Regulators of ECM Structure Enable Functional Adaptation to Tensile Loading in Tendon Explants.

Area of Science:

• Biomedical Engineering
• Tissue Engineering
• Mechanobiology

Background:

• Extracellular matrix (ECM) remodeling is crucial for tissue adaptation to mechanical stress.
• The molecular mechanisms linking mechanical strain to functional outcomes in tendons are not fully understood.
• Tendon adaptation is vital for responding to physical demands like exercise and disuse.

Purpose of the Study:

• To elucidate the molecular and cellular programs governing tendon adaptation to increased (exercise) and decreased (disuse) mechanical strain.
• To link specific mechanical perturbations to changes in ECM organization, composition, and function.

Main Methods:

• Cultured male murine flexor tendon explants in tensile bioreactors.
• Applied step changes in cyclic strain (1% to 5% for exercise, stress deprivation for disuse).
• Conducted multiscale analyses including matrix organization, composition, protein synthesis, signaling, and proteolytic activity.

Main Results:

• Increased strain (exercise) enhanced mechanical properties (elastic modulus, failure stress) via anabolic remodeling.
• Exercise-induced adaptation involved TGF-β/IL-6 signaling, increased proteoglycan expression, suppressed MMPs, and improved collagen alignment.
• Disuse (unloading) reduced collagen synthesis and alignment, promoting a catabolic phenotype with increased MMP activity.

Conclusions:

• Regulators of ECM organization and turnover are critical for functional tendon adaptation beyond synthesis alone.
• Defined mechanical loading protocols reveal distinct molecular pathways for anabolic (exercise) and catabolic (disuse) remodeling.
• Findings identify potential therapeutic targets for maladaptive ECM changes in aging, injury, and disease.