What happens to glycosaminoglycans (GAGs) during immobilization?

• A. Immobilization causes an increase in GAGs.
• B. GAGs remain unchanged with immobilization.
• C. Immobilization causes loss of GAGs.
• D. GAGs convert to collagen with immobilization.

Answer: (C)

When a joint or tissue is immobilized, mechanical stimulation drops and the cells that maintain the extracellular matrix respond by reducing synthesis of proteoglycans while catabolic processes increase. Glycosaminoglycans are core components of these proteoglycans in cartilage, contributing to fixed negative charge and water retention that give the tissue its resilience. With unloading, proteoglycan content, including GAGs, declines, the matrix loses its hydration and cushioning properties, and the tissue becomes more susceptible to degeneration over time. Since GAGs are part of the matrix rather than something that would be created from other molecules, they don’t increase or stay unchanged, and they don’t transform into collagen. Thus immobilization leads to loss of GAGs.