Objective      To observe the effect of different exogenous decorin (DCN) levels on matrix metalloproteases 13 (MMP13) gene expression in normal human articular chondrocytes primarily cultured in vitro.       Methods      Human hyaline chondrocytes were isolated and cultured with trypsin and type 2 collagenase in combination with digestion to observe their morphology. The cells were identified with Alcian blue staining and type 2 collagen immunohistochemistry. Effect of different exogenous DCN levels (0

2.5

25 and 250 μg/ml) on expression of MMP13 and collagen X in hyaline chondrocytes was detected by RT-PCR.       Results      The cultured normal hyaline chondrocytes were polygonal and flat in shape

and turned into polygonal and star in shape in 5 d after they were cultured with another medium and closely arranged as a “stone shop”. Alcian blue staining and type 2 collagen immunohistochemistry were positive for primarily cultured hyaline chondrocytes. The expression of collagen X was significantly decreased (0.78±0.03，0.71±0.04，0.63±0.01) with the increasing exogenous DCN level (0 to 250 μg/ml) in a dose-dependent manner (P0.01)，while the MMP13 expression significantly decreased (0.85±0.02) at the highest DCN level (250 μg/ml

P0.01).       Conclusion      Exogenous DCN inhibits expression of collagen X in hyaline chondrocytes in a dose-dependent manner and high DCN level (250 μg/ml) plays a significant role in inhibiting the expression of MMP13

which indicates that exogenous DCN inhibits the MMP13 expression in hyaline chondrocytes by suppressing their hypertrophy.