While space travel is likely to remain only a pipe dream for most of us, scientists are intrigued about what effects weightlessness and being millions of miles up have on human physiological systems. A recent Henry Ford Hospital study of mice aboard a Russian spaceflight could pose an issue for tomorrow’s astronauts: Could traveling in space be bad for your joints?
So far, researchers have found instances of cartilage breakdown in the mice, hinting that the reduced biomechanical forces of spaceflight could affect human musculoskeletal systems. The research is published online in npg Microgravity, part of the Nature Partner Journals publishing group.
According to Jamie Fitzgerald, Ph.D., head of musculoskeletal genetics at Henry Ford’s Department of Orthopedic Surgery and the study’s lead author, evidence of articular cartilage breakdown in the mice was “clear-cut.”
Fitzgerald and fellow researchers theorize that the variations in biomechanical forces encountered in space, arising from the absence of gravity, account for the cartilage breakdown. “If this were to happen to humans, given enough time, it would lead to major joint problems,” he says.
“We do know that tissues of the musculoskeletal system—bone, muscle, tendon, cartilage, and ligament—are constantly subjected to ‘loading’ everywhere on Earth,” adds Dr. Fitzgerald. “This comes from daily activities like walking and lifting, and the action of gravity pulling down on the musculoskeletal system. When that loading is removed due to weightlessness and near zero gravity in space, these tissues begin to degrade. The most dramatic example is the atrophy of muscle and demineralization of bones that occurs during spaceflight.”
Fitzgerald notes that muscle and bone loss is reversed when the astronauts return to Earth, thus placing further strain on joints. He adds that cartilage is a tissue that repairs poorly.
For the NASA-funded study, Dr. Fitzgerald and his research team analyzed the molecular changes in the cartilage of mice that spent a month aboard an unmanned Russian Bion-M1 spacecraft in 2013. The scientists performed tissue stains and gene expression studies on the cartilage, and compared the results with a control group of mice observed on Earth during the same period.
“Overall, we can say that after 30 days of microgravity, the process of cartilage degrading began,” he says. “We saw changes in the gene expressions that were consistent with cartilage breakdown.”
According to video footage, the mice floated freely in their enclosure during the day, but struggled to navigate the enclosure’s grates at night. “The mice did experience some loading on the joints as they tried to hang onto each other. It wasn’t a complete unloading,” Dr. Fitzgerald says.
The control group of mice on Earth showed no discernible cartilage degradation.
Dr. Fitzgerald says NASA is interested in developing a better understanding of what happens to the human body in space. With the possibility of a manned Mars mission, he believes more research is needed.
