Objective      To study the expression of matrix metalloproteinase 3 (MMP-3) and its effect on supraspinal ligament degeneration due to ankylosing spondylitis (AS).       Methods      Expression of MMP-3 and type Ⅰ collagen in ligaments was detected by immunohistochemistry. Proteoglycan level in ligaments was measured by ELISA. Supraspinal ligament morphology was observed under scanning electron microscope and transmission electron mic

roscope

respectively. Collagen fibril distribution density and positively-stained collagen area were analyzed by Image-Pro Plus(IPP).       Results      MMP-3 was highly expressed in vascular smooth muscle cells and endothelial cells in AS group but not in control group. The proteoglycan level was significantly higher in control group than in AS group (19.462±2.174 vs 7.477±2.512 μg/mg). The collagen fibrils were regularly arranged in control group and apparently exposed with massive degradation of matrix in AS group. The distribution density of collagen fibrils was 218.02±10.39/μm

2

and 122.47±22.42/μm

2

in control group and AS group

respectively. The proportion of positively-stained collagen area was significantly higher in control group than in AS group [(60.23±3.41)% vs (43.37±5.96)%

P0.05

]

.       Conclusion      MMP-3 is highly expressed in supraspinal ligament blood vessels of active AS patients by promoting the growth of blood vessels

activating the degradation of proteoglycan

and destroying the normal ultra-structure of ligaments

and is thus involved in the degenerative ossification process of ligaments.