Proteomics Research. Brachial Plexus Injury After Muscle Atrophy

Rapid atrophy of skeletal muscle fibers is a common debilitating feature of muscles upon nerve injury or denervation. In clinical cases brachial plexus root avulsion is one of the main causes that lead to serious skeletal muscle atrophy of upper lamb. Up to now treatment for brachial plexus root avulsion has been unceasingly improved due to development of microsurgical technique for nerve transfer and nerve graft, but curative effect is unable to be completely satisfactory. The main reason is that the degeneration and necrosis of proximal neuron and distal target muscle are occurred to a certain different extent simultaneously after peripheral nerve injury. It becomes a key point for hampering improvement of curative effect that the severe atrophy of skeletal muscle is not responsible for regenerated nerve. In other words, irreversible atrophy of target muscle is occurred before gaining nerve domination again. Therefore exploring pathogenic atrophy mechanism of human denervated skeletal muscle attracts attention and interest around the world.We have known some alterations in metabolic pathways, ubiquitin (Ub) ligases signaling pathway, or some genes during muscle atrophy, but the molecular mechanism involved in denervated skeletal muscle atrophy is still poorly understood.The maintenance of muscle mass is controlled by a balance between protein synthesis and protein degradation pathways, which is thought to shift toward protein degradation during atrophy. Loss of muscle proteins occurs primarily through enhanced protein breakdown because of activation of the Ub-proteasome pathway. In addition, muscle atrophy appears to be caused by changes in mRNA levels of specific regulators of proteolysis, protein synthesis, and contractile apparatus assembling, such as polyubiquitin, elongation factor 2, and nebulin. However, the dynamic changes in a whole picture of skeletal muscle proteins during the process of muscle atrophy have never been characterized because of the limitations of the techniques available. The identification of protein alterations specific to muscle atrophy would clarify the pathogenetic mechanisms involved in the disease and might be of prognostic and therapeutic benefit. It is common belief that there is a critical period for the functional recovery of the denervated atrophy muscles. In other words, the muscles after denervation more long time would be suffer irreversible change in structure and function. The identification of such irreversible change-related protein would be veryuseful for the clinical purpose.Proteomics is the study of the dynamic expression pattern, activities, modifications and localization of all proteins encoded by the genome, and protein-protein interactions in a given cell, tissue or organism. So there is intense interest in use of proteomic approach to foster a better understanding of disease processes, develop new biomarkers for diagnosis, and accelerate drug development. Two-dimensional electrophoresis (2-DE) is first, important step in the traditional proteomics strategy, which separates proteins on the gel in two dimensions on the basis of independent charge and size properties. We employed it in this study to permit the simultaneous investigation of the largest possible range of skeletal muscle proteins. By comparing the complex 2-DE protein patterns, among about total of 800 protein spots in 2-DE gel, 26 proteins displayed decrease and 6 proteins were increased in expression in atrophy muscles versus normal controls. The identified proteins could be generally grouped together as metabolic proteins, chaperone proteins and contractile apparatus proteins. The significances of the altered proteins were discussed. The most prominent changes occurred is the contractile protein myosin light chain. The disregulation of protein DnaJC 1 showed a possible role of molecular chaperone in the functional recovery of the denervated atrophy muscles.In summary, the present work demonstrated the feasibility and validity of using proteomic analysis to search for skeletal muscle atrophy-related proteins. Our research work first provided the 2-D gel pattern of human skeletal muscle tissue, and showed that protein synthesis, preventing from attack by free radicals, correction of protein misfolding, and protein sorting in the cell are involved in the process of human denervated skeletal muscle atrophy after brachial plexus nerve injury. Although there was a similar report on proteomic analysis of denervated atrophying rat soleus muscle, but due to the different function between rat's hind-limbs and human hands, the dynamic changes in a whole picture of denervated skeletal muscles of these two different research objects are certainly not the same. The mRNA transcription of P20, a chaperone protein disregulated in denervated rat soleus, showed no heat inducibility, while DnajCl is necessary in protecting protein against multiple stress condition in human skeletal muscle. The desregulation of MnSOD was found in denervated skeletal muscles from human patients, and was not reported in denervated rat soleus. It seems that MnSOD plays a more relevant role in muscle atrophy than other metabolic enzymes because of its complicated effect on signaling pathways involving NO. All...