Expansion Microscopy reveals changes in cellular and extracellular structures between healthy and perturbed tendons

Area of Science:

• Biomaterials Science
• Cell Biology
• Orthopedics

Background:

• Tendons are vital for force transmission, composed of an aligned collagen matrix.
• Resident cells normally repair tendon damage, but this fails in tendinopathies, impairing function.
• Understanding how mechanical forces alter tendon cell and matrix architecture is crucial but limited by current imaging methods.

Purpose of the Study:

• To develop and validate a novel imaging technique for visualizing tendon structure across multiple length scales.
• To investigate the impact of mechanical changes on tendon cellular and extracellular matrix organization.

Main Methods:

• Combined Fluorescent Labeling of Abundant Reactive Entities (FLARE) with Expansion Microscopy (ExM).
• Applied FLARE-ExM to native tendon tissue, including elastic fibers and cellular protrusions.
• Analyzed tendon tissue from a resection model and ruptured human Achilles tendons.

Main Results:

• FLARE-ExM successfully resolved the dense fibrillar matrix and cellular structures in various tendon types.
• Acute loss of tension in a resection model showed increased fibril width and expanded matrix regions.
• Ruptured human Achilles tendons exhibited extracellular disorganization and disrupted cellular architecture.

Conclusions:

• FLARE-ExM is an effective approach for visualizing complex tendon architecture.
• This technique provides insights into how mechanical perturbations remodel tendon structure in physiological and disease states.
• FLARE-ExM can advance the study of tendinopathies and tendon repair mechanisms.