Studying osteoarthritis in a mouse is difficult, because scientists can't ask a rodent how it's feeling. But a new invention from the Oklahoma Medical Research Foundation lets mice tell researchers how they feel — without saying a word.
Mice are vital to medical research, giving scientists insights into the biology and genetics of animals whose physiology often correlates with those of humans. OMRF researcher Tim Griffin, Ph.D., studies how obesity and osteoarthritis are linked using mice that are fed a high-fat diet.
In a paper published in the Journal of Applied Physiology, Griffin unveiled a newly designed exercise wheel that measures the forces generated during movement in mice with arthritic joints.
Osteoarthritis is a common joint disorder that affects 27 million Americans. It occurs when the cartilage that cushions bones at the joints breaks down and wears away, allowing bones to rub together. This results in pain, stiffness and swelling and can cause bone spurs to form around the joint, making it even more difficult to move freely.
“It's a vicious cycle,” said Griffin. “Obesity can lead to osteoarthritis, which causes pain, reducing movement and making it harder to lose weight and live a healthy, active lifestyle.”
His goal is to understand the biological and cellular processes at the root of osteoarthritis, paving the way for treatments that can reduce or halt pain and the disease's effect on mobility.
By observing the natural movement of mice with osteoarthritis — not only how often they run, but also the force with which they push on the wheel — Griffin could deduce how much physical disability and pain the osteoarthritis causes and the effect it has on their joints. The best way to do that is with a mouse wheel, which mice are already inclined to use.
Since building this specialized exercise wheel required additional expertise in mechanical and electrical engineering, Griffin recruited local engineering interns to help perfect the design and build the device.
The specialized wheel uses a series of sensors to measure how hard the mouse pushes against the wheel when it runs, which may indicate the animal's level of pain by detecting whether it limps or otherwise favors a joint. Scientists can use this wheel to test the effectiveness of experimental treatments for osteoarthritis by studying the improvements in the mouse's gait and its ability to run.
The specialized mouse wheel incorporates features similar to a device called a force platform, which measures the force of movement in human patients, Griffin said. He came up with the idea for a force-sensing mouse wheel based on a force platform treadmill used to study human movement, which he helped develop as a graduate student at the University of California at Berkeley.
In addition to capturing force data, the wheel includes a high-speed infrared camera to film the mice running, since they prefer to exercise in the dark. Griffin's team designed software that tells the camera to only record images when the mice step on the force-sensing part of the wheel. The video and force data are collected and stored automatically, which allows the researchers to collect these data while they are at home sleeping.
Griffin said the next step will involve fitting the wheel with a motor, almost like a treadmill, to see how movement patterns change when the mouse walks and runs at set speeds.
“The current systems for measuring osteoarthritis disability in mice during movement are time-consuming and not particularly sensitive,” he said. “This new wheel lets us easily collect highly sensitive data from voluntary, spontaneous movement. Now we're seeing how they move when they want to move.”
Griffin said he hopes this new method of study will lead to better treatments for patients suffering with osteoarthritis.
Funding for the project was provided through a grant from the Oklahoma Center for the Advancement of Science & Technology. Engineering students Grahm Roach and Mangesh Edke assisted in the design of the wheel.