Sarah Little, M.S.
Bone is a complex and active tissue. Most people think once you stop growing that the bone is no longer changing; but actually, bone is constantly remodeling itself – it is just in a balance between resorption and formation. In fact, bone is constantly adapting to the world around it. Many things affect bone, like exercise (or the lack thereof), diet, inflammatory diseases, and radiation. While most people never encounter radiation, individuals with cancer or astronauts experience a huge effect. It has been well documented that individuals undergoing radiation therapy have a much greater risk of fracture at the sites of radiation exposure. Similarly, astronauts who spend time in space experience changes to their entire skeletal system, since the whole body is exposed to radiation – this is a major concern with regards to manned spaceflight.
The space environment has several types of radiation, including mass ejections from the sun to background radiation from outside our solar system. This background radiation is made up mostly of protons with a small percentage of heavy ions, like iron. What exactly does radiation exposure do to bone? Within one day in space, the balance between bone resorption and formation is tilted in favor of resorption. This tilt leads to bone loss. What causes radiation to negatively impact bone? Increased inflammation is the first response of the body to radiation. There are many proteins involved in inflammatory pathways and some of them directly interact with bone. These proteins, like TNF-a and Sclerostin, talk to the master controllers of bone, osteocytes, and cause this tilt to bone resorption. This effect is also common in diseases characterized by high levels of inflammation, such as Inflammatory Bowel Disease. There is evidence that a diet high in omega- 3 fatty acids can be protective of bone. Scientists think that these omega-3 fatty acids are able to lower the levels of the inflammatory proteins, like TNF-a and Sclerostin, which decreases the amount that these proteins can communicate with osteocytes and increase bone resorption. Recent unpublished data from our lab has exhibited a positive effect of low dose radiation on bone, suggesting a possible anabolic response. This process, instead of TNF-a and Sclerostin, would involve a protein called IGF-1, which communicates with osteocytes to increase bone formation.
The Bone Biology Lab at Texas A&M investigates the effect that exposure to the space environment, including space radiation, can have on bone. Our lab has identified these inflammatory proteins as a culprit in this radiation-induced bone loss. Our lab has also tied a link to these same inflammatory proteins and bone loss in models of Inflammatory Bowel Disease. Most recently, our lab has determined that low doses of radiation may cause an anabolic effect, potentially via IGF-1. Using techniques to analyze bone microarchitecture, bone strength, and bones stained for different proteins, our lab will be able to determine if very low doses of radiation can actually have a positive effect, thereby avoiding the negative effects that higher doses of radiation have on bone.