Dynamic proteome profiling of human muscle responses to high-intensity interval training

Field: Biochemistry, Genetics and Molecular Biology (Life Sciences)

Skeletal muscle is the most abundant tissue in the body and it plays a central role in whole-body metabolism. Physical inactivity and obesity are associated with poor metabolic health due to insulin resistance of peripheral tissues, in particular skeletal muscle. Conversely, a physically active lifestyle or formal exercise training are associated with adaptations in skeletal muscle that improve its substrate metabolism and insulin sensitivity. Such changes in muscle function are underpinned by changes to the muscle proteome, i.e. relative increases or decreases in the abundance of select proteins. Proteomic analysis of human muscle biopsy samples involves non-targeted analysis of a large number of proteins and can generate new hypotheses. To date, the majority of proteomic studies report protein abundances only and the dynamic aspects (i.e. synthesis and degradation) of proteins in human muscle has seldom been investigated, but it is likely that the quality of muscle proteins i.e. turnover rate may also contribute to muscle function. We have used deuterium oxide to label newly synthesised proteins in vivo and then analysed muscle biopsy samples using peptide mass spectrometry techniques that are capable of identifying individual proteins and measuring their relative abundance and fractional rate of synthesis. We have used this method to investigate 2 research questions: (i) what changes occur in the skeletal muscle proteome associated with sedentary lifestyle and obesity, and (ii) what is the dynamic proteome response of human muscle to high-intensity interval training? Our cross-sectional study of obese vs trained individuals (N = 4, in each group) revealed novel proteins that had differences in abundance and synthesis rate. Proteins including carbonic anhydrase 3, heat shock protein β-1, glyceraldehyde 3 phosphate dehydrogenase, sarcoplasmic/endoplasmic reticulum calcium ATPase 1, creatine kinase muscle type, and type IIx myosin heavy chain) are more abundant and have a lower rate of turnover in the muscle of individuals with obesity. Therefore, these may be more likely to accrue deleterious posttranslational modifications that may affect their activity or interaction with other proteins. We then performed a longitudinal study to investigate responses to 10-week high-intensity interval training (HIT) programme in the muscle of participants with obesity. HIT increased the turnover rate of individual muscle proteins and in particular we discovered greater abundance of 2 novel proteins, desmin and α-actinin-3, which have not been previously reported in regard to endurance exercise. In conclusion, we have applied a new dynamic proteome profiling method to investigate complex physiological responses associated with obesity and exercise training in human muscle in vivo. Our data support the hypothesis that obesity is associated with changes to the turnover rate as well as abundance of muscle proteins. Our findings bring new insight and a new avenue of research investigating protein quality control as a mechanism underpinning the deleterious effects of obesity and physical inactivity. HIT training was able to counter some of the effects associated with obesity and sedentary behaviour and this thesis highlights a number of key muscle proteins that are suitable for future targeted research.