| Yhteenveto: | Introduction. Proteomics appears as a modern discipline to produce deep-level adaptations of human skeletal muscle to resistance training. However, alterations of muscle fiber protein profiles during detraining and retraining remain poorly investigated. Additionally, a clear consensus of myofibrillar and sarcoplasmic protein classification appears to be lacking. Therefore, the present thesis demonstrates an alternative approach to classification of protein profiles and seeks the impact of training and detraining periods on myofibrillar and sarcoplasmic protein profiles while muscle size is altered.
Methods. In total, 18 Finnish men and 12 Finnish women, all previously untrained, were randomized in a training-detraining-retraining-group (TDR, n = 17) undergoing 10 weeks of resistance training, 10 weeks of detraining, and 10 weeks of retraining, and control group (CTR, n = 11) remaining non-trained for 10 weeks. Muscle cross sectional area of vastus lateralis (VL CSA) was assessed with ultrasound and biopsies from VL muscle were collected for proteomic analysis at weeks 0, 10, 20 and 30. High-end LC-MS-based proteomics were utilized for protein analysis. Data of identified protein IDs were inserted into Panther Classification and UniProt Gene Ontology (GO) databases were applied for protein classification. In total, eight protein profiles were determined. Two main variables included in analysis were 1) relative protein abundance and 2) approximate absolute protein content.
Results. From quantified proteins (> 3000), 50 unique proteins were classified as myofibrillar proteins (37 sarcomeric and 13 sarcomere-associated proteins). To some extent overlapped with other profiles (non-unique), 1257 enzymes, and 2014 cytosolic/cytoplasmic, 714 mitochondrial, 120 ribosomal, and 992 nuclear proteins were classified as sarcoplasmic proteins. In TDR group, the relative abundance of myofibrillar proteins together, and sarcomeric and sarcomere-associated proteins separately displayed no changes between the timepoints, whereas the relative abundance of each sarcoplasmic protein profile increased during the initial 10-week training period (p < 0.05) with significance compared to control group (p < 0.05). However, no significant changes in sarcoplasmic relative protein abundance occurred during detraining or retraining. Both VL CSA and the absolute protein content of all protein profiles increased during both resistance training periods (p < 0.001) (significant compared to control group (p < 0.001)) and decreased during detraining (p < 0.01). Control group displayed no changes in any of the protein profiles.
Conclusions. In untrained individuals, the relative protein abundance tends to increase in sarcoplasmic protein profiles during the initial 10 weeks of resistance training while myofibrillar proteins seem to mostly align the changes of muscle size. The absolute protein content changes similarly to muscle size. Thus, skeletal muscle hypertrophy seems to occur due to enhancement of myofibrillar structures, sarcoplasmic components and cellular organelles, yet these changes take place in different relation. During detraining and retraining, all these protein profiles likely track the alteration of muscle size.
Keywords: protein, protein profile, relative abundance, resistance training, detraining
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