Global mRNA sequencing of human skeletal muscle: Search for novel exercise-regulated myokines

Abstract

ObjectiveSkeletal muscle is an important secretory organ, producing and releasing numerous myokines, which may be involved in mediating beneficial health effects of physical activity. More than 100 myokines have been identified by different proteomics approaches, but these techniques may not detect all myokines. We used mRNA sequencing as an untargeted approach to study gene expression of secreted proteins in skeletal muscle upon acute as well as long-term exercise.MethodsTwenty-six middle-aged, sedentary men underwent combined endurance and strength training for 12 weeks. Skeletal muscle biopsies from m. vastus lateralis and blood samples were taken before and after an acute bicycle test, performed at baseline as well as after 12 weeks of training intervention. We identified transcripts encoding secretory proteins that were changed more than 1.5-fold in muscle after exercise. Secretory proteins were defined based on either curated UniProt annotations or predictions made by multiple bioinformatics methods.ResultsThis approach led to the identification of 161 candidate secretory transcripts that were up-regulated after acute exercise and 99 that where increased after 12 weeks exercise training. Furthermore, 92 secretory transcripts were decreased after acute and/or long-term physical activity. From these responsive transcripts, we selected 17 candidate myokines sensitive to short- and/or long-term exercise that have not been described as myokines before. The expression of these transcripts was confirmed in primary human skeletal muscle cells during in vitro differentiation and electrical pulse stimulation (EPS). One of the candidates we identified was macrophage colony-stimulating factor-1 (CSF1), which influences macrophage homeostasis. CSF1 mRNA increased in skeletal muscle after acute and long-term exercise, which was accompanied by a rise in circulating CSF1 protein. In cultured muscle cells, EPS promoted a significant increase in the expression and secretion of CSF1.ConclusionWe identified 17 new, exercise-responsive transcripts encoding secretory proteins. We further identified CSF1 as a novel myokine, which is secreted from cultured muscle cells and up-regulated in muscle and plasma after acute exercise.

Association of circulating proinflammatory marker, leucine‐rich‐α2‐glycoprotein (LRG1), following metabolic/bariatric surgery

“…Interestingly, LRG1 transcripts were found to be upregulated in muscles after acute exercise but was not differentially regulated from baseline, after a 12‐week exercise, suggesting a transient increase. Following observation of transient increase in LRG1 after exercise, it is tempting to speculate that the increase in LRG1 after metabolic/bariatric surgery could be because of complex remodelling in the adipose tissue. The early increased circulating LRG1 after metabolic/bariatric surgery may be important in initiating an antiinflammatory and antiangiogenic environment.…”

Myokines in skeletal muscle physiology and metabolism: Recent advances and future perspectives

“…[102][103][104] One study used global mRNA sequencing to detect genes that were upregulated in human skeletal muscle as an outcome of acute and/or long-term exercise. For example, more than 100 myokines have been identified by different proteomics approaches, but these techniques may not detect all myokines.…”

“…For example, more than 100 myokines have been identified by different proteomics approaches, but these techniques may not detect all myokines. 103 Some transcripts encode well-known myokines, such as irisin, BDNF and IL-6, which have been described extensively and are reviewed elsewhere, 2,3,5,102-104 ; others have not been studied previously in skeletal muscle and may encode novel myokines. [102][103][104] One study used global mRNA sequencing to detect genes that were upregulated in human skeletal muscle as an outcome of acute and/or long-term exercise.…”

“…mRNA sequencing has been employed as an alternative, unbiased approach to identify and study gene expression of secreted myokines and is a useful approach by which to expand our knowledge of the skeletal muscle secretome. 102,103 In addition, Genome-wide association studies (GWAS) have been instrumental in the identification of a multitude of pleiotropic candidate single-nucleotide polymorphisms (SNPs)/loci associated with traits related to skeletal muscle physiology and metabolism, with multiple loci overlapping between the traits. 103 In total, the group detected almost 250 genes encoding putative myokines that were upregulated after acute and/or long-term training.…”

Measuring myokines with cardiovascular functions: pre-analytical variables affecting the analytical output

“…Hence, physical activity (PA) represents the main stimulus to the endocrine functioning of the SKM (3). Other than IL-6, more than 100 myokines have been so far identified (4), among the 300 predicted proteins constituting the SKM secretome (5), and 17 additional novel exercise-responsive transcripts have been recently discovered (3).…”