Cartilage is held together by elastic glycan strings. Physiological and pathological implications

Area of Science:

• Biochemistry
• Biophysics
• Cell Biology

Background:

• Animal shapes are maintained by connective tissue extracellular matrices (ECMs).
• Proteoglycans (PGs) with glycosaminoglycan (AGAG) chains form bridges, maintaining collagen fibril organization and interfibrillar distances.
• These repeating structures, termed 'shape modules', are crucial for ECM integrity.

Purpose of the Study:

• To elucidate the structural and mechanical properties of ECM 'shape modules'.
• To explain the role of PGs and AGAGs in maintaining tissue shape and elasticity.
• To interpret cartilage's anisotropic responses to stress and the mechanisms underlying osteoarthrosis.

Main Methods:

• Structural analysis of PG-AGAG interactions.
• Mechanical testing of shape modules under stress.
• Observational studies of cartilage ECM in health and osteoarthrosis.

Main Results:

• Shape modules, composed of aggregated AGAG chains (DS, KS, CS), provide elasticity through specific bonding and L-iduronate sugars.
• Cartilage aggrecan depots imbibe water, creating swelling pressure that interacts with elastic shape modules.
• Degradation of shape modules in osteoarthrosis leads to water imbibition, fissuring, and erosion.

Conclusions:

• Shape modules are fundamental to ECM structure, elasticity, and mechanical responses.
• The described mechanism explains cartilage's anisotropic behavior and the pathology of osteoarthrosis.
• Understanding shape modules offers insights into connective tissue mechanics and disease.