescence during the time-course of mouse osteoarthritis development after surgical induction. Inset boxes in safranin O staining indicate regions of immunofluorescence. Scale bars, 100 µm and 50 µm, respectively. All data are expressed as mean ± SD of biologically independent three samples per group