The loss of normal weight-bearing activity, which occurs during
bed rest, limb immobilization, and spaceflight, stimulates a catabolic response within the musculoskeletal system, which results in a loss of skeletal muscle mass and bone
mineral. The mechanism by which loading of muscle and bone is sensed and translated into signals controlling tissue formation remains a major question in the field of musculoskeletal research. In this investigation, we have examined the ability of two potentially anti-atrophic
proteins,
IGF-I and Shh, to inhibit
disuse atrophy within muscle and bone, when electroporated into skeletal muscle. We have found that electroporation and ectopic expression of
IGF-I and/or Shh within the gastrocnemius/soleus muscle significantly stimulated muscle fiber
hypertrophy and increases in muscle size. In addition, we report that electroporation and ectopic expression of
IGF-I and/or Shh within the gastrocnemius/soleus muscle attenuated the lost of muscle fiber area, muscle mass, and muscle mass density that normally occurs during disuse
muscle atrophy. Finally, we found that ectopic expression of
IGF-I and Shh within the gastrocnemius/soleus muscle inhibits parameters of
osteopenia within the tibia and fibula associated with hindlimb unloading. These results support the theory that skeletal muscle can regulate bone maintenance and could offer potentially novel and efficient therapeutic options for attenuating muscle and bone
atrophy during aging, illness and spaceflight.