Joints allow us to run, jump, and throw a ball, cushioning our bones from wear and tear with a protective bubble of lubricating fluid. But joints can falter with disease and old age, leaving millions searching for ways to keep them healthy. Now researchers at Brown University have discovered that a protein found in this fluid acts as a shock absorber, allowing it to absorb energy during activity, thus reducing friction on the surface of cartilage.

"What we have may be something useful to help prevent arthritis," says Gregory Jay, associate professor of emergency medicine and engineering at Brown University and the project's leader. He hopes that adding the protein to current injection therapies will boost their joint-protecting power, shielding the cartilage from damage. Such a treatment could be especially useful in sports medicine, Jay says.

Arthritis is a joint disorder that affects nearly 40 million people in the United States. It's often the result of an activity-related injury that damages some part of the joint, and it's characterized by inflammation, which is painful and makes the joints stiff and swollen.

Currently, there is no preventative method for arthritis; there are only treatments to reduce joint pain and inflammation. In one particular treatment, a gooey polymer made of hyaluronate--long thought to be the substance that gives joint fluid its resiliency--is injected into the joint.

While this treatment seems to be helpful for some patients, the mechanisms by which it works and the effect it has on the functional outcome of the joints are unclear, says Matthew Warman, the director of the orthopedic research laboratories at Children's Hospital Boston, an investigator with the Howard Hughes Medical Institute, and a professor of genetics and orthopedic surgery at Harvard Medical School. Warman also took part in the study.

Hoping to find a better treatment, the researchers set out to determine how a protein called lubricin, also found in joint fluid, changes the shock-absorbing properties of the fluid. They compared the biophysical properties of the protein using two samples of joint fluid: one normal, and the other from a human with a rare disease in which the body does not make lubricin. The team implanted fluorescent beads in the fluid and tracked the particles' movements with a video camera.

After calculating the viscosity and other mechanical properties of the fluids, the researchers discovered that lubricin actually adds elasticity by binding to the hyaluronate. Based on these results, published this month in the Proceedings of the National Academy of Sciences, researchers hope to recreate the protective feature of joint fluid by adding lubricin to the hyaluronate prior to injection, says Jay.

Jay and his team now plan to test their new formulation in animals. If they can prove that they are able to recreate the elastic effects and control them, clinical trials will be conducted to test whether this could be an effective preventative treatment for injured joints, as well as a more successful therapy for patients with advanced arthritis.