Characterization of the Changes in the Signalling Pathways During Spinal Cord Injury-induced Skeletal Muscle Atrophy

Atrogin-1 and muscle RING finger-1 are skeletal muscle specific genes, with ubiquitin ligase activities, that are upregulated during muscle atrophy in mice. Atrogin-1 and MuRF1 knock-out mice have a significant protection against skeletal muscle atrophy. The Akt/GSK3 and Akt/mTOR pathways are involved in muscle hypertrophy in mice. They have also been shown to stimulate the expression of myogenic regulatory factors. Recent studies by the investigators team and others have demonstrated the implication of these signalling pathways in the control of muscle mass in humans. However no study has yet investigated the involvement of these systems in the early stages of spinal cord injury induced human skeletal muscle atrophy.

Goals of the project The investigators propose to investigate the level of expression of the different components of the ubiquitin-proteasome system together with the level of expression and activity of the Akt/mTOR and Akt/GSK3 signalling pathways after SCI in humans during the first months following the injury.

Moreover the investigators will also study the effects of exercise training in paraplegic patients on the same molecular targets. In order to do that the investigators will use a novel apparatus of electrical stimulation which generate movements by closed-loop electrical muscle stimulation.

Detailed research plan The patients will be recruited jointly at the Clinique Romande de Réadaptation (CRR) in Sion and the Swiss paraplegic centre in Nottwil. They will be randomly divided into two groups, a first group of patients will undergo a conventional treatment of rehabilitation while a second set of patients will be treated using a brand new system of electro-stimulation called MotionMaker TM. Biopsies will be obtained in the first weeks after admission; two other biopsies will be taken respectively 3 and 6 months post-lesion. For each group, the muscle biopsies will be divided into 4 samples which will be used for a) real-time PCR to quantify the gene expression of the different components of the ubiquitin-proteasome system (Atrogin-1, MuRF1, Nedd4, UBB and Psma) b) Western blotting, using anti-phospho-site specific antibodies to quantify the activities of the Akt/GSK3 and Akt/mTOR pathways and of their downstream regulators of protein synthesis, eIF2B, p70S6K and PHAS-1/4E-BP1 c) fiber type analysis to quantify the variation in MHC expression and d) immunochemistry to localize the investigators molecular targets inside the different fiber types.

Expected value of the proposed project Our results will provide an increased understanding of the molecular mechanisms contributing to skeletal muscle atrophy during the early stages following SCI and a characterization of the impact of endurance training in the no more voluntary innervated muscle. Moreover this study will also investigate the potential improvement in the rehabilitation process by using a new system of electro-stimulation.