Generating fast-twitch myotubes in vitro with an optogenetic-based, quantitative contractility assay

Area of Science:

• Muscle physiology
• Cellular biology
• Biomedical engineering

Background:

• Skeletal muscle fiber composition is crucial for physiological function and disease susceptibility.
• In vitro models require accurate fiber-type representation for effective muscle condition studies.
• Understanding fiber specification is key to developing better disease models.

Purpose of the Study:

• To develop an in vitro method for inducing skeletal muscle fiber specification.
• To quantitatively assess structural and functional adaptations in cultured myotubes.
• To refine in vitro models for studying muscle aging and diseases.

Main Methods:

• Designed a quantitative contractility assay using optogenetics and particle image velocimetry.
• Applied long-term intermittent light-stimulation patterns to cultured myotubes.
• Characterized myotube structural and functional changes, including gene expression.

Main Results:

• In vitro exercise led to faster contraction and increased fatigue resistance in myotubes.
• Myotubes exhibited enhanced maturation, including increased width and neuron receptor gene upregulation.
• Observed upregulation of fast myosin heavy-chain isoforms, indicating a shift to a fast-twitch phenotype.

Conclusions:

• Long-term in vitro exercise effectively induces skeletal muscle fiber specification towards a fast-twitch phenotype.
• This strategy enhances myotube maturation and contractile function.
• The developed method can improve the study of fiber specification and muscle disease modeling.