A new animal model for modulating myosin isoform expression by altered mechanical activity

Area of Science:

• Muscle physiology
• Biomechanics
• Molecular biology

Background:

• Understanding mechanical loading's impact on skeletal muscle is crucial.
• Myosin heavy chain (MHC) isoforms determine muscle fiber characteristics and function.
• Existing models may not fully capture the complex interplay between loading and MHC expression.

Purpose of the Study:

• To develop and validate a novel rodent model for studying mechanical loading effects on MHC isoform expression.
• To delineate the specific roles of concentric and eccentric contractions under high load.
• To analyze changes in MHC expression in plantar and dorsiflexor muscles.

Main Methods:

• Chronic implantation of stimulating electrodes for controlled muscle activation.
• A custom training apparatus translating ankle moment into linear force.
• Utilizing a computer-controlled ergometer for precise isovelocity contractions.
• Measuring muscle mass, myofibrillar adenosinetriphosphatase activity, and MHC isoform content.

Main Results:

• The model successfully induced significant muscle hypertrophy in medial gastrocnemius (MG) and tibialis anterior (TA) muscles.
• High-frequency stimulation (100 Hz) with high loading (concentric/eccentric) upregulated type IIa MHC and downregulated type IIb MHC.
• Myofibrillar adenosinetriphosphatase activity decreased, indicating a shift towards slower contractile properties.
• Type I MHC expression remained unaffected by the training protocols.

Conclusions:

• The developed rodent model effectively demonstrates the influence of mechanical loading on MHC isoform plasticity.
• High-load, high-frequency training promotes a fast-to-fast MHC transition (IIb to IIa) in skeletal muscle.
• This model provides a valuable tool for future research into muscle adaptation and performance.