What is the most abundant proteoglycan in the annulus fibrosus (AF)?

Aggrecan is the most abundant proteoglycan found in the annulus fibrosus (AF), which is part of the intervertebral disc structure. The primary role of aggrecan is to provide the disc with the ability to withstand compressive forces by retaining water, contributing to its overall hydration and biomechanical properties.

Aggrecan is a large chondroitin sulfate proteoglycan that forms aggregates with hyaluronic acid and other aggrecan molecules, resulting in a gel-like matrix that enhances the mechanical resilience of the AF. This is critical for maintaining the structural integrity of the intervertebral discs, allowing them to absorb shocks and resist deformation during movements.

While biglycan is another type of proteoglycan present in the AF, it is not found in as high quantities as aggrecan. Collagen types I and II are essential components of the extracellular matrix but are fibrous proteins rather than proteoglycans. In the context of the annulus fibrosus, type I collagen is the predominant fiber, providing tensile strength, while type II collagen is more associated with cartilage and the nucleus pulposus. Therefore, the prominence of aggrecan in the AF underscores its critical role in the tissue's mechanical function