Osteochondral angiogenesis and increased protease inhibitor expression in OA

Area of Science:

• Biomedical research
• Cartilage biology
• Osteoarthritis pathogenesis

Background:

• Normal cartilage resists vascular invasion, possibly due to anti-angiogenic factors.
• Dysregulated expression of protease inhibitors may influence osteochondral vascularity in osteoarthritis (OA).

Purpose of the Study:

• To investigate the hypothesis that altered expression of four key anti-angiogenic protease inhibitors contributes to increased osteochondral vascularity in OA.

Main Methods:

• Immunohistochemistry was used to assess TIMP-1, TIMP-3, PAI-1, SLPI, and VEGF in tibial plateaux from OA patients and controls.
• Chondropathy was scored using the Mankin score, and osteochondral vascular density was quantified.

Main Results:

• Protease inhibitors and VEGF were primarily localized to superficial chondrocytes.
• Expression of VEGF, TIMP-1, TIMP-3, SLPI, and PAI-1 was increased in OA compared to controls.
• VEGF expression correlated with higher osteochondral vascular density, but protease inhibitors did not.

Conclusions:

• Cartilage's resistance to vascular invasion may depend more on its matrix than protease inhibitor expression.
• Upregulation of protease inhibitors by superficial chondrocytes in OA may partially counteract VEGF's angiogenic effects.
• Lack of expression by deep chondrocytes might permit vascular invasion in OA cartilage.