Increase of extracellular matrix proteins in hibernating ground squirrels could help maintain bone health.

Abstract

Whether from injury, old age, or space flight, immobility or a lack of gravitational loading has negative effects on the physiology of bone and bone marrow. Consequences include a weakening of the immune system, decreased hematopoietic cells in the bone marrow, and an overall decrease in bone density. Understanding the mechanisms behind these effects and combating their side effects is a subject of intense research. Thirteen lined ground squirrels are a common model organism for these studies because they hibernate for months and experience long periods of inactivity. Like humans under low loading and activity, the ground squirrels experience changes in the bone marrow cell make up and decreased bone density, but, unlike humans, once a 13-lined ground squirrel becomes active again, the side effects from their long rest are minute or non-existent. Transcriptomes were constructed from genes expressed in bone marrow from hibernating and non-hibernating ground squirrels. Certain extracellular matrix proteins, including COL4A2, were seen to increase drastically during hibernation and may possibly play a role in maintaining the health of the bone.