How many phosphoproteins does it take to make muscle grow?

The application of proteomics in muscle exercise physiology

INTRODUCTION

Exercise offers protection from non-communicable diseases and extends healthspan by offsetting natural physiological declines that occur in older age. Striated muscle is the largest bodily organ; it underpins the capacity for physical work, and the responses of muscle to exercise convey the health benefits of a physically active lifestyle. Proteomic surveys of muscle provide a means to study the protective effects of exercise and this review summaries some key findings from literature listed in PubMed during the last 10 years that have led to new insight in muscle exercise physiology.

AREAS COVERED

'Bottom-up' analyses involving liquid-chromatography tandem mass spectrometry (LC-MS/MS) of peptide digests have become the mainstay of proteomic studies and have been applied to muscle mitochondrial fractions. Enrichment techniques for post-translational modifications, including phosphorylation, acetylation and ubiquitination, have evolved and the analysis of site-specific modifications has become a major area of interest in exercise proteomics. Finally, we consider emergent techniques for dynamic analysis of muscle proteomes that offer new insight to protein turnover and the contributions of synthesis and degradation to changes in protein abundance in response to exercise training.

EXPERT OPINION

Burgeoning methods for dynamic proteome profiling offer new opportunities to study the mechanisms of muscle adaptation.

Diurnal Differences in Human Muscle Isometric Force In Vivo Are Associated with Differential Phosphorylation of Sarcomeric M-Band Proteins

We investigated whether diurnal differences in muscle force output are associated with the post-translational state of muscle proteins. Ten physically active men (mean ± SD; age 26.7 ± 3.7 y) performed experimental sessions in the morning (08:00 h) and evening (17:00 h), which were counterbalanced in order of administration and separated by at least 72 h. Knee extensor maximal voluntary isometric contraction (MVIC) force and peak rate of force development (RFD) were measured, and samples of vastus lateralis were collected immediately after exercise. MVIC force was greater in the evening (mean difference of 67 N, 10.2%; p < 0.05). Two-dimensional (2D) gel analysis encompassed 122 proteoforms and discovered 6 significant (p < 0.05; false discovery rate [FDR] = 10%) diurnal differences. Phosphopeptide analysis identified 1693 phosphopeptides and detected 140 phosphopeptides from 104 proteins that were more (p < 0.05, FDR = 22%) phosphorylated in the morning. Myomesin 2, muscle creatine kinase, and the C-terminus of titin exhibited the most robust (FDR < 10%) diurnal differences. Exercise in the morning, compared to the evening, coincided with a greater phosphorylation of M-band-associated proteins in human muscle. These protein modifications may alter the M-band structure and disrupt force transmission, thus potentially explaining the lower force output in the morning.