Osteoarthritis is the most common degenerative joint disease. Although the condition has been extensively studied through a medical perspective, the molecular changes associated with osteoarthritis remain unclear.
The cartilage in the joints, along with a lubricant known as the synovial fluid, provides a smooth surface that helps withstand weight-bearing movements. The fluid contains several molecules, including hyaluronan (HA) and phospholipids. Since the cartilage environment cannot be quickly healed or repaired, researchers have tried to diagnose the early stages of joint disease by monitoring the molecular weight and concentration of HA.
“Although we know that in healthy joints there is very low friction, it is unclear which other molecules are involved and how they change during osteoarthritis,” said Rosa Espinosa-Marzal (EIRH). “During the early stages of osteoarthritis, cartilage starts degrading, and previous research has shown that the molecular composition of the synovial fluid changes. We wanted to see if the two changes are related to each other.”
In a healthy joint, the molecular weight of HA varies between 2-20 MDa with a concentration ranging from 1-4 mg/ml. However, in diseased joints, HA is broken down resulting in a lower molecular weight. Additionally, its concentration is also reduced by ten times.
To do so, the researchers combined vesicles with high and low molecular weight HA. Using neutron scattering and light scattering, they discovered that the molecular weight of HA can vastly change the structure of the vesicles. Lower molecular weight HA, which mimics osteoarthritis-diseased joints, results in larger vesicle size. They also observed that the molecular weight of HA changes the thickness of the phospholipid layers in the joints.
The researchers also studied how these differences can influence the formation of a protective film; in joints this film is responsible for the very low friction we need for unhindered motion.
The researchers are now working on using cartilage to understand whether their observations with gold surfaces also hold true in a biologically relevant system. They are also interested in studying the other molecular components that are found in joints to build a more comprehensive model of the changes that are associated with osteoarthritis.
Kangdi Sun, Tooba Shoaib, Mark W. Rutland, Joesph Beller, Changwoo Do, Rosa M. Espinosa-Marzal. Insight into the assembly of lipid-hyaluronan complexes in osteoarthritic conditions. Biointerphases, 2023; 18 (2) DOI: 10.1116/6.0002502
Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign. “New insights into the structural changes associated with osteoarthritis.” ScienceDaily. ScienceDaily, 5 July 2023. <www.sciencedaily.com/releases/2023/07/230705143002.htm>.
Photo by Toa Heftiba