Cartilage is a connective tissue that provides a smooth, lubricated surface for articulation and facilitates the transmission of loads with a low frictional coefficient. In diseases, such as osteoarthritis, the mechanical properties of cartilage (e.g., its compressive resistance and load-bearing ability) are reduced due to changes in both the chemical composition and the physical properties of its macromolecular constituents. Cartilage proteoglycans (PGs) exhibit a hierarchical bottlebrush structure at multiple length scales. We investigated the hierarchical structure of cartilage PGs and their roles in cartilage function using an array of complementary experimental techniques, including osmotic swelling pressure measurements, small angle neutron and X-ray scattering measurements (SANS and SAXS), light scattering and atomic force microscopy. We proved that aggrecan and its complexes with hyaluronic acid (HA) exhibit microgel-like behavior. The small size and dispersed character of the microgel particles ensure rapid response to sudden changes in external forces, e.g., in shock absorption. Under compressive load, microgel particles deswell and release lubricating fluid, reducing the friction of movement within the joint. An unexpected feature of PG assemblies is their insensitivity to the presence of calcium ions. Over the length scale range (10 – 500 Å) explored by SANS, SAXS and light scattering, no detectable structural change occurs, even at ionic strength (0.2 M) which is much higher than the physiological concentration range. Such stability is a prerequisite for the function of cartilage in bone formation.

Insight into cartilage supramolecular structure and biological function

2019 Spring National Meeting

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