Comparative analysis of the transcriptomes of EDL, psoas, and soleus muscles from mice

Abstract

Background Individual skeletal muscles have evolved to perform specific tasks based on their molecular composition. In general, muscle fibers are characterized as either fast-twitch or slow-twitch based on their myosin heavy chain isoform profiles. This approach made sense in the early days of muscle studies when SDS-PAGE was the primary tool for mapping fiber type. However, Next Generation Sequencing tools permit analysis of the entire muscle transcriptome in a single sample, which allows for more precise characterization of differences among fiber types, including distinguishing between different isoforms of specific proteins. We demonstrate the power of this approach by comparing the differential gene expression patterns of extensor digitorum longus (EDL), psoas, and soleus from mice using high throughput RNA sequencing. Results EDL and psoas are typically classified as fast-twitch muscles based on their myosin expression pattern, while soleus is considered a slow-twitch muscle. The majority of the transcriptomic variability aligns with the fast-twitch and slow-twitch characterization. However, psoas and EDL exhibit unique expression patterns associated with the genes coding for extracellular matrix, myofibril, transcription, translation, striated muscle adaptation, mitochondrion distribution, and metabolism. Furthermore, significant expression differences between psoas and EDL were observed in genes coding for myosin light chain, troponin, tropomyosin isoforms, and several genes encoding the constituents of the Z-disk. Conclusions The observations highlight the intricate molecular nature of skeletal muscles and demonstrate the importance of utilizing transcriptomic information as a tool for skeletal muscle characterization.

Lifespan analysis of dystrophic mdx fast-twitch muscle morphology and its impact on contractile function

“…The fast twitch EDL skeletal muscle from the mdx mouse, is the most used muscle to study the pathophysiology caused by the absence of dystrophin. The mouse EDL is a mix of fast fiber types; ~79% type 2B (fast glycolytic), ~16% type 2X and ~4% type 2A (fast oxidative glycolytic) 82 . We have previously proposed a two-step model to describe the skeletal muscle pathology in the dystrophinopathies 12,15-17,25 . Step-one; involves the absence of dystrophin triggering skeletal muscle fiber necrosis driven by a pathological increase in [Ca 2+ ]in likely caused by a combination of increased free radical damage and abnormal ion channel functioning.…”

Absence of the Z-disc protein α-actinin-3 impairs the mechanical stability of Actn3KO mouse fast-twitch muscle fibres without altering their contractile properties or twitch kinetics

“…For the skinned fibre experiments, we used the EDL fast-twitch muscle with longer fibres suitable for tying to a sensitive force transducer (not feasible for the ~500 µm long FDB fibres). The mouse EDL has been shown to have a fibre type distribution that is ~79% type 2B (fast glycolytic), ~16% type 2X and ~4% type 2A (fast oxidative glycolytic) muscle fibres (26). Figure 2 shows the maximal force produced by isolated myofibres from Actn3KO and WT mouse EDL.…”

Minocycline Treatment Reduces Mass and Force Output From Fast-Twitch Mouse Muscles and Inhibits Myosin Production in C2C12 Myotubes

“…The EDL and soleus mouse muscle are unusual in that they are predominantly comprised of fast or slow-twitch profile fibres ( Augusto et al, 2004 ), respectively, which allows us to differentiate the fibre type response to minocycline. More specifically the mouse EDL is an mixture of approximately ∼79% type 2B (fast glycolytic), ∼16% type 2X and ∼4% type 2A (fast oxidative glycolytic) muscle fibres while the soleus contains a population of ∼39% type 2A, ∼30% type 1 (slow oxidative), ∼26% type 2X and 5% type 2B ( Hettige et al, 2020 ). If the minocycline is reducing the amount of fast 2B/X/A myosin produced, then this would mean that the minocycline treated soleus would contain a higher proportion of slow type 1 myosin (as there was no change in mass) accounting for our finding of the slowing of the twitch and relaxation.…”