Interface membrane fibroblasts around aseptically loosened endoprostheses express MMP-13

Area of Science:

• Biomedical Engineering
• Orthopedic Surgery
• Cell Biology

Background:

• Aseptic loosening of joint arthroplasties is a significant clinical problem.
• The cellular and molecular mechanisms underlying aseptic loosening are not fully understood.
• Matrix metalloproteinases (MMPs) are implicated in extracellular matrix degradation.

Purpose of the Study:

• To determine if matrix metalloproteinase-13 (MMP-13) is produced by cells at the peri-implant interface.
• To characterize the cells responsible for MMP-13 production in loosened arthroplasties.
• To investigate the potential role of MMP-13 in the pathogenesis of aseptic loosening.

Main Methods:

• Tissue specimens from revision surgery of loosened hip and knee arthroplasties (n=27) and control synovial tissues (n=6) were analyzed.
• In situ hybridization was used to detect messenger RNAs (mRNAs) encoding MMP-13 and alpha(1) collagen I (COL1A1).
• Immunohistochemistry for CD68 and tartrate-resistant acid phosphatase (TRAP) were used to characterize cell populations.

Main Results:

• Cells expressing MMP-13 mRNA were identified in 70% of the peri-implant interface tissues.
• These MMP-13-producing cells exhibited a fibroblastic morphology and co-expressed COL1A1 mRNA.
• MMP-13 expressing cells were located near osteoclasts and multinuclear giant cells, but not within them.

Conclusions:

• Fibroblasts at the interface of aseptically loosened endoprostheses selectively express MMP-13.
• The expression and release of MMP-13 by these fibroblasts may contribute to local extracellular matrix degradation.
• This process could play a role in the bone resorption associated with aseptic loosening of joint implants.