Expression of the stress proteins, ubiquitin, heat shock protein 72, and myofibrillar protein content after 12 weeks of leg cycling in persons with spinal cord injury

Objective: To determine the effects of leg cycling exercise on ubiquitin (UBI), heat shock protein 72 (HSP-72) mRNA, protein expression, and myofibrillar protein content in individuals with spinal cord injury (SCI). Design: Case series. Setting: Motor behavior laboratory. Participants: Seven subjects with motor-complete SCI (4 men, 3 women). Intervention: A 12-week exercise program involving an electromagnetically braked recumbent bicycle ergometer, which allowed for passive exercise of the legs. Training occurred 2 days a week at approximately 75% of each subject's maximum heart rate. Main Outcome Measures: Total body mass (TBM) and muscle biopsies were obtained pre- and posttraining. The mRNA and protein expression of UBI, HSP-72, and myofibrillar protein content were determined. Results: Nonsignificant increases (P>.05) of 2.45% were observed for TBM. There were significant increases (P<.05) in the expression of both HSP-72 mRNA (33.71%) and protein (30.23%). For UBI, there were also significant decreases (P<.05) in the expression of both mRNA (26.86%) and protein (69.43%). Myofibrillar protein content increased significantly (P<.05, 41.86%). Conclusion: Leg cycling exercise in SCI increases myofibrillar protein content, possibly because of up-regulation in the expression of HSP-72 with concomitant down-regulation in the expression of UBI.