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

Overview

Atrogin-1 and muscle RING finger-1 are skeletal muscle specific genes, with ubiquitin ligase activities, that are upregulated during muscle atrophy in mice. The Akt/GSK3 and Akt/mTOR pathways are involved in muscle hypertrophy in mice. 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. 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. A second aim of this project is to assess if a novel apparatus of electrical stimulation which generate movements by closed-loop electrical muscle stimulation may improve strength and muscle mass in these patients. 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. 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.

Measures: For each group, the muscle biopsies will be divided into 3 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-BP1and c) fiber type analysis to quantify the variation in MHC expression.