Blocking The Protein Myostatin Keeps Mice Muscled In Space

One of the challenges astronauts face during space missions is a loss of muscle and bone mass. Microgravity causes muscles and bones to weaken over time. Currently, the way NASA fights bone and muscle loss for astronauts on the ISS is with specialized exercise programs. However, with longer duration missions, such as trips to Mars, exercise programs won't be sufficient. Researchers are looking at a protein called Myostatin (MSTN) in mice testing to help astronauts maintain muscle and bone mass.

MSTN is a protein that is part of a system of checks and balances, limiting muscle growth in humans and other species. Increased muscle mass results when the braking function of MSTN is removed. Researchers created mice lacking MSTN and called them Mighty Mice resulting in dramatic muscle growth.

Researchers wanted to figure out what happens to these mice in microgravity and if an inhibitor of MSTN could help normal mice retain their muscle mass in space. To answer that question, researchers sent mice into space. A total of 40 mice were placed aboard the SpaceX-19 mission that launched on December 5, 2019. Those mice stayed aboard the ISS for 33 days before returning to Earth on January 7, 2020.

Among the subjects were normal wild-type mice for the control, Mighty Mice, and mice given a dose of a specific compound known as ACVR2B/Fc. Similar groups of mice were also maintained on the ground in conditions reproducing those on the ISS, other than microgravity. Researchers found that normal mice lost considerable muscle mass and bone density.

Mice given doses of ACVR2B/Fc to inhibit MSTN and activin A, both of which limit muscle growth, were found to be protected against microgravity-induced muscle and bone loss. The wild-type mice on the ISS loss between eight and 18 percent of the weight in individual muscles compared to those on earth and 11 percent of bone mineral density in specific bones. MSTN-lacking mice maintained their bulked up muscles.

The mice dosed with ACVR2B/Fc gained more lean body weight than the group on the ground, including increased muscle mass. The bone mass density of those mice also increased in space. Scientists believe that ACVR2B/Fc has important implications for therapeutic strategies during space exploration and recovery after returning from microgravity and treatment for people suffering from atrophy on earth.