In tendons, differing physiological requirements lead to distinct patterns of MMP-1 degradation.

Area of Science:

• Biomaterials Science
• Connective Tissue Biology
• Musculoskeletal Biomechanics

Background:

• Tendon collagen fibril diameter and crosslinking vary between high-stress (energy-storing) and low-stress (positional) tendons.
• Energy-storing tendons exhibit reduced remodeling and higher injury rates, potentially due to lower collagen turnover.
• Matrix metalloproteinase-1 (MMP-1) resistance has been proposed as a factor in reduced collagen turnover in energy-storing tendons.

Purpose of the Study:

• To validate and expand upon previous findings regarding MMP-1 resistance in single collagen fibrils.
• To conduct a population-level assessment of MMP-1 degradation across different tendon types.
• To develop predictive models for fibril diameter changes during degradation.

Main Methods:

• Incubation of positional and energy-storing tendon sections with buffer or MMP-1 for 24 hours.
• Scanning electron microscopy (SEM) for imaging fibril morphology.
• Custom image analysis pipeline for quantitative measurement of fibril diameter, alignment, curvature, and D-band length.

Main Results:

• MMP-1 treatment led to reduced fibril diameter, alignment, D-band length, and increased curvature in both tendon types.
• Energy-storing tendon fibrils showed significantly greater resistance to MMP-1 degradation (15% diameter reduction) compared to positional tendon fibrils (41% diameter reduction).
• Degradation exhibited a linear relationship with fibril size, with larger fibrils experiencing more pronounced diameter reduction and variation, suggesting higher core crosslinking.

Conclusions:

• Collagen fibrils in energy-storing tendons are inherently more resistant to MMP-1-mediated degradation than those in positional tendons.
• Fibril size and increased crosslinking density, particularly in the core, contribute to this resistance and influence degradation patterns.
• These findings provide insights into the distinct mechanical properties, remodeling capacities, and injury susceptibility of different tendon types.