Abstract
Rat L6, mouse C2C12, and primary human skeletal muscle cells (HSMCs) are commonly used to study biological processes in skeletal muscle, and experimental data on these models are abundant. However, consistently matched experimental data are scarce, and comparisons between the different cell types and adult tissue are problematic. We hypothesized that metabolic differences between these cellular models may be reflected at the mRNA level. Publicly available data sets were used to profile mRNA levels in myotubes and skeletal muscle tissues. L6, C2C12, and HSMC myotubes were assessed for proliferation, glucose uptake, glycogen synthesis, mitochondrial activity, and substrate oxidation, as well as the response to in vitro contraction. Transcriptomic profiling revealed that mRNA of genes coding for actin and myosin was enriched in C2C12, whereas L6 myotubes had the highest levels of genes encoding glucose transporters and the five complexes of the mitochondrial electron transport chain. Consistently, insulin-stimulated glucose uptake and oxidative capacity were greatest in L6 myotubes. Insulin-induced glycogen synthesis was highest in HSMCs, but C2C12 myotubes had higher baseline glucose oxidation. All models responded to electrical pulse stimulation-induced glucose uptake and gene expression but in a slightly different manner. Our analysis reveals a great degree of heterogeneity in the transcriptomic and metabolic profiles of L6, C2C12, or primary human myotubes. Based on these distinct signatures, we provide recommendations for the appropriate use of these models depending on scientific hypotheses and biological relevance.
Highlights
Skeletal muscle is one of the largest organs in the body and plays an important role in locomotion and whole-body metabolic homeostasis
The L6 cell line has been extensively used in metabolic studies [17, 51, 53], and several modified clones have been developed, such as the L6-GLUT4myc cells that were engineered to express a labeled, insulin-responsive glucose transporter 4 (GLUT4) [53]
The best correlations of transcript expression were observed between cells and tissues from the same species, suggesting important species-specific differences in skeletal muscle mRNA composition (Fig. 1C)
Summary
Skeletal muscle is one of the largest organs in the body and plays an important role in locomotion and whole-body metabolic homeostasis. Adult skeletal muscle comprises nerves, vasculature, smooth muscle cells, fibroblasts, and resident immune cells, which all contribute to the different functions fulfilled by muscle. This complex arrangement makes it difficult to decipher the specific contribution of muscle cells to physiological outcomes and limits the methods available to study intramyocellular processes in vivo [11]. The L6 cell line has been extensively used in metabolic studies [17, 51, 53], and several modified clones have been developed, such as the L6-GLUT4myc cells that were engineered to express a labeled, insulin-responsive glucose transporter 4 (GLUT4) [53]. Cultured primary myoblasts from human biopsies have been developed [6] and are widely used in metabolic studies
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